One‐ and two‐photon activity of cross‐conjugated photoinitiators with bathochromic shift

Intrigued by the good performance of 1,5‐diphenylpenta‐1,4‐diyn‐3‐one ( DPD ) as photoinitiator for radical polymerization we prepared and investigated several donor substituted derivatives. UV‐Vis spectroscopy revealed a gradual red‐shift of λ_max and higher extinction in the order of the donor capability. A methoxy‐substituted derivative ( O‐DPD ) exhibited significant photoinitiation activity in photo‐DSC experiments. Steady state photolysis experiments showed decreased decomposition rates with increasing donor capability. A dimethylamino derivative N‐DPD was even photostable under these conditions. Because of to the D‐π‐A‐π‐D system of these compounds two‐photon induced 3D photopolymerization experiments were performed and N‐DPD showed outstanding performance compared to often applied single photon initiators. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3280–3291, 2007     

Enzymatic hydroxylations with molecular oxygen

For thermodynamic reasons, biological hydroxylations cannot usually proceed according to the β-oxidation scheme, but are possible only with the aid of molecular oxygen by a route requiring a large amount of energy. The corresponding enzymes, known as “mixed function oxygenases” or more appropriately “monooxygenases”, require two reduction equivalents for the activation of oxygen. The cytochrome P-450-dependent monooxygenases are taken as examples for the discussion of the chemistry of the enzymatic catalysis. The central problem of the activation of oxygen has not yet been solved, but an “oxenoid” mechanism can be deduced from model investigations.     

Microprobe analysis of low alloyed sintered steels

Homogenization of Mo, W and Cr in alloyed P/M carbon steels during sintering with a transient liquid phase has been investigated by microscopic and microanalytical means. The reaction was found to start with carburization of the VIa metal, continues with the formation of different carbides, and generation of a liquid phase between the carbide and -Fe. The steady state equilibrium remains stable until all VIa metal has been consumed. Microprobe analysis was found to yield optimum results if selected model samples, in which homogenization should not proceed too fast, are investigated.Dedicated to Professor Günther Tölg on the occasion of his 60th birthday     

Diphenyloligothiophene-based dichromophoric macrocycles and their ability to form donor/acceptor complexes

A series of four dichromophoric rigid macrocycles 6a-6d, two with diphenyloligothiophene chromophores, the other two with more electron-rich diphenyl-EDOT or diphenyl-bis-EDOT chromophores, have been synthesized. The absorption spectrum of the diphenyl-bis-EDOT based macrocycle 6d displayed the most pronounced vibronic resolution with a well-resolved 0-0 transition, indicating a fully planarized geometry of the diphenyl-bis-EDOT chromophores. The (1)H NMR spectra of the macrocycles displayed weak to moderate chemical shifts of characteristic signals upon addition of pi-conjugated oligonitro-9-fluorenone acceptors. X-ray single-crystal analysis showed that columnar pi-stacked donor/acceptor complexes are formed with the stacks composed of alternating donor and acceptor molecules. The stoichiometry of the crystalline, dark-colored complexes was found to be 1:1 by elemental analysis and integration of the (1)H NMR peaks. The complex formation is accompanied by remarkably large Stern-Volmer constants of fluorescence quenching.     

Single-detector micro-electro-mechanical scanning grating spectrometer

A compact, robust grating spectrometer based on an optimised micro-electro-mechanical grating mirror component has been developed, built, and characterised. The application of an oscillating reflection grating micro-mirror component as scanning dispersive element in a modified Czerny–Turner monochromator layout enables the design of compact grating spectrometers capable of acquiring full spectra using a single detector element. Designed for a wavelength range between 1200 and 1900 nm, the spectrometer features a spectral resolution of 10 nm with wavelength stability better than ±0.5 nm. One-hundred scan spectra can be acquired in less than one second, or spectral changes can be monitored at time a resolution of less than 10 ms. In combination with a fibre-optic interface and a typical weight of less than 1 kg, this makes this novel type of fully portable micro-electro-mechanical near-IR scanning spectrometer an interesting alternative to existing spectrometers and opens a range of new applications, in particular the detection of major and minor components in the near-IR. MEMS SG spectrometer prototype     

Photocurrent theory based on coordinate dependent lifetime

Recent work by Pejova [Mater. Res. Bull. 43, 2887 (2008)] showed that the widely cited classical photocurrent theory of DeVore [Phys. Rev. 102, 86 (1956)] does not necessarily apply for photocurrent experiments carried out on thin-film semiconductors. In this Letter, we theoretically and experimentally justify the successful use of the photocurrent model published by Bouchenaki et al. [J. Opt. Soc. Am. B 8, 691 (1991)].     

The Haar System as a Schauder Basis in Spaces of Hardy–Sobolev Type

We show that, for suitable enumerations, the Haar system is a Schauder basis in the classical Sobolev spaces in \({\mathbb R}^d\) with integrability \(1<p<\infty \) and smoothness \(1/p-1<s<1/p\). This complements earlier work by the last two authors on the unconditionality of the Haar system and implies that it is a conditional Schauder basis for a nonempty open subset of the (1 / p, s)-diagram. The results extend to (quasi-)Banach spaces of Hardy–Sobolev and Triebel–Lizorkin type in the range of parameters \(\frac{d}{d+1}<p<\infty \) and \(\max \{d(1/p-1),1/p-1\}<s<\min \{1,1/p\}\), which is optimal except perhaps at the end-points.     

High intrachain hole mobility on molecular wires of ladder-type poly(p-phenylenes)

We have studied the high-frequency (34 GHz) mobility of positive charge carriers on isolated ladder-type polymer chains in dilute solution. We find that the high-frequency mobility is limited by the chain ends on chains as long as 35 monomers. The intrachain motion of charge carriers can be described by one-dimensional diffusion between infinitely high reflecting barriers, representing the chain ends. Our data indicate that the intrachain mobility for ladder-type polymer chains is close to 600 cm(2)/V s. With this high mobility the ladder-type polymer is a promising candidate for future use as an interconnecting wire in molecular electronics.