Doctor of Philosophy
Wisner, James A.
The use of light as an external stimulus provides a non-invasive technique to induce large changes in physical and chemical properties of a substrate. The incorporation of a photochromic subunit into supramolecular polymeric systems therefore adds a potential "smart" quality for polymer manipulation. The azo moiety (-N=N-) is one of the most popular photochromic units as the trans to cis isomerization results in a large degree of spatial rearrangement. This present thesis exploits the azo group by its incorporation into complementary hydrogen bonded complexes. Hydrogen bonding acceptor groups attached to the periphery of the central azo photoswitch provided strong complexation with donor arrays in the trans state. Isomerization to the cis isomer disrupted complex stability by rearrangement from the optimal binding geometry. Furthermore, one of the azo nitrogen atoms also participated in hydrogen bonding which is a new use for these types of photoswitches.
The arrays used as photoswitchable hydrogen bonding acceptors in this work were synthesized through high yielding synthetic methods with inexpensive, commercially available starting materials. The donor arrays chosen for this work were 2-aminoindoles which are small, planar compounds. They were chosen as they have a multitude of positions were substitutions can take place which can result in a large library of compounds. Complex stability of these arrays were analyzed in solution using 1H NMR titration methods and these results were validated in the solid state by X-ray diffraction analysis. It was determined that substitution patterns on the donor arrays, the number of acceptor sites, and solvent interactions all have a large overall effect on the resulting complex stability. Association constants ranged from 90 to 1.7 x 105 M-1.
Additionally, the spatial arrangement of the acceptor atoms resulted in a decrease of complex stability. The trans to cis isomerization provided a less optimal binding geometry towards the donor arrays. This was determined through a newly developed 1H NMR extrapolation method which allowed for the determination of lower association constants for the cis isomeric complexes. The reversibility of the system was also tested and showed stability and reproducibility.
Pleizier, Jeffrey S., "Photo-Isomerizable Complementary Hydrogen Bond Arrays" (2018). Electronic Thesis and Dissertation Repository. 5983.