Document Type

Article

Publication Date

July 2009

Journal or Book Title

Angewandte Chemie International Edition

Volume

48

Issue

34

Abstract

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.

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