Tetrachloroanthracene Walled Glycoluril Dimer Undergoes Self-Association and 1:1, 2:2, and 1:3 Host•Guest Binding

We report the design, synthesis and characterization of a tetrachloroanthracene walled methylene bridged glycoluril dimer (H1). According to ¹H NMR spectroscopy and symmetry considerations we formulate H1 as a C _2v -symmetric monomer in DMSO but it exists as a C _2h -symmetric dimer (H1•H1) in water. The H1•H1 dimer persists below 25 μM in water and displays high thermodynamic stability (K_s ≥ 1.8 x 10⁶ M^-1). H1•H1 is also stable up to 70 °C in water. We investigated the binding of H1 with a panel of five dyes by isothermal titration calorimetry and ¹H NMR spectroscopy and found that H1 engages with dyes with several different stoichiometries of binding. For example, NMeAc and Berb are capable of causing the dissociation of H1•H1 resulting in the formation of the 1:1 intracavity dye complexes H1•NMeAc and H1•Berb. In contrast, Rh6G and ThT do not dissociate the H1•H1 dimer and instead stack on the exterior of the dimer to form Rh6G•H1•H1•Rh6G and ThT•H1•H1•ThT, respectively. Finally, 3 equivalents of NDI+ causes dissociation of H1•H1 and binds both intracavity and on the exterior to form the H1•(NDI+)₃ complex.