RESUMEN
Two molecules of cavitand tetraboronic acid and four molecules of various bis(catechol) linkers self-assemble into capsules through the formation of eight dynamic boronic ester bonds. Each capsule has a different cavity size depending on the linker used, and shows particular guest encapsulation selectivity. A chiral capsule made up of the cavitand and a chiral bis(catechol) linker was also constructed. This capsule induces supramolecular chirality with respect to a prochiral biphenyl guest by diastereomeric encapsulation through the asymmetric suppression of rotation around the axis of the prochiral biphenyl moiety.
RESUMEN
The self-assembled boronic ester cavitand capsule 3 quantitatively and tightly encapsulates 2,6-diacetoxy-9,10-bis(arylethynyl)anthracene derivatives 4 a-4 c as highly fluorescent cruciform guests to form complexes 4 a@3, 4 b@3, and 4 c@(3)2. The structural features of capsule 3, which possesses two polar bowl-shaped aromatic cavity ends and four large equatorial windows connected by dynamic boronic ester bonds, made it possible to encapsulate cruciform 4 with protection of the reactive anthracene core inside the capsule and with two protruding arylethynyl groups, the π-conjugated arms of compound 4, through two of the equatorial windows of the capsule. Thus, complexes 4 a@3, 4 b@3, and 4 c@(3)2 show greater resistance to photochemical reactions in solution and fluorescence quenching in the powder state compared to free guests 4. In addition to the improved photostability, restriction of the free rotation of the arylethynyl groups of guests 4 upon encapsulation results in sharpening of the UV/Vis absorption peaks with a red-shift and a significant increase in some of the two-photon-absorption peaks of complexes 4 a@3, 4 b@3, and 4 c@(3)2 compared with free guests 4.
