title: Effect of amino substitution on the excited state dynamics of uracil.
abstract: 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.
authors.affiliation: Laboratoire Francis Perrin, CEA/DSM/IRAMIS/SPAM - CNRS URA 2453, Gif-sur-Yvette, France.
authors.forename: Akos
authors.initials: A
authors.lastname: Bányász
authors.forename: Thomas
authors.initials: T
authors.lastname: Gustavsson
authors.forename: Erno
authors.initials: E
authors.lastname: Keszei
authors.forename: Roberto
authors.initials: R
authors.lastname: Improta
authors.forename: Dimitra
authors.initials: D
authors.lastname: Markovitsi
mesh_terms: D005453:Fluorescence; D005454:Fluorescence Polarization; D013997:Time Factors; D014498:Uracil / Q000031:analogs & derivatives* / Q000737:chemistry; D014867:Water / Q000737:chemistry
chemical_list: D014867:Water; D014498:Uracil; C013400:6-aminouracil; C011166:5-aminouracil