Nonswitchable and switchable pyroelectric organic crystals produced from diphenylureas with chiral side chains and racemic side chains

Tetraalkoxylated diphenylureas U-3,4-Scit and U-3,4-raccit were synthesized from chiral and racemic citronellyl bromides as starting materials, respectively. To prepare pyroelectric crystals, these two compounds were slowly cooled from their molten states. Although the two compounds have very similar molecular structures, they exhibited quite different electric-field responsiveness. U-3,4-Scit spontaneously polarized during the crystallization process, and almost no polarization switching was observed. On the other hand, U-3,4-raccit exhibited polarization switching in its crystalline state at a high-temperature range, and the polarization direction could be fixed by cooling the crystal to room temperature while applying a direct current voltage. This flexibility occurs because the alkyl chain parts in the crystal are disordered. These pyroelectric thin films are promising materials, as they function in a polycrystalline state without poling treatment.