Aminophosphine Reduction Mechanisms and the Synthesis of Indium Phosphide Nanomaterials

Indium phosphide (InP) nanomaterials are attractive for countless technological applications due to their well-placed band gap energies. The quantum confinement of these semiconductors can give rise to size-dependent absorption and emission features throughout the entire visible spectrum. Therefore, InP materials can be employed as low-toxicity fluorophores that can be implemented in high value avenues such as biological probes, lighting applications, and lasing technologies. However, large scale development of these quantum dots (QDs) has been stymied by the lack of affordable and safe phosphorus precursors. Syntheses have largely been restricted to the use of dangerous chemicals such as tris(trimethylsilyl)phosphine ((TMS)₃P), which is costly and highly sensitive to oxygen and water. Recently, less-hazardous tris(dialkylamino)phosphines have been introduced to produce InP QDs on par with those utilizing (TMS)₃P. However, a poor understanding of the reaction mechanics has resulted in difficulties tuning and optimizing this method. In this work, density functional theory (DFT) is used to identify the mechanism of this aminophosphine precursor conversion. This understanding is then implemented to design an improved InP QD synthesis, allowing for the production of high-quality materials outside of glovebox conditions. Time is spent understanding the impact of different precursor salts on the reaction mechanisms and discerning their subsequent effects on nanoparticle size and quality. The motivation of this work is to formulate safer and less technical indium phosphide quantum dot syntheses to foster non-specialist and industrial implementation of these materials

Aminophosphine Reduction Mechanisms and the Synthesis of Indium Phosphide Nanomaterials

Indium phosphide (InP) nanomaterials are attractive for countless technological applications due to their well-placed band gap energies. The quantum confinement of these semiconductors can give rise to size-dependent absorption and emission features throughout the entire visible spectrum. Therefore, InP materials can be employed as low-toxicity fluorophores that can be implemented in high value avenues such as biological probes, lighting applications, and lasing technologies. However, large scale development of these quantum dots (QDs) has been stymied by the lack of affordable and safe phosphorus precursors. Syntheses have largely been restricted to the use of dangerous chemicals such as tris(trimethylsilyl)phosphine ((TMS)₃P), which is costly and highly sensitive to oxygen and water. Recently, less-hazardous tris(dialkylamino)phosphines have been introduced to produce InP QDs on par with those utilizing (TMS)₃P. However, a poor understanding of the reaction mechanics has resulted in difficulties tuning and optimizing this method. In this work, density functional theory (DFT) is used to identify the mechanism of this aminophosphine precursor conversion. This understanding is then implemented to design an improved InP QD synthesis, allowing for the production of high-quality materials outside of glovebox conditions. Time is spent understanding the impact of different precursor salts on the reaction mechanisms and discerning their subsequent effects on nanoparticle size and quality. The motivation of this work is to formulate safer and less technical indium phosphide quantum dot syntheses to foster non-specialist and industrial implementation of these materials

An In Vitro Investigation of Cytotoxic Effects of InP/Zns Quantum Dots with Different Surface Chemistries

Indium phosphide quantum dots (QDs) passivated with zinc sulphide in a core/shell architecture (InP/ZnS) with different surface chemistries were introduced to RAW 264.7 murine “macrophage-like„ cells to understand their potential toxicities. The InP/ZnS quantum dots were conjugated with an oligonucleotide, a carboxylic acid, or an amino-polyethylene glycol ligand, and cell viability and cell proliferation were investigated via a metabolic assay. Membrane integrity was measured through the production of lactate dehydrogenase. Fluorescence microscopy showed cellular uptake. All quantum dots exhibited cytotoxic behaviour less than that observed from cadmium- or lead-based quantum dots; however, this behaviour was sensitive to the ligands used. In particular, the amino-polyethylene glycol conjugated quantum dots proved to possess the highest cytotoxicity examined here. This provides quantitative evidence that aqueous InP/ZnS quantum dots can offer a safer alternative for bioimaging or in therapeutic applications

