US3809561A - Negative unfogged silver halide emulsion containing a sensitizing combination of a cyanine desensitizing dye and a supersensitizing compound - Google Patents

Abstract

NEGATIVE UNFOGGED PHOTOGRAPHIC SILVER HALIDE EMULSIONS CONTAINING A DENSENSITIZING CARBOCYANINE DYE AND A SUPERSENSITIZING AGENT ARE PROVIDED. THE SUPERSENSITIZING AGENT SUBSTANTIALLY ELIMINATES THE DENSENSITIZING EFFECT OF THE DESENSITIZING DYES AND RENDERS THEM USEFUL AS SENSITIZERS FOR NEGATIVE SILVER HALIDE EMULSIONS. ALSO DISCLOSED IS THE USE OF DENSENSITIZING DYES AS FILTERED DYES IN A PHOTOGRAPHIC ELEMENT IN COMBINATION WITH A SUPERSENSITIZING AGENT, DESENSITIZATION BY MIGRATED DYE MOLECULES BEING THEREBY GREATLY REDUCED.

Description

United States Patent Oflice Patented May 7, 1974 3,809,561 NEGATIVE UNFOGGED SILVER HALIDE EMUL- SION CONTAINING A SENSITIZING COMBINA- TION OF A CYANINE DESENSITIZING DYE AND A SUPERSENSITIZING COMPOUND Cynthia G. Ulbing, Rochester, and Daniel A. Corretore,

Jr., Webster, N. assignors to Eastman Kodak Company, Rochester, NY. No Drawing. Filed June 1, 1972, Ser. No. 258,770 Int. Cl. G03c 1/28, 1/36, 1/84 US. CI. 96-84 15 Claims ABSTRACT OF THE DISCLOSURE This invention relates to the use of supersensitizers to reduce the desensitization effects of photographic desensitizing dyes in negative unfogged silver halide photographic emulsions.

Certain cyanine dyes are known to act as desensitizers for photographic silver halide emulsions. Electron accepting dyes such as described in Illingsworth US. Pat. 3,501,305 issued Mar. 17, 1970 and Brooker et al. US. Pat. 3,431,111 issued Mar. 4, 1969 which act as spectral sensitizers for fogged, direct positive emulsions, act as strong desensitizers in negative silver halide emulsions. This fact has heretofore limited the use of such dyes to direct positive silver halide emulsions. It is an object of this invention to provide novel negative photographic silver halide emulsions containing desensitizing dyes which exhibit increased photographic speed.

In accordance with this invention, there is provided a negative unfogged photographic silver halide emulsion comprising (1) an electron trapping photographic cyanine dye having a cathodic polarographic half-wave potential more positive than l.0 volt and an anodic half-wave potential greater than +0.4 volt and preferably greater than +0.9 volt and (2) a supersensitizing agent such as 'a sulfonated derivative of bis(triazinylamino)stilbene,

ascorbic acid or alkali metal thiocyanate. Electron trapping photographic dyes having a cathodic polarographic half-wave potential more positive than 1.0 volt and an anodic half-wave potential greater than +0.4 volt include cyanine dyes containing a desensitizing nucleus. As used herein, desensitizing nucleus refers to those nuclei which, when converted to a symmetrical carbocyanine dye and added to a gelatin unfogged silver chlorobromide emulsion containing 40 mole percent chloride and 60 mole percent bromide, at a concentration of from 0.01 to 0.2 g. of dye per mole of silver, caused, by electron trapping, at least an 80% loss in the blue speed of the emulsion when it is sensitometrically exposed and devoloped 3 minutes at 20 C. in Kodak D-19 developer.

