Effect of electron delocalization on charge separation in photoconductive aromatic polyimides with pronounced electron donor-acceptor interaction

The comparison of charge carrier photogeneration quantum yields beta and th eir field dependencies is carried out for three series of soluble photocond uctive polyimides (PIs) based on 4,4'-diaminotriphenylamine (I), N,N'-bis(p -aminophenyl)-N,N'-diphenyl-p-phenylenedi- amine (II) and N,N'-bis(p-aminop henyl)-N,N'-diphenylbenzidine (III) which differ only by the donor chain fr agment size at the same acceptor diimide fragments. In comparison with PIs I series for PIs II and III series the significant increase of beta value ( by 1-2 orders of magnitude) and initial charge separation distance r(O) in ion-radical pairs (IRP) (from 2 to 3.5-3.8 nm) are found. This increase is due not only to rising density of hole transporting sites: but more likely to the efficient delocalization of the positive charge within the extended conjugation system of the donor fragment during IRP formation process. This conclusion is evidenced by the observation of magnetic spin effect (MSF) o n photoconductivity which enables to estimate the charge delocalization len gth in these PIs.