US3628958A - Bipyridinium compound/nitrosubstituted n-heterocyclic compound desensitized silver halide emulsion - Google Patents

Abstract

A negative silver halide emulsion is desensitized with a desensitizing combination of a bipyridinium salt and an organic nitrosubstituted N-heterocyclic desensitizer. The emulsion is effectively desensitized for handling in roomlight and the sensitometric properties of the desensitized emulsion are improved with respect to emulsions desensitized with, for example, known organic nitrosubstituted N-heterocyclic desensitizers.

Description

United States Patent John A. Haeiner Rochester, N.Y.

Mar. 2, 1970 Dec. 21, 1971 Eastman Kodak Company Rochester, N.Y.

inventor Appl. No. Filed Patented Assignee BIPYRIDINIUM COMPOUND/NITROSUBSTITUTED N- HETEROCYCLIC COMPOUND DESENSITIZED SILVER HALIDE EMULSION 9 Claims, No Drawings U.S.Cl 96/10] Int. Cl G03c 1/36 Field of Search 96/l0l References Cited UNITED STATES PATENTS 1l/l962 Hillson 7 96/10] 3,124,458 3/1964 Fry etal 96/ lOl FOREIGN PATENTS 946,476 1/1964 GreatBritain 96/l0l Primary ExaminerJ. Travis Brown Assistant Examiner-Won H. Louie, Jr. Attorneys-W. H. .l. Kline, B. D. Wiese and Henry E. Byers BIPYRIDINIUM COMPOUND/NITROSUBSTITUTED N- HETEROCYCLIC COMPOUND DESENSITIZED SILVER HALIDE EMULSION The present invention relates to novel photographic emulsions and elements. More particularly, the invention relates to a new class of desensitized negative silver halide emulsions, to photographic elements provided with such emulsions, and to novel desensitizing combinations for such materials.

It is known that negative silver halide emulsions can be desensitized by incorporating certain agents, called desensitizers, in the emulsion. These agents achieve a reduction in sensitivity by a factor of more than 1.0 log E. However, in addition to reducing the sensitivity of the emulsion, these agents cause a change in the sensitometric curve for the emulsion. The desensitized emulsions exhibit, for example, less contrast than the nondesensitized emulsion. The desensitized emulsions are widely useful, particularly in the field of graphic arts and engineering drawing reproduction for halftone and linecopying applications where advantage can be taken of the roomlight-handling properties of a desensitized emulsion or photographic element. However, it would be a distinct advantage if the contrast of the desensitized emulsion could be increased. It would thus be desirable to obtain a desensitized emulsion having a higher contrast than other emulsions desensitized to the same extent.

It is, accordingly, an object of the present invention to provide a desensitized silver halide photographic emulsion which has improved sensitometric properties relative to conventional desensitized emulsions. It is a further object of the present invention to provide photographic elements including such photographic emulsion. Other objects of the invention will be apparent from this disclosure and the appended claims.

I have discovered that a negative silver halide photographic emulsion can be effectively desensitized with a novel desensitizing combination comprising: a bipyridinium salt having two pyridinium nuclei joined by a linkage which is attached to a carbon atom of each of the pyridinium nuclei; and an organic nitrosubstituted N-heteroeyclic desensitizer. By providing this novel combination of materials in a negative silver halide photographic emulsion, l have achieved a reduction in sensitivity of more than 1.0 log E. In addition, the emulsion exhibits higher contrast, lower minimum density, and a sensitometric curve having a less linear toe than conventionally desensitized emulsions.

Examples of the bipyridinium salts useful herein have two pyridinium nuclei joined by a linkage which is attached to carbon atom of each of said pyridinium nuclei. For example, the two pyridinium nuclei can be joined by any suitable linkage, such as a single covalent bond, a vinylene linkage or an ethylene linkage. Typical bipyridinium salts which can be used in the practice of this invention have one of the following formulas:

wherein n represents a positive integer of from 1 to 2; m represents a positive integer of from 2 to 4; R represents a vinylene group (CH= CH-) or an ethylene group CH,CH,-); R and R, each represents an alkyl group (preferably a lower alkyl containing from one to four carbon atoms), e.g., methyl, ethyl, propyl, isopropyl, butyl, hexyl, cyclohexyl, decyl, dodecyl, etc., and substituted alkyl groups,

