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

• Published in: Molecules (Basel, Switzerland) Switzerland), 2020-05, Vol.25 (10), p.2456
• Main Authors: Costa, Alexandra I, Barata, Patrícia D, Fialho, Carina B, Prata, José V
• Format: Article
• Language: English
• Subjects: Alkynes - chemistry; Binding sites; calixarene; Calixarenes; Calixarenes - chemistry; Cations, Divalent; Copper; Copper - analysis; Density functional theory; Electron transfer; Ethers, Cyclic - chemistry; Experiments; Explosives; Fluorescence; Fluorescent Dyes - chemistry; Fluorescent indicators; Free energy; inclusion complex; Inclusion complexes; Molecular Structure; Phenols - chemistry; Piperidines - chemistry; Polymers; Probes; Quantum Theory; Receptors, Artificial - chemistry; Selectivity; sensor; Sensors; Signal transduction; Solutions; Spectroscopy; supramolecular; Titration
• ISSN: 1420-3049; 1420-3049
• DOI: 10.3390/molecules25102456

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.