Estimation of ground and excited state dipole moments of some laser dyes

The ground state (μg) and the excited state (μe) dipole moments of three laser dyes namely 2, 5-diphenyl-1, 3, 4- oxadiazole (PPD), 2, 2″-dimethyl-p-terphenyl (DMT) and 1, 3-diphenyl benzene (MT) were studied at room temperature in various solvents. The ground state dipole moments (μg) of all the three laser dyes were determined experimentally by Guggenheim method. The excited state dipole moments (μe) were estimated from Lippert’s, Bakshiev’s and Chamma Viallet’s equations by using the variation of the Stokes shift with the solvent dielectric constant and refractive index. Ground and excited state dipole moments were evaluated 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 moment values of excited states (μe) were higher than corresponding ground state values (μg), indicating a substantial redistribution of the π-electron densities in a more polar excited state for all the dyes investigated.