Highly selective and sensitive turn-on fluorescent sensor for detection of Al based on quinoline-base Schiff base.

A new aluminum ion fluorescent probe (4-(diethylamino)-2-hydroxybenzylidene)isoquinoline-1-carbohydrazide (HL) has been conveniently synthesized and characterized. HL exhibited a highly selective and pronounced enhancement for Al in the fluorescence emission over other common cations by forming a 2:1 complex, with a recognition mechanism based on excited-state intramolecular proton transfer (ESIPT) and intramolecular charge transfer (ICT). The strong fluorescent emission can be observed even at ppm level concentration of the probe in the presence of Al with 41 fold intensity enhancement at 545 nm. HL displays good linear relationship with Al in the low concentration and the limit of detection is 8.08 × 10 mol/L. Similar molecules with different substituents on salicylaldehyde phenyl ring were synthesized for studying the structure-activity relationship. Density-functional theory (DFT) calculations are in agreement with the proposed mechanism. It is confirmed that HL could be used to detect Al ions in real sample by fluorescence spectrometry and Al ions in cells by bioimaging.