Constructing anion–π interactions in cationic iridium(iii) complexes to achieve aggregation-induced emission properties

Abstract

Organometallic iridium(III) complexes with AIE properties have received much attention for their potential in the photoelectric and biomedical fields; however, the development of such materials remains challenging due to the lack of a precise design strategy. Herein, a family of cationic iridium(III) complexes with pyridine-azole ancillary ligands, in which 1-(2,4-difluorophenyl)-1H-pyrazole is a cyclometalated ligand, have been strategically synthesized. Detailed photophysical studies demonstrate that they exhibit weak emission in dilute solution with photoluminescence quantum yields of ∼1% but show enhanced phosphorescence in the aggregation state. The large structure relaxation between the ground state and triplet excited state results in almost non-emissive behavior in the isolated state. Interestingly, such structure relaxation and detrimental π–π stacking can be effectively suppressed by the anion–π interaction formed between the counter anion and the π-systems in the cationic component, which are rationally supported by single-crystal analysis and theoretical calculation. Decreased nonradiative pathways thus give rise to strong emission upon aggregation. Information security and storage are also achieved by employing the studied material as a medium. This work will contribute a simple design strategy to construct AIE-active iridium(III) complexes based on anion–π interactions and further enrich phosphorescent AIE systems.