Journal of the American Chemical Society, Vol.131, No.23, 8180-8195, 2009
Tuning Charge Transfer Energetics in Reaction Center Mimics via T-h-Functionalization of Fullerenes
We have introduced an approach of mono- and hexakis-adducts of C-60 involving a T-h-symmetrical addition pattern, where up to 12 ferrocene or 10 ferrocene and one porphyrin units are linked flexibly to C-60 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 C-60, (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-C-60-(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.