Phosphorescent Pt(ii) acetylacetonate complexes bearing 9-(pyrimidin-2-yl)-9H-carbazole ligand: syntheses, photophysical properties and OLED applications

Abstract

Four mononuclear platinum(II) complexes, Pt(TBPCH)(acac) 1a, Pt(TBPCH)(dpmn) 2a, Pt(TBPCH)(dbmn) 3a, and Pt(TBPCH)(dnmn) 4a, and one binuclear Pt(II) complex, Pt₂(TBPC)(acac)₂1b, where TBPCH₂ = 3,6-di-tert-butyl-9-(pyrimidin-2-yl)-9H-carbazole, acac = acetylacetonate, dpmn = dipivaloylmethanate, dbmn = dibenzoylmethanate, and dnmn = di(2-naphthoyl)methanate, have been prepared by utilizing TBPCH₂ (C^N) as the primary ligand and acetylacetonate derivatives (O^O) as the ancillary ligands. All five complexes were characterized using NMR, HR-MS, elemental analysis, CV, TGA, and single-crystal X-ray diffraction, except for 2a, for which a single crystal was not obtained. Moreover, TD-DFT calculations were performed to investigate the triplet emission nature of the complexes. All five complexes exhibited phosphorescence, with complex 1a emitting at 534 nm with Φ = 5%, τ = 3.17 μs, 2a emitting at 530 nm with Φ = 21%, τ = 2.48 μs, 3a emitting at 581 nm with Φ = 25%, τ = 7.48 μs, 4a emitting at 586 nm with Φ = 38%, τ = 2.32 μs, and 1b emitting at 573 nm with Φ = 5%, τ = 1.44 μs in 2 wt% polymethyl methacrylate (PMMA) films. The OLED devices were fabricated through a vapor deposition process utilizing complexes 2a and 4a as emitting materials. The 2a-based devices exhibited an emission peak at 525 nm with a maximum external quantum efficiency (EQE_max) of 4.0% at CIE coordinates of (0.34, 0.51), and the 4a-based devices exhibited an emission peak at 585 nm with an EQE_max of 15.1% at CIE coordinates of (0.50, 0.48).