Synthesis Of Fluoride Chemosensors And Their Recognition Mechanism

Anions play great roles in the areas of biology, medicine and environment. Corresponding specific receptors attracted most interest. And this has been especially true during last several years. Numerous efforts have been devoted to the designing of abiotic receptors for anion species, and some of important anions have been recognized. As the smallest anion, fluoride anion has unique chemical properties and is useful for dental caries and the treatment of osteoporosis in biology medicine and environment. So it is important for recognizing fluoride anion. Recently, various kinds of novel chemosensors for fluoride anion have been developed. In this thesis, we designed and synthesized a series chemosensors for fluoride and studied their recognition behaviors. The major contents are as follows:In Chapter 1, we introduce the recent development of anion recognition, anion structure characteristics and the general principles of designing receptors. We also introduced the literature review about chromogenic sensing and fluorescence sensing m recent years.In Chapter 2, we synthesized neutral receptor,2,6-bisbenzoicamidepyridine (1) and studied its recognition behaviors for anions, such as F, Cl-, Br-, AcO- and HSO4-. The results showed that receptor 1 can selectively recognized fluoride anion which prompts intramolecular charge transfer (ICT) in receptor 1. Receptor 1 could combine fluoride anion and form 1:1 complex, along with visible color change and remarkable spectral change. When fluoride anion was added, the characteristic absorption peak of the receptor 1 at 302nm shifted to 330 nm and a new peak at 409nm was appeared. Simultaneously, the color of receptor 1 changed to yellow and made the recognition of fluoride anion by naked eye come true. The results of Job plot and ESI-MS indicate that receptor 1 form 1:1 stoichiometric complex with fluoride anion by hydrogen bonding interactions, which was proved in 1H NMR spectra. Geometry structure of receptor 1 simulated by Gaussian 03 showed that it is easy for receptor 1 to take intramolecular charge transfer.In Chapter 3, we synthesized ionic receptor 2,6-bisbenzoicamide pyridine hydrochloride (3) by the ionization of neutral receptor 2,6-bisbenzoicamidepyridine (1). Its recognition behaviors for anions, such as F-,Cl-, Br-, AcO- and HSO4- were also studied. The results showed that receptor 3 can selectively recognized fluoride anion. The receptor 3 showed plane configurations and high fluorescence performance because of its (N-H)+. Receptor 3 could combine fluoride anion and form 1:1 complex, along with visible color change and remarkable spectral change. Job plot indicated that receptor 3 form 1:1 stoichiometric complexes with fluoride anion. Geometry structure of receptor 3 simulated by Gaussian 03 showed that receptor 3 combines with F-through hydrogen bond interaction of N-H…F- and (N-H)+…F-.Receptor 3 is a good chromofluorescent fluoride chemosensor.In Chapter 4, we synthesized the receptors containing benzimidazole and compared the anion recognition of the ionic receptor 5 and 6 with the neutral receptor 4. The ionic receptor 6 can combine fluoride anion with (C-H)+and form 1:1 complex, along with remarkable spectral change. When fluoride anion was added, a new absorption peak at 315 nm appeared, the fluorescence emission spectrums at 400 nm or 378 nm enhanced. Geometry structure of receptor 6 simulated by Gaussian 03 showed that receptor 6 combine with F- through hydrogen bond interaction (C-H)+…F-.