Solvent effects on photophysical properties of merocyanine 540

Absorption and corrected fluorescence emission spectra of merocyanine 540 (MC 540) were recorded in solvents with different physico-chemical parameters – dielectric constant ε_r, refractive index n, dipolarity/polarizability π^*, hydrogen-bonding ability α. Hypsochromic shifts of their maxima positions did not obey Lippert–Mataga equation. However, a correlation with π^* and α was observed. Relative quantum yields φ_f and rate constants of nonradiative deactivation processes k_nr of the dye in different solvents based on steady-state measurements were estimated. Dependence on hydrogen-bonding ability was indicated – with increasing α, φ_f decreased and k_nr increased. The interaction between MC 540 and solvent molecules is discussed in terms of the different interactions contributing to the solvent stabilization of merocyanine dyes. Our results indicate that hydrogen bonding may contribute to solvent stabilization of MC 540.