Novel photo-crosslinkable liquid crystalline polymers containing vanillylidene cycloalkanones and azobenzene units

Two series of novel liquid crystalline photo-crosslinkable bis(vanillylidene-azobenzene) cycloalkanone containing polymers, namely poly(vanillylidene alkyloxy-4,4'-azobenzenedicarboxylic ester)s, have been synthesised from bis[m-hydroxyalkyloxy(vanillylidene)cycloalkanone] (m = 6, 8, 10) with azobenzene dicarbonylchloride by solution polycondensation method at ambient temperature. Polymers with varying spacer lengths have been synthesised and characterised by spectroscopic techniques. These variations have been correlated with the thermal properties and transition temperatures. Thermal transitions were analysed by differential scanning calorimetry (DSC) and the mesophases were identified by hot stage optical polarised microscopy (HOPM). All of the polymers were found to exhibit liquid crystalline properties. Transition temperatures were observed to decrease with increasing spacer length. The thermogravimetric analysis reveals that all of the polymers were stable up to 280°C undergo two-stage decomposition. Using the UV-visible photolysis studies we investigated the simultaneous behaviour of reactivity rates of crosslinking in the vanillylidene unit and isomerisation caused by the azobenzene unit in the photo-crosslinkable main chain liquid crystalline polymers. The photolysis of liquid crystalline bis(vanillylidene)cycloalkanone-based polymers reveals that there are two kinds of photoreactions in these systems: the EZ photoisomerisation of azobenzene unit and 2p+2p addition by vanillylidene units. The EZ photoisomerisation in the liquid crystal phase disrupts the parallel stacking of the mesogens, resulting in the transition from the liquid crystal phase to isotropic phase. The photoreaction involving 2p+2p addition of the bis(vanillylidene)cycloalkanone units in the polymers results in the conjoining of the chains. The cyclopentanone polymers exhibited a faster rate of photolysis than the cyclohexanone polymers.     

Liquid crystalline behavior and fluorescent property of calix[4]arene containing azobenzene photochromic group

The reaction of 4′-hydroxy-4-methyl azobenzene (1) and 1,6-dibromohexane afforded 6-bromo-1-((4-((4-met hylphenyl)azo)phenyl)oxy)hexane (2), which further reacted with p-tert-butylcalix[4]arene to give the calix[4]arene derivative (3) whose lower rim had been modified by the azobenzene photochromic group. The structure of 3 was characterized by ¹H-nuclear magnetic resonance (NMR) and electrospray ionization-mass spectrometry (ESI-MS). The fluorescence intensity of compound 3 was two to four times higher than that of compounds 1 and 2 as the azobenzene group concentration in the range of 1.6 × 10⁻⁵ to 8.0 × 10⁻⁴ mol/L, indicating that the fluorescence quantum yield of the azobenzene group had been improved through being attached to the calix[4]arene skeleton. The liquid crystalline behavior of compound 3 was studied by polarized microscopy (POM) and differential scan calorimeter (DSC). Compound 3 exhibited the enchased texture of a smectic liquid crystal from 209.4°C to 219.5°C on heating, while 2 exhibited a liquid crystalline phase from 87.4 to 83.2°C on cooling. It was found that the calix[4]arene skeleton was a good platform for conformation immobilization of azobenzene photochromic group and the formation of liquid crystalline. Translated from Chinese Journal of Applied Chemistry, 2006, 23(9): 1023–1026 [译自: 应用化学]     

Synthesis,characterisation and liquid crystalline behaviour of some lanthanides complexes containing two azobenzene Schiff base

Schiff base ligand N,N′-di-(4-butylsalicylidene)-1′,3′-diaminopropane [H₂L] was synthesised by the reaction of substituted azobenzene and 1,3-diaminopropane in 2:1 molar ratio. Four mononuclear lanthanide complexes of the type [Ln(H₂L)LCl] (Ln = LaIII, CeIII, SmIII and GdIII) were synthesised and characterised by ¹H,¹³C NMR, fourier transform infrared (FT-IR) spectroscopy, elemental analysis (CHNO), gas chromotography-mass, magnetic susceptibility and molar conductivity. Thermal properties of the title compounds were studied using the thermogravimetric analysis/differential scanning calorimetry (TGA/DSC) and optical polarising microscopy (OPM). The ligand and coordination compounds exhibit liquid-crystalline properties (smectic A).     

