Communication: the dark singlet state as a doorway state in the ultrafast and efficient intersystem crossing dynamics in 2-thiothymine and 2-thiouracil.

Imagen de Carlos E Crespo-Hernández
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TítuloCommunication: the dark singlet state as a doorway state in the ultrafast and efficient intersystem crossing dynamics in 2-thiothymine and 2-thiouracil.
Publication TypeJournal Article
Year of Publication2014
AutoresPollum, M, Crespo-Hernández, CE
JournalJ Chem Phys
Volume140
Issue7
Pagination071101
Date Published2014 Feb 21
ISSN1089-7690
Abstract

Femtosecond broadband transient absorption experiments are reported for 2-thiothymine and 2-thiouracil in aqueous buffer solution and in acetonitrile. It is shown that the S1(nπ*) state acts as a doorway state in the ultrafast and efficient population of the T1(ππ*) state upon 316 nm excitation. A sequential kinetic model is presented to explain the excited-state dynamics in 2-thiothymine and 2-thiouracil upon UVA excitation: S2(ππ*) → S1(nπ*) → T1(ππ*). The experimental results are also used to scrutinize the excited-state relaxation pathways recently predicted for 2-thiouracil at the CASPT2//CASSCF level of theory [G. Cui and W. Fang, J. Chem. Phys. 138, 044315 (2013)]. The efficient population of the T1(ππ*) state for both 2-thiothymine and 2-thiouracil in a few hundreds of femtoseconds lends further support to the emerging idea that thiobase derivatives exhibit photo-toxic properties that can be effectively harnessed in photo-chemotherapeutic applications.

DOI10.1063/1.4866447
Alternate JournalJ Chem Phys
PubMed ID24559331