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

Tetrasulfonated zinc phthalocyanine (Pc) was bound to graphene (G) sheets by the pi-pi 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. (C) 2011 Elsevier Ltd. All rights reserved.