Norman Herron

Crystal Structure and Optical Properties of Cd32S14(SC6H5)36. DMF4, a Cluster with a 15 Angstrom CdS Core

Recrystallization of the solid Cd10S4(SC6H5)12 from a solution of pyridine and N, N-di-methylformamide (DMF) results in the formation of the cluster Cd32S14(SC6H5)36-DMF4 as pale yellow cubes. The structure consists of an 82-atom CdS core that is a roughly spherical piece of the cubic sphalerite lattice ∼12 angstroms in diameter. The four corners of the lattice are capped by hexagonal wurtzite-like CdS units, which results in an overall tetrahedral cluster ∼15 angstroms in diameter. This cluster dissolves intact in tetrahydrofuran where its absorption spectrum reveals a sharp peak at 358 nanometers at room temperature and its emission spectra show a strong broad band at 500 nanometers.

Highly efficient electroluminescent materials based on fluorinated organometallic iridium compounds

We report a class of highly efficient electroluminescent materials based on fluorinated iridium compounds. Using aluminum as the cathode, a device, using fac-tris[5-fluoro-2(5-trifluoromethyl-2-pyridinyl)phenyl-C,N]iridium (Ir-2h) as the luminescent layer, displayed intense electroluminescence at 525 nm with an efficiency of 20 cd/A and a maximum radiance of 4800 cd/m2. Differing from the previously reported Ir(ppy)3, Ir-2h can be used in the undiluted form without the use of a charge-transporting host. This indicates that Ir-2h by itself has good enough charge-transporting properties. Photoluminescence studies at room temperature and 77 K revealed that electroluminescence originates from the metal-to-ligand charge transfer state with a quantum yield of 0.56 for Ir-2h and 0.5 for Ir(ppy)3 in toluene at room temperature. In the thin-film form, photoluminescence quantum yield of Ir-2h is a factor of 10 greater than that of Ir(ppy)3 due to the larger self-quenching effect of Ir(ppy)3.

Synthesis and Single-Crystal X-ray Structure of a Highly Symmetrical C60 Derivative, C60Br24

C60 and liquid bromine react to form C60Br24, a crystalline compound isolated as a bromine solvate, C60Br24(Br2)x, The x-ray crystal structure defines a new pattern of addition to the carbon skeleton that imparts a rare high symmetry. The parent C60 framework is recognizable in C60Br24, but sp3 carbons at sites of bromination distort the surface, affecting conformations of all of the hexagonal and pentagonal rings. Twenty-four bromine atoms envelop the carbon core, shielding the 18 remaining double bonds from addition. At 150� to 200�C there is effectively quantitative reversion of C60Br24 to C60 and Br2.

The Selective Partial Oxidation of Alkanes using Zeolite Based Catalysts. Phthalocyanine (PC) “Ship-in-Bottle” Species

Phthalocyaninatoiron (FePc) complexes may be prepared inside the pore structure of large pore zeolites X or Y by a process of sequential introduction of components followed by assembly inside the void space of the zeolite. Such species are capable of performing as catalysts in the oxidation of alkanes using iodosobenzene as the oxygen atom transfer reagent. The fact that such catalysis is constrained to occur inside the size- and shape-selective zeolite crystallites imposes unique selectivities on the distribution of oxidized products. These catalysts prefer to oxidize the smaller of two competitive substrates and to oxidize toward the ends of the long molecular axis of such substrates. In addition. stereoselectivity is apparent in cases of oxidations with diastereotopic C–H bonds. All of the observed selectivities can be explained in terms of the sieving and orienting effects of the zeolite hosts. While selectivities are moderate with the native zeolites, they may be considerably adjusted by simply alter...

