US3542544A - Photoconductive elements containing organic photoconductors of the triarylalkane and tetraarylmethane types - Google Patents

Description

United States Patent 3,542,544 PHOTOCONDUCTIVE ELEMENTS CONTAINING ORGANIC PHGTOCONDUCTORS OF THE TRI- %;III5\LKANE AND TETRAARYLMETHANE Edward J. Seas and Martin Goldman, Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N .Y., a corporation of New Jersey No Drawing. Continuation-impart of application Ser. No. 624,233, Mar. 20, 1967. This application Apr. 3, 1967, Ser. No. 627,857

Int. Cl. G03g 5/06 US. Cl. 96-15 16 Claims ABSTRACT OF THE DISCLOSURE Photoconductive elements containing amino-substituted 1,1,1-triarylalkanes and tetraarylmethanes as photoconductors are described. The described photoconductors canlbe sensitized and charged either negatively or positive y.

This application is a continuation-in-part application of our copending application titled the same as the present application filed on or about Mar. 20, 1967, having Ser. No. 624,233 and now abandoned.

This invention relates to photoconduction and to organic photoconductor-containing electrophotographic elements having photoconductivity when electrically charged.

An electrophotographic process, xerography, disclosed by Carlson in U.S. 2,297,691, employs an electrophotographic element comprising a conducting support material bearing a coating of a photoconductive material which is a normally insulating material whose electrical resistance varies with the amount of incident actinic radiation it received during an imagewise exposure. The electrophotographic element, commonly termed a photoconductive element, when used in a xerographic reproduction process is first given a uniform surface charge in the dark after a suitable period of dark adaptation. It is then exposed to a pattern of actinic radiation which has the effect of reducing the potential of the surface charge in accordance with the relative energy contained in various parts of the radiation pattern. The resultant differential surface charge or latent electrostatic image remaining on the electrophotographic element is then made visible by contacting the surface with a suitable electroscopic marking material. Such marking material or toner may be selected to be electrostatically responsive to the presence or absence of electrical charge on the surface in accordance with the imagewise charge pattern. The deposited marking material may then be either permanently fixed to the surface of the sensitive element by known means such as heat, pressure, solvent vapor, or the like, or transferred to a second element to which it may similarly be fixed.

Various photoconductive insulating materials have been employed in the manufacture of electrophotographic elements. Selenium and selenium alloys vapor deposited on a suitable support and particles of photoconductive zinc oxide held in a resinous, film-forming binder have found wide application in presentday document copying applications.

Recently, some organic compounds have been discovered which demonstrate a useful level of photoconductivity. Most organic photoconductors have the advantage of being capable of being uniformly coated in the form of a film or layer. Many organic photoconductor compositions, when coated as a. film or layer on a suitable support, yield an element which may be transparent and is generally reusable; that is, it can be used to form subsequent images. At the present time the search for organic compounds for use in photoconductor compositions to form electrophotographic layers has been forced to proceed on a compoundby-compound basis. Nothing has yet been discovered from the large number of known photoconductive substances which permits effective prediction of new compounds or structural relationships which will produce enhanced photo-conduction when used in electrophotographic applications.

It is an object of this invention to provide novel photoconductive elements containing at least one organic photoconductor in an amount suflicient to be useful in electrophotographic applications.

It is another object of this invention to provide novel photoconductive elements containing particularly effective specific photoconductive compounds.

It is still another object of the invention to provide novel electrophotographic elements containing colorless photoconductors that are stable to oxidation.

Likewise, it is an object of this invention to provide new eleetrophotographic elements that can be charged either positively or negatively.

It is a further object of this invention to provide new photoconductive elements containing organic photoconductive compounds that can be effectively sensitized to a high electrophotographic speed with sensitizer, particularly pyrylium, thiapyrylium, and selenapyrylium sensitizers.

These and other objects of the invention are accomplished with electrophotographic elements having coated thereon photoconductor compositions containing 1,1,1-triarylalkanes or tetraarylmethanes as photoconductors wherein there is substituted an amino group on at least one aryl group attached to the alkane or methane moieties of such photoconductors.

