Theoretical Investigation of Para-substitution Effect on the Electronic Transition, A2B2 ← X2B1 of Thiophenoxyl Radical

Abstract

Effect of chemical substitution at the para-position of the thiophenoxyl radical has been theoretically investigated in terms of energetics, structures, charge densities and orbital shapes for the ground and first electronically excited states. It is found that the adiabatic energy gap increases when CH3 or F is being substituted at the para-position. This change is attributed to the stabilization of the ground state of thiophenoxyl radical through the electron-donating effect of F or CH3 group as the charge or spin of the singly-occupied molecular orbital is delocalized over the entire molecule especially at the ground state whereas that at the excited state is rather localized on sulfur and little affected by chemical substitutions. Quantitative comparison of predictions based on four different quantum-mechanical calculation methods is presented.