Photoinitiated Transformation of Nanocrystal Superlattice Polymorphs Assembled at a Fluid Interface

Directing the assembly of nanoscale building blocks into programmable superstructures is of broad scientific and technological interest. Advances in nanocrystal self‐assembly at fluid interfaces are combined with digital light processing to demonstrate that how the extent and spatial region of superlattice structure transformation can be controlled. It is shown that the addition of a photoacid generator to the fluid subphase provides new experimental degrees of freedom to modulate the dynamic equilibrium of ligands bound to the colloidal nanocrystal surface. Within the photoexposed regions, the nanocrystal ligand coverage is reduced which impacts the interactions between proximate nanocrystals and drives the transformation from a sixfold to a fourfold symmetric superlattice. Structural analysis is presented from transmission electron microscopy and chemical analysis is presented from infrared spectroscopy to establish the relationship between superlattice structure and ligand coverage. Beyond new insights understanding of and control over deprotection of colloidal nanocrystals at fluid interfaces, the processing method described in this work presents new opportunities to create nanocrystal assemblies with spatially programmable structures.