Design, Synthesis of Umbelliferone Fused Benzo[b][1,4]oxazepines and Thiazepines Acting as Fluorometric Bio‐Sensor

ABSTRACT

A series of novel 7‐hydroxycoumarin‐fused benzoxazepine and benzothiazepine derivatives were synthesized and explored as potential fluorometric biosensors for biomolecular detection. The target compounds were obtained through a multistep synthetic route involving a key Michael addition reaction and were structurally characterized using FTIR, ¹ H NMR, and ¹³ C NMR spectroscopy. To investigate their electronic properties, Density Functional Theory (DFT) calculations were performed, and the HOMO–LUMO energy gaps were determined. The computed energy‐gap values were further correlated with experimental band‐gap values obtained from Diffuse Reflectance Spectroscopy (DRS), providing insight into the structure–property relationships of the synthesized fluorophores. The combined theoretical and experimental analyses enabled the identification of promising candidates for fluorescence‐based sensing applications. The selected compounds were subsequently evaluated for their sensing performance toward biologically relevant analytes, including glucose and basic amino acids. Fluorescence studies revealed significant analyte‐induced responses, demonstrating their suitability as fluorescent probes. Furthermore, the limits of detection (LOD) were determined, confirming the high sensitivity of the developed sensors. These findings highlight the potential of coumarin‐fused benzoxazepine and benzothiazepine derivatives as efficient fluorometric biosensors for biomolecular recognition.