METHOD AND FORMULATION FOR PREPARING OPTICAL METAL OXIDE LAYERS

Abstract

The present invention relates to a method for preparing an optical metal oxide layer, to a formulation for preparing an optical metal oxide layer and to an optical device comprising an optical metal oxide layer. The optical metal oxide layers are particularly suitable for optical applications and may be used in optical devices such as, for example, in diffractive gratings for augmented reality (AR) and/or virtual reality (VR) devices.

Description

FIELD OF THE INVENTION

The present invention relates to a method for preparing an optical metal oxide layer, to a formulation for preparing an optical metal oxide layer and to an optical device comprising an optical metal oxide layer.

The method for preparing an optical metal oxide layer according to the present invention involves using a formulation comprising one or more titanium polyoxometalates (POMs) and one or more formulation media. The obtained optical metal oxide layers are particularly suitable for optical applications and may be used in optical devices such as, for example, in diffractive gratings for augmented reality (AR) and/or virtual reality (VR) devices. The obtained optical metal oxide layers show (a) favorable optical properties such as high refractive index (RI) of >1.7, preferably >2.0, at wavelengths of ≤520 nm, low absorption, and low degree of haze formation; (b) favorable mechanical properties such as low shrinkage, (c) favorable coating properties such as dense layer and flat surface structure; and (d) favorable filling properties such as homogeneous filling of topographical features on patterned substrates.

The method according to the present invention allows the preparation of optical metal oxide layers on the surface of both patterned or non-patterned substrates. The metal oxide layer may form various structures such as, for example, layers covering a surface of a non-patterned substrate and/or fillings covering topographical features such as e.g. gaps on the surface of a patterned substrate, thereby providing highly refractive optical structures. In particular, the method according to the present invention allows the preparation of advanced optical gap filling with low overburden, thus enabling an easy and cost efficient mass production of complex optical devices by avoiding typical problems occurring when layer deposition or gap filling is performed by physical vapor deposition (PVD) or chemical vapor deposition (CVD) techniques such as, for example, incomplete or excessive gap filling due to unfavourable deposition and layer growth characteristics such as, for example, decreased or increased deposition or growth rates at corners and edges.

The present invention further relates to a formulation for preparing an optical metal oxide layer, wherein said formulation is based on titanium polyoxometalates POMs. The formulation according to the present invention allows improved wetting characteristics and allows the preparation of optical metal oxide layers on patterned or non-patterned substrates showing the above mentioned beneficial effects, namely (a) favorable optical properties such as high refractive index (RI) of >1.7, preferably >2.0, at wavelengths of ≤520 nm, low absorption and low degree of haze formation; (b) favorable mechanical properties such as low shrinkage, (c) favorable coating properties such as dense layer and flat surface structure; and (d) favorable filling properties such as homogeneous filling of topographical features on patterned substrates.

Beyond that, the formulation according to the present invention allows the preparation of advanced optical gap filling with low overburden, thus enabling easy and cost-efficient mass production of complex optical devices as described above. The formulation is therefore particularly suitable for the preparation of optical metal oxide layers having high refractive index for optical devices such as, for example, for diffractive gratings in AR and/or VR devices.

Finally, the present invention provides an optical device, preferably an AR and/or VR device, comprising an optical metal oxide layer, which is obtainable by the method according to the present invention or which is prepared by using the formulation according to the present invention.

BACKGROUND OF THE INVENTION

Leading edge optical devices typically include optical gratings made from composite materials having a substrate as a support and complex and interlaced patterns thereon, the patterns being made up of different layers or stacks of layers.

Usually, the creation of such complex and interlaced patterns demands for structuring processes, which become increasingly challenging with decreasing size of structural dimensions to be prepared.

In addition to a wide range of possible uses in various fields of application, such as in spectrometers or in optical storage systems (CD, DVD, etc.), diffractive gratings are the core components of so-called XR devices, mostly glasses. In this context, R stands for the term reality and X denotes different attributes such as, for example, virtual, augmented, mixed and so forth. Hence, diffractive gratings form part of the core of the so-called optical engine in XR devices, specifically in augmented reality and mixed reality glasses. Virtual reality glasses, when built as a head mounted display, are often composed of a conventional liquid crystal (LC) organic light emitting diode (OLED) display being embedded in the device, and thus do not necessarily require diffractive gratings. In contrast, augmented and mixed reality glasses are designed that way to enable consumers to obtain visual impressions of their environment, at its best as if they would not wear any glasses at all. However, they also make it possible to provide and serve digital information and to also project it into the field of vision of individuals. Additional digital information is gathered from recognizing and analyzing the environment, the individual inspects or takes a look currently at. In order to convey and project supporting digital information into the eyes of an individual, the augmented or mixed reality glasses are equipped with an information supply unit, which is coupled to an optical waveguide system that transports the optically coded supporting information through it directly to the lens of the glasses. Here, the information passes a diffractive grating which couples the incident light into the lens and splits it according to its angular information and its spectral bands by diffraction. After incoupling of the light, the lens serves as waveguide enabling transport of the light to and into the pupil of an individual. The location of light incoupling is independent of any preferred position and thus of the implication of technical needs. The direction of traversal of light within the lenses is determined by the diffractive grating diffracting or splitting the light. At certain positions in the lens, a second and a third diffractive grating serves for changing the direction of light traversal and thereby enforcing the light to be projected into pupil of the user. The light traversal in the glasses is accomplished by total internal reflection (TIR) of the light, thus bouncing several times between the glass interfaces until reaching another diffractive grating, which changes the internal TIR direction of the light (see FIG. 2). The second and third grating are geometrically aligned in different directions with respect to the first and incoupling grating, e. g. by a certain angular distortion of the longitudinal axis, thus allowing to change the direction of propagation of totally internally reflected light. Needless to say, the lens itself or the material of which lenses are made of shall not be absorbing. Otherwise, the supportive information never reaches the pupil of the user or only with strongly depleted light intensity. The process works regardless of the use of reflection or transmission gratings. Usually, the lenses are equipped with both types of gratings to properly guide the light. It should also be mentioned that there are differences in the optical performance of reflection and transmission gratings, which, however, are of no further interest in the context of the current invention. The basic structure of the gratings is very similar, which is more important at this point.

Nevertheless, there are different designs and structures such as surface relief (SR) or volume phase holographic (VPH) gratings to achieve waveguide. Both types are very similar in appearance. In the simplest case, the gratings are somehow mounted onto the surface of a waveguiding material, here the lens. The grating itself is composed of an array of fine structures, mostly trenches of a first material type Material 01 with a refractive index RI 01, however, not limited thereto. The geometrical shape of the trenches may be manifold, from rectangular, over V-shaped trenches, U-shaped and there like. The width, including structures with different widths, the geometrical form of the trenches, their pitch as well as their depth, including different depths, are specially designed to influence the diffraction pattern of the incident light to be diffracted.

In case of VPH gratings, the trenches or structures of a first material type (Material 01) having a refractive index (RI 01) are filled by a second material type (Material 02) having a refractive index (RI 02), wherein RI 02 is incrementally different from RI 01 (see FIGS. 1 and 3). For the sake of completeness, it should be mentioned that Material 01 or Material 02 may be composed of a stack of structured layers, each containing a different material composition with different refractive index, stacked on top of each other, thereby forming Material 01 or Material 02 having an effective or graded refractive index RI 01 or RI 02, respectively. Incidentally, the (effective or graded) refractive indices RI 01 and RI 02 depend on the refractive index of the waveguide or the lens from which the glasses are made of. If a glass lens with high refractive index (n03>1.46) is used, the (effective or graded) refractive indices of Material 01 and Material 02 are considered to be higher than that of the lens itself, whereby a RI value of 2.0 can be reached and exceeded. Surface relief (SR) gratings may look similar and may also include a second type of material as a filler for the trenches, but the trenches can also be just air. High performance gratings, especially those of VPH-type, may be manufactured using standard lithography and deposition techniques known from micro-fabrication such as, for example, the manufacturing of integrated circuits.

Such standard techniques typically include physical vapor deposition (PVD) or chemical vapor deposition (CVD) processes and often suffer from incomplete gap filling due to unfavourable deposition and/or layer growth deposition properties including increased deposition and/or growth rates at corners and edges. Such incomplete gap filling results in the formation of voids within the structures to be filled by the PVD- and CVD-materials. In addition to the formation of voids, the surface of the substrate is covered by a PVD and/or CVD layer that is almost as thick as the maximum depth of the deepest structure to be filled by the deposited gap filling material (see FIGS. 4 and 5). In some applications, however, it may be necessary to expose the surface of the substrate so that it is available for further processing. As a consequence, undesired overburden layers from PVD or CVD need to be removed, for example by chemical mechanical planarization (CMP) without harming the original substrate surface underneath. Although CMP is very well established in the process of manufacturing integrated circuits, CMP is a time consuming and costly process and can be seen as a potential economic drawback for mass production of leading-edge optical devices, particularly the mass production of diffractive gratings. It would therefore be desirable to have a solution for an advanced and cost-efficient manufacturing of optical gratings where gap filling does not require CMP (see FIG. 6).

The present invention addresses various disadvantages of the technologies for preparing optical gratings for leading edge optical devices as described above. The focus here is on improved optical properties, improved mechanical properties, improved coating properties and improved filling properties. Furthermore, are of interest.

OBJECT OF THE INVENTION

It is an object of the present invention to provide a method for preparing optical metal oxide layers, wherein said metal oxide layers are particularly suitable for optical applications and may be used in optical devices such as, for example, in diffractive gratings for AR and/or VR devices. The obtained optical metal oxide layers show (a) favorable optical properties such as high refractive index (RI) of >1.7, preferably >2.0, at wavelengths of ≤520 nm, low absorption, and low degree of haze formation; (b) favorable mechanical properties such as low shrinkage, (c) favorable coating properties such as dense layer and flat surface structure; and (d) favorable filling properties such as homogeneous filling of topographical features on patterned substrates.

Moreover, it is an object of the present invention to provide a method providing an easy and cost-efficient preparation of optical metal oxide layers.

It is a further object of the present invention that said method allows the preparation of optical metal oxide layers on the surface of both patterned or non-patterned substrates. The metal oxide layers may form various structures such as, for example, layers covering a surface of a non-patterned substrate and/or fillings covering topographical features such as, for example, gaps on the surface of a patterned substrate, thereby providing highly refractive optical structures.

Hence, it is an object of the present invention to provide a method for preparing optical metal oxide layers, wherein said method allows the preparation of advanced optical gap filling with low overburden, thus enabling an easy and cost-efficient mass production of complex optical devices. It is a further object of the present invention to provide a method for preparing optical metal oxide layers which avoids typical problems occurring when layer deposition or gap filling is performed by PVD or CVD techniques such as, for example, incomplete or excessive gap filling due to unfavourable deposition and layer growth characteristics such as, for example, decreased or increased deposition or growth rates at corners and edges.

It is a further object of the present invention to provide a formulation for preparing optical metal oxide layers, wherein said formulation allows improved wetting characteristics and allows the preparation of optical metal oxide layers on patterned or non-patterned substrates showing the above mentioned beneficial effects, namely (a) favorable optical properties such as high refractive index (RI) of >1.7, preferably >2.0, at wavelengths of ≤520 nm, low absorption and low degree of haze formation; (b) favorable mechanical properties such as low shrinkage, (c) favorable coating properties such as dense layer and flat surface structure; and (d) favorable filling properties such as homogeneous filling of topographical features on patterned substrates.

Moreover, it is an object of the present invention to provide a formulation for preparing optical metal oxide layers, wherein said formulation allows the preparation of advanced optical gap filling with low overburden, thus enabling easy and cost-efficient mass production of complex optical devices.

Thus, it is an object of the present invention that the formulation is particularly suitable for the preparation of optical metal oxide layers having high refractive index for optical devices such as, for example, for diffractive gratings in AR and/or VR devices.

Finally, it is an object of the present invention to provide an optical device, preferably an AR and/or VR device, comprising an optical metal oxide layer, which is obtainable by the method according to the present invention or which is prepared by using the formulation according to the present invention, and thereby shows the above-mentioned beneficial effects.

SUMMARY OF THE INVENTION

The present inventors surprisingly found that the above objects are achieved by a method for preparing an optical metal oxide layer comprising the following steps:

• • (a) providing a formulation comprising one or more titanium polyoxometalates (POMs) and one or more formulation media;
  • (b) applying the formulation to a surface of a substrate; and
  • (c) converting the formulation on the surface of the substrate to an optical metal oxide layer.

The present invention further provides a formulation for preparing an optical metal oxide layer, wherein said formulation comprises:

• • (i) one or more titanium polyoxometalates (POMs):
  • (ii) one or more formulation media; and
  • (iii) one or more additives selected from surfactants, wetting and dispersion agents, adhesion promoters, and polymer matrices.

Finally, an optical device is provided comprising an optical metal oxide layer, which is obtainable or obtained by the method according to the present invention or which is prepared by using the formulation according to the present invention.

Preferred embodiments of the present invention are described hereinafter and in the dependent claims.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1: Schematic cross-sectional view of a VPH grating with a Material 01 and a Material 02, wherein the refractive index IR 01 of Material 01 is incrementally different to the refractive index IR 02 of Material 02.

FIG. 2: Schematic cross-sectional view of a VPH grating enabling light diffraction (transmissive case) including propagation of diffracted light within waveguide (e.g. lens) by total internal reflection.

FIG. 3: Schematic cross-sectional view of a VPH grating providing gaps (trenches) to be filled with a high refractive index material (Material 02), wherein the refractive index of Material 02 is incrementally different form the refractive index of Material 01 flanking the gaps (trenches).

FIG. 4: Schematic representation of PVD- or CVD-mediated gap filling process and removal of undesired overburden.

FIG. 5: Schematic representation of PVD- or CVD-mediated gap filling process creating and leaving voids within gaps and deposited layers.

FIG. 6: Schematic representation of gap filling process using formulations containing inventive metal complex or formulations thereof being converted to metal oxides.

FIG. 7: Schematic representation of a metal oxo cluster comprising a core (sphere) and a ligand sphere surrounding the core.

FIG. 8: Absorbance at 460 nm of Ti₄₄ polyoxometalate films prepared in Example 2.

FIG. 9: Refractive index at 520 nm of Ti₄₄ polyoxometalate films prepared in Example 2.

FIG. 10: Layer thickness of Ti₄₄ polyoxometalate films prepared in Example 2 as function of spin coating speed at various hard baking temperatures (average layer shrinkage: 52%).

FIG. 11: Surface feature fill characteristics of Ti₄₄ polyoxometalate formulation applied in Example 3; spin coated 2.5% solution in PGME (w/w), pre-baking at 100° C. for 1 min and baking at 400° C. for 10 min.

FIG. 12: Surface feature fill characteristics of Ti₄₄ polyoxometalate formulation applied in Example 4; spin coated 2.5% solution in PGME (w/w), pre-baking at 100° C. for 1 min and baking at 400° C. for 10 min each, a 2^nd and 3^rd layer were deposited on top of the first one from the same formulation with the same deposition and post-treatment parameters.

FIG. 13: Surface feature fill characteristics of Ti₄₄ polyoxometalate formulation applied in Example 5; drop casted 5% solution in PGME (w/w)+0.5% (w/w) BYK-307 (siloxane-based surfactant), pre-baking at 100° C. for 1 min and baking at 300° C. for 10 min.

FIG. 14: Absorbance at 460 nm of Ti₁₈ polyoxometalate films prepared in Example 7.

FIG. 15: Refractive index at 520 nm of Ti₁₈ polyoxometalate films prepared in Example 7.

FIG. 16: Layer thickness of Ti₁₈ polyoxometalate films prepared in Example 6 as function of spin coating speed at various hard baking temperatures (average layer shrinkage: ca. 50%).

FIG. 17: Filling properties of spin coated Ti₁₈ polyoxometalate, 25% in PGME (w/w) after pre-baking at 60° C. for 60 min and baking at 400° C. for 5 min prepared in Example 8. The substrate was cleaned (IPA+ultrasonication) before the deposition steps.

FIG. 18: Filling properties of spin coated Ti₁₈ polyoxometalate, 25% in PGME (w/w) after pre-baking at 60° C. for 60 min and baking at 400° C. for 5 min prepared in Example 8. The substrate was cleaned (IPA+ultrasonication) and O₂ plasma treated before the deposition steps.

FIG. 19: IR spectrum of Ti₁₂ polyoxometalate prepared in Example 9.

FIG. 20: Absorbance at 460 nm of Ti₁₂ polyoxometalate films prepared in Example 10.

FIG. 21: Refractive index at 520 nm of Ti₁₂ polyoxometalate films prepared in Example 10.

FIG. 22: Layer thickness of Ti₁₂ polyoxometalate films prepared in Example 10 as function of spin coating speed at various hard baking temperatures (average layer shrinkage: ca. 70%).

FIG. 23: Filling properties of spin coated Ti₁₂ polyoxometalate from a 10% (w/w) solution in PGME after pre-baking at 60° C. for 60 min and baking at 400° C. for 5 min prepared in Example 11.

DETAILED DESCRIPTION

Definitions

The term “polyoxometalate” or “POM” as used herein, refers to a polyatomic ion, usually an anion, that consists of three or more transition metal oxyanions linked together by shared oxygen atoms to form closed 3-dimensional frameworks. The metal atoms are usually group 6 (Mo, W) or less commonly group 5 (V, Nb, Ta) or group 4 (Ti, Zr, Hf) transition metals in their high oxidation states. They are usually colorless or orange, diamagnetic anions. Two broad families are recognized, isopolymetalates, composed of only one kind of metal and oxide, and heteropolymetalates, composed of one metal, oxide and a main group oxyanion (e.g. phosphate, silicate, etc.). Beyond that, polyoxometalates may also contain further ligands. To balance the charge, polyoxometalate compounds may comprise one or more different cations (e.g. alkali metal cations, alkaline earth metal cations, ammonium cations, etc.).

Titanium polyoxometalates are a well-known material class for various applications, ranging from biology to nanotechnology. Numerous scientific publications of titanium polyoxometalates are known from literature a selection of which is cited in the following:

• (1) D. E. Katsoulis, A Survey of Application of Polyoxometalates, Chem. Rev. 1998, 98, 359-387.
• (2) D.-L. Long, E. Burkholder, L. Cronin, Polyoxometalate clusters, nanostructures and materials: From self-assembly to designer materials and devices, Chem. Soc. Rev., 2007, 36, 105-121.
• (3) P. Coppens, Y. Chen, E. Trzop, Crystallography and Properties of Polyoxotitanate Nanoclusters, Chem. Rev. 2014, 114, 9645-9661.
• (4) W.-H. Fang, L. Zhang, J. Zhang, A 3.6 nm Ti₅₂-Oxo Nanocluster with Precise Atomic Structure, J. Am. Chem. Soc. 2016, 138, 7480-7483.
• (5) M.-Y. Gao, F. Wang, Z.-G. Gu, D.-X. Zhang, L. Zhang, J. Zhang, Fullerene-like Polyoxotitanium Cage with High Solution Stability, J. Am. Chem. Soc. 2016, 138, 2556-2559.
• (6) S. Chen, W.-H. Fang, L. Zhang, J. Zhang, Synthesis, Structures, and Photocurrent Response of Polyoxo-Titanium Clusters with Oxime Ligands: From Ti₄ to Ti₁₈, Inorg. Chem. 2018, 57, 8850-8856.
• (7) W.-H. Fang, L. Zhang, J. Zhang, Synthetic strategies, diverse structures and tunable properties of polyoxo-titanium clusters, Chem. Soc. Rev., 2018, 47, 404-421.
• (8) M.-Y. Gao, L. Zhang, J. Zhang, Acid-Controlled Synthesis of Carboxylate-Stabilized Ti₄₄-Oxo Clusters: Scaling up Preparation, Exchangeable Protecting Ligands, and Photophysical Properties, Chem. Eur. J. 2019, 25, 10450-10455.

The term “ligand” as used herein, refers to ionic or neutral molecules (having one or more functional groups) that bind to a central metal atom or ion to form a metal complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electron pairs often through Lewis bases. The nature of metal-ligand bonding can range from covalent to ionic. Furthermore, the metal-ligand bond order can range from one to three. Ligands are typically regarded as Lewis bases, although rare cases are known to involve Lewis acids ligands. Ligands are classified as L or X (or a combination thereof), depending on how many electrons they provide for the bond between ligand and central atom. L ligands provide two electrons from a lone electron pair, resulting in a coordinate covalent bond. X ligands provide one electron, with the central atom providing the other electron, thus forming a regular covalent bond.

In the context of the present invention, the term “formulation medium” as used herein, denotes a compound that serves as a solvent, suspending agent, carrier and/or matrix for the titanium polyoxometalates (POMs) and any other component included in the formulation. Formulation media are generally inert compounds that do not react with said titanium polyoxometalates (POMs) and said other components. Formulation media may be liquid or solid compounds. Typically, formulation media are organic compounds.

The term “surfactant” as used herein, refers to an additive that reduces the surface tension of a given formulation.

The term “wetting and dispersion agent” as used herein, refers to an additive that increases the spreading and penetrating properties of a given formulation. In this way, the tendency of the molecules to adhere to each other is reduced.

The term “adhesion promoter” as used herein, refers to an additive that increases the adhesion of a given formulation.

The term “polymer matrix” as used herein, refers to an additive that acts as a macromolecular matrix for one or more components of a given formulation.

The term “monomer for polymer matrix” as used herein, refers to an additive that is able to form a polymer matrix.

The term “coordinating surfactant” a used herein, refers to an additive that coordinates metal ions and acts as a surfactant.

The term “viscosity enhancer” as used herein, refers to an additive that increases the viscosity of a given formulation.

The term “optical device” as used herein, relates to a device containing one or more optical components for forming a light beam including, but not limited to, gratings, lenses, prisms, mirrors, optical windows, filters, polarizing optics, UV and IR optics, and optical coatings. Preferred optical devices in the context of the present invention are augmented reality (AR) glasses and/or virtual reality (VR) glasses.

