US3769011A

US3769011A - Photoconductive compositions and elements containing methine dye in j-aggregate state

Info

Publication number: US3769011A
Application number: US00221037A
Authority: US
Inventors: P Gilman; D Heseltine
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1972-01-26
Filing date: 1972-01-26
Publication date: 1973-10-30
Anticipated expiration: 1990-10-30

Abstract

Organic photoconductive compositions containing a methine dye present in the J-aggregated state and which spectrally respond primarily in the J-band are described. The resultant compositions can be used as photoconductors or as sensitizers for other photoconductors.

Description

United States Patent 1191 Gilman et a1.

[451 Oct.30,19 73 PHOTOCONDUCTIVE COMPOSITIONS AND ELEMENTS CONTAINING METHINE DYE IN J-AGGREGATE STATE [75] Inventors: Paul B. Gilman; Donald W.

I-Ieseltine, both of Rochester, N.Y.

[73] Assignee: Eastman Kodak Company,

Rochester, N.Y.

[221 Filed: Jan. 26, 1972 [21] Appl. N0.: 221,037

Related US. Application Data [63] Continuation-in-part of Ser. No. 804,267, March 4,

1969, abandoned.

[52] US. Cl 96/l.6, 96/130, 96/129 [51] Int. Cl G03g 5/06 [58] Field of Search 96/130, 132, 1.5, 96/l.6

[56] References Cited UNITED STATES PATENTS 3,469,987 9/1969 Owens et a1. 96/102 3,676,147 7/1972 Boyer et al. 96/130 OTHER PUBLICATIONS Rosenoff et al., The Resolved Spectra of Small Cyanine Dye Aggregates and a Mechanism of Supersensitization, Photo. Science & Eng, Vol. 12, N0. 4, 185-195, July, 1968.

Primary ExaminerGeorge F. Lesmes Assistant Examiner-M. B. Wittenberg v Attorney-Robert W. Hampton et a1.

[57] ABSTRACT ductors.

17 Claims, No Drawings PHOTOCONDUCTIVE COMPOSITIONS AND ELEMENTS CONTAINING METHINE DYE IN J-AGGREGATE STATE This application is a continuation-in-part of our application Ser. No. 804,267 filed Mar. 4, 1969 now abandoned.

This invention relates to electrophotography, and more particularly, to photoconductive compositions and sensitizers for photoconductive compositions.

Electrophotographic imaging processes and techniques have been extensively described in both the pa-' tent and other literature, for example, U.S. Pat. Nos. 2,221,776; 2,277,013; 2,297,691; 2,357,809; 2,551,582; 2,825,814; 2,833,648; 3,220,324; 3,220,831; 3,220,833 and many others. Generally, these processes have in common the steps of employing a normally insulating photoconductive element which is prepared to respond to imagewise exposure with electromagnetic radiation by forming a latent electrostatic charge image. A variety of subsequent operations, now well known in the art, can then be employed to produce a permanent record of the image.

One type of photoconductive insulating structural element particularly useful in electrophotography utilizes a composition containing a photoconductive insulating material dispersed in a resinous material.- A unitary electrophotographic element is generally produced in a multi-layer type of structure'by coating a layer of the photoconductive composition onto a film support previously overcoated with a layer of conducting material or else the photoconductive composition can be coated directly onto a coating support of metal or other suitable conducting material. Such photoconductive compositions show improved speed and/or spectral response, as well as other desired electrophotographic characteristics, when one or more photosensitizing materials or addenda are incorporated into the photoconductive compositions. Typical addenda of this latter type are disclosed in U.S. Pat. Nos. 3,250,615; 3,141,770; and 2,987,395. Generally photosensitizing addenda used in photoconductive compositions are incorporatedto effect a change in the sensitivity min the speed of a particular photoconductor system and/or a change in its spectral response characteristics. Such addenda can enhance the sensitivity of an element to radiation at a particularwavelength or to a braod range of wavelengths where desired. The mechanism of such sensitization is presently not fully understood. The phenomenon, however, is extremely useful. The importance of such effects is evidenced by the extensive search currently conducted by' workers in the art for compositions and compounds which are capable of photosensitizing photoconductive compositions in the manner described.

Usually the desirability of a change in electrophotographic properties is dictated by the end use contemplated for the photoconductive element. For example, in document copying applications the spectral sensitivity of the electrophotographic response of the photoconductor should be capable of reproducing the wide range of colors which are normally encountered in such use. If the response of the photoconductor fall short of these design criteria, it is highly desirable if the spectral response of the composition can be altered by the addition of spectral sensitizing addenda to the composition. Likewise, various applications specifically require other characteristics such as high extriction coeffiaggregate are used for forming heterogeneous compo- 'cients and an improved mechanism of charge conduction. It is also desirable for the photoconductive element to exhibit high shoulder speed and high toe speed as measured in an electrical characteristic curve (charge v. exposure).

Spectral sensitization of many photoconductive compositions by the addition of certain dyes selected from the large number of dyes presently known has hitherto been widely used to provide for the desired flexibility in the design of photoconductive elements in particular photoconductor-containing systems. At. the present time, however, few sensitizing addenda to photoconductor compositions or elements have been shown to the art which are capable of producing a significant improvement in, substantially all of the aforementioned desirable characteristics. Conventional dye addenda to photoconductor compositions have generally shown only a limited capability for over-all improvement in the totality of electrophotographic properties which cooperate to produce a useful electrophotographic element or structure. The art is still searching for improveme'nts in effective spectral sensitizers for photoconductive compositions: Thus far, conventional dye sensitization alone has not produced the quality of improvement in photoconductor-containing systems which might be considered satisfactory for the wide varietyof electrophotographic applications presently contemplated by workers in the art.

It is, therefore, an object of this invention to porvide the art of electrophotography with novel compositions of matter, method for their preparation and elements for their optimum employment.

It is a further object of this invention to provide novel means for spectrally sensitizing photoconductive compositions and elements for the employment of such sensitized compositions.

It is also an object of this invention to provide nove photoconductive compositions having high extinction coefficients.

i It is still another object to provide novel photoconductive compositions having higher speeds.

The above and further objects and advantages of this invention will become apparent from the following description of the invention. I

We have discovered that spectral sensitization of photoconductive compositions containing an electrically insulating polymer as a binder can be obtained by the formation of J-aggregate's of certain methine dyes in the photoconductive compositions to form a twophase or particulate-containing composition. In addition, we have'found a variety of novel means for obtaining a high percentage of such aggregated dye in photoconductive compositions.

The dyes useful in accordance with this invention can be generally characterized as methine spectral sensitizing dyes which have shown the ability under variouscircumstances to form J-type aggregates. This characteristic present in certain dyes is extensively discussed in C. E. K. Mees, The Theory of the Photographic Process, 3rd edition, pp. 215, 234, 240, 245, 248 and 254 and MG. deW. Anderson, Stereochemical Factors Affecting Optical Sensitization, Proceedings of the International Conference on Scientific Photography at Liege, 1959, pp. 487 ff. Dyes exhibiting the ability to J- sitions of this invention when combined with a photoconductive electrically insulating composition in accordance with this invention. When the useful dyes are aggregated and contiguous with a photoconductor in accordance with the novel methods of this invention, not only is the spectral sensitivity ofthe photoconductor increased but in addition the new photoconductive composition appears to have a better mechanism of charge conduction. This latter added feature is probably the result of the ordering of the molecules when in this aggregated state. I

The spectral sensitizers used in accordance with this invention are methine dyes, including polymethine dyes, characterized by their ability to form J- aggregates. Methine dyes are dyes containing at least one methine group, including substituted methine groups, as part of a chromophore group in the dye. Methine groups can be represented by the formula wherein n is an integer having a value of O, l, 2 or 3 and Q is a hydrogen atom, a lower alkyl group (e.g., one to six carbons) or an aryl group such as phenyl. Particularly useful methine dyes include .l-aggregating cyanine dyes. The term cyanine dye as used herein, is to be construed broadly as inclusive of simple cyanines, carbocyanines, including polycarbocyanines such as dicarbocyanines, tricarbocyanines, etc. The term includes symmetrical as well as unsymmetrical dyes, as well as chain-methine substituted dyes. Cyanine dyes useful herein feature the amidinium ion chromophoric system. See Mees and James, The Theory of the Photographic Process" published by MacMillan Company (1966) page 201 et seq. The term cyanine dye is also meant to include the following dyes: 2,2'-cyanines and carboxyanines, thiacyanines, oxacyanines, thia-2'- cyanines, N,N-cthylene bridged thiacyanines, 9- substituted thiacarbocyanines, naphthothiazolocyanines, naphthoxazolocyanines, allopolar cyanines, complex cyanines (rhodacyanines), bridged cyanines, and the like. Also included under the term cyanine are thosedyes featuring the amidinium-ion chromophoric system but which have only one nitrogen atom in a heterocyclic ring through which a portion of the conjugated chain passes, such as' hemicyanine dyes. Preferred aggregating cyanine dyes useful in the invention can be represented by the formula:

wherein Z'is an acid anion; Q is a hydrogen atom, a lower alkyl radical (e.g., one to six carbon atoms) or an aryl radical such as phenyl; n is an integer having a value of 0, l, 2 or 3; and X and Y are the atoms necessary to complete a heterocyclic nucleus having five to six atoms in the hetero ring such as benzothiazole, benzoxazole, benzimidazole, etc. Styryl dyes, for example, alkylaminostyryl dyes and merocyanine dyes are also useful. The term merocyanine is also used broadly and includes dyes which are characterized by the amidic chromophoric system. See Mees and James,

supra, pages 201 and 21 8.