Production of Perfluoroalkylated Nanospheres from Buckminsterfullerene

Perfluoroalkylated nanospheres have been prepared by reaction of fullerenes with a variety of fluoroalkyl radicals. The latter are generated by thermal or photochemical decomposition of fluoroalkyl iodides or fluorodiacyl peroxides. Up to 16 radicals add to C60 to afford easily isolable fluoroalkylated derivatives. The monosubstituted radical adducts were detected by electron spin resonance in the early stages of the fluoroalkylation reactions. These spheroidal molecules are thermally quite stable, soluble in fluoroorganic solvents, chemically resistant to corrosive aqueous solutions, and more volatile than the parent fullerenes. Films of the sublimed material display properties typical for a perfluoroalkylated material.

Three-dimensionally confined diluted magnetic semiconductor clusters: Zn1−xMnxS

We report the first example of a dilute magnetic semiconductor (DMS) confined in all three dimensions (DMS quantum dot). Zn0.93Mn0.07S clusters of not, vert, similar 25 A diameter are successfully synthesized inside a glass matrix and fully characterized by chemical analysis, x-ray diffraction, extended x-ray absorption fine structure (EXAFS), and photoluminescence spectroscopy. Effect of size quantization on the exciton energy has been observed. Preliminary magnetic susceptibility data are presented and discussed.

New, efficient electroluminescent materials based onorganometallic Ir complexes

Reaction of IrCl3 with fluorinated 2-arylpyridines in the presence of AgO2CCF3 affords fac-tris-cyclometalated arylpyridine Ir complexes exhibiting excellent processing and electroluminescent properties which can be fine-tuned via systematic control of the nature and position of the substituents on the aromatic rings.

Nanoparticles: Uses and Relationships to Molecular Cluster Compounds

More than a thousand articles on various aspects of nanoparticles and nanoscale chemistry have appeared in the last year. Nanoparticles have attracted so much attention because they are both important and interesting. Important, as nanoparticles can have useful properties not exhibited by either smaller molecular systems or larger particulate matter; interesting, as working on supramolecular scales raises exciting synthetic challenges and allows intimate exploration of the relationships among atoms, molecules, and extended systems. In the first part of this article we briefly discuss a selected few of the useful properties exhibited by nanoparticles and/or nanostructured materials. In the second part of this article we examine a subset of the relationships between molecular and extended systems, especially between binary and ternary inorganic molecular cluster compounds and the smallest nanometer-sized particles, and consider some implications for the synthesis and chemistry of ananoclusterso. In neither part of this article do we attempt a systematic review of the nanoparticle literature, but rather we focus on a few examples from research conducted at DuPont and from the literature. And, while we rely heavily upon experience with inorganic molecular cluster compoundsÐwhere chemistry and detailed structures are often much better understood than they are in larger particlesÐwe caution that overly relying upon cluster experience would be misleading, as there are fundamental differences between molecular-sized clusters and nanometer-sized particles.

X-Ray Photoconductive Nanocomposites

The successful development of digital radiography depends, to a large extent, on the availability of suitable x-ray photoconductors. The x-ray photoconductive nanocomposites reported here combine the advantages of both inorganic and organic compounds. An inorganic compound was finely dispersed in an organic polymer. The inorganic compound, with its large x-ray absorption efficiency, functioned as the x-ray absorber, and the polymer provided good dielectric properties and ease of thin-film preparation. The preparation procedures and the x-ray photoconductive properties of a specific example, a 50 percent by weight nanocomposite of bismuth triiodide and nylon-11, are discussed in detail.

Semiconductor nanocrystals in carrier-transporting polymers: Charge generation and charge transport

Abstract By incorporating semiconductor nanocrystals in carrier-transporting polymers, an interesting class of photoconductive nanocomposites is created. The presence of semiconductor nanocrystals enhances the photoinduced charge generation efficiency and extends the sensitivity range, while the polymer matrix is responsible for charge transport. A wide variety of semiconductors and polymers have been used. In this paper, we review material synthesis and discuss the effects of semiconductor nanocrystals on the charge transport and charge generation properties.