The Synthesis And Properties Of Novel Schiff Base Fluorescent Sensors Based On Quinoline

Fluorescent sensors have been proved to be useful tools for sensing metal cations, anions and amino acids in vivo and vitro. The more and more researchers have paid more attention to study the fluorescent sensors because of their high selectivity, good sensitivity, easy operational use and fast response times with respect to traditional analytical methods. Schiff base is an ideal fluorescent sensor. Not only Schiff base is easily to be synthesized, but also it can provide nitrogen which coordinates with metal ions. So recently, much attention has been paid to the synthesis and study of Schiff base fluorescent sensors by some researchers.In this paper, four novel Schiff base L, L1, L2 and L3 have been synthesized by modifying the 2 and 8 positions of 8-hydroxy-2-methyl quinoline by different substituent groups. They are as follows:First, according to the Hard-Soft-Acid-Base theory, the 8-hydroxy-2-methyl quinoline’s nitrogen and oxygen can provide a hard-base environment for hard-acid Al3+. After being modified the 8-hydroxy-2-methyl quinoline, the sensor L has a high selectivity and sensitivity for detecting Al3+ in ethanol solvents. The binding ratio between Al3+ and L was 1:2, which was determined by the Job’s plot. The binding mechanism was studied to be based on PET mechanism.Second, the sensor L1 was synthesized by reacting 8-hydroxy-2-quinoline formaldehyde with hydrazide. When other metal ions and Fe3+ coexist in DMSO solvents, the sensor L1 showed a high selectivity and anti-interference ability for recognizing Fe3+, and the remarkly fluorescence quenching can be achieved.Third, the sensor L2 was synthesized by reacting 8-hydroxy-2-quinoline formaldehyde with 4-aminoantipryrine. And the sensor L3 was synthesized by substituting the hydroxyl position of sensor L2 with 2-bromomethyl pyridine. Comparing the L2 and L3, L3 can’t be acted as a good sensor for detecting the metal ions in solutions. However, the sensor L2 performed a high selectivity and sensitivity for the Al3+ in ethanol solvents, and the recognition process was studied to be based on both ESIPT and PET mechanism.