Representative examples of dyes useful in the invention include compounds listed in Table I.

TABLE 1 Compound Name of No. Compound 1 3,3'-diethyl-5,5'-dimethyl-9-ethyl thiacarbocyanine chloride 2 anhydro-S,5,6,6'-tetrachloro-l ,l ,3-triethyl- 3-(3-sulfobutyl)benzimidazolocarbocyanine hydroxide 3 anhydrol -ethyl-l 4-sulfobutyl )-2,2

cyanine hydroxide 4 3,3'-dimethyl 9-phenyl-4,5,4',5'-dibenzothiacarbocyanine bromide 5 anhydro-5,5 ',6,6'-tetrachlorol l -diethyl- 3,3'-di-(3-sulfobutyl)benzimidazolocan bocyanine hydroxide 6 5,5-dichlorol ,1 ',3,3'-tetramethylbenzimidazolocarbocyanine perchlorate 7 l',3-diethylthia-2'-cyanine chloride 8 3,3,9-triethylselenathiacarbocyanine perchlorate 9 3 ,3 '-dimethyl-8, l O-diphenoxyoxacarbocyanine chloride 10 2-(5,5-dicyano-2,A-pentenylidene)3-ethylbenzothiazoline l l 3,3'diethyl-9-rnethylthiacarbocyanine chloride 12 l-ethyl-3-methylthia-2'-cyanine chloride 13 l,l'-diethyl-6,6-dimethyl-2,2' -cyanine perchlorate l4 anhydro-3,9-diethyl-3-sulfobutyl-5,5'-

diphenyloxacarbocyanine hydroxide l5 3,3'-triethyl-5,5'-dichlorothiacarbocyanine bromide l6 3,3'-dimethyl-Q-ethylthiacarbocyanine bromide 17 3 ,3 "diethyl-9-methyl-4,5 ,4',5 '-dibenzothiacarbocyanine bromide l8 3 ,3 '-dimethyl-9-phenyl-4,5 ,4',5 '-dibenzothiacarbocyanine bromide l9 l,l'-diethyl-2,2-cyanine chloride 20 3'-ethyl-l-methyl-5,6-dinitro-2-phenyl-3- indolothiacarbocyanine p-toluenesulfonate 21 2 2-[2-(4-bromophenyl)-6- methoxyimidazo[ l ,2-b]-pyrida zin-3- yl]vinyl}-3-ethyl-6-nitrobenzothiazolium p-toluenesulfonate 22 anhydro-2-[2-(3,5-dimethyl-l-p-sulfophenyl- 4-pyrazolyl)vinyl]-3-ethylthiazolo[4,5 blquinovlinium hydroxide 23 3'-ethyl-l-methyl-5,6'-dinitro-2-phenyl-3- indolthiacarbocyanine p-toluenesulfonate 24 l,3,3,3 -tetramethyl-5,6'-dinitroindothiacyanine p-toluenesulfonate 25 2-[(3,5-dimethyl-l-phenyl-4-pyrazoly)vinyl1- 3-ethylthiazolo[4,5-b]quinolinium chloride 26 3,3',9-triethyl-5,5-diphenyloxacarbocyanine bromide 27 3,3 '-diethyl-9-methylthiacarbocyanine p-toluenesulfonate 28 anhydro-tS-chloroQ-l2-(3,5-dimethyl-1-psulfophenyl-4-pyrazolyl )vinyl l ,3-

diphenyl-imidazo[4,5-b]qunioxalinium hydroxide 29 6,7-dichlor0-1,3,3'-trimethyl-l,3-diphenylimidazo[4,5-b]quinoxalinoindocarbocyanine iqditlq. 30 3'-ethyll -methyl-5;6'-dini!ro-2-phenyl-3- indolothiacarbocyanine p-toluenesulfonate 3l 2-[(3,5dimethyll -phenyl-4- pyrazolyl)vinyl l ,3 ,3-trimethyl-3 H- pyrrolo[2,3-b]pyridinium iodide 32 l,3-diallyl-3-methyl-6'-nitroimidazo[4,5-b1- quinoxalinothiacyanine p-toluenesulfonate 33 3-ethyl-6-nitro-2-l 2-( l-phenyl-4-pyrazolyl vinyllbenzothiazolium p-toluenesulfonate 34 2{2-[l-(2-benzothiazolyl)-3,5-dimethyl-4- pyrazolyl]vinyl}-3-ethyI-6-nitr0benzothiazolium p-toluenesulfonate 35 l,3-diallyl-2-[ 2-( l-phenyl-4-pyrazolyl)vinyl imidazo[4,5-b1quinoxalinium p-toluehesulfonate 36 anhydro-2-[2-( 3 ,S-dimethyll -p-sulfophenyl- 4-pyrazolyl)vinyl]-3-ethylthiazolo[4,5-blquinolinium hydroxide 37 6,7-dichloro-2-[2-( l-methyl-2-phenyl-3- indolyl )vinyl l ,3,-diphenylirnidazo[4,5- b]-quinoxalinium p-toluenesulfonate 38 l,3-diallyl-l '-methyl-5 '-nitro-2'- phenylimidazo[4,5-b]quinoxalino-3 indolocarbocyanine p-toluenesulfonate 3'-ethyll .3.3-trimethyl-5.6-dinitroindo thiacarbocyanine p-toluenesulfonate 5-chloro-2[2-( 3 ,5 -dimethyll -phenyl-4- pyrazolyl )vinyl ]-l ,3 ,3-trimethyl-3H- indolium iodide l, l ,3 ,3-tetraethylimidazo['4,5-

b]quinoxalinocarbocyanine chloride 3-[ (6,7-dichloro-l ,3-diphenyll H- imidazo[4,5-b]-quinoxalin-2(3H)- ylidene)ethylidene]-2 H-pyrido[ l ,2-a]pyrimidine-2,4(3H)-dione 5 .5 '-dichloro-3 ,3."-diethyl-6,6'-dinitrothiacarbocyanine iodide 3-ethyl-6-nitro-2-[ 2-( l ,3 ,5-triphenyl-4- pyrazolyl)vinyllbenzothiazolium iodide 2-{2-[2-(4-bromophenyl)-6- methoxyimidazo-[ l,2-b]pyridazin-3 yllvinyl}-3-ethyl-6-nitrobenzothiazolium p-toluenesulfonate We have found 'means for preparing sensitized photoconductive compositions containing a methine dye which spectrally responds predominantly in the region of J-aggregation. We have found 'that the dye need not all be J-aggregated. It is not always necessary to have the dyes completely aggregated as long as so much is tion appear to be comprised only of dye. The present J -aggregated dyes alone as carried in a suitable polymer matrix'have photoconductive properties as well as sensitizing properties for other photoconductors.

One method for forming the present organic photoconductive compositions sensitized with J-aggregated dye that is particularly useful involves aggregating basic dyes. According to this method, the basic dyes are protonated prior to their incorporation into a photoconductive composition. The particular method for protonating the dye can be selected from any of a wide variety of well-known protonation techniques. One suitable technique is the addition of p-toluene-sulfonic acid to the basic dye. Another equally suitable technique is to fume a basic dye solution with hydrogen chloride. Generally, protonation will cause the dye to become colorless. The protonated dye which is not yet in the J-aggregated state is then much more soluble in the organic solvents used in preparing a photoconductive coating and thus can be more easily mixed into the photoconductive composition. At this point, the dye is generally still not in the aggregated state; however, a variety of procedures can be followed subsequently to convert the dye to its colored state after mixing: into the photoconductive composition and to cause it to be converted to the J-aggregate. Fuming the dye-containing photoconductive composition with ammonia is a particularly useful'method for neutralizing the protonated dye while it is in a polymeric matrix of a photoconduc- 0 tive composition. Neutralization thus results in the foraggregated that the dye-containing composition spec- I trally responds primarily in the so-called .l-band. In general, a predominant portion of the dye is present in the .l-aggregated state and preferably substantially all of the dye present is in the .l-aggregated state.

The exact mechanism involved in the formation of the J-aggregatc is not entirely known. However, the presence of the aggregate is readily determined by the characteristic intense, narrow absorption band (J- band) seen at a longer wavelength than the typical absorption band for the non-aggregated form of a dye. It has been suggested that the .l-band arises from interaction of dye molecules in a large aggregate of the dye either as a nematic crystal, or on a polymer matrix or micellar structure. The basic mechanism is presently not wholly defined; however, as referred to above, the J- band per se is readily observed and has been well known since the original workof Dr. E. E. Jelley for whom this band is named.

