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by: H.J. Brouwer -
February 25, 1998
π-conjugated polymers attract much interest nowadays for use as active component in electronic, optical and optoelectronic applications, like light-emitting diodes, light-emitting electrochemical cells, photodiodes, photovoltaic cells, field-effect transistors, optocouplers and optically pumped lasers. π-conjugated polymers combine the properties of classical macromolecules, such as low weight, good mechanical behaviour (strength and flexibility) and processability with semiconductor properties, arising from their particular electronic structure. Conjugated polymers like poly(p-phenylene vinylene) and poly(p-phenylene) have a backbone consisting of alternating single and double carbon-carbon bonds. The overlap of π orbitals forms a continuous system of electron density along the backbone. The extent of this overlap (the conjugation length) together with the bond alternation determines the HOMO-LUMO bandgap. These materials are often strongly fluorescent and emit in the range from near infrared to the ultraviolet (1-4 eV). Especially PPV and soluble derivatives thereof, are of great interest, due to the combination of emission in the visible wavelength region and high luminescence quantum yields.
The primary interest of this study has been the solid-state photophysical characterization of a series of novel well-defined alternating PPV copolymers and crystalline 5-ring oligo(p-phenylene vinylene)s, and their application as emissive medium in light-emitting diodes and photopumped lasers.
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