Abstract: This invention relates to an imaging element comprising an imaging layer having associated therewith a compound of Structure I: wherein: the substituents are as defined in the application.

Abstract: This invention relates to an imaging element comprising an imaging layer having associated therewith a compound of Structure I: wherein PUG is a residue of removing a hydrogen from wherein X, Y, and Z represent substituents selected independently from the groups hydrogen, alkyl group of 1 to 6 carbon atoms, cyclopropyl, aryl, arylalkyl, and heterocyclic groups, wherein at least one of X, Y, and Z is an aryl group and one of X, Y, Z, which may or may not be an aryl group, is attached in the direction of the backbone, and the other substituents are as defined in the specification. Such compounds have good reactivity and can by used to block photographically useful compounds such as developing agents until thermally activated under preselected conditions. Compounds according to the present invention are especially useful in color photothermographic imaging elements.

Abstract: Disclosed is a silver halide photographic light-sensitive material comprising at least one silver halide emulsion layer on a support, which contains a compound of which one-electron oxidized derivative produced by one electron oxidation of the compound is capable of releasing two or more electrons with a bond cleavage and has a characteristic curve drawn in orthogonal coordinates of logarithm of light exposure (x-axis) and optical density (y-axis) using equal unit lengths for the both axes, on which gamma is 5.0 or more for the optical density range of 0.3-3.0. This silver halide photographic light-sensitive material shows high contrast and high sensitivity.

Abstract: Disclosed is a highly sensitive photothermographic material containing on a support a silver salt of an organic acid, a photosensitive silver halide, a reducing agent, a binder and, for example, a compound of which one-electron oxidized derivative produced by one electron oxidation of the compound is capable of releasing two or more electrons with a bond cleavage.

Abstract: This invention comprises an imaging element comprising an imaging layer having associated therewith a phenolic activating agent in combination with a blocked color-forming agent of Structure I: wherein PUG is a photographically useful color-forming agent, LINK 1 and LINK 2 are linking groups; TIME is a timing group; HET is a heterocyclic group, and the other groups are as defined in the specification.

Abstract: This invention comprises an imaging element comprising an imaging layer having associated therewith a compound of Structure I: In the above Structure I, the substituents are as defined in the application. Such compounds have good reactivity and can by used to block photographically useful compounds such as developing agents until thermally activated under preselected conditions. Compounds according to the present invention are especially useful in color photothermographic imaging elements.

Abstract: A light-sensitive silver-halide color photographic element comprising at least two different chromogenic couplers including, in reactive association, a multifunctional coupler and a developer precursor that liberates a developing agent enabling cyan color from the multifunctional coupler on development, wherein the multifunctional coupler has the property that it is capable of forming a distinctly colored dye with an oxidized form of the developer 4-(N-ethyl-N-2-hydroxyethyl)-2-methylphenylenediamine. In one embodiment, the multifunctional coupler has the property that it is capable of forming a distinctly colored magenta dye with an oxidized form of the developer 4-(N-ethyl-N-2-hydroxyethyl)-2-methylphenylenediamine. By means of the present invention, light-sensitive color photothermographic elements can form yellow, magenta and cyan dye records of consistent density forming ability and consistent stability in all three color records.

Abstract: This invention relates to a photothermographic color element containing a mixture of blocked developers in the same emulsion layer, which blocked developers having different onset temperatures. Such a mixture has been found to allow for lower film processing temperatures and/or shorter times of development with respect to the blocked developer having a higher onset temperature. Conversely, improved discrimination can be obtained with respect to the blocked developer having the lower onset temperature.

Abstract: This invention relates to a photothermographic color element containing a mixture of blocked developers in the same emulsion layers. By having different blocked developers or mixtures of at least two blocked developers in different color layers, it is possible to manipulate the image discrimination (at the processing temperature) in each layer and to balance the density formation or color in the different color layers. Different mixtures of blocked developers can be used in different imaging layers, to balance the Gamma, the Dmin and the Latitude in different imaging layers or color units.

Abstract: This invention relates to an imaging element comprising an imaging layer having associated therewith a compound of Structure I: In the above Structure I, the substituents are as defined in the application, wherein B is a six-membered heteroaromatic ring. Such compounds have good reactivity and can by used to block photographically useful compounds such as developing agents until thermally activated under preselected conditions. Compounds according to the present invention are especially useful in color photothermographic imaging elements.

