Liquid crystals are halfway in between crystals and liquids and therefore sometimes called mesophases. They possess numerous technological applications as, for example, in electronic displays. In order to broaden their range of applications, measuring techniques characterizing the phase transitions of liquid crystals are needed.

Valentina Domenici, University of Pisa, Italy, and colleagues analyzed the behavior of an azobenzene derivative in the mesophasic range by using a combined approach of ²H- and ¹⁴N-NMR and DFT (density functional theory) calculations. The researchers measured the NMR spectra at various points in the temperature range where the phase transition from liquid to liquid crystal occurs. Due to the anisotropy of the liquid crystal phase, the NMR spectra are complicated. Therefore, the researchers carried out additional DFT calculations to interpret the spectra in terms of different temperature-dependent anisotropic NMR parameters. This allowed them to deduce the temperature dependence of the liquid crystal’s molecular order parameters, which are numbers commonly used to characterize phase transitions.

• A Photosensitive Liquid Crystal Studied by ¹⁴N NMR, ²H NMR, and DFT Calculations,
  A. Marini, B. Zupančič, V. Domenici, B. Mennucci, B. Zalar, C. A. Veracini,
  ChemPhysChem 2012.
  DOI: 10.1002/cphc.201200546