Ultrafast charge transfer dynamics in 2-aminopurine modified double helical DNA

Ultrafast charge transfer dynamics in double helical DNAs and the corresponding single strands has been studied by femtosecond time-resolved fluorescence (TRF). The DNA molecules were modified by replacing one adenine with 2-aminopurine (2Ap), a fluorescent analogue of adenine. TRF signals of 2Ap in the DNAs require three time constants with the fastest in the range of 0.42-10 ps. The DNA duplex, where 2Ap and guanine are connected directly, shows the fastest 420 fs decay. The observed time scales are significantly different from the values reported previously. The time constant and amplitude of the fastest component vary with the nature and position of the bridges between the 2Ap and guanine in accordance with the oxidation potential of the bridge suggesting that the ultrafast component represents the charge transfer dynamics in DNA. The multi-exponential dispersive kinetics can be accounted for by invoking conformational heterogeneity.