Photo-thermalization processes of charge transfer complexes in liquids studied by the transient grating method

Transient grating spectroscopy was applied to the study of the photo-therma lization process of charge transfer (CT) complexes such as toluene/tetracya noethylene (TCNE), mesithylene/TCNE, and naphthalene/TCNE in polar liquids. We measured the population and the acoustic grating signals after the exci tation of the CT band by a sub-ps laser pulse (358 nm). The delay time of t he first acoustic peak arrival time relative to the value expected from imp ulsive heating was of the order of 10 ps, which represents an energy weight ed average of the thermalization time. The energy relaxation time in the gr ound state is discussed in relation to the excited state lifetime and the r eaction free energy. (C) 2000 Elsevier Science B.V. All rights reserved.