Pullerits T, Mirzov O, Scheblykin I G
Chemical Physics, Lund University, P.O. Box 124, 22100 Lund, Sweden.
J Phys Chem B. 2005 Oct 20;109(41):19099-107. doi: 10.1021/jp052189c.
The fluorescence of single chains of the conductive polymer poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylene vinylene] (MEH-PPV) was studied by means of single-molecule spectroscopy at 15 K. MEH-PPV was deposited onto a surface from a toluene solution and covered with a polymer cap layer of poly(vinyl alcohol) spin-coated from an aqueous solution for protection against air. Because MEH-PPV is insoluble in water, such sample preparation guarantees that MEH-PPV chains do not mix with the cap polymer. We found that this "host matrix free" environment results in substantially stronger fluorescence spectral diffusion than that observed for conjugated polymer single chains embedded into polymer matrices. The average spectral diffusion range was 500 cm(-1), and the maximum registered value reached 1100 cm(-1), which is approximately 6 times larger than the values reported before. We analyzed spectral diffusion by observation of temporal evolution of the fluorescence intensity, the position of the maximum, and the width of fluorescence spectra. We propose that the transition energy shifts are caused by the differences of the London dispersive forces in slightly different polymer chain conformations. Such conformational changes are possible even at low temperatures because the MEH-PPV single chains in our samples have more freedom for fluctuations than in the usual "in host" arrangement.
通过单分子光谱法在15 K下研究了导电聚合物聚2-甲氧基-5-(2'-乙基己氧基)-1,4-亚苯基亚乙烯基单链的荧光。MEH-PPV从甲苯溶液沉积到表面上，并用从水溶液中旋涂的聚乙烯醇聚合物盖层覆盖，以防止空气影响。由于MEH-PPV不溶于水，这种样品制备保证了MEH-PPV链不会与盖聚合物混合。我们发现，这种“无主体基质”环境导致的荧光光谱扩散比嵌入聚合物基质中的共轭聚合物单链所观察到的要强得多。平均光谱扩散范围为500 cm⁻¹，记录到的最大值达到1100 cm⁻¹，约为之前报道值的6倍。我们通过观察荧光强度随时间的演变、最大值位置和荧光光谱宽度来分析光谱扩散。我们提出，跃迁能量的移动是由聚合物链构象略有不同时伦敦色散力的差异引起的。即使在低温下，这种构象变化也是可能的，因为我们样品中的MEH-PPV单链比通常的“在主体中”排列具有更大的波动自由度。
