The design, synthesis, structure, and anion-binding properties of the first indolocarbazole-containing interlocked structure are described. The novel 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 π-donor−acceptor, CH···π, and electrostatic interactions in the assembly of pseudorotaxanes between the electron-deficient tetracationic macrocycle and a series of π-electron-rich indolocarbazole derivatives. Subsequent urethane stoppering of one of these complexes afforded a 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 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.
Brown, A., Mullen, K. M., Ryu, J., Chmielewski, M. J., Santos, S. M., Felix, V., Thompson, A. L., Warren, J. E., Pascu, S. I., & Beer, P. D. (2009). Interlocked host anion recognition by an indolocarbazole-containing rotaxane. Journal of the American Chemical Society, 131(13), 4937-4952. https://doi.org/10.1021/ja809905x