Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, UK.
School of Chemistry, University of East Anglia, Earlham Road, Norwich NR4 7TJ, UK.
Science. 2017 Apr 14;356(6334):159-163. doi: 10.1126/science.aah4345. Epub 2017 Mar 30.
Organic light-emitting diodes (OLEDs) promise highly efficient lighting and display technologies. We introduce a new class of linear donor-bridge-acceptor light-emitting molecules, which enable solution-processed OLEDs with near-100% internal quantum efficiency at high brightness. Key to this performance is their rapid and efficient utilization of triplet states. Using time-resolved spectroscopy, we establish that luminescence via triplets occurs within 350 nanoseconds at ambient temperature, after reverse intersystem crossing to singlets. We find that molecular geometries exist at which the singlet-triplet energy gap (exchange energy) is close to zero, so that rapid interconversion is possible. Calculations indicate that exchange energy is tuned by relative rotation of the donor and acceptor moieties about the bridge. Unlike other systems with low exchange energy, substantial oscillator strength is sustained at the singlet-triplet degeneracy point.
有机发光二极管（OLED）有望成为高效照明和显示技术。我们引入了一类新型的线性给体-桥-受体发光分子，它们能够实现溶液处理的 OLED，在高亮度下具有近 100%的内量子效率。实现这一性能的关键是它们能够快速有效地利用三重态。通过时间分辨光谱，我们确定在环境温度下，经过反向系间窜越到单重态后，三重态的发光在 350 纳秒内发生。我们发现存在分子构象，其中单重态-三重态能量差（交换能）接近零，因此可以实现快速的相互转换。计算表明，交换能可以通过供体和受体部分相对于桥的相对旋转来调节。与其他具有低交换能的系统不同，在单重态-三重态简并点处保持了相当大的振子强度。