The electrochemical potential measurements can be made with an approximately molar solution of the dye in an electrolyte; for example, methanol which is 0.05 molar in lithium chloride. A dropping mercury electrode can be used for the cathodic measurement with the polarographic half-wave potential for the cathodic response most positive in potential designated E A pyrolytic graphite electrode can be used for the anodic measurement with the voltammetric half-peak potential for the anodic response most negative in potential designated E,,. In each measurement, the reference electrode can be an aqueous silver-silver chloride (saturated potassium chloride) electrode at 20 C. Plus and minus signs are assigned to the potential values according to the IUPAC Stockholm Convention 1953. The E and E values so measured shall not include processes in which electron transfer is primarily the result of the presence in solution of the counter ion of a positively charged dye or other such chemical entities in solution that are not an integral part of, or attached to, the chromophoric system of the dye. A response of lesser current magnitude preceding the primary response, such as a prewave resulting from adsorption of the electrolysis product to the electrode surface, shall be excluded from designation as E or E Electrochemical measurements of this type are known in the art and are described in one or more of the following reference texts: New Instrumental Methods in Electrochemistry, by Delahay, Interscience Publishers, New York, N.Y., 1954; Polarography, by Kolthoif and Lingane, 2nd edition, Interscience Publishers, New York, N.Y., 1952; and Electrochemistry at Solid Electrodes, by Adams, Marcel] Dekker, Inc., New York, N.Y., 1969.

Cyanine dyes containing a desensitizing nucleus which may be used in the practice of this invention include those represented b the formulas:

wherein Z and Z each represent the nonmetallic atoms necessary to complete a heterocyclic nucleus containing 5 to 6 atoms in the heterocyclic ring. Typical suitable heterocyclic nuclei completed with the atoms of Z include those of the thiazole series (e.g., thiazole, 4-methylthiazole, 5 methylthiazole, 4 phenylthiazole, S-phenylthiazole, 4,5 dimethylthiazole, 4,5 diphenylthiazole, 4- (2-thienyl)thiazole, etc.), those of the benzothiazole series (e.g., benzothiazole, 4-cl1lorobenzothiazole, S-chlorobenzothiazole, 6-chlorobenzothiazole, 7 chlorobenzothiazole, 4 methylbenzothiazole, 5 methylbenzothiazole, 6 methylbenzothiazole, 5 bromobenzothiazole, 6- bromobenzothiazole, 4 phenylbenzothiazole, 5 phenylbenzothiazole, 4-methoxybenzothiazole, S-methoxybenzothiazole, 6 methoxybenzothiazole, 5-iodobenzothiazole, 6 iodobenzothiazole, 4 ethoxybenzothiazole, S-ethoxybenzothiazole, tetrahydrobenzothiazole, 5,6 dimethoxybenzothiazole, 5,6 dioxymethylenebenzothiazole, 5 hydroxybenzothiazole, etc.), those of the naphthothiazole series (e.g., a-naphthothiazole, fi-naphthothiazole, 5 methoxy-fl-naphthothiazole, S-ethoxy p naphthothiazole, 7 methoxy a naphthothiazole, 8 methoxy-fl-naphthothiazole, etc.), those of the thianaphtheno 7,6,4,5- thiazole series (e.g., 4 methoxythianaphtheno 7',6',4,5- thiazole, etc.), those of the oxazole series (e.g., 4-methyloxazole, 5 methyloxazole, 4 phenyloxazole, 4,5 diphenyloxazole, 4 ethyloxazole, 4,5 dimethyloxazole, 5-phenyloxazole, etc.), those of the benzoxazole series (e.g., benzoxazole, 5 chlorobenzoxazole, 5 phenylbenzoxazole, 5 methylbenzoxazole, 6 methylbenzoxazole, 5,6-dimethylbenzoxazole, 4,6 dimethylbenzoxazole, 5; -methoxybenzoxazole, 6 methoxybenzoxazole, S-ethoxybenzoxazole, 6 chlorobenzoxazole, 5 hydroxybenzoxazole, 6 hydroxybenzoxazole, etc.), those of the naphthoxazole series (e.g., a-naphthoxazole, ,S-naphthoxazole,

