Structure and Dynamics of S2 and S1 Diphenylacetylene in Solution Studied by Picosecond Time-Resolved CARS Spectroscopy

Picosecond time-resolved CARS spectra of diphenylacetylene and its 13 C-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 states 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 frequency of the S 1 state is smaller than 1600 cm -1, indicating a marked decrease of the CC bond order in this state. The width of the central CC stretch band of the S 2 state is found to be ∼40 cm -1 (hwhm). These spectral features are discussed in connection with the structure and dynamics in the two singlet excited states.