Connectivity-Rewired Construction of Hydrogen-Bonded Azo-Macrocycles Enables Photoswitchable Recognition of Lithium Ions

Photoresponsive hydrogen-bonded azo-macrocycles capable of selectively recognizing lithium cation were constructed by reversing the amide–azobenzene connectivity, which redistributes electron density and preorganizes four carbonyl oxygen donors into a smaller, more convergent cavity. Compared with a connectivity-isomeric reference macrocycle, the new receptor displays a pronounced preference for Li+, in which complexation with LiClO4 shows a slow exchange on the 1H NMR timescale and an association constant (Ka) exceeding 104 M−1, whereas the reference binds Li+ weakly (<5 M−1). In contrast, both hosts exhibit only modest binding toward Na+ (102~103 M−1) and fast exchange, consistent with size/geometry matching of the compressed cavity to Li+. The newly designed azo-macrocycles reveal a highly selective recognition of Li+ thanks to the more evenly arrayed four amide oxygens enclosing a cavity of small dimension. Notably, E/Z photoisomerization of macrocycle switches the binding regime, enabling reversibly light-triggered Li+ binding under UV irradiation and recapture under visible light. This work establishes a new photoresponsive receptor based on H-bonded azo-macrocycles for photoswitchable recognition of Li+.