•The study analysed 16 new non-symmetric dimers and confirmed their structures.•All the dimers showed enantiotropic mesophase with a pronounced odd-even effect.•Nematic phase stability was influenced ...by spacer length.•cis-trans photoisomerization was observed.•Computational analysis provided insights into the dimers' electronic structure.
The synthesis and properties of two new mesogenic homologous series comprising of sixteen unsymmetrical dimers of cyanoazobenzene and azo/azomethine naphthalene are described. Their right structure was confirmed by FT-IR, 1HNMR , 13CNMR , and elemental analysis. On the polarising optical microscope (POM), their thermotropic properties were examined and further confirmed using differential scanning calorimetry (DSC). All sixteen dimers exhibit an enantiotropic nematic phase. The relationship between the nematic-isotropic transition temperature and the structures of dimers was discussed. A view of their photochromic behaviour was gained by UV–visible spectroscopy. The 6–31 g (d, p) basis set is combined with the B3LYP functional, which is used for computational studies of all the dimers. The examination of Electrostatic Potential (ESP) and optical characteristics also yielded important information about the electronic structure.
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•New LC dimers with azo or azomethine naphthalene synthesized and characetrized.•Even-spacer dimers are nematogenic, whereas odd-spacer dimers are non-mesogenic.•Structure-property relationship ...discussed for synthesized dimers of both series.•NpAmDn series exhibits wider mesophase ranges than NPAzDn.•DFT analyzed, structure optimized, and vibrational frequencies studied.•Azo dimers undergo photoisomerization when exposed to 360 nm light.
The reactions of different α,ω-dibromo alkanes with (E)-4-(naphthalen-2-yldiazenyl)phenol and (E)-4-(naphthalen-2-ylimino)methyl)phenol, respectively, led to the synthesis of two new homologous series of liquid crystalline symmetrical dimers with azobenzene or azomethine central linkage and containing the naphthalene moiety as a rigid core. Spectroscopic techniques like FT-IR, 1H NMR, 13C NMR and elemental analysis confirmed their structure. These dimers exhibited mesomorphic phases, studied through POM and DSC. Their photophysical behaviour was explored using UV–visible spectroscopy. Remarkably, dimers with even spacer units (n = 2, 4, 6, 8, 10, 12) displayed excellent liquid crystalline properties as nematic phases, with extended mesophase lengths and thermal stability for both series. The study revealed the vital role of spacer length in determining liquid crystalline behaviour. The computational studies employed the B3LYP method and electron density method for optimization.
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One new homologous series of liquid crystalline λ-shaped tris azo trimers containing azobenzene moiety as a rigid core and ether linkages were synthesized by the reaction of various n-butylazobenzene ...having bromoalkoxy tail with magneson-I dye respectively. Their right structure was confirmed by FT-IR, 1H NMR, 13C NMR spectroscopy, mass spectrometry and elemental analysis. On the polarising optical microscope (POM), their thermotropic properties were examined, and additional studies were conducted using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). All the trimers with an even number of flexible spacers (n = 2 and 4) show excellent liquid crystalline properties as an enantiotropic nematic phase with greater mesophase length and good thermal stability. The introduction of odd-membered methylene disrupts the orderly stacking of layers and results in a change in mesogenic behaviour. Their structure-property relationships, the influence of different flexible spacers, the mesophase ranges and the photo-isomerisation of liquid crystalline trimers were described. A view of their photochromic behaviour was gained by UV–Visible spectroscopy. The 6-31G (d, p) basis set is combined with the B3LYP functional, which is used for computational studies of λ-shaped tris azo trimers. This approach allows for the determination of various quantum mechanical descriptors that can help us comprehend the mesogenic nature of molecules in computational studies. The results of the Gaussian calculation showed that the target compounds have low energy differences between HOMO-LUMO levels and good chemical reactivity. The examination of ESP and optical characteristics also yielded important information about the electronic structure and potential uses of these compounds.
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•New series of λ-Shape Tris azo liquid crystalline trimers with azobenzene core were synthesized.•DSC and POM techniques were used to examine liquid crystalline properties.•Trimers with an even number of flexible spacer (n = 2 and 4) show enantiotropic mesophase.•Odd membered trimers (n = 3 and 5) show monotropic mesophase.•DFT calculations were used to conduct theoretical studies on these molecules.
One new homologous series of mesogenic compounds containing imine (-CH = N-) and ester (-COO-) linkages as well as lateral thiol (−SH) group and terminal alkoxy chain was synthezised. Molecules in ...the present work was convinced with respective right structure confirmed with FT-IR,
1
H-NMR and
13
C-NMR spectroscopy. Thermotropic properties of the compounds were investigated on a hot-stage plate of a polarising optical microscope and further by differential scanning calorimetry. All the compounds of the series exhibited excellent liquid crystalline nature. Structure-property relationships, the influence of different flexible spacers and the mesophase ranges were studied. Computational studies and the electron density method was performed with B3LYP method for all molecular structures in present work. The mesophase ranges were found to be dependent on the length and flexibility of the alkoxy chain, as well as the presence of the lateral thiol group. The comparative study of the present series with the geometrically related series provided valuable insights into the effect of molecular shape on the mesomorphic properties.
