Rational design, synthesis, and structure-property relationships of C3-symmetric chiral foldamers and surface-functionalized organic-inorganic hybrid materials

Chapter 1. Two-Dimensional Electronic Conjugation.;The design of two-dimensional (2D) pi-conjugated scaffolds has been widely explored. The expansion from one-dimensional systems provides certain advantages in tuning electronic properties through structural control of linear segments. Tris(N-salicylideneaniline)s have been studied as a way to understand the effects of structural folding on the electronic properties of confomationally switchable pi-conjugation.;Chapter 2. Chiral tris(N -salicylideneaniline)s: Hydrogen-bonding promoted helical folding, and effects of pi-extended chromophores on screw-sense and exciton coupling.;C3-symmetric tris(N-salicylideneaniline)s fold to adopt helical propeller-shaped secondary structures that are strengthened by intramolecular hydrogen bonds. Using kinetic resolution, an efficient synthetic route was developed for the synthesis of chiral propargylic alcohols. An extended family of such molecules were designed and synthesized through modification of these building blocks through C-C cross-coupling reactions. Extension of pi-conjugation from the chiral centers using phenylene-ethynylene spacers enhances the stability of one helical conformation over the other as evidenced by UV-vis and circular dichroism spectroscopic studies. Increasing the number of hydrogen bonds not only increases the population of one folded conformation, but also serves to define the spatial relationship between adjacent chromophores which gives rise to large exciton-coupled circular dichroism. A torsional relationship between chromophores further validates the absolute configuration of chiral alcohols. Solvent studies revealed unusual helicity switching behavior caused by solvent-molecule interactions.;Chapter 3. Chiral C3-Symmetric Azo Dyes: pH-controlled Azo-Coupling and Effect of Chiral Centers on Helicity.;By controlling the pH of reaction conditions, a series of mono-, di-, and tri-azo coupled chiral C3-symmetric molecules were synthesized. 1H and 13C NMR spectroscopy was used to determine the tautomeric form of each compound. As the number of azo-linkages was increased, a red-shift in lambdamax was observed by UV-vis spectroscopy. A direct correlation was made between the number of chiral centers and helical conformation using circular dichroism spectroscopy. The absolute configuration of chiral alcohols controls directional folding of these molecules to one dominant screw-sense in solution.;Chapter 4. Quantification of Reactive Sites on Mesoporous Silicates Using Fluoride Detecting Molecular Probe.;Azide-appended mesoporous silicates (MPSs) were synthesized by co-condensation reactions between tetraalkoxysilanes and (EtO)3Si-(CH2) 3--N3 using P123 as a templating agent. In order to probe the number of reactive azido groups on the surface, reporter molecules were anchored onto the surface through Huisgen [3 + 2] dipolar cycloaddition (= "click") reactions between surface bound azide groups and a terminal acetylene on the reporter moiety. Release of a chromophore from the reporter molecule was achieved by reaction with fluoride ion, which triggers a quinone-methide (QM) rearrangement and controlled chain fragmentation. UV-vis spectroscopy can be used to determine the concentration of this chromophore, which directly correlates to the number of functionally relevant azido groups on the MPS surface. This non-destructive approach provides a straightforward spectroscopic method for quantifying the reactive sites of porous materials.