title: Acetylation makes the difference: a joint experimental and theoretical study on low-lying electronically excited states of 9H-adenine and 9-acetyladenine.
abstract: Vibronic spectra of 9H-adenine, 9-acetyladenine and several alkyladenines have been recorded by resonant two-photon ionization spectroscopy of the laser-desorbed molecules, entrained in a molecular beam. While adenine and the alkyladenines exhibit similar electronic spectra, 9-acetyladenine behaves considerably different. Theoretical absorption spectra of 9H-adenine and 9-acetyladenine were calculated using the combined density functional theory/multi-reference configuration interaction approach and using second order coupled cluster theory, in order to explain striking differences in the experimental spectra. The major differences between the 9H-adenine and the 9-acetyladenine absorption spectra can be traced back to the different configurations, which contribute to the excitations, both of the lowest ππ* and the nπ* states. While the excitations in 9H-adenine are localized in the chromophore, they show considerable charge transfer character from the chromophore to the acetyl group in the case of 9-acetyladenine.
authors.affiliation: Heinrich-Heine-Universität, Institut für Physikalische Chemie I, 40225 Düsseldorf, Germany.
authors.forename: Gernot
authors.initials: G
authors.lastname: Engler
authors.forename: Kai
authors.initials: K
authors.lastname: Seefeld
authors.forename: Michael
authors.initials: M
authors.lastname: Schmitt
authors.forename: Jörg
authors.initials: J
authors.lastname: Tatchen
authors.forename: Oliver
authors.initials: O
authors.lastname: Grotkopp
authors.forename: Thomas J J
authors.initials: TJ
authors.lastname: Müller
authors.forename: Karl
authors.initials: K
authors.lastname: Kleinermanns
mesh_terms: D000107:Acetylation; D000225:Adenine / Q000031:analogs & derivatives*; D008956:Models, Chemical; D011789:Quantum Theory
chemical_list: D000225:Adenine