Comparative study of the relaxation mechanisms of the excited states of cytosine and isocytosine |
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Authors: | Rumyana I. Bakalska Vassil B. Delchev |
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Affiliation: | 1. Faculty of Chemistry, University of Plovdiv, Tzar Assen 24 Str., 4000, Plovdiv, Bulgaria
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Abstract: | An experimental and theoretical investigation was performed to study the photostability of cytosine and isocytosine. The experimental UV irradiation of acetonitrile solutions of the two compounds showed that the amino-oxo tautomer of cytosine is photostable while the amino-oxo tautomer of isocytosine tautomerizes to the amino-hydroxy form. The theoretical investigations were carried out at the CC2 level of theory. They were performed to explain the experimental observations. It was found that the 1ππ* excited states of the ring deformation mechanisms of cytosine and isocytosine relax (internal conversion) to the ground states of the amino-oxo forms of the compounds. We propose a channel for the radiationless deactivation of the repulsive 1πσ* excited state of the amino-oxo form of isocytosine to the ground state of the amino-hydroxy tautomer. |
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