Picosecond processes in the isomerism of stilbenes

Abstract

Following a review of the problem of stilbene isomerism an account is given of recent picosecond tinescale experiments on this system. Transient absorption methods are used to expose vibrational relaxation de— tails for molecules in solution and streak camera measurements of fluo— rescence decay are presented to demonstrate the irreversibility of the Si (trans) decay. A simple statistical mechanical model is presented to describe the effect of viscosity on the twisting dynamics of trans—stilbene. A summary of recent experiments involving stilbene in the gas phase is presented. The isolated molecules twist very rapidly (15 ps at 265 nm ex— citation) and display characteristics typical of systems with a potential barrier. Finally the solution and gas phase processes are contrasted.