Anti-Kasha electroluminescence in carbene-gold-arylacetylide complexes

Kasha's rule states that luminescence occurs from the lowest excited state; violating this rule could enable radiative release of excess electronic energy, otherwise lost as heat in electroluminescent devices. Here we demonstrate anti-Kasha narrowband electroluminescence from carbene-gold(I)-arylacetylide complexes. A rigid acetylide bridge links a (carbene)gold(I) moiety to a multiple-resonance chromophore, thereby spatially separating frontier orbitals to produce a dark long-range charge-transfer S1 and bright short-range charge-transfer S2 states. Optical spectroscopy and theory show that S2 is populated by reverse intersystem crossing from T1 and T2 triplets, enabled by gold-mediated spin-orbit coupling. Proof-of-concept solutionprocessed OLEDs exhibit narrowband (26 nm) anti-Kasha electroluminescence with 20.4% maximum external quantum efficiency (EQE), and 13% EQE at 10,000 cd m-2 .