Uncovering the Mechanisms of Triplet-Triplet Annihilation Upconversion Enhancement via Plasmonic Nanocavity Tuning.

The nonlinear conversion of photons from lower to higher energy is important for a wide range of applications, from quantum communications and optoelectronics to solar energy conversion and medicine. Triplet-triplet annihilation upconversion (TTA UC), which utilizes an absorber/emitter molecular pair, is a promising tool for upconversion applications requiring low intensity light such as photovoltaics, photocatalysis, and bioimaging. Despite demonstrations of efficient TTA UC in solution, practical applications have proven difficult, as thin films retard the necessary energy transfer steps and result in low emission yields.

Tracking light-induced charge transport.

Precise charge dynamics could help to improve the operation of solar cells and sensors.

Ultrathin Pyroelectric Photodetector with Integrated Polarization-Sensing Metasurface.

An abundance of metallic metasurfaces have been realized with miniscule, intricate features capable of tailored scattering, reflection, and absorption; however, high losses through heat limit their use in optoelectronics. Here, codesign of a detector and a polarization-sensing metasurface overcomes this challenge by utilizing the heat generation for integrated pyroelectric detection of the incoming light polarization. Using a nanogap metasurface with asymmetric metallic elements, polarization-sensitive photodetection exhibits high extinction ratios up to 19 for orthogonally polarized light and allows extraction of Stokes parameters with <12% deviation from theoretical values.

Impact of Molecular Orientation on Lateral and Interfacial Electron Transfer at Oxide Interfaces.

Molecular dyes, called sensitizers, with a -[Ru(LL)(dcb)(NCS)] structure, where dcb is 4,4'-(COH)-2,2'-bipyridine and LL is dcb or a different diimine ligand, are among the most optimal for application in dye-sensitized solar cells (DSSCs). Herein, a series of five sensitizers, three bearing two dcb ligands and two bearing one dcb ligand, were anchored to mesoporous thin films of conducting tin-doped indium oxide (ITO) or semiconducting TiO nanocrystallites. The number of dcb ligands impacts the surface orientation of the sensitizer; density functional theory (DFT) calculations revealed an ∼1.

Reorganization Energies for Interfacial Proton-Coupled Electron Transfer to a Water Oxidation Catalyst.

The reorganization energy (λ) for interfacial electron transfer (ET) and proton-coupled ET (PCET) from a conductive metal oxide (InO:Sn, ITO) to a surface-bound water oxidation catalyst was extracted from kinetic data measured as a function of the thermodynamic driving force. Visible light excitation resulted in rapid excited-state injection ( > 10 s) to the ITO, which photo-initiated the two interfacial reactions of interest. The rate constants for both reactions increased with the driving force, -Δ°, to a saturating limit, , with rate constants consistently larger for ET than for PCET.

Reorganization Energies for Interfacial Electron Transfer across Phenylene Ethynylene Rigid-Rod Bridges.

A family of three ruthenium bipyridyl rigid-rod compounds of the general form [Ru(bpy)(LL)](PF) were anchored to mesoporous thin films of tin-doped indium oxide (ITO) nanocrystals. Here, LL is a 4-substituted 2,2-bipyridine (bpy) ligand with varying numbers of conjugated phenylenethynylene bridge units between the bipyridine ring and anchoring group consisting of a bis-carboxylated isophthalic group. The visible absorption spectra and the formal potentials, (), of the surface anchored rigid-rods were insensitive to the presence of the phenylene ethynylene bridge units in 0.

Accessing Photoredox Transformations with an Iron(III) Photosensitizer and Green Light.

Efficient excited-state electron transfer between an iron(III) photosensitizer and organic electron donors was realized with green light irradiation. This advance was enabled by the use of the previously reported iron photosensitizer, [Fe(phtmeimb)] (phtmeimb = {phenyl[tris(3-methyl-imidazolin-2-ylidene)]borate}, that exhibited long-lived and luminescent ligand-to-metal charge-transfer (LMCT) excited states. A benchmark dehalogenation reaction was investigated with yields that exceed 90% and an enhanced stability relative to the prototypical photosensitizer [Ru(bpy)].

Solvent influence on non-adiabatic interfacial electron transfer at conductive oxide electrolyte interfaces.

The kinetics for interfacial electron transfer (ET) from a transparent conductive oxide (tin-doped indium oxide, ITO, Sn:InO) to molecular acceptors 4-[N,N-di(p-tolyl)amino]benzylphosphonic acid, TPA, and [Ru(bpy)(4,4'-(POH)-bpy)], RuP, positioned at variable distances within and beyond the electric double layer (EDL), were quantified in benzonitrile and methanol by nanosecond absorption spectroscopy as a function of the thermodynamic driving force, -ΔG°. Relevant ET parameters such as the rate constant, k, reorganization energy, λ, and electronic coupling, H, were extracted from the kinetic data. Overall, k increased as the distance between the molecular acceptor and the conductor decreased.

