Photoinduced electron transfer in isolated, jet-cooled molecular systems

Information about photoinduced electron transfer (ET) in isolated (collision free) molecular systems may be deduced from fluorescence and fluorescence excitation spectra of jet-cooled donor-acceptor (D-A) complexes and bridged donor-acceptor bichromophores (D-B-A). The structures of their different isomeric forms may be obtained by semi-empirical calculations. The relation between structures and essential parameters of ET processes (rates, energy thresholds, etc.) is treated in terms of a model based on the theory of radiationless transitions. Two distinct cases of a rapid (direct) ET corresponding to broad-band excitation spectra and of sequential processes in the systems with narrow-band spectra are discussed. The necessity of further studies and especially of time-resolved experiments at the picosecond timescale is emphasized.