Tuning Charge Transfer Energetics in Reaction Center Mimics via Th-Functionalization of Fullerenes

Abstract

We have introduced an approach of mono- and hexakis-adducts of C₆₀ involving a T_h-symmetrical addition pattern, where up to 12 ferrocene or 10 ferrocene and one porphyrin units are linked flexibly to C₆₀ with the objective to systematically raise the energy of the radical ion pair state. A detailed electrochemical and photophysical investigation has shed light onto charge transfer events that depend largely on (i) the functionalization pattern of C₆₀, (ii) the donor strength of the donor, (iii) the excited-state energy of the predominant chromophore, and (iv) the solvent polarity. Considering (i)−(iv), the presence of the porphyrins is key to providing sufficient driving forces for affording spatially separated radical ion pair states. An ideal scenario, that is, testing ZnP−C₆₀−(Fc)₁₀ (19) in benzonitrile and DMF, allows storing nearly 1.7 eV in a nanosecond lived radical ion pair state. In this context, the flexible linkage, powering a through space charge transfer, prevents, however, stabilization of the radical ion pair state beyond nanoseconds.