VIBRATIONAL POPULATION RELAXATION OF TETRACENE IN N-ALKANES - EVIDENCE FOR SHORT-RANGE MOLECULAR ALIGNMENT

We report on the vibrational population relaxation dynamics of three t etracene vibrational modes (1462, 1383, and 1293 cm(-1)) in eight n-al kane solvents. The 1462 and 1383 cm(-1) resonances in tetracene are Ra man-active fundamental vibrational modes, and the 1293 cm(-1) mode is a Raman-active combination mode (307 + 986 cm(-1)). The vibrational po pulation relaxation times (T-1) for these modes range from <10 to simi lar to 40 ps, depending on the identity of the solvent and the vibrati onal mode. These data are indicative of local solvent organization aro und the tetracene molecule. Comparison of these data to those we repor ted previously for perylene in the same solvents indicates that n-alka ne solvent-solute coupling is more efficient for tetracene, in general , than for perylene. We interpret the comparatively efficient relaxati on of tetracene in terms of short-range molecular alignment.