Stimuli-responsive Properties Study Of Spiropyran Substituted Polydiacetylene Functional Materials

Stimuli-responsive functional materials can adapt to external environment in real time because they produce different response to different environmental stimuli.When suffering the outside stimuli(for example temperature,light,electric field,magnetic field,pH,humidity,different kinds of chemicals),this kind of materials are able to generate a serials of changes of structure and property.Among them,multi-stimuli-responsive polymer materials have been widely used in many fields due to their excellent properties,such as light weight,good flexibility,easy processing and operation,bionic function and so on.In recent decades,researchers devote to study the multi-stimuli-responsive and multifunctional materials,although great progress have been acquired,however,there still exist many problems,for instance few stimuli-responsive types,system with only one function,materials unable to reused.So there are some difficult problems needed to resolve urgently,namely how to achieve the multi-stimuli-responsive systems and control the structure and property accurately used the simple methods.According to the above background and problems,this work combine the spiropyran and polydiacetylene(PDA)to one molecule which are both multi-stimuli-responsive material by chemical bond,proving the possibility for achieving multiple functions and response to multiple stimuli with the simple system.Also,we controlled the fluorescence resonance energy transfer(FRET)between spiropyran and PDA using the property relationships under different external stimuli,thus regulating the fluorescence of the whole composite system.The first part we fabricated the novel vesicles using the above synthesized spiropyran functionalized PDA through self-assembly.The open form of spiropyran(MC)could react with CN selectively,inducing structural perturbations to the PDA matrices,thus leading to the color and spectral changes of the whole solution and achieving the detection of CN-.This can be observed by naked eyes and completely detected in the aqueous phase,also the whole process is biocompatible and environmentally friendly.In the second part,coumarin-substituted PDA which can response to temperature reversibly has been introduced into the spiropyran-substituted PDA vesicles.the prepared hybrid vesicles could response to light、pH and temperature reversibly which can be readout through the change of fluorescence.We constructed three different logic gates based on the different inputs and realized the function of multiple logical operations.In the third part,PDA microtube has been synthesized successfully by adding metal ions into the PDA vesicles under proper conditions,after the UV light irradiation and heating,the PDA was in the fluorescent red-phase.These microtubes can be used as one-dimensional optical waveguide devices under the excitation light.Spiropyran was attached on the surface of microtube by means of chemical reaction,structural transformation of spiropyran can be modulated by different light irradiation.Effective energy transfer can occur(FRET)between the open form of spiropyran(MC state)and the red-phase PDA,which causing the fluorescence quenching of the PDA microtube and resulting in the decrease of optical waveguide.While the ring-closed form of spiropyran(SP)has negligible effect on the fluorescence of microtube,the whole waveguiding performance can be controlled through light irradiation.The last part,DA-embedded microfiber was fabricated through electrospinning.Orientation arrangement of the PDA main chains can be controlled by the polarization state of UV light used in the polymerization,and also the polarization property of the waveguiding from end point was controllable.More details are as follows:1.We fabricated vesicles composed of spironpyran substituted DA molecule by self-assembly which dissolved in water.Under UV light irradiation,DA polymerized into polymer PDA,spiropyran transformed from SP to MC,the state of MC can bind with CN-specifically.After the reaction,chemical environment changes of the system perturbed the main chains of PDA,which resulting the transformation of PDA from blue phase to red phase,with the change of color and fluorescence.The content of CN-can be quantitative detected by absorption and fluorescence spectra,also the whole process can be tested directly using the naked eye according to the variations of solution color.Spectral sensitivity was very high,so the accurate sensing level of CN-of is very low(up to 0.5 M)and the whole process exhibited no interference with other anions.Water solution is environment friendly and can be used directly in environmental monitoring for life and production.Because of the isomerization of spiropyran,removal of CN-from solution can be realized by simple acid treatment,so the vesicle solution