A THEORETICAL-STUDY OF THE INDIGOID DYES AND THEIR CHROMOPHORE

A theoretical study of the electronic spectra of indigo, bispyrroleind igo, and the H-chromophore, thought to be the basic structure leading to the intense absorption in the visible spectrum of the indigoid dyes , has been performed by means of the complete active space (GAS) SCF m ethod and the multiconfigurational second-order perturbation theory (C ASPT2). The calculations include excitation energies, oscillator stren gths, and transition moment directions for the valence singlet states of the molecules. The assumption that the H-chromophore is responsible for the absorption in the visible spectrum is quantitatively revisite d with the help of the modern ab initio methodologies and the main fea tures of these molecules are theoretically analyzed, some of them for the first time.