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Creators/Authors contains: "Shimizu, Linda S."

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  1. Free, publicly-accessible full text available April 19, 2023
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  5. Absorption of electronic acceptors in the accessible channels of an assembled triphenylamine (TPA) bis -urea macrocycle 1 enabled the study of electron transfer from the walls of the TPA framework to the encapsulated guests. The TPA host is isoskeletal in all host–guest structures analyzed with guests 2,1,3-benzothiadiazole, 2,5-dichlorobenzoquinone and I 2 loading in single-crystal-to-single-crystal transformations. Analysis of the crystal structures highlights how the spatial proximity and orientation of the TPA host and the entrapped guests influence their resulting photophysical properties and allow direct comparison of the different donor–acceptor complexes. Diffuse reflectance spectroscopy shows that upon complex formation 1·2,5-dichlorobenzoquinone exhibits amore »charge transfer (CT) transition. Whereas, the 1·2,1,3-benzothiadiazole complex undergoes a photoinduced electron transfer (PET) upon irradiation with 365 nm LEDs. The CT absorptions were also identified with the aid of time dependent density functional theory (TD-DFT) calculations. Cyclic voltammetry experiments show that 2,1,3-benzothiadiazole undergoes reversible reduction within the host–guest complex. Moreover, the optical band gaps of the host 1·2,5-dichlorobenzoquinone (1.66 eV), and host 1·2,1,3-benzothiadiazole (2.15 eV) complexes are significantly smaller as compared to the free host 1 material (3.19 eV). Overall, understanding this supramolecular electron transfer strategy should pave the way towards designing lower band gap inclusion complexes.« less
    Free, publicly-accessible full text available October 27, 2022
  6. We demonstrated ion-mobility spectrometry mass spectrometry (IMS-MS) as a powerful tool for interrogating and preserving selective chemistry including non-covalent and host–guest complexes of m -xylene macrocycles formed in solution. The technique readily revealed the unique favorability of a thiourea-containing macrocycle MXT to Zn 2+ to form a dimer complex with the cation in an off-axis sandwich structure having the Zn–S bonds in a tetrahedral coordination environment. Replacing thiourea with urea generates MXU which formed high-order oligomerization with weak binding interactions to neutral DMSO guests detected at every oligomer size. The self-assembly pathway observed for this macrocycle is consistent with themore »crystalline assembly. Further transformation of urea into squaramide produces MXS, a rare receptor for probing sulfate in solution. Tight complexes were observed for both monomeric and dimeric of MXS in which HSO 4 − bound stronger than SO 4 2− to the host. The position of HSO 4 − at the binding cavity is a 180° inversion of the reported crystallographic SO 4 2− . The MXS dimer formed a prism-like shape with HSO 4 − exhibiting strong contacts with the 8 amine protons of two MXS macrocycles. By eliminating intermolecular interferences, we detected the low energy structures of MXS with collisional cross section (CCS) matching cis – trans and cis – cis squaramides-amines, both were not observed in crystallization trials. The experiments collectively unravel multiple facets of macrocycle chemistry including conformational flexibility, self-assembly and ligand binding; all in one analysis. Our findings illustrate an inexpensive and widely applicable approach to investigate weak but important interactions that define the shape and binding of macrocycles.« less
  7. Self-assembly of brominated triphenylamine bis-urea macrocycles affords robust porous materials. Urea hydrogen bonds organize these building blocks into 1-dimensional columns, which pack via halogen–aryl interactions. The crystals are stable when emptied, present two distinct absorption sites for Xe with restricted Xe diffusion, and exhibit single-crystal-to-single-crystal guest exchange.