A graphene sheet as an efficient electron acceptor and conductor for photoinduced charge separation

Abstract

Tetrasulfonated zinc phthalocyanine (Pc) was bound to graphene (G) sheets by the π–π stacking supermolecular method. The few-layer graphene sheets were obtained by chemically reducing graphite oxide and characterized by AFM, IR and UV–vis absorption methods. Photoinduced electron transfer (PET) within the nano assembly is revealed by laser flash photolysis, time resolved and steady state fluorescence, as well as UV–vis absorption techniques. A graphene sheet can be attached by up to 52,000 Pc molecules to form a super molecule G(Pc) 52,000, in which many Pc molecules can be simultaneously photoexcited to the S 1 state. One graphene sheet can simultaneously quench thousands of excited Pcs with a large rate constant of the order of 10 16 M −1 s −1 by PET. A graphene sheet not only accepts electrons from the excited Pcs on it but also delivers the captured electrons to its unexcited Pcs to form (Pc +) n G(Pc −) n , so that a large electron charge (i.e. n >> 1) is separated between unlinked Pc molecules with a small energy loss. These novel features of PET are explained by the following unique properties of graphene: (i) its excellent electron-transport and multi-electron-accepting ability, (ii) its multi-chromophore binding and concurrent multi-photon absorbing ability.