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1.
A new series of asymmetric bent-core compounds were synthesised using azo linkages with equal as well as unequal terminal alkyl chains and their photo and electrical switching properties investigated. The mesomorphic properties were characterised using polarised optical microscopy, X-ray diffraction and differential scanning calorimetry. The lower homologues of the series of compounds show a B1 phase whereas higher homologues exhibit a B2 phase. The B2 phase shows an anticlinic-antiferroelectric switching behaviour during electro-optic measurements. The photo-switching properties of the azobenzene containing bent-core molecules were investigated using ultraviolet-visible spectroscopy. The trans to cis photo isomerisation was observed at 25 s whereas reverse processes took 14 h in chloroform.  相似文献   

2.
Extensive survey carried out in bent liquid crystals (BLCs) exhibiting ferroelectric (FE) phases suggested for the design of non-symmetric (NS) frame. Novel series of BLCs (C8Cm) with distinct lateral moieties and heterocyclic central (oxadiazole) moiety, viz., octyl 4-(5-(4´-(alkyloxy) biphenyl-4-yl)-1,2,4-oxadiazol-3-yl)benzoates, are reported. NS BLC frame is realised by incorporating differing number of aromatic cores and varied length of end chains in the lateral moieties. Lateral moiety with biphenyl core is prepared by Suzuki coupling. Purity of the BLC product is confirmed by 1H NMR and elemental analysis. LC phases exhibited by C8Cm series of BLCs for m = 8, 10, 12, 15 and 16 are characterised by polarisation optical microscopy (POM), differential scanning calorimetry (DSC) and spontaneous polarisation (PS) techniques. C8Cm series are found to exhibit SmA, CrystalB, B2, B5, SmG and SmE phase variance. SmG occurs as monotropic phase. Temperature variation of PS(T) studied in FE B2 and B5 phases by field reversal method infers a moderate PS value of ~80–100 nC · cm?2. Order parameter growth in FE B2 and B5 phases is analysed through PS(T). Normalised order parameter θN exhibits asymptotic behaviour with universal temperature TU. Influence of aromatic cores and length of end chains (in lateral moieties) on the thermal stability of FE phases is discussed in the wake of the data on other BLCs.  相似文献   

3.
A homologous series of new chiral liquid crystal compounds, M6BnB (n = 2, 4, 6, 8, 10, 12, 14, 16, 18), with varying length of n-alkoxy chains at one end, was formed by covalently linking a chiral (?)-menthyl with biphenyl-benzoate via adipoyloxy spacer group. A combination of analysis methods such as Fourier transform infrared, 1H NMR spectra, differential scanning calorimetry, polarised optical microscopy and X-ray diffraction was carried out to systematically investigate their phase structures and phase transition behaviours. The length of the flexible terminal alkoxy group has a profound influence on the clearing points (Tiso) and Tiso decrease with the increase of alkoxy chain (n). In addition, increasing the length of the terminal alkoxy group tends to narrow the temperature range of the N* phase and favour the development of chiral smectic C phase.  相似文献   

4.
Three analogous series of symmetric banana‐shaped liquid crystalline molecules containing bisnaphthyl units were synthesized and characterized. The effects of linking groups (on the side wings) and lateral meta‐fluoro substitutions (on the middle outer rings) on the mesogenic properties were examined. The type of mesophase depends on the lengths of terminal alkoxy chains. Thus, achiral molecules with shorter flexible chains (n = 8) exhibit a rectangular columnar (B1) phase, while analogous derivatives with longer flexible chains (n = 12) display the B2 phase. All lateral meta‐fluoro substituted analogues (series II) possess the lowest isotropization temperatures and the narrowest mesophasic ranges of the B1 and B2 phases. The B1 and B2 phases were confirmed by X‐ray diffraction, polarizing optical microscopy (POM) and electro‐optical (EO) switching experiments. An electric field‐induced transition from an antiferroelectric (tristable) state to a ferroelectric (bistable) state was observed in the EO measurements. Spontaneous polarization (by switching current response), tilt angle of chiral domains (by POM), and transmittance–voltage measurements of the B2 phase in related compounds have been surveyed in this study.  相似文献   

