Design flüssigkristalliner Blockmoleküle: columnare Mesophasen calamitischer Bolaamphiphile mit lateralen lipophilen Substituenten

Calamitic Bolaamphiphiles with (Semi)Perfluorinated Lateral Chains: Polyphilic Block Molecules with New Liquid Crystalline Phase Structures

“…The model shown in Figure a was first proposed for the p 2 gg lattice of compounds 1 /10− 1 /12 . Generally, a p 2 gg lattice requires a herringbone-like arrangement within the lattice, which was realized in the model in Figure a by including two elliptical cylinders per unit cell, separated by bilayer-like aggregates of the bolaamphiphilic units .…”

“…However, the cooperative and dynamic networks of intermolecular hydrogen bonding between the diol groups provide sufficient cohesive energy to inhibit a complete collapse of the molecular order and support the segregation of the incompatible parts, leading to a series of novel mesophases. As shown in Figure , elongation of the lateral chain of the compounds 1 / n gives rise to a transition from a smectic monolayer structure ( n = 0, 1: SmA 1 ) via a mesophase with a strongly distorted structure ( n = 3−7: SmA + ), a centered rectangular columnar phase ( n = 6−9: Col r / c 2 mm ), and a noncentered rectangular columnar phase ( n = 10−12: Col r / p 2 gg ) to a hexagonal columnar phase ( n ≥ 12: Col h / p 6 mm ) 21b. This phase sequence results from the microsegregation of the lateral alkyl chains from the rigid aromatic units which occurs above a certain minimum length for these chains (≥3).…”

“…For short-chain compounds ( 1 /3, 1 /5) and for medium-chain compounds at higher temperatures ( 1 /6, 1 /7), there is no long-range correlation between these lipophilic regions. This leads to a special type of mesophase which is characterized by a typical SmA-like optical texture and by an X-ray diffraction pattern in which a diffuse scattering in the small-angle region appears adjacent to or instead of the sharp layer reflection (SmA + ) 21b. Longer chains organize in infinite columns which adopt a positional long-range order in two dimensions, leading to columnar phases.…”

“…The space required by the alkyl chains with respect to the length of the bolaamphiphilic units determines the number of biphenyl units which have to be organized in the shells around the lipophilic cylinder cores. This influences the geometry of the cylinders and gives rise to the above-mentioned sequence of two-dimensional(2D) lattices 21b 1 Dependence of the liquid crystalline phases of compounds 1 / n with respect to the length of the lateral alkyl chains and models for the organization of the molecules 1 / n in their mesophases 21b.…”

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1 Dependence of the liquid crystalline phases of compounds 1 / n with respect to the length of the lateral alkyl chains and models for the organization of the molecules 1 / n in their mesophases 21b. Cr = crystal, SmA = smectic A phase (liquid crystalline phase with layer structure, without long-range positional order in the layers and with an arrangement of the biphenyl units parallel to the layer normal), SmA + = disordered mesophase (typical SmA texture, but a diffuse reflection is found adjacent or instead of the sharp layer reflection in the small-angle region of the X-ray diffraction pattern),21b Col r = centered ( c 2 mm ) or noncentered ( p 2 gg ) rectangular columnar phases; Col h = hexagonal columnar phase ( p 6 mm ) . Models: blue = hydrogen-bonding networks of the terminal diol groups; white = microsegregated regions of the lateral alkyl chains; gray = rigid biphenyl units.

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