Abstract: Novel thermally imageable monochrome product compositions, elements, and processes are disclosed herein. These compositions and elements characteristically have high contrast and fast imaging speeds. The thermally imageable compositions of this invention comprise (a) at least one near IR-absorbing dye having the structure given in the specification; (b) at least one HABI compound; (c) at least one leuco dye; (d) at least one acid-generating compound; and (e) a polymeric binder. Optionally at least one UV stabilizer and/or at least one inhibitor of color formation can also be present. These compositions have the propensity for affording, upon imaging, highly colored images having high optical density values. At the same time, background color is low in preferred compositions even after extensive exposure to ambient light. These compositions are imagewise exposed to near IR radiation from a laser or other device to effect color formation (i.e., generation of an image).

Abstract: A reversible thermosensitive composition including a coloring agent and a developer and capable of assuming a colored state and a discolored state depending upon the thermal hysteresis thereof. The developer is a phenol compound represented by the formula: ##STR1## wherein R.sup.1 represents a substituted or non-substituted divalent hydrocarbon group having at least two carbon atoms, R.sup.2 represents a substituted or non-substituted hydrocarbon group, X and Y represent, independently from each other, a divalent group having a hetero atom and r is an integer of between 1 and 3. A reversible thermosensitive recording medium includes a support and a thermosensitive layer including the above composition.

Abstract: The sensitivity to radiation of combinations of cationic electron acceptors (such as phosphonium, sulfonium, diazonium and iodonium salts) with sensitizing dyes, which sensitize these cationic electron acceptors to wavelengths (typically visible wavelengths) to which they are not sensitive in the absence of the dye, can be increased by including with the cationic electron acceptor and the sensitizing dye a supersensitizer which has an oxidation potential lower than that of the sensitizing dye, the supersensitizer being an ionic compound having a cation comprising an ionic grouping, said grouping comprising at least one atom of an element from Group VB, VIB or VIIB of the Periodic Table.

Abstract: Styryl dyes and compositions which exhibit superior two-photon absorption cross-sections and are useful in two-photon pumped cavity lasing, two-photon pumped upconversion lasing, optical power limiting, optical power stabilization, optical signal reshaping, and infrared beam detection and indication are disclosed. Also disclosed are multiphasic nanostructured composites which include a glass having pores, an optically active coating material on the pore surface, and a polymeric material in the pores. These composites are useful in producing multifunctional optical materials, such as broadly tunable lasers. Methods for killing cells and viruses using a photosensitizer and a two-photon upconverting dye are also described. These methods are especially useful to kill cells and viruses in biological materials, such as in photodynamic therapy of tumors and cancers or blood purification protocols.

Abstract: Disclosed are diazahemicyanine hydrophobic cationic dyes represented by the formula (1): ##STR1## wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are lower alkyl groups having not more than 5 carbon atoms, R.sup.5 is a lower alkyl group having not more than 5 carbon atoms or a lower alkoxy lower alkyl group having not more than 6 carbon atoms, and Z.sup.- is a counter ion having a hydrophobic organic group, and a thermal transfer ink ribbon having a substrate and and ink layer laminated thereon containing said cationic dye.

Abstract: Compositions for making structured color images comprising (a) a soluble pigment precursor which can be transformed to an insoluble pigment by means of chemical, thermal, photolytic or radiation-induced method, and (b) a binder polymer or prepolymer, or a positive or negative resist-type resin which can be structured by crosslinking, polymerization or depolymerization by applying heat or electromagnetic irradiation. The compositions can be applied to optical and thermal recording, printing, and the production of color filters for Liquid Crystal Displays, with high accuracy, high transparency and high stability.

Abstract: A heat sensitive recording material is provided which can be simply prevented from falsification and is excellent in contrast between fixed portion and image portion, and a recording method using it is further provided. Moreover, there is provided a heat sensitive recording material capable of carrying out multicolor recording which is excellent in contrast of the image portions, density of the image portions, and image storage stability.

