# Chiral Chromonics Confined in Spherical Geometries
## 2 Brief Description of Chromonics  
Chromonics are a subset of lyotropic liquid crystals. Their name is derived from the Greek word \"chroma\" meaning color, indicating that many chromonics are colored [18]. They usually consist of a rigid hydrophobic discotic core that is composed of hydrophobic aromatic rings with hydrophilic groups [19]. Some examples of chromonic LCs include drugs, such as disodium chromoglycate, that are often used in anti-asthmatic treatments; dyes, such as Sunset Yellow, that are used in the food industry; DNA nucleotidessuch as guanine derivatives; DNA itself and cellulose. The interest in chromonic materials relies on the fact that their molecules are able to self-assemble. The driving force for molecular aggregation appears to be an enthalpically driven face-to-face adhesion between the aromatic rings [20]. Not only are the \(\pi\)-\(\pi\) interactions between the aromatic complexes involved in the aggregation but the flexibility and nature of the chains connecting the complexes, the nature of the other functional groups around the complexes and the electrostatic and dipolar interactions between the complexes also define the organization between the molecules [21]. These interactions (electrostatic, excluded volume, hydrophobic) constrain the aromatic complexes to arrange themselves in very specific orientations relative to each other [22]. Then, during stacking, chromonic molecules can position themselves on each other, so the stack is perpendicular to the flat chromonic molecule, or they can undergo displacement, so the stack is angled. In other cases, the arrangement is even more complex. However, for chromonic self-assemblies, there is neither an optimum aggregation size nor a critical temperature for the onset of the aggregation. Additionally, the energy of the assembly is high [20; 21; 22]; hence, there are significant energy barriers for the dynamic dissociation and re-association of these molecules. Due to the presence of these elongated aggregates, chromonics are able to form two mesophases (Figure 1): the nematic (N) phase at low concentrations, consisting of a nematic matrix of columns, and the M phase at higher concentrations, in which the columns pack into a regular two-dimensional hexagonal lattice. The best way to illustrate the mesophase existence intervals of a chromonic material in water is to consider its phase diagram, which identifies them as a function of their temperature and concentration [23; 24]. Figure 2a shows the molecular structure of disodium chromoglycate (DSCG), whose phase diagram in a deionized water solution is reported Figure 2b. DSCG is the disodium salt of dibasic acid: 1,3-bis (2-carboxychromon-5-yloxy)-2-hydroxypropane [25]. Its crystals are an interstitial solid solution, with water as the interstitial component. In the solution, the unit cell expands to accommodate up to approx. nine water molecules before collapsing to form liquid crystalline hydrates. The DSCG crystals are unique in their degree of reversible water absorption without causing a lattice collapse. For the DSCG concentrations between 10 and 15 wt%, the nematic phase appears at room temperature. For the concentrations of 20 wt% or more, a columnar phase appears. The phase diagram contains large intervals in which the two phases coexist. At room temperature, the N and M phases coexist in the range of 15 to 20 wt%. Another well studied chromonic is Sunset Yellow (SSY), Figure 3a shows its molecular formula. SSY can exist in two tautomeric forms [26]: an NH hydrazone form, where the hydrogen resides on the distant nitrogen of the azo bond, and an OH azo-tautomer form, where the hydroxide proton resides on the oxygen in ortho rather than the azo bond. [PERSON] et al. [27] showed that the NH hydrazonic form prevails. The azo form can produce cis-trans isomers. This change in the isomers occurs when the molecule  
Figure 1: Scheme of the N (**left**) and M phases (**right**) for a chromonic liquid crystal. interacts with light in the 480-500 nm wavelength range.