Designed molecular switches: Controlling the conformation of hydrogen-bonded diphenylacetylenes.

摘要

Molecular switches are compounds that possess two or more conformations. Under a given set of conditions, a switch adopts the most energetically preferred conformation. However, upon changing conditions, a new conformation is stabilized leading to a conformational switch. Herein is described the design, preparation, and characterization of a new class of molecular switch, which depending on the appended functionality, changes conformation in response to pH, anion concentration, and redox gradients.;The second chapter details the design and synthesis of a new scaffold for switching based upon Kemp's hydrogen-bonded diphenylacetylene (H-bonded DPA). It is shown that, upon functionalization with a second H-bond donor, a conformational equilibrium is created. That equilibrium can be controlled in the solid-state and solution-phase by conjugating electron-donating or -withdrawing groups to the H-bond donors. Furthermore, a method is developed to relate the observed conformational biases for a series of DPA's with literature Hammett parameters.;The third chapter details the design and characterization of a pH-dependent molecular switch. Protonation of a dimethylamino group transforms the electron-donating group into an electron-withdrawing group. This electronic change is communicated to the H-bonded equilibrium; causing a change in conformation that is observable by 1H NMR spectroscopy.;The fourth chapter describes the design and characterization of an anion-dependent switch. Juxtaposing a urea and an amide within the DPA scaffold biases the conformation toward the bidentate urea. However, addition of chloride or bromide to the switch causes the urea to bind the halide, forcing the H-bond acceptor to switch conformation. This switch is confirmed in the solution and gas phases using key control compounds. Furthermore, the fluorescence behavior of this class of anion-dependent switch is explored.;The fifth chapter describes the design and synthesis of a redox-dependent switch. Grafting a ferrocene unit onto the DPA scaffold installs a redox addressable handle. The electron-withdrawing nature of ferrocene, as well as its size, biases the conformation away from the iron(II) center as determined by 1H NMR and X-ray crystallography. Cyclic voltammetry shows that the switch undergoes a reversible one-electron oxidation. Paramagnetic NMR spectroscopy of the partially oxidized switch and control compounds suggests that oxidation to the ferrocenium causes a conformational switch.