Synthetically simple, click-generated quinoline-based Fe3+ sensors

Simple quinoline-based fluorescent probes for Fe3+ have been efficiently synthesized through 'click' reaction. Both probes gave intense fluorescence compared to 8-hydroquinoline in various organic solvents due to the inhibition of the excited state intramolecular photon transfer process, while showing dramatically quenched and red-shifted fluorescence in an aqueous solution, which can be attributed to the hydrogen bond-induced intermolecular excited state proton transfer process. In the presence of Fe3+ or in an acidic condition (pH less than 4.0), both probes showed similar quenching of the emission and over 100 nmred-shifts of their emission maxima. The binding mode between the probes and Fe3+ has been found to be 1:1 based on Job's plot. A highly sensitive and selective response in their absorption and emission towards Fe3+ over many other metal ions, including Cr3+ and Cu2+, was observed and may be the result of the ground state metal to ligand charge transfer effect from Fe3+ to quinoline ligands.