Design, Synthesis And Applications Of A Novel Multi-state Molecular Switch Based On The Photochromic Spiropyran

As an important sector of switchable molecules, photochromic organic compounds havebeen widely investigated and used due to their attractive characteristics. With the rapiddevelopment of information technology, the simple bistable photochromic switchable moleculesalready cannot satisfy the need. People have been focused on design and synthesis of multi-stateand multi-function switchable molecules. Tremendous efforts have been given recently onintegration of several switchable functions into a single molecule through chemical bonding toconstruct more complex multi-state systems. These multi-component systems and multiplestimulus-response photochromic systems are believed having a chance to achieve thehigh-density data storage and multi-function smart materials. Spiropyrans as one of the moststudied photochromic compounds have been widely applied in logic gate, data storage, ionprobes, biological imaging and color materials. Even though they display attractivephoto-response, good fatigue resistance and obvious color change properties. One weakness isthe weak fluorescence of their open isomers due to the intrinsic non-radiative energy decay.In this dissertation, a monomolecular multi-state fluorescent switch based on a spiropyranand fluorescein fused conjugation has been designed and synthesized. We studied the propertiesof compound Flu-1-SP in solution and polymer films respectively. After the research onultraviolet absorption and fluorescence spectra, we demonstrated that molecule Flu-1-SP showedfour stable states and three different fluorescence emissions with the stimulation of light,chemical acid and base.We use the traditional route to synthesize the target molecule upon the condensationreaction of indoline and fluorescein monoaldehyde, and the chemical structure of compoundFlu-1-SP was confirmed by HRMS，1H NMR，13C NMR. Then the spectroscopy properties ofmolecule Flu-1-SP in dichloromethane solution were carefully studied with the externalstimulation of light and chemical acid/base. The optical spectra of contrast compoundFlu-1-OCH3-SP proved the obvious photochromism of compound Flu-1-SP in solution. The spiropyran moiety of Flu-1-SP could convert to the merocyanine state through the ring-openreaction with the irradiation of ultraviolet light, resulting into the photo-induced ring-openmerocyanine-xanthene conjugation. In addition, the compound Flu-1-SP can transform to theacidic or basic ring-open form with the addition of excessive amount of trifluoroacetic acid ortriethylamine. Through analyzing the optical spectra of contrast compounds Flu-1-OCH3-SP andfluorescein on dealt with excessive acid and base respectively, we further confirmed theprecision acidic or basic ring-open structures, which showed that molecule Flu-1-SP canresponse to chemical acid and base, accompanied with orange and green, two differentfluorescence emissions. Finally it is concluded that with the stimulation of ultraviolet light andchemical acid/base, compound Flu-1-SP can switch from the closed form to the photo-inducedring-open, or acidic/basic ring-open forms respectively, along with three differentfluorescence-red, orange and green.Besides, we studied the color change properties of PMMA polymer films doping withcompound Flu-1-SP. The photochromic polymer films were prepared using the physical blendingmethod. It is found that compound Flu-1-SP still maintained the photochromic properties in thepolymer. The space limit effect can stabilize the photo-induced ring-open form of moleculeFlu-1-SP and reduce the decolorization rate of the open isomer. These doped polymer films notonly exhibited the photochromic character, but also responded to acidic and basic gases. With theconsistent behavior of molecule Flu-1-SP in solution, the results showed that compoundFlu-1-SP displayed the character of four stable states and three fluorescence emissions inpolymer. In brief, the Flu-1-SP molecule doped polymer films have the potential to be themultiple stimulus-response and multi-function fluorescent material.