Confining ultrasmall Au nanoclusters in an ionic Ir(iii)-based cage for selective photoreduction.

Balancing activity and stability in metal nanoclusters (NCs) for efficient catalysis remains challenging, particularly in tuning their surrounding microenvironment to control selectivity. Here, we report ultrasmall Au nanoclusters (0.73 ± 0.14 nm) confined within a photoactive dinuclear Ir(iii)-based ionic cage, synergistically coupling spatial confinement with electronic cooperativity for selective photoreduction. The ionic cage enables controlled synthesis of ultrasmall Au-NCs, ensures long-term stability (>6 months) and facilitates photoinduced electron transfer (PET) from Ir(iii) photosensitizers to Au active sites. This multi-function design drives complete nitrobenzene-to-azobenzene conversion with >98% selectivity under visible light (450 nm) at room temperature, avoiding aniline byproducts. Operando spectroscopy, kinetic studies, and DFT calculations reveal that substrate-sieving at cage windows directs the stepwise reduction pathway via azoxybenzene intermediates. The demonstrated integration of photoinduced electronic and steric microenvironment control of cage-encapsulated NC-based composites establishes a promising strategy for developing nanocatalysts with exceptional selectivity steering capability.