Estimation of the helical twisting power of chiral inducers by time-dependent density functional theory (TD-DFT) for electrochemical polymerization in cholesteric liquid crystals

Abstract

Five chiral compounds were designed and synthesized using the Mitsunobu reaction to act as chiral inducers (i.e., chiral dopants) for the transformation of a nematic liquid crystal (LC) (4-n-octoxy-4′-cyanobiphenyl) into a cholesteric LC. These chiral inducers contain two types of chiral alkyl chains with different kinds of achiral mesogenic cores (biphenylcarboxylate, biphenoxy, and cyanobiphenoxy). We observed that the achiral mesogenic cores affected the helical twisting power in terms of both induction strength and helicity (left-/right-hand introduction). All the ester type inducers exhibited a positive Cotton effect and right-hand helical twisting power (HTP). However, ethers exhibited a negative Cotton effect and left-hand HTP. The microscopic HTPs (βM) of these inducers demonstrate a linear relation with their optical activities (ellipticity near the absorption maximum). Further, the time-dependent density functional theory (TD–DFT) calculation using the B3LYP/6-311++G (d, p) method has been used to predict the circular dichroism spectra of these inducers. The predicted optical activity was observed to be in accordance with that observed in the experimental result. This study proposes a method for predicting the HTP of chiral inducers that can be applied to achieve polymerization in the reaction fields of cholesteric LCs.