etc.), those of the selenazole series (e.g., 4-methylselenazole, 4 phenylselenazole, etc.), those of the benzoselenazole series (e.g., benzoselenazole, 5 chlorobenzoselenazole, S-methoxybenzoselenazole, 5 hydroxybenzoselenazole, tetrahydrobeuzoselenazole, etc.), those of the naphthoselenazole series (e.g., a-naphthoselenazole, B-naphthoselenazole, etc.), those of the thiazoline series (e.g., thiazoline, 4 methylthiazoline, etc.), those of the 2- quinoline series (e.g., quinoline, 3-methylquinoline, 5- methyllquinoline, 7 methylquinoline, S-methylquinoline, 6 chloroquinoline, 8 chloroquinoline, 6 methoxyquinoline, 6 ethoxyquinoline, 6 hydroxyquinoline, 8- hydroxyquinoline, etc.), those of the 3,3 dialkylindolenine series (e.g., 3,3 dimethylindolenine, 3,3,5 trimethylindolenine, 3,3,7 trimethylindolenine, etc.), and those of the 2 pyridine series (e.g., pyridine, 3 methylpyridine, 4 methylpyridine, 5 methylpyridine, 6 methylpyridine, 3,4 dimethylpyridine, 3,5 dimethylpyridine, 3,6 dimethylpyridine, 4,5 dirnethylpyridine, 4,6 dimethylpyridine, 4 chloropyn'dine, 5 chloropyridine, 6 chloropyridine, 3 hydroxypyridine, 4 hydroxypyridine, 5 hydroxypyridine, 6 hydroxypyridine, 3-phenylpyridine, 4 phenylpyridine, 6 phenylpyridine, etc.), Typical suitable heterocyclic nuclei completed with the atoms of Z include indoles such as those indole nuclei in the dyes disclosed in U.S. Pats. 2,930,694, 3,501,312, 3,582,343 and 3,598,596; pyrazoles such as those pyrazole nuclei in the dyes disclosed in U.S. Pat. 3,615,608; 4- pyrazoles; and, quinoxalines and pyrazines such as the 3 pyrrolo[2,3-b]quinoxaline and 3 pyrrolo[2,3-b]pyrazine nuclei in the dyes disclosed in U.S. Pat. 3,598,595. Z and Z each represent the nonmetallic atoms necessary to complete a desensitizing heterocyclic nucleus containing from 5 to 6 atoms in the heterocyclic ring such as a nitrobenzothiazole nucleus (e.g., 5 nitrobenzothiazole, 6 nitrobenzothiazole, 5 chloro 6 nitrobenzothiazole, etc.), a nitrobenzoxazole nucleus (e.g., 5 nitrobenboxazole, 6 nitrobenzoxazole, 5 chloro 6 nitrobenzoxazole, etc.), a nitrobenzoselenazole nucleus (e.g., 5 nitrobenzoselenazole, 6 nitrobenzoselenazole, 5 chloro-6- nitrobenzoselenazole, etc.), an imidazo [4,5-b]quinoxaline nucleus (e.g., imidazo[4,5-b]quinoxaline, 1,3 dialkylimidazo[4,5-b]quinoxaline such as 1,3 diethylimidazo [4,5-b]quinoxaline, 6 chloro 1,3 diethylimidaz[4,5- b]quinoxaline, etc., 1,3 dialkenylimidazo [4,5-b] quinoxaline such as 1,3 diallylimidazo[4,5-b]quinoxaline, 6- chloro 1,3 diallylimidazo[4,5-b]quinoxaline, etc., 1,3- diarylimidazo[4,5-b]quinoxaline such as 1,3 diphenylimidazo[4,5-b]quinoxaline, 6 chloro 1,3 diphenylimidazo[4,5-b]quinoxaline, etc.), a 3,3 dialkyl 3H- pyrrolo[2,3-b] pyridine nucleus (e.g., 3,3 dimethyl-3H- pyrrolo[2,3-b]pyridine, 3,3 diethyl 3H pyn'olo [2,3-b] pyridine, etc.), a 3,3 dialkyl 3H nitroindole (eg., 3,3- dimethyl nitro 3H indole, 3,3 diethyl 5 nitro- 3H indole, 3,3 dimethyl 6 nitro 3H indole, etc.), a thiazolo[4,5-b]quinoline nucleus or a nitroquinoline nucleus (e.g., 5 nitroquinoline, 6 nitroquinoline, etc.); R R R R and R can be the same or diiferent groups and each preferably represents a lower alkyl group having 1 to 8 carbon atoms such as methyl, ethyl, propyl, etc., and including substituted lower alkyl groups such as a carboxyalkyl group (e.g., carboxymethyl, carboxyethyl, carboxypropyl, carboxybutyl, etc.), a carbalkoxyalkyl group (e.g., carbomethoxymethyl, carbethoxyethyl, carbopropoxyethyl, carbopropoxybutyl, etc.), a sulfoalkyl group (e.g., sulfomethyl, sulfoethyl, sulfopropyl, sulfobutyl, etc.), a hydroxyalkyl group (e.g., hydroxymethyl, hydroxyethyl, hydroxypropyl, hydroxybutyl, etc.), an alkoxyalkyl group (e.g., methoxyethyl, methoxypropyl, ethoxyethyl, ethoxypropyl, etc.), a sulfoalkoxyalkyl group, as well as an aryl group such as phenyl, 4-methylphenyl, 4 chlorophenyl, etc. E represents anionic groups such as chloride, bromide, iodide, p-toluenesulfonate, thiocyanate, perchlorate, acetate, methylsulfate, ethylsulfate, etc. q is 0, 1 or 2; and ris 1 or 2.

