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

The photochemical kinetic parameters for the model compounds of benzop henone-containing polyimide were determined on the basis of the Stern- Volmer analysis. The quantum yield for photoreduction, Phi(M), in dich loromethane decreased with an increase in the intramolecular charge-tr ansfer (CT) character which depends upon the chemical structure of the amine components and the conformation around N-aryl group linkage. Th is could be explained well by a schematic photophysical mechanism in w hich the intersystem crossing followed by the hydrogen abstraction com petes with the intramolecular CT process followed by effective deactiv ation. The phosphorescence spectra and lifetime at 77 K and the transi ent 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 independe nt of the intramolecular CT character. It was found that benzophenoneb isimides have the hydrogen abstraction rate constants no less than tha t of benzophenone (BP).