The aggregation behavior of conjugated polyelectrolytes of various forms in various solvents have long been known. Noteably, this behavior seems to depend dramatically on the type of substituents that comprise solvating side chains for these polymers. In this work, the authors attempt to explain how this effect is dependant on something more fundamentally physical regarding the conjugated backbone rather than intermolecular interactions. Using a DFT - Tight Binding approach, 500 ps of molecular dynamics were calculated for three different poly(phenylene ethynylene) derivatives in the gas phase. By monitoring the dihedral angle between adjacent phenylene units over time, histograms of conjugation lengths could be generated by periodically sampling the results of the MD trajectory. It was found that alkyl substituents reduce rigidity of poly(phenylene ethynylene) with respect to an unsubstituted polymer, whereas alkoxy substutuents increase the rigidity and average conjugation length of the polymer.

Understanding the effect of substituents on the rigidity and conjugation length of poly(phenylene ethynylene) using DFT - Tight Binding

254th National Meeting (2017)

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