Achieving deep red to near-infrared electroluminescence in platinum complex through enhanced conjugation of the ligand

Abstract

Three mononuclear platinum (II) complexes piqPtOXD, 2niqPtOXD and PyriqPtOXD were synthesized using phenyl isoquinoline, naphthalene isoquinoline and pyrene isoquinoline as cyclometalated ligands and 1,3,4-oxadiazole derivatives as auxiliary ligands. The photophysical, electrochemical and electroluminescent properties were primarily investigated. It's observed that an increase in the rigid planar structure of the ligand cyclic aromatic hydrocarbons resulted in higher thermal stability, lower band gap values and red-shifted emission spectra. Theoretical calculations indicated that the decrease in the energy gap value of the complex PyriqPtOXD was due to the distribution of both the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy level on the platinum atoms and cyclometalated ligands. In addition, the electroluminescence (EL) peak of the devices based on PyriqPtOXD reached 742 nm, which was 140 nm red-shifted compared to the piqPtOXD-based devices, with a maximum irradiance of 36 μW/cm² and a maximum external quantum efficiency (EQE_max) of 0.35 %.