Abstract: A cyan dye-donor element for thermal dye transfer comprising a support having thereon a dye layer comprising a mixture of cyan dyes dispersed in a polymeric binder, at least one of the cyan dyes having the formula: ##STR1## and at least one of the other of the dyes having the formula: ##STR2##

Abstract: Novel thermally imageable monochrome product compositions, elements, and processes are disclosed herein. These compositions and elements characteristically have high contrast and fast imaging speeds. The thermally imageable compositions of this invention comprise (a) at least one hexaarylbiimidazole (HABI) compound, (b) at least one leuco dye, (c) at least one acid-generating compound, (d) a polymeric binder, (e) optionally at least one UV stabilizer and/or at least one inhibitor of color formation, and, in certain embodiments, (f) at least one near IR-absorbing dye. These compositions have the propensity for affording, upon thermal imaging, highly colored images having high optical density values. At the same time, background color is low in preferred compositions even after extensive exposure to ambient light. These compositions can be imagewise heated to effect color formation (i.e.

Abstract: A black thermal transfer sheet comprises a substrate film and a black dye layer formed on one surface of the substrate film. The die layer comprises dye and a binder. The dye comprises a first dye and a second dye respectively expressed by the following formulae (1) and (2): ##STR1## (where, "R.sup.1 " and "R.sup.2 " represent a substitutional or non-substitutional alkyl group, etc., "R.sup.3 " represents a hydrogen atom, etc., "R.sup.4 " represents a substitutional or non-substitutional alkyl group, etc., and "R.sup.5 " represents a substitutional or non-substitutional aminocarbonyl group, etc.; and "n" represents an integer of 1 or 2); and ##STR2## (where, "R.sup.1 ", "R.sup.2 ", "R.sup.3 " and "n" represent the same definitions as those in the formula (1), and "R.sup.6 " and "R.sup.7 " represent a substitutional or non-substitutional alkyl group, etc.).

Abstract: There is disclosed a color developing resin composition comprising a base polymer, a dialdehyde represented by the general formula OHC--R.sup.1' --CHO, a diamine represented by the general formula H.sub.2 N--R.sup.2' --NH.sub.2 (at least one of R.sup.1' and R.sup.2' is an aromatic group), a compound which produces an acid by light irradiating and a resin which is crosslinked with the acid.

Abstract: The present invention provides a process for the preparation of a material comprising a substrate on whose surface there is at least one pigment coating consisting of one or more pigments of the formula (I) or (II) or derivatives thereofA(D.sub.1)(D.sub.2).sub.x (I)Pc (II)in whichA is the radical of a chromophore of the quinacridone, anthraquinone, perylene, indigo, azo, quinophthalone, isoindolinone, isoindoline, dioxazine, phthalocyanine or diketopyrrolopyrrole series which contains nitrogen atoms attached to D.sub.1 and to x D.sub.2, each nitrogen atom present in A being able independently of the others to be attached to 0, 1 or 2 groups D.sub.1 or D.sub.2,D.sub.1 and D.sub.

Abstract: One embodiment of the present invention is a method and composition comprising a novel pre-dye molecule that is colorless and stable to ordinary light. The pre-dye molecule is capable of forming a color when exposed to certain wavelengths of electromagnetic radiation. A second embodiment of the present invention is a method of converting a conventional leuco dye to a colored composition by exposing the leuco dye admixed with a radiation transorber to certain wavelengths of electromagnetic radiation.

Abstract: The present invention provides methods for producing top anti-reflective coating compositions having a very low level of metal ions, utilizing a specially washed and modified ion exchange resin. A method is also provided for producing semiconductor devices using such ion exchange treated top anti-reflective coating compositions.

Abstract: A cyan dye-donor element for thermal dye transfer comprising a support having thereon a dye layer comprising a mixture of cyan dyes dispersed in a polymeric binder, at least one of the cyan dyes having the formula: ##STR1## and at least one of the other of the dyes having the formula: ##STR2##

Abstract: A light- and heat-sensitive recording material is disclosed, comprising a support provided thereon a light- and heat-sensitive layer containing a photo-color-forming element comprising a photodecomposable compound and an element capable of forming a color upon reaction with a decomposition product of the photodecomposable compound, wherein the photo-color-forming element is imagewise heated so as to be mixed to thereby form a latent image and the latent image is further exposed to light to form a color; at least one of the photodecomposable compound and the element capable of forming a color upon reaction with the decomposition product of the photodecomposable compound being dispersed through solution in an organic solvent.

