Solvent effect on absorption and fluorescence spectra of coumarin laser dyes: Evaluation of ground and excited state dipole moments

The effect of solvents on absorption and fluorescence spectra and dipole moments of coumarin 307 (C307) and coumarin 522B (C522B) have been studied extensively in various solvents, viz., general solvents, alcohols and binary mixtures (acetonitrile–benzene) at 298 K. The bathchromic shift observed in absorption and fluorescence spectra of C307 and C522B with increasing solvent polarity indicates that transition involved are π → π*. Solvatochromic correlations were used to obtain the ground and excited state dipole moments. The excited state dipole moments are observed to be greater than their ground state counterparts in all the solvents studied. Further, the experimentally obtained Δμ   were compared with those using normalized polarity terms ETN from Reichardt equation.