The excited state effective dipole moment of 2,3-benzofuran from thermochromic shifts in absorption and emission spectra

Abstract

The excited state dipole moment of the lowest excited singlet state of 2,3-benzofuran in ethylacetate solution is determined using thermochromic spectroscopy and compared to the values which are obtained for the isolated molecule from electronic Stark spectroscopy (Hebestreit et al., 2020) and to the results of ab initio calculations at coupled cluster level of theory. It is shown that the dipole moment from thermochromic shifts in solution deviates considerably from that of the isolated molecule. This finding can be traced back to a field induced mixing by the strong reaction field of the solvent, which exceeds the external Stark field applied in gas phase measurements by a factor of 10.000. Depending on the dipole moments of the perturbing state and its energy gap to the excited state, dipole moments from thermochromic shifts (and consequently also of solvatochromic shifts) might be considerably different to gas phase values. However, the alteration of the electronic configuration of the molecule via the reaction field of the solvent can be deperturbed in the high-field limit.