Abstract: This invention provides a color diffusion transfer image forming material comprising a light-sensitive material containing a compound which forms or releases a diffusible dye upon reaction with a developing agent derived from a light-sensitive silver halide, aminopheno derivative or phenylenediamine derivative and an oxidation product of the developing agent supported on a first support, and a dye-fixing material containing a discoloration preventing agent having a specific structure supported on a second support which may be the same as or different from the first support, wherein the light-sensitive material and the dye-fixing material are located so that the diffusible dye formed or released by developing is at least transferred from the light-sensitive material to the dye-fixing material in developing the light-sensitive material, thereby providing the image forming material with excellent properties in terms of dye concentration, image fastness and the like.

Abstract: This invention relates to an imaging element comprising an imaging layer having associated therewith a compound of Structure I: In the above Structure I, the substituents are as defined in the application. Such compounds have good reactivity and can by used to block photographically useful compounds such as developing agents until thermally activated under preselected conditions. Compounds according to the present invention are especially useful in color photothermographic imaging elements.

Abstract: This invention relates to an imaging element comprising an imaging layer having associated therewith a compound of Structure I: wherein the substituents are as defined in the specification.

Abstract: Compounds of the formula I are suitable as release compounds for photographically useful groups (photographic units). On reacting with nucleophilic reagents, preferably with dinucleophiles, the photographically useful group is released. ##STR1## In formula I: PUG means a photographically useful group;A means a strong electron acceptor;V means a vinylene group or two or more successive vinylene groups, wherein the vinylene group or two successive vinylene groups may form part of an aromatic ring system;L means one or more timing groups;m means 0 (zero) 1 or 2;n means 0 (zero), 1 or 2;R.sup.1 means H or methyl;R.sup.2 means H, alkyl with 1-18 C atoms or aryl;R.sup.3, R.sup.4 mean H or an organic group,wherein R.sup.2 and R.sup.3 may also together mean the residue necessary to complete a ring.

Abstract: There is described a multicolor diffusion transfer film unit having a plurality of different color image components, each of which includes a color-sensitive silver halide emulsion in association with a corresponding image dye-providing material and a first silver halide developer which takes part in photographic development to provide an imagewise pattern of diffusible image dye-forming material as a function of photoexposure. At least one of said color image components includes a second silver halide developer, or a precursor thereof, which is capable of developing silver halide indiscriminately and which is made available after photographic development in the color image component in which it is located is substantially completed.

Abstract: The invention provides a color photographic material comprising at least one silver halide emulsion layer having associated therewith a dye image-forming coupler and which contains in a layer thereof an ETA (electron transfer agent) releasing compound of the general formula: ##STR1## wherein R.sup.1 is an alkyl group,R.sup.2 to R.sup.6 are individually H or an alkyl group with the proviso that when one or both of R.sup.5 or R.sup.6 are H, R.sup.3 and R.sup.4 must not be H,R.sup.7 to R.sup.11 are individually H, or an alkyl or alkoxy group,A is H or an alkyl group and B is an alkyl group or, together with the atoms to which they are attached, A and B complete a carbocyclic or heterocyclic ring group,or,when A and B are not linked together, A and R.sup.2 may together complete an aromatic or nonaromatic carbocyclic group or an aromatic or nonaromatic heterocyclic group,with the proviso that if R.sup.7 to R.sup.11 are all hydrogen then neither R.sub.3 nor R.sub.4 are methyl or hydroxymethyl.

Abstract: A method for making a photographic silver halide developer composition, preferably immediately before use, by electrolysing an aqueous medium containing a developing agent precursor composition which forms or releases a silver halide developing agent at an electrode upon electrolysis.

Abstract: A p-phenylenediamine series color developing agent or a precursor thereof having a substituent A at the ortho-position; Substituent A: ##STR1## wherein R.sup.1 represents a hydrogen atom or an alkyl group and X represents --O--R.sup.7 or ##STR2## wherein R.sup.7 represents an alkyl group, an aryl group, or a heterocyclic ring and R.sup.8 and and R.sup.9, which may be the same or different, each represents a hydrogen atom, an alkyl group, an aryl group, or a heterocyclic ring, R.sup.8 and R.sup.9 may combine with each other to form a heterocyclic ring, and a process for forming an image which comprises imagewise exposing a silver halide color photographic material and thereafter color developing the color photographic material in the presence of a p-phenylenediamine series color developing agent or a precursor thereof having the aforesaid substituent A.

