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Conformation and dynamics of conjugated polymers: A single-molecule study

共轭聚合物的构象和动力学：单分子研究

基本信息

批准号：
18340123
负责人：
VACHA Martin
金额：
$ 8.6万
依托单位：
Tokyo Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2006
资助国家：
日本
起止时间：
2006 至 2007
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-18340123/
关键词：
Single-molecule detection Conjugated polymers Polymer conformation

项目摘要

We use single-molecule spectroscopy to study the conformation and related photophysics of the conjugated polymer MEH-PPV dispersed in spin-coated thin-film matrices. The conformation is measured via the polymer chain absorption anisotropy (absorption ellipsoid ratio r) using a novel fluorescence microscopic method. The method is based on alternative excitation of the sample with far-field epi-fluorescence and near-field total internal reflection modes. Polarization modulated fluorescence from individual molecules is fitted with theoretical expressions to obtain the shape and orientation of the absorption ellipsoid for each chain. A coarse-grain molecular dynamics (MD) is further used to simulate the actual conformations corresponding to the measured absorption ellipsoids. We found that MEH-PPV individual chains can attain a single form of a collapsed conformation in poor-solvent matrices (Zeonex), or can coexist in two forms of extended conformations in good-solvent matrices (PS). The … More MD simulations completely reproduce the experimental results when the factors of solvent, chemical defects and spin-coating conditions are included. The defect cylinder conformation observed in Zeonex explains the photophysical properties of emission intermittency and fluorescence spectra distributions. The two defect-coil-type conformations observed in PS correspond well with the two types of intermittency behavior and with the bi-modal spectral distributions observed. Moment analysis of the MD simulation results provides a link between the two conformation forms and the different photophysical properties. The work on MEH-PPV is further complemented by the study of a graft copolymer consisting of a polythiophene backbone and polystyrene branches. The presence of the branches prevents the molecule from forming a collapsed globule-like conformation. Polythiophenes with grafted PS branches (PT-PS) and without the branches (PT-R) show markedly different photophysical properties. Emission intensity of the PT-PS molecules decays gradually due to photobleaching. In PT-R the emission intensity oscillates between the background and one intensity level before one-step photobleaching takes place. The blinking and bleaching behavior of the PT-R polymer is due to the fact that emission of the chain proceeds from one or a few conjugated segments where the energy is quickly localized after absorption. The continuous decrease of emission intensity in case of PT-PS is a result of each segment emitting independently. The emission properties of the two polymers are further characterized by measuring the single molecule emission anisotropy ratio, the histogram of which shows a peak at 0 anisotropy for PT-PS and minimum at 0 for PT-R, and by studying the time-evolution of fluorescence spectra of individual molecules. Less

我们利用单分子光谱学研究了共轭聚合物MEH-PPV在旋涂薄膜基质中的构象和相关的光物理性质。使用一种新的荧光显微镜方法，通过高分子链的吸收各向异性(吸收椭球比r)来测量构象。该方法基于样品的远场外荧光和近场全内反射模式的交替激发。将单个分子的偏振调制荧光与理论公式进行了拟合，得到了每个链的吸收椭球的形状和取向。进一步使用粗粒分子动力学(MD)模拟了与测量的吸收椭球相对应的实际构象。我们发现，MEH-PPV单链可以在弱溶剂基质(Zeonex)中获得单一形式的折叠构象，也可以在良溶剂基质(PS)中以两种形式的扩展构象共存。The…在考虑了溶剂、化学缺陷和旋涂条件等因素的情况下，更多的分子动力学模拟完全再现了实验结果。Zeonex中观察到的缺陷圆柱体构象解释了发射间歇的光物理性质和荧光光谱分布。在PS中观察到的两种缺陷线圈构象与两种类型的间歇行为以及观察到的双峰谱分布很好地对应。分子动力学模拟结果的矩分析提供了两种构象形式和不同的光物理性质之间的联系。对MEH-PPV的研究进一步补充了由聚噻吩基和聚苯乙烯支链组成的接枝共聚物的研究。支链的存在阻止了分子形成坍塌的球状构象。具有接枝PS支化结构(PT-PS)和不带支化结构(PT-R)的聚噻吩光物理性能有明显的差异。由于光漂白，PT-PS分子的发光强度逐渐衰减。在PT-R中，在一步光漂白发生之前，发射强度在背景和一个强度水平之间振荡。PT-R聚合物的闪烁和漂白行为是由于链的发射来自一个或几个共轭链段，这些链段的能量在吸收后迅速局部化。在PT-PS的情况下，发射强度的不断降低是每个分段独立发射的结果。通过测量PT-PS的单分子发射各向异性比，直方图显示PT-PS在0各向异性处有峰值，PT-R在0处有极小值，并通过研究单个分子的荧光光谱的时间演化来进一步表征这两种聚合物的发射性能。较少