The Mississippi College Organic Research Group (MC-ORG) has an ongoing mission to design and prepare flat, two-dimensional dendrimers. In order for dendrimers to attain light-harvesting properties, conjugation of the π-bonding system must be conserved. It has been found that when twisting occurs about the single bonds of the dendrons, there is a decrease in energy transfer and therefore loss of conjugation and reduced light harvesting properties. In previous projects, the MC-ORG has been synthesizing dendrimers that show twisting, and therefore loss of π-conjugation, due to the hydrogens in the ortho positions of the phenyl rings. In order to alleviate these steric interactions, the MC-ORG group is attempting to synthesize structures that incorporate diynes. The hope is that the extended length of the diyne units, as opposed to the ethynyl units previously used, will position the hydrogens far enough from one another that their steric interactions will be reduced and twisting of the structure will not occur. The goal of this project is to assist the MC-ORG in determining whether these structures will alleviate the twisting and produce “flat” dendrimers that retain conjugation. Another goal of this research is to determine if twisting can be eradicated by changing the types of atoms and the length of the bridges that connect the phenyl rings. Nucleus-independent chemical shift calculations are also conducted to determine the aromaticity of the structures and prove whether conjugation is truly conserved. To investigate these questions, optimum structures are computed at the SCF and DFT levels of theory. The functionals employed are B3LYP, M06-2X, and ωB97XD. All calculations use correlation consistent basis sets. We gratefully acknowledge support from the Mississippi College Catalysts, the alumni support group of the Department of Chemistry & Biochemistry.

How can steric hindrance be alleviated in the formation of dendrimer precursors to conserve π-conjugation?

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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