Publications (6)50.57 Total impact
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Article: Excited-state dynamics of cytosine tautomers.
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ABSTRACT: We report the relaxation dynamics of keto and enol or keto-imino cytosine, photoexcited in the wavelength range of 260-290 nm. Three transients with femtosecond to hundreds of picoseconds lifetimes are observed for the biologically relevant keto tautomer and are assigned to internal conversion and excited-state tautomerization. Only two transients with femtosecond and picosecond lifetimes are identified for the enol or keto-imino tautomer and are assigned to internal conversion processes. The results are discussed in the context of published ab initio theory.Journal of the American Chemical Society 10/2009; 131(46):16939-43. · 9.91 Impact Factor -
Article: Observation of proton transfer in 2-aminopyridine dimer by electron and mass spectroscopy.
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ABSTRACT: A photoinitiated intermolecular electron-proton transfer reaction in 2-aminopyridine dimer was investigated by femtosecond pump-probe electron-ion coincidence spectroscopy and accompanying theory. Excited-state population dynamics were observed in real time by time-resolved mass spectroscopy, and the respective excited-state character of locally excited and proton/hydrogen transfer states was identified in coincident electron spectra. Two reaction channels for an ultrafast (sub-50 fs) and a slower (approximately 75 ps) proton/hydrogen transfer were observed and indicate that vibrational energy redistribution may lead to efficient population trapping in the excited state. Spectroscopic evidence of an unexpected hydrogen-transfer reaction in photoexcited aminopyridine monomer is also presented.The Journal of Physical Chemistry A 08/2009; 113(29):8195-201. · 2.95 Impact Factor -
Article: Thymine relaxation after UV irradiation: the role of tautomerization and pi-sigma* states.
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ABSTRACT: Ab initio calculations and femtosecond pump-probe ionization experiments were carried out to identify excited state relaxation processes in isolated thymine monomer and small thymine-water clusters. Three transient species with life times of < or =100 fs, 7 ps and >1 ns were observed in the experiments on gas phase thymine. The longer-lived transients were weak or absent in thymine-water clusters. Available theoretical results on thymine agree with the assignment of low-lying pi-pi* and n-pi* excited states to the femtosecond and picosecond transients but the assignment of the third transient remains opaque. Our theoretical results seem to exclude the possibility of ground or excited state tautomerization as well as the involvement of states with pi-sigma* character. Remaining explanations for the observed transients are: very fast intersystem crossing to the triplet manifold or the observation of transient signals from local minima on the potential energy surfaces.Physical Chemistry Chemical Physics 06/2009; 11(20):3927-34. · 3.57 Impact Factor -
Article: On the puzzling deactivation mechanism of thymine after light irradiation
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ABSTRACT: The possible deactivation mechanisms of thymine after UV light irradiation are reviewed in the light of theoretical calculations. Recent experiments reveal that three transient species with lifetimes in the fs, ps, and ns regime are present in thymine. The possibility of ground or excited state tautomerization is explored and discarded. The role of πσ∗ states, as well as of the proposed minimum of the ππ∗ excited state surface are assessed. In view of the obtained calculations and results available from the literature, the measured time scales can be tentatively attributed to a model involving different conical intersections between the ππ∗, nπ∗, and the electronic ground state, as well as deactivation via the triplet states. Time‐resolved photoelectron experiments supported by theoretical calculations are proposed to appraise the validity of this model.AIP Conference Proceedings. 12/2008; 1080(1):169-175. -
Article: Electronic structure of adenine and thymine base pairs studied by femtosecond electron-ion coincidence spectroscopy.
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ABSTRACT: Femtosecond pump-probe spectroscopy was combined with photoelectron-photoion coincidence detection to investigate the electronic structure and dynamics of isolated adenine (A) and thymine (T) dimers and the adenine-thymine (AT) base pair. The photoelectron spectra show that pipi* and npi* states are only weakly perturbed in the hydrogen-bound dimers as compared to the monomers. For cationic base pairs with internal energies greater than 1 eV, we observed considerable cluster fragmentation into protonated monomers. This process selectively removed signals from the npi* --> n-1 ionization channel in all dimers. The photoelectron spectra are compared to time-resolved mass spectra and confirm the assignment of short-lived pipi* and npi* populations in the adenine, thymine, and mixed AT dimers.The Journal of Physical Chemistry A 11/2007; 111(46):11743-9. · 2.95 Impact Factor -
Article: Efficient deactivation of a model base pair via excited-state hydrogen transfer.
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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.Science 01/2005; 306(5702):1765-8. · 31.20 Impact Factor
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Institutions
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2009
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Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie
Berlin, Land Berlin, Germany -
Friedrich-Schiller-Universität Jena
- Institut für Physikalische Chemie
Jena, Thuringia, Germany
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