Synthesis of phosphorescent syn, anti-isomeric clamshell platinum(ii) dimers for OLED applications

Abstract

Six clamshell diplatinum(II) complexes with a formula of [Pt(TBPCH)(N^N)]₂ bearing both a carbazole-pyrimidine chelate and a N^N bridge, (TBPCH₂ = 3,6-di-tert-butyl-9-(pyrimidin-2-yl)-9H-carbazole), have been prepared by utilizing TBPCH₂ (C^N) as the primary ligand and N^N as the bridging ligand. Six complexes, including 1-anti (1-syn) (N^N = N,N′-diphenylformamidine) and 2-anti (2-syn) (N^N = 3,5-ditert-butyl-1H-pyrazole), 3 (N^N = 9H-pyrido[2,3-b]indole) and 4 (N^N = 2-anilinopyridine), were synthesized and characterized by NMR spectroscopy, HR-MS, elemental analysis, CV, and single-crystal XRD. Moreover, DFT and TD-DFT calculations were performed to determine the frontier orbital location and the nature of the triplet emission. All six complexes exhibited phosphorescence when they were embedded in a polymethyl methacrylate (PMMA) film at 2 wt%, with complex 1-anti emitting at 599 nm with Φ = 28%, τ = 1.64 μs, 2-anti emitting at 567 nm with Φ = 43%, τ = 2.21 μs and complex 3 emitting at 563 nm with Φ = 25%, τ = 1.36 μs. OLED devices were fabricated through vapor deposition with complexes 1-anti, 2-anti, and 3 as the emitting materials. The 1-anti-based device exhibited an emission peak at 598 nm with the maximum external quantum efficiency (EQE_max) of 5.3% at CIE coordinates of (0.55, 0.44), the 2-anti-based device exhibited an emission peak at 573 nm with the maximum external quantum efficiency (EQE_max) of 5.9% at CIE coordinates of (0.46, 0.51), and the 3-based device exhibited an emission peak at 559 nm with an EQE_max of 9.65% at CIE coordinates of (0.44, 0.53).