A Study of Liquid Crystalline Properties and Their Relation to the Molecular Structure of Novel Ethylene Derivatives

Abstract

A novel homologous series α-4-[4 -n-Alkoxy benzoyloxy] benzoyl β-4 -methoxy phenyl ethylenes of 12 homologue substances is presented and comprises of 5 compounds (heptyl to tetradecyl) that exhibit both a smectic and a nematic phases. The pentyl, hexyl, and hexadecyl homologues only exhibit the nematic without exhibition of any smectogenic property. The methyl to butyl homologues are not liquid crystalline. All novel liquid crystal (LC) substances of novel series are enantiotropically mesomorphic. The textures of nematogenic homologues are threaded or Schlieren and that of the smectogenic homologues are typical of the smectic A or C. Analytical and spectral data support the molecular structures. Solid-mesomorphic or isotropic, Sm-N, and N-isotropic transition curves of a phase diagram behave in a normal manner. An odd-even effect is exhibited by the Sm-N and N-isotropic transition curves. Thermal stabilities for the smectic and nematic mesophases are 118.0 • C and 157.0 • C, respectively. The Sm-N mesophase length is between 13 • C and 21 • C, whereas the N-I mesophase length varies between 20 • C and 46 • C. The liquid crystal properties of the novel series are compared with known structurally similar homologous series.

Effect of a Central Group on Mesomorphism

“…The changing trend of mesogenic properties from homologue to homologue in present series is due to the sequencial addition of methylene unit or units in left n-alkoxy terminal end group keeping unaltered, polar OCH 3 group at the other end of a molecule. The nematic-isotropic transition curve for odd members of a series is extrapolated [21][22][23] to the nonmesomorphic first member of a present series to determine and predict nematic-isotropic transition temperature of first homologue, keeping in view of the trend of the transition curve, it matches to the point at 201 • C, which is a solid-isotropic temperature of first odd member of a series i.e., 201=201= 0, or mesophase length zero degree centigrade indicates or means, there is no possibility of mesophase formation beyond 201 • C. The mesomorphic behaviors of a present novel series are compared with structurally similar known homologous series X [24] and Y [25] which differs with respect to one of the central groups, keeping rest of the molecular part identical for the same homologue from series to series , shown as under in Fig. 2.…”