Photoconductivity of Aliphatic Polyimides(2); Photoconduction Mechanism and Their Sensitization.

Abstract

Photoconduction mechanism of an aliphatic polyimide, PI(PMDA/DCHM), and its sensitization by the addition of N, N, N′N′-tetramethyl-p-phenylenediamine(TMPD) were investigated by comparing them with those for an aliphatic polyimide containing two methyl substituents, PI(PMDA/DMDHM), and an aromatic polyimide, PI(PMDA/ODA). Photoconductivity of PI(PMDA/DCHM) would be the result of the weak intermolecular interaction formed by mixed layer packing arrangement between pyromellitic moiety of one polymer backbone and N-cyclohexyl ring of another one in the ground state. The irradiation of this weak intermolecular interaction forms immediately a charge-transfer complex in the excited state, produces charge carriers of radical cation and anion, and would result in the photoconductivity in the bulk polyimide film.The addition of the electron donor increases the photocurrent generation of polyimide films by about three orders of magnitude shifting to longer wavelength by forming intermolecular charge-transfer complex in the ground state of the polyimide films. The doped-aliphatic polyimide film shows a larger enhancement of photocurrent probably due to the existence of only intermolecular charge-transfer complex in the polyimide film, compared to the case of the aromatic polyimide having charge-transfer complex both intra- and intermolecularly.