Effect of Temperature and Chain Length on the Bimodal Emission Properties of Single Polyfluorene Copolymer Molecules
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- 作者：John K. Grey ; Doo Young Kim ; Carrie L. Donley ; William L. Miller ; Ji Seon Kim ; Carlos Silva ; Richard H. Friend ; Paul F. Barbara
- 刊名：Journal of Physical Chemistry B
- 出版年：2006
- 出版时间：September 28, 2006
- 年：2006
- 卷：110
- 期：38
- 页码：18898 - 18903
- 全文大小：146K
- 年卷期：v.110,no.38(September 28, 2006)
- ISSN：1520-5207
文摘
Fluorescence emission spectra were recorded for isolated polymer chains of the polyfluorene copolymer,F8BT [poly(9,9-di-n-octylfluorene-alt-benzothiadiazole)], at 298 and 20 K for two molecular weights (chainlengths). For long-chain F8BT at 298 K, the observed distribution of single-molecule emission maxima G(Emax)is bimodal, with peaks at ~2.35 eV ("blue") and ~2.25 eV ("red"). Previously, the red forms have beenassigned to polymer chains that possess intrachain contacts, which lowers the local singlet exciton energy. At~20 K, G(Emax) collapses into a single broad distribution centered at ~2.3 eV for long-chain F8BT. However,this distribution can be further divided into a high-energy edge that is dominated by the "blue" form, whilethe remainder of the distribution is composed of the "red" form. Low-molecular-weight F8BT samples emitexclusively from the blue form, and no shift in peak maxima with low temperature was observed. A Franck-Condon analysis reveals a decrease in emitting state displacements between spectra measured at 298 and 20K, suggesting that temperature-induced structural displacements are responsible for the change in the bimodalemission.