Synthesis And Phase Transition Properties Of Fluoroanilinium And Methoxyanilinium Crown Ether Inclusion Compounds

Phase transition materials have received extensive attention for their potential applications in sensors,switchable dielectric devices,optoelectronics,environmental detectors,digital processing,and so on.In recent years,many efforts have been made in this field.Crown ether-based host-guest compounds were found to be advantageous in achieving this effect.The possible localized twisting or rotational motion of crown ether-based host-guest compounds leads to order-disorder-type structural phase transitions,accompanied by the abrupt change of ferroelectricity,ferroelasticity,dielectricity,and nonlinear optical effects.The most important feature of crown ether is that it can accommodate cations,but its hole is ion-selective.Crown ethers not only have high affinity for potassium ions,but also can form inclusion complexes with protonated ammonium salts.Generally speaking,the crown ether molecule acts as the host,which interacts with the guest cation through the N-H-O hydrogen bond,futher assembling with the corresponding anion to form a molecular rotor-stator system.Based on the excellent properties of crown ether-based host-guest compounds,we are committed to finding more crown ether-based host-guest molecular phase change materials.Using the "momentum matching" theory and fluorination effect proposed by Xiong et al.,we designed and synthesized a series of crown ether-based host-guest compounds composed of protonated ammonium and 18-crown-6.Their structures and properties were comprehensively explored by single crystal structure analysis,dielectric measurement,infrared spectroscopy,differential scanning calorimetry and Xray powder diffractometer analysis.Considering that the electronegativity of fluorine is greater than that of hydrogen,the introduction of fluorine atoms into organic amines can increase the dipole moment of the molecule and introduce chirality.The introduction of fluorine atoms into organic amines may also increase the molecular rotational energy barrier,thereby increasing the phase transition temperature.The introduction of fluorine atoms can also improve the fat solubility of the compound and reduce the hydrophilicity.To this end,this paper uses "momentum matching" theory and H/F substitution strategy to design and synthesize 6 kinds of host-guest molecular compounds composed of fluoroaniline and18-crown-6.The six compounds are [(2,3-DFA)(18-crown-6)][TFSA](1)(DFA =difluorobenzonium,TFSA = bis(trifluoromethanesulfonyl)ammonium),[(2,5-DFA)(18-crown-6)][TFSA](2),[(2,6-DFA)(18-crown-6)][TFSA](3),[(2,4-DFA)(18-crown-6)][TFSA](4),[(3,4-DFA)(18-crown-6)][TFSA](5)and [(3,5-DFA)(18-crown-6)][TFSA](6).Their structures were confirmed by single crystal structure analysis.From the results of dielectric measurement and differential scanning calorimetry analysis,compounds 4,5 and 6 all underwent reversible phase transitions.However,the generally low phase transition temperatures limit their practical applications.In order to obtain molecular materials with high phase transition temperature,based on compounds 4,5 and 6,we designed and synthesized two host-guest molecular materials composed of methoxyaniline and 18-crown-6.They are [(3-MOA)(18-crown-6)][TFSA](MOA = methoxyanilinium)(7)and [(2-MOA)(18-crown-6)][TFSA](8).Their structures were confirmed by single crystal structure analysis.According to the results of dielectric measurement and differential scanning calorimetry analysis,compound 7 undergoes a reversible phase transition near 307.7 K,which is higher than that of compounds 4 and 6.And compound 7 has switchable dielectric behavior between high dielectric state and low dielectric state,indicating that it has great potential for application in room temperature bistable dielectric switching.This work paves the way for the design of crown ether based host guest molecular dielectric switch.