Mesomorphism of novel stilbene-based bent-core liquid crystals

Abstract

A series of asymmetric bent-core liquid crystals, bearing the stilbene moiety in the side wing, was synthesised © and characterised © . Structural modifications of the non-stilbene wing resulted in formation of various mesophases. Compounds 1 and 3 with an ester linking group between the phenyl rings in this wing have an enantiotropic non-polar smectic-type mesophase, while compound 2, incorporating the biphenyl moiety, has a ferroelectric SmC a P F phase. The molecules of 2 undergo photoisomerisation © in solution under UV irradiation, while the mesophases are unstable and UV irradiation leads to irreversible changes. The mesophases of 1 and 3 do not show any electro-optical switching and polarisation © current. Applying low frequency AC voltage on a planarly aligned film of compound 2, smectic domains grow, while the birefringence and an image flickering increase. The observed features of these compounds identify stilbene as an attractive moiety in the design of advanced materials based on bent-core molecules.

On the photophysical properties of a liquid crystal dimer based on 4-nitrostilbene: A combined experimental and theoretical study

“…The FTIR spectrum of the synthesized compound was recorded with a Bomem MB series 100 spectrophotometer in the ATR mode. The NMR spectral measurements were performed on a Bruker 300 spectrometer at 400 MHz for the 1 H NMR and 100 MHz for the 13 C NMR spectra. The spectra were recorded at room temperature in CDCl3 using TMS as the internal standard.…”

“…FTIR (ATR) ʋ 2920, 2850,1587,1572,1505,1473,1334,1323,1269,1246,1173,1108,1033,1004,975,952,875,841,749,716,686,630,582,530, 452 cm -1 ; 1 H NMR (CDCl3) δ [ppm]: 1.26-1.39 (m, 12H, -CH2-), 1.44-1.51 (m, 4H, -CH2-), 1.81 (quin, 4H, J =7.1 Hz, -CH2-), 3.99 (t, 4H, J = 6.6 Hz, -CH2O-), 6.92 (d, 4H, J = 8.8 Hz, -C6H4-), 7.0 (d, 2H, J =16.4 Hz, -CH=CH-), 7.23 (d, 2H, J =16.4 Hz, -CH=CH-) 7.49 (d, 4H, J = 8.8 Hz, -C6H4-), 7.60 (d, 4H, J = 8.8 Hz, -C6H4-), 8.21 (d, 4H, J = 8.8 Hz, -C6H4-). 13…”

“…Wu and co-workers prepared LCs with anisotropic fluorescence emission by ionic self-assembly from a copolymer and oppositely charged fluorescent rod-like dye containing this scaffold [12]. A series of bent-core molecules bearing 4-nitrostilbene in a side wing was also reported [13]. In this case, relatively small modifications in their structure significantly influenced the supramolecular assembly, which was further reflected in formation of various LC phases.…”

Liquid crystalline dimers containing a cholesteryl benzoate unit: smectic phase, chiral nematic phase and blue phase

“…What is more remarkable is that it shows some significant characteristics: chirality is the driving force for helical formation and the helical structure of materials is the reason for the stability of some mesophases, such as blue phases, etc.. 15 The frustrated phase (TGB) transition is generally from the isotropic or chiral nematic phase to the chiral smectic A or chiral smectic C phase. In a previous review, Channabasaveshwar V. 15 summarized the abundance of cholesterolbased dimeric liquid crystals connected to mesogenic units such as Schiff base, 31 azobenzene, [32][33][34] tolane, 35 chalcone, 36 and stilbene 37 through flexible chains. Numerous experiments have demonstrated the abundance of mesophases of cholesterol-based dimers, the ability of chirality of which tends to stabilize some frustrated phases.…”

Photosensitive Bent-Core Liquid Crystals with Laterally Substituted Azobenzene Unit

“…Bent-core liquid crystals (BCLCs) are an extraordinary class of the mesomorphic materials since they may exhibit polar order and macroscopic chirality in self-assembled mesophases consisting of achiral molecules. According to their structure, they can form various mesophases with unique properties in comparison with other classes of LCs [19][20][21]. Bent-core nematics (BCN) can have biaxial character [22][23][24][25][26] and exhibit a huge flexoelectric effect compared to conventional calamitic nematics [27][28][29][30], which predetermines them for new generation of optoelectrical devices, holographic media [31,32], photonics and optical data storage [33,34].…”