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Electron Transport over 2D Molecular Materials and Assemblies
Accounts of Chemical Research ( IF 16.4 ) Pub Date : 2024-08-20 , DOI: 10.1021/acs.accounts.4c00376 Shu Seki 1 , Rajendra Prasad Paitandi 1 , Wookjin Choi 1 , Samrat Ghosh 1 , Takayuki Tanaka 1
Accounts of Chemical Research ( IF 16.4 ) Pub Date : 2024-08-20 , DOI: 10.1021/acs.accounts.4c00376 Shu Seki 1 , Rajendra Prasad Paitandi 1 , Wookjin Choi 1 , Samrat Ghosh 1 , Takayuki Tanaka 1
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Two-dimensional (2D) molecular materials, in which the major interactions are confined in 2D planes with contrasted force fields acting in between the planes, have been key electronic functional materials since the past decade. Even without referring to the functionals of graphene-based systems, 2D electronic conjugated systems are expected to show extrawide dynamic ranges in electronic density of states (DOS) tuning, effective electron mass, electron mobility, and conductivity. A major advantage of 2D electronic systems is their compatibility with the ubiquitous electronic devices designed using planar structures, such as transistors and memories, which is associated with the utility of 2D active materials. The mobility of electrons in 2D systems is the key to their utility, and various conjugated molecular and 2D materials have been designed to optimize the mobility. This Account begins with an introduction for mobility assessment: using noncontact time-resolved microwave conductivity (TRMC) measurements as a technique to probe differential conductivity upon transient charge carrier injection into the materials. Electronic transport over 2D electronic materials such as graphenes, covalent organic frameworks (COFs), and metal–organic frameworks (MOFs) is discussed with a special emphasis on molecular building blocks, fine-tuning conducting species and linkages, topology of the framework, and controlling molecular doping. The superiority of β-ketoenamine-linked COF over imine-linked COF films in charge transport and dominant in-plane charge carrier mobility over out-of-plane mobility is also illustrated. Systematic molecular engineering of the building blocks of β-ketoenamine-linked COFs with varying degrees of donor–acceptor (D–A) conjugation, torsional angles, and reaction conditions resulted in the modulation of the efficiency of charge carrier generation/transport as well as exciton migration. The advantages of 2D systems are finally discussed in terms of the mobility interplaying with spatial arrangements of molecules as well as the substantial role of intermolecular interactions in stabilizing their condensed phases. The strong correlation between the dispersion of mobility and hierarchical intermolecular interactions sheds light on the way to overcome structural fluctuation on the optimization of charge transport in molecular electronic materials. The point of singularity in the dispersion at an intermolecular distance of d ∼ 0.3 nm is deduced from the overall mobility assessment in condensed phases of conjugated molecules, suggesting key roles of intermolecular electronic coupling: the new concept of electronic conjugation. Exceptional electronic coupling with relatively high charge carrier mobility was also observed, particularly in 2D spatial arrangements of chiral molecules in contrast to 3D analogues, where the reduction of gravitational density of the molecular condensates was impacting DOS: the Wallach’s rule. 2D electronic systems are strong candidates for the violation of the long-lasting Wallach’s rule in terms of DOS.
