Stable room temperature ferroelectricity in hydrogen-bonded supramolecular assemblies of ambipolar π-systems

This article reports H-bonding driven supramolecular polymerization of naphthalimide (A)-thiophene (D)-naphthalimide (A) (AD(n)A, n = 1-4) conjugated ambipolar pi-systems and its remarkable impact on room temperature ferroelectricity. Electrochemical studies confirm the ambipolar nature of these AD(n)A molecules with the HOMO-LUMO gap varying between 2.05 and 2.29 eV. Electron density mapping from ESP calculations reveals intra-molecular charge separation as typically observed in ambipolar systems. In the aggregated state, AD(1)A and AD(2)A exhibit bathochromically shifted absorption bands while AD(3)A and AD(4)A show typical H-aggregation with a hypsochromic shift. Polarization vs. electric field (P-E) measurements reveal stable room temperature ferroelectricity for these supramolecular assemblies, most prominent for the AD(2)A system, with a Curie temperature (T-c) approximate to 361 K and saturation polarization (P-s) of similar to 2 mu C cm(-2) at a rather low coercive field of similar to 2 kV cm(-1). Control molecules, lacking either the ambipolar chromophore or the amide functionality, do not show any ferroelectricity, vindicating the present molecular and supramolecular design. Computational studies enable structural optimization of the stacked oligomer(s) of AD(2)A molecules and reveal a significant increase in the macro-dipole moment (in the range of 10-12 Debye) going from the monomer to the oligomer(s), which provides the rationale for the origin of ferroelectricity in these supramolecular polymers.

Automated summary

This study reports a hydrogen bonding-driven supramolecular polymerization of naphthalimide-thiophene-naphthalimide conjugated ambipolar pi-systems, showcasing a significant impact on room temperature ferroelectricity. The supramolecular assemblies exhibit stable ferroelectricity, with the AD(2)A system showing the most prominent behavior.