Toward Coarse-Grained Elasticity of Single-Layer Covalent Organic Frameworks

Abstract

Two-dimensional covalent organic frameworks (2D COFs) are an interesting class of 2D materials since their reticular synthesis allows the tailored design of structures and functionalities. For many of their applications, the mechanical stability and performance is an important aspect. Here, we use a computational approach involving a density-functional based tight-binding method to calculate the in-plane elastic properties of 45 COFs with a honeycomb lattice. Based on those calculations, we develop two coarse-grained descriptions: one based on a spring network and the second using a network of elastic beams. The models allow us to connect the COF force constants to the molecular force constants of the linker molecules and thus enable an efficient description of elastic deformations. To illustrate this aspect, we calculate the deformation energy of different COFs containing the equivalent of a Stone−Wales defect and find very good agreement with the coarse-grained description.

Highly Flexible Dielectric Films from Solution Processable Covalent Organic Frameworks**

“…[45,52] Indeed, most reports of conventional tensile testing studies involving 2D COFs have been carried out on samples of COF/polymer composites rather than free-standing COF films for these reasons. [9,20] The morphology of the synthesized films was analyzed using scanning electron microscopy (SEM) (Figures 4A, 4B, and S18). Both the COF-PEO-3 and TFP-PEO-3 films have Angewandte Chemie a smooth, dense, and continuous appearance.…”

“…Since the initial discovery of covalent organic frameworks (COFs) in 2005, [1] they have evolved into a promising class of materials for applications in energy storage, [2] molecular separation, [3,4] and heterogeneous catalysis, [5] due to their crystallinity, high surface area, and wide scope of functionality. While the permanent porosity of COFs has drawn the most attention for application development, two-dimensional (2D) COFs have recently gained interest for use in other types of applications such as dielectric devices [6,7] and ballistic materials, [8][9][10] where other types of 2D materials (e.g., graphene) [11] have often been a focus. While most classes of 2D materials face challenges in their synthesis and scalability, [12] 2D COFs can be produced as highly crystalline polymers, even in bulk quantities.…”

Highly Flexible Dielectric Films from Solution Processable Covalent Organic Frameworks**

“…Despite this impressive performance the observed scale is very small, and defects or imperfections formed during the casting of the whole film can directly affect the bulk mechanical performance of the material [45,52] . Indeed, most reports of conventional tensile testing studies involving 2D COFs have been carried out on samples of COF/polymer composites rather than free‐standing COF films for these reasons [9,20] …”

“…[45,52] Indeed, most reports of conventional tensile testing studies involving 2D COFs have been carried out on samples of COF/polymer composites rather than free-standing COF films for these reasons. [9,20] The morphology of the synthesized films was analyzed using scanning electron microscopy (SEM) (Figures 4A, 4B, and S18). Both the COF-PEO-3 and TFP-PEO-3 films have a smooth, dense, and continuous appearance.…”

Early-Career and Emerging Researchers in Physical Chemistry Volume 2

“…The translation from atomistic models, with small system sizes, to coarse-grained models and prediction of material properties of extended structures represents a challenging area for computational chemistry. In their work, Croy et al 23 develop this connection for the case of 2D covalent organic frameworks. In particular, they show that mechanical properties of the frameworks can be related to the properties of the individual organic building blocks�a result that a chemist might have always dreamed of but like many dreams can be fiendishly difficult to realize.…”