Quantum-mechanical studies of NMR properties of solutes in liquid crystals: A new strategy to determine orientational order parameters

Abstract

We present a quantum-mechanical method to calculate the tensorial NMR magnetic properties of molecules in liquid crystals. The method exploits a density functional description for the solute and the integral equation formalism version of the polarizable continuum model to include the effects of the dielectric anisotropy of the solvent on the wave function of the solute molecule and on its response to an applied magnetic field. Taking into account the dependence of the calculated molecular tensors on the solute orientation, we have derived the necessary expressions to relate such tensors to the spectral observables. These equations are then used to determine order parameters by calculating the nuclear shieldings of various solutes in the nematic ZLI-1167. Comparisons with experimental data of the same parameters are finally presented.

Quantum Mechanical Continuum Solvation Models

“…On the one hand, generalizations to include more detailed aspects of solvation, such as specific solute−solvent interactions, through couplings with discrete pictures have been presented using solute−solvent clusters obtained through QM minimization methods or taken from MD simulations. On the other hand, extensions to more complex environments have been also realized; we recall here, as an example, the recent extension of the IEFPCM for anisotropic dielectrics to the study of NMR properties of solutes immersed in liquid crystalline solvents. , Both of these extensions indicate new perspectives of applications of continuum models toward systems of increasing complexity, heretofore considered as completely prohibitive for a continuum description.…”

“…On the other hand, extensions to more complex environments have been also realized; we recall here, as an example, the recent extension of the IEFPCM for anisotropic dielectrics to the study of NMR properties of solutes immersed in liquid crystalline solvents. 102,701 Both of these extensions indicate new perspectives of applications of continuum models toward systems of increasing complexity, heretofore considered as completely prohibitive for a continuum description.…”

Oriented molecules

“…127 The method has been applied to a mixture of beryllium fluoride complexes. Despite severe overlap in the 9 Be spectrum, a quadrupolar splitting was observed for BeF 3 À whereas no such splitting was resolved for BeF 4 2À . NMR spectra of 13 Ciodomethane dissolved in thermotropic and lyotropic liquid crystalline solvents have been used to measure 1 H-1 H and 13 C-1 H dipolar couplings.…”

“…A quantum-mechanical method to calculate the tensorial properties of molecules dissolved in liquid crystals has been presented. 9 Using the method, the order parameters of various solutes in the nematic liquid crystal ZLI-1167 have been obtained and compared with experimental data. The effect of the magnetic field strength on the magnitude of residual dipolar couplings introduced by partial orientation in a dilute liquid crystalline media has been investigated.…”

Selected features of the polarizable continuum model for the representation of solvation

“…A correct value of the property is present, and so we introduce the concept of error due to the choice of gauge. Different methods have been devised to reduce the gauge error: PCM versions have been elaborated for the GIAO, LORG, IGLO and CSGT methods 59–64…”