could been reused for CN-sensing.2.The vesicles composed of spironpyran substituted DA and coumarin-substituted DA has been successfully prepared through self-assembly,which polymerized into PDA vesicles after UV irradiation.Due to the spironpyran substituted PDA responsive to light and pH reversibly,coumarin-substituted PDA responsive to temperature reversibly,the hybrid vesicles could responsive to light,pH and temperature simultaneously.Spiropyran was in the MC form after UV light irradiation,there existed FRET between MC and red phase of PDA due to the overlap of absorption spectra for MC and fluorescence spectra for red phase PDA,resulting in the fluorescence quenching.Spiropyran was in the SP form which can not occur FRET with PDA after visible light irradiation and produced no effect on the fluorescence.The transformation of spiropyran caused by different light irradiation will at last give rise to the reversibly change of absorption and fluorescence of the whole system.MC isomerized to the protonated MC(MCH)form when reduce pH of the system,FRET between red phase PDA and the MCH did not occur because MCH has no absorption and color in the visible light region.Similarly,MCH transferred to MC reversibly when pH increased,leading to the quenching of fluorescence.Change of pH caused the reversibly isomerization of spiropyran and induced the reversibly change of absorption and fluorescence for the hybrid vesicle solution.PDA exhibits chromatic switch from blue phase which is non-fluorescent to fluorescent red phase when heating.Normally,the red phase of PDA can not return to the blue phase even if lowering the temperature,however,due to the π-πstacking,red phase of coumarin-substituted PDA could return to the blue phase when the temperature is cool to room temperature.Therefore,fluorescence of coumarin-substituted PDA changed from OFF to ON when raising temperature.Red phase PDA return to blue phase when lowering the temperature,with fluorescence changed from ON to OFF reversibly.Based on the hybrid vesicle responsive to light,pH and temperature reversibly,using the different combinations of stimuli as inputs,change of fluorescence as output,,we obtained "AND" "OR" "INHIBIT" logic gates respectively,realizing a series of resettable logic operations.3.After formation of PDA vesicles through self-assembly,we obtained PDA microtube under proper conditions.When treating with UV light irradiation and heating,PDA was in the red phase,the microtube could be used as active optical waveguiding.Spiropyran was grafted onto the surface of PDA microtube by means of chemical reaction between amino and epoxy group,waveguiding performance can be modulated by isomerization of spiropyran which induced by UV light and visible light irradiation.Spiropyran was in the SP form under visible light irradiation,so FRET between PDA and SP can’t occur,fluorescence and waveguiding of microtube was ON.However,there existed FRET between PDA and MC of spiropyran when treating with UV light irradiation,fluorescence and waveguiding of microtube was OFF.We realized logic operations in one-dimensional polymer mocrotube based on the above modulation of optical waveguiding.UV light,visible light,HCl gas were taken as inputs,intensity of waveguiding as output,"OR" and "INHIBIT" logic gates has been realized successfully.The above logic operations were resettable because of the reversible transformations of spiropyran.4.DA molecules were doped in the solution and then polymer microfibers containing DA were prepared by electrospinning.The study found that orientation arrangement of PDA main chains have much to do with the polarization direction of UV light used in the polymerization.Through tuning the polarization state the UV light,different order of the PDA main chains inside the microfiber can be obtained which were sensitive to the polarization of the excitation source,also the polarization states of the emitting waveguiding will be controlled according to the requirements.When polymerized the microfiber with un-polarized UV light,the orientation arrangement of PDA main chains in the microfiber was attributed to high-voltage electric field during electrospinning.PDA main chains were disorder when irradiated microfiber with circular polarized UV light,experimentally discovered that the intrinsic anisotropy induced by the electrospun process was erased by isotropic electric-field component.When the microfiber was polymerized with linearly-polarized UV light of various orientations,we found that the direction of PDA main chains in the microfiber was the same as the polarization direction pf linearly-polarized UV light.Microfiber with different orientations of PDA main chains was sensitive to the polarization of the excitation source,and the polarization of waveguiding was also controllable by different polarization state of UV light used in the polymerization.