Intrachain photoluminescence dynamics of MEH-PPV in the solid state.
Intrachain photoluminescence dynamics of MEH-PPV in the solid state.
复制标题
DOI：
10.1021/jp073492b
复制
发表时间：
2007-11
期刊：
影响因子：
--
通讯作者：
K. Kanemoto;Yoshitaka Imanaka;I. Akai;M. Sugisaki;H. Hashimoto;T. Karasawa
中科院分区：
文献类型：
--
作者：
K. Kanemoto;Yoshitaka Imanaka;I. Akai;M. Sugisaki;H. Hashimoto;T. Karasawa
研究了甲基对苯二甲酸乙二醇酯(poly[2-methoxy-5-(2‘-ethyl-hexyloxy)-1，4-phenylene-PPV)共混在主体聚合物(PP、PP)基质中和纯薄膜中的光致发光动力学。为了观察MEH-PPV在固态下的链内发光特性，设计了较低的MEH-PPV在PP共混物中的浓度(0.01wt%)。共混样品的稳态0-0PL带相对于平整的MEH-PPV膜有0.12 eV的蓝移。共混样品的光致发光(PLE)谱显示出一定的振动结构，因此我们可以确定其斯托克斯位移的大小为0.06 eV。共混样品在4K下呈现单指数发光衰减，其时间常数为850ps。我们强调，这种单指数型的光致发光衰减是链内光致发光物种的一种固有性质。时间分辨光致发光测量证实了光致发光带的动态红移，而在PP共混物中没有发现这一趋势。这些观察结果表明，在孤立的MEH-PPV聚合物链中，有限链段之间的能量转移会导致激子迁移，与链间转移的情况相比，效率要低得多。时间分辨测量进一步表明，共混物样品中识别的斯托克斯位移发生在光激发后50ps内的早期阶段。我们将这种斯托克斯位移归因于MEH-PPV链的平面度的快速增加，这是由于光激发后某些组成的苯环发生扭转所致。最后，基于混合样品和纯薄膜之间斯托克斯位移的不同大小的争论，我们得出结论：纯薄膜中MEH-PPV的荧光主要发生在通过激子的链间迁移而发生的链间激发位置。
The photoluminescence (PL) dynamics of poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) blended in host polymer (polypropylene, PP) matrix as well as that in the neat film has been studied. The concentration of MEH-PPV in the PP blend is designed to be fairly low (0.01 wt %) in order to observe the intrinsic intrachain PL property of MEH-PPV in the solid state. The steady-state 0-0 PL band of the blend sample shows a blue-shift of 0.12 eV with respect to that of the neat film of MEH-PPV. The PL-excitation (PLE) spectra of the blend sample exhibit definite vibronic structure, and hence we can determine the magnitude of the Stokes shift as 0.06 eV. The blend sample shows a single-exponential PL decay at 4 K with a time constant of 850 ps. We emphasize that this single-exponential-type PL decay is an intrinsic property of the intrachain PL species. Time-resolved PL measurements confirm dynamical red-shift of the PL band in the neat film, whereas this trend is not found in the case of the PP blend. These observations indicate that the energy transfer between finite segments, which can cause exciton migration, is much less efficient within the isolated MEH-PPV polymer chain compared to the case of the interchain transfer. The time-resolved measurements further demonstrate that the Stokes shift identified in the blend sample takes place at the early stage within 50 ps following photoexcitation. We attribute this Stokes shift to the rapid increase of the planarity of the MEH-PPV chain caused by the torsion of some constituent phenyl rings following photoexcitation. Finally, based on an argument on the different magnitudes of Stokes shift between the blend sample and the neat film, we conclude that the PL of MEH-PPV in the neat film predominantly occurs at the site of interchain excitations via the interchain migration of excitons.