Role of interactions seen by vibrational and relaxation dynamics in the thermodynamic states of the asymmetric para-terphenyl

ABSTRACT

The liquid crystal 2’,3’-difluro-4-nonyl-4”-heptyl-para-terphenyl (abbreviated as 7T9) was examined by differential scanning calorimetry, polarized optical microscopy, X-ray diffraction, Fourier-transform absorption infrared spectroscopy and broadband dielectric spectroscopy in order to describe its phase behaviour as well as vibrational and relaxation dynamics in appropriate thermodynamic states. The two-dimensional correlation analysis of infrared spectra was used to check changes of the arrangement and specific interactions of molecules during phase transitions. The compound under study formed two crystal phases and three liquid crystal phases, smectic C, smectic A and nematic. The absorption band associated with asymmetric C-H bending vibrations in methyl groups was sensitive to various intra- and intermolecular interactions related with the thermodynamic states of the 7T9 compound. The Arrhenius type low-frequency relaxation was detected in the high-temperature crystal phase.

Graphical abstract

KEYWORDS:

• Liquid crystals
• phase transitions
• vibrational dynamics
• relaxation dynamics

Acknowledgments

The PL-Grid Infrastructure and the ACC Cyfronet AGH (Krakow, Poland) are acknowledged for computational resources.

Disclosure statement

No potential conflict of interest was reported by the author(s).