Institute of Chemistry, Academia Sinica, 128 Section 2 Academia Road, Nankang, Taipei 11529, Taiwan.
Phys Chem Chem Phys. 2011 Dec 14;13(46):20704-13. doi: 10.1039/c1cp22535a. Epub 2011 Nov 3.
The charge mobility is a key property in many electro-optical materials, with charge transfer (CT) taking place in a solid matrix of molecules. Large intermolecular electronic interaction is one of the key factors for a good CT rate, which is dependent on both intra- and intermolecular structures. The connection of the molecular structure with the intermolecular CT property would facilitate the search for a new material with desirable CT property, but currently it is still quite limited by the lack of knowledge for intermolecular configurations. In the present work, we study factors influencing the intermolecular configurations, and subsequently the CT property, in tris(8-hydroxyquinolinato) aluminium(III) (AlQ(3)) from all currently available crystal structures. We found that there exists a pair of CH-π interactions in a good majority of the π-π stacked bimolecular configurations. Such CH-π and π-π interacting structures are also seen in the crystal structures of many other similar molecules. With both experimental and simulated structures, we show that the CH-π interaction stabilizes the bimolecular configurations, and drives the structure towards a region with a higher electron transfer coupling and lower hole transfer coupling. This effect likely affects the electron transport property of AlQ(3), since it is consistent with recent experimental results, where AlQ(3) analogs with their CH-π interaction blocked either require a higher operating voltage in light-emitting devices [Sapochak et al., J. Am. Chem. Soc., 2001, 123, 6300], or become bipolar in their charge mobilities [Liao et al., J. Am. Chem. Soc., 2009, 131, 763]. CH-π interaction is commonly seen in aromatic molecules, which are frequently used as building blocks in molecules for electro-optical applications. Our work points out a possible way to enhance the desired CT property in the design of new materials.
电荷迁移率是许多光电材料的关键性质，其中电荷转移（CT）发生在分子的固体基质中。大分子间的电子相互作用是良好 CT 速率的关键因素之一，这取决于分子内和分子间结构。将分子结构与分子间 CT 性质联系起来，有助于寻找具有理想 CT 性质的新材料，但目前由于对分子间构型的了解有限，这种方法仍然相当有限。在本工作中，我们研究了影响三（8-羟基喹啉）铝（III）（AlQ（3））分子间构型，进而影响 CT 性质的因素，从目前所有可用的晶体结构中进行研究。我们发现，在大多数π-π堆叠双分子构型中存在一对 CH-π 相互作用。在许多其他类似分子的晶体结构中也可以看到这种 CH-π 和π-π 相互作用的结构。通过实验和模拟结构，我们表明 CH-π 相互作用稳定了双分子构型，并使结构向具有更高电子转移耦合和更低空穴转移耦合的区域移动。这种效应可能会影响 AlQ（3）的电子输运性质，因为它与最近的实验结果一致，在这些实验中，其 CH-π 相互作用被阻断的 AlQ（3）类似物要么在发光器件中需要更高的工作电压[ Sapochak 等人，J. Am. Chem. Soc.，2001，123，6300]，要么在其电荷迁移率上表现出双极特性[Liao 等人，J. Am. Chem. Soc.，2009，131，763]。CH-π 相互作用在芳香族分子中很常见，这些分子经常被用作光电应用中分子的构建块。我们的工作指出了在设计新材料时增强所需 CT 性质的一种可能途径。
