Ferrocenes liquid crystals

Liquid-crystalline phases are characterized to some degree by the shape of the molecules and by their packing arrangements and ordering in the mesomorphic state. Typically, molecules can have cither disc- or rod-like shapes and can form discotic or calamitic mesophases, respectively. Ferrocene liquid crystal systems that have so far been synthesized tend to have molecular structures that are lath- or rod-like in shape, and consequently the phases observed are calamitic. However, this does not preclude the possibility that a polysubstituted ferrocene could be prepared where the molecular shape is disc-like, thereby holding out the prospect of possibly producing discotic/columnar phases. 

The smectic state, apart from exhibiting a rich variety of modifications, is also thermodynamically ordered. Thus, there is a well-defined sequence of phases formed on cooling from the isotropic liquid. For instance, the following transition sequence would be observed for a ferrocene liquid crystal exhibiting enantiotropic smectic C, smectic A and nematic phases ... 

Ferrocene-containing co-polyesters, preparation, 12, 350 Ferrocene-containing liquid crystals dendrimers, 12, 235 disubstituted ferrocenes, 12, 227 hydrogen-bonded ferrocene derivatives, 12, 234 monosubstituted ferrocenes, 12, 222 polycatenar ferrocenes, 12, 234 properties, 12, 221... 

The esterification of ferrocene-1,1 -dicarboxylic acid with substituted phenols to produce hexacatenar substituted ferrocenes, which are thermotropic liquid crystals, is also mediated by carbodiimides. ... 

Organothiols chemisorbed on gold surfaces are especially usefiil for electrochemical and chemical studies. For example, carboxylic acid terminated monolayers are often used. An example is the attachment of cytochrome C with its side chain lysine groups to acid terminated self assembled monolayer gold electrodes. Carbodiimide mediated esterification of ferrocene-l,l -dicarboxylic acid with phenols is used to construct thermotropic liquid crystals. ... 

This contribution presents the results published up to June 1993 on ferrocene-containing thermotropic liquid crystals and should be considered as a comple-... 

Fig. 9-3. Monosubstituted ferrocene-containing thermotropic liquid crystals.

None of the ferrocene derivatives 13 showed liquid crystal properties on heating. They all melted into an isotropic melt. When cooled from the isotropic liquid, the first members of the series [n = 1 — 6) exhibited a monotropic nematic phase. A representative example of a nematic schlieren texture is shown in Fig. 9-10. 

The thermal characteristics exhibited by the series 11 [18] and 14 [20] proved that interesting liquid crystal properties can be obtained with symmetrically 1,T-disubstituted ferrocene derivatives. The structure of the organic unit, which is combined with the ferrocenyl moiety, must be carefully chosen. 

Ferrocene derivatives 15 exhibited remarkable liquid crystal properties (Fig. 9-13). Indeed, they all gave rise to enantiotropic mesophases. Structures with n = 1 to 11 showed nematic phases. From n = 12 a smectic C phase formed. The latter was monotropic only for 15 (n = 12). The smectic C domain increased from n = 13 to n = 16, and, inversely, the nematic range narrowed. The last member of this series (n = 18) presented one smectic C phase between 159 °C and 179 °C. A nematic to smectic C transition and a focal-conic texture of a smectic C phase are presented in Figs. 9-14 and 9-15, respectively. 

Fig. 9-12. First 1,3-disubstituted ferrocene-containing liquid crystals (15 and 16) and non mesomorphic 1,3-disubstituted ferrocene derivatives 17.

Ferrocene derivative 16 showed an enantiotropic nematic phase between 204 °C and 235 °C. This result indicated that a biphenyl system, when associated with the ferrocenyl moiety substituted in the 1,3-positions, was also propitious to liquid crystal formation (compare 16 with its l,T-isomeric analogue 7 (n = 6)). 

The cyclopentane ring has already been used to prepare thermotropic liquid crystals [23]. In 17, the bulky ferrocene core, due to its depth, acts as a spacer... 

P Ferrocene-Containing Thermotropic Liquid Crystals COzR ... 

We designed and studied [27] a family of unsymmetrically l,l -disubstituted ferrocene derivatives obtained by combining the organic units A and B (above), used to prepare the families 13 and 14, respectively within the same molecular framework. Structures 25 (Fig. 9-21) led to remarkable mesomorphic properties. All derivatives exhibited liquid crystal properties. Compound 25 (n = 11) gave rise to an enantiotropic smectic A phase. Complex 25 (n = 12) showed an enantiotropic... 

Fig. 9-21. Unsymmetrically l,l -disubstituted ferrocene-containing thermotropic liquid crystals and examples of their transition temperatures.

Polyesters 26 represent the first ferrocene-containing liquid crystal polymers [28]. These copolymers were found to be insoluble in THF, toluene, dichloromethane, chloroform, p-chlorophenol, and tetrachloroethane. The terephthaloyl chloride/iso-phthaloyl chloride ratio was maintained constant (7 3), but the content of the ferrocene unit was varied from 0 to 100%. 

The research on ferrocene-containing thermotropic liquid crystals has concentrated, so far, on design, synthesis, and investigations of thermal properties. These efforts, and more particularly the results obtained, could be a source of inspiration for the development of new metallomesogens. As an example, we recently reported the first liquid crystalline ruthenocene derivatives [29]. 

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