title: On the population of triplet excited states of 6-aza-2-thiothymine.
abstract: The mechanisms of population of the lowest excited triplet states of 6-aza-2-thiothymine were investigated by means of CASPT2//CASSCF quantum-chemical calculations, with extensive atomic natural orbital basis sets of double-ζ quality (ANO-L-VDZP). Several key structures corresponding to equilibrium geometries, surface crossings, minimum energy paths, and linear interpolation in internal coordinates were used to explain the ability to sensitize molecular oxygen. After population of the S2(1)(ππ*) state, the system evolves to the state minimum. At this point, and along the minimum energy path of the (1)(ππ*) state, two main mechanisms related to the triplet and singlet manifolds can be visualized, leading the system to the lowest triplet state, T1(3)(ππ*).
authors.affiliation: Instituto de Química, Universidade de São Paulo , and NAP-PhotoTech , USP Consortium for Photochemical Technology, Av. Prof. Lineu Prestes 748, 05508-900 São Paulo, São Paulo, Brazil. jpgobbo@iq.usp.br
authors.forename: João Paulo
authors.initials: JP
authors.lastname: Gobbo
authors.forename: Antonio Carlos
authors.initials: AC
authors.lastname: Borin
mesh_terms: D011789:Quantum Theory; D013941:Thymine / Q000031:analogs & derivatives* / Q000737:chemistry; D014227:Triazines
chemical_list: D014227:Triazines; C005823:2-thio-6-azathymine; D013941:Thymine