Quantum Chemistry Insight into the Multifaceted Structural Properties of Two-Dimensional Covalent Organic Frameworks

2D covalent organic frameworks (COFs) possess a wide range of desirable mechanical and optoelectronic properties, rendering them a versatile compound class that is widely investigated in many areas of chemistry. However, experimental structure determination remains challenging as mostly inseparable isomers are measured while computational models mostly account for a very limited number of model structures, making the establishment of comprehensive structure-property relationships difficult. Thus, here, we go computationally beyond the conventional but insufficient description of eclipsed stacked COF building blocks. We emphasize the presence of a variety of stacking and structural motifs and investigate their impact on the electronic properties. Given the very large size of the investigated systems, we employ the fast and accurate tight-binding based semiempirical quantum mechanical (SQM) GFN-xTB method. Taking an imine-linked COF as a representative system, we discuss our structural, energetic, electronic, and spectroscopic results calculated at the periodic GFN1-xTB quantum chemistry level in comparison to experimental findings.

Automated summary

2D covalent organic frameworks (COFs) possess desirable mechanical and optoelectronic properties, but experimental structure determination remains challenging due to inseparable isomers and limited computational models. In this study, we go beyond the conventional description of COF building blocks and investigate the impact of different stacking and structural motifs on electronic properties. Using the SQM GFN-xTB method, we analyze the structural, energetic, electronic, and spectroscopic results of an imine-linked COF and compare them to experimental findings.