Synthesis And Properties Of Fluorescence Probe Based On Spiropyran And Schiff Base

Spiropyran derivatives are a class of photochromic compounds.The spectral properties of spiropyran are affected by many environmental factors（light,temperature,solvent,p H,force,etc.）.When irradiated with ultraviolet light of certain intensity,spiropyran could undergo isomerization from the colorless cyclic spiropyran（SP）to the colored ring-open merocyanine（MC）.MC form could convert to SP form with irradiation of visible light at a certain wavelength and intensity,and the conversion with light stimulation is reversible.The-C=N-of Schiff base can coordinate with a variety of ions,and also has good bioactivity,catalytic activities and photochemical properties.Because of the photochromic properties,spiropyran-based compounds and Schiff base have attracted great attention.In this thesis,three fluorescence probes were designed and synthesized with specific functionalization.The main contents and results of this thesis are as follows:Chapter 1: This chapter first started with the brief introduction of fluorescence probe and their structure as well as response mechanism.Second,the structure,properties,synthesis and application of spiropyran and Schiff base are summarized.Finally,the background and main contents of this thesis were summarized.Chapter 2: A spiropyran based probe（SP-CN）has been synthesized with indoline and 4-cyanophenol.The probe can identify and detect calcium ion with high sensitivity and selectivity.The binding mechanism between the probe and Ca²⁺ was verified by ultraviolet-visible spectra,fluorescence spectra and ¹H NMR spectra.Ca²⁺ induced the ring-opening of SP-CN and converted it into MC form.In the MC form,phenolic oxygen and carbonyl of MC bind with Ca²⁺ by coordination bond to form 1:1 MC-Ca²⁺ complex.Along with the solution color change from colorless to pink under visible light,from blue to red under UV light.SP-CN reacted with Ca²⁺ in 1:1 ratio which was confirmed by Job’s plot analysis.The association constant was determined as 2.47 × 103 L/mol.The detection limit was calculated as 4.53 × 10-8 mol/L for Ca²⁺.Paper strips of probe SP-CN have been prepared and used for the detection of Ca²⁺.This probe provided a new idea for the development and research of novel spiropyran probes.Chapter 3: An “on-off-on”,simple structure and large Stokes shift Schiff base fluorescent probe L1 was prepared.This probe can detect p H in a wide range.In the range of p H 3.0-11.0,L₁ produced two different colors of fluorescence.In the range of p H 3.0-5.0,the orange fluorescence intensity from probe gradually decreased as the p H increased.When the p H value increased from 5.0 to 11.0,The probe fluorescence gradually changed from weak emission to strong yellow-green emission.The response mechanism was studied by density functional theory（DFT）and spectral analysis.The pyridine N was protonated at acidic condition,and phenol hydroxyl group and hydrazone group were deprotonized in alkaline condition.The probe L1 has good biocompatibility and permeability of cell membrane with potential application in detecting intracellular p H value.Chapter 4: A Schiff base probe L₂ for the detection of Zn²⁺ has been synthesized with（9H-Fluoren-9-yl）methyl hydrazinecarboxylate and 4-cyanophenol.After adding Zn²⁺ into the solution of L₂,an intense emission band appeared at 530 nm,and the original emission at 630 nm disappeared.Along with the solution color change from blue to red under UV light.L₂ reacted with Zn²⁺ in 1:1 ratio which was confirmed by Job’s plot analysis.The association constant was determined as 8.09× 104 L/mol.The detection limit was calculated as 2.36× 10-8 mol/L for Zn²⁺.The probe can be applied to the determination of Zn²⁺ for practical water samples.