Application of computational chemistry methods to the prediction of chirality and helical twisting power in liquid crystal systems

Abstract

Until recently, it has not been possible to determine, with any real certainty, a complete picture of chirality (absolute configuration, optical rotation direction, and helical twisting power) for new chiral compounds without first synthesizing, purifying, characterizing, and testing every new material. Recent advances in computational chemistry now allow the prediction of certain key chiral molecular properties prior to synthesis, which opens the possibility of predetermining the chiroptical properties of new liquid crystal dopants and mixtures for advanced optical and photonics applications. A key element to this activity was the development of both the chirality index (Go) by Osipov et al., and the scaled chirality index (G 0S ) by Solymosi et al., that can be used as a figure of merit for molecular chirality. Promising correlations between G 0S and both circular dichroism (CD) and the helical twisting power (HTP) of a chiral dopant in a liquid crystal host have been shown by Neal et al., Osipov, and Kuball. Our work improves the predictive capabilities of G 0S by taking into account the actual mass of each atom in the molecule in the calculations; in previous studies the mass of each atom was assumed to be equal. This weighted scaled chirality index (G 0SW ) was calculated and correlated to existing experimental HTP data for each member of a series of existing, well-known chiral compounds. The computed HTP using G 0SW for these model systems correlated to the experimental data with remarkable accuracy. Weighted, scaled chiral indices were also calculated for the first time for a series of novel chiral transition metal dithiolene dyes for near-IR liquid crystal device applications.