Solvent solute interactions probed by picosecond transient Raman spectroscopy:S 1 1,4-diphenyl-1,3-butadiene in the linear alkanes

Abstract

We present theS1 Raman spectra of 1,4-DiPhenyl-1,3-Butadiene (DPB) in a series of linear alkanes (pentane, hexane, heptane, octane, decane, and dodecane). Bands assignable to both the 11Bu and 21Ag states are present, suggesting that the state we are observing in solution is a mixed state with both 11Bu and 21Ag character. The relative intensities of several bands associated with Co∔Co stretching motions in the 21Ag and 11Bu states change systematically through the solvent series. The relative intensity changes reflect a changing distribution ofs-trans conformers inS1 DPB as the solvent is varied. We suggest that the distribution ofs-trans conformers inS1 DPB controls the nature of the mixing between the 21Ag and 11Bu 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 inS1 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.