Reversible Photochemically Gated Transformation of a Hemicarcerand to a Carcerand

摘要

In the 1980s, Cram pioneered the synthesis of container molecules, hemicarcerands and carcerands, the latter able to imprison guest molecules. Hemicarcerands are selective host molecules whose binding affinity mainly depends on the size of the guest molecule. Hemicarcerands are important host molecules in research fields such as drug delivery, phase-transfer catalysis, and molecular recognition. Calculations led to an understanding of how guests enter and escape from the container molecules by means of a thermal gating mechanism. Gating converts hemicarcerands (open gate) into carcerands (closed gate) (Figure 1). Gating has been achieved previously with stimuli such as heat and redox or acid/base chemistry. Photochemical processes can serve as switching mechanisms in appropriately constructed container molecules ; Rebek used the cis-trans photoisomerization of azobenzene, and Mattay used the photoreactivities of anthracene. However, the use of photoswitchable gates to interconvert hemicarcerands and carcerands has not been demonstrated. We report herein the synthesis of a reversible photoswitchable gated hemicarcerand based on the photochemical properties of anthracene. The reversible photochemical gating is demonstrated to control the stability of the host-guest complex, which could be important for delivery systems engineered to encapsulate and release guest molecules upon irradiation.