Columnar rectangular mesophase

Note 1 See Figs 15a-c for illustrations of molecular arrangements in columnar rectangular mesophases. 

Note 4 There also exist chiral columnar rectangular mesophases, with the molecular discs tilted periodically in the columns and with the tilt directions changing regularly down the columns. 

Complexation of 100 with carbonyl complexes of chromium, molybdenum, and tungsten yielded liquid crystalline complexes lOla-c [114] (Scheme 50). All derivatives 101 melted at similar temperatures into the columnar rectangular mesophase (deduced from WAXS and SAXS measurements). However, the clearing points were strongly dependent on the metal center and increased with increasing atom number. Upon complexation, the aza crown macrocycle loses its flexibility, with the metal carbonyl fragment located above the crown leading to a cone-shaped... 

Figure 8. Model of the mesomorphic self-organization of 2,3,4-t isdodecyloxy-benzaldehyde-2 4 -dinit ophe-nylhydrazone in its columnar rectangular mesophase [20] Don donor part, Acc acceptor part.

The discotic mesophases are classified in two types columnar, and nematic discotic. The structure of the nematic discotic mesophase (Np, Figure 8.3, left) is similar to that of rod-like molecules, but constituted by disk-like units. In columnar mesophases, the molecules are stacked in a columnar disposition and, depending on the type of columnar arrangement, several columnar mesophases are known. The most common lattices of the columnar phases are nematic discotic (No), columnar nematic (Ncoi), columnar hexagonal (Coin), and columnar rectangular (Col,) mesophases. 

Fig. 15. Plan views of the two-dimensional lattice of the columns in columnar rectangular (a) to (c) and oblique (d) mesophases. Ovals indicate the planes of the molecular discs.

Compound 114d possesses significantly lower transition temperatures (Scheme 60) due to the branched side chains [126]. A columnar phase is present even below room temperature. At 14 °C, anew chiral columnar phase was observed while above 111 °C, an achiral columnar rectangular phase was observed. The spiral-pattern texture of 114d in the chiral Col mesophase is shown in Fig. 17. 

Figure 4. Schematic phase diagrams of members of the radial hexayne series 1,2, and 3 as electron donors with TNF as the electron acceptor [26] Cr crystalline, Nd nematic discotic, Col, columnar rectangular, and Col), columnar hexagonal mesophase (o intracolumnar ordered). Iso isotropic liquid (see footnote 1 in Sec. 3 commenting on the nomenclature of columnar mesophases).

A helical arrangement within columns was also found for other metal 3-diketonate complexes provided with chiral side chains (32) by Serrano and co-workers.35,36 These compounds form rectangular columnar mesophases with helical order within the columns. A spin-coated sample of 32 showed a positive exciton-splitted signal in the CD spectra, which was interpreted as a left-handed (M) helix. Annealing of the film resulted in much higher optical activities and a shift of the absorption maxima. The observed optical changes clearly point to a chiral organization of the columns in the mesophase. 

Discotic liquid crystals arise from disk-shaped molecules as nematic or cholesteric mesophases. Their structural characteristics are similar to the respective ealamitie mesophases, that is, the normals of the disks are oriented parallel. Instead of the smectic mesophases, diseotie columnar liquid crystals arise from eonnecting the disks to each other. The columns of the discotic columnar mesophase form a two-dimensional lattice whieh is in a hexagonal or rectangular modification. In addition, the columns may be tilted (Fig. 2f,g). 

Note Depending on the order in the molecular stacking in the columns and the two-dimensional lattice symmetry of the columnar packing, the columnar mesophases may be classified into three major classes hexagonal, rectangular and oblique (see Definitions 3.2.2.1. to 3.2.2.3). 

Columnar mesophase characterised by a liquid-like molecular order along the columns, in which the columns are arranged in a rectangular packing. 

Columnar mesophases of rectangular section have been obtained by combining the monotopic components of 173 with the TP2 and TU2 units their occurrence may be attributed to the formation of mixed 2/1 supermolecules 175 [9.153],... 

Fig. 12 Schematic representation of the self-assembly of dendromesogens into various type of mesophases (smectic, hexagonal and rectangular columnar, micellar cubic, and tetragonal phases) by the control of the molecular shape conformation (from flat tapered to cylindrical to conical and to spherical shape). From [126]...

Another example of a rigid macrocycle used as the central core of a den-drimer is the porphyrin. First and second generation phenylene-based dendritic porphyrins with 8 and 16 long alkyl chains on their periphery have been studied (Fig. 80). Only the second generation exhibits mesomorphic behavior with the formation of a rectangular columnar mesophase upon heating (Cr 39 Coir 110 I) [334]. A stable supramolecular 1 1 complex was formed between the second generation and Ceo, which led to the enhancement of the mesophase stabiUty of the formed (imidentified) columnar phase (Cr 99 Col 250 I). 

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