Charge separation in supramolecular ferrocene(s)-zinc porphyrin-fullerene triads: A femtosecond transient absorption study

Abstract

Mechanistic aspects of photoinduced charge separation in supramolecular triads, constructed using covalently linked zinc porphyrin-ferrocene(s) dyads — self-assembled via axial coordination to either pyridine or phenylimidazole appended fulleropyrrolidine ( Fc x- ZnP : PyC 60 or Fc x- ZnP : ImC 60; x = 1 or 2), has been investigated using femtosecond pump-probe transient spectroscopy. Upon photoexcitation of ZnP , charge separation from ferrocene to 1 ZnP * to yield the initial Fc +- ZnP •-: C 60 radical ion-pair or charge separation from 1 ZnP * to C 60 to yield the initial Fc - ZnP •+: C 60•- radical ion-pair, depending upon the ferrocene-zinc porphyrin intermolecular distance, was observed. These radical ion-pairs resulted in the formation of ultimate distantly separated Fc +- ZnP : C 60•- radical ion-pairs either via an electron migration (former case) or hole shift (latter case) process. Kinetics of charge separation as a function of spacer connecting the ferrocene and porphyrin, and spacer between the porphyrin and fullerene is reported. In agreement with our earlier study (J. Phys. Chem. B 2004; 108: 11333–11343), the Fc +- ZnP : C 60•- radical ion-pair persisted beyond the monitoring time window of our instrument, suggesting charge stabilization in these supramolecular triads.