Solute-solvent interactions probed by picosecond transient Raman spectroscopy: S-1 trans-4,4 '-diphenylstilbene in aromatic solvents

The picosecond transient Raman spectra of S-1 trans-4,4'-diphenylstilbene ( DPS) in benzene and toluene at an excitation wavelength of 310 nm and probe wavelengths of 630 and 660 nm are presented. No significant dynamic variat ions between benzene and toluene in the change in peak position of vibratio nal modes in S-1 DPS with delay were observed. These data indicate that vib rational relaxation occurs at similar rates in both solvents. The vibration al relaxation dynamics of S-1 DPS in the aromatic solvents were also compar ed with those in dioxane and methylene chloride. It is suggested that speci fic solute-solvent effects contribute to vibrational relaxation in these so lvents. It was found that the relative intensities of Raman bands that cont ain contributions from the phenyl-phenyl stretch are different for S-1 DPS in toluene compared with S-1 DPS in benzene. The difference in relative int ensities is attributed to an equilibrium conformation in S-1 DPS that is pe rturbed by the methyl group on toluene, giving rise to a variation in the c onformation of the biphenyl group in S-1 DPS, Copyright (C) 2000 John Wiley & Sons, Ltd.