期刊
CHEMICAL PHYSICS
卷 347, 期 1-3, 页码 405-412出版社
ELSEVIER SCIENCE BV
DOI: 10.1016/j.chemphys.2007.09.056
关键词
photochemistry; ab initio molecular dynamics; surface hopping; density functional theory
Nonradiative decay of the photoexcited RNA base uracil has been studied in fully explicit aqueous solution using nonadiabatic ab initio molecular dynamics. Detailed comparison of the time-dependent nonadiabatic transition probability with specific molecular vibrational motions provides insight into the mechanism of the ultrafast internal conversion. From a monoexponential fit to the excited state ensemble population, the lifetime of the first electronically excited pi pi* singlet state has been determined to be 359 fs. Additional, reference, nonadiabatic simulations have been carried out in the gas phase, pinpointing the effects of the solvent on the photophysics of uracil. The gas phase excited state lifetime is calculated to be 608 fs, somewhat longer than in solution. In terms of excitation energies and geometrical parameters, the differences between gas phase and aqueous solution are found to be generally small. A notable exception is the excited state out-of-plane torsional motion about the C=C double bond, which appears severely damped by the solvent. Moreover, hydrogen bond interactions between the uracil oxygens and the solvent hydrogens are seen to enhance internal conversion. (C) 2007 Elsevier B.V. All rights reserved.
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