Morphological Diversity in Nanoporous Covalent Organic Materials Derived from Viologen and Pyrene

Abstract

Adjustment of the morphology of covalent organic nanomaterials is a challenge but can be achieved by perturbing the planarity of the monomers used as core moieties in these polymers. Here we describe a templatefree Zincke reaction for the synthesis of covalent organic nanosheets (CONs) that stack several layers thick and of covalent organic tubes (COTs). Both materials contain the same viologen linker but different pyrene-based cores. Both polymeric materials are nanoporous, cationic, and highly stable in water, even in the presence of acid (1 M HCl) or base (1 M NaOH). Their porosity and ionic surfaces are responsible for high affinities and adsorption capacities for iodine vapor.Porous covalent organic polymers (COPs) are well known for their diverse applications in fields such as gas storage and separation, [1][2][3][4] catalysis, [5][6][7][8] sensing, [9,10] drug delivery, [11] and environmental remediation. [12] In order to design COPs with improved functionality, considerable research has been undertaken to understand the relationship between the morphologies and properties of these materials. [13][14][15] It has been observed that the morphology of COPs can be tuned by changing the symmetry of their constituent building blocks, but precise regulation of COP nanostructure remains a challenging task.Syntheses of covalent organic hollow tubes (COTs) and nanosheets (CONs) are of interest because their large surface areas facilitate the adsorption of small molecule guests. Porous, template-free COPs with uniform tube morphology have been used for device manufacturing [16] and catalysis, [17,18] but reports of the synthesis and application of this type of material remain scarce. Studies of covalent nanosheets are more prevalent, but, this type of material is obtained by either liquid phase exfoliation [19] or mechanical delamination, [20] and these two methods often result in low surface areas because the mechanical forces involved often cause pore blockage. In short, syntheses that rely on mechanical techniques for isolating nanosheets tend to be expensive and non-scalable and produce materials that have limited adsorption efficiency. Designing an efficient and green approach to the large-scale synthesis of porous CONs stacked several (or fewer) layers thick is an open challenge. [21] In general, porous COPs are synthesized from neutral building blocks, which limits the range of application for the materials. For example, neutral COPs are not optimal for the uptake of charged species, including toxic ionic guest molecules. To address this issue, we have begun to develop charged COPs that incorporate redox-active viologens and are capable of adsorbing iodine vapor, toxic dyes, and metal ions by anion exchange. [22,23] Despite their great potential, viologen-based COPs are still rarely documented in the literature, though Li et al. [24] have reported supramolecular organic frameworks (SOFs) that contain viologen struts and form in water.Herein, we report a one-pot, template-free solvothermal synthesis ...

Covalent Organic Polymers and Frameworks for Fluorescence-Based Sensors

“…Detecting leakages of such toxic species is essential to ensure a safe energy supply . Several COPs have been developed for remediation of iodine emissions − as well as for its detection through fluorescence. Friedel–Crafts − and related coupling reactions have often been used in generating COP sensors for iodine because they can easily generate fully sp 2 -conjugated systems that are fluorescent in nature and possess a high affinity for iodine (dipole–dipole interactions, ionic interactions with polyiodides).…”

Structural Approaches to Control Interlayer Interactions in 2D Covalent Organic Frameworks

“…Trabolsi and co‐workers [ 86 ] have described how the copolymerization of a viologen derivative with two different pyrene derivatives produced two viologen‐based covalent organic polymers. When using a tetraaniline pyrene derivative few‐layer covalent organic nanosheets were spontaneously formed.…”

Design Strategies and Redox-Dependent Applications of Insoluble Viologen-Based Covalent Organic Polymers

“…This could be because a water–ethanol mixture has been found to be an optimal solvent for the Zincke reaction for its ability to stabilize reaction intermediates most effectively, thereby allowing time for the self-correction mechanism . When 1,3,5-tris­(4-aminophenyl)­benzene was replaced by pyrene-based amines, crystallinity was not observed either, most likely due to the nonplanar structure of the precursor amines. Recently, use of a polyhedral oligomeric silsesquioxane core in the Zincke reaction performed in DMF under solvothermal conditions yielded a weakly crystalline material based on PXRD, but no structural model of the material was proposed …”