Parrott, L-J.; (2008) Optical and electrical characterisation of threaded molecular wires (TMWs) and related optoelectronic devices. Doctoral thesis , University of London.

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Abstract

Commercial light-emitting devices (LEDs) are currently based on inorganic materials with high processing costs and associated environmental issues. In 1990 Burroughes et al. published findings using conjugated polymers (carbon-based chains with single- and double-bonds) as the emissive layer in LEDs. Organic light-emitting devices (OLEDs) are now commercially available as displays. They have advantages over conventional display technologies larger viewing angles, lower operating powers and "true" colour display. OLED device efficiencies and colour purity can be detrimentally altered by close proximity of polymer chains within the device. By separating the chains in the LED film this effect may be lessened. Polyrotaxanes have already found uses in molecular motors, whereas in the materials studied here on the macrocycle is utilised to increase chain separation distance between the conjugated main chains. Previous work has shown that photoluminescence (PL) and electroluminescence (EL) of the polyrotaxane compared to the unthreaded polyrotaxane shifts to higher energies and polyrotaxane light emission is more efficient, indicating that the macrocycles do increase the distance between adjacent chains. Different ionic side-groups using metallic and non-metallic ions have been incorporated to the main chain. These side-groups prevent disruption to the electronic structure of the unthreaded and threaded polyrotaxanes when temperature is raised, and the macrocycles provide further stabilisation. Once an electric field has been applied to the device, the cation is mobile, and the anions remain anchored to the main chain. The ionic mobility allows the devices to emit under forward and reverse bias. This type of device is referred to as a light-emitting electrochemical cell (LEC). Presence of large metallic cations (e.g. Cs) produce LECs which are more stable and exhibit higher PL and EL efficiencies than small metallic cations e.g. Lf based LECs. Further studies in to the addition of hole-transport layers for use with the water-soluble polymers has been carried out to boost operating efficiencies.

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