Recognizing that the isomers of Ir(pmi)3 have an exceptionally high ET of approximately 3. Historically, the photochemical transformation of norbornadiene to quadricyclane has required ketonebased photosensitizers such as acetophenone as these have suitably high ET (ET of acetophenone = 3.22 eV) to achieve >90% yield of quadricyclane. Wenger and co-workers achieved 99% conversion in just one hour at an NMR-scale reaction using blue LEDs (λexc = 415 nm) and 0.3 mol% [Ir(dFN(Me)2ppy)2(BCF)2] -. Using 1 mol% of mer-Ir(pmi)3 resulted in a yield of 45% (Table ).