AM1/CI, CNDO/S and ZINDO/S computations of absorption bands and their intensities in the UV spectra of some 4(3H)-quinazolinones

A detailed analysis of both frontier MOs and electronic transitions in UV spectra of 16 4-quinazolinone derivatives has been carried out in MO terms, by semiempirical methods AM1/CI, CNDO/S and ZINDO/S. On the basis of experimental and theoretical investigations by the ZINDO/S and CNDO/S methods the long-wavelength bands of 4(3H)-quinazolinone and its derivatives have been assigned to n-->pi(*) transition of the CO fragment and to the transition caused by intramolecular charge transfer from Ph and NCN fragments to CO group. It was shown that theoretically obtained electronic transitions applying method AM1/CI are not in agreement with experimental data observed for the 4(3H)-quinazolinone and 2,4(1H,3H)-quinazolinedione. Good correlation of theoretical and experimental data has been obtained by the method ZINDO/S for the wavelengths and the molar extinction coefficients of the compounds studied. Satisfactory correlation of theoretical and experimental data has also been obtained by the method CNDO/S with singly and doubly excited configurations, for the wavelengths only. Such correlations on experimental and theoretical wavelength and molar absorption coefficients of 4-quinazolinone derivatives are carried out for the first time.