High performance electrophosphorescent light emitting diodes (LEDs) were demonstrated by using conjugated polymers, poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO), PFO end-capped with hole-transporting moieties (HTM), PFO-HTM, and PFO end-capped with electron-transporting moieties (ETM), PFO-ETM, as the hosts and the organometallic emitter, tris-[2,5-bis-2'-(9,9'-dihexylfluorene) iridium] [Ir(HFP)<sub>3</sub>] as the guest. Electrophosphorescent LEDs fabricated from PFO, PFO-HTM, and PFO-ETM as the hosts emit red light with turn-on voltage around 5V, luminances (L) of 2040 cd/m<sup>2</sup>, 1937 cd/m<sup>2</sup> and 2487 cd/m<sup>2</sup> at 290 mA/cm<sup>2</sup> (16 V), and luminance efficiencies (LE) of 1.40 cd/A, 1.38 cd/A and 1.80 cd/A at 4.5 mA/cm<sup>2</sup> for PFO, PFO-HTM, and PFO-ETM, respectively. The results demonstrate that high performance electrophosphorescence can be obtained from conjugated polymer-based LEDs that are fabricated by processing the active materials directly from solution.
The measurements of the ultra-fast fluorescence anisotropy decay in conjugated dendrimers and in model branched dendritic molecules of different symmetry are reported. The excited state relaxation of carbon and adamantane-centered tetramers was investigated by polarized fluorescence upconversion spectroscopy. Fluorescence anisotropy was found to decay to the residual value in femtosecond time range. A comparison between the tetramer systems and a nitrogen cored distyrylbenzene dendrimer is provided. For the model system bis-MSB representing the linear building block of the investigated systems a fluorescence anisotropy decay time of 82 ps was obtained which agrees with rotational diffusion. Ultrafast anisotropy decay for these branched systems was explained in terms of interchromophore interactions. The results of these ultrafast anisotropy measurements are important to the understanding of the characteristics of excitations in organic dendrimers.
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Bio-Inspired/Biomimetic Sensor Technologies and Applications