ChemPhysChem

Opto-mechanical cis–trans isomerization of a dithioazobenzene bridge suspended between two gold electrodes: On p. 345, I. Štich et al. reveal by means of ab initio simulations a subtle interplay of mechanochemical and photochemical switching.

The well known molecular magnet V15 (V green; As dark yellow; O red) is shown in a hydrophobic cavity of a human serum albumin with the single tryptophan fluorescence centre (Trp214) in its vicinity, as described by P. Lemmens, S. K. Pal et al. on p. 389. The Förster resonance energy transfer (FRET) from Trp214 to V₁₅ is represented schematically.

Line them up! Liquid crystals are anisotropic fluids. Their self-organization is a powerful means to control carbon nanotube alignment on the macroscopic scale (see picture).

Out with the old: The observation of a morphotropic phase boundary in bismuth ferrite under stress is Highlighted herein together with an exciting development for monoclinic structured BiFeO₃ films (see picture). These materials may pave the way to a new generation of lead-free actuator/transducer devices.

Flip-flop: Mechanical and opto-mechanical switching cycle of a nanoswitch made up of single dithioazobenzene chromophore suspended between two gold tips (see picture). Mechanical switching proceeds on the ground-state S₀ surface while successful optical switching via S₁ state requires mechanical assistance.

Combination of spectroscopic methods: THz, FIR and Raman spectroscopy (see figure) allow the assignment of all intra and inter molecular vibrational modes in imidazolium-based ionic liquids in the low frequency range between 2 and 300 cm⁻¹. Although THz spectroscopy is very sensitive for this frequency range, clearly no significant contribution could be detected below 50 cm⁻¹.

The adsorption geometry of valine on a Ge(100) surface was studied using high-resolution core-level photoemission spectroscopy. Analysis of Ge 3d, C 1s, N 1s, and O 1s core-level spectra of valine adsorbed onto the Ge(100) surface suggests that both the amine and carboxyl groups in valine concurrently participate in the adsorption (see picture).

Stabilized by fluorine: For the first time a conclusive explanation for the beneficial effects of fluorine in aliphatic bridges within the mesogenic core structure of nematic liquid crystals is offered. A combination of steric and stereoelectronic effects stabilizes rod-like conformations (see pciture) which are essential for the formation of the nematic phase.

Water solvent determines the self-assembly pathway and stability of organic rosette nanotubes (RNTs) (see figure). Structural water molecules penetrate the pockets on the RNT outer surface, form a wetting monolayer in the RNT channel and bridge RNT rosettes. Three-dimensional molecular theory of solvation (3D-RISM) predicts the solvation structure in inner spaces of these nanostructures in solution.

The terahertz spectra of pentaerythritol tetranitrate (PETN, see figure) is calculated using Discover with the COMPASS force field, CASTEP and PWscf. The calculations are compared to each other and to a terahertz (0.3–3 THz) spectra of crystalline PETN recorded at 4 K. A number of analysis methods have been used to characterise the calculated normal modes.

The anisotropic adsorption and condensation of tert-butylamine close to steps on the Cu(111) surface are discussed in terms of STM and DFT calculations. Preferential adsorption at the upper step edges and uneven distribution of tert-butylamine molecules in the vicinity of the step (see figure) illustrate that the asymmetric electronic structure of the step could affect the adsorption and diffusion of polar molecules.

H-bond networks: The first exhaustive quantum-chemical calculations of H-bond networks in dodecahedral water clusters (see picture) are described. The millions of configurations considered provide unique statistical data for the energies, spatial and electronic structures of water clusters, thus allowing for insights into the nature of cooperativity in H-bonded systems.

Confined spaces: The complexation and confinement of [V₁₅As₆O₄₂(H₂O)]⁻⁶ (V₁₅) in the cavity of human serum albumin (HSA) leads to enhanced stability without perturbing the magnetic properties of V₁₅ or the tertiary structure of the protein. Resonance energy transfer via excited-state dipole–dipole interaction is probed by steady-state and time-resolved fluorescence spectroscopy of the HSA (see picture).

Silver bullet: The first SERS substrates using silver nanoparticles formed by the activity of an enzyme are presented. These particles allow an easy characterization of their SERS activity and help to overcome the bottleneck of the production of reproducible SERS substrates. Unlike other SERS substrates, these can be characterized by a simple electrical measurement (see picture).

Really small ice cubes: Nano-ice clusters self-assemble on a hexagonal boron nitride nanomesh template. The holes of the template host ice clusters of about 40 water molecules. The picture shows one possible (H₂O)₄₂ cluster overlaid on a scanning tunneling microscopy image. Tunneling barrier height microscopy resolves the local electrostatic potential above the clusters and thus accesses the individual proton positions.

Filter tips: Nanofiltration through solvent-resistant polyimide membranes is studied by measuring the permeation of organic solvents. The solvents are systematically selected to allow investigation of the effects of key physicochemical transport parameters. Viscosity and polarity are found to have a greater influence than the other parameters (in the picture, the grey ovals are membrane polymer molecules and the white circles are solvent molecules).

