Energy flow in DNA duplexes

This chapter focuses on the singlet excited states of model DNA helices with simple base sequence: poly(dGdC).poly(dGdC), poly(dAdT).poly(dAdT) and poly(dA).poly(dT). We discuss their absorption spectra, which reect the properties of Franck-Condon states, in connection with theoretical studies, performed in the frame of the exciton theory taking into account conformational disorder and spectral broadening. Then we turn to uorescence properties studied using uorescence upconversion and time-correlated single photon counting. We review the behavior of the uorescence decays and we look more closely on the uorescence anisotropy, explaining how this property can provide information on energy transfer in molecular systems and we show the results obtained in this way for the three examined polymeric helices. Finally, we present a qualitative model describing energy ow in DNA helices; this model involves population of excited states that are delocalized over a few bases, ultrafast (