Mechanism and Dynamics of Electron Injection and Charge Recombination in DNA. Dependence on Neighboring Pyrimidines

The mechanism and dynamics of photoinduced electron injection and charge recombination have been investigated for several series of DNA hairpins. The hairpins possess a stilbenediether linker, which serves as an electron donor and base pair stems that possess different pyrimidine bases adjacent to the linker. Hairpins with adjacent thymine-adenine (T-A) base pairs undergo fast electron injection and relatively slow charge recombination with rate constants that are not strongly dependent upon the following base pair. Hairpins with adjacent cytosine-guanine (C-G) base pairs undergo reversible electron injection and much faster charge recombination than those with adjacent T-A base pairs. Hairpins with 5-fluorouracil or other halogenated pyrimidines in their first and second base pair undergo fast electron injection and multiexponential charge recombination. The difference in kinetic behavior for the different series of hairpins and its implications for the formation of long-lived charge-separated states are discussed and compared to results reported previously for other electron-donor chromophores.