The amino groups comprising the present photoconductors can be unsubstituted amino groups (i.e., -NH and substituted amino groups such as those having the formula wherein each R can be an alkyl group or an aryl group such as phenyl or naphthyl, and including substituted alkyl and aryl groups. The R groups together can be the necessary atoms to form a heterocyclic amino group typically having 5 to 6 atoms in the ring such as morpholino, pyridyl, pyryl, etc. R is typically an alkyl group having 1 to 8 carbon atoms although longer chain lengths can be used. Likewise, one of such R groups can be a hydrogen atom and the other R group-can be an alkyl, alkoxy or aryl group as described. The amino group is preferably in the para or 4-position of the aryl group.

The aryl groups attached to either the alkane or methane moieties of the present photoconductors are preferably phenyl groups, although naphthyl groups can also be used. Such aryl groups can contain such substituents as alkyl and alkoxy typically having 1 to 8 carbon atoms, hydroxy, halogen, etc. Such substituents can be in the ortho, meta or para positions on the aryl groups. These aryl groups can also be joined together or cyclized to form a fiuorene moiety, for example.

The alkane moiety of the present 1,1,1-triarylalkane photoconductors has at least two carbon atoms, and typically 2 to 8 carbon atoms. 1,1,1-triphenylethanes are particularly useful.

The present photoconductors are not leuco base ma- ,terials and should thus be distinguished from such closely related compounds as triphenylmethanes and related dye precursors which can be readily oxidized to dyes.

3 Typical photoconductors of the invention can be illustrated by the following formula:

wherein each of X, R and Z are aryl groups and T is an alkyl group or an aryl group as described above, at least one of X, R or Z containing an amino substituent as described above.

The present photoconductors can be prepared by known procedures. For example, bis(4-N,N-dimethylamino)- 1,1,1-triphenylethane has been previously described by Braun (Ann. 472, 49 (1929)). 4-N,N-dimethylaminotetraphenylmethane was first prepared by Fischer and Luckmann (Hoppe-Seylers Z physiol. Chem., 115, 92 (1921) Electrophotographic elements of the invention can be prepared with the photoconducting compounds of the in- H vention in the usual manner, i.e., by blending a dispersion or solution of a photoconductive compound together with a binder, when necessary or desirable, and coating or forming a self-supporting layer with the photoconductorcontaining material. Mixtures of the photoconductors described herein can be employed. Likewise, other photoconductors known in the art can be combined with the present photoconductors. In addition, supplemental materials useful for changing the spectral sensitivity or electrophotosensitivity of the element can be added to the composition of the element when it is desirable to produce the characteristic effect of such materials.

Preferred binders for use in preparing the present photoconductive layers comprise polymers having fairly high dielectric strength which are good electrically insulating film-forming vehicles. Materials of this type comprise styrene-butadiene copolymers; silicone resins; styrenealkyd resins; silicon-alkyd resins; soya-alkyd resins; poly- (vinyl chloride); poly(vinylidene chloride); vinylidene chloride-acrylonitrile copolymers; poly(vinyl acetate); vinyl acetate-vinyl chloride copolymers; poly(vinyl acetals), such as poly(vinyl butyral); polyacrylic and methacrylic esters, such as poly(methylmethacrylate), poly(nbutylmethacrylate), poly(isobutyl methacrylate), etc.; polystyrene; nitrated polystyrene; polymethylstyrene; isobutylene polymers; polyesters, such as poly(ethylenealkaryloxyalkylene terephthalate); phenol-formaldehyde resins; ketone resins; polyamide; polycarbonates; polythiocarbonates; poly(ethyleneglycol 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. Pats. 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, Cyrnac, Piccopale 100, Saran F-220 and Lexan 105. 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, Z-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 1 weight percent of the coating composition. The upper limit in the amount of photoconductor substance present can be widely varied in accordance with usual practice. In those cases where a binder is employed, it is normally required 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 0.001 inch to about 0.01 inch before drying is useful for the practice of this invention. The preferred range of coating thickness was found to be in the range from about 0.002 inch to about 0.006 inch before drying although useful results can be obtained outside of this range.

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 relative humidity above 20 percent); aluminum-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 silver or aluminum and the like. An especially useful conducting support can be prepared by coating a support material such as polyethylene 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. 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. 3,007,901 and 3,267,807.

