Fluorescence of DNA Duplexes: From Model Helices to Natural DNA

Recent fluorescence studies of DNA duplexes with a simple repetitive base sequence have revealed important collective effects which are very sensitive to comformational disorder. In contrast to the monomeric chromophores, whose fluorescence lifetimes are shorter than 1 ps, the fluorescence decays of duplexes span several decades of time. The occurrence of excitation energy transfer, evidenced by the decay of the fluoresence anisotropy on the femtosecond time scale, is a common feature of all of the examined systems. It is explained by the existence of Franck-Condon exciton states, in line with the UV absorption spectra. Understanding the nature of the long lived excited states, whose emission dominates the steady-state fluoresence spectrum of natural DNA, will be one of the challenges for the years to come.