Phenoxazinium Based Fluorescence Probes For Cation Ions:Synthesis And Properties

Fluorescent probes can transfer molecular recognition events into the changes in the photophysics properties of the fluorophores to detect the analytes. The advantages of molecular fluorescence for sensing can be summarized:high sensitivity, high selectivity, observation in situ,"on-off’switch ability, low cost, etc. At present, the research is mainly focused on the design of the multifunctional fluorescent probes which show near-infrared (NIR) emission, water solubility, good biocompatibility.Phenoxazinium as a fluorophore has tremendous superiority, such as big molar extinction coefficient, long wavelength emission, water solubility, low cytotoxicity, membrane permeability, and high pH stability in the physiological conditions. Herein, on the basis of the mechanism of desulfuration reaction and photoinduced electron transfer (PET), three kinds of multifunctional fluorescent probes based on phenoxazinium for metal ions were designed and synthesized. All compounds were characterized by1HNMR,13CNMR, and HRMS. Their photophysical properties and responses to cations were investigated by means of UV-vis and fluorescence methods.1. A series of oxzaine-based fluorescent probes2a-c (λem=556nm) through the mechanism of desulfuration reaction were synthesized. They showed "turn-on" fluorescence and excellent selectivity toward Hg2+in the presence of various other metal ions in CH3CN/H2O(1/1, v/v). Addition of Hg2+induced the hypochromatic shift of absorption spectrum up to about100nm, and the fluorescence intensity significantly increased. Therefore,2a-c can readily distinguish Hg2+by both naked eye and fluorescence.2. A near-infrared fluorescent probe6(λem=683nm) for Zn2+was developed. It was based on the PET mechanism and phenoxazinium was chose as the fluorophore. It can selectively recognize Zn2+over other metal ions in Tris-HCl (10mM,1%DMSO, pH7.4). Moreover, its fluorescence intensity enhanced in a linear fashion with the concentration of Zn2+, thus it can be used potentially for quantification of Zn2+. Probe6exhibited good membrane permeability, and the living cells image experiment demonstrated that6can be used as a fluorescent probe for monitoring Zn2+in living cells. In addition, the conjugated mode was also discussed by1HNMR.3. Another NIR probe15(λem=672nm) which could sensitively and selectively recognize K+in99%Tris-HCl (10mM,1%DMSO, pH7.4) aqueous solution was designed and synthesized. When K+was added, the fluorescence increased gradually. The living cell image experiment indicated the low cytotoxicity and its value in the practical applications of biological systems.