Absorption spectra and structure of substituted benzo[b]thiin-4-one 1,1-dioxides as new chromophores

Abstract

The absorption spectra of 2- and 3-substituted benzo[b]thiin-4-one 1,1-dioxides have been studied to characterise their chromophores. From PPP MO calculations with the parameters empirically adjusted from the X-ray analysis, the first absorption bands of these derivatives are approximated by HOMO–LUMO transition, which involves the charge transfer from the donor group to the carbonyl group. It is found that the sulphonyl group plays a less significant role in the first absorption band. This finding is supported by ab initio. calculations using STO-3G and STO-3G* basis sets and from results of resonance Raman spectroscopy and X-ray analysis.