The present invention provides an electrophotographic photoreceptor consisting essentially of an electrically conductive substrate and a photosensitive layer containing at least one charge transport material selected from the compound shown by formulae (1), (2), (3), (4), and (5): ##STR1## and at least one charge generating material selected from pyrrolopyrrole compounds of formula (6) ##STR2##

The present invention relates to electrophotographic photoreceptors e.g. 
for laser beam printers, plain paper copiers and combinations thereof, and 
to novel nitrogen-containing compounds which can be used as charge 
transport material in electrophotographic photoreceptors. 
Various electrophotographic photoreceptors have been suggested, such as 
those comprising inorganic or organic photoconductive compounds. 
Particularly in recent years, systems comprising a charge generating 
material and a charge transport material have been intensively 
investigated. JP Patent Kokais Sho 59-114 545, Sho 59-228 652, 60-151 645, 
60-162 260, 61-35 451 and 63-95 457, and EP Patent Application No. 99 552 
disclose electrophotographic photoreceptors comprising diazo pigments as 
charge generating material in combination with various charge transport 
materials. Having accomplished a new pyrrolopyrrole type charge generating 
material, U.S. Pat. No. 4,632,893 discloses an electrophotographic 
photoreceptor comprising the following compound 
##STR3## 
as charge generating material and the hydrazone compound of the following 
formula 
##STR4## 
as charge transport material. Although such compositions generally possess 
good properties, they do not always satisfy modern technological demands. 
The purpose of the present invention is therefore to provide an 
electrophotographic photoreceptor with higher sensitivity and lower 
residual potential containing a hydrazone and/or enamine compound or a 
specific nitrogen-containing compound, as well as some new hydrazone 
compounds which function as an excellent electrophotographic charge 
transport material when used in combination with a pyrrolopyrrole compound 
.

The electrophotographic photoreceptor of the present invention has very 
flat photosensitivity characteristic from the visible light region to the 
near IR and the material is therefore applicable to both laser beam 
printers and plain paper copiers as well as combinations of both devices. 
A small variation in the chemical structure of the charge transport 
material surprisingly has a very big effect on the photographic properties 
of the photosensitive layer. The electrophotographic photoreceptor of the 
present invention exhibits improved electrophotographic properties, 
especially higher sensitivity and lower residual potential, compared with 
the known combination of a hydrazone derivative with a pyrrolopyrrole 
compound shown in U.S. Pat. No. 4,632,893. 
The electrophotographic photoreceptor of the present invention comprises an 
electrically conductive substrate and a photosensitive layer containing at 
least one charge transport material selected from the compound of the 
formulae (1), (2), (3), (4) and (5): 
##STR5## 
wherein R.sub.1 represents hydrogen, C.sub.1 -C.sub.4 alkyl, phenyl or 
phenyl substituted by halogen, C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 
alkoxy, C.sub.2 -C.sub.8 -dialkylamino or diaralkylamino of which the 
ring(s) may have at least one substituent selected from C.sub.1 -C.sub.4 
alkyl, C.sub.1 -C.sub.4 alkoxy, nitro and halogen, 
R.sub.2 represents naphthyl, anthryl or styryl which may be substituted by 
C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy or C.sub.2 -C.sub.8 
dialkylamino, pyridyl, furanyl, or thiophenyl or a group of formula 
##STR6## 
wherein R.sub.5, R.sub.7 and R.sub.9 represent independently hydrogen, 
