Nitrogen inversion, in which a pyramidalized tricoordinate nitrogen center turns "inside out", is an intriguing phenomenon that has inspired a century of fundamental research but has yet to find practical application. In this work, classical nitrogen inversion is used to template polarization switching in a new class of molecular ferroelectrics, material candidates for next-generation digital information storage systems. We demonstrate that azangulene, a bowl-shaped nitrogen-centered heterotriangulene, when adopting a polar crystal packing motif, exhibits above-room-temperature ferroelectricity that we attribute to whole-molecule inversion. Although the mechanism of classical nitrogen inversion predicts a planar transition-state structure, we isolate a crystallographic polymorph in which the bowl depth of azangulene is flat, suggesting that the planar geometry is a stable and isolable structure on the conformational energy surface. A combination of crystallographic polymorphism and computational investigations unravels the complex interplay between the enthalpic and entropic factors contributing to the unique functionality of this molecule.
Rosa et al. (Mon,) studied this question.