The J-aggregates formed in accordance with this invention not only produce an observable longwavelength absorption band, but' in addition the J- aggregates, are often visible whenobserved microscopically. The aggregates, which give a heterogeneous nature to the photoconductive compositions sensitized therewith, generally have a particle size of from about 2 X 10' to about 1 X 10" mm. with a preferred range aggregate particles prepared according to this invenmation of a J-aggregated state of the dye. Such secondary neutralization procedures are sometimes not necessary if the photoconductive composition itself is sufficiently basic in relation to the dye; In this latter situation, mer'e mixing of the protonated dye with the basic photoconductive composition will cause formation in situ of the desired .I-aggregated state of the dye.

v A further method of forming the present J -aggregate s is to mix the aggregating dye or dyes into a photoconductive composition, coat a layer of the material and then subject it to the-fumes of various solvents. Particular ly useful solvents include chlorinated hydrocarbon solvents such as methylene chloride, ethylene chloride, etc. .Also useful are aromatic hydrocarbon -solvents such as benzene, toluene, 'etc.

Another suitable method for theformation of the sensitized photoconductive compositions according to this invention involves rnetachromism. Metachromism as referred to here is the use of a material, such as an organic polymer with dyesin solution in order to'change the state of the'dye from the non-aggregate to the J'-(long wavelength) aggregate form. A metachromic interaction can be readily observed by a shift in the absorption spectrum of the-dye used. A useful metachromatic method for converting a dye to the described aggregate form involves the cooperation of a charged form of an aggregating dye with an oppositely charged material, such as a charged polymer. The charged dye is thoroughly mixed into a photoconductive composition comprising a polymeric binder'having aphotoconductor dispersed or'dissolved therein. Thereafter, a, solution of an oppositely charged material is prepared, such as a solution of a cationic polymer. The cationic polymer and the dye-containingphotoconductive com-- position are then mixed together to form the J- aggregate form of the dye. Alternatively, a cationic polymer solution can be coated on a support and the dye-containing photoconductive composition coated thereover. In either situation after contacting the anionic dye species with the cationic polymeric material, the formation of the J-aggregated form of the dye is en- .hanced. Although the exact mechanismof this system is not fully understood, the anionic-cationic relationship between the charged dye and the charged polymeric material facilitates the formation of the J- aggregated state of the dye. In addition to the above procedure, a similar procedure can be followed using a cationic species of dye and using an anionic material, such as a charged polymer, to facilitate the formation of the J-aggregate. A wide variety of charged organic polymers can be used to induce the present metachromic interaction. Materials useful in the practice of this method include poly(vinylbenzyltrimethylammonium chloride), 2,7-naphthalenedisulfonic acid, the sodium salt of naphthalenesulfonates, etc. A variety of antistatic materials have proved useful such as Napcostat which is a water-soluble low volatility cationic material produced by condensing various aromatic hydroxy compounds with 9 to 19 moles of ethylene oxide per hydroxy radical as disclosed in U.S. Pat. No. 3,333,983 and made by Napco Chemical Co. Other useful materials are Compound 79OL which is an antistatic agent made by Merix Chemical Co. and Mollisan which is a nonionic material manufactured by Onyx Chemical Co.

Still another means for forming the aggregated dye in a photoconductive composition involves the use of high moisture conditions during the coating operation. This method can be accomplished in several ways. One useful way involves forming a coating dope of the photoconductor, binder and sensitizing dye and coating the dope on a support in contact with a cold coating block so as to cause condensation of moisture on the coating surface. Alternatively, the dope can be coated in the usual manner only in the presence of steam. It is also possible to produce the aggregated dye by forming a coating of this dope and then subjecting it to steam at a later time.

A further suitable technique for forming the described aggregates involves dissolving a J-aggregating dye in alcohol and very thoroughly mixing the dyealcohol solution into a typical photoconductive composition. A very satisfactory method for obtaining the requisite thorough mixing is through the use of an ultrasonic mixing device although other methods could be used. Useful alcohols include lower alkanols such as those having from one to three carbon atoms such as methanol, ethanol, propanol, etc., with methanol giving the best results. Although the exact reasons that make this method useful are not known, it is believed to be partly due to the solubility of the dyes in alcohol. This solubility gives rise to increased dispersion in solution which makes it possible to disperse the dye more readily and thoroughly throughout the polymer matrix of the photoconductive composition.

Any of the above techniques for forming the J- aggregated dye in a photoconductive composition can also be used to form the J-aggregate in a polymeric binder which does not contain a photoconductor. The aggregate-containing polymeric material can then be used to sensitize a typical photoconductive composition in a variety of ways by bringing the aggregate and photoconductor into contiguous relationship such as by coating the photoconductive composition over a layer of the aggregate-containing binder. Sensitization can also be accomplished by overcoating a photoconductive composition with an aggregate-containing polymeric material. If so desired, sensitization can likewise be accomplished by mixing an aggregate-containing polymeric material into a photoconductive composition.

In accordance with this invention, photoconductive compositions can be sensitized with more than one J- aggregating dye. If two dyes are used which have J- bands at slightly displaced regions of the spectrum, the two will produce a combined result. By using various combinations of dyes, it is possible to prepare sensitized photoconductive compositions having peak sensitivity at different wavelengths than would be possible using only one dye.

The present invention can readily be used for enhancing the sensitivity and extending the spectral range of sensitivity of a variety of organic photoconductors including both nand p-type photoconductors. For example, the present invention can be used in connection with organic photoconducting materials which have little or substantially no persistence of photoconductivity. An especially useful class of organic photoconductors is referred to herein as organic amine photoconductors. Such organic photoconductors have as a common structural feature at leas one amino group. Useful organic photoconductors which can be spectrally sensitized in accordance with this invention include, therefore, arylamine compounds comprising (1) diarylamines such as diphenylamine, dinaphthylamine, N,N-

diphenylbenzidine, N-phenyl- 1 -naphthylamine N-phenyl-2-naphthylamine, N,N'-diphenyl-pphenylenediamine, 2-carboxy-5-chloro-4 methoxydiphenylamine, p-anilinophenol, N,N'-di-2- naphthyLp-phenylenediamine, those described in Fox U.S. Pat. No. 3,240,597, issued Mar. 15, 1966, and the like, and (2) triarylamines including (a) nonpolymeric triarylamines, such as triphenylamine, N,N,N',N'-

tetraphenyl-m-phenylenediamine 4- acetyltriphenylamine, 4-hexanoyltriphenylamine 4- lauroyltriphenylamine, 4-hexyltriphenylamine, 4-

dodecyltriphenylamine, 4,4-bis(diphenylamino)benzil, 4,4-bis(diphenylamino)benzophenone and the like, and (b) polymeric triarylamines such as 'poly[N,4- '-(N,N' ,N-triphenylbenzidine polyaidpyltriphenylamine, polysebacyltriphenylamine, polydecamethylenetriphenylamine, poly-n-(4-vinylphenyl)diphenylamine, poly-N-(vinylphenyl)-a,a'- dinaphthylamine andthe like. Other useful amine-type photoconductors are disclosed in U.S. Pat. No. 3,180,730issued Apr. 27, 1965.

Useful photoconductive substances capable of being sensitized in accordance with this invention are disclosed in Fox U.S. Pat. No. 3,265,496 issued Aug. 9, 1966 and include those represented by the following general formula:

R|:III-T Q wherein T represents a mononuclear or polynuclear divalent aromatic radical, either fused or linear (e.g., phenyl, naphthyl, biphenyl, biriaphthyl, etc.), ora substituted divalent aromatic radical of these types wherein said substituent can comprise a member such as an acyl group having from one to about six carbon atoms (.e.g, acetyl, propionyl, butyryl, etc.), an alkyl group having from one to about sixcarbon atoms (e.g., methyl, ethyl, propyl, butyl, etc), an alkoxy group having from one to about six carbon atoms (e.g., methoxy, ethoxy, propoxy, pentoxy, etc.), or a'nitro group; M represents a mononuclear or polynuclear monovalent aromatic radical, either fused or linear (e.g., phenyl, naphthyl, biphenyl, etc), or a substituted monovalent aromatic radical wherein said substituent can comprise a member, such as an acyl group having from one to about six carbon atoms (e. g., acetyl, propionyl, butyryl, etc.), an alkyl group having from one to about six carbon atoms (e.g., methyl, ethyl, propyl, butyl, etc.), an alkoxy group having from one to about six carbon atoms (e.g., methoxy, propoxy, pentoxy, etc.), or a nitro group; O can represent a hydrogen atom, a halogen atom or an aromatic amino group, such as MNH-; b represents an integer from 1 to about 12; and, R represents a hydrogen atom, a mononuclear or polynuclear aromatic radical, either fused or linear (e.g., phenyl, naphthyl, biphenyl, etc.), a substituted aromatic radical wherein said substituent comprises an alkyl group, an alkoxy group, an acyl group, or a nitro group, or a poly(4-vinylphenyl) group which is bonded to the nitrogenatom by a carbonatom of the phenyl group.