Kinetic Evidence That the Solvent Barrier for Electron Transfer Is Absent in the Electric Double Layer.

Classical capacitance studies have revealed that the first layer of water present at an aqueous metal-electrolyte interface has a dielectric constant less than 1/10th of that of bulk water. Modern theory indicates that the barrier for electron transfer will decrease substantially in this layer; yet, this important prediction has not been tested experimentally. Here, we report the interfacial electron transfer kinetics for molecules positioned at variable distances within the electric double layer of a transparent conductive oxide as a function of the Gibbs free energy change.

Electron Transfer Reorganization Energies in the Electrode-Electrolyte Double Layer.

The total reorganization energy, λ, for interfacial electron transfer, ET, from a conductive electrode to redox-active molecules at fixed positions within the electric double layer, EDL, has been determined experimentally. Conductive indium-tin-oxide (ITO, InO:Sn) mesoporous films were functionalized with 4-[,-di(-tolyl)-amino]benzylphosphonic acid (TPA) and/or [Ru(bpy)(4,4'-(POH)-bpy)] (RuP), where bpy is 2,2'-bipyridine. The small inner-sphere reorganizations, λ, for RuP and TPA make them excellent probes of outer-sphere reorganization energy, λ, as λ ≪ λ such that λ = λ + λ ≈ λ.

Electron Localization and Transport in SnO/TiO Mesoporous Thin Films: Evidence for a SnO/SnTiO/TiO Structure.

A study of SnO/TiO core/shell films was undertaken to investigate the influences of shell thickness and post deposition sintering on electron localization and transport properties. Electrochemical reduction of the materials resulted in the appearance of a broad visible-near IR absorbance that provided insights into the electronic state(s) within the core/shell structures. As the shell thickness was increased from 0.

Determination of Proton-Coupled Electron Transfer Reorganization Energies with Application to Water Oxidation Catalysts.

The reorganization energy, λ, for interfacial electron transfer (ET) and for proton-coupled electron transfer (PCET) between a water oxidation catalyst and a conductive InO:Sn (ITO) oxide were extracted from kinetic data by application of Marcus-Gerischer theory. Specifically, light excitation of the water oxidation catalyst [Ru(tpy)(4,4'-(POH)-bpy)OH] (Ru-OH), where tpy is 2,2':6',2″-terpyridine and bpy is 2,2'-bipyridine, anchored to a mesoporous thin film of ITO nanocrystallites resulted in rapid excited-state injection ( k > 10 s). The subsequent reaction of the injected electron (ITO(e)) and the oxidized catalyst was quantified spectroscopically on nanosecond and longer time scales.

Slow-release delivery enhances the pharmacological properties of oral 5-hydroxytryptophan: mouse proof-of-concept.

5-hydroxytryptophan (5-HTP) has shown therapeutic promise in a range of human CNS disorders. But native 5-HTP immediate release (IR) is poorly druggable, as rapid absorption causes rapid onset of adverse events, and rapid elimination causes fluctuating exposure. Recently, we reported that 5-HTP delivered as slow-release (SR) in mice augmented the brain pro-serotonergic effect of selective serotonin reuptake inhibitors (SSRIs), without the usual adverse events associated with 5-HTP IR.

Surface Grafting of Ru(II) Diazonium-Based Sensitizers on Metal Oxides Enhances Alkaline Stability for Solar Energy Conversion.

The electrografting of [Ru(ttt)(tpy-CH-N)], where "ttt" is 4,4',4″-tri-tert-butyl-2,2':6',2″-terpyridine, was investigated on several wide band gap metal oxide surfaces (TiO, SnO, ZrO, ZnO, InO:Sn) and compared to structurally analogous sensitizers that differed only by the anchoring group, i.e., -POH and -COOH.

Engineering oxidative stability in human hemoglobin based on the Hb providence (βK82D) mutation and genetic cross-linking.

Previous work suggested that hemoglobin (Hb) tetramer formation slows autoxidation and hemin loss and that the naturally occurring mutant, Hb Providence (HbProv; βK82D), is much more resistant to degradation by HO We have examined systematically the effects of genetic cross-linking of Hb tetramers with and without the HbProv mutation on autoxidation, hemin loss, and reactions with HO, using native HbA and various wild-type recombinant Hbs as controls. Genetically cross-linked Hb Presbyterian (βN108K) was also examined as an example of a low oxygen affinity tetramer. Our conclusions are: (a) at low concentrations, all the cross-linked tetramers show smaller rates of autoxidation and hemin loss than HbA, which can dissociate into much less stable dimers and (b) the HbProv βK82D mutation confers more resistance to degradation by HO, by markedly inhibiting oxidation of the β93 cysteine side chain, particularly in cross-linked tetramers and even in the presence of the destabilizing Hb Presbyterian mutation.