Triptycenes as a molecular building block to introduce internal free volume in organic materials

Abstract

Chapter 1. Triptycenes are shown to possess "internal free volume" swept out between their aromatic faces, which enable them to align their long axis normal to the host alignment to most efficiently fill this volume. This alignment is the opposite of that expected by conventional aspect ratio considerations alone. Anthracene chromophores were attached directly into the triptycene backbone and their polarized UV-Visible spectra were probed to determine their overall orientation. This alignment is guided by the minimization of the free volume of the system and works for both liquid crystalline and poly(vinyl chloride) hosts.

Chapter 2. Building from the principles learned in Chapter 1, a design for fluorescent and dichroic dyes is introduced to increase their alignment when dissolved in nematic liquid crystals and the mixture is aligned on a rubbed poly(imide) surface. A wide variety of dyes was synthesized to demonstrate the universality of the effect and exception to the rule, particularly azo dyes and pentiptycene containing materials, are addressed. Application of a fluorescent green dye towards a fluorescent security device is shown.

Chapter 3. The synthesis of a new class of nematic liquid crystals with triptycenes built into a bis(p-dialkoxyphenylethynyl)benzene mesogenic core is reported. Triptycenes are designed into the center or terminal ring of the mesogen, to make symmetric and asymmetric liquid crystals respectively. Both types displayed monotropic behavior, with the asymmetric compounds having unusual phase behavior, lacking distinct crystallization transitions. A chiral analogue were found to be crystalline, but gave chiral nematic phases when doped into achiral analogues. This design may allow for the synthesis of a single component liquid crystal which displays a biaxial nematic phase. Rotation is physically hindered normal to the director and free-rotation can be further inhibited introduction of lateral dipoles.

Chapter 4. Norbornene-based ROMP polymers incorporating the triptycene subunit and stepwise polymerization of hydroquinones with activated fluoroarenes to produce poly(aryl ether)s are prepared. Iptycenes are shown to introduce "internal free volume" into the polymer films, thereby lowering their dielectric constants. The triptycene containing polymers exhibit low-water absorption, high thermal stability, and form very flat thin films when spin-coated onto glass substrates. Dielectric constants were determined by the construction of metal-insulator-metal (MIM) devices, low water absorption by measurement with a quartz crystal microbalance (QCM).

Chapter 5. Ladder polymers based on triptycene, poly(iptycenes), are introduced with the synthesis of monomers capable of undergoing efficient Diels-Alder polymerization to produce materials with large internal free volumes. The effect of hyperbranching and applications of high-pressure on polymerization behavior are discussed. Applications of these materials in binary polymer blends with common polymers such as polyethylene and poly(vinyl chloride) are discussed with potential applications toward the production of auxetic materials.