Turn-On Metal Ion Responsive Behavior Enabled by Coordination-Driven Multicomponent Self-Assembly

The advancement of industrialization, fossil fuel reliance, and agricultural expansion has intensified environmental contamination by heavy metal ions, and they demand urgent attention. In this work, we proposed a multicomponent-assembly-based strategy for the construction of a turn-on fluorescence sensing system and designed mixed-ligand probes with tetraphenylethylene (TPE) and binaphthyl units. As many as 17 different metal ions were introduced into the mixed ligands; only Zn(II) and Cd(II) induced a significant fluorescence enhancement. The experimental results indicated that the binaphthyl-induced spatial restriction after coordination markedly enhanced the emission efficiency. Heteroleptic assemblies S2 and S4 (Φ_F = 65.7% for S2 and Φ_F = 49.8% for S4) based on mixed ligands L2 and L3 displayed a 100-fold enhancement in fluorescence efficiency relative to the free ligand L2 (Φ_F = 0.5%). Furthermore, according to fluorescence titration experiments, the calculated limits of detection (LODs) for Zn(II) and Cd(II) of our mixed (L2 and L3) ligand sensing system were approximately 1.7 × 10^-7 and 1.8 × 10^-7 M, which are markedly superior to the L1 and L3 ligand combination. Consequently, mixed ligands L2 and L3 can serve as ideal turn-on fluorescent probes for the detection of Zn(II) and Cd(II) ions in a fast, sensitive, and selective manner.