title: Excited-state interactions in diastereomeric flurbiprofen-thymine dyads.
abstract: Excited-state interactions between (S)- or (R)-flurbiprofen ((S)- or (R)-FBP) and thymidine (dThd) covalently linked in dyads 1 or 2 have been investigated. In both dyads, the only emitting species is (1)FBP*, but with a lower fluorescence quantum yield (φ(F)) and a shorter fluorescence lifetime (τ(F)) than when free in solution. These results indicate that dynamic quenching occurs either by electron transfer or via exciplex formation, with FBP as the charge-donating species. In acetonitrile, both mechanisms are favored, while in dioxane exciplex formation is predominating. Isomer 1 displays lower values of φ(F) and τ(F) than its analogue 2, indicating that the relative spatial arrangement of the chromophores plays a significant role. The triplet quantum yields (φ(T)) of 1 and 2 are significantly higher than the expectations based solely on (1)FBP*-dThd intersystem crossing quantum yields (φ(ISC)), with φ(T) (1) > φ(T) (2). This can be explained in terms of intramolecular charge recombination at the radical ion pairs and/or the exciplexes, which would be again dependent on geometrical factors. The triplet lifetimes (τ(T)) of (3)FBP*-dThd and free (3)FBP* are similar, indicating the lack of excited-state interactions at this stage. The FBP-dThd dyads could, in principle, constitute appropriate model systems for the elucidation of the excited-state interactions in noncovalent DNA-ligand complexes.
authors.affiliation: Chemistry Department/Institute of Chemical Technology UPV-CSIC, Universitat Politècnica de València, 46022 Valencia, Spain.
authors.forename: Paula
authors.initials: P
authors.lastname: Bonancía
authors.forename: Ignacio
authors.initials: I
authors.lastname: Vayá
authors.forename: M José
authors.initials: MJ
authors.lastname: Climent
authors.forename: Thomas
authors.initials: T
authors.lastname: Gustavsson
authors.forename: Dimitra
authors.initials: D
authors.lastname: Markovitsi
authors.forename: M Consuelo
authors.initials: MC
authors.lastname: Jiménez
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Miranda
mesh_terms: D000042:Absorption; D004579:Electron Transport; D005480:Flurbiprofen / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013237:Stereoisomerism; D013941:Thymine / Q000737:chemistry*
chemical_list: D005480:Flurbiprofen; D013941:Thymine