Exploring ultraviolet photoinduced charge-transfer dynamics in a model dinucleotide of guanine and thymine

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Abstract

An understanding of the initial photoexcited states of DNA is essential to unravelling deleterious photoinduced chemical reactions and the intrinsic ultrafast photoprotection of the genetic code for all life. In our combined experimental and theoretical study, we have elucidated the primary non-radiative relaxation dynamics of a model nucleotide of guanine and thymine (2'-deoxyguanosine 3'-monophospate 5'-thymidine, d(GpT)) in buffered aqueous solution. Experimentally, we unequivocally demonstrate that the Franck-Condon excited states of d(GpT) are significantly delocalised across both nucleobases, and mediate d(G+pT–) exciplex product formation on an ultrafast (< 350 fs) timescale. Theoretical studies show that the nature of the vertical excited states are very dependent on the specific geometry of the dinucleotide, and dictate the degree of delocalised, charge-transfer or localised character. Our mechanism for prompt exciplex formation involves a rapid change in electronic structure and includes a diabatic surface crossing very close to the Franck-Condon region mediating fast d(G+pT–) formation. Exciplexes are quickly converted back to neutral ground state molecules on a ~10 ps timescale with a high quantum yield, ensuring the photostability of the nucleotide sequence.
Original languageEnglish
Pages (from-to)14407-14417
Number of pages11
JournalPhysical Chemistry Chemical Physics
Volume21
Issue number26
Early online date6 Mar 2019
DOIs
Publication statusPublished - 3 Jul 2019

Structured keywords

  • BCS and TECS CDTs

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