Encapsulation with the Protrusion of Cruciform 9,10-Bis(arylethynyl)anthracene Derivatives in a Self-Assembled Boronic Ester Cavitand Capsule: Photochemical and Photophysical Properties

摘要

The self-assembled boronic ester cavitand capsule 3 quantitatively and tightly encapsulates 2,6-diacetoxy-9,10-bis(arylethynyl)anthracene derivatives 4a-4c as highly fluorescent cruciform guests to form complexes 4a@3, 4b@3, and 4c@(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 4a@3, 4b@3, and 4c@(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 4a@3, 4b@3, and 4c@(3)_2 compared with free guests 4.