On the estimation of excited-state dipole moments from solvatochromic shifts of absorption and fluorescence spectra

The effect of the solvent polarity parameters f (epsilon, n) and phi (epsilon, 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 mu(e) 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 mu(e), but only on the solvent parameters f (epsilon, n) and phi (epsilon, 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 m(1) and m(2). Also the effect of alpha/a(3) (alpha 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 mu(e) has been studied, and it is found that the assumption alpha/a(3) = 1/2 is valid in many cases.