Yellowish-orange phosphorescent iridium(III) complexes of bis-cyclometalated ligand with pyrazolone derivatives: synthesis, characterization, photophysical and thermal properties

Three novel heteroleptic iridium complexes containing 2-phenylbenzothiazole (bt) as the cyclometalated ligands and variety of pyrazolone-based Schiff-based derivatives as ancillary ligands were synthesized and characterized by spectroscopic techniques such as 1 H-NMR, 13 C-NMR, mass, FT-IR and elemental analysis. The electronic and photonic properties of these complexes were tuned by introducing electron donating groups on the 4-position of phenyl ring attached to nitrogen. All the complexes show good photoluminescence properties in solid state as well as in solution state having λ PL in the range of 540–562 nm with CIE coordinates (0.40, 0.59). Electrochemical and photophysical properties were performed to evaluate suitability of designed compounds for organic light-emitting diodes (OLEDs). The designed complexes show bandgap ( E g ) and quantum yield ( Φ PL ) in the range of 2.38 to 2.40 eV and 0.48 to 0.57, respectively. The emission lifetime of complexes I, II and III were measured in solution and solid state and were found to be 0.243 μs, 0.391 μs and 0.280 μs and 0.190 μs, 0.557 μs, 0.414 μs, respectively. All the synthesized complexes display high thermal stability up to 300 °C.