Torsion potential in polydiacetylene: Accurate computations on oligomers extrapolated to the polymer limit

The optoelectronic properties of polydiacetylenes can be strongly modulated by torsions along the polymer chains. These as well as other distortions of the nominally coplanar polydiacetylene backbones result in the major color changes observed for these materials in response to a variety of external, low-energy stimuli; such color changes form the basis for the many applications of polydiacetylenes as sensor materials. There has been little theoretical work related to backbone distortions in polydiacetylenes; actually, previous estimates of the torsional barriers in these systems differ by an order of magnitude. Understanding the impact that polymer torsions have upon the properties of polydiacetylenes necessitates accurate estimates of the torsion potentials. Here, by using computationally efficient, wave-function-based electronic structure methods on increasingly larger oligomers, we present reliable estimates of the torsional barriers in model diacetylene oligomers and provide an accurate extrapolation of these values to the polymer limit.