Add time:08/02/2019         Source:sciencedirect.com

Six iridium complexes with 2-(2-trifluoromethyl)pyrimidine-pyridine as the main ligand and 2-(5-phenyl-1,3,4-oxadiazol-2-yl)-phenol or 2-(5-phenyl-1,3,4-thiadiazol-2-yl)-phenol derivatives as ancillary ligands were synthesized. The crystal structures of the complexes adopted pseudo-octahedral coordination geometry with the conventional trans-N, cis-C arrangement of main ligand and the ancillary ligand was connected to iridium center by an N atom from 1,3,4-oxadiazole or 1,3,4-thiadiazole group and an O atom from phenol moiety. Electrochemical study confirmed the ancillary ligand variations have effects on the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels. The density functional theory (DFT) calculations suggested that the frontier orbitals and the electronic properties of the complexes can be manipulated by introducing different ancillary ligands. The compositions of LUMO on the 1,3,4-thiadiazole ancillary ligands are higher than that of 1,3,4-oxadiazole derivatives, and the HOMO - LUMO gaps are also decreased. Therefore, the emissions of the complexes with 1,3,4-thiadiazole ancillary ligands are shift from green to red. The organic light-emitting diodes with Ir3 and Ir6 as emitters show maximum current efficiencies of 41.08 and 50.92 cd/A, respectively, with mild efficiency roll-off. This work provides a way to tune the emission and device efficiency of IrIII complexes by introducing of 1,3,4-thiadiazole group in ancillary ligand.

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