tPL of 2300 ns in MeCN 76 ); however, upon exposure to air the tPL decreases by an order of magnitude to 188 ns. Aerobic quenching of the lifetime was also observed for the DME solution, with the tPL of [Ir1] decreasing from 2111 to 202 ns under anaerobic and aerobic conditions, respectively. In powder form, the PL instead decays with biexponential kinetics, reflecting the heterogeneity of the environment, and the intensity of the PL is significantly less attenuated in the presence of oxygen. Considering that the outcome of photocatalysis reactions is governed by a complex combination of different quenching rates between different substrates and the photocatalyst, it seems plausible that the quenching of excited species by dissolved oxygen in aerobic solution reactions may be increased relative to the quenching by oxygen at a solidgas interface that largely exists in aerobic solvent-minimized conditions, and could be a contributing factor to the poorer performance of [Ir1] in the solution XAT cross-coupling relative to the mechanophotocatalysis analogue, Figure .