The elements of 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, the electrophotographic element is given a blanket electrostatic charge by placing the same under a corona discharge which serves to give a uniform charge to the surface of the photoconductive layer. This charge is retained by the layer owing to 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. By exposure of the surface in this manner, a changed pattern is created by virtue of the fact that light causes the charge to be conducted away in proportion to the intensity of the illumination in a particular area. The charge pattern remaining after exposure is then developed, i.e., rendered visible, by treatment with a medium comprising electrostatically attractable particles having optical density. The developing electrostatically attractable particles can be in the form of a dust, e.g., powder, a pigment in a resinous carrier, i.e., toner, or a liquid developer may be used in which the developing particles are carried in an electrically insulating liquid carrier. Methods of development of this type are widely known and have been described in the patent literature in such patents, for example, as U.S. Pat. 2,297,- 691, and in Australian Pat. 212,315. In processes of electrophotographic reproduction such as in 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 the 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 known in the art and have been described in a number of U.S. and foreign patents, such as U.S. Pats. 2,297,691 and 2,551,582, and in RCA Review, vol. 15 (1954), pages 469-484.

The present invention is not limited to any particular mode of use of the new electrophotographic materials, and the exposure technique, the charging method, the transfer (if any), the developing method, and the fixing method as well as the materials used in these methods can be selected and adapted to the requirements of any particular technique.

Electrophotographic materials according to the present invention can be applied to reproduction techniques wherein different kinds of radiations, i.e., electromagnetic radiations as well as nuclear radiations, can be used. For this reason, it is pointed out herein that although materials according to the invention are mainly intended for use in connection with methods comprising an exposure, the term electrophotography wherever appearing in the description and the claims, is to be interpreted broadly and understood to comprise both xerography and xeroradiography.

The photoconductive layers of the invention can also be sensitized to highly improved speed. Sensitizing compounds useful with the photoconductive compounds of the present invention can include a wide variety of substances such as pyrylium, thiapyrylium, and selenapyrylium salts of U.S. Pat. 3,250,615, issued May 10, 1966; fluorenes, such as 7,12dioxo-13-dibenzo(a,h)fluorene, 5,10-dioxo-4a, l l-diazabenzo(b)fiuorene, 3,13-di oxo-7-oxadibenzo(b,g) fiuorene, trinitrofluorenone, tetranitrofiuorenone and the like; aromatic nitro compounds of U.S. Pat. 2,610,120; anthrones of U.S. Pat. 2,670,285; quinones of U.S. Pat. 2,670,286; benzophenones of U.S. Pat. 2,- 670,287; thiazoles of U.S. Pat. 2,732,301; mineral acids; carboxylic acids, such as maleic acid, dichloroacetic acid, and salicylic acid; sulfonic and phosphoric acids; and various dyes such as triphenylmethane, diarylmethane, thiazine, azine, oxazine, xanthene, phthalein, acridine, azo, anthraquinone dyes and many other suitable sensitizing dyes. The preferred sensitizers for use with the compounds of this invention are pyrylium and thiapyrylium salts, fluorenes, carboxylic acids, and triphenylmethane dyes.

Where a sensitizing compound is to be used within a photoconductive layer as disclosed herein it is conventional practice to mix a suitable amount of the sensitizing compounds with the coating composition so that, after thorough mixing, the sensitizing compound is uniformly distributed throughout the desired layer of the coated element. In preparing the photoconducting layers, no sensitizing compound is needed for the layer to exhibit photoconductivity. The lower limit of sensitizer required in a particular photoconductive layer is, therefore, zero. However, since relatively minor amounts of sensitizing compound give substantial improvement in the electrophotographic speed of such layers, the use of some sensitizer is preferred. The amount of sensitizer that can be added to a photoconductor-incorporating layer to give effective increases in speed can vary widely. The optimum concentration in any given case will vary with the specific photoconductor and sensitizing compound used. In general, substantial speed gains can be obtained where an appropriate sensitizer is added in a concentration range from about 0.0001 to about 30 percent by weight based on the weight of the film-forming coating composition Normally, a sensitizer is added to the coating composition in an amount by weight from about 0.005 to about 5.0 percent by weight of the total coating composition.

