SOLVENT SOLUTE INTERACTIONS PROBED BY PICOSECOND TRANSIENT RAMAN-SPECTROSCOPY - S-1 1,4-DIPHENYL-1,3-BUTADIENE IN THE LINEAR ALKANES

We present the S-1 Raman spectra of 1,4-Di-Phenyl-1,3-Butadiene (DPB) in a series of linear alkanes (pentane, hexane, heptane, octane, decane, and dodecane). Bands assignable to both the 1 B-1(u) and 2 (1)A(g) states are present, suggesting that the state we are observing in solution is a mixed state with both 1 B-1(u) and 2 (1)A(g) character. The relative intensities of several bands associated with C-0-C-0 stretching motions in the 2 (1)A(g) and 1 B-1(u) states change systematically through the solvent series. The relative intensity changes reflect a changing distribution of s-trans conformers in S-1 DPB as the solvent is varied. We suggest that the distribution ef s-trans conformers in S-1 DPB controls the nature of the mixing between the 2 (1)A(g) and 1 B-1(u) states and that the distribution of conformers is controlled by the solvent viscosity. Changes in the peak position and bandwidth of the phenyl C=C stretch with delay reflect vibrational relaxation processes in S-1 DPB. We observe anomolous behavior in pentane that we attribute to the effect of the solvent structure on the ability of DPB to exchange energy with pentane.