Steric stabilization of colloidal UiO-66 nanocrystals with oleylammonium octadecylphosphonate.

We report the synthesis and characterization of octahedral UiO-66 nanocrystals ( = 17-25 nm) terminated with amine, oleate, and octadecylphosphonate ligands. Acetate capped UiO-66 nanocrystals were dispersed in toluene using oleic acid and oleylamine. Ligand exchange with octadecylphosphonic acid produces ammonium octadecylphosphonate terminated nanocrystals with coverages of 2.

Metal Fluorides Passivate II-VI and III-V Quantum Dots.

Quantum dots (QDs) with metal fluoride surface ligands were prepared via reaction with anhydrous oleylammonium fluoride. Carboxylate terminated II-VI QDs underwent carboxylate for fluoride exchange, while InP QDs underwent photochemical acidolysis yielding oleylamine, PH, and InF. The final photoluminescence quantum yield (PLQY) reached 83% for InP and near unity for core-shell QDs.

Synthesis of graded CdSSe nanoplatelet alloys and heterostructures from pairs of chalcogenoureas with tailored conversion reactivity.

A mixture of ,,'-trisubstituted thiourea and cyclic ,,','-tetrasubstituted selenourea precursors were used to synthesize three monolayer thick CdSSe nanoplatelets in a single synthetic step. The microstructure of the nanoplatelets could be tuned from homogeneous alloys, to graded alloys to core/crown heterostructures depending on the relative conversion reactivity of the sulfur and selenium precursors. UV-visible absorption and photoluminescence spectroscopy and scanning transmission electron microscopy electron energy loss spectroscopy (STEM-EELS) images demonstrate that the elemental distribution is governed by the relative precursor conversion kinetics.

Design Rules for Obtaining Narrow Luminescence from Semiconductors Made in Solution.

Solution-processed semiconductors are in demand for present and next-generation optoelectronic technologies ranging from displays to quantum light sources because of their scalability and ease of integration into devices with diverse form factors. One of the central requirements for semiconductors used in these applications is a narrow photoluminescence (PL) line width. Narrow emission line widths are needed to ensure both color and single-photon purity, raising the question of what design rules are needed to obtain narrow emission from semiconductors made in solution.

Indefinite and bidirectional near-infrared nanocrystal photoswitching.

Materials whose luminescence can be switched by optical stimulation drive technologies ranging from superresolution imaging, nanophotonics, and optical data storage, to targeted pharmacology, optogenetics, and chemical reactivity. These photoswitchable probes, including organic fluorophores and proteins, can be prone to photodegradation and often operate in the ultraviolet or visible spectral regions. Colloidal inorganic nanoparticles can offer improved stability, but the ability to switch emission bidirectionally, particularly with near-infrared (NIR) light, has not, to our knowledge, been reported in such systems.

Growth kinetics determine the polydispersity and size of PbS and PbSe nanocrystals.

A library of thio- and selenourea derivatives is used to adjust the kinetics of PbE (E = S, Se) nanocrystal formation across a 1000-fold range ( = 10 to 10 s), at several temperatures (80-120 °C), under a standard set of conditions (Pb : E = 1.2 : 1, [Pb(oleate)] = 10.8 mM, [chalcogenourea] = 9.

Persistent nucleation and size dependent attachment kinetics produce monodisperse PbS nanocrystals.

Modern syntheses of colloidal nanocrystals yield extraordinarily narrow size distributions that are believed to result from a rapid "burst of nucleation" (La Mer, , 1950, (11), 4847-4854) followed by diffusion limited growth and size distribution focusing (Reiss, , 1951, , 482). Using a combination of X-ray scattering, optical absorption, and C nuclear magnetic resonance (NMR) spectroscopy, we monitor the kinetics of PbS solute generation, nucleation, and crystal growth from three thiourea precursors whose conversion reactivity spans a 2-fold range. In all three cases, nucleation is found to be slow and continues during >50% of the precipitation.

Relations between absorption, emission, and excited state chemical potentials from nanocrystal 2D spectra.

For quantum-confined nanomaterials, size dispersion causes a static broadening of spectra that has been difficult to measure and invalidates all-optical methods for determining the maximum photovoltage that an excited state can generate. Using femtosecond two-dimensional (2D) spectroscopy to separate size dispersion broadening of absorption and emission spectra allows a test of single-molecule generalized Einstein relations between such spectra for colloidal PbS quantum dots. We show that 2D spectra and these relations determine the thermodynamic standard chemical potential difference between the lowest excited and ground electronic states, which gives the maximum photovoltage.

