Electronic spectral shifts, reorganization energies, and local density augmentation of Coumarin 153 in supercritical solvents

Solvent reorganization energies and local densities of Coumarin 153 (C153) in supercritical C2H6, CO2, and CHF3 (T-c = 5 K) are measured using fluorescence spectroscopy. Reorganization energies are 320 +/- 70 and 770 +/- 70 cm(-1) in CO2 and CHF3, respectively - nearly independent of density (0.3 less than or equal to rho/rho(c) less than or equal to 2.1). The spectral shifts imply similar effective local densities in all three solvents. These effective densities can exceed 3-5 times the bulk density. In CO, and CHF,, the maximum density augmentation calculated from emission shifts is similar to 20% greater than that calculated from excitation shifts. No such difference is found in C2H6. (C) 1999 Elsevier Science B.V. All rights reserved.