Excited state dipole moments of two dicyanobenzene isomers from thermochromic shifts and ab initio calculations

Abstract

The excited state dipole moments of two positional isomers of dicyanobenzene have been determined from thermochromic shifts of the absorption and fluorescence emission spectra in ethyl acetate solution and compared to the results of ab initio calculations. We found that the dipole moments of excited states from thermochromic shifts closely resemble the ab initio values of the isolated molecule, while the results of conductor-like screening model (COSMO) using the same wave function model as for the isolated molecule, shows considerable deviations from the experimental values. It is shown that the dipole moments of the two cyano groups add up vectorially for both the ground and excited states.