Three novel iridium(III) complexes with pyrimidine carboxylic acid as the auxiliary ligand were designed, showing adjustable emission peak wavelengths from 559 nm to 610 nm with relatively high photoluminescence quantum yields (PLQYs) of 58–89% in CH₂Cl₂. The structures of the title complexes were confirmed by single-crystal X-ray diffraction (XRD), nuclear magnetic resonance spectroscopy (NMR), and high-resolution mass spectrometry (HRMS). Their electronic states were investigated using time-dependent density functional theory (TD-DFT) calculations. When employing these emitters to fabricate solution-processed organic light-emitting diodes (OLEDs), the obtained orange and red OLEDs exhibit prominent performances with the maximum current efficiencies of 95.4 cd A⁻¹ and 39.8 cd A⁻¹, and the maximum external quantum efficiencies (EQE_max) of 31.3% and 24.7%, both of which are ranked among the highest values for orange and red solution-processed OLEDs.

The fluorescence quenching of multi-resonance thermally activated delayed fluorescence (MR-TADF) materials has remained a formidable challenge due to the strong π–π packing and intense intermolecular aggregation. To this end, we designed MR-TADF molecules modified with adamantane with large spatial hindrance, named BN-Ad, to mitigate the intermolecular π–π stacking between rigid planar skeletons and prevent aggregation-caused quenching. Photoelectric properties of BN-Ad in solutions and thin films were systematically investigated, and the electroluminescence properties were characterized by fabricating organic light-emitting diodes (OLEDs). The optimized device employing BN-Ad exhibited a maximum external quantum efficiency (EQE_max) of 32.3% peaking at 500 nm with a small full width at half maximum (FWHM) of only 35 nm. When the doping ratio increased to 50 wt%, the EQE_max can still be maintained at 11.2% with a slightly red-shifted emission peak at 508 nm and a moderately widened FWHM of 53 nm.

Two narrowband chiral iridium isomers with an FWHM of 48 nm, EQE _max of 15.58% and g _EL of 2.29 × 10 ⁻⁴ were synthesized and separated.

One bis-cyclometalated blue iridium complex and two tris-heteroleptic blue iridium isomers containing the asymmetric tris-heteroleptic [Ir(C₁^N₁)(C₂^N₂)(LX)]-configuration are developed and applied in OLEDs with good EL performances.