PHOTOPHYSICAL PROCESSES IN AROMATIC POLYIMIDES .2. PHOTOREDUCTION OF BENZOPHENONE-CONTAINING POLYIMIDE MODEL COMPOUNDS

The photochemical kinetic parameters for the model compounds of benzophenone-containing polyimide were determined on the basis of the Stern-Volmer analysis. The quantum yield for photoreduction, Phi(M), in dichloromethane decreased with an increase in the intramolecular charge-transfer (CT) character which depends upon the chemical structure of the amine components and the conformation around N-aryl group linkage. This could be explained well by a schematic photophysical mechanism in which the intersystem crossing followed by the hydrogen abstraction competes with the intramolecular CT process followed by effective deactivation. The phosphorescence spectra and lifetime at 77 K and the transient T-1 --> T-n absorption and emission spectra of the model compounds at 20 degrees C suggested that T-1 is of pure (n,pi*) state independent of the intramolecular CT character. It was found that benzophenonebisimides have the hydrogen abstraction rate constants no less than that of benzophenone (BP).