Jaiser Frank, Neher Dieter, Meisel Andreas, Nothofer Heinz-Georg, Miteva Tzenka, Herrmann Andreas, Müllen Klaus, Scherf Ullrich
Institut fur Physik und Astronomie, Universitat Potsdam, Karl-Liebknecht-Str. 24-25, 14476 Potsdam-Golm, Germany.
J Chem Phys. 2008 Sep 21;129(11):114901. doi: 10.1063/1.2976769.
Two generations of polyphenylene dendrimers with a perylene diimide core are compared with a nondendronized tetraphenoxyperylene diimide model compound regarding their application in organic light-emitting diodes (OLEDs). Single layer devices with blends of the first and second generation dendrimers in polyfluorene are investigated as active layers in OLEDs, and the effect of dendronization on the emission color and electroluminescence intensity is studied. In photoluminescence, higher degrees of dendronization lead to a reduction in Forster transfer from the polyfluorene host to the perylene, resulting in a larger contribution of the blue host emission in the photoluminescence spectra. In electroluminescence, the dopants appear to act as active traps for electrons, resulting in a predominant generation of excitons on the dye. This gives rise to a remarkably stronger contribution of red emission in electroluminescence than in photoluminescence where energy is exchanged exclusively via Forster transfer. The pronounced color change from red to blue with higher degrees of dendronization and larger driving voltages is explained by the competition of the recombination of free electrons with holes and trapping of electrons by the emitting guest.
将具有苝二酰亚胺核的两代聚苯撑树枝状大分子与一种非树枝状化的四苯氧基苝二酰亚胺模型化合物在有机发光二极管（OLED）中的应用进行了比较。研究了第一代和第二代树枝状大分子与聚芴的混合物作为OLED活性层的单层器件，并研究了树枝状化对发射颜色和电致发光强度的影响。在光致发光中，更高程度的树枝状化导致从聚芴主体到苝的福斯特转移减少，从而导致光致发光光谱中蓝色主体发射的贡献更大。在电致发光中，掺杂剂似乎充当电子的活性陷阱，导致染料上主要产生激子。这使得电致发光中红色发射的贡献比仅通过福斯特转移进行能量交换的光致发光中显著更强。随着树枝状化程度的提高和驱动电压的增大，从红色到蓝色的明显颜色变化是由自由电子与空穴复合以及发射客体对电子的俘获之间的竞争来解释的。
