Ester David F, McKearney Declan, Herasymchuk Khrystyna, Williams Vance E
Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada.
Materials (Basel). 2019 Jul 19;12(14):2314. doi: 10.3390/ma12142314.
Liquid crystalline self-assembly offers the potential to create highly ordered, uniformly aligned, and defect-free thin-film organic semiconductors. Analogues of one of the more promising classes of liquid crystal semiconductors, 5,5"-dialkyl-α-terthiophenes, were prepared in order to investigate the effects of replacing the central thiophene with either an oxadiazole or a thiadiazole ring. The phase behaviour was examined by differential scanning calorimetry, polarized optical microscopy, and variable temperature x-ray diffraction. While the oxadiazole derivative was not liquid crystalline, thiadiazole derivatives formed smectic C and soft crystal lamellar phases, and maintained lamellar order down to room temperature. Variation of the terminal alkyl chains also influenced the observed phase sequence. Single crystal structures revealed the face-to-face orientation of molecules within the layers in the solid-state, a packing motif that is rationalized based on the shape and dipole of the thiadiazole ring, as corroborated by density functional theory (DFT) calculations. The solution opto-electronic properties of the systems were characterized by absorption and emission spectroscopy, cyclic voltammetry, and time-dependent density functional theory (TD-DFT).
液晶自组装为创建高度有序、均匀排列且无缺陷的薄膜有机半导体提供了潜力。为了研究用恶二唑或噻二唑环取代中心噻吩的影响，制备了一类更有前景的液晶半导体——5,5”-二烷基-α-三联噻吩的类似物。通过差示扫描量热法、偏光显微镜和变温X射线衍射研究了其相行为。虽然恶二唑衍生物不是液晶，但噻二唑衍生物形成了近晶C相和软晶层状相，并在室温下保持层状有序。末端烷基链长的变化也影响了观察到的相序列。单晶结构揭示了固态中层内分子的面对面取向，这种堆积模式基于噻二唑环的形状和偶极得到合理解释，密度泛函理论（DFT）计算也证实了这一点。通过吸收和发射光谱、循环伏安法以及含时密度泛函理论（TD-DFT）对体系的溶液光电性质进行了表征。
