Pronounced Chirality Effect on the Ferroelectricity of Hydrogen-Bonded Supramolecular Assemblies of Ambipolar Chromophoric Systems

Abstract

Chirality effects are well documented in different biological functions, but examples in soft materials physics are lesser known. This paper reports a significant chirality effect on modulating ferroelectricity in hydrogen-bonded supramolecular assemblies of two acceptor (A)−donor (D)−acceptor (A)-type conjugated molecules, namely, AD 2 A-C and AD 2 A. Both molecules contain the same naphthalimide−bithiophene− naphthalimide conjugated chromophore, symmetrically functionalized with two substituted benzamide wedges with either a chiral (AD 2 A-C ) or achiral (AD 2 A) peripheral alkyl chain. They exhibit self-assembly in a hydrocarbon solvent methylcyclohexane (MCH), driven by H-bonding among the amide groups and aromatic stacking of the conjugated chromophore. Despite showing similar entangled fibrillar morphology, ultraviolet−visible (UV−vis) and Fourier transform infrared spectroscopy (FT-IR) spectra of the aggregated samples indicate a significant difference in the internal order of the self-assembled AD 2 A-C and AD 2 A. The CD spectra and microscopy images confirm helical assembly for the chiral derivative. In the mixed samples of AD 2 A-C + AD 2 A, chirality induction followed a "sergeant and soldiers" principle. The chiral AD 2 A-C exhibits stable ferroelectricity with a Curie temperature of 361 K and a saturation polarization of ∼2 μC cm −2 , while the achiral AD 2 A lacks any notable ferroelectricity. The retained ferroelectricity in the mixed samples and the polarization tunability through chirality induction support their direct correlation and are key observations for predicting the future soft ferroelectric low-power electronic systems.

Piezoelectric Micropower Harvester from Supramolecular Assembly of Chiral Ambipolar Chromophores

“…These results undoubtedly highlight the remarkable impact of supramolecular assembly as well as chirality on the piezoelectricity. Homochiral helical supramolecular polymerization perhaps helps provide the desired angle between the molecular axis and the stacking axis for generating effective macro-dipole and prominent macroscopic polarization and thereby helps to achieve a strong piezoresponse, similar to what has been previously reported by our group for chiral ferroelectric systems …”

“…Detailed syntheses and characterization of the AD 1 A, AD 2 A, and AD 3 A series and two control molecules AD 2 A-1 and AD 2 A-2 are reported in our earlier papers , and discussed in Supporting Information.…”

“…Recently we have reported prominent room temperature (rt) ferroelectricity in hydrogen-bonded supramolecular assemblies of acceptor (A)–donor (D)–acceptor (A)-type ambipolar π-systems (Figure a), in which naphthalimide and oligothiophene serve as the A and D type chromophores, respectively (Figure ). , Intramolecular charge separation in such ADA-type ambipolar molecules (as shown in Figure b) generates a significant dipole moment and polarization, the effect of which is significantly enhanced in the chiral supramolecular polymers. For example, from the density functional theory (DFT) calculation it was found that the dipole moment of the AD 2 A system increases from 4 to 11 debye (D) by going from a dimeric to tetrameric stack and further increases with increasing stack length .…”

Supramolecular Organic Ferroelectric Materials from Donor–Acceptor Systems

“…We have further investigated the effect of chirality on the FE behaviour. [71] For this we have compared AD 2 A with an analogous achiral system, AD 2 A-2 (Figure 9a). Unlike AD 2 A, AD 2 A-2 does not contain any chiral peripheral chain, but otherwise they are structurally identical.…”