ROTATIONAL RELAXATION OF ROD-LIKE MOLECULES - DIPHENYLACETYLENE IN VARIOUS SOLVENTS

By using fluorescence anisotropy decay and polarized transient absorpt ion spectrum measurement techniques with a picosecond time resolution, we have studied the rotational relaxation of 4-[[4-(dimethylamino)phe nyl]ethynyl]-benzonitrile in various solvents. Our aim is to clarify t he solvent solute interactions revealed as a solvent dependence of the rotational relaxation time of solute molecules. Among the solvents we used, ethanol shows characteristic behavior compared with other polar solvents. The rotational relaxation time in ethanol seem to be close to that calculated on the basis of the slip boundary condition, while in other polar solvents, the stick boundary condition can reproduce th e experimental value. The results suggests that the strong hydrogen bo nding between the solvent molecules allows the solute to rotate more f reely within the solvent cage than in other polar solvents.