Role of Ultrafast Torsional Relaxation in the Emission from Polythiophene Aggregates
Role of Ultrafast Torsional Relaxation in the Emission from Polythiophene Aggregates
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DOI：
10.1021/jz101026g
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发表时间：
2010-10-07
影响因子：
5.7
通讯作者：
Herz, Laura M.
中科院分区：
文献类型：
--
作者：
Parkinson, Patrick;Mueller, Christian;Herz, Laura M.
了解半导体聚合物中的聚集效应对于它们在光电子器件中的应用是至关重要的；然而，这种链间状态的动态演变还没有被很好地理解。在这里，我们研究了半导体聚(3-己基噻吩基)(P3HT)与电子惰性超高相对分子质量聚乙烯(UHMW-PE)基质的混合物，该基质被证明可以精确控制P3HT链聚集的程度。我们用飞秒时间分辨光致发光测量方法测定了孤立的和聚集的P3HT区域内的单重态激发态布居，发现只有聚集的情况下才有一条强烈的超快衰变路径。两个最低振动带发射的比较表明，在大约13ps的时间内，从初始的振动“热”光激发态转变到几何松弛聚集态，对应于这些材料扭转弛豫的时间尺度。我们的结论是，共轭聚合物中聚集体激发态的形成是由系综从低对称性到高对称性有序态的振动弛豫所促成的。
An understanding of aggregation effects in semiconducting polymers is essential for their use in optoelectronic devices; however, the dynamic evolution of such interchain states is not well understood. Here, we have investigated a blend of semiconducting poly(3-hexylthiophene) (P3HT) with an electronically inert ultrahigh-molecular-weight polyethylene (UHMW-PE) matrix that is shown to allow precise control over the extent to which the P3HT chains aggregate. We determined the singlet excition population within isolated and aggregated P3HT regions using femtosecond time-resolved photoluminescence measurements and found a strong ultrafast decay pathway in the aggregated case only. Comparison of the emission from the two lowerst vibronic bands demonstrates a changeover from an initial vibrationally "hot" photoexcited state to a geometrically relaxed aggregate state within similar to 13 ps, corresponding to time scales for torsional relaxation in these materials. We conclude that formation of an aggregate excited state in conjugated polymers is mediated by vibrational relaxation from a low-symmetry to a high-symmetry ordered state for the ensemble.