Control of charge transfer by conformational and electronic effects: Donor–donor and donor–acceptor phenyl pyrroles

Derivatives of N-pyrrolobenzene with a para-donor and a para-acceptor substituent on the benzene ring are compared. It is shown that by a suitable increase of the donor strength of the pyrrolo group, CT fluorescence can be achieved even for donor–donor-substituted benzenes. The ICT emission for sterically hindered compounds is more forbidden than that of unhindered phenyl pyrroles. This suggests conformational effects which induce a narrower twist angle distribution around a perpendicular minimum in the excited state.     

CsMBi(3)Te(6) and CsM(2)Bi(3)Te(7) (M = Pb, Sn): new thermoelectric compounds with low-dimensional structures

The new materials CsPbBi(3)Te(6) and CsPb(2)Bi(3)Te(7) were discovered through reactions of CsBi(4)Te(6) with PbTe, whereas the isostructural materials CsSnBi(3)Te(6) and CsSn(2)Bi(3)Te(7) were discovered through corresponding reactions with SnTe. The compounds can also be prepared from stoichiometric mixtures of Cs(2)Te, Pb (Sn), Bi, and Te. The crystal structures show a layered architecture of NaCl-type slabs alternating with layers of Cs atoms. This group of compounds offers a new quaternary system, Cs-M-Bi-Te (M = Pb and Sn), available for thermoelectric investigations, including fine-tuning of compositions and doping.     

The decay scheme of 127Ba and half-lives of some low-lying excited states in 123, 125, 127, 129Cs

Radioactive sources of ^{123, 125, 127, 129}Ba obtained in the spallation reaction have been studied with Ge(Li), Si(Li), NaI(Tl) and plastic detectors. On the basis of γ-ray energies, intensities, energy sums and coincidence information, the decay scheme has been proposed for ¹²⁷Ba. No high-spin isomer of ¹²⁷Ba has been observed. The lifetimes of $\text{5}\text{2}$⁺ → $\text{1}\text{2}$⁺ transitions in ^{123, 125, 127, 129}Cs have been measured. No evidence for the shape isomerism in ¹²⁷Cs has been found.     

Investigation of deep states in thin films of hydrogenated amorphous silicon by photo-induced current transient spectroscopy

Summary Photo-induced current transient spectroscopy (PICTS) was performed for thin films of undoped hydrogenated amorphous silicon (a-SiH). Existing theoretical models i.e. the standard model of PICTS (the transient currents are limited by thermal emission of carriers from localized to mobile states) and the recombination model due to Rose (the transient currents are limited by recombination) fail to describe the experimental data. It is concluded that the recombination model has to be extended to arbitrary distributions of the density of states in order to be applicable to the present case.

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Untersuchung tiefer Zustände in dünnen Schichten von wasserstoffhaltigem amorphem Silicium mit Hilfe der Photostrom-Transienten-Spektroskopie

     

Optimized hole injection with strong electron acceptors at organic-metal interfaces

The energy-level alignment at interfaces between three electroactive conjugated organic materials and Au was systematically varied by adjusting the precoverage of the metal substrate with the electron acceptor tetrafluoro-tetracyanoquinodimethane (F4-TCNQ). Photoelectron spectroscopy revealed that electron transfer from Au to adsorbed F4-TCNQ was responsible for lowering the hole-injection barrier by as much as 1.2 eV. This novel interface modification scheme is independent of the charge transfer complex formation ability of the organic materials with the electron acceptor.     

Directed regio- and stereoselective hydroformylation of mono- and 1,3-disubstituted allylic alcohols: a catalytic approach to the anti-aldol-retron

Regioselective and diastereoselective hydroformylation of mono- and 1,3-disubstituted allylic alcohol o-DPPB esters is described. The products represent synthetically important anti-aldol retrons.