Design And Synthesis Of New Fluorescent Probes Based On Rhodamin B And Fluorescein

Among so many detection methods, the research on fluorescent probes based on organic dyes remains very active and receives lots of attentions. Fluorescent probes can selectively transfer chemical information of the analyte into fluorescence signals which can be detected by analytical instruments, and have advangtages in many respects, such as sensitivity, selectivity and so on. Searching for new fluorophores to improve sensitivity and selectivity of fluorescent probes is still a challenge for the analytical research efforts. As important fluorescent materials, rhodamine and fluorescein have excellent properties such as high fluorescence quantum yield, favorable solubility in water, low cost, low toxicity, excellent rigid planar structure and their maximum emission wavelengths are in the visible light region so there's low background interference, as a result, they are ideal fluorophore choices for chemical probes. In this paper, three fluorescent probes based on rhodamine and fluorescein were designed and synthesized to detect metal ions and anions. The details are summarized as follows:In chapter 2, a ratiometric fluorescent FRET-based zinc probe was designed and synthesized. Ratiometric measurement involves the observation of changes in ratio of the intensities of the absorption or the emission at two wavelengths and has many advantages in that it permits signal rationing, and therefore increases the dynamic range and provides built-in correction for environmental effects. In this probe, fluorescein acts as electron donor and rhodamine B as electron acceptor. The compound is colorless and non-fluorescent. Upon mixing Zn2+ in its DMF-water(1:1, v/v) solution, the compound-Zn2+ complexation quenches the fluorescence of fluorescein at 518 nm and induces a new fluorescent enhancement at 590 nm. It is designed to chelate with metal ions via its S atoms, imino and N atoms, as a result, this probe exhibits high selectivity for sensing Zn2+ over other common metal ions. The ratiometric fluorescence response is attributed to the 1:1 complex formation between probe and Zn2+ which has been utilized as the basis for the selective detection of Zn2+. The analytical performance characteristics of the proposed Zn2+-sensitive probe were investigated. The probe can be applied to the quantification of Zn2+ with a linear range covering from 2.0×10-7 mol/L to 2.0×10-5 mol/L and a detection limit of 4.0×10-8 mol/L. It was also used for imaging of Zn2+ in living cells and showed satisfactory results.In chapter 3, a highly sensitive fluorescent probe based on 8-quinoline-containing rhodamine B derivative for selective detection of Hg2+ in mixed N, N-dimethylform-amide(DMF) neutral buffered media was developed and prepared. In the existence of Hg2+ at pH 7.4, the fluorescent probe emitted fluorescence at 530 nm. The fluorescent response of the probe towards Hg2+ seems to be caused by the binding of Hg2+ ion with the quinoline moiety, which was confirmed by the absorption spectra and 1H NMR spectrum. Hg2+ is known as a kind of fluorescent quencher via enhancement of spin-orbit coupling, hence, detection of Hg2+ by fluorescent sensors is operated in fluorescence guenching mode in most cases. But this probe we reported can cause a dramatic increase upon binding Hg2+ in DMF/H2O (1:1, v/v) solution at pH 7.4 in both fluorescence intensity and absorbance of the mixing solution, in company with color change. Therefore, it is a kind of "off-on" switch probe. The signal change of the probe is based on a specific metal ion induced reversible ring-opening mechanism of rhodamine spirolactams. With the experimental conditions optimized, a wide linear dynamic range of Hg2+ from 1.0×10-8 to 1.0×10-5 mol/L was reached, with a detection limit of 8.5×10-9 mol/L. The fluorescent probe exhibits satisfactory response time and selectivity over other common metal ions. Besides, probe displays a reversible dual chromo-and fluorogenic response toward Hg2+. It is also used for imaging of Hg2+ in living cells.In chapter 4, a new fluorescent probe for hypochlorite anion based on a fluorescein-hydroxyamine conjugate was synthesized and its fluorescence could be enhanced by the addition of hypochlorite anion. In this probe, fluorescein was selected as the fluorophore and hydroxyamine was selected as the receptor. Adding hypochlorite anion can result in increasing in fluorescence emission intensity at 530 nm. The signal change of the probe is based on the fact that hypochlorite anion can cut off C=N bond in oxime. As a result, in this case, the C=N bond of fluorescein based oxime was cutted. Consequently, a new fluorescent enhancement showed up. Probe exhibits high selectivity for sensing hypochlorite anion among other anions. The probe can be applied to the quantification of hypochlorite with a linear range covering from 4.0×10-7 mol/L to 1.0×10-5 mol/L and a detection limit of 2.0×10-7 mol/L.