Deriving binary phase diagrams for chromonic materials in water mixtures via fluorescence spectroscopy: cromolyn and water.

We report here the first example of a new and novel method of determining the binary temperature-composition phase diagram of a chromonic material in water using its intrinsic fluorescence. Disodium cromoglycate, or cromolyn, is an anti-allergy medicine representative of a class of compounds known as the chromonics. We have discovered that cromolyn's fluorescence is very sensitive to the polarity, hence structure, of the phase it exhibits. The fluorescence signal shifts its wavelength maximum and its shape depending on whether the cromolyn is a single phase or in coexisting phases. Since the signal due to individual phases can be identified, the fluorescence signal can reveal the temperature-induced transitions between single phase and phase coexistence regions. By studying such fluorescence data for different compositions, an isobaric temperature-composition phase diagram may be constructed. We present here a phase diagram derived from fluorescence studies that is in agreement with previous determinations using other techniques. Our results suggest that the binary phase diagrams of other intrinsically fluorescent chromonic materials, such as perylene monoimide and bisimide derivatives used in organic optoelectronic devices, solar cells, and light-emitting diodes, can be studied in water using an analogous fluorescence approach.

Biologically relevant lyotropic liquid crystalline phases in mixtures of n-octyl ß-D-glucoside and water. Determination of the phase diagram by fluorescence spectroscopy.

When mixed with water, n-octyl ß-D-glucoside forms self-assembled nanostructures, several of which are liquid crystalline and all of which depend on the water/glucoside ratio and temperature. For practical use of these phases, a detailed understanding of the conditions under which they exist (i.e., the isobaric phase diagram) is required. We use the fluorescence of the dye molecule prodan as a new approach to probe the phases formed in these mixtures. The prodan fluorescence signal depends on the polarity of its environment and thus the phase(s) in which the dye exists. Visual inspection of the total fluorescence signal can qualitatively determine the phases present, including coexisting phases. Temperature-induced phase changes are also detected from variations observed in the prodan fluorescence spectrum. The sensitivity of this new technique allows the single- and multiple-phase regions to be mapped carefully for the first time.