# A Solid State Zwitterionic Plastic Crystal With High Static Dielectric Constant

## TL;DR

A new zwitterionic material with a high dielectric constant in solid state is developed, offering potential for energy storage applications.

## Contribution

The discovery of a zwitterion forming a plastic crystal phase with a high static dielectric constant in solid state.

## Key findings

- The zwitterion exhibits a plastic crystal phase with a high dielectric constant of 147 at -10°C.
- The material remains in the plastic crystal phase within 50 K of ambient temperature.
- The high dielectric constant arises from rotational degrees of freedom due to weak intermolecular interactions.

## Abstract

Solid materials with a high dielectric constant have a wide range of applications in the energy storage field. In this research, an imidazolium‐based zwitterion is designed, synthesized, and confirmed to have a plastic crystal phase based on the following experimental and computational evidence: (i) the presence of long‐range order with weak intermolecular forces and competing attractive‐repulsive interactions along different crystallographic directions; (ii) the observation of more than one endotherm on heating including a solid‐solid phase transition at Ts‐s = −26 °C and melting of the plastic crystal at Tm = 72°C; (iii) a low entropy of fusion at melting (2.1 JK−1mol−1); (iv) a strongly anisotropic morphology; (v) relatively fast dynamics originating from short‐range degrees of freedom. Furthermore, it exhibits a very high dielectric constant in the plastic crystal solid state (147 at −10°C and 103 at 70°C) due to the rotational degrees of freedom of plastic crystals that arise from weak net intermolecular interactions of zwitterions due to only having two carbons between the anion and cation. This material conveniently remains in the plastic crystal phase within 50 K of ambient temperature. This discovery opens new opportunities in the search for solid‐state high dielectric constant materials.

Developing solid high dielectric constant materials has been a research focus in the energy storage field. In this research, we discovered a zwitterion with a plastic crystal phase. Due to the short‐range degree of freedom of the dipole moment for this zwitterion, a relatively high static dielectric constant has been achieved in its solid state.