Self-assembled molecules columns

Since the overall number of peripheral chains per dendritic molecule is changed, while the lattice parameter of the Colh phases remains roughly similar, the number of dendrimers self-assembling into columns is different in order to keep the total munber of radiating chains constant as shown in Fig. 55. 

A second example of homochiral columns formed by discotics are the complexes of tetrazoles (59 and 60) with l,3,5-tris(4,5-dihydroimidazol-2-yl)benzene (61).74 Four molecules self-assemble to give a supramolecular disc and these discs subsequently form columns in nonpolar solvents. Chiral discs were obtained from the self-assembly of the chiral tetrazole (60) with 61. The chirality of the side chains was found to induce a bias in the helic-ity of the supramolecular assembly. Sergeants-and-soldiers measurements75 were performed for which chiral (60) and achiral (59) molecules were mixed. The experiments showed no amplification of chirality, thus revealing that in these systems chirality transfer from the side chains into the column is... 

Phthalocyanines provided with crown ethers and chiral alkyl side chains (64) have also been reported to self-assemble in nonpolar solvents.77 These molecules form helical columns as could be deduced from the presence of a Cotton effect upon aggregation. To investigate the expression of chirality at the mesoscopic level, sergeants-and-soldiers experiments75 were performed. Chiral phthalocyanine molecules 64 were used as the sergeants and achiral... 

Figure 6.9 Schematic representation of hierarchical self-assembly process for chiral phthalocya-nine 64. Phthalocyanine molecules self-assembly into helical columns with right-handed screw sense (left). These right-handed helices subsequently aggregate to give left-handed super-helices.

Figure 6.12 Self-assembly process of 24 from single molecules into helical columns via nonhelical intermediates. The average number of molecules, (IV), participating in one column in n-butanol at three different concentrations is given as function of temperature. Arrows mark transition from achiral to helical aggregates.

Figure 6.14 Mode of aggregation of eight J(GpGpApGpG) molecules. First self-assembly in barrels occurs, followed by stacking of these barrels in columns. (Gottarelli, G. Masiero, S. Spada, G. P. J. Chem. Soc., Chem. Commun. 1995, 2555 - 2557. Reproduced by permission of the Royal Society of Chemistry.)...

Figure 5.4 Self-assembly of wedge-shaped molecules (modified from Zeng et al 2004). (a) Dendrons with fewer tethered chains adopt a flat slice-like shape (X is a weakly binding group), (b) The slices stack up and form cylindrical columns, which assemble on a two-dimensional hexagonal columnar (Col ) lattice (c). (d) Dendrons with more end-chains assume a conical shape, (e) The cones assemble into spheres, which pack on three different three-dimensional lattices (f) with different symmetries.

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... 

Rh = 3 1, because the molecules between adjacent squares have to give their Rsi-chains into one of the adjacent RF filled squares [42], Note that in this structure the number of distinct columns is larger than the number of incompatible chains attached to the rod-like core. This means that mixing of the distinct chains gives rise to additional colors which further enhances the complexity of LC self-assembly. 

The columnar order in 52a,b was explained by molecular folding the molecules are assumed to be in their U- (or wedge-) shaped conformation and six molecules self-assemble to a supramolecular disc. These discs are stacked in columns and arranged within a columnar hexagonal lattice (Fig. 8). Folding of similar mesogens was also seen by Heiney [65]. 

Helicenes have an intrinsic, rigid helical shape and can be separated into enantiomers. Katz et al. found that the nonracemic helicene 6 with quinone residues self-assembles into one-handed helical columns in apolar solvents, where the molecules are stacked along their helix axes as shown in Fig. 4 [40-42], In this case, the 7r-donor-acceptor interactions appear to induce aggregations and stabilize the columnar stacks. Interestingly, unlike the nonracemic 6, the corresponding racemic 6 produced no such aggregation. 

A columnar mesophase has been used by the group of Percec for the creation of hydrogen-bonded supramolecular polymers.60-61 The phase separation of the apolar side groups of substituted benzamides with the core of the molecule accounts for the self-assembly into a cylindrical structure in which hydrogen bonding acting along the columnar axis occurs and stabilizes the column. 

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