The effect of a lateral aromatic branch on the orientational ordering of laterally alkoxy substituted nematics

Abstract

Two new mesogenic series have been synthesized. They have the same main core which contains four aromatic rings, with two lateral substituents on the same side of one of the inner rings. One of the substituents is a 4-chlorobenzyloxy group and the second is an alkoxy chain. The positions of the lateral substituents are di erent in the two series. Despite the large aromatic branch, an enantiotropic nematic phase is obtained for most of the compounds. The orientational ordering behaviour of these new compounds has been investigated by C-13 NMR, and two isomeric compounds containing a lateral dodecyloxy chain were chosen for the study. The order parameters of the chain were obtained by a 2D C-13 NMR technique with variable angle spinning. The temperature dependence of the order parameters was determined using the C-13 chemical shifts with slow spinning of the sample parallel to the magnetic ® eld. The ® rst methylene fragment in each lateral substituent of each compound has a positive C± H bond order parameter, implying that this fragment adopts a cisconformation in the nematic phase. The two lateral substituents are folded back along the mesogenic core in opposite directions. The lateral chain is found to be roughly aligned along the molecular long axis imposed by the core, whereas the para-axis of the phenyl ring in the lateral aromatic branch makes a considerable angle with the molecular long axis. It was also found that the di erent patterns of substitution do not a ect the position of the molecular long axis to any large extent.

Orientational ordering in some nematogens deviating from the classical rod-shape

“…The two lateral chains were found to be folded back along the mesogenic core, involving a gaucheconformation for the ® rst segment. The molecular long axis of the core seemed not to be in¯uenced by the found that the para-axis of the lateral aromatic ring makes a non-negligible angle with respect to the core [1 ].…”

“…As a consequence, Our previous NMR studies have revealed that when an the mesogenic core needs to be su ciently long in order to preserve the liquid crystal properties [1]. compounds containing four aromatic rings in the main core and two lateral substituents on one of the inner rings, one alkoxy chain and a 4-chlorobenzyloxy branch; they exhibited the nematic phase [1 ].…”

“…was performed, using PEG 200 as solvent, between the diazonium salt and the dialkoxyphenol under basic In the present paper, in order to obtain a better view of the aromatic ordering, we present the synthesis of conditions [ 1]. Coupling occurs mainly in the position para-to the remaining hydroxyl group.…”

Nematogens containing oxyethylene units at a lateral or terminal position and their mixtures with salts

“…As a consequence, in a homologous series, the conventional mesogens, alkyl or alkoxy chains are used melting temperatures can be adjusted by changing the as terminal fragments [1]. The chain conformation in number of carbons within the terminal and/or lateral the solid phase of these compounds is usually trans and chains without aOE ecting too much the nematic range the crystal cohesion which contributes to the value of [5][6][7]. the melting temperature is mainly due to core-core Nematogens containing the oxyethylene unit have two interactions.…”

Synthesis and comparative studies of phase transition behaviour of new dimeric liquid crystals consisting of dimethyluracil and biphenyl cores

“…4, the 1,3-dimethyluracil ring and the two phenyl rings (or biphenyl moiety) which is adjacent to the spacer appear at different positions depending on the number of carbons at the alkoxy spacer [34][35][36]. The models indicate that 1.3-dimethyluracil and biphenyl core groups take at different side where the number of carbons at spacer change from n = 6 to 10.…”