Calculation and Modeling of Rigidity in Conjugated Polymers
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Calculation and Modeling of Rigidity in Conjugated Polymers


π-Conjugated polymers are an emerging class of materials for use in solar cells, transis-tors, LEDs, and sensors. Both the electronic and thermomechanical properties of π-conjugated polymers are governed by the fundamental rigidity of the polymer backbone. For example, we find that two highly similar compounds have radically different thermomechanical and electronic properties with only a small change in backbone structure. It would be advantageous to be able to characterize this property for use in designing novel polymeric compounds. One method to do this would be computational techniques, particularly molecular dynamics (MD). However, MD simulations of π-conjugated polymers are often highly distorted due to nonbonded interactions, particularly steric interactions. This dissertation describes a universal method to use computa- tionally chemically modified π-conjugated polymers to isolate the fundamental energy governing polymer rigidity. Not only does this method result in MD simulations that are significantly more accurate, it additionally allows for simple understanding of the underlying fundamental forces governing π-conjugated polymers. This improved understanding can lead to the use of this fundamental property in physical-organic chemistry experiments. Additionally, isolation of the fundamental energy governing π-conjugated polymer rigidity opened avenues to study effects that previous were entirely subsumed by nonbonded interactions. A novel type of torsion in π- conjugated polymers was characterized using this technique, resulting in yet another increase in accuracy in MD modeling of π-conjugated polymers. Additionally, the models show that this may be a significant source of torsion in the popular class of donor-acceptor polymers. An additional method was developed to quickly characterize the coupled styles of torsion in conjugated poly- mers. Finally, the method was used to correct for long-range interactions between monomers in π-conjugated polymers, resulting in a moderate increase in accuracy. These studies for the first time additionally allowed comparison of short-range and long-range rigidity in π-conjugated polymers. Overall, this work allows for characterization of the fundamental property governing π-conjugated polymers for rational design.

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