Responsive Behavior Of Spiropyran-based Compound With Different Size

Spiropyran(SP)is one of the most classic molecules with reversible generation and fracture of covalent bond under the stimulation of PH,temperature,electric field,force,light and solvent polarity.Much attention has been attracted to force responsi ve polymer since spiropyran was covalently incorporated in PMA in 2007.The force responsive behavior of spiropyran-based compound depends on its molecular configuration and size.In this work,spiropyran-based compounds with different size were synthesized and their stimuli-response behaviors were systematically investigated.It mainly includes two aspects as follows:(1)Light and force dual-responsive waterborne polyurethane(WPU)was synthesized and its response behavior was investigated using ultrasonic experiment,stretch-responsive experiment and UV-Vis absorbance spectra.The UV light triggered color change in the emulsion state was slightly faster than that of the SP-WPU film.The decay rate was quite different in the two states.The decay rate of the emulsion state was rapider than that of the hindered solid state,which was ascribed to the faster chain motion.The ultra-sonication responsive properties relied on the solvent environment as well as the size of micelle formed by WPU.The SP-WPU mixed solution containing 15 vol%water showed the most sensitive ultra-sonication activation properties due to the synergetic effect of the mixed solvents.The SP-WPU film also showed stretch responsive properties,giving the color change when the elongation was over 500%,where sufficient chain alignments along the tensile direction were formed.The SP embedded WPU is a smart and environmental friendly material.It is easy to scale up and has great applications in the light sensitive coatings like sunglasses,damage detection and so on.(2)Spiropyran containing single polyhedral oligomeric silsesquioxane(SP-POSS)or terminated by double POSS(POSS-SP-POSS)was first synthesized and characterized by 1H NMR,13C NMR and MALDI-TOF-MS.Their response behaviors under pressure were investigated by in situ combination of UV-Vis spectrophotometer and high pressure device.Colorless POSS-SP and POSS-SP-POSS could transform into larger conjugated brown-red forms of POSS-MC and POSS-MC-POSS under high pressure with increasing UV-Vis absorption strength at 400-470 nm.For POSS-SP-POSS,the intensity of characteristic absorption peak showed good linear relationship with pressure between 0-20 GPa.However,POSS-SP only showed more sensitive linear relationship in 2-5 GPa.Chemical kinetics and the transmission mechanism of pressure were studied when exploring the different responsive behaviors.The activation energy of the isomerization of POSS-MC and POSS-MC-POSS was much lower than that of MC,giving POSS-MC and POSS-MC-POSS better reversibility under pressure.Due to the protection of large size POSS group,the force would be specifically transmitted to mechanophore along the covalent bond between SP and POSS when giant molecule POSS-SP-POSS was under high pressure,while the force would be sustained in all directions directly for small molecule SP.For POSS-SP,it exhibited the combinative behaviors of giant molecule and small molecule.POSS-SP and POSS-SP-POSS have potential application in sensing materials.