halogen, C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy, nitro, hydroxyl, 
C.sub.2 -C.sub.8 dialkylamino, or diphenylamino, R.sub.6 represents 
hydrogen, halogen, C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy, nitro, 
hydroxyl, C.sub.2 -C.sub.8 dialkylamino, mono-C.sub.1 -C.sub.4 
alkyl-monophenylamino or diarylamino or diaralkylamino of which the 
ring(s) may have at least one substituent selected from C.sub.1 -C.sub.4 
alkyl, C.sub.1 -C.sub.4 alkoxy, nitro and halogen, R.sub.8 represents 
hydrogen, C.sub.1 -C.sub.4 alkyl or C.sub.1 -C.sub.4 alkoxy, or R.sub.6 
and R.sub.7 jointly form methylendioxy, 
R.sub.3 represents C.sub.1 -C.sub.4 alkyl, aryl or aralkyl optionally 
substituted by C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy and/or 
halogen, 
R.sub.4 represents C.sub.1 -C.sub.4 alkyl, aryl or aralkyl optionally 
substituted by halogen, C.sub.1 -C.sub.4 alkyl and/or C.sub.1 -C.sub.4 
alkoxy, and 
n represents 0 or 1; 
##STR7## 
wherein R.sub.10 represents C.sub.1 -C.sub.4 alkyl which may be 
substituted by C.sub.1 -C.sub.4 alkoxy, aryl, hydroxyl and/or halogen, 
R.sub.11 represents hydrogen, halogen, C.sub.1 -C.sub.4 alkyl, C.sub.1 
-C.sub.4 alkoxy, C.sub.2 -C.sub.8 dialkylamino or nitro, 
R.sub.12 represents C.sub.1 -C.sub.4 alkyl, aryl which may be substituted 
by C.sub.1 -C.sub.4 alkyl and/or C.sub.1 -C.sub.4 alkoxy, or aralkyl, 
R.sub.13 represents C.sub.1 -C.sub.4 alkyl, aryl or aralkyl, and 
n represents 0 or 1, 
provided that, when R.sub.10 represents ethyl and R.sub.11 represents 
hydrogen, R.sub.12 and R.sub.13 do not simultaneously represent phenyl; 
##STR8## 
wherein C represents C.sub.1 -C.sub.4 alkyl, aralkyl optionally 
substituted by halogen, C.sub.1 -C.sub.4 alkyl or C.sub.1 -C.sub.4 alkoxy 
or a group of the formula 
##STR9## 
wherein R.sub.14, R.sub.15, R.sub.16 and R.sub.17 are the same or different 
and represent hydrogen, C.sub.1 -C.sub.4 alkoxy, C.sub.2 -C.sub.8 
dialkylamino, mono-C.sub.1 -C.sub.4 alkyl-monoarylamino, diarylamino or 
diaralkylamino optionally substituted by C.sub.1 -C.sub.4 alkyl, C.sub.1 
-C.sub.4 alkoxy and/or halogen; 
##STR10## 
wherein R.sub.18 is hydrogen, C.sub.1 -C.sub.4 alkyl, phenyl or phenyl 
substituted by C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy or C.sub.2 
-C.sub.8 dialkylamino or containing a methylendioxy bridge, R.sub.19 is an 
optionally substituted aryl, or a condensed carbocyclic or heterocyclic 
aromatic group, R.sub.20 is hydrogen, C.sub.1 -C.sub.4 alkyl, C.sub.1 
-C.sub.4 alkoxy, optionally substituted aryl or C.sub.2 -C.sub.8 
dialkylamino, and Z represents an optionally substituted oxygen- or 
sulfur-containing group which may form a condensed ring with a benzene 
ring; and 
##STR11## 
wherein R.sub.21 and R.sub.22 independently from each other are hydrogen, 
C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy, mono-C.sub.1 -C.sub.4 
alkyl-monoarylamino or C.sub.2 -C.sub.8 dialkylamino; and at least one 
charge generating material selected from pyrrolopyrrole compounds of 
formula (6) 
##STR12## 
wherein A and B represent independently from each other C.sub.1 -C.sub.4 
alkyl, aralkyl, cycloalkyl or a carbocyclic or a heterocyclic aromatic 
radical, and R.sub.23 and R.sub.24 represent independently from each other 
hydrogen or substituents which shall not provide water solubility. 
According to the above definitions in the formulae (1) to (5): 
examples of C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy and C.sub.2 
-C.sub.8 dialkylamino are e.g. methyl, ethyl, n-propyl, isopropyl, n-butyl 
and tert-butyl; methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy and 
tert-butoxy; dimethylamino, diethylamino, methylethylamino, dipropylamino 
or dibutylamino; 
Mono-C.sub.2 -C.sub.4 -alkyl-monophenylamino may be e.g. 
