Search

Four novel bisthienylethene-based rod-like liquid crystals containing different numbers of terminal fluorine atoms were designed and the effect of the terminal fluorination on liquid crystalline self-assembly, optical characteristics in solid state and mechanochromic behaviors was explored. The transition from non-liquid crystal via monotropic liquid crystal with smectic A phase to enantiotropic liquid crystal with smectic A phase can be achieved and the temperature ranges of smectic A phase gradually increase by increasing the terminal fluorination, which might be due to the increase in intermolecular interactions by increasing the number of terminal fluorine atom. All the compounds exhibited AIE characteristic and distinct solid-state fluorescence with yellow or orange color. In addition, the non-fluorosubstituted and difluorosubstituted bisthienylethene-based liquid crystals exhibited reversible mechanochromism, whereas the monofluorosubstituted and trifluorosubstituted bisthienylethene-based liquid crystals exhibited extremely weak mechanochromism due to different intermolecular interaction, molecular symmetry and molecular conformation. These investigations implied that the incorporation of fluorine atom could result in interesting self-assemblies and photophysical properties in different states, which also provided the understanding of the relationship between chemical structures and properties. [Display omitted] • AIE-active bisthienylethene-based mesogens containing different number of terminal fluorine atom are synthesized. • Increase in terminal fluorination increases the stability of smectic A phase. • Distinct solid-state emission and mechanochromic behavior are achieved. [ABSTRACT FROM AUTHOR]

Two novel rod-like mesogens containing one cyanostyrene, one pyridine and one pyrene as π-conjugate rigid core were designed and synthesized by Suzuki coupling and Knoevenagel reactions. The effect of the position of nitrogen-atom on the thermodynamic behavior, liquid crystalline self-assembly, optical behavior, mechanochromism behavior and acidochromism behavior was investigated. The rod-like mesogen in which the nitrogen atom is adjacent to the pyrene displays a phase transition from smectic A to smectic C by increasing temperature, whereas the other rod-like mesogen can only self-assemble into smectic C phase. This difference in mesophase transition behavior might be attributed to the position of nitrogen-atom which induces the change in molecular configuration. Both mesogens exhibit positive solvatochromism and high fluorescence in both solution state and aggregated state which might be attributed to the intramolecular charge transfer and twisted molecular configurations, respectively. Reversible mechanochromism behavior due to changes in molecular stacking and acidochromism behavior due to protonation and deprotonation were also achieved. These multi-stimuli responsive behaviors of the designed rod-like mesogens demonstrate potential applications in the field of multifunctional materials. [Display omitted] • Two novel rod-like mesogens containing multiple functional building blocks are synthesized. • The position of nitrogen atom induces distinct mesophase transition behavior. • High-contrast mechanochromic and acidochromic behaviors are achieved. [ABSTRACT FROM AUTHOR]

Two series of unsymmetric α-cyanostilbene-based tetracatenars containing three hexadecyl chains at one end and one alkyl chain with varying lengths at the other end were prepared by using Suzuki coupling and Knoevenagel reactions. These tetracatenars with the terminal three hexadecyl chains, which are adjacent to the cyano group are non-mesogens, whereas the isomers with one alkyl chain, which is adjacent to the cyano group display transition from non-mesogens to monotropic hexagonal columnar liquid crystal upon elongation of the alkyl chain. This transition could be attributed to that the three hexadecyl chains which are adjacent to the cyano group decrease the interactions between π-conjugated rigid cores, hindering the formation of mesophase. In addition, weak slovatochromism implies weak ICT in both series tetracatenars. Both series isomers exhibit distinct AIE characteristics attributing to the presence of α-cyanostilbene, which could induce stereoisomerism and restricted intermolecular rotation in the aggregated state. Different mechanochromism behaviors could be achieved due to the positional isomerism of terminal alkyl chains. Therefore, tuning the position of terminal alkyl chains could give rise to distinct changes in the molecular aggregate, which provides a scheme to build multifunctional materials with diverse potentials. [ABSTRACT FROM AUTHOR]

• Three series of AIE-active cyanostilbene-based amphiphilic mesogens with different degree of fluorination were synthesized. • The mesomorphic transition from Col hex / p 6 mm to Cub I / I m 3 ¯ m was achieved. • The increase in the degree of fluorination led to the disappearance of Cub I / I m 3 ¯ m. Three series of amphiphilic mesogens containing a cyanostilbene core with zero, one or two lateral fluorine atoms, which attach one polar glycerol group at one end and three lipophilic alkyl chains at the other end were synthesized by Suzuki coupling and Knoevenagel reactions. The thermodynamics, liquid crystalline and photophysical properties of these amphiphilic mesogens were evaluated by polarized optical microscopy, differential scanning calorimetry, small-angle X-ray diffraction, density functional theory calculation, absorption and emission spectra. The non-fluoro and mono-fluoro amphiphilic mesogens display a mesophase transition from hexagonal columnar phase to three-dimensional micellar cubic phase with I m 3 ¯ m lattice by the increase of temperature or the elongation of terminal lipophilic alkyl chains. The bi-fluoro amphiphilic mesogens can only self-organize into hexagonal columnar mesophase. Similar spectral properties and weak solvatochromism in these amphiphilic mesogens are observed attributed to the weak intramolecular charge transfer and weak influence of fluorine atom on the electronic properties in both ground and excited states. In addition, aggregation-induced emission behavior could be achieved in these amphiphilic mesogens due to the twisted molecular configuration. Therefore, complex self-assembly structures and interesting photophysical properties may be altered by varying the degree of fluorination of amphiphilic mesogens, which could promote the application of liquid crystalline materials. [Display omitted] [ABSTRACT FROM AUTHOR]

