Controlling Helical Morphology of Conjugated Molecules with Different Chiral Chain Spacer

Abstract

Chirality is a common characteristic of nature, such as the right-handed β-form double helix of DNA, amino acids, and proteins. Chirality plays an important role in hierarchical architectures starting from the molecular to the supramolecular level. However, the mechanism of the formation of hierarchical structures from molecular to supramolecular level in the chiral self-assembly process is still far from being fully understood because chiral supramolecular structures are associated with a variety of factors such as noncovalent interactions (hydrogen-bonding, hydrophobic or hydrophilic interactions, van der Waals interactions, and π-π interactions) between molecules and external effects (temperature, solvent, pH, and additives). Therefore, investigating the chiral assembly according to molecular interaction will provide guidance on the design of new functional chiral materials. In this work, conjugated molecules with different chiral chain spacers were designed and synthesized. We control the chirality of supramolecular nanostructures through variation of the alkyl spacer length between the chiral chain and π-conjugated molecule. We discuss an investigation into how alkyl spacer between conjugated core and chiral side chains influence the internal arrangement of the π-π stacking within self-assembled molecules. Their electronic properties and morphology of the film were analyzed and characterized through various measurements such as UV–vis, circular dichroism spectroscopies, POM, FE-SEM, FT-IR spectroscopies, and 2D-GIWAXS. Based on these investigations, we could suggest that the H-bonding between amide groups and π-π interactions between isoindigo moieties contributed to the inversion of supramolecular chirality. This molecule design and synthesis of IID-C3-LG and IID-C4-LG gives a new approach to tuning the supramolecular chirality of self-assembled materials.