methyl-phenylamino, ethyl-phenylamino; 
Diaralkylamino optionally substituted by C.sub.1 -C.sub.4 alkyl or C.sub.1 
-C.sub.4 alkoxy is e.g. dibenzylamino or di(3-methylphenylmethyl)-amino; 
Optionally substituted aralkyl is e.g. benzyl, chlorobenzyl; 
Halogen in the above formulae is e.g. chlorine or bromine; 
R.sub.6 and R.sub.14 to R.sub.17 as diarylamino may be e.g. diphenylamino; 
Optionally substituted aryl is e.g. phenyl, naphthyl, anthryl, bromophenyl, 
chlorophenyl, methylphenyl, methoxyphenyl, ethoxyphenyl, 
methyl-ethylaminophenyl, diethylaminophenyl, diphenylaminophenyl, or a 
group of the formula 
##STR13## 
R.sub.10 as C.sub.1 -C.sub.4 alkyl which may be substituted is e.g. methyl, 
ethyl, n-propyl, n-butyl, chloroethyl, or hydroxyethyl; 
Z as optionally substituted oxygen- or sulfur-containing group which may 
form a condensed ring with a benzene ring is e.g. a group of the following 
formulae: 
##STR14## 
A und B in formula (6) as alkyl groups may be branched, unbranched, 
saturated or unsaturated, and contain preferably 1 to 18, most preferably 
1 to 12, carbon atoms, e.g. methyl, ethyl, n-propyl, isopropyl, n-butyl, 
sec-butyl, tert-butyl, tert-amyl, n-pentyl, n-hexyl, 
1,1,3,3-tetramethylbutyl, n-heptyl, n-octyl, nonyl, decyl, undecyl, 
dodecyl or stearyl. 
A and B as aralkyl groups are preferably those which contain a preferably 
mono- or bicyclic aryl radical which is attached through a branched or 
unbranched alkyl group containing 1 to 6 and preferably 1 to 4, carbon 
atoms. Examples of such aralkyl groups are benzyl and phenylethyl. 
A and B or R.sub.19 as carbocyclic aromatic radicals are preferably mono- 
or bicyclic radicals, e.g. phenyl, diphenyl or naphthyl radicals. 
A and B or R.sub.19 as heterocyclic aromatic radicals are preferably mono- 
to tricyclic radicals. Said radicals may be purely heterocyclic or may 
contain a heterocyclic ring and one or more fused benzene rings and at 
least one nitrogen atom, one oxygen atom or one sulfur atom, e.g. pyridyl, 
furanyl and thiophenyl, or carbazolyl, N-methyl-and N-ethylcarbazolyl. 
R.sub.23 and R.sub.24 in formula (6) as substituents which do not impart 
solubility in water are for example branched or unbranched, saturated or 
unsaturated alkyl groups containing preferably 1 to 18, most preferably 1 
to 12, carbon atoms. These groups may be unsubstituted or substituted by 
hydroxy, halogen, alkoxy or cyano. Examples of such groups are methyl, 
ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, tert-amyl, 
n-pentyl, n-hexyl, allyl, hydroxymethyl, hydroxyethyl, 
1,1,3,3-tetramethylbutyl, n-heptyl, n-octyl, nonyl, decyl, undecyl, 
dodecyl, stearyl, trifluoromethyl, trifluoroethyl or cyanoethyl. 
R.sub.23 and R.sub.24 may also be aryl groups, preferably unsubstituted 
phenyl or phenyl substituted by halogen, C.sub.1 -C.sub.12 alkyl, C.sub.1 
-C.sub.12 alkoxy, C.sub.1 -C.sub.12 alkylmercapto, trifluoromethyl or 
nitro. 
Those compounds of formula (6) wherein R.sub.23 and R.sub.24 are hydrogen 
are of particular interest. 
Preferred compounds of formula (6) are those wherein A and B are identical 
radicals of formula 
##STR15## 
wherein one of the substituents X.sub.3 and Y.sub.3 is a hydrogen, 
chlorine or bromine atom, a methyl, cyano, N,N-dimethylamino, 
N,N-diethylamino, C.sub.1 -C.sub.5 alkoxy, C.sub.1 -C.sub.5 alkylmercapto 
or C.sub.2 -C.sub.4 alkoxycarbonyl group, and the other substituent is a 
hydrogen atom. X.sub.3 and Y.sub.3 are for example in ortho-, meta- or 
para-position, preferably in meta- or para-position. 
Preferred one is the so-called DTPP compound of the formula 
##STR16## 
The compounds of formula (6) are described in U.S. Pat. No. 4,632,893 and 
can be obtained according to the methods described therein. 
Preferred charge transport materials are selected from the compounds of 
formula (1), formula (2), formula (3) and formula (4), wherein: 
In formula (1) 
R.sub.1 represents hydrogen, phenyl or phenyl substituted by C.sub.1 
-C.sub.4 alkoxy or C.sub.2 -C.sub.8 dialkylamino. 
