title: Multi-pathway excited state relaxation of adenine oligomers in aqueous solution: a joint theoretical and experimental study.
abstract: The singlet excited states of adenine oligomers, model systems widely used for the understanding of the interaction of ultraviolet radiation with DNA, are investigated by fluorescence spectroscopy and time-dependent (TD) DFT calculations. Fluorescence decays, fluorescence anisotropy decays, and time-resolved fluorescence spectra are recorded from the femtosecond to the nanosecond timescales for single strand (dA)20 in aqueous solution. These experimental observations and, in particular, the comparison of the fluorescence behavior upon UVC and UVA excitation allow the identification of various types of electronic transitions with different energy and polarization. Calculations performed for up to five stacked 9-methyladenines, taking into account the solvent, show that different excited states are responsible for the absorption in the UVC and UVA spectral domains. Independently of the number of bases, bright excitons may evolve toward two types of excited dimers having π-π* or charge-transfer character, each one distinguished by its own geometry and spectroscopic signature. According to the picture arising from the joint experimental and theoretical investigation, UVC-induced fluorescence contains contribution from 1) exciton states with a different degree of localization, decaying within a few ps, 2) "neutral" excited dimers decaying on the sub-nanosecond timescale, being the dominant species, and 3) charge-transfer states decaying on the nanosecond timescale. The majority of the photons emitted upon UVA excitation are related to charge-transfer states.
authors: CNRS, IRAMIS, SPAM, Laboratoire Francis Perrin, URA 2453 CEA/Saclay, 91191 Gif-sur-Yvette, France.
authors: Akos
authors: A
authors: Banyasz
authors: Thomas
authors: T
authors: Gustavsson
authors: Delphine
authors: D
authors: Onidas
authors: Pascale
authors: P
authors: Changenet-Barret
authors: Dimitra
authors: D
authors: Markovitsi
authors: Roberto
authors: R
authors: Improta
mesh_terms: D000225:Adenine / Q000737:chemistry*; D008958:Models, Molecular; D011789:Quantum Theory; D012996:Solutions; D013056:Spectrophotometry, Ultraviolet; D013997:Time Factors; D014466:Ultraviolet Rays; D014867:Water / Q000737:chemistry
chemical_list: D012996:Solutions; D014867:Water; D000225:Adenine