The excited state dipole moment of 2-[(4-methoxyphenyl)ethynyl]-3-(1-methyl-1H-indol-3-yl)-quinoxaline from thermochromic shifts.

Abstract

The excited state dipole moment of 2-[(4-methoxyphenyl)ethynyl]-3-(1-methyl-1H-indol-3-yl)-quinoxaline has been determined in ethyl acetate solution using the method of thermochromic shifts. Three different models have been tested and are compared to each other and to the results of ab initio calculations at the coupled cluster CC2/cc-pVTZ and SCS-CC2/cc-pVTZ level of theory. Good agreement is obtained for solvent polarity functions as defined by Bilot and Kawski (L. Bilot and A. Kawski, Z. Naturforsch., 1962, 17A, 621-627), while the original Lippert-Mataga type polarity functions fail to describe the excited state dipole moment correctly. We report an excited state dipole moment of the title compound of 8.5 D and a change upon excitation of 5.5 D.