5.
Two new coordination polymers with an asymmetric dicarboxylate and 4,4′-bipyridine ligand, {[Co(bpy)(H2O)4]·(cpa)·0.5H2O}n (1) and {[Ag(cpa)(bpy)][Ag(bpy)]·4H2O}n (2) (H2cpa = 4-(2-carboxyethyl)benzoic acid, bpy = 4,4′-bipyridine), have been hydrothermally synthesized and characterized by elemental analysis, FT-IR spectroscopy, and single-crystal X-ray diffraction. Compound 1 displays a linear chain with guest molecule (cpa)2? ions existing in the structure. Compound 2 contains two independent units, [Ag(cpa)(bpy)] (A) and [Ag(bpy)]+ (B), which form a 1-D + 1-D structure. A shows a 1-D chain structure bearing hooks formed by the carboxylates and organized into a tubular structure by hydrogen-bonding interactions. B has linear chains formed from Ag+ and bpy. The A and B chains co-crystallize with waters of crystallization to provide two linear [Ag(bpy)]+ chains embedded in the tubular structure formed by A via π…π stacking contacts. In 1 and 2, hydrogen-bonding and π…π stacking interactions connect the discrete 1-D chains into 3-D supramolecular structures. The fluorescent properties, TG analysis, and X-ray powder diffraction patterns for 1 and 2 were also measured.  相似文献   

6.
Two series of discotic dimers T3Dn and T5Dn based on hexapropoxytriphenylene (HAT3) and hexapentyloxytriphenylene(HAT5), respectively, with polymethylene linkage O(CH2)nO (n = 3–12) have been synthesised. Their mesomorphism was investigated by differential scanning calorimetry, polarising optical microscopy and X-ray diffraction. The results showed that side chains induced a phase transition from colhp phase to colh phase, namely dimers T3Dn (n = 6–12) based on HAT3 exhibiting a single colhp phase, dimers T4Dn (n = 6, 7, 11, 12) based on HAT4 showing a highly ordered colhp phase in low-temperature region and a colh phase in high-temperature region, dimers T4Dn (n = 8–10) based on HAT4 displaying a single colhp phase and dimers T5Dn (n = 6–11) based on HAT5 indicating a single colh phase. Dimers T4Dn showed a phase competition between colh phase and colhp phase induced by linkages. Surprisingly, a unique phenomenon was found by us, that is, those compounds in which linkage lengths were twice those of side chains showed the largest enthalpies, the smallest intracolumnar spacings and the highest charge-carrier mobilities among their homologues, respectively, which implied that they formed the most highly ordered phase among their homologues.  相似文献   

7.
Substitution of each phenyl in 1,3,5-triphenyl-6-oxoverdazyl with three alkoxy groups induces an ordered columnar hexagonal phase (Colh(o)) below 130°C in 1b[n], while in the alkylsulfanyl analogues 1a[n] additional periodicity along the columns was found rendering the phase a true three-dimensional columnar hexagonal phase (Colh(3D)) below 60°C. Both series exhibit broad absorption bands in the visible region with maxima at 540 and 610 nm in series 1a[n] and at 486 and 614 nm in series 1b[n]. Unusual reversible thermochromism is observed in series 1b[n], in which the dark green isotropic phase turns red in the discotic phase. Analysis of 1a[8] revealed redox potentials E0/+11/2 = +0.99 V and E0/ ?11/2 = –0.45 V vs. saturated calomel electrode (SCE), while the potentials in the alkoxy analogue 1b[8] are shifted cathodically by 0.16 V. Photovoltaic studies of 1a[8] demonstrated hole mobility of μh = 1.52 × 10?3 cm2 V?1 s?1 in the mesophase with an activation energy Ea = 0.06 ± 0.01 eV. Magnetisation studies of 1a[8] revealed nearly ideal paramagnetic behaviour in either the solid or fluid phase above 200 K and weak antiferromagnetic interactions at low temperatures. In contrast, a noticeable drop of about 4% in μeff was observed during the I→Col phase transition in 1b[8], which coincide with the thermochromic effect.  相似文献   

8.
A homologous series of banana-shaped compounds (n =1-12) is described. The short-chain derivatives exhibit a B6 phase, while B6/B1 dimorphism is found for the pentyloxy and hexyloxy homologues. The B1 phase of the compounds having longer alkyloxy chains is changed to a B2 phase for the compounds with n =11 and 12. The phase characterization was performed using their optical textures and by means of X-ray investigations. Transition enthalpies were measured using DSC. In addition, density measurements were performed on one selected homologue. The compound n =8 exhibiting a B1 phase was investigated also by high-pressure DTA.  相似文献   

