Highly Emissive Dinuclear Platinum(III) Complexes.

Abstract

Dinuclear Pt(III) complexes were commonly reported to have short-lived lowest-lying triplet states, resulting in extremely weak or no photoluminescence. To overcome this obstacle, a new series of dinuclear Pt(III) complexes, named Pt2a-Pt2c, were strategically designed and synthesized using donor (D)-acceptor (A)-type oxadiazole-thiol chelates as bridging ligands. These dinuclear Pt(III) complexes possess a d7-d7 electronic configuration and exhibit intense phosphorescence under ambient conditions. Among them, Pt2a exhibits orange phosphorescence maximized at 618 nm in degassed dichloromethane solution (Φp ≈ 8.2%, τp ≈ 0.10 μs) and near-infrared (NIR) emission at 749 nm (Φp ≈ 10.1% τp ≈ 0.66 μs) in the crystalline powder and at 704 nm (Φp ≈ 33.1%, τp ≈ 0.34 μs) in the spin-coated neat film. An emission blue-shifted by more than 3343 cm-1 is observed under mechanically ground crystalline Pt2a, affirming intermolecular interactions in the solid states. Time-dependent density functional theory (TD-DFT) discloses the lowest-lying electronic transition of Pt2a-Pt2c complexes to be a bridging ligand-metal-metal charge transfer (LMMCT) transition. The long-lived triplet states of these dinuclear platinum(III) complexes may find potential use in lighting. Employing Pt2a as an emitter, high-performance organic light-emitting diodes (OLEDs) were fabricated with NIR emission at 716 nm (η = 5.1%), red emission at 614 nm (η = 8.7%), and white-light emission (η = 11.6%) in nondoped, doped (in mCP), and hybrid (in CzACSF) devices, respectively.