High-efficiency deep-red to near-infrared emission from Pt(ii) complexes by incorporating an oxygen-bridged triphenylborane skeleton

Abstract

Due to the limitation of the energy gap law, platinum(II) complexes simultaneously with long luminous wavelength and high efficiency are still confronted with challenges. In order to better understand the effects of the molecular structure on the luminescence properties, in this work, two homogeneous platinum(II) complexes of (BOiqn)₂Pt and (BOPy)₂Pt were designed and synthesized, in which a planar and rigid multiple-resonance skeleton of oxygen-bridged triphenylborane (BO) was incorporated into iso-quinoline and trifluoromethyl pyridine to construct the BOiqnH and BOPyH main ligands, respectively. The effects of the BO-based azacyclic ligands on the photophysical, electrochemical and electroluminescence properties of both platinum(II) complexes were primarily studied. High efficiency deep-red to near-infrared (NIR) emissions were observed peaked at 649 nm for (BOPy)₂Pt and 710 nm for (BOiqn)₂Pt in dichloromethane solution by enlarging conjugation and decreasing vibration relaxation of the rigid BO skeleton under photo-excitation. More importantly, intense electroluminescence was further exhibited with a peak/shoulder at 656/710 nm and 624/660 nm in the (BOiqn)₂Pt- and (BOPy)₂Pt-doped organic light emitting diodes by the solution process at the same time, in which the maximum external quantum efficiencies (EQEs) reached 3.84% and 7.99%, respectively. This work provides a feasible strategy to develop deep-red to NIR-emitting platinum(II) complexes by incorporating a planar and rigid multiple-resonance skeleton of BO units into azacyclic units.