Anthracene adamantylbisurea receptors: switching of anion binding by photocyclization

Abstract

Anion binding of adamantane bisurea receptors 1–4 bearing anthracene chromophores was investigated in DMSO solution by UV–vis and fluorescence titrations. All derivatives form stable complexes with F− (K1:2≈105–106 M−2), AcO− (K1:1≈103 M−1), and H2PO4− (K1:1≈103–104 M−1, K1:2≈105–106 M−2). Photochemical reactivity of 1–4 in the [4π+4π] photocyclizations was also investigated. Anthracene 1 is photochemically stable, 3 and 4 undergo reaction giving mixture of products, but 2 reacts selectively yielding only cyclic product 5. Product 5 was isolated and characterized by X-ray analysis. Cyclic receptor 5 also binds anions but forms complexes with different stability constants than its opened analogue 2. Anthracene 2 forms more stable complex with H2PO4−, whereas cyclic receptor 5 forms the most stable complex with AcO− (K1:1 >106 M−1).