Fluorinated chain

A model with overlapping perfluoroalkyl tail should be excluded, since in this case the difference A is independent of the length of the fluorinated chain. The calculations for the molecular form factor gives a reasonable agreement with the intensities of successive (OOn) harmonics for the model with overlapping aromatic parts of the molecules and the tilt (approximately 35°) of perfloro chains [41c]. This model also satisfies fhe requiremenfs for dense Ailing of space. The smecfic layers in fhe dimeric smecfic phase are well defined (cr = 2.5-3 A) and consisf of fwo sublayers of fhe fluorinafed and aromafic parfs of fhe molecules. 

Only one example of the functionalization of a bis(oxazoline) ligand with fluorinated chains has been described to date [44], but the use of these functionalized hgands does not meet our description of a supported catalyst... 

A C60 derivative with an attached fluorinated chain gave a limiting area of 0.78 nm molecule [266]. It was reported that this film was so mechanically rigid that it pushed the Wilhehny plate out of the water at 11 14 mN m The monolayer spreading of this compound arises from the even greater hydrophobicity of the fluorocarbon chains and their orientation away from the water surface. The LB films with a fluorinated tetrathiafulvalene derivative did not show evidence of charge transfer in their UV spectra. 

Fig. 12 Selected examples of taper shaped crown ethers and polyethers with three fluorinated chains (77°C) data refer to compounds 30, 32 and 34 [132-135]...

Dendritic molecules, forming predominately hexagonal columnar and micellar cubic phases, have been introduced and intensively investigated by Percec et al. and this field has recently been reviewed [143], The mesophases of these dendrons can also be stabilized and modified by replacing alkyl chains by fluorinated chains selected examples will be discussed in the next sections. 

Fig. 16 Representative examples of semiperfluorinated benzoic acids and methyl benzoates with fluorinated chains (77°C) [126, 133, 134, 136, 144-146]...

Rod-Like Liquid Crystals with Fluorinated Chains... 

Examples of rod-like molecules with a branched fluorinated chain at one end (compounds 90-93) are collated in Fig. 26 [166]. It is interesting that smectic phases are retained despite the significant size of these chains. This is mainly a result of the intercalation of the aromatic cores and aliphatic spacers of these molecules, which can compensate this steric distortion. These branched chains remove the B and E phases with crystalline layers and replace them by fluid smectic phases, including SmC phases. The comparison in this figure also shows that the bulky and flexible bis(perfluoropropylene oxide) derived chains (compounds 92, 93) can provide LC materials with especially low melting points and broad mesophase ranges due to the higher conformational flexibility of perfluoroethers compared to linear perfluoroalkyl chains [99, 176]. 

Fig. 27 Comparison of phenylpyrimidine based rod-like mesogens with an alkyl chain at one end and different types of fluorinated chains at the other end (77° C) a observed on heating, all other transitions were observed on cooling [167-170]...

Fig. 30 Selected examples of chiral rod-like mesogens with one fluorinated chain (77° C) one enantiomer is shown as example (SmCA = antiferroelectric SmC phase SmC = ferroelectric SmC phase SmCpi = ferrielectric SmC phase SmCa = helical SmC phase SmI = chiral tilted low temperature phase) [197-199]...

Hydrogen bonded dimers of 4-RF-substituted benzoic acids [119, 120, 122, 126], /rcyclohexane carboxylic acids [120], and hydrogen bonded complexes of benzoic acids with 4,4 -bipyridine and stilbazole [166, 243-246] can be regarded as supramolecular rod-like mesogens with two fluorinated chains. Figures 33 and 34 show comparisons of selected benzoic acid dimers and their bipyridine and stilbazole complexes. Comparison of the benzoic acid dimers 122 and 123 with -alkyl chains and F-terminated -alkyl chains, respectively, indicates that a single F-atom at the end of the alkyl chain reduces the mesophase stability... 

For polycatenar hydrogen bonded complexes with fluorinated chains at both ends (e.g., 138,139, see Fig. 36) formation of columnar phases was observed [246]. However, compound 137, having a branched Rp-chain at one end and three RH-chains at the other has a sequence of three distinct phases in the unusual sequence Cub-Col-SmA-Iso. For the SmA phase of compound 137 a structure with intercalated aromatic cores and RF-chains and separated layers of the hydrocarbon chains was proposed. At lower temperature, when incompatibility rises and the aromatics and Rp-chains disintegrate, all three components form their own layers. However, this produces interface curvature and a columnar phase with square lattice is formed. On further cooling a transition to a cubic phase with Im3m lattice takes place which is most likely of the bicontinuous type [262]. This leads to the unusual phase sequence Cubv-Col-SmA where the positions of the Cubv and Col phases are exchanged with respect to the usually observed phase sequences. The Col-Cub transition at lower temperature could be the result of the decreased conformational disorder of the terminal chains which reduces the steric frustration and hence reduces the interface curvature. 

Investigation of symmetric and non-symmetric triphenylenes combining three fluorinated and three non-fhiorinated chains (compounds 149 and 150 in Fig. 40) has shown that these compounds can possess a higher stability of the columnar phases compared to those with all chains semiperfluorinated (compound 148), whereas the distribution of the fluorinated chains (symmetric vs. non-symmetric) does not play a significant role [272],... 

Fig. 40 Comparison of the effects of the number and distribution of the fluorinated chains in disc-like triphenylene mesogens (77° C) [272]...

Percec et al. described the self-assembly of Rp-substituted bis-dendritic benzamides, such as compounds 179a and 179b, combining a dendron decorated with perfluorinated chains and a dendron with alkyl chains. In the hexagonal columnar LC phases of these molecules the smaller alkyl chains form the centers of the columns, the aromatics are arranged in cylindrical shells surrounding the aliphatic columns, while the larger fluorinated chains form a fluorous continuum... 

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