Selective Fluorescent Detection of Fe (III) Using a Benzothiadiazole-Based Conjugated Molecule: A Combined DFT and Experimental Study

The rational design of molecular sensors with well-defined recognition mechanisms is essential for improving selectivity toward metal ions. In this study, a benzothiadiazole–pyridine-based organic molecule (BTDP) was designed as a fluorescent sensor by strategically integrating nitrogen- and sulfur-containing donor sites to enable selective interaction with ferric ions. The sensing behaviour was systematically investigated using a combination of photophysical measurements and density functional theory calculations. The interaction mechanism between BTDP and Fe 3+ was elucidated through X-ray photoelectron spectroscopy, non-covalent interaction analysis, and electrostatic potential mapping, providing complementary experimental and theoretical insight into charge redistribution and coordination behaviour at the molecular level. Fluorescence quenching studies further supported the proposed interaction pathway. The Limit of detection (LOD) and Limit of quantification (LOQ) in this study was found to be 2.3 μM and 6.99 μM respectively. This work emphasizes a structure-interaction-response approach, offering a mechanistic framework for the rational development of fluorescent metal-ion sensors.