Supramolecular chemistry of functionalized "Texas-sized" molecular boxes and their applications in hydrogel materials
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Positively-charged, electron-deficient, and box-like macrocyclic receptors, such as “the blue box” (CBPQT⁴⁺) and its diversiform congeners, have been widely recognized for their roles in the construction of mechanically interlocked molecules (MIMs). These receptors display a high affinity for various π-donor guests, allowing researchers to use them to create a wide range of molecular and supramolecular ensembles, including rotaxanes, catenanes, polypseudorotaxanes, and electrochemically switchable molecules. To explore novel supramolecular architectures that are not accessible using the classic CBPQT⁴⁺ motif, our group developed a more flexible tetracationic imidazolium-based “Texas-sized” molecular box and several synthetic analogues since 2010. This system has been found to afford a number of stimuli-responsive self-associated ensembles. On the basis of the prior work, we synthesized the functionalized Texas-sized molecular boxes, leading us to investigate their self-assembling properties and to incorporate them into gel-forming copolymeric materials. This dissertation details the author’s work focused on the preparation, analyses, and applications of three Texas-sized macrocycles appended with the monocarboxylic acid, dicarboxylic acid, and methacrylate functionalities, respectively. Chapter 1 provides a brief review regarding our current understanding of the solution-based and solid-state host-guest assembly of the unfunctionalized Texas-sized macrocycle with a diversity of anionic guests. Chapter 2 depicts our studies on the self-complementary dimerization of a monocarboxylic acid-functionalized Texas-sized molecular box in the solid state and the head-to-tail polymerization of its conjugate base in solution and the solid state. Chapter 3 describes our work incorporating a dicarboxylic acid-substituted Texas-sized macrocycle into a covalently cross-linked copolymeric network. Such a copolymer is found to form a hydrogel capable of absorbing inorganic and organic anions from aqueous media. Chapter 4 details the multicolor hydrogels containing both anion-binding tetracationic receptor motifs and gel-specific fluorophores, which may be used as building blocks to produce multifluorescent color 3D codes through physical adhesion. The encoded information produced by patterns of such hydrogels may be further transformed through either physical action or by exposure to a chemical stimulus. Chapter 5 includes all the syntheses and characterization data of the compounds prepared by the author, as well as the single crystal X-ray diffraction data of four functionalized Texas-sized molecular boxes.