From photophysical evidence, we suggest a structural model based on intrachain ordering that can account for the changes of the absorption spectrum of poly(9,9-dioctylfluorene) (PFO) films under certain physicochemical treatment protocols. We correlate this model to the results of X-ray fiber diffraction experiments.

A method is demonstrated by which liquid-crystalline self-organization in rigid-rod nematic conjugated polymers can be used to control the microstructure of the active semiconducting layer in solution-processed polymer thin-film transistors (TFTs). Enhanced charge carrier mobilities of 0.01–0.02 cm2/V s and good operating stability have been achieved in polyfluorene copolymer TFTs by preparing the polymer in a nematic glassy state and by aligning the polymer chains parallel to the transport direction with the help of an alignment layer. Mobility anisotropies of 5–8 for current flow parallel and perpendicular to the alignment direction have been observed that are of the same order of magnitude as optical dichroic ratios.

We report on the physical characterization of a dioctyl‐substituted polyfluorene, both in solution and in the solid state. We focus on studies of chain geometry both by molecular modeling and by gel permeation chromatography coupled with light scattering. We determine experimentally a Kuhn segment length, lk = 17.1 ± 2.1 nm and a characteristic ratio C∞ = 21.5 %plusmn; 4.3 indicative of a stiff polymer chain. The effects on absorption and emission spectra of intermolecular interactions that lead to gelation or precipitation from solution are reported. We discuss these results in the context of the strong current interest in the nature of aggregation phenomena and their role in controlling the emissive properties of conjugated polymers. We further show that a markedly enhanced dichroism can be achieved through suitable control of the polymer microstructure.

Electroluminescence and liquid crystallinity: these are the properties of a new spacerless conjugated main‐chain liquid‐crystalline (LC) polymer reported here. The thermal and spectroscopic properties of the new glass‐forming poly‐fluorene with octyl side chains (see Figure) are described, showing that polarized electroluminescent multilayer devices should be possible.

We report cyclic voltammetry measurements for the blue electroluminescent conjugated polymer poly(9,9-dioctylfluorene). Both oxidation and reduction potentials are determined and thus estimates of both the ionization potential Ip and electron affinity Ea of the polymer are obtained for the same sample under the same experimental conditions. We estimate Ip=5.80 eV and Ea=2.12 eV. These results disagree with the common assumption that Ea is, to good approximation, given by the difference between Ip and the optical gap. Measurements on indium tin oxide/polyfluorene/calcium light emitting diode structures are consistent with the deductions from the electrochemical data.