Tuning of emission color for blue dendrimer blend light-emitting diodes

We demonstrate efficient tunable blue electroluminescence from blends of two solution-processible light-emitting dendrimers. These materials can be blended to form optical quality thin films with no phase-separation effects, irrespective of the blend ratio. External quantum efficiencies of 1% have been measured for the blend systems and the emission color can be tuned from deep blue (emission peak 401 nm) to blue green (477 nm) by blend composition. A power efficiency of 1.5 lm/W (at 200 Cd/m(2) and 5.4 V) is measured for a single layer, first-generation blue-green fluorene-thiophene dendrimer. These results show that by choice of a dendrimer structure with common branching units and surface groups, dissimilar cores can be blended with excellent miscibility. This provides a simple way of tuning the color of organic light-emitting diodes. (C) 2004 American Institute of Physics.