PREFERRED EMBODIMENTS

Method for Preparing Optical Metal Oxide Layer

The present invention relates to a method for preparing an optical metal oxide layer comprising the following steps:

• • (a) providing a formulation comprising one or more titanium polyoxometalates (POMs) and one or more formulation media;
  • (b) applying the formulation to a surface of a substrate; and
  • (c) converting the formulation on the surface of the substrate to an optical metal oxide layer.

In a preferred embodiment of the method for preparing an optical metal oxide layer according to the present invention, the one or more titanium polyoxometalates comprise independently from each other three or more, preferably four or more, titanium atoms and one or more, preferably two or more, ligand species, preferably organic ligand species.

The titanium polyoxometalates (POMs) used in the present invention are cluster materials, which in literature are also referred to as polyoxotitanate nanoclusters or titanium oxo-clusters. Basically, the clusters can be considered as being composed of two parts or spheres such as a core (sphere) and a ligand sphere which surrounds the core as illustrated in FIG. 7.

The core itself can be composed of several metal centers (high degree of nuclearity), which are bridged and/or connected by oxygen-containing species forming a small three-dimensional network. The metal centers in the core may have various oxidation states, typically they are positively charged metal cations. Typical oxygen-containing species which bridge and/or connect metal centers in the core are hydroxo ions (OH⁻) and oxido ions (O²⁻).

With respect to name conventions in coordination chemistry, such oxygen containing species which bridge and/or connect metal centers in the core can also be called ligands, and since these ligands are bridging two or more metal centers, hydroxo- and oxido-ligands are furthermore sub-categorized to pi-ligands, where the index “i” stands for the number of metal centers being bridged and connected by this type of ligand. Consequently, i=2 refers to a ligand bridging two metal centers, i=3 refers to a ligand bridging three metal centers and i=4 stands for a ligand bridging four metal centers. At the same time, the index “i” also denotes, how much coordination sites of a metal center or of the total number of all coordination sites of all metal ions within a cluster core are occupied by these types of ligands. As a simplified example, it is known that titanium often forms octahedrally coordinated complexes. Thus, there are six coordination sites around a titanium ion as central ion. Assuming that a titanium cluster is composed of two titanium centers, there are 12 coordination sites available in the complex, two of which can be occupied by a μ₂-hydroxo (μ₂-OH) species, which bridges both metal centers and consequentially leaves over ten remaining coordination sites, which can be occupied by other ligands.

The second part of the cluster is the ligand sphere, which surrounds the cluster core and may contain a variety of different complexing coordinating species acting as ligands. Typically, such coordinating species in the ligand sphere are inorganic or organic species, preferably organic species. Such species acting as ligands may be unidentate, bidentate, tridentate ligands and so forth, and as such unidentate ligands can occupy one open coordination site at a metal center, whereas ligands of higher denticity may occupy two, three and more coordination sites at a metal center as long as other restrictions, such as steric requirements, are met.

The ligands of the ligand sphere stabilize and shield the cluster core from external influences, such as e.g. solvents and other chemicals. Sometimes, the ligands in the ligand sphere are labile, which means that they can be easily exchanged by other ligands or even solvent molecules when dissolving the clusters in a different solvent. The ligands in the ligand sphere cap and seal open coordination sites on the metal centers that are not an integral part of the metal oxo cluster core's backbone or network.

In a preferred embodiment of the present invention, the titanium polyoxometalates (POMs) are independently from each other represented by the following Formula (1):

$\begin{array}{cc}\left\{{{\mathrm{Ti}}_u\left({\mu }_2-\mathrm{OH}\right)}_v{\left({\mu }_3-\mathrm{OH}\right)}_w{\left({\mu }_2-O\right)}_x{\left({\mu }_3-O\right)}_y{\left({\mu }_4-O\right)}_z\right\}\prod _{j=1}^{j=n}{\left(L^j\right)}_{a_j}& \mathrm{Formula}\left(1\right)\end{array}$

wherein:

• • μ₂-OH represents a bidentate bridging hydroxo (OH⁻);
  • μ₃-OH represents a tridentate bridging hydroxo (OH⁻);
  • μ₂-O represents a bidentate bridging oxido (O²⁻);
  • μ₃-O represents a tridentate bridging oxido (O²⁻);
  • μ₄-O represents a tetradentate bridging oxido (O²⁻);
  • L^j represents at each occurrence independently from each other a ligand species, preferably an organic ligand species;
  • a_j is at each occurrence independently from each other an integer from 1 to 100, preferably 1 to 70, more preferably 1 to 50;
  • n is an integer from 2 to 10, preferably 2 to 5, more preferably 2, 3 or 4;
  • u is an integer from 2 to 100, preferably 2 to 70, more preferably 3 to 50;
  • v is an integer from 0 to 100, preferably 0 to 70, more preferably 0 to 50;
  • w is an integer from 0 to 100, preferably 0 to 70, more preferably 0 to 50;
  • x is an integer from 0 to 100, preferably 0 to 70, more preferably 0 to 50;
  • y is an integer from 0 to 100, preferably 0 to 70, more preferably 0 to 50; and
  • z is an integer from 0 to 100, preferably 0 to 70, more preferably 0 to 50.

It is preferred that at least one of v, w, x, y and z is not 0. It is more preferred that at least two of v, w, x, y and z are not 0.

In a more preferred embodiment of the present invention, the titanium polyoxometalates (POMs) are independently from each other represented by Formula (1) as described above, wherein in addition the following equation is fulfilled:

$4^{*}u-\left[v+w+2^{*}\left(x+y+z\right)+\sum _{j=1}^{j=n}\left({m_j\left(L^j\right)}^{*}{a}_j\right)\right]=c$

wherein:

• • m_j(L^j) represents the amount of negative charge of L^j, preferably m_j(L^j) is at each occurrence independently from each other an integer selected from 0, 1, 2, 3, 4 and 5, more preferably 0, 1, 2 and 3, and most preferably 0, 1 and 2; and c represents the total charge of the titanium polyoxometalate (POM), preferably c is an integer from −10 to +10, more preferably from −5 to +5, and most preferably c=0; and a_j, n, u, v, w, x, y, and z are defined as shown above.

Preferably, the ligand species L^j is selected at each occurrence independently from each other from organic ligands or inorganic ligands. Preferred inorganic ligands are halides, phosphoric acid, sulfonic acid, nitric acid and water, which are optionally deprotonated. Preferred organic ligands are alcohols, carboxylic acids, cyanates, isocyanates, 1,3-diketones, beta-keto acids, beta-keto esters, organylphosphonic acids, organylsulfonic acids, oximes, hydroxamic acids, dihydroxy benzenes, hydroxybenzoic acids, dihydroxy benzoic acids, gallic acid, dihydroxynaphthalenes, anthracene diols, hydroxy-anthrones, anthracene triols, dithranols, halogenated hydrocarbons, aromatics, heteroaromatics, esters, catechols, coumarins and their derivatives, which are optionally deprotonated.

More preferably, the ligand species L^j is selected at each occurrence independently from each other from the list in Table 1:

TABLE 1
Ligand species Lj.
2-aminoisonicotinic acid (ANA);
(CH3)2CHCOO−;
(CH3)2CHCOOH;
1,10-phenanthroline (1,10-phn);
1-hydroxy benzotriazolate (1-HBTA);
1-naphthalenecarboxylic acid (1-NA);
1-naphthylacetic acid (NAA);
2,2′-bipyridine (2,2′-bpy);
2-amino-ethylphoshonate (AEP);
2-chloroisonicotinic acid (CIA);
2-methoxy-5-(pyridin-4-yl)-benzaldehyde (PYRALD);
2-naphthalenecarboxylic acid (2-NA);
3,5-di-tert-butylcatechol (H2DTBC);
343-coumarin;
3-methylglutaric acid (MGA);
4-aminobenzoic acid (ABZ);
4-aminophenylacetonate (APA);
4-dimethylamino trans-cinnamic acid (DMACA);
4-phenylpyridine (4-PHPY);
4-picoline (PICO);
4-tert-butylbenzoate (4-TBBZ);
9-anthracenecarboxylate (9-AC);
acetoxime;
acetylacetonate (acac);
AcO− (CH3COO−);
AcOH (CH3COOH);
adenine (ADN);
aminopyrazine (APZ);
benzene dicarboxylate (BDC);
benzoic acid (BA);
biphenyl-2-carboxylate (2-BPYC);
Br−;
bromoacetic acid (BRA);
BuCH2COO−;
BuCH2COOH;
C2H5COO−;
C2H5COOH;
C6H6;
catechol (CAT);
CH2Cl2;
CH3CN;
CHCl3;
chlorosalicylate (SAL-Cl);
Cl−;
Cl3CCH2O−;
Cl3CCH2OH;
C-propylpyrogallol[4]arene (PgC3);
cyclohex-3-ene-1-carboxylate (Cec);
diethylenetriamine;
dimethyl sulfoxide (DMSO);
dimethylamino benzoic acid (DMABA);
dimethylthio-TTF dicarboxylate (DTTF);
Et(Me)2CCOO−;
Et(Me)2CCOOH;
EtCOOtBu;
EtO−;
EtOH;
F−;
fluorenyl (Fl);
formic acid (HFA);
formiate (FA)
glutaric acid (GA);
H2O (water);
H2SO4 (sulfonic acid);
HBr (hydrobromic acid);
HCl (hydrochloric acid);
HF (hydrofluoric acid);
HI (hydroiodic acid);
HNO3 (nitric acid);
HOMc (methacrylic acid);
HON═C5H8 (cyclopentanone oxime);
HON═CMe═CH2═CMe═NOH (2,4-pentanedione dioxime);
HOOCC5H3NCOOiPr;
I−;
iBuO−;
iBuOH;
imidazolate (Im);
iminodiacetate (IDA);
iPrO−;
iPrOH;
isonicotinic acid (INA);
MeC(CH2OH)3 (1,1,1-tris(hydroxymethyl)-ethane);
MeC6H5 (toluene);
MeCl2;
MeCOOtBu;
MeO−;
MeOH;
nBuCOO−;
nBuCOOH;
nBuO−;
nBuOH;
nitrophenyl acetylacetonate (NPA);
N-methyldiethoxoamine (MDEA);
NO3−(nitrate);
nPrO−;
nPrOH;
O2P(OiPr)allyl2;
O3P-allyl (allyl phosphonate);
O3P-Bu (butyl phosphonate);
O3PCH2CH═CH2;
O3PCH2CH2CH2Br (3-bromopropyl phosphonate);
O3PCH2CH2CH2Cl (3-chloropropyl phosphonate);
O3P-Et (ethyl phosphonate);
O3P-Ph (phenyl phosphonate);
O3P-tBu (t-butyl phosphonate);
O3P-xylyl (xylyl phosphonate);
OMc (methacrylate);
ON═C6H10;
ON═CMe2;
ON═CMe—CH2—CMe═NO;
−OOCC5H3NCOOiPr;
ortho-benzene dicarboxylate (o-BDC);
PhCN;
PhCOO− (benzoate);
PhCOOH (benzoic acid);
PhO− (phenolate);
PhOH (phenol);
PhPO3H2 (phenylphosphonic acid);
piperazine (PIP) (C4N2H10);
pivalic acid (PIV);
propionate (PA);
propionic acid (HPA);
pyridine (Py);
salicylaldoxime;
salicylhydroxamic acid;
saliycylate (SAL);
SO42− (sulfate);
tBuCH2COO−;
tBuCH2COOH;
tBuCH2O−;
tBuCH2OH;
tBuO−;
tBuOH;
tetrabutylammonium bromide (TBAB);
tetrabutylammonium chloride (TBAC);
tetraethylammonium chloride (TEAC);
trans-cinnamic acid (CA); and
triiodide (I3−).

It goes without saying that the abovementioned ligand species L^j can each be present in their protonated or unprotonated form in the titanium polyoxomometalate (POM), even if only one form is shown in each case.

The titanium polyoxometalates (POMs) may comprise one or more alkaline metals selected from Li, Na, K, Rb and Cs. The titanium polyoxometalates (POMs) may comprise one or more alkaline earth metals selected from Be, Mg, Ca, Sr, and Ba. The titanium polyoxometalates (POMs) may comprise one or more alkaline metals selected from Li, Na, K, Rb and Cs; and one or more alkaline earth metals selected from Be, Mg, Ca, Sr, and Ba.

In a preferred embodiment of the present invention, the titanium polyoxometalates (POMs) are independently from each other selected from the list in Table 2:

TABLE 2
Preferred titanium polyoxometalates (POMs),
(C4N2H12)8[TiO(SO4)2]8•23H2O;
(C4N3H16)5(H3O)[TiO(SO4)2]8•15H2O;
[Ti22(μ-O)11(μ3-O)20(μ1-OiPr)16(μ2-OiPr)2(PIV)9(I)(OH2)H3](I3)•HOiPr;
[Ti10O12(CAT)8(Py)8];
[Ti18O27(OH2)30(SO4)6]Cl6•6TBAC•12H2O;
[Ti25O26(OEt)36(O3P-Ph)6];
[Ti26O26(OEt)39(O3P-Ph)6]Br;
[Ti26O26(OEt)39(PhPO3)6]Br;
[Ti28(μ4-O)4(μ3-O)20(μ2-O)24(PhO)14(1,10-phn)14]Cl2•6PhOH;
[Ti4(μ3-O)(μ2-O)(μ2-OiPr)2(OiPr)4(O3P-Ph)3(1,10-phn)](HOiPr);
[Ti4(μ3-O)(μ2-OiPr)3(OiPr)5(O3P-Bu)3(DMSO)];
[Ti4(μ3-O)(μ2-OiPr)3(OiPr)5(O3P-Ph)3(Im)];
[Ti4(μ3-O)(O3P-Ph)3(OiPr)8]2(ADN);
[Ti4(μ3-O)(O3P-Ph)3(OiPr)8]2(APZ);
[Ti4(μ3-O)(O3P-Ph)3(OiPr)8]2(PIP)•2HOiPr;
[Ti4(μ3-O)(O3P-Ph)3(OiPr)8]2[Ti6(μ3-O)2(μ2-O)2(O3P-Ph)2 (OiPr)10](ANA)2;
[Ti4O(OEt)12(O3P-Ph)];
[Ti4O4(OH2)8(SO4)4]•2TEAC•H2SO4•10H2O;
[Ti4O4(OtBu)4(OOCC(Me)2Et)4];
[Ti4O4(OtBu)4(OOCC(Me)2Et)4]•0.5toluene;
[Ti5(μ3-O)(μ2-OiPr)4(OiPr)7(OAc)(O3PCH2CH2CH2Br)3];
[Ti5(μ3-O)2(μ2-O)(μ2-OiPr)2(OiPr)4(OAc)4(O3P-xylyl)2];
[Ti5O(OiPr)11(OMc)(O3PEt)3];
[Ti6(μ2-O)6(O3P-Ph)2(PhO)6(1,10-phn)6]Cl2•5PhOH;
[Ti6(μ2-O)6(O3P-Ph)2(PhO)6(2,2′-bpy)6]Cl2•2PhOH;
[Ti6(μ3-O)2(μ2-O)2(μ2-OiPr)4(OiPr)6(OAc)2(O3PEt)2];
[Ti6(μ3-O)2(μ2-O)2(O3P-Ph)2(OiPr)10(1-HBTA)2];
[Ti6(μ3-O)2(O3P-Ph)4(PhO)6(OiPr)6];
[Ti6(μ3-O)6(OiPr)6(μ-OOCC5H3NCOOiPr)6];
[Ti6(μ3-O)6(OiPr)6(1-NA)6];
[Ti6(μ3-O)6(OiPr)6(NAA)6];
[Ti6O3(DTTF)2(OiPr)14];
[Ti6O4(O3P-Ph)2(OiPr)10(CIA)2];
[Ti6O4(OiPr)10 (O3P-Ph)2(BRA)2];
[Ti6O4(OiPr)10(O3P-Ph)2(PIV)2];
[Ti6O4(OiPr)6(CAT)4(9-AC)2];
[Ti6O6(2-BPYC)10(OiPr)2];
[Ti6O6(2-BPYC)6(OiPr)6];
[Ti6O6(4-TBBZ)10(OiPr)2];
[Ti6O6(4-TBBZ)6(OiPr)6];
[Ti6O6(ABZ)6(OiPr)6](iPrOH)5;
[Ti6O6(OiBu)6(OOCC(Me)2Et)6];
[Ti6O6(OiPr)6(9-AC)6];
[Ti6O6(OtBu)6(OOCC(Me)2Et)6]•C6H5Me;
[Ti6O6(OtBu)6(OOCCH2tBu)6]•C6H5Me;
[Ti6O8(OH2)20]Br8•6TBAB•4H2O;
[Ti6O8(OH2)20]Cl8•6TBAC•4H2O;
[Ti7(μ3-O)2(μ2-OiPr)6(OiPr)6(O3PCH2CH2CH2Cl)6];
[Ti7O9(OiBu)4(HOiBu)(OOCCMe2Et)6]2;
[Ti8(μ2-O)8(μ2-OMc)16];
[Ti8(μ3-O)2(μ2-O)2(O3P-Ph)2(OiPr)16(ADN)2(NO3)2];
[Ti8(μ3-O)2(μ2-OiPr)6(OiPr)8(O3P-allyl)6O2P(OiPr)allyl2];
[Ti8O10(ABZ)12](PhCN)3.6;
[Ti8O10(OOCCH(CH3)2)12];
[Ti8O12(H2O)24]Cl8•HCl•7H2O;
[Ti8O12(OH2)24]I8•0.5HI;
[Ti8O8(OOCCH2Bu)16];
{Ti44(μ2-OH)4(μ2-O)32(μ3-O)30(HPA)2(PA)44(MGA)2(H2O)4}•2HPA;
{Ti44(μ2-OH)4(μ2-O)32(μ3-O)30(HPA)2(PA)46(HFA)2(FA)2(H2O)2}•4HPA;
{Ti44(μ2-OH)4(μ2-O)32(μ3-O)30(HPA)4(PA)44(GA)2(H2O)2}•5HPA;
Cs2[Ti3(μ2-O)3(OH2)4Cl8]•4CsCl;
Cs2[Ti4(μ2-O)4(OH2)6Cl2(SO4)4]•4CsCl•HCl;
H[Ti5(μ2-O)(μ3-O)2(OMe)3(L1)6];
H2[Ti18(μ2-O)11(μ3-O)14(Cec)20(OiPr)4];
H2[Ti18(μ3-O)14(μ2-O)6(O3P-Ph)2(PA)16(OiPr)14];
K7H[Ti6O9(IDA)6]Cl2•13H2O;
Ti10(μ2-OiPr)2(OiPr)14(OMc)4(O3PCH2CH═CH2)10;
Ti10O12(CAT)8(4-PHPY)8;
Ti10O12(CAT)8(PICO)8;
Ti10O12(CAT)8(PYRALD)8;
Ti10O2(EtO)32(AEP)2;
Ti11(μ2-O)5(μ3-O)8(PA)14(OtBu)4;
Ti11O13(OEt)5(OiPr)13•EtOH;
Ti11O13(OiPr)18;
Ti12(μ2-O)4(μ3-O)4(OEt)20(L2)4;
Ti12O12(OAc)6(OnPr)18;
Ti12O16(OCH2tBu)16;
Ti12O16(OEt)4(OtBu)12•2tBuOH;
Ti12O16(OEt)6(OiPr)10;
Ti12O16(OiPr)16;
Ti12O16(OiPr)16•1.4MeCl2;
Ti12O4(PgC3)(OiPr)28;
Ti13O10(o-BDC)4(SAL)4(OiPr)16;
Ti13O10(o-BDC)4(SAL-Cl)4(OiPr)16;
Ti14O14(OEt)22(O3P-Ph)3;
Ti14O14(OEt)22(PhPO3)3;
Ti14O18(OiBu)8(HOiBu)2(OOCCMe2Et)12;
Ti14O20(OAc)4(OtBu)13(H)•MeCOOtBu;
Ti15O14(OEt)32;
Ti16(μ2-OH)2(μ2-O)10(μ3-O)10(PA)20(OtBu)2;
Ti16O16(OEt)24(OnPr)8•2MeC6H5;
Ti16O16(OEt)26(OCH2CC13)6;
Ti16O16(OEt)28(OnPr)4•2MeC6H5;
Ti16O16(OEt)32;
Ti17(μ2-O)2(μ3-O)18(μ4-O)2(PA)8(OiPr)16;
Ti17O24(OiPr)16(acac)4;
Ti17O24(OiPr)16(APA)4•MeCl2;
Ti17O24(OiPr)16(BA)4;
Ti17O24(OiPr)16(CAT)4•2C6H6;
Ti17O24(OiPr)16(DMABA)4•disordered solvent;
Ti17O24(OiPr)16(DMACA)4•2CH3CN;
Ti17O24(OiPr)16(INA)4;
Ti17O24(OiPr)16(NPA)4•7C6H6;
Ti17O24(OiPr)18(343-coumarin)2•3iPrOH;
Ti17O24(OiPr)18(CA)2;
Ti17O24(OiPr)20;
Ti17O24(OiPr)20;
Ti17O24(OiPr)20(Py)•C6H6;
Ti17O24(OiPr)20(Py)•C6H6;
Ti17O24(OiPr16)DMACA42CH3CN;
Ti18(μ2-OH)2(μ2-O)8(μ3-O)14(PIV)14(OtBu)6(OnBu)6;
Ti18(μ2-O)10(μ3-O)8(μ4-O)2(OEt)30(L3)2;
Ti18O22(OnBu)26(acac)2;
Ti18O25(C2H5COO)10(tBuO)12•tBuOH•EtCOOtBu;
Ti18O25(OtBu)12(C2H5COO)10-tBuOH•EtCOOtBu;
Ti18O25(OtBu)12(OAc)10•4tBuOH;
Ti18O28(OtBu)17(H);
Ti18O28(OtBu)17(H)•tBuOH;
Ti2(OiPr)6(ON═C6H10)2;
Ti25O26(OEt)36(PhPO3)6;
Ti28O34(OEt)44;
Ti28O40(OtBu)20(OAc)12•MeC6H5;
Ti34O50(OiPr)30(DMABA)6•12C6H6;
Ti34O50(OiPr)30DMABA6•12C6H6;
Ti34O50(OiPr)36•MeC6H5;
Ti4(μ2-O)(μ4-O)(2-NA)2(OiPr)10;
Ti4(μ2-O)(μ4-O)(BA)2(OiPr)10;
Ti4(μ3-O)4(PA)4(OtBu)4;
Ti4(OiPr)8(ON═CMe—CH2—CMe═NO)4;
Ti4(μ4-O)(OMe)6(L1)4;
Ti4O(EtO)12(tBuPO3);
Ti4O2(OiPr)8(ON═CMe═CH2═CMe═NO)2;
Ti4O2(OiPr)8(ON═CMe—CH2—CMe═NO)2;
Ti52(μ-OH)2(μ-O)14(μ3-O)50(μ4-O)8(PA)34(OiPr)28;
Ti6(μ2-O)2(μ3-O)2(Cec)4(OiPr)12;
Ti6(μ2-OH)2(μ3-O)2(SO4)4(OiPr)10;
Ti6(μ3-O)2(μ2-O)2(μ2-OiPr)2(μ2-OMc)8(OiPr)6;
Ti6(μ3-O)4(BDC)2(PA)2(OiPr)10;
Ti6(μ3-O)6(Cec)6(OiPr)6;
Ti6(μ3-O)6(nBuCOO)6(OiPr)6;
Ti6(μ3-O)6(PA)6(OtBu)6;
Ti6(μ2-O)(μ3-O)2(OiPr)10(OAc)2(L2)2;
Ti6O4(o-BDC)2(o-BDC-iPr)2(OiPr)10;
Ti6O4(OEt)4(OiPr)4(OOCC6H5)8;
Ti6O4(OiPr)10(OMc)2(O3PCH2CH2CH2Br)2;
Ti6O6(MDEA)6•2CH2Cl2;
Ti6O6(OBu)6(ON═C5H8)6;
Ti6O6(OiPr)6(L3)6;
Ti6O6(OiPr)6(ON═CMe2)6•2CH2Cl2;
Ti7(μ3-O)2(OEt)18(L2)2;
Ti9(μ2-O)2(μ3-O)8(μ4-O)2(CH3COO)4(OtBu)8; and
Ti9(μ3-O)2(μ2-O)6(OiPr)4(μ2-OMc)16;
wherein the following abbreviations apply:
C4N2H12 = protonated piperazine
C4N3H16 = protonated diethylenetriamine
(HON═CMe═CH2═CMe═NOH) = 2,4-pentanedione dioxime;
(ON═C5H8) = cyclopentanone oxime;
1,10-phn = 1,10-phenanthroline;
1-HBTA = 1-hydroxy benzotriazolate;
2-BPYC = biphenyl-2-carboxylate;
4-PHPY = 4-phenylpyridine;
4-TBBZ = 4-tert-butylbenzoate;
9-AC = 9-anthracenecarboxylate;
ABZ = 4-aminobenzoic acid;
acac = acetylacetonate;
ADN = adenine;
AEP = 2-amino-ethylphoshonate;
ANA = 2-aminoisonicotinic acid;
APA = 4-aminophenylacetonate;
APZ = aminopyrazine;
BA = benzoic acid;
BDC = benzene dicarboxylate;
BRA = bromoacetic acid;
CA = trans-cinnamic acid;
CAT = catechol;
Cec = cyclohex-3-ene-1-carboxylate;
CIA = 2-chloroisonicotinic acid;
DMABA = dimethylaminobenzoic acid;
DMACA = 4-dimethylamino trans-cinnamic acid;
DMSO = dimethyl sulfoxide;
DTTF = dimethylthio-TTF dicarboxylate;
HFA = formic acid;
FA = formiate
GA = glutaric acid;
H2DTBC = 3,5-di-tert-butylcatechol;
H2L1 = salicylaldoxime;
H3L2 = salicylhydroxamic acid;
HL3 = acetoxime;
HOMc = methacrylic acid;
IDA = iminodiacetate;
Im = imidazolate;
INA = isonicotinic acid;
MDEA = N-methyldiethoxoamine;
MeC(CH2OH)3 = 1,1,1-tris(hydroxymethyl)-ethane;
MGA = 3-methylglutaric acid;
1-NA = 1-naphthalenecarboxylic acid;
2-NA = 2-naphthalenecarboxylic acid;
NAA = 1-naphthylacetic acid;
NPA = nitrophenyl acetylacetonate;
O3P-Ph = phenyl phosphonate;
OAc = acetate;
OEt = ethoxide;
OiPr = isopropoxide;
PA = propionate;
PgC3 = C-propylpyrogallol[4]arene;
PhOH = phenol;
PhPO3H2 = phenylphosphonic acid;
PICO = 4-picoline;
PIP = piperazine;
PIV = pivalic acid;
Py = pyridine;
PYRALD = 2-methoxy-5-(pyridin-4-yl)-benzaldehyde;
SAL = salicylate; and
TEAC = tetraethylammonium chloride.

