| Photomechanical materials have become a new research hotspot in the field of intelligent materials because they can control the deformation or motion of materials through light.The driving force of photomechanical materials were based on molecule motor,which could miniaturize the device and improve the responsiveness of the device.Photomechanical materials have great application potential in the fields of artificial muscles,software robots,optical switches,micro-devices,and so on.Photomechanical materials mainly include Photomechanical polymer materials,Photomechanical liquid crystal materials,Photomechanical organic crystal materials.Among them,Photomechanical organic crystal materials have received more attention because of its rapid response,easy reaction control,easy analysis of the structure and highly ordered structure.However,due to the short development time,only a little photomechanical organic crystal materials have been reported,and how to connect the molecular structure and molecular packing with the photomechanical properties of material was still unclear.In this thesis,a series of styrylbenzoxazole and styrylbenzothiazole molecules were designed,the relationship of functional group,molecular packing mode and photomechanical behavior were carried out,and the relationship of photomechanical behavior and crystals shape.The photosalient behaviour and fluosescene were combined and some creative results have been obtained and outline below.(1)The chlorine substituted styrylbenzoxazoles derivatives BOACl2,BOACl4 and BOACl24 were designed and synthesized.Under UV irradiation,shape-dependent photo-induced bending,curling,rolling and salient behaviors of the molecular crystals of BOACl24 were observed.Interestingly,the reversible controllable bending of the needlelike crystals away from the light source driven by [2+2] cycloaddition was observed,which was resulted from the uniformly release of the strain accumulated by the movement of the atoms during photodimerization of BOACl24.We also found the photosalient effect of the crystals based on metal-free olefin BOACl24 on account of the rapid release of the strong internal strain originated from the photo-triggered structural transformations.Although the photomechanical motion has seldom been reported in organogel,the nanofibers in methanol organogel of BOACl24 were found to curl under UV irradiation.In particular,we found a rotation of benzoxazole ring around C-C single bond upon UV irradiation before photodimerization,so that [2+2] cycloaddition took place between two different conformational isomers of BOACl24.(2)The fluorine substituted styrylbenzoxazoles and styrylbenzothiazole derivatives BOAF4?BOAF24?BTAF4 and BTAF24,were designed and synthesized.All compounds could occur [2+2] cycloaddition in crystal state,and it Is found that the shapes of crystal would induce different photosalient effects under UV Irradiation.Unexpectedly,BOAF4 and BTAF4 crystals exhibited bending behavior towards UV light,whereas BOAF24 and BTAF24 crystals showed negative phototropism behavior.This interesting phenomenon is due to the different molecular packing resulting from different F...H-C interactions in the crystals.In detail,the F...H-C interactions of BOAF4 and BTAF4 crystals are linearly extensive,whereas the F...H-C interaction of BOAF24 and BTAF24 crystals has multiple directions.The different bending behaviors resulting from minor changes in molecular structure give us a new inspiration to design new photosalient crystals.Moreover,we obtained the physical properties of the crystals by theoretical calculation and found that they are elastic,which is a simple way to evaluate the mechanical properties of crystals.Taking advantages of the photo responsive property,we achieved the potential application in pushing objects,as well as enriching and removing pollutants.By coating BOAF4 on a nitrile butadiene glove,a macroscopic mechanical motion was achieved by amplifying the collective molecular motion from the nanoscale up to the macroscopic dimension.(3)We further investigated the fluorescence changes of fluorine substituted styrylbenzoxazoles derivatives,BOAF4 and BOAF24 during the light-induced [2+2]cycloaddition reaction.a new class of AIE luminogens with “living” property was reported.BOAF4 and BOAF24 were typical ACQ molecules due to the severe,extensive ?-? interactions in the solid-state.Upon UV irradiation,photo-induced[2+2] cycloaddition occurred to generate D-BOAF4,D-BOAF24(?)and D-BOAF24(?)with AIE-activity.Intramolecular or intermolecular through-space conjugation was confirmed to be the key factor for the luminescence of these non-conjugated molecules.D-BOAF24(?)formed two kinds of crystals with blue and yellow emission,respectively.This novel in-situ ACQ-to-AIE transformation is thus a general approach to obtain solid-state light-emitting materials in a simple and atomeconomical manner.The approach we described here should be helpful to enlighten the use of many already invented solid-state emitters and facilitate the design of“living” luminogens with more rational strategies.(4)We tried to combine styrylbenzoxazole derivatives(BOAF4 and PVBO)with TCB to cocrystalization,although the cocrystal did not show the photosalient effect,but through collaboration with cocrystal engineering,visualization and manipulation of solid-state molecular motion(SSMM)in two-component systems,namely BOAF4/TCB and PVBO/TCB,were realized.The obtained yellow-emissive BOAF4/TCB cocrystal displayed turn-on fluorescence and the green-emissive PVBO/TCB cocrystal presented redder emission,both of which exhibited aggregationinduced emission property.At varied pressure and temperature,the grinding mixtures of BOAF4/TCB and PVBO/TCB displayed different molecular motions that were readily observed through the fluorescence signal.Notably,even without grinding,BOAF4 and TCB molecules could move over for 4 mm in a 1D tube.The unique emission changes induced by SSMM was applied in information storage and dynamic anticounterfeiting.(5)New full-conjugated non-traditional ?-gelators based on styrylbenzoxazoles and styrylbenzothiazoles have been synthesized.It was found that the introduction of chlorine atoms at 2,4-position of benzene ring as well as the existence of benzothiazole with better ?-electron delocalization would enhance the gelation abilities.Through the organogel of BTACl24 did not have photosalient behaviour,but it could be destroyed into solution upon UV irradiation because of the trans-cis isomerization,which could further lead to the morphological change of xerogel.The smooth nanofibers stretched out lots of thin ‘arms'.Some ‘arms' would hold together,and some ‘arms' would catch other nanofibers.It should be noted BOACl24 exhibited strong fluorescence in wet organogel and in xerogel,which could be quenched by TFA.In particular,the decay time and the detection limit of BOACl24 in xerogel-based film towards TFA vapor were of 1.7 s and of 0.5 ppm,respectively,and they were decreased to 0.7 s and 0.3ppm,respectively,for the xerogel-based film of BTACl24 due to its strong basicity.Therefore,the organogelation of non-traditional organogelators is a powerful way to fabricate multi-stimuli-responsive soft materials and we provided a new method to fabricate more entangled supramolecular networks via photochemical reactions of ?-gelators in xerogels. |
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