Topo-Photochemical Reaction Of Chalcone And Anthracene Derivatives And Their Crystal Photomechanical Properties

The cyclic structure is a important unit of many new drugs and organic functional materials.In organic synthesis,topo-photo-induced[2+2]and[4+4]cycloaddition is a key strategy in the synthesis of muti-cyclic compounds.Comparing with the photochemical reaction in solution,solid station[2+2]cycloaddition could synthesize cyclobutane derivatives with high region and high stereoselectivity.At present,the study on [2+2] cycloaddition reaction mainly focuses on diarylethene derivatives,especially the diarylethene derivatives containing pyridine group,while the study on[2+2]cycloaddition of chalcone is rare.In recent years,due to the development and needs of biomimetic science,photomechanical intelligent materials based on solid-state organic photochemical reaction,which indirectly convert photo energy into mechanical energy,have gradually become a research hotspot.Common photomechanical materials include polymers,liquid crystal elastomers and molecular crystals.Photomechanical intelligent crystal materials have unique advantages,for example,fast response speed,high elastic modulus,regular molecular arrangement,high energy conversion efficiency,good reversibility,easy characterization,and attracted wide attention.Comparing with other solid state organic photochemical reactions,during[2+2]and[4+4]cycloaddition reactions,the two molecules are close to each other,which could achieve a large physical displacements on molecular level,and the spatial size of reactants and products is quite different.Therefore,the process of photochemical reaction is often accompanied by the accumulation of stress.The macroscopic crystal may show mechanical motion after the stress is released.Therefore,photomechanical crystal materials driven by[2+2]and[4+4]cycloaddition reactions have attracted special attention.However,the study on this field still in the initial stage,and how to connect molecular packing with the photomechanical properties of material was still unclear.On the other hand,at present,most crystal photoactuator driven by [2+2]cycloaddition reaction have some disadvantages,for example,poor reversibility of motion,less cycle times and single control mode.On the one hand,in order to understand how substituents affect the packing of molecules in crystals and the photomechanical properties of molecular crystals.On the other hand,in order to obtain crystal actuators that can move repeatedly under muti-stimuli.In this thesis,a series of chalcone with potential [2+2]cycloaddition reactivity and anthracene derivatives with potential[4+4]cycloaddition reactivity were designed.The effects of substituent of molecules on the stacking mode were carried out.The factors affecting the photo-induced [2+2] and [4+4]cycloaddition reactivity were discussed.The photomechanical behaviors were investigated.Some creative results have been obtained and outline below.1)Chalcones bearing 4-fluorostyryl,3,5-difluorostyryl and 3,4,5-trifluorostyryl have been synthesized.It is found that fluorine can tune the reactivity of photo-induced[2+2]cycloaddition reactions in crystals.The chalcones bearing 4-fluorostyryl,3,5-difluorostyryl and 3,4,5-trifluorostyryl could transform into the derivatives of cyclobutanes in yields of ca.6%-57%,14%-83%and 29%-100%respectively,after 1h of irradiation.In contrast,the fluorine-free chalcones were synthesized,they can't undergo[2+2]cycloaddition reaction in solid state.The single crystal structures and Hirshfeld surface calculation illustrated that the introduction of fluorine not only increased the molecular planarity but also could steer the packing mode of molecular to meet Schmidt's criteria.Therefore,the stereospecific[2+2]cycloaddition reactions took place to afford one diastereoisomer from the reactive chalcones except for 1FChH((E)-3-(4-fluorophenyl)-1-phenylprop-2-en-1-one).On account of the motions at the molecular level during[2+2]cycloaddition reactions,strain in the crystals is produced and accumulated.Additionally,the chalcone-based molecular crystals exhibited various photomechanical behaviors,such as bending toward or away from the light source,swinging,cracking and jumping.It is understandable that obvious photomechanical effects can be observed in the crystals formed from highly photoactive chalcones.Powder X-ray diffraction results suggested that the solid state[2+2]cycloaddition reactions changed the unit cell of the single crystals.it was suggested that the contraction or expansion of phototropic surfaces actuated the bending of the needle-like crystals toward or away from the UV light source.Herein,we provided a useful strategy for tuning the topo-[2+2]cycloaddition reactivity and photoactuator of molecular crystals via the introduction of a simple group.What's more,the molecular crystals formed from the molecules with high[2+2]cycloaddition reactivity are desired platforms for photoactuators,which may be employed in opto-mechanical microdevices,smart microrobotics,etc.2)3,5-dichlorostyryl-containing chalcones 2ClChMe-4 and 2ClChOMe-4 have been prepared.The ribbon-like crystal(Form I)and block-like crystal(Form II)of2ClChMe-4 were prepared via solvent evaporation and sublimation,respectively.They undergo single crystal to single crystal transformation under heating,resulted in thermo-induced curling/flipping and