Solvent effects on the dipole moments and photo physical properties of laser dye

The absorption and emission spectra of fluorescent laser dye namely, 4,4”’-bis-2-butyyloctyl-oxy)-P-quaterphenyl have been recorded at room temperature in solvents of different polarities. The exited state dipole moments (µ e ) have been estimated from Lippert’s, Bakhshiev’s and Kawski-Chamma-Viallet’s equations using the variation of Stoke’s shift with the solvent dielectric constant and refractive index. The geometry of the molecule has been fully optimized and the µ g has also been calculated theoretically by Gaussian 03 software using B3LYP/6-31g* level of theory. The µ g and µ e have been calculated by means of solvatochromic shift method. It has been observed that µ e is higher than µ g , indicating a substantial redistribution of the π-electron densities in a more polar excited state for the selected laser dye. Further, the changes in the dipole moment ( µ) has been calculated both from solvatochromic shift method and microscopic empirical solvent polarity parameter ( E ) and values are compared.