The synthesis and photophysical study of two novel tert-butyl modified cyclometalated iridium(III) complexes, i.e., bis(4-tert-butyl-2-phenylbenzothiozolato-N, C-2') iridium (III) (acetylacetonate) [(tbt)(2)Ir(acac)] and bis(4-tert-butyl-1-phenyl-1H-benzimidazolato-N, C-2') iridium (III) (acetylacetonate) [(tpbi)(2)Ir(acac)], are reported, their molecular structures were characterized by C-13 NMR, H-1 NMR, ESI-MS, FT-IR, and elementary analysis. Compared with their prototypes without tert-butyl substituents [(bt)(2)Ir(acac) and (pbi)(2)Ir(acac)], (tbt)(2)Ir(acac) and (tpbi)(2)Ir(acac) both have shortened phosphorescent lifetimes [(tbt)(2)Ir(acac) versus (bt)(2)Ir(acac), 1.1 mu s:1.8 mu s; (pbi)(2)Ir(acac) versus (tpbi)(2)Ir(acac), 0.8 mu s:1.82 mu s]. Moreover, (tbt)(2)Ir(acac) has much more improved phototoluminescence quantum efficiencies in CH2Cl2 solution, [(tbt)(2)Ir(acac), 0.51; (bt)(2)Ir(acac), 0.26]. Employing them as dopants, high performance double-layer PLEDs were fabricated. The (tbt)(2)Ir(acac)-based and (tpbi)(2)Ir(acac)-based PLEDs have the maximum external quantum efficiencies of 8.71 % and 10.25 %, respectively, and high EL quantum efficiencies of 5.92 % and 7.21 % can be achieved under high driven current density of 100 mA cm(-2). PLEDs fabricated with both the two phosphors have much broadened EL spectra with FWHM of > 110 nm, which afford the feasibility to be used as dopants in white LEDs, and the best doping concentrations of the two complexes in fabrication of PLEDs were optimized.