Electron Transport Properties through Graphene Oxide-Cobalt Phthalocyanine Complexes

We present a theoretical study using density functional theory at the M05-2X/6-31G(d)/LANL2DZ level of theory of the structural, stability, reactivity, and electrical properties of cobalt phthalocyanine (CoPc) adsorbed on functionalized graphene (G). The functionalization, localized at the center of graphene, is based on epoxide (-O), hydroxyl (-OH), and carboxyl (-COOH) complexes. Three types of graphene molecules are used: pristine, defect (Def), and vacancy (Vac). Binding energies show large stabilities for G-O-CoPc, from similar to-43 to -65 kcal/mol, and for G-OH-CoPc, from similar to-19 to -32 kcal/mol. No adsorption of CoPc occurs on G-COOH. The HOMO-LUMO gap is shorter by similar to 0.5 eV for the complexes containing epoxide and hydroxyl (except for G-Vac) than for the functionalized G, thus implying a higher reactivity of the former. All these results together with the nature of the frontier molecular orbitals, which make functionalized G electron acceptor and CoPc electron donor species, explain the charge transfer properties of the complexes. Complexes containing epoxide functionalization present a better conduction of similar to 18 mu A (at similar to 1 V) than those complexes containing hydroxyl functionalization (similar to 7 mu A). These results show that the adsorption of cobalt phthalocyanine on functionalized graphene is feasible; yielding a tunable hybrid material that allows sensing because of the intrinsic electrical properties provided by functionalized G and CoPc.