On the Estimation of Excited-State Dipole Moments from Solvatochromic Shifts of Absorption and Fluorescence Spectra

The effect of the solvent polarity parameters f (e, n) and j (e, n) appearing in solvatochromic theories, and the effect of the molecular shape of the Onsager cavity (sphere, ellipsoid of revolution) on the determined electric dipole moments me in the singlet excited state are studied. It is found that the shape of the solute does not exhibit a significant effect on the determined values of me, but only on the solvent parameters f (e, n) and j (e, n) as well as on the Onsager radius a. Passing from a sphere to an ellipsoid leads to such a change in the scale that induces a proportional change in the slope coefficients m1 and m2. Also the effect of a/a (a and a are the mean isotropic polarizability of the solute and the Onsager cavity radius in a homogeneous dielectric, respectively) on the determined values of me has been studied, and it is found that the assumption a/a = 1/2 is valid in many cases.