The dynamics of charge transfer from a photoexcited donor to an acceptor coupled through a bridge is investigated by using a correlation-function approach in Liouville space that takes into account solvent dynamics with an arbitrary distribution of time scales. The time- and frequency-resolved fluorescence spectrum from the acceptor is used to probe the scaling of the ET rate with bridge size. The crossover between the coherent tunneling (transfer) and the incoherent sequential (transport) regimes and its implications on the nature of ET processes in DNA are discussed.