Graphene oxide with covalently linked porphyrin antennae: Synthesis, characterization and photophysical properties

The successful covalent functionalization of graphene oxide (GO) with 5-(4-aminophenyl)-10,15,20-triphenyl-21,23H-porphyrin (H₂P) has been reported. The resulting GO-H₂P hybrid material forms stable dispersions in DMF and has been thoroughly characterized by spectroscopic (UV-vis, ATR-IR, Raman) and thermal (TGA) tools. Microscopy techniques (AFM and TEM) have been employed to probe the morphological characteristics as well as to investigate the exfoliation of graphene sheets. Steady-state and time-resolved fluorescence emission studies have shown efficient fluorescence quenching, suggesting that electron transfer occurs from the singlet excited state of the H₂P moiety to the GO sheet. Photoexcitation resulted in the one-electron oxidation of the H₂P with the simultaneous one-electron reduction of GO, yielding (GO)^--(H₂P)⁺, as revealed by transient absorption measurements. The electrochemical redox potentials of the graphene-H₂P material were studied by cyclic voltammetry (CV) and differential pulsed voltammetry (DPV) and the energy gap for the charge-separated state of (GO)^--(H₂P)⁺ has been calculated as 0.87 eV, while, the negative free-energy change for the photoinduced charge-separation of GO-H₂P has been evaluated to be -1.00 eV, which confirms the thermodynamically favorable formation of (GO) ^--(H₂P)⁺. Eventually, the GO-H₂P hybrid material was deposited by electrophoretic deposition onto SnO₂ electrodes, and the OTE/SnO₂/GO-H₂P electrode exhibited an incident photon-to-photocurrent-efficiency IPCE of 1.3% in a standard photoelectrochemical cell.