Abstract

When the electronic interaction between an electron donor (D) and acceptor (A) is very weak, the electron transfer (ET) process is considered to be non-adiabatic. When the interaction become fairly strong, the reaction will become adiabatic. If the electronic interaction becomes sufficiently strong and the energy gap relations are also favorable, the ET process will become barrierless. In such case it is believed that the ET process is governed mainly by the orientational motions of polar solvent molecules or polar groups in the environment surrounding D and A, and the longitudinal dielectric relaxation time τ_L will be important as a factor controlling the ET rate. In a limit of strong interaction between D and A groups combined by rigid spacer or single bond, its excited singlet state can be regarded as a very polar single molecule and we can observe a large fluorescence Stokes shift due to the solution in polar solvents. For the elucidation of the above mechanisms, especially the interaction of D and A with solvent including its dynamical effects on the ET process, systematic femtosecond-picosecond laser photolysis studies on various combined D, A system with different degrees of electronic interaction between them are of crucial importance.

© 1990 Optical Society of America