R.sub.2 represents a group of the following formula 
##STR17## 
wherein Y.sub.1 represents hydrogen or C.sub.1 -C.sub.4 alkoxy and Y.sub.2 
represents hydrogen, C.sub.1 -C.sub.4 alkoxy, methyl-phenylamino or 
diphenylamino, 
R.sub.3 represents phenyl, R.sub.4 represents methyl or phenyl, and n 
represents 0 or 1; in formula (2), R.sub.10 represents C.sub.1 -C.sub.4 
alkyl, R.sub.11 represents hydrogen, R.sub.12 represents C.sub.1 -C.sub.4 
alkyl or phenyl, R.sub.13 represents phenyl, and n represents 0; 
in formula (3) C represents methyl, benzyl or a group of formula 
##STR18## 
wherein R.sub.14, R.sub.15, R.sub.16 and R.sub.17 represent independently 
H or C.sub.1 -C.sub.4 alkoxy; and in formula (4) R.sub.18 and R.sub.19 are 
phenyl or phenyl substituted by methoxy, R.sub.20 is hydrogen and Z is a 
bridge of formulae --CH.sub.2 CH.sub.2 --, 
##STR19## 
--CH.sub.2 CH.sub.2 CH.sub.2 -- or 
##STR20## 
Examples of charge transfer material (CTM) of formula (1), wherein n 
represents 1, are: 
##STR21## 
Examples of CTM of formulae (1), wherein n represents 0, are: 
##STR22## 
Examples of CTM of formula (2) are: 
##STR23## 
Examples of CTM of formula (4) are: 
##STR24## 
Particularly preferred ones are compounds of the formulae: 
##STR25## 
Especially preferred ones are the compounds of formulae: 
##STR26## 
The above compounds Nos. 114, 115 and 120 are novel and also constitute an 
object of the present invention. They can be prepared from 
3-N,N-4'-dimethylaminophenylacrolein, 
3-(4'-methoxyphenyl)-3-(4"-dimethylaminophenyl)acrolein and 
2,4-dimethoxybenzaldehyde by reacting with a 1,1-diphenylhydrazine salt by 
a conventional method, respectively. 
The compounds of formula (4) are disclosed in JP Patent Kokai-Sho 63-95 
457. The compounds of formulae (1), (2), (3) and (5) can be prepared 
according to known methods e.g. according to JP Patent Kokais Sho 60-162 
260 and Sho 59-114 545. 
The charge transport materials of formulae (1), (2), (3), (4) and (5) can 
be used together with other charge transport materials in any amounts 
provided that the charging property and the photosensitive property are 
not impaired. 
Examples of such compounds are: 
hydrazone type compounds other than those shown by formulae (1) and (2), 
amine derivatives such as 
4,4',4'-tris(4-diethylaminophenyl)triphenylamine, nitrogen-containing 
cyclic compounds such as indole type compounds, oxazole type compounds, 
isooxazole type compounds, thiazole type compounds, thiadiazole type 
compounds, imidazole type compounds, pyrazole type compounds, triazole 
type compounds, condensed polycyclic compounds, pyrazoline type compounds 
such as 1-phenyl-3-(p-dimethylaminophenyl)pyrazoline, carbazole type 
compounds such as polyvinyl carbazole, oxadiazole type compounds such as 
2,4-di(4-dimethylaminophenyl)-1,3,4-oxadiazole, conjugate type compounds 
such as 1,1-diphenyl-4,4-bis(4-dimethylaminophenyl)-1,3-butadiene, 
nitrated compounds such as 2,4,8-trinitrothioxanthone and 
dinitroanthracene, succinic anhydride, maleic anhydride, dibromomaleic 
anhydride, fluorenone type compounds such as 2,4,7-trinitro-fluorenone, 
styryl type compounds such as 9-(4-diethylaminostyryl)anthracene, and 
tetracyanoethylene. 
The pyrrolopyrrole compounds of formula (6) have a low absorption in the 
NIR-region (near infrared, where the AlGaAs-laser diodes emit light). The 
NIR-absorption and photoconduction can however be greatly enhance by the 
method described in U.S. Pat. No. 4,632,893. 
The pyrrolopyrrole compounds of formula (6) may be jointly used with other 
charge generating materials in any ratio that does not adversely affect 
the photosensitive property. 
