Polyphenylenes are molecules that are composed of benzene rings connected in a repeating pattern. Although extensive research has been done into one group of isomers, para-phenylenes, which is used in polymer chemistry, limited research has been done on the ortho-phenylenes. ortho-Phenylenes are conjugated chains of benzenes that have been found previously to form organized helical structures governed by aromatic staking. These foldamers have the potential for catalytic and analytical applications. To design polyphenylenes with specific applications it is necessary to understand the basic properties which govern their folding. The folded conformation (AAA) has three internal dihedral angles set to (+/- 55°) and the unfolded confirmation has interior angles of (+/- 130°). There are also 3 more semi-folded conformations for each molecule: (AAB, ABB, BAB). To investigate the effect of expanding the aromatic rings of the base molecule o-sexiphenyl a computational model which made use of Avogadro for model building and Gaussian for structure optimization. The calculations set up through Gaussian used the “B97D” functional which is helpful for assessing the interactions between aromatic rings. The results of the computational jobs showed that for all of the aromatic substituted molecules the folded conformation was even more energetically favored than the folded conformation of the p-sexiphenyl. This suggests that there is an interplay between the aromatic stacking associated with the folded AAA conformation of the molecules and the size of the overlapping units. Moving forward, further research could be done to expand the scope of this computational study to more molecules and to determine a method of synthesis of these molecules to verify the computational results.
Author: Griffin Betz
Faculty Advisor: Scott Hartley, Chemistry and Biochemistry
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