An off-on-off fluorescence probe based on a pyrazole derivative for Al3+ and Fe3+ detection

A new fluorescence probe (E)-N & PRIME;-(2,3-dihydroxybenzylidene)-1-(pyridin-2-yl)-5-(thiophen-2-yl)-1H-pyrazol-3-carbohydrazide (L) was designed and synthesized, which could be applied as an off-on-off sensor for the successive detection of Al3+ and Fe3+. The detection limits of L towards Al3+ and Fe3+ were determined to be 1.10 x 10(-8) M and 4.45 x 10(-8) M, respectively. The 1 : 2 binding stoichiometry of L to Al3+ and Fe3+ was established from Job plot analysis, H-1 NMR spectroscopy and mass spectrometry titration. Application experiments proved that L had excellent ability to monitor Al3+ and Fe3+ in tap water, and the sensing process could be performed on test paper as well.