Substituent effects of bridged binaphthyl-type chiral dopants on the helical twisting power in dopant-induced chiral liquid crystals

A new series of chiral dopants, (R)-6,6′-halogenated (1b-1e, X = F, Cl, Br and I) and -methylated (1f) binaphthyl compounds, were designed and synthesized to create chiral liquid crystals by doping them into an achiral nematic liquid crystal (NLC). The influence of halogen (X = F, Cl, Br and I) and methyl substituent factors, such as steric, polar, and polarizability properties, on the helical twisting power (HTP) and their temperature dependences on the chiral dopants were investigated in two host NLCs with different characteristics, fluorinated JC-1041XX and N-(4-methoxybenzylidene)-4-butylaniline (MBBA). The chiral dopants possessing less steric and larger polarizability factors increased the HTP values. The structural similarity and electrostatic arene-arene interactions between the chiral dopants and the NLC molecules also exerted important influences on these values. The temperature dependence of the HTP (HTP_t.d.) values also correlated well with the steric and polarizability substituents factors in the two host NLCs. Their correlation coefficients (R²) depended on the molecular structural similarity between the chiral dopant and the NLC.