Singlet oxygen stimulus for switchable functional organic cages.

Molecular cages and incorporating a 9,10-diphenylanthracene (DPA) chromophore were synthesized through a templated ring-closure metathesis approach that allows variation in cavity size through the introduction of up to three different pillars. Reversible Diels-Alder reaction between the DPA moiety and photogenerated singlet oxygen smoothly converted and to the corresponding endoperoxide cages and , which are converted back to and upon heating. Endoperoxide formation constitutes a reversible covalent signal that combines structural changes in the interior of the cage with introduction of two additional coordination sites. This results in a large modulation of the binding ability of the receptors attributed to a change in the location of the preferred binding site owing to the added coordination by the endoperoxide oxygen lone pairs. Cages and form complexes with sodium and cesium whose association constants are modified by 4-20 fold for Na and 200-450 fold for Cs upon conversion to and . DFT calculations show that in the anthracene form, cages and can bind 2 metal cations in their periphery so that each cation is coordinated by 4 oxygens and one amine nitrogen, whereas the endoperoxide cages and bind cations centrally in a geometry that favors coordination to the endoperoxide oxygens.