Asymmetries were observed across a monolayer of dimethylanilinoaza[C 60 ]fullerene, (DMA-NC 60 , 1) sandwiched between gold electrodes of relatively large size (0.265 mm 2 ). Two modes of behavior are observed: (1) a sigmoidal and slightly asymmetric behavior, bespeaking of a moderate unimolecular rectifier (rectification ratio of about 2), and (2) above a threshold voltage V 1 (≈0.6 to 1.0 V), a dramatic increase of current to 0.3 to 1 A (as high as 1.36 × 10 7 electrons molecule -1 s -1 at 1.5 V), followed by ohmic behavior from V 1 to a relatively smaller negative bias V 2 (≈ -0.5 V to -0.6 V). At more negative potentials (e.g., at -1.5 V) the current is very small (a few µA). This high asymmetry in current persists for between 10 and 20 cycles of voltage scan. This increased, but ohmic conductivity is probably due to defects that grow at domain boundaries, since this behavior is not seen when very small electrodes (1 µm 2 area) are used. The defects could be stalagmitic filaments of gold which grow from the bottom electrode above V 1 but are broken at the negative bias V 2 , or else they could be due to some unknown electrochemical couple. This device is vaguely reminiscent of Zener diodes or varistors: if operated between, say, + 2 V and -2 V, it is a super-rectifier, with a rectification ratio of up to 20 000 at 1.5 V.

Although it is tempting to compare organic semiconductors with their inorganic counterparts, the spin-injection and spin-transport properties are fundamentally different. The challenges in understanding and improving such properties make organic spintronics an exciting field in its own right.

Hydrogenation reactions can be used to store energy in chemical bonds, and if these reactions are reversible, that energy can be released on demand. Some of the most effective transition metal catalysts for CO2 hydrogenation have featured pyridin-2-ol-based ligands (e.g., 6,6′-dihydroxybipyridine (6,6′-dhbp)) for both their proton-responsive features and for metal–ligand bifunctional catalysis. We aimed to compare bidentate pyridin-2-ol based ligands with a new scaffold featuring an N-heterocyclic carbene (NHC) bound to pyridin-2-ol. Toward this aim, we have synthesized a series of [Cp*Ir(NHC-pyOR)Cl]OTf complexes where R = tBu (1), H (2), or Me (3). For comparison, we tested analogous bipy-derived iridium complexes as catalysts, specifically [Cp*Ir(6,6′-dxbp)Cl]OTf, where x = hydroxy (4Ir) or methoxy (5Ir); 4Ir was reported previously, but 5Ir is new. The analogous ruthenium complexes were also tested using [(η6-cymene)Ru(6,6′-dxbp)Cl]OTf, where x = hydroxy (4Ru) or methoxy (5Ru); 4Ru and 5Ru were both reported previously. All new complexes were fully characterized by spectroscopic and analytical methods and by single-crystal X-ray diffraction for 1, 2, 3, 5Ir, and for two [Ag(NHC-pyOR)2]OTf complexes 6 (R = tBu) and 7 (R = Me). The aqueous catalytic studies of both CO2 hydrogenation and formic acid dehydrogenation were performed with catalysts 1–5. In general, NHC-pyOR complexes 1–3 were modest precatalysts for both reactions. NHC complexes 1–3 all underwent transformations under basic CO2 hydrogenation conditions, and for 3, we trapped a product of its transformation, 3SP, which we characterized crystallographically. For CO2 hydrogenation with base and dxbp-based catalysts, we observed that x = hydroxy (4Ir) is 5–8 times more active than x = methoxy (5Ir). Notably, ruthenium complex 4Ru showed 95% of the activity of 4Ir. For formic acid dehydrogenation, the trends were quite different with catalytic activity showing 4Ir ≫ 4Ru and 4Ir ≈ 5Ir. Secondary coordination sphere effects are important under basic hydrogenation conditions where the OH groups of 6,6′-dhbp are deprotonated and alkali metals can bind and help to activate CO2. Computational DFT studies have confirmed these trends and have been used to study the mechanisms of both CO2 hydrogenation and formic acid dehydrogenation.

We report a new synthesis of colloidal gold(I) sulfide nanoparticles by reacting aqueous solutions of sodium sulfide and sodium gold sulfite. Optical absorption spectra and pH were measured during the reaction. The pH changes from 10.3 to 8.8 immediately after mixing the reactants and very slowly decreases during particle growth. The nanoparticles exhibit a continuous increase in absorption as the photon energy increases from 1 to 5 eV. The optical band gap of the nanoparticles has been estimated from the onset of absorption to be 1.8 ± 0.2 eV. X-ray photoelectron and energy-dispersive X-ray spectroscopy indicate that the composition of the particles is Au2S. The measured S(2p3/2) and Au(4f7/2) binding energies suggest that Au2S has mixed covalent/ionic bonding. Transmission electron microscopy shows that the particles are roughly spherical with an average diameter of 4 nm.

We have studied the adsorption of Hg atoms onto gold and silver nanoparticles by optical spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and energy-dispersive X-ray analysis. Mercury adsorption induces a blue shift of the surface plasmon mode of gold and silver nanoparticles. Two trends are observed in the UV-vis spectra. First, silver particles experience a larger blue shift than gold particles (given the same particle size and Hg surface coverage). Second, smaller Au and Ag particles experience a greater blue shift than larger particles. We have calculated the UV-vis absorption spectra using a core/Hg(shell) model and found good agreement between the experimental results and theoretical calculations. The results suggest the basis for a novel colorimetric assay for Hg.

We have prepared Langmuir−Blodgett monolayers of hexadecylquinolinium tricyanoquinodimethanide (C16H33Q+-3CNQ-) on gold surfaces and characterized the structure by surface plasmon resonance (SPR), X-ray photoelectron spectroscopy (XPS), reflection−absorption infrared spectroscopy (RAIRS), Raman spectroscopy, and water contact angle measurements. We compare the IR and UV−vis spectra of C16H33Q+-3CNQ- to a series of compounds that contain the key functional groups in the titled compound to help assign the spectral features. The surface spectroscopic measurements indicate that the molecules in the monolayer are aligned such that the two terminal cyano groups are adsorbed on the Au surface, and that the aliphatic chain is away from that surface. The thickness of the monolayer was measured by XPS to be ∼ 26 Å and suggests that the molecules are tilted ∼40° away from the surface normal. High-resolution XPS and spectroelectrochemical measurements of C16H33Q+-3CNQ- strongly suggest that it is a ground-state zwitterion in both the adsorbed and solvated forms.

Exchange-biased magnetic tunnel junctions with a CoFeB/MgO pinned layer, a Co free layer and an aluminum tris-(8-hydroxyquinoline) spacer layer of thickness ranging from 0–8 nm have been prepared by photolithography. The devices show a room-temperature, zero-bias magnetoresistance of 12.5±0.3%, which is unchanged after the crossover from tunneling to hopping transport at a barrier thickness of about 4 nm. The spin-diffusion length in the hopping regime is much greater than 10 nm. The magnetoresistance in the tunneling regime changes sign at a positive bias of 250 mV, and it is maximum at −100 mV.

Thermal conversion of [Fe(phen) 3 ](SCN) 2 thin films into the spin crossover complex Fe(phen) 2 (NCS) 2 3