(preferably a substituted lower alkyl containing from one to four carbon atoms), such as a hydroxyalkyl group, e.g., hydroxyethyl, w-hydroxybutyl, etc., an alkoxyalkyl group, e.g., fi-methoxyethyl, w-butoxybutyl, etc., a carboxyalkyl group e.g., B-carboxyethyl, w-carboxybutyl, etc., a sulfoalkyl group, e.g., B-sulfoethyl, m-sulfobutyl, etc., a sulfatoalkyl group, e.g., B-sulfatoethyl, w-sulfatobutyl, etc., an aroyloxy alkyl e.g., phenacyl, an acyloxyalkyl group, e.g., fi-acetoxyethyl, yacetoxypropyl, w-butyryloxybutyl, etc., an alkoxy carbonylalkyl group, e.g., fl-methoxycarbonylethyl, m-ethoxycarbonylbutyl, etc., or an aralkyl group, e.g., benzyl, phenethyl, etc., and the like; or, any aryl group, e.g., phenyl, tolyl, naphthyl, methoxyphenyl, chlorophenyl, etc.; R, and R each represents a hydrogen atom, a lower alkyl group containing from one to four carbon atoms, e.g., methyl, butyl, etc., a lower alkoxy group containing from one to four carbon atoms, e.g., methoxy, butoxy, etc., or a halogen atom, e.g., chlorine or bromine; R and R each represents a hydrogen atom or a lower alkyl below.

TABLE 1 A. 1,1 '-Dibutyl-4,4'-bipyridinium dibromide l ,l '-Dibutyl-4,4 -bipyridinium diperchlorate l,l '-Di(Z-hydroxyethyl)-4,4'-bipyridinium dibromide l,l '-Diphenacyl-4,4'-bipyridinium dibromide B. C. D. E. l,2-Di( 4-pyridyl )ethylene bis( phenacyl bromide) i i ,im i-pyridyfiethylene bis(phenethobromide) G. Dianhydrol ,2-di[ l (3-sulfopropyl)-4-pyridyl lethylene dihydroxide l. l,l '-Dimethyl-4,4'-bipyridinium dibromide J. l,2-Di(4-pyridyl)ethane bis(phenethobromide) mmomcm-N om-om )gomom 0,11, 2Br

K. l ,l '-Ethylene-2,2'-bipyridinium dibromide al., U.S. Pat. No. 3,035,9l7, patented May 22, 1962; Fry et al., U.S. Pat. No. 3,124,458, patented Mar. l0, l964; and E. N. Mason and Sons Ltd. et al., British Pat. No. 714,290, dated Aug. 25, 1954.

Examples of the organic nitrosubstituted N-heterocyclic: desensitizcrs useful in the invention include nitrosubstituted thiazoles and compounds including a benzene nucleus such as benzothiazole, quinoline, indolenine, benzotriazole and rhodanine compounds having one or more nitro groups at tached to the benzene nucleus which is either a part of the heterocyclic moiety or attached to it through a doubly bonded carbon to carbon chain. The quaternary salts of the nitrosubstituted thiazoles, benzothiazoles, quinolines and indolenines are also useful. The compounds include an N-heterocyclic moiety and are substituted with one or more nitro groups either in the heterocyclic ring or in the benzene ring of these compounds which include a benzene ring. The compounds may be otherwise unsubstituted or substituted with noninter fering substituents such as alkyl, preferably lower alkyl of one-three carbon atoms, halo, alkoxy, preferably lower alkox-- y of one-three carbon atoms, mercapto, amino, alkyl amino, preferably lower alkyl amino of one-three carbon atoms, and the like. The heterocyclic moiety may include a single hetero cyclic: nitrogen atom such as thiazole, benzothiazole, quinoline, indolenine and rhodanine, or a plurality of heterocyclic nitrogen atoms such as benzotriazole, and may include a hetero sulfur atom such as thiazole, benzothiazole and rhodanine. Representative compounds include 2-mercapto-4 methyl-S-nitrothiazole, 2-rnethyl-6-nitrobenzothiazole methop-toluene sulfonate, 2-(o-nitrostyryl)--3 -ethylbenzothiazolium iodide and the mand p-nitrostyryl compounds, 2-(o,pdinitrostyryl)-3-ethylbenzothiazolium iodide, 2(o,p-dinitrostyryl)-benzothiazole, 2-(p-nitrostyryll-quinoline metho-ptoluene sulfonate, the 6-ethoxy derivative thereof and the oand mnitrostyryl compounds, 4-(p-nitrostyryl)-quinoline methiodide, 3,3-dimethyl-2-(p-nitrostyryl)-indolenine methiodide, Z-(p-dimethylarninostyryl)-3-ethyl-6- nitrobenzothiazoliurn chloride, 6-nitrobenzo-l,2,3-triazole and the 4- or S-chloro derivatives thereof, and S-o-nitrobenzylidene-3-ethylrliodanine.

