Abstract

Time resolved spectroscopic studies of the photoisomerization reactions of cis-stilbene in solution have provided a great deal of information on these simple reactions (1-3). Transient absorption (1,2) and fluorescence (3) experiments have demonstrated that the initially created electronically excited cis-stilbene population (cis*) persists for 0.5 to 1.5 ps in room temperature solution-phase environments. Polarized transient absorption experiments and time-resolved fluorescence experiments indicate that during this time the cis* molecules retain most of the energy of the incident photon and also retain largely the same geometry and orientation as the initial cis molecules (2,3). This initially created cis* population is then partitioned between two primary reaction pathways, one involving geometric rearrangement leading to trans-stilbene and the second involving electronic rearrangement leading to dihydrophenanthrene (DHP). The trans product is produced on a time scale indistinguishable from the time scale for the decay of the cis* population in room temperature alkane solutions. This means that the stilbene molecule is transformed from electronically identifiable cis* to ground electronic state trans (possibly highly distorted) on a time scale of < 150 fs. The appearance of the DHP product follows a delay of no more than 300 fs from the disappearance of the cis* population.

© 1992 The Author(s)