Chiral doping of nematic phases and its application to the determination of absolute configuration

Abstract

Doping nematic liquid crystals with nonracemic chiral compounds induces a twisted nematic (cholesteric) phase. The ability of solutes to twist the nematic phase may be related to the overall shape of the chiral dopant and consequently to its absolute configuration. The cholesteric induction is therefore a powerful tool complementary to chiroptical techniques to obtain stereochemical information on chiral molecules.

Design and Synthesis of Chiral Nematic Liquid Crystals

“…This is usually achieved by addition of chiral dopants to either shorten or lengthen the pitch length (the latter is sometimes termed compensation). Questions might also be raised about how a given chiral dopant allows transfer of chirality to the phase; for optimal transfer of the twist, it is best to use a dopant that has some structural similarity with the host mixture [28][29][30][31]. • How does the pitch change with temperature?…”

“…Conversely, a high ee will result in the formation of a shorter pitch length, thus giving a larger value of the twisting power, β. Note should also be taken of the fact that twisting power is often strongly influenced by the structural relationship between the chiral solute and the solvent; in other words, high twisting powers are obtained when the chiral dopant has a structure similar to that of the host nematic phase [28,31,96]. For a single chiral center, the ee of a given species may be defined as the degree of excess of one isomer over the other; for two enantiomeric species (R)-and (S)-, it may be expressed arithmetically as [97] …”

The interplay of configuration and conformation in helical perylenequinones: Insights from chirality induction in liquid crystals and calculations

“…By addition of a chiral nonracemic compound, a nematic liquid crystal is transformed into a chiral nematic (or cholesteric) phase. Here the director, i.e., the local alignment direction, rotates in space in helical way, along a perpendicular axis [2–3]. The handedness of this helix reflects the configuration of the dopant: Enantiomers induce oppositely handed cholesterics.…”

“…Only in the last few decades has the generation of cholesteric liquid crystals and the amplification of the molecular chirality observed upon doping nematic phases with chiral derivatives attracted great interest in the field of material science [3–4]. In this context, one of the major research lines focuses on the investigation of the chirality transfer between “shape persistent” dopants and nematic solvents [2,5–11]. Thus, the chirality amplification from the molecular to mesophase level can be exploited for the determination of the absolute configuration [2–3 5–6 12–24].…”

“…In this context, one of the major research lines focuses on the investigation of the chirality transfer between “shape persistent” dopants and nematic solvents [2,5–11]. Thus, the chirality amplification from the molecular to mesophase level can be exploited for the determination of the absolute configuration [2–3 5–6 12–24]. In fact, this technique has been fruitfully applied to different classes of systems, possessing either stereogenic centers or axial chirality.…”