Four new naphthyridine-based iridium(III) complexes, namely (dfpmp)₂Ir(mmND), (mtfmpp)₂Ir(mmND), (tfmptp)₂Ir(mmND), and (mtfmptp)₂Ir(mmND), were designed and synthesized. The complexes show tunable emission peak wavelengths from 521 nm to 600 nm with relatively high photoluminescence quantum yields (PLQYs) of 80–85% in CH₂Cl₂. Employing these emitters, all the organic light-emitting diodes (OLEDs) exhibit prominent performances with the maximum external quantum efficiency (EQE_max) exceeding 30%, and simultaneously the efficiency roll-off is extremely low. Of note, the double emissive layer OLED using (mtfmpp)₂Ir(mmND) as the dopant achieves the optimal electroluminescence (EL) performances with an EQE_max of 32.3% and an ultrahigh brightness of 242 548 cd m⁻².