Synthesis and Structures of Triptycene-Derived Oxacalixarenes with Expanded Cavities: Tunable and Switchable Complexation towards Bipyridinium Salts.

New triptycene-derived oxacalixarene H1 was efficiently synthesized by a template cyclization step, and anilino-substituted macrocycle H2 was subsequently afforded through straightforward nucleophilic displacement of the active chlorine atom in H1. Oxacalixarene H1 adopts a fixed boat-like 1,3-alternate conformation and shows moderate complexation abilities towards various bipyridinium salts. However, the affinities of H2 towards the guests were found to be substantially stronger, which could be tentatively attributed to the additional hydrogen-bonding site, π-π stacking site, and especially the increased electron richness of the host. Furthermore, the acid-base switchable complexation process between H1 and the bipyridinium salt was also realized, which could potentially facilitate the construction of high-level stimuli-responsive supramolecular structures based on the newly synthesized oxacalixarene.