Relation between photoconduction and excimer formation in a conjugated oligomer

Photoconduction action spectra and site-selective fluorescence spectra have been measured in polystyrene blends of an oligomer of phenylenevinylene carrying cyano- and octyloxy-substituents (CNSB). Increasing the content from 20% to 80% (by weight) changes the fluorescence spectra from being monomer-like to excimer-like. Strong excimer emission correlates with efficient photoconduction measured in a sandwich cell configuration with indium tinoxide (ITO) and aluminium electrodes. The lowering of the photocurrent upon inserting a thin blocking silicon monoxide layer between the ITO and the sample in conjunction with the polarity dependence, as well as the dependence on temperature and electric field indicate that the charge carrier delivering process is the efficient dissociation of inter-chain excitations at the ITO electrode rather than bulk photoionization. (C) 1998 Elsevier Science B.V.