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Macrocycle-Assisted Cooperative Fe3+ Coordination and Fluorescence Regulation in a Coumarin-Functionalized
Ömer Güngör1,2, Neşe Taşci3, Ayça Şeyma Ünaldı3
1Polymer Science and Technology, Natural Sciences Institutes, Kocaeli University, Umuttepe Campus, 41001 Kocaeli, Turkey.
None:
A coumarin-functionalized calix[4]-arene was designed and synthesized as a supramolecular fluorescent platform for the selective recognition of Fe3+ ions in aqueous media. The preorganized calix[4]-arene cavity, combined with the coordinating oxygen- and nitrogen-donor sites of the coumarin unit, enables effective host-guest interactions with Fe3+, resulting in pronounced fluorescence quenching. Spectroscopic investigations revealed that the quenching process proceeds through a combination of static complex formation and dynamic collisional pathways, supported by Stern-Volmer analysis. Job's plot analysis indicated a 1:2 binding stoichiometry (Fe3+/ligand), highlighting the cooperative role of the calixarene framework in metal-ion coordination. The sensor exhibits a low detection limit of 0.30 μM and a wide linear response range from 33 to 354 μM toward Fe3+, while maintaining a high selectivity in the presence of competing metal ions. The applicability of the supramolecular system was further demonstrated through the determination of Fe3+ ions in real water samples with satisfactory recovery values. This study illustrates how the integration of a coumarin fluorophore into a calix[4]-arene scaffold provides an effective coordination-driven fluorescence modulation platform, offering insight into calixarene-based metal-ion recognition systems relevant to supramolecular and coordination chemistry.
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Colors and Magnetism
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human eye.

