This chapter provides several interesting indications on the excited-state behavior of uracil derivatives in aqueous solution. The excited-state lifetimes of all the compounds examined, except 5-fluoro uracil, are dominated by a component shorter than 250 femtosecond. Calculations indicate that the relevant state for discussing the absorption and fluorescence spectra of uracil derivatives in aqueous solution is the ππ. The key steps in the ultrafast internal conversion are the pyramidalization of C5 and the out of plane motion of C5 substituent, which explains why the excited-state lifetime depends mainly on the nature of the C5 substituent. The shape of the potential energy surface of the S1 electronic states seems consistent with a very fast nonradiative decay. The result strongly supports the reliability of the general picture of the ultrafast ground state recovery of excited uracils in aqueous solution. © 2006 Elsevier B.V. All rights reserved.

*** IBB - CNR ***

Laboratoire Francis Perrin, CEA/DSM/DRECAM/SPAM-CNRS URA 2453, CEA Saclay, F-91191 Gif-sur-Yvette, France

Dipartimento di Chimica, Universita Federico II, Complesso Universitario Monte S. Angelo, Via Cintia, I-80126 Napoli, Italy

Istituto Biostrutture e Bioimmagini/CNR, V. Mezzocannone 6-80134 Napoli, Italy

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