含偶氮苯基团的三枝状凝胶因子的合成和凝胶性质研究

设计合成了一种中心为三乙基氨基,酰胺基作为氢键连接基团,柔性的烷基链连接偶氮苯基团的含多种分子间弱相互作用的三枝状有机凝胶因子1.由于偶氮苯基团处于分子的外缘,在THF溶液中,凝胶因子1表现出良好的光致变色行为.凝胶性能测试中,分子间存在氢键作用、π-π相互作用等使得该化合物在醇类、有机酸类和乙腈等极性溶剂中极易形成稳定的有机凝胶.在少数的非极性溶剂,如正己烷和环己烷中也可以形成稳定凝胶,并且随着溶剂极性的不同,凝胶形貌呈现出规则的纤维状或带状结构.     

Photo-responsive polysiloxane-based azobenzene liquid crystalline polymers prepared by thiol-ene click chemistry

In this work, a novel polysiloxane-based azobenzene-containing liquid crystalline polymer (LCP) PMMS-A44V6 has been designed and synthesized via a facile thiol-ene click chemistry method by grafting a side-on azobenzene mesogenic group A44V6 onto poly-[3-mercaptopropylmethylsiloxane] (PMMS) backbone. ¹H NMR, ¹³C NMR, GPC, TGA, DSC, POM and WAXS were used to investigate the mesogenic properties and photo-responsive behaviour of PMMS-A44V6. Taking advantage of the azobenzene’s trans–cis isomerization effect, PMMS-A44V6 can perform an isotropization process under UV irradiation in its nematic phase. Initially, the isotropization process starts in a linearly decreasing manner with a rate of ca ?6.5 × 10⁵ intensity/s, and eventually finishes in an exponential decrease regime to form cis-azobenzene moieties. The reversible UV-response behaviour of PMMS-A44V6 can be performed in a relatively low temperature range of 30 ~ 75°C, which might help this azobenzene-containing LCP material to find potential application in control devices.     

Tailoring the liquid crystalline property via controlling the generation of dendronized polymers containing azobenzene mesogen

The first‐ and second‐generation dendronized polymers containing azobenzene mesogen were designed and successfully synthesized via free radical polymerization. The chemical structures of the monomers were confirmed by elemental analysis, ¹H NMR, and ¹³C NMR. The molecular characterizations of the polymers were performed with ¹H NMR and gel permeation chromatography. The phase structures and transition behaviors were studied using differential scanning calorimetry, polarized light microscopy, and small‐angle X‐ray scatter experiments. The experiment results revealed that the first‐generation dendronized polymer exhibited liquid crystalline behavior of the conventional side‐chain liquid crystalline polymer with azobenzene mesogen, that is, the polymer exhibited smectic phase structure at lower temperature and nematic phase structure at higher temperature. However, the second‐generation dendronized polymers exhibited more versatile intriguing liquid crystalline structures, namely smectic phase structure at lower temperature and columnar nematic phase structure at higher temperature, and moreover, the phase structure still remained before the decomposition temperature. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1149–1159, 2010     

Synthesis and characterisation of polymethacrylates containing para-, meta- and ortho-monosubstituted azobenzene moieties in the side chain

Three sets of novel side-chain liquid crystalline polymers with monosubstituted azobenzene moieties in the side-chain have been studied. These are poly(p-(4′-methoxy-4-oxyhexyloxy azobenzene) benzyl methacrylate) (PPHABM), poly(m-(4′-methoxy-4-oxyhexyloxy azobenzene) benzyl methacrylate) (PMHABM) and poly(o-(4′-methoxy-4-oxyhexyloxy azobenzene) benzyl methacrylate) (POHABM). The chemical structure of the monomers was confirmed by ¹H NMR, ¹³C NMR spectroscopy and elemental analysis. The structural characterisation of the polymers was performed by ¹H NMR spectroscopy and gel permeation chromatography, and their phase behaviour and liquid crystalline properties were studied using differential scanning calorimetry, polarised optical microscopy and wide-angle X-ray diffraction. The results show that the transitional behaviour of side-chain liquid crystalline polymers containing monosubstituted azobenzene moieties depends strongly on the position of the substituent on the azobenzene moiety; for example, the ortho-monosubstituted polymers do not form liquid crystalline phases, but all the para- and meta-monosubstituted polymers exhibit a smectic A phase. Furthermore, the glass transition temperature (T_g ) of the polymers decreases in the order, para > meta > ortho. For the PPHABM and PMHABM polymers the isotropic temperature (T_i ) and liquid crystalline range (ΔT, from T_g to T_i ) are found to be in the order, para > meta, although it is surprising that the associated enthalpy changes in these polymers is the opposite order, meta > para.     

