Y. Matsunaga

Nematic-Isotropic Transition Temperature and Dipole-Dipole Interaction. 4-(4-X-Substituted Phenyliminomethyl)phenyl 4-Y-Substituted Benzoates and 4-X-Substituted Phenyl 4-(4-Y-Substituted Phenyliminomethyl) benzoates

Abstract Nematic-isotropic transition temperature was determined for 4-(4-X-phenyliminomethyl)phenyl 4-Y-benzoates and 4-X- phenyl 4-(4-Y-phenyliminomethyl)benzoates, where X and Y are CN, CH3O, NO2, Cl, Br, N(CH3)2, CH3, F, or CF3 groups. The transition temperature in the absence of the dipole-dipole interaction was estimated by extending Van der Veens approximation. While a large positive deviation is found for the CH3O-NO2 and CH3−NO2 derivatives, indicating the significant contribution of dipole-dipole interaction to the nematic thermal stability, no deviation in the CH3O-CN derivatives suggests the anti-parallel molecular association in the mesophase.

Effects of Terminal Substituents on Mesomorphic Properties. 4-(4-X-Substituted Benzylideneamino) phenyl 4-Y-Substituted Benzoates

Abstract Nematic-isotropic transition temperature was determined for 4-(4-X-benzylideneamino)phenyl 4-Y-benzoates, where X and Y were chosen from methoxy, nitro, chloro, bromo, dimethylamino, methyl, fluoro, trifluoromethyl groups. The order of group (X or Y) efficiency in promoting the nematic-isotropic transition temperature is markedly affected by the nature of the group (Y or X) located at the other end. For example, the methoxy and methyl series give NO2 > CH3O > N (CH3)2 > Cl ≒ Br > CH3 > F > CF3, whereas the trifluoromethyl series gives N(CH3)2 > CH3O > CH3 > Cl ≒ Br > NO2 > F, suggesting that the dipole-dipole interaction contributes significantly to the stabilization of the nematic phase.

Effects of Lateral Substituents on Mesomorphic Behavior. II. 4-(4-Alkoxybenzylideneamino)phenyl Benzoates

Abstract The mesomorphic properties of 4-(4 alkoxybenzylideneamino)phenyl 2- and 3-X-benzoates, where X = Me or Cl, were examined. While the nematic-isotropic transition temperatures of the 2-Me and 2-Cl derivatives are nearly identical, the 3-Cl derivatives give higher transition temperatures than the 3-Me derivatives, the difference being 20°C or more. The nematic phase given by the lower homologous members of the 2-Me derivative is thermally more stable than that of the 3-Me derivative but this relation is reversed for the higher members. In contrast to the purely nematogenic parent compounds, the 3-halogeno derivatives of the higher homologous members exhibit a smectic A phase.

Effects of Lateral Substituents on Mesomorphic Behavior. I. 4-(Benzylideneamino) phenyl 4-Alkoxybenzoates

Abstract Liquid crystalline transition temperatures in 4-(2-and 3-X-benzylideneamino)phenyl 4-alkoxybenzoates, where X = Me or C1, were examined. Although the two substituents are geometrically similar, they affect the nematic-isotropic transition temperature differently. The transition temperature of the 2-Me derivative is higher by 10 to 15°C than that of the 2-C1 derivative, whereas the reverse is true for the 3-X derivatives, the difference being 14 to 21°C. The 3-halogeno derivatives of the higher homologous members exhibit a smectic A phase which is not observed for the parent compounds.

Mesomorphic Behavior of Compounds Incorporating One-Unit Linking Groups. II

Abstract 4,4′-Bis[4-(4-alkoxybenzoyloxy)benzylideneamino diphenyl ether, its 3,4′-analogue, and 1,4-bis[4-[4-(4-alkoxybenzoyloxy)benzylideneamino phenoxy benzene have been found to exhibit mostly an enantiotropic nematic phase. The clearing points of these three homologous series are rather close to each other; for example, the methoxy members give 340,325, and 333°C respectively and the decyloxy members 222,213, and 231°C, suggesting no substantial difference in the molecular shape though the molecules are not quite linear. On the other hand, the mesophase appearing in 4,4′-bis[4-(4-alkoxybenzoyloxy)benzylideneamino diphenylmethanes is of the smectic C type. Thus, the importance of the nature of one-unit linking groups as a factor determining the type of mesophase was demonstrated.

