Exploring photoinduced proton and charge transfer in prototypical biomolecular systems

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. Using a combination of ultrafast spectroscopy and theoretical calculations, we have elucidated the primary non-radiative relaxation dynamics of a model nucleotide of guanine (G) and thymine (T) in buffered aqueous solution (d(GpT)). Experimentally, we unequivocally demonstrate that the Franck-Condon excited states of d(GpT) are significantly delocalised across both nucleobases, and mediate d(G+pT–) charge-transfer product formation on an ultrafast (< 350 fs) timescale.

Photoinduced proton transfer is a fundamental reaction, ubiquitous throughout nature and chemistry. Using time-resolved vibrational spectroscopy, we have studied a prototypical excited state proton transfer between hydrogen bonded coumarin–imidazole chromophores in chloroform solution. Using this approach, we are able to watch the nascent product formation from the earliest time epoch, and subsequent nuclear re-arrangements that accompany the highly exothermic reaction.