Nonradiative Decay Mechanisms in DNA Model Systems

Experimental and theoretical research into excited electronic states of DNA has flourished during the past decade. The dynamics of excited states in monomeric nucleobases and defined-sequence oligo- and polynucleotides can now be routinely observed by ultrafast laser spectroscopy on time scales of hundreds of femtoseconds and beyond. Powerful quantum chemical methods are pinpointing the coupled nuclear and electronic motions responsible for nonradiative decay with unprecedented detail. For single bases, a fully microscopic description of nonradiative decay is almost at hand, and experiment and quantum dynamics calculations are increasingly congruent about deactivation events, including the bifurcation of excited-state populations on ultrafast time scales. For nucleobase multimers, there is evidence of both slower and faster rates of nonradiative decay than those in single bases, but the underlying mechanisms are poorly understood due to uncertainty about excited-state delocalization and energy transfer.