The Role of Fluorine Substituents on the Physical Properties of 4-Pentyl-4″-propyl-1,1′:4′,1″-terphenyl Liquid Crystals

The phase behavior of three liquid crystal derivatives of 4-pentyl-4″-propyl-1,1':4',1″-terphenyls differing in number of fluorine atoms in the mesogenic core has been described. Calorimetric and microscopic studies show that the fluoro-substitution of the rigid core affects whether a given liquid crystal undergoes crystallization or a glass transition during cooling. Compounds with the highest number of fluorine atoms crystallize, while other derivatives vitrify from the conformationally disordered crystal phase. Calorimetric studies show different mechanisms of cold crystallization processes. Dielectric measurements uncover the complex relaxation processes present in the nematic and crystal phases and glassy states. DFT calculations allow for the determination of which stochastic movements are responsible for specific relaxation processes. Infrared absorption spectra show that the C-H bending vibrations are a sensitive probe of changes to the local surrounding of a molecule related to the thermodynamic states.