High-efficiency and stable red to near-infrared organic light-emitting diodes using dinuclear platinum(ii) complexes

Abstract

Increasing the radiative decay rates of triplet excited states to overcome the energy-gap law is important for the development of high-efficiency and short-lived phosphorescent metal complexes in the red to near-infrared (NIR) region. Herein, a series of robust dinuclear Pt(II) complexes featuring strong intramolecular noncovalent Pt–Pt and π–π interactions has been developed by using N-deprotonated α-carboline as the bridging ligands. Combined crystallography, electrochemical and computational studies reveal their rigid structures and triplet metal–metal-to-ligand charge transfer (³MMLCT) excited states. The new complexes exhibit efficient red to NIR phosphorescence with excited lifetimes shorter than 2 μs. Organic light-emitting diodes (OLEDs) doped with these complexes show high maximum external quantum efficiencies (EQEs) up to 26.4% (λ_max = 615 nm) and 10.8% for red and NIR (λ_max = 740 nm) devices, respectively, which are among the best devices doped with discrete Pt(II) complexes. Both the red and NIR devices also show small efficiency roll-offs at high brightness. Appealing operational lifetimes have also been revealed which promise their practicality.