Effect of Electron Delocalization on Charge Separation in Photoconductive Aromatic Polyimides with Pronounced Electron Donor-Acceptor Interaction

Abstract

The comparison of charge carrier photogeneration quantum yields β and their field dependencies is carried out for three series of soluble photoconductive polyimides (PIs) based on 4,4′-diaminotriphenylamine (I), N,N′-bis(p-aminophenyl)-N,N′-diphenyl-p-phenylenediamine (II) and N,N′-bis(p-aminophenyl)-N,N′-diphenylbenzidine (III) which differ only by the donor chain fragment size at the same acceptor diimide fragments. In comparison with PIs I series for PIs II and III series the significant increase of β 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) on photoconductivity which enables to estimate the charge delocalization length in these PIs.