Conjugated polymers and oligomers are very interesting materials, with a number of possible electronic, optoelectronic, and photonic applications. New synthesis techniques allow the preparation of extremely pure soluble poly(paraphenylenes), showing a steepness at the bandedge comparable to conventional semiconductors. One consequence of this high purity is an improved photoluminescence quantum yield, higher than 24% for thin films. Copolymers of stepladder poly(paraphenylenes) are presented, which can be understood as the polymeric version of quantum well structures. Oligomers of poly(paraphenylene), like p-hexaphenyl can be produced as highly pure, well ordered thin films, which show a high photo-luminescence quantum yield in excess of 30%. All these materials, including an improved poly(phenylenevinylene), are applied as the active layer in light-emitting devices, giving bright light emission in the visible range and we report on their performance and efficiencies. Finally, we present a new preparation technique to produce highly ordered self assembled aromatic oligoazomethines, which are applied as transport layers in multiheterolayer electroluminescence devices.