²H, ¹³C NMR and Ab Initio Calculations Applied to the SmC* Phase: Methodology and Case Studies

Abstract

Recently several liquid crystals having a chiral smectic C phase (SmC*) have been studied by means of NMR spectroscopy combined with ab initio calculations. The advantage of exploiting different experimental techiques, such as ²H and ¹³C NMR, and the possibility to calculate relevant spectroscopic quantities, such as ¹³C chemical shift tensors, by means of ab initio methods, is here discussed based on recent results obtained on several ferroelectric liquid crystal compounds. Orientational order parameters, conformational and structural features can be determined in a self consistent way by applying this combined approach.

Keywords:

• Order parameters
• deuterium NMR
• carbon-13 NMR
• tilt angles
• ferroelectric
• SmC* phases

Acknowledgments

The authors are grateful to Prof. C. A. Veracini for his constant scientific support and to Dr. A. Bubnov, Dr. V. Hamplova, Dr. V. Novotna and Prof. M. Glogarova for their collaboration and helpful discussions.

Notes

To correctly take into account possible conformational and/or phase packing effects, this must be taken temperature by temperature from the corresponding ¹³C MAS spectra, rather than from ¹³C spectra in solution or in the solid state.

Note that Equations (6) and (7) differ only in the definition of and .

The ability to locate the orientation of each tensor in a particular molecular frame is an added advantage of DFT calculations of CSTs. This information is indeed a necessary requirement to unambiguously find the orientation order parameters.

In a simple benzen ring, the “regular geometry” for the chemical shileding tensor assumes that the principal component of the tensor is placed along the C‒H bond (or the representative C‒C or C‒X bonds in substitutes benzenes).