The invention will now be described by reference to the following examples.

EXAMPLE 1 Organic photoconductors of the type described herein are separately incorporated into a coating dope having the following composition:

Organic photoconductor0.15 g. Polymeric binder-0.50 g.

Sensitizer-0.002 g. Methylene chloride-5 ml.

These compositions are then separately coated at a wet thickness of 0.004-inch on an aluminum surface maintained at F. to provide the coatings described in Tables 1 and 2 below. In a darkened room, the surface of each of the photoconductive layers, so prepared, is charged to a potential of about +600 volts under a corona charger. The layer is then covered with a transparent sheet bearing a pattern of opaque and light-transmitting areas and exposed to the radiation from an incandescent lamp with an illumination intensity of about 75 meter-candles for 12 seconds. The resulting electrostatic latent image is developed in the usual manner by cascading over the surface of the layer a mixture of negatively charged black thermoplastic toner particles and glass beads. A good reproduction of the pattern resulted in each instance. The relative speed of a coating is determined on the basis of the reciprocal of the exposure required to reduce the potential of the surface charge by 100 volts as measured by an electrometer probe. The speeds of the coatings are reported in Table 1 compared to the speed of a coating containing only the sensitizer and the polymeric binder. In Table 2 relative speeds are reported compared to the speed of a coating containing only photoconductor and polymeric binder. The polymeric binder used in the coating composition is a polyester of terephthalic acid and a mixture of ethylene glycol and 2,2-bis(4-hydroxyethoxyphenyl)propane (1 part by Weight of ethylene glycol and 9 parts by weight of 2,2-bis (4-hydroxyethoxyphenyl) propane). The sensitizers referred to in the tables are as follows:

Ano sensitizer added B2,6-bis(4-ethylphenyl) 4 (4-amyloxyphenyl)-thiapyrylium perchlorate C2,4,7-trinitrofluorenone D-Crystal Violet ERhodamine B 1 Surface potential reduced 100 volts below initial potential.

EXAMPLE .2

The photoconductors described in Table 3 are incorporated separately into a coating dope, coated separately, charged positively or negatively as indicated in Table 3, exposed and developed as described in Example 1 except that the surface potential is reduced to 100 volts rather than being reduced by 100 volts. Sensitizer F referred to in Table 3 is 2,4-bis(4-ethoxyphenyl) 6 (4-amyloxystyryl)pyrylium tetrafluoroborate and Sensitizer B is identified in Example 1.

TABLE 3 Speeds of photoconductive coatings (surface potential Photoconduetor Bis (4-N,N-dimethyl-amino)-1,1,1-triphenylethane 1-(i-N,N-dimethyl-aminophenyD-l,l-diphenylethane 1,1,1-tris (4-N,N-dimethylaminophenyl) ethane 1,1-bis (4-N,N-diethylaminophenyl)-1-phenylethane Q-methyl-Q-(4-N,N-di-rnethylaminophenyl)-fluorene 11,04,112 ,d-tetra-phenyl-a,a-bis-(4-N,N-diethylaminophenyl) 4-N,N-diethylamino-tetraphenylmethane 4- N-di-n-propylaminotetrapthenylmethane :N-diethylamino-2-methyltetraphenylmethane. 4 ,N-diethylarninoi-methyltetraphenylmethan 4,4-bis(N,N-diethyl-amino)-tetraphenylmethane 4-N,N-diethylamino-Z-methyltetraphenylmethane.

N-dibenzylamino-tetraphenylmethane 1 Speed not determined.

Test coating containing no photoconductor have zero speed. Other triarylethanes and tetraarylmethanes which can be used as the photoconductor in the same concentrations as described above are l,l-bis(N,N-diethylaminophenyl) 1 (4-methylphenyl)ethane; a,ot,a',a'-tetrakis (4N,N-diethylaminophenyl)-a,a'-bis (4 dimethylaminophenyl(p-xylene; oz,ot,ot,ct',u',et'-h6Xak1S (4 diethylaminophenyl)-p-xylene; 4-N,N-di-isopropylamino 2 methyltetraphenylmethane; 4,4',4",4"' tetrakis(N,N-dimethy1 amino)tetraphenylmethane; and, 4-N,N-diethylamino-2- ethoxytetraphenylmethane.

