Revealing High-Lying Intersystem Crossing in Brightly Luminescent Cyclic Trinuclear CuI/AgI Complexes

The increased attention to luminescent copper­(I) complexes, mostly mononuclear and dinuclear ones, in the past few years was mainly due to the new pathways established in the intersystem crossing (ISC) for highly efficient singlet/triplet harvesting, which showed great potential in light-emitting devices. Governing the photophysical processes of planar cyclic trinuclear complexes is more challenging owing to the rich intra- and intermolecular metal–metal interactions involved, but new opportunities also accompany this. Herein reported is a hidden route to the ultra-long-lived, highly efficient phosphorescence of cyclic trinuclear two-coordinate CuI–pyrazolate complexes through pushing the unfavorable metal-to-ligand charge transfer events to the high-lying ISC pathways. Moreover, an anomaly of much higher quantum yields of a trinuclear AgI–pyrazolate complex relative to its CuI analogue is observed.