Reversing V═O Orientation of Vanadyl Phthalocyanine as "Molecular Switch" on Carbon Nitride Boosts CO₂ Photoreduction

The precise engineering of catalytic microenvironments in single-atom site photocatalysts is critical yet challenging for optimizing CO₂ photoreduction. Herein, we propose a novel strategy by leveraging the tunable molecular orientation of non-planar vanadyl phthalocyanine (VOPc) as a "molecular switch" to dynamically modulate the local catalytic microenvironment. Positive surface charge and hydrogen bonding introduced by the hydroxylation of carbon nitride (C₃N₄) allows a preferential "O-down" configuration of VOPc on the modified substrate (VOPc/OH-C₃N₄). Density functional theory (DFT) calculations reveal that this specific molecular orientation lowers the energy barrier for the rate-determining step (*CO₂→*COOH). VOPc/OH-C₃N₄ shows enhanced electron transfer efficiency, an upward shift of the V-centered d-band toward the Fermi level, and stabilized *COOH adsorption. Consequently, VOPc/OH-C₃N₄ achieves a CO evolution rate of 65.22 µmol·g^-1·h^-1, which is 7.5 times higher than that of VOPc/C₃N₄ with "O-up" configuration of VOPc. This work highlights that controlling the orientation of active sites presents a promising strategy for modulating interfacial electronic structures and boosting photocatalytic CO₂ reduction performance.