Characterization of the oxidation products of styryl-substituted terthiophenes and sexithiophenes using electronic absorption spectroscopy and time-dependent DFT

The electronic absorption spectra of a series of alkoxy-styryl substituted terthiophenes, their corresponding sexithiophenes, and the oxidation products of both have been measured. The terthiophenes studied sigma-dimerize to sexithiophenes during the oxidation process and there is clear evidence of sexithiophene radical cations, dications, and pi-dimers in the electronic absorption spectra. The oxidation of concentrated solutions produces predominantly pi-dimer bands, as expected. The absorption spectrum of the styryl-functionalized sexithiophene dication without alkoxy substitution closely resembles that of unsubstituted sexithiophene, while alkoxy substitution induces changes in the wavelength of the dication band maximum and the overall band shape. Time-dependent density functional theory (TDDFT) calculations have shown that styryl-based molecular orbitals are important in the transitions of the neutral molecules as well as the charged species, the dication in particular. Kinetics analyses confirm the stabilization effect induced by the alkoxy substituents. The presence of a reversible pi-dimer equilibrium was verified by cyclic voltammetry. It is clear from the experimental observations and the theoretical calculations that both the styryl and alkoxy groups are influencing the electronic properties of this class of molecules.     

The design and synthesis of porphyrin/oligiothiophene hybrid monomers

In an effort to build effective photovoltaic cells based on porphyrin-functionalised polythiophenes we have focused on synthetic routes to three monomer types. By controlling the geometric structure of the monomer, oxidation of these materials should produce polymers with different architectural structures, and as a result, different opto-electronic properties. Employing Wittig protocols allowed access to monomers in which the porphyrin moiety is connected to the beta-position of the thiophene via an alkene linkage. In addition, monomers were constructed using porphyrin condensation methods to afford alpha-thiophene meso-substituted porphryins. Another set of monomers was also prepared via porphyrin condensation routes, but instead utilising beta-formylthiophenes. By utilising different formyloligothiophenes we were able to generate a series of monomers that can be used to control the loading of the porphyrin in the polythiophene matrix.     

Metallation effects on the thermal interconversion of atropisomers of di(orthomethylarene)-substituted porphyrins

A new series of meso-substituted diaryl free-base and metalloporphyrins have been prepared. Each arene has been substituted with both a methyl group in the ortho position and a formyl group in the meta position. Rotation of the arene units is prevented at room temperature due to the steric restrictions imposed by the flanking methyl groups at the porphyrin beta-pyrrolic positions on the methyl groups at the ortho position on the meso-substituted arene unit. This allowed the alpha alpha and alpha beta atropisomers of this porphyrin to be separated and characterised. X-Ray crystallographic determination of the structure of the free-base porphyrin revealed a very flat porphyrin core. Metallation resulted in the isolation and characterisation of the nickel, zinc and copper derivatives. The assignments of the alpha alpha and alpha beta isomers are confirmed by X-ray crystallographic determination of the structures of the Cu(II) analogues. The copper alpha alpha structure exhibits a very twisted porphyrin core, the copper alpha beta structure is also distorted, but to a lesser degree. The activation energy for rotation has been calculated for each of the 2H, Ni and Zn derivatives. The energy required to rotate the arene ring increases in the order Ni < Zn approximately 2H. No significant difference in the free energy of rotation was observed between experiments carried out with the alpha alpha and small alpha beta isomers.     

Resonance Raman studies of beta-substituted porphyrin systems with unusual electronic absorption properties.

Zn(II) and Cu(II) porphyrins with beta-conjugated barbiturate functional groups have low-energy electronic transitions which are unusual in that there are two strong bands in the Soret region. Resonance excitation of the two bands shows that each has features characteristic of both the porphyrin and barbiturate groups, with some perturbation to these features caused by the interaction of the two chromophores. The resonance Raman (RR) spectrum (lambda(exc)=413.1 nm) of the 412 nm band shows two bands at 1722 and 1743 cm(-1) attributable to C==O stretches in the substituent. Changes in frequency of porphyrin core modes due to the differing metal centres are reproduced by density functional theory calculations. The Q band RR spectra show modes with anomalous polarization which may be attributed to A(2g) modes, however no overtone or combination bands are observed.     

Differential inhibition of postnatal brain,spinal cord and body growth by a growth hormone antagonist

Background  

Growth hormone (GH) plays an incompletely understood role in the development of the central nervous system (CNS). In this study, we use transgenic mice expressing a growth hormone antagonist (GHA) to explore the role of GH in regulating postnatal brain, spinal cord and body growth into adulthood. The GHA transgene encodes a protein that inhibits the binding of GH to its receptor, specifically antagonizing the trophic effects of endogenous GH.     

Dehydrohalogenation of endo- 1-chloro-1a, 9b-dihydrocyclopropa 11 phenanthrene

Base induced dehydrochlorination of the title compound (4) leads to products by way of the Δ¹ olefin (5). Under solvolytic conditions the dibenzcycloheptatriene (9) is produced.     

A study of the C(p, p′) reactions at 135 MeV

A relativistic mean field approach is used to determine and compare the single-particle Dirac potentials for nuclei and hypernuclei (Λ, Σ, Ξ). A simple model is used and the Dirac-Hartree-Fock equations are reduced to a Schrödinger-like equation. The subsequent central and spin-orbit shell-model potentials are compared to those of phenomenological approach and other recent microscopic approaches. In the case of hypernuclei the Hartree approximation works already quite well without any need of taking into account the strangeness exchange part coming from strange mesons. The influence of the anomalous magnetic moment of the baryon on the spin-orbit term is found to be rather important for both Λ- and Σ-hyperons.     

The origin of open circuit voltage of porphyrin-sensitised TiO(2) solar cells

Electron lifetime and diffusion coefficient measurements in highly efficient porphyrin-sensitised TiO(2) solar cells showed reduced electron lifetime, and consequently, lower photo-induced electron density under illumination compared to commonly used ruthenium dye (N719)-sensitised solar cells, which is proposed to be the origin of the generally lower open circuit voltage.     

A readily-prepared, convergent, oxygen reduction electrocatalyst

Monomeric cobalt(II) tetraphenylporphyrin immobilized in high concentrations within vapour-phase polymerized polypyrrole deposited on an ITO electrode catalyzes the 4-electron reduction of dioxygen to water, a reaction requiring concerted action by two separate catalytic groups.