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.