Control of electrophosphorescence in conjugated dendrimer light-emitting diodes

We present a novel platinum porphyrin based phosphorescent dendrimer for us e as a triplet harvesting dopant in organic light-emitting diodes. Two type s of dendritic host materials are used. Through the choice of a common bran ching architecture around the emissive chromophore unit of both guest and h ost materials, we are able to achieve excellent miscibility. The relative c ontribution of guest to host emission is found to depend strongly on the en ergy level offsets of the two blend materials, indicating strong trapping p rocesses. Under pulsed operation, we observe a striking dependence of the e mission spectrum on pulse period, independent of the host material used. Th is spectral modification is attributed to the quenching of triplet excitati ons at high excitation densities. We find excellent agreement between our m easured data and a model based on bimolecular recombination.