Encapsulation of Palladium Porphyrin in a Tetrapyridylphenylethylene-Based Molecular Cage for Enhanced Photocatalytic Performance in Organized Thin Films

Abstract Metalloporphyrin photocatalysts often suffer from aggregation and difficulty in recovery, limiting the utilization of their photoactive sites. Here, we report the encapsulation of negatively charged palladium tetraphenylporphyrin tetrasulfonic acid (PdTPPS) within a tetrapyridylphenylethylene (TPPE)-based molecular cage (TPPE-AB) to construct a single-site host–guest photocatalyst. The host–guest PdTPPS@TPPE-AB complexes enable efficient energy transfer from the cage to the porphyrin, as confirmed by steady-state and time-resolved fluorescence spectroscopy. Organized thin films fabricated via the Langmuir–Blodgett (LB) technique exhibit uniform morphology with highly exposed catalytic sites. In photocatalytic oxidation of thioanisole and oxidative coupling of benzylamine, the LB film catalyst delivered average turnover frequencies of 5.92 and 1066.3 h–1, respectively─approximately 27 and 2 times those of the corresponding powder counterpart─owing to superior active-site dispersion, high specific surface area, and reduced mass-transfer resistance. EPR spin-trapping measurements identify 1O2 and O2•– as key reactive species, and a corresponding mechanism is proposed. The LB film also shows good recyclability. This work offers a promising strategy for single-site photocatalysis in confined organized assemblies.