For example, the bipyridinium compound and nitrosubstituted compound are incorporated into a negative silver halidle emulsion which may be of any conventional type,

The novel desensitizer combination according to the present invention is incorporated into the emulsion at any time prior to coating the emulsion on a support. Conveniently the materials are blended into the finished emulsion prior to coating.

The silver halide emulsions used with this invention can comprise silver chloride, silver bromide, silver bromoiodide, silver chlorobrornoiodide or mixtures thereof. The emulsions may be coarse or fine grain and can be prepared by any of the well'known procedures, e.g., single jet emulsions, double jet emulsions, such as Lipprnann emulsions, ammoniacal emul sions, thiocyanate or thioether ripened emulsions such as those described in Nietz et al., U.S. Pat. No. 2,222,264; lllingsworth US. Pat. No. 3,320,069; and McBride U.S. Pat. No. 3,27l,l57. Surface image emulsions may be used or internal image emulsions such as those described in Davey et al., U.S. Pat. No. 2,592,250; Porter et al., U.S. Pat. No. 3,206,3l3; Berriman U.S. Pat. No. 3,367,778 and Bacon et al., US Pat. No. 3,447,927. If desired, mixtures of surface and internal image emulsions may be used as described in Luckey et al., US. Pat. No. 2,996,382. Negative type emulsions may be used or direct positive emulsions such as those described in Leermakers U.S. Pat. No. 2,l84,0l3; Kendall et al., U.S. Pat. No. 2,54l,472; Berriman U.S. Pat. No. 3,367,778; Schouwenaars British Pat. No. 723,0l9; lllingsworth et al., French Pat. No. 1,520,821; lves U.S. Pat. No. 2,563,785; Knott et al., U.S. Pat. No. 2,456,953 and Land US. Pat. No. 2,86l,885. The emulsions may be regular grain emulsions such as the type described in Klein and Moisar, J. Phat. Sui, Vol. 12, No. 5, Sept/Oct, 1964, pp. 242-251.

The emulsions used with this invention may be sensitized with chemical sensitizers, such as with reducing agents; sulfur, selenium or tellurium compounds; gold, platinum or palladium compounds; or combinations of these. Suitable procedures are described in Sheppard et al., U.S. Pat. No. 1,623,499; Waller et al,, U.S. Pat. No. 2,399,083; McVeigh U.S. Pat. No. 3,297,447; and Dunn U.Sv Pat. No. 3,297,446.

The silver halide emulsions used with this invention may contain speed increasing compounds such as polyalkylene glycols, cationic surface active agents and thioethers or combinations of these as described in Piper U.S. Pat. No. 2,886,437; Dann et al., U.S. Pat. No. 3,046,l34; Carroll et al., US. Pat. No. 2,944,900; and Goffe US. Pat. No. 3,294,540.