中文翻译：
二维分子材料和组件上的电子传输
二维（2D）分子材料，其中主要的相互作用被限制在二维平面内，并且在平面之间作用对比力场，自过去十年以来一直是关键的电子功能材料。即使不参考基于石墨烯的系统的功能，二维电子共轭系统也有望在电子态密度（DOS）调谐、有效电子质量、电子迁移率和电导率方面表现出超宽的动态范围。二维电子系统的一个主要优点是它们与使用平面结构设计的无处不在的电子设备（例如晶体管和存储器）兼容，这与二维活性材料的实用性相关。二维系统中电子的迁移率是其实用性的关键，并且设计了各种共轭分子和二维材料来优化迁移率。本帐户首先介绍迁移率评估：使用非接触式时间分辨微波电导率 (TRMC) 测量作为一种技术来探测瞬态电荷载流子注入材料时的微分电导率。讨论了石墨烯、共价有机框架 (COF) 和金属有机框架 (MOF) 等二维电子材料上的电子传输，特别强调分子构建块、微调导电物质和连接、框架拓扑以及控制分子掺杂。还说明了 β-酮烯胺连接的 COF 在电荷传输方面优于亚胺连接的 COF 薄膜，并且面内载流子迁移率优于面外迁移率。 具有不同程度的供体-受体（D-A）共轭、扭转角和反应条件的β-酮烯胺连接的COF的构建模块的系统分子工程导致了电荷载流子产生/传输效率的调节以及激子迁移。最后从与分子空间排列相互作用的迁移率以及分子间相互作用在稳定其凝聚相中的重要作用方面讨论了二维系统的优点。迁移率分散性与分级分子间相互作用之间的强相关性揭示了克服分子电子材料中电荷传输优化的结构波动的方法。从共轭分子凝聚相的整体迁移率评估中推导出分子间距离d ∼ 0.3 nm 处的分散奇点，表明分子间电子耦合的关键作用：电子共轭的新概念。还观察到具有相对较高载流子迁移率的特殊电子耦合，特别是在手性分子的 2D 空间排列中，与 3D 类似物相比，其中分子凝聚体的引力密度的降低正在影响 DOS：瓦拉赫法则。二维电子系统是违反 DOS 方面长期存在的瓦拉赫规则的有力候选者。
更新日期：2024-08-20
中文翻译：
二维分子材料和组件上的电子传输
二维（2D）分子材料，其中主要的相互作用被限制在二维平面内，并且在平面之间作用对比力场，自过去十年以来一直是关键的电子功能材料。即使不参考基于石墨烯的系统的功能，二维电子共轭系统也有望在电子态密度（DOS）调谐、有效电子质量、电子迁移率和电导率方面表现出超宽的动态范围。二维电子系统的一个主要优点是它们与使用平面结构设计的无处不在的电子设备（例如晶体管和存储器）兼容，这与二维活性材料的实用性相关。二维系统中电子的迁移率是其实用性的关键，并且设计了各种共轭分子和二维材料来优化迁移率。本帐户首先介绍迁移率评估：使用非接触式时间分辨微波电导率 (TRMC) 测量作为一种技术来探测瞬态电荷载流子注入材料时的微分电导率。讨论了石墨烯、共价有机框架 (COF) 和金属有机框架 (MOF) 等二维电子材料上的电子传输，特别强调分子构建块、微调导电物质和连接、框架拓扑以及控制分子掺杂。还说明了 β-酮烯胺连接的 COF 在电荷传输方面优于亚胺连接的 COF 薄膜，并且面内载流子迁移率优于面外迁移率。 具有不同程度的供体-受体（D-A）共轭、扭转角和反应条件的β-酮烯胺连接的COF的构建模块的系统分子工程导致了电荷载流子产生/传输效率的调节以及激子迁移。最后从与分子空间排列相互作用的迁移率以及分子间相互作用在稳定其凝聚相中的重要作用方面讨论了二维系统的优点。迁移率分散性与分级分子间相互作用之间的强相关性揭示了克服分子电子材料中电荷传输优化的结构波动的方法。从共轭分子凝聚相的整体迁移率评估中推导出分子间距离d ∼ 0.3 nm 处的分散奇点，表明分子间电子耦合的关键作用：电子共轭的新概念。还观察到具有相对较高载流子迁移率的特殊电子耦合，特别是在手性分子的 2D 空间排列中，与 3D 类似物相比，其中分子凝聚体的引力密度的降低正在影响 DOS：瓦拉赫法则。二维电子系统是违反 DOS 方面长期存在的瓦拉赫规则的有力候选者。
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