Synthesis of highly selective indole-based sensors for mercuric ion

Two indole-based fluorescent chemosensors 1 and 2 were prepared and investigated characteristic features with transition metal ions. Sensors 1 and 2 were selective for Hg ²⁺ ion, among a series of metal ions, in aqueous ethanol (H ₂O-EtOH, 1:2, v/v) with association constants of 5.74×10 ³ and 4.46×10 ³ M ^-1 and detection limits of 7.4 and 6.8 μM, respectively. Computational results revealed that sensor 1 or 2 with Hg ²⁺ ion formed 1:1 complex with a central, sandwichcoordinated Hg ²⁺ ion. Computational calculations provided evidence that a sandwich-coordinated Hg ²⁺ ion center was formed and the polyoxyethylene spacer acted as a scaffold for bringing functional ligands into a suitable geometry.