• blend
• cyclodextrin
• energy transfer
• insulated
• light-emitting diode
• molecular wire
• polirotassani
• polyrotaxanes
• white OLED

Conjugated polymers emerged in the past two decades as promising materials for organic electronics and photonics, and are currently studied and developed for application in organic light emitting diodes (OLEDs), organic thin film transistors (OTFT), photovoltaic cells, sensors and optical amplifiers/lasers. Conjugated polymers offer unique properties over inorganic semiconductors, in particular they are flexible, their electronic and optical properties can be tuned over a wide range by means of synthetic chemistry, and they can be processed from solution on large and flexible substrates with high-throughput and low-cost techniques like roll-to-roll printing.
Growing attention is being directed to white organic light emitting diodes in the prospective of using them as efficient solid-state light sources for general lighting. White luminescence requires the excitation of more emitting species with complementary emission spectra; embedding the different species into a single emitting layer offers an advantage in terms of ease of device fabrication which translates into a lower final cost of the device. However this is found to be non trivial because migration of the excitations from the higher energy emitting material towards the lower energy emitting species occurs in the emitting layer, usually resulting in a dominant emission from the material with the lower band-gap.
Molecularly insulated conjugated polymers can offer an elegant solution to the problem of energy transfer in luminescent blends. These materials, which have been defined insulated molecular wires, are characterized by a semiconducting conjugated backbone partially encapsulated in an "inert" insulating sheath which strongly reduces intermolecular interactions; the beneficial effect of the molecular insulation on the luminescence quantum yield, resulting from a reduced tendency to aggregation and an increased protection from fluorescence quenching agents, has been demonstrated in several studies.
We found that cyclodextrin-threaded conjugated polyrotaxanes, a particular class of insulated molecular wires, can be engineered to control energy transfer in binary blends of conjugated polymers, allowing the formulation of white emitting polymer composites with application in white OLEDs. The present work focused first on the synthesis of a green luminescent cyclodextrin-polyrotaxane, based on a fluorene copolymer, which was undertaken at the Chemistry Department of the University of Oxford, under the supervision of Prof. Harry L. Anderson.
The second part of the project, which was performed at the London Centre for Nanotechnology (LCN) and the Department of Physics of the University College London (UCL) with the supervision of Prof. Franco Cacialli, was dedicated both to the investigation of the photophysical properties of polymer blends of the synthetized polyrotaxane, by means of Time Correlated Single Photon Counting (TCSPC) fluorescence spectroscopy, and to the fabrication and characterization of white light emitting diodes based on those materials.