Photoinitiated Transformation of Nanocrystal Superlattice Polymorphs Assembled at a Fluid Interface

Abstract

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.

Processing–Structure–Performance Relationships of Microporous Metal–Organic Polymers for Size-Selective Separations

“…Concurrent advances in the nanostructured building blocks , and optical patterning have opened opportunities to program materials over multiple length scales. The assembly of colloidal nanoparticles is an attractive strategy to produce hierarchical structures. − Studies using molecular ligand–ligand interactions, such as organic ligands or DNA, to directionally bind and orientate nanobuilding blocks have generated nanoscale features including mesopores and macropores. − On the other hand, advances in photoresponsive ligand chemistries have created new prospects to spatially pattern assemblies by light. , Recent works have demonstrated the fabrication of hierarchical nanoporous materials by combining nanoparticles’ assemblies with light-initiated three-dimensional (3D) printing. − Unfortunately, this strategy has so far not been realized for the formation of microporous materials, as the length of ligands and their polymerization limit our capability to generate sub-nanometer features.…”

“…14−16 On the other hand, advances in photoresponsive ligand chemistries have created new prospects to spatially pattern assemblies by light. 17,18 Recent works have demonstrated the fabrication of hierarchical nanoporous materials by combining nanoparticles' assemblies with light-initiated threedimensional (3D) printing. 19−21 Unfortunately, this strategy has so far not been realized for the formation of microporous materials, as the length of ligands and their polymerization limit our capability to generate sub-nanometer features.…”

Photobase-Triggered Formation of 3D Epitaxially Fused Quantum Dot Superlattices with High Uniformity and Low Bulk Defect Densities

“…By dissolving a suitable PBG molecule in the EG, subsequently depositing an oleate-capped SL on the EG surface, and then uniformly illuminating the EG from below with ultraviolet light, we trigger the uniform release of piperidine ((CH 2 ) 5 NH) under the QD film to convert the oleate-capped SL into the epi-SL without causing mechanical disturbances that can damage the film or lateral ligand concentration gradients that produce corresponding gradients in ligand coverage, mechanical strain, and QD necking. Our work follows the use of photochemically active ligands − and dissolved photoacids for direct photopatterning of QD films. In particular, Gao et al .…”

“…In particular, Gao et al . recently used a dissolved photoacid generator and a digital light projector to photopattern monolayer (2D) PbS epi-SLs within floating QD monolayers . These authors showed that the oleate coverage and SL structure could be tuned with light dose and photoacid concentration.…”