Substituent and solvent effects on the photo-physical properties of some coumarin dyes.

Absorption and fluorescence spectra of three coumarin dyes with various substituents and alkyl groups have been recorded in solvents in the range of 200-730 nm. The photo-physical behavior of dissolved dye depends on the nature of its environment, i.e. the solvatochromic behaviors of coumarin dyes and solvent/solute hydrogen bonding interactions can be analyzed by means of linear solvation energy relationships concept proposed by Kamlet and Taft. The intensity, shape, and maximum wavelength of the absorption and fluorescence band of these dyes in solution depend strongly on the solvent-solute interactions and solvent nature. Hydrogen bonding interactions (specific solute-solvent interactions) between these dye-solvent complex and dipolarity/polarizability (non-specific solute-solvent interactions) control reorientation of solvent molecules around the dye. Copyright 2009 Elsevier B.V. All rights reserved.