A supra-molecular switchable dielectric material with non-linear optical properties

A novel molecular phase transition material (PTM), 1-methylpiperidinium perchlorate [18-crown-6] monohydrate (1), has been synthesized, which exhibits reversible switchable dielectric anomalies near room temperature. The phase transition in 1 is from noncentrosymmetric to noncentrosymmetric, displaying non-linear optical (NLO) properties with a second harmonic generation response of similar to 0.8 times compared to that of potassium dihydrogen phosphate. Thermal analyses of 1, including differential scanning calorimetry and specific heat measurements, confirm the first-order solid-state phase transition at 260 K. The dielectric constants display temperature-dependent anomalies with the temperature approaching the transition point (T-c), where the evident step-like anomalies demonstrate two distinct states below and above the T-c value, respectively. Variable-temperature single crystal X-ray diffraction discloses that the origin of its phase transition is ascribed to the order-disorder transformation of perchlorate anion, the methyl group of cation and the torsional angular change in crown molecule; that is, all three components contribute to the emergence of this phase transition. This result suggests that 1 could be conceived as a potential switchable dielectric and NLO material, which provides an effective approach to design novel NLO switch materials.