AIE-active Ir(III) complexes with tunable emissions, mechanoluminescence and their application for data security protection

Four heteroleptic cationic Ir(iii) complexes [(X)₂Ir(L2)]⁺PF₆^- were designed and synthesized, where L2 = 3,6-di-tert-butyl-9-(4-(4,5-dimethyl-2-(pyridin-2-yl)-1H-imidazol-1-yl)butyl)-9H-carbazole, X = difluorophenylpyridine (dfppy) (1), dimethylphenylpyridine (dmppy) (2), difluorophenylquinoline (dfpq) (3), dimethylphenylquinoline (dmpq) (4). Their photophysical properties have been systematically investigated via a series of spectroscopic methods. All complexes show fluorescence-phosphorescence dual-emission, aggregation-induced fluorescence emission (AIFE) and aggregation-induced phosphorescence emission (AIPE) in a solvent. Meanwhile, green to red emission colors are exhibited in the solid state. Noticeably, complex 2 shows evident piezochromic and vapochromic behaviors. The emission colors of complex 2 can be reversed from green to yellow upon grinding and CH₂Cl₂ fuming, which is further demonstrated using solid state and powder X-ray diffraction spectroscopy. Additionally, complex 2 is used in data security protection and provides a strategy to design smart luminescent materials.