Study On The [2+2] Cycloaddition Reaction And Light-Activated Properties Of Haloaryl Acrylic Acid And Its Derivatives

Light-induced mechanical motion refers to an energy conversion method that converts light energy into mechanical energy.Because it can be remotely controlled,it has attractive prospects in applications such as actuators,flexible electronics,artificial muscles,and soft microfluidic devices.Photochemical reactions are ideal means of converting the absorbed photon energy into motion for the photomechanical materials.For example,the cis-trans isomerization of azobenzenes,the cycloaddition reaction of anthracene,and the electrocyclic of diarylethylene compounds may all cause macroscopic movements such as bending,curling,twisting,crawling,and jumping of molecular crystals.Among them,the solid[2+2]cycloaddition reaction can not only induce the light-induced mechanical movements of molecular crystals,but also synthesize some stereospecific cyclobutane derivatives without pollution and high yield.Therefore,designing and synthesizing organic molecules capable of[2+2]cycloaddition reactions and preparing new-type mechanically responsive molecular crystals induced by cycloaddition reactions are a meaningful subject.It is well known that cinnamic acid,as a photochemically active molecule,can undergo photodimerization in the solid state.In addition,halogens can be used as"crystal engineering"groups in topological chemical reactions to promote molecular reactions.Therefore,starting from the design of novel haloaryl acrylic acid and its derivatives,this paper studies the effect of halogen substituents on the cycloaddition of molecular crystals,and prepares crystals with photomechanical motion.Some creative results have been obtained,and outline below:?1?A series of halogen-substituted phenyl acrylate compounds were synthesized and obtained their crystal structures.The results show that when the para position of the phenyl group attached to the acyloxy group is replaced by chlorine or bromine,the crystals of FPCCl,FPCBr,ClPCCl,ClPCBr,BrPCCl,BrPCBr,IPCCl and IPCBr were all head-to-head?-form stacking.When the position was replaced by fluorine or iodine,in addition to FPCF,the crystals of FPCI,ClPCF,ClPCI,BrPCF,BrPCI,IPCF and IPCI were?-form stacking.Therefore,the substituent?F,Cl,Br or I?on the para position of the phenyl group connected to the acyl group has little effect on the accumulation of the single crystal.In?-form crystals,there are hydrogen bonds,halogen bonds,and Van der waals interactions between molecules.The proportion of intermolecular interactions in the crystal arrangement was quantitatively evaluated by Hirshfeld surface analysis,and it was found that hydrogen bonds?C-H···halogen and C-H···O?dominated the crystal packing of?-form structure effect.[2+2]cycloaddition reaction of crystals with?-form structure occurred under 365 nm light irradiation,and only one rctt-type cyclobutane product was obtained,indicating that the reaction process was stereospecific.For crystals with?-form structure,because the distance between the"olefin pairs"was greater than 4.2?,cycloaddition reaction could not take place.Interestingly,the distance between the parallel double bonds in the IPCCl crystal was 5.872?,which did not satisfy the Schmidt's criteria,but the cycloaddition reaction occurred.The introduction of these halogen provides new ideas for designing molecules capable of[2+2]cycloaddition reactions.?2?The photomechanical effects of the dynamic molecular crystals of halogen-substituted naphthalene acrylic acids have been investigated.Upon UV irradiation,obvious macroscopic movements of the molecular crystals of 1FNaAA,1ClNaAA,1BrNaAA and 6BrNaAA were observed.The needle-like crystal of 1FNaAA curled into a loop without breaking rapidly upon UV irradiation,and the long needle-like crystals of 1FNaAA showed light-induced bending,flipping and bursting.The slice-like crystals of 1ClNaAA and 1BrNaAA not only exhibited bending backwards from UV light,but also cracking,coiling,rotating and twisting in response to UV light.Differently,the slice-like crystal of 6BrNaAA bent towards the light source.Since the geometric parameters?d,?,?₁ and?₂?in the crystals of 1FNaAA,1ClNaAA,1BrNaAA and 6BrNaAA satisfy the topological photochemical rules of Schmidt,the[2+2]cycloaddition reaction occurred in the crystals.The single crystal structure indicated that the molecules 1FNaAA,1ClNaAA,1BrNaAA and 6BrNaAA were stacked in a head-to-head mode to form hydrogen-bonded dimers,and only one isomer of the rctt-type photodimerization product was produced.On account of the significant movement on the molecular level during photodimerization,strain was produced on the phototropic surface of the crystal in the short period of time.Therefore,light-induced bending,curling,coiling,and twisting were observed when the strain accumulated during light-induced structural transformation was released slowly.If the accumulated strain was released rapidly,flipping,bursting,and cracking of the crystals were observed.This work provided new clues for the development of photomechanical molecular crystals based on acrylic acids.