Physical chemistry of the lowest excited singlet state of trans-stilbene in solution as studied by time-resolved Raman spectroscopy

Structure and dynamics of the lowest excited singlet state of trans-stilbene (the S, state of tSB) in solution are discussed with an emphasis placed on the elucidation of the mechanism of the trans-cis photoisomerization. Structure of S-1 tSB in solution is first discussed based on the time-resolved Raman spectral data and their isotope substitution effects. Original data for an asymmetrically deuteriated tSB, tSB-d(5), are presented to confirm the ethylene-like structure of the central C-C linkage of S-1 tSB. Next, the time-, temperature-, and solvent-dependent band shape changes of the olefinic C=C stretch band are discussed in terms of the solvent induced dynamic polarization. It is shown that the dynamic polarization model accounts very well, not only for the observed band shape changes, but also for their relevance to the isomerization mechanism. A new microscopic view on the photoisomerization of tSB is thus presented. Picosecond energy dissipation process of S-1 tSB is then discussed in relation to the microscopic solvation structure in chloroform. Finally, the mechanism of a new bimolecular reaction between S-1 tSB and carbon tetrachloride is discussed on the basis of the diffusion-controlled reaction model.