The Studies On Synthesis Of Heterocyclic Shiff-bases As Metal Ions(Al³⁺, Mg²⁺, Cu²⁺,Zn²⁺) Probes

Due to the unique biological and pharmacological activity, heterocyclic compounds has a very broad and important purpose in the fields of biology, chemistry,medicine, pesticides, conductive polymers and superconducting material. In this paper,five heterocyclic Schiff-base ligands have been synthesized and characterized. In addition, their sensing properties and recognition mechanisms have been studied. This thesis includes five chapters. And the main contents are as follows:In the first chapter, we make a brief intoduction to the applications of heterocyclic compounds and their Schiff-bases chemosensors. Furthermore, the basic background knowledge of chemosensors and sensing mechanism have been summarized. Finally, some researches on various metal ions in recent years have been presented.In the second chapter, two similar structure Schiff base fluorescent probe,1-phenyl-3-methyl-5-hydroxypyrazole-4-carbaldehyde(2'-methylquinoline-4'-formyl)hydrazone(L1) and1-phenyl-3-methyl-5-hydroxypyrazole-4-acetone-(2'-methylquinoline-4'-formyl)hydrazone(L2), for selective detection of Al3+ has been designed and synthesized.The free receptor almost not show fluorescence emission. Upon the addition of Al3+,L1 shows 286-fold enhancement of fluorescence intensity and L2 shows 111-fold enhancement. This phenomenon was attributed to forms 1:1 complex which inhibit photo-induced electron transfer process and chelation-enhanced fluorescence precess.In the third chapter, a new senser Isatin-3-(7'-Methoxychromone-3'-methylidene)hydrazone based on chromone Schiff base was synthesized to detect Mg2+. The complexation behavior of chemosensor with different metal ions in ethanolic solution was studied on UV-vis absorption spectra and fluorescent spectra. Results showed that the chemosensor displayed a 70-fold fluorescence enhancement upon the addition of Mg2+ due to the photo-induced electron transfer(PET) effect.In the fourth chapter, we have synthesized a colorimetric chemosensor based on7-acetamidyl-4-methyl-1,8-naphthyridine-2-aldehyde and fluorescein hydrazide. The colour dramatically changed in the present of Cu2+, while other ions did not have much influence. In addition, it showed a good selectivity to Cu2+ in the presence of other metal cations. Therefore, the Schiff base compound can act as an efficient sensor for Cu2+.In the last chapter, we have developed a fluorescence chemosensor based on7-acetamidyl-4-methyl-1,8-naphthyridine-2-aldehyde and gallic acid hydrazide. The free receptor almost did not show fluorescence emission at 504 nm when it was excited at 431 nm. Upon the addition of Zn2+, the probe displays a highly sensitive and selective response with remarkably enhanced fluorescence intensity at 504 nm in ethanol. This restricts the photoinduced electron transfer(PET) process and enhances fluorescence output via chelation enhanced fluorescence(CHEF) effect.