The cation-directed self-assembly process has emerged as a fascinating approach for constructing supramolecular architectures and manifested a diverse range of assembly related applications. Herein, we synthesized a macrocyclic structure containing bis-amidopyridine and photopolymerizable diacetylene template, PyMCDA. Owing to the metal coordination affinity of bis-amidopyridine and the π−π stacking characteristic of diacetylene template and complementary to the cyclic molecular framework, Cs + -directed organic nanotubes are generated via unidirectional selfassembly of PyMCDA. The monomeric PyMCDA nanotubes are transformed into the covalently cross-linked chromogenic polydiacetylene nanotubes (PyMCPDA-Cs + ) by UV-promoted topochemical polymerization. The result of a metal−ligand coordination characteristic, geometric parameters in solid-state assemblies, and topochemical polymerization behavior reveals a generation of Cs + ion inserted nanotubes. Interestingly, PyMCDA-Cs + nanotubes display thermochromic property with a brilliant blue-to-red color transition.

The shape-persistent self-assembling characteristic of the macrocyclic structure has been extensively employed for creating columnar nanoarchitectures. The macrocyclic structure offers a definite structural confinement as well as conformational flexibility to the molecular frame and ensures the unidirectional self-assembly into hollow tubular channels. Upon introducing the judicious choice of functional groups, the macrocycle often functions as an adaptive receptor/host and accommodates structure-specific external guest within the predefined confined space. A new macrocycle, PMCDA, was constructed from a more flexible polymerizable diacetylene (DA) template by connecting with pyridine rings. Owing to the proton receptor nature of pyridine ring and π–π stacking characteristic of DA template, protonation-induced tubular structures are generated through the columnar assembly of PMCDA. Upon UV light irradiation, the monomeric PMCDA-H + are transformed into the robust covalently cross-linked blue-phase polydiacetylene (PMCPDA-H + ). Quite interestingly, the blue-phase PMCPDA-H + displays multistimuli-responsive colorimetric sensory responses: reversible thermochromism, selective solvatochrom for dimethyl sulfoxide and dimethylformamide, and organic/inorganic base sensing. The chromatic changes of PMCPDA-H + demonstrate potential applications in developing thermo-chemocolorimetric sensors.

Supramolecular gels originating from the hierarchical selfassembly 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 (PyMCDA). Basic nitrogen of a pyridine ring with a strong affinity toward proton transforms the neutral PyMCDA into gelator in its protonated pyridinium salt form (PyMCDA-H + ), 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 PyMCPDA-H + gel exhibits a naked-eye detectable reversible blue−red colorimetric response for alternating acid/base (H 2 SO 4 /NH 4 OH) and colorimetric sensitivity toward selected anions: CH 3 COO − , CN − , HCOO − , and CH 3 CH 2 COO − . 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.

Co-solvent controlled fabrication of thermo-responsive chromogenic nanotubes of a cyclic dipeptide–polydiacetylene supramolecular system.