Platinum(II) Complexes with Ligand-Dependent Aggregation-Induced Electrochemiluminescence Properties and Their Application for the Ultrasensitive Determination of Dopamine

Platinum(II) complexes have been reported to possess the property of aggregation-induced electrochemiluminescence (AIECL), showcasing significant potential in ECL sensing applications due to their robust stability and high emission yields. However, a comprehensive understanding of their ECL emission mechanism and the effect of ligand types on ECL emission efficiency remains elusive, hampering further advancements. In this study, we synthesized three platinum(II) complexes using three N̂N̂N-type tridentate ligands and conducted a thorough investigation of their optical and electrochemical properties. The as-prepared complexes exhibit solvent-dependent self-assembly characteristics, yielding tunable UV absorption and aggregation-induced emission (AIE) properties. Notably, all three complexes exhibit typical AIECL emission; in particular, the cathodic ECL emission efficiency of the complex containing 2,6-bis(benzimidazol-2-yl) pyridine as the ligand, designated as Pt-1, is 23 times greater than that of the commercially available [Ru(bpy)₃]²⁺ complex. Moreover, the complex with 2,2':6',2″-terpyridine as the ligand (Pt-2) exhibits an obvious positively shifted ECL excitation potential to -0.8 V, compared to -1.5 V for Ru(bpy)₃²⁺. The underlying ECL mechanism suggests that the self-catalytic capability of platinum(II) complexes in facilitating the decomposition of the coreactant is responsible for the enhanced ECL emission. Density functional theory calculations further reveal that the type of ligand significantly affects the energy gaps of the resulting complexes, with Pt-1 exhibiting the lowest energy gap and high ECL emission efficiency. Ultimately, a "turn-off" ECL sensor for the profiling of dopamine was developed with impressive performance in terms of detection range and limit of detection. This study introduces a novel concept for the development of platinum(II) complexes, broadening their application as innovative ECL materials and marking a pivotal advancement in the field of ECL material science.