A Poling-Free Supramolecular Crown Ether Compound with Large Piezoelectricity.

Supramolecular host-guest ferroelectrics based on solution processing are highly desirable because they are generally created with intrinsic piezoelectricity/ferroelectricity and do not need further poling. Poly(vinylidene fluoride) (PVDF) in the electric-active beta phase after stretching/annealing still shows no piezoelectric response unless poled. Although many supramolecular host-guest ferroelectrics have been discovered, their piezoelectricity is relatively small. Based on H/F substitution, we reported a supramolecular host-guest compound [(CF 3 -C 6 H 4 -NH 3 )(18-crown-6)][TFSA] (CF 3 -C 6 H 4 -NH 3 = 4-trifluoromethylanilinium, TFSA = bis(trifluoromethanesulfonyl)ammonium) with a remarkable piezoelectric response of 42 pC/N under no poling condition. The introduction of F atoms increases phase transition temperature, polar axes, second harmonic generation (SHG) intensity, and piezoelectric coefficient d 33 . To our knowledge, such a large piezoelectric performance of [(CF 3 -C 6 H 4 -NH 3 )(18-crown-6)][TFSA] makes its d 33 , piezoelectric voltage coefficient g 33 , and mechanical quality factor Q m the highest among the reported supramolecular host-guest ferroelectric compounds and even larger than the values of PVDF. This work provides inspiration for optimizing piezoelectricity on molecular materials.