Oligo(2,5-bis(3-dodecylthiophen-2-yl)thieno[3,2-b]thiophene)s Tn and Tn-2CN (n = 4, 8, 12, 20, n represents the number of thiophene rings), which have H and CN end-groups, respectively, were synthesized, and the effect of chain-length and end-groups on their properties was studied. For both Tn and Tn-2CN, a red-shift of absorption spectra was observed as the chain length increased. Introduction of electron-withdrawing CN end-groups resulted in a remarkable red-shift of absorption spectra in both solution and film states for shorter oligomers (n = 4 and 8). However, for oligomers with n = 12 and 20, obvious red-shift of absorption spectra was only observed in the film state. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels were both lowered by introducing CN end-groups, and the level of reduction decreased with an increase of the chain length. Both the chain length and end-groups influenced the thin film microstructures of the oligomers as revealed by two-dimensional grazing incidence X-ray diffraction (2D-GIXD) and atomic force microscopy (AFM) studies. The oligomers with n = 4 and 8 stood on the substrates with a tilt angle, and the films of T4-2CN and T8-2CN were characterized with 3D crystal structures. In contrast, the oligomers with n = 12 and 20 adopted an edge-on arrangement with the long axes of the molecules parallel to the substrates, like polymeric counterparts. Compared to the films of T12 and T20, those of T12-2CN and T20-2CN comprised larger and more oriented crystal-domains to the substrates along with shorter lamellar distances. Charge-transport properties of the oligomers were influenced by both the chain length and end-groups due to their remarkable effect on the film morphology and packing structures. The film of T8-2CN combined three features: large domain sizes, low surface-roughness and diminished grain boundaries, and therefore exhibited the highest field-effect mobility.

中文翻译：

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寡（2,5-双（3-十二烷基噻吩-2-基）噻吩并[3,2- b ]噻吩）的合成与表征：链长和端基对其光学和电荷传输性能的影响†

寡（2,5-双（3-十二烷基噻吩-2-基）噻吩并[3,2- b ]噻吩）Tn和Tn-2CN（n = 4，8，12，20，n代表噻吩环的数量合成了分别具有H和CN端基的），并研究了链长和端基对其性能的影响。对于Tn和Tn-2CN，随着链长的增加，观察到吸收光谱的红移。吸电子的CN端基的引入导致较短的低聚物（n = 4和8）在溶液和薄膜状态下的吸收光谱均出现明显的红移。但是，对于具有n的低聚物＝ 12和20，仅在膜状态下观察到吸收光谱的明显红移。引入CN端基降低了最高占据分子轨道（HOMO）和最低未占据分子轨道（LUMO）的能级，并且还原水平随着链长的增加而降低。二维掠入射X射线衍射（2D-GIXD）和原子力显微镜（AFM）研究表明，链长和端基均影响低聚物的薄膜微观结构。n = 4和8的低聚物以倾斜角放置在基板上，并用3D晶体结构表征了T4-2CN和T8-2CN的薄膜。相反，具有n的低聚物= 12和20采用边缘排列，分子的长轴平行于底物，如聚合物对应物。与T12和T20的薄膜相比，T12-2CN和T20-2CN的薄膜具有更大，取向更强的晶域，且片层距离更短。低聚物的电荷传输性质受链长和端基的影响，这是由于它们对薄膜形态和堆积结构的显着影响。T8-2CN薄膜具有三个特征：较大的畴尺寸，低的表面粗糙度和减小的晶界，因此表现出最高的场效应迁移率。