Quantum efficiencies of electroluminescent poly(para-phenylenes)

Poly(para-phenylene) (PPP) and its derivatives with their band-gap corresponding to blue light have shown to be suitable as active layers in Light Emitting Diodes (LEDs). One important factor for the efficiency of these devices is the photoluminescence quantum yield of the active layer. Intermolecular effects in the layers (excitation energy transfer (EET), self-quenching and excimer-formation) lead to a decreased quantum yield in solid state compared to solutions. We investigated the photoluminescence quantum yields of para-hexaphenyl and several PPP-type ladderpolymers in solution and solid state. We report on the measured quantum yields (up to 85% in solution and 30% in solid state) and discuss the occuring quenching mechanisms.