This paper studies the synthesis and photophysical properties of a series of bi-substituted phenylisoquinoline iridium(III) complexes. Interestingly, the bis[3-methyl-1-p-tolylisoquinolinato-N,C2′] iridium(III) (acetylacetonate) (6a1) could be prepared even though the singlecrystal X-ray crystallography data showed that there was steric hindrance due to the methyl group on the C-3 position to isoquinoline. Noticeably, the cyclic voltammetric (CV) measurements indicated that although these iridium(III) complexes have similar energy gaps, their E1/2(ox) are different from the mono-substituted (in phenyl ring) phenylisoquinoline iridium(III) complexes. This illustrates that the major influence of oxidation potential for iridium(III) complexes is the substituted isoquinoline ring. While all these complexes emitted in the red region, the bis[5-methyl-1l-p-tolylisoquinolinato- N,C2′] iridium(III) (acetylacetonate) (6c1) showed a higher brightness of 9299.36 cd/m2 at a higher current density of J = 63.69 mA/cm2 and a better luminance efficiency of 21.96 cd/A at a current density of J = 0.28 mA/cm2. The corresponding CIE (Commission International de L'Eclairage) coordinates are x = 0.67, y = 0.33.
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