Direct Observation of the Hole Carriers in DNA Photoinduced Charge Transport.

The excited state behavior of DNA hairpins possessing a diphenylacetylenedicarboxamide (DPA) linker separated from a single guanine-cytosine (G C) base pair by zero-to-six adenine-thymine (A-T) base pairs has been investigated. In the case of hairpins with zero or one A-T separating DPA and G, formation of both DPA anion radical (DPA(-center dot)) and G cation radical (G(+center dot)) are directly observed and characterized by their transient absorption and stimulated Raman spectra. For hairpins with two or more intervening A-T, the transient absorption spectra of DPA(-center dot) and the adenine polaron (A(n)(+center dot)) are observed. In addition to characterization of the hole carriers, the dynamics of each step in the charge separation and charge recombination process as well as the overall efficiency of charge separation have been determined, thus providing a complete account of the mechanism and dynamics of photoinduced charge transport in these DNA hairpins.