Engineering the Electronic and Thermal Properties of Two-Dimensional Covalent Organic Frameworks
Engineering the Electronic and Thermal Properties of Two-Dimensional Covalent Organic Frameworks
复制标题
DOI：
10.1021/acs.jpcc.3c00652
复制
发表时间：
2023-06
期刊：
影响因子：
--
通讯作者：
M. A. Rahman;S. Thakur;P. Hopkins;A. Giri
中科院分区：
文献类型：
--
作者：
M. A. Rahman;S. Thakur;P. Hopkins;A. Giri
二维共价有机骨架（2D COF）是一类具有高孔隙率和大表面积的模块化聚合物晶体。它们的可调微观结构（具有广泛的分子构建块选择）为它们的自下而上设计和潜在的可定制物理特性提供了机会。在这项工作中，通过结合密度泛函理论（DFT）计算和分子动力学（MD）模拟，我们研究了不同的分子官能团和不同的孔隙率对二维COFs的电子和热性质的影响。更具体地说，通过对24种不同的二维COF进行DFT计算，我们证明了决定其带隙的主要描述符之一是其质量密度或网络孔隙率。此外，我们还发现，形成节点的特定官能团可以导致更大的电荷密度局部化，从而导致更宽的带隙。通过进行MD模拟，调查他们的热性能，我们表明，（类似于他们的电子性能）质量密度也是决定热传导的主要因素之一，其中较高的密度与相对较高的热导率沿着的二维片。我们的光谱能量密度计算提供了这些材料的高度非谐性质的见解。我们发现，增加孔隙率导致更大的非谐相互作用，从而降低这些材料的热导率。类似于它们的电子带隙，形成2D COF的节点在决定它们的热导率方面也具有显著的贡献，其中较大的节点（伴随着较高的密度）通常导致2D COF中相对较高的热导率。两者合计，从2D COF中的构建块的变化中产生的电子和热性质的变化提供了对微观热力学中的根本变化的见解，这些变化是由于系统地改变其分子结构而产生的。因此，我们的研究提供了一个蓝图的战略合成的二维COF与“用户定义的”电子
: Two-dimensional covalent organic frameworks (2D COFs) are a class of modular polymeric crystals with high porosities and large surface areas. Their tunable microstructure (with a wide array of choices for the molecular building block) provides the opportunity for their bottom-up design and potentially tailorable physical properties. In this work, through combined density functional theory (DFT) calculations and molecular dynamics (MD) simulations, we study the influence of different molecular functional groups and varying porosities on the electronic and thermal properties of 2D COFs. More specifically, by performing DFT calculations on 24 different 2D COFs, we demonstrate that one of the main descriptors dictating their band gaps are their mass densities or network porosities. Furthermore, we also find that specific functional groups forming the nodes can lead to larger localization of charge densities resulting in wider band gaps. By performing MD simulations to investigate their thermal properties, we show that (similar to their electronic properties) mass density is also one of the main factors dictating heat conduction, where higher densities are associated with relatively higher thermal conductivities along the 2D sheets. Our spectral energy density calculations provide insights into the highly anharmonic nature of these materials. We find that increasing porosities lead to larger anharmonic interactions and thus reduced thermal conductivities in these materials. Similar to their electronic band gaps, the nodes forming the 2D COFs also have a significant contribution in dictating their thermal conductivities with bigger nodes (accompanied by higher densities) generally resulting in relatively higher thermal conductivities in 2D COFs. Taken together, the resulting changes in the electronic and thermal properties from variations in the building blocks in 2D COFs lend insights into fundamental changes in the microscopic thermodynamics that arise from systematically changing their molecular structure. Therefore, our study provides a blueprint for the strategic syntheses of 2D COFs with “user-defined” electronic