Photoinduced electron transfer dynamics in aromatic vinyl polymers and related systems: time-resolved detection of primary events

Abstract

Primary processes of photoinduced electron transfer (ET) dynamics in aromatic vinyl polymers, such as charge separation, charge recombination, and hole migration reactions, in solution, solid, and adsorbed systems are reviewed. The application of time-resolved transient absorption spectroscopy and dichroism measurements clearly demonstrates that the electron transfer dynamics in aromatic vinyl polymers in solution phase are well described by a simple scheme in which the cation migrates continuously along pendant aromatic moieties in a polymer chain and the charge recombination at the initial position of the charge separation. Dependence of the hole transfer (HT) rate constants on the size of the aromatics and the solvent polarity suggest that the delocalization of the cationic state over several aromatic side groups takes on an important role in the rapid HT processes. The role of stable dimer cation formation and its relation to the rapid HT process are discussed on the basis of the experimental results for the ET dynamics in the poly(1-vinylpyrene) system, where effective dimer cation formation occurs. For photoconductive amorphous solid PVCz films doped with electron acceptors, the direct investigation of the primary processes of the electron transfer dynamics also reveal that the hole migration from the cation state of the carbazolyl moiety (Cz) to neighboring Cz’s in solid films takes place in the nanosecond time region. An extremely long-lived charge-separated state (>8 h) was attained due to the charge shift reactions in a PVCz system co-adsorbed with an electron acceptor on a macroreticular resin. On the basis of these direct measurements, the mechanism of the primary events of the photoinduced electron transfer processes coupled with photoconduction in the aromatic vinyl polymer and related molecular systems are discussed from the viewpoint of the elementary ET reactions.