Anthraquinonyl-pyridinium-based iridium(III) complexes with reversible piezochromic phosphorescence behaviors

The synthesis and characterization of two novel orange emissive cationic iridium(III) complexes (Ir1 and Ir2) are reported, where an anthraquinone group was introduced into the pyridine moiety to construct the cyclometalating ligands, and the photophysical properties and piezochromic behavior were systematically investigated. The prepared ionic phosphorescent iridium(III) complexes exhibited orange-red emissions at 577 nm and 580 nm, respectively. Upon grinding, the phosphorescence intensity of Ir1 decreased, accompanied by a red-shift of 14 nm, and its lifetime extended to 5.83 μs. Meanwhile, the emission peak of Ir2 showed a blue shift of 20 nm. Powder X-ray diffraction (P-XRD) analysis confirmed that a phase transition from crystalline to amorphous states occurred after applying external pressure, which can be attributed to the distorted molecular conformation leading to looser molecular packing. Through the design and regulation of molecular structures, novel phosphorescent materials with efficient, stable, and reversible piezochromic properties were developed, thereby advancing the research and application of piezochromic materials.