Advancing fluoride ion sensing with a fluorene-derived fluorophore: A comprehensive experimental and computational study

This paper discusses the detailed sensing studies of a fluorene-based fluorophore for the sensitive and selective detection of fluoride ions in the solution state. The fluorophore FOPD has been synthesised from 9H-fluoren-9-one and o-phenylene diamine by simple reaction set-up, which was then structurally characterised by various spectroscopic techniques including FT-IR, NMR, and HRMS analyses. Further, the sensing potential of the fluorophore was carried out by UV–visible and fluorescence spectroscopic techniques. Various parameters including sensitivity, selectivity, interference, the influence of pH, and limit of detection were successfully validated experimentally, thereby confirming the excellent ability of FOPD in detecting fluoride ions. Computational studies, including Density Functional Theory (DFT), were employed to optimise the molecular structure of FOPD, explore its Frontier Molecular Orbitals (FMOs), and identify the plausible interaction between fluoride ions. Further, topological analyses such as ELF, LOL, RDG and QTAIM provide valuable insights into the non-bonding and intramolecular hydrogen bonding interactions, enabling a clearer understanding of the sensing mechanism. Finally, the toxicity analysis of FOPD revealed that it is relatively non-toxic with an excellent LOD of 0.125 µM, underscoring its potential as a safe and environmentally friendly fluorophore for the selective detection of fluoride ions.