EXAMPLE 3 For purposes of comparison several photoconductive coatings of the invention can be compared with closely related photoconductive coatings containing a leuco base material as a photoconductor. The coatings are prepared and tested as described in Example 2, Dye B being the sensitizer in each coating.

1 Surface potential reduced to 100 volts. 5 Photoconductor A is a leuco base or dye precursor.

EXAMPLE 49 dropwise during a 15-minute period. The solution was refluxed for 2 hours. After the addition of 200 ml. of ether and 100 ml. of water, enough sodium chloride and ammonium chloride were added to saturate the solution. The aqueous phase and the organic phase separated. After washing with water and drying over anhydrous magnesium sulfate, the organic layer was evaporated. The residue was slurred with 150 ml. of petroleum ether, collected, and washed with more petroleum ether. After air drying, 25.2 g. of yellow solid, M.P. 109-1l9 (sintering at was obtained. After recrystallization from cyclohexane, 9.25 g. of 9-(p-dimethylaminophenyl)-9-fiuorenol was obtained as pale yellow plates, M.P. 155-158". The analytical sample obtained by recrystallization from cyclohexane-ethyl acetate (5 to 1) had an M.P. of 156-l59.

Calcd. C H NO (percent): C, 83.8; H, 6.3; N, 4.65. Found (percent): C, 84.0; H, 6.1; N, 4.6.

6.0 g., 0.02 mole, of 9-(p-dimethylarninophenyl)-9- fiuorenol and 0.5 g., .0026 mole, of p-toluenesulfonic acid were combined in ml. of methanol. The solution was refluxed for 2 hours. Upon cooling to room temperature, crystals separated which were collected by filtration and washed with small portions of methanol. After air drying, 4.25 g. of 9-(p-dimethylaminophenyl)-9-fluorenyl methyl ether were obtained as oif-white plates, M.P. 111-112. Recrystallization from methanol gave 3.15 g. of oil-white plates, M.P. Ill-113.

Calcd. C H NO (percent): C, 83.9; H, 6.7; N, 4.45. Found (percent): C, 84.2; H, 6.4; N, 4.5.

2.15 g., .00682 mole, of 9-(p-dimethylamin0phenyl)-9- fluorenyl methyl ether in 40 ml. of dry benzene was added to a methyl magnesium iodide solution prepared from 4.55 g., 0.032 mole, of methyl iodide and 0.8 g., 0.0333 mole, of magnesium in 40 ml. of anhydrous ether. After refluxing for 17 hours, 10 ml. of water was added dropwise over a 10-minute period. 15 g. of ammonium chloride and 50 ml. of water were added, whereupon the aqueous phase and the organic phase separated. The organic phase was washed with several changes of water, dried over anhydrous magnesium sulfate and the solvent evaporated. 1.55 g. of white solid, M.P. 109-116", resulted. Upon recrystallization from petroleum ether, 0.5 g. of 9-(p-dimethylaminophenyl)-9 methylfluorene, M.P. 1185-121" was obtained as an off-white solid. An additional 0.4 g. of product was obtained from the filtrate after cooling as a pale yellow solid, M.P. 1l6.5119.

Calcd. C H N (percent): C, 88.3; H, 7.0; N, 4.7. Found (percent): C, 88.4; H, 7.3; N, 4.5.

70 Methyl-9-(4-N,N-dimethylaminophenyl)fluorene EXAMPLE 5 Lithium wire 3.0 g., 0.44 mole) was added to a soluaflflfld-Tetraphenyl-u,a'bwP'dlethylammtion of p-bromo-N,N-dimethylaniline in ml. anhy phenyl'p'xylene drous ether with stirring. After 30 minutes, 9-fluorenone 75 To 50 ml. acetic anhydride was added 2.7 g. (0.018

(36 g., 0.20 mole) in 150 ml. dried benzene was added mole) N,N-diethylaniline and 2.0 g. (0.0045 mole) on,a,a,a-tetraphenyl-u,u'-dihydroxy p xylene. The solution was refluxed under nitrogen for 17 hours, cooled and filtered. The precipitate was extracted with boiling methanol and washed with ethyl ether. After drying, 1.4 g. (41%) of product were obtained, M.P. 232.8234.8 C. (corrected).