Examples of such charge generating material may be selenium, 
selenium-tellurium, amorphous silicon, pyrylium salts, azo type compounds, 
diazo type compounds, phthalocyanine type compounds, anthanthrone type 
compounds, perylene type compounds, indigo type compounds, 
triphenylmethane type compounds, threne type compounds, toluidine type 
compounds, pyrazoline type compounds, and quinacridone type compounds. 
The electrically conductive substrate may be in the form of a plate, drum 
or sheet which may have rough or pretreated surfaces. The substrate may be 
made of an electrically conductive material or a electrically 
non-conductive material covered with an electrically conductive material. 
Examples of such substrates are aluminum, copper, tin, platinum, titanium, 
nickel, palladium, indium, their alloys, stainless steel, brass, etc. In 
the case of aluminum, pretreatment may consist on anodisation. The plastic 
material which have been vapor-blasted, vacuum deposited or superposed 
with the above-mentioned metals, glass plates coated with aluminum iodide, 
tin oxide, indium oxide or indium-tin-oxide (ITO), may be also cited as 
examples. Preferred substrate is the pretreated aluminum mentioned above. 
The photosensitive layer for the electrophotographic photoreceptor of the 
present invention contains the pyrrolopyrrole compound of formula (6) to 
generate charge carriers when subjected to exposure, and this material 
will be used together with the charge transport material of formulae (1), 
(2), (3), (4) and (5) present in said layer. Such a layer makes it 
possible, after integral electrostatic charging and imagewise exposure, to 
produce corresponding latent images which can be visualised by toners. 
The photosensitive layer may contain further additives such as conventional 
sensitizers, plasticizers, deterioration inhibitors such as antioxidants 
and ultraviolet absorbers and the like. 
Examples of the sensitizers may be terphenyl, halogennaphthoquinones and 
acenaphthylene, quenchers represented by fluorene type compounds like 
9-(N,N-diphenylhydrazino)fluorene and 9-carbazolyliminofluorene. 
The photosensitive layer may be a mono layer or a multi layer. If the layer 
is a mono layer, then this contains one or more charge generating 
materials of formula (6) and one or more charge transport materials of 
formulae (1), (2), (3), (4) and (5) and an organic binder. In the case of 
a multi layer, a double layer is the focus of interest, and this double 
layer comprises a charge generating layer containing one or more 
pyrrolopyrrole compounds of formula (6) and a charge transport layer 
containing one or more charge transport materials of formulae (1), (2), 
(3), (4) and (5) and an organic binder. If the photosensitive layer 
consists of a mono layer, the mixing ratio of the charge generating 
material, charge transport material and the binding agent is not critical, 
but can be determined depending on the characteristics required for a 
desired electrophotographic photoreceptor. 
Electrophotographic photoreceptor of mono layer type can be obtained by 
preparing a dispersion containing one or more charge generating materials 
of formula (6) and one or more charge transport materials of formulae (1), 
(2), (3), (4) and (5) dispersed finely in an organic binder and optionally 
an organic solvent and applying it onto the above mentioned electrically 
conductive substrate, drying, removing the solvent, if any, and/or curing 
it. 
Suitable organic solvents are exemplified by aliphatic hydrocarbons such as 
n-hexene, octane and cyclohexane; aromatic hydrocarbons such as benzene, 
toluene and xylene; halogenated hydrocarbons such as dichloromethane, 
dichloroethane, carbon tetrachloride and chlorobenzene; esters such as 
ethyl acetate and methyl acetate; dimethyl formamide, dimethyl sulfoxide, 
ethers such as dimethyl ether, diethyl ether, tetrahydrofuran (THF), 
ethylene glycol dimethyl ether, ethylene glycol diethyl ether and 
diethylene glycol dimethyl ether; ketones such as acetone, methyl ethyl 
ketone and cyclohexanone, or mixtures of these solvents. 
In the preparation of the dispersion, a leveling agent, surfactant etc. may 
be added to improve the dispersibility and coating property. 
In the case of multi layers, the order of the layers is not critical. For 
example, the charge transport layer can be prepared on the electrically 
conductive substrate, and the charge generating layer is then applied 
thereon, or vice-versa. 
The charge generating layer may be formed by vaporizing or sputtering under 
vacuum the pyrrolopyrrole compound of formula (6) or finely dispersing it 
in an organic binder, if necessary together with one or more organic 
solvents. The mixing ratio of the pyrrolopyrrole compound to the binding 
agent is not critical. 
