Tenery Daeri, Gesquiere Andre J
NanoScience Technology Center, Department of Chemistry and CREOL, The College of Optics and Photonics, University of Central Florida, 12424 Research Parkway Suite 400, Orlando, FL 32826, USA.
Chemphyschem. 2009 Oct 5;10(14):2449-57. doi: 10.1002/cphc.200900413.
The emission of composite conjugated polymer (MEH-PPV)/fullerene (PCBM) nanoparticles is investigated by single particle spectroscopy (SPS), and changes in vibronic structure with nanoparticle composition are evaluated by means of a detailed Franck-Condon analysis. Consistent with previous reports we find that the emission spectra can be modeled as the superposition of two types of emitters, one with aggregate character and one with molecular character. Major findings from the fitting of the SPS data to a Franck-Condon model are that 1) the occurrence of each of the two types of emitters changes with nanoparticle composition to the point that no aggregate emitters are detected (at 50 wt% PCBM), 2) at the highest PCBM doping levels (75 wt% PCBM) aggregate emitters reappear due to nanoscale phase separation in the composite nanoparticles, 3) the molecular emitters show small Huang-Rhys factors that increase with PCBM doping, indicative of extensive delocalization and exciton migration that is reduced by the disorder introduced in the polymer material by PCBM doping and 4) the aggregate emitters show large Huang-Rhys factors, indicative of the localized nature of these energy trap sites, with a broad distribution of values of these Huang-Rhys factors. The latter observation suggests a broad heterogeneous distribution of aggregate morphologies in blended conducting polymer materials, which can be attributed to variations in polymer chain folding and stacking at the aggregate sites. The reported results obtained by the SPS approach show how blending conjugated polymers with fullerenes at various doping levels induces changes in interchain interactions and aggregate site density even at length scales below a few tens of nanometers that affect conjugated polymer material properties, an observation that has gone unnoticed in bulk studies of blended conjugated polymer films.
通过单粒子光谱法（SPS）研究了复合共轭聚合物（MEH-PPV）/富勒烯（PCBM）纳米粒子的发射，并通过详细的弗兰克-康登分析评估了纳米粒子组成引起的振动结构变化。与之前的报道一致，我们发现发射光谱可以建模为两种发射体的叠加，一种具有聚集特征，另一种具有分子特征。将SPS数据拟合到弗兰克-康登模型的主要发现是：1）两种发射体的出现随纳米粒子组成而变化，以至于在50 wt% PCBM时未检测到聚集发射体；2）在最高PCBM掺杂水平（75 wt% PCBM）时，由于复合纳米粒子中的纳米级相分离，聚集发射体重新出现；3）分子发射体显示出较小的黄-里斯因子，该因子随PCBM掺杂而增加，表明存在广泛的离域和激子迁移，而PCBM掺杂在聚合物材料中引入的无序会降低这种迁移；4）聚集发射体显示出较大的黄-里斯因子，表明这些能量陷阱位点具有局域性质，且这些黄-里斯因子的值分布广泛。后一观察结果表明，在混合导电聚合物材料中，聚集形态存在广泛的非均匀分布，这可归因于聚合物链在聚集位点处的折叠和堆积变化。通过SPS方法获得的报道结果表明，即使在几十纳米以下的长度尺度上，将共轭聚合物与富勒烯在不同掺杂水平下混合也会引起链间相互作用和聚集位点密度的变化，从而影响共轭聚合物材料的性能，这一观察结果在混合共轭聚合物薄膜体相研究中未被注意到。
