UV Excited Single- and Double-Stranded DNA

There is a new paper out by us: "Electronic Excitation Processes in Single-Strand and Double-Strand DNA: A Computational Approach" in Topics in Current Chemistry. I made this figure to show all the possible processes happening:

• Monomer-like decay, which is also observed in the gas phase
• Delocalization and excitation energy transfer (with a focus on electron dynamics)
• Proton transfer between the strands, possibly leading to deactivation
• Electron transfer leading to charge transfer states
• Excimers, which may constitute stable trapping sites
• And finally the thing we are trying to avoid: photoproduct formation, which can lead to damage of the DNA

Which ones of these pathways are the important ones is not known yet. The problem is that every research group involved has their own convictions and it is not quite clear who is correct. In this paper we are of course not able to solve the problem, but at least we discuss the different computational methods applied to help make it more clear why the results by different groups are different.

My own contribution to the debate is the hypothesis of an exciplex with strong geometric distortions, small intermolecular separations, and strong orbital interactions that we described in this paper. Some other groups have obtained similar results: In particular Spiridoula Matsika did lots of work (e.g. this paper) where she invokes a bonded exciplex model. And a Chinese group who were the first to obtain these types of results, using semi-empirical calculations.