An adaptive metal-organic cage for mutually induced recognition

Preparing artificial hosts that can realize enzyme-like mutual induced-fit recognition remains a challenge. Herein, an adaptive metal-organic cage based on a flexible tri-((pyridin-4-yloxy)methyl)ethane ligand and cis-blocked palladium nodes was prepared. Upon complexation with different guests, the cage can realize sophisticated mutual induction behaviours, including expansion of host and compression of guest, stretching of host and distortion of guest, compression of host and stretching of guest, and distortion of host and distortion of guest. For the Z/E isomers of azobenzene/stilbene with similar size, the cage shows selective pick-up of (E)-azobenzene over (Z)-azobenzene, but (Z)-stilbene over (E)-stilbene; while the poor encapsulation capacity for (E)-stilbene can be further enhanced by a guest-driven allosteric control. Inside the cage, the Z→E photoisomerization of stilbene can be significantly improved while the E→Z photoisomerization of azobenzene tends to be inhibited. Direct conversion of crude (E)-stilbene (about 90%) into pure (E)-stilbene (>99%) can be achieved through the synergy of selective binding and photoisomerization.