Polyarylalkane photoconductors are particuarly useful in producing the present invention. Such photoconductors are described in US. Pat. No. 3,274,000, French Pat. No. 1,383,461 and in copending application of Seus and Goldman titled Photoconductive Element Containing Organic Photoconductors Ser. No. 627,857, filed Apr. 3, 1967, now US. Pat No. 3,542,544. These photoconductors include leuco bases of diaryl or triaryl methane dye salts, 1,1,1- triarylalkanes wherein the alkane moiety has at-least two carbon atoms and tetraarylmethanes, there being substituted an amine group on at least one of the aryl groups attached to the alkane and methine moieties of the latter two classes of photoconductors which are non-leuco base materials.

Preferred polyarylalkane photoconductors can be represented by the formula:

wherein each of D, E and G is an aryl group and J is a hydrogen atom, an alkyl group, or an aryl group, at least one of D, E and G containing an amino substituent. The aryl groups attached to the central carbon atom are preferably phenyl groups, although naphthyl groups can also be used. Such aryl groups can contain such substituents as alkyl and alkoxy typically having one to eight carbon atoms, hydroxy, halogen, etc., in the ortho, meta or para positions, ortho-substituted phenyl being preferred. The aryl groups can also be joined together or cyclized to form a fluorene moiety, for example. The amino substituent can be represented by the formula wherein each L can be alkyl group typically having one to eight carbon atoms, a hydrogen atom, an aryl group,

or together the necessary atoms to form a heterocyclic' amino group typically having five to six atoms in the ring such as morpholino, pyridyl, pyrryl, etc. At least one of D, E and G is preferably p-dialkylam'inophenyl group. When J is an alkyl group, such an alkyl group more generally has one to seven carbon toms.

Representative useful polyarylalkane photoconductors include the compounds listed in Table 11.

TABLE II Compound Number Name of Compound 1 4,4'-benzylidenebis(N,N-diethyl-m-toluidine) 2 4,4"-diamino-4-dimethylamino-2',

,2"-dimethyltriphenylmethane Y 3 4',4"-bis(diethylamino)-2,6-dichloro2',2"-

. dimethyltriphenylmethane 4 4',4"bis(diethylamino )-2',2"-dimethyldiphenylnaphthylmethane 5 2',2"-dimethyl-4,4,4"-tris(dimethylamino)- triphenylmethane 6 4,4"-bis(diethylamino)-4-dimethylamino- 2',2"-dimethyltriphenylmethane 7 4',4"-bis(diethylamin0)-2-chloro-2,2"-

dimethyl-4-dimethylaminotriphenylmethane 8 4',4"-bis(diethylamino)-4-dimethylamino- 2,2',2"-trimethyltriphenylmethane 9 4',4"-bis(dimethylamino)-2-chloro-2,2"-

dimethyltriphenylmethane 4,4"-bis(dimethylamino)-2,2"-dimethyl-4- methoxytriphenylmethane bis( 4-diethylamino l l l -tripl1enylethane bis(4-diethylamino)tetraphenylmethane 4',4"-bis( benzylethylamino)-2',2"-dimethyltriphenylmethane 4',4"-bis(diethylamino)-2',2"-diethoxytriphenylmethane 4,4-bis(dimethylamino)-1.1,l-triphenyleth ne- .7 a; 1-(4N,N-dimethylaminophenyT 1 1 diphenylethane 4-dimethylaminotetraphenylmethane 4-diethylaminotetraphenylmethane wherein R, and R are each phenyl radicals including substitued phenyl radicals and particularly when R, is a phenyl radical having the'formula:

lam

wherein R and R are each aryl radicals, aliphatic residues of one to 12 carbon atoms such as alkyl radicals preferably having one to four carbon atoms or hydrogen. Particularly advantageous results. are obtained when R, is a phenyl" radical including substituted phenyl radicals an where R is diphenylaminophenyl, dimethylaminophenyl or phenyl.

Representative photoconductive compounds useful with sensitizing amounts of the feature'material of this invention includethe following:

TABLE 3 Compound Number Name of Compound 1 4',4"-bis(diethylamino)-2',2"-dimethyltriphenylmethane 2 4',4"-diamino-4-dimethylamino-Z,2",5',5"-

tetramethyltriphenylmethane 3 4',4' '-bis(diethylamino )-2,6-dichloro-2,2"-

dimethyltriphenylmethane 4 4',4"-bis(diethylamino)-2,2"-climethyldi' phenylnaphthylmethane 5 2,2"-dimethyl-4,4,4"-tris(dimethylamino)- triphenylmethane 6 4',4"-bis(diethylamino)-2-dimethy1amino- 2,2",5,5"-tetramethyltriphenylmethane 7 4,4"-bis(diethylamino)-2-chloror-2',2"-

dimethyl-4-dimethylaminotriphenylmethane 8 4',4"-bis(diethylamino)-4-dimethylamino- 2,2,2"-trimethyltriphenylmethane 9 4',4"-bis(dimethylamino)2-chloro-2,2"-

dimethyltriphenylmethane 4',4"-bis(dimethylamino)-2,2"-dimethyl-4 methoxytriphenylmethane I l 4,4"-bis( benzylethylamino)-2',2"-dimethyltriphenylmethane 4',4"-bis(diethylamino)-2', 2",

5 ,5 '-tetramethyltriphenylmethane 4',4"-bis(diethylamino)-2',2"-diethoxytriphenylmethane Other photoconductors which can be used with the present .l-aggregate containing compositions include parachlorosil, benzil, trinitrofluoroenone, tetrafluorene, 9-dicyanomethylene-2,4,7-trinitrofluorenone, etc.

The following Table 111 comprises a partial listing'of U.S. patents disclosing a wide variety of organic photoconductive compounds and compositions which are useful in practicing this invention.

TABLE Ill 7 Inventor U.S. Pat. No. Inventor US. Pat. No. Hoegl et all. 3,037,861 Cassiers 3,158,475 Sues et :11. 3,041,165 Tomanek 3,161,505 Schlesinger 3,066,023 Schlesinger 3,163,530 Bethe 3,072,479 Schlesinger 3,163,531 Klupl'el et a1. 3,047,095 Schlesinger 3,163,532 Neugebauer et a1. 3,112,197 Hoegl 3,169,060 Cassiers et a1. 3,133,022 Stumpf 3,174,854 Schlesinger 3,144,633 Klupfel et 21. 3,180,729 Noe et a1. 3,122,435 Klupfel et-al. 3,180,730 Sues et al. 3,127,266 Neugebauer 3,189,447 Schlesinger 3,130,046 Neugebauer 3,206,306 Cassiers 3,131,060 Fox 3,240,597 Schlesinger 3.139,338 Schlesinger 3,257,202 Schlesinger 3,139,339 Sues et al. 3,257,203 Cassiers 3,140,946 Sues et al. 3,257,204 Davis et a1. 3,141,770 Fo'x 3,265,496 Ghys 3,148,982 Kosche 3,265,497 Cassiers 3,155,503 Noe et al. 3,274,000

The amount of sensitizing dye that is used in conjunction with a photoconductive layer in accordance with the invention can vary widely. Th optimum concentration in any given case will vary with the specific photoconductor and sensitizing dye used. In general, effective results can be obtained where an appropriate sensitizing dye is used in a concentration range from about 0.0001 to about 30 percent by weight based on the weight of the film-forming photoconductive coating composition. Preferably, the sensitizing dye is added directly to the photoconductive composition to be coated in an amount of from about 0.1 to about 10 percent by weight of the total coating composition.

Binders for use in preparing the present sensitized photoconductive layers are film-forming polymeric binder materials having fairly high'dielectric strength which are good electrically insulating film-forming vehicles. Materials of this type comprise styrenebutadiene copolymers; silicone resins; styrene-alkyd resins; silicone-alkyd resins; soyaalkyd resins; poly(vinyl chloride); poly(vinylidene chloride); vinylidene chlorideacrylonitrile copolymers; poly(vinyl acetate); vinyl acetate-vinyl chloride copolymers; poly(vinyl acetals), such as poly(vinyl butyral); polyacrylic and methacrylic esters, such as poly(methyl methacrylate), poly(n-butyl methacrylate), poly(isobutyl methacrylate), etc.: polystyrene; nitrated polystyrene; chlorinated polyethylene; polyvinyl-m-bromobenzoate-covinyl acetate; polymethylstyrene; isobutylene polymers; polyesters, such as poly(ethylenealkaryloxyalky-,

lene terephthalate); phenol formaldehyde resins; ketone resins; polyamides; polycarbonates; polythiocarbonates; poly(ethylene glycal-co-bishydroxyethoxyphenyl propane terephthalate); etc. Methods of making resins of this type have been described in the prior art, for example, styrene-alkyd resins can be prepared according to the method described in U.S. Pat. Nos. 2,361,019 and 2,258,423. Suitable resins of the type contemplated for use in the photoconductive layers of the invention are sold under such trade names as Vitel PE-lOl Cymac, Piccopale 100, Saran F-220 and Lexan 145. Other types of binders which can be used in the photoconductive layers of the invention include such materials as paraffin, mineral waxes, etc.