The silver halide emulsions used in the practice of this invention can be protected against the production of fog and can be stabilized against loss of sensitivity during keeping. Suitable antifoggants and stabilizers each used alone or in combination include thiazolium salts described in Brooker et al., U.S. Pat, No. 2,l3l,038 and Allen et al., U.S. Pat. No. 2,694,7l6; the azaindenes described in Piper U.S. Pat. No. 2,886,437 and Heimbach et al., U.S. Pat. No. 2,444,605; the mercury salts as described in Allen et al., US. Pat. No. 2,728,663; the urazoles described in Anderson et al., US, Pat. No. 3,287,135; the sulfocatechols described in Kennard et al., US. Pat. No. 3,236,652; the oximes described in Carroll et al., British Pat. No. 623,448; nitron; nitroindazoles; the mercaptotetrazoles described in Kendall et al., U.S. Pat. No. 2,403,927; Kennard et al., U.S. Pat. No. 3,266,897 and Luckey et al., U.S. Pat. No. 3,397,987; the polyvalent metal salts described in Jones U.S. Pat. No. 2,839,405; the thiuronium salts described in Herz et al., U.S. Pat. No. 3,220,839; the palladium, platinum and gold salts described in Trivelli et al., U.S. Pat. No. 2,566,263 and Yutzy et al., U.S. Pat. No. 2,597,915.

The photographic elements of this invention may contain incorporated developing agents such as hydroquinones, catechols, aminophenols, 3-pyrazolidones, ascorbic acid and its derivatives, reductones and phenylenediamines. Combinations of developing agents can be employed in the practice of the invention. The developing agents can be in a silver halide emulsion and/or in another suitable location in the photographic element. The developing agents may be added from suitable solvents or in the form of dispersions as described in Yackel U.S. Pat. No. 2,592,368 and Dunn et al., French Pat. No. l,505,778.

The photographic and other hardenable layers used in the practice of this invention can be hardened by various organic or inorganic hardeners, alone or in combination, such as the aldehydes, and blocked aldehydes, ketones, carboxylic and carbonic acid derivatives, sulfonate esters sulfonyl halides and vinyl sulfonyl ethers, active halogen compounds, epoxy compounds, aziridines, active olef'ms, isocyanates, carbodiiniides, mixed function hardeners and polymeric hardeners such as oxidized polysaccharides like dialdehyde starch and oxyguargum and the like.

The photographic emulsions and elements described in the practice of this invention can contain various colloids alone or in combination as vehicles, binding agents and various layers. Suitable hydrophilic materials include 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(vinylpyrrolidone), acrylamide polymers and the like.

