Dugan Hayes

A critical aspect of designing and realizing useful solid state materials is controlling phase and structure to tailor physical properties. While common for semiconductor and quantum materials, plasmonic materials have inhabited a narrow phase space typically comprising one or two elements, e.g., face-centered cubic metals. While this simplicity has enabled robust use and understanding of Au and Ag nanoparticles, it has also limited the design and manipulation of solid state properties. Here, we show that by tuning the phase and elemental composition of binary Au–Sn nanoparticles, the steady-state absorbance and ultrafast thermalization properties of plasmonic nanoparticles can be controlled. Solid state characterization suggests this is due to the dealloying of Sn and destabilization of the AuSn phase, leading to higher quality Au₅Sn intermetallic phases alongside Au. Consequently, this work shows that phase control can profoundly influence the properties of plasmonic nanoparticles, providing important tunability for applications in catalysis, photothermal heating, and sensing.

The oxidation of alcohols, amines, and halides is a fundamental transformation in organic chemistry with significant applications in the synthesis of fine chemicals, pharmaceuticals, and natural products. Here we show that a broad variety of N‐heteroarenes bearing hydroxymethyl, aminomethyl, or halomethyl groups are oxidatively dehydrogenated to their respective aldehydes by simply heating them in acidic or basic aqueous solution under ambient atmosphere. The quantitative oxidation of 9‐acridinemethanol to 9‐acridinecarboxaldehyde serves as an illustrative example, proceeding to completion within 3 hours in refluxing 5% aqueous acetic acid or even household vinegar. Quinoline derivatives may be similarly oxidized but require higher temperatures and longer reaction times, while indole derivatives are oxidized under basic conditions. Based on comprehensive regioselectivity screens, internal kinetic isotope competition, and density functional theory (DFT) calculations, we propose a mechanism in which migration of a methylene hydrogen to the pyridinic nitrogen by acid‐catalyzed dearomative tautomerization yields an unstable enol or enamine intermediate that then irreversibly loses two hydrogen atoms to atmospheric oxygen. In addition to the simplicity and environmentally benign nature of our method, we observe no indication of any over‐oxidation to carboxylic acids. Finally, we demonstrate the synthetic utility of this reaction through two different one‐pot formylations of acridine.

A critical aspect of designing and realizing useful solid state materials is controlling phase and structure to tailor physical properties. While common for semiconductor and quantum materials, plasmonic materials have inhabited a narrow phase space typically comprising one or two elements, e.g., face-centered cubic metals. While this simplicity has enabled robust use and understanding of Au and Ag nanoparticles, it has also limited the design and manipulation of solid state properties. Here, we show that by tuning the phase and elemental composition of binary Au-Sn nanoparticles, the steady-state absorbance and ultrafast thermalization properties of plasmonic nanoparticles can be controlled. Solid state characterization suggests this is due to the dealloying of Sn and destabilization of AuSn phase, leading to higher quality Au5Sn intermetallic phases alongside Au. Consequently, this work shows that phase control can profoundly influence the properties of plasmonic nanoparticles, providing important tunability for applications in catalysis, photothermal heating, and sensing.

This work reports on various physicochemical properties and energy conversion processes in phosphate glasses containing Sn²⁺ and Nd³⁺ ions of interest for luminescence-based applications. The glasses were prepared by melting with 50P₂O₅-(49 – x)­BaO-1Nd₂O₃-xSnO (x = 0, 1.0, 3.0, 5.0, 7.0, and 9.0 mol %) nominal compositions and characterized by X-ray diffraction, ¹¹⁹Sn Mössbauer spectroscopy, density and related physical properties, Raman spectroscopy, differential scanning calorimetry, dilatometry, optical absorption, and photoluminescence (PL) spectroscopy. X-ray diffraction confirmed the noncrystalline nature of the glasses. The ¹¹⁹Sn Mössbauer evaluation allowed for estimating the relative amounts of Sn²⁺ and Sn⁴⁺ in the glasses, which showed that Sn²⁺ occurrence was favored. The densities showed variations without definite trends; additional physical parameters were then determined such as Sn²⁺-Nd³⁺ distances based on ¹¹⁹Sn Mössbauer results. The characterization by Raman spectroscopy showed no significant structural variation was induced as SnO replaced BaO. The thermal properties of the codoped glasses assessed were however found to be impacted mostly by Sn²⁺ at high nominal SnO contents. Absorption spectra supported consistent occurrence of Nd³⁺ ions among the codoped glasses. The PL evaluation showed that exciting Sn²⁺ centers in the UV (e.g., near 290 nm) results in near-infrared emission from Nd³⁺, which was maximized for SnO added at 5 mol %. The visible PL data were consistent with the presence of Sn²⁺ in the glasses and showed dips in the emission spectra, indicating the energy transfer to Nd³⁺ ions. The Nd³⁺ decay times were however similar among the different samples.

