ELECTRONIC-STRUCTURE AND DYNAMICS OF IONIC SPECIES IN THIN PE POLY(N-VINYLCARBAZOLE) FILMS DOPED WITH SOME ELECTRON-ACCEPTORS AS REVEALED BY TRANSIENT ABSORPTION-SPECTROSCOPY

A laser photolysis method, monitoring transient absorption under a multireflection condition, was applied to thin poly(N-vinylcarbazole) (PVCz) films doped with some electron accepters. Absorption spectra composed of PVCz cation and acceptor anion were ascribed to migrating hole and trapped electron, respectively. The decay process of the ionic species obeyed second-order kinetics in the 1-40-mu s range, indicating that homogeneous charge recombination is the rate-determining step for the decay of the ionic species. The diffusion coefficient of the hole obtained from the bimolecular rate constant decreased as the electron affinity of doped accepters increased. The absorption band of the PVCz cation for the charge transfer system with large electron affinity was sharp compared with that of the exciplex system with a small one. These changes in the diffusion coefficient of the hole and in the absorption band of the PVCz cation were discussed in terms of electron-donor-acceptor interaction.