Zinc Phthalocyanine-Graphene Hybrid Material for Energy Conversion: Synthesis, Characterization, Photophysics, and Photoelectrochemical Cell Preparation

Graphene exfoliation upon tip sonication in o-dichlorobenzene (o-DCB) was accomplished. Covalent grafting of (2-aminoethoxy)(tri-tert-butyl) zinc phthalocyanine (ZnPc) to exfoliated graphene sheets was then achieved. The newly formed ZnPc-graphene hybrid material was found to be soluble in common organic solvents without any precipitation for several weeks. Application of diverse spectroscopic techniques verified the successful formation of the ZnPc-graphene hybrid material, while thermogravimetric analysis revealed the amount of ZnPc loading onto graphene. Microscopy analysis based on AFM and TEM was applied to probe the morphological characteristics and to investigate the exfoliation of graphene sheets. Efficient fluorescence quenching of ZnPc in the ZnPc-graphene hybrid material suggested that photoinduced events occur from the photoexcited ZnPc to exfoliated graphene. The dynamics of the photoinduced electron transfer was evaluated by femtosecond transient absorption spectroscopy, thus revealing the formation of transient species such as ZnPc center dot+, yielding the charge-separated state ZnPc center dot+-graphene(center dot-). Finally, the ZnPc-graphene hybrid material was integrated into a photoactive electrode of an optical transparent electrode (OTE) cast with nanostructured SnO2 films (OTE/SnO2), which exhibited stable and reproducible photocurrent responses, and the incident photon-to-current conversion efficiency was determined.