Tarnishing Silver Metal into Mithrene.

Silver metal exposed to the atmosphere corrodes and becomes tarnished as a result of oxidation and precipitation of the metal as an insoluble salt. Tarnish has so poor a reputation that the word itself connotes corruption and disrespectability; however, tarnishing is a facile synthetic approach for preparing thin metal-sulfide films on silver or copper metal that might be exploited to prepare more elaborate materials with desirable optoelectronic properties. In this work, we prepare luminescent semiconducting thin films of mithrene, a metal-organic chalcogenolate assembly, by replacing the tarnish-causing atmospheric sulfur source with diphenyl diselenide.

Design Rules for Self-Assembly of 2D Nanocrystal/Metal-Organic Framework Superstructures.

We demonstrate the guiding principles behind simple two dimensional self-assembly of MOF nanoparticles (NPs) and oleic acid capped iron oxide (Fe O ) NCs into a uniform two-dimensional bi-layered superstructure. This self-assembly process can be controlled by the energy of ligand-ligand interactions between surface ligands on Fe O NCs and Zr O (OH) (fumarate) MOF NPs. Scanning transmission electron microscopy (TEM)/energy-dispersive X-ray spectroscopy and TEM tomography confirm the hierarchical co-assembly of Fe O NCs with MOF NPs as ligand energies are manipulated to promote facile diffusion of the smaller NCs.

Two-dimensional sp carbon-conjugated covalent organic frameworks.

We synthesized a two-dimensional (2D) crystalline covalent organic framework (spc-COF) that was designed to be fully π-conjugated and constructed from all sp carbons by C=C condensation reactions of tetrakis(4-formylphenyl)pyrene and 1,4-phenylenediacetonitrile. The C=C linkages topologically connect pyrene knots at regular intervals into a 2D lattice with π conjugations extended along both and directions and develop an eclipsed layer framework rather than the more conventionally obtained disordered structures. The spc-COF is a semiconductor with a discrete band gap of 1.

para-Azaquinodimethane: A Compact Quinodimethane Variant as an Ambient Stable Building Block for High-Performance Low Band Gap Polymers.

Quinoidal structures incorporating expanded para-quinodimethane (p-QM) units have garnered great interest as functional organic electronic, optical, and magnetic materials. The direct use of the compact p-QM unit as an electronic building block, however, has been inhibited by the high reactivity conveyed by its biradical character. Herein, we introduce a stable p-QM variant, namely p-azaquinodimethane (p-AQM), that incorporates nitrogen atoms in the central ring and alkoxy substituents on the periphery to increase the stability of the quinoidal structure.

Enhancing fullerene-based solar cell lifetimes by addition of a fullerene dumbbell.

Cost-effective, solution-processable organic photovoltaics (OPV) present an interesting alternative to inorganic silicon-based solar cells. However, one of the major remaining challenges of OPV devices is their lack of long-term operational stability, especially at elevated temperatures. The synthesis of a fullerene dumbbell and its use as an additive in the active layer of a PCDTBT:PCBM-based OPV device is reported.

Quadrites and crossed-chain crystal structures in polymer semiconductors.

Many high-performance conjugated polymers for organic photovoltaics and transistors crystallize such that chains are parallel, resulting in significant anisotropy of the nanoscale charge transport properties. Here we demonstrate an unusual intercrystallite relationship where thin lamellae adopt a preferred epitaxial relationship with crossed-chains at the interface. The crossed-chains may allow either crystal to use the other as an "electronic shunt", creating efficient quasi-three-dimensional transport pathways that reduce the severity of grain boundaries and defects in limiting transport.

Solubility-limited extrinsic n-type doping of a high electron mobility polymer for thermoelectric applications.

The thermoelectric properties of a highperformance electron-conducting polymer, (P(NDIOD-T2), extrinsically doped with dihydro-1H-benzoimidazol-2-yl (NDBI) derivatives, are reported. The highest thermoelectric power factor that has been reported for a solution-processed n-type polymer is achieved; and it is concluded that engineering polymerdopant miscibility is essential for the development of organic thermoelectrics.

A modular strategy for fully conjugated donor-acceptor block copolymers.

A novel strategy for the synthesis of fully conjugated donor-acceptor block copolymers, in a single reaction step employing Stille coupling polymerization of end-functional polythiophene and AA + BB monomers, is presented. The unique donor-acceptor structure of these block copolymers provides a rich self-assembly behavior, with the first example of a fully conjugated donor-acceptor block copolymer having two separate crystalline domains being obtained.

Solvent-dependent friction force response of poly(ethylenimine)-graft-poly(ethylene glycol) brushes investigated by atomic force microscopy.

Lateral and normal forces between a surface-bound, brushlike copolymer, poly(ethylenimine)-graft-poly(ethylene glycol) (PEI-g-PEG), and a silica colloidal probe were investigated with atomic force microscopy (AFM) and related to the relative mass of the solvent absorbed within the polymer as measured with the quartz crystal microbalance. PEI-g-PEG was adsorbed onto an oxide-passivated silicon wafer through its exposure to physiologically buffered solutions of the polymer. Frictional forces were measured between the colloidal probe and the substrate by AFM as the polarity of the solvent was systematically varied.