A Series of Polyamide Receptor Based PET Fluorescent Sensor Molecules:  Positively Cooperative Hg²⁺ Ion Binding with High Sensitivity

[structure: see text] A series of PET fluorescent sensor molecules were designed and synthesized based on BODIPY fluorophore and polyamide receptors. Comparison of the photophysical properties of these sensor molecules, equipped with di-, tri-, and tetraamide receptor, provided a deep insight into the polyamide-Hg2+ interactions, and an unusual positively cooperative tetraamide-Hg2+ complexation was disclosed. In addition, sensor S3 displayed several favorable sensing properties.