Mesophase design: I. Molecular structure and crystal packing motifs of 4-alkylcyanobiphenyls |
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Authors: | L G Kuz’mina N S Kucherepa |
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Institution: | 1.Kurnakov Institute of General and Inorganic Chemistry,Russian Academy of Sciences,Moscow,Russia |
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Abstract: | A comparative study of the crystal and molecular structures of 4-alkylcyanobiphenyls (ACB-n) C
n
H2n + 1-C6H4-C6H4-CN (n = 2, 4–12) belonging to liquid-crystal compounds revealed no direct relationship between the molecular geometry of these
compounds and their liquid-crystalline properties. Mesogenic properties are determined by the alternation of the loosely packed
aliphatic and closely packed aromatic regions in the crystals. Graphs describing the crystals and mesophases were designed
for ACB-n. The graph for nematic mesogens of ACB-n (n = 5−7) has one structure-forming element. The graph for smectic-nematic (n = 8 and 9) and smectic (n = 10−12) mesogens have more than one structure-forming element. If different types of secondary bonds in the smectic mesophase
have equal energies, the disruption of these interactions caused by the temperature rise occurs simultaneously and the system
undergoes a transition from the smectic phase to the isotropic liquid. If the energies of different types of secondary bonds
are different, the destruction of the mesophase occurs in steps and the phase transitions are more complicated (smectic-nematic-isotropic
transitions). |
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Keywords: | |
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