Pathway-resolved hierarchical self-assembly of biomimetic double-walled nanotubes

Self-assembly, the spontaneous organization of molecular components into ordered structures without external intervention, offers a powerful route to complex nanomaterials. Yet the molecular pathways that govern hierarchical assembly, particularly under non-equilibrium conditions, often remain poorly understood. Here we establish an integrated experimental platform that couples microfluidic control of the assembly environment with multi-scale optical and structural probes, enabling direct correlation between morphological evolution and excitonic functionality during supramolecular growth. Using this approach, we track in real time the formation of double-walled nanotubes (DWNTs) from the amphiphilic cyanine dye C8S3, a synthetic analogue of the light-harvesting chlorosomes in green sulfur bacteria. The results show that the outer nanotube structures first, while the inner nanotube follows with a delay, ultimately giving rise to electronically coupled coaxial architectures. While the principal excitonic signatures and morphological motifs emerge within minutes of self-assembly, axial elongation and orientational refinement continue over tens of hours through a nucleation-elongation mechanism. Notably, suppressing local concentration gradients through more efficient mixing abolishes DWNT formation, establishing spatial heterogeneity as a key parameter governing hierarchical self-assembly. By linking structural evolution with excitonic functionality in real time, this combined platform provides a framework for dissecting non-equilibrium pathways in supramolecular materials.