Four mononuclear cationic Cu(I) complexes featuring functional C-linked pyrazolyl pyridine diimine ligands have been synthesized and characterized. Under UV 365 nm at room temperature, these complexes emit similar orange light in solution and green light in thin film, which could be attributed to the limited charge and steric influence of these methyl or trifluoromethyl substituted phenyl appendages at the pyrazol ring. Moreover, multilayer organic light-emitting diodes (OLEDs) based on these Cu(I) complexes had different performance efficiencies. The device with complex 1 as the light emitting material had the highest current efficiency of 17.8 cd A−1 and an external quantum efficiency (EQE) of 6.4%, while the device with complex 2 which shows the highest photoluminescence quantum yields gave the poorest device efficiency with a current efficiency of 13 cd A−1 and an EQE of 4.7%.