In a more preferred embodiment of the present invention, the titanium polyoxometalates (POMs) are independently from each other selected from Ti₁₂ polyoxometalates, Ti₁₆ polyoxometalates, Ti₁₈ polyoxometalates, Ti₄₄ polyoxometalates, and Ti₅₂ polyoxometalates.

In a most preferred embodiment of the present invention, the titanium polyoxometalates (POMs) are independently from each other selected from the list in Table 3:

TABLE 3
Most preferred titanium polyoxometalates (POMs),
[Ti18O27(OH2)30(SO4)6]Cl6•6TBAC•12H2O;
{Ti44(μ2-OH)4(μ2-O)32(μ3-O)30(HPA)2(PA)44(MGA)2(H2O)4}•2HPA;
{Ti44(μ2-OH)4(μ2-O)32(μ3-O)30(HPA)2(PA)46(HFA)2(FA)2(H2O)2}•4HPA;
{Ti44(μ2-OH)4(μ2-O)32(μ3-O)30(HPA)4(PA)44(GA)2(H2O)2}•5HPA;
H2[Ti18(μ2-O)11(μ3-O)14(Cec)20(OiPr)4];
H2[Ti18(3-O)14(μ2-O)6(O3P-Ph)2(PA)16(OiPr)14];
Ti12(μ2-O)4(μ3-O)4(OEt)20(L2)4;
Ti12O12(OAc)6(OnPr)18;
Ti12O16(OCH2tBu)16;
Ti12O16(OEt)4(OtBu)12•2tBuOH;
Ti12O16(OEt)6(OiPr)10;
Ti12O16(OiPr)16;
Ti12O16(OiPr)16•1.4MeCl2;
Ti12O4(PgC3)(OiPr)28;
Ti16(μ2-OH)2(μ2-O)10(μ3-O)10(PA)20(OtBu)2;
Ti16O16(OEt)24(OnPr)8•2MeC6H5;
Ti16O16(OEt)26(OCH2CCl3)6;
Ti16O16(OEt)28(OnPr)4•2MeC6H5;
Ti16O16(OEt)32;
Ti18(μ2-OH)2(μ2-O)8(μ3-O)14(PIV)14(OtBu)6(OnBu)6;
Ti18(μ2-O)10(μ3-O)8(μ4-O)2(OEt)30(L3)2;
Ti18O22(OnBu)26(acac)2;
Ti18O25(C2H5COO)10(tBuO)12•tBuOH•EtCOOtBu;
Ti18O25(OtBu)12(C2H5COO)10-tBuOH•EtCOOtBu;
Ti18O25(OtBu)12(OAc)10•4tBuOH;
Ti18O28(OtBu)17(H);
Ti18O28(OtBu)17(H)•tBuOH; and
Ti52(μ-OH)2(μ-O)14(μ3-O)50(μ4-O)8(PA)34(OiPr)28;
wherein the abbreviations of Table 2 apply.

In a very most preferred embodiment of the present invention, the titanium polyoxometalates (POMs) are independently from each other selected from the list Table 4:

TABLE 4
Very most preferred titanium polyoxometalates (POMs),
{Ti44(μ2-OH)4(μ2-O)32(μ3-O)30(HPA)2(PA)46(HFA)2(FA)2(H2O)2}•4HPA;
Ti12(μ2-O)4(μ3-O)4(OEt)20(L2)4;
Ti16(μ2-OH)2(μ2-O)10(μ3-O)10(PA)20(OtBu)2;
Ti18(μ2-OH)2(μ2-O)8(μ3-O)14(PIV)14(OtBu)6(OnBu)6;
Ti18(μ2-O)10(μ3-O)8(μ4-O)2(OEt)30(L3)2; and
Ti52(μ-OH)2(μ-O)14(μ3-O)50(μ4-O)8(PA)34(OiPr)28;
wherein the abbreviations of Table 2 apply.

Preferably, the mass ratio of titanium polyoxometalates (POMs) in the formulation is in the range from 0.1% to 50% (w/w), preferably 0.5% to 40% (w/w), more preferably 1% to 30% (w/w), based on the total mass of the formulation.

In a preferred embodiment of the present invention, the one or more formulation media are solution media and/or dispersion media. The formulation media are selected to improve applicability, wettability, deposition properties, filling properties and/or stability of the formulation. Any formulation media can be used as long as it dissolves or disperses the titanium polyoxometalates (POMs) comprised in the formulation provided in step (a) of the method for preparing an optical metal oxide layer according to the present invention.

In a more preferred embodiment of the present invention, the one or more formulation media are selected from water, amides, aromatic hydrocarbons, non-aromatic hydrocarbons, alcohols, carboxylic acids, esters, ethers, ketones, diketones, lactones, and mixtures thereof.