Abstract: A photographic element including a support bearing at least one photographic silver halide emulsion layer and bearing on the opposite side of the support a layer containing at least one blocked developing agent or precursor thereof provides automatic developing agent replenishment of the developing bath upon processing.

Abstract: A photographic element is disclosed including a support bearing at least one photographic silver halide emulsion layer and at least one non-photosensitive layer between the emulsion layer and the support, wherein the non-photosensitive layer comprises at least one blocked developing agent.

Abstract: A dispersion comprising solid particles of a developer precursor having the structureCD--(T).sub.m --Sin whichCD is a silver halide color developer,T is a timing group,m is an integer from 0 to 6, andS is a blocking group,and a vehicle in which the solid particles are insoluble, is disclosed. The dispersion can be incorporated in a photographic element.

Abstract: A color photographic element for use with a latent or silver image intensification or amplification method which incorporates a blocked color developing agent. The color photographic element includes at least one silver halide emulsion layer which includes at least about 70 mole percent chloride and has a concentration of silver within the range of about 0.1 mg/m.sup.2 to 2000 mg/m.sup.2. The blocked color developing agent is capable of being unblocked during photographic processing by means of reaction with a dinucleophile reagent. A preferred dinucleophile reagent is hydrogen peroxide, which also acts as an oxidant in the latent or silver image intensification method.

Abstract: A heat-developable color photographic material comprising a support having thereon at least a light-sensitive silver halide, a binder, at least one of an electron-donating agent and a precursor thereof, a reducible dye-forming compound which releases a diffusible dye by reduction and an electron-transferring agent, wherein an electron-transferring agent precursor co-exists together with the electron-transferring agent.

Abstract: A silver halide photographic material composed of a support having thereon at least one silver halide photosensitive emulsion layer, at least one layer of the material containing a blocked photographic reagent precursor represented by formula (I): ##STR1## wherein X.sub.1 represents a divalent linking group containing a hetero atom bonded to the carbon atom, provided that X.sub.1 is linked to the carbon atom by a group other than ##STR2## PUG represents a photographically useful group containing a hetero atom bonded to X.sub.1 ; W represents .dbd.N-- or ##STR3## Y.sub.1 represents hydrogen or a group capable of being substituted; Z represents an atomic group necessary for forming a heterocyclic ring, provided that when W represents a ##STR4## the group adjacent to W in the heterocyclic ring is a group other than ##STR5## wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.

Abstract: A method for processing a silver halide color photographic material is described, comprising a support having thereon at least one light-sensitive silver halide emulsion layer, wherein after imagewise exposure, said silver halide color photographic material is processed with a color developer containing at least one aromatic primary amine developing agent and at least one compound capable of releasing the aromatic primary amine developing agent which has substantially no developing agent ability prior to the release of the aromatic primary amine developing agent.

Abstract: A silver halide photographic material, which contains at least one blocked photographic reagent having in the molecule thereof at least one group selected from ##STR1## group and capable of releasing a photographically useful reagent by cleavage of the --N--C--bond by a nucleophilic attack of a nucleophilic reagent on the carbonyl group and a subsequent intramolecular electron transfer reaction or intramolecular nucleophilic reaction and which has at least one photosensitive silver halide emulsion layer, is photographically processed in the presence of an amine. A photographic material which includes, in combination, a photographic reagent precursor capable of releasing a photographically useful reagent timely on photographic processing and a photosensitive silver halide emulsion layer is provided along with a method of processing the photographic material.

Abstract: A silver halide photographic material is disclosed, which comprises a support having formed thereon at least one silver halide emulsion layer, wherein the silver halide photographic material contains, in the silver halide emulsion layer, other hydrophilic colloid layer(s), or both, a compound represented by formula (I) ##STR1## wherein EAG represents an electron accepting group, --SO.sub.2 -- represents a sulfonylene group; X represents an oxygen atom (--O--), a sulfur atom (--S--) or an atomic group (--N(R.sub.2)--) containing a nitrogen atom; the single bond between --SO.sub.2 and X being cleaved after EAG receives an electron, wherein R.sub.1 and R.sub.2 each represents a simple bond or a group other than a hydrogen atom; said R.sub.1, R.sub.2, EAG may be combined with each other to form a ring; (Time) represents a group capable of releasing a photographically useful group (PUG) upon the cleavage of the SO.sub.

