Concise design and synthesis of water-soluble fluorescence sensor for sequential detection of Zn(II) and picric acid via cascade mechanism

Under microwave assistance, 2,6-bis(benzimidazolyl)-pyridine has been concisely synthesized and further productively converted to the functional molecule BMBP via accessible N-alkylation reaction. For the introduction of alkoxyalkyl chain, this original substance BMBP with better solubility in water exhibits specific fluorescence response toward Zn2+ from colourless to blue in aqueous solution. A sequential detection for picric acid (PA) can be conducted in this following system, showing the high selectivity and sensitivity of quenching over other analogues. On the basis of the comparison with the control BMBB, a cascade sensing mechanism has been disclosed to accelerate the recognition of structure-property relationship, which is fully supported by LC-MS, H-1 NMR, lifetime measurement and theoretical calculation. Noteworthily, BMBP is also readily available for practical application not only in quantitative determination of Zn2+ and PA in real water samples, but also in visible detection of two analytes in multiple forms on paper test strips, offering convenient process for low-cost, portable and versatile sensing device.