The charge generating layer may jointly contain charge transport materials 
such as those shown by formulae (1), (2), (3), (4) and (5). 
The charge transport layer may be formed by dissolving or finely dispersing 
the charge transport material of formulae (1), (2), (3), (4) and (5) in 
one or more organic binders, if necessary together with one or more 
organic solvents. The mixing ratio of the charge transport material and 
the binder is not critical. 
Electrophotographic photoreceptors of double layer type can be formed by 
preparing a dispersion of a charge generating layer and a solution or 
dispersion of a charge transport layer, applying them, in any order 
desired, on an electrically conductive substrate, drying, removing 
solvents if any, and/or curing. The organic solvents optionally used for 
the preparation of the layers may be those mentioned for the single 
layers. The charge generating layer comprising the pyrrolopyrrole compound 
of formula (6) may be applied by vaporizing it under vacuum onto the 
conductive substrate or the charge transport layer as the case may be. 
An undercoating layer may be provided between the photosensitive layer and 
the electrically conductive substrate to enhance their adhesion. For the 
same purpose, the surface of the conductive substrate can be pretreated 
with a surface-treating agent such as silane coupling agent, or a titanium 
coupling agent, etc. The undercoating may consist of natural or synthetic 
polymer solutions. A surface protecting layer may be formed on the 
photosensitive layer to protect its surface. Such protecting layers 
comprise suitable binding agents, deterioration preventing agents, etc. 
The binder should be film-forming, insulating and adhesive. Depending on 
the application, the binder is soluble in organic solvents or in basic 
mixtures of organic solvents which may also contain water. Particularly 
suitable binders are those based on polycondensation and polyaddition 
products such as polyamides, polyurethanes, polyesters, epoxy resins, 
phenoxy resins, polyketones, polycaarbonates, polyvinyl ketones, 
polystyrenes, polyvinyl carbazoles, polyacrylamides, polyolefines such as 
polyethylene, chlorinated polyethylene, or polypropylene, etc., alkyd 
resins, polysulfons, polyallylate resins, diallylphthalate resins, 
polyether resins, polymethyl methacrylates, polyvinyl butyrates, polyvinyl 
chlorides, as well as copolymers such as styrene-acryl copolymers e.g. 
styrene/maleic anhydride copolymers, styrene/methacrylic acid/methacrylate 
copolymers, ethylene-vinyl acetate copolymers, vinylchloride-vinylacetate 
copolymers. 
The photosensitive layer for the electrophotographic photoreceptor of the 
present invention contains one or more dithioketopyrrolopyrrole compounds 
of formula (6) which generate charge carriers when subjected to exposure 
and which is used together with the charge transport materials of formulae 
(1), (2), (3), (4) and (5) present in said layers. Such a layered 
structure makes it possible, after integral electrostatic charging and 
imagewise exposure, to produce a corresponding latent image which can be 
visualised by known toners. 
Exposure can be effected with light from the visible to the near infrared 
region. A particular advantage of the dithioketopyrrolopyrroles is that 
they are also capable of absorbing rays in the near infrared range and 
that they are also photoconductive in this wave length range. The range of 
650 to 850 nm in which gallium arsenide laser diodes operate is of 
particular interest. 
On account of the fact that they exhibit high dark resistance, the 
dithioketopyrrolopyrroles of formula (6) help to maintain electrostatic 
potential in unexposed areas. 
The invention is illustrated by the following examples. 
PREATION EXAMPLES OF CHARGE TRANSPORT MATERIALS 
EXAMPLE 1 
A mixture of 2.5 g of 3-N,N-4'-dimethylaminophenyl-3-phenylacrolein, 2.2 g 
of 1,1-diphenylhydrazine hydrochloride and 0.82 g of sodium acetate is 
refluxed for 3 hours in 20 ml of ethanol. After cooling down to room 
temperature, the crude product is collected by filtration and 
recrystallized from ethanol. The yield of the resulting compound of the 
formula 
##STR27## 
is 2.2 g (48%). 
M.W.: 417; 
M.P.: 181.degree.-182.degree. C.; 
I.P.: 5.45 eV; (I.P=Ionization Potential) 
Mass spectrum: M/e 417 (M.sup.+). 
