DNA programmable assembly has been combined with top-down lithography to construct superlattices of discrete, reconfigurable nanoparticle architectures on a gold surface over large areas. Specifically, the assembly of individual colloidal plasmonic nanoparticles with different shapes and sizes is controlled by oligonucleotides containing "locked" nucleic acids and confined environments provided by polymer pores to yield oriented architectures that feature tunable arrangements and independently controllable distances at both nanometer- and micrometer-length scales. These structures, which would be difficult to construct by other common assembly methods, provide a platform to systematically study and control light-matter interactions in nanoparticle-based optical materials. The generality and potential of this approach are explored by identifying a broadband absorber with a solvent polarity response that allows dynamic tuning of visible light absorption.

The ability to precisely control nanocrystal (NC) shape and composition is useful in many fields, including catalysis and plasmonics. Seed-mediated strategies have proven effective for preparing a wide variety of structures, but a poor understanding of how to selectively grow corners, edges, and facets has limited the development of a general strategy to control structure evolution. Here, we report a universal synthetic strategy for directing the site-specific growth of anisotropic seeds to prepare a library of designer nanostructures. This strategy leverages nucleation energy barrier profiles and the chemical potential of the growth solution to control the site-specific growth of NCs into exotic shapes and compositions. This strategy can be used to not only control where growth occurs on anisotropic seeds but also control the exposed facets of the newly grown regions. NCs of many shapes are synthesized, including over 10 here-to-fore never reported NCs and, in principle, many others are possible.

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Halide perovskites have exceptional optoelectronic properties, but a poor understanding of the relationship between crystal dimensions, composition, and properties limits their use in integrated devices. We report a new multiplexed cantilever-free scanning probe method for synthesizing compositionally diverse and size-controlled halide perovskite nanocrystals spanning square centimeter areas. Single-particle photoluminescence studies reveal multiple independent emission modes due to defect-defined band edges with relative intensities that depend on crystal size at a fixed composition. Smaller particles, but ones with dimensions that exceed the quantum confinement regime, exhibit blue-shifted emission due to reabsorption of higher-energy modes. Six different halide perovskites have been synthesized, including a layered Ruddlesden-Popper phase, and the method has been used to prepare functional solar cells based on single nanocrystals. The ability to pattern arrays of multicolor light-emitting nanocrystals opens avenues toward the development of optoelectronic devices, including optical displays.

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Frustrated Lewis pairs (FLPs) created by sterically hindered Lewis acids and Lewis bases have shown their capacity for capturing and reacting with a variety of small molecules, including H2 and CO2, and thereby creating a new strategy for CO2 reduction. Here, the photocatalytic CO2 reduction behavior of defect‐laden indium oxide (In2O3− x(OH)y) is greatly enhanced through isomorphous substitution of In3+ with Bi3+, providing fundamental insights into the catalytically active surface FLPs (i.e., In—OH···In) and the experimentally observed “volcano” relationship between the CO production rate and Bi3+ substitution level. According to density functional theory calculations at the optimal Bi3+ substitution level, the 6s2 electron pair of Bi3+ hybridizes with the oxygen in the neighboring In—OH Lewis base site, leading to mildly increased Lewis basicity without influencing the Lewis acidity of the nearby In Lewis acid site. Meanwhile, Bi3+ can act as an extra acid site, serving to maximize the heterolytic splitting of reactant H2, and results in a more hydridic hydride for more efficient CO2 reduction. This study demonstrates that isomorphous substitution can effectively optimize the reactivity of surface catalytic active sites in addition to influencing optoelectronic properties, affording a better understanding of the photocatalytic CO2 reduction mechanism.

are guided to assemble into desired architectures over a large scale. [2] Over the past three decades, we and others have repurposed DNA for the programmable assembly of synthetic materials. [3][4][5][6] These efforts have led to designer architectures made entirely out of DNA (i.e., structural DNA nanotechnology) [7][8][9][10] as well as structures where DNA is used as a bonding element to position functional building blocks in one, two, and three dimensions with sub-nanometric precision. [3,11,12] In particular, the concept of programmable atom equivalents, or PAEs, has paved the way for the field of colloidal crystal engineering with DNA. [13] In this field, DNA is used to chemically program the assembly of colloidal particles into precise, and in many cases, crystalline architectures, where various aspects of the resulting structures (e.g., crystallographic symmetry, lattice parameters, and crystal sizes/habits) can be systematically controlled. [13] PAEs have led to key fundamental chemical insights and form the basis for a whole new field of chemistry based on nanoparticles as "atoms" and DNA as programmable "bonds"; many analogies can be made between traditional chemical bonding and this new form of bonding based on DNA. PAEs also are particularly useful in biomedicine as diagnostic probes and therapeutic modalities, [14][15][16][17][18] and colloidal crystals engineered with DNA have been used as catalysts, actuators, and optical/plasmonic devices. [19][20][21][22] In the following sections, the characteristics of PAEs, the physical and chemical parameters that control the growth of PAE superstructures into complex assemblies, the types and properties of colloidal crystals that have been realized from PAEs (note that crystals with over 50 different symmetries have been prepared, some of which do not exist in nature), and the applications enabled by PAEs and PAE assemblies are discussed. The similarities and key differences between atoms and nanoparticle "atoms" and electron-based bonds and DNA "bonds" are also discussed. An outlook on future directions in the field is provided at the end. Programmable Atom EquivalentsA PAE is comprised of a nanoparticle core that is densely functionalized with a radially oriented DNA shell (Figure 1). Typically, the DNA shell consists of "anchor" strands that are attached to the nanoparticle surface and complementary "linker" strands that terminate in short single-stranded regions Colloidal crystal engineering with DNA has led to significant advances in bottom-up materials synthesis and a new way of thinking about fundamental concepts in chemistry. Here, programmable atom equivalents (PAEs), comprised of nanoparticles (the "atoms") functionalized with DNA (the "bonding elements"), are assembled through DNA hybridization into crystalline lattices. Unlike atomic systems, the "atom" (e.g., the nanoparticle shape, size, and composition) and the "bond" (e.g., the DNA length and sequence) can be tuned independently, yielding designer materials with unique catalytic, optical, an...

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