Under these conditions, fac-Ir(pmi)3 afforded a comparable product yield of 79% (Figure ), while fac-Ir(ppy)3 only gave a moderate yield of 45% (Figure ). When performed under air, the yield with fac-Ir(pmi)3 dropped to 47%, while no product formed with fac-Ir(ppy)3 as the PC (Table ). No product formation was observed either in the absence of light (λexc = 390 nm) or photocatalyst (Table ). 39 We next explored a more challenging energy transfer reaction, the 1,3-sigmatropic shift of s-verbenone to chrysanthenone. Direct photoexcitation of the substrate (λexc < 300 nm) in acetic acid for one hour can result in yields of up to 67%. Under similar conditions as the transformation of norbornadiene to quadricyclane, Wenger and co-workers reported an 80% yield of chrysanthenone after three hours. At this timescale, using our set up, fac-Ir(pmi)3 achieved a moderate yield of 55% at 2 mol% loading (Table ), which could be improved upon increasing the reaction time to 5 hours for both mer-and fac-Ir(pmi)3, affording, respectively, 64 and 62% of chrysanthenone (Figure ). No product formation was observed when employing fac-Ir(ppy)3 at this same PC loading (Figure ). Under air, the yield decreases significantly, with fac-Ir(pmi)3 giving only 23% product (Table ), suggesting that competitive quenching of the PC* by molecular oxygen becomes more effective as the substrate ET increases. In the absence of PC under deaerated conditions there is a background reaction as 21% of product is formed over 5 hours, while there is no conversion under air (Table ); further, in the absence of light, no product formation was observed (Table ).