The described photographic emulsion layers and other layers of a photographic element employed in the practice of this invention can also contain alone or in combination with hydrophilie, water permeable colloids, other synthetic polymeric compounds such as dispersed vinyl compounds such as in latex form and particularly those which increase the dimensional stability of the photographic materials. Suitable synthetic polymers include those described, for example, in Nottorf US. Pat. No. 3,142,568, issued July 28, 1964; White U.S. Pat. No. 3,193,386, issued July 6, 1965; l-louck et al., U.S. Pat. No. 3,062,674, issued Nov. 6, 1962; Houck et al., U.S. Pat. No. 3,220,884, issued Nov. 30, 1965; Ream et al., U.S. Pat. No. 3,287,289, issued Nov. 22, 1966; and Dykstra thiazoles, selenazoles and imidazoles. Such nuclei may contain alkyl, alkylene, hydroxyalkyl, sulfoalkyl, carboxyalkyl, aminoalkyl and enamine groups and may be fused to carbocyclic or heterocyclic ring systems either unsubstituted or sub- U.S. Pat. No. 3,41 1,91 l, issued Nov. 19, 1968; particularly ef- 5 stituted with halogen, phenyl, alkyl, haloalkyl, cyano, or alfective are those water-insoluble polymers of alkyl acrylates koxy groups. The dyes may be symmetrical or unsymmetrical and methacrylates, acrylic acid, sulfoalkyl acrylates or and may contain alkyl, phenyl, enamine or heterocyclic submethacrylates, those which have cross-linking sites which 'stituents on the me hine or polymethine chain. facilitate hardening or curing, those having recurring sul- The merocyanine dyes may contain the basic nuclei menfobetaine units as described in Dykstra Canadian Pat. No. tioned above as well as acid nuclei such as thiohydantoins, 774,054. rhodanines, oxazolidenediones, thiazolidenediones, barbituric The photographic layers and other layers of a photographic acids, thiazolineones, and malononitrile. These acid nuclei element employed and described herein can be coated on a may be substituted with alkyl, alkylene, phenyl, carboxyalkyl, wide variety of supports. Typical supports include cellulose sulfoalkyl, hydroxyalkyl, alkoxyalkyl, alkylamlno groups, or nitrate film, cellulose ester film, poly(vinyl acetal) film, heterocyclic nuclei. Combinations of these dyes may be used, polystyrene film, poly(ethylene terephthalate) film, polycarif desired. in addition, supersensitizing addenda which do not bonate film and related films or resinous materials, as well as absorb visible light may be included, for instance, ascorbic glass, paper, metal and the like. Typically, a flexible support is acid derivatives, azaindenes, cadmium salts, and organic sulemployed, especially a paper support, which can be partially 2o fonic acids as described in McFall et al., U.S. Pat. No. acetylated or coated with baryta and/or an alpha-olefin 2,933,390 and Jones et al., U.S. Pat. No. 2,937,089. polymer, particularly a polymer of an alpha-olefin containing The various layers, including the photographic layers, emtwo to 10 carbon atoms such as polyethylene, polypropylene, ployed in the practice of this invention can contain light abethylenebutene copolymers and the like. sorbing materials and filter dyes such as those described in The photographic layers employed in the practice of this in- Sawdey U.S. Pat. No. 3,253,921; Gaspar U.S. Pat. No. vention may contain surfactants such as saponin; anionic com- 2,274,782; Silberstein et al., U.S. Pat. No. 2,527,583 and Vanpouncls such as the alkyl aryl sulfonates described in Bald Campen U.S. Pat. No. 2,956,879. if desired, the dyes can be siefen U.S. Pat. No. 2,600,831; amphoteric compounds such mordanted, for example, as described in Jones et al., U.S. Pat. as those described in Ben-Ezra U.S. Pat. No. 3,133,816; and No. 3,282,699. water-soluble adducts of glycidol and an alkyl phenol such as Photographic elements prepared according to this invention those described in Olin Mathieson British Pat. No. 1,022,878. can be processed by various methods including processing in The photographic elements employed in the practice f th alkaline solutions containing conventional developing agents invention may contain matting agents such as starch, titanium h a hydroquinones, catechols, aminophenols, 3- diOXide, Zinc OXide. Silica, p lyme c beads including beads f' pyrazolidones, phenylenediamines, ascorbic acid derivatives, the type described in Jelley ct al.,U.S. Pat. No. 2,992,101 and hydroxylamines, hydrazines, reductones and the like; web y 2,701,245- processing such as described in Tregillus et al., U.S. Pat. No. The Photographic elements used in this invention y 3,l79,517; stabilization processing as described in Russell ct brightening agents including slllbenes, ttiazines. OXaZOleS al., "Stabilization Processing of Films and Papers," PSA Jourand coumarin brightening s Water-Soluble brightening nal, Vol. 16B, Aug. 1950; monobath processing as described agents may be used such as those described in Albers et al., 40 in Levy Combined Development and Fixation f p German Pat. No. 972,067 and McFall et al., U.S. Pat. No. graphic [mazes i Monobaghs, p Sci. and Eng V L 2 2,993,390 or dispersions of brishteners may be used such as No. 3, Oct. 1953, and Barnes et al., u.s. Pat. No. 3,392,019. 1f P described in Jansen German 1,150,274 desired, the photographic elements of this invention can be Oetrker et al., U.S. Pat. No. 3,406,070 and Heldke French Pat. processed in hardening developers such as those described in Allen et al., U.S. Pat. No. 3,232,761; in roller transport Swen-a] f f dyes P be F confer processors such as those described in Russell et al., U.S. Pat. addmonal sensitivity to the light sensitive silver halide emul- 3,025,779; or by surface application processing as sion of the multilayer photographic elements of the invention. described in example 3 f Kit e US. Pat. No. 3,418,132. For instance, additional spectral sensitization can be obtained The foliowing examples are included for a further by treating the emulsion with a solution of a sensitizing dye in demanding ofthe invention an organic solvent or the dye may be added in the form of a dispersion as described in Ownes et al., British Pat. No. 1,154,781. For optimum results, the dye may either be added EXAMPLES F3 to the emulsion as a final step or at some earlier stage.

