Protonation-Induced Self-Assembly of Flexible Macrocyclic Diacetylene for Constructing Stimuli-Responsive Polydiacetylene

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 pi-pi 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.