Bent-core LCs

Fig. 2 Polarizing optical micrographs in the B4 phase of bent-core LC. Under crossed polarizers, texture with bluish color is observable (middle). By decrossing polarizers, two brighter and darker domains are observable (right and left). The brightness is interchanged by decrossing polarizers to counter senses [11]...

Bent-core LC molecules are one fascinating LC class featured by a banana-shaped or bent-core molecular shape which have attracted a great deal of interest for then-exciting electro-optical behavior [65,66]. When the bent-core molecule 13 was used (Scheme 4.5), a columnar phase of hybrid GNPs were obtained (Fig. 4.10) [50]. 

In this context, two series of unsymmetrical bent-core LCs have been obtained containing isoxazole (35a—g) or 1,2,4-oxadiazole (36a—g) tings (Figure 4). All the compounds of the two series exhibited enantiotropic... 

Recently, Li et al. reported the thermally, photochemicaUy, and electrically switch-able reflection colors in an azo-based chiral bent-core LC 29 [103]. This compound exhibited the cholesteric phase in the temperature range of 50 °C to 109 °C. Figure 5.22 shows the dependence of the central reflection wavelength of this compound upon UV irradiation. These changes can be attributed to trans to cis isomerization... 

Supermolecular Chirality and Macroscopic Polar Order in Bent-Core LCs... 

STIMULI-RESPONSIVE BENT-CORE LCS 6.3.1 Electric Stimulus... 

It is weU known that E Z photoisomerization of azobenzene-containing LC molecules can lead to a nematic-to-isotropic transition as well as photochromism [167]. It was reported that UV irradiation of a nematic mixture doped by chiral azobenzene bent-core LCs leads to the N -I transition and shift in selective reflection band position of the N phase [177]. These chiral bent-core molecules can induce the N helix upon doping them into a nematic base mixture, and their helical twisting power (HTP) is given by P = UPC where P is the helical pitch length, and C is the concentration of a chiral dopant. The P value for the exclusively E isomer is maximum and decreases with the increase in the ratio of the Z isomer. UV irradiation causes E Z conversion, therefore increasing the helical pitch and shifting the selective reflection band of the N phase. 

There are many different types of bent-core molecules known, and most of exotic bent-core phase structures have been well elucidated. The future research and development on bent-core LCs shall be focused on the exploration of a variety of applications. Certainly, these applications shall not be limited to today s known bent-core molecules, and the development of new types of bent-core molecules incorporating varied functionalities based on new ideas or concepts is critically important. For instance, linking bent-core molecules with nanoscience and photoisomerization chemistry is a good step. Further exploration in organic field effect transistors (OFETs) and organic photovoltaics (OPVs) could be very fmitful. 

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