Rational ligand engineering of AIE-active iridium(iii) complexes for tunable emission, reversible mechanochromism and anti-counterfeiting†

Developing multifunctional phosphorescent materials with efficient solid-state emission and tunable colors in response to external stimuli is highly desirable but remains challenging due to the lack of clear design strategies. Herein, we propose a straightforward strategy to construct a series of AIE-active iridium(III) complexes with donor–acceptor (D–A) type ancillary ligands, namely 3N-Ir-TPA, 3N-Ir-TPAPy, and 3N-Ir-TPAIq, where triphenylamine derivatives serve as donors and 2-(3-methyl-1H-1,2,4-triazol-5-yl)pyridine functions as acceptors. By systematically tuning the donor units from hydrogen atom to pyridine and isoquinoline units, the tunable emission color shifts from green to orange with ease. Detailed spectroscopic studies and theoretical calculations reveal that the restriction of intramolecular motion is the fundamental cause of the AIE properties. 3N-Ir-TPA exhibits reversible mechanochromic luminescence (MCL) property with a color change from green to yellow upon grinding (41 nm red shift), which can be fully reversed by vapor fuming. Utilizing the remarkable AIE and MCL properties of 3N-Ir-TPA, we employ 3N-Ir-TPAPy as a reference material to successfully construct a high-contrast anti-counterfeiting device. This study provides an effective strategy for developing color-tunable and multifunctional AIE-active iridium(III) complexes.