Abstract: A process for processing a DIR coupler-containing silver halide color photographic material for photographing use in a continuous manner with replenishment of a developer is disclosed in which said DIR coupler is a coupler which has in a coupling site a group that functions as a development inhibitor or a development inhibitor precursor upon being eliminated from the coupling active site by color development processing and that will be decomposed to a compound exerting substantially no influences on photographic properties after flowing into a color developing solution, said development inhibitor having a half-value period of 4 hours or shorter than that at a pH of 10.0, and in which the developing solution is replenished in an amount of 700 ml or less per m.sup.2 of developed light-sensitive materials.

Abstract: A silver halide photographic material comprising a support having thereon at least one silver halide emulsion layer, wherein the silver halide photographic material contains at least one compound represented by the following general formula (I):A--Time).sub.t X (I)wherein A represents an oxidation reduction moiety comprising an atomic group which does not enable --Time).sub.t X to be released until the oxidation reduction moiety is oxidized during photographic development processing; Time represents a timing group which is connected to A through a sulfur atom, a nitrogen atom or an oxygen atom; t represents an integer of 0 or 1; and X represents a group represented by the following general formula (II): ##STR1## wherein R represents a straight chain or branched chain alkylene group, a straight chain or branched chain alkenylene group, a straight chain or branched chain aralkylene group or an arylene group; Z represents a polar substituent; Y represents ##STR2## R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.

Abstract: A silver halide photographic material which contains at least one blocked photographic reagent having in the molecule thereof at least one ##STR1## structure and capable of releasing a photogrpahically useful reagent by cleavage of the ##STR2## bond by a nucleophilic attack of a nucleophilic reagent on the structure and a subsequent intramolecular electron transfer reaction or an intramolecular nucleophilic reaction and which has at least one photosensitive silver halide emulsion layer. There is provided a photogrphic material which includes, in combination, a photographic reagent precursor capable of releasing a photographically useful reagent timely on photographic processing and a photosensitive silver halide emulsion layer.

Abstract: A silver halide photographic material which comprises a support having coated thereon a light-sensitive silver halide emulsion layer, wherein the photographic material contains at least one blocked photographic agent represented by the following general formula (I): ##STR1## wherein A represents a photographic agent moiety which is bonded to a blocking moiety through a hetero atom, or a precursor thereof; R.sup.1, R.sup.2 and R.sup.3 each represents a hydrogen atom, or a substituent group; and Z represents atoms necessary to form a carbocyclic ring or a heterocyclic ring (except for a heterocyclic ring which contains an NH group at the position adjacent to the carbon atom to which R.sup.1 is attached). The blocked photographic agent is completely stable upon storage of the photographic material, and releases a photographic agent at a desired time upon processing. The blocked photographic agent also exhibits its function to a substantial degree over a wide range of pH.

Abstract: Photographic elements and processes are described which employ a compound containing a hydrazide moiety attached by a linking group, comprising an acidic group or an active methylene group adjacent to an acidic group, to a heteroatom of a moiety containing a photographically useful group comprising a photographic dye or precursor thereof or a photographic reagent; wherein:(a) the hydrazide moiety is capable of being oxidized to an azo group by an oxidized developing agent,(b) the azo group formation causes the release of the photographically useful group, and(c) the released photographically useful group does not contain the linking group or the nitrogen atoms of the hydrazide moiety.

Abstract: A silver halide photographic light-sensitive material is described, comprising a support having thereon a light-sensitive silver halide emulsion layer having associated therewith a blocked photographic agent represented by formula (I) ##STR1## wherein A represents a photographically useful agent moiety, which may have a timing group; X.sup.1 and X.sup.2 each represents a carbonyl group, a sulfonyl group, or a sulfinyl group; Z represents an atomic group forming a 5-membered, 6-membered, or 7-membered ring; R.sup.1 and R.sup.2, which may be the same or different, each represents a hydrogen atom, a halogen atom, an alkyl group, an alkenyl group, a cycloalkyl group, an aryl group, an alkoxy group, an acyl group, a sulfonyl group, or a heterocyclic group; R.sup.3 represents an alkyl group, an alkenyl group, a cycloalkyl group, a heterocyclic group, an aryl group, or an aralkyl group; m represents 0, 1, or 2; n represents 0 or 1; and the total of m+n is 1, 2, or 3.