Supercell DFT calculations on the adsorption properties of Au atoms on SiO₂/Mo(112) and Li-doped thin films (see figure) show that Li atoms penetrate into the pores of the silica film and become stabilized at the interface where they donate one electron to the Mo metal. The work function of the Li-doped SiO₂/Mo(112) film is reduced and Au atoms and clusters bind strongly to the surface and become negatively charged.

Gas-phase kinetics: Time-resolved studies of chlorosilylene are carried out to obtain rate constants for its bimolecular reaction with ethene. Cl-for-H substitution in silylene reduces the rate constant of addition by a small factor of ca. 2.5. Collisional stabilisation of the initial adduct of this reaction leads predominantly to ethylchlorosilylene, in contrast to the cycloaddition of SiH₂ with C₂H₄ (see figure).

Blue crystal: Blue amplified spontaneous emission from the largest face of a 1,1,4,4-tetraphenyl-1,3-butadiene (TPB, see figure) single crystal is demonstrated at room temperature with a threshold excitation fluence of 400 μJ cm⁻². TPB may be a good candidate for the development of vertical cavity geometry lasers based on organic single crystals.

Structural signature: Hydrogen-bonding network ensembles and bound water molecules in phospholipids are visualized by means of far-infrared spectroscopy (see picture). This technique allows a very specific description of the intermolecular hydrogen-bonding interactions in large molecular assemblies and is thus a powerful tool for structural investigation.

Up in the air: The reactions of Cl with a series of hydrofluoroalcohols (HFAs) and their deuterated analogues are studied kinetically at 268–378 K. Optimized geometries are obtained for the reagents, transition states (TSn) and molecular complexes (MCn) appearing along the different reaction pathways (see picture). Atmospheric degradation of the HFAs should generate the corresponding carbonyl compounds.

Dimer configurations: 3-O-(2-methylnaphthyl)-β-cyclodextrin (Cap-βCD) forms either head-to-head or head-to-tail arrangements. Computer simulations and free-energy calculations show that the head-to-head configuration in which the naphthyl caps are mutually inserted into each other's CD cavities (see picture) is the most favourable because it optimises hydrophobic cap–cavity association and forms the most inter-CD hydrogen bonds.

Electrostatic interactions: The combined electronic, re-orientational and collaborative contributions of the NLO chromophores in indole-based polymeric materials lead to notable improvements of photorefractive optical gain Γ₂ (see figure). More efficient and stable electro-optical devices can be obtained.

A relaxation pathway for the metal string complex Co₃(dpa)₄(NCS)₂ [where dpa=di(2-pyridyl)amido] after photoexcitation is proposed (see figure). The system first undergoes an ultrarapid conversion from ligand-centered states to a metal-centered d–d state (within 100 fs). Then, conversion or intersystem crossing occurs to a second low-lying d–d state (this happens within a few picoseconds). The population relaxes to the ground-state surface with a time coefficient of 10–23 ps.

The charge response kernel (CRK) method is used to calculate the site energy disorder for electron and hole transfer in amorphous tris(8-hydroxyquinolinato)aluminum (Alq₃, see picture). A simple procedure to calculate the CRK parameters for large molecules from ab initio calculations is presented, and the effect of the polarization on the site energy disorder is discussed.

State's evidence: Thioxanthone photophysics is revealed by ab initio calculations and femtosecond transient absorption experiments. The initially populated singlet ππ* state decays through internal conversion (IC) and intersystem crossing (ISC) via intermediate nπ* singlet and triplet states (see picture). Two easily accessible conical intersections explain the favorable IC rates and low fluorescence quantum yields in nonpolar media.

Biological template: The authors use a biomolecule-assisted hydrothermal method to synthesize β-phase Ni(OH)₂ peonylike nanostructures with second-order nanoplate structure. The complex Ni(OH)₂ nanostructures exhibit high-power Ni/MH battery performance, as well as superhydrobic properties (see picture).

Concentration affects NLO response: A series of 4-X-1-methylpyridinium cationic NLO chromophores with various organic, inorganic and organometallic counter anions (see picture) is studied at various concentrations in order to investigate the role of ion pairing, ionic dissociation and aggregation of ion pairs in determining their second-order NLO responses.

A thermodynamic formalism is developed to analyse speed of ultrasound data for solutions and liquid mixtures. The correlation among the ratios between excess (E) and ideal (id) values of the speed of ultrasound u, molar volume V_m and molar isentropic compression K_S,m of liquid mixtures, which all exhibit extreme values at approximately the same composition (see picture), is theoretically derived.

Highly strung: The relaxation dynamics of excited trinickel string complexes show ultrarapid conversion from ligand-centered states to a metal-centered dd state in 0.1–0.4 ps; then vibrational cooling occurs in this dd electronic manifold in a few picoseconds. The population relaxes to the ground-state surface with a time coefficient of 100–200 ps (see picture).