Electronic excitation processes in single-strand and double-strand DNA: a computational approach.

Absorption of UV light by nucleic acids can lead to damaging photoreactions, which may ultimately lead to mutations of the genetic code. The complexity of the photodynamical behavior of nucleobases in the DNA double-helix provides a great challenge to both experimental and computational chemists studying these processes. Starting from the initially excited states, the main question regards the understanding of the subsequent relaxation processes, which can either utilize monomer-like deactivation pathways or lead to excitonic or charge transfer species with new relaxation dynamics. After a review of photophysical processes in single nucleobases we outline the theoretical background relevant for interacting chromophores and assess a large variety of computational approaches relevant for the understanding of the nature and dynamics of excited states of DNA. The discussion continues with the analysis of calculations on excitonic and charge transfer states followed by the presentation of the dynamics of excited-state processes in DNA. The review is concluded by topics on proton transfer in DNA and photochemical dimer formation of nucleobases.