Synthesis, Electronic Structure, Molecular Packing/Morphology Evolution, and Carrier Mobilities of Pure Oligo-/Poly(alkylthiophenes)
Synthesis, Electronic Structure, Molecular Packing/Morphology Evolution, and Carrier Mobilities of Pure Oligo-/Poly(alkylthiophenes)
复制标题
DOI：
10.1021/ja3104796
复制
发表时间：
2013-01-16
影响因子：
15
通讯作者：
Briseno, Alejandro L.
中科院分区：
文献类型：
--
作者：
Zhang, Lei;Colella, Nicholas S.;Briseno, Alejandro L.
单分散的共轭低聚噻吩类化合物由于其独特的光学、光电和电荷传输特性而受到基础科学和应用科学的广泛关注。这些“低分子量”聚合物充当相应聚合物类似物的模型结构，其固有地是多分散的。在这里，我们报告了具有多达六个双十二烷基四噻吩（DDQT）结构单元重复单元（即，24个噻吩单元）。在达到有效共轭长度的点处，电子结构表现出与相应聚合物聚（3，3“-双十二烷基-四噻吩）（PQT-12）的收敛行为。二聚体（DDQT-2）的X-射线晶体结构分析表明，终端噻吩表现出顺式构象，类似于在三聚体（DDQT-3）中观察到的终端顺式构象。二聚体还表现出罕见的末端烷基侧链的弯曲，以防止与连接到核心噻吩的相邻氢的空间位阻。掠入射X射线散射测量揭示了从小分子样包装的薄膜中的聚合物样包装的形态演变，与有效共轭长度附近发生的形态转变。电荷传输测量表明，随着链长的减少，迁移率增加。我们将分子堆积和形态与电荷传输相关联，并确定载流子迁移率对结晶度和晶粒取向差最敏感。这表明分子量不是低分子量区域载流子迁移率提高的决定性因素，而是结晶度和面内晶体取向的程度。这些结果代表了一个根本性的进步，在了解共轭长度和载流子迁移率之间的关系，在oligophiophene半导体。
Monodispersed conjugated oligothiophenes are receiving attention in fundamental and applied science due to their interesting optical, optoelectronic, and charge transport properties. These "low molecular weight" polymers serve as model structures for the corresponding polymer analogues, which are inherently polydispersed. Here we report the synthesis, electronic structure, molecular packing/morphology, and charge transport properties of monodispersed oligothiophenes with up to six didodecylquaterthiophene (DDQT) building block repeat units (i.e., 24 thiophene units). At the point where the effective conjugation length is reached, the electronic structure showed convergence behavior to the corresponding polymer, poly(3,3 ''-didodecyl-quaterthiophene) (PQT-12). X-ray crystal structure analysis of the dimer (DDQT-2) showed that terminal thiophenes exhibit syn-conformations, similar to the terminal syn-conformations observed in the trimer (DDQT-3). The dimer also exhibits a rare bending of the terminal alkyl side chains in order to prevent steric hindrance with neighboring hydrogens attached to core thiophenes. Grazing incidence X-ray scattering measurements revealed a morphology evolution from small molecule-like packing to polymer-like packing in thin films, with a morphology transition occurring near the effective conjugation length. Charge transport measurements showed a mobility increase with decreasing chain length. We correlated the molecular packing and morphology to charge transport and determined that carrier mobilities are most sensitive to crystallinity and crystal grain misorientation. This indicates that molecular weight is not a decisive factor for improved carrier mobility in the low molecular weight region, but rather the degree in crystallinity and in-plane crystal orientation. These results represent a fundamental advancement in understanding the relationship between conjugation length and carrier mobilities in oligothiophene semiconductors.