p‐Sulfonatocalix[4]arene Supramolecular Polymers: Formation by Host–Guest Interactions and Light Response

A combination of the advantages of supramolecular chemistry and materials science has expedited the emergence of supramolecular polymers, in which the repetition of monomeric units is mainly governed by highly directional and dynamic noncovalent interactions. The noncovalent route is a promising approach towards highly functional materials, and has led to a recent surge in the production of self-healing and adaptive supramolecular polymers. Until now, several noncovalent interactions, including metal coordination, p–p stacking, hydrogen bonding, as well as host– guest interactions, have been extensively used to fabricate supramolecular polymers. Among the macrocyclic hosts, cyclodextrins and crown ethers are most commonly used in supramolecular polymerization, whereas supramolecular polymers directed by host–guest recognition of calixarenes have only occasionally been reported. Some typical host– guest pairs are p-tert-butylcalix[5]arene and primary alkylammonium ions, covalently linked double-calix[5]arenes and C60, and water-soluble calixarenes and organic cations. Previously reported calixarene-based supramolecular polymers have been formed mainly through the preorganized scaffolds of calixarenes, and host–guest interactions offered by calixarene cavities were not exploited as the dominant driving force for polymerization. p-Sulfonatocalix[n]arenes (SCnAs) are important biocompatible and water-soluble calixarene derivatives that have fascinating binding properties, especially with organic cations. Consequently, SCnAs are widely used in highly diverse applications in molecular recognition/sensing, crystal engineering, catalysis, amphiphilicity, and biomedical applications. By using homoditopic bis-p-sulfonatocalix[n]arenes (bisSCnA, n=4, 5), we previously designed a series of water-soluble supramolecular polymers based on the molecular recognition of SCnAs by organic cations. Subsequent to our study, Tian an co-workers reported a dual-stimulusresponsive supramolecular polymer based on iterative intermolecular inclusion of bisSC4A and a heteroditopic flexible guest. Most previous supramolecular polymers consist of calixarenes and guests with flexible spacers. It has been well-established that building blocks with flexible spacers have disadvantages for polymerization. Herein, we report a linear supramolecular polymer based on molecular recognition of bisSC4A by a homoditopic bis-4-(N-methylpyridinium)azobenzene (AzobPy) with rigid azobenzene as spacer (Scheme 1). It was anticipated that the isomerization