Platinum Terpyridine Metallopolymer Electrode as Cost-Effective Replacement for Bulk Platinum Catalysts in Oxygen Reduction Reaction and Hydrogen Evolution Reaction

Conducting polymers consisting of metal-selective coordination units and a highly conductive backbone, so-called metallopolymers, are interesting materials exposing single atoms for photo/electrocatalysis and thus represent a potential low-cost alternative for bulk or nanoparticulate platinum group metals (PGMs). We synthesized and fully characterized an electropolymerisable monomer bearing a pendant terpyridine unit for the selective complexation of PGMs. Electrocatalytic tests of the resulting metallopolymer, poly-[(tThTerpy)­PtCl]­Cl, revealed activity both in the oxygen reduction reaction and hydrogen evolution reaction. Rotating disk experiments showed the direct four-electron reduction of molecular oxygen to water at low angular velocities of the rotating electrode. Furthermore, the fabrication of Pt metallopolymers proved to be simple, nonhazardous and versatile. This proof-of-concept opens up the possibility for developing future low-cost electro- and photocatalysts to replace current systems

Inter-ligand energy transfer in dye chromophores attached to high bandgap SiO2 nanoparticles.

Artificial light harvesters require ordered arrangement of chromophores. We covalently attach three organic chromophore ligands to silicon dioxide nanoparticles. This allows us to study inter-ligand energy transfer when attached to SiO2 nanoparticles, creating a simple system with a large ratio of donors to acceptors. Using steady-state and transient spectroscopy measurements we quantify this energy transfer between ligands. We show a maximum transfer efficiency of 30% and measure the 2D diffusion length of anthracene carboxylic acid on SiO2 to be between 0.6 and 2.2 nm

Interface-Dependent Selectivity in Plasmon-Driven Chemical Reactions

Plasmonic nanoparticles can drive chemical reactions powered by sunlight. These processes involve the excitation of surface plasmon resonances (SPR) and the subsequent charge transfer to adsorbed molecular orbitals. Nonetheless, controlling the flow of energy and charge from SPR to adsorbed molecules is still difficult to predict or tune. Here, we show the crucial role of halide ions in modifying the energy landscape of a plasmon-driven chemical reaction by carefully engineering the nanoparticle–molecule interface. By doing so, the selectivity of plasmon-driven chemical reactions can be controlled, either enhancing or inhibiting the metal–molecule charge and energy transfer or by regulating the vibrational pumping rate. These results provide an elegant method for controlling the energy flow from plasmonic nanoparticles to adsorbed molecules, in situ, and selectively targeting chemical bonds by changing the chemical nature of the metal–molecule interface

The Evolution of Quantum Confinement in CsPbBr₃ Perovskite Nanocrystals

Colloidal nanocrystals (NCs) of lead halide perovskites are considered highly promising materials that combine the exceptional optoelectronic properties of lead halide perovskites with tunability from quantum confinement. But can we assume that these materials are in the strong confinement regime? Here, we report an ultrafast transient absorption study of cubic CsPbBr₃ NCs as a function of size, compared with the bulk material. For NCs above ∼7 nm edge length, spectral signatures are similar to the bulk material–characterized by state-filling with uncorrelated charges–but discrete new kinetic components emerge at high fluence due to bimolecular recombination occurring in a discrete volume. Only for the smallest NCs (∼4 nm edge length) are strong quantum confinement effects manifest in TA spectral dynamics; focusing toward discrete energy states, enhanced bandgap renormalization energy, and departure from a Boltzmann statistical carrier cooling. At high fluence, we find that a hot-phonon bottleneck effect slows carrier cooling, but this appears to be intrinsic to the material, rather than size dependent. Overall, we find that the smallest NCs are understood in the framework of quantum confinement, however for the widely used NCs with edge lengths >7 nm the photophysics of bulk lead halide perovskites are a better point of reference