Photophysical Processes in Aromatic Polyimides. 2. Photoreduction of Benzophenone-containing Polyimide Model Compounds
摘要:
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).
Photophysical Processes in Aromatic Polyimides. 2. Photoreduction of Benzophenone-containing Polyimide Model Compounds
摘要:
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).
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).