Orientational order properties of two fluorinated nematogens, exhibiting a wide nematic range, have been
investigated by means of optical methods, dielectric spectroscopy, and 13C NMR. 13C NMR spectra have
been recorded by 1H-SPINAL decoupling CP techniques under both static and magic angle spinning conditions.
The order parameters of the fluorinated aromatic fragments have been calculated by analyzing the 13C−19F
dipolar couplings at different levels of approximations by means of a least-squares fitting procedure using
geometrical parameters determined by DFT methods, eventually including empirical corrections for vibrations
and anisotropic scalar couplings. The nematic order parameters determined from optical birefringence data,
dielectric anisotropy, and NMR have been compared: their trends with temperature, analyzed by the Haller
model and by more sophisticated ones, are very similar, even if the order parameters from optical birefringence
are shifted to slightly higher values. The differences among the results obtained by the three methods can be
related to the different anisotropic properties monitored, described by tensors whose principal or “long” axes
can be located at slightly different places on the molecule. The assumptions and approximations used in each
case are discussed in detail.
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