Polymer Science and Engineering Division, CSIR-National Chemical Laboratory, Pune 411008, Maharashtra, India.
ACS Appl Mater Interfaces. 2013 Aug 14;5(15):7086-93. doi: 10.1021/am401379a. Epub 2013 Jul 12.
Small molecules and oligomers can be synthesized with very high purity and precise molecular weights, but they often do not form uniform thin films while processed from solution. Decreased intermolecular contacts between the small molecules are another disadvantage. To increase the intermolecular contacts in small molecules, we have chosen i-indigo, as one of the conjugated molecular units. The electron poor i-indigo has been connected with electron rich triphenylamine to synthesize a donor-acceptor-donor type small molecule. The propeller shaped triphenylamine helps to increase the solubility of the small molecule as well as isotropic charge transport. The intermolecular spacing between the molecules has been found to be low and did not vary as a function of thermal annealing. This implies that the intermolecular contacts between the small molecules are enhanced, and they do not vary as a function of thermal annealing. Organic field effect transistors (OFET) fabricated using a small molecule exhibited a hole carrier mobility (μ) of 0.3 cm(2)/(V s) before thermal annealing. A marginal increase in μ was observed upon thermal annealing at 150 °C, which has been attributed to changes in thin film morphology. The morphology of the thin films plays an important role in charge transport in addition to the intermolecular spacing that can be modulated with a judicious choice of the conjugated molecular unit.
小分子和低聚物可以非常高的纯度和精确的分子量合成，但它们往往不形成均匀的薄膜，而从溶液中处理。小分子之间的分子间接触减少是另一个缺点。为了增加小分子之间的分子间接触，我们选择了吲哚，作为共轭分子单元之一。电子缺乏的吲哚与富电子的三苯胺连接，合成了供体-受体-供体型小分子。螺旋桨状的三苯胺有助于增加小分子的溶解度和各向同性电荷输运。发现分子间的间距很低，并且不随热退火而变化。这意味着小分子之间的分子间接触增强，并且不随热退火而变化。使用小分子制造的有机场效应晶体管 (OFET) 在热退火之前表现出 0.3 cm(2)/(V s) 的空穴载流子迁移率 (μ)。在 150°C 下热退火时观察到 μ 略有增加，这归因于薄膜形貌的变化。除了可以通过明智地选择共轭分子单元来调节的分子间间距之外，薄膜的形态在电荷输运中起着重要作用。
