Manipulating the Isomerization of a Tris-azobenzene Cage by Anion Binding.

Here, we report a C3-symmetric tris-azobenzene cage 1 comprising azobenzene cores and bis(urea) units. This system demonstrates efficient reversible photoisomerization and unprecedented anion-mediated switching modes. Specifically, the phosphate anion induces a concerted ZZZ → EEE isomerization with prolonged thermal relaxation (t1/2 = 37.5 h at 298 K). In contrast, the bulky benzene-1,3,5-tricarboxylate anion enforces a stepwise pathway (ZZZ → EZZ → EEZ → EEE) with rapid thermal relaxation (t1/2 = 54.4, 44.5, and 12.9 min for each step). This study represents the first demonstration of selective control over stepwise and concerted multi-azobenzene switch, mimicking biological adaptability through environmental changes.