A quantum mechanical study of the interplay between the bright ππ* (Sπ) and the dark nπ* (Sn) excited states of thymine in the gas phase is reported. TD-PBE0 calculations indicate that within a relevant region of the Sπ surface, connecting the Franck-Condon point with the planar and non-planar S π plateau, Sπ and Sn are almost isoenergetic and that a Sπ→Sn population transfer is therefore likely. This latter process has been studied by two complementary quantum dynamical approaches, a three-dimensional anharmonic (quartic) model, and a full-dimensional harmonic linear vibronic coupling model. Although providing slightly different quantitative indications, both approaches predict a very fast and effective Sπ→Sn population transfer: already at 50 fs the Sn state is significantly populated (20-40 %) and this population persists or even increases on a longer time scale. Walking the line: A quantum mechanical study of the interplay between the bright ππ* (Sπ) and the dark nπ* (Sn) excited states of thymine (see picture) in the gas phase is reported. The process is studied by two complementary quantum dynamical approaches, a three-dimensional anharmonic (quartic) model, and a full-dimensional harmonic linear vibronic coupling model. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

*** IBB - CNR ***

CNR (Consiglio Nazionale Delle Ricerche), Istituto di Chimica Dei Composti, OrganoMetallici (ICCOM-CNR), UOS di Pisa, Area della Ricerca, via G. Moruzzi 1, I-56124 Pisa, Italy

Scuola Normale Superiore, Piazza dei Cavalieri, 7, I-56126 Pisa, Italy

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