Oligomers can acquire precise alternate structures that fold into intricate secondary conformations with various functionalities, also known as foldamers. Not until recently has research been conducted on polyphenylenes that possess ortho connectivity compared to polyphenylenes in the para and meta positions. The purpose of our current study is to assemble oP6(NO2)2A, oP6(NO2)4A, oP6(NO2)2B and oP6(NO2)4B hexamers via the addition of nitro substituents to oP6(H)6 with different connectivity and structural geometry to investigate how they affect foldamer behavior. By effectively manipulating the structural orientation of foldamer molecules is key to building larger, more complex molecules that can be potentially utilized to develop new catalysts or molecular recognition sensors. It was anticipated that nitro substituted o-phenylenes favor the completely folded hexamer since previous research has found that electron withdrawing groups were more likely to form the folded conformer. This study was completed with use of computational programs, Avogadro, where they were initially built and GaussView, where the conformations were optimized. The perfectly folded (AAA) with internal torsional angle ± 55°, perfectly unfolded (BBB) with an angle of ± 130°, and partially folded (AAB, BAB, ABB) hexamer conformations were optimized using the B97D method and cc-pVDZ basis set. Adjustments to the isomerization of these substituents could be utilized to control the structural geometry of the synthesized molecules that form these complex foldamers. The increase in secondary helical folding of the orthophenylenes is regulated by the aromatic stacking interactions with every third repeat unit. Additionally, our results conclude that by introducing electron withdrawing groups to o-phenylene this increases the likelihood of a perfectly folded conformer due to the energy stabilization. Verification of these results could be performed by the synthesis of extended o-phenylene moieties of different lengths with various substituents and the correlating folding geometrical effects is currently in progress.
Author: Nadeen Saleh
Faculty Advisor: Scott Hartley, Chemistry and Biochemistry
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