Uniform exciton fluorescence from individual molecular nanotubes immobilized on solid substrates

Self-assembled quasi one-dimensional nanostructures of π-conjugated molecules1,2,3,4,5,6,7,8,9,10,11,12,13,14,15 may find a use in devices owing to their intriguing optoelectronic properties, which include sharp exciton transitions1,2,3,4,5, strong circular dichroism5,6,7, high exciton mobilities8,9 and photoconductivity10. However, many applications require immobilization of these nanostructures on a solid substrate, which is a challenge to achieve without destroying their delicate supramolecular structure. Here, we use a drop-flow technique to immobilize double-walled tubular J-aggregates of amphiphilic cyanine dyes without affecting their morphological or optical properties. High-resolution images of the topography and exciton fluorescence of individual J-aggregates are obtained simultaneously with polarization-resolved near-field scanning optical microscopy. These images show remarkably uniform supramolecular structure, both along individual nanotubes and between nanotubes in an ensemble, demonstrating their potential for light harvesting and energy transport. Individual double-walled tubular aggregates are immobilized on a solid substrate out of solution using a drop-flow technique. Using near-field scanning optical microscopy, these aggregates are shown to have a remarkably uniform supramolecular structure.