Ordered phases, chromonics

LCs typically have an aromatic organic core with ionic groups lining the periphery, giving them a disk- or plank-like shape (e.g., ionic organic dye molecules). They are technically classified as LLCs because they can self-assemble into ordered phases in the presence of water. However, unlike traditional amphiphiles, lyotropic chromonic LCs are rigid rather than flexible, and their hydrophobic components are based on aromatic units rather than aliphatic chains. Unlike traditional amphiphilic LCs, they self-organize in so-... 

At first sight there appears to be a paradoxical feature in the standard chromonic phase diagram (Fig. 5). This concerns the N+I/M+I boundary, where on heating the N phase regions become M, i.e., a less ordered phase changes to a more ordered phase. But note that the two mesophases do not have the same composition, i.e., the M phase is more concentrated than the N. This... 

Examples of thermochemical considerations of cupric enolates include the study of the binding of Cu + with kojic acid (16), a cyclic a-ketoenol. Comparison was made between the divalent cations of U02 +, Cu +, Zn +, Ni +, Co +, Cd +, Ca + where these metals are listed in decreasing order of binding constants over 6 powers of 10. In this case carbon-bonded metal seems most unreasonable because it would ruin the chelation as well as any aromaticity in the pyrone ring. It is admittedly an assumption that pyrones are aromatic. There are no one-ring pyrones for which there are enthalpy of formation data for gas phase species, as opposed to the benzoannelated compounds coumarin (I7)i07a, I07b chromone (is) " " "and xanthone (19) . Plausible, but unstable, Cu(II) enolates eliminate copper and form the 1,4-dicarbonyl compounds as shown in equation 8. 

Figure 2. The structure of the chromonic N and M phases The basic structural unit of both phases is the untilted stack of molecules. The N phase is a nematic array in which these stacks lie in a more or less parallel pattern, but where there is no positional ordering. Tlie M phase is a hexagonal array of these columns. The six-fold symmetry is a result of orientational (but not positional) disorder. A schematic diagram of a localized region, as shown in (a) has only orthorhombic symmetry, but, averaged over the whole structure, each column actually lies in a site with sixfold symmetry (b). The restrictions to the possible orientations of the columns are shown in (c). Because of packing considerations, for any particular orientation of a column, as shown on the left, an adjacent column (right) can take up only two of the three possible orientations (i) and (ii). A representation of the orientationally disordered state of the M phase is given in Fig. 9. Note that the molecular columns are shown here in a highly stylized way. They are not necessarily such simple one-molecule-wide stacks.

A survey of chromic species, especially dyes, makes it clear that there is no need for the molecules to even approximate to circular discs, as might be expected if chromonic systems are regarded merely as lyotropic discotic phases extended blade-like molecules are capable of forming chromonic me-sophases with apparently perfect hexagonal order. 

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