Orientational order of fluorinated mesogens containing the 1,3,2-dioxaborinane ring: a multidisciplinary approach

Orientational order properties of two fluorinated liquid crystals containing the 1,3,2-dioxaborinane ring have been investigated by means of optical, dielectric, and 13C and 19F NMR spectroscopies. The optical birefringence and dielectric anisotropy values determined in the mesomorphic phases were analyzed in terms of well- established theoretical models to obtain the order parameters relative to the principal axis of the polarizability tensor and molecular dipole moment, respectively. A large set of data, including 13C and 19F chemical shift anisotropies and 13C-19F and 1H-19F couplings relative to nuclei on the aromatic rings, was acquired in the NMR experiments and analyzed to determine local order parameters (principal order parameter and biaxiality) for different rigid fragments of the mesogen aromatic core using advanced DFT methods for the calculation of geometrical parameters and chemical shift tensors. A critical analysis of the dependence of the order parameters on the data set employed and on the theoretical assumptions and approximations has also been performed. The orientational order parameters obtained using the different techniques are compared and discussed in relation to the reference frame associated with the anisotropic properties monitored.