Abstract

The ground state (μ_g) and the excited state (μ_e) dipole moments of a laser dye ADS560EI is estimated in various solvents by Lippert, Backshieve, Kawski-Chamma-Viallet, McRae and Suppan equations using the variation of stokes shift with the solvent dielectric constant and refractive index. The excited state dipole moments were also calculated by using the variation of stokes shift with microscopic solvent polarity parameter (). It was observed that the dipole moment values of excited state (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 than the ground state. The rotational reorientation of this probe molecule has also been examined in various solvents. It is observed that the increase in viscosity of the solvent is responsible for the increase in the rotational relaxation time of the probe molecule.

Key words: Stokes shift, excited state, ground state, dipole moment, reorientation time.