Performance of Spherical Quantum Well Down Converters in Solid State Lighting.

We report the color conversion performance of amber and red emitting quantum dots (QDs) on InGaN solid-state lighting (SSL) light emitting diode (LED) packages. Spherical quantum well (SQW) architectures (CdS/CdSeS/CdS) were prepared using a library of thio- and selenourea synthesis reagents and high throughput synthesis robotics. CdS/CdSeS QDs with narrow luminescence bands were coated with thick CdS shells (thickness = 1.

Au/TiO-Catalyzed Benzyl Alcohol Oxidation on Morphologically Precise Anatase Nanoparticles.

Au nanoparticles (NP) on TiO have been shown to be effective catalysts for selective oxidation reactions by using molecular oxygen. In this work, we have studied the influence of support morphology on the catalytic activity of Au/TiO catalysts. Two TiO anatase supports, a nanoplatelet-shaped material with predominantly the {001} facet exposed and a truncated bipyramidal-shaped nanoparticle with predominantly the {101} facet exposed, were prepared by using a nonaqueous solvothermal method and characterized by using DRIFTS, XPS, and TEM.

Precursor reaction kinetics control compositional grading and size of CdSe S nanocrystal heterostructures.

We report a method to control the composition and microstructure of CdSe S nanocrystals by the simultaneous injection of sulfide and selenide precursors into a solution of cadmium oleate and oleic acid at 240 °C. Pairs of substituted thio- and selenoureas were selected from a library of compounds with conversion reaction reactivity exponents ( ) spanning 1.3 × 10 s to 2.

Dynamic emission Stokes shift and liquid-like dielectric solvation of band edge carriers in lead-halide perovskites.

Lead-halide perovskites have emerged as promising materials for photovoltaic and optoelectronic applications. Their significantly anharmonic lattice motion, in contrast to conventional harmonic semiconductors, presents a conceptual challenge in understanding the genesis of their exceptional optoelectronic properties. Here we report a strongly temperature dependent luminescence Stokes shift in the electronic spectra of both hybrid and inorganic lead-bromide perovskite single crystals.

Size-Dependent Lattice Dynamics of Atomically Precise Cadmium Selenide Quantum Dots.

Material properties depend sensitively on the atomic arrangements and atomic bonding, but these are notoriously difficult to measure in nanosized atomic clusters due to the small size of the objects and the challenge of obtaining bulk samples of identical clusters. Here, we have combined the recent ability to make gram quantities of identical semiconductor quantum-dot nanoparticles with the ability to measure lattice dynamics on small sample quantities of hydrogenated materials using high energy resolution inelastic x-ray scattering, to measure the size dependence of the phonon density of states in CdSe quantum dots. The fact that we have atomically precise structural models for these nanoparticles allows the calculation of the phonon density of states using density functional theory, providing both experimental and theoretical confirmations of the important role that the inertia of the surface capping species plays on determining the lattice dynamics.

Flexible Nanopipettes for Minimally Invasive Intracellular Electrophysiology In Vivo.

Intracellular recordings in vivo remains the best technique to link single-neuron electrical properties to network function. Yet existing methods are limited in accuracy, throughput, and duration, primarily via washout, membrane damage, and movement-induced failure. Here, we introduce flexible quartz nanopipettes (inner diameters of 10-25 nm and spring constant of ∼0.

Anthracene as a Launchpad for a Phosphinidene Sulfide and for Generation of a Phosphorus-Sulfur Material Having the Composition PS, a Vulcanized Red Phosphorus That Is Yellow.

Thermolysis of a pair of dibenzo-7-phosphanorbornadiene compounds is shown to lead to differing behaviors: phosphinidene sulfide release and formation of amorphous PS. These compounds, BuP(S)A (1, A = CH or anthracene; 59% isol. yield) and HP(S)A (2; 63%), are available through thionation of BuPA and the new secondary phosphine HPA (5), prepared from MeNPA and DIBAL-H in 50% yield.

Stereoelectronic Effects on the Binding of Neutral Lewis Bases to CdSe Nanocrystals.

