Aiding the self-assembly of supramolecular polyoxometalates under hydrothermal conditions to give precursors of complex functional oxides

In?situ Raman spectroscopy allows insight into molecular processes under hydrothermal conditions during synthesis of complex nanostructured MoVTeNb oxides (see picture: Nb?yellow, Mo?blue, V/Mo?pale blue, Te?red). Based on the knowledge acquired, the synthesis can be more efficiently directed towards the desired product with improved functionality.     

Probing the barrier for internal rotation of the retinal chromophore

Molecular ion calorimetry: A technique for measuring the heat capacity of an isolated gas-phase chromophore is presented and applied to the retinal protonated Schiff base. The potential use of this technique for studying barriers for internal rotations is discussed.     

Counterion Effects on the Columnar Mesophases of Triphenylene‐Substituted [18]Crown‐6 Ethers: Is Flatter Better?

The twisted lateral tetraalkyloxy ortho‐terphenyl units in dibenzo[18]crown‐6 ethers 1 a – f were readily converted into the flat tetraalkyloxytriphenylene systems 2 a – f by oxidative cyclization with FeCl₃ in nitromethane. Reactions of the latter with potassium salts gave complexes KX ?2 , which displayed mesomorphic properties. The aromatization increased both the clearing and melting points; the mesophase stabilities, however, were mainly influenced by the respective anions upon complexation with various potassium salts. In contrast, the alkyl chain lengths played only a secondary role. Among the potassium complexes of triphenylene‐substituted crown ethers KX ?2 , only those with the soft anions I^? and SCN^? displayed mesophases with expanded phase temperature ranges of 93 °C and 132 °C (for KX ?2 e ), respectively, as compared to the corresponding o‐terphenyl‐substituted crown ether complexes KI ?1 e (ΔT=51 °C) and KSCN ?1 e (plastic crystal phase). Anions such as Br^?, Cl^?, and F^? decreased the mesophase stability, and PF₆^? led to complete loss of the mesomorphic properties of KPF₆ ?2 although not for KPF₆ ?1 . For crown ether complexes KX ?2 (X=F, Cl, Br, I, BF₄, and SCN), columnar rectangular mesophases of different symmetries (c2 mm, p2 mg, and p2 gg) were detected. In contrast to findings for the twisted o‐terphenyl crown ether complexes KX ?1 , the complexation of the flat triphenylene crown ethers 2 with KX resulted in the formation of organogels. Characterization of the organogel of KI ?2 e in CH₂Cl₂ revealed a network of fibers.     

Cluster properties of peptides on (100) semiconductor surfaces

Peptide adhesion on semiconductor surfaces is quantitatively investigated by atomic force microscopy. The selected peptides are shown to cluster at the surface, with the larger, higher, and softer clusters appearing on the surfaces with lower peptide adhesion. Average cluster diameters vary from 40 nm on GaAs (100) to 300 nm on Si (100). Direct adhesion of the peptides to the surface competes with forming molecular aggregates that offer an overall reduced surface contact.     

Diode laser with 1 Hz linewidth

We report an ultranarrow-linewidth laser spectrometer at 657 nm, consisting of a diode laser locked in a single stage to a stable high-finesse reference cavity. The system is characterized by comparison with a second independent system. From beat frequency measurements a linewidth below 1.5 Hz (FWHM) and a fractional instability of less than 2 x 10(-15) for 1 s of averaging time are observed.     

Dipheno-silyliminoquinones - A 14π-system

Lithium salts of 2.6-dialkylanilines react with di-tert-butylfluorosilanes to give mono (1-3) - and bis (7, 8)-(2.6-dialkylphenylamino)silanes. Amino-2.6-dimethylphenyl-(di-tert-butylfluoro)silane (1) forms with BuLi a dimeric lithium salt (4) containing an eight-membered (LiFNSi)₂ ring system. Thermally, 4 loses LiF and a bicyclic compound (9) via iminosilenes is obtained. The lithium salt of the bulkier amino-2.6-diisopropylphenyl-(di-tert-butylfluorosilanes) (5-7) thermally loses LiH and iminosilanes (10-12) with a 14π-system are isolated. The reaction mechanisms and crystal structures are discussed.     

Time-resolved study of solvent-induced recombination in photodissociated IBr-(CO2)n clusters

We report the time-resolved recombination of photodissociated IBr-(CO2)n (n = 5-10) clusters following excitation to the dissociative IBr-A' 2Pi12 state of the chromophore via a 180 fs, 795 nm laser pulse. Dissociation from the A' state of the bare anion results in I- and Br products. Upon solvation with CO2, the IBr- chromophore regains near-IR absorption only after recombination and vibrational relaxation on the ground electronic state. The recombination time was determined by using a delayed femtosecond probe laser, at the same wavelength as the pump, and detecting ionic photoproducts of the recombined IBr- cluster ions. In sharp contrast to previous studies involving solvated I2-, the observed recombination times for IBr-(CO2)n increase dramatically with increasing cluster size, from 12 ps for n = 5 to 900 ps for n = 8,10. The nanosecond recombination times are especially surprising in that the overall recombination probability for these cluster ions is unity. Over the range of 5-10 solvent molecules, calculations show that the solvent is very asymmetrically distributed, localized around the Br end of the IBr- chromophore. It is proposed that this asymmetric solvation delays the recombination of the dissociating IBr-, in part through a solvent-induced well in the A' state that (for n = 8,10) traps the evolving complex. Extensive electronic structure calculations and nonadiabatic molecular dynamics simulations provide a framework to understand this unexpected behavior.