title: Comparative study of the relaxation mechanisms of the excited states of cytosine and isocytosine.
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 (1)ππ(*) 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 (1)πσ(*) excited state of the amino-oxo form of isocytosine to the ground state of the amino-hydroxy tautomer.
authors: University of Plovdiv, Tzar Assen 24 Str., 4000 Plovdiv, Bulgaria.
authors: Rumyana I
authors: RI
authors: Bakalska
authors: Vassil B
authors: VB
authors: Delchev
mesh_terms: D003596:Cytosine / Q000031:analogs & derivatives* / Q000737:chemistry* / Q000528:radiation effects; D007536:Isomerism; D007700:Kinetics; D008958:Models, Molecular; D008968:Molecular Conformation / Q000528:radiation effects; D055668:Photochemical Processes; D011789:Quantum Theory; D013056:Spectrophotometry, Ultraviolet; D013816:Thermodynamics; D014466:Ultraviolet Rays
chemical_list: C093270:isocytosine; D003596:Cytosine