Using P nuclear magnetic resonance (NMR) spectroscopy, we monitor the competition between tri- n-butylphosphine (BuP) and various amine and phosphine ligands for the surface of chloride terminated CdSe nanocrystals. Distinct P NMR signals for free and bound phosphine ligands allow the surface ligand coverage to be measured in phosphine solution. Ligands with a small steric profile achieve higher surface coverages (BuP = 0.

Two-Dimensional Fullerene Assembly from an Exfoliated van der Waals Template.

Two-dimensional (2D) materials are commonly prepared by exfoliating bulk layered van der Waals crystals. The creation of synthetic 2D materials from bottom-up methods is an important challenge as their structural flexibility will enable chemists to tune the materials properties. A 2D material was assembled using C as a polymerizable monomer.

Nucleation and Growth Kinetics from LaMer Burst Data.

In LaMer burst nucleation, the individual nucleation events happen en masse, quasi-simultaneously, and at nearly identical homogeneous conditions. These properties make LaMer burst nucleation important for applications that require monodispersed particles and also for theoretical analyses. Sugimoto and co-workers predicted that the number of nuclei generated during a LaMer burst depends only on the solute supply rate and the growth rate, independent of the nucleation kinetics.

Local Polar Fluctuations in Lead Halide Perovskite Crystals.

Hybrid lead-halide perovskites have emerged as an excellent class of photovoltaic materials. Recent reports suggest that the organic molecular cation is responsible for local polar fluctuations that inhibit carrier recombination. We combine low-frequency Raman scattering with first-principles molecular dynamics (MD) to study the fundamental nature of these local polar fluctuations.

Tris(2-mercaptoimidazolyl)hydroborato Cadmium Thiolate Complexes, [Tm]CdSAr: Thiolate Exchange at Cadmium in a Sulfur-Rich Coordination Environment.

A series of cadmium thiolate compounds that feature a sulfur-rich coordination environment, namely [Tm]CdSAr, have been synthesized by the reactions of [Tm]CdMe with ArSH (Ar = CH-4-F, CH-4-Bu, CH-4-OMe, and CH-3-OMe). In addition, the pyridine-2-thiolate and pyridine-2-selenolate derivatives, [Tm]CdSPy and [Tm]CdSePy have been obtained via the respective reactions of [Tm]CdMe with pyridine-2-thione and pyridine-2-selone. The molecular structures of [Tm]CdSAr and [Tm]CdEPy (E = S or Se) have been determined by X-ray diffraction and demonstrate that, in each case, the [CdS] motif is distorted tetrahedral and approaches a trigonal monopyramidal geometry in which the thiolate ligand adopts an equatorial position; [Tm]CdSPy and [Tm]CdSePy, however, exhibit an additional long-range interaction with the pyridyl nitrogen atoms.

Unbalanced Hole and Electron Diffusion in Lead Bromide Perovskites.

We use scanning photocurrent microscopy and time-resolved microwave conductivity to measure the diffusion of holes and electrons in a series of lead bromide perovskite single crystals, APbBr, with A = methylammonium (MA), formamidinium (FA), and Cs. We find that the diffusion length of holes (L ∼ 10-50 μm) is on average an order of magnitude longer than that of electrons (L ∼ 1-5 μm), regardless of the A-type cation or applied bias. Furthermore, we observe a weak dependence of L across the A-cation series MA > FA > Cs.

Tight Binding of Carboxylate, Phosphonate, and Carbamate Anions to Stoichiometric CdSe Nanocrystals.

To completely displace the carboxylate surface ligands from cadmium selenide nanocrystals, oleic acid impurities are first removed using dimethylcadmium or diethylzinc. In addition to metal carboxylate and methane coproducts, reactions with CdMe produce surface bound methyl groups (δ = 0.4 ppm, 0.

A Library of Selenourea Precursors to PbSe Nanocrystals with Size Distributions near the Homogeneous Limit.

We report a tunable library of N,N,N'-trisubstituted selenourea precursors and their reaction with lead oleate at 60-150 °C to form carboxylate-terminated PbSe nanocrystals in quantitative yields. Single exponential conversion kinetics can be tailored over 4 orders of magnitude by adjusting the selenourea structure. The wide range of conversion reactivity allows the extent of nucleation ([nanocrystal] = 4.