Polarized Light Scattering by Macromolecular Self-Assembly of J-Aggregates

We have recently reported that by sending a tightly collimated (0.05 - 2 mm diameter) red-or near-IR laser beam through an aqueous solution of pseudoisocyanine (PIC) J-aggregates, a macroscopic tube-like structure is formed surrounding the laser beam on the time scale of minutes. This self-assembled structure is comprised of heterogeneous material containing micrometer-size rod-like strands or microcrystals. Because the illumination wavelength is far red-shifted from the linear absorption range of the PIC and J-aggregates, the self-assembly is likely induced by some very weak background absorption or dissipation. Furthermore, strong correlation of the effect with the characteristic J-aggregate peak in the absorption spectrum and critical dependence of the "tube" formation on pH of the solution indicate molecular charge related non-equilibrium nature of the underlying mechanism. Most interestingly, the structure formation is accompanied by strongly polarized scattering. When observed between crossed polarizers, the angular intensity distribution of the scattered light resembles Maltese cross figure, indicating that the scattering rods are arranged in a circular pattern around the beam axis direction. It appears that the illumination is creating in the medium a radially directed gradient of either concentration-, temperature- or other type of parameter that controls the microcrystal formation.