______________________________________ 
Elemental analysis in %: 
H C N 
______________________________________ 
Found 6.49 83.38 10.15 
Calculated for C.sub.29 H.sub.27 N.sub.3 
6.52 83.42 10.06 
______________________________________ 
EXAMPLE 2 
A mixture of 28 g of 
3-(4'-methoxyphenyl)-3-(4"-dimethylaminophenyl)-acrolein, 22 g of 
1,1-diphenylhydrazine hydrochloride and 8.2 g of sodium acetate is 
refluxed for 1 hour in 200 ml of ethanol. After cooling down to room 
temperature, the crude product is collected by filtration and 
recrystallized from ethanol-acetone. The yield of the resulting compound 
of formula 
##STR28## 
is 23 g (51%). 
M.W.: 447; 
M.P.: 161.degree.-162.degree. C.; 
I.P.: 4.90 eV; 
Mass spectrum: M/e: 447 (M.sup.+); 
______________________________________ 
Elemental analysis in %: 
H C N 
______________________________________ 
Found 6.55 80.32 9.35 
Calculated for C.sub.30 H.sub.29 ON.sub.3 
6.53 80.51 9.39 
______________________________________ 
EXAMPLE 3 
A mixture of 16.6 g of 2,4-dimethoxybenzaldehyde, 22 g of 
1,1-diphenylhydrazine hydrochloride and 8.2 g of sodium acetate if 
refluxed for 1 hour in 150 ml of ethanol. After cooling down to room 
temperature, the crude product is collected by filtration and 
recrystallized from ethanol. The yield of the resulting compound of 
formula 
##STR29## 
is 24 g (75%). 
M.W.: 332; 
M.P.: 105.degree.-106.degree. C.; 
Mass spectrum: M/e: 332 (M.sup.+); 
______________________________________ 
Elemental analysis 
H C N 
______________________________________ 
Found 6.06 75.85 8.43 
Calculated for C.sub.21 H.sub.20 N.sub.2 O.sub.2 
6.06 75.88 8.43 
______________________________________ 
DETERMINATION OF THE ELECTROPHOTOGRAPHIC CHARACTERISTICS 
(1) Preparation of sample specimen 
A tetrahydrofuran solution of CTM/polycarbonate (1 wt./1 wt.) is coated on 
the charge generating layer film formed on an aluminum substrate (see FIG. 
1) and dried. 
______________________________________ 
Charge transfer layer: 
CTM/polycarbonate (1/1) of thickness 
(CTL) 15 microns 
Charge generating layer: 
DTPP film vapour deposited of 
(CGL) thickness 1500 .ANG. or less 
______________________________________ 
AL: Aluminum substrate of thickness 80 microns 
(DTPP = dithiodiketopyrrolopyrrole; CTM = charge transfer material). 
(2) Electrophotographic characteristics 
A sample specimen prepared in the above manner is minus charged at -6.0 KV 
by means of corona discharge from Electrostatic Paper Analyzer 
(EPA-8100.RTM., mfd by Kawaguchi Elec. Co.). The surface potential (Vs.p.) 
is determined first, then the specimen is irradiated with a monochromatic 
light (800 nm, 5 microW/cm.sup.2) from a tungsten-halogen lamp to 
determine the time when the surface potential reduces to the half value to 
calculate the half decay exposure E 1/2. The surface potential at 5 
seconds after the exposure is determined to obtain the residual potential. 
The results are shown in Table 1. 
TABLE 1 
______________________________________ 
Electrophotographic characteristics 
Specimen CTM .sup.(1) E1/2 
.sup.(2) Vs.p. 
.sup.(3) Vr.p. 
No. CGM No. (.mu.J/cm.sup.2) 
(V) (V) 
______________________________________ 
1 DTPP 114 0.43 -377 -6 
2 DTPP 73 0.50 -550 -10 
3 DTPP 115 0.35 -255 -3 
4 DTPP 117 0.55 -656 -8 
5 DTPP 118 0.45 -827 -23 
6 DTPP 120 0.45 -599 -83 
7 DTPP 131 0.63 -590 -16 
8 DTPP 121 0.65 -688 -31 
9 DTPP 119 0.65 -775 -63 
10 DTPP 122 0.48 -353 -8 
11 DTPP 127 0.35 -504 -7 
12 DTPP 123 0.53 -759 -20 
13 DTPP 128 0.53 -771 -19 
14 DTPP 126 0.63 -632 -31 
15 DTPP 124 0.40 -620 -14 
______________________________________ 
.sup.(1) Half decay exposure 
.sup.(2) Surface potential 
.sup.(3) Residual potential 
CGM: charge generating material; CTM: charge transfer material 
Better electrophotographic characteristics are obtained when the surface 
potential (Vs.p.) is higher, the residual potential (Vr.p.) is lower and 
the Half Decay Exposure (E 1/2) is lower. 
