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Issue 34, 2006
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Time-resolved photoelectron and photoion fragmentation spectroscopy study of 9-methyladenine and its hydrates: a contribution to the understanding of the ultrafast radiationless decay of excited DNA bases

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Abstract

The excited state dynamics of the purine base 9-methyladenine (9Me-Ade) has been investigated by time- and energy-resolved photoelectron imaging spectroscopy and mass-selected ion spectroscopy, in both vacuum and water-cluster environments. The specific probe processes used, namely a careful monitoring of time-resolved photoelectron energy distributions and of photoion fragmentation, together with the excellent temporal resolution achieved, enable us to derive additional information on the nature of the excited states (ππ*, nπ*, πσ*, triplet) involved in the electronic relaxation of adenine. The two-step pathway we propose to account for the double exponential decay observed agrees well with recent theoretical calculations. The near-UV photophysics of 9Me-Ade is dominated by the direct excitation of the ππ* (1Lb) state (lifetime of 100 fs), followed by internal conversion to the nπ* state (lifetime in the ps range) via conical intersection. No evidence for the involvement of a πσ* or a triplet state was found. 9Me-Ade–(H2O)n clusters have been studied, focusing on the fragmentation of these species after the probe process. A careful analysis of the fragments allowed us to provide evidence for a double exponential decay profile for the hydrates. The very weak second component observed, however, led us to conclude that the photophysics were very different compared with the isolated base, assigned to a competition between (i) a direct one-step decay of the initially excited state (ππ* La and/or Lb, stabilised by hydration) to the ground state and (ii) a modified two-step decay scheme, qualitatively comparable to that occurring in the isolated molecule.

Graphical abstract: Time-resolved photoelectron and photoion fragmentation spectroscopy study of 9-methyladenine and its hydrates: a contribution to the understanding of the ultrafast radiationless decay of excited DNA bases

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Publication details

The article was received on 08 May 2006, accepted on 22 Jun 2006 and first published on 17 Jul 2006


Article type: Paper
DOI: 10.1039/B606437J
Citation: Phys. Chem. Chem. Phys., 2006,8, 3978-3987
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    Time-resolved photoelectron and photoion fragmentation spectroscopy study of 9-methyladenine and its hydrates: a contribution to the understanding of the ultrafast radiationless decay of excited DNA bases

    C. Canuel, M. Elhanine, M. Mons, F. Piuzzi, B. Tardivel and I. Dimicoli, Phys. Chem. Chem. Phys., 2006, 8, 3978
    DOI: 10.1039/B606437J

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