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

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 s...

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Bibliographic Details
Published in:The Journal of chemical physics 2014-02, Vol.140 (7), p.071101-071101
Main Authors: Pollum, Marvin, Crespo-Hernández, Carlos E
Format: Article
Language:English
Subjects:
Acetonitriles - chemistry
Buffers
Electrons
Kinetics
Quantum Theory
Spectrophotometry, Ultraviolet
Thiouracil - chemistry
Thymine - analogs & derivatives
Thymine - chemistry
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Summary: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.
ISSN:0021-9606
1089-7690
DOI:10.1063/1.4866447