Photoconductive Properties of Bis-halogenated Anthauthrone Pigments

Photoconductivity measurements using an electrostatic paper analyser and an electrophotographic recorder have been carried out on a series of duallayer photoconductor devices consisting of thin po~y~arbo~ate films doped with bis-halogenated anthanthrone pigments as the charge-generation material (CGM). The pigments, all synthesised by the same chemical route, exhibit photodecays that decrease with an increase in the size of the substituted halogens with the~uoro pigment exhibiting anomalous behaviour. In most cases anthanthro~e itse~is found to exhibit the fastest photodecay. Vacuum-depositedfilms ofthe pigments exhibit muchfaster photodecay rates with no signl~cant dark decay, indicating that the photo~onductivity is an intrinsic property of the pigments. The nature of the charge-transport material (CT&f), also using polycarbonate as the polymer binder, has a marked but variable influence on the photodecay rates. Charge acceptance increases with a decrease in the electron-donating power of the CTM and is in the order oxadiazole < leueo-tr~pheny~methane, although the eflect is reversed for the vacuum-deposited systems. The results indicate that the photoconductivity of the pigments is very much dependent on their synthetic route purity and nature of the CTM and that the mechanism of photodecay occurs through the lowest ex~itedsing~et state. This issupportedby the lack of any ESB signal from the pigmen fs on optical excitation and the observation that halogen substitution decreases photo~ondurtivity. 183 Byes and Pigments 0143-7208/89/$03.50