In a most preferred embodiment of the present invention, the one or more formulation media are selected from the list consisting of: diethylene glycol; diethylene glycol butyl ether acetate; diethylene glycol dibutyl ether; diethylene glycol diethyl ether; diethylene glycol divinyl ether; diethylene glycol hexyl ether; diethylene glycol methyl t-butyl ether; diethylene glycol monobutyl ether; diethylene glycol monoethyl ether; diethylene glycol monoethyl ether acetate; diethylene glycol monomethyl ether; diethylene glycol monopropyl ether; ethylene glycol; ethylene glycol butyl ether acetate; ethylene glycol butyl ethyl ether; ethylene glycol butyl methyl ether; ethylene glycol diacetate; ethylene glycol dibutyl ether; ethylene glycol diethyl ether; ethylene glycol dimethyl ether; ethylene glycol di-t-butyl ether; ethylene glycol methyl t-butyl ether; ethylene glycol mono 2-ethyl hexyl ether; ethylene glycol mono benzyl ether; ethylene glycol mono ethyl ether acrylate; ethylene glycol mono n-hexyl ether; ethylene glycol mono n-propyl ether; ethylene glycol mono t-butyl ether; ethylene glycol monobutyl ether; ethylene glycol monoethyl ether; ethylene glycol monoethyl ether acetate; ethylene glycol monoisobutyl ether; ethylene glycol monoisopropyl ether; ethylene glycol monomethyl ether; ethylene glycol monomethyl ether acetate; ethylene glycol sulfite; triethylene glycol; triethylene glycol monomethyl ether; triethylene glycol monooleyl ether; triethylene glycol dimethyl ether; tetraethylene glycol; tetraethylene glycol dimethyl ether; ethylene glycol diacrylate; pentaethylene glycol dimethyl ether; phenyl acetaldehyde ethylene glycol acetal; 2-phenyl propionaldehyde ethylene glycol acetal; cinnamaldehyde ethylene glycol acetal; citral ethylene glycol acetal; diethylene glycoldimethacrylate; dipropylene glycol; dipropylene glycol methyl ether; dipropylene glycol mono n-butyl ether; dipropylene glycol mono n-propyl ether; dipropylene glycol monomethyl ether acetate; propylene glycol; propylene glycol monobutyl ether; propylene glycol monoethyl ether; propylene glycol monoethyl ether acetate; propylene glycol monoisobutyl ether; propylene glycol monoisopropyl ether; propylene glycol monomethyl ether; propylene glycol monomethyl ether acetate; propylene glycol monophenyl ether; propylene glycol monopropyl ether; propylene glycol mono-t-butyl ether; tripropylene glycol monomethyl ether; dipropylene glycol; tripropylene glycol; tripropylene glycol monomethyl ether; dipropylene glycol monomethyl ether; propylene glycol 2-tert-butyl ether; dipropylene glycol t-butyl ether; dipropylene glycol monoethyl ether; tripropylene glycol monoethyl ether; propylene glycol stearate; propylene glycol diacetate; propylene glycol acetone ketal; propylene glycol stearate; hexanal propylene glycol acetal; benzaldehyde propylene glycol acetal; cinnamaldehyde propylene glycol acetal; furfural propylene glycol acetal; decanal propylene glycol acetal; propylene glycol dipropionate; citral propylene glycol acetal; isovaleraldehyde propylene glycol acetal; propylene glycol dibenzoate; propylene glycol monobutyrate; propylene glycol monohexanoate; propylene glycol dihexanoate; propylene glycol dibutyrate; isobutyraldehyde propylene glycol acetal; 6-methyl-5-hepten-2-one propylene glycol acetal; nonanal propylene glycol acetal; vanillin propylene glycol acetal; ethyl vanillin propylene glycol acetal; valeraldehyde propylene glycol acetal; octanal propylene glycol acetal; undecanal propylene glycol acetal; melon heptenal propylene glycol acetal; hydroxycitronellal propylene glycol acetal; (E)-2-hexen-1-al propylene glycol acetal; acetoin propylene glycol acetal; butyl lactate; ethyl lactate; methyl lactate; ethyl phenyl lactate; isobutyl lactate; propyl lactate; benzyl lactate; ethyl acetyl lactate; lauryl lactate; amyl lactate; butyl butyryl lactate; phenethyl lactate; sec-butyl lactate; isoamyl lactate; hexyl lactate; methyl laevo-lactate; butyl laevo-lactate; cetyl lactate; laevo-menthyl lactate; (Z)-3-hexen-1-yl lactate; ethyl butyryl lactate; menthyl methyl lactate; 1-menthyl lactate; diethyl malonate; diethyl diethylmalonate; dibenzyl malonate; dioctyl malonate; butyl ethyl malonate; γ-butyrolactone (GBL); caprolactone (epsilon); crotonlactone; β-propiolactone; δ-undecalactone; γ-nonalactone; α-angelica lactone; γ-valerolactone; δ-nonalactone; □-decalactone; □-dodecalactone; γ-undecalactone; octalactone; δ-dodecalactone; γ-heptalactone; dehydrocostus lactone; menthone lactone; γ-octadecalactone; β-angelica lactone; mesitene lactone; γ-hexalactone; δ-octalactone; δ-decalactone; γ-palmitolactone; δ-hexalactone; lilac lactone; 2-decen-1,4-lactone; δ-tetradecalactone; δ-heptalactone; epsilon-decalactone; dihydrojasmone lactone; δ-juniper lactone; δ-tridecalactone; mint lactone; dairy lactone; δ-2-dodecenolactone; epsilon-dodecalactone; α-decalactone; animal carbolactone; creamy lactone; jasmin lactone; whiskey lactone; massoia lactone; δ-decenolactone; wine lactone; γ-jasmolactone; (±)-3-methyl-γ-decalactone; costus valerolactone; waxy lactone; dehydromenthofurolactone; (±)-dihydromint lactone; tuberose lactone; wine lactone; spironolactone; cyclopropylmethylketone; dibutyl ketone; diethyl ketone; di-isobutyl ketone; dipropyl ketone; ethyl amyl ketone; ethyl butyl ketone; ethyl vinylketone; methyl butyl ketone; methyl ethyl ketone (MEK); methyl isoamyl ketone; methyl isobutyl ketone (MIBK); methyl isopropenyl ketone; methyl n-amyl ketone; methyl n-propyl ketone; methyl vinyl ketone; 1,1,1,3,3,4,4-heptafluoro-2-butanone; methyl perfluoro (pyrrolidinemethyl) ketone; methyfluoro(2-(N,N-diamino)ethyl)ketone; methyl isopropyl ketone; ethyl isopropyl ketone; benzyl methyl ketone; raspberry ketone acetate; para-anisyl methyl ketone; ethyl isoamyl ketone; musk ketone; raspberry ketone methyl ether; powdery ketone; elsholtzia ketone; sabina ketone; artemisyl ketone; 2-naphthyl phenyl ketone; tonka ketone; balsam ketone; celery ketone; 2-furyl pentyl ketone; isolongifolene ketone; woody ketone; watermelon ketone; neroli ketone; galbanum ketone; hydroxymethyl hexyl ethyl ketone; herbal ketone; musk methyl ketone; chrysanthemum ketone; tert-butyl vinyl ketone; isopropyl vinyl ketone; phenyl vinyl ketone; n-propyl propanoate; ethyl 2-chloropropanoate; isobutyl propanoate; tert-butyl propanoate; sec-butyl propanoate; decyl propanoate; 2,2-dimethylpropyl propanoate; dodecyl propanoate; hexadecyl propanoate; hexyl propanoate; isopropyl propanoate; 1-methylbutyl propanoate; 2-methylbutyl propanoate; octyl propanoate; tetradecyl propanoate; undecyl propanoate; ethyl 2-bromo-2-methylpropanoate; ethyl (2s)-2-hydroxypropanoate; glyceryl tripropanoate; ethyl 3-(2-furyl) propanoate; octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanoate; 3-{[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanoyl]oxy}-2,2-bis({[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanoyl]oxy}methyl)propyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanoate; ethyl perfluorooctanoate; methyl pentadecafluoro octanoate; isoamyl octanoate; propyl octanoate; isopropyl octanoate; butyl octanoate; amyl octanoate; hexyl octanoate; octyl octanoate; allyl octanoate; heptyl octanoate; phenethyl octanoate; isobutyl octanoate; ethyl 3-hydroxyoctanoate; propylene di(octanoate); nonyl octanoate; linalyl octanoate; benzyl octanoate; methyl 3-acetoxyoctanoate; ethyl 5-acetoxyoctanoate; furfuryl octanoate; geranyl octanoate; (Z)-3-hexen-1-yl octanoate; 2-methyl butyl octanoate; citronellyl octanoate; ethyl 3-acetoxyoctanoate; (E)-2-hexen-1-yl octanoate; ethyl 4-acetoxyoctanoate; sulfuryl octanoate; methyl pivalate; vinyl pivalate; phenethyl pivalate; peach pivalate; methyl butanoate; ethyl isobutanoate; heptyl butanoate; propyl butanoate; isopropyl butanoate; isobutyl butanoate; pentyl butanoate; 3-methylbutyl butanoate; tert-butyl butanoate; sec-butyl butanoate; decyl butanoate; 1,1-dimethylpropyl butanoate; dodecyl butanoate; 1-methylbutyl butanoate; 2-methylbutyl butanoate; octyl butanoate; tetradecyl butanoate; undecyl butanoate; methyl 4-chlorobutanoate; rose butanoate; vinyl 2,2,3,3,4,4,4-heptafluorobutanoate; acetophenone; 9,10-anthraquinone; benzophenone; α-chloro acetophenone; p-chloro acetophenone; 2-chlorocyclohexanone; cyclobutanone; cyclodecanone; cycloheptanone; cyclohexanone; cyclooctanone; cyclopentanone; 4-ethoxy acetophenone; 4-fluoropropiophenone; 5,6-indolequinone; 4-methoxy acetophenone; methoxyhexanone (pentoxone); 2-methyl cyclohexanone; 3-methyl cyclohexanone; 1-nonene; pentafluorobenzophenone; 9,10-phenanthrenequinone; 2,2,6,6-tetrachlorocyclohexanone; 4-(trifluoromethyl) acetophenone; 1,1,1,3,3,4,4,5,5-nonafluoro-2-pentanone; 1,1,1,2,2,5,5,5-octafluoro-3-pentanone; 3,3,4,4,5,5,5-heptafluoro-2-pentanone; 1,3,3,4,4,5,5-heptafluoro-2-pentanone; 3,4,4,4-Tetrafluoro-3-(trifluoromethyl)-2-butanone; 3,3,4,5,5,5-hexafluoro-2-pentanone; 1,1,1,2,2-pentafluoro-3-pentanone; 1,1,1,2,2,4,5,5,5-nonafluoro-4-(trifluoromethyl)-3-pentanone; 1,1,1,2,2,5,5,5-octafluoro-4-(trifluoromethyl)-3-pentanone; 1,1,1,3,3,4,4,5,5,6,6-undecafluoro-2-hexanone; 1,1,1,3,3,4,4,5,5,6,6-undecafluoro-2-hexanone; 3,3,4,4,5,5,6,6-octafluoro-2-hexanone; 4,4,5,5,6,6,6-heptafluoro-3-hexanone; 1,1,1,5,5,5-hexafluoro-4-methyl-2-pentanone; 1,1,1-trifluoro-2-butanone; 3,3,4,4-tetrafluoro-2-butanone; 4,4,5,5,6,6,7,7,7-nonafluoro-3-heptanone; 4,4,5,5,6,6,7,7,8,8,8-undecafluoro-3-octanone; 3,3,4,4,5,5,6,6,7,7,7-undecafluoro-2-heptanone; α-ionone; 3-hexanone; 2,4-dimethyl-3-pentanone; 2-octanone; cyclohexanone oxime; 2-heptyl cyclopentanone; 8-pentadecanone; (4-(t-pentyl)-cyclohexanone); thymoquinone; para-tert-butyl cyclohexanone; 2-methyl-1-nonene; 2-decanone; 2-undecanone; 6-undecanone; cyclododecanone; 2-dodecanone; 7-tridecanone; 2-tridecanone; methoxyacetone; acetoin; 2-piperidinone; 3-methylcyclopentanone; 3,3-dimethyl-2-butanone; 3-methyl-2-pentanone; 2-cyclohexenone; 4-methylcyclohexanone 4,4-dimethyl-2-pentanone; 3-methyl-2-hexanone; 3,3-dimethyl-2-pentanone; 5-methyl-3-hexanone; 4-methyl-2-hexanone; 4-methyl-3-hexanone; 4-octanone; 2,2,4-trimethyl-3-pentanone; 2-nonanone; 3-nonanone; β-ionone; o-hydroxyacetophenone; p-hydroxyacetophenone; 1-phenyl-1-butanone; 1,4-naphthoquinone; p-benzoquinone; 1,4-dihydroxyanthraquinone; propiophenone; 2,2-dimethyl-3-pentanone; m-methylacetophenone; o-methylacetophenone; p-methylacetophenone; o-aminoacetophenone; m-aminoacetophenone; p-aminoacetophenone; 2-hydroxyacetophenone; 2-tert-butyl cyclohexanone; 3′,4′-dimethoxyacetophenone; fluorenone; 2-bromoacetophenone; p-bromoacetophenone; hydroquinone diacetate; duroquinone; 1-acetonaphthone; 4-hydroxybenzophenone; 2-aminobenzophenone; valerophenone; 3-aminobenzophenone; 4′-hydroxy-3′-methoxyacetophenone; 3-benzylidene-2-butanone; tetrachloro-1,2-benzoquinone; para-ethyl acetophenone; 2-tetradecanone; 2-hexadecanone; trans-1-bromo-1-nonene; cis-1-bromo-1-nonene; cis-1-chloro-1-nonene; trans-1-chloro-1-nonene; 3,4-dimethyl-2-pentanone; 2-eicosanone; 3-ethyl-2-pentanone; trans-1-fluoro-1-nonene; cis-1-fluoro-1-nonene; cis-1-iodo-1-nonene; 2-methyl-3-hexanone; 2-octadecanone; α-ionone; 2-pentanone oxime; 2-cyclohexyl cyclohexanone; 4-nonanone; 2,6,8-trimethyl-4-nonanone; 8-methyl-1-nonene; α-iso □ methyl ionone; β-ionone; methyl heptenone; p-hydroxy phenyl butanone; 4-mercapto-4-methyl-2-hexanone; γ-ionone; tropical ionone; β-isomethyl ionone; verbenone; 2′,4′-dimethyl acetophenone; melon nonenoate; trans,trans-2,4-nonadienal; β-methyl ionone; pseudoionone; chrysanthenone; piperitenone; 4-isopropyl-2-cyclohexenone; isopiperitenone; 5-methyl-3-heptanone; civet decenone; 2′-methoxyacetophenone; hydroquinone monoethyl ether; para-isopropyl acetophenone; 6-methyl-2-heptanone; 3-decanone; pseudo-isomethyl ionone; nutty cyclohexenone; laevo-verbenone; floral undecenone; n-methyl ionone; methyl heptadienone; cyclohexanone diethyl acetal; labdanum ethanone; (E)-4-nonen-1-al; (Z)-6-nonen-1-al; cistus cyclohexanone; (E)-2-nonen-1-al; penten-1-yl cyclopentanone; grapefruit octenone; cyclohexadecanone; 8-cyclohexadecenone; coffee furanone; 5-methyl-3(2H)-furanone; 4-hydroxy-2,5-dimethyl-3(2H)-furanone; 2-nonenoic acid; berry furanone; 3-nonenoic acid; strawberry furanone acetate; 2-pentyl cyclopentanone; 2-cyclopentyl cyclopentanone; pepper hexanone; vetiver pentanone; 8-nonen-2-one; 1-hydroxy-2-butanone; filbert hexenone; 1-(2-thienyl) butanone; spicy pentanone; 3-hydroxy-4-phenyl-2-butanone; cycloionone; (E)-4-nonen-1-al; α-ionone; 4-methyl-4-phenyl pentanone; 3-benzyl-4-heptanone; 2,6,6-trimethyl-2-hydroxycyclohexanone; 4-(para-tolyl)-2-butanone; α-methyl ionone; δ-methyl ionone; 2-hydroxy-2-cyclohexenone; (Z)-3-nonen-1-ol; 2-methyl-3-heptanone; (Z)-3-nonen-1-yl acetate; 2-hexylcyclopentanone; megastigmatrierone; 3-nonen-2-one; mango furanone; 4-undecanone; peppermint cyclohexanone; (E)-2-nonenoic acid; dihydro-β-ionone; 2-hexylidene cyclopentanone; (E)-3-nonen-2-one; toffee furanone; dehydrodihydroionone; curzerenone; 1-nonen-3-ol; β-ionone epoxide; cassis pentanone; β-damascenone; amyl cyclopentenone; 2-pentylidene cyclohexanone; pseudomethyl ionone; (E)-5-nonen-2-one; shoyu furanone; (E)-2-nonen-4-one; β-oplopenone; dihydroxyacetophenone; caramel furanone; (E)-2-nonen-1-yl acetate; dihydro-α-ionone; (E)-2-nonen-1-ol; petal pyranone; potato butanone; coconut naphthalenone; hexen-1-yl cyclopentanone; piperitenone oxide; (Z)-6-nonen-1-ol; woody cyclohexanone; methyl (E)-3-nonenoate; 3-hydroxy-2-octanone; 3-heptyl dihydro-5-methyl-2(3H)-furanone; amyl cyclopentanone propanone; (Z)-2-nonen-1-ol; herbal undecanone; herbal ethanone; 3-nonen-4-olide; jasminone; saffron indenone; patchouli ethanone; valeranone; (E)-β-methyl ionone; sandal pentenone; 2,5-dimethyl-4-ethoxy-3(2H)-furanone; fruity cyclopentanone; octen-1-yl cyclopentanone; dimethyl benzofuranone; orris butenone; 1-hydroxy-4-methyl-2-pentanone; decen-1-yl cyclopentanone; patchouli ethanone; patchouli ethanone; chamomile octenone; (Z)-6-nonen-1-al dimethyl acetal; dimethyl ionone; diethyl dimethyl-2-cyclohexenone; 2-methyl-4-(camphenyl-8)\cyclohexanone; jasmin pyranone; tonka undecanone; isobutyl ionone; saffron pyranone; dimethyl α-ionone; clary octenone; (Z)-6-nonen-1-yl acetate; tonka furanone; filbert heptenone; tobacco nonene; coconut decanone; coconut decanone; peach cyclopentanone; (E)-12-musk decenone; 1-(3-hydroxy-5-methyl-2-thienyl) ethanone; 3-hydroxy-5-methyl-2-hexanone; 2-hydroxy-5-methyl-3-hexanone; 2-cyclohexylhepta-1,6-dien-3-one; (±)-2,4,8-trimethyl-7-nonen-2-ol; 2-ethyl-4-hydroxy-5-methyl-3(2H)-furanone; chlormadinone acetate; 2-hydroxy-4-n-octoxybenzophenone; 2,4-dihydroxybenzophenone; 2-hydroxy-4-methoxy benzophenone; 2-hydroxy-4-dodecyloxy-benzophenone; 1,5-dimethyl-2-pyrrolidinone; 1-chloroanthraquinone; rotenone; 4,4′-Bis(dimethylamino)-benzophenone (Michler's ketone); 2-aminoanthraquinone; 1-hydroxyanthraquinone; [1,1′-bi(cyclohexan)]-1′-en-2-one; 2-pentylanthraquinone; 5-ethyl-1-nonene; 2,3-dicyano-1,4-dithia-anthraquinone(dithianon); 2,4-dihydroxybenzophenone; hexazinone; 4-hydroxypropiophenone; 1,3-benzenediol; 1,4-butandiol diacrylate; 1,3-butanediol; 1,4-butanediol; 1,2-cyclohexanediol; 1,4-dihydroxybenzene (1,4-benzenediol); hexane 1,6 diol; 1,9-nonanediol; 1,3-propanediol (trimethyleneglycol); 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (texanol); 1H,1H,2H,3H,3H-perfluorononane-1,2-diol; cis-2-butene-1,4-diol; trans-2-butene-1,4-diol; 2-butyne-1,4-diol; 2,3-butanediol; 1,5-pentanediol; 2,2-dimethyl-1,3-propanediol; 1,2-butanediol; 2,5-hexanediol; 2-methyl-2-propyl-1,3-propanediol; (±)-3-chloro-1,2-propanediol; 1,4-pentanediol; 1,2-pentanediol; 2-methyl-2-ethyl-1,3-propanediol; 2,3-dimethyl-2,3-butanediol; 1-phenyl-1,2-ethanediol; 1,2-decanediol; 1,10-decanediol; 2,2-diethyl-1,3-propanediol; 2,3-dimethyl-1,2-butanediol; 3,3-dimethyl-1,2-butanediol; 2,3-dimethyl-1,3-butanediol; 2,2-dimethyl-1,3-butanediol; 2,2-dimethyl-1,3-pentanediol; 2,3-dimethyl-1,3-pentanediol; 2,2-dimethyl-1,4-butanediol; 3,4-dimethyl-1,4-pentanediol; 2,2-dimethyl-1,5-pentanediol; 3,3-dimethyl-1,5-pentanediol; 2,4-dimethyl-2,3-pentanediol; 2,4-dimethyl-2,4-pentanediol; dl-2,3-butanediol; 1,12-dodecanediol; 1,2-dodecanediol; 1,20-eicosanediol; 1,2-eicosanediol; 1,4-eicosanediol; 1,3-eicosanediol; 2-ethyl-1,3-butanediol; 2-ethyl-1,3-pentanediol; 2-ethyl-1,3-propanediol; 1,2-heptanediol; 1,4-heptanediol; 2,6-heptanediol; 1,7-heptanediol; 1,3-heptanediol; 2,4-heptanediol; 2,3-heptanediol; 1,2-hexadecanediol; 2,3-hexanediol; 1,4-hexanediol; 1,3-hexanediol; 1,2-hexanediol; 3,4-hexanediol; 1,5-hexanediol; 2-isopropyl-1,3-propanediol; 2-isopropyl-1,4-butanediol; meso-2,3-butanediol; meso-2,4-pentanediol; 2-methyl-1,2-butanediol; 3-methyl-1,2-butanediol; 2-methyl-1,2-propanediol; 3-methyl-1,3-butanediol; 2-methyl-1,3-butanediol; 2-methyl-1,3-pentanediol; 2-methyl-1,4-butanediol; 2-methyl-1,5-pentanediol; 3-methyl-1,5-pentanediol; 2-methyl-2,3-butanediol; 3-methyl-2,3-pentanediol; 2-methyl-2,3-pentanediol; 2-methyl-2,4-hexanediol; 3-methyl-2,4-pentanediol; 1,2-nonanediol; 1,2-octadecanediol; 1,2-octanediol; 1,8-octanediol; 1,3-octanediol; 1,3-pentanediol; 2-propyl-1,3-propanediol; 2-sec-butyl-1,3-propanediol; 1,2-tetradecanediol; 1,11-undecanediol; 1,2-undecanediol; 1,3-undecanediol; 1,4-undecanediol; 2-methyl-1,3-propanediol; 1,3-propanediol dinitrate; 2,3-pentanediol; 1,2-ethanediol monoacetate; 2,4-pentanediol; 1,2-propanediol dinitrate; 1,3-butanediol dinitrate; 2-ethyl-1,2-hexanediol; 3-chloro-1,2-propanediol dinitrate; agathadiol; 2,2,4-trimethyl-1,3-pentanediol; 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate; 2,2,4-trimethyl-1,3-pentanediol diisobutyrate; diolein; diola; (E)-para-menthane-3,8-diol; heptanal 2,3-butane diol acetal; (S)-dihydroactinidiolide; para-menthane-3,8-diol; 1,4-nonane diol diacetate; menthoxypropane diol; para-menth-8-en-1,2-diol; hexanal butane-2,3-diol acetal; 3-laevo-menthoxy-2-methyl propane-1,2-diol; acetaldehyde 1,3-octane diol acetal; hexanal octane-1,3-diol acetal; estradiol; 2,2-Bis(bromomethyl)-1,3-propanediol; 1-chloro-2-(1,2-ethanediol)benzene; 2-bromo-2-nitropropane-1,3-diol; 2-amino-2-ethyl-1,3-propanediol; 1,4-butanediol diglycidylether; 3-allyloxy-1,2-propanediol; 1,2-benzenediol; 2-hydroxymethyl-2-methyl-1,3-propanediol; 1,1,2,2-tetraphenylethane-1,2-diol; 3-(3-methylbutoxy)propane-1,2-diol; 3-butoxy-1,2-propanediol; 3-methoxy propan-1,2-diol; 2,4-diethyl-1,5-pentanediol; 2,7-naphthalenediol; 1,5-naphthalenediol; 2,3-naphthalenediol; 2,4-quinolinediol; 2,3-quinoxalinediol; 1,2,6-hexanetriol; 1,2,3-propanetriol 1-acetate; 1,2,3-butanetriol; 1,2,4-butanetriol; estriol; glycerol; N-methyl-2-pyrrolidone (NMP); N-(2-hydroxyethyl)-2-pyrrolidone; N-acetyl pyrrolidone; N-benzyl pyrrolidone; N-cyclohexyl-2-pyrrolidone; n-ethyl-2-pyrrolidone; N-n-butyl pyrrolidone; 2-pyrrolidone; vinyl pyrrolidone; menthyl pyrrolidone carboxylate; N-vinylpyrrolidone; 1-2-pyrrolidone-5-carboxylic acid; α-terpineol; β-terpineol; terpineol; α-dihydroterpineol; α-terpineol; d-terpineol; (+)-α-terpineol; α-dihydroterpineol; anisole; o-bromoanisole; 4-chloroanisole; 2,6-dichloroanisole; p-fluoroanisole; p-nitroanisole; p-bromoanisole; m-methylanisole; o-methylanisole; p-methylanisole; 2,4-dimethyl anisole; m-chloroanisole; o-chloroanisole; m-nitroanisole; 2,4-dinitroanisole; p-iodoanisole; ortho-vinyl anisole; 4-ethyl anisole; 4-ethoxyanisole; 2-ethoxyanisole; butylated hydroxyanisole; pentachloroanisole; allyl acetoacetate; ethyl 2,2-difluoroacetoacetate; methyl chlorodifluoroacetoacetate; ethyl-methyl-4,4,4-trifluoro-acetoacetate; t-butyl acetoacetate; ethyl 2-ethyl acetoacetate; spicy acetoacetate; amyl acetoacetate; isoamyl acetoacetate; benzyl acetoacetate; isobutyl acetoacetate; jasmin acetoacetate; laevo-menthyl acetoacetate; geranyl acetoacetate; bergamot acetoacetate; n-butyl aceto acetate; ethyl aceto acetate (keto); methyl aceto acetate; ethyl 4,4,4-trifluoroaceto acetate; acetylacetone; adonitol; allyl alcohol; benzyl alcohol; 2-bromo allyl alcohol; 2,3-butadiene-1-ol; 1-butanol; 2-butanol; butoxy ethoxy propanol; t-butyl alcohol; 2-t-butyl-4-methyl phenol; 2-chloro allyl alcohol; 3-chloro allyl alcohol; 3-chloro-1-propanol; 2-chloro-5-methyl phenol; 4-chlorobenzyl alcohol; 2-chlorophenol; cinnamyl alcohol; coniferyl alcohol; p-coumaryl alcohol; m-cresol; cyclohexanol; 2-cyclopentenyl alcohol; 2-decanol; 1-decanol; diacetone alcohol; 1,3-dichloro-2-propanol; 2,4-dichlorophenol; 2,5-dichlorophenol; 2,6-dichlorophenol; 2,3-dichloropropanol; 2-(diethylamino)ethanol; di-isobutyl carbinol; 2,6-dimethoxy phenol; 2,6-dimethyl phenol; 3,4-dimethyl phenol; 3,5-dinitrophenol; 3,4-dinitrophenol; dodecanol; ethanol; 1-ethoxy