Fluorescence of DNA Duplexes: From Model Helices to Natural DNA

Recent fluorescence studies of DNA duplexes with simple repetitive base sequence have revealed important collective effects which are very sensitive to conformational 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 fluorescence anisotropy on the femtosecond time-scale, is a common feature of all 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 fluorescence spectrum of natural DNA, will be one of the challenges for the years to come.