title: On the intrinsic population of the lowest triplet state of thymine.
abstract: The population of the lowest triplet state of thymine after near-UV irradiation has been established, on the basis of CASPT2//CASSCF quantum chemical calculations, to take place via three distinct intersystem crossing mechanisms from the initially populated singlet bright 1pipi* state. Two singlet-triplet crossings have been found along the minimum-energy path for ultrafast decay of the singlet state at 4.8 and 4.0 eV, involving the lowest 3npi* and 3pipi* states, respectively. Large spin-orbit coupling elements predict efficient intersystem crossing processes in both cases. Another mechanism involving energy transfer from the lowest 1npi* state with much larger spin-orbit coupling terms can also be proposed. The wavelength dependence measured for the triplet quantum yield of pyrimidine nucleobases is explained by the location and accessibility of the singlet-triplet crossing regions.
authors.affiliation: Instituto de Ciencia Molecular, Universitat de València, Apartado 22085, ES-46071, Valencia, Spain.
authors.forename: Juan José
authors.initials: JJ
authors.lastname: Serrano-Pérez
authors.forename: Remedios
authors.initials: R
authors.lastname: Gonzalez-Luque
authors.forename: Manuela
authors.initials: M
authors.lastname: Merchan
authors.forename: Luis
authors.initials: L
authors.lastname: Serrano-Andrés
mesh_terms: D008958:Models, Molecular; D008968:Molecular Conformation; D013941:Thymine / Q000737:chemistry*
chemical_list: D013941:Thymine