title: The peculiar spectral properties of amino-substituted uracils: a combined theoretical and experimental study.
abstract: A detailed experimental and computational study of the absorption and fluorescence spectra of 5-aminouracil (5 AU) and 6-aminouracil (6 AU) in aqueous solution is reported. The lowest energy band of the steady-state absorption spectra of 5 AU is considerably red-shifted, noticeably less intense, and broader than its counterpart in uracil (U). On the contrary, the 6 AU lowest energy absorption peak is close in energy to that of U, but it is much narrower and the transition is much more intense. The emission properties of 5 AU, 6 AU, and U are also very different. Both amino-substituted compounds exhibit indeed a much larger Stokes shift as compared to U, and the emission band of 5 AU is much narrower than that of 6 AU. Those features are fully rationalized with the help of PCM/TD-PBE0 calculations in aqueous solution and MS-CASPT2/CASSCF calculations in the gas phase. A stable minimum on the potential energy surface of the lowest energy bright state is found for 5 AU, both in the gas phase and in aqueous solution. For 6 AU a barrierless path leads to the conical intersection with the ground electronic state, but a nonplanar plateau region is predicted in aqueous solution, which is responsible for the very large Stokes shift. Some general considerations on the excited-state dynamics of uracil derivatives are also reported.
authors.affiliation: Laboratoire Francis Perrin, CEA/DSM/IRAMIS/SPAM - CNRS URA 2453, 91191 Gif-sur-Yvette.
authors.forename: Akos
authors.initials: A
authors.lastname: Bányász
authors.forename: Szilvia
authors.initials: S
authors.lastname: Karpati
authors.forename: Yannick
authors.initials: Y
authors.lastname: Mercier
authors.forename: Mar
authors.initials: M
authors.lastname: Reguero
authors.forename: Thomas
authors.initials: T
authors.lastname: Gustavsson
authors.forename: Dimitra
authors.initials: D
authors.lastname: Markovitsi
authors.forename: Roberto
authors.initials: R
authors.lastname: Improta
mesh_terms: D000042:Absorption; D005740:Gases / Q000737:chemistry; D008962:Models, Theoretical; D011789:Quantum Theory; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics; D014498:Uracil / Q000031:analogs & derivatives* / Q000737:chemistry
chemical_list: D005740:Gases; D014498:Uracil; C013400:6-aminouracil; C011166:5-aminouracil