Interlayer Interactions as Design Tool for Large-Pore COFs

Abstract

Covalent organic frameworks (COFs) with a pore size beyond 5 nm are still rarely seen in this emerging field. Besides obvious complications like the elaborated synthesis of large linkers with sufficient solubility, more subtle challenges regarding large-pore COF synthesis, including pore occlusion and collapse, prevail. Here we present two isoreticular series of large-pore imine COFs with pore sizes up to 5.8 nm and correlate the interlayer interactions with the structure and thermal behavior of the COFs. By adjusting interlayer interactions through the incorporation of methoxy groups acting as pore-directing "anchors", different stacking modes can be accessed, resulting in modified stacking polytypes and, hence, effective pore sizes. A strong correlation between stacking energy towards highly ordered, nearlyeclipsed structures, higher structural integrity during thermal stress, and a novel, thermally induced phase transition of stacking modes in COFs was found, which sheds light on viable design strategies for increased structural control and stability in large-pore COFs.

Olefin Metathesis in Confinement: Towards Covalent Organic Framework Scaffolds for Increased Macrocyclization Selectivity

“…The pore size distribution (PSD) was determined from the adsorption branch by quenched solid density functional theory (QSDFT) based on the carbon model for cylindrical pores. It shows a narrow PSD around 4.8 nm, which is in good agreement with the structure model and closely related, isoreticular COFs [18] …”

“…Methoxy groups incorporated in the COF act as non-covalent anchors to achieve better layer registry and thus high porosity and large, well-defined pore sizes for this framework. [18] Imine formation during the initial COF synthesis was confirmed by FTIR analysis (Figure S7). The spectrum shows the absence of the prominent aldehyde C=O stretching band at 1674 cm À 1 and amine NÀ H stretching bands at 3355 cm À 1 and 3431 cm À 1 , corresponding to the starting materials, indicating full conversion into imine bonds.…”

“…This assumed model is based on previous findings for phenylphenanthridine based COFs and shows a good match when compared to the simulated patterns of an AA stacked model (Figure S10). [18] Rietveld refinement of the pattern with the assumed model yielded unit cell parameters (a = b = 58.824 Å and c = 7.3 Å) with a satisfying agreement factor (R wp = 7.10 %, R p = 4.88 %) (Figure 2). [19] Porosity of dHP-TAB COF was investigated by nitrogen physisorption measurements at 77 K, showing a type-IV isotherm, which is typical for mesoporous systems.…”

“…It shows a narrow PSD around 4.8 nm, which is in good agreement with the structure model and closely related, isoreticular COFs. [18] Next, the molecular catalyst RuCl 2 (N-mesityl-N-…”

“…The large‐pore COF system was chosen to accommodate the bulky catalyst and substrates and prevent pore blocking during immobilization and catalysis. Methoxy groups incorporated in the COF act as non‐covalent anchors to achieve better layer registry and thus high porosity and large, well‐defined pore sizes for this framework [18] …”