Hockey stick-shaped azo compounds: effect of linkage groups and their direction of linking on mesomorphic properties

Abstract

Several new hockey stick-shaped azo compounds are designed and synthesised with an aim to study the effect of different types of linkages and their direction of linking on the mesomorphic properties in such systems. The new compounds synthesised are characterised by spectroscopic methods. The liquid crystalline properties are investigated using polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) studies. They exhibited a variety of mesophases such as nematic (N), smectic A (SmA), anticlinic smectic C (SmC a ), B 1 , etc. We found that the direction of linkage groups has a major effect on the mesomorphic properties when compared to the effect of different types of linkage groups. We observed a reversible photoswitching phenomenon of these compounds in their solution UV-vis spectra.

Synthesis of 4-Chloro-1,3-Diazobenzene Bent-Cores Liquid Crystal and Characterizations of Its Mesogenic Behaviors and Photosensitivity

“…5 Interestingly, dissolved 4c reached photostationary state in 10 seconds, significantly faster than reported response rates of similar ABLCs, which are in minutes and even hours. 11,13,14,[16][17][18]22,24,[44][45][46][47] Compound 4c can turn from crystalline solid into nematic phase (Figure 3 The ratio of the isomer concentrations can be estimated by the following equation:…”

“…[7][8][9][10][11] To date, the majority of ABLC compounds implemented at least one ester as the direct linkage of the central bent-core and or deployed azo groups in the distant side arms, 5,[12][13][14][15][16][17] which usually exhibited high temperatures of phase transition, far above room temperature 25 °C, and narrow temperature ranges of nematic phases. To lower the phase transition temperature and broaden the temperature range of nematic phases, recent studies emphasized on structural alterations such as introducing different lateral substitutions on the bending core, 12,13,18 adjusting the number of aromatic units, 14,[19][20][21] modifying the type, number, and position of linkage groups, 14,[22][23][24][25] and changing the type and length of the terminal chains. 14,15,[25][26][27] Yet, the mesogenic phase behaviors of current ABLCs are still unfavorable for practical applications.…”

“…Previous studies suggest that the location of azo linkage does not exert significant influence on the mesogenic behavior; if azo bond is close to central ring, it can even inhibit the formation of mesogenic phases. 14,22 However, their conclusions were based on compounds with a single azo linkage. This study proposed an alternative approach to improve the design of ABLC by using two azo bonds instead of esters as the central linkages connecting the central bent-core, which intends to weaken the intermolecular interactions and therefore to enhance the overall performance of ABLC.…”

Alignment and Deformation Properties of the Third Type of Hockey Stick‐Shaped Molecules in Vertical Alignment and Fringe‐Field Switching Modes

“…In the first type, the rod‐like mesogens containing two flexible terminal chains: one chain being connected to the para position of one side of the terminal ring and the other to the meta one of the other side . In the second type, the asymmetric bent‐core mesogens contain two terminal chains . In the third type, only the longer arms of the asymmetric bent‐core mesogen possess their own terminal chains.…”

Synthesis and mesogenic property of new hockey-stick-like molecules

“…These characteristics of HSL-LCs render them suitable for LCD applications because the fast-response characteristic of LCD technology requires low rotation viscosity, strong spontaneous polarization, proper tilt angle, and dielectric anisotropy of the molecules. Researches on HSL-LCs were commenced only quite recently, and thus, the relationship between the structure and property of HSL-LCs is yet to be established [28][29][30]. Basically, the results of this type of study can be useful in the design of LC structures for broad application within the field of display technology.…”