Synthesis, Properties And Sensing Applications Of Calix[4]arene Derivatives

As a kind of macrocyclic host compounds developed in 1940s, calixarene has been widely used in a lot of field with the gradual development of synthetic methods. In recent years, calixarene has attracted increasing attention and achieved remarkable research progress due to the unique structure and the excellent properties. Therefore, calixarene is honored as the third generation of macrocyclic host compounds after crown ether and cyclodextrin.Calixarene is a cyclic oligomer which is formed by polycondensation reaction between phenol and formaldehyde. Because of the excellent advantages such as rich conformation isomerism, resizable hydrophobic cavity, easy modification and strong environmental adaptability, calixarene has broad applications in many diverse areas such as molecule and ion recognition, ion transport, drug delivery and release, supramolecular gels, etc. Calixarene takes the advantages of both crown ethers and cyclodextrins. The lower rim of the phenolic hydroxyl group can be formed by intramolecular hydrogen bonds to stabilize its structure, it can also chelate cations to realize ion transport. Ionic and neutral molecules could be encapsuled into π electron-rich hydrophobic cavity formed by the phenyl groups through host-guest interaction. At the same time, it is possible to adjust the size of the hydrophobic cavity to selectively capture the different sizes of molecules or ions. In addition, calixarene could easily be modified by introducing suitable substituents at the different conditions which strengthens its identification ability. While suitable chelation units and fluorescent groups are introduced to modify the structure of calixarene, it can not only enhance the ability to identify specific molecules or ions, but also make it easier for quantitative detection by monitoring the changes of fluorescence. Due to abundant conformational isomerism and strong environmental adaptability, calixarene has been introduced to supramolecular gel system. When the system is subjected to external stimuli, the conformation of calixarene can adjust to maintains a stable gel state. Meanwhile, calixarene has a variety of guest molecules or ions, and it could endow the gel with some special properties to meet the needs of different materials from environments.Based on the above considerations as well as similar work in our laboratory in recent years, in this thesis, with the calix[4]arene as the main structure, a series of calix[4]arene derivatives were synthesized by introduction of suitable substituents. Sensing performance studies showed that one of the derivative L1 is responsive to Ag+, thus realizing the visual detection of Ag+ and formaldehyde. In addition, different types and numbers of substituents were employed to modify the calix[4]arene to study the effects of different substituents on the gel-formation ability. This thesis mainly consists of the following two parts.In the first section, a bis-nitrobenzoxadiazole (NBD) derivative of calix[4]arene (L1) and a control compound (L2), mono-NBD derivative of the calixarene were designed and prepared via click chemistry. Fluorescence studies demonstrated that L1 as created can function as a switch with the presence of Ag+in THF, of which the free state of L1 emits at ～527 nm, but the binding state at 576 nm. Based upon this discovery, L1 was studied as a chemo-sensor of Ag+ in a mixture solvent of THF and H2O with a detection limit (DL) of ～6.2×10-/ mol/L. Presence of other commonly found metal ions shows little effect upon the determination. Moreover, the L1 in the Ag+-L1 complex could be fully released with introduction of HCHO, a base for the sensitive and selective detection of the toxic chemical. The DL of this test is 6.6×10-7 mol/L. Interestingly, binding and releasing of the fluorescent ligand could be repeated for at least 5 times. Furthermore, both sensing processes could be performed in a visualized manner. It is believed that the fluorescent compound as created should have a potential to find real-life applications.In the second section, based on the similar work in our laboratory in recent years, it is found that introduction of calixarene supramolecular gel system will make the system obtain some special properties. Therefore,13 kinds of calix[4]arene derivatives were designed and synthesized. Their gelation behaviors in 30 solvents were studied in detail. With increasing the substitution number, the solubility decreases while the gelling ability enhances. Further studies on the gel structures, the gel properties and the relevant gel formation mechanisms are still in progress.