Abstract: One embodiment of the present invention is a method and composition comprising a novel pre-dye molecule that is colorless and stable to ordinary light. The pre-dye molecule is capable of forming a color when exposed to certain wavelengths of electromagnetic radiation. A second embodiment of the present invention is a method of converting a conventional leuco dye to a colored composition by exposing the leuco dye admixed with a radiation transorber to certain wavelengths of electromagnetic radiation.

Abstract: The invention relates to a light sensing device comprising a spironaphthoxazine dispersed in a layer of gelatin on a base material.

Abstract: A process for producing and fixing an image uses an imaging medium comprising an acid-generating layer or phase comprising a mixture of a superacid precursor, a sensitizer and a secondary acid generator, and a color-change layer comprising an image dye. The sensitizer can absorb radiation of a sensitizer wavelength which does not, in the absence of the sensitizer, cause decomposition of the superacid precursor to form the corresponding superacid. The secondary acid generator is capable of acid-catalyzed thermal decomposition by the first acid to form a second acid, and the image dye undergoes a color change upon contact with the second acid. The medium is imagewise exposed to radiation of the sensitizer wavelength, thereby causing the sensitizer, in exposed areas, to decompose superacid precursor with formation of the fist acid. The medium is then heated to cause, in the exposed areas, acid-catalyzed thermal decomposition of the secondary acid generator and formation of the second acid.

Abstract: This invention relates to a mixture of imageable polyacetylenic compounds which have similar photosensitivities and which are visually imageable in complementary colors combinable to provide a black image, which mixture contains at least one polyacetylenic metal salt which produces a color, preferably a metal salt of a diacetylene C.sub.6 to C.sub.48 mono- or dicarboxylic acid, which is complementary to a color produced by another polyacetylenic metal salt or non-metallic polyacetylenic compound contained in the mixture or in an another integral color forming layer. The invention also pertains to the use of said mixture and the manner of its preparation.

Abstract: A recording material comprising on the same side of a support, called the heat-sensitive side, (1) one or more layers comprising an imaging composition essentially consisting of (i) a substantially light-insensitive organic silver salt being in thermal working relationship with (ii) a reducing agent, and (2) at said same side covering said imaging composition a protective later, characterized in that said protective layer mainly comprises an organic thermosetting or moisture-hardened polymer or an organic thermosetting or moisture-hardened polymer composition.

Abstract: An optical recording medium including a substrate having thereon a recording layer containing a dye precursor, a color developer reactable with the dye precursor to develop a color, and a light absorbent for converting light to heat, characterized in that the color developer is at least one compound of Formula (1):(R--NH (C.dbd.S) NH)n--Z (1)(wherein R denotes a substituted or unsubstituted alkyl, cycloalkyl, aryl, aralkyl, or alkenyl. n is an integer of 2 or more, and Z denotes a group having a valence of 2 or more.). The optical recording medium is superior in heat resistance and plasticizer resistance of the recorded image, heat resistance of background, water resistance, and moisture resistance.).

Abstract: Dye-donor element for thermal dye transfer comprising at least one magenta dye having extremely low side absorption in the blue and red regions of the spectrum, said dye corresponding to the general formula (I) : ##STR1## wherein R.sup.1 is H, (cyclo)alkyl, or aryl; X represents the atoms completing a heterocycle; Z is an electron-withdrawing group; Y is an electron-withdrawing group or --N(R.sup.2)R.sup.3 ; R.sup.2 and R.sup.3 together represent the atoms completing a heterocycle; or R.sup.2 and R.sup.3 together represent .dbd.C(R.sup.4)R.sup.5, or each of R.sup.2 and R.sup.3 represents (same or different) (cyclo) alkyl, aryl, or an electron-withdrawing group; each of R.sup.4 and R.sup.5 (same or different) represents H, (cyclo)alkyl, aryl, a heterocycle, SO.sub.2 R.sup.6, COR.sup.6, CSR.sup.6, POR.sup.6 R.sup.7, OR.sup.8, NR.sup.8 R.sup.9, SR.sup.8, or R.sup.4 and R.sup.5 together represent the atoms completing an aliphatic ring or a heterocycle, each of R.sup.6 and R.sup.

