Photocontrol of complexation of neutral and cationic species by p-tert-butylcalix[4]arene tetraethyl ester

A number of sodium salt complexes of p-tert-butylcalix[4]arene tetraethyl ester (1) were isolated both with and without upper-rim encapsulated acetonitrile or methanol. Upon dissolution in CDCl₃, 1 remained largely complexed to the sodium cation but ca. 90% of the upper-rim bound solvent was released, reflecting the relative values of the binding constants for complexation of the two guest species. Selective decomplexation of lower-rim bound sodium cations could be successfully achieved using low-pressure light sources, triggering the immediate expulsion of the upper-rim bound solvent. The extent of decomplexation at both rims is controlled both by the oxidation of the counter-anionic species at the lower rim and by the fate of the photoproducts generated. The calixarene host molecule, 1, remains intact during the decomplexation process.