Structure and Dynamics of Photogenerated Triplet Radical Ion Pairs in DNA Hairpin Conjugates with Anthraquinone End Caps

• DOI: 10.1021/ja303721j
• Publication Date: 2012-06-07T15:49:01Z
• Authors: Raanan Carmieli; Amanda L. Smeigh; Sarah M. Mickley ...; Arun K. Thazhathv...; Masaaki Fuki; Yasuhiro Kobori; Frederick D. Lewis; Michael R. Wasiel...
• Keywords: Anthraquinones; Dynamics; Radical ion; Conjugate

A series of DNA hairpins (AqGn) possessing a tethered anthraquinone (Aq) end-capping group were synthesized in which the distance between Aq and guanine-cytosine (G-C) base pair was systematically varied by changing number (n - 1) adenine-thymine (A-T) pairs them. The photophysics photochemistry these investigated using nanosecond transient absorption time-resolved electron paramagnetic resonance (TREPR) spectroscopy. Upon photoexcitation, (1*)Aq undergoes rapid intersystem crossing to yield (3*)Aq, is capable oxidizing purine nucleobases resulting formation (3)(Aq(-•)Gn(+•)). All (3)(Aq(-•)Gn(+•)) radical ion exhibit asymmetric TREPR spectra with an spin polarization phase pattern enhanced emission (A/E) due their different triplet sublevel populations, are derived from corresponding non-Boltzmann populations (3*)Aq precursor. depend strongly on spin-spin dipolar interaction weakly exchange coupling. anisotropy makes it possible determine that π systems Aq(-•) G(+•) within parallel one another. Charge recombination long-lived displays unusual bimodal dependence results change rate-determining step for charge n < 4 coherent superexchange > 4.