9.
A series of hockey-stick shaped 6-oxoverdazyl radicals 1[n]3[n], containing CH3 (a), CF3 (b) and CN (c) groups in the short ‘arm’, were prepared and their physical properties were investigated. Mesogenic behaviour was found only in the CN derivatives with the COO (1[n]c) and N=N (2[12]c) linking groups, which exhibited a nematic phase. Analysis of binary mixtures of selected compounds with bent-core nematic host 4[12] gave virtual nematic-isotropic transition temperatures, [TNI], which follow the order 1[12]b < 1[12]c < 1[12]a in one series and 1[12]c < 2[12]c < (3[12]c) in another. The observed effectiveness of the short-arm substituent, CF3 < CN < CH3, was related to the magnitude and orientation of the molecular dipole moment calculated with density functional theory methods.  相似文献   

10.
Qian Cui 《Liquid crystals》2013,40(12):1609-1618
The axially chiral mesogens 5-alkoxy-5′-[(4-alkoxybenzoyl)oxy]-2,2′-spirobiindan-1,1′-dione (QL7-n) were synthesised as racemic mixtures and resolved as single enantiomers by preparative chiral phase HPLC. The shorter homologues (R)-QL7-8 and QL7-9 form enantiotropic N* and SmC* phases, whereas the longer homologues (R)-QL7-10 and QL7-12 form an enantiotropic SmC* phase only. Texture analysis showed that the helical pitch of the N* phase is below the wavelength range of visible light; a helical pitch of 187 nm was measured at T – TNI = –5 K by selective reflection using enantiomerically enriched mixtures of (R)- and (S)-QL7-8 (0.35 ≤ ee ≤ 0.80). Spontaneous polarisations were measured as a function of temperature in the SmC* phase by the triangular wave method. PS values at saturation range from 102 nC cm2 for (R)-QL7-8 to 120 nC cm?2 for (R)-QL7-9, which are up to three times greater than the highest polarisation previously reported for an axially chiral SmC* mesogen. Optical tilt angles θ were measured as a function of temperature and showed a sharp rise consistent with first-order N*–SmC* or I–SmC* transitions, with values at saturation ranging from 42 to 44°.  相似文献   

11.
Weakly polar–polar isosteric pairs of 12-vertex p-carborane [closo-1,12-C2B10H12] (1[12]) and monocarbaborate [closo-1-CB11H12]? (2[12]) nematic liquid crystals, in which the difference in the calculated molecular dipole moment is 11.3 D, were synthesised, and the effect of the dipole moment on nematic phase stability was investigated. The trend observed for the 12-vertex series ([12]) was identical to that of the previously investigated 10-vertex series ([10]) containing [closo-1,10-C2B8H10] (1[10]) and [closo-1-CB9H10]? (2[10]): the uniform increase in the molecular dipole moment in the pairs of mesogens does not correspond to a uniform change in the clearing temperature, TNI. This demonstrates the role of a remote substituent in modulating the intermolecular dipole–dipole interactions. The magnitude of such interactions was calculated (using density functional theory methods) for a pair of polar (2[12]d2[12]d) and an analogous pair of weakly polar (1[12]d1[12]d) molecules. All results for the 12-vertex series ([12]) were analysed relative to the 10-vertex analogues ([10]).  相似文献   

12.
Two new homologous series of seven‐ring bent‐core compounds derived from 5‐chlororesorcinol have been synthesized. Many of the lower homologues in both series exhibit the rectangular columnar B1 phase. However, the three analogous compounds having long terminal alkyl chains exhibit a switchable lamellar phase, which is different from the usual B2 phase. Although the ground state structure of the mesophase is antiferroelectric, it shows chiral conglomerates with opposite tilt and polarity. Simultaneously, racemic structures are also seen. The mesophases have been characterized using a combination of polarized light microscopy, X‐ray diffraction and electro‐optical studies.  相似文献   

13.
The isobaric phase diagram for a binary system of liquid crystals is presented. One mixing component is a bent-core mesogen forming a B7 phase and the other one is a nematogenic calamitic compound. The occurring mesophases have been identified by their optical textures as well as by X-ray investigations. The B7 phase exists down to about 60 mol% of the bent-core compound A / 40 mol% of the calamitic compound B. Two additional mesophases are induced in the mixed phase region. At medium concentrations (around 50 mol%) an oblique columnar phase appears which shows a similar X-ray pattern to the B7 phase but an utterly different nucleation on cooling the isotropic liquid and a completely dissimilar texture. At concentrations below 35 mol% A, a further phase is induced which possesses an irregularly modulated layer structure. This phase can be regarded as an intermediate state between the regularly modulated Colr (B1) phase and the intercalated B6 phase. It transforms on cooling into the phase with a regularly modulated structure.  相似文献   

