Base sequence and higher-order structure induce the complex excited-state dynamics in DNA.

The high photostability of DNA is commonly attributed to efficient radiationless electronic relaxation processes. We used femtosecond time-resolved fluorescence spectroscopy to reveal that the ensuing dynamics are strongly dependent on base sequence and are also affected by higher-order structure. Excited electronic state lifetimes in dG-doped d(A)20 single-stranded DNA and dG.dC-doped d(A)20.d(T)20 double-stranded DNA decrease sharply with the substitution of only a few bases. In duplexes containing d(AGA).d(TCT) or d(AG).d(TC) repeats, deactivation of the fluorescing states occurs on the subpicosecond time scale, but the excited-state lifetimes increase again in extended d(G) runs. The results point at more complex and molecule-specific photodynamics in native DNA than may be evident in simpler model systems.