A helical polydiacetylene with enhanced thermochromic reversibility temperature from self-assembly of diacetylene-containing rosettes.

Rosettes are a class of higher-order hierarchical supramolecular structures formed through highly precise and controlled molecularly coordinated self-assembly via sequential non-covalent interactions, predominantly directed by hydrogen-bonding networks. Herein, we constructed robust hydrogen-bonded colorimetric hexad rosette supramolecules through the self-assembly of linear barbituric acid-linked diacetylene monomers (PCDA-ABA). The barbituric acid head group, with multiple hydrogen-bond donor and acceptor sites, facilitates sequential packing, forming a cyclic hexameric rosette arrangement. These hexad rosettes stack along the axis in a columnar fashion, forming nanohelices stabilized by hydrogen bonding originating from the barbuteric acid moiety and π-π stacking interactions of the diacetylene (DA) chains. Interestingly, upon UV-induced photopolymerization, the columnar stacked rosettes transform into a rigid covalent structure, imparting distinct colorimetric properties to the resulting polymeric assemblies. Results from structural arrangement analysis using FT-IR indicate that hydrogen bonding is the major driving force behind the formation of hexad rosette nanohelices. Studies of structural packing patterns and morphological characteristics using XRD, AFM, SEM, and TEM strongly support the formation of rosette-based nanohelices. Photopolymerization results in a covalently linked blue-phase PDA rosette structure, which exhibits enhanced reversible thermochromic properties up to 180 °C over multiple thermal cycles. Also, the pH-dependent behavior of the self-assembled PDA was evaluated, revealing a reversible colorimetric response regulated by protonation and deprotonation processes.