Excitation and temperature dependence of the excitonic emissions in undoped and Mg-doped VPE InP

The photoluminescence of vapor phase epitaxial indium phosphide, both unimplanted and magnesium implanted, is investigated as a function of excitation intensity and temperature to gain a more complete understanding of the free exciton, exciton-bound donor, exciton-bound acceptor (residual and Mg), the 1.4155 eV emission identified with both the recombination of free holes with neutral donors and with bound excitons to ionized donors, and the recently identified 1.4122 eV emission (unique to Mg implanted layers). Emission peak broadening, quenching, and saturation is examined as the irradiance is varied from 0.002 to 33.3 W/cm² and the temperature from 2.6 to 50 K. The source of the 1.4122 eV emission is speculated to be a donor-acceptor recombination involving a donor center bond to an off-axis band and the Mg acceptor, or more likely, excitons bound to point defects which are created by the acceptor implant.     

Chemie der Pleuromutiline, 3. Mitt.: Synthese des 14-O-Acetyl-19,20-dihydro-A-nor-mutilins

Derivatives of the antibiotic pleuromutilin are rapidly metabolised in animals. This phenomenon is responsible for the lack of biological activity of these compoundsin vivo although their activitiesin vitro are extremely high (MHK=0,005–0.1 g/ml). In order to reduce the rate of metabolism a compound with slightly modified conformation (15) in the appropriate region of the molecule (C-1, C-2)^3a was chosen for biological tests. The synthesis of this compound is described in detail.

2. Mitteilung,Berner H., Schulz G., Schneider H., Tetrahedron37, 915 (1981).     

Analysis of the metal–ligand bonds in [Mo(X)(NH2)3] (X = P, N, PO, and NO), [Mo(CO)5(NO)]+, and [Mo(CO)5(PO)]+

Quantum chemical calculations at the DFT level have been carried out for model complexes [Mo(P)(NH₂)₃] (1), [Mo(N)(NH₂)₃] (2), [Mo(PO)(NH₂)₃] (3), [Mo(NO)(NH₂)₃] (4), [Mo(CO)₅(PO)]⁺ (5), and [Mo(CO)₅(NO)]⁺ (6). The equilibrium geometries and the vibration frequencies are in good agreement with experimental and previous theoretical results. The nature of the Mo–PO, Mo–NO, Mo–PO⁺, Mo–NO⁺, Mo–P, and Mo–N bond has been investigated by means of the AIM, NBO and EDA methods. The NBO and EDA data complement each other in the interpretation of the interatomic interactions while the numerical AIM results must be interpreted with caution. The terminal Mo–P and Mo–N bonds in 1 and 2 are clearly electron-sharing triple bonds. The terminal Mo–PO and Mo–NO bonds in 3 and 4 have also three bonding contributions from a σ and a degenerate π orbital where the σ components are more polarized toward the ligand end and the π orbitals are more polarized toward the metal end than in 1 and 2. The EDA calculations show that the π bonding contributions to the Mo–PO and Mo–NO bonds in 3 and 4 are much more important than the σ contributions while σ and π bonding have nearly equal strength in the terminal Mo–P and Mo–N bonds in 1 and 2. The total (NH₂)₃Mo–PO binding interactions are stronger than for (NH₂)₃Mo–P which is in agreement with the shorter Mo–PO bond. The calculated bond orders suggest that there are only (NH₂)₃Mo–PO and (NH₂)₃Mo–NO double bonds which comes from the larger polarization of the σ and π contributions but a closer inspection of the bonding shows that these bonds should also be considered as electron-sharing triple bonds. The bonding situation in the positively charged complexes [(CO)₅Mo–(PO)]⁺ and [(CO)₅Mo–(NO)]⁺ is best described in terms of (CO)₅Mo → XO⁺ donation and (CO)₅Mo ← XO⁺ backdonation (X = P, N) using the Dewar–Chatt–Duncanson model. The latter bonds are stronger and have a larger π character than the Mo-CO bonds.     

Programmed metalloporphyrins for self-assembly within light-harvesting stacks: (5,15-dicyano-10,20-bis(3,5-di-tert-butylphenyl)porphyrinato)zinc(II) and its push-pull 15-N,N-dialkylamino-5-cyano congeners obtained by a facile direct amination

The title dicyano compound was synthesized via cyanation and it self-assembles in nonpolar solvents giving red-shifted and broad absorption maxima just as the bacteriochlorophylls which are encountered in the light-harvesting organelles of early photosynthetic bacteria. In the crystal, stacks are formed through a hierarchic combination of pi-stacking and a CN-Zn electrostatic interaction. Push-pull 15-N,N-dialkylamino-5-cyano congeners could be obtained in high yields using a solvent- and catalyst-free direct amination of meso-bromoporphyrins. Importantly, the fluorescence of the self-assembled species due to the very orderly manner in which the chromophores are arranged is not entirely quenched and has a surprisingly long lifetime of over 1 ns. This lends hope of using the trapped energy in biomimetic hybrid solar cells.     

Are carbodiphosphoranes better ligands than N-heterocyclic carbenes for Grubb's catalysts?

Theoretical investigations suggest that substitution of an N-heterocyclic carbene by a carbodiphosphorane in the Grubb's catalyst for olefin metathesis might lead to enhanced reactivity.