DETERMINATION OF CARRIER MOBILITY 
On an aluminum plate of thickness 80 microns as a substrate conductive 
layer, a solution comprising 1 part by weight of a charge transport 
material, 1 part by weight of a polycarbonate resin (Makrolon 2800.RTM.), 
and 8 parts by weight of tetrahydrofuran is coated by means of a wirebar, 
which is then heated at 60.degree. C. for 5 minutes, and then at 
80.degree. C. for 20 minutes to dry out to form a charge transport layer 
of 15 microns thickness. Then, thin gold film is vapor deposited under 
vacuum to a thickness of ca. 50 .ANG. as a semi-transparent electrode. 
Regarding the layer samples thus obtained, transient photocurrents are 
evaluated according to the Time-of-Flight method which is disclosed on 
pages 301-308 of "Solar Cells, 2" (1980) by T. TIEDJE, C. R. WRONSKI, B. 
ABELES and J. M. CEBULKA, published by Elsevier Sequola S.A., Lausanne - 
printed in the Netherlands. 
A nitrogen laser pulse (337 nm, 1 nanosecond) is irradiated onto the 
samples on which an electric field (10.sup.5 -10.sup.6 V/cm) is applied 
through the gold electrode, and the transit time of the charge carrier 
from the gold electrode to the aluminum substrate is determined; and 
carrier mobility is calculated thereby taking the layer thickness and 
applied electric field into consideration. The experimental set-up for the 
determination of carrier mobility is schematically illustrated in FIG. 2 
and the test results are shown in Table 2. 
It is found that the carrier mobility .mu. (cm.sup.2 /Vsec) correlates to 
the strength of electric field E (V/cm) in accordance with the following 
equation: 
EQU log .mu.=a.times.E+b (a,b=constant) 
Below, the constant values for a, b and the carrier mobilities with an 
applied voltage of 500 V (electric field 3.33.times.10.sup.5 V/cm) are 
tabulated. 
TABLE 2 
______________________________________ 
Carrier mobility 
CTM (cm.sup.2 /V sec) at 3.33 .times. 
No. a b 10.sup.5 V/cm of fieldstrength 
______________________________________ 
66 1.99 .times. 10.sup.-6 
-5.95 51.6 .times. 10.sup.-6 
73 6.89 .times. 10.sup.-7 
-5.07 5.02 .times. 10.sup.-6 
114 1.99 .times. 10.sup.-6 
-6.13 3.41 .times. 10.sup.-6 
115 1.77 .times. 10.sup.-6 
-6.28 2.04 .times. 10.sup.-6 
117 1.46 .times. 10.sup.-6 
-5.14 2.22 .times. 10.sup.-5 
118 1.55 .times. 10.sup.-6 
-6.22 1.98 .times. 10.sup.-6 
119 1.83 .times. 10.sup.-6 
-5.58 1.07 .times. 10.sup.-5 
120 1.47 .times. 10.sup.-6 
-6.41 1.20 .times. 10.sup.-6 
121 1.47 .times. 10.sup.-6 
-5.87 4.16 .times. 10.sup.-6 
122 8.36 .times. 10.sup.-7 
-5.73 3.53 .times. 10.sup.-6 
123 9.27 .times. 10.sup.-7 
-6.02 1.94 .times. 10.sup.-6 
124 1.16 .times. 10.sup.-6 
-5.20 1.54 .times. 10.sup.-5 
126 1.13 .times. 10.sup.-6 
-6.20 1.50 .times. 10.sup.-6 
127 8.93 .times. 10.sup.-7 
-5.83 2.93 .times. 10.sup.-6 
128 1.14 .times. 10.sup.-6 
-5.84 3.46 .times. 10.sup.-6 
______________________________________ 
As illustrated in above Tables 1 and 2, the tested combinations show good 
or improved sensitivity (E 1/2), surface potential and residual potential 
as compared to the prior art combinations.