Date of Award
Doctor of Philosophy (PhD)
16-Diodo-EEE-135-hexatriene;Conducting Polymers;Diiodopolyenes;Diodohexatriene;Polyacetylene;Urea Inclusion Complexes
Chemistry | Physical Sciences and Mathematics
1,6-Diodo-E,E,E-1,3,5-hexatriene (DIHT) has been prepared for the first time with a high degree of stereoselectivity. This compound was used as the guest in the formation of a urea inclusion crystal (UIC), and it functions as the precursor in a light-induced solid-state polymerization to form polyacetylene in high levels of structural uniformity inside the urea channels. The resulting highly ordered polyacetylene is expected to possess very different electronic properties than polyacetylene produced using standard techniques. The synthesis of DIHT was optimized, with the key step being a (bis)hydroboration/iodination of an enediyne precursor, E-3-hexen-1,5-diyne, which could afford DIHT as a single isomer in 20% yield. It was also demonstrated that when a mixture of isomers (EEE, EEZ and ZEZ) is obtained from a lower quality reaction or isomerization, urea inclusion crystal formation could be used to isolate the EEE isomer of DIHT from a mixture, as other isomers are excluded from crystallization. Conditions for DIHT:UIC synthesis were also systematically investigated, including variations in crystallization time, stoichiometry, and solvent, as well as methods to control crystal morphology through use of a capping agent, 5- decoxyisophthalic acid. Successful polymerization of DIHT via broadband irradiation of DIHT:UIC was demonstrated using mass-loss experiments and Raman spectroscopy. In addition to laying the groundwork for DIHT:UIC synthesis and photopolymerization, progress was made in refining the synthesis and photopolymerization of 1,4-diodo-E,E-1,3- butadiene (DIBD), a previous model used to study confined diiodopolyene photopolymerization. DIBD:UIC-d4 was synthesized for the first time using deuterated urea, and studied using inelastic neutron scattering spectroscopy. These experiments had the goal of yielding a more complete understanding of how the vibrational states of conjugated polyenes change with chain length, however they ultimately did not yield definitive data. Synthetic efforts were also contributed to the rigorous study of DIBD:UIC photopolymerization. These experiments were able to quantify the rate at which mass is lost during photopolymerization, a direct measure of the progress of photopolymerization. In addition, they established the relationship between temperature and speed of photopolymerization, showing that as temperature increases so does the rate of the reaction. The relationship between DIHT:UIC formation and DIBD:UIC formation was explored through the use of competition and exchange experiments. When UIC crystals were grown from a solution containing both DIBD and DIHT, the ratio of guest that was incorporated into the crystals demonstrated a modest preference for DIHT inclusion at all concentration ranges. In addition, when either DIBD:UIC or DIHT:UIC were submerged in a solution containing the alternative guest, no exchange of guests was observed. Ultimately, this project showed that DIHT:UIC undergoes photopolymerization at a slower rate than DIBD:UIC, which ran counter to our predicted outcome. In addition, efforts towards measuring the conductivity of heavily irradiated DIHT:UICs did not show evidence of increased conductivity. This is likely the result of defects in the inclusion crystals, such as gaps in crystal channels or short polyene chains. Further study is required to definitively explore the potential of confined polyene chains to act as efficient conductors of electricity.
Moskowitz, Michael, "Synthesis of Polyacetylene Through Photopolymerization of Conjugated Diiodopolyenes in Urea Inclusion Complexes" (2023). Dissertations - ALL. 1729.