Master of Science
Wisner, James A.
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%.
Summary for Lay Audience
Materials that have the potential to cycle between one or more metastable states have a promising future. When these metastable isomers absorb at different wavelengths of visible light and possess a higher or lower activity rate towards a target substrate, their productivity can be externally controlled. Molecular switches are molecules which can be controlled by a change in pH, temperature, enzymatic activity, or an electric current between its highly stable isomers. Photoswitches allow researchers to manipulate the properties of a molecule (through its structure) and thus its function by a non-invasive external handle: light.
In contrast to traditional electronics, dynamic smart materials respond directly with their environment. Monomeric units are first synthesized and are then held together by non-covalent interactions. Unlike dipole-dipole interactions, ion-dipole interactions and van der Waals forces, hydrogen bonds have been documented to form durable bonds. Hydrogen bonds are reversible, transient interactions between a hydrogen atom and an electronegative atom (fluorine, oxygen, nitrogen) with the hydrogen bond donor (HBD) forming a bond with a hydrogen bond acceptor atom (HBA). Hydrogen bond arrays exist in two forms; complementary and self-complementary. Complementary hydrogen bond arrays contain either consecutive HBAs or HBDs whereas self-complementary arrays contain alternating HBAs and HBDs atoms to create the resulting complex.
This thesis seeks to evaluate the photoefficiency and complexation strength of a hemithioindigo self-complementary hydrogen bond array in solvents of varying polarity. The thermodynamic most stable product (Z isomer) is irradiated with visible light (410-660 nm) converting it to the other isomer (E). The specific wavelength of visible light causes a physical rearrangement in the structure capable of an overall electronic shuffling contributing to the weaker or stronger hydrogen bond interactions of the isomer with identical neighboring molecules. The photochemical and photophysical properties will be discussed along with the dimerization constant (Kd); a value that designates the strength of the hydrogen bond interactions. Overall, a library of nine urea-based hydrogen bond arrays were synthesized with the highest Kd value of 1100 M-1. The stability of these hydrogen bond arrays as the Z isomer proved to be adequate for biomedical and materials-based applications.
Noori, Suendues, "Hemithioindigo-based Photoswitchable Self- Complementary Hydrogen Bond Arrays" (2020). Electronic Thesis and Dissertation Repository. 7572.
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