Energy Transfer Between Squaraine Polymer Sections: From Helix to Zigzag and All the Way Back.
Energy Transfer Between Squaraine Polymer Sections: From Helix to Zigzag and All the Way Back.
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DOI：
10.1021/jacs.5b03644
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发表时间：
2015-06
影响因子：
15
通讯作者：
C. Lambert;Federico Koch;S. Völker;A. Schmiedel;M. Holzapfel;A. Humeniuk;M. Röhr;R. Mitrić;T. Brixner
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文献类型：
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作者：
C. Lambert;Federico Koch;S. Völker;A. Schmiedel;M. Holzapfel;A. Humeniuk;M. Röhr;R. Mitrić;T. Brixner
我们提供了一个联合的实验和理论研究方酸聚合物在溶液中。吸收光谱表明聚合物中存在两种不同的构象：螺旋结构和锯齿结构。这种独特的情况下，允许研究溶液中单个聚合物链内不同结构段之间的超快能量传递过程。了解潜在的动力学对于开发用于光捕获和光电应用的新型材料具有根本的重要性。在这里，我们结合联合收割机飞秒瞬态吸收光谱与时间分辨的二维电子光谱，以证明超快的能量转移的方酸聚合物链内的收益从最初激发的螺旋段锯齿形段或反之亦然，这取决于溶剂以及激发波数。这些观察结果与其他共轭聚合物如MEH-PPV形成对比，其中报道了慢得多的链内能量转移。方酸聚合物中非常快的能量转移的原因很可能是供体和受体聚合物链段之间的态密度的紧密匹配，因为这些花青样发色团中的重组能非常小。
We provide a joint experimental and theoretical study of squaraine polymers in solution. The absorption spectra show evidence that two different conformations are present in the polymer: a helix and a zigzag structure. This unique situation allows investigating ultrafast energy-transfer processes between different structural segments within a single polymer chain in solution. The understanding of the underlying dynamics is of fundamental importance for the development of novel materials for light-harvesting and optoelectronic applications. Here, we combine femtosecond transient absorption spectroscopy with time-resolved 2D electronic spectroscopy in order to demonstrate that ultrafast energy transfer within the squaraine polymer chains proceeds from initially excited helix segments to zigzag segments or vice versa, depending on the solvent as well as on the excitation wavenumber. These observations contrast other conjugated polymers such as MEH-PPV where much slower intrachain energy transfer was reported. The reason for the very fast energy transfer in squaraine polymers is most likely a close matching of the density of states between donor and acceptor polymer segments because of the very small reorganization energy in these cyanine-like chromophores.