Abstract: A heat-sensitive recording material suited for use in direct thermal imaging and having image-stabilization properties which material contains in a binder on a support (i) a substantially light-insensitive organic silver salt capable of thermally activated reduction to silver in thermal working relationship with (ii) at least one reducing agent capable of reducing the substantially light-insensitive organic silver salt when thermally activated, characterized in that the recording material contains in conjunction, preferably in admixture, with the reducing agent(s) at least one colourless photo-oxidizing substance that on exposure to ultraviolet (UV) radiation, such as present in daylight or artificial lighting, yields free radicals capable of inactivating said reducing agent(s) by oxidation, thereby rendering said reducing agent(s) incapable of reducing said organic silver salt to silver.

Abstract: A process for producing an image uses an imaging medium comprising an acid-generating layer or phase comprising a mixture of a superacid precursor, a sensitizing dye and a secondary acid generator, and a color-change layer comprising an image dye. The sensitizing dye has first and second forms, the first form having substantially greater substantial absorption in a first wavelength range than the second form. The superacid precursor is capable of being decomposed to produce superacid by radiation in a second wavelength range, but is not, in the absence of the sensitizing dye, capable of being decomposed by radiation in the first wavelength range. The secondary acid generator is capable of acid-catalyzed thermal decomposition by unbuffered superacid to form a secondary acid.

Abstract: Dyes comprising an inner salt of a compound of the formula:Q.sup.1 =Z-Q.sup.2wherein:Q.sup.1 is a 4-(benz[b]-4H-pyrylium)methylidene, 4-(benz[b]-4H-thiopyrylium)methylidene or 4-(benz[b]-4H-selenopyrylium)methylidene grouping;Z is a 1,3-(2-hydroxy-4-oxo-2-cyclobutylidene) hydroxide or 1,3-(2-hydroxy-4,5-dioxo-2-cyclopentylidene) hydroxide ring; andQ.sup.2 is a 4-(benz[b]-4H-pyran-4-ylidene)methyl, 4-(benz[b]-4H-thiopyran-4-ylidene)methyl or 4-(benz[b]-4H-selenopyran-4-ylidene)methyl grouping;wherein at least one of the groupings Q.sup.1 and Q.sup.

Abstract: The present invention provides methods for producing top anti-reflective coating compositions having a very low level of metal ions, utilizing specially treated ion exchange resins. A method is also provided for producing semiconductor devices using such top anti-reflective coating compositions.

Abstract: In an optical recording sheet having a thermal recording layer containing a colorless or pale colored dye precursor and a color developer reactable with the dye precursor upon heating to develop a color, a dimerized or trimerized urea compound is used as the color developer to obtain an optical recording sheet which is superior in ground color stability and an optical recording sheet having a reversible recordability.

Abstract: An optical image forming material in which the background portions thereof are not color developed (not fogged) during storage in the dark after fixing, comprising a support having thereon at least a coating layer containing (1) microcapsules containing a leuco dye which is form color when it is oxidized and a photooxidizing agent, and (2) a reducing agent and a fixing accelerator present outside of the microcapsules. The reducing agent is a hydroquinone derivative substituted by an alkyl group at each of 2- and 5-positions thereof, and the fixing accelerator is 2,2-bis(4-hydroxy-phenyl)propane.

Abstract: A recording material comprising on a support (i) a heat sensitive layer comprising a substantially light insensitive organic silver salt, (ii) a protective layer containing a thermomeltable particle dispersed in a binder and (iii) a reducing agent being present in the heat sensitive layer and/or any other layer of the recording material on the same side of the support carrying the heat sensitive layer.

Abstract: A process for producing and fixing an image uses an imaging medium comprising an acid-generating layer or phase comprising a mixture of a superacid precursor, a sensitizer and a secondary acid generator, and a color-change layer comprising an image dye. The sensitizer can absorb radiation of a sensitizer wavelength which does not, in the absence of the sensitizer, cause decomposition of the superacid precursor to form the corresponding superacid. The secondary acid generator is capable of acid-catalyzed thermal decomposition by the first acid to form a secondary acid, and the image dye undergoes a color change upon contact with the secondary acid. The medium is imagewise exposed to radiation of the sensitizer wavelength, thereby causing the sensitizer, in exposed areas, to decompose superacid precursor with formation of the fist acid. The medium is then heated to cause, in the exposed areas, acid-catalyzed thermal decomposition of the secondary acid generator and formation of the secondary acid.