Solvents of choice for preparing coating compositions of the present invention can include a number of solvents such as benzene, toluene, acetone, 2- butanone, chlorinated hydrocarbons, e.g., methylene chloride, ethylene chloride, etc., ethers, e.g., tetrahydrofuran, or mixtures of these solvents, etc.

In preparing the coating composition useful results are obtained where the photoconductor substance is present in an amount equal to at least about lweight percent of the coating composition. The upper limit in the amount of photoconductor substance present can be widely varied in accordance with usual practice. It is usual practice that the photoconductor substance be present in an amount from about 1 weight percent of the coating composition to about 99 weight percent of the coating composition. A preferred weight range for the photoconductor substance in the coating composition is from about 10 weight percent to about 60 weight percent.

Coating thicknesses of the photoconductive composition on a support can vary widely. Normally, a coating in the range of about 10 microns to about 250 microns before drying is useful for the practice of this invention. The preferred range of coating thickness is formed to be in the range from about 25 microns to about microns before drying although useful results can be obtained outside of this range. As previously mentioned, more than one layer may be coated on the support. Good results are obtainable when a first layer containing a photoconductor, a binder and a sensitizer is overcoated with a second layer of a composition containing a photoconductor and a binder. The photoconductor and binderemployed in the overcoat can be different than those employed'in the first layer.

Suitable supporting materials for coating the photoconductive layers of the present invention can include any of a wide variety of electrically conducting supports, for example, paper (at a relativev humidity above 20 percent); aluminum foil-paper laminates; metal foils such as aluminum foil, zinc foil, etc; metal plates, such as aluminum, copper, zinc, brass and galvanized plates; vapor deposited metal layers such as nickel, silver, aluminum and the like. An especially useful conducting 13 support can be prepared by coating a support material such as poly(ethylene terephthalate) with a layer containing a semiconductor dispersed in a resin. Such conducting layers both with and without insulating barrier layers are described in U.S. Pat. No. 3,245,833. Likewise, a suitable conducting coating can be prepared from the sodium salt of a carboxyester lactone of maleic anhydride and a vinyl acetate polymer. Such kinds of conducting layers and methods for their'optimum preparation and use are disclosed in U.S. Pats. Nos. 3,007,901 and 3,267,807.

Whether a transparent, translucent or opaque supportmaterial is used will be determined by the method of exposure to be employed, e.g., exposure by reflex or by transmission through the original, and by the end use desired of the reproduction. Exposure by reflex, for example, requires that the support transmit light while no such requirement is necessary for exposures by projection. Similarly transparent supports are required if the reproduction is to be used for projection purposes; translucent supports are preferred for reflex prints; and opaque supports are adequate if the image is subsequently transferred by any means to another support, the reproduction is satisfactory as obtained, or the reproduction is to be used as a printing plate for preparing multiple copies of the original.

As used herein and in the appended claims, the terms insulating" and electrically conductive have reference to materials the surface resistivities of which are greater than ohms per square unit (e.g., per square foot) and less than 10' ohms per square unit (e.g., per square foot) respectively.

Electrophotographic elements sensitized in accordance with the present invention can be employed in any of the well-known electrophotographic processes which require photoconductive layers. One such process is the xerographic process. In a process of this type, an electrophotographic element is given a blanket electrostatic charge by placing the same under a corona discharge device maintained at a potential of from 6,000-7,000 volts. This device gives a uniform charge to. the surface of the photoconductive layer which charge is retained by the layer because of the substantial insulating property of the layer, i.e., the low conductivity of the layer in the dark. The electrostatic charge formed on the surface of the photoconducting layer is then selectively dissipated from the surface of the layer by exposure to light through an image-bearing transparency by a conventional exposure operation such as, for example, by contact-printing technique, or by lens projection of an image, etc., to form a latent image in the photoconducting layer. Of course, the exposure can also be a reflex exposure. By exposure of the surface in any such manner, a charged pattern is created by virtue of the fact that light causes the charge to be conducted away in proportion to the amount of the exposure in a particular area. The charge pattern remaining after exposure is then developed, i.e., rendered visible, by treatment with a medium comprising tents, for example, as U.S. Pat. No. 2,907,674 and in Australian Pat. No. 212,315. In processes of electrophotographic reproduction such as xerography, by selecting a developing particle which has as one of its components, a low-melting resin, it is possible to treat the developed photoconductive material with heat and cause the powder to adhere permanently to the surface of the photoconductive layer. In other cases, a transfer of the image formed on the photoconductive layer can be made to a second support, which would then become the final print. Techniques of the type indicated are well knownin the art and have been described in a number of U.S. and foreign patents, such as U.S. Pats. Nos. 2,297,691 and 2,551,582 and in RCA Review, vol. 15 (1954), pages 469-484.

The following examples are included for af urther understanding of the invention.

Example 1 An organic electrically insulating photoconductive composition is prepared from 50 ml of a 10 percent solution of a polycarbonate binder dissolved in methylene bis(4hydroxyphenyl)-propane (e.g., Lexan 145, Genelectrostatically attractable particles having optical eral Electric Co.). Next, 0.05 g. of anhydro-S ,5, 6,6-tetrachloro-l ,l '-diethyl -3,3 -di(3-sulfobutyl)benzimidazolocarbocyanine hydroxide is added to 3 ml. of methyl alcohol and the mixture is agitated in an ultrasonic mixing apparatus to disperse the dye as a colloidal suspension in the alcohol. This colloidal suspension is then added with stirring to the photoconductive mixture previously prepared. The combined mixture is then wet coated at a thickness of microns onto a poly(ethylene terephthalate) film support carrying a conductive layer of the sodium salt of a polymeric lactone as described in U.S. Pat. No. 3,260,706, The resultant electrophotographic element is then negatively charged under a corona source and exposed for 1 second using a Bausch and Lomb wedge spectrograph at a slit width of 3 mm. After exposure, the electrostatic latent image is developed to a visible'image by cascading over the element a dry developer of the type dc scribed in U.S. Reissue Pat. No. 25,136. The resultant wedge spectrogram shows a spectral sensitivity extending from 400 to 630 nm. with a large prominent peak Example 2 The procedure of Example 1 is repeated using triphenylamine as the photoconductor. Similar results are obtained with thesensitivity of the photoconductive e l ement extending well beyond that of the dye in the nonaggregate state. i

Example 3 A photoconductive composition is prepared from 200 ml. of methylene chloride, l8 g. of the binder of Example 1 and 12 g. of the photoconductor of Example 1. Additional methylene chloride is then added to the mixture to bring the total weight of the solution to 300 g. Next, 0.05 g. of the sensitizing dye of Example 1 is added to 1.5 ml. of methyl alcohol. A 10 percent methyl alcohol solution of p-toluenesulfonic acid is then added dropwise to the dye-alcohol mixture with stirring and heating until the dye completely dissolves and becomes colorless due to protonation. The colorless solution of protonated dye is then added to the previously prepared photoconductive composition. After slight mixing of the two solutions, the basic photoconductive composition converts the protonated, colorless dye to the colored form and at the same time induces the formation of dye in the J-aggregate state. After 2 minutes of mixing, the combined materials are coated at a 100 microns wet-thickness on the conducting support of Example 1. The resultant electrophotographic element is then negatively charged under a corona source and a wedge spectrogram is made as described in Example 1 with an exposure time of l/ 10 of a second. The spectral response of this electrophotographic element extends from 400 to 610 nm. with a peak between 560 and 600 nm.

Example 4 An electrophotographic element similar to that in Example 3 is prepared using the following sensitizing dye: anhydro-5,5 ',6,6-tetrachloro-l l ',3-triethyl-3(3- sulfobutyl)-benzimidazolocarbocyanine hydroxide. A wedge spectrogram is made on this element in accordance with the previous examples. The sensitized photoconductive composition shows a spectral sensitivity from 400 to 620 nm. with a strong band at 560 to 610 nm. This element requires only 1/100 ofa second exposure on the wedge spectrograph to record a good visible image.

Example 5 An electrophotographic element is prepared in accordance with Example 1 using as the sensitizing dye 3 ,3 '-dimethyl-9-phenyl-4,4',5 ,5 -dibenzothiacarbocyanine bromide. Wedge spectrograms are made in accordance with the previous examples. The spectral sensitivity of the sensitized photoconductive composition extends from 500 to about 680 nm. with a peak at.

about 670 nm.

