title: Quantum chemical investigations on the nonradiative deactivation pathways of cytosine derivatives.
abstract: The nonradiative deactivation pathways of cytosine derivatives (cytosine, 5-fluorocytosine, 5-methylcytosine, and 1-methycytosine) and their tautomers are investigated by quantum chemical calculations, and the substituent effects on the deactivation process are examined. The MS-CASPT2 method is employed in the excited-state geometry optimization and also in the search for conical intersection points, and the potential energy profiles connecting the Franck-Condon point, excited-state minimum energy structures, and the conical intersection points are investigated. Our calculated vertical and adiabatic excitation energies are in quite good agreement with the experimental results, and the relative barrier heights leading to the conical intersections are correlated with the experimentally observed excite-state lifetimes, where the calculated barrier heights are in the order of cytosine < 5-methylcytosine < 5-fluorocytosine.
authors.affiliation: Catalysis Research Center, Hokkaido University , Sapporo 001-0021, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Nakayama
authors.forename: Shohei
authors.initials: S
authors.lastname: Yamazaki
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Taketsugu
mesh_terms: D044503:5-Methylcytosine / Q000737:chemistry*; D003596:Cytosine / Q000031:analogs & derivatives* / Q000737:chemistry*; D005437:Flucytosine / Q000737:chemistry*; D010782:Photolysis; D011789:Quantum Theory; D013237:Stereoisomerism; D013816:Thermodynamics
chemical_list: C031532:1-methylcytosine; D044503:5-Methylcytosine; D003596:Cytosine; D005437:Flucytosine