Abstract: The present invention provides a thermofixable photosensitive recording material comprising a substrate and a recording layer formed thereon in which a pyrazolone derivative represented by the formula (1 ) shown in the specification and functions as a color former, and a hydroquinone derivative and an acidic substance which function as a color forming auxiliary agent or fixing auxiliary agent are dissolved mutually therein.Further, a binder can be added as required to the recording layer, thereby four components are dissolved mutually therein.

Abstract: A heat-sensitive recording material suited for use in direct thermal imaging by means of an information-wise energized heating element, which recording material comprises on the same side of a support, called the heat-sensitive side, one or more binder layers containing a substantially light-insensitive metal salt in thermal working relationship with at least one organic reducing agent, characterized in that said recording material also comprises an acid-sensitive leuco dye transformable into dye by means of an acid-reacting compound serving as dye developer that stands in thermal working relationship with said leuco dye.

Abstract: The present invention provides a dye donor element comprising a dye according to the following general formula: ##STR1## wherein the symbols have a meaning as defined in the claims and the description. The present invention further provides a thermal dye transfer process using such dye donor elements. Furthermore, novel thermochromic compounds are provided.

Abstract: There is provided a thermal transfer film comprising: a substrate film; a sublimable dye layer region comprised of at least one color layer; and a hot-melt ink layer region, the sublimable dye layer region and the hot-melt ink layer region being provided in parallel to each other on the substrate film,the hot-melt ink layer region comprising at least a release layer, a release protective layer, and a hot-melt ink layer laminated in that order on the substrate film,the hot-melt ink layer region being broader than one color layer in the sublimable dye layer region.

Abstract: The present invention provides a recording material comprising on a support (i) a heat sensitive layer comprising a substantially light insensitive organic silver salt, (ii) a protective layer containing a matting agent dispersed in a binder and (iii) a reducing agent being present in the heat sensitive layer and/or another layer on the same side of the support carrying the heat sensitive layer. The present invention further provides a method for making images therewith. The obtained images may be used in medical diagnostics.

Abstract: Acid can be generated by exposing a superacid precursor to actinic radiation effective to generate superacid from the superacid precursor and heating the superacid in admixture with a secondary acid generator capable of undergoing thermal decomposition to produce a secondary acid. The superacid catalyzes decomposition of the secondary acid generator, thus increasing the quantity of strong acid present in the medium. The resultant secondary acid can be used to effect a color change in an acid-sensitive material, so providing an imaging process.

Abstract: A direct thermal imaging process wherein a non-photosensitive direct thermal recording material is heated dot-wise, and said direct thermal recording material comprises an imaging layer containing uniformly distributed in a film-forming polymeric binder (i) one or more substantially light-insensitive organic silver salts, said silver salt(s) being uniformly in thermal working relationship with (ii) one or more organic reducing agents therefor, however neither including 3,5-dihydroxybenzoic acid as acidic reagent nor di-tert-butyl-p-cresol as a sole reducing agent, characterized in that said imaging layer contains at least one polycarboxylic acid and/or anhydride thereof in a molar percentage of at least 20 with respect to said silver salt(s).

Abstract: A laser dye-ablative recording element comprising a support having thereon a dye layer comprising an image dye dispersed in a polymeric binder, said dye layer having an infrared-absorbing material associated therewith, and wherein said dye layer also contains an arylazo phenol, naphthol or aniline UV-absorbing dye.

Abstract: A laser recording element comprising a support having thereon a dye layer comprising an image dye dispersed in a polymeric binder, said dye layer having an infrared-absorbing material associated therewith, and wherein said dye layer also contains an oxalanilide UV-absorbing dye.

Abstract: The present invention provides methods for producing top anti-reflective coating compositions having a very low level of metal ions, utilizing specially treated ion exchange resins. A method is also provided for producing semiconductor devices using such top anti-reflective coating compositions.

Abstract: The present invention provides a dye donor element comprising a dye according to the following general formula: ##STR1## wherein the symbols have a meaning as defined in the claims and the description. The present invention further provides a thermal dye transfer process using such dye donor elements. Furthermore, novel thermochromic compounds are provided.

