de Vries Xander, Coehoorn Reinder, Bobbert Peter A
Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, NL-5600, MB, Eindhoven, The Netherlands.
Institute for Complex Molecular Systems, Eindhoven University of Technology, P.O. Box 513, NL-5600, MB, Eindhoven, The Netherlands.
Nat Commun. 2020 Mar 10;11(1):1292. doi: 10.1038/s41467-020-15034-0.
Exciton management in organic light-emitting diodes (OLEDs) is vital for improving efficiency, reducing device aging, and creating new device architectures. In particular in white OLEDs, exothermic Förster-type exciton transfer, e.g. from blue to red emitters, plays a crucial role. It is known that a small exothermicity partially overcomes the spectral Stokes shift, enhancing the fraction of resonant donor-acceptor pair states and thus the Förster transfer rate. We demonstrate here a second enhancement mechanism, setting in when the exothermicity exceeds the Stokes shift: transfer to multiple higher-lying electronically excited states of the acceptor molecules. Using a recently developed computational method we evaluate the Förster transfer rate for 84 different donor-acceptor pairs of phosphorescent emitters. As a result of the enhancement the Förster radius tends to increase with increasing exothermicity, from around 1 nm to almost 4 nm. The enhancement becomes particularly strong when the excited states have a large spin-singlet character.
有机发光二极管（OLED）中的激子管理对于提高效率、减少器件老化以及创建新的器件架构至关重要。特别是在白色OLED中，放热的福斯特型激子转移，例如从蓝色发射体到红色发射体的转移，起着关键作用。众所周知，小的放热部分克服了光谱斯托克斯位移，增加了共振供体 - 受体对态的比例，从而提高了福斯特转移速率。我们在此展示了第二种增强机制，当放热超过斯托克斯位移时起作用：转移到受体分子的多个较高电子激发态。使用最近开发的计算方法，我们评估了84种不同的磷光发射体供体 - 受体对的福斯特转移速率。由于这种增强，福斯特半径倾向于随着放热的增加而增加，从约1纳米增加到近4纳米。当激发态具有较大的自旋单重态特征时，这种增强变得尤为强烈。
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