Sulfonated derivatives of a bis(triazinylamiuo)stilbeue which may be used in the practice of this invention include those represented by the general formula:

(III) N N It -f TNH NH( Tm -o0=oH- J N N N V m V 37 3H 3 B wherein R R", R and R may be the same or different groups and each represents a hydrogen atom, a hydroxyl group, an aryloxy group (e.g., phenoxyl, o-toloxyl, psulfophenoxyl, etc.), an alkoxyl group (e.g., methoxyl, ethoxyl, etc.), a halogen atom (e.g., chlorine, bromine, etc.), a heterocyclic radical (e.g., morpholinyl, piperidyl, etc.), an alkylthio group (e.g., methylthio, ethylthio, etc.), an arylthio group (e.g., phenylthio, tolylthio, etc.), a heterocyclylthio group (e.g., benzothiazylthio, etc.), an amino group, an alkylamino group (e.g., methylamino, ethylamino, propylamino, dimethylamino, diethylamino, dodecylamino, cyclohexylamino, [3 hydroxyethylamino, di ,8 hydroxyethylamino, p sulfoethylamino, etc.), an arylamino group (e.g., anilino, om-, and p-sulfoanilino, 0-, m-, and p-chloroanilino, o-, mand p-anisylamino, o-, m-, and p-toludino, o-, m-, and p-carboxyanilino, hydroxyanilino, sulfonaphthylamino, o-, m-, and p-aminoanilino, p-acetamidoanilino, etc.), etc. Such compounds are disclosed in Carrol et a1. U.S. Pat. 2,875,058 issued Feb. 24, 1959, Mc'Fall et a1. U.S. Pat. 2,933,390 issued Apr. 19, 1960, and Jones et a1. U.S. Pat. 2,961,318 issued Nov. 22, 1960. These compounds include, for example,

4,4'-bis(4,6-bis-o-chloroanilino-s-triazin-Z-ylamino)stilbene-2,2-disulfonic acid, disodium salt;

4,4'-bis [4- 3 '-sulfoanilino -6-amino-s-triazin-2-ylamino] stilbene-2,2'-disulfonic acid;

4,4'-bis [4,6-dip-hydroxyethylamino) -s-sriazin-2- ylamino]sti1bene-2,2'-disulfonic acid;

4,4'-bis{4 [4 (N-4"-sulfobenzyl-N-ethyl) aminoanilino]-6-hydroxy-s-triazin-2-ylamino}stilbene-2,2'-disulfonic acid;

