Highly Sensitive and Selective Fluorescent Probes for Cu(II) Detection Based on Calix[4]arene-Oxacyclophane Architectures.

A new topological design of fluorescent probes for sensing copper ion is disclosed. The calix[]arene-oxacyclophane (Calix-OCP) receptor, either wired-in-series in arylene--ethynylene conjugated polymers or standing alone as a sole molecular probe, display a remarkable affinity and selectivity for Cu(II). The unique recognition properties of Calix-OCP system toward copper cation stem from its pre-organised cyclic array of -ligands at the calixarene narrow rim, which is kept in a conformational rigid arrangement by a tethered oxacyclophane sub-unit. The magnitude of the binding constants ( = 5.30 - 8.52 × 10 M) and the free energy changes for the inclusion complexation (-Δ = 27.0 - 28.1 kJmol), retrieved from fluorimetric titration experiments, revealed a high sensitivity of Calix-OCP architectures for Cu(II) species. Formation of supramolecular inclusion complexes was evidenced from UV-Vis spectroscopy. The new Calix-OCP-conjugated polymers (polymers and ), synthesized in good yields by Sonogashira-Hagihara methodologies, exhibit high fluorescence quantum yields ( = 0.59 - 0.65). Density functional theory (DFT) calculations were used to support the experimental findings. The fluorescence on-off behaviour of the sensing systems is tentatively explained by a photoinduced electron transfer mechanism.