INTRAMOLECULAR CHARGE-TRANSFER AND CONFORMATION OF POLYIMIDE CHAINS - PHOTOPHYSICAL AND PHOTOCHEMICAL PROCESSES IN MODEL COMPOUNDS

The photoinduced intramolecular charge transfer which dominates the photochemical process of benzophenone type polyimides was investigated in relation with the conformation and the rotational potential of the polyimide chains. With a focus upon the chain conformation around the bond between the imide ring and the aromatic ring, the most stable dihedral angle and the rotational potential were estimated based upon the quantum chemical calculation with semiempirical AM1 and ab initio STO-3G. Althogh N-(3-ethylphenyl)phthalimide has a very low rotational potential and rotates freely, the rotational potential of N-(2,2-diethylphenyl)phthalimide is very high and the most stable dihedral angle is 73-degrees. Further, the possibility of intramolecular charge transfer was estimated qualitatively on the basis of molecular orbital consideration. These results coinside well with the experimental results for the photochemical reaction of model benzophenone bisimide compounds.