Department of Chemistry and Biochemistry and the Center for Nano and Molecular Science and Technology, The University of Texas at Austin, Austin, Texas 78712, USA.
ACS Nano. 2012 Jan 24;6(1):523-9. doi: 10.1021/nn203860u. Epub 2011 Dec 30.
For conjugated polymer materials, there is currently a major gap in understanding between the fundamental properties observed in single molecule measurements and the bulk electronic properties extracted from measurements of highly heterogeneous thin films. New materials and methodologies are needed to follow the evolution from single chain to bulk film properties as multiple chains begin to interact. In this work, we used a controlled solvent vapor annealing process to assemble single chains of phenylene-vinylene conjugated polymers into aggregates that can be individually spectroscopically interrogated. This approach allowed us to probe the effects of interchain coupling in isolated conjugated polymer nanodomains of controlled size. By assembling these aggregates from building blocks of both pristine MEH-PPV and MEH-PPV derivatives containing structure-directing ortho- or para-terphenyl inclusions, we were able to control the ordering of these nanodomains as measured by single aggregate polarization anisotropy measurments. Depending on the individual chain constituents, these aggregates varied from highly anisotropic to nearly isotropic, respectively facilitating or inhibiting interchain coupling. From the single chain fluorescence lifetimes, we demonstrated that these structure directing inclusions effectively break the phenylene-vinylene conjugation, allowing us to differentiate interchain electronic effects from those due to hyper-extended conjugation. We observed well-defined bathochromic shifts in the fluorescence spectra of the aggregates containing extensive interchain interactions, indicating that low-energy exciton traps in MEH-PPV are the result of coupling interactions between neighboring chain segments. These results demonstrate the power of the synthetic inclusion approach to control properties at not just the single chain level, but as a comprehensive approach toward ground-up design of bulk electronic properties.
对于共轭聚合物材料，目前在单分子测量中观察到的基本性质与从高度不均匀的薄膜测量中提取的体电子性质之间存在很大差距。需要新的材料和方法来跟踪从单链到体膜性质的演变，因为多条链开始相互作用。在这项工作中，我们使用受控溶剂蒸气退火过程将苯并乙烯共轭聚合物的单链组装成可以进行单独光谱检测的聚集体。这种方法使我们能够在受控尺寸的孤立共轭聚合物纳米域中探测链间耦合的影响。通过使用包含结构导向邻或对三联苯的单体 MEH-PPV 和 MEH-PPV 衍生物的构建块组装这些聚集体，我们能够控制这些纳米域的有序性，如通过单个聚集体偏振各向异性测量来测量。根据各个链成分的不同，这些聚集体从高度各向异性到几乎各向同性不等，分别促进或抑制链间耦合。从单链荧光寿命来看，我们证明这些结构导向的包含物有效地打断了苯并乙烯的共轭，使我们能够区分链间电子效应和超扩展共轭引起的效应。我们观察到含有广泛链间相互作用的聚集体的荧光光谱明显红移，表明 MEH-PPV 中的低能激子陷阱是相邻链段之间耦合相互作用的结果。这些结果证明了合成包含物方法的强大功能，不仅可以控制单链水平的性质，而且可以全面设计体电子性质。
