Solute-solvent interactions and chiral induction in liquid crystals.
The induction of a cholesteric phase by doping an achiral nematic liquid crystal with an enantiopure solute is a phenomenon that, as in all general supramolecular phenomena of chiral amplification, depends in a subtle way on intermolecular interactions. The micrometric helical deformation of the phase director in the cholesteric phase is generated by the interplay of anisotropy and chirality of probe-medium interactions. In the case of a flexible chiral dopant, the solvent can influence the twisting power in two ways, difficult to disentangle: it is responsible for the solute orientational order, an essential ingredient for the emergence of phase chirality; but also it can affect the dopant conformational distribution and then the chirality of the structures present in the solution. In this work we have investigated methyl phenyl sulfoxide, a flexible, chiral molecule that, when dissolved in different nematics, can produce cholesteric phases of opposite handedness. This peculiar, intriguing sensitivity to the environment makes MPS a suitable probe for a thorough investigation of the effects of solute-solvent interactions on chiral induction in liquid crystals. NMR experiments in various nematic solvents have been performed in addition to twisting power measurements. From the analysis of partially averaged 1H-1H and 13C-1H dipolar couplings, the effects of solvent on solute conformation and orientational order are disentangled, and this information is combined with the modeling of the chirality of intermolecular interactions, within a molecular field theory. The integration of different techniques allows an unprecedented insight into the role of solvent in mediating the chirality transfer from molecule to phase.
Celebre
Giorgio
G
Dipartimento di Chimica, Università della Calabria, via P. Bucci, 87036 Rende (CS), Italy. giorgio.celebre@unical.it
De Luca
Giuseppina
G
Maiorino
Michela
M
Iemma
Francesca
F
Ferrarini
Alberta
A
Pieraccini
Silvia
S
Spada
Gian Piero
GP
D003460:Crystallization; D009682:Magnetic Resonance Spectroscopy / Q000379:methods / Q000592:standards; D015394:Molecular Structure; D012015:Reference Standards; D012997:Solvents / Q000737:chemistry; D013454:Sulfoxides / Q000737:chemistry*
D012997:Solvents; D013454:Sulfoxides; C417240:methyl phenyl sulfoxide