Assembly of Extra-Large Nanosheets by Supramolecular Polymerization of Amphiphilic Pyrene Oligomers in Aqueous Solution

The precise arraying of functional entities in a reproducible and predictable way in morphologically well-defined shapes is a key challenge in materials science. In this work, we describe the importance of kinetic effects in the two-dimensional (2D) self-assembly of a negatively charged pyrene trimer (Py3) in aqueous media. Under optimized experimental conditions the chain-folded oligomers assemble into exceptionally thin planar assemblies (∼2 nm thick) with a very high aspect ratio (area/thickness ratio ≈ 107 nm). The morphology of the nanosheets was characterized by different microscopic techniques (AFM, TEM, and optical microscopy), while UV-vis and fluorescence spectroscopy revealed details on the intramolecular folding of the oligomer strands. Temperature control was shown to be crucial for preventing the formation of kinetically trapped states, thus allowing the development of extra-large 2D assemblies.