Electronic spectroscopy of pyrromethene 546

UV-Vis absorption and fluorescence (steady state and time-correlated) spectroscopies are applied to study the photophysics of pyrromethene 546 in a multitude of apolar, polar, and protic solvents, including water/ethanol mixtures. The solvent effect on the absorption and fluorescence bands is analysed in terms of the stabilization of several resonance structures of the pi-system of the chromophore by general and specific H-bond solute/solvent interactions. Highest and lowest values for the rate constant of radiative and radiationless deactivation of PM546 are observed in high polar and H-bond donor solvents, respectively, and they are recommended as the best media to obtain the highest laser efficiency of PM546 in liquid solutions. (C) 1999 Elsevier Science S.A. All rights reserved.