Thiophene-phenylquinazoline probe for selective ratiometric fluorescence and visual detection of Fe(iii) and turn-off fluorescence for I and its applications.

A 2,5-bis(4-phenylquinazolin-2-yl)thiophene (BQT) probe is designed, synthesized and explored for selective ratiometric fluorescence and visual detection of Fe and as a turn-off fluorescence probe for I anion. BQT is colorless and has blue emission in CHCN solution. BQT selectively complexes with Fe, turns its solution from colorless to greenish yellow and enables the ratiometric sensing of Fe with limit of detection (LOD) and limit of quantitation (LOQ) of 2 × 10 M and 6.1 × 10 M, respectively. Binding constant of BQT with Fe is found to be 4.1 × 10 M. BQT is also able to sense I anion present in aqueous solution by selectively turning colorless to yellow and fluorescence quenching with a LOD of 1.7 × 10 M and LOQ of 5.2 × 10 M. BQT sensing ability is not influenced by the presence of other metal ions and anions in the vicinity. The BQT-Fe complex is thoroughly characterized using MALDI-TOF, NMR and Job's plot. A reversibility experiment with EDTA suggests BQT is a reversible fluorescent chemosensor for Fe ions. The spectroscopic data of BQT and its complexes are employed to construct a field test kit for qualitative analysis and INHIBIT logic gate.