Torsional dynamics of molecules on barrierless potentials in liquids. III. Pressure dependent picosecond studies of triphenyl-methane dye solutions in a diamond anvil cell

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Abstract
Pressure dependent measurements of the nonradiative torsional dynamics of triphenyl-methane dyes are reported. The viscosity dependence of the excited state absorption and fluorescence decays of crystal violet, dissolved in methanol, ethanol, and n-propanol, are studied over a viscosity range of between 0.5 and 500 cP (pressures up to 1.5 GPa ∼15 000 atm). The overall viscosity dependence of the excited state decay time is linear. The nonlinear viscosity dependencies observed in earlier studies may have resulted from the complex nature of the solvents used and, in the case of fluorescence quantum yield measurements, from a pressure dependence of the radiative rate. Differences between the viscosity dependence observed when varying pressure, temperature, or solvent type at low viscosities are tentatively ascribed to pressure and temperature induced conformational changes.