PHOTOGENERATION OF CHARGE-CARRIERS IN LAY ERS OF SOLUBLE PHOTOCONDUCTING POLYIMIDES SENSITIZED BY DYES

Photogeneration of charge carriers in the layers of soluble photocondu cting polyimides and their sensitization by various dyes were studied by method of photoinduced decay of the surface potential. The PI layer s were based on 4,4'-diaminotriphenylamine and a series of dianhydride s of aromatic tetracarboxylic acids with different groups X separating the phthalanhydride fragments (X = O, -, SO2, CO in samples PI I-IV, respectively). The role of the electron donor-acceptor interaction in the polymers was established. The quantum yields of the carrier photog eneration and their field dependences were measured. The PI-I and PI-I V samples with dominating interchain electron donor-acceptor interacti on were efficiently sensitized by various dyes in the entire visible s pectral range. The sensitization was accompanied by quenching of the d ye luminescence as a result of either a nonradiative energy transfer ( PI-IV) or the electron transfer from a donor chain fragment to the exc ited dye (PI-I). In PI-II and PI-III samples (with dominating intramol ecular electron donor-acceptor interaction), the field dependence of t he quantum yield of photogeneration exhibits a threshold character, an d the efficiently of dye-induced sensitization is much lower than that in PI-I and PI-IV. The PI-I and PI-IV samples showed a weak photosens itivity (with the corresponding weak absorption) in the near IR range, which is attributed to the presence of long-living ion pairs of the P oole-Frenkel type. The ion pairs play an important role in the mechani sm of universal spectral sensitization.