Abstract: Compounds of the formula ##STR1## wherein L is a direct bond or consists of a chain of carbon atoms or of a divalent ring system, R.sub.1 to R.sub.4 are hydrogen or alkyl, R.sub.5 or R.sub.6 are hydrogen, alkyl or aryl, or R.sub.5 together with R.sub.6 complete a ring system, and R.sub.7 is hydrogen or a group of the formula ##STR2## wherein L, R.sub.5 and R.sub.6 are as defined. These compounds are useful developing agents for activation processing.

Abstract: Photographic silver halide material containing a ballasted electron-donor precursor compound yielding by alkaline hydrolysis an electron-donor compound (ED-compound) capable (1) of donating electrons to an oxidized electron-accepting silver halide developing agent e.g. for scavenging it, said electron-donor precursor compound corresponding to the following general formula: ##STR1## wherein: R represents hydrogen or a substituent, e.g. an acyl group, which on hydrolytic removal allows the replacement of R by H,R.sup.1, R.sup.2 and R.sup.3 (same or different) are hydrocarbon substituents or R.sup.3 is H, andZ and Y represent the necessary atoms to close a benzene ring that may be substituted or form a fused ring system.

Abstract: A silver halide photographic light-sensitive material containing a diffusion resistant coupler, a light-sensitive silver halide and at least one organic metal complex represented by the following general formula (I) in the same layer or different layers on a support. ##STR1## wherein M represents a divalent metal atom; R.sup.1 and R.sup.2, which may be the same or different, each represents an alkyl group having from 1 to 5 carbon atoms, a hydroxyalkyl group having from 1 to 5 carbon atoms, an alkoxyalkyl group having from 2 to 10 carbon atoms or an alkylsulfonamidoalkyl group having from 2 to 10 carbon atoms, or R.sup.1 and R.sup.2 may be bonded each other to form a heterocyclic ring together with the nitrogen atom; R.sup.3, represents a hydrogen atom, an alkyl group having from 1 to 5 carbon atoms or an alkoxy group having from 1 to 5 carbon atoms; and R.sup.4 and R.sup.

Abstract: A silver halide photographic light-sensitive material containing at least one compound represented by the general formula (I): ##STR1## is disclosed. The compound of the invention has good stability over time. The material has improved developability and makes it possible to carry out simple and rapid processing. The material has good resistance with respect to fogging, stains and desensitization.

Abstract: Compounds corresponding to the formula: ##STR1## wherein Z represents a radical which completes a condensed aromatic ring system;R.sup.1 represents an n-valent aliphatic or aromatic radical;R.sup.2 represents H, alkyl or aryl,R.sup.3 represents one or more radicals to control the diffusion properties and the activation pH;andn represents 1 or 2,are suitable ED precursor compounds for use in color-photographic recording materials. They are preferably used in a combination with reducible dye-releasers. They are also suitable as so-called scavengers.

Abstract: Compounds corresponding to the formula: ##STR1## wherein R.sup.1 represents an aromatic group, andR.sup.2 represents H, alkyl, alkenyl, aryl or acyl, are suitable ED precursor compounds for use in color photographic recording materials. They are preferably used in combination with reducible dye releasers. They are also suitable as so-called scavengers.

Abstract: .alpha.-Ketoimidomethyl blocked photographic reagents are useful in photographic elements, film units and processes. The blocked photographic reagents have the structure: ##STR1## wherein J represents ##STR2## X represents the atoms to complete a 5- or 6-membered ring or ring system; R represents alkyl of 1 to 30 carbon atoms or aryl of 6 to 30 carbon atoms; andPR represents the residue of an organic photographic reagent containing a heteroatom through which it is joined to the blocking group.

