Solvatochromic effect on the photophysical properties of two coumarins.

The absorption and emission spectra of two coumarins namely 7, 8 benzo-4-azidomethyl coumarin (C(1)) and 6-methoxy-4-azidomethyl coumarin (C(2)) have been recorded at room temperature in solvents of different polarities. The ground state dipole moments (μ(g)) of two coumarins were determined experimentally by Guggenheim method. The exited state (μ(e)) dipole moments were estimated from Lippert's, Bakhshievs and Chamma-Viallet's equations by using the variation of Stoke's shift with the solvent dielectric constant and refractive index. The ground and excited state dipole moments were calculated by means of solvatochromic shift method and also the excited state dipole moments are determined in combination with ground state dipole moments. It was observed that dipole moments of excited state were higher than those of the ground state, indicating a substantial redistribution of the π-electron densities in a more polar excited state for two coumarins.