Solvent effect on the ground and excited state dipole moments of fluorescein

The ground-state and excited-state dipole moments of fluorescein were studi ed at room temperature in n-alcohols (methanol-n-hexanol) and acetonitrile and acetonitrile-benzene solvent mixtures. The excited-state dipole moments were estimated from Lippert's, Bakhshiev's and Chamma-Viallet's equations by using the variation of the Stokes' shift with the solvent dielectric con stant and refractive index. Experimental ground-state dipole moments for fl uorescein in n-alcohols, acetonitrile and acetonitrile-benzene solvent mixt ures were estimated by the Guggenheim- Smith method (GSM). It was determine d that dipole moments of the excited-state were higher than those of the gr ound-state in n-alcohols while they were lower than those of the ground-sta te in acetonitrile and acetonitrile-benzene solvent mixtures. The solute-so lvent interactions on the ground-state and the excited-state dipole moments of fluorescein are discussed. (C) 2001 Elsevier Science B.V. All rights re served.