The Phase Transtion Properties Of Single Crystals Based On DABCO And Crown Ether Derivatives

Switchable materials whose physical properties can reversibly convert among different statuses by external stimuli（such as temperature,light,pressure,electric,and magnetic fields）.They have attached widely investigation due to the promising potential in the field of sensors,data storage,optical technologies and so on.Among them,inorganic perovskites（Ba Ti O₃,Li Nb O₃,etc.）have shown excellent switchable dielectric,magnetism,and even ferroelectric.However,the high processing temperature and toxic ingredients limit their further development.Therefore,it is urgent to overcome the inherent shortcomings of inorganic perovskites and seek ideal alternatives.Compared with the rigid structure of inorganic perovskites,organic-inorganic hybrid perovskites（HOIPs）show superior performance due to the synergistic effect of the organic and inorganic parts.Among them,DABCO amine has been supposed as a preferred candidate to design switchable materials which have anticipative performance because of the motion of the cations in“melting ON”and“freezing OFF”.DABCO is a star molecule similar to CH₃NH₂（CH₃NH₃Pb I₃ in the solar cell）.We have designed a lot of new materials based on this star molecule.Here,as one of this series of work,we further successfully optimized the DABCO derivatives and derived halogen substituents with disordered switchable dielectric phase transitions.In addition,similar to the DABCO molecule,the crown ether molecule always undergoes order-disorder movement which is easily triggered by temperature.Therefore,crown ether molecules were introduced as a molecular rotor.Besides,halogen-substituted ammonium cations were used to build the host-guest complex.To keep charge balance,tetrahedral/octahedron anions were introduced simultaneously.The synthesized host-guest crown ether supramolecular inclusion compounds are a promising candidate to explore new switchable materials.Based on the“quasi-spherical”theory and the“H-F”substitution principle,we successfully synthesized twelve organic-inorganic hybrid compounds through precise molecular modification:[C₇H₁₅N₂F]²⁺[Rb（BF₄）₃]^2-（1）,[C₇H₁₄N₂Cl]₂²⁺[Ni（SCN）₄]^2-（2）,[C₇H₁₄N₂Cl]₂²⁺[Mn（SCN）₄]^2-（3）,[（C₃H₈NBr）（18-crown-6）]⁺[Cl O₄]^-（4）,[（C₃H₈NCl）（18-crown-6）]⁺[Cl O₄]^-（5）,[（C₃H₈NCl）（18-crown-6）]⁺[PF₆]^-（6）,[（C₂H₇NBr）₂（18-crown-6）]²⁺[BF₄]₂^2-?H₂O（7）,[（C₂H₇NBr）（18-crown-6）]⁺[Cl O₄]^-（8）,[（C₂H₇NBr）（18-crown-6）]⁺[PF₆]^-（9）,[（C₂H₆NF₂）（18-crown-6）]⁺[BF₄]^-（10）,[（C₂H₆NF₂）（18-crown-6）]⁺[PF₆]^-.CH₃CN（11）,[（C₂H₅NF₃）（18-crown-6）]⁺[PF₆]^-（12）.Systematic characterization was performed on the synthesized materials.Among them,compounds 1,9,and 11 all achieved reversible phase transitions within the selected temperature range.It is noteworthy that,1([C₇H₁₅N₂F]²⁺[Rb（BF₄）₃]^2-)was successfully targeted by introducing a methyl group and a fluorine atom at the two symmetrical ends of the Dabco（1,4-diazoniabicyclo[2.2.2]octane）.The synthesized hybrid 3D perovskite displays three reversible phase transitions accompanying dual ferroelastic behavior（m3?8）F4/mmm and 4/mmm F2/m).The promotion is entirely due to the precise design of the cation and the logical symmetry adjustment.This will inspire further research on chemical design strategy,and provide the potential for optimized performance of switchable materials.