Large assembly formation via a two-step process in a chromonic liquid crystal

Area of Science:

• Materials Science
• Physical Chemistry
• Supramolecular Chemistry

Background:

• Chromonic liquid crystals exhibit unique self-assembly properties in solution.
• Near-infrared (NIR) cyanine dyes are of interest for their optical and self-assembly characteristics.

Purpose of the Study:

• To investigate the self-assembly behavior and liquid crystal formation of the NIR cyanine dye IR-806 in aqueous solutions.
• To characterize the concentration-dependent changes in IR-806 assemblies and compare them to known chromonic liquid crystals.

Main Methods:

• UV-Vis absorption spectroscopy to study assembly processes.
• X-ray scattering to determine aggregate size and structure.
• Polarizing microscopy to observe liquid crystal phase transitions.

Main Results:

• IR-806 forms liquid crystal phases at concentrations as low as 0.5 wt %.
• Absorption spectra reveal an isodesmic assembly at low concentrations and a non-isodesmic process at higher concentrations.
• X-ray scattering indicates significantly larger assemblies at higher concentrations compared to typical chromonic systems.
• A narrow 10-15 °C transitional region between liquid crystal and isotropic phases was observed, without a biphasic region.

Conclusions:

• IR-806 exhibits distinct self-assembly behavior and liquid crystal formation in aqueous solutions.
• The dye's assembly process is concentration-dependent, with unique characteristics at higher concentrations.
• The observed large aggregate size and lack of a biphasic region differentiate IR-806 from many conventional chromonic liquid crystals.