Creation of cationic iridium(iii) complexes with aggregation-induced phosphorescent emission (AIPE) properties by increasing rotation groups on carbazole peripheries

Abstract

Three cationic iridium complexes containing 4,7-bis(3,6-di-tert-butyl-9H-carbazol-9-yl)-1,10-phenanthroline (L₁) and 4,7-bis(3′,6′-di-tert-butyl-6-(3,6-di-tert-butyl-9H-carbazol-9-yl)-3,9′-bi(9H-carbazol)-9-yl)-1,10-phenanthroline (L₂) as the ancillary ligands, namely, [Ir(ppy)₂(L₁)]PF₆ (1), [Ir(ppy)₂(L₂)]PF₆ (2) and [Ir(oxd)₂(L₂)]PF₆ (3) (ppy is 2-phenylpyridine, oxd is 2,5-diphenyl-1,3,4-oxadiazole), have been designed and prepared. With more intramolecular rotational units on the ancillary ligand (L₂), 2 and 3 possess a unique aggregation-induced phosphorescent emission (AIPE) property. This phenomenon was unprecedentedly observed in the cationic iridium(III) complexes. In order to investigate the underlying mechanism of this AIPE behavior, their photophysical, temperature-dependent aggregation properties as well as theoretical calculations, were performed. The results suggest that restricted intramolecular rotation is responsible for the AIPE of cationic complexes. Moreover, photoluminescent quantum yields in the neat film, thermal stabilities and off/on luminescence switching of 2 were investigated, revealing its potential application as a candidate for LECs and organic vapor sensing.