Size dependence of optical activities in helical polymers

Chiroptical properties of helical polymers do not always align with the sum of the local contributions of their unit cells. This study investigates the discrepancy in optical rotatory strength between local and global structures using a right-handed helical polyacetylene model. The chirality is examined through density functional theory (DFT) calculations. The analysis reveals that, at higher degrees of polymerization, the contribution of chirality from the helical strand generally surpasses the partial chirality from the local structure. The ratio of local contribution to total contribution is deduced within the framework of crystal orbital theory, and a numerical method using Wannier functions is presented for evaluation.