4,4'-bis [4-(4-sulfoanilino)-6fl-hydroxyethylamino-striazin-Z-ylamino]stilbene-2,2disulfonic acid;

4,4-[4,6-dianilino-s-triazin-Z-ylamino1stilbene- 2,2-disulfonic acid;

4,4-bis [4phenoxy-6 fl-hydroxyethylamino) -s-triazin-2- ylarnino]stilbene-2,2-disulfonic acid;

4,4'-bis[4,6-dihydroxy-s-triaziu-2-ylamino) stilbene- 2,2'-disulfonic acid;

4,4-bis(4-anilino-6-hydroxy-s-triazin-2-ylamino) stilbene-2,2'-disulfonic acid;

4,4-bis[4(2'-chloroanilino)-6-hydroxy-2-triazin-2- ylamino]stilbene-2,2'-disulfonic acid; and

4,4'-bis(s-triazin-Z-ylamino)stilbeue-2,2'-disulfonic acid, disodium salt.

The alkyl groups or moieties referred to herein typically have 1 to 20 carbon atoms, lower alkyl radicals or moieties have 1 to 8 carbon atoms and aryl groups or moieties typically include phenyl and naphthyl.

Negative unfogged photographic silver halide emulsions which can be spectrally sensitized by the dyes and supersensitizers of this invention can comprise, for example, silver chloride, silver bromide, silver chlorobromide, silver chloroiodide, silver chlorobromoiodide crystals or mixtures thereof. The emulsions can be coarse or fine grain emulsions and can be prepared by a variety of techniques, e.g., single jet emulsions such as those described in Trivelli and Smith, The Photographic Journal, vol. LXXIX, May 1939 (pp. 330-338), double jet emulsions such as Lippmann emulsions, ammoniacal emulsions, thiocyanate or thioether ripened emulsions such as those described in Neitz et a1. U.S. Pat. 2,222,264 issued Nov. 19, 1940; Illingsworth U.S. Pat. 3,320,069 issued May 17, 1967 and McBride U.S. Pat. 3,271,157 issued Sept. 6, 1966.

As used herein, and in the appended claims, the term unfogged refers to emulsions containing silver halide grains which produce a density of less than 0.3 when developed, without exposure, for 5 minutes at 20 C. in Kodak developer DK-SO when the emulsion is coated at a silver coverage of 50 mg. to 500 mg. per square foot.

The desensitizing dyes and supersensitizers are advantageously incorporated in the washed, finished emulsion and should be uniformly distributed throughout the emulsion. They can be added from solutions in appropriate solvents which are compatible with the emulsion and which are substantially free from deleterious effects on the light sensitive materials.

The types of silver halide emulsions that can be sensitized in accordance with this invention include those prepared with hydrophilic colloids that are known to be satisfactory vehicles for dispersed silver halides, for example, emulsions comprising both naturally-occurring substances such as proteins, for example, gelatin, gelatin derivatives, cellulose derivatives, polysaccharides such as dextran, gum arabic and the like; and synthetic polymeric substances such as water soluble polyvinyl compounds like poly-(vinyl-pyrrolidone), acrylamide polymers and the like. The photographic emulsions can also contain alone or in combination with hydrophilic, water-permeable colloids, other synthetic polymeric vehicle compounds such as dispersed vinyl compounds such as in latex form and particularly those which increase the dimensional stability of the photographic materials. Typical synthetic polymers include those described in Nottorf US. Pat. 3,142,568 issued July 28, 1964; White US. Pat. 3,193,386 issued July 6, 1965; Houck et al. US. Pat. 3,062,674 issued Nov. 6, 1962; Houck et al. U.S. Pat. 3,220,844 issued Nov. 30, 1965; Ream et al. US. Pat. 3,287,289 issued Nov. 22, 1966 and Dykstra US. Pat. 3,411,911 issued Nov. 19, 1968. Other vehicle materials include water-insoluble polymers of alkyl acrylates and methacrylates, acrylic acid, sulfoalkyl acrylates or methacrylates, those which have cross-linking sites which facilitate hardening or curing as described in Smith US. Pat. 3,488,708 issued Jan. 6, 1970, and those having recurring sulfobetaine units as described in Dykstra Canadian Pat. 774,054.

