Olof Wennerström

C60 embedded in γ-cyclodextrin: a water-soluble fullerene

A water-soluble complex of C60 is formed on refluxing a solution of γ-cyclodextrin with solid C60; the lifetime of the triplet excited state of C60 in the complex is 83 µs in an oxygen free solution.

The interaction between ammonia and poly(pyrrole)

Abstract Reversible and irreversible interactions between ammonia and poly-(pyrrole) have been studied using electrical conductivity measurements, optical spectroscopy, Fourier transform infrared spectroscopy (FT i.r.), X-ray photoelectron spectroscopy (XPS) and elemental analysis. The results show that in addition to the previously reported reversible change of the electronic properties of poly(pyrrole) upon treatment with ammonia, there is also a large irreversible change if the material is exposed to high concentrations of ammonia or ammonia plus water vapour for a long period of time. The measurements also indicate that amide-type carbonyl groups, amine groups and ammonium ions could be present in the irreversibly changed polymer. The results are used as a basis for a discussion on the interaction between conducting polymers and ammonia in general and between poly-(pyrrole) and ammonia in particular.

White light from an electroluminescent diode made from poly[3(4‐octylphenyl)‐2,2′‐bithiophene] and an oxadiazole derivative

We report on an electroluminescent diode emitting red, green, and blue light simultaneously. The device is based on a thin polymer layer, poly[3‐(4‐octylphenyl)‐2,2’‐bithiophene] and a thick molecular layer, 2‐(4‐biphenylyl)‐5‐(4‐tertbutyl‐phenyl)1,3,5‐oxadiazole. The quantum efficiency for light conversion is 0.3% and the turn‐on voltage for light emission is 7 V. In this article we present electric and spectroscopic characterizations. A mechanism for the light emission, based on electron and hole recombination between the two organic layers, is proposed.

Polythiophene polymers in light emitting diodes: making multicolour devices

Summary form only given. Polythiophenes with alkyl and alkylphenyl substituents, with bandgaps from 1.8 to 3 eV, have been synthesised and used in polymer light emitting diodes. The bandgap is systematically tuned by the pattern and character of substituents on the polythiophene main chain. Steric repulsion between substituents and the main chain forces the polymer out of planarity, increasing the bandgap. By using these soluble polymers in light emitting diodes we have obtained the colours blue, green, red and infrared, with quantum efficiencies reaching the 0. I- I % range. Using multilayers we have obtained multicolour emission in these diodes. Special geometries allows the use of these polymer LEDs as /spl les/100 nm diameter light sources.

Controlling colour by voltage in polymer light emitting diodes

We report electroluminescence using different substituted polythiophenes as the emitting mterial. Different substituents cause different sterical interacion which force the thiophene rings out of planarity. This results in different bandgaps. Colours from blue to near infrared have been demonstrated in electroluminescent devices. We also demonstrate voltage controlled electroluminescence using mixtures of these polymers.

Thermal control of near‐infrared and visible electroluminescence in alkyl‐phenyl substituted polythiophenes

We report electroluminescence from a regioregular alkyl-phenyl substituted polythiophene. The polymer film exists in two forms, giving widely different optical absorption, as well as photoluminesce ...

Geometry of polyaniline

Abstract In order to get a quantitative picture of the geometry of polyaniline, we have carried out MNDO calculations on segments of the polymer. The completely oxidized form (2A) shows an alternating benzoid-quinoid structure of the six-membered carbon rings, while the completely reduced form (1A) is all benzoid. The torsion angles between adjacent rings in the 2A and 1A forms are calculated to be 87° and 82°, respectively. In the protonated 2S′form the torsion angle between rings adjacent to a protonated nitrogen is reduced to ∼72°, while the torsion angle between rings adjacent to an unprotonated nitrogen is still close to 90°. The benzoid-quinoid structure is preserved in the 2S′ form and the charge transferred to the polymer chain is found to be well delocalized. We also present data from n.m.r. experiments on oxidized polyaniline before and after protonation. These data can be interpreted in a way consistent with the geometry obtained from the MNDO calculations. The n.m.r. spectrum of oxidized and protonated polyaniline is rather featureless, but the similarity in the distributions of chemical shifts between the spectra implies that the structure is unchanged upon protonation and that the injected charge is delocalized, i.e. , in agreement with the MNDO results.

A gas phase container for C60; a γ-cyclodextrin dimer

Abstract A molecular complex consisting of two molecules of γ-cyclodextrin and one molecule of C 60 has been identified by negative FAB/LSIMS mass spectroscopy.

meso-tetra(meso-tetraphenylporphyrinyl)porphyrin, a macrocycle with five covalently linked porphyrin units

Abstract A convenient synthesis of a meso-tetraphenylporphyrin monoaldehyde, 1c, is reported. Condensation of this aldehyde with excess benzaldehyde and pyrrole gives the bis-porphyrin 2. A low yield of the title compound, the penta-porphyrin 3 is obtained from 1c and pyrrole in refluxing propionic acid.

Synthesis of poly(alkylthiophenes) for light emitting diodes

We have demonstrated a general way to tune the emission of poly(alkylthiophenes) by using steric interaction between the repeating units. Light-emitting diodes prepared of the polymers have blue to near-infrared emission.