Confinement Induced Chiroptical Photoswitching – An Encapsulation Approach for Advanced Photochemical Functions

Molecular control of chiroptical properties lies at the heart of advanced photonic applications including molecular information processing, optical memories, sensing, or absolute asymmetric synthesis. Chiroptical photoswitching is especially interesting in this regard as it uses light in a dual sense, first as trigger for modulation of the chiroptical response and second as the chiral optical output signal. Commonly, chiroptical properties are established in photoswitches by introduction of chirality at the core chromophore. The resulting photoswitches show permanent chiroptical responses with varying degree of effectiveness. In this work, we use molecular confinement to introduce a second level of control and dramatically enhance chiroptical photoswitching. Two different molecular photoswitches were substituted with remote chiral groups, but their reversible photoresponses remain achiral in solution. However, upon take-up into a hexameric capsule, the photoswitches undergo host-induced folding, which leads to effective chirality transfer to the chromophores. As a result, viable chiroptical photoswitching is achieved in the encapsulation assemblies showing the power of molecular confinement for advanced chiroptical property manipulation. Adding a competing guest expels the photoswitchable guest molecules and returns the whole system back to the non-responsive chiroptical state. This concept can be used for virtually any photoswitch to turn on dormant chiroptical responses, make them light-addressable, but also supramolecularly controllable by guest exchange processes.