ELECTRON-TRANSFER COMPLEXES OF THE SYSTEM PYRENE PMDA STUDIED BY TRANSIENT ABSORPTION AND DEGENERATE 4-WAVE-MIXING MEASUREMENTS/

The kinetics of the intermolecular electron transfer between pyrene an d pyromelitic dianhydride is studied by two experimental technigues: t ransient absorption measurements and degenerate four-wave mixing after optical excitation by picosecond light pulses. The observed time evol ution of the electron transfer reaction depends strongly on the wavele ngth of the pump pulse. Excitation of pyrene leads to a diffusion-cont rolled electron transfer (in agreement with theoretical calculations), while excitation of the ground state donor-acceptor complex shows a d ifferent time behavior. Comparison of the decay times and the molecula r hyperpolarizabilities provides clear evidence for two different exci ted charge transfer complexes.