Although there have been numerous studies of solvation, the role of solvent specific and collective interactions, especially for charge-transfer processes, remains difficult to unravel. Here, we report, using femtosecond fluorescence up-conversion and steady-state spectroscopic measurements, studies of well-designed single-sited formylperylene (FPe) in binary solvents. One of the solvents (methanol, MOH) can selectively hydrogen (H) bond to the carbonyl (C=O) site, while the other (acetonitrile, ACN) cannot, but both have similar polarity ( for MOH and for ACN). The results reveal that ultrafast charge transfer from the perylene unit to the carbonyl group of FPe is facilitated by site-specific H-bonding interactions between the carbonyl oxygen of the excited moiety and the protic solvent networks. The time scales involved are 13 ps for the reformations, including rearrangements, of H-bond networks and 35-60 ps, depending on MOH mole fraction, for the bimolecular diffusion. This notion of direct involvement of solvent networks and delocalization of charges on the solvent is not apparent in a continuum dielectric description of solvation, and is relevant to other chemical and biological processes involving charge separation.
Available at: http://works.bepress.com/christina_othon/6/