High-Temperature Molecular Ferroelectricity in Organic Cocrystal and Its Application in Tactile Sensing.

For decades, molecular ferroelectrics have been regarded as promising alternatives to inorganic ferroelectrics, owing to their lightweight, flexibility, heavy-metal-free composition, and low cost. However, most reported organic compounds met the problem of low Curie point (Tc). Here, we report a novel ferroelectric donor-acceptor (D-A) cocrystal, namely 7H-benzo[c]carbazole-1,2,4,5-tetracyanobenzene (BCZ-TCNB), which shows significiant polarization at room temperature and its polar structure can be maintained up to a high melting point of 502 K. Owing to the displacive ···D+A-···D+A-···D+A-··· packing along a-axis and asymmetric orientation along c-axis, bi-directional polarization behavior is observed in the symmetry breaking binary system. The thermodynamically and dynamically stable polar structure enables a high-temperature melting state, benefiting from strong charge-transfer interaction and other intermolecular interactions. Considering its good piezoelectric coefficient, organic field-effect transistors (OFETs) covered with BCZ-TCNB thin-film exhibits good capability for real-time monitoring of various signals and expressing spatial information.