Design, Synthesis And Application Of Novel Fluorescent Probes Based Benzofurazan Compounds

Fluorescent probe is an excellent biological molecular sensor with high sensitivity, high selectivity,rapid response time,“on-off”switchability and so on in the field of molecular recognition. With thecontinuous development of fluorescence technology, fluorescence probes are broadly used in biologicalmonitoring and environmental analysis. In recent years, fluorescent probes identifying the transition metalions have been of great interest to many scientists such as chemists, biologists, clinical biochemists andenvironmentalists. Therefore, designing highly effective and new fluorescent probes is a very urgent taskfor chemical researchers.Benzofurazan derivatives have frequently been designed to biological molecules and been applied tocell detection, because of their good biocompatibility, easy modification on the molecular structure and soon. Recently, visible light excited NBD (7-nitrobenzo-2-oxa^-1,3-diazolyl) derivatives have been widelyapplied to construct applicable fluorescent probe.2,1,3-Benzoxadiazole derivatives with theelectron-donating group （D） occupying the⁴-position and the electron-withdrawing group （A） occupyingthe7-position are the typical ICT （intramolecular charge transfer） fluorophores and special concerned bybiomedicine. simultaneously, fluorescent probes utilizing DPA as a receptor for metal ions are readilydeveloped.A new DPA-NBD derivatives fluorescent probe have been synthesized and designed in our work, thephotophysical properties and its application in the detection of metal ions have been studied and discussed.The emission wavelength of probe L with about170nm Stokes shift showed about110nm red shift incomparison with NBD reference standards. Probe L exhibited excellent selectivity and sensitivity to copperion and iron ion in Tris-HCl （0.1M） buffered solution （acetonitrile: water=1:1, v/v, pH=7.2）. In thetitration experiment of the copper ion, the maximum absorption peak of probe L displayed about196nmblue shift and the fluorescence of probe L was completely quenched by copper ion. probe L and copperions formed a1:1complex according to controlled trials and the job’s plot analysis, the stability constant ofcomplex was determined to be7.3×10⁴M^-1by Benesi-Hildebrand calculation. In the titrationexperiment of the Iron ion, addition of Fe³⁺ions to probe L resulted in not only an about2-foldfluorescence enhancement but also an around23nm blue shift of the maximum emission peak. Fe³⁺ion is paramagnetic metal ions, which is known as common fluorescence quencher. This is the first examplereported in our paper that Fe³⁺ion can enhance the fluorescence intensity of DPA-NBD fluorescent probe.It was proved through controlled trials and the job’s plot analysis that Fe³⁺ion complexed the probe L bythe1:1stoichiometric ratio. The stability constant of complex was determined to be2.7×104M-1byBenesi-Hildebrand equation. The complexing of probe L with Cu²⁺ion was easier than Fe³⁺ion throughthe dropping experiment with each other between Fe³⁺ion and Cu²⁺ion.Their structures were characterized by¹H-NMR,¹³C-NMR, HRMS.It will open up an effective novel way for the recognition of either Fe³⁺or Cu²⁺ions by a DPA-NBDderivative probe and these results will have good application prospect.