Nascimbeni Giulia, Wöll Christof, Zojer Egbert
Institute of Solid State Physics, NAWI Graz, Graz University of Technology, Petersgasse 16, 8010 Graz, Austria.
Institute of Functional Interfaces (IFG), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz Platz-1, 76344 Eggenstein-Leopoldshafen, Germany.
Nanomaterials (Basel). 2020 Dec 3;10(12):2420. doi: 10.3390/nano10122420.
In recent years, optical and electronic properties of metal-organic frameworks (MOFs) have increasingly shifted into the focus of interest of the scientific community. Here, we discuss a strategy for conveniently tuning these properties through electrostatic design. More specifically, based on quantum-mechanical simulations, we suggest an approach for creating a gradient of the electrostatic potential within a MOF thin film, exploiting collective electrostatic effects. With a suitable orientation of polar apical linkers, the resulting non-centrosymmetric packing results in an energy staircase of the frontier electronic states reminiscent of the situation in a pin-photodiode. The observed one dimensional gradient of the electrostatic potential causes a closure of the global energy gap and also shifts core-level energies by an amount equaling the size of the original band gap. The realization of such assemblies could be based on so-called pillared layer MOFs fabricated in an oriented fashion on a solid substrate employing layer by layer growth techniques. In this context, the simulations provide guidelines regarding the design of the polar apical linker molecules that would allow the realization of MOF thin films with the (vast majority of the) molecular dipole moments pointing in the same direction.
近年来，金属有机框架（MOF）的光学和电子性质越来越成为科学界关注的焦点。在此，我们讨论一种通过静电设计方便地调节这些性质的策略。更具体地说，基于量子力学模拟，我们提出一种利用集体静电效应在MOF薄膜内创建静电势梯度的方法。通过极性顶端连接体的合适取向，所得的非中心对称堆积导致前沿电子态的能量阶梯，这让人联想到pin光电二极管中的情况。观察到的静电势的一维梯度导致全局能隙的闭合，并且还使芯能级能量移动一个等于原始带隙大小的量。这种组装体的实现可以基于通过逐层生长技术以定向方式在固体衬底上制造的所谓柱撑层MOF。在这种情况下，模拟为极性顶端连接体分子的设计提供了指导方针，这将允许实现（绝大多数）分子偶极矩指向同一方向的MOF薄膜。
