STRUCTURE AND DYNAMICS OF S-2 AND S-1 DIPHENYLACETYLENE IN SOLUTION STUDIED BY PICOSECOND TIME-RESOLVED CARS SPECTROSCOPY

Picosecond time-resolved CARS spectra of diphenylacetylene and its C-1 3-substituted analogue in cyclohexane are reported for the 2330-590 cm (-1) wavenumber shift. The transient CARS bands of the S-2 and S-1 sta tes are observed in addition to those of the cation radical, the anion radical, and the T-1 state. It is found that the central CC stretch f requency of the S-1 state is smaller than 1600 cm(-1), indicating a ma rked decrease of the CC bond order in this state. The width of the cen tral CC stretch band of the S-2 State is found to be similar to 40 cm( -1) (hwhm). These spectral features are discussed in connection with t he structure and dynamics in the two singlet excited states.