Functional π-Conjugated Two-Dimensional Covalent Organic Frameworks

Abstract

Fingerprints of π-conjugated compounds are ubiquitous in nature and play a crucial part in human existence. For instance, cis-retinal, an endogenous π-conjugated molecule present in the eye, performs a vital role in the function of visual perception. π-Conjugated molecules have also received a great deal of attention owing to their intriguing optical properties and created a surge in optoelectronics. Varieties of π-conjugated molecules/oligomers have been developed and explored for a number of applications such as organic lightemitting diodes (OLEDs), organic field-effect transistors (OFETs), organic photovoltaics (OPVs), and sensors, among others. While the extended πdelocalization in one-dimensional (1D) polymers versus oligomers produce superior optical and electronic properties, further extension of π-delocalization to the second dimension (2D) is expected to give rise even more intriguing properties as revealed by theoretical studies. As a matter of fact, graphene is the best example of 2D-conjugated polymers, but its zero-band-gap behavior is a major impediment for semiconducting applications. In contrast, it was challenging to prepare 2D crystalline polymers until the discovery of boroxine/boronate ester linked covalent organic frameworks (COFs) by Yaghi and co-workers. COFs are a new class of porous crystalline polymers in which organic building blocks are held together by covalent bonds. These polymers exhibit potential applications in gas storage, energy storage, photocatalyst, heterogeneous catalysis, sensors, etc. However, the first π-conjugated COF was realized in 2009 via the introduction of imine linker (−CN−) between the building blocks. Since then, wide varieties of COFs with various πdelocalization promoting spacers have been developed and explored their electronic and optical properties and pertinent applications. In this review, we will highlight the importance of 2D π-conjugated COFs and their achievements in developing novel functionalities.

Application of Metal-Organic Frameworks and Covalent Organic Frameworks as (Photo)Active Material in Hybrid Photovoltaic Technologies

“…Additionally, the investigated MOFs exhibit tunable luminescence (from blue to yellow to white) as a function of temperature. These very interesting features could open the doors to the application of MOF in different fields, e.g., light emitting electrochemical cells/diodes, LEEC [144] or LED [145], respectively [146].…”

Towards the room-temperature synthesis of covalent organic frameworks: a mini-review

“…On the other hand, the presence of hydrogen bonding and p-p interactions in COFs improves the interactions and adsorption capacity of COFs. Hence, the flexible structure, high stability, and also high adsorption capacity make COFs as amazing platforms for use in different fields including catalysts [9,10], semiconductors [11,12], sensors [13,14], pollutant treatment [15,16], separation science [7,17], and other applications [18,19]. After the year 2007 that Yaghi and co-workers as pioneers in the synthesis of COFs introduced the first COFs, many efforts have been done for the preparation of different COFs and their applications.…”

Adsorption Properties of Hydrated Cr3+ Ions on Schiff‐base Covalent Organic Frameworks: A DFT Study

“…Pioneering work by Yaghi's group in 2005 paved the way for covalent organic frameworks (COFs), which are crystalline polymers integrated by the light elements (C, N, H, O, and B) . Since then, the well‐defined nanostructures and tunable properties drive it to be a hotspot of material science, owning enormous applications in the fields of catalysis, electrodes, sensors, and separation . The synthesis of COFs planes is principally based on the dynamic covalent chemistry, where the reversible covalent bonds are formed at the thermodynamic minimum, which can be achieved via the error‐correction during the polymerization process .…”

“…Since then, the well‐defined nanostructures and tunable properties drive it to be a hotspot of material science, owning enormous applications in the fields of catalysis, electrodes, sensors, and separation . The synthesis of COFs planes is principally based on the dynamic covalent chemistry, where the reversible covalent bonds are formed at the thermodynamic minimum, which can be achieved via the error‐correction during the polymerization process . Among various condensation methods, the Schiff‐base reaction between the aldehyde and the amine derivatives has been extensively explored in the synthesis of COFs materials ascribing to the intriguing properties obtained, which also allow them to be the promising candidates as adsorbents in the extraction conditions .…”

“…[5] The synthesis of COFs planes is principally based on the dynamic covalent chemistry, where the reversible covalent bonds are formed at the thermodynamic minimum, which can be achieved via the error-correction during the polymerization process. [5] Among various condensation methods, the Schiff-base reaction between the aldehyde and the amine derivatives has been extensively explored in the synthesis of COFs materials ascribing to the intriguing properties obtained, which also allow them to be the promising candidates as adsorbents in the extraction conditions. [6] For example, a type of hydrazone-linked COFs materials (TpODH) was synthesized and possessed relatively high adsorption capacities for Cu(II) (324 mg g À 1 ) and Hg(II) (1692 mg g À 1 ), respectively, ascribing to the high affinities between imide groups and metal ions.…”