Crossover from superexchange to hopping as the mechanism for photoinduced charge transfer in DNA hairpin conjugates

Frederick D. Lewis*, Huihe Zhu, Pierre Daublain, Torsten Fiebig, Milen Raytchev, Qiang Wang, Vladimir Shafirovich

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

149 Scopus citations

Abstract

The mechanism and dynamics of photoinduced charge separation and charge recombination have been investigated in synthetic DNA hairpins possessing donor and acceptor stilbenes separated by one to seven A:T base pairs. The application of femtosecond broadband pump-probe spectroscopy, nanosecond transient absorption spectroscopy, and picosecond fluorescence decay measurements permits detailed analysis of the formation and decay of the stilbene acceptor singlet state and of the charge-separated intermediates. When the donor and acceptor are separated by a single A:T base pair, charge separation occurs via a single-step superexchange mechanism. However, when the donor and acceptor are separated by two or more A:T base pairs, charge separation occurs via a multistep process consisting of hole injection, hole transport, and hole trapping. In such cases, hole arrival at the electron donor is slower than hole injection into the bridging A-tract. Rate constants for charge separation (hole arrival) and charge recombination are dependent upon the donor-acceptor distance; however, the rate constant for hole injection is independent of the donor-acceptor distance. The observation of crossover from a superexchange to a hopping mechanism provides a "missing link" in the analysis of DNA electron transfer and requires reevaluation of the existing literature for photoinduced electron transfer in DNA.

Original languageEnglish (US)
Pages (from-to)791-800
Number of pages10
JournalJournal of the American Chemical Society
Volume128
Issue number3
DOIs
StatePublished - Jan 25 2006

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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