Banana-shaped compounds

Pelzl, G. Diele, S. Weissflog, W. Banana-shaped compounds — a new field of liquid crystals. Adv. Mater. 1999,11, 707-724. 

I. Wirth, W. Weissflog, Structural and electro-optical investigations ofthe smectic phase of chlorine-substituted banana-shaped compounds, Liq. Cryst. 26 (1999) 401. 

Paleos CM, Laronge TM, Labes MM (1968) Liquid crystal monomers V-(p-alkoxybenzylidene)-p-aminostyrene. Chem Commun (London) 18 1115-1116 Pelzl G, Diele S, Weissflog W (1999) Banana-shaped compounds-a new field of liquid crystals. Adv Mater 11 707-724... 

Bedel JP, Rouillon JC, Marcerou JP, Laguerre M, Nguyen HT, Achard MR New switchable smectic phases in banana-shaped compounds. Liq Cryst 2001 28 1285-92. 

P Bault, Ch Selbman, S Rauch, H Sawade and G Heppke, Biphenyl-Based Banana Shaped Compounds, P.611, ILCC 2003, Edinburgh... 

This situation changed dramatically in 1996 with the discovery of strong electro-optic (EO) activity in smectics composed of bent-core, bowshaped, or banana-shaped achiral molecules.4 Since then, the banana-phases exhibited by such compounds have been shown to possess a rich supermolecular stereochemistry, with examples of both macroscopic racemates and conglomerates represented. Indeed, the chiral banana phases formed from achiral or racemic compounds represent the first known bulk fluid conglomerates, identified 150 years after the discovery of their organic crystalline counterparts by Pasteur. A brief introduction to LCs as supermolecular self-assemblies, and in particular SmC ferroelectric and SmCA antiferroelectric LCs, followed by a snapshot of the rapidly evolving banana-phase stereochemistry story, is presented here. 

Spontaneous formation of chiral LC phases from achiral mesogens—an equivalent to spontaneous resolution of achiral compounds in crystals but in a fluid phase—is a relatively recent phenomenon [9,130-132]. The first compounds discovered with this extraordinary property were the bent-core or banana-shaped mesogens [133,134],... 

Other types of interesting, sometimes even curious, amphotropic materials with unusual molecular architectures have also been found. Whereas T-shaped [109] molecular structures have flexible wings, T-shaped compounds are made of rigid lipophilic units [166]. In the T-shaped case, smectic instead of columnar phases are observed. While mono-alkylated amphiphiles usually show only SmA phases, an interesting exception are so-called banana shaped amphiphiles of which 51 in Fig. 35 may be an example. This gentiobioside exhibits a bi-continuous cubic mesophase [129]. 

Scorch Check for banana shaped injection sprues. Check compound and settings... 

Reddy, R. A. Sadashiva, B. K. Ferroelectric properties exhibited by mesophases of compounds composed of achiral banana-shaped molecules. J. Mater. Chem. 2002, 12, 2627-2632. 

Many other types of liquid crystalline compounds exist besides those with rod-like molecules e.g. compounds with disk-shaped, banana-shaped, and bowlshaped molecules. However, over 80% of all liquid crystals have a rod-like form (e.g. the molecule shown in Fig. 5.1-3). 

In addition, there exist a special type of LC compounds consisting of relatively flat disk-shaped molecules, which have a rigid central part and four to eight flexible chains attached to the core with a suitable linkage (Tables 1 and 2). And finally, in this century, a novel type of LC phase, a banana mesophase formed by banana-shaped molecules, was discovered. " ... 

In 1,3-benzene derivatives like compound 9, first synthesized by Matsunaga et al. [197], recently ferroelectric properties have been claimed [197 a, 197 b], The reinvestigation and new synthesis of several such banana-shaped molecules by different groups [197 c, 197d] proved antiferroelec-tric behaviour, which is striking, because the molecules are achiral. 

There is a third problem for which chirality information is of current interest anisotropic phases are often stabilized by chiral structures. Apart from chiral structures with enantiomorphic crystals of chiral compounds, suprastructural chirality exists in liquid crystal phases built up by chiral molecules as in the cholesteric phases and the smectic C phases. Even liquid crystalline phases with suprastructural chirality originating in achiral, so-called banana-shaped molecules, seem to be possible. Anisotropic polymer films with chiral structures have been found. It can be anticipated that chiroptical spectroscopy with anisotropic chiral systems will lead to new questions and answers. 

However, two possible molecular arrangements can arise in the smectic layers of these V-shape LC molecules, i.e., with the bow-string direction parallel or perpendicular to the layers. Consequendy, it remains controversial whether the molecular arrangements in the mesophases of these compounds is, banana like or calamitic, as discussed by Choi et al. [49,50] and Ros et al. [51,52] with different interpretations. Both prepared homologous... 

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