Simple color tuning of phosphorescent dendrimer light emitting diodes

Published versio

Synthesis and properties of highly efficient electroluminescent green phosphorescent iridium cored dendrimers

A simple convergent procedure has been developed for the preparation of solution processable phosphorescent dendrimers with biphenyl-based dendrons and fac-tris(2-phenylpyridyl)iridium(III) cores. We found that the attachment point and branching of the dendrons are important for controlling the color of the light emission. Photolumineseence excitation measurements showed that energy could be transferred efficiently from the dendrons to the core. Solution photoluminescence quantum yield (PLQY) measurements of the dendrimers were of order 70%, showing that the attachment of the dendron did not decrease the luminescence efficiency of the core iridium complex. The PLQYs of the neat dendrimer films increased with generation with the second-generation dendrimer having a neat film PLQY of 31%, 1(1)/(2) times higher than the first-generation dendrimers and almost 3 times that of the nondendritic iridium complex, demonstrating the power of the dendrimer architecture to control intermolecular interactions. Electrochemical experiments showed that charge was injected directly into the core of the dendrimers.</p

Photophysics of <i>fac</i>-tris(2-phenylpyridine) iridium(III) cored electroluminescent dendrimers in solution and films

We present time-resolved photoluminescence (PL) studies of novel first- and second-generation electrophosphorescent fac-tris(2-phenylpyridine) iridium(III) [Ir(ppy)(3)] cored dendrimers and compare them with neat films of molecular Ir(ppy)(3). A PL quantum yield of similar to0.8 is observed in blends of the dendrimers with 4,4'-bis(N-carbazolyl)biphenyl (CBP) at room temperature, and the natural radiative lifetime of the emissive state (1.5 mus) is observed to be the same for dendrimers and molecular Ir(ppy)(3). Quenching of the PL occurs in neat films, because of an energy transfer to less-emissive sites, which have similar to10 times lower oscillator strength. The PL quenching rate in spin-coated films of the first- and second-generation dendrimers is slower by a factor of 11 and 20, respectively, as compared to neat Ir(ppy)(3) films prepared by evaporation. Dendrimer films showed a much smoother surface than Ir(ppy)(3) films, which is consistent with more extensive aggregation of molecular lr(ppy)3 than dendrimers.</p

Photophysics of <i>fac</i>-tris(2-phenylpyridine) iridium(III) cored electroluminescent dendrimers in solution and films

We present time-resolved photoluminescence (PL) studies of novel first- and second-generation electrophosphorescent fac-tris(2-phenylpyridine) iridium(III) [Ir(ppy)(3)] cored dendrimers and compare them with neat films of molecular Ir(ppy)(3). A PL quantum yield of similar to0.8 is observed in blends of the dendrimers with 4,4'-bis(N-carbazolyl)biphenyl (CBP) at room temperature, and the natural radiative lifetime of the emissive state (1.5 mus) is observed to be the same for dendrimers and molecular Ir(ppy)(3). Quenching of the PL occurs in neat films, because of an energy transfer to less-emissive sites, which have similar to10 times lower oscillator strength. The PL quenching rate in spin-coated films of the first- and second-generation dendrimers is slower by a factor of 11 and 20, respectively, as compared to neat Ir(ppy)(3) films prepared by evaporation. Dendrimer films showed a much smoother surface than Ir(ppy)(3) films, which is consistent with more extensive aggregation of molecular lr(ppy)3 than dendrimers.</p