A Tale of Two Folds: Multiorthogonal Interactions Driven Hierarchical Assembly of a Polymer with an Appended Donor–Acceptor Dyad and Prominent Piezoelectricity

This study reveals biomimetic folding and hierarchical self-assembly of a segmented polyurethane by employing multiple noncovalent interactions, operating in orthogonal manner. The polymer contains a pendant donor (D)-acceptor (A) dyad in each repeating unit and urethane groups in its backbone. Intrachain D-A charge-transfer (CT) interaction in the pendant chains and intrachain hydrogen bonding in the polymer backbone work simultaneously (but independently), enabling a multistage folding in a nonpolar solvent, leading to the formation of a remarkably stable secondary structure. This folded structure further self-assembles into a hierarchical fibrillar network through interchain extended H-bonding among the terminal urethane groups and van der Waals interactions, forming a stable organogel with an entangled fibrillar network. Such hierarchical self-assembly of folded chains results in a remarkably stable supramolecular structure with an embedded CT-complex, which was confirmed by variable-temperature UV-vis and circular dichroism spectroscopy. Furthermore, the self-assembled material exhibits prominent piezoelectric properties, with a robust d₃₃ coefficient of 9 ± 3 pm/V, even in the "off-state". This work highlights a promising strategy for creating functional, biomimetic polymers with potential applications in organic micropower energy harvesting.