Why covalent organic frameworks grow twisted on graphite
Veniero Lenzi1, Karol Strutyński1, Manuel Melle-Franco2
1CICECO-Aveiro Institute of Materials, Department of Chemistry, University of Aveiro, Aveiro, Portugal.
None:
Van der Waals 2D materials made of graphene and Covalent Organic Frameworks (COFs) show a large potential for advanced applications, such as in superconductive and twistronic devices. High-quality pyrene diboronic acid (PDBA) COFs have been recently achieved on graphite, showcasing highly reproducible twisted stackings and moiré superlattices. A fundamental understanding of the processes ruling the formation of these unexpected materials is yet lacking. Hereby, we address this issue by studying growing COFs at different twist angles with an ad-hoc hybrid molecular mechanics force field with near-DFT accuracy. This reveals that as PDBA COFs grow, the number of available thermodynamic minima decreases dramatically, which may effectively lock the COF in the unique twisted stacking found experimentally. In addition, the mobility on the surface is found to show large alterations with size and twist angle. We discuss how both findings are expected to play a fundamental role in the synthesis of twisted PDBA COFs monolayers on graphitic surfaces.
Related Concept Videos
02:18Network Covalent Solids
To break or to melt a covalent network solid, covalent bonds must be broken. Because covalent bonds are relatively strong, covalent network solids are typically...
02:11Conformations of Cyclohexane
The chair form is the most stable and derives its name from its resemblance to the “easy chair.” In the chair conformation, two carbon atoms are arranged out-of-plane — one above and one below, minimizing the torsional strain. In the chair form, the bond angle is very close to the ideal...
02:58Crystal Field Theory - Octahedral Complexes
To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
CFT focuses on...
02:46Crystal Field Theory - Tetrahedral and Square Planar Complexes
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...
01:17Ziegler–Natta Chain-Growth Polymerization: Overview
01:18Molecular Shapes
Two regions of electron density in a diatomic...