The excited state deactivation of two amino-substituted uracils, 5-aminouracil (5AU) and 6-aminouracil (6AU) in aqueous solution was studied by femtosecond fluorescence upconversion. The fluorescence of 6AU decays as fast as that of uracil with a unique time constant of about 100 femtoseconds. The fluorescence of 5AU exhibits a more complex behavior, fundamentally different from what we found in any other uracils: the decays are globally slower (up to several picoseconds) and depend strongly on the wavelength. This difference is attributed to the particular character of the amino group, affecting the out-of-plane motion of the 5-substituent which has been shown to be crucial for the ultrafast internal conversion occurring in uracils. Our observations indicate instead the formation of a transient fluorescent state which in turn is deactivated by a different relaxation process specific to the amino group. © The Royal Society of Chemistry and Owner Societies.

*** IBB - CNR ***

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

Eötvös Lorand University Budapest, Department of Physical Chemistry, P.O. Box 32, 1518 Budapest 112, Hungary

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

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

E tv s Lorand University Budapest, Department of Physical Chemistry, P. O. Box 32, 1518 Budapest 112, Hungary

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Chandra, A. K., Uchimaru, T., Zeegers-Huyskens, T., Theoretical study on protonated and deprotonated 5-substituted uracil derivatives and their complexes with water (2002) J. Mol. Struct., 605, pp. 213-220

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Palafox, M. A., Tardajos, G., Guerrero-Martinez, A., Rastogi, V. K., Mishra, D., Ojha, S. P., Kiefer, W., FT-IR, FT-Raman spectra, density functional computations of the vibrational spectra and molecular geometry of biomolecule 5-aminouracil (2007) Chem. Phys., 340, pp. 17-31

Estrin, D. A., Paglieri, L., Corongiu, G., A density functional study of tautomerism of uracil and cytosine (1994) J. Phys. Chem., 98, pp. 5653-5660

Marian, C. M., Schneider, F., Kleinschmidt, M., Tatchen, J., Electronic excitation and singlet-triplet coupling in uracil tautomers and uracil-water complexes. a quantum chemical investigation (2002) Eur. Phys. J. D: Atom. Mol. Opt. Phys., 20, pp. 357-367

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Pal, S. K., Peon, J., Zewail, A. H., Ultrafast decay and hydration dynamics of DNA bases and mimics (2002) Chem. Phys. Lett., 363, pp. 57-63