Two approaches are reported to achieve efficient blue to near-UV emission from triscyclometalated iridium(III) materials related to the previously reported complex, fac-Ir(ppz)3 (ppz = 1-phenylpyrazolyl-N,C2‘). The first involves replacement of the phenyl group of the ppz ligand with a 9,9-dimethyl-2-fluorenyl group, i.e., fac-tris(1-[(9,9-dimethyl-2-fluorenyl)]pyrazolyl-N,C2‘)iridium(III), abbreviated as fac-Ir(flz)3. Crystallographic analysis reveals that both fac-Ir(flz)3 and fac-Ir(ppz)3 have a similar coordination environment around the Ir center. The absorption and emission spectra of fac-Ir(flz)3 are red shifted from those of fac-Ir(ppz)3. The fac-Ir(flz)3 complex gives blue photoluminescence (PL) with a high efficiency (λmax = 480 nm, φPL = 0.38) at room temperature. The lifetime and quantum efficiency were used to determine the radiative and nonradiative rates (1.0 × 104 and 2.0 × 104 s-1, respectively). The second approach utilizes N-heterocyclic carbene (NHC) ligands to form triscyclometalated ...

Blue and near-UV phosphorescence from iridium complexes with cyclometalated pyrazolyl or N-heterocyclic carbene ligands.

Either to sustain autotrophy, or as a prelude to heterotrophy, organic synthesis from an environmentally available C1 feedstock molecule is crucial to the origin of life. Recent findings augment key literature results and suggest that hydrogen cyanide--"Blausaure"--was that feedstock.

The Origin of Life--Out of the Blue.

Recent advances in carbon nanomaterial-based adsorbents for water purification

Chemical reactivity is conventionally understood in broad terms of kinetic versus thermodynamic control, wherein the decisive factor is the lowest activation barrier among the various reaction paths or the lowest free energy of the final products, respectively. We demonstrate that quantum-mechanical tunneling can supersede traditional kinetic control and direct a reaction exclusively to a product whose reaction path has a higher barrier. Specifically, we prepared methylhydroxycarbene (H(3)C-C-OH) via vacuum pyrolysis of pyruvic acid at about 1200 kelvin (K), followed by argon matrix trapping at 11 K. The previously elusive carbene, characterized by ultraviolet and infrared spectroscopy as well as exacting quantum-mechanical computations, undergoes a facile [1,2]hydrogen shift to acetaldehyde via tunneling under a barrier of 28.0 kilocalories per mole (kcal mol(-1)), with a half-life of around 1 hour. The analogous isomerization to vinyl alcohol has a substantially lower barrier of 22.6 kcal mol(-1) but is precluded at low temperature by the greater width of the potential energy profile for tunneling.

http://science.sciencemag.org/content/sci/332/6035/1300.full.pdf

Methylhydroxycarbene: Tunneling Control of a Chemical Reaction

Laser vaporization of graphite generates C60+ cluster ions that are fullerenes and a mixture of roughly planar polycyclic polyyne ring isomers. Experimental studies of the annealing of the non-fullerene C60+ ions indicate that they can be converted (in the gas phase) into the fullerene and an isomer that appears to be a large monocyclic ring. Some fragmentation is associated with conversion to the fullerene geometry, but the majority of the non-fullerene C60+ isomers are cleanly converted into an intact fullerene. The emergence of the monocyclic ring (as the clusters are annealed) suggests that this is a relatively stable non-spheroidal form of these all carbon molecules. The estimated activation energies for the observed structural interconversions are relatively low, suggesting that these processes may play an important role in the synthesis of spheroidal fullerenes.

http://science.sciencemag.org/content/sci/260/5109/784.full.pdf

Annealing C60+: Synthesis of Fullerenes and Large Carbon Rings

This work describes how the addition of hydrogen donors to systems in which C{sub 60} and C{sub 70} are generated results in the formation of polycyclic aromatic hydrocarbons whose carbon skeleton may represent intermediates in fullerene formation. These investigations implicate a mechanism of fullerene formation in which linear, monocyclic and polycyclic carbon clusters precede fullerene synthesis. 13 refs., 2 figs.

On the mechanism of fullerene formation. Trapping of some possible intermediates

The cocondensation of atomic carbon with water at 77 K generates a mixture of straight chain aldoses with up to five carbons. A proposed mechanism involves initial reaction of C with H 2 O to give hydroxymethylene which rearranges to formaldehyde. Subsequent nucleophilic addition of hydroxymethylene to formaldehyde with hydrogen transfer generates glycolaldehyde which reacts with additional hydroxymethylenes to build up the higher carbohydrates. Confirmation of this mechanism is provided by deuterium labeling studies

Formation of carbohydrates in the reaction of atomic carbon with water

Etude du mecanisme de la reaction de l'hydroxymethylene(I) (genere a partir d'atomes de carbone et d'eau dans un arc) avec le formaldehyde et evaluation du potentiel de I comme donneur d'hydrogene

The unusual reactivity of hydroxymethylene

Diatomic carbon, C{sub 2}, reacts with propylene and (E)- and (Z)-2-butene in the condensed phase at 77 K. Products can be rationalized by a mechanism involving initial addition of C{sub 2} to the alkene to generate a 1,4-diradical. This diradical may then either abstract hydrogens or add another alkene molecule to give a 1,6-diradical which disproportionates to an enyne. Thus, reaction of C{sub 2} with propene gives 1-pentyne, 3-methyl-l-butyne, 4-methylhept-6-en-1-yne, 6-methylhept-1-en-4-yne, and oct-1-en-4-yne. Ab initio calculations at the HF/3-21G level predict that both {sup 1}C{sub 2} and {sup 3}C{sub 2} will add to ethylene without barrier. At the MP2/6-31G*//3-21G level, the triplet adduct is calculated to be more stable than {sup 3}C{sub 2} and ethylene by 46.0 kcal/mol. The reactions of {sup 1}C{sub 2} and {sup 3}C{sub 2} with methane and hydrogen have also been investigated theoretically.

Sheikh N. Ahmed

Papers

On the mechanism of fullerene formation. Trapping of some possible intermediates

Formation of carbohydrates in the reaction of atomic carbon with water

The unusual reactivity of hydroxymethylene

Some reactions and properties of molecular diatomic carbon C2. An experimental and theoretical treatment

An experimental and ab initio study of the addition of atomic carbon to water