Protonation-Triggered Supramolecular Gel from Macrocyclic Diacetylene: Gelation Behavior, Topochemical Polymerization, and Colorimetric Response.

Supramolecular gels originating from the hierarchical self-assembly of low molecular weight organic molecules is a strongly emerging field of advanced material research for the fabrication of soft functional materials. Herein, a novel supramolecular gel was fabricated through the protonation-triggered unidirectional self-assembly of pyridine-attached macrocyclic diacetylene (). Basic nitrogen of a pyridine ring with a strong affinity toward proton transforms the neutral into gelator in its protonated pyridinium salt form (), which further evolves to nano-fibrillar networks to yield a supramolecular gel. Under the irradiation of UV light, the white color gel turned to a robust covalently cross-linked blue-phase PDA gel. Interestingly, polymeric gel exhibits a naked-eye detectable reversible blue-red colorimetric response for alternating acid/base (HSO/NHOH) and colorimetric sensitivity toward selected anions: CHCOO, CN, HCOO, and CHCHCOO. It is with the hope that this work point toward the utility and versatility of macrocyclic PDAs for constructing chromogenic supramolecular gels for their possible use in sensing systems.