抄録
The semiempirical SC F-MO-CI calculations were performed with the aid of the variable β-core procedure for a systematic investigation of the π-electronic structures and spectra of a series of pyrones and coumarins including sulfur derivatives. The calculated results on the π-π* transitions indicated several significant effects of the heteroatom replacement upon the polarization direction and oscillator strength. The calculated values of the singlet π-π* transition energies for the compounds excepting the thiothia-derivatives and the polarization directions of the lowest two π-π* transitions of coumarins and so on were found to be in good agreement with the observed results. Also, the changes in the π-electronic distribution in going from the ground to the lowest 1 (π, π*) and/or 3 (π, π*) state were in good correlation with a few experimental facts.
