Novel bent-core (banana-shaped) liquid crystals without Schiff-base units have been synthesized and investigated by polarized light optical microscopy, differential scanning calorimetry, X-ray scattering, and electrooptical investigations. These molecules are 4-(4-alkylbenzoyloxy)benzoates and 4-(4-alkoxybenzoyloxy)benzoates of resorcinol, 3,4′-dihydroxybiphenyl, and 4,4′′-dihydroxy-1,1′:3′,1′′-terphenyl. Three different mesophases were found depending on the molecular structure and the length of the terminal alkyl chains: a rectangular columnar phase, a highly ordered low-temperature mesophase, and an antiferroelectric switchable fluid smectic mesophase designated as SmCP A . The influence of the molecular structure on the occurrence of the SmCP A phase was investigated. The spontaneous polarization of these molecules is quite high (P S ) 500-700 nC cm -2 ) and specially those molecules with long alkyl chains and short bent-core structures have low melting points and broad regions of this switchable mesophase. Furthermore, first examples of antiferroelectric switchable bent-core molecules with semifluorinated terminal chains will be described.
Several low-aspect-ratio organic molecules [tetrahedral pentaerythritol derivatives, peracylated polyhydroxy compounds and aminoalcohols, a tetraphenylmethane derivative, a tetraphenylstannane, and a tetrahedral zinc bis(1,3-diketonate) all carrying long aliphatic chains] have been synthesized. These compounds were investigated by polarizing optical microscopy and differential scanning calorimetry, and some of them by X-ray diffraction. Most compounds show columnar liquid-crystalline mesophases. Their mesogenic properties are neither caused by a specific anisometric shape of these molecules nor by a strong amphiphilicity as known from conventional liquid crystals. Instead their mesogenity is mainly driven by micro segregation of the incompatible molecular parts (polar central regions and lipophilic alkyl chains) into wellorganized different microdomains. It is shown that, in analogy to block copolymers, the mesophase stability rises on enlarging the number of repeat units connected with each other and on increasing the degree of incompatibility between the incompatible segments. During the process of self-organization the average conformation of the molecules is changed in such a way that it allows a most efficient packing of the molecules. Consequently, rigid molecules with a fixed tetrahedral geometry are not mesogenic. The molecules described herein can be regarded as the most simple star-shaped low-aspect-ratio block molecules that form liquidcrystalline phases. They bridge the gap between classical amphiphilic mesogens, several nonconventional dendritic and oligomeric liquid crystals, and mesomorphic block copolymers.
Tetrahedral pentaerythritol tetra(3,4-dialkoxybenzoates) and tetra(3,4,5-trialkoxybenzoates) can display columnar liquid-crystalline phases despite the fact that they are neither disc-like nor amphiphilic.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.