Anisotropic media effect on the dipole moment of some coumarin dyes.

The ground state (μ(g)) and the excited state (μ(e)) dipole moments of two coumarin laser dyes, C500 and C503, were studied at room temperature in various solvents, viz., aprotic solvents, alcohols and liquid crystals at 298 K. We report dipole moment of laser dyes in different anisotropic (liquid crystals) and isotropic environments. The dipole moments values in different media help to investigate environment effects on the molecular dipole moment and provide a straightforward method for comparing their properties. Ground and excited state dipole moments of coumarin dyes were evaluated by means of solvatochromic shift method. It was observed that dipole moment values of excited states (μ(e)) were higher than corresponding ground state values (μ(g)), indicating a substantial redistribution of the π-electron densities in a more polar excited state for the dyes investigated.