A detailed investigation is presented of the redox states of three oligothiophenes (nT) with 6, 9, and 12 thiophene units. While open-shell radical cations (polarons) and closed-shell dications (bipolarons) are usually invoked as the primary redox species in these systems, we have obtained evidence that the dication of the longest oligothiophene (12T) has an electronic structure with two individual polarons. The redox states of 6T, 9T, and 12T have been fully characterized using UV/visible/near-IR and ESR spectroscopy in combination with electrospray mass spectrometry. For 6T and 9T, singleelectron oxidation in dichloromethane produces the corresponding radical cations, which form spinless p dimers at lower temperatures. A second oxidation step forms dications which possess a bipolaronic electronic structure. However, the redox behavior of the longest oligothiophene, 12T, is entirely different. Radical cations of 12T disproportionate into neutral oligomers and dications, except at the lowest oxidation levels. The spectral data for doubly oxidized 12T are incompatible with those expected for a bipolaronic structure but are consistent with the formation of two individual polarons on a single chain; this interpretation is also supported by the results from correlated quantum chemical calculations.

A well-defined triblock copolymer is synthesized by using a strategy in which the α-coupling of 11 thiophene rings of the middle block and the monodispersity (DP = 30 and M̄ w/M̄ n = 1.1) of the two polystyrene outer blocks is ensured. Monofunctional polystyrene 1 is first modified with an α-terthiophene unit 2 to form 3, and two of these units are coupled in a double Stetter reaction of 4 with a difunctional α-terthiophene 5 to yield a tetraketone 6 as the precursor of the triblock copolymer, which was formed with excess Lawesson's reagent. The polymer 7 is fully characterized with IR and NMR spectroscopy and MALDI-TOF mass spectrometry. Size exclusion chromatography, transmission electron microscopy, and scanning force microscopy show that 7 is self-assembled into spherical, micellar structures with average diameters of 12 nm, which corresponds to about 60 block copolymer molecules per aggregate. The optical properties of 7 are in full agreement with an associated unsubstituted oligothiophene. Electrochemical doping is hampered by the polystyrene shell; however, chemical doping afforded small nanoscopic charged aggregates that are soluble in organic solvents.

In two consecutive one‐electron oxidations, oligopyrroles substituted with phenyl capping groups (PhPynPh, n = 2–4) can be oxidized reversibly to give stable cation radicals and dications. Spectroelectrochemical studies give direct evidence that diamagnetic π‐dimers of cation radicals are formed in solution. Such dimers may be involved as charge carriers in conducting polypyrrole.

The mechanism of excitation energy transfer is studied using host-guest systems consisting of green and yellow emitting poly(phenylene vinylene) (PPV) based polymers into which red emitting dyes are dispersed. The photoluminescence from such polymer-dye systems is studied in the steady-state and time resolved. Furthermore, the electroluminescence from devices containing these polymer-dye systems as emissive layer is measured. It is shown that in such disordered polymers, characterized by dispersive exciton transport, energetic resonance between the polymer and the dye is not the only requisite for efficient energy transfer. In addition, the exciton kinetics of the combined polymer-dye system has to be taken into account. Efficient transfer of excitation energy from a disordered polymer to a dye can only occur if, at a certain energy, the polymer-to-dye exciton transfer rate is higher than the intrapolymer exciton migration rate. A consequence of the mechanism described here is that when a dye is dispersed into a disordered polymer, always a residual polymer emission remains, both in photoluminescence as well as in electroluminescence, provided that excitons are created on the polymer. This knowledge is important when constructing a device employing such a polymerdye system as the emissive layer.