THE PHOTOCHROMISM OF THE DEHYDRODIANTHRONES. PARISER-PARR-POPLE CALCULATIONS

— The spectral features and related parameters of the ground state structure of 1,3,6′,8′-tetramethyldehydrodianthrone (TMD) which, according to the theoretical approach used in this paper, is identical with dehydrodianthrone, have been calculated with the aid of the Pariser-Pam-Pople semiempirical SCF LCAO MO method with CI. The calculated singlet-singlet absorption spectra and triplet-triplet absorption spectra are in very good agreement with previous experimental findings. The object of the present paper, however, is to theoretically establish the nature of the green photochromic species of TMD. Calculations have been made for several plausible structures for this species which have been proposed earlier. The results suggest that the valence-isomeric form V is the most probable structure of the green photochromic form of the dehydrodianthrone and its derivatives.