THEORETICAL-ANALYSIS OF THE IR AND VISIBLE ABSORPTION SPECTRAL CHANGEBY THE PHASE-TRANSITION OF THE CRYSTALS OF 2,3-DIPHENYLTHIO-)-1,4-NAPHTHOQUINONES AND 2,3-DI(P-CHLOROTHIOPHENYL)-1,4-NAPHTHOQUINONES

The isomerization mechanism of 2,3-Diphenylthio- and 2,3-Di(p-chloro t hiophenyl)-1,4-Naphthoquinones was determined by using ab initio calcu lations and compared IR and visible absorption spectra. The optimized geometries using RHF/3-21G method were determined with C-2 symmetry f or the violet form, and with C-s symmetry for the red one. Visible spe ctra were identified by the charge transfers from thiophenyl group to naphthoquinone ring of these two isomers. The lowest allowed excitated states of these isomers were characterized by the the charge transfer (CT) from next-HOMO to LUMO in the violet form, and from HOMO to LUMO in the red form. The IR active CO stretching mode in the naphthoquino ne ring appear as the symmetric type on the violet form, and anti-symm etric type on the red one.