Photomechanical effects in liquid crystalline polymer networks and elastomers

Liquid crystals are widely employed as stimuli‐responsive materials. Liquid crystallinity can be retained in polymeric form. Photoinduced mechanical effects in liquid crystalline polymer networks and elastomers have been a topic of considerable recent research. This review details the historical underpinnings and recent advances in the synthesis and the corresponding photomechanical response of these materials. In nearly all cases, the conversion of light into mechanical work has employed azobenzene as either a guest additive or covalently attached to the network. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 695–705     

Photochromic LC copolymers containing azobenzene and crown‐ether groups

An approach for the creation of a novel family of multifunctional crown‐ether‐containing comb‐shaped copolyacrylates consisting of chromophoric (azobenzene), ionophoric (crown‐ether), and mesogenic groups in the same macromolecule was developed. Phase behavior of the copolymers was studied, and correlation between their molecular structure and thermal properties was established. The increase of crown‐ether‐containing groups' concentration up to 26 mol % leads to disruption of nematic order and formation of amorphous phase. Influence of copolymers complexation with potassium perchlorate on mesomorphic properties of such systems was investigated. It was shown that complexation leads to decrease in mesophase thermostability due to the significant reducing of the side group anisometry by perchlorate counter ion. The comparative investigations of photooptical properties and photoorientation processes of copolymers and their complexes were also performed. An essential difference in kinetics of photooptical behavior was revealed; the bulky crown‐ether substituents decrease rotational mobility and prevent photoorientation process of azobenzene fragments diminishing photoinduced orientation and order parameter. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6532–6541, 2008     

Mesomorphic polyacrylates containing isomeric methyl-substituted azobenzene mesogens

The synthesis and characterization are reported of two new series of structurally isomeric polyacrylates containing the azobenzene moiety spaced away from the backbone by a hexamethylene spacer and substituted in 4-position with linear alkoxy groups (C₁? C₆, C₁₀) and with a lateral methyl group in 2′- or 3′-position. Thermal optical and X-ray analyses of the prepared polymer samples, with molecular weight ranging from 50 × 10³ to 35 × 10⁴ Dalton (M?_w/M?_n = 2?3), provide evidences for the establishment of liquid crystalline behavior in the melt in a fairly broad range of temperature. In any case, quenching from the mesophase allows for the lock-in of the liquid crystalline structure in the glassy state. The presence of the lateral methyl-substitutents causes a drop as high as 50–100 K. in the stability of the mesophase with respect to the corresponding samples of the methyl-unsubstituted series. A parallel depletion of the smectogenic character is also observed. Typical even-odd effects on the isotropization temperature and relevant thermodynamic parameters have been detected along with the formation of interdigitated smectic structures.     

New azobenzene containing bent-core liquid crystals based on disubstituted resorcinol

New bent-core molecules with 4,6-dichlororesorcinol or 4-chloro-2-methylresorcinol as the central unit, and azobenzene with different alkyloxy chain length as side arms were synthesised. The mesophase behaviour of the new compounds was investigated by polarising optical microscopy, differential scanning calorimetry, X-ray diffraction studies and electro-optical measurements. It is found that 4,6-dichlororesorcinol is more conducive towards mesomorphism than 4-chloro-2-methylresorcinol. The liquid crystalline properties of all of the prepared compounds are greatly affected by the lateral substitution on the outer ring. 4,6-Dichlororesorcinol-based compounds without lateral substitution show nematic phases with cybotactic cluster of the SmC-type (N_CybC). Moreover, depending on the chain length, the nematic phase appears as enantiotropic phase for the shortest homologue and as monotropic phase for the higher homologues.     

Synthesis of chiral azobenzene derivatives and the performance in photochemical control of blue phase liquid crystal

A series of chiral azobenzene compounds with branched terminal were synthesised, and the photosensitive performances were investigated accordingly. It was found that the photochemical properties were mainly affected by the trans–cis configuration of azobenzene and the linked position between the azobenzene and chiral centre. The para-type azobenzenes showed general photochemical decrease in helical twisting power (HTP), but the meta-type ones appeared interestingly showed photochemical increase in HTP. This work provided an effective method for designing molecules to control blue phase (BP) including adjusting colours, inducing BP and extending BP range, which was promising in the applications of optically addressable devices.     

