title: Efficient deactivation of a model base pair via excited-state hydrogen transfer.
abstract: We present experimental and theoretical evidence for an excited-state deactivation mechanism specific to hydrogen-bonded aromatic dimers, which may account, in part, for the photostability of the Watson-Crick base pairs in DNA. Femtosecond time-resolved mass spectroscopy of 2-aminopyridine clusters reveals an excited-state lifetime of 65 +/- 10 picoseconds for the near-planar hydrogen-bonded dimer, which is significantly shorter than the lifetime of either the monomer or the 3- and 4-membered nonplanar clusters. Ab initio calculations of reaction pathways and potential-energy profiles identify the mechanism of the enhanced excited-state decay of the dimer: Conical intersections connect the locally excited 1pipi* state and the electronic ground state with a 1pipi* charge-transfer state that is strongly stabilized by the transfer of a proton.
authors.affiliation: Max Born Institute Berlin, Max-Born-Strasse 2a, D-10247 Berlin, Germany. schultz@mbi-berlin.de
authors.forename: Thomas
authors.initials: T
authors.lastname: Schultz
authors.forename: Elena
authors.initials: E
authors.lastname: Samoylova
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Radloff
authors.forename: Ingolf V
authors.initials: IV
authors.lastname: Hertel
authors.forename: Andrzej L
authors.initials: AL
authors.lastname: Sobolewski
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Domcke
mesh_terms: D000631:Aminopyridines / Q000737:chemistry*; D020029:Base Pairing; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D004247:DNA / Q000737:chemistry*; D019281:Dimerization; D006859:Hydrogen / Q000737:chemistry*; D006860:Hydrogen Bonding; D013058:Mass Spectrometry; D008956:Models, Chemical; D011522:Protons; D013816:Thermodynamics; D014466:Ultraviolet Rays
chemical_list: D000631:Aminopyridines; D011522:Protons; D006859:Hydrogen; D004247:DNA; C032439:alpha-aminopyridine