Cyclobutane Thymine Photodimerization Mechanism Revealed by Nonadiabatic Molecular Dynamics.
The formation of cyclobutane thymine dimers is one of the most important DNA carcinogenic photolesions induced by ultraviolet irradiation. The long debated question whether thymine dimerization after direct light excitation involves singlet or triplet states is investigated here for the first time using nonadiabatic molecular dynamics simulations. We find that the precursor of this [2 + 2] cycloaddition reaction is the singlet doubly π2π*2excited state, which is spectroscopically rather dark. Excitation to the bright1ππ* or dark1nπ* excited states does not lead to thymine dimer formation. In all cases, intersystem crossing to the triplet states is not observed during the simulated time, indicating that ultrafast dimerization occurs in the singlet manifold. The dynamics simulations also show that dimerization takes place only when conformational control happens in the doubly excited state.
Institute of Theoretical Chemistry, Faculty of Chemistry, University of Vienna , Währinger Straße 17, 1090 Vienna, Austria.
Clemens
C
Rauer
Institute of Theoretical Chemistry, Faculty of Chemistry, University of Vienna , Währinger Straße 17, 1090 Vienna, Austria.
Juan J
JJ
Nogueira
Institute of Theoretical Chemistry, Faculty of Chemistry, University of Vienna , Währinger Straße 17, 1090 Vienna, Austria.
Philipp
P
Marquetand
Institute of Theoretical Chemistry, Faculty of Chemistry, University of Vienna , Währinger Straße 17, 1090 Vienna, Austria.
Leticia
L
González