Electronic Absorption Spectra of Substituted Anthraquinones and Their Simulation Using ZINDO/S Method

Electronic absorption spectra of chrysophanol (1,8-dihydroxy-3-methylanthracene-9,10-dione), physcion (1,8-dihydroxy-3-methoxy-6-methylanthracene-9,10-dione) and emodin (1,3,8trihydroxy- 6-methylanthracene-9,10-dione) were investigated. Molecular geometries of the substituted anthraquinones in the ground state were optimized using semiempirical AM1 method without imposing any symmetry constrains. The ground state geometries of all the molecular systems were found to be planar. For interpretation of the spectra, ZINDO/S-CI investigation employing singly excited configuration using the completely optimized geometries was carried out. Such calculations on the electronic spectra of chrysophanol, physcion, and emodin were carried out for the first time. On the basis of these investigations, the assignments of the spectra were successfully predicted.