Design and Synthesis of Novel Coumarin–Isoxazole Conjugates as Chemosensers: A Highly Selective and Instantaneous Detection of Mn2+ and Cu2+ Ions

This study demonstrates the synthesis and characterization of a series of novel isoxazole-containing 4-hydroxycoumarin-based chemosensors for the highly selective and rapid detection of Mn²⁺ and Cu²⁺ ions from among several metal ions in DMSO: EtOH (1:9 v/v). The probes were synthesized using inexpensive and readily available starting materials and were structurally characterized by ¹H and ¹³C NMR, FT-IR, HRMS, and SC-XRD spectroscopic analyses. UV–Vis, fluorescence studies, and X-ray crystallography revealed a significant binding interaction with Cu²⁺ and Mn²⁺, leading to pronounced spectral shifts. Fluorescence studies demonstrated strong fluorescence enhancement for Mn²⁺, whereas Cu²⁺ exhibited quenching behavior. The calculated binding constant for the 8f-Mn²⁺ complex was 1.2233 × 10⁷ M⁻¹ and for the 8f-Cu²⁺ complex was 5.4647 × 10⁷ M⁻¹. Again, the calculated limit of detection (LOD) for Mn²⁺ and Cu²⁺ with respect to the ligand 8f was 2.697552 × 10⁻⁷ M and 0.60491 × 10⁻⁷ M respectively, indicating high sensitivity. The fluorescence variations in 8f with two chemical inputs, Mn²⁺ and Cu²⁺, can be utilized to create a molecular circuit demonstrating an INHIBIT logic operation based on studies. The competitive selectivity experiments confirmed the ligand's superior affinity towards Mn²⁺ in the presence of various metal ions.