The interaction of light with DNA can lead to photochemical damage, often via the formation of a thymine dimer photoproduct. On the other hand, DNA has the ability to dissipate a large part of the absorbed energy very efficiently through radiationless decay, thus avoiding the dangerous reactions. We will show how excimers and exciplexes between pi-stacked bases have an effect on both the photochemical and photophysical events in oligonucleotides. Using QM/MM studies to describe oligonucleotides of 18-20 base pairs where two or three bases are treated quantum-mechanically we show that besides the monomer like decay pathways for relaxation there are also excimers/exciplexes formed between pi-stacked bases that participate in the photophysical pathways. We will also show that exciplexes may be important in quenching the formation of photochemical products. Previous experimental work has shown that the nature of the neighboring bases affects the yield of the thymine dimer photoproduct. Our QM/MM studies explain these findings through the formation of exciplexes between thymine and a neighboring base.

Insights into the role of excimers/exciplexes in the photophysics and photochemistry of DNA

249th National Meeting (2015)

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