bending of ribbon-like crystal,and the thermo-induced expanding of block-like crystal.The single crystal structure analysis indicated that the packing of molecules in ribbon-like crystals is relatively loose comparing with the block-like crystal,so the phase transition occurs at a slightly lower temperature.During thermo-induced phase transformations,the molecular conformation of 2ClChMe-4 changed and the molecules slipped along(100)plane in crystal.It resulted in the expanding of a-axis and b-axis and the contracting of c-axis of crystal cell,which in turn led to the mechanical motions of crystal.Additionally,the ribbon-like crystal of 2ClChMe-4 have higher photo-induced [2+2]cycloaddition reactivity,it showed photo-induced bending away from the UV light source.The bent ribbon-like crystal of 2ClChMe-4 could return to it's original shape under subsequent heating.Accordingly,the ribbon-like crystal of 2ClChMe-4 showing multiple reversible bending behaviors was fabricated triggered by irradiation and heating successively.3)Fluorostyryl and methoxystyryl containing hydroxychalcone derivatives 2-FCh,3-FCh,4-FCh,4-MeOCh and 4-MeODBr Ch and boron difluoride complexs Ch-BF₂,2-FCh-BF₂,3-FCh-BF₂,4-FCh-BF₂,4-MeOCh-BF₂and 4-MeODBr Ch-BF₂were synthesized.It was found that hydroxychalcone derivatives don't have reactivity of[2+2]cycloaddition in crystal,but[2+2]cycloaddition could occur in the crystal of the boron difluoride complex.The single crystal structure of Ch and 4-MeODBr Ch indicated that the packing of Ch and 4-MeODBr Ch don't meet with Schmidt's criteria in crystal.Although the packing of 4-MeOCh meet with Schmidt's criteria in the single crystal of 4-MeOCh.The excited-state intramolecular proton transfer(ESIPT)in crystal of 4-MeOCh caused that the[2+2]cycloaddition don't occur.After hydroxychalcone is coordinated with boron difluoride,boron difluoride restricted the ESIPT,but also steer the packing of potentially reactive to meet Schmidt's criteria by formation intermolecular C–H…F interaction.Therefore,we developed a new metal template to improve the[2+2]cycloaddition reactivity of hydroxychalcone.On the other hand,the dimer of boron difluoride complex obtained by photodimerization could decompose in methanol,so the dimer of hydroxychalcone with pharmaceutical application value can be obtained,which provides a new method for the synthesis of the dimer of hydroxychalcone.In addition,driven by[2+2]cycloaddition reaction,the block-like crystal of Ch-BF₂and the microcrystals of 4-MeODBr Ch-BF₂showed photo-induce cracking and jumping behaviour.4)Halogen-substituted 9-anthracenecarbonitrile derivatives FCNA,ClCNA and BrCNA were synthesized.[4+4]cycloaddition of 10-fluoroanthracene-9-carbonitrile(FCNA)could tack place under 365 nm,410 nm UV light and even under white light,and the reverse reaction of[4+4]cycloaddition occurred under 254 nm UV light or heating.Driven by reverse[4+4]cycloaddition reaction,the needle-like crystals of FCNA could bend rapidly under 365 nm,410 nm UV light and white light irradiation,and the bent crystal could straighten upon irradiation of 254 nm UV light or heating.In addition,because the crystal FCNA showed fast response photomechanical behavior,the PVDF film incorporated with FCNA exhibited photo-induced twisting,bending toward or away from the light source depending on its initial shape.Particularly,the film-based actuator could be used as an artificial muscle to lift small objects directed by remote light.Although the distance between the adjacent anthracence are less than4.7(?) in the single crystal of ClCNA and BrCNA,the[4+4]cycloaddition reactivity was low,and BrCNA was inert under UV light.That's because the singlet excited state is the reactive species in the photo-induced [4+4]cycloaddition of anthracene derivatives.However,the heavy atom effect of Cl or Br was favourable for the intersystem crossing to give triplet state.Hence,the introduction of F atom in anthracence derivative could improve the reactivity of [4+4] cycloaddition and enhance the photomechanical performance.5)The 9-(2-nitrovinyl)anthracene(NVA)and halogen substituted 9-(2-nitrovinyl)anthracene,FNVA,ClNVA and BrNVA were synthesized.UV-Vis absorption spectrum,fluorescence spectrum and ¹H NMR indicated that the photo-induced Z-E isomerization firstly could tack place,and then the photo-induced[4+2]cycloaddition reaction occurred whenNVA was irradiated in solution.Only the photo-induced Z-E isomerization occurred when FNVA,ClNVA and BrNVA was irradiated in solution.In addition,the photo-induced conformation transition ofNVA,FNVA,ClNVA and BrNVA occurred after their microcrystals was irradiated by 254 nm UV light,365 nm UV light and visible light.Although the packing of molecules are meet with the Schmidt's rule in single crystal of ClNVA and BrNVA.The photo-induced[4+4]and[2+2]cycloaddition reaction couldn't occur in microcrystals of ClNVA and BrNVA.That's because This is because two adjacent molecules need to be close to each other during photoinduced[2+2]and[4+4]cycloaddition reactions,while strong ?-? interaction between two adjacent anthracene rings restrict the movement of molecules in the single crystals of ClNVA and BrNVA.In addition,the formation of intermolecular ?-? interaction caused the elastic of needle-like crystals of ClNVA and BrNVA,these crystals showed reverse elastic bending under the stimulation of mechanical force.