Metallomesogen mesophases

Polarization, and NLO properties, 12, 102 Polarized optical microscopy, metallomesogen mesophase characterization, 12, 208 Polar monomers, polymerization, 1, 147 Polar polyolefins, co-polymerizations, 11, 723 Polyacetylenes... 

A different mechanism is that of charge transfer, of which there are many examples based, in particular, on metallomesogens [14]. In these cases, mesophases can be induced by adding the electron-poor TNF (2,4,7-trinitro-9-fluorenone) and Fig. 9 shows Pd mesogen 4, which shows a particular type of SmA phase when TNF is added [15]. 

Trzaska and co-workers showed a similar propeller mechanism for the formation of helical columns from disclike metallomesogens (29-31).34 These metallomesogens also have C3 symmetry and 30 and 31 are provided with chiral side chains. In the hexagonal columnar mesophase these chiral side chains induce a Cotton effect in the chromophore of the helically arranged core. Heating the mesophase to the isotropic liquid results in the disappearance of the Cotton effect because of the loss of helical order. This effect illustrates the need for the molecules to be positionally ordered in order for the side-chain chirality to be transferred to the supramolecular column. 

Thermotropic liquid crystals, 15 86-98 bent-core, 15 98 discotic phases of, 15 96 frustrated phases of, 15 94-96 metallomesogens, 15 97 nematic liquid crystals, 15 86-92 smectic liquid crystals, 15 92-94 Thermotropic mesophases, 20 79 Thermotropic polycarbonates, 19 804 Thermotropic polyesters, liquid-crystalline, 20 34... 

Keywords Columnar mesophase Cubic mesophase Dendrimer Liquid crystal Metallomesogen Micro-segregation Organic semiconductor Perfluorinated molecule Polyphilic molecule Self-assembly... 

Fig. 45 Fluorous metallomesogens at the lamellar-columnar cross-over (a) induction of a nematic phase by mixing metallomesogens with smectic and columnar phases, (b) metallomesogens showing re-entrant isotropic mesophases (Isore) (77° C) [40, 41, 293]...

Keywords Crown compounds Liquid crystals Mesophases Metallomesogens Polymers Salt effects Self-assembly Substituent effects Supramolecular chemistry Phthalocyanines Cyclophanes... 

Metallomesogens have been shown to form helical supramolecular organisations in their mesophases [95]. Chiral oxazoline complexes with various metal ions and six alkyl chains did not show LC behaviour, but when mixed with trinitrofluorenone form achiral smectic A phases [96]. Furthermore, when a branch was included in the structure of the ligands (Fig. 12) the corresponding complexes with copper(II) and palladium(II) form columnar mesophases which have a helical organisation [97]. The presence of the stereogenic centre near the central metal ion in these complexes (Fig. 12) is enough to cause the parallel molecules to stack in a tilted manner with... 

Although most of the times it is of interest to obtain stable mesophases, it may be useful also to exploit their controlled degradation or transformation. Taubert and coworkers reported a very interesting application of metallomesogens [80, 81]. They prepared mixtures of bis(dodecylpyridinium) tetrachlorocuprate 37 and of... 

Phthalocyanines represent a class of inherently disc-like molecules and consequently were among some of the first examples of metallomesogens exhibiting columnar mesophases, being first reported by Simon and co-workers in 1982 [122]. Thus, they described an octasubstituted phthalocyanine copper(Il) complex (Figure 65) which exhibited a mesophase between 53°C and the start of decomposition at about 300°C X-ray diffraction studies showed lines with reciprocal spacing of 1 3 v 4 7,... 

While there are several examples of metal complexes which are amphiphilic in nature, it is in very few cases that lyotropic liquid crystals mesophases have been characterized. Although numerous and strictly classifiable as metallomesogens, in this article we exclude discussion of the amphiphiles with a simple metal ion as the cation (e. g. sodium salts of carboxylic acids), rather concentrating on amphiphiles in which the metal cation is an integral part of the amphiphile. 

Refractive index studies allow measurements of the birefringence, but also of the polarisability. The mean polarisability (a) can be determined using an isotropic liquid solution, whereas the polarisability anisotropy (Aa) is measured in the mesophase. Polarisability studies have been made on palladium, platinum, iridium and silver metallomesogens, and show a higher polarisability for the metal complexes than for their parent ligands. ... 

The number of studies on luminescence of metallomesogens in the liquid crystal state is still limited, but considerable progress is to be expected in the near future. New strategies for the design of room-temperature mesophases exhibited by metal complexes will make more types of metallomesogens available for photophysical studies. The possibility to obtain polarised emission via these systems and the use of these compounds in luminescent devices can be an additional drive for further exploration of this research field. ° The most promising metal ions to be included in luminescent metallomesogens are Eu, Tb, Sm, Ru, ... 

Spontaneous polarisation can also be observed for chiral discotic metallomesogens forming columnar mesophases, when the chiral molecules are tilted with respect to the column axis. The tilt induces a dipole moment within the plane of the molecule. A net macroscopic polarisation can be obtained for rectangular columnar phases with Cz or P2i symmetry. Serrano and Sierra reported on ferroelectric switching in the columnar mesophase for chiral /3-diketonate complexes (Figure 2.52). ... 

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