Role of Dispersion and Electrostatic Forces on Solute−Solvent Interactions in a Nematic Liquid Crystal Phase

A series of 23 substituted biphenyl, phenylpyridine, and bipyridine derivatives were doped in the nematic liquid crystal host 4‘-(pentyloxy)-4-biphenylcarbonitrile over the mole fraction range 0.005 ≤ x d ≤ 0.04. The effect of each biaryl dopant on the nematic−isotropic phase transition temperature (clearing point) of the liquid crystal phase was determined by differential scanning calorimetry as a function of dopant mole fraction for a wide range of substituents and expressed as a constant of proportionality δ I . The molecular polarizability (α) and electrostatic character ( E HOMO ) of each dopant were estimated using ab initio calculations at the HF/3-21G* level. Analysis of the combined δ I data with respect to α and E HOMO by multilinear regression showed that a reasonable correlation exists between δ I and a linear combination of α and E HOMO ( R 2 = 0.81) which represents a statistically significant improvement over correlations between δ I and α ( R 2 = 0.72) and between δ I and E HOMO ( R 2 = 0.56). These results provide evidence that arene−arene interactions in the absence of a ternary solvent are controlled by both electrostatic and dispersion forces. In this work, dispersion forces were shown to strongly influence the stability of the nematic phase, with a secondary influence coming from electrostatic forces. Furthermore, the results suggest that charge-transfer complexation and molecular dipole−dipole interactions do not have an appreciable effect on the stability of arene−arene interactions in the nematic phase.