Leng Siwei, Wex Brigitte, Chan Li Hsin, Graham Matthew J, Jin Shi, Jing Alexander J, Jeong Kwang-Un, Van Horn Ryan M, Sun Bin, Zhu Meifang, Kaafarani Bilal R, Cheng Stephen Z D
Institute of Polymer Science and Engineering, Department of Polymer Science, The University of Akron, Akron, Ohio 44325-3909, USA.
J Phys Chem B. 2009 Apr 23;113(16):5403-11. doi: 10.1021/jp810653z.
A series of conjugated compounds, 6,7,15,16-tetrakis(alkylthio)quinoxalino[2',3':9,10]phenanthro[4,5-abc]phenazine (TQPP-SC(n)) (n = 6, 8, 10, and 12), which display p-channel characteristics was synthesized. These materials show promise for use in liquid crystalline photovoltaic applications. To determine their applicability, the different phase structures and transitions of these compounds were studied with differential scanning calorimetry (DSC), polarized light microscopy (PLM), wide-angle X-ray diffraction (WAXD), selected area electron diffraction (SAED), and Fourier transform infrared spectroscopy (FT-IR). Using TQPP-SC(12) as a model compound, DSC and 1D WAXD results showed that this compound possesses four crystalline, but no liquid crystalline, phases. Based on structural results obtained from 2D WAXD experiments on oriented samples and SAED patterns from single crystals, the unit cell of the lowest temperature TQPP-SC(12) crystalline phase (K(1)) was determined to be monoclinic with dimensions of a = 1.87 nm, b = 0.53 nm, c = 3.51 nm, and beta = 96.2 degrees . With increasing temperature, the K(1) phase transformed to other crystalline phases which all were monoclinic with different crystallographic parameters. The arrangement of the TQPP-SC(12) rigid fused rings changed only slightly in these crystalline phases, yet the conformation of the alkyl chains attached to the rigid cores changed significantly at the phase transitions. For the other TQPP-SC(n) compounds, only two phase transitions could be identified. It was determined that the transition temperature can be tuned by modifying the attached alkyl chains at the four corners of the rigid fused rings. One-dimensional WAXD studies indicated that the condensed state phase transitions of these compounds were all crystal-crystal transitions. Although single crystals will provide the highest charge carrier mobility, they are very difficult to grow and incur a high cost in production. On the other hand, liquid crystalline phases are preferred for the ease of processing and reasonable performance in change carrier mobility. Therefore, in order to achieve liquid crystalline phases in these compounds, as desired for their application as organic photovoltaic materials, additional modifications to the alkyl chains and their locations are necessary.
合成了一系列具有p沟道特性的共轭化合物，即6,7,15,16-四（烷硫基）喹喔啉并[2',3':9,10]菲并[4,5-abc]吩嗪（TQPP-SC(n)）（n = 6、8、10和12）。这些材料有望用于液晶光伏应用。为了确定它们的适用性，采用差示扫描量热法（DSC）、偏光显微镜（PLM）、广角X射线衍射（WAXD）、选区电子衍射（SAED）和傅里叶变换红外光谱（FT-IR）研究了这些化合物的不同相结构和转变。以TQPP-SC(十二)为模型化合物，DSC和一维WAXD结果表明该化合物具有四个晶相，但没有液晶相。基于对取向样品的二维WAXD实验和单晶的SAED图谱获得的结构结果，确定最低温度的TQPP-SC(十二)晶相（K(1)）的晶胞为单斜晶系，尺寸为a = 1.87 nm、b = 0.53 nm、c = 3.51 nm，β = 96.2°。随着温度升高，K(1)相转变为其他晶相，这些晶相均为具有不同晶体学参数的单斜晶系。在这些晶相中，TQPP-SC(十二)刚性稠环的排列仅略有变化，但连接到刚性核上的烷基链的构象在相变时发生了显著变化。对于其他TQPP-SC(n)化合物，只能识别出两个相变。确定可以通过修饰刚性稠环四个角上连接的烷基链来调节转变温度。一维WAXD研究表明这些化合物的凝聚态相变均为晶-晶转变。虽然单晶将提供最高的电荷载流子迁移率，但它们很难生长且生产成本高昂。另一方面，液晶相因其易于加工和在载流子迁移率方面具有合理性能而更受青睐。因此，为了在这些化合物中实现液晶相，以满足其作为有机光伏材料的应用需求，有必要对烷基链及其位置进行额外修饰。