14.
New mesogenic homologous series bearing 1,3,4-oxadiazole ring with a nitro terminal group, 4-(5-(4-nitrophenyl)-1,3,4-oxadiazol-2-yl)phenyl 4-((4-methoxybenzylidene)amino)benzoate (G1–G11), were synthesised. Their chemical structures are identified by fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance (1H-NMR) and elemental analysis. The liquid crystalline properties of the series Gn and their precursory Fn were screened by differential scanning calorimetry and optical polarising microscopy (OPM). The compounds of the series Gn were screened by thermogravimetric analysis to observe their thermal stability. The target compounds (Gn) in this study, were displayed different liquid crystalline mesophase, the first two homologous (G1 and G2) did not show any liquid crystalline behaviour, the homologous (G3–G10) which have an alkoxy terminal group (n = 3–10) exhibited nematic phase, whilst the last derivative of the series (G11), n = 12, displayed SmA phase. The mesomorphic properties of these derivatives were affected by the presence of the nitro group at the end of the molecules which was classified as a strong polar group. Also, the role of alkoxy terminal chain and the bent heterocyclic ring (1,3,4-oxadiazole) in the liquid crystalline properties of these molecules were debated.  相似文献   

15.
Here, we report four new homologous series of azo-functionalised achiral bent-core compounds. The paper deals with the design, synthesis and liquid crystalline properties of four new homologous series of photochromic materials. In this study, we have investigated the effect of the presence of –N=N– linkage at different locations of the molecular architecture, on the mesomorphic properties. The molecular structures of all the newly synthesised compounds are established using the organic spectroscopic methods. The liquid crystalline properties are investigated using polarising optical microscopy (POM), differential scanning calorimetry (DSC), X-ray diffraction and electro-optical studies. They exhibit B1 (colr) and B2 (SmCAPA) mesophases. We find that the presence of the –N=N– linkage at different locations in the molecular architecture does not seem to have much effect on the mesogenic behaviour of such compounds. However, we clearly see a profound effect of the location of the –N=N– linkage on the photo-induced electro-optical properties of these compounds.  相似文献   

16.
A series of novel cationic gemini surfactants, p-[C n H2n+1N+(CH3)2CH2CH(OH)CH2O]2C6H4·2Cl? [A(n = 12), B(n = 14) and C(n = 16)], containing a spacer group with two flexible and hydrophilic groups (2-hydroxy-1,3-propylene) on both sides of a rigid and hydrophobic group (1,4-dioxyphenylene) has been synthesized by the reaction of hydroquinone diglycidyl ether with N,N-dimethylalkylamine and N,N-dimethylalkylamine hydrochloride. Their surface-active properties have been investigated by surface tension measurement. The critical micelle concentration (cmc) values of the synthesized cationic gemini surfactants are one order of magnitude lower than those of their corresponding monomeric surfactants (C n H2n + 1N+(CH3)3·Cl?). Both the cmc and surface tension at the cmc (γcmc) of A are lower than those of p-[C12H25N+(CH3)2CH2]2C6H4·2Cl? (D). The novel cationic gemini surfactants A and B also show good foaming properties.  相似文献   

17.
Two new complexes, [MnL2](ClO4) (1) and [CuL2] (2) (where LH = (E)-1-((3-(dimethylamino)propylimino)methyl)naphthalen-2-ol), have been synthesized and characterized by spectroscopic techniques and their molecular structures are established by single-crystal X-ray diffraction study. Complex 1 adopts an octahedral geometry around the central manganese atom which is in + 3 oxidation state, whereas in complex 2, the Cu+2 ion preferred a square pyramidal environment around it through the ligand donor atoms. Both complexes were tested for catecholase and phenoxazinone synthase activity. Complex 1 catalyzes the oxidation of 3,5-ditertiary-butyl catechol with a kcat value of 6.8424 × 102 h?1 in acetonitrile whereas the same for complex 2 is 3.7485 × 102 h?1 in methanol. Phenoxazinone synthase activity was shown only by complex 2 having kcat = 74.225 h?1. Structures of both the title complexes have been optimized by means of DFT calculations. Experimental electronic spectra of the complexes have been corroborated by TDDFT analysis. Electrochemical investigations by means of cyclic voltammetry have been carried out to study the electron transfer processes in the complexes.  相似文献   

