In comparison to traditional solar cells, the dye-sensitized photocatalytic system is one of the most appealing artificial photosynthesis mechanisms due to its low cost and straightforward fabrication. Herein, the photoelectrochemical and photocatalytic hydrogen evolution reactions of Zn-based phthalocyanine (Pc) derivatives, abbreviated as ZnPc-1 and ZnPc-2, were primarily studied in the presence of TEOA sacrificial electron donor. To this aim, the PC activities of ZnPc-1/TiO2 and ZnPc-2/TiO2 photocatalysts were investigated in the absence and presence of a cocatalyst. For the first hour, the amount of hydrogen generated by ZnPc derivatives (ZnPc-1/TiO2 and ZnPc-2/TiO2) was determined to be 1.221 and 0.864 mmol g-1 h-1, respectively. Additionally, the solar-to-hydrogen conversion efficiencies of ZnPc-1/TiO2 and ZnPc-2/TiO2 were ascertained to be 3.15% and 2.22%, respectively. Interestingly, STH efficiencies of photocatalysts were increased about 4-fold in the presence of a cocatalyst. Consequently, to elucidate the structural properties of ZnPc-1 and ZnPc-2, density functional theory (DFT) and time-dependent DFT studies were also conducted, and it was discovered that noncovalent interactions and steric hindrance effects on ZnPc-2 are tightly related to the experimentally determined PC activity differences between ZnPc-1 and ZnPc-2.