Polymer/fullerene bimolecular crystal formation has been investigated using a variety of conjugated polymers and fullerenes to understand the design rules that influence donor–acceptor interaction. Modifications of the polymer by varying the substitution side-chain position, density, and branching have demonstrated the importance of the “pocket” dimensions (free volume between side chains where the fullerene resides) for controlling intercalation. Yet the effect of pocket height has not been systematically explored because of the solubility limitations in polymers. In this report, we present an experimental investigation into the effect of the pocket height by synthesizing poly[2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene] dimers with varied side chain lengths and track the morphological changes of the dimer/fullerene blends using grazing-incidence X-ray scattering, thermal measurements, and photoluminescence quenching. We identify two regimes: (1) oligomers with side chains greater than or equal to heptyl (C7) form bimolecular crystals and (2) oligomers with less than or equal to hexyl (C6) form amorphous blends. This work provides the first observation of an order-to-disorder transition mediated by side-chain length in donor-fullerene intercalated blends.

中文翻译：

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打破双分子晶体：边链长度对低聚噻吩/富勒烯插层的影响

聚合物/富勒烯双分子晶体的形成已使用多种共轭聚合物和富勒烯进行了研究，以了解影响供体-受体相互作用的设计规则。通过改变取代侧链的位置，密度和支链对聚合物进行的改性已证明“口袋”尺寸（富勒烯所在的侧链之间的自由体积）对于控制插层的重要性。由于聚合物中的溶解度限制，尚未系统地研究袋高的影响。在本报告中，我们通过合成聚[2,5-双（3-烷基噻吩-2-基）噻吩并[3,2- b[噻吩]二聚体具有不同的侧链长度，并使用掠入射X射线散射，热测量和光致发光猝灭来跟踪二聚体/富勒烯共混物的形态变化。我们确定了两种机制：（1）侧链大于或等于庚基（C7）的低聚物形成双分子晶体，（2）小于或等于己基（C6）的低聚物形成无定形共混物。这项工作提供了由供体-富勒烯插层共混物中侧链长度介导的有序到无序过渡的首次观察。