Copper(I) Donor–Chromophore–Acceptor Assembly for Light-Driven Oxidation on a Zinc Oxide Nanowire Electrode

Dye-sensitized photoelectrochemical cells have emerged as a potential candidate for solar-to-fuel conversion. Herein, we report a Cu­(I)-based donor–chromophore–acceptor triad comprising a triphenylamine electron donor and a dipyrido­[3,2-a:2′,3′-c]­phenazine electron acceptor as the active material for photoanodes. Energy levels of this triad are carefully aligned for thermodynamically favorable photoinduced electron transfer. Once this triad is surface-grafted onto zinc oxide nanowires, photoelectrochemical studies confirm the utility of this architecture for oxidative processes such as alcohol oxidation with modest yields

Diffusion of Organic Molecules as a Function of Temperature in a Sucrose Matrix (a Proxy for Secondary Organic Aerosol)

Knowledge of diffusion coefficients as a function of temperature in secondary organic aerosol (SOA) or proxies of SOA is needed to predict atmospheric chemistry, climate, and air quality. We determined diffusion coefficients as a function of temperature of a fluorescent organic molecule in a sucrose matrix (a proxy for SOA). Diffusion coefficients were a strong function of temperature (e.g., at water activity = 0.43, diffusion coefficients decreased by a factor of ∼40 as the temperature decreased by 20 K). Interestingly, the apparent activation energy for diffusion of the fluorescent organic molecule was similar to the apparent activation for diffusion of water in the sucrose matrix. On the basis of these measurements, the mixing time of organic molecules by diffusion in some types of SOA particles will often be >1 h in the free troposphere, if a sucrose matrix is an accurate proxy for these types of SOA

Scalable, green fabrication of single-crystal noble metal films and nanostructures for low-loss nanotechnology applications

High quality metal thin films and nanostructures are critical building blocks for next generation nanotechnologies. They comprise low-loss circuit elements in nanodevices, provide new catalytic pathways for water splitting and $CO_2$ reduction technologies, and enable the confinement of spatially extended electromagnetic waves to be harnessed for application in information processing, energy harvesting, engineered metamaterials, and new technologies that will operate in the quantum plasmonics limit. However, the controlled fabrication of high-definition single-crystal subwavelength metal nanostructures remains a significant hurdle, due to the tendency for polycrystalline metal growth using conventional physical vapor deposition methods, and the challenges associated with placing solution-grown nanocrystals in desired orientations and locations on a surface to fabricate functional devices. Here, we introduce a new scalable, green, wet chemical approach to monocrystalline noble metals that enables the fabrication of ultrasmooth, epitaxial, single-crystal films of controllable thickness. They are ideal for the subtractive manufacture of nanostructure through ion beam milling, and additive crystalline nanostructure via lithographic patterning to enable large area, single-crystal metamaterials and high aspect ratio nanowires. Our single-crystal nanostructures demonstrate improved feature quality and pattern transfer yield, reduced optical and resistive losses, tailored local fields, and greatly improved stability compared to polycrystalline structures, supporting greater local field enhancements and enabling new practical advances at the nanoscale

Near-Field Enhancement of Optical Second Harmonic Generation in Hybrid Gold-Lithium Niobate Nanostructures

Nanophotonics research has focused recently on the ability of non-linear optical processes to mediate and transform optical signals in a myriad of novel devices, including optical modulators, transducers, color filters, photodetectors, photon sources, and ultrafast optical switches. The inherent weakness of optical nonlinearities at smaller scales has, however, hindered the realization of efficient miniaturized devices, and strategies for enhancing both device efficiencies and synthesis throughput via nanoengineering remain limited. Here, we demonstrate a novel mechanism by which second harmonic generation, a prototypical non-linear optical phenomenon, from individual lithium niobate particles can be significantly enhanced through nonradiative coupling to the localized surface plasmon resonances of embedded gold nanoparticles. A joint experimental and theoretical investigation of single mesoporous lithium niobate particles coated with aispersed layer of $\sim$10-nm diameter gold nanoparticles shows that a $\sim$32-fold enhancement of second harmonic generation can be achieved without introducing finely tailored radiative nanoantennas to mediate photon transfer to or from the non-linear material. This work highlights the limitations of current strategies for enhancing non-linear optical phenomena and proposes a route through which a new class of subwavelength nonlinear optical platforms can be designed to maximize non-linear efficiencies through near-field energy exchange

Diffusion Coefficients and Mixing Times of Organic Molecules in β‑Caryophyllene Secondary Organic Aerosol (SOA) and Biomass Burning Organic Aerosol (BBOA)

