Complex local dynamics in DNA on the picosecond and nanosecond time scales

Time-resolved Stokes shift measurements of the local structural relaxation of three DNA oligonucleotides are presented. Logarithmic relaxation is seen for over three decades in time (40 ps-40 ns), indicating a complex relaxation among a large number of conformational substates. The observed relaxation is the same in all the sequences. Sequence dependence of the localized dynamics of DNA does not appear within this time range. We infer that 30%-50% of the relaxation is faster than 40 ps, has a nonlogarithmic decay and has a sequence dependent amplitude.