ethoxy-2-propanol; 4-ethyl phenol; 2-ethyl-1-butanol; 2-ethyl-hexanol; eugenol; furfuryl alcohol; glycerol; glycidol; 1-heptanol; 2-heptanol; 3-heptanol; hexafluoro isopropanol; 1-hexanol; isobutyl alcohol; isooctyl alcohol; 1-menthol; methanol; 3-methoxy butanol; methoxy methanol; 3-methoxy-3-methyl butanol; 3-methyl allyl alcohol; 1-methyl cyclohexanol; methyl isobutyl carbinol; 2-methyl-1-butanol; 2-methyl-1-pentanol; 2-methyl-2-butanol; 3-methyl-2-butanol; 1-naphthol; 2-nitro-1-propanol; 4-nitrophenol; 1-nonanol; nonyl phenol; nonyl phenoxy ethanol; 2-octanol; 1-octanol; oleyl alcohol; pentachlorophenol; 2-pentanol; 1-pentanol; phenol; 2-phenoxy ethanol; 2-phenyl ethanol; 1-propanol; 2-propanol; 2-propyn-1-ol; sinapyl alcohol; 2,5-tetrahydrofuran dimethanol; tetrahydrofurfuryl alcohol; thymol; 2,4,6-tribromo phenol; 2,4,6-trichloroanisol; 2,4,6-trichlorophenol; tridecyl alcohol; 2,2,2-trifluoro ethanol; vinyl carbitol; vinyl ethyl carbitol; 2-fluoro-ethanol; 2,2,3,3,3-pentafluoro-propan-1-ol; 2,2,3,3-tetrafluoro-propan-1-ol; 2,2-difluoro-ethanol; 1,1,1-trifluoro-propan-2-ol; 1,3-difluoro-propan-2-ol; 2,2,3,3,4,4,4,-heptafluoro-butan-1-ol; 2,2,3,4,4,4-hexafluorobutan-1-ol; 4,4,4-trifluoro-butan-1-ol; 2,3,3,3-tetrafluoro-2-trifluoromethyl-propan-1-ol; 1,1,1,3,3,4,4,4-octafluorobutan-2-ol; 3,3,4,4,4-pentafluorobutan-2-ol; nonafluoro-tert-buthanol; hexafluoro-tert-buthanol; 1,1,1-trifluoro-2-methylpropan-2-ol; octafluoro-cyclo-pentanol; 1-ethoxy-2,2,2-trifluoro-ethanol; 3,3,3-trifluoro-propan-1-ol; pentafluorophenol; 3-bromo-1,1,1-trifluoro-2-propanol; 1-chloro-3-fluoroisopropanol; 1H,1H,7H-dodecafluoro-1-heptanol; (perfluorocyclohexyl)methanol; 1H,1H-perfluoro-1-heptanol; 1H,1H-perfluoro-1-octanol; 1H,1H,2H,2H-perfluorooctanol; 2-perfluoropropoxy-2,3,3,3-tetrafluoropropanol; 2,2-bis(trifluoromethyl)propanol; 2-methyl 4,4,4-trifluorobutanol; o-cresol; p-cresol; o-ethylphenol; m-ethylphenol; 2,3-xylenol; 2,4-xylenol; 2,5-xylenol; 3,5-xylenol; 1-heptadecanol; 1-octadecanol; 1-eicosanol; 3-pentanol; 3-methyl-1-pentanol; cis-2-methylcyclohexanol; trans-2-methylcyclohexanol; cis-3-methylcyclohexanol; trans-3-methylcyclohexanol; cis-4-methylcyclohexanol; trans-4-methylcyclohexanol; cis-2-butene-1-ol; 2-chloro-1-propanol; 1-propylcyclopentanol; 1-amino-2-propanol; 3-amino-1-propanol; 2-aminoethoxyethanol; pentaerythritol; 2-hexanol; hexylene glycol; 5-methyl-1-hexanol; 2-nonanol; 1-undecanol; 1-tetradecanol; sorbitol; p-methoxyphenol; 2-phenyl-2-propanol; p-tert-butylphenol; p-tert-butylcatechol; p-tert-amylphenol; p-tert-octylphenol; p-cumylphenol; 2,6-di-tert-butyl-p-cresol; nonylphenol; dinonylphenol; 5-hexen-1-ol; 1-hepten-3-ol; Hinokitiol (2-hydroxy-4-(1-methylethyl)-2,4,6-cycloheptatrien-1-one); cis-3,7-dimethyl-2,6-octadien-1-ol; 4-decanol; 5-methyl-5-nonanol; 2-methyl-2-nonanol; 3-methyl-3-nonanol; 4-methyl-4-nonanol; 3-decanol; 5-decanol; 2-undecanol; 2-dodecanol; 2-tetradecanol; 1-pentadecanol; 2-hexadecanol; 2-amino-2-methyl-1-propanol; 3-buten-2-ol; cyclobutanol; 2-buten-1-ol; 2-methyl-3-buten-2-ol; 1-penten-3-ol; 4-penten-2-ol; 4-penten-1-ol; prenol; mepafynol; 1-methylcyclopentanol; 1-hexen-3-ol; 3-methyl-2-pentanol; 3-hexanol; 3,3-dimethyl-2-butanol; 2,3-dimethyl-2-butanol; 3-methyl-3-pentanol; 4-methyl-1-pentanol; 3,3-dimethyl-1-butanol; 2-methyl-2-pentanol; 2-methyl-3-pentanol; 2,3-dimethyl-1-butanol; 4-heptanol; 2-methyl-2-hexanol; 2,3-dimethyl-2-pentanol; 4,4-dimethyl-2-pentanol; 3-ethyl-2-pentanol; 2,3-dimethyl-3-pentanol; 3-ethyl-3-pentanol; 2,2-dimethyl-3-pentanol; 2,4-dimethyl-3-pentanol; 2-ethyl-1-pentanol; 4-methyl-2-hexanol; 5-methyl-2-hexanol; 3-methyl-3-hexanol; 5-methyl-3-hexanol; 2,4,4-trimethyl-1-pentanol; 3,4-dimethyl-3-hexanol; 4-methyl-3-heptanol; 3-octanol; 4-octanol; 3,3-dimethyl-2-hexanol; 5-methyl-1-heptanol; 2,3-dimethyl-3-hexanol; 2,3,3-trimethyl-2-pentanol; 2,3,4-trimethyl-3-pentanol; 4-methyl-1-heptanol; 3-ethyl-3-hexanol; 2,2,3-trimethyl-3-pentanol; 2,2,4-trimethyl-3-pentanol; 3,4-dimethyl-2-hexanol; 2,2-dimethyl-1-hexanol; 2,4-dimethyl-3-hexanol; 2,5-dimethyl-2-hexanol; 2,5-dimethyl-3-hexanol; 5-methyl-3-heptanol; 2-methyl-4-heptanol; 3-methyl-4-heptanol; 6-methyl-2-heptanol; 4-methyl-4-heptanol; 3-methyl-3-heptanol; 5-nonanol; 3-nonanol; 3-methyl-3-octanol; 4-nonanol; m-chlorophenol; p-chlorophenol; o-nitrophenol; m-nitrophenol; m-bromophenol; p-bromophenol; 1,2,3,4-butanetetrol; m-nitrobenzyl alcohol; menthol; triphenylmethanol; trimethylsilanol; 2-naphthol; 2-methoxy-4-prop-1-enyl-phenol; p-isopropylbenzyl alcohol; 2-methyl-5-isopropylphenol; geraniol; (3-citronellol; 3-phenyl-1-propanol; fenchyl alcohol; 1-phenylethanol; 2,2-dimethyl-1-butanol; m-aminophenol; p-aminophenol; o-aminophenol; 3-methyl-2-hexanol; 2-methyl-3-hexanol; 3-methyl-1-hexanol; 3,3-dimethyl-2-pentanol; 2,3-dimethyl-1-pentanol; 2,4-dimethyl-2-pentanol; 4-methyl-1-hexanol; 2,4-dimethyl-1-pentanol; 3,4-dimethyl-1-pentanol; 4,4-dimethyl-1-pentanol; 2-methyl-2-ethyl-1-butanol; 2,3,3-trimethyl-1-butanol; 2,3,3-trimethyl-2-butanol; 2-methylbenzyl alcohol; 4-methylbenzyl alcohol; 3-methylbenzyl alcohol; 2-hydroxybenzyl alcohol; 3-hydroxybenzyl alcohol; 4-hydroxybenzyl alcohol; 3-methoxyphenol; 2-methyl-1-heptanol; 3-methyl-1-heptanol; 6-methyl-1-heptanol; 2-methyl-2-heptanol; 3-methyl-2-heptanol; 4-methyl-2-heptanol; 5-methyl-2-heptanol; 2-methyl-3-heptanol; 2,2,4-trimethyl-1-pentanol; 2,3,4-trimethyl-1-pentanol; 4-ethyl-3-hexanol; 3,5-dimethyl-3-hexanol; 4-methyl-2-ethyl-1-pentanol; 2,4,4-trimethyl-2-pentanol; 2,2-dimethyl-3-hexanol; 2-allylphenol; 4-propylphenol; 3-propylphenol; 2-propylphenol; 4-isopropylphenol; 3-isopropylphenol; 2-isopropylphenol; 1-phenyl-1-propanol; 1-phenyl-2-propanol; 2-phenyl-1-propanol; 4-methoxybenzyl alcohol; 4-methyl-4-octanol; 2,2,4,4-tetramethyl-3-pentanol; 2,2,3-trimethyl-3-hexanol; 2-methyl-2-octanol; (E)-anethol; 3-tert-butylphenol; 2-tert-butylphenol; 3-butylphenol; 2-butylphenol; 4-butylphenol; 2-nitrobenzyl alcohol; 4-nitrobenzyl alcohol; isoborneol; borneol; 2,3-dichlorophenol; 3,4-dichlorophenol; 3,5-dichlorophenol; muguet carbinol; p-phenylphenol; o-phenylphenol; o-bromophenol; 2-chloro-4-nitrophenol; bromstyrol; 2,4-dinitrophenol; 2,4,6-triiodophenol; p-vinylphenol; 2-acetamidophenol; 3-acetamidophenol; m-iodophenol; o-iodophenol; p-iodophenol; 2,4-dibromophenol; 2,4,6-trimethylphenol; 2,4,5-trimethylphenol; 2-(1,1-dimethylethyl)-6-methyl-phenol; 4-methyl-3-nitrophenol; 2-methyl-3-nitrophenol; 5-methyl-2-nitrophenol; 2,6-di-t-butyl-4-hydroxymethylphenol; 2,3,5-trimethylphenol; 3-methyl-5-ethylphenol; 4-sec-butylphenol; methyl isoeugenol; 2-sec-butylphenol; ortho-acetyl-para-cresol; 2,6-diisopropylphenol; dihydrocarveol; 3,7-dimethyl-1-octanol; 2,3,6-trimethylphenol; 3,4-diethylphenol; 2,4-diethylphenol; 2,5-diethylphenol; 2,3-diethylphenol; 2,6-diethylphenol; 6,6-dimethyl-1-heptanol; 2,2-dimethyl-1-heptanol; 2,3-dimethyl-1-hexanol; 5,5-dimethyl-1-hexanol; 4,5-dimethyl-1-hexanol; 2,4-dimethyl-1-hexanol; 3,5-dimethyl-1-hexanol; 3,4-dimethyl-1-hexanol; 2,5-dimethyl-1-hexanol; 3,3-dimethyl-1-hexanol; 4,5-dimethyl-1-octanol; 4,6-dimethyl-1-octanol; 4,7-dimethyl-1-octanol; 7,7-dimethyl-1-octanol; 2,6-dimethyl-1-octanol; 2,2-dimethyl-1-octanol; 2,2-dimethyl-1-pentanol; 3,3-dimethyl-1-pentanol; 3,5-dimethyl-2-ethylphenol; 2,5-dimethyl-2-heptanol; 2,6-dimethyl-2-heptanol; 2,3-dimethyl-2-heptanol; 4,6-dimethyl-2-heptanol; 5,6-dimethyl-2-heptanol; 2,4-dimethyl-2-heptanol; 5,5-dimethyl-2-hexanol; 2,4-dimethyl-2-hexanol; 3,5-dimethyl-2-hexanol; 4,4-dimethyl-2-hexanol; 2,3-dimethyl-2-hexanol; 3,7-dimethyl-2-octanol; 2,7-dimethyl-2-octanol; 2,4-dimethyl-2-octanol; 3,4-dimethyl-2-pentanol; 5,5-dimethyl-3-ethyl-3-hexanol; 2,4-dimethyl-3-ethyl-3-pentanol; 2,2-dimethyl-3-heptanol; 2,3-dimethyl-3-heptanol; 2,6-dimethyl-3-heptanol; 3,5-dimethyl-3-heptanol; 3,6-dimethyl-3-heptanol; 4,4-dimethyl-3-hexanol; 2,4-dimethyl-3-isopropyl-3-pentanol; 2,7-dimethyl-3-octanol; 2,3-dimethyl-3-octanol; 2,2-dimethyl-3-octanol; 3,7-dimethyl-3-octanol; 3,6-dimethyl-3-octanol; 2,4-dimethyl-4-heptanol; 3,5-dimethyl-4-heptanol; 2,4-dimethyl-4-octanol; 2,5-dimethyl-4-octanol; 2,6-dimethyl-4-octanol; 4,7-dimethyl-4-octanol; 2,7-dimethyl-4-octanol; 2,4-dimethyl-5-ethylphenol; 3,4-dimethyl-6-ethylphenol; 2,6-dimethyl-2-octanol; 2-eicosanol; 3-ethyl-1-heptanol; 2-ethyl-1-heptanol; 3-ethyl-1-hexanol; 2-ethyl-1-octanol; 3-ethyl-2-heptanol; 3-ethyl-3-heptanol; 6-ethyl-3-octanol; 3-ethyl-3-octanol; 4-ethyl-4-heptanol; 2-heptadecanol; 4-isobutylphenol; 2-isobutylphenol; isodecanol; 2-isopropyl-1-pentanol; 2-methyl-1-hexanol; 6-methyl-1-octanol; 4-methyl-1-octanol; 3-methyl-1-octanol; 2-methyl-1-octanol; 7-methyl-1-octanol; 5-methyl-2-ethyl-1-hexanol; 3-methyl-2-ethyl-1-hexanol; 2-methyl-2-ethyl-1-pentanol; 4-methyl-2-ethylphenol; 5-methyl-2-isopropyl-1-hexanol; 3-methyl-2-isopropylphenol; 4-methyl-2-isopropylphenol; 3-methyl-2-octanol; 4-methyl-2-propyl-1-pentanol; 4-methyl-2-propylphenol; 2-methyl-3-ethyl-2-hexanol; 2-methyl-3-ethyl-2-pentanol; 2-methyl-3-ethyl-3-hexanol; 5-methyl-3-ethyl-3-hexanol; 2-methyl-3-ethyl-3-pentanol; 4-methyl-3-ethylphenol; 2-methyl-3-ethylphenol; 6-methyl-3-heptanol; 4-methyl-3-hexanol; 4-methyl-3-isopropylphenol; 2-methyl-3-isopropylphenol; 2-methyl-3-octanol; 6-methyl-3-octanol; 3-methyl-4-ethyl-3-hexanol; 2-methyl-4-ethylphenol; 3-methyl-4-ethylphenol; 2-methyl-4-isopropylphenol; 7-methyl-4-octanol; 5-methyl-4-octanol; 2-methyl-4-octanol; 2-methyl-4-propylphenol; 2-methyl-5-ethylphenol; 3-methyl-5-isopropylphenol; 3-methyl-6-ethylphenol; 2-methyl-6-ethylphenol; 2-nonadecanol; 2-pentadecanol; 2-propyl-1-hexanol; 2-propyl-1-pentanol; 4-propyl-4-heptanol; 3-sec-butylphenol; 2,2,5,5-tetramethyl-3-hexanol; 2,3,4,6-tetramethylphenol; 2,3,5,6-tetramethylphenol; 2,3,4,5-tetramethylphenol; 2-tridecanol; 3,4,4-trimethyl-1-hexanol; 3,5,5-trimethyl-1-hexanol; 2,3,4-trimethyl-2-hexanol; 2,3,4-trimethyl-2-pentanol; 2,3,5-trimethyl-3-hexanol; 2,4,4-trimethyl-3-hexanol; 2,5,5-trimethyl-3-hexanol; 3,4,4-trimethyl-3-hexanol; 3,5,5-trimethyl-3-hexanol; 3,4,5-trimethylphenol; 2,3,4-trimethylphenol; acetaldol; acetol; 2-methyl-1-butanol; 6-chloro-1-hexanol; 1,2,3,4-tetrahydro-2-naphthol; d-mannitol; 1-phenyl-2-propanol; inositol; xylitol; 2-amino-1-propanol; α-tocopherol; sitosterol; 2-butyl-nonan-1-ol; 2-methyl-1-undecanol; 2-butyl-octan-1-ol; β-cholesterol; 1,4-cyclohexanedimethanol; triacetone alcohol; 2-butyl-1-decanol; 2-methyl-1-tridecanol; 2-methyl-dodecan-1-ol; 2-(2-(2-butoxyethoxy)ethoxy)ethanol; 2-pentoxyethanol; stigmasterol; 2-(2-pentoxyethoxy)ethanol; aurantiol; bacdanol; cedrol; cineol; dihydrolinalool; dihydromyrcenol; dimethyl benzyl carbinol; fenchyl alcohol; hexenol; isononyl alcohol; isopulegol; levo-carveol; linalool; mayol; methyl eugenol; norlimbanol; para-menth-3-en-1-ol; patchouli alcohol; 3-methyl-5-phenyl-1-pentanol; undecavertol; santalol; sandanol; cyclodithalfarol; 2-methyl-isoborneol; chlorothymol; octenol; terpinen-4-ol; β-santalol; musk xylol; maraniol; 6-tert-butyl-meta-cresol; vetiverol; 4-methyl guaiacol; propenyl guaethol; patchouli hexanol; α-amyl cinnamyl alcohol; dihydroanethol; (E,E)-farnesol; hydroxycitronellol; 2,4-hexadien-1-ol; 10-undecen-1-ol; homomenthol; maltol; benzyl isoeugenol; dextro-linalool; laevo-linalool; nopol; sulfurol; rhodinol; (+)-nerolidol; phytol; longiborneol; carotol; sabinol; junenol; β-caryophyllene alcohol; β-eudesmol; α-eudesmol; verbenol; α-cadinol; (−)-guaiol; diosphenol; piperitol; heliotropyl alcohol; vanillyl alcohol; (−)-lavandulol; carvomenthol; chavicol; isophytol; totarol; α-fenchol; myrtanol; myrtenol; sclareol; bisabolol; magnolol; hawthorn\carbinol; perilla alcohol; myrcenol; (Z)-3-hexen-1-ol; viridiflorol; 6-shogaol; ledol; ortho-eugenol; manool; α-elemol; 1-phenyl-2-pentanol; 4-methyl-3-penten-1-ol; (E)-3-penten-1-ol; (Z)-3-penten-1-ol; 2-decalinol; 3-methyl-1-penten-3-ol; (E)-4-hexen-1-ol; (E)-geranyl linalool; (r)-(+)-β-citronellol; (3a,5a)-androst-16-en-3-ol; cherry propanol; (Z)-carveol; (E)-carveol; γ-eudesmol; menthol; α-methyl cinnamic alcohol; coriander heptenol; (Z)-2-penten-1-ol; (E)-2-penten-1-ol; (E)-pinocarveol; vinyl sulfurol; (E)-verbenol; (Z)-verbenol; hawthorn ethanol; α-campholenic alcohol; limonene glycol; phenoxyacetaldehyde; nerolin fragarol; dextro-neomenthol; patchouli ethanol; (E)-2-hexen-1-ol; 4-phenyl-2-butanol; pinol; vanilla cresol; dihydroeugenol; 4-ethyl guaiacol; acetyl ethyl carbinol; oakmoss phenol; menthadienol; dihydro-β-ionol; 4-phenyl-1-butanol; (3r)-1-octen-3-ol; (Z)-nerolidol; 5-methyl furfuryl alcohol; (E)-3-penten-2-ol; tetrahydroionol; (E)-cinnamyl alcohol; cyclohexyl ethyl alcohol; 2-methyl-3-buten-1-ol; α-caryophyllene alcohol; farnesol; leather cyclohexanol; 2-methyl-2-buten-1-ol; 2-octen-4-ol; ethyl maltol; (Z)-2-pinanol; α-methoxy-para-cresol; cyclohexyl propanol; (Z)-isoeugenol; (E)-isoeugenol; t-cadinol; pinocarveol; 2-octanol; ocimenol; palustrol; 4-hexen-1-ol; (Z)-4-hepten-1-ol; 4-allyl-2,6-dimethoxyphenol; 4-propenyl syringol; 4-methyl-2,6-dimethoxyphenol; spathulenol; 4-propyl syringol; (S)-rhodinol; widdrol; cedanol; (E)-para-mentha-2,8-dien-1-ol; nerolidol; laevo-citronellol; isobutyl benzyl carbinol; ethyl isoeugenol; 2,6-nonadien-1-ol; 2-methoxy-4-vinyl phenol; elemol; ethyl linalool; lilac pentanol; amyl isoeugenol; phenyl amyl alcohol; 3-hepten-1-ol; 9-decen-1-ol; muguet propanol; pine hexanol; 4-ethyl syringol; β-bisabolol; citrus propanol; (Z)-piperitol; (E)-piperitol; (E,E)-2,4-hexadien-1-ol; 4-phenyl-3-buten-2-ol; 2-ethyl fenchol; (E)-2-octen-1-ol; (E)-2-decen-1-ol; 2,4-octadien-1-ol; 2,4-decadien-1-ol; muguet octadienol; para-menth-1-ene-9-ol; (E,E)-2,4-dodecadien-1-ol; (r)-2-phenyl propyl alcohol; peony alcohol; t-muurolol; hotrienol; (E)-2-octen-4-ol; (Z)-3-octen-1-ol; 2-penten-1-ol; valerianol; cumin carbinol; α-ethoxy-ortho-cresol; (−)-cubenol; thujyl alcohol; pogostol; 0-ionol; (E)-2-hepten-1-ol; 2-octen-1-ol; 2-decen-1-ol; 2-dodecen-1-ol; bulnesol; dextro-2,8-para-menthadien-1-ol; cubebol; agarospirol; waxy undecadienol; lime octenol; α-ionol; sandal butenol; cedrenol; 2,6-dimethoxy-4-vinyl phenol; 0-acorenol; dehydro β-linalool; (E)-2,6-dimethyl-1,5,7-octatrien-3-ol; artemisyl alcohol; dehydrolinalool; yomogi alcohol; β-elemol; decatol; 2-(2-hexen-1-yl)cyclopentanol; ipsdienol; santolina alcohol; d-cadinol; (±)-α-melonol; amber cyclohexanol; musk amberol; 2-undecen-1-ol; jasmin pyranol; 2-(laevo-menthoxy) ethanol; (E)-nerolidol; isodihydrolavandulol; α-ambrinol; sandal octanol; (E)-1,5-octadien-3-ol; (Z)-1,5-octadien-3-ol; 1-decen-3-ol; globulol; (±)-2,3-dihydrofarnesol; α-isomethyl ionol; (Z)-5-decen-1-ol; (Z,Z)-3,6-nonadien-1-ol; (Z)-4-octen-1-ol; roasted butanol; caryophyllene alcohol; (E,Z)-3,6-nonadien-1-ol; muguet butanol; dehydrodihydroionol; (Z)-4-decen-1-ol; herbal undecanol; lavandulol; 2,4-undecadien-1-ol; methialdol; violet propanol; 1-penten-2-ol; 2,4-nonadien-1-ol; floral pyranol; muguet ethanol; 8-hydroxylinalool; (Z)-5-octen-1-ol; sandal pentanol; 3-octanon-1-ol; 4-(5,5,6-trimethylbicyclo[2.2.1]hept-2-yl)cyclohexanol; 4-(1,7,7-trimethylbicyclo[2.2.1]hept-2-yl)cyclohexanol; patchouli cyclohexanol; 2,4-dimethyl-3-cyclohexene-1-methanol; sandal pentenol; (e+z)-4,8-dimethyl-3,7-nonadien-2-ol; amyl isoeugenol; floral methanol; (E)-2-tridecen-1-ol; isocyclogeraniol; 6,8-dimethyl-2-nonanol; dihydrogeranyl linalool; ambrinol; heptanal cyclic acetal with glycerol; 2,4-dimethyl-4-nonanol; germacrene d-4-ol; (Z)-2-tridecen-1-ol; 3-octen-2-ol; 3,6-nonadien-1-ol; geranyl farnesol; 1,5-octadien-3-ol; silwanol; (Z)-4-propenyl phenol; amber carbinol; epi-globulol; magnolia cyclohexanol; grapefruit pentanol; methyl β-ionol; lily propanol; 1-allyl-2,2,7,7-tetramethyl cycloheptanol; amber butanol; 2-octanol; cis-2-hexen-1-ol; trans-2-hexen-1-ol; undecan-4-ol; dodecan-3-ol; undecan-3-ol; (E)-3,7,11,15-tetramethylhexadec-2-en-1-ol; danazol; haloperidol; pindolol; atenolol; practolol; acebutolol; nadolol; labetalol; timolol; pindolol; chloramphenicol; oxprenolol; alprenolol; metoprolol; propranolol; sotalol; 1H-indol-2-ol; 1H-indol-5-ol; 2-ethenoxyethanol; 2-allyloxyethanol; amino-4,5-dinitrophenol; dicofol; triphenylsilanol; 3,4-dichlorobenzyl alcohol; 2,4-dichloro-1-naphthol; 2,6-dicycloehxylphenol; 2,6-di-sec-butylphenol; fenarimol; isodecanol; isotridecanol; isopropenylphenol; 2-(perfluorooctyl)ethanol; 1,1,11-trihydroperfluoro_undecanol; 2-(dibutylamino)ethanol; dipentaerythritol; 4-pyridinol; 3,6-dinitrophenol; 7-isoquinolinol; 3-quinolinol; 2,4-dimethylimidazol; 9-anthracenemethanol; diethylstilbestrol; 1-(phenylazo)-2-naphthalenol; 2-pyridineethanol; ancymidol; flutriafol; thiabendazol; captafol; 4-chloro-2-nitrophenol; 2,4-di-tert-pentylphenol; 1,5-hexadien-3-ol; p-octylphenol; 2(1,1-dimethylethyl)-4,6-dimethylphenol; 2,2,6,6-tetramethylpiperidin-4-ol; 4,4-isobutylethylidendiphenol; 4-pentylphenol; 1-(3-methylphenyl)ethanol; 3-bromo-3-buten-1-ol; 2,4-diaminophenol; 2-(2h-benzotriazol-2-yl)-4-methylphenol; 2-fluorophenol; cetyl alcohol (1-hexadecanol); isoamyl alcohol (3-methyl-1-butanol); cyclopentanol (cyclopentyl alcohol); α-methylbenzyl alcohol formate; yomogi alcohol a; caryophyllene alcohol acetate; (3-caryophyllene alcohol acetate; (S)-(−)-perillyl alcohol; 3-phenoxy-benzyl alcohol; dihydroabietyl alcohol (technical mix); bis-(m-phenoxyphenyl) ether; 1,2-epoxy-3-phenoxypropane; phenoxyacetic acid; 1,2-diphenoxyethane; phenoxyethyl isobutyrate; phenoxyacetylene; allyl phenoxyacetate; 2-(4-methoxyphenoxy) propionic acid; phenoxyethyl propionate; 2-phenoxyethyl butyrate; 2-phenoxyethyl formate; para-methyl phenoxyacetaldehyde; 2,4-dichloro-1-(3-methoxy-4-nitrophenoxy)benzene; fenvalerate; deltametrin; 1-Amino-2-(4-bromophenoxy)-4-hydroxy-9,10-anthracenedione; (4-chloro-2-methylphenoxy)acetic acid; 2-chlorophenoxyacetic acid; 3-chlorophenoxyacetic acid; o-cyanophenoxyacetic acid; p-cyanophenoxyacetic acid; 2,4,5-trichlorophenoxyacetic acid; fenoprop; o-bromotoluene; p-bromotoluene; 3-n-butyl toluene; o-n-butyltoluene; p-n-butyltoluene; 4-chloro-2-nitrotoluene; 6-chloro-2-nitrotoluene; o-chlorotoluene; p-chlorotoluene; 3,4-dichloro a,a,a-trifluorotoluene; 3,4-dichlorotoluene; 2,4-dinitrotoluene; methyl-4-toluenesulfonate; p-nitro toluene; toluene; a,a,a-trifluoro toluene; 2-vinyl toluene; 2,3,4,5,6-pentafluorotoluene; o-ethyltoluene; m-ethyltoluene; p-ethyltoluene; o-fluorotoluene; m-fluorotoluene; p-fluorotoluene; toluene diamine (2,6-toluene diamine); 2,5-dinitrotoluene; 2,6-dinitrotoluene; 3,4-dinitrotoluene; 3,5-dinitrotoluene; m-nitrotoluene; o-nitrotoluene; toluene diisocyanate; p-iodotoluene; m-chlorotoluene; m-bromotoluene; toluenediamine; o-iodotoluene; 2,3-dimethoxytoluene; 2,5-dimethoxytoluene; 2,5-dichlorotoluene; 2,6-dichlorotoluene; 2,4-dichlorotoluene; 2,3-dichlorotoluene; 4-chloro-3-nitrotoluene; p-toluenesulfonamide; 2,3-dinitrotoluene; p-toluenesulfonyl chloride; ethyl p-toluenesulfonate; m-iodotoluene; 3,4-diaminotoluene; 3,4-dimethoxytoluene; p-toluenesulfonic acid; 2,3,4,5,6-pentachlorotoluene; o-toluenesulfonic acid; 2,6-toluene diisocyanate; 4-nitrotoluene-2-sulphonic acid; 1(p-toluenesulphonyl)imidazole; toluene-2,5-diamine (2,5-diaminotoluene); 2-phenoxytoluene; 3-phenoxytoluene; 4-phenoxytoluene; 3-phenoxybenzaldehyde; 3-phenoxyphenol; 1-methoxy-3-phenoxybenzene; 1,1′-oxybis[3-methylbenzene]; 3-phenoxybenzenemethanamine; 1,3-dimethyl-5-phenoxybenzene; 1-ethenyl-3-phenoxybenzene; 3-phenoxybenzonitrile; 1-methyl-3-(4-methylphenoxy)benzene; 3,3′-oxybis[phenol]; 1,2-dimethyl-4-phenoxybenzene; 3,3′-methylenebis[phenol]; 1-ethynyl-3-phenoxybenzene; 4′-hydroxy-3-phenoxybenzyl alcohol; 1-(4-methoxyphenoxy)-3-methylbenzene; 1-methyl-2-(3-methylphenoxy)benzene; 4-(3-methylphenoxy)phenol; 1-ethyl-3-phenoxybenzene; 1-methoxy-3-(4-methylphenoxy)benzene; α-methyl-3-phenoxybenzenemethanol; 1,1′-methylenebis[3-methoxybenzene]; (αR)-α-methyl-3-phenoxybenzenemethanol; 1,3-dimethoxy-5-(phenylmethyl)benzene; 1-(iodomethyl)-3-phenoxybenzene; 3-phenoxybenzeneethanol; 5-(phenylmethyl)-1,3-benzenediol; 3-(2-methylphenoxy)phenol; (αS)-α-methyl-3-phenoxybenzenemethanol; 3-(4-methylphenoxy)phenol; 2-(3-methylphenoxy)phenol; 3-(3-methylphenoxy)phenol; 1-methoxy-3-(3-methylphenoxy)benzene; 3-(3-methylphenoxy)benzenamine; 2-methyl-4-phenoxyphenol; 5-phenoxy-1,3-benzenediol; 1,2-dimethyl-3-phenoxybenzene; 1-methoxy-3-methyl-5-phenoxybenzene; 3-methyl-5-phenoxyphenol; 3-(3-hydroxyphenoxy)-5-methylphenol; 3-(3-methylphenoxy)benzenemethanol; 3-hydroxy-5-phenoxybenzenemethanol; 3-(3-hydroxyphenoxy)benzenemethanol; 1-(1-methylethyl)-3-phenoxybenzene; 2-methyl-3-phenoxyphenol; 2-methyl-6-phenoxyphenol; 2-methyl-5-phenoxyphenol; 1-(methoxymethyl)-3-phenoxybenzene; 3-methoxy-5-(phenylmethyl)phenol; bis(m-ethylphenyl)ether; and mixtures thereof.

