Institut für Physikalische Chemie, Johannes Gutenberg-Universität, 55099 Mainz, Germany.
Chemphyschem. 2011 Jun 6;12(8):1499-508. doi: 10.1002/cphc.201001010. Epub 2011 Apr 5.
Single poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) molecules dispersed in thin poly(methylmethacrylate) films have been investigated by fluorescence emission, excitation and time-resolved spectroscopy at 1.2 K. For the molecular weight studied (∼200 kDa) a bimodal distribution of emission maxima is observed. Based on a comparison of the spectroscopic properties of blue and red sites and on polarisation-resolved measurements, we argue in agreement with recent quantum-chemical calculations that the red subpopulation most probably does not arise from interchromophoric excitation delocalisation but is to be attributed to longer chromophoric units originating from ordered regions of a polymer chain, where due to constraints on the chain conformation larger conjugation lengths can be realised. In excitation spectra within the red spectral region we can identify multiple chromophoric units, among them chromophores without correspondence in the emission spectrum-donors of the intramolecular energy transfer. Zero-phonon lines of donor chromophores proved to be significantly broadened, indicating fast excited-state population decay due to energy transfer. Thus, a distribution of energy transfer times within MEH-PPV chains could be determined from donor zero-phonon line widths, with an average value of 3.9 ps. Our study represents the first direct measurement of energy transfer times in conjugated polymers, parameters that are crucial for the performance of many technical applications based on this class of material.
在 1.2 K 下，通过荧光发射、激发和时间分辨光谱研究了分散在薄聚甲基丙烯酸甲酯薄膜中的单聚2-甲氧基-5-(2'-乙基己氧基)-1,4-亚苯基乙烯基分子。对于研究的分子量（约 200 kDa），观察到发射峰的双峰分布。基于对蓝、红位点的光谱性质的比较以及偏振分辨测量，我们认为与最近的量子化学计算一致，红亚群最不可能是由于发色团间激发离域引起的，而是归因于来自聚合物链有序区域的更长发色团单元，在这些区域中，由于链构象的限制，可以实现更大的共轭长度。在红色光谱区域内的激发光谱中，我们可以识别出多个发色团单元，其中包括在发射光谱中没有对应物的发色团-分子内能量转移的供体。供体发色团的零声子线被证明明显变宽，表明由于能量转移，激发态的快速Population 衰减。因此，可以从供体零声子线宽确定 MEH-PPV 链中的能量转移时间分布，平均为 3.9 ps。我们的研究代表了对共轭聚合物中能量转移时间的首次直接测量，这些参数对于基于这类材料的许多技术应用的性能至关重要。
