Study On Chemical Design Syntheses And Properties Of Several Organic Enantiomer Molecular Ferroelectrics

As an important functional dielectric material,ferroelectrics have a wide range of applications in ultrasound probes,infrared detectors,aerospace,and other fields due to their spontaneous polarization and polarization ability to flip or reorient under external electric fields.Devices based on the inherent properties of ferroelectrics are widely used.Although the first discovered ferroelectricity in 1920 was an organic compound,namely the Rochelle salt,inorganic ceramic ferroelectric materials have long dominated the application market due to their higher stability and excellent properties.In recent years,with the emergence of more and more molecular ferroelectrics,especially hybrid organic inorganic compound and organic compounds,molecular based ferroelectrics have the advantages of simple solution preparation,low cost,strong biological compatibility,structural adjustability,etc.,especially chirality,which is incompatible with traditional inorganic ferroelectric ceramics,making them a useful supplement or replacement for inorganic ferroelectrics.At present,the chemical design of molecular ferroelectrics is an important topic in the field of ferroelectric material research.The research of organic molecular ferroelectrics poses new challenges to material chemistry,and the design and synthesis of organic molecular ferroelectrics with chirality is a frontier research hotspot and difficulty.The introduction of chirality can increase the probability of its crystallization in the ferroelectric space group,and trigger more molecular based ferroelectrics with diverse properties.In this paper,three groups of organic enantiomer ferroelectrics were synthesized by studying different single group enantiomer and chemical design modification and tailoring.Explore it by combining relevant testing methods such as single crystal structure,electrical properties,thermodynamic properties,ferroelectric phase transition,and ferroelectric domain structure.The main content includes the following three aspects:1.A pair of organic enantiomer multiferroic crystals（R/S）-BINOL-DIPASi were synthesized by introducing momentum matching module diisopropyl silicon into axially chiral BINOL as the reaction substrate.CD and VCD tests verified the properties of their enantiomer,and DSC,dielectric and PXRD tests verified that they would undergo structural phase transition at 363 K.The single crystal structure analysis further shows that during the phase transition process,the ordered and disordered movement of diisopropyl groups leads to the ferroelectric phase transition of the enantiomer from P2₁ to P1 symmetry,which is also a ferroelastic phase transition.Through hysteresis loop measurement and PFM characterization,the enantiomer has significant polarization reversal and ferroelectric domain reversal properties.In addition,polarization microscopy and nanoindentation instrumentation confirmed the reversible changes in its ferroelastic domains.The introduction of organic silicon components endows materials with easy processing,adjustable structure,and non-toxic properties,which makes them have potential applications in the field of biomedicine.2.4-（（1R,4R）-7,7-dimethyl-2-oxobicyclo[2.2.1]heptan-1-yl）methanesulfonyl P-entaerythritol ester[（R/S）camphor sulfonic acid pentaerythritol]was synthesized using camphor sulfonyl chloride and pentaerythritol as raw materials.The structure of its enantiomer was determined by CD test.DSC,PXRD and dielectric constant test at variable temperature showed that the enantiomer had a reversible structure transition at 357 K.The crystal structure analysis shows that the crystal is crystallized in P1space group at room temperature,which is one of the polar point groups required by ferroelectricity,and they are potential ferroelectrics.3.A group of organic enantiomer ferroelectric crystals（7a S,10S,11a R）-12,12-dimethyl-6,6-dioxo-3,4,9,10-tetrahydro-7H7a,10-methyl-2H-1,3-oxazino[2,3-i][2,1]b enzisothiazol-11（8H）-one（1-SSRforshort）and（7a R,10R,11a S）-12,12-dimethyl-6,6-diox o-3,4,9,10-tetrahydrodro-7H-7a,10-methylo-2H-1,3-oxazino[2,3-i][2,1]benzisothiazol-11（8H）-one（1-RRSforshort）.1-SSR and 1-RRS are crystallized in P2₁ space group,C₂point group,hysteresis loop and PFM tests,which prove that they all have ferroelectricity before the melting point,and the enantiomer compound has a saturation polarization value Ps of 2.2μC/cm²,with a piezoelectric coefficient d₃₃value of 10 p C/N.In addition,they have a relatively low acoustic impedance value of2.7*10⁶ kg/（s m²）,which is well matched with human tissue.The introduction of chiral chemical design method can make organic enantiomer ferroelectrics have higher ferrovoltaic properties,which is useful in intelligent wearable and biological matching applications.The introduction of chirality into organic molecules to form enantiomer compounds improves the possibility of enantiomer crystals becoming ferroelectrics in five polar chiral space group,which meets the basic requirements of ferroelectricity.In this process,it is important that the introduction of chirality transforms optically inactive molecules into optically active molecules,which,together with other special structures,expands the potential applications of molecular ferroelectrics in piezoelectricity and biomedicine.