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Issue 8, 2017
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Ab initio molecular dynamics relaxation and intersystem crossing mechanisms of 5-azacytosine

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Abstract

The gas phase relaxation dynamics of photoexcited 5-azacytosine has been investigated by means of SHARC (surface-hopping including arbitrary couplings) molecular dynamics, based on accurate multireference electronic structure computations. Both singlet and triplet states were included in the simulations in order to investigate the different internal conversion and intersystem crossing pathways of this molecule. It was found that after excitation, 5-azacytosine undergoes ultrafast relaxation to the electronic ground state with a time constant of about 1 picosecond. Two important conical intersections have been identified as the funnel responsible for this deactivation mechanism. The very low intersystem crossing yield of 5-azacytosine has been explained by the size of the relevant spin–orbit coupling matrix elements, which are significantly smaller than in related molecules like cytosine or 6-azauracil. This difference is due to the fact that in 5-azacytosine the lowest singlet state is of nNπ* nature, whereas in cytosine and 6-azauracil it is of nOπ* character.

Graphical abstract: Ab initio molecular dynamics relaxation and intersystem crossing mechanisms of 5-azacytosine

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The article was received on 19 Nov 2016, accepted on 19 Jan 2017 and first published on 24 Jan 2017


Article type: Paper
DOI: 10.1039/C6CP07919A
Citation: Phys. Chem. Chem. Phys., 2017,19, 5888-5894
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    Ab initio molecular dynamics relaxation and intersystem crossing mechanisms of 5-azacytosine

    A. Carlos Borin, S. Mai, P. Marquetand and L. González, Phys. Chem. Chem. Phys., 2017, 19, 5888
    DOI: 10.1039/C6CP07919A

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