Rapid Intramolecular Hole Hopping in meso-meso and meta-Phenylene Linked Linear and Cyclic Multiporphyrin Arrays

A series of zinc porphyrin arrays comprised of a meso-meso linked porphyrin dimer, a meta-phenylene linked dimer, gable-like tetramers consisting of the meso-meso linked dimers bridged via a meta-phenylene linker, and a dodecameric ring composed of this alternating dimeric pattern were singly oxidized, and intramolecular hole hopping between the porphyrin moieties was probed using electron paramagnetic resonance (EPR) spectroscopy. Electron nuclear double resonance (ENDOR) spectroscopy was also used to probe hole hopping within the dimers. Rapid hole hopping occurs between both porphyrins within both dimers and among three porphyrins of the tetramers with rates > 10(7) s(-1) at 290 K. Additionally, the hole hops among 8-12 porphyrins in the dodecameric ring with a rate that is > 10(7) s(-1) at 290 K, but hopping is slow at 180 K. These results show that hole hopping is rapid even though the meta-phenyl bridges and direct meso-meso linkages do not provide optimal electronic coupling between the porphyrins within these multiporphyrin arrays. This greatly expands the scope of possible structures that can be employed to tailor the design of long distance charge transport systems.