Effects of Lateral Substituents on Mesomorphic Behavior. III. N-4-(4-Alkoxybenzoyloxy)benzylidene]-anilines

Abstract The mesomorphic properties of N-4-(4-alkoxybenzoyloxy)benzylidene]-2- and -3-X-anilines, where X = Me, F, Cl, Br or I, were examined. The 2-Me derivatives give higher nematic-isotropic transition temperatures than the 3-Me derivatives, whereas the reverse is true for the F compounds. The intersection between the plots of the transition temperatures of the 2-X and 3-X derivatives against the alky chain length is found for the CL, Br, and I compounds, respectively. The smectic A-nematic transition temperature recorded for the heptyloxy member is promoted by the 3-X substitution as much as 32°C (X = F) and 16° (X = Cl).

Nematic-isotropic transition temperature and dipole-dipole interaction. 4-X-Substituted phenyl 4-(4-Y-substituted benzylideneamino)-benzoates

Abstract The nematic-isotropic transition temperature of 4-X-phenyl 4-(4-Y-benzylideneamino)benzoates, where the terminal groups X and Y are CN. CH3O, NO2, Cl. Br. N (CH3)2, CH3, F, or CF3, was examined. The transition temperature difference between the two series, in which X or Y=CH3O and F, respectively, decreases in this order: CF3>NO2>Cl ≒ Br ≒ F>CN>CH3>CH3O>N (CH3)2. Thus, the groups are almost in the order of substituent constants except for the CN group, suggesting that the dipole-dipole interaction contributes significantly to the nematic thermal stability and also that the effective dipole moment of the molecule bearing CN and CH3O groups is markedly reduced in the mesophase from that of the free molecule because of the anti-parallel molecular association.

Mesomorphic Behavior of Symmetric Liquid Crystal Dimers: α,ω-Bis[4-(4-alkoxybenzoyloxy)benzylideneamino] alkanes

The mesomorphic properties of eight series of α,ω-bis[4-(4-alkoxybenzoyloxy)benzylidene-amino]alkanes have been examined. The terminal alkoxy group was varied from ethoxy to octyloxy and the number of methylene units in the spacer was increased from three to ten. While all the dimers with even-membered spacers are nematogenic, the dimers with odd-membered spacers exhibit both a nematic and a smectic phase when the terminal alkyl chain is short and only a smectic phase when the alkyl chain is long. The higher alkoxy derivatives are particularly interesting as the dimers with even-membered spacers possess higher clearing temperatures associated with small entropies of N-I transition and those with odd-membered spacers possess lower clearing temperatures associated with large entropies of S-I transition.

Effects of Lateral Substituents on Mesomorphic Behavior. IV. Phenyl 4-(4-Alkoxybenzylideneamino)-benzoates

Abstract Phenyl 4-(4-alkoxybenzylideneamino)benzoates exhibit both a nematic phase and a smectic A phase when the alkyl chain is propyl to decyl. While the 2-X substitution tends to eliminate the smectic phase, the 3-X substitution tends to eliminate the nematic phase. A smectic A phase is generated by the methoxy to decyloxy members of the 3-Me, 3-F and 3-Cl derivatives, by the ethoxy and higher members of the 3-Br derivative and by the butoxy and higher members of the 2-F derivative. The smectic thermal stability can be enhanced or depressed by the 3-X substitution depending on the kind of halogen and the alkyl chain length; for example, 29°C for X=F, 3°C for Cl and −11°C for Br in the case of the propoxy member and 5°C for X=F, − 15°C for Cl and −24°C for Br in the case of the decyloxy member.

Mesomorphic properties of 3-pyridyl 4-(4-alkoxybenzyleneamino) benzoates and isomeric compounds

Abstract The nematic-isotropic transition temperature of 3-pyridyl 4-(4-propoxybenzylideneamino) benzoate is higher by 13°C than that of the phenyl analogue and the smectic A-nematic/isotropic transition is also promoted by the replacement of the terminal moiety as much as 23°C. The enhancement of both the nematic and smectic thermal stabilities decreases as the terminal alkyl chain length increases. Similar changes in the mesomorphic properties by the replacement are recorded for N-[4-(4-alkoxy-benzoyloxy) benzylidene] anilines and other isomeric compounds.