In situ detection of birefringent mesoscopic H and J aggregates of thiacarbocyanine dye in solution.

Polarized-light microscopy, fluorescence microscopy, atomic force microscopy as well as absorption and fluorescence spectroscopy were used to characterize mesoscopic structures of both supramolecular H and J aggregates of 3,3‘-disulfopropyl-5,5‘-dichloro-9-methyl thiacarbocyanine dye in aqueous solution. Polarized-light microscopy visualizes in situ the mesoscopic morphology of the H and J aggregates and distinguishes between them by their own colors. The H aggregate having a fibrous structure showed negative birefringence, namely, the refractive index along the fiber short axis was higher than that of the long axis, so that π-electron chromophores of the dye molecule are likely to orient along the short axis of the elongated fibers. The degree of birefringence of the H aggregate fiber was ∼−0.3. Investigations on the concentration dependence of the absorption spectra showed that the amount of J aggregates increased at the expense of a decrease in the amount of H aggregates. With respect to the J aggregat...