A series of asymmetrical liquid crystal dimers (E)-4((4(n(1,1'-biphenyl-4-yloxy)alkoxy)phenyl) diazenyl)benzonitrile (BpnCN) were synthesized, consisting of two distinct rigid cores: ...4-cyanoazobenzene and biphenyl units. Characterization was accomplished through various spectroscopic techniques. The mesomorphic properties were explored via polarizing optical microscopy and differential scanning calorimetry. UV-Visible spectroscopy assessed the photophysical properties. The presence of an even number of atoms in the flexible spacer resulted in linear molecular shapes for Bp4CN and Bp6CN, while Bp3CN and Bp5CN showed nonlinearity, explaining their non-mesomorphic properties. Computational studies showed a clear correlation between theoretical and experimental wave numbers. The enhanced stability of the mesophase in Bp4CN and Bp6CN was attributed to their higher aspect ratios, promoting ordered structures within the material. UV-visible spectroscopy of dimer Bp4CN revealed absorption bands at 445 nm (n-π* transitions) and 365 nm (π-π* transitions), with photoisomerization observed under UV exposure, reaching a photostationary state in 2.5 min and reversible isomerization back to the trans form in approximately 2.3 h. Notably, even in the absence of substitutions on the biphenyl core, the dimers in our present series demonstrated an enantiotropic nematic mesophase.
In the current study, two new unsymmetrical liquid crystalline homologous series of dimers with a rigid biphenyl core were synthesised using an ether-linking group. Several spectroscopic methods, ...including FT-IR,
1
H-NMR,
13
C-NMR, elemental analysis and mass spectrometry, were used to describe the synthesized dimers. Differential scanning calorimetry (DSC) and polarised optical microscopy (POM) were used to assess their mesomorphic properties. The results showed that the number of methylene spacers significantly affected the thermal properties of the synthesized dimers. To ascertain photophysical behaviour, UV-Visible spectroscopy was employed. Nematic-type mesophase patterns with good mesophase range and thermal stability were seen in both series. Dimers with flexible spacers (
n
= 2, 4, 6) had the best liquid crystalline nature out of all the dimers. The relationships between structure and its mesogenic property, the effects of various flexible spacers, the mesophase ranges, and the photo-isomerization of liquid crystalline dimers were all investigated. DFT Studies were carried out to gain a better understanding of structural features.
•Synthesis of new series of azo naphthyl derivatives with bromoalkoxy tail.•DSC and POM techniques were used to examine liquid crystalline properties.•4e shows reversible photoisomerization, makes it ...suitable for optoelectronics.•Determination of refractive index and dielectric constant for optical properties.•Theoretical models aid in identifying excellent mesogenic dielectric materials.
One new homologous series of mesogenic bromoalkoxy terminated naphthyl derivatives containing flexible spacers as well as azo and ether linkages was synthesized by the etherification of an azo dye (E)-4-(naphthalen-2-yldiazenyl) phenol with various α, ω-dibromo-alkanes, respectively. Compounds in the present work were convinced with respective right structures confirmed with various spectroscopic techniques. Thermotropic properties of the compounds were investigated. Among all the compounds, compounds with flexible spacer (n = 4, 5, 6) exhibited excellent liquid crystalline nature. Structure–property relationships, the influence of different flexible spacers, the mesophase ranges and the photo-isomerization of liquid crystalline compounds were studied. The photophysical behavior was gained by UV–visible spectroscopy and optical properties were determined with a spectroscopic ellipsometer. Computational studies of all molecular structures were performed with satisfactory explanation to attribute mesogenic and optical properties. It's worth noting that synthesized mesogenic materials are excellent dielectrics making them suitable for electronic and industrial applications, as well as having a suitable refractive index making them suitable for light-guiding phenomena.
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Microplastics (MPs) pollution has wreaked havoc on biodiversity and food safety globally. The false ingestion of MPs causes harmful effects on organisms, resulting in a decline in biodiversity. The ...present review comprehended the current knowledge of MP contamination in Crustacea and Mollusca from 75 peer‐reviewed articles published in Asia between 2015 and 2023. A total of 79 species (27 Crustacea and 52 Mollusca) have been recorded to be contaminated with MPs. Out of the total 27 species of Crustacea, Metopograpsus quadridentatus (327.56 MPs/individual) and Balanus albicostatus (0.42 MPs/individual) showed the highest and lowest contamination, respectively. Out of the total 52 species of Mollusca, Dolabella auricularia (2325 MPs/individual) and Crassostrea gigas and Mytilus edulis (0.2 MPs/individual) showed the highest and lowest contamination, respectively. In terms of country‐wise MP contamination, China has the highest number of contaminated species in both phylums among Asia. Findings of pollution indices revealed a very high risk of MP contamination in all the countries. Fiber was reported predominantly in both groups. Blue and black‐colored MPs having <500 μm and <500 μm–1 mm size were found dominantly in Crustacea and Mollusca, respectively. Polypropylene was recorded as the dominant plastic polymer in both Crustacea and Mollusca. In essence, this review has provided a comprehensive insight into MP concentration in Crustacea and Mollusca of Asia, highlighting variations among species and geographic locations. This understanding is crucial for tackling urgent environmental challenges, safeguarding human health, and promoting global sustainability initiatives amid the escalating issue of plastic pollution.
Practitioner Points
Microplastic pollution has created havoc on biodiversity and food safety.
A total of 27 and 52 species of crustaceans and Mollusca have been recorded to be contaminated with MPs.
Metopograpsus quadridentate and Dolabella auricularia have shown higher MPs contamination.
Polypropylene was recorded as the dominant plastic polymer in both crustacean and Mollusca.
Findings of pollution indices revealed a very high risk of MP contamination in all the countries.
A comprehensive analysis of microplastic pollution in marine crustaceans and mollusks in Asia is conducted in this systematic review. The study examines the current situation, concentration levels, characterization methods, polymeric risk assessment, and potential future developments.