It is preferred that any binary, tertiary, quaternary or higher mixtures of the aforementioned formulation media are used in the present invention.

In a preferred embodiment of the present invention, the formulation provided in step (a) of the method for preparing an optical metal oxide layer further comprises one or more additives selected from surfactants, wetting and dispersion agents, adhesion promoters, and polymer matrices.

Preferred surfactants are surface active substances, which preferably include surface active metal oxides and/or surface-active organic compounds. Surface-active organic compounds may include nonionic surfactants, anionic surfactants, and ampholytic surfactants and they may be coordinating or non-coordinating.

Examples of nonionic surfactants include, polyoxyethylene alkyl ethers, such as polyoxyethylene lauryl ether, polyoxyethylene oleyl ether and 30 polyoxyethylene cetyl ether; polyoxyethylene fatty acid diester; polyoxyethylene fatty acid monoester; polyoxyethylene polyoxypropylene block polymer; acetylene alcohol; acetylene glycol; polyethoxylate of acetylene alcohol; acetylene glycol derivatives, such as polyethoxylate of acetylene glycol; fluorine-containing surfactants, for example, FLUORAD (trade name, manufactured by Sumitomo 3M Limited), MEGAFAC (trade name: manufactured by DIC Cooperation), SURFLON (trade name, 5 manufactured by Asahi Glass Co. Ltd); or organosiloxane surfactants, for example, KP341 (trade name, manufactured by Shin-Etsu Chemical Co., Ltd.), and the like. Examples of said acetylene glycol include 3-methyl-1-butyne-3-ol, 3-methyl-1-pentyn-3-ol, 3,6-dimethyl-4-octyne-3,6-diol, 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,5-dimethyl-1-hexyne-3-ol, 2,5-dimethyl-3-10 hexyne-2,5-diol, 2,5-dimethyl-2,5-hexane-diol, and the like.

Examples of anionic surfactants include ammonium salt or organic amine salt of alkyl diphenyl ether disulfonic acid, ammonium salt or organic amine salt of alkyl diphenyl ether sulfonic acid, ammonium salt or organic amine 15 salt of alkyl benzene sulfonic acid, ammonium salt or organic amine salt of polyoxyethylene alkyl ether sulfuric acid, ammonium salt or organic amine salt of alkyl sulfuric acid, and the like.

Examples of amphoteric surfactants include 2-alkyl-N-carboxymethyl-N-20 hydroxyethyl imidazolium betaine, lauric acid amide propyl hydroxysulfone betaine, and the like.

Preferred surface-active metal oxides are selected from the list consisting of aluminum oxide, calcium oxide, silica, and zinc oxide. Such surface-active metal oxides are preferably present as fine powders, more preferably as nanoparticles, which are optionally surface treated.

Preferred surface-active organic compounds are surface-active non-polymeric compounds or surface-active polymeric organic compounds, wherein said surface-active non-polymeric compounds are preferably selected from the list consisting of alcohols, alkoxylates, aromatics, ketones, esters, modified urea, silanes, siloxanes and soap-based foam stabilizers, which are optionally functionalized and/or modified; and wherein said surface-active polymeric compounds are preferably selected from the list consisting of hydroxy polyesters, maleinate resins, polyacrylates, polyethers, polyester, polysilanes, silicone resins, and waxes, which are optionally functionalized and/or modified; and which are optionally present as copolymers. In a preferred embodiment, the surface-active organic compound is used as a solution.

Preferred silanes are polyether-modified silanes, polyester-modified silanes, and polyether-polyester-modified silanes. Preferred siloxanes are polyether-modified siloxanes, polyester-modified siloxanes, and polyether-polyester-modified siloxanes.

Preferred polyacrylates are modified polyacrylates, preferably silicone-modified polyacrylates, polyether macromer-modified polyacrylates, and silicone and polyether macromer-modified polyacrylates, which are optionally present as copolymers.

Preferred polysilanes are polyether-modified polysilanes (e.g. PEG-Silane 6-9), polyester-modified polysilanes, and polyether-polyester-modified polysilanes.

Preferred silicone resins are polyether-modified polysiloxanes, preferably polyether-modified polydialkylsiloxanes, more preferably polyether-modified polymethylalkylsiloxanes, and most preferably polyether-modified polydimethylsiloxanes and polyether-modified, hydroxy-functional polydimethylsiloxanes; polyester-modified polysiloxanes, preferably polydialkylsiloxanes, more preferably polyester-modified polymethylalkylsiloxanes, and most preferably polyester-modified polydimethylsiloxanes and polyester-modified, hydroxy-functional polydimethylsiloxanes; polyether-polyester-modified polysiloxanes, preferably polyether-polyester-modified polydialkylsiloxanes, more preferably polyether-polyester-modified polymethylalkylsiloxanes, and most preferably polyether-polyester-modified polydimethylsiloxanes and polyether-polyester-modified, hydroxy-functional polydimethylsiloxanes; epoxy functional polysiloxanes, preferably epoxy functional polydialkylsiloxanes, more preferably epoxy functional polymethylalkylsiloxanes, and most preferably epoxy functional polydimethylsiloxanes; acryl functional polysiloxanes, preferably acryl functional polydialkylsiloxanes, more preferably acryl functional polymethylalkylsiloxanes, and most preferably acryl functional polydimethylsiloxanes; polyether-modified, acryl functional polysiloxanes, preferably polyether-modified, acryl-functional polydialkylsiloxanes, more preferably polyether-modified, acryl-functional polymethylalkylsiloxanes, and most preferably polyether-modified, acryl-functional polydimethylsiloxanes; polyester-modified, acryl-functional polysiloxanes, preferably polyester-modified, acryl-functional polydialkylsiloxanes, more preferably polyester-modified, acryl-functional polymethylalkylsiloxanes, and most preferably polyester-modified, acryl-functional polydimethylsiloxanes; and aralkyl-modified polysiloxanes, preferably aralkyl-modified polydialkylsiloxanes, more preferably aralkyl-modified polymethylalkylsiloxanes, and most preferably aralkyl-modified polydimethylsiloxanes; which are optionally present as copolymers.

Preferred surfactants are commercially available from BYK-Chemie GmbH, Wesel, Germany and offered as surface additives. Preferred surfactants are BYK-300, BYK-301, BYK-302, BYK-306, BYK-307, BYK-310, BYK-313, BYK-315 N, BYK-320, BYK-322, BYK-323, BYK-325 N, BYK-326, BYK-327, BYK-329, BYK-330, BYK-331, BYK-332, BYK-333, BYK-342, BYK-345, BYK-346, BYK-347, BYK-348, BYK-349, BYK-350, BYK-352, BYK-354, BYK-355, BYK-356, BYK-358 N, BYK-359, BYK-360 P, BYK-361 N, BYK-364 P, BYK-366 P, BYK-368 P, BYK 370, BYK 375, BYK-377, BYK-378, BYK-381, BYK-390, BYK-392, BYK-394, BYK-399, BYK-2616, BYK-3400, BYK-3410, BYK-3420, BYK-3450, BYK-3451, BYK-3455, BYK-3456, BYK-3480, BYK-3481, BYK-3499, BYK-3550, BYK-3560, BYK-3565, BYK-3566, BYK-3750, BYK-3751, BYK-3752, BYK-3753, BYK-3754, BYK-3760, BYK-3761, BYK-3762, BYK-3763, BYK-3764, BYK-3770, BYK-3771, BYK-3780, BYK-3900 P, BYK 3902 P, BYK-3931 P, BYK 3932 P, BYK-3933 P, BYK-8020, BYK-8070, BYK-9890, BYK-DYNWET 800, BYK-S 706, BYK-S 732, BYK-S 740, BYK-S 750 N, BYK-S 760, BYK-S 780, BYK-S 782, BYK-SILCELAN 3700, BYK-SILCLEAN 3701, BYK-SILCLEAN 3710, BYK-SILCLEAN 3720, BYK-UV 3500, BYK-UV 3505, BYK-UV 3510, BYK-UV 3530, BYK-UV 3535, BYK-UV 3570, BYK-UV 3575, BYK-UV 3576, BYKETOL-AQ, BYKETOL-OK, BYKETOL-PC, BYKETOL-SPECIAL, BYKETOL-WA, NANOBYK-3603, NANOBYK-3605, NANOBYK-3620, NANOBYK-3650, NANOBYK-3652, and NANOBYK-3822.

The wetting and dispersion agents used in the present invention are additives, which provide both wetting and/or stabilizing effects for formulations containing fine solid particles. They result in a fine and homogenous distribution of solid particles in a formulation media, preferably liquid formulation media, and ensure long-term stability of such systems. The formulation media may comprise water and the entire range of organic solvents of varying polarity. Moreover, they result in an improved wetting of solids and prevent particles from flocculating by various mechanisms (e.g. by electrostatic effects, steric effects, etc.).

Preferably, the wetting and dispersion agents are organic polymers or organic copolymers having polar functional groups selected from amino groups; amide groups; carbamate groups; carbonate groups; acidic groups, preferably boric acid groups, boronic acid groups, carboxylic acid groups, sulfuric acid groups, sulfonic acid groups, phosphoric acid groups, phosphonic acid groups, and phosphinic acid groups; ester groups, preferably boric ester groups, boronic ester groups, carboxylic ester groups, sulfuric ester groups, sulfonic ester groups, phosphoric ester groups, phosphonic ester groups, and phosphinic ester groups; ether groups; hydroxy groups; keto groups; and urea groups; wherein the organic polymers or copolymers may be present as a conjugate, derivative and/or salt, preferably as a salt. Preferred salts are ammonium salts, alkyl ammonium salts, alkylol ammonium salts, or alkaline metal salts such as preferably Li, Na, K and Rb salts. The polar functional groups may be also referred to as pigment-affinic groups or as filler-affinic groups. In a preferred embodiment, the wetting and dispersion agent is used as a solution.

More preferably, the wetting and dispersion agents are organic polymers or organic copolymers selected from acrylates; amides; carboxylic acids; and esters; wherein the organic polymers or copolymers may be present as a conjugate, derivative and/or salt, preferably as a salt; and wherein they may be further functionalized with one or more polar functional group as described above. Preferred salts are ammonium salts, alkyl ammonium salts, alkylol ammonium salts, or alkaline metal salts such as preferably Li, Na, K and Rb salts. In a preferred embodiment, the wetting and dispersion agent is used as a solution.

The wetting and dispersion agents may be present as a mixture, preferably as a mixture with a polysiloxane copolymer.

Preferred wetting and dispersing agents are commercially available from BYK-Chemie GmbH, Wesel, Germany. Preferred wetting and dispersing agents are ANTI-TERRA-202, ANTI-TERRA-203, ANTI-TERRA-204, ANTI-TERRA-205, ANTI-TERRA-210, ANTI-TERRA-250, ANTI-TERRA-U, ANTI-TERRA-U 80, ANTI-TERRA-U 100, BYK-151, BYK-153, BYK-154, BYK-155/35, BYK-156, BYK-220 S, BYK-1160, BYK-1162, BYK-1165, BYK-9076, BYK-9077, BYK-GO 8702, BYK-GO 8720, BYK-P 104, BYK-P 104 S, BYK-P 105, BYK-SYNERGIST 2100, BYK-SYNERGIST 2105, BYK-W 900, BYK-W 903, BYK-W 907, BYK-W 908, BYK-W 909, BYK-W 940, BYK-W 961, BYK-W 966, BYK-W 969, BYK-W 972, BYK-W 974, BYK-W 980, BYK-W 985, BYK-W 995, BYK-W 996, BYK-W 9010, BYK-W 9011, BYK-W 9012, BYKJET-9131, BYKJET-9132, BYKJET-9133, BYKJET-9142, BYKJET-9150, BYKJET-9151, BYKJET-9152, BYKJET-9170, BYKJET-9171, BYKUMEN, DISPERBYK, DISPERBYK-101 N, DISPERBYK-102, DISPERBYK-103, DISPERBYK-106, DISPERBYK-107, DISPERBYK-108, DISPERBYK-109, DISPERBYK-110, DISPERBYK-111, DISPERBYK-115, DISPERBYK-118, DISPERBYK-130, DISPERBYK-140, DISPERBYK-142, DISPERBYK-145, DISPERBYK-161, DISPERBYK-162, DISPERBYK-162 TF, DISPERBYK-163, DISPERBYK-163 TF, DISPERBYK-164, DISPERBYK-165, DISPERBYK-166, DISPERBYK-167, DISPERBYK-167 TF, DISPERBYK-168, DISPERBYK-168 TF, DISPERBYK-169, DISPERBYK-170, DISPERBYK-171, DISPERBYK-174, DISPERBYK-180, DISPERBYK-181, DISPERBYK-182, DISPERBYK-184, DISPERBYK-185, DISPERBYK-187, DISPERBYK-190, DISPERBYK-190 BF, DISPERBYK-191, DISPERBYK-192, DISPERBYK-193, DISPERBYK-194 N, DISPERBYK-199, DISPERBYK-199 BF, DISPERBYK-2000, DISPERBYK-2001, DISPERBYK-2008, DISPERBYK-2009, DISPERBYK-2010, DISPERBYK-2012, DISPERBYK-2013, DISPERBYK-2014, DISPERBYK-2015, DISPERBYK-2015 BF, DISPERBYK-2018, DISPERBYK-2019, DISPERBYK-2022, DISPERBYK-2023, DISPERBYK-2025, DISPERBYK-2026, DISPERBYK-2030, DISPERBYK-2050, DISPERBYK-2055, DISPERBYK-2059, DISPERBYK-2060, DISPERBYK-2061, DISPERBYK-2062, DISPERBYK-2070, DISPERBYK-2080, DISPERBYK-2081, DISPERBYK-2096, DISPERBYK-2117, DISPERBYK-2118, DISPERBYK-2150, DISPERBYK-2151, DISPERBYK-2152, DISPERBYK-2155, DISPERBYK-2155 TF, DISPERBYK-2157, DISPERBYK-2158, DISPERBYK-2159, DISPERBYK-2163, DISPERBYK-2163 TF, DISPERBYK-2164, DISPERBYK-2190, DISPERBYK-2200, DISPERBYK-2205, DISPERBYK-2290, DISPERBYK-2291, DISPERPLAST-1142, DISPERPLAST-1148, DISPERPLAST-1150, DISPERPLAST-1180, DISPERPLAST-I, and DISPERPLAST-P.

Preferred adhesion promoters are block copolymers, preferably high molecular weight block copolymers; copolymers with functional groups, preferably hydroxy-functional copolymers with acidic groups, styrene-ethylene/butylene-styrene block copolymer (SEBS) functionalized with maleic acid anhydride, carboxylated SEBS functionalized with maleic anhydride, SEBS functionalized with glycidyl methacrylate, polyolefin block copolymer functionalized with maleic acid anhydride, and ethylene octene copolymer functionalized with maleic anhydride; and polymers with functional groups, preferably polymers with acidic groups, and polypropylene functionalized with maleic anhydride. In a preferred embodiment, the adhesion promoter is used as a solution.

Preferred adhesion promoters are commercially available from BYK-Chemie GmbH, Wesel, Germany. Preferred adhesion promoters are BYK-4500, BYK-4509, BYK-4510, BYK-4511, BYK-4512, BYK-4513, SCONA TPKD 8102 PCC, SCONA TSIN 4013 GC, SCONA TSPOE 1002 GBLL, SCONA TPPP 2112 FA, SCONA TPPP 2112 GA, SCONA TPPP 8112 GA, SCONA TSKD 9103, SCONA TPPP 8112 FA, SCONA TPKD 8304 PCC, and SCONA TSPP 10213 GB.

Preferred polymer matrices are polymethyl methacrylate, polyvinylpyrrolidone, polycarbonate, polystyrene, polymethylpentene, and silicone.

It is particularly preferred that a combination of two or more of the above-mentioned additives are present in the formulation. Particularly preferred combinations are polymer matrices+wetting agents, and adhesion promoters+wetting and dispersion agents.

In a preferred embodiment of the present invention, the mass ratio of the additives in the formulation is from >0% to ≤10% (w/w), preferably >0.01% to <9% (w/w), more preferably >0.05% to <7.5% (w/w), and most preferably >0.1% to <5.0 (w/w), based on the total mass of the formulation.

In a preferred embodiment of the present invention, the formulation provided in step (a) of the method for preparing an optical metal oxide layer comprises one or more further metal complexes, which may act as further metal oxide precursor(s). In such case, a mixed optical metal oxide layer may be formed comprising a metal oxide obtained from the titanium polyoxometalate(s) (POMs) and a further metal oxide obtained from the further metal oxide precursor(s).

Preferred further metal complexes comprise one or more trivalent or tetravalent metals M′, preferably selected from the list consisting of Sc, Y, La, Ti, Zr, Hf and Sn, more preferably one or more tetravalent metals M′ selected from the list consisting of Ti, Zr, Hf and Sn.

Preferred further metal complexes comprise one or more ligand species L^j, as defined in Formula (1) and the description above.

In a preferred embodiment of the present invention, the formulation provided in step (a) of the method for preparing an optical metal oxide layer comprises one, two, three, four or more further metal complexes in addition to the one or more titanium polyoxometalate(s) (POMs), where preferably each of the further metal complexes contains ligand species L selected from organic ligands or inorganic ligands. Preferred inorganic ligands are halogenids, phosphoric acid, sulfonic acid, nitric acid and water, which are optionally deptrotonated. Preferred organic ligands are alcohols, carboxylic acids, cyanates, isocyanates, 1,3-diketones, beta-keto acids, beta-keto esters, organylphosphonic acids, organylsulfonic acids, oximes, hydroxamic acids, dihydroxy benzenes, hydroxybenzoic acids, dihydroxy benzoic acids, gallic acid, dihydroxynaphthalenes, anthracene diols, hydroxy-anthrones, anthracene triols, dithranols, halogenated hydrocarbons, aromatics, heteroaromatics, esters, catechols, coumarins and their derivatives, which are optionally deprotonated.

