Influence of photoinduced isomerization on the chiral separation of novel liquid crystalline materials with a diazene moiety

Abstract

The influence of photoinduced isomerization on the enantiomeric separation of two newly synthesized liquid crystalline materials, liquid crystals 1 and 2, was studied by high-performance liquid chromatography on a chiral stationary phase Chiralpack AD-3. Both materials have one chiral center and one diazene moiety. The compounds were separated into their E and Z isomeric forms. The conditions and time scale of the ultraviolet-induced E to Z transition were briefly evaluated. Under the optimized conditions, we were able to baseline separate the S and R enantiomers of both the studied materials in their E isomeric form. The chiral separation of liquid crystal 2 after ultraviolet irradiation was unsuccessful. In contrast, the chiral separation of liquid crystal 1 possessing a similar structure to liquid crystal 2 provided baseline separation in its Z isomeric form as well. Previously, we have shown the influence of photoinduced isomerization and its utilization in the enantioseparation on relatively simple molecules. Here, we demonstrate that (1) much more complex compounds can also be successfully separated despite the bulkiness of the achiral part of the structure and (2) photoinduced isomerization even for such complex molecules still strongly influences their chromatographic properties.

Determination of Optical Purity of Lactic Acid-Based Chiral Liquid Crystals and Corresponding Building Blocks by Chiral High-Performance Liquid Chromatography and Supercritical Fluid Chromatography

“…The chiral separation method was based on a previously optimised methodology available in our laboratory for the enantioseparation of chiral photosensitive LCs [11,12,13]. Optimal separation conditions for precursors 2a – d were heptane/propan-2-ol (9/1, v / v ).…”

“…Although the optical purity of CLCs is a very important issue in the development and utilisation of novel chiral materials, only scarce information on chiral separation of CLCs can be found in the literature [9,10]. Most of the work thus far has been devoted to chiral liquid chromatography separation of photosensitive CLCs and the effect of light-induced E -to- Z -isomerisation on chiral recognition [11,12,13]. It has been found that the structure of CLCs plays an important role in the chiral resolution.…”