THE MOLECULAR-STRUCTURES AND THE ABSORPTION MAXIMA OF THE H-CHROMOPHORES OF THE INDIGOID DYES

The molecular structures of the H-chromophore of the indigoid dyes and five other isomers are studied by ab initio MP2/6-31 + G*//HF/6-31 + G* method. The bond angles are affected by the pi-electron conjugation. The molecular structures of the H-chromophores and indigoid dyes indicate that the benzene rings and the five-membered rings are structurally important. The absorption maxima of the H-chromophores are successfully calculated by CI-singles-MP2/6-31 + G* theory for the first time and correspond to the HOMO, LUMO transition. All these transitions are the pi-pi* transitions. Like the indigoid dyes, trans isomers have the bathochromic shifts of the absorption maxima, and the bathochromic shifts are found with the best donor group of -NH. From these calculations, the absorption maxima of some indigoid dyes can be explained by their H-chromophores qualitatively. (C) 1995 by John Wiley & Sons, Inc.