Abstract: A photographic element comprising a support provided thereon with at least one light-sensitive silver halide emulsion layer containing a nondiffusible compound which receives at least one electron in an alkaline condition to release a photographically useful material and a nondiffusible electron donor or a precursor thereof having the following formula (I) or (II): ##STR1## wherein R.sup.1 represents hydrogen, an alkyl, an aryl or a heterocyclic group, R.sup.2 represents hydrogen, an alkyl, an aryl, a heterocyclic, an amino, a carbamide, a sulfonamide, a sulfamoyl, a carbamoyl or a ureido group, R.sup.3 and R.sup.4 each is hydrogen, --COR.sup.5, --SO.sub.2 R.sup.6 or --CSR.sup.7 wherein R.sup.5 and R.sup.6 each is a substituted or unsubstituted, respectively, alkyl, alkenyl, aryl, heterocyclic, alkylamino, alkyloxy, aryloxy, alkylthio, arylthio, alkyloxycarbonyl or aryloxycarbonyl group, and R.sup.7 is a substituted or unsubstituted alkyllamino or arylamino group, said R.sup.

Abstract: There are disclosed novel compounds which are represented by the formula ##STR1## wherein X represents the nonmetallic atoms necessary to form a nucleus which completes a 5- or 6-membered heterocyclic moiety, R is H, an alkali metal or a group which is cleavable in aqueous alkaline medium and Z is H, alkyl having from 1 to 10 carbon atoms, aralkyl such as benzyl or phenethyl, phenyl or substituted phenyl. The compounds are useful in photographic applications.

Abstract: Mesoionic 1,2,4-triazolium-3-thiolate silver halide stabilizer precursors are novel compounds useful in a heat developable and heat stabilizable photographic silver halide materials and processes. After imagewise exposure of the photographic material, a developed and stabilized silver image is produced by heating the element. Mesoionic stabilizer precursors are also useful in photographic silver halide processing compositions.

Abstract: A photographic image-forming method comprising imagewise exposing a silver halide photographic light-sensitive element containing a specific hydroquinone derivative in the silver halide emulsion layer of substantially the surface latent image type or at least one hydrophilic colloid layer thereof and then developing the exposed light-sensitive element in the presence of a specific hydrazine compound. The method forms a photographic image having markedly high negative gradation.

Abstract: The compounds represented by the general formula (I) or (II) as defined in the specification are novel and useful developing agent precursors in silver halide photographic light sensitive materials.

Abstract: New DIR-compounds of the formula ##STR1## are useful in photographic materials and processes.

Abstract: A process for the production of an improved photographic image is provided which comprises imagewise exposing photographic material which comprises on a support base at least one light-sensitive negative-working silver halide emulsion layer containing a color coupler (receptor layer) and in which after color processing a negative dye image only is formed, there being associated therewith at least one light-sensitive negative-working silver halide emulsion layer containing at least one DIR compound (development inhibitor releasing compound) and in which after processing no photographic image is present (donor layer), developing the photographic material in a color photographic developing solution to form a negative silver image in the layer which comprises the DIR compound and a coupled compound with the DIR compound in the areas in which the silver has been developed, so releasing the DI compound imagewise from the DIR compound and allowing the DI compound to diffuse imagewise into the layer containing the co

Abstract: Novel electron donor precursors have the structure: ##STR1## where: R is an alkali labile group;Y is an aliphatic or aromatic group; andZ is an electron withdrawing group.The compounds are useful in photographic elements, film units and processes to provide electrons to immobile compounds which must accept at least one electron before releasing a diffusible dye or photographic reagent.

Abstract: Novel electron donor precursors have the structure: ##STR1## wherein: Z represents the atoms to complete a mono-, bi- or tricyclic ring system, each ring of which contains 5 to 6 nuclear atoms;n is 1 or 2;R.sup.1 is a monovalent aromatic group when n is 1 and a bivalent aromatic group when n is 2; andR.sup.2 represents hydrogen, an alkyl group, an aryl group, an acyl group, an ester group or an amido group.The compounds are useful in photographic elements, film units and processes to provide electrons to immobile compounds which must accept at least one electron before releasing a diffusible dye or photographic reagent.

Abstract: A novel silver halide color photographic material containing a desilvering accelerator releasing compound, which comprises at least one light-sensitive silver halide emulsion layer on a support, wherein at least one of said emulsion layer and a non-light sensitive hydrophilic layer(s) contains at least one compound represented by the formula (I)PWR--Time--.sub.t BA (I)wherein PWR represents a group which undergoes reduction to release (Time--.sub.t BA; BA represents a group which becomes a desilvering accelerator after being released; Time represents a group which releases BA through a reaction after being released from PWR as (Time--.sub.t BA; and t represents an integer of 0 or 1.