Energy Transfer Between Squaraine Polymer Sections: From Helix to Zigzag and All the Way Back

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• 作者：Christoph Lambert ; Federico Koch ; Sebastian F. V枚lker ; Alexander Schmiedel ; Marco Holzapfel ; Alexander Humeniuk ; Merle I. S. R枚hr ; Roland Mitric ; Tobias Brixner
• 刊名：Journal of the American Chemical Society
• 出版年：2015
• 出版时间：June 24, 2015
• 年：2015
• 卷：137
• 期：24
• 页码：7851-7861
• 全文大小：756K
• ISSN：1520-5126

文摘

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.