Zinc Phthalocyanine–Graphene
Hybrid Material
for Energy Conversion: Synthesis, Characterization, Photophysics,
and Photoelectrochemical Cell Preparation
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Abstract
Graphene exfoliation upon tip sonication in <i>o</i>-dichlorobenzene
(<i>o</i>-DCB) was accomplished. Covalent grafting of (2-aminoethoxy)(tri-<i>tert</i>-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<sup>•+</sup>, yielding
the charge-separated state ZnPc<sup>•+</sup>–graphene<sup>•–</sup>. Finally, the ZnPc–graphene hybrid
material was integrated into a photoactive electrode of an optical
transparent electrode (OTE) cast with nanostructured SnO<sub>2</sub> films (OTE/SnO<sub>2</sub>), which exhibited stable and reproducible
photocurrent responses, and the incident photon-to-current conversion
efficiency was determined