The presence of such further metal complexes allows to adjust certain properties of the optical metal oxide layer prepared therefrom such as e.g. material hardness, shrinkage, refractive index, transparency, absorbance, and haze suppression.

Preferably, the mass ratio (w/w) between the one or more titanium polyoxometalates (POMs) and the one or more further metal complexes in the formulation is in the range from 1:100 to 100:1, preferably from 1:10 to 10:1, and more preferably from 1:5 to 5:1.

In a preferred embodiment of the present invention, the formulation provided in step (a) of the method for preparing an optical metal oxide layer is a mixture being suitable for inkjet printing.

In a preferred embodiment of the method for preparing an optical metal oxide layer according to the present invention, the formulation is applied in step (b) to a surface of a substrate by a deposition method. A preferred deposition method is drop casting, coating, or printing. A more preferred deposition method is spin coating or inkjet printing.

Depending on the specific problem to be solved, the formulation needs to be deposited either as a homogeneous, dense and thin layer covering the entire surface of the substrate by a coating method or the formulation needs to be deposited locally in a structured manner, thus requiring for a printing method. Both, coating and printing methods require formulations to be formulated in an adequate manner to comply with the physico-chemical needs of the respective coating and printing method as well as to comply with certain needs regarding the surface of the substrate to be coated or printed.

In a preferred embodiment of the method for preparing an optical metal oxide layer according to the present invention, the surface of the substrate is pre-treated by a surface cleaning process. Preferred surface cleaning processes are silicon wafer cleaning processes such as described in W. Kern, The Evolution of Silicon Wafer Cleaning Technology, J. Electrochem. Soc., Vol. 137, 6, 1990, 1887-1892 and in New Process Technologies for Microelectronics, RCA Review 1970, 31, 2, 185-454. Such silicon wafer cleaning processes include wet cleaning process involving cleaning solvents (e.g. isopropanol (IPA)); wet etching processes involving hydrogen peroxide solutions (e.g. piranha solution, SC1, and SC2), choline solutions, or HF solutions; dry etching processes involving chemical vapor etching, UV/ozone treatments or glow discharge techniques (e.g. O₂ plasma etching); and mechanical processes involving brush scrubbing, fluid jet or ultrasonic techniques (sonification). The surface of the substrate can also be pre-treated by silanization or an atomic layer deposition (ALD) process. The pre-treatment of the surface of the substrate serves to modify the hydrophobicity/hydrophilicity of the surface. This can improve the adhesion and filling characteristics of the optical metal oxide layer on the surface of the substrate.

In a more preferred embodiment, a wet cleaning process involving cleaning solvents (e.g. isopropanol (IPA)) is combined with one or more of a wet etching process involving hydrogen peroxide solutions (e.g. piranha solution, SC1, and SC2), choline solutions, or HF solutions; dry etching process involving chemical vapor etching, UV/ozone treatments or glow discharge techniques (e.g. O₂ plasma etching); and mechanical process involving brush scrubbing, fluid jet or ultrasonic techniques (sonification).

In a most preferred embodiment, a wet cleaning process involving cleaning solvents (e.g. isopropanol (IPA)) is combined with a mechanical process involving brush scrubbing, fluid jet or ultrasonic techniques (sonification) and with a wet etching process involving hydrogen peroxide solutions (e.g. piranha solution, SC1, and SC2), choline solutions, or HF solutions; In a preferred embodiment of the present invention, step (b) of the method for preparing an optical metal oxide layer is carried out several times in succession, preferably 2 to 20 times, more preferably 2 to 10 times, most preferably 2, 3, 4 or 5 times.

In a preferred embodiment of the method for preparing an optical metal oxide layer according to the present invention, the formulation is converted in step (c) on the surface of the substrate to an optical metal oxide layer by exposure to thermal treatment and/or irradiation treatment.

Preferred thermal treatment includes exposure to elevated temperatures as high as 1200° C., preferably up to 600° C., more preferably up to 550° C. and most preferably up to 500° C. Thermal treatment is not limited to any specific thermal treatment methods or times. Depending on the type of substrate and formulation, a person skilled in the art is able to determine suitable thermal treatment methods and times.

Preferred irradiation treatment includes exposure to infrared (IR) light, visible (VIS) light and/or ultraviolet (UV) light. IR light has a wavelength of >800 nm. VIS light has a wavelength from 400 to 800 nm. UV light has a wavelength of <400 nm and may include EUV (extreme UV). Irradiation treatment is not limited to any specific irradiation treatment methods or times. Depending on the type of substrate and formulation, a person skilled in the art is able to determine suitable irradiation treatment methods and times.

In a more preferred embodiment of the method for preparing an optical metal oxide layer according to the present invention, the formulation is converted in step (c) on the surface of the substrate to an optical metal oxide layer by pre-baking (soft baking) at a temperature from 40 to 150° C., preferably from 50 to 120° C., more preferably from 60 to 100° C.; and then baking (hard baking, sintering or annealing) at a temperature from 150 to 600° C., preferably from 250 to 550° C., more preferably from 300 to 500° C.

In a preferred embodiment of the method for preparing an optical metal oxide layer according to the present invention, the substrate is a patterned substrate comprising topographical features and the metal oxide forms a coating layer covering the surface of the substrate and filling said topographical features. As a result, the topographical features are filled and levelled by said metal oxide.

Preferred topographical features include, for example, gaps, grooves, trenches and vias. Topographical features may be distributed uniformly or non-uniformly over the surface of the substrate. Preferably, they are arranged as an array or grating on the surface of the substrate. It is preferred that the topographical features have different lengths, widths, diameters as well as different aspect ratios. It is preferred that said topographical features have an aspect ratio of 1:20 to 20:1, more preferably 1:10 to 10:1. The aspect ratio is defined as width of structure to its height (or depth). From the viewpoint of dimension, the depth of the topographical features is preferably in the range from 10 nm to 10 μm, more preferably 50 nm to 5 μm, and most preferably 100 nm to 1 μm.

It is also preferred that the topographical features are inclined at a certain angle, such as an angle from 10 to 80°, preferably from 20 to 60°, more preferably from 30 to 50°, most preferably about 40°. Such inclined topographical features are also referred to as slanted or blazed topographical features.

It may be also necessary to fill topographical features locally with optical metal oxide layer, either completely or to a certain level, but not to cover adjacent surfaces of the substrate, where no topographical features to be filled are available.

Hence, it is preferred that the method for preparing an optical metal oxide layer according to the present invention further comprises the following step:

• • (d) removing a portion of said optical metal oxide layer covering the top of the topographical features, thereby obtaining filled topographical features, wherein an overburden of the optical metal oxide layer on top of said topographical features is reduced, preferably to an overburden of between 0 to 100 nm, more preferably between 0 to 50, and most preferably between 0 to 20 nm.

Step (d) takes place after steps (a) to (c) of the method according to the present invention. Preferably, removing a portion of said optical metal oxide layer covering a top of the topography in step (d) is performed by using a surface cleaning process as described above. Preferred surface cleaning processes are silicon wafer cleaning processes such as described in W. Kern, The Evolution of Silicon Wafer Cleaning Technology, J. Electrochem. Soc., Vol. 137, 6, 1990, 1887-1892 and in New Processe Technologies for Microelectronics, RCA Review 1970, 31, 2, 185-454. Such silicon wafer cleaning processes include wet-etching processes involving hydrogen peroxide solutions (e.g. piranha solution, SC1, and SC2), choline solutions, or HF solutions; dry-etching processes involving chemical vapor etching, UV/ozone treatments or glow discharge techniques (e.g. O₂ plasma etching); and mechanical processes involving brush scrubbing, fluid jet or ultrasonic techniques.

The substrate is preferably a substrate of an optical device. Preferred substrates are made of inorganic or organic base materials, preferably inorganic base materials. Preferred inorganic base materials contain materials selected from the list consisting of ceramics, glass, fused silica, sapphire, silicon, silicon nitride, quartz, and transparent polymers or resins. The geometry of the substrate is not specifically limited, however, preferred are sheets or wafers.

In step (b) of the method for preparing an optical metal oxide layer, the formulation is applied on a surface of a substrate, wherein said surface may be either a surface of a base material of the substrate or a surface of a layer of a material being different from the base material of the substrate, wherein such layer has been formed prior to applying said formulation.

In this way, sequences of different layers (layer stacks) can be formed on top of one another. Such layer stacks may be also structured, wherein such structures typically have dimensions in the nanometer scale, at least with respect to diameter, width and/or aspect ratio.

Formulation

The present invention furthermore relates to a formulation for preparing an optical metal oxide layer, wherein the formulation comprises:

• • (i) one or more titanium polyoxometalates (POMs);
  • (ii) one or more formulation media; and
  • (iii) one or more additives selected from surfactants, wetting and dispersion agents, adhesion promoters, and polymer matrices.

In a preferred embodiment of the formulation for preparing an optical metal oxide layer according to the present invention, the one or more titanium polyoxometalates (POMs) comprise independently from each other three or more, preferably four or more, titanium atoms and one or more, preferably two or more, ligand species, preferably organic ligand species.

The titanium polyoxometalates (POMs) used in the present invention are cluster materials as described above for the method for preparing an optical metal oxide layer.

In a preferred embodiment, the titanium polyoxometalates (POMs) in the formulation according to the present invention are independently from each other represented by the following Formula (1):

$\begin{array}{cc}\left\{{{\mathrm{Ti}}_u\left({\mu }_2-\mathrm{OH}\right)}_v{\left({\mu }_3-\mathrm{OH}\right)}_w{\left({\mu }_2-O\right)}_x{\left({\mu }_3-O\right)}_y{\left({\mu }_4-O\right)}_z\right\}\prod _{j=1}^{j=n}{\left(L^j\right)}_{a_j}& \mathrm{Formula}\left(1\right)\end{array}$

wherein:

• • μ₂-OH represents a bidentate bridging hydroxo (OH⁻);
  • μ₃-OH represents a tridentate bridging hydroxo (OH⁻);
  • μ₂-O represents a bidentate bridging oxido (O²⁻);
  • μ₃-O represents a tridentate bridging oxido (O²⁻);
  • μ₄-O represents a tetradentate bridging oxido (O²⁻);
  • L^j represents at each occurrence independently from each other a ligand species, preferably an organic ligand species;
  • a_j is at each occurrence independently from each other an integer from 1 to 100, preferably 1 to 70, more preferably 1 to 50;
  • n is an integer from 2 to 10, preferably 2 to 5, more preferably 2, 3 or 4;
  • u is an integer from 2 to 100, preferably 2 to 70, more preferably 3 to 50;
  • v is an integer from 0 to 100, preferably 0 to 70, more preferably 0 to 50;
  • w is an integer from 0 to 100, preferably 0 to 70, more preferably 0 to 50;
  • x is an integer from 0 to 100, preferably 0 to 70, more preferably 0 to 50;
  • y is an integer from 0 to 100, preferably 0 to 70, more preferably 0 to 50; and
  • z is an integer from 0 to 100, preferably 0 to 70, more preferably 0 to 50.

It is preferred that at least one of v, w, x, y and z is not 0. It is more preferred that at least two of v, w, x, y and z are not 0.

In a more preferred embodiment of the present invention, the titanium polyoxometalates (POMs) in the formulation according to the present invention are independently from each other represented by Formula (1) as described above, wherein in addition the following equation is fulfilled:

$4^{*}u-\left[v+w+2^{*}\left(x+y+z\right)+\sum _{j=1}^{j=n}\left({m_j\left(L^j\right)}^{*}{a}_j\right)\right]=c$

wherein:

• • m_j(L^j) represents the amount of negative charge of L^j, preferably m_j(L^j) is at each occurrence independently from each other an integer selected from 0, 1, 2, 3, 4 and 5, more preferably 0, 1, 2 and 3, and most more preferably 0, 1 and 2; and c represents the total charge of the titanium polyoxometalate (POM), preferably c is an integer from −10 to +10, more preferably from −5 to +5, and most preferably c=0; and a_j, n, u, v, w, x, y and z are defined as shown above.

Preferably, the ligand species L^j is selected at each occurrence independently from each other from organic ligands or inorganic ligands. Preferred inorganic ligands are halogenids, phosphoric acid, sulfonic acid, nitric acid and water, which are optionally deptrotonated. Preferred organic ligands are alcohols, carboxylic acids, cyanates, isocyanates, 1,3-diketones, beta-keto acids, beta-keto esters, organylphosphonic acids, organylsulfonic acids, oximes, hydroxamic acids, dihydroxy benzenes, hydroxybenzoic acids, dihydroxy benzoic acids, gallic acid, dihydroxynaphthalenes, anthracene diols, hydroxy-anthrones, anthracene triols, dithranols, halogenated hydrocarbons, aromatics, heteroaromatics, esters, catechols, coumarins and their derivatives, which are optionally deprotonated.

More preferably, the ligand species L^j is selected at each occurrence independently from each other from the list in Table 1 as described above for the method for preparing an optical metal oxide layer.

It goes without saying that the abovementioned ligand species L^j can each be present in their protonated or unprotonated form in the titanium polyoxomometalate (POM), even if only one form is shown in each case.

The titanium polyoxometalates (POMs) may comprise one or more alkaline metals selected from Li, Na, K, Rb and Cs. The titanium polyoxometalates (POMs) may comprise one or more alkaline earth metals selected from Be, Mg, Ca, Sr, and Ba. The titanium polyoxometalates (POMs) may comprise one or more alkaline metals selected from Li, Na, K, Rb and Cs; and one or more alkaline earth metals selected from Be, Mg, Ca, Sr, and Ba.

In a preferred embodiment of the present invention, the titanium polyoxometalates (POMs) are independently from each other selected from the list in Table 2 as described above for the method for preparing an optical metal oxide layer.

In a more preferred embodiment of the present invention, the titanium polyoxometalates (POMs) are independently from each other selected from Ti₁₂ polyoxometalates, Ti₁₆ polyoxometalates, Ti₁₈ polyoxometalates, Ti₄₄ polyoxometalates, and Ti₅₂ polyoxometalates.

In a most preferred embodiment of the present invention, the titanium polyoxometalates (POMs) are independently from each other selected from the list in Table 3 as described above for the method for preparing an optical metal oxide layer.

In a very most preferred embodiment of the present invention, the titanium polyoxometalates (POMs) are independently from each other selected from the list in Table 4 as described above for the method for preparing an optical metal oxide layer.

Preferably, the mass ratio of titanium polyoxometalates (POMs) in the formulation is in the range from 0.1% to 50% (w/w), preferably 0.5% to 40% (w/w), more preferably 1% to 30% (w/w), based on the total mass of the formulation.

In a preferred embodiment of the present invention, the one or more formulation media are solution media and/or dispersion media. The formulation media are selected to improve applicability, wettability, deposition properties, filling properties and/or stability of the formulation. Any formulation media can be used as long as it dissolves or disperses the titanium polyoxometalates (POMs) comprised in the formulation according to the present invention.

In a more preferred embodiment of the present invention, the one or more formulation media are selected from water, amides, aromatic hydrocarbons, non-aromatic hydrocarbons, alcohols, carboxylic acids, esters, ethers, ketones, diketones, lactones, and mixtures thereof.

In a most preferred embodiment of the present invention, the one or more formulation media are selected from the list as described above for the method for preparing an optical metal oxide layer.

It is preferred that any binary, tertiary, quaternary or higher mixtures of the aforementioned formulation media are used in the present invention.

Preferred surfactants, wetting and dispersion agents, adhesion promoters, and polymer matrices in the formulation according to the present invention are the same as described above for the method for preparing an optical metal oxide layer.

It is particularly preferred that a combination of two or more of the above-mentioned additives are present in the formulation. Particularly preferred combinations are polymer matrices+wetting agents, and adhesion promoters+wetting and dispersion agents.

In a preferred embodiment of the present invention, the mass ratio of the additives in the formulation is from >0% to ≤10% (w/w), preferably >0.01% to <9% (w/w), more preferably >0.05% to <7.5% (w/w), and most preferably >0.1% to <5.0 (w/w), based on the total mass of the formulation.

In a preferred embodiment of the present invention, the formulation comprises one or more further metal complexes, which may act as further metal oxide precursor(s). In such case, a mixed optical metal oxide layer may be formed comprising a metal oxide obtained from the titanium polyoxometalate(s) (POMs) and a further metal oxide obtained from the further metal oxide precursor(s).

Preferred further metal complexes comprise one or more trivalent or tetravalent metals M′, preferably selected from the list consisting of Sc, Y, La, Ti, Zr, Hf and Sn, more preferably one or more tetravalent metals M′ selected from the list consisting of Ti, Zr, Hf and Sn.

Preferred further metal complexes comprise one or more ligand species L^j, as defined in Formula (1) and the description above.

In a preferred embodiment of the present invention, the formulation comprises one, two, three, four or more further metal complexes in addition to the one or more titanium polyoxometalate(s) (POMs), where preferably each of the further metal complexes contains ligand species L^j selected from organic ligands or inorganic ligands. Preferred inorganic ligands are halogenids, phosphoric acid, sulfonic acid, nitric acid and water, which are optionally deptrotonated. Preferred organic ligands are alcohols, carboxylic acids, cyanates, isocyanates, 1,3-diketones, beta-keto acids, beta-keto esters, organylphosphonic acids, organylsulfonic acids, oximes, hydroxamic acids, dihydroxy benzenes, hydroxybenzoic acids, dihydroxy benzoic acids, gallic acid, dihydroxynaphthalenes, anthracene diols, hydroxy-anthrones, anthracene triols, dithranols, halogenated hydrocarbons, aromatics, heteroaromatics, esters, catechols, coumarins and their derivatives, which are optionally deprotonated.

The presence of such further metal complexes allows to adjust certain properties of the optical metal oxide layer prepared therefrom such as e.g. material hardness, shrinkage, refractive index, transparency, absorbance, and haze suppression.

Preferably, the mass ratio (w/w) between the one or more titanium polyoxometalates (POMs) and the one or more further metal complexes in the formulation is in the range from 1:100 to 100:1, preferably from 1:10 to 10:1, and more preferably from 1:5 to 5:1.

In a preferred embodiment of the present invention, the formulation is a mixture being suitable for inkjet printing. Furthermore, the formulation according to the present invention may be used in the method for preparing an optical metal oxide layer according to the present invention as described above.

Optical Device

Finally, the present invention relates to an optical device comprising an optical metal oxide layer, which is obtainable or obtained by the method for preparing an optical metal oxide layer according to the present invention as described above. It is preferred that the optical device is an augmented reality (AR) and/or virtual reality (VR) device.

Finally, the present invention further relates to an optical device comprising an optical metal oxide layer, which is prepared by using the formulation according to the present invention as described above. It is preferred that the optical device is an augmented reality (AR) and/or virtual reality (VR) device.

The present invention is further illustrated by the examples following hereinafter which shall in no way be construed as limiting. The skilled person will acknowledge that various modifications, additions and alternations may be made to the invention without departing from the spirit and scope of the invention as defined in the appended claims.

EXAMPLES

Analytics and Measurement Methods

Ellipsometry was used to determine layer thickness, refractive index (n) and absorption index (k) of a metal oxide layer. Measurements were performed using an ellipsometer M2000 from J. A. Woollam and three different angles of incidence (65°, 70° and 75°). The measurement data was analyzed with software CompleteEase from J. A. Woolam, assuming either full or almost nearly complete transparent behaviour above a wavelength of 600 nm and applying B-spline fitting for obtaining refractive indices (n) as well as absorption indices (k). The optical constants were averaged from three to four measured samples each of them providing a different layer thickness either after soft bake or after hard bake or layer cure.

Optical spectra of any sheets and substrates being either coated or uncoated by metal oxide layers described in the present invention were recorded using UV/Vis/NIR-spectrophotometer Cary 7000 from Agilent with UMA-setup. Measurements were carried out using dual beam mode, a scan speed of 600 nm/min and a spectral band width of 4 nm, non-polarized light and applying a spectral window from 350 nm to 700 nm. Transmission measurements were carried out with an angle of incidence of 6° versus surface normal of the sample. The detector was aligned 180° to light incidence. Reflection measurements were carried out with an angle of incidence of 6° versus surface normal of the sample, the detector angle amounted to 12° versus incidence of light. The absorption of the samples was calculated using Equation 1, where A stands for the absorption of the coated sample, R stands for the reflection and T for the transmission of the sample.

$\begin{array}{cc}A=1-\left(R+T\right)& \mathrm{Equation}1\end{array}$

Thermogravimetric analysis was run on a TGA Q 50 from TA Instruments. Results upon elementary analysis were received as service from an analyticlál service provider where measurements were conducted according to DIN 51732:2014-07.

NMR-measurements, ¹H-NMR, were measured using 500 MHz spectrometer from Bruker Biospin GmbH.

ICP-OES metal analysis was run on a FHS12 System from Spectro Arcos SOP after chemical pulping of the analyte subjected to analysis.

FTIR-spectra were recorded on Bruker Vertex 70 in ATR-mode, typically applying a spectral window from 4,000 to 400 cm⁻¹ with spectral resolution of 2 cm⁻¹.

SEM images were recorded using either a Mira 3 LMU from Tescan or Sigma 300VP from Carl Zeiss or Supra 35 from Carl Zeiss, too.