Thermal recordable novel cholesteric liquid crystalline polyacrylates containing various chiral moieties

To investigate the effect of spacer length and linkages between the rigid mesogenic core and the terminal group on the molecular interaction and physical properties of polymers, two series of novel side chain liquid crystalline polyacrylates were synthesized. These were composed of liquid crystalline monomers with six or eleven methylene segments as spacers, and chiral monomers end capped with menthyl or cholesteryl groups. Liquid crystalline phases of the polymers were investigated using differential scanning calorimetry and polarized optical microscopy, and confirmed with X‐ray diffractometry. Color image recording of the synthesized polymer films was achieved using a thermal treatment, and then fixed by quenching. This investigation demonstrates that the introduction of carbonate linking groups between the rigid mesogenic core and terminal group decreases both the lateral molecular interaction and thermal stability of the liquid crystalline polymers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6214–6228, 2008     

Photo-triggered assembly/disassembly of macroscopically ordered monodomain lamellar structure in side-chain liquid crystalline polymer containing strong polar azobenzene mesogens

Assembly of ordered structures by an external stimulus allows for design of functional materials with enhanced physical and chemical properties. A new side-chain liquid crystal polymer containing strong polar azobenzene mesogens was synthesised. A macroscopically ordered monodomain smectic-like lamellar structure having orientational order and positional order was immediately assembled by linear polarised light irradiation (473 nm, 20 mW/cm²) at room temperature. The lamellar layer with its periodic d-spacing of 1.9 nm and mesogens arranged at an inclination angle of about 75° were characterised by X-ray diffraction and polarising optical microscopy which showed a diffraction peak at 2θ?=?4.53° and an off-centred interference figure. Reversible assembly and disassembly of the lamellar phase were achieved by alternative irradiation with polarised light and non-polarised light. Potential factors influencing the assembly of the ordered lamellar structure were investigated by controlling the mesogens out-of-plane orientation and by changing the polarities of mesogens. The difference in arrangement of the mesogens between the lamellar phase and a thermotropic smectic phase was also compared by heating the selectively exposed film. The light controllable assembly of mesogens provides an easy route to assemble a lamellar phase in azobenzene containing polymers for application in optical and photonic devices.     

两种偶氮苯冠醚的合成及其光致变色机理

报道了4-氮杂15-冠-5-4'-甲氧基偶氮苯和4-氮杂15-冠-5-4'-硝基偶氮苯的合成及其分子内扭曲电荷转移的光致变色机理.     

两各氮苯冠醚的合成及其及其光致变色机理

报道了４－氮杂１５－－５－４＇－甲氮基偶氮苯和４－氮杂１５－冠－５－４＇－硝基偶氮苯的合成及其分子内扭曲电荷转移的光致变色机理。     

Photochromic characteristics of monodisperse microcapsules containing azobenzene derivative-doped nematic liquid crystals

Highly mono-sized dye-doped liquid crystal (LC) microcapsules were prepared by the solute codiffusion method for application in photoswitchable devices. Azobenzene derivatives, which can be photoisomerized by irradiation with UV (366 nm) and visible (433 nm) light, were used as a photoresponsive dichroic dye. The microcapsules have a spherical shape and a single dye-doped LC domain. After UV light (366 nm) irradiation, PDLC films prepared using the microcapsules attained a photostationary state within 10 min and this state maintained stability. PDLC films made by employing a dichroic dye having electron donor and acceptor groups in the molecule showed especially good photoisomerization properties. The reversible trans-cis -photoisomerization occurred sharply by irradiating alternately with visible and UV light.     

Photochromic characteristics of monodisperse microcapsules containing azobenzene derivative-doped nematic liquid crystals

Highly mono-sized dye-doped liquid crystal (LC) microcapsules were prepared by the solute codiffusion method for application in photoswitchable devices. Azobenzene derivatives, which can be photoisomerized by irradiation with UV (366 nm) and visible (433 nm) light, were used as a photoresponsive dichroic dye. The microcapsules have a spherical shape and a single dye-doped LC domain. After UV light (366 nm) irradiation, PDLC films prepared using the microcapsules attained a photostationary state within 10 min and this state maintained stability. PDLC films made by employing a dichroic dye having electron donor and acceptor groups in the molecule showed especially good photoisomerization properties. The reversible trans-cis -photoisomerization occurred sharply by irradiating alternately with visible and UV light.     

光致变色液晶材料研究进展

本文介绍了液晶相态和光致变色的基本原理,液晶材料在光学领域中的应用,光致变色化合物的光异构化反应对液晶光学性质的影响,以及光致变色液晶材料制备的进展。参考文献53篇。     

Optical and dielectric properties of new azobenzene copolyethers embedded in polymer matrices

A new group of photochromic azobenzene copolyethers was synthesized. Their photochomic and dielectric properties were studied in poly(vinyl alcohol) and poly(methyl methacrylate) matrices.