Approaching the Shortest Intermetallic Distance of Half‐Lantern Diplatinum(II) Complexes for Efficient and Stable Deep‐Red Organic Light‐Emitting Diodes

Abstract A fast radiative decay process for long‐wavelength molecular light‐emitters is vital to achieving a high emission efficiency by outcompeting the nonradiative decay imposed by the energy‐gap law. An ensuing short emission lifetime is also beneficial for fabricating high‐performance organic light‐emitting diodes. Herein a series of half‐lantern dinuclear platinum(II) complexes is reported, which shows high‐efficiency deep red phosphorescence (λ_em > 660 nm). The molecules are designed to have a cofacially aligned structure featuring short Pt–Pt distances of 2.80–2.83 Å by using 10H‐pyrido[3,2‐b][1,4]benzoxazine (PyXZ) as the rigid bridges, which are revealed by single crystal X‐ray diffraction analysis. Together with the strong electron‐donating property of PyXZ bridges, the metallophilic interaction endows low‐energy triplet excited states with mixed metal–metal‐to‐ligand charge‐transfer (³MMLCT) and ligand‐to‐ligand charge‐transfer (³LLCT) characters. The deep red devices based on the diplatinum(II) complexes show maximum external quantum efficiencies (EQEs) up to 21.8%. The EQE of 19.4% and operational lifetime (LT₈₅) of 334 h (the operational time after which the luminance drops to 85% of the initial value) at a luminance of 1000 cd m⁻² promise the pratical use of these complexes.