The concentrations of the desensitizing dyes and supersensitizers in the emulsion can vary widely, e.g., from about 0.01 to 0.3 g. of desensitizing dye per mole of silver halide in the emulsion and from about 0.03 to 10.0 g. of supersensitizer per mole of silver halide in the emulsion. The specific concentrations will vary according to the type of light-sensitive material in the emulsion and the efi'ects desired. The suitable and most economical concentrations for a given emulsion will be apparent to those skilled in the art upon making the tests and observations customarily used in the art of emulsion making.

The silver halide emulsions of the invention can contain conventional photographic emulsion addenda such as chemical sensitizers, antifoggants, hardeners, color-forming couplers, plasticizers, lubricants, surfactants, etc. as disclosed in Product Licensing Index, vol. 92, December 1971, publication 9232, pages 107-110, particularly paragraphs III-VII, XI-XVI and )OCH.

The negative photographic silver halide emulsions of this invention can be coated on a wide variety of supports. Useful photographic elements will typically comprise a support having thereon at least one negative unfogged photographic silver halide emulsion layer according to the present invention. Typical supports include cellulose nitrate film, cellulose acetate film, poly(vinyl acetal) film, polystyrene film, poly(ethylene terephthalate) film, polycarbonate film and related films or resinous materials, as well as glass, paper, metal and the like. Typically, a flexible support is employed, especially a paper support, which can be partially acetylated or coated with baryta and/or an alpha-olefin polymer, particularly a polymer of an alpha-olefin containing 2 to carbon atoms such as polyethylene, polypropylene, ethylenebutene copolymers and the like.

The practice of this invention also permits the use of strong desensitizing dyes as filter dyes in a layer on a photographic element. Heretofore, these desensitizing dyes were of limited usefulness as filter dyes due to the possibility that they may migrate or wander to the silver halide grain thus causing severe desensitization. By incorporating a supersensitizer in the photographic element such as in a silver halide emulsion layer, if the desensitizing dye does migrate to the silver halide grain, its desensitizing effects are substantially prevented. Since many desensitizing dyes are bleached rapidly by developers, the use of such dyes as filler dyes or as sensitizers permits more rapid processing of the photographic elements containing such dyes.

The following examples illustrate the best modes contemplated for carrying out this invention:

EXAMPLES l-6 The dyes and sensitizers identified in the following table, dissolved in suitable solvents, are added to separate portions of a sulfur and gold sensitized negative unfogged gelatino silver bromoiodide emulsion. In the table, Dye A is 6-chloro-2-[2(1-methyl-2-phenyl-3-indolyl)vinyl]-1,3-diphenyl-1H-imidazo[4,5-b1quinoxalinium p-toluenesulfonate and has the formula Dye B is 1,1',3,3,3,3'-hexamethyl-5,5'-dinitroindocarbocyanine p-toluenesulfonate and has the formula \e em ms-Q-cm Dye C is 3-ethyl-2-[2-(1-methyl-2-phenyl-3-indolyl) vinyl]-6-nitrobenzothiazolium iodide and has the formula N0: N H: cu. 0 on o (E 0H5 N measure of the spectral response to the dye. After exposure, the samples are processed for 4 minutes at 20 C. in Kodak D-19 developer, fixed, washed and dried in the usual manner. The photographic results are set forth in the following table. Similar results can be obtained with comparable amounts of ascorbic as thesupersensitizer. Dyes A-C were all decolorized by Kodak D-19 developer. Their maxima of absorption (A in methanolic solution are, respectively, 520, 562 and 512 nm. The band widths at half of the maximum density (density at A were respectively 491 to 542 nm., 543 to 576 nm., and 472535 nm.

