High-Contrast Switching of Dielectric Properties via a Reversible Isomerization Phase Transition in 1H-2,4-Diamino-6-Phenyl-1,3,5-Triazine Perchlorate

Abstract

Dielectric response materials, which exhibit reversible and tunable dielectric properties under external stimuli, have shown broad application prospects in information storage, sensors, and smart switches. In this study, a novel molecular crystal, DAPT·ClO4, (DAPT=1H-2,4-diamino-6-phenyl-1,3,5-triazine) was successfully synthesized and systematically characterized. Infrared spectroscopy confirmed the successful formation of the target compound with characteristic functional groups. Thermogravimetric analysis revealed excellent thermal stability up to approximately 450 K. Powder X-ray diffraction patterns matched well with the simulated data, confirming high phase purity and good crystallinity. The differential scanning calorimetry curves exhibit a reversible pair of exothermic and endothermic peaks at approximately 223 K and 248 K. Variable-temperature single-crystal analysis reveals an isomorphous phase transition, with both high- and low-temperature phases crystallizing in the P2₁/c space group. Dielectric measurements show that the dielectric constant changes by nearly twice near the phase transition temperature at 1 MHz, high lighting its potential as a dielectric switching material. Through the analysis the structures, it was found that the slight distortion of perchloric acid and the weakening of hydrogen bond forces around the guest cations jointly induced the phase transition. This study provides new ideas for designing molecular crystals with switchable dielectric properties and lays a foundation for the development of advanced functional materials.