Synthesis and Optical Binding Evaluation of Indole-Based Ligand with Coumarin

Coumarin is frequently used as a fragrance material, for example as a fragrance enhancer or a stabilizer. High consumption of coumarin can pose several health hazards due to its potential toxicity and anticoagulant effect. In recent years, alternative methods for coumarin detection that are simpler and faster have been invented using different organic compounds such as cyclodextrins as optical sensing materials. This study mainly emphasized the synthesis and characterization of indole Schiff base ligand as well as their interactions with coumarin. In the first stage, indole Schiff base ligand (compound 2) was synthesized via condensation reactions. The reaction progress was tracked using thin-layer chromatography (TLC), confirming its completion. The resulting yellowish-orange precipitate was subsequently characterized using nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR), and also Differential Scanning Calorimetry (DSC). The second stage of this research involved the interaction studies between the indole Schiff base ligand with coumarin via UV-Vis titration method, fluorescence titration and Job's plot analysis. The result indicates that compound 2 was able to bind to coumarin strongly with a high binding constant, K_b = (1.11 ± 0.1) × 10⁵ M^-1, with a 40% hypochromic effect and a red shift was observed for 4.5 nm. In conclusion, compound 2 was believed to show good potential as sensing material in the future solid-state chemosensor to detect coumarin in food and personal care products.