Interlocked host anion recognition by an indolocarbazole-containing [2]rotaxane

The design, synthesis, structure, and anion-binding properties of the first indolocarbazolecontaining interlocked structure are described. The novel [2]rotaxane molecular structure incorporates a neutral indolocarbazole- containing axle component which is encircled by a tetracationic macrocycle functionalized with an isophthalamide anion recognition motif. 1H NMR and UV-visible spectroscopies and X-ray crystallography demonstrated the importance of p-donor-acceptor, CH⋯π, and electrostatic interactions in the assembly of pseudorotaxanes between the electron-deficient tetracationic macrocycle and a series of p-electron-rich indolocarbazole derivatives. Subsequent urethane stoppering of one of these complexes afforded a [2]rotaxane, which was shown by 1H NMR spectroscopic titration experiments to exhibit enhanced chloride and bromide anion recognition compared to its non-interlocked components. Computational molecular dynamics simulations provide further insight into the mechanism and structural nature of the anion recognition process, confirming it to involve cooperative hydrogen-bond donation from both macrocycle and indolocarbazole components of the rotaxane. The observed selectivity of the [2]rotaxane for chloride is interpreted in terms of its unique interlocked binding cavity, defined by the macrocycle isophthalamide and indolocarbazole N-H protons, which is complementary in size and shape to this halide guest. © 2009 American Chemical Society.