Photoswitchable Self-Complementary Hydrogen Bond Arrays

Background: Photochromism is the reversible transformation of a chemical material to another form by the absorption of electromagnetic radiation (light), where the two metastable forms have distinct absorption spectra and other properties. Photochromism in materials allows for the switching of their function solely based on irradiation with light. Polymers are used frequently as the building blocks for materials as they are versatile, multifunctional, can carry charge and be processed by solution-based deposition methods. Supramolecular polymers share the same definition as polymers with the exception that they are held together by reversible and directional non-covalent interactions such as hydrogen bonds. Synthesizing supramolecular polymers with hydrogen bonds can be carried out in two possible arrangements. Hydrogen bonds can form between different (complementary) or the same monomeric end groups (self-complementary). This poster presentation will focus on our recent efforts toward the investigation of the strength and fatigue-resistance of the hydrogen bonding interaction between self-complementary hydrogen bond arrays intended for elaboration in supramolecular polymeric materials. The supramolecular and photophysical properties will be examined using UV-Vis Spectroscopy, Nuclear Magnetic Resonance, and dilution experiments. Future steps include incorporating these photochromic compounds into functional polymers to evaluate the photocontrolled elasticity, molecular alignment and self-healing abilities of the resulting materials

Direct Investigation of the Supramolecular Assembly of Stretchable and Self-healing Conjugated Polymers

Wearable and flexible electronics attract a lot of attention in the scientific community since these new technologies have the potential to drastically modify the way that humans interact with everyday electronics. With the goal of producing flexible and wearable electronics, π-conjugated polymers are promising candidates given their synthetic versatility and functionality. In addition, polymers can be easily tuned and processed by previously published methods such as solution-based deposition and possess the ability to carry charge effectively. π-conjugated polymers interact via a π- π stacking mechanism forming a fairly rigid material. Incorporating hydrogen bonding into the polymer backbone will cause a disruption in the π- π stacking resulting in a more fluid material. However, due to the innovative research in this field, there needs to be a consideration of the reciprocal properties and thus the competition between the electronic charge and the mechanical properties of the polymers. The relationship between these features will, in turn, affect the degree of the dynamic bonds available for self-healing analysis. This presentation will focus on our recent effort toward the design and preparation of intrinsically stretchable conjugated polymers. In specific, these properties were investigated through a series of soft contact lamination techniques, allowing for the determination of the mechanical properties of the materials. A direct investigation of the elasticity, crack-on-set-strain, nanoscale morphology, molecular alignment and other important mechanical properties of the new conjugated polymers will be presented. The molecular design rules determined in this research will also be applicable to other important class of rigid materials, such as polyaromatics, and will have multiple impacts in many fields of polymer chemistry as well as provide a template for the next generation of electronics and technologies

Hemithioindigo-based Photoswitchable Self- Complementary Hydrogen Bond Arrays

Hydrogen bonded materials are slowly conquering grounds in the literature because of their dynamic features which stem from their reversible interactions. Incorporating the ability for light to chemically modify these interactions provides a unique template for innovative, efficient and self-healing materials. This thesis explores the design, synthesis, and characterization of nine derivatives of a well-known organic compound – hemithioindigo – with dual function; as a photoswitch and a novel self-complementary hydrogen bond array. The supramolecular complexes formed moderate to strong associations (63 M-1 to 1100 M-1) with spontaneous Gibbs free energy values (-10.3 kJ/mol to -17.3 kJ/mol) to infer the effect of strong electron-withdrawing and electron-donating additions on each framework. Solid state complexation (via Single-Crystal X-Ray Crystallography) further confirmed the dimer structures of each photoarray. Photochemical and photophysical properties of these dynamic arrays were explored using UV-Vis and NMR spectroscopy with photostationary state (PSS) conversions to the E isomers from 12% to 82%