Sensitizing dyes useful in sensitizing such emulsions are To a Portion of a finished convemlmla' mgauve gelatinv described, for example, in Brooker et al., U.S. Pat. No. silver chloride emulsion containing a conventional hardener 2,526,632, issued Oct. 24, 1950; Sprague U.S. Pat. No. and coating aid is added a desensitizing combination accord- 2,503,776, issued Apr. 1 l, 1950; Brooker et al., U.S. Pat. No. ing to the invention in the amount shown below. The emulsion 2,493,748; and Taber et al., U.S. Pat. No. 3,384,486. Spectral is then coated on a cellulose acetate film support at 410 mg. sensitizers which can be used include the cyanines, merosilver per square foot and 418 mg. gelatin per square foot. A cyanines, complex (tri or tetranuclear) merocyanines, comseparate portion of the emulsion is coated in the same manner plex (tri or tetranuclear) cyanines, holopolar cyanines, styryls, without the desensitizers as a control. Samples of each coating hemicyanines (e.g. enamine hemicyanines), oxonols and are exposed for 10 seconds to a black light ultraviolet lamp hemioxonols. through a step wedge, developed in a conventional developer, Dyes of the cyanine classes may contain such basic nuclei as and fixed, washed, and dried, all in a conventional manner. the thiazolines, oxazolines, pyrrolines, pyridines oxazoles, The following results are obtained:

Minimum A Rel. Addenda, mgJmole Ag density Gamma log E speed Example:

1 Control 0. 10 1.82 224 2 B (200) plus P 0.04 7.00 -2. 1 2.8 3 B (100) plus R (100)-.- 0.04 7.60 1.6 0.4

B =1, 1'-d1-n-buty1-4, 4-blpyridln1um dihromlde. P 2-mereap to-4-methyl-b-nltrothlazolo. R= 2-rnothyl-d nltrobenzothlazolo motho-p-toluono sulionato.

Examples 2 and 3 show that the emulsion is desensitized more than 1.0 log E by the addition ofa novel desensitizer combination according to the invention. The desensitized emulsion furthermore has excellent sensitometric properties as shown in the table. Other combinations of the bipyridinium compounds and nitrosubstituted compounds mentioned above achieve similar results.

EXAMPLES 4-6 results are as follows:

Addenda Minimum Rel. Example mgJmole Ag density Gamma Speed P I) 5 P I00) 0.03 4.9 200 6 8(200) 0.03 6.2 42

A similar improvement in sensitometric characteristics, with excellent desensitizing, is achieved with other novel desensitizer combinations according to the invention.

The amount of desensitizer combination added to the emulsion can vary wisely from the amounts shown in the examples. ln general, an amount is used such that densitizing to an extent of more than 1.0 log E is achieved, and improved sensitometric properties are achieved where the amount of each of the two tubes of material making up the combination is present in an amount of 25-75 percent, preferably 35-65 percent, by weight of the combination. The maximum amount of sensitizer combination can vary quite widely without deleterious effect, but amounts in excess of about 500 mg. per mole of silver are not usually justified economically. Therefore, the sensitizer combination will generally be present in an amount of not more than 500 mg. per mole of silver. The minimum amount of sensitizer combination sufficient to ensure desensitization of l.O log E will vary somewhat but is generally about 50 mg. per mole of silver,

EXAMPLES 7 and 8 The following examples show that the addition of a watersoluble cadmium salt increases the maximum density. A silver chloride emulsion (7) is prepared and coated similar to that described as example 2.

Another silver chloride emulsion (8) is prepared similar to example 2 except addenda B (l,l -di-n-butyl-4l,4'-bipyridini um dibromide) is lowered to 100 mg. per silver mole and cadmium chloride is added to the emulsion layer at 10 g. per silver mole.

The: above two coatings are then exposed for l minute to a pulse xenon light source, developed as described in the following table, fixed, washed and dried.

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

lclaim: l. A desensitized negative silver halide photographic emulsion containing a desensitizing combination comprising a 5 bipyridinium salt having two pyridinium nuclei joined by a linkage which is attached to a carbon atoms of each of said pyridinium nuclei and an organic nitro-substituted N-heterocyclic desensitizer.