Information on the diffusion rates of organic molecules within secondary organic aerosol (SOA) and biomass burning organic aerosol (BBOA) is needed to predict the impact of these aerosols on atmospheric chemistry, air quality, and climate. Nevertheless, no studies have measured diffusion rates of organics within SOA generated from β-caryophyllene or within BBOA. Here, we measured diffusion rates of organic molecules in laboratory-generated SOA and BBOA as a function of water activity (aw) using fluorescence recovery after photobleaching. The SOA was generated by the ozonolysis of β-caryophyllene, and the BBOA was generated by the pyrolysis of pine wood. Only the water-soluble component of the BBOA was studied. The measured diffusion coefficients of organic molecules in β-caryophyllene range from 1.1 × 10–16 to 1.3 × 10–14 m2 s–1 for aw values ranging from 0.23 to 0.86. For BBOA, the diffusion coefficients range from 7.3 × 10–17 to 6.6 × 10–16 m2 s–1 for aw values ranging from 0.23 to 0.43. Based on these values, the mixing times of organic molecules within a 200 nm SOA or BBOA are less than 1 min for aw values >0.23. Since aw values are often greater than 0.23 in the planetary boundary layer and temperatures in the planetary boundary are often within 5 K of our experimental temperatures, mixing times are likely often short in that part of the atmosphere for the types of aerosols studied here. For β-caryophyllene SOA, we compared the measured diffusion coefficients with predictions based on the Stokes–Einstein relation and the fractional Stokes–Einstein relation. For both the Stokes–Einstein and the fractional Stokes–Einstein relations, the measured diffusion coefficients agree with the predicted diffusion coefficients. This work illustrates that when the radius of the diffusing molecules is greater than the average radius of the matrix molecules, the Stokes–Einstein equation is able to predict diffusion coefficients in β-caryophyllene SOA with reasonable accuracy

Phase Behavior and Viscosity in Biomass Burning Organic Aerosol and Climatic Impacts

Smoke particles generated by burning biomass consist mainly of organic aerosol termed biomass burning organic aerosol (BBOA). BBOA influences the climate by scattering and absorbing solar radiation or acting as nuclei for cloud formation. The viscosity and the phase behavior (i.e., the number and type of phases present in a particle) are properties of BBOA that are expected to impact several climate-relevant processes but remain highly uncertain. We studied the phase behavior of BBOA using fluorescence microscopy and showed that BBOA particles comprise two organic phases (a hydrophobic and a hydrophilic phase) across a wide range of atmospheric relative humidity (RH). We determined the viscosity of the two phases at room temperature using a photobleaching method and showed that the two phases possess different RH-dependent viscosities. The viscosity of the hydrophobic phase is largely independent of the RH from 0 to 95%. We use the Vogel–Fulcher–Tamman equation to extrapolate our results to colder and warmer temperatures, and based on the extrapolation, the hydrophobic phase is predicted to be glassy (viscosity >1012 Pa s) for temperatures less than 230 K and RHs below 95%, with possible implications for heterogeneous reaction kinetics and cloud formation in the atmosphere. Using a kinetic multilayer model (KM-GAP), we investigated the effect of two phases on the atmospheric lifetime of brown carbon within BBOA, which is a climate-warming agent. We showed that the presence of two phases can increase the lifetime of brown carbon in the planetary boundary layer and polar regions compared to previous modeling studies. Hence, the presence of two phases can lead to an increase in the predicted warming effect of BBOA on the climate

Polymer Dots with Enhanced Photostability, Quantum Yield, and Two-Photon Cross-Section using Structurally Constrained Deep-Blue Fluorophores

Semiconducting polymer dots (Pdots) have emerged as versatile probes for bioanalysis and imaging at the single-particle level. Despite their utility in multiplexed analysis, deep blue Pdots remain rare due to their need for high-energy excitation and sensitivity to photobleaching. Here, we describe the design of deep blue fluorophores using structural constraints to improve resistance to photobleaching, two-photon absorption cross sections, and fluorescence quantum yields using the hexamethylazatriangulene motif. Scanning tunneling microscopy was used to characterize the electronic structure of these chromophores on the atomic scale as well as their intrinsic stability. The most promising fluorophore was functionalized with a polymerizable acrylate handle and used to give deep-blue fluorescent acrylic polymers with Mn > 18 kDa and Đ < 1.2. Nanoprecipitation with amphiphilic polystyrene-graft-(carboxylate-terminated poly­(ethylene glycol)) gave water-soluble Pdots with blue fluorescence, quantum yields of 0.81, and molar absorption coefficients of (4 ± 2) × 108 M–1 cm–1. This high brightness facilitated single-particle visualization with dramatically improved signal-to-noise ratio and photobleaching resistance versus an unencapsulated dye. The Pdots were then conjugated with antibodies for immunolabeling of SK-BR3 human breast cancer cells, which were imaged using deep blue fluorescence in both one- and two-photon excitation modes