Synthesis of cationic iridium(III) complexes with high quantum yield via enhancing the steric hindrance of ligands

A series of cationic Ir(III) complexes 1a–4a functionalized with carbazole-9-yl-n-butyl group (CZB) were designed and synthesized. An investigation of their photophysical properties showed that the attachment of CZB moiety into the complexes resulted in large improvement in the photoluminescence quantum yield (PLQY) of solid film although the emission spectra and excited-state character presented little change compared with those of the parent complexes. Besides, the functionalized complexes also exhibited good thermal stability and film-forming property. In light of our quantum chemical calculations and X-ray data, these advantages of functionalized complexes mainly derived from the CZB moiety which was superior in reducing the intermolecular interaction and inhibiting the quenching process. Furthermore, to verify our results and design cationic Ir(III) complexes with much higher efficiency, four Ir(III) complexes G0–G3 were synthesized, in which different number of CZB moieties (from 0 to 3) were introduced into the complexes, respectively. Noticeably, in case of G3, the obvious high neat film PLQY of 43% was obtained. In comparison with its dispersed film, a large retaining percentage (90%) was realized, indicating that the CZB moiety could suppress the quenching of luminescence effectively.