Dimension-engineered synthesis of atomically thin II-VI nanoplatelets (NPLs) remains an open challenge. While CdSe NPLs have been made with confinement ranging from 2 to 11 monolayers (ML), CdTe NPLs have been significantly more challenging to synthesize and separate. Here we provide detailed mechanistic insight into the layer-by-layer growth kinetics of the CdTe NPLs. Combining ensemble and single-particle spectroscopic and microscopic tools, our work suggests that beyond 2 ML CdTe NPLs, higher ML structures initially appear as heteroconfined materials with colocalized multilayer structures. In particular, we observe strongly colocalized 3 and 4 ML emissions, accompanied by a broad trap emission. Accompanying transient absorption, single-particle optical, and atomic force microscopy analyses suggest islands of different MLs on the same NPL. To explain the nonstandard nucleation and growth of these heteroconfined structures, we simulated the growth conditions of NPLs and quantified how the monomer binding energy modifies the kinetics and permits single NPLs with multi-ML structures. Our findings suggest that the lower bond energy associated with CdTe relative to CdSe limits higher ML syntheses and explains the observed differences between CdTe and CdSe growth.

A new family of water‐degradable elastic polymers prepared by oxidative crosslinking of the parent polythionolactones shows promise in a broad range of applications, but the compositions of these materials elude conventional analytical methods. Here we use sulfur K‐edge X‐ray absorption spectroscopy to quantify the amounts of thioether, disulfide, sulfone, sulfate ester, and thionoester in each polymer and to rule out the presence of several other functional groups, including sulfonate, thiosulfonate, sulfate, and sulfoxide. We rationalize this speciation as a function of linker flexibility in the context of sulfinyl cycloaddition reactions and propose a mechanism of aggregation for the oxidized polymers. Our results correlate with swelling ratios but not with porosity nor crosslink density measurements, demonstrating the importance of pairing mechanical and chemical techniques when characterizing heterogeneous organic polymers. Finally, we take advantage of the proximity of the gold M_4,5‐edges to the sulfur K‐edge to analyze the binding and reactivity of Au(III) with the crosslinked polymers.

Dimension-engineered synthesis of atomically thin II-VI nanoplatelets (NPLs) remains an open challenge. While CdSe NPLs have been made with confinement ranging from 2-11 monolayers (ML), CdTe NPLs have been significantly more challenging to synthesize and separate. Here we provide detailed mechanistic insight into the layer-by-layer growth kinetics of CdTe NPLs. Combining ensemble and single particle spectroscopic and microscopic tools, our work suggests that beyond 2 ML CdTe NPLs, higher ML structures initially appear as hetero-confined materials with co-localized multilayer structures. In particular, we observe strongly colocalized 3 and 4 ML emissions accompanied by a broad trap emission. Accompanying transient absorption, single particle optical and atomic force microscopy suggests islands of different MLs on the same NPL. To explain the non-standard nucleation and growth of these hetero-confined structures, we simulated the growth conditions of NPLs and quantified how monomer binding energy modifies the kinetics and permits single NPLs with multi-ML structures. Our findings suggest that the lower bond energy associated with CdTe relative to CdSe limits higher ML syntheses and explains the observed differences between CdTe and CdSe growth.

Hypervalent iron intermediates have been invoked in the catalytic cycles of many metalloproteins, and thus, it is crucial to understand how the coupling between such species and their environment can impact their chemical and physical properties in such contexts. In this work, we take advantage of the solvent kinetic isotope effect (SKIE) to gain insight into the nonradiative deactivation of electronic excited states of the aqueous ferrate-(VI) ion. We observe an exceptionally large SKIE of 9.7 for the nanosecond-scale relaxation of the lowest energy triplet ligand field state to the ground state. Proton inventory studies demonstrate that a single solvent O-H bond is coupled to the ion during deactivation, likely due to the sparse vibrational structure of ferrate-(VI). Such a mechanism is consistent with that reported for the deactivation of f-f excited states of aqueous trivalent lanthanides, which exhibit comparably large SKIE values. This phenomenon is ascribed entirely to dissipation of energy into a higher overtone of a solvent acceptor mode, as any impact on the apparent relaxation rate due to a change in solvent viscosity is negligible.

Barium phosphate glasses were prepared with 0.5 mol% Tb ₄ O ₇ added alongside SnO up to 5 mol% with the purpose of evaluating the resulting terbium and tin oxidation states and their impact on glass structural, thermal, and luminescent properties.

Bimetallic electron donor-acceptor complexes can facilitate electron and energy transfer with excellent structural control through synthetic design. In this work, we investigate the photochemical dynamics in a Ru-Cu bimetallic complex after photoexcitation of the Ru-centered charge transfer state. The physical underpinnings of the metal-to-metal directional charge transfer process are unraveled via analyses of the quantum electronic dynamics and electron-nuclear trajectories. The effects of molecular vibrations in the photoexcited state on the charge transfer processes are also analyzed.