Electronic Structures of Uracil and Its Anions

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Abstract
Electronic structures of uracil and its anions were theoretically investigated by a modified CNDO-CI method. Theoretical results were in good agreement with the observed spectra of uracil and of both the uracil-3-ide and uracil-1-ide anions, indicating that the second π-π* band of uracil may tentatively be assigned to the 215 nm band observed in circular dichroism spectrum, and that the lowest singlet and triplet states of uracil are n-π* and π-π* states, respectively, in accord with the observed solvent dependence on emission properties. The first π-π* band of uracil-1-ide anion was correctly predicted by the method at longer wavelengths than the corresponding band of uracil-3-ide anion. For the purpose of comparison, a modified INDO-CI, CNDO/S-CI, and a modified π-SCF-MO-CI methods were also applied to the molecules under consideration. The results were only partly successful in predicting the observed spectra.