• Three series of AIE-active cyanostilbene-based amphiphilic mesogens with different degree of fluorination were synthesized. • The mesomorphic transition from Col hex / p 6 mm to Cub I / I m 3 ¯ m was achieved. • The increase in the degree of fluorination led to the disappearance of Cub I / I m 3 ¯ m. Three series of amphiphilic mesogens containing a cyanostilbene core with zero, one or two lateral fluorine atoms, which attach one polar glycerol group at one end and three lipophilic alkyl chains at the other end were synthesized by Suzuki coupling and Knoevenagel reactions. The thermodynamics, liquid crystalline and photophysical properties of these amphiphilic mesogens were evaluated by polarized optical microscopy, differential scanning calorimetry, small-angle X-ray diffraction, density functional theory calculation, absorption and emission spectra. The non-fluoro and mono-fluoro amphiphilic mesogens display a mesophase transition from hexagonal columnar phase to three-dimensional micellar cubic phase with I m 3 ¯ m lattice by the increase of temperature or the elongation of terminal lipophilic alkyl chains. The bi-fluoro amphiphilic mesogens can only self-organize into hexagonal columnar mesophase. Similar spectral properties and weak solvatochromism in these amphiphilic mesogens are observed attributed to the weak intramolecular charge transfer and weak influence of fluorine atom on the electronic properties in both ground and excited states. In addition, aggregation-induced emission behavior could be achieved in these amphiphilic mesogens due to the twisted molecular configuration. Therefore, complex self-assembly structures and interesting photophysical properties may be altered by varying the degree of fluorination of amphiphilic mesogens, which could promote the application of liquid crystalline materials. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Five series of rod-like liquid crystals containing cyanostilbene and different terminal atoms were constructed. • Different terminal atoms and chain length induced mesogenic transition between smectic A phase and nematic phase. • Increasing temperature induced fluorescence quenching. • The terminal halogen atoms induced different AIE and mechanochromism behaviors. Five series of cyanostilbene-based rod-like liquid crystals containing one different terminal atom (H, F, Cl, Br and I) at one end and one terminal aliphatic chain with different numbers of carbon atoms at the other end were reported by Suzuki coupling and Knoevenagel reactions. The influence of terminal halogen atoms and terminal chain length on the self-assembly, AIE behavior, temperature-dependent emission and mechanochromism behavior was explored by POM, DSC, XRD, SEM, absorption spectra and emission spectra. All the compounds are enantiotropic liquid crystals. The lowest non-halogen substituted homologue exhibited solo N phase, but the higher non-halogen substituted homologues exhibited mesogenic transition from SmA phase to N phase upon rising temperature. All the lowest halogen substituted homologues exhibited mesogenic transition from SmA phase to N phase upon rising temperature and all the higher homologues only exhibited SmA. The distinct mesogenic phase transition could be attributed to the intermolecular interaction produced by terminal halogen and the rigidity of the terminal aliphatic chain. All the non-halogen substituted compounds and halogen substituted compounds with smaller terminal halogen atom (F, Cl and Br atom) exhibited AIE behaviors, whereas the iodinated compounds exhibited extremely weak emission in solution and aggregated states due to the heavy atoms effect. These compounds also exhibited distinct solid-state emission with blue or cyan fluorescence, which could be quenched by increasing temperature. The reversible mechanochromism behavior was also achieved in all the compounds. The mechanical force induced quench in emission in non-halogen substituted compounds and halogen substituted compounds with smaller terminal halogen atom (F, Cl and Br atom), whereas enhancement in iodinated compounds. The reversible mechanochromism behavior endowed these compounds with potential applications in rewritable paper and anti-counterfeiting. The interesting properties in these liquid crystals would be attributed to the balance of the halogen-halogen interactions, heavy atom effect, steric-hindrance effect and chain length. These investigations would be helpful to understand the relationship between chemical structures and properties. [ABSTRACT FROM AUTHOR]

C18H18N2O4, monoclinic, P21/n (no. 14), a=5.2291(2) Å, b=10.5932(4) Å, c=15.3775(6) Å, β=96.619(2)°, V =846.13(6) Å3, Z =4, Rgt(F)=0.0479, wRref(F2)=0.1438, T =293(2) K. [ABSTRACT FROM AUTHOR]