2. A desensitized negative silver halide photographic emulsion according to claim 1 wherein said desensitizer combina tion is present in an amount of at least 50 mg. per mole of silver, and said organic desensitizer is present in an amount of from 25-75 percent by weight of the combination and is selected from the group consisting of nitro-substituted thiazoles and compounds of benzothiazolc, quinoline, indolenine, benzotriazole, and rhodanine having one or more nitro groups attached to a benzene nucleus of said com pounds, said benzene nucleus being either a part of the heterocyclic moiety of said compound or attached thereto through a doubly bonded carbon chain.

3. A desensitized negative silver halide photographic emulsion as claimed in claim 1 wherein said organic desensitizer is present in an amount of from 35-65 percent by weight of said combination and is selected from the groups consisting of 2- mercapto-4-methyl-5-nitrothiazole, 2methyl-6- nitrobenzothiazole metho-p-toluene sulfonate, 2-nitorstyryl-3 ethylbenzothiazolium iodide, 2-(o,p-dinitrostyryl)-3-ethylbenzothiazolium iodide, 2-(o,p-dinitrostyryl)-benzothiazole, Z-(p-nitrostyryl)-quinoline metho-p-toluene sulfonate, 6- ethoxy-Z-nitrostyryl-quinoline metho-p-toluene sulfonate, 4- (p-nitrostyryl)-indolenine methiodide, Z-(p-dimethyIaminos' tyryl)-3-ethyl-6-nitrobenzothiazolium chloride, o-nitrobenzo- 1,2,3-triazole, 4-chloro-6-nitrobenzo-l ,2,3-triazole, 5-chloroo-nitrobenzo-l,2,3-triazole, and S-o-nitrobenzylideneB- ethylrhodanine.

4. A desensitized negative silver halide photographic emulsion according to claim l wherein said descnsitizer combination is present in an amount of at least 50 mg. per mole of silver, the pyridinium component is present in an amount of 2575 percent by weight of said combination and wherein the linkage of said pyridinium compound is selected from the group consisting of a single covalent bond, a vinylene linkage and an ethylene linkage.

5. A desensitized negative silver halide photographic emulsion according to claim 4 wherein said bipyridinium salt is present in an amount of from 35 to 65 percent by weight of said desensitizer combination and is selected from compounds having the formulas:

wherein n represents a positive integer of from 1 to 2', m represents a positive integer of from 2 to 4', R represents vinylene or ethylene; R, and R each represents alkyl, hydroxyalkyl, alkoxyalltyl, carboxyalkyl, sulfoalkyl, sulfatoalltyl, aroyloxy alkyl, acyloxyalkyl, alkoxycarbonyalkyl, aralkyl, and aryl; R and R. each represents hydrogen, lower alkyl containing from one to four carbon atoms, lower alkoxy containing from one to four carbon atoms, or halogen; R and R each represents hydrogen or a lower alltyl group containing from one to four carbon atoms, and X represents an acid anion.

6. A negative silver halide photographic emulsion according to claim 5 wherein said bipyridinium compound is a member selected from the group consisting of: l,l -dibutyl 4,4'

bipyridinium dibromide, diperchlorate, 1,1 -di(2-hydroxyethyl)-4,4'-bipyridinium, dibromide l,l'-diphenacyl-4,4-bipyridinium dibromide, l,2- di(4-pyridyl)ethylene bis(phenacyl bromide), l,2-di(4-' pyridyl)ethylene bis(phenethobromide), dianhydro-l,2-di[ l- (3-sulfopropyl)-4-pyridyl}ethylene dihydroxide l,2-di(4- pyridyl)ethylene bis(methobromide), l,l'-dimethyl-4,4- bipyridinium dibromide, 1,2-di( 4-pyridyl)ethane bis(phenethobromide 1,1 -ethylene-2,2 '-bipyridinium dibromide, and l,l'-tetramethylene-2,2'-bipyridinium dibromide.

