Synthesis And Properties Of Water-soluble Fluoride Ion Fluorescent Probes

Fluoride aion is the anion with smallest the ionic radius and has unique chemicalproperties. It plays great roles in the area of body’s health. Has an important role in the cure ofdental caries and osteoporosis. But the excessive intake would lead to the’fluorosis’ of teeth orbone.In recent years, scientists have begun to focus on the research of efficient and sensitivechemosensors for fluoride anions.There is Lewis acid-base interaction between compounds with organoboron group andfluoride aions, and these compounds can specifically recognize fluoride anion. In this thesis,the photophysical properties of organoboron chemosensors for fluoride anions wereinvestigated in detail. Seven different compounds were synthesized. The photophysicalproperties (including linear absorption, single-photon fluorescence and two-photonfluorescence) of these compounds were systematically investigated. Fluoride anionrecognition properties were investigated as the key points. In chapter2, we reported thesynthesis of all the compounds. In chapter3, we reported linear photophysical properties ofthe compounds. In chapter4, we reported the two-photo fluorescence properties of somecompounds. And chapter5is the focused chapter of this thesis, we reported the response ofsix compounds with fluorine aion.The title compounds are classified to two series according to the type of organic borongroup.Series1: Dimesitylboryl-based compounds1~5 Series2: Boric acid-based compounds6~7 1. Sythesis and characteristic of the compoundsSeven compounds of two series above were sythesized and some of them weresythesized for the first time. All of the compounds are stable in solid state or common organicsolvents.2. Measurement and analysis of linear photophysical propertiesIn this thesis, we have systematically studied the linear photophysical properties of thecompounds, which including linear absorption and single-photon excited fluorescenceproperties. We found that dimesitylboryl group is a perfect fluorescence group and allcompounds with dimesitylboryl group exhibit strong single-photon excited fluorescence.Linear absorption spectra of all the compounds depend only slightly on solvent polarity, butsingle-photon excited fluorescence spectra exhibit different dependence on the solventpolarity because of the different polarity of the compounds. Compound2is an A-π-A’molecule, its fluorescence spectra exhibit weak dependence on the solvent polarity and itshows strong fluorescence emission in almost all the common solvents. Compounds1and3-5exhibit obvious solvent effect and their fluorescence are red-shifted with the increase ofsolvent polarity.3. Two-photon excited fluorescence propertiesWe have studied the two-photon excited fluorescence propertiy of compounds1-5.Within a certain range, the two-photon fluorescence intensity is proportional to the square ofincident light energy. For these compounds, the largest two-photon absorption is observed attwice the largest single-photon absorption wavelength. These experimental results haveproved the two-photon excitation mechanism. The comparison between compound3and itsformer indicates that the input of organoboron group increases the two-photon excitedfluorescence intensity. The comparison between compound4and the correspondingsingle-branched compound indicates that the coupling enhanced effect of two branches caneffectively increases the two-photon excited fluorescence intensity of the compounds. Single-photon fluorescence can be used as the premise of the two-photon fluorescence andcompounds with two-photon effect must also have a single-photon fluorescence effect.4. Spectral response to fluoride complexationBoth the dimesitylboryl and boric acid groups can recognize fluoride ion, but therecognition mechanism is different. The spectral response of six compounds to fluoridecomplexation was investigated in details and especially the response at water conditions wasinvestigated. The investigation indicates that all the six compounds can quickly, efficientlyand specifically recognize fluoride aion. But some compounds showed weak recognitionperformance in water solution, such as compounds1,3and4. But compounds2,6and7havesuccessfully showed response in water conditions. Compounds6and7can recognize fluorideaions in pure water and their absorption show spectral changes when fluoride ions are added.The investigation also indicates that the input of electron accepting group with positive chargecan increase the Lewis acid of the organoboron group and then increase the bonding abilitybetween the compound and fluoride anions and also then the compound exhibits obviousbetter water-compatibility towards complexation to fluoride than its neutral analogue. Theinvectigation also indicates that the extended conjugated bridge length can also promote thebonding between the compound and fluoride anions.In summary, this thesis focused on exploring boron-containing fluoride aion chemsensors.We designed and synthesized seven compounds. We have investigated their properties oflinear absorption, single-photon fluorescence and two-photon fluorescence. And the spectralresponse to fluoride complexation was also investigated. Some significative conclusions aresummarized.