Pressure effects on absorption and fluorescence of polar dyes

Fluorescence spectra of laser dyes coumarin 1 and coumarin 102 in methanol and ethanol were studied at high pressures using diamond anvil cell. These dyes show a large frequency shift with pressure toward the red end. While the fluorescence maxima vary smoothly with pressure up to the glassification pressure followed by an expected change of slope at this pressure for coumarin 102, coumarin 1 exhibits a pressure-independent regime prior to glassification. This is attributed to a conformational change taking place in coumarin 1 at about 1 GPa