Substrate coating, usually wafers, was done using a spin coater (LabSpin 150i) from Suess. The spin coating process using planar substrates was follows: deposition of 0.5 ml of the coating onto static quartz wafers followed by a spinning interval of 30 seconds at a given spin speed where the acceleration of the spinning speed as set to 500 rpm/s². Different layer and coating thicknesses were achieved using either different spin speeds or different coating formulations having different concentrations of the metal oxide precursor or mixtures of different metal oxide precursors. After spin coating, the coated substrates either underwent a pre-baking at 100° C. for 2 minutes for driving out solvent residues, subsequently followed by baking at elevated temperatures or the layers deposited on the wafers became directly baked at elevated temperature for a dedicated time. Usually, however not limited hereto, the coated layers were baked at 300° C., 400° C. and 500° C. for 5 minutes as well as for 60 minutes as shown in some of the following examples. Pre-baking as well as layer baking were performed using high temperature hotplates from Harry Gestigkeit allowing for reaching temperatures of up to 600° C. Aforementioned conditions and parameters apply to all following experimental examples unless other conditions are explicitly mentioned elsewhere.

Usually, quartz and/or silicon wafers, both 2″ in diameter, were used throughout all coating experiments where flat and non-structured carriers for metal oxides were required (e. g. spectroscopic and ellipsometry measurements).

Structured substrates, usually silicon wafers, were used as square-shaped dies with edge length of 1.5 cm to 2 cm. The wafer dies were cutted and cleaved from a parent wafer, typically having a diameter of 8″. The structures were created and arranged in a layer stack composed of SiO₂/SiN_x being deposited onto the wafer surface. Dimensions of the structures (e. g. cross-section width and length of trenches) referred to the architecture of Sematech mask 854. Usually, however not limited hereto, the cross-sectional cleaves perpendicular to trench arrays providing a width of 40 nm to 50 nm were used as trench structures of primary interest to investigate their filling by metal oxides. Besides to aforementioned, cross-sections of arrays to trenches having widths of 100 nm and 150 nm where used to investigate trench filling by metal oxides.

Structured wafer dies were, unless otherwise mentioned, coated by spin coating. For that purpose, the coating formulation, typically a volume between 0.15 ml to 0.5 ml per die, was pipetted and casted onto wafer's surface. The formulation was allowed to spread and settle on the surface for one minute followed by a step of distribution of the formulation over the entire surface of the wafer die at 500 rpm for 30 seconds, followed by a final spin-off step at 2,000 rpm for further 60 minutes. The acceleration of the spin speed was set to 500 rpm/s². The soft bake and hard conditions of structured wafer dies was chosen similar or identical to those already mentioned for flat substrates.

All chemicals for synthesis described were purchased from Sigma Aldrich and used without further purification, unless mentioned differently.

Example 1: Synthesis of Ti₄₄ Polyoxometalate (Ti₄₄C₁₆₀H₂₈₀O₁₈₀)

The synthesis of {Ti₄₄(μ₂-OH)₄(μ₂-O)₃₂(μ₃-O)₃₀(HPA)₂(PA)₄₆(HFA)₂(FA)₂ (H₂O)₂}·4HPA was performed in conventional laboratory glassware in a conventional fume hood. The reaction apparatus was constantly flushed with an argon stream. 409.2 g of propionic acid (Sigma-Aldrich, ≥99.5 ACS reagent) were weighed into a two-necked reaction flask with a reflux condenser. Then, 63.936 g of titanium isopropoxide (Sigma-Aldrich, 97%) were transferred into the reaction flask by use of a disposable syringe. During the addition of the titanium isopropoxide, the resulting mixture was constantly stirred by the use a magnetic stir bar. The resulting mixture turned slightly turbid. The reaction mixture was completed by the addition of 6.165 g of formic acid (Sigma-Aldrich, 98-100%, REAG. ACS, REAG. PH. EUR. puriss p. a.) under constant stirring. After completion, the reaction mixture was heated in an oil bath to reach an internal reaction temperature of 80° C. The reaction temperature was constantly monitored by an appropriate thermocouple immersed in the mixture. The mixture was allowed to react for three days under these conditions. After completion of the reaction, the mixture was allowed to cool down and the solvent was removed as next step resulting in a cream-like colored residue. The crude product (40.5 g) was dissolved in 202 g of toluene. To this solution, 405 g of heptane were added to precipitate a white powder. The white precipitate was collected by filtration, washed by the mother liquor and finally dried at room temperature in a vacuum convection furnace yielding 34 g of product. The product was analyzed by ¹H-NMR-spectroscopy, CHN- and TGA-analysis and the metal content was determined by ICP-OES. The ¹H-NMR-spectrum (CDCl₃) provided a broad multiplett at 1.06 ppm (1.65H, —CH₃) and a broad multiplett at 2.17 ppm (1H, —CH₂—). CHN-analysis resulted in 27.4% w/w for C (26.73% w/w) and 4.6% w/w for H (3.93% w/w), where the theoretically expected values are provided in brackets. The metal content provided 28% w/w for Ti (29.29% w/w) and TG-analysis yielded a mass residue of 46.70% w/w after thermal decomposition of up to 950° C. in air which was found to be close to the expected value of 48.87% w/w for TiO₂.

Example 2: Physical and Optical Properties of Ti₄₄ Polyoxometalate Films

The Ti₄₄ polyoxometalate obtained in Example 1 was spin coated with 3,000 rpm onto a flat quartz wafer from a 12% (w/w) formulation in PGME. The coated substrates were then pre-baked for 2 min at 100° C. and submitted to various hard bake temperatures. The Ti₄₄ polyoxometalate has a tunable refractive index of >2.00 after baking at >300° C. and an absorption of <0.1% after baking at 300° C. with an average layer shrinkage of 52%. The absorbance at 460 nm of the Ti₄₄ polyoxometalate films is shown in FIG. 8, the refractive index at 520 nm of the Ti₄₄ polyoxometalate films is shown in FIG. 9, and the layer thickness of the Ti₄₄ polyoxometalate films as function of the spin coating speed at various hard baking temperatures is shown in FIG. 10.

Example 3: Filling Properties of Ti₄₄ Polyoxometalate

The Ti₄₄ polyoxometalate obtained in Example 1 was spin coated onto a substrate with surface features of 400 nm depth and ca. 45 nm width. The substrate surface is made of silicon nitride and was cleaned with IPA+ultrasonication. A formulation of 2.5% (w/w) of Ti₄₄ polyoxometalate in PGME was spin coated onto the wafer. 150 μl of the formulation was applied on the wafer, the soaking time was 60 s, then the substrate was spun for 25 s at 2,000 rpm. The coated substrate was then pre-baked at 100° C. for 1 min and subsequently hard baked at 400° C. for 10 min.

The formulation deposited via the process described above fills the surface features with aspect ratio 1:9 homogeneously (see FIG. 11).

Example 4: Filling Properties of Ti₄₄ Polyoxometalate

The Ti₄₄ polyoxometalate obtained in Example 1 was spin coated onto a substrate with surface features of 400 nm depth and ca. 45 nm width. The substrate surface is made of silicon nitride and was cleaned with IPA+ultrasonication. A formulation of 2.5% (w/w) of Ti₄₄ polyoxometalate in PGME was spin coated onto the wafer. 150 μl of the formulation was applied on the wafer, the soaking time was 60 s, then the substrate was spun for 25 s at 2,000 rpm. The coated substrate was then pre-baked at 100° C. for 1 min and hard baked at 400° C. for 10 min, then a second and a third layer were deposited on top of the first layer from the same formulation with the same deposition and post-treatment parameters.

The formulation deposited via the process described above fills the surface features with aspect ratio 1:9 homogeneously and the second and third coating step increases the thickness of the overburden, i.e. the film thickness above the top of the surface features (see FIG. 12). Thus, multiple coating steps are a way of fine-tuning the overburden thickness.

Example 5: Filling Properties of Ti₄₄ Polyoxometalate

The Ti₄₄ polyoxometalate obtained in Example 1 was drop casted onto a substrate with surface features of 400 nm depth and ca. 45 nm width. The substrate surface is made of silicon nitride and was cleaned with IPA+ultrasonication. A formulation of 5% (w/w) Ti₄₄ polyoxometalate with 0.5% (w/w) BYK-307 (siloxane based surfactant) in PGME was applied on 5×5 mm substrate. The formulation was then dried under ambient conditions for 20 min, then the substrate was pre-baked for 1 min at 100° C. and subsequently baked for 10 min at 300° C.

The formulation described above fills the surface features with aspect ratio 1:9 homogeneously. Additionally, homogeneous surface feature fill was observed using a formulation with 1% and 2.5% (w/w) of BYK-307, based on the total mass of the formulation, but 2.5% (w/w) BYK-307 did not yield a refractive index of >2.00 (see FIG. 13).

Example 6: Synthesis of Ti₁₈ Polyoxometalate (Ti₁₈C₆₆H₁₆₂N₂O₅₂)

The synthesis of Ti₁₈(μ₂-O)₁₀(μ₃-O)₈(μ₄-O)₂(OEt)₃₀(L3)₂ was performed under solvothermal conditions in a microwave furnace and conducted as described for compound PTC-130 on page 8852 in reference (6) (S. Chen et.al., Inorg. Chem. 2018, 57, 8850-8856).

Example 7: Physical and Optical Properties of Ti₁₈ Polyoxometalate Films

The Ti₁₈ polyoxometalate obtained in Example 6 was spin coated with 3,000 rpm onto a flat quartz wafer from a 25% (w/w) formulation in PGME. The coated substrates were then pre-baked for 2 min at 100° C. and submitted to various hard bake temperatures. The Ti₁₈ polyoxometalate has a tunable refractive index of >2.00 after baking at >300° C. and an absorption of <0.1% after baking at 300° C. with a layer shrinkage of ca. 50%. The absorbance at 460 nm of the Ti₁₈ polyoxometalate films is shown in FIG. 14, the refractive index at 520 nm of the Ti₁₈ polyoxometalate films is shown in FIG. 15, and the layer thickness of the Ti₁₈ polyoxometalate films as function of the spin coating speed at various hard baking temperatures is shown in FIG. 16.

Example 8: Filling Properties of Ti₁₈ Polyoxometalate

The Ti₁₈ polyoxometalate obtained in Example 6 was spin coated onto a substrate with surface features of 400 nm depth and ca. 90 nm width. The substrate surface is made of silicon nitride and the substrate was submitted to different surface pre-treatments, i.e. wet cleaning (IPA+ultrasonication) and optional plasma treatment (O₂ plasma). A formulation of 25% (w/w) of Ti₁₈ polyoxometalate in PGME was then spin coated onto the wafer, where 0.50 ml of the formulation was applied on the wafer. The soaking time was 60 s, then the substrate was spun for 30 s at 2,000 rpm. The coated substrate was then pre-baked at 60° C. for 60 min and subsequently hard baked at 400° C. for 5 min.

The filling properties of spin coated Ti₁₈ polyoxometalate, 25% in PGME (w/w) on wet-cleaned (IPA+ultrasonication) substrate after baking at 400° C. are shown in FIG. 17.

The filling properties of spin coated Ti₁₈ polyoxometalate, 25% in PGME (w/w) on wet-cleaned (IPA+ultrasonication) and O₂ plasma pre-treated substrate after baking at 400° C. are shown in FIG. 18.

FIGS. 17 and 18 show that the coated film on the substrate, which was pre-treated with O₂ plasma for 20 mins at 450 W prior to spin coating the formulation, fills the substrate features homogeneously. Without the O₂ plasma pre-treatment, the surface features are not properly filled after baking.

Example 9: Synthesis of Ti₁₂ Polyoxometalate (Ti₁₂C₆₈H₁₁₆N₄O₄₀)

The synthesis of (Ti₁₂(μ₂-O)₄(μ₃-O)₄(OEt)₂₀(L2)₄) was performed under solvothermal conditions in a microwave furnace. 8.625 g of salicylhydroxamic acid (Sigma-Aldrich, 99%), 8.85 g of succinic acid (Merck, p. a.) and 375 ml of ethanol (Merck) were placed into a 500 ml PTFE-lined microwave reaction flask and the mixture was homogenized under stirring. While constant stirring, 66.6 ml of titanium isopropoxide were added to the reaction solution. After completion of the addition, the reaction vessel was tightly sealed and placed into a microwave furnace. The reaction conditions were set to a reaction duration of 72 h and to a reaction temperature of 80° C. After completion of the reaction, the vessel and mixture were allowed to cool down to room temperature. An intensively yellow-orange colored precipitate was formed in the reaction mixture which was collected by filtration and after successive washing by mother liquor, followed by drying of the precipitate in a vacuum convention furnace at room-temperature, 13.75 g of yellow-orange product were obtained. The product was analyzed by IR spectroscopy, CHN- and TGA-analysis. The IR spectrum is shown in FIG. 19, where absorption bands between 1,100 and 1,000 cm⁻¹ indicate the presence of Ti—O—C bonds. The metal content was determined by ICP-OES. CHN-analysis, which gave 35.5% w/w for C (37.06% w/w), 5.4% w/w for H (5.30% w/w) and 2.7% w/w for N (2.54% w/w), where the theoretically expected values are provided in brackets. The analysis of the metal content provided 26% w/w for Ti (26.06% w/w) and TG-analysis yielded a mass residue of 45.38% w/w after thermal decomposition of up to 950° C. in air which was close to the expected value of 43.48% w/w for TiO₂.

Example 10: Physical and Optical Properties of Ti₁₂ Polyoxometalate Films

The Ti₁₂ polyoxometalate obtained in Example 9 was spin coated with 3,000 rpm onto a flat quartz wafer from a 10% (w/w) formulation in PGME. The coated substrates were then pre-baked for 2 min at 100° C. and submitted to various hard bake temperatures. The Ti₁₂ polyoxometalate has a tunable refractive index of >2.00 after baking at >300° C. and an absorption of <0.1% after baking at 500° C. with a layer shrinkage of ca. 70%. The absorbance at 460 nm of the Ti₁₂ polyoxometalate films is shown in FIG. 20, the refractive index at 520 nm of the Ti₁₂ polyoxometalate films is shown in FIG. 21, and the layer thickness of the Ti₁₂ polyoxometalate films as function of the spin coating speed at various hard baking temperatures is shown in FIG. 22.

Example 11: Filling Properties of Ti₁₂ Polyoxometalate

The Ti₁₂ polyoxometalate obtained in Example 9 was spin coated onto a substrate with surface features of 400 nm depth and ca. 90 nm width. The substrate surface is made of silicon nitride and was cleaned with IPA+ultrasonication. A formulation of 10% (w/w) of Ti₁₂ polyoxometalate in PGME was spin coated onto the wafer. 0.50 ml of the formulation was applied on the wafer, the soaking time was 60 s, then the substrate was spun for 30 s at 4,000 rpm. The coated substrate was then pre-baked at 60° C. for 60 min and subsequently hard baked at 400° C. for 5 min.

The filling properties of spin coated Ti₁₂ polyoxometalate from a 10% (w/w) solution in PGME is shown in FIG. 23.

The above examples show that the technical objects of the present invention are achieved.

LIST OF REFERENCE SIGNS

• • 1 Material 02 with RI 02
  • 2 Material 01 with RI 01
  • 3 Substrate (e.g. glass)
  • 4 Diffraction of incident light represented by broad arrow
  • 5 Total internal reflection of light (TIR)
  • 6 Waveguide
  • 7 Structured layer stack with gaps (trenches)
  • 8 Substrate (e.g. glass or silicon)
  • 9 Overburden of material (e.g. high refractive index material or high etch resistant material)
  • 10 Material (e.g. high refractive index material or high etch resistant material) providing gap fill
  • 11 Voids
  • 12 Formulation (e.g. ink) of high refractive index material (e.g. metal oxide precursor)
  • 13 High refractive index material (e.g. metal oxide) providing gap fill with optional concave geometry
  • 14 Overburden layer (optional)
  • 15 Energy

Claims

1. Method for preparing an optical metal oxide layer comprising the following steps:

(a) providing a formulation comprising one or more titanium polyoxometalates (POMs) and one or more formulation media;

(b) applying the formulation to a surface of a substrate; and

(c) converting the formulation on the surface of the substrate to an optical metal oxide layer.

2. Method according to claim 1, wherein the one or more titanium polyoxometalates (POMs) comprise independently from each other three or more titanium atoms and one or more ligand species.

3. Method according to claim 1, wherein the titanium polyoxometalates (POMs) are independently from each other represented by the following Formula (1): { Ti u ( μ 2 - OH ) v ⁢ ( μ 3 - OH ) w ⁢ ( μ 2 - O ) x ⁢ ( μ 3 - O ) y ⁢ ( μ 4 - O ) z } ⁢ ∏ j = 1 j = n ( L j ) a j Formula ⁢ ( 1 ) wherein:

μ2-OH represents a bidentate bridging hydroxo;

μ3-OH represents a tridentate bridging hydroxo;

μ2-O represents a bidentate bridging oxido;

μ3-O represents a tridentate bridging oxido;

μ4-O represents a tetradentate bridging oxido;

Lj represents at each occurrence independently from each other a ligand species;

aj is at each occurrence independently from each other an integer from 1 to 100;

n is an integer from 2 to 10;

u is an integer from 2 to 100;

v is an integer from 0 to 100;

w is an integer from 0 to 100;

x is an integer from 0 to 100;

y is an integer from 0 to 100; and

z is an integer from 0 to 100.

4. Method according to claim 3, wherein the following equation is fulfilled: 4 * ⁢ u - [ v + w + 2 * ⁢ ( x + y + z ) + ∑ j = 1 j = n ( m j ( L j ) * ⁢ a j ) ] = c

wherein:

mj(Lj) represents the amount of negative charge of Lj; and

c represents the total charge of the titanium polyoxometalate (POM);

and aj, n, u, v, w, x, y and z are defined as in claim 3.

5. Method according to claim 1, wherein the one or more titanium polyoxometalates (POMs) are independently from each other selected from Ti12 polyoxometalates, Tins polyoxometalates, Ti18 polyoxometalates, Ti44 polyoxometalates, and Ti52 polyoxometalates.

6. Method according to claim 1, wherein the mass ratio of titanium polyoxometalates (POMs) in the formulation is in the range from 0.1% to 50% (w/w) based on the total mass of the formulation.

7. Method according to claim 1, wherein the formulation provided in step (a) further comprises one or more additives selected from surfactants, wetting and dispersion agents, adhesion promoters, and polymer matrices.

8. Method according to claim 1, wherein the formulation is applied in step (b) to a surface of a substrate by a deposition method, preferably by a drop casting method, a coating method, or a printing method.

9. Method according to claim 1, wherein step (b) is carried out several times in succession.

10. Method according to claim 1, wherein in step (c) the formulation is converted on the surface of the substrate to an optical metal oxide layer by exposure to thermal treatment and/or irradiation treatment.

11. Method according to claim 1, wherein in step (c) the formulation is converted on the surface of the substrate to an optical metal oxide layer by pre-baking at a temperature from 40 to 150° C.; and then baking at a temperature from 150 to 600° C.

12. Method according to claim 1, wherein the substrate is a patterned substrate comprising topographical features on the surface thereof.

13. Method according to claim 12, wherein the optical metal oxide layer covers the surface of the substrate and fills said topographical features.

14. Method according to claim 12, wherein the topographical features have an aspect ratio of 1:20 to 20:1.

15. Formulation for preparing an optical metal oxide layer, wherein the formulation comprises:

(i) one or more titanium polyoxometalates (POMs);

(ii) one or more formulation media; and

(iii) one or more additives selected from surfactants, wetting and dispersion agents, adhesion promoters, and polymer matrices.

16. Formulation according to claim 15, wherein the titanium polyoxometalates (POMs) comprise independently from each other three or more titanium atoms and one or more ligand species.

17. Formulation according to claim 15, wherein the titanium polyoxometalates (POMs) are independently from each other represented by the following Formula (1): { Ti u ( μ 2 - OH ) v ⁢ ( μ 3 - OH ) w ⁢ ( μ 2 - O ) x ⁢ ( μ 3 - O ) y ⁢ ( μ 4 - O ) z } ⁢ ∏ j = 1 j = n ( L j ) a j wherein:

Formula (1)

μ2-OH represents a bidentate bridging hydroxo;

μ3-OH represents a tridentate bridging hydroxo;

μ2-O represents a bidentate bridging oxido;

μ3-O represents a tridentate bridging oxido;

μ4-O represents a tetradentate bridging oxido;

Lj represents at each occurrence independently from each other a ligand species;

aj is at each occurrence independently from each other an integer from 1 to 100;

n is an integer from 2 to 10;

u is an integer from 2 to 100;

v is an integer from 0 to 100;

w is an integer from 0 to 100;

x is an integer from 0 to 100;

y is an integer from 0 to 100; and

z is an integer from 0 to 100.

18. Formulation according to claim 17, wherein the following equation is fulfilled: 4 * ⁢ u - [ v + w + 2 * ⁢ ( x + y + z ) + ∑ j = 1 j = n ( m j ( L j ) * ⁢ a j ) ] = c

wherein:

mj(Lj) represents the amount of negative charge of Lj; and

c represents the total charge of the titanium polyoxometalate (POM);

and aj, n, u, v, w, x, y, and z are defined as in claim 17.

19. Formulation according to claim 15, wherein the one or more titanium polyoxometalates (POMs) are independently from each other selected from Ti12 polyoxometalates, Ti16 polyoxometalates, Ti18 polyoxometalates, Ti44 polyoxometalates, and Ti52 polyoxometalates.

20. Formulation according to claim 15, wherein the mass ratio of titanium polyoxometalates (POMs) in the formulation is in the range from 0.1% to 50% (w/w) based on the total mass of the formulation.

21. Optical device comprising an optical metal oxide layer, which is obtainable by a method for preparing an optical metal oxide layer comprising the following steps: which is prepared by using a formulation for preparing an optical metal oxide layer, wherein the formulation comprises:

(a) providing a formulation comprising one or more titanium polyoxometalates (POMs) and one or more formulation media;

(b) applying the formulation to a surface of a substrate; and

(c) converting the formulation on the surface of the substrate to an optical metal oxide layer, or

(i) one or more titanium polyoxometalates (POMs);

(ii) one or more formulation media; and

(iii) one or more additives selected from surfactants, wetting and dispersion agents, adhesion promoters, and polymer matrices,

wherein the optical device is preferably an augmented reality (AR) and/or virtual reality (VR) device.