Design And Synthesis Of Quasi-Spherical Molecules And Their Role In Introducing Ferroelectricity

Most of the traditional molecular ferroelectrics are unipolar molecular ferroelectric s,which affect their good expression in piezoelectricity and ferroelectricity,and their application potential is severely limited by their uniaxial properties,leading to the search for suitable thin film growth substrates.There are significant problems in achieving high film performance.It has been found that a class of compounds composed of small molecules with spherical structures has a high probability of being plastic/multiaxial molecular ferroelectric crystals,showing various unique properties,most of which are caused by the rotational motion and directional disorder of the constituent molecules.Induced ferroelectricity in the low temperature phase(including the room temperature phase),which is different from the traditional molecular ferroelectric crystal.According to the guidance of ’quasi-spherical theory’,by synthesizing spherical molecules 1,5-diazabicyclo[3.2.2]nonane,1,4-diazabicyclo[3.2.2]nonane and 2,5-diazabicyclo[2.2.1]heptane,reacted with HClO4,HReO4,HBF4,HPF6,CF3COOH,and RbX(Cl、Br、I),respectively,to give compounds 1～13:[(1,5-3.2.2-Hdabcn)ClO4](1),[(1,5-3.2.2-Hdabcn)ReO4](2),[(1,5-3.2.2-Hdabcn)BF4](3),[(1,5-3.2.2-Hdabcn)PF6](4),[1,4-3.2.2-Hdabcn]ClO4(5)和[1,4-3.2.2-Hdabcn]ReO4(6),[2,5-2.2.1-Hdabch]ClO4(7),[2,5-2.2.1-Hdabch]ReO4(8),[2,5-2.2.1-Hdabch]BF4(9),[2,5-2.2.1-Hdabch]CF3COO(10),[2,5-2.2.1-H2dabch]RbCl3·H2O(11)、[2,5-2.2.1-H2dabch]RbBr3·H2O(12)、[2,5-2.2.1-H2dabch]RbI3·H2O(13).Through a series of characterizations such as phase transition tests,second harmonic generation(SHG)and piezoelectric force microscopy(PFM),we found that compound 1 and compound 2 are ferroelectric with Curie temperatures of 405.7 K and 395.7 K,respectively,which also proves The design and synthesis of spherical molecules are of certain significance in the introduction of ferroelectricity.The structures of compound 3 and compound 1 are similar,and they are both in the non-centrosymmetric space group of Pmn21 at room temperature,which is a typical ferroelectric space group.It is disappointing that according to the current data,compound 3 may not be a ferroelectric,but a ferroelectric.General phase change materials.Compounds 5 and 6 wanted to increase the dipole moment and introduce ferroelectricity by changing the position of the C-N bond,but the results were unsatisfactory.Compounds 5 and 6 are not ferroelectrics.However,when 2,5-diazabicyclo[2.2.1]heptane was used as a spherical organic amine ligand,the potential ferroelectrics were not found due to the fact that the molecular structure was too small and did not match the energy of the inorganic acid of the large anion group.However,compounds 7～10 all show reversible phase transitions and possess dielectric properties at the same time.Compounds 11～13 are three-dimensional perovskite phase change materials with identical structures,all in the chiral space group of the orthorhombic system P212121,and the phase transition temperature of compound 13>compound 12>compound 11.According to this,organic plastic multiaxial molecular ferroelectrics were obtained by designing synthetic DABCO-like spherical organic amine molecules and reacting them with inorganic acids whose anions are polyhedral configuration.This work enriches the types of ceramic-like multipolar axial molecular ferroelectrics to a certain extent,and provides a new idea for the design and synthesis of multiaxial ferroelectrics.