Department of Chemical and Biomolecular Engineering, University of Melbourne, Melbourne, Victoria, Australia.
J Phys Chem B. 2011 Jun 2;115(21):6838-42. doi: 10.1021/jp111787b. Epub 2011 May 9.
Conjugated polymers in solution exhibit interesting photophysical behavior, which is dictated by their molecular conformation. The conformations and resulting photophysics can be altered by deformational flows such as simple shear. Solutions of poly[2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) in dimethylformamide (DMF) show large decreases in fluorescence intensity as a function of shear rate, combined with significant spectral shifts upon exposure to shear. The excitation and emission spectra shift toward shorter wavelengths, indicating a change in conformation with shortened conjugated segment lengths attributed to compressive hydrodynamic forces in flow. Addition of poly(methyl methacrylate) to the solutions is shown to alter the fluorescence emission spectral behavior, which we ascribe to energy transfer from the higher energy, short segments to a small population of lower energy conjugated segments. The measured fluorescence changes were not reversible upon cessation of shear, demonstrating that permanent conformational changes are induced by flow.
溶液中的共轭聚合物表现出有趣的光物理行为，这取决于它们的分子构象。构象和由此产生的光物理性质可以通过简单的剪切等变形流来改变。聚2-甲氧基-5-(2-乙基己氧基)-1,4-亚苯基乙烯基在二甲基甲酰胺(DMF)中的溶液在剪切速率的作用下，荧光强度会大幅降低，同时在暴露于剪切时会发生显著的光谱位移。激发和发射光谱向较短的波长移动，表明构象发生了变化，共轭片段的长度缩短，这归因于流场中的压缩流体动力。向溶液中添加聚甲基丙烯酸甲酯被证明会改变荧光发射光谱行为，我们将其归因于能量从高能、短链段向一小部分低能共轭链段的转移。测量的荧光变化在停止剪切后不能恢复，这表明流场会引起永久性的构象变化。
