SOLVENT/SOLUTE INTERACTIONS PROBED BY PICOSECOND TRANSIENT RAMAN-SPECTROSCOPY - VIBRATIONAL DYNAMICS AND STATE ORDERING IN S-1 1,4-DIPHENYL-1,3-BUTADIENE

We present the S-1 Raman spectra of 1,4-diphenyl-1,3-butadiene (DPB) in n-hexane and THF at three different probe wavelengths. We assign the Raman spectra of S-1 DPB on the basis of gas-phase and low-temperature fluorescence spectra. Bands assignable to the 1(1)B(u) and 2(1)A(g) states from the gas-phase spectra are both present in solution. These results suggest that the state we are observing in solution is a mixed state, having both 1(1)B(u) and 2(1)A(g) character. Broad vibrational bands associated with the olefin region of DPB suggest that there is a distribution of s-trans conformers in S-1 DPB. We also observe mode-specific, solvent-dependent dynamics in the excited-state Raman spectra. In particular, the peak position and bandwidth of the mode associated with the C=C phenyl stretch change as the delay is increased. We suggest that the mode-specific dynamics are related primarily to vibrational relaxation in S-1 DPB.