Synthesis And Properties Of Fluorescence Probe Based On Triphenylamine And Cyanine Dyes

In recent years, fluorescence probes play an increasingly crucial role in synthetic chemistry, medical science, food science, life science, material science and information science. Compared to numerous analytical methods, like atomic absorption spectrometry, atomic emission spectroscopy, chemical titration analysis, ion chromatography, electrochemical analysis, etc., fluorescent probes offer individual advantages such as easy operation, simple equipment, low cost, excellent selectivity, high sensitivity, short response times and low detection limits. Hence, it is widely used in the detection of anions, cations, biological macromolecules and pH. However, the major issues that fluorescence sensor faced are aggregation caused quenching（ACQ）, low water solubility, poor cell permeability and unable to be applied in biological cell imaging and living tissues. In this respect, several organic small molecular fluorescent probes based on triphenylamine and cyanine dyes are synthesized and show high selectivity and sensitivity. It is investigated the recognition of heavy metal ions, anions and pH in aqueous solution and studied the mechanism. Additionally, the probes are applied in the biological cells and living tissues.（1） A novel fluorescence chemosensor 1 was synthesized through a nucleophilic addition reaction between cyanide and triphenylamine and characterized by nuclear magnetic spectrum, infrared spectrum, high resolution mass spectrometry and element analysis. It exhibited strong aggregation-induced emission and was able to detect Fe³⁺, CN^- and SO₃^2- in almost pure aqueous solution with low detection limits of 1.44 μM, 9.88 n M and 0.107 μM, respectively. Job plot and 1H NMR data showed that the binding stoichiometry of 1 with Fe³⁺, CN^- or SO₃^2-was 1 : 1. Further observations of ¹HNMR titration suggested that a coordination bond was formed between two cyano of 1 and Fe³⁺ which resulted in fluorescence quenching of 1 after detection of Fe³⁺, whereas the nucleophilic addition ofcyanide or sulfite to the vinyl group was responsible for the fluorescent quenching of CN^- or SO₃^2- toward 1. In addition, 1 could also be made into test strips to detect Fe³⁺ and CN^- and was employed as a sensor for the detection of Fe³⁺ in living cells.（2） A triphenylamine derivatives containing Schiff base, fluorescence probe 2, was designed and synthesized, which could be dispersed well in aqueous solution. It was studied its fluorescence behavior in different pH solution and found the fluorescence was quenched when pH below 2, suggesting a great instruction effects under strong acidic condition. There was a linear relationship with its fluorescence intensity and pH between 2 and 7. And its fluorescence emission was reversibility in acidic and alkaline solution. The recognition performances of metal ions were analyzed by fluorescence spectroscopy and it exhibited highly selective towards Fe³⁺ with detection limit of 0.511 μM. The mechanism is the coordination effect between Fe³⁺ and nitrogen atom of C=N bond, which promote the intramolecular charge transfer（ICT） or energy transfer process and cause fluorescence quenching. 2 also can be applied in He La cell imaging and detection of Fe³⁺ in it.（3） A highly sensitive fluorescent probe 3 based on cyanine dyes for Cu²⁺ and Pb²⁺ has been developed. Probe 3 exhibited fluorescent turn-off sensing ability to Cu²⁺. On the other hand, 3 displayed ratiometric fluorescent response, which was perfect sensitive and accurate, towards Pb²⁺ with a distinct fluorescent color change from blue to orange. Detection limits of 3 to Cu²⁺ or Pb²⁺ were calculatedas 1.24 and 3.41×10-6 M, respectively. The ¹HNMR titrations revealed that the fluorescent response of 3 to Cu²⁺ and Pb²⁺ is triggered by the interaction of the pyridine unit and the metal ion. Probe 3 displayed sensitive response to pH below 5, which the protonation of pyridinyl moiety in acidic solution was responsible for the sensing process. Furthermore, 3 can also be used as a sensor for detection of Cu²⁺ and Pb²⁺ in a test strip, whose green fluorescence was quenched completely and turned to be yellow, respectively. In addition, the fluorescent microscopic images of probe in live cells and zebrafish were achieved successfully and the performance was stable.（4） A novel cyanine-based fluorescent probe 4 containing indole and quinoline was designed and synthesized via facile methods. Ferric ions quenched the fluorescence of probe 4 with detection of 6.78 μM, whereas the addition of ferrous ions led to only small changes in the fluorescence signal. When hydrogen peroxide was introduced into the solution containing probe 4 and Fe²⁺, Fe²⁺ was oxidized to Fe³⁺, resulting in the quenching of the fluorescence. Therefore, the probe 4/Fe²⁺ solution fluorescence could also be quenched by H₂O₂ releasedfrom glucose oxidation by glucose oxidase（GOD）, which means that probe 4/Fe²⁺ platform could be used to detect H₂O₂ and glucose, whose detection limits were calculated as 0.268 μM and 0.96 μM, respectively. Probe 4 showed fluorescence reversibility in acidic and alkaline solution and could be loaded in thin-layer chromatography（TLC） plate, which emitted bright green light upon photoexcitation and was able to be used as a chemosensor for detecting volatile organic compounds with high acidity and basicity with using many times. The ¹HNMR titrations revealed that the fluorescent response of 4 to pH is due to protonation of quinoline moiety and the detection of Fe³⁺ is triggered by the complexation of nitrogen atom of quinoline unit, which reduce the electronic exchange, lower π electron density and improve the photoinduced electron transfer（PET） or energy transfer process, causing the fluorescence quenching and realizing recognition. Subsequently, 4 displayed excellent cell image in DU145 cells and perfect fluorescence properties in zebrafish, suggesting that the probe has good cell membrane permeability and apotential application for imaging in living cells and living organisms.