EXAMPLE 6 A 0.1 percent solution of anhydro-5,5',6,6'- tetrachloro-1,1 '-diethyl-3 ,3 '-di( 3-sulfobutyl) benzimidazolocarbocyanine hydroxide in an 80/20 ethyl alcohol-water mixture is prepared. Ten ml. of a watersolution of an interpolymer of methyl vinyl ether and maleic anhydride (Gantrez AN-l 19 of General Aniline and Film Corporation) is added to 2 ml. of the dye solution and the mixture is coated at 100 microns wet thickness on a conducting support as in Example 1. The layer is dried and overcoated with a 100 microns wet thickness coating of a 10 percent methylene chloride solution of the binder poly[ethyleneglycol-co-bis- (hydroxyethoxyphenyl)propane terephthalate] (Vitel 101 of Goodyear Tire and Rubber Co.) containing 0.3 g of the photoconductor of Example 1. The overcoat is dried and the resultant electrophotographic element is charged under a corona charging apparatus. The double layer element is then exposed for 5 seconds at slit width 5 mm. in a wedge spectrograph as in Example 1, followed by development using toner of Example 1. The resultant wedge spectrogram showed a spectral sensitivity extending from 480 to 600 nm. with a peak at 580 nm.

Example 7 A photoconductive composition is prepared containing 18 g of the binder of Example 1, 12 g. of the photoconductor of Example 1 in 200 ml. of methylene chloride with additional methylene chloride added to adjust the total weight to 300 g. Next, 0.025 g. of the dye anhydro-5,5,6,6'-tetrachloro-l ,1 ,3-triethyl-3 3- sulfobutyl)benzimidazolocarbocyanine hydroxide is dissolved in 0.5 ml. of a 10 percent methanolic solution of p-toluenesulfonic acid and the resultant dye solution is added to 25 ml. of the previously prepared photoconductor-containing solution. The combined solutions are then coated at 100 microns wet-thickness on the conductive support of Example 1 to form a control element. After drying the resultant electrophotographic element is corona charged and exposed for 10 seconds at 10 mm. slit width in a Bausch and Lomb Wedge Spectrograph. After exposure, the electrostatic latent image on the control element was developed with the developer of Example 1. The spectral sensitivity of this element extends from 440 to 560 nm. with a very slight peak at 580 nm. Next, a coating formulation is prepared as above with the addition of 0.02 g. of poly(vinylbenzyltrimethylammonium chloride) to 25 ml. of the above mixture. This combined formulation is coated on a conductive support as previously described, exposed in the spectrograph and developed. A high-contrast wedge spectrogram results with only a l/ 10 of a second exposure and exhibits a spectral sensitivity from 440 to 620 nm. with a large prominent peak at 580 nm., characteristic of the dye in the J-aggregate state. The spectrophotometric absorption curves of the two elements show an approximate 50 percent higher conversion of the dye to the J-aggregate state in the second coating as compared to the control coating.

Example 8 latent electrostrostatic image is developed as in the previous examples. The wedge spectrogram which is obtained shows good image defination and exhibits a spectral sensitivity having a strong peak at 5 nm.

Example 9 The procedure of Example 8 is repeated with the exception of the binder used in the photoconductive composition is the binder. of Example 6. After coating on the specially prepared paper, J-aggregation of the dye occurs on dry down and a wedge spectrogram produced as in the preceding examples shows a strong peak at 580 nm.

Example 10 A composition is prepared using 0.025 g. of the dye anhydro-l-ethyl-I-sulfohutyl-2.2'-cyaninc hydroxide in 2.5 ml. of the binder, photoconductor combination o fEx ample l The sensitized photoconductive composition is then coated on the specially prepared support of Example 7 dried, charged, exposed and developed-as the preceding examples. Theresultant wedge spectrogram shows good electrophotographic response from 460 to 600 nm. with a definite narrow J-band response at 580 nm. with an exposure of 1/10 of asecond at mm. A second electrophotographic element containing structurally similar dye l ,1 -diethyl-2,2-cyanine chloride in place of the previous dye when exposed for 30. seconds on the-wedge spectrograph exhibits only faint electrophotographicresponse and shows a peak at 530 nm. with no J -band response. Thisindicates the necessity for the acidic portion of the dye when used in conjunction with a basic polymeric substrate or addenda.

Example I l The procedure of Example 4 is repeated using the dye 5,5, 6,6'-tetrachloro-l ,-l 3,3 '-tetraethylbenzimidaiolocarbocyanine chloride. The resultant electrophotographic element exhibits J-aggregate spectral sensitivity at 580 nm. Similar results are obtained with an electrophotographic element prepared as in'Example 4 only using sulfobutyl)benzimidazolocarbocyanine hydroxide.

Example 12 Two electrophotographic elements areprepared by the procedure of Example 4 using a lzlmixture of the dye of that example with one of the following dyes: anhydro-S ,6-dichlorol -ethyl-l ,3 ,3 ,-trimethyl-'3- -sulrobur 1beitziihiaaiaiaifizfisaaisaeyaame "hydroxide and 5 ,6-dichlorol -B-diethylaminoethyl-3 ,3 diethylbenzimidazolothiacarbocyanine iodide. When one of the above dyes is blended withthe dye of Example 4, the spectral sensitivity is shifted to a shorter wavelength. The above dyemixtures when combined in the electrophotographic element of Example 4 procedure a broad sensitivity bandwith a shifted maximum response. Using this techniqueof mixingdyes, the spectral sensitivity of a photoconductive compositioncan be controlled or shifted to a desiredportion of the spectrum.

Example 1 3 A photoconductive composition is prepared by mixing the following ingredients: Binder of Example 6 10.5 g.

Triphenylamine (photoconductor) 3.5

3'-ethyl-l-methyl-5,6'-dinitro-2 phenyl- 3-indolothia- 55 carbo cyanine p-toluenesulfonate 0.14

Methylene chloride 81.9 ml. This composition is coated'onto a conducting support as in Example 1 with a coating.blocktemperature of about 50C. After the coating dries the resultant electrophotographic element is tested for: spectral sensitivity as in Example 1. This controlelementzhas a radia-- potential, V0,.to some lower potential, V, whose exact.

resultant electrophotographic' element is, then measured'for spectral sensitivity and found'to have a radiation absorption maximum of 570 nm.

Example 14 Two compositions are prepared using 14 g. of the binder of Example 6, 0.28 g. of the dye of Example 13 and 81.9 ml. of methylene'chloride in each of the compositions. After mixing, each of the compositions is 0 coated at a microns wet thickness onto a transparent conductive support as in Example 1. One of these coatings is subjected to fuming with methylene chloride Avhich results in aggregate formation. The control coating (unfumed) and the treated coating are then measured for spectral sensitivity and found to have radiation absorption 'maxima at 510 and 560 mm., respectively. The two elements are then measured for positive and negative electrical speeds as follows. Each element is electrostatically charged .under a corona source until the surface potential, as measured by an electrometer probe, reaches about 600 volts. The charged elements are then exposed to a 3,000K tungsten light source through a stepped density gray scale. The exposure causes reduction of the surface potential of the elements under each step of the gray scale from its initial value depends on the actual amount of exposure received by the area. The results of these measurements are then plotted on-a graph of surface potential V vs log exposure for each step. The actual positive or negative speed of the photoconductive composition used can then be expressed in terms of the reciprocal of the exposure required to reduce the surface potential to any fixed arbitrarily selected value. The actual positive and negative speed is the numerical expression of 10 divided by the exposure in m'eter-candle-seconds required to reduce the 600v volt surface potential to a value of 500 volts (100 volt shoulder speed). The positive and negative 100 volt shoulder speeds of the control coatingare 0 and 0, respectively. The positive and negative 100 volt shoulder speeds of the aggregated coating are 25 and 110, respectively, thus demonstrating the photoconductive response obtainable from the aggregated dye above.

Example 15 A composition is prepared by dissolving 1.5 g. of the binder of Example 1, 1.0 g. of the photoconductor of Example 1, 50mg. of the dye 2-(5,5'-dicyano-2,4- pentenylidene)-3-ethylbenaothiazoline in 12 cc. of dichloromethane. This solution is coated at a wet thickness of microns on a conductingpaper support in contact with a metal block held at 15c. The dry coating is then fumed with toluene vapors for -l5 minutes during which time it changes from orange to blue violet in color. The resultant element is positively charged, exposed in a wedge spectrograph and developed as in Example 1. A similar element is prepared without fumabove. The spectral sensitivity of the fumed coatings extends from 400 to 720 nm; whereas, the non-fumed coating has essentially no xerographic sensitivity and absorbs essentially no light of wavelengths longer than Example l6v The four spectral ,sensitizing'dyes listed in Table I ing and is then charged, exposed and developed as below are each characterized by their ability to form J-aggregates in light-sensitive silver halide compositions. For comparative purposes, the typical absorption peak of the non-aggregated form of each dye is also 3-ethylbenzothiazoline Samples of each dye are dissolved in methanol to form dye solutions of three concentrations: a first concentration corresponding to that typically used to sensitize a silver halide emulsion; a second, higher, concentration corresponding to that typically used to sensitize an organic photoconductive composition; and a third concentration intermediatev to the first and second.

