Photo‐Responsive Behavior of Azobenzene Based Polar Hockey‐Stick‐Shaped Liquid Crystals

Abstract

A study on the photoswitching behavior of azobenzene‐based polar hockey‐stick‐shaped liquid crystals (HSLCs) has been presented. Two new series of five phenyl rings based polar HSLCs have been designed and synthesized. Solution state photoisomerization of the synthesized materials was investigated thoroughly via UV‐visible and 1H NMR spectroscopic techniques, whereas solid‐state photochromic behavior was elucidated via physical color change of the materials, solid‐state UV‐visible study, powder XRD, and FE‐SEM techniques. The materials exhibited decent photochromic behavior for different potential applications. The thermal phase behavior of the superstructural assembly has been characterized via polarizing optical microscopy (POM), differential scanning calorimetry (DSC), and temperature‐dependent small and wide‐angle X‐ray scattering (SAXS/WAXS) studies. Depending upon the length of the terminal alkyl chain, nematic (N) and partially bilayer smectic A (SmAd) phases were observed. DFT calculations revealed the favorable anti‐parallel arrangement of the polar molecules that substantiate the formation of SmAd phase.

Cyanostilbene‐Based AIEgen Smart Film: Optical Switching by Engineering Molecular Packing Structure and Molecular Conformation Through Thermal and Photoinduced Monotropic Phase Transition

“…The other two diffraction peaks at 2θ = 5.70° and 7.47° ( d = 1.55 and 1.18 nm) can be explained as the in‐plane ordering when two D4CS molecules are regarded as a building block, as shown in Figure 2c. [ 48 ]…”

“…Considering the fully extended molecular length of D4CS ( L = 5.72 nm), the low‐angle diffraction peaks at 2θ = 1.62° and 3.24° ( d = 5.44 nm and 2.72 nm) were identified as (001) and (002), which indicates that the annealed D4CS is a highly ordered smectic crystal (SmCr) phase. [ 43,44,48 ] The much stronger and sharper second‐order diffraction peak than the first‐order one may be due to the strong periodicity between cyanostilbene mesogens with more electrons. The weak broad scattering halo at 2θ = 11.26° ( d = 0.78 nm) comes from the short‐range positional order between the nanophase‐separated cyclosiloxanes.…”

“…The other two diffraction peaks at 2θ = 5.70° and 7.47° (d = 1.55 and 1.18 nm) can be explained as the in-plane ordering when two D4CS molecules are regarded as a building block, as shown in Figure 2c. [48] The molecular packing changes of D4CS were further studied by 1D WAXD with increasing the temperature from 30 to 120 °C (Figure S8, Supporting Information). As the temperature rises to 60 °C, the 1D WAXD pattern becomes simpler.…”

Nematic Phase of Polar Unsymmetrical Bent‐Core Molecules

“…BCNs also exhibit photoswitchable mesophases upon the incorporation of an azo linker in bent-core architecture for potential applications in photonic and optical display devices, light tunable gratings, optical switches, etc. [29][30][31] Polar groups such as F, Cl, CN, NO 2 , etc. in the bent-core molecular architecture enhance polarization and promote strong dipole moment which is further reflected in an antiparallel molecular arrangement.…”

“…[34][35][36][37] The terminal cyano-substituted bent-core systems have been reported for the biaxial Smectic A (SmA b ) phase, [38][39][40] nematic phase, [17,33,41,42] and polar orthogonal phases [43] whereas, there are a few reports on nitro-terminated bent-core mesogens. [31,33,42] In addition to the bent angle, [44,45] the terminal or lateral substitutions [46] play a crucial role in bend-splay anisotropy, a significant parameter for electrooptical devices. Since the first observation of the cybotactic nematic phase in 1,3,4-oxadiazole-based bent-core LCs, [12] nematic mesomorphism has been widely noticed in symmetrical as well as unsymmetrical polar bent-core compounds.…”