Photophysics of fac-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.