Chromonic liquid crystals formed by CI Acid Red 266 and related structures

Abstract

Chromonic liquid crystals are currently receiving increased attention because they have applications in a wide range of products. In this study, we have compared the chromonic mesophase behaviour of four azo dyes with similar chemical structures. Our objective is to determine if there is an obvious link between mesophase formation and dye chemical structure. Orange G does not form mesophases over the concentration range examined (saturated solution >~20-30 wt%). The other three compounds all form nematic (N) and hexagonal (H) mesophases, but over very different concentration ranges. X-ray diffraction shows that the ordered Edicol Sunset Yellow (ESY) aggregates present in the mesophases have a single molecule cross section, while those of CI Acid Red have a cross section equivalent to six to eight molecules, probably organised in a 'water-filled pipes' structure. NMR quadrupole splittings of 2 H 2 O demonstrate that water binding to the aggregates is similar to that found for surfactant lyotropic mesophases. The sodium ( 23 Na) quadrupole splittings for Orange II and CI Acid Red are similar to the values found for surfactant hexagonal phases, suggesting that most sodium ions are 'bound' to the aggregates. This is unlike the behaviour of ESY where only one of the two sodium ions is bound.

Effects of Sodium and Magnesium Cations on the Aggregation of Chromonic Solutions Using Molecular Dynamics

“…As noted by Dickinson et al., aggregation patterns of LCLC appear to be dependent on the number of solubilizing groups and their locations around chromonic polyaromatic cores. Thus, understanding chromonics’ noncovalent interactions with the solvent and counterions (or any additional ionic dopants) is decisive in explaining complex chromonic self-assembly patterns not yet fully understood, such as in Acid Red 266 …”

“…Thus, understanding chromonics' noncovalent interactions with the solvent and counterions (or any additional ionic dopants) is decisive in explaining complex chromonic self-assembly patterns not yet fully understood, such as in Acid Red 266. 94…”

Chromonic liquid crystals: more questions than answers

“…The phase diagrams (Figure 3), however, show profound differences. [9] Maybe most strikingly, Orange G does not show any liquid crystalline phases at all. The differences between CI Acid Red 266 and ESY are also very noticeable.…”

Self-Assembly and Formation of Chromonic Liquid Crystals from the Dyes Quinaldine Red Acetate and Pyronin Y

“…7 Å (i.e., twice the separation between neighbor molecules), results from longer range order within the molecular stacks, as it has been reported for Sunset Yellow and CI acid red 266. 27,29 The broadness of the peaks may be attributed to a finite number of molecules in the aggregates; i.e., the columns continue growing as the concentration increases. The position of the first SAXS peak of the nematic phase, indicative of positional correlation between columns, shifts to higher q as the concentration increases due to decreasing distance between aggregates (Figure 5).…”