Abstract
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.