Rational Design of AIPE-Active Cationic Ir(III) Complexes for Detecting Picric Acid in Aqueous Media

The efficient detection of nitroaromatic explosives is of great importance to social safety. For this purpose, three cationic Ir(III) complexes Ir1–Ir3 were synthesized. Ir1–Ir3 exhibit aggregation-induced phosphorescent emission (AIPE) properties and can be utilized for sensitively and selectively detecting picric acid (PA) in an H₂O/CH₃CN system. The results demonstrate that there is a positive correlation between the AIPE activities of Ir(III) complexes and their efficiencies in detecting PA. 4-Fluorophenyl-substituted complex Ir3 possesses the highest AIPE activity and exhibits the highest quenching constant (K_SV = 635,621 M⁻¹) and the lowest limit of detection (LOD = 2.6 nM) for detecting PA among these complexes. The crystal structures reveal that the higher AIPE activity of Ir3 is owing to its more abundant molecular interactions compared to Ir2. The density functional theory calculations suggest that luminescence quenching is due to the photo-induced electron transfer.