Leveraging Conformational and Nitrogen Atom Inversion for Room-Temperature Ferroelectricity

TL;DR

This paper introduces a new class of molecular ferroelectrics based on nitrogen inversion, enabling room-temperature polarization switching for digital storage.

Contribution

The study demonstrates room-temperature ferroelectricity in azangulene through nitrogen inversion and identifies a stable planar polymorph.

Findings

Azangulene exhibits above-room-temperature ferroelectricity via whole-molecule inversion.

A flat polymorph of azangulene was isolated, showing a stable planar structure.

Crystallographic and computational analyses reveal enthalpic and entropic contributions to the molecule's functionality.

Abstract

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.

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