Photophysical Insights Into Excited‐State Reactivity of Silicon Phthalocyanine Catalysts

Silicon phthalocyanines have recently been explored as photocatalysts, yet axial ligand effects on photophysical properties remain underexplored. In this study, we investigate a series of silicon phthalocyanine catalysts with different alkoxy or silyloxy ligands at the axial positions to understand how these ligands affect properties such as quenching dynamics, excited state potentials, and mechanistic outcomes in the context of photoredox dehalogenation of 4‐nitrophenacyl bromide. Stern–Volmer quenching experiments reveal that the phenacyl bromide substrate efficiently quenches the excited state of the catalysts, suggesting the bromine–carbon bond breaking is the first step in the mechanism. Notably, photophysical data indicate that the catalysts operate through a possible singlet excited state, while a contribution from a triplet state cannot be excluded. Furthermore, we demonstrate that steric variation in the axial ligands of the silicon phthalocyanines significantly influences quenching efficiency with an amine quencher. Bulky ligands are hypothesized to hinder recombination of the charge‐separated state, thereby enhancing catalytic performance. These findings highlight the critical role of ligand design in modulating photocatalyst reactivity and provide mechanistic insight into possible singlet excited state electron transfer processes in silicon‐based photoredox catalysis.