Efficient colorimetric fluoride anion chemosensors based-on simple naphthodipyrrolidone dyes

Two novel lactam-containing compounds based on simple naphthodipyrrolidones have been developed as colorimetric sensors for fluoride anion with high selectivity and sensitivity. The two compounds can selectively act with fluoride anion and exhibit the naked-eye visible color change from purple to blue, and the detection limit could reach the concentration as low as 3.0 × 10^?6 M. The proton nuclear magnetic resonance titrations reveal the happen of intermolecular proton transfer between the hydrogen atom on the lactam N and the fluoride anion. Quantum chemical calculations indicate that the deprotonation can alleviate the distorted degree between the peripheral phenyl and the naphthodipyrrolidone core, and raise the frontier molecular orbital energy levels and decrease the band gap, rendering the protonated molecules a new more batho-chromic absorption band.