VIBRATIONAL POPULATION RELAXATION OF PERYLENE IN N-ALKANES - THE ROLE OF SOLVENT LOCAL-STRUCTURE IN LONG-RANGE VIBRATIONAL-ENERGY TRANSFER

We have measured the vibrational population relaxation times of the Raman active v(7) mode (1375 cm(-1)) and (v(7) + v(15)) combination mode (1733 cm(-1)) of perylene in eight liquid iz-alkanes using ultrafast stimulated emission spectroscopy. The vibrational population relaxation time of the perylene v(7)-mode ranges from similar to 300 to < 10 ps depending on the n-alkane solvent chain length, but there is no simple correspondence between alkane length and T-1 for v(7). Energy transfer from the perylene v(7) vibrational mode to a specific n-alkane solvent vibrational mode is dominated by long-range resonance coupling. The perylene (v(7) +/- v(15)) combination mode exhibits additional efficient relaxation Pathways for different length n-alkanes. These data point collectively to short-range order in the n-alkane solvent surrounding perylene molecule.