Supramolecular Substitution Reactions between Hydrazide-Based Molecular Duplex Strands: Complexation Induced Nonsymmetry and Dynamic Behavior
journal contributionposted on 15.08.2008 by Yong Yang, Jun-Feng Xiang, Min Xue, Hai-Yu Hu, Chuan-Feng Chen
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Supramolecular substitution reactions between hydrazide-based oligomers 1a−c and 2a−c were systematically investigated. Each oligomer existed as hydrogen-bonding mediated molecular duplex strands or a polymeric zipper structure in apolar solvents. But when another oligomer with complementary hydrogen bonding sites was added, a heterodimer structure formed due to supramolecular substitution reaction driven by the formation of more hydrogen bonds, which was evidenced by NMR experiments, sometimes gel−sol transition. When a nonsymmetric oligomer and a symmetric oligomer were involved, complexation-induced nonsymmetry was observed. When two nonsymmetric oligomers were involved, two hydrogen-bonded isomers were observed in solution. Variable-temperature 1H NMR experiments further revealed unique dynamic behavior for the individual oligomer and the complexes. When diacetyl-terminated oligomer 1c was involved, slides perpendicular to hydrogen bonds between two constituent molecules were observed, which led to complicated 1H NMR spectra at lower temperature; otherwise, high selectivity was obtained. Combined with the results we reported previously, a detailed picture of the structure−property relationship for our hydrazide-based oligomers was depicted, which would provide guidelines for the design of hydrazide-based fine-tuning functional materials.