Abstract: Several methods of using dyes within polymers and specifically in packaging materials are disclosed. These dyes respond to specific stimuli and indicate exposure to stimuli by a change or shift in the frequencies of light which they adsorb. The stimuli include temperature, radiation, chemicals (e.g. H.sub.2 O, CO.sub.2, NO.sub.2, ethylene, and SO.sub.2), and tensile or compressive stress. Within packaging materials (or affixed thereto as a label, decal or tag) these dyes could indicate spoilage or the possibility of spoilage, that the product has been irradiated, or that the product has been exposed to an undesirably high or low temperature. Many of the shifts in absorption frequencies result in visible color change which a consumer could quickly identify. The tensile or compressive stress sensitive dyes could indicate whether common opposing interlocking polymeric strips used to seal plastic bags have been effectively interlocked to seal the bags.

Abstract: A benzoin compound is synthesized from phenylglyoxal and a substituted benzene derivative, and the resulting benzoin compound is converted to a bis-dithiobenzilnickel complex using phosphorus pentasulfide/nickel chloride. The bis-dithiobenzilnickel complex is useful as a near-infrared absorbing material to be coated on paper, and the benzoin compound is useful as an intermediate of the complex. The obtained bis-dithiobenzilnickel complex can be applied to an optical recording material, a near-infrared absorbing resin, a near-infrared absorbing hard coating agent and a near-infrared absorbing glass composite.

Abstract: A recording material employing an electron-donating achromatic dye and an electron-accepting compound, which further contains at least one triarylamine derivative represented by general: formula (1), (2), (3) or (4); ##STR1## wherein all the symbols are defined in the specification.

Abstract: An image forming element and an image forming method using the same are disclosed. The element comprises a support having thereon a image forming layer comprising a binder, an aromatic aldehyde, a cobalt (III) complex represented by formula I, and a compound represented by formula II or formula III;Co.sup.3 +(L)p(X)q (I)wherein L is a coordination compound capable of forming a complex compound with the cobalt cation and at least one of which is NH.sub.3 or a primary amine; X is a counter anion; p is an integer of 1 to 6; when p is 2 to 6, the plural Ls may be the same or different; and q is an integer of 1 to 3, ##STR1## wherein lig is a coordination compound capable of forming with the cobalt cation; R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are each independently an alkyl group, an aryl group, an aralkyl group, an alkenyl group, an alkinyl group, a cycloalkyl group, a heterocyclic group or a cyano group; n.sub.1 is an integer of 1 to 6, when n.sub.

Abstract: Disclosed is a magnetic recording element comprising a support having coated on at least one major surface thereof a layer of a magnetic recording medium and a photosensitive layer which may be separate from or integral with the magnetic recording layer and which contains an infrared absorbing dye or its precursors. Information can be imparted to the photosensitive layer by imagewise exposure to actinic radiation which will either promote or inhibit generation or destruction of the infrared absorbing dye.

Abstract: A slide blank comprises a support at least part of which is essentially transparent; an imageable layer superposed on one face of the support, the imageable layer not being substantially photosensitive but comprising a color-forming composition, which, upon imagewise exposure to actinic radiation, forms a colored material, thereby forming in the imageable layer an image which can be viewed in transmission; and a protective layer superposed on the imageable layer on the opposed side thereof from the support, at least part of the protective layer being essentially transparent; the support, imageable layer and protective layer being secured together to form a slide blank having a thickness of at least about 0.8 mm, and the thickness of the protective layer being such that no part of the imageable layer containing the color-forming composition is more than about 0.2 mm from one external surface of the slide blank. This slide blank can be imaged to produce a ready-mounted slide.

Abstract: A laser beam absorbing resin composition is disclosed which includes 100 parts by weight of a thermosetting resin, a colorant capable of discoloring upon being heated at a temperature of 250.degree. C. or more, and at least 10 parts by weight of a particulate, laser beam absorbing substance which has an average particle size of 50 .mu.m or less and which is at least one member selected from cordierite and zeolite. By irradiating a shaped, hardened body of the above composition with a laser beam, the colorant is thermally decomposed, so that the color of the irradiated surface is changed and becomes discriminitive from that of non-irradiated surface.

Abstract: Photochemical systems for the direct visualization of exposure to ultraviolet radiation that effect visible color changes involving a process in which a photoacid is formed upon irradiation of a nitro-substituted aromatic aldehyde with ultraviolet light and wherein proton transfer to a dye causes the dye to undergo a visible color change. The system undergoes such color change to an extent directly proportional to the cumulative amount of ultraviolet incident thereupon.