Calcd. (percent): C, 88.57; H, 7.45; N, 3.97. M.W. 705.

Found (percent): C, 88.4; H, 7.3; N, 3.9. M.W. 680.

All temperatures are given in degrees centigrade.

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 as described hereinbefore and as defined in the appended claims.

We claim:

1. An electrophotographic element comprising a conductive support having coated thereon a photoconductive composition comprising a film-forming polymeric binder and a photoconductor selected from the group consisting of 1,1,1-triarylalkanes wherein the alkane moiety has 2 to 8 carbon atoms and tetraarylmethanes, there being substituted an amino group on at least one of the aryl groups attached to the alkane and methane moieties.

2. An electrophotographic element comprising a conductive support having coated thereon a photoconductive composition comprising a film-forming polymeric binder and a 1,1,1-triphenylalkane wherein the alkane moiety has 2 to 8 carbon atoms, at least one of the phenyl groups of said 1,1,1-triphenylalkane being a p-aminophenyl group.

3. An electrophotographic element comprising a conductive support having coated thereon a photoconductive composition comprising a film-forming polymeric binder and a tetraphenylmethane, at least one of the phenyl groups of said tetraphenylmethane being a p-aminophenyl group.

4. An electrophotographic element as described in claim 1 wherein the photoconductive composition contains a sensitizing amount of a sensitizer selected from the group consisting of pyrylium, thiapyrylium and selenapyrylium salts.

5. An electrophotographic element as described in claim 2 wherein the alkane moiety is ethane.

6. An electrophotographic element as described in claim 2 wherein the amino of the p-aminophenyl group has-the formula:

wherein each R substituent is an alkyl group having 1 to 8 carbon atoms.

7. An electrophotographic element as described in claim 3 wherein the amino of the p-aminophenyl group has the formula:

wherein each R substituent is an alkyl group having 1 to 8 carbon atoms.

8. An electrophotographic element as described in claim 2 wherein the 1,1,1-triphenylalkane is bis(4-N,N- dimethylamino)-1,1,1-triphenylethane.

9. An electrophotographic element as described in claim 2 wherein the 1,1,1-triphenylalkane is 1- (4-N,N-dimethylaminophenyl 1,1-diphenylethane.

10. An electrophotographic element as described in claim 2 wherein the 1,1,1-triphenylalkane is 1,1-bis(4- N,N-diethylaminophenyl) -1-phenylethane.

11. An electrophotographic element as claim 3 wherein the tetraphenylmethane methylaminotetraphenylmethane.

12. An electrophotographic element as claim 3 wherein the tetraphenylmethane ethylaminotetraphenylmethane.

13. An electrophotographic element as claim 3 wherein the tetraphenylmethane ethylamino-4'-methyltetraphenylmethane.

14. An electrophotographic element as described in claim 4 wherein the sensitizer is a 2,6-bis(4-ethylphenyl)- 4-(4-amyloxyphenyl)thiapyrylium salt.

15. An electrophotographic element as described in claim 4 wherein the sensitizer is a 2,4-bis(4-ethoxyphenyl) -6- 4-amyloxystyryl) pyrylium salt.

16. In an electrophotographic process where in an electrostatic charge pattern is formed on a photoconductive element, the improvement characterized in that said photoconductive element has a photoconductive layer comprising a film-forming polymeric binder and an organic compound selected from the group consisting of 1,1,1-triarylalkanes wherein the alkane moiety has 2 to 8 carbon atoms and tetraarylmethanes, there being substituted an amino group on at least one of the aryl groups attached to the alkane and methane moieties.

described in is 4-N,N-didescribed in is 4-N,N-didescribed in is 4-N,N-di- References Cited UNITED STATES PATENTS 3,274,000 9/1966 Noe et a1. 96l.5 3,418,371 12/1968 Krimm et a1 260-393 X FOREIGN PATENTS 1,318,863 1/1963 France.

GEORGE F. LESMES, Primary Examiner R. E. MARTIN, Assistant Examiner U.S. Cl. X.R.