A portion of each dye-methanol solution is added to identical silver halide test emulsions to produce dyesensitized emulsion dopes which, except for the presence of the different dyes employed, have the following composition:

Silver Halide Test Composition (excluding sensitizer) 1.22 g. silver halide emulsion containing 1 mole of silver halide and 30 grams of gel per 6l0 grams of the emulsion of l2%% by weight gel mixture of dye solvent of l5%.by weight saponin mixture of distilled water total weight Another portion of each dye-methanol solution is added to identical organic photoconductive test compositions to produce dye-sensitized organic photocond'uctive dopes .which, except for the particular dye employed, have the following compoisition:

Organic Photoconductive Test Composition (excluding sensitizer) VitellOl binder 1.70 g. l 17.90 g. methylene chloride solvent 0.6 g. of triphenylamine organic photoconductor 20.2 g. total weight Each of the above dopes is coated on a support and dried. The sensitized coating are tested for the presence of J-aggregation by observing their absorption curves to determine whether they exhitit the characteristic, intense J-absorption band seen at a longer wavelength than the broad absorption bandtypical of the non-aggregated form of the dye. Table 11 shows the results of these tests. The wavelength of peak absorption presented for each dye in its silver halide and organic photoconductive test composition remains substantially unchanged despite the variance in concentration of dye in the composition. Accordingly, the wavelength presented for each dye represents an average value for the three test compositions in which it is present.

TABLE 1] Silver Halide (AgX) Composition or Organic Photoconduc- Wavelength of As can be seen in Table II, the dye sensitized silver halide compositions exhibit the characteristic shift in absorption peak indicating that J-aggregation is present. The organic photoconductive compositions, however, show no such shift in absorption peak indicating that the dyes present therein remain in nonaggregated form. The results of this example are to be compared with those of Examples 4,5,1'0, and 15 above which in accordance with the discovery of the present invention teach that .l-aggregation of Dyes Nos. l-4 in organic photoconductive compositions may be obtained. From the above, it is apparent that .I-aggregated dye formation in silver halide emulsions and other inorganic light sitions. v

Example 17 1.0 g of polyvinyl m-bromobenzoate-co-vinyl acetate binder, 1.0g of 4,4-bis(diphenylaminochalcone) organic photoconductor and 0.04 g of 6-chloro-l methyl-l ,2 ,3 -triphenylimdiazo [4,5'-quinoxalino-3'-indolocarbocyanine sensitizing dye is dissolved in 15.6 g of methylene chloride by stirring the solids in the solvent for 1 hour at room temperature. The resulting solution is hand coated at a wet coating thickness of 0.004 inch on a conducting layer comprising the sodium salt of a carboxyester lactone which is in turn coated on a cellulose acetate film base. After dying, the absorption curve of the sensitized coating is measured and found to exhibit a broad peak at 528 nm. Comparison with'the broad 505 nm. absorption peak exhibited by the nonaggregated dye in methanol solution'shows that no J- aggregation occurs in the organic photoconductive composition. Viewing the sensitized coating under a microscope at 500x magnification further indicates that the J-aggregated dye is not present since dye particles are not observed. This Example shows that simple addition of sensitizing dyes to the above-noted organic chalcone photoconductive composition does not produce J-aggregation of thedye in the above-described organic photoconductive composition.

Example 18 Example 17 is repeated except that 6,6'-dichloro- 1,1'-3,3'-tetraphenylimidazo [4,5-b]- quinoxalinocarbocyanine p-toluenesulfonate is employed as the sensitizer in the organic photoconductive composition. The coating exhibits a broad absorption peak at 618 nm, as compared with the broad peak at 605 nm which th'edye shows in methanol solution. Viewing at SOOX magnification does not reveal the Presence of p-toluenesulfonate 4. A photoconductive composition as in claim 1 wherein the organic photoconductor is selected from the group consisting of a polyarylalkane and an arylamine.

5. An electrophotographic element comprising a conducting support having coated thereon an electrically insulating polymer binder material, an organic photoconductor and a sensitizing amount of at least one sensitizing methine dye which is present in the J- aggregated state and which spectrally responds primarily in the region of J-aggregation.

6. An electrophotographic element as in claim wherein the sensitizing methine dye is selected from the group consisting of cyanine and merocyanine dyes.

7. An electrophotographic element as in claim 5 wherein the organic photoconductor is selected from the group consisting of polyarylalkane, arylamine, and 4-diarylamino-substituted chalcone photoconductors.

8. An electrophotographic element comprising a conducting support having coated thereon the photoconductive composition of claim 3.

9. A method for producing a sensitizing photoconductive composition comprising the steps of combining in solution an organic photoconductor, an electrically insulating polymeric material and a charged form of a methine dye capable of forming J-aggregates, adding an organic polymer having a charge of opposite polarity from said dye, mixing the combination, coating a layer of the combined materials on aconducting support and drying the coating to form a heterogeneous coating in which the dye present spectrally responds primarily in the region of J-aggregation.

10. A method for the sensitization of photoconductors comprising the steps of protonating a methine dye capable of forming J-aggregates, combining the protonated dye with an electrically insulating polymeric material, neutralizing the protonated dye to form a heterogeneous composition in which the sensitizng dye present spectrally'responds predominantly in the region of J-aggregation and adding a sensitizing amount of the resulting heterogeneouscomposition to a photoconductive composition comprising an organic photoconductor in a polymeric hydrophobic binder.

11. An electrophotographic element comprising an electrically conductive support having coated thereon a photoconductive electrically insulating composition comprised of an organic photoconductor, an electrically insulating, film-forming polycarbonate resin binder, and a sensitizing amount of at least one cyanine dye capable of forming J-aggregates, said dye being present in the J-ag'gregated state and said composition being characterized in that it spectrally responds primarily in the region of J-aggregation of the dye.

12. An electrophotographic element as in claim 11 wherein the J-aggregated state of the dye is comprised of particles having a size of from about 2X10 to about lXlO mm.

13. An electrophotographic element as in claim 12 wherein the dye is anhydro-5,5,6,6'-t etrach1oro-l,1- diethyl-3,3'di(3-sulfobutyl)benzimidazolocarbocyanine hydroxide.

14. An electrophotographic element as in claim 12 wherein the dye is 3,3'-dimethyl-9-phenyl-4,4',5,5'- dibenzothiacarbocyanine bromide.

15. An electrophotographic element as in claim 12 wherein the dye is l-ethyl-l '-sulfobutylcyanine hydroxide.

16. An electrophotographic element as in claim 12 wherein the dye is 5,5',6,6-tetrachloro-l,1',3,3'- tetraethylbenzimidazolocarbocyanine chloride.

17. An electrophotographic element as in claim 12 wherein the dye is 2(-5,5'-dicyano-2,4-pentenylidene)- 3-ethylbenzothiazoline.

3 7 30 UNITED STATES PATENT OFFICE CERTIFICATE. OF CORRECTION 3,769,011 Dated October 30, .1973

Patent No. lnventqfls) Paul B. Gilman and Donald w.; H eseltine t error appears in the above-identified patent It is certified tha hereby corrected as shown below:

' and that said Letters Patent are Column 23, claim 9, first sentence, "sensitizing" should read --sensitized-- Signed and sealed this 1113511 day of May 1971+.

(SEAL) Attest: v

EDWARD II.FLETCIER,JR. 1 I c. MARSHALL DANN Atte sting Officer- Commissioner of Patents

