Influences of bulky aromatic head group on morphology, structure and color-transition behaviors of polydiacetylene assemblies upon exposure to thermal and chemical stimuli

Abstract

This contribution investigates the morphologies, packing structure and color-transition behaviors of polydiacetylene(PDA) assemblies prepared from 10,12-pentacosadiynoic acid (PCDA), 3-(pentacosa-10,12-diynamido)benzoic acid (PCDA-mBzA), and 6-(pentacosa-10,12-diynamido)-2-naphthoic acid (PCDA-NPA). This series of PDAs provides a systematic increase of head group size and overall inter- and intramolecular interactions within the assemblies. The increase of head group size affects the packing parameter of diacetylene(DA) monomers, causing morphological change from spherical vesicles to rod-like structures. X-ray diffraction reveals that the size of the head group also dictates molecular tilting angle within the lamellar structure of DA assemblies. The monocarboxylic poly(PCDA) exhibits irreversible thermochromism. The incorporation of aromatic head groups in poly(PCDA-mBzA) and poly(PCDA-NPA) enhances the overall interactions within assemblies, resulting in reversible thermochromism. Furthermore, the size of aromatic head groups strongly affects the response time and color reversibility in thin film. Interestingly, the sensitivity of PDAs to chemical stimuli including cationic surfactants and organic solvents is found to vary with type of head group. The poly(PCDA-mBzA) is more sensitive to cationic surfactants compared to the system of poly(PCDA-NPA). An opposite result is observed when organic solvents, tetrahydrofuran and pyridine, are used as chemical stimuli. Our study provides fundamental understanding about molecular factors affecting the self-assembling structure and color-transition behaviors of PDA materials.