Pentacarbonyl(di‐2‐pyridyl­amine)tungsten(0)

In the title molecular complex, (I), the W atom is in an octahedral environment with four equatorial carbonyl ligands and a fifth in an axial position trans to the monodentate dipyridyl­amine ligand. The long dimension of this last bisects the angle between two of the equatorial carbonyl groups and while the non‐bonded pyridyl N atom is directed away from the W atom, the bridging amine group is directed towards it. Thus, in addition to the N atom to which it is attached, the amino H has two nearest neighbour C atoms of equatorial carbonyl groups but does not participate in hydrogen bonding in any real or usual sense. The W—C bond distance for the axial carbonyl group is notably less than those of the equatorial groups.     

Stereoselective synthesis of the tetrahydropyran core of polycarvernoside A

[reaction: see text] A concise and stereoselective synthesis of the tetrasubstituted tetrahydropyran core of polycavernoside A was achieved in 55% overall yield from 3-benzyloxypropanal. A stereoselective allyl transfer reaction was used in the synthesis of enol ether 18 followed by a TFA-mediated cyclization to create the three new asymmetric centers in the tetrahydropyran with complete stereocontrol in a single-pot process.     

Coherent anti-stokes raman scattering spectral interferometry: determination of the real and imaginary components of nonlinear susceptibility chi(3) for vibrational microscopy

We demonstrate coherent anti-Stokes Raman scattering (CARS) heterodyne spectral interferometry for retrieval of the real and imaginary components of the third-order nonlinear susceptibility (chi(3)) of molecular vibrations. Extraction of the imaginary component of chi(3) allows a straightforward reconstruction of the vibrationally resonant signal that is completely free of the electronic nonresonant background and resembles the spontaneous Raman spectrum. Heterodyne detection offers potential for signal amplification and enhanced sensitivity for CARS microscopy.     

Alignment locking to suspended Fabry-Perot cavity

In this paper we report on the alignment locking of an in vacuum 77 m long suspended mirror Fabry-Perot cavity. Lock was achieved by mode-matching a 500 mW Nd:YAG NPRO onto a pre-mode cleaner, the output of which was then mode-matched to the suspended cavity. The longitudinal locking was achieved by feeding back to the laser frequency actuator to follow the cavity resonance. Subsequent implementation of a hybrid auto-alignment system enhanced the stability of the circulating power inside the cavity. Preliminary results are presented.     

Picosecond-pulse amplification with an external passive optical cavity

We experimentally demonstrate the amplification of picosecond pulses at high repetition rates through the coherent addition of successive pulses of a mode-locked pulse train in a high-finesse optical cavity equipped with cavity dumping. Amplification greater than 30 times is obtained at a repetition rate of 253 kHz, boosting the 5.3-nJ pulses from a commercial mode-locked picosecond Ti:sapphire laser to pulse energies of more than 150 nJ.     

Some dynamic features of the preparation of liquid crystalline elastomers

Liquid crystalline elastomers derived from siloxane polymers, PMHS and PEHS, were prepared following a two-stage reaction scheme to investigate the effects of processing conditions and thermal treatment on mesomorphic characteristics. The LC elastomer samples were analysed by FTIR, DSC, stress-strain relationship, polarized optical microscopy, and X-ray diffraction techniques. Key findings include: (1) Chain length of the precursor siloxane polymer is critical to achieving a bulk alignment via stretching during the second-stage reaction; (2) the imposed strain is also critical to achieving a monodomain nematic character, which is completely recoverable upon heating beyond the clearing temperature followed by cooling back to room temperature (i.e. thermal treatment); (3) enthalpy is stored in an elastomer freshly prepared without an imposed strain, but the imposed strain helps to release the stored enthalpy, which can be almost completely released upon thermal treatment; and (4) while the stored enthalpy does not increase order parameter (HOF_A), its release through molecular relaxation contributes to an increased HOF_A value.     

The crystal and molecular structure of tetracarbonyl(6-p-styryl-2,2′-bipyridyl)tungsten(0). An examination of the affect of a bulky group α to one coordinating nitrogen atom in a bidentate ligand

The crystal and molecular structure of tetracarbonyl(6-p-styryl-2,2′-bipyridyl)tungsten(0) have been determined by single crystal X-ray techniques. Cell dimensions are a 13.735(17), b 8.839(6) and c 17.105(12) Å for the monoclinic unit cell with β 109.06(8)° and Z = 4. The space group was determined as P2₁/n. The structure was solved by conventional Patterson and Fourier methods and refined to a final R-value of 0.055 (1734 unique reflections) by block diagonal least squares. The molecule consists of monomeric units containing one tungsten atom bound to four terminal carbonyl groups and to one 6-p-styryl-2,2′-bipyridyl ligand via its two nitrogen atoms. The presence of the styryl group α to one coordinating nitrogen causes a significant difference in the bond lengths between the central tungsten atom and the nitrogen atoms (WN(1), 2.29(1) Å; WN(2) 2.23(1) Å).     

Facile Tuning of Luminescent Platinum(II) Schiff Base Complexes from Yellow to Near‐Infrared: Photophysics,Electrochemistry, Electrochemiluminescence and Theoretical Calculations

The photophysical and related properties of platinum(II) Schiff base complexes can be finely and predictably tuned over a wide range of wavelengths by small and easily implemented changes to ligand structure. A series of such complexes, differing only in the number and positioning of methoxy substituents on the phenoxy ring, were synthesised and their photophysical, electrochemical and electrochemiluminescent (ECL) properties investigated. Theoretical calculations were performed in order to gain further insight into the relationship between structure and properties in these materials. By positioning methoxy groups para and/or ortho to either the imine or the oxygen group on the ligand, electron density could be directed selectively toward the LUMO or HOMO as required. This allowed the emission colour (both photoluminescent and electrochemiluminescent) to be tuned over a wide range between 587 and 739 nm. The variation in orbital energies was also manifested in the positions of the absorption bands and the redox properties of the complexes, as well as in the NMR shifts for the uncoordinated ligands. All reported complexes displayed intense electrochemiluminescence (ECL), which could be initiated either by annihilation or co‐reactant pathways. The relationship between the electrochemical and photophysical properties and the efficiency of the ECL is discussed. For two of the complexes solid‐state ECL could be generated from electrodeposited layers of the complex.     

Stepwise reduction of a base-stabilised ferrocenyl aluminium(iii) dihalide for the synthesis of structurally-diverse dialane species

We report the reduction of bulky ferrocenyl-based NHC-stabilised aluminium(iii) diiodide [Fc*(NHC)AlI₂] (Fc* = 2,5-bis(3,5-di-tert-butylphenyl)-1-ferrocenyl) in different hydrocarbon solvents (hexane, benzene, toluene, and p-xylene), which results in different outcomes. Reduction in hexane with an equivalent amount of KC₈ generates the diiododialane [(Fc*(NHC)AlI)₂], whereas complete reduction in hexane leads to an unusual C–H activation at an N–Me group of one NHC unit. In contrast, reaction in aromatic solvents result in hitherto unknown Birch-type reductions of the corresponding solvent molecules by transient aluminium radicals of the type [LAlR₂]˙, which is ultimately bound to two aluminium centers.

A bulky ferrocenyl-based NHC-stabilised aluminium(iii) dihalide was reduced in different solvents, leading to vastly different outcomes, including formation of a rare example of a dialane and a novel dialuminyl analogue of the Birch reduction.