Studies on 1,8-naphthalimide derivative as a robust multi-responsive receptor for an array of low cost microanalytical techniques for selective prompt and on-site recognition of duplicitous fluoride in semi-aqueous medium

Abstract

In this work, an optochromogenic receptor NC, (E)-2-(2-hydroxyethyl)-6-(2-(1-(6-nitro-2-oxo-2H-chromen-3-yl)ethylidene)hydrazinyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione has been designed and developed from 1,8-naphthalimide and 3-acetyl-6-nitro-2H-chromen-2-one moieties which provides multidimensional options for the rapid, selective, economical and reliable monitoring of fluoride in water (i.e. naked-eye, colorimetric, fluorometric, test strip, electrochemical and smartphone based response). Pick and choose assay process can be adopted depending upon the available instruments and skill of the analyzer impacting uniqueness to the developed receptor. Colorimetric detection of F− in water is possible, which can be monitored by UV-vis spectroscopy (detection limit as low as 8.468 × 10−7 M), test strips, and perceived by the naked eye. Excellent colorimetric response can be elucidated by augmented intramolecular charge transfer process within the molecule after anionic deprotonation interactions. The receptor exhibits a "turn-off" fluorescence response towards F− due to enhanced photoinduced charge transfer (PET) process with the detection limit up to 7.413 × 10−7 M. The binding interaction between receptor NC and F− is confirmed by DFT/TD-DFT calculations, 1H NMR and 19F NMR titration. The anodic and cathodic potential become flattened and shifted in NC + F− complex in the cyclic voltammetry study. Increased number of smartphone users and its user-friendly property initiated us to develop a simple and efficient protocol based on a digital image colorimetry using smartphones of different companies for the detection and quantification of fluoride ion. The lowest limit of detection from the smartphone protocol was found to be 3.368 × 10−6 M. A comparative study was carried out to check the versatility and accuracy of F− ion concentration determined through different microanalytical techniques. Fluoride ion concentration in real life samples like toothpaste, mouthwash, and groundwater collected from various regions were analyzed and found to be in agreement with standard Ion-selective electrode method. Thus, it holds promise for being developed as a futuristic tool for the real-time water quality monitoring.