As used in the structural formulas herein, C H is an ethyl group and C H is a phenyl group.

TABLE Mg. of super- Relative speeds Mg. of dye/ sensitizer/ mole of mole of Minus Range of spectral Example Dye silver halide Super-sensltizer silver halide Blue blue sensitivity (nm.)

Cnnfrnl Nmm None 100 To 540, D0 A 100 do 6.9 100 To 625. l 73 500 Do. Control 69 To 540. 2 73 436 To 625. Control 50 To 530. q 83 330 To 620. Control 126 To 540. 4 21 240 To 620 Control 5 44 132 To 620. Control 12 25 To 600. 6 60 Do.

1 Desensitlzed.

The foregoing examples show that the supersensitizing compounds reduce the desensitization of the coatings containing desensitizing dyes and incnease the minus blue speed. Moreover, most of the desensitizing dyes and the supersensitizers coact in such a way as to give higher blue speed and a higher range of spectral sensitivity than obtained by the use of the supersensitizer in the absence of the desensitizer.

The invention has been described in detail with reference to particular embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

1. A negative unfogged photographic silver halide emulsion comprising:

(a) an electron-trapping photographic cyanine dye having a cathodic polarographic half-wave potential more positive than --l.0 volt and an anodic halfwave potential greater than +0.4 volt wherein said dye has the formula wherein:

(1) Z and Z each represent the nonmetallic atoms necessary to complete a heterocyclic nucleus containing 5 to 6 atoms in the heterocyclic ring;

(2) Z and 2 each represent the nonmetallic atoms necessary to complete a desensitizing heterocyclic nucleus containing 5 to 6 atoms in the heterocyclic ring selected from the group consisting of a nitrobenzothiazole nucleus, a nitrobenzoxazole nucleus, a nitrobenzoselenazole nucleus, an imidazo[4,5-b]quinoxaline nucleus, a 3,3-dialkyl-3H-pyrrolo[2,3 b] pyridine nucleus,

2. A negative unfogged photographic silver halide emulsion containing:

(I) a cyanine dye having the formula:

2-. 9 n -iv--o=on-on=on-o=n -m wherein:

(A) R and R are each alkyl groups or phenyl groups,

(B) Z represents the. nonmetallic atoms necessary to complete a heterocyclic nucleus containing 5 to 6 atoms in the heterocyclic ring,

(C) Z represents the nonmetallic atoms necessary to complete a desensitizing heterocyclic nucleus containing 5 to 6 atoms in the heterocyclic nucleus selected from the group consisting of a nitrobenzothiazole nucleus, a nitrobenzoxazole nucleus, a nitrobenzoselenazole nucleus, an imidazo[4,5-b]quinoxaline nucleus, a 3,3-dialkyl-3H- pyrrolo[2,3-b] pyridine nucleus, a 3,3-dialkyl-3H- nitroindole nucleus, a thiazole[4,5-b]quinoline nucleus and a nitroquinoline nucleus, and

(D) E is an anion; and

(H) a supersensitizing agent selected from the group consisting of:

(A) a sulfonated derivative of bis(triazinylamino) stilbene,

(B) ascorbic acid, and

(C) an alkali metal thiocyanate.

3. A negative unfogged photographic silver halide emulsion containing:

(I) a cyanine dye having the formula:

r' s 'ZL 1 I R'-N-o=o-oH=oH-o=N-R E wherein:

(A) R R and R are each alkyl groups or phenyl groups, (B) Z represents the nonmetallic atoms necessary to complete a heterocyclic nucleus containing 5 to 6 atoms in the heterocyclic ring, (C) Z represents the nonmetallic atoms necessary to complete a desensitizing heterocyclic nucleus containing to 6 carbon atoms in the heterocyclic nucleus selected from the group consisting of a nitrobenzothiazole nucleus, a nitrobenzoxazole nucleus, 2. nitrobenzoselenazole nucleus, an imidazo[4,5-b]quinoxaline nucleus, a 3,3-dialkyl-3H- pyrrolo[2,3-b]pyridine nucleus, a 3,3-dialky1-3H- nitroindole nucleus, a thiazole[4,5-b]quinoline nucleus and a nitroquinoline nucleus, and (D) E is an anion; and (II) a supersensitizing agent selected from the group consisting of:

(A) a sulfonated derivative of bis(triazinylamino) stilbene, (B) ascorbic acid, and (C) an alkali metal thiocyanate.

