Figure 6. Design principle of switchable phase transfer and binding.

Schematic outline of the application of light-controlled guest 8 with light-controlled phase-transfer properties. Compound 8 (trans-open) is soluble in toluene. Irradiation with λ=365 nm (trans–cis isomerization) and λ=430 nm (cis–trans isomerization) controls the state of the azobenzene. Cyclization of the DASA moiety with visible light results in phase transfer of compound 8. In the aqueous layer (pH ⩾9), the azobenzene binds the water-soluble α-CD in its trans-state, but not in the cis-state.