Spiral fractal patterns via hierarchical assembly

Chirality is ubiquitous in nature and manifested at various scale from subatom to galaxy. Fractal geometry is also very popular and active in the world. However, there are few reports on the concept of combining fractal patterns and chiral structures in self-assembled systems. It was found that tree-shaped fractal patterns could be self-assembled from the N-[(9H-fluoren-9-ylmethoxy) carbonyl] protected glutamic acid (Fmoc-Glu) and zinc-porphyrin (ZnTPyP). The fractal pattern was composed of nanorod aggregate arranged in a spiral fractal way, in which the nanorods were stacked one-by-one in a single direction. The patterns started with the formation of initial nucleon and growing, during which the diffusion limited aggregation (DLA) mechanism led to the fractal patterns. Interestingly, the spiral packing and their branches were closely related to the absolute configuration of Fmoc-Glu that anticlockwise and clockwise arrangement for L-Fmoc-Glu/ZnTPyP and D-Fmoc-Glu/ZnTPyP, respectively. Our work provides a new finding on the spiral fractal pattern via hierarchical self-assembly.