4. A negative unfogged photographic silver halide emulsion as defined in claim 1 wherein said silver halide supersensitizer is a sulfonated stilbene derivative having the formula NH-( I-R wherein R R", R and R each represents a hydrogen atom, a hydroxyl group, an aryloxyl group, an alkoxyl group, a halogen atom, a heterocyclic radical, an alkylthio group, an arylthio group, or an amino group.

5. A negative unfogged photographic silver halide emulsion as defined in claim 4 wherein said carbocyanine dye is 6-chloro-2-[2-(1-methyl 2 phenyl-3-indolyl)vinyl]- 1,3 dipheny1-1H-imidazo[4,5-b]quinoxalinium p-toluenesulfonate.

6. A negative unfogged photographic silver halide emulsion as defined in claim 3 wherein said carbocyanine dye is 1,1,3,3,3',3-hexamethy1 5,5 dinitroindocarbocyanine p-toluenesulfonate.

7. A negative unfogged photographic silver halide emulsion as defined in claim 3 wherein said carbocyanine dye is 3-ethyl-2-[2-(1-methyl 2 pheny1-3-indolyl)vinyl]-6- nitrobenzothiazolium iodide.

8. A negative unfogged photographic silver halide emulsion as defined in claim 1 wherein said supersensitizer is the sodium salt of 4,4'-bis(2-triazin-2-ylamino)stilbene- 2,2'-disulfonic acid.

9. A negative unfogged photographic silver halide emulsion as defined in claim 1 wherein said supersensitizer is potassium thiocyanate.

10. A negative unfogged photographic gelatino silver halide emulsion containing a sensitizing combination of 6-chloro 2 [2-(1-methyl-2-pheyl-3-indolyl)vinyl]-1,3- diphenyl-1H-imidazo[4,5-b]quinoxalinium p toluenesulfonate and the sodium salt of 4,4'-bis(2-triazin-2-ylamino) stilbene-2,2'-disulfonic acid.

11. A negative unfogged photographic gelatino silver halide emulsion containing a sensitizing combination of 6-chloro 2 [2-(1-methyl2-pheyl-3-indolyl)vinyl]-l,3- diphenyl-lH-imidazo [4,5-b1quinoxalinium p toluenesulfonate and potassium thiocyanate.

12. A negative unfogged photographic gelatino silver halide emulsion containing a sensitizing combination of 1,l',3,3,3',3-hexamethyl 5,5 dinitroindocarbocyanine ptoluenesulfonate and the sodium salt of 4,4'-bis(triazin- 2-ylamino)stilbene-2,2'-disulfonic acid.

13. A negative unfogged photographic gelatino silver halide emulsion containing a sensitizing combination of 3-ethyl-2-[2-( l-methyl 2-phenyl-3-ind0lyl)vinyl] -6-nitrobenzothiazolium iodide and the sodium salt of 4,4'-bis(triazin-2-ylamino)stilbene-2,2-disulfonic acid.

14. A photographic element comprising a support having thereon at least one negative unfogged photographic silver halide emulsion layer as defined in claim 1.

15. A photographic element comprising a support having thereon at least one negative unfogged photographic silver halide emulsion as defined in claim 4.

References Cited UNITED STATES PATENTS 3,687,676 8/1972 Spence et al 96-l0l 3,649,289 3/1972 Hiller 96-107 3,706,567 12/1972 Hillel 96-101 NORMAN G. TORCHIN, Primary Examiner W. H. LOUIE, JR., Assistant Examiner US. Cl. X.R.