Boosting the Performance of Iron-Phthalocyanine as Cathode Electrocatalyst for Alkaline Polymer Fuel Cells Through Edge-Closed Conjugation.

Recent progress in anion-exchange membranes has evoked increasing interests in alkaline polymer fuel cells (APFCs). A large body of recent research has demonstrated attractive activity of Fe-N macrocycle complexes as electrocatalysts for the oxygen reduction reaction (ORR) in alkaline media. To be a substitute for Pt in APFCs, however, most of the macrocycle molecules remain largely unsatisfactory in both of the catalytic activity and durability.

Photosensitised Multiheme Cytochromes as Light-Driven Molecular Wires and Resistors.

Multiheme cytochromes possess closely packed redox-active hemes arranged as chains spanning the tertiary structure. Here we describe five variants of a representative multiheme cytochrome engineered as biohybrid phototransducers for converting light into electricity. Each variant possesses a single Cys sulfhydryl group near a terminus of the heme chain, and this was efficiently labelled with a Ru (2,2'-bipyridine) photosensitiser.

Direct Assembly of Large Area Nanoparticle Arrays.

A major goal of nanotechnology is the assembly of nanoscale building blocks into functional optical, electrical, or chemical devices. Many of these applications depend on an ability to optically or electrically address single nanoparticles. However, positioning large numbers of single nanocrystals with nanometer precision on a substrate for integration into solid-state devices remains a fundamental roadblock.

Photochemical upconversion is suppressed by high concentrations of molecular sensitizers.

Photochemical upconversion uses sensitized triplet-triplet annihilation in bimolecular compositions to convert lower energy photons to higher energy photons. For high efficiency under low illumination, usually a high sensitizer concentration is desirable. However, here we show that the upconversion sensitizer can reduce the emitter triplet lifetime by dynamic quenching, with rate constants on the order 106 M-1 s-1, leading to diminishing returns beyond a certain concentration.

Infrared spectroscopy reveals multi-step multi-timescale photoactivation in the photoconvertible protein archetype dronpa.

Photochromic fluorescent proteins play key roles in super-resolution microscopy and optogenetics. The light-driven structural changes that modulate the fluorescence involve both trans-to-cis isomerization and proton transfer. The mechanism, timescale and relative contribution of chromophore and protein dynamics are currently not well understood.

Colloidal Stability of Apolar Nanoparticles: The Role of Particle Size and Ligand Shell Structure.

Being able to predict and tune the colloidal stability of nanoparticles is essential for a wide range of applications, yet our ability to do so is currently poor due to a lack of understanding of how they interact with one another. Here, we show that the agglomeration of apolar particles is dominated by either the core or the ligand shell depending on the particle size and materials. We do this by using small-angle X-ray scattering and molecular dynamics simulations to characterize the interaction between hexadecanethiol passivated gold nanoparticles in decane solvent.

Polycrystallinity of Lithographically Fabricated Plasmonic Nanostructures Dominates Their Acoustic Vibrational Damping.

The study of acoustic vibrations in nanoparticles provides unique and unparalleled insight into their mechanical properties. Electron-beam lithography of nanostructures allows precise manipulation of their acoustic vibration frequencies through control of nanoscale morphology. However, the dissipation of acoustic vibrations in this important class of nanostructures has not yet been examined.

Structural and Chemical Changes to CH NH PbI Induced by Electron and Gallium Ion Beams.

Organic-inorganic hybrid perovskites, such as CH NH PbI have shown highly promising photovoltaic performance. Electron microscopy (EM) is a powerful tool for studying the crystallography, morphology, interfaces, lattice defects, composition, and charge carrier collection and recombination properties at the nanoscale. Here, the sensitivity of CH NH PbI to electron beam irradiation is examined.

Multihydroxy-Anthraquinone Derivatives as Free Radical and Cationic Photoinitiators of Various Photopolymerizations under Green LED.

Multihydroxy-anthraquinone derivatives [i.e., 1,2,4-trihydroxyanthraquinone (124-THAQ), 1,2,7-trihydroxyanthraquinone (127-THAQ), and 1,2,5,8-tetrahydroxyanthraquinone (1258-THAQ)] can interact with various additives [e.

Calculating curly arrows from ab initio wavefunctions.

Despite being at the heart of chemical thought, the curly arrow notation of reaction mechanisms has been treated with suspicion-the connection with rigorous molecular quantum mechanics being unclear. The connection requires a view of the wavefunction that goes beyond molecular orbitals and rests on the most fundamental property of electrons. The antisymmetry of electronic wavefunctions requires that an N-electron wavefunction repeat itself in 3N dimensions, thus exhibiting tiles.

Efficient and Stable Inverted Planar Perovskite Solar Cells Using a Triphenylamine Hole-Transporting Material.

Inverted perovskite solar cells (PSCs) with a p-i-n structure have attracted great attention. Normally, inorganic p-type metal oxides or polymers are used as the hole-transport material (HTM), a vital component in the inverted PSCs. However, this type of HTM often requires high processing temperatures and/or high costs.

Two Mechanisms Determine Quantum Dot Blinking.

Many potential applications of quantum dots (QDs) can only be realized once the luminescence from single nanocrystals (NCs) is understood. These applications include the development of quantum logic devices, single-photon sources, long-life LEDs, and single-molecule biolabels. At the single-nanocrystal level, random fluctuations in the QD photoluminescence occur, a phenomenon termed blinking.

The evolution of size, shape, and surface morphology of gold nanorods.

We investigate the transformation of single crystal gold nanorod surface morphology over extended growth times. After initial rapid anisotropic growth and disappearance of {111} bridging facets, the aspect ratios converge across AgNO concentrations. The surface morphology transitions from faceted to curved.

