Kinetics of charge separation in poly(A)-poly(T) DNA hairpins.

A kinetics model is designed to investigate the charge separation (CT) process in stilbene-capped DNA hairpins composed of AT base pairs. This model combines standard tunneling and hopping electron transport with exciplex formation upon photoexcitation of the acceptor stilbene and its neighboring adenine and is capable of interpreting the CT rate and yield data within experimental accuracy. An analysis of hopping transport within the framework of a 1-D diffusion model results in a calculation of the nearest-neighbor CT rate to be approximately 1.2 ns(-1). In agreement with previous experimental and theoretical work, it is ascertained through a novel application of an extension to classical Marcus theory that the nearest-neighbor CT is adiabatic with reorganization energy lambda approximately 0.83 eV. The kinetics model can be extended to accurately characterize CT in other poly(A)-poly(T) systems with different hole donors (naphthaldiimide and 2-aminopurine) and acceptors (phenothiazine and guanine).