Thermodynamic phase transition triggered by distinct distortion and ordering of dipropylammonium picrate

Dipropylammonium picrate (compound 1) undergoes a first-order phase transition at 185.0 K. Differential scanning calorimetry (DSC) measurements show reversible anomaly peaks with a thermal hysteresis of 10.2 K. Dielectric responses with distinct anisotropy and striking anomaly further confirm the phase transition. Detailed structural analyses demonstrate that the phase transition in 1 is dominated by order-disorder transformations of the dipropylammonium (DPA) cations and the picrate anions. Moreover, the unique distortions of the terminal propyl moieties in the flexible chain-like DPA cation also play an important role in this structural phase transition. All these results indicate that 1 is a potential phase-transition material.