Endothermic singlet fission is hindered by excimer formation.

Singlet fission is a process whereby two triplet excitons can be produced from one photon, potentially increasing the efficiency of photovoltaic devices. Endothermic singlet fission is desired for a maximum energy-conversion efficiency, and such systems have been considered to form an excimer-like state with multiexcitonic character prior to the appearance of triplets. However, the role of the excimer as an intermediate has, until now, been unclear.

Mass Spectrometry Using Nanomechanical Systems: Beyond the Point-Mass Approximation.

The mass measurement of single molecules, in real time, is performed routinely using resonant nanomechanical devices. This approach models the molecules as point particles. A recent development now allows the spatial extent (and, indeed, image) of the adsorbate to be characterized using multimode measurements ( Hanay , M.

Tuning Single Quantum Dot Emission with a Micromirror.

The photoluminescence of single quantum dots fluctuates between bright (on) and dark (off) states, also termed fluorescence intermittency or blinking. This blinking limits the performance of quantum dot-based devices such as light-emitting diodes and solar cells. However, the origins of the blinking remain unresolved.

Photophysical and Fluorescence Anisotropic Behavior of Polyfluorene β-Conformation Films.

We demonstrate a systematic visualization of the unique photophysical and fluorescence anisotropic properties of polyfluorene coplanar conformation (β-conformation) using time-resolved scanning confocal fluorescence imaging (FLIM) and fluorescence anisotropy imaging microscopy (FAIM) measurements. We observe inhomogeneous morphologies and fluorescence decay profiles at various micrometer-sized regions within all types of polyfluorene β-conformational spin-coated films. Poly(9,9-dioctylfluorene-2,7-diyl) (PFO) and poly[4-(octyloxy)-9,9-diphenylfluoren-2,7-diyl]-co-[5-(octyloxy)-9,9-diphenylfluoren-2,7-diyl] (PODPF) β-domains both have shorter lifetime than those of the glassy conformation for the longer effective conjugated length and rigid chain structures.

Aqueous Synthesis of High-Quality CuZnSnS Nanocrystals and Their Thermal Annealing Characteristics.

Copper zinc tin sulfide (CZTS) nanocrystal inks are promising candidates for the development of cheap, efficient, scalable, and nontoxic photovoltaic (PV) devices. However, optimization of the synthetic chemistry to achieve these goals remains a key challenge. Herein we describe a single-step, aqueous-based synthesis that yields high-quality CZTS nanocrystal inks while also minimizing residual organic impurities.

A Mechanism for Symmetry Breaking and Shape Control in Single-Crystal Gold Nanorods.

The phenomenon of symmetry breaking-in which the order of symmetry of a system is reduced despite manifest higher-order symmetry in the underlying fundamental laws-is pervasive throughout science and nature, playing a critical role in fields ranging from particle physics and quantum theory to cosmology and general relativity. For the growth of crystals, symmetry breaking is the crucial step required to generate a macroscopic shape that has fewer symmetry elements than the unit cell and/or seed crystal from which it grew. Advances in colloid synthesis have enabled a wide variety of nanocrystal morphologies to be achieved, albeit empirically.

Topologically Enclosed Aluminum Voids as Plasmonic Nanostructures.

Recent advances in the ability to synthesize metallic nanoparticles with tailored geometries have led to a revolution in the field of plasmonics. However, studies of the important complementary system, an inverted nanostructure, have so far been limited to two-dimensional sphere-segment voids or holes. Here we reveal the localized surface plasmon resonances (LSPRs) of nanovoids that are topologically enclosed in three-dimensions: an "anti-nanoparticle".

Vibrational coupling in plasmonic molecules.

Plasmon hybridization theory, inspired by molecular orbital theory, has been extremely successful in describing the near-field coupling in clusters of plasmonic nanoparticles, also known as plasmonic molecules. However, the vibrational modes of plasmonic molecules have been virtually unexplored. By designing precisely configured plasmonic molecules of varying complexity and probing them at the individual plasmonic molecule level, intramolecular coupling of acoustic modes, mediated by the underlying substrate, is observed.

Analysis of time-correlated single photon counting data: a comparative evaluation of deterministic and probabilistic approaches.

We review various methods for analysing time-resolved fluorescence data acquired using the time-correlated single photon counting method in an attempt to evaluate their benefits and limitations. We have applied these methods to both experimental and simulated data. The relative merits of using deterministic approaches, such as the commonly used iterative reconvolution method, and probabilistic approaches, such as the smoothed exponential series method, the maximum entropy method and recently proposed basis pursuit denoising (compressed sensing) method, are outlined.

Dipole-field-assisted charge extraction in metal-perovskite-metal back-contact solar cells.

Hybrid organic-inorganic halide perovskites are low-cost solution-processable solar cell materials with photovoltaic properties that rival those of crystalline silicon. The perovskite films are typically sandwiched between thin layers of hole and electron transport materials, which efficiently extract photogenerated charges. This affords high-energy conversion efficiencies but results in significant performance and fabrication challenges.

A study of size-dependent properties of MoS monolayer nanoflakes using density-functional theory.

Novel physical phenomena emerge in ultra-small sized nanomaterials. We study the limiting small-size-dependent properties of MoS monolayer rhombic nanoflakes using density-functional theory on structures of size up to MoS (1.74 nm).

Ab initio calculation of energy levels for phosphorus donors in silicon.

The s manifold energy levels for phosphorus donors in silicon are important input parameters for the design and modeling of electronic devices on the nanoscale. In this paper we calculate these energy levels from first principles using density functional theory. The wavefunction of the donor electron's ground state is found to have a form that is similar to an atomic s orbital, with an effective Bohr radius of 1.