The Synthesis, Structures And Properties Of Several Molecule-Based Phase Transition Compounds

Switchable dielectric materials, due to their convertible dielectric behavior between high and low dielectric states, would find potential applications in data storage, data communication, signal processing, etc. These materials can change their properties between different states by external stimuli, such as electric field, extra light and temperature, etc. Among them, solid-to-solid reversible phase transition, induced by the change of temperature, is a common principle for constructing the switchable dielectric materials. In order to explore new phase transition crystal materials, we have synthesized a series of phase transition compound. Furthermore, differential scanning calorimetry, specific heat, variable-temperature dielectric, variable-temperature second-harmonic generation, pyroelectric, variable-temperature X-ray structure determinations were used to investigate deeply their mechanism and physical properties of phase transition.1. Dibenzylamine-based molecular compounds are found to readily undergo phase transition, hence we use dibenzylamine as the functional unit, trichloroacetic acid as the anion and synthesized the phase transition compound [?C₇H₇?₂NH₂]Cl₃CCOO?1?. Thermal measurements reveal that 1 undergoes a reversible ferroelastic phase transition at 329 K. The reversible second-order phenomenon has been investigated by DSC measurements, specific heat capacity, dielectric measurements and variable-temperature cell parameter analyses, etc. X-ray single-crystal diffraction reveals clearly that the ordered trichloroacetate anion goes gradual change to disorder state with temperature warming up to Tc. Variable temperature PXRD tests strongly confirm the structural phase transition. The slight ordering caused by chlorine atoms based on single-crystal structural analyses makes 1 to be a promising material. These process findings will possibly provide a new avenue for designing the switchable dielectric materials.2. N-methylcyclohexylamine-based molecular compounds are found to readily undergo phase transition, hence we use N-methylcyclohexylamine as the functional unit, 2, 4, 6-trinitrophenol as the anion and synthesized the phase transition compound(C₇H₁₄NH₂)[C₆H₂?NO₂?₃O]?2?. Thermal measurements reveal that 2 undergoes a reversible solid-to-solid phase transition at 240 K?285K. The reversible first-order phenomenon has been investigated by DSC measurements, specific heat capacity, dielectric measurements and variable-temperature cell parameter analyses, etc. X-ray single-crystal diffraction reveals clearly that the ordered nitryl on picric acid and carbocycle goes gradual change to disorder state step by step with temperature warming up to Tc. Besides, 2 exhibit a perfect SHG effect when low temperature. These process findings will possibly provide a new avenue for designing the switchable dielectric materials.3. Cyclohexylamine-based molecular compounds are found to readily undergo phase transition, hence we use cyclohexylamine as the functional unit, fluosilicic acid as the anion and synthesized the phase transition compound [(C₆H₁₁)NH₃]HSi F₆?3?. Thermal measurements reveal that 3 undergoes a reversible solid-to-solid phase transition at 216 K. The reversible first-order phenomenon has been investigated by DSC measurements, specific heat capacity, dielectric measurements and variable-temperature cell parameter analyses, etc. X-ray single-crystal diffraction reveals clearly that the ordered carbocycle goes gradual change to disorder state with temperature warming up to Tc, like DABCO. Variable temperature PXRD tests strongly confirm the structural phase transition. D2 O was used to prove whether H-bond effects the phase transition. These process findings will possibly provide a new avenue for designing the switchable dielectric materials.4. Ethyldiisopropylamine-based molecular compounds are found to readily undergo phase transition, hence we use ethyldiisopropylamine as the functional unit, perchloric acid as the anion and synthesized the phase transition compound [?C₃H₇?₂C₂H₅NH]ClO₄?4?. Thermal measurements reveal that 4 undergoes a reversible solid-to-solid phase transition at 239 K?306 K. The reversible first-order phenomenon has been investigated by DSC measurements, specific heat capacity, dielectric measurements and variable-temperature cell parameter analyses, etc. X-ray single-crystal diffraction reveals clearly that the ordered trichloroacetate anion goes gradual change to disorder state with temperature warming up to Tc. Variable temperature PXRD tests strongly confirm the structural phase transition. The unit goes disordered stepwise when temperature changes. Also, a big step-like dielectric constant anomal appears and it seems to be a promising material. These process findings will possibly provide a new avenue for designing the switchable dielectric materials.