We describe the synthesis of three tetraureacalixarenes having four appended terminal azobenzene groups. In CD2Cl2 solution and at millimolar concentration, the thermally equilibrated all–trans-tetraureas dimerize quantitatively, encapsulating one Me4P+ cation. The light-induced isomerization of the all–trans encapsulation complexes produced a plethora of isomeric cis-enriched counterparts displaying a reduction in cavity size. cis-enriched dimers not suitable for the encapsulation of the cation or a solvent molecule are also produced, leading to partial release of the cargo (Me4P+) to the bulk solution. The substitution of the terminal phenyl in the azobenzene groups plays a key role in controlling the amount of released cargo in quantities up to 70%. The switching between the two states (all–trans and cis-enriched capsules) proceeds with no detectable photodegradation, even when it is repeated multiple times.
Reversible Light-Controlled Cargo Release in Hydrogen-Bonded Dimeric Capsules
J. Org. Chem. 2015, 80, 10866-10873.