Photochemistry of hydrogen-bonded aromatic pairs: Quantum dynamical calculations for the pyrrole-pyridine complex.

Department of Chemistry, Technical University of Munich, D-85747 Garching, Germany.
Proceedings of the National Academy of Sciences (Impact Factor: 9.81). 10/2008; 105(35):12707-12. DOI: 10.1073/pnas.0801062105
Source: PubMed

ABSTRACT The photochemical dynamics of the pyrrole-pyridine hydrogen-bonded complex has been investigated with computational methods. In this system, a highly polar charge-transfer state of (1)pipi* character drives the proton transfer from pyrrole to pyridine, leading to a conical intersection of S(1) and S(0) energy surfaces. A two-sheeted potential-energy surface including 39 in-plane nuclear degrees of freedom has been constructed on the basis of ab initio multiconfiguration electronic-structure data. The non-Born-Oppenheimer nuclear dynamics has been treated with time-dependent quantum wave-packet methods, including the two or three most relevant nuclear degrees of freedom. The effect of the numerous weakly coupled vibrational modes has been taken into account with reduced-density-matrix methods (multilevel Redfield theory). The results provide insight into the mechanisms of excited-state deactivation of hydrogen-bonded aromatic systems via the electron-driven proton-transfer process. This process is believed to be of relevance for the ultrafast excited-state deactivation of DNA base pairs and may contribute to the photostability of the molecular encoding of the genetic information.

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