Selective Recognition of H2PO4- in Competitive Environments and Water-Promoted Selective Recognition of F-

In this contribution, we demonstrate the selective recognition of H2PO4- in competitive environments containing various anions, as well as water-promoted selective recognition of F-, by using a previously reported polycyclic aromatic cage (1). Through exploring the [4 + 2] cyclization synthesis strategy, the synthetic approach toward polycyclic aromatic cages has been improved. NMR titration, fluorescence titration, and nonlinear fitting analysis revealed the binding behavior and binding stoichiometry of 1+H2PO4- (1:1) and 1+F- (1:2). The resulting binding affinity of 1+H2PO4- (K1:1 > 104 M−1) and 1+F- (K1:1 > 103 M−1, β2 > 107 M−2) is in sharp contrast to that of 1+other anions (no evident binding). Moreover, 2D NMR studies revealed the structural features of [1-H2PO4-] and [1-2F-] complexes, and disclosed that water is involved in the formation of [1-2F-] complexes. At last, liquid-liquid extraction studies exhibited that 1 can selectively recognize and separate H2PO4- from water. This study may provide valuable considerations for the design of molecular cages for selective recognition and separation of H2PO4-.