Buckycatcher. A New Opportunity for Charge-Transfer Mediation?

Abstract

This contribution deals with a computational study of hole transfer (HT) and excess electron transfer (EET) in complexes of a buckyball and a molecular catcher having two concave buckybowls as described by Sygula et al. (J. Am. Chem. Soc. 2007, 129, 3842). Three systems are considered: (1) the inclusion complex consisting of the fullerene and catcher subunits, (2) a system formed by two catchers, and (3) a supermolecular system consisting of two fullerene and two catcher molecules. Such a type of organic system is of potential interest in the design of nanoelectronic devices. HT and EET electronic couplings of the subunits in the systems are calculated using the HF/6-31G* method and the semiempirical INDO/S scheme; the calculation of the reorganization energy is carried out within the B3LYP/6-31G* method. On the basis of the computed values of electronic couplings and reorganization energies, we predict that excess charge (hole or electron) should be strongly confined to a single subunit in the complexes. Then, we suggest that excess charge propagation within the fullerene-catcher system in the solid state occurs as superexchange mediated hopping; in this process, fullerene molecules function as stepping stones, while the catcher effectively mediates the charge transport between buckyballs. The properties of the buckycatcher, acting as a charge-transfer mediator from and to fullerenes, are found to be quite different for electron- and hole-transfer processes. We estimate the absolute rate of the hole and the excess electron hopping between fullerenes, kHT = 1.28 1012 s-1, while kEET = 1.07 109 s-1 and find that the HT is much faster than the EET because of (1) the stronger HT coupling between neighboring buckybowls of the catchers and (2) the smaller HT reorganization energy relative to that for EET