Effect of generation on the electronic properties of light-emitting dendrimers
Organic Light-Emitting Materials and Devices III
We have compared the optical and electronic properties of a series of porphyrin centred dendrimers containing stilbene dendrons. The first and second generation dendrimers could be spin-coated from solution to form good quality thin films. Incorporation into single layer light-emitting diodes gave red-light emission with maximum external quantum efficiencies of 0.02% and 0.04% for the first and second generation dendrimers respectively. We have determined by photoluminescence studies that
... can be transferredefficientlyfrom the stilbene dendrons to the porphyrin core and that PL emission is from the core. Cyclic voltammetiy studies on the dendrimers show that the reductions are porphyrin centred with the dendrons only affecting the rate of heterogeneous electron tiansferbetween the electrode and the dendrimers. This suggests that charge mobility within a dendrimer film in an LED will be affectedby the porphyrin edge to porphyrin edge distance. We have studied the hydrodynamic radii of the dendrimers by gel permeation chromatography and found as expected that the average porphyrin edge to dendron edge distance increases with generation. This is consistent with the slowing of heterogeneous electron transfer observed in the cyclic voltammetry on increasing the generation number and suggests that the dendrons are interleaved in the solid state to facilitate charge transport.