7. A negative silver halide photographic emulsion according to claim 1 containing, per mole of silver, 50 toS QO mg. of a 1,1 -dibutyl-4,4'-bipyridinium

Claims (8)

1. 2. A desensitized negative silver halide photographic emulsion according to claim 1 wherein said desensitizer combination is present in an amount of at least 50 mg. per mole of silver, and said organic desensitizer is present in an amount of from 25-75 percent by weight of the combination and is selected from the group consisting of nitro-substituted thiazoles and compounds of benzothiazole, quinoline, indolenine, benzotriazole, and rhodanine having one or more nitro groups attached to a benzene nucleus of said compounds, said benzene nucleus being either a part of the heterocyclic moiety of said compound or attached thereto through a doubly bonded carbon chain.
2. 3. A desensitized negative silver halide photographic emulsion as claimed in claim 1 wherein said organic desensitizer is present in an amount of from 35-65 percent by weight of said combination and is selected from the groups consisting of 2-mercapto-4-methyl-5-nitrothiazole, 2-methyl-6-nitrobenzothiazole metho-p-toluene sulfonate, 2-nitorstyryl-3-ethylbenzothiazolium iodide, 2-(o,p-dinitrostyryl)-3-ethylbenzothiazolium iodide, 2-(o,p-dinitrostyryl)-benzothiazole, 2-(p-nitrostyryl)-quinoline metho-p-toluene sulfonate, 6-ethoxy-2-nitrostyryl-quinoline metho-p-toluene sulfonate, 4-(p-nitrostyryl)-indolenine methiodide, 2-(p-dimethylaminostyryl)-3-ethyl-6-nitrobenzothiazolium chloride, 6-nitrobenzo-1,2,3-triazole, 4-chloro-6-nitrobenzo-1,2,3-triazole, 5-chloro-6-nitrobenzo-1,2,3-triazole, and 5-o-nitrobenzylidene-3-ethylrhodanine.
3. 4. A desensitized negative silver halide photographic emulsion according to claim 1 wherein said desensitizer combination is present in an amount of at least 50 mg. per mole of silver, the pyridinium component is present in an amount of 25-75 percent by weight of said combination and wherein the linkage of said pyridinium compound is selected from the group consisting of a single covalent bond, a vinylene linkage and an ethylene linkage.
4. 5. A desensitized negative silver halide photographic emulsion according to claim 4 wherein said bipyridinium salt is present in an amount of from 35 to 65 percent by weight of said desensitizer combination and is selected from compounds having the formulas:
5. 6. A negative silver halide photographic emulsion according to claim 5 wherein said bipyridinium compound is a member selected from the group consisting of: 1,1''-dibutyl-4,4''-bipyridinium dibromide, 1,1''-dibutyl-4,4''-bipyridinium diperchlorate, 1,1''-di(2-hydroxyethyl)-4,4''-bipyridinium dibromide 1,1''-diphenacyl-4, 4''-bipyridinium dibromide, 1,2-di(4-pyridyl)ethylene bis(phenacyl bromide), 1,2-di(4-pyridyl)ethylene bis(phenethobromide), dianhydro-1,2-di(1-(3-sulfopropyl)-4-pyridyl)ethylene dihydroxide 1,2-di(4-pyridyl)ethylene bis(methobromide), 1,1''-dimethyl-4,4''-bipyridinium dibromide, 1,2-di(4-pyridyl)ethane bis(phenethobromide), 1,1''-ethylene-2,2''-bipyridinium dibromide, and 1,1''-tetramethylene-2,2''-bipyridinium dibromide.
6. 7. A negative silver halide photographic emulsion according to claim 1 containing, per mole of silver, 50 to 500 mg. of a desensitizer combination consisting essentially of from 25 to 75 percent by weight of 1,1''-di-n-butyl-4,4''-bipyridinium dihalide, and from 25 to 75 percent by weight of a member selected from the group consisting of 2-mercapto-4-methyl-5-nitrothiazole and 2-methyl-6-nitrobenzothiazole metho-p-toluene sulfonate.
7. 8. A photographic element comprising a support having thereon a desensitized negative silver halide emulsion layer as claimed in claim 1.
8. 9. A photographic element comprising a support having thereon a desensitized negative silver halide emulsion layer as claimed in claim 7.