Synthesis Of Squaramide-based Host And Its Application In Host-Guest Recognition And Orthogonal Self-Assembly

Urea/thiourea groups have been applied in a wide range in supramolecular chemistry due to their formations of hydrogen bond host-guest complex and self-assembly polymer. Aromatic squaramide moieties containing polarized N-H binding units, whose binding affinity are better than their counterparts of urea/thiourea binding moieties, have become of great significance in the host-guest recognition for their strong hydrogen bond donor ability in recent years, and the superiority of squaramide moieties over urea groups as H-bond donors was also supported by further theoretical studies. Herein we selected squaramide units as binding sites to synthesize and explore different types of anion and molecular receptors and their recognition application in different host-guest system. This dissertation is focused on the design and synthesis of functionalized squaramide ligands and application in host-guest chemistry, and it consists of four parts of research work as follows:Part 1. Novel calix[4]arene-based anion receptors 2-1,2-2,2-3 with bis-squaramide moieties were designed and synthesized. Their sensing properties with various anions were investigated by UV-vis, ESI-MS and 1H NMR spectra. The experimental results revealed that there were two types of interaction modes where receptor 2-1 bound biologically important H2PO4-, F- and AcO- ions selectively over other anions in hydrogen bonding interaction mode, while receptors 2-2 and 2-3 displayed deprotonation behavior with basic anions (F-, AcO- and H2PO4-) via acid-base interaction mode. Receptors 2-2 and 2-3 were proved to be efficient "naked-eye" sensors for F- and AcO-with marked color changes.Part 2. A series of squaramide-based tripodal anion receptors 3-1,2,3 have been prepared and their anion binding properties with various inorganic anions were investigated. Single crystal structure of complex 2TBA-[3-1·SO4] suggested an unusual dimeric encapsulation of SO42- by receptor 3-1 with 2:2 binding stoichiometry in solid state, while both 1H NMR titration experiments and DOSY NMR experiments at different concentrations suggested SO42- was encapsulated by receptor 3-1 with 1:1 binding stoichiometry in solution. All receptors 3-1,3-2,3-3 could selectively encapsulate SO42-via hydrogen bonds over other examined anions.Part 3. A bis-squaramide-functionalized pillar[5]arene has been synthesized and and its binding properties with linear alkyl dicarboxylates in highly polar solvent DMSO were investigated., in which the hydrogen bonding interactions between the bis-squaramide hydrogens and the oxygen of dicarboxylate play an important role in the binding alongside C-H…π interactions. A series of mono-squaramide-functionalized pillar[5]arenes have also been synthesized and and their binding behavior with organic acids were investigated as well.Part 4. A novel linear supramolecular polymers, have been constructed at "high" concentrations from a heteroditopic monomers:5-2, which bears one alkyl urea moiety and one UPy unit. It was based on the orthogonal self-assembly of the quadruple hydrogen bonding ureidopyrimidinone and pillar[5]arene-alkyl chain host-guest recognition motifs, with both of these two kinds of non-covalent interactions in the main chain.In summary, this dissertation has studied the application of squaramide-based host deeply in the research of anion recognition, molecular recognition and orthogonal self-assembly, and paved a way for succeeding works.