Hydrogen-bonding effects in liquid crystals for application to LCDs

Hydrogen bonding plays an important role in the performance of liquid crystal displays (LCDs) by controlling the solubility and dissolution stability of dichroic dyes in the liquid crystal medium, for guest-host type LCDs. The hydrogen-bonding behaviors of 4-pentyl-4'-cyanobiphenyl (5CB) (liquid crystal), benzonitrile, and acetonitrile, with 1-hexanol in CCl4 were studied using FTIR spectroscopy, equations of state, and A initio calculations. In all three mixtures, the -OH group acts as a hydrogen-bond donor, and the -CN group acts as a hydrogen-bond acceptor. On the basis of FTIR analysis, the enthalpy of hydrogen-bond formation is observed to be -14.7 kJ/mol for 1-hexanol/acetonitrile, -5.4 kJ/moI for 1-hexanol/benzonitrile, and -4.6 kJ/moI for 1-hexanol/5CB. The entropy of hydrogen-bond formation is more favorable for 1-hexanol/5CB than for 1-hexanol/acetonitrile or 1-hexanol/benzonitrile. Trends in the spectroscopic results agree with ab initio calculations. Lattice fluid hydrogen-bonding parameters also were obtained from the spectroscopic data.