Claims

2. A photoconductive composition as in claim 1 wherein the sensitizing dye is selected from the group consisting of cyanine, merocyanine and styryl dyes.
3. A photoconductive composition as in claim 1 wherein the sensitizing dye is selected from the group consisting of: 3,3-diethyl-5,5''-dimethyl-9-ethyl-thiacarbocyanine chloride, anhydro-5,5'',6,6''-tetrachloro-1,1'',3-triethyl-3''-(3 -sulfobutyl)benzimidazolocarbocyanine hydroxide, anhydro-1-ethyl-1-(4-sulfobutyl)-2,2''-cyanine hydroxide, 3,3''-dimethyl-9-phenyl-4,5 4'',5''-dibenzothiacarbocyanine bromide, anhydro-5,5'',6,6''-tetrachloro-1,1-diethyl-3,3''-di-(3 -sulfobutyl)benzimidazolocarbocyanine hydroxide, 5,5''-dichloro-1,1'',3,3''-tetramethylbenzimidazolocarbocyanine perchlorate 1'',3-diethylthia-2''-cyanine chloride 3,3'',9-triethylselenathiacarbocyanine perchlorate 3,3''-dimethyl-8,10 -diphenoxyoxacarbocyanine chloride 2-(5,5''-dicyano-2,4-pentenylidene)-3-ethylbenzothiazoline 3,3''-diethyl-9-methylthiacarbocyanine chloride 1''-ethyl-3-methylthia-2''-cyanine chloride 1,1''-diethyl-6,6''-dimethyl-2,2''-cyanine perchlorate 3,3'',9-triethyl-5,5''-diphenyloxacarbocyanine hydroxide anhydro-3,9-diethyl-3''-sulfobutyl-5,5''-dichlorothiacarbocyanine bromide 3,3''-dimethyl-9-ethylthiacarbocyanine bromide 3,3''-diethyl-9-methyl-4,5,4'',5''-dibenzothiacarbocyanine bromide 3,3''-dimethyl-9-phenyl-4,5,4'',5''-dibenzothiacarbocyanine bromide 1,1''-diethyl-2,2''-cyanine chloride 3''-ethyl-1-methyl-5,6''-dinitro-2-phenyl-3-indolothiacarbocyanine p-toluenesulfonate 2(2-(2-(4-bromophenyl) -6-methoxyimidazo(1,2-b)pyridazin-3-yl)vinyl)-3-ethyl-6-nitrobenzothiazolium p-toluenesulfonate anhydro-2-(2-(3,5-dimethyl-1-p-sulfophenyl-4-pyrozolyl)-vinyl) -3-ethylthiazolo( 4,5-b)quinolinium hydroxide 3''-ethyl-1-methyl -5,6''-dinitro-2-phenyl-3-indolothiacarbocyanine p-toluenesulfonate 1,3,3,3'' -tetramethyl-5,6''-dinitroindothiacyanine p-toluenesulfonate 2-((3,5-dimethyl-1-phenyl-4-pyrazolyl)vinyl)-3-ethylthiazolo( 4, 5-b)quinolinium chloride 3,3'',9-triethyl-5,5''-diphenyloxacarbocyanine bromide 3,3''-diethyl-9-methylthiacarbocyanine p-toluenesulfonate anhydro-6 -chloro-2-(2-(3,5-dimethyl-1-p-sulfophenyl-4-pyrazolyl)vinyl)-1,3 -diphenylimidazo(4,5-b)quinoxalinium hydroxide 6,7-dichloro-1'',3'', 3''-trimethyl-1,3-diphenylimidazo(4,5-b)-quinoxalinoindocarbocyanine iodide 4-p-dimethylaminobenzylidene-3-methyl-1,2,3,4-tetrahydropyrido/2,1 -b/benzothiazolium iodide 3''-ethyl-1-methyl-5,6''-dinitro-2-phenyl-3-indolothiacarbocyanine p-toluenesulfonate 2-((3,5-dimethyl-1-phenyl-4-pyrazolyl)vinyl)-1,3,3-trimethyl-3H-pyRrolo(2,3 -b)pyridinium iodide 1,3-diallyl-3''-methyl-6''-nitroimidazo( 4,5-b)quinoxalinothiacyanine p-toluenesulfonate 3-ethyl-6-nitro-2-(2-(1-phenyl-4-pyrazolyl)vinyl)benzothiazolium p-toluenesulfonate 2-(2-(1-(2-benzothiazolyl)3,5-dimethyl-4-pyrazolyl)vinyl)-3-ethyl-6 -nitrobenzothiazolium p-toluenesulfonate 1,3-diallyl-2-(2-(1-phenyl-4-pyrazolyl)vinyl)imidazo( 4,5-b)-quinoxalinium p-toluenesulfonate anhydro-2-(2-(3,5-dimethyl-1-p-sulfophenyl-4-pyrazolyl)- vinyl)-3-ethylthiazolo(4,5-b)quinolinium hydroxide 6,7-dichloro-2-(2-(1-methyl-2-phenyl-3-indolyl)vinyl)-1,3-diphenylimidazo( 4,5-b)quinoxalinium p-toluenesulfonate 1,3-diallyl-1''-methyl-5''-nitro-2''-phenylimidazo( 4,5-b)-quinoxalino-3''-indolocarbocyanine p-toluenesulfonate 3''-ethyl-1,3,3-trimethyl-5,6''-dinitroindothiacarbocyanine p-toluenesulfonate 5-chloro-2-(2-(3,5-dimethyl-1-phenyl-4pyrozolyl)vinyl)-1,3,3-trimethyl-3H-indolium iodide 1,1'',3,3''-tetraethylimidazo( 4,5-b)quinoxalinocarbocyanine chloride 3-((6,7-dichloro-1,3-diphenyl-1H-imidazo( 4,5-b)quinoxalin-2(3H)ylidene)ethylidene)-2H-pyrido( 1,2-a)pyrimidine-2,4-(3H)-dione 5,5''-dichloro-3,3''-diethyl-6,6''-dinitrothiacarbocyanine iodide 3-ethyl-6-nitro-2-(2-(1,3,5-triphenyl-4-pyrazolyl)vinyl)-benzothiazolium iodide 2-(2-(2-(4-bromophenyl)-6-methoxyimidazo(1,2-b)pyridazin-3-yl)vinyl)-3-ethyl-6-nitrobenzothiazolium p-toluene-sulfonate 2-(2-(2-(4-bromophenyl)-6-methoxyimidazo(1,2-b)pyridazin-3-yl)vinyl) -1,3,3-trimethyl-5-nitro-3H-indolium p-toluenesulfonate 3''-ethyl-6,6''-dinitro-1,3-diphenylimidazo( 4,5-b)quinoxalinothiacarbocyanine p-toluenesulfonate 1,3-diallyl-6''-nitro-1'',3''-diphenylimidazo( 4,5-b)quinoxalinocarbocyanine p-toluenesulfonate 1,3,3''-triethylimidazo( 4,5-b)quinoxalinothiacarbocyanine iodide 2-p-diethylaminostyryl-3-ethyl-6-(2-oxo-1-pyrrolidinyl) benzothiazolium.
4. A photoconductive composition as in claim 1 wherein the organic photoconductor is selected from the group consisting of a polyarylalkane and an arylamine.
5. An electrophotographic element comprising a conducting support having coated thereon an electrically insulating polymer binder material, an organic photoconductor and a sensitizing amount of at least one sensitizing methine dye which is present in the J-aggregated state and which spectrally responds primarily in the region of J-aggregation.
6. An electrophotographic element as in claim 5 wherein the sensitizing methine dye is selected from the group consisting of cyanine and merocyanine dyes.
7. An electrophotographic element as in claim 5 wherein the organic photoconductor is selected from the group consisting of polyarylalkane, arylamine, and 4-diarylamino-substituted chalcone photoconductors.
8. An electrophotographic element comprising a conducting support having coated thereon the photoconductive composition of claim 3.
9. A method for producing a sensitized photoconductive composition comprising the steps of combining in solution an organic photoconductor, an electrically insulating polymeric material and a charged form of a methine dye capable of forming J-aggregates, adding an Organic polymer having a charge of opposite polarity from said dye, mixing the combination, coating a layer of the combined materials on a conducting support and drying the coating to form a heterogeneous coating in which the dye present spectrally responds primarily in the region of J-aggregation.
10. A method for the sensitization of photoconductors comprising the steps of protonating a methine dye capable of forming J-aggregates, combining the protonated dye with an electrically insulating polymeric material, neutralizing the protonated dye to form a heterogeneous composition in which the sensitizng dye present spectrally responds predominantly in the region of J-aggregation and adding a sensitizing amount of the resulting heterogeneous composition to a photoconductive composition comprising an organic photoconductor in a polymeric hydrophobic binder.
11. An electrophotographic element comprising an electrically conductive support having coated thereon a photoconductive electrically insulating composition comprised of an organic photoconductor, an electrically insulating, film-forming polycarbonate resin binder, and a sensitizing amount of at least one cyanine dye capable of forming J-aggregates, said dye being present in the J-aggregated state and said composition being characterized in that it spectrally responds primarily in the region of J-aggregation of the dye.
12. An electrophotographic element as in claim 11 wherein the J-aggregated state of the dye is comprised of particles having a size of from about 2 X 10 6 to about 1 X 10 1mm.
13. An electrophotographic element as in claim 12 wherein the dye is anhydro-5,5'',6,6''-tetrachloro-1,1''-diethyl-3,3''-di(3 -sulfobutyl)benzimidazolocarbocyanine hydroxide.
14. An electrophotographic element as in claim 12 wherein the dye is 3,3''-dimethyl-9-phenyl-4,4'',5,5''-dibenzothiacarbocyanine bromide.
15. An electrophotographic element as in claim 12 wherein the dye is 1-ethyl-1''-sulfobutylcyanine hydroxide.
16. An electrophotographic element as in claim 12 wherein the dye is 5,5'',6,6''-tetrachloro-1,1'',3,3'' -tetraethylbenzimidazolocarbocyanine chloride.
17. An electrophotographic element as in claim 12 wherein the dye is 2(-5,5''-dicyano-2,4-pentenylidene)-3-ethylbenzothiazoline.