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International Journal of Photoenergy
Volume 2015, Article ID 937474, 6 pages
Research Article

Bonded Excimer in Stacked Cytosines: A Semiclassical Simulation Study

1Institute of Computational Chemistry, Chongqing University of Posts and Telecommunications, Chongqing, 400065, China
2Department of Physical Sciences, Nicholls State University, P.O. Box 2022, Thibodaux, LA 70310, USA
3Department of Physics and Astronomy, Texas A&M University, College Station, TX 77843-4242, USA

Received 13 May 2014; Accepted 21 July 2014

Academic Editor: Fuli Li

Copyright © 2015 Weifeng Wu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The formation of a covalent bond between two stacked cytosines, one of which is excited by an ultrafast laser pulse, was studied by semiclassical dynamics simulations. The results show that a bonded excimer is created, which sharply lowers the energy gap between the LUMO and HOMO and consequently facilitates the deactivation of the electronically excited molecule. This is different from the case of two stacked adenines, where the formation of a covalent bond alters the nonadiabatic deactivation mechanism in two opposite ways. It lowers the energy gap and consequently leads to the coupling between the HOMO and LUMO levels, thus enhancing the deactivation of the electronically excited molecule. On the other hand, it leads to restriction of the deformation vibration of the pyrimidine in the excited molecule, because of a steric effect, and this delays the deactivation process of the excited adenine molecule with return to the electronic ground state.