Orientational and Vibrational Relaxation Dynamics of Perylene and 1-Methylperylene in Aldehydes and Ketones

Abstract

We report on the rotational diffusion and vibrational population relaxation dynamics of the probe molecules perylene and 1-methylperylene in selected aliphatic aldehyde and ketone solvents. The reorientation data demonstrate that, for both solvent systems, there is a change in the nature of the solvent−solute interactions with both probe molecules as the hydrodynamic volume of the solvent molecules approaches that of the probes. The solvent-dependent change in behavior occurs for different solvent aliphatic chain lengths in the two systems. Vibrational population relaxation measurements for two probe molecule vibrational modes reveal efficient intermolecular coupling in all cases. The data point to the role of the solvent aldehyde proton in mediating solvent−solvent and solvent−solute interactions, leading to chromophore dynamics reminiscent of those seen in the n-alcohols. Reorientation of the two probes in the ketones yields results that are more consistent with those seen in the alkanes, suggesting the relative weakness of dipole−induced dipole interactions relative to hydrogen-bonding interactions in the solvation of perylene and 1-methylperylene.

Solvent-assisted intramolecular vibrational energy redistribution of S1 perylene in ketone solvents

“…Therefore, τ 3 can be assigned to VET or SA-IVR. Blanchard et al reported an analysis of VER of ground-state (S 0 ) perylene in several ketone solvents by using picosecond stimulated emission spectroscopy, and found that the VET rates were in 10 -50 ps range [9]. This time constant is much longer than the τ 3 value observed in the present study, 1.8 -4.9 ps, even taking the difference in the electronic states, S 0 and S 1 , into account.…”

“…This sudden drop-off of decay rates, which is common for τ 2 and τ 3 processes, may be attributed to the change in structure of solvation cavity surrounding perylene. Goldie and Blanchard measured reorientation dynamics of perylene in ketone solvents, and reported that the reorientation of perylene can be expressed by a single exponential decay function for the C 5 -C 8 ketone solvents while by a double exponential decay for the C 9 ketone solvent [9]. These results indicate that the structure of solvation cavity surrounding perylene changes from prolate for the C 5 -C 8 ketones to oblate for the C 9 ketone [9,26].…”

“…Goldie and Blanchard measured reorientation dynamics of perylene in ketone solvents, and reported that the reorientation of perylene can be expressed by a single exponential decay function for the C 5 -C 8 ketone solvents while by a double exponential decay for the C 9 ketone solvent [9]. These results indicate that the structure of solvation cavity surrounding perylene changes from prolate for the C 5 -C 8 ketones to oblate for the C 9 ketone [9,26]. Note that the change in cavity structure even affects the pure IVR rates as well as the SA-IVR rates as indicated in Figure 7.…”

“…Many experimental and theoretical studies have been reported on VER in the last decade [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. that IVR is further classified into two processes in solutions; the fast IVR that takes place in tens of femtoseconds to sub picoseconds time scales and the slow IVR in a few picoseconds time scale [5][6][7][8].…”

“…Blanchard et al studied VER of S 0 perylene and S 0 1-methylperylene in various solvents by using picosecond stimulated emission spectroscopy [9][10][11]. They investigated VET taking place in time scales slower than tens of picoseconds.…”