Experimental Physics II, University of Bayreuth, Bayreuth, Germany.
J Phys Chem B. 2011 Jul 7;115(26):8417-23. doi: 10.1021/jp202763e. Epub 2011 Jun 15.
We have studied the temperature dependence of phosphorescence (Ph) and delayed fluorescence (DF) in two series of poly(p-phenylene) derivatives within a temperature range from 10 to 300 K under quasi-stationary conditions. One set of materials consists of the dimer, trimer, and polymer of ethylhexyl-substituted poly(fluorene) (PF2/6) and thus allows us to assess the effects of oligomer length. The second series addresses the influence of energetic disorder and conjugation length by being composed of the polymers alkoxy-substituted poly(p-phenylene) (DOO-PPP), poly(indenofluorene) (PIF), and ladder-type poly(p-phenylene) (MeLPPP). Under low light intensities, the DF features a maximum at a certain temperature T(max). For the dimer and trimer, the T(max) coincides with the temperature at which the phosphorescence has decayed to 1/2 of the value at 10 K, while T(max) shifts to lower temperature values along the series DOO-PPP, PIF, and MeLPPP and approaches T = 0 K for MeLPPP. By applying conventional kinetic equations we show that the occurrence of a maximum in the DF intensity is the consequence of generalized thermally activated triplet exciton transport toward quenching sites. We find the quenching rates at 0 K to be in the range of 1 s(-1) for the polymers, while they are more than an order of magnitude lower for the oligomers.
我们在 10 到 300 K 的温度范围内，通过准静态条件，研究了两个系列的聚（对亚苯基）衍生物中的磷光（Ph）和延迟荧光（DF）的温度依赖性。一组材料由乙基己基取代聚芴（PF2/6）的二聚体、三聚体和聚合物组成，从而使我们能够评估低聚物长度的影响。第二组系列通过由烷氧基取代的聚（对亚苯基）（DOO-PPP）、聚（茚并芴）（PIF）和梯型聚（对亚苯基）（MeLPPP）组成，解决了能量无序和共轭长度的影响。在低光强下，DF 在某个温度 T(max) 处具有最大值。对于二聚体和三聚体，T(max) 与磷光衰减至 10 K 时的 1/2 值时的温度重合，而 T(max) 沿着 DOO-PPP、PIF 和 MeLPPP 系列向低温值移动，并在 MeLPPP 中接近 T = 0 K。通过应用常规动力学方程，我们表明，DF 强度中最大值的出现是热激活三重态激子向猝灭位置输运的普遍现象的结果。我们发现，在 0 K 时，聚合物的猝灭速率在 1 s(-1) 的范围内，而对于低聚物，其猝灭速率则低一个数量级以上。
