Assembling Shape-Persistent High-Order Sierpiński Triangular Fractals.

Fractals are a series of intricate patterns with aesthetic, mathematic, and philosophic significance. The Sierpiński triangles have been known for more than one hundred years, but only recently discrete shape-persistent low-generation (mainly ST-1) fractal supramolecules have been realized. Herein, we report a retro-assembly pathway to the nanometer-scale, supra-macromolecular second-generation Sierpiński triangle and its third-generation saturated counterpart (Pascal's triangle). These gigantic triangular assemblies are unambiguously confirmed by NMR, DOSY, ESI-MS, TWIM-MS, TEM, and AFM analyses. Notably, the dense-packed counterions of these discrete triangular architectures could further form supramolecular hydro-gels in water. This work not only provides a fundamental chemical pathway to explore various giant supramolecular constructs and further overcome the synthetic limitation of complicated molecular fractals, but also presents a new type of supramolecular hydro-gels with potential in controlled release applications.