Solar-light-driven photocatalytic hydrogen evolution by push-pull thiophenoxy-substituted zinc phthalocyanines

Two zinc phthalocyanine derivatives (ZnPc 1 and 2) carrying bulky 2,6-diisopro-pylthiophenoxy peripheral substituents have been synthesized and their performances as photosensitizers in photochemical hydrogen production evaluated. To examine the influence of the spacer on the performance of ZnPc 1 and 2, the carboxyl group has been linked to the macrocycle ring either directly or via the phenyl ring, respectively. The photocatalytic activities of ZnPcs (ZnPc 1 and ZnPc 2) as sensitizers of TiO2 for hydrogen production were investigated in the presence of Pt. ZnPc 1 and ZnPc 2 sensitized TiO2 produced 0.687 mmolg-1h-1 and 0.436 mmol g-1h-1 hydrogens, which also reached 3.986 and 2.091 mmolg-1 after 8h illumination, respectively, under visible light (≥ 420 nm) irradiation. In addition, STH efficiencies of ZnPc 1/TiO2 and ZnPc 2/TiO2 were determined as 1.77% and 1.12%, respectively. ZnPc 1/TiO2 exhibited 1.9-fold more photocatalytic hydrogen amount than ZnPc 2/TiO2, and the hydrogen evolution performance of the photocatalyst in the presence of Pt enhanced to 3.021 mmol g-1h-1 and 0.911mmol g-1h-1 for ZnPc 1 and ZnPc 2, respectively.