18.
A series of bent-core V-shaped mesogens consisting of salicylaldimine mesogenic segments have been synthesized and their mesomorphic behaviour characterized. In an attempt to understand structure–property relationships, the lengths of the terminal alkoxy chains have been varied from C2 to C12, C16 and C18, resulting in 13 new bent-core V-shaped molecules. The thermal behaviour of these new compounds has been investigated by optical microscopy, calorimetry and X-ray diffraction studies. In general the compounds show conventional mesophases similar to those shown by calamitic LCs. The materials exhibit good thermal stability, even though their melting and clearing transition temperatures are high as a result of the presence of intramolecular hydrogen bonding between the H-atom of the hydroxyl group and the N-atom of the imine functionality. The phase appearing in the first member of the series with ethoxy chains is a nematic, while the C3 to C6 derivatives exhibit a smectic A phase as well as a nematic phase. The higher homologues, C7 to C12, C16 and C18, show only the smectic A phase. X-ray studies reveal that the SmA phase has a partially bilayer (interdigitated) structure. Remarkably, in some cases, the smectic A phase supercools well below room temperature. It is apparent from our studies that increasing the length of the alkoxy chains promotes smectic behaviour, in agreement with the general observation made for such bent-core molecules.  相似文献   

19.
Ting Bao 《Liquid crystals》2013,40(12):1687-1695
A series of small angle bent-core (V-shaped) mesogens carrying 1,7-naphthalene as a central core linked with lateral halogenated (chlorinated or fluorinated) Schiff-base side wings and alkylthio terminal tails of variable carbon number (n = 12, 16) was synthesised in order to reduce the transition temperature and improve the phase stability of bent-core liquid crystal molecules. Differential scanning calorimetry (DSC), polarising optical microscopy (POM), small-angle X-ray scattering system (SAXS) and two-dimensional X-ray diffractometer were applied to ascertain the mesomorphic structure and phase transition temperatures of the compounds. The results confirm that all the molecules show thermotropic liquid crystalline behaviour and exhibit hexagonal columnar phase (Colh) in a certain temperature range. Compared with the homologous compounds without lateral halogen, the cleaning point temperature of lateral halogenated V-shaped compounds generally decrease and the Colh phase ranges are more extensive. The influence of lateral chlorine on the cleaning point temperature is more obvious, as well as the effect of lateral fluorine on the range of Colh phase.  相似文献   

20.

The graft copolymerization of acrylonitrile (AN) and ethyl acrylate (EA) comonomers onto cellulose has been carried out using ceric ammonium nitrate (CAN) as an initiator in the presence of nitric acid at 35±0.1°C. The addition of ethyl acrylate as comonomer has shown a significant effect on overall and individual graft copolymerization of acrylonitrile on cellulose. The graft yield (%GY) and other grafting parameters viz. true grafting (%GT), graft conversion (%CG), cellulose number (Ng) and frequency of grafting (GF) were evaluated on varying the concentration of comonomers from 6.0–30.0×10?1 mol dm?3 and ceric (IV) ions concentration from 2.5–25×10?3 mol dm?3 at constant feed composition (fAN 0.6) and constant concentration of nitric acid (7.5×10?2 mol dm?3) in the reaction mixture. The graft yield (%GY) and other grafting parameters were optimal at 15×10?1 mol dm?3 concentration of comonomers and at 10×10?3 mol dm?3 concentration of ceric ammonium nitrate. The graft yield (%GY) and composition of grafted chains (FAN) was optimal at a feed composition (fAN) of 0.6. The energy of activation (Ea) for graft copolymerization has been found to be 16 kJ mol?1. The molecular weight (Mw) and molecular weight distribution (Mw/Mn) of grafted chains was determined by GPC and found to be optimum at 15×10?1 mol dm?3 concentration of comonomer in the reaction mixture. The composition of grafted chains (FAN) determined by IR method was used to calculate the reactivity ratios of monomers, which has been found to be 0.62 (r1) and 1.52 (r2), respectively for acrylonitrile (AN) and ethyl acrylate (EA) monomers used for graft copolymerization. The energy of activation for decomposition of cellulose and grafted cellulose was determining by using different models based on constant and different rate (β) of heating. Considering experimental observations, the reaction steps for graft copolymerization were proposed.  相似文献   

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