Chirality Magic from Magic-Sized Clusters

Magic-sized clusters (MSC) are identical CdS inorganic cores that maintain a closed-shell stability, inhibiting conventional growth processes. Because MSCs are smaller than nanoparticles, they can mimic molecular-level processes, and because of their small size and high organic-ligand/core ratio, MSCs have “softer” inter-particle interactions, with access to a richer phase diagram beyond the classical close packed structures seen with larger particles. In this talk I will highlight some remarkable behavior we have recently found in their ability to isomerize and their ability to self-organize into hierarchical assemblies with optical activity. These MSCs display a surprising ability to self-organize into films with hierarchical assembly that spans over seven orders of magnitude in length scale. Meniscus-guided evaporative assembly of these nanoclusters results in large-scale homochiral domains with anisotropy values (g-factors) near 0.15 – among the highest reported for all semiconductor particles – and domains surpassing 6 mm². Through Mueller matrix polarimetry spatial mapping we unravel the mechanism behind the formation of the self-organized chiral domains. Our hypothesis is that the fibrous nanocluster hybrid materials undergo pinning and twisting under fluid flow, leading to helical assemblies. Beyond optical properties, the multiscale self-organization behavior of these MSCs displays similarities to biosystems, providing a new platform for the design and study of materials.