Hania P Ralph, Thomsson Daniel, Scheblykin Ivan G
Department of Chemical Physics, University of Lund, Box 124, SE-22100 Sweden.
J Phys Chem B. 2006 Dec 28;110(51):25895-900. doi: 10.1021/jp0653252.
An electric field oscillating at a frequency approximately 1 Hz is found to induce strong modulation of the fluorescence intensity of single poly[2-methoxy,5-(2'-ethyl-hexyloxy)-p-phenylene vinylene] (MEH-PPV) molecules (MW approximately 10(6)) embedded in a poly(methyl methacrylate) (PMMA) matrix. The MEH-PPV polymer chains are carefully isolated from the electrodes to avoid effects of injection. In a polystyrene matrix, fluorescence intensity modulations are on average much less pronounced. The difference in average modulation depth can be explained in terms of lower field-induced exciton dissociation rates in the MEH-PPV/polystyrene system compared to MEH-PPV/PMMA because of a lack of suitable acceptor sites. The observed electric field dependence of single-molecule fluorescence strongly suggests that energy transfer from singlet or even triplet excitons to long-living on-chain hole polarons contributes to the observed modulations. The observed large qualitative differences between the responses of different molecules probably reflect differences in chain topology and strongly anisotropic distributions of acceptor sites, while the hysteretic response of some molecules indicates conformational switching.
人们发现，振荡频率约为1赫兹的电场能强烈调制嵌入聚甲基丙烯酸甲酯（PMMA）基质中的单个聚[2-甲氧基，5-（2'-乙基己氧基）-对苯撑乙烯撑]（MEH-PPV）分子（分子量约为10⁶）的荧光强度。MEH-PPV聚合物链与电极小心隔离，以避免注入效应。在聚苯乙烯基质中，荧光强度调制平均而言不太明显。平均调制深度的差异可以用以下原因来解释：由于缺乏合适的受体位点，与MEH-PPV/PMMA相比，MEH-PPV/聚苯乙烯体系中电场诱导的激子解离速率较低。观察到的单分子荧光对电场的依赖性强烈表明，单重态甚至三重态激子向长寿命链上空穴极化子的能量转移导致了观察到的调制。观察到的不同分子响应之间的巨大定性差异可能反映了链拓扑结构的差异以及受体位点的强烈各向异性分布，而一些分子的滞后响应表明存在构象转换。
