Pålsson Lars-Olof, Vaughan Helen L, Monkman Andrew P
Photonics Materials Institute, Department of Physics, Durham University, South Road, DH1 3LE Durham, United Kingdom.
J Chem Phys. 2006 Oct 28;125(16):164701. doi: 10.1063/1.2354473.
Two related poly(phenylene-vinylene) (PPV) light-emitting polymers have been investigated by means of polarized optical spectroscopy. The purpose of the investigation was to investigate the nature of the interactions in thin films and to examine what impact the difference in side chain structure and molecular weight in poly(2'-methoxy-5-2-ethyl-hexoxy)-1,4-phenylene vinylene (MEH-PPV) and poly(2-(3',7'-dimethyloctyloxy)-5-methoxy-1,4-phenylene-vinylene) (OC1C10-PPV) has on the electronic and optical properties of the two polymers. Aligning the polymers by dispersing them in anisotropic solvents and stretched films shows that the side chains have an impact on the relative orientations of the transition dipole moments. In anisotropic solvents the linear dichroism is larger for MEH-PPV than for the related polymer OC1C10-PPV, while in stretched films the opposite situation prevails. A lower polarization of the luminescence from OC1C10-PPV, relative to MEH-PPV, was also obtained independent of alignment medium used. The data therefore suggest that while mechanical stretching may align the OC1C10-PPV to a greater degree, the emitting species is distinct from the absorbing species. The circular dichroism (CD) spectra of both polymers undergo dramatic changes when the liquid phase and the solid state (film) are compared. The solution CD spectra shows no evidence of interchain interactions; instead the spectra of both systems indicate a helical conformation of the polymers. The CD spectra of films are dramatically different with the strong Cotton effect being observed. This points to the formation of an aggregate in the film, with an associated ground state interaction, an interchain species such as a physical dimer, or a more complex higher aggregate.
通过偏振光谱法对两种相关的聚（亚苯基亚乙烯基）（PPV）发光聚合物进行了研究。该研究的目的是探究薄膜中相互作用的本质，并考察聚（2'-甲氧基-5-（2-乙基己氧基）-1,4-亚苯基亚乙烯基）（MEH-PPV）和聚（2-（3',7'-二甲基辛氧基）-5-甲氧基-1,4-亚苯基亚乙烯基）（OC1C10-PPV）的侧链结构和分子量差异对这两种聚合物的电子和光学性质有何影响。通过将聚合物分散在各向异性溶剂中并拉伸薄膜来使聚合物取向，结果表明侧链对跃迁偶极矩的相对取向有影响。在各向异性溶剂中，MEH-PPV的线性二色性比相关聚合物OC1C10-PPV的大，而在拉伸薄膜中情况则相反。相对于MEH-PPV，OC1C10-PPV的发光偏振度较低，且与所使用的取向介质无关。因此，数据表明，虽然机械拉伸可能使OC1C10-PPV的取向程度更高，但发射物种与吸收物种不同。当比较液相和固态（薄膜）时，两种聚合物的圆二色性（CD）光谱都发生了显著变化。溶液CD光谱没有显示链间相互作用的迹象；相反，两个体系的光谱都表明聚合物呈螺旋构象。薄膜的CD光谱有很大不同，观察到了强烈的科顿效应。这表明在薄膜中形成了聚集体，伴有基态相互作用、链间物种如物理二聚体或更复杂的高级聚集体。
