Predictions of molecular chirality and helical twisting powers: A theoretical study

Abstract

A theoretical study of a number of chiral molecules has been undertaken using a molecular Monte Carlo simulation approach coupled with calculations of molecular chirality based on a chirality order parameter. Results for a variety of TADDOL (α,α,α′,α′-tetraaryl-1,3-dioxolan-4,5dimethanol) derivatives show good agreement with experimental findings for the sign, magnitude, and the temperature dependence of the helical twisting power (HTP). For a photochromic chiral dopant with variable HTP we are able to model the reduction in the HTP when photoisomerization occurs. Our studies on a liquid crystalline material with a single chiral center have reproduced a temperature dependent twist inversion in the material. We discuss the temperature and solvent dependence of the helical twisting power and argue that in all the systems studied here, preferential selection of certain molecular conformations at different temperatures and in different solvents are able to explain the observed experimental behavior of the HTP.

Synthesis of a Terpene-Based New Chiral Inducer and Preparation of an Asymmetric Polymer

“…However, twisting power of pure aliphatic chiral compounds tend to be weak due to flexibility of alkyl chain [24]. Bornyl group has some advantageous properties to application for chiral inducers.…”

“…Stereogenic center at bornyl group bonding OH group have rigid structure [25]. Conformational flexibility of molecules can weaken twisting power of chiral inducers [24]. The structural property of bornyl group is desirable for chiral inducers.…”

Progress in computer simulations of liquid crystals

“…An interesting extension to the Nordio/Ferrarini theory comes from exam-ining how χ varies with conformation, through an internal Monte Carlo approach [125]. Not only does this provide a route to calculating β M for flexible molecules, it also provides some intriguing insights into chirality.…”

“…Moreover, because the balance of conformations in a molecule usually changes with temperature, this leads to the prediction of a temperature dependent β M . In the extreme case, where high temperature conformers have the opposite sign of β M to those preferred at low temperature, Earl and Wilson have shown [125] that the changing balance of conformations can explain the remarkable property of helical twist inversion which can occur in some chiral nematic materials [126,127]. Thisayukta el al.…”

“…have reported the experimental observation that doping a chiral solvent with an achiral banana molecule leads to an increase in the twist of the phase [128]. Looking at the achiral bananas with the combined chirality tensor/Monte Carlo technique provides an interesting insight [125,129]. Individual conformations of bananas, such as the one shown in figure 12, can exhibit extraordinary large values of χ, which arise when the molecules themselves twist into a helical shape.…”