Knitting the layers of two-dimensional covalent organic framework with one-dimensional polymer to make conducting quasi-three-dimensional architecture

Abstract

The present disclosure provides a process for synthesizing a cross-linked covalent organic framework (COF) in which polypyrrole chains connect the two-dimensional (2D) COF layers through covalent bonds via post-synthetic modifications to form quasi-three-dimensional (quasi-3D) COF with improved electronic conductivity over its 2D COFs without the loss of 5 crystallinity. Interlayer cross-linking improves the layer alignment leading to a decrease in the band gap and an increase in inter-layer charge mobility or electronic conductivity of the 3D COFs. The structural robustness of COFs is crucial for it to qualify for several practical applications. The 3D COFs obtained by the presently claimed process display remarkable improvement of crystallinity evidenced through SAED (Selected area electron diffraction) 0 pattern and lattice fringes in high-resolution transmission electron microscopy (HRTEM) which results in improved electronic conductivity.

Description

KNITTING THE LAYERS OF TWO-DIMENSIONAL COVALENT ORGANIC FRAMEWORK WITH ONE-DIMENSIONAL POLYMER TO MAKE CONDUCTING QUASI-THREE-DIMENSIONAL ARCHITECTUREFIELD OF THE INVENTION

[0001] The present disclosure relates to a method of converting two dimensional covalent organic frameworks (2D COFs) into a quasi three dimensional covalent organic frameworks (3D COFs). The present disclosure also provides 3D COFs without loss of crystallinity and with improved electronic conductivity. The 3D COF has enormously improved crystallinity, and the lattice fringes and the highly ordered SAED pattern.BACKGROUND OF THE INVENTION

[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.

[0003] Converting 2D layered COFs into more robust and porous 3D architectures is a target of immense interest due to the numerous avenues that can benefit from 3D COFs. To the best of our knowledge, till date, there has been no reported method that is controlled enough to convert the 2D COF into more ordered (crystalline) 3D COF. For example, Haidar et al. [Adv. Energy Mater. 2022, 12, 2200754] incorporated chains of polypyrrole in a polyamide- based COF to achieve 1000-fold improvement in electronic conductivity, but there was no true control on the extent of polypyrrole loading and the method cannot proffer its loading exclusively into the pore in a stoichiometric fashion. Meanwhile, Jin et al. [J. Am. Chem. Soc. 2023, 145, 11, 6507-6515] reported a strategy to cross-link the layers of 2D COF by polyethylene glycol (PEG) or alkyl chains through covalent bonds and achieved 3D architecture of 2D COF. But the structural information of the 3D form is limited and there is no electronic activity considered. In a very recent work, Xiao et al. [J. Am. Chem. Soc. 2023, 145, 25, 13537-13541] converted 2D COF into 3D by combining cross-linking trialdehyde with tetramethyl-phenylenedimaine in place of phenylenediamine, giving rise to interdigitated 3D lattice.

[0004] Covalent Organic Frameworks (COFs) are best described as crystalline organic polymers. There are numerous 2D COFs and a few 3D COFs reported to date. While theformer is constructed from readily available aromatic building units, the latter can be prepared from selected functionalized tetrahedral building units, which are expensive. Intrinsically the 3D COFs are more porous and can have higher stability. The lack of stability in the 2D COF arises from the slippage of layers triggered by crystallinity loss and porosity loss.

[0005] COF offers excellent promise in diverse applications in gas storage, charge storage, catalysis etc. In all these aspects, converting the 2D COF into 3D ones can dramatically improve its performance. Of the few methods identified to convert 2D COFs into 3D, the third-direction ordering is achieved by highly flexible, stoichiometrically uncontrolled units. This gives no control, and the conjugation of the system is not preserved. Losing conjugation means losing electronic conduction, which is key to some of the major applications. Although cross-linking COF layers to form 3D structures are present, the use of any 1-D ordered conjugated polymer chains to cross-link COF layers without loss of crystallinity and with improved electronics is not yet known in the art. Thus given the abundance of 2D COFs, coming up with a controlled route that can help convert it into conjugated electronically conductive 3D COF is extremely valuable and a need of the art in COF.

[0006] Thus, there is immense interest in devising versatile approaches towards forming 3D COFs, but the ordering in the third-dimension has not been possible. Along these lines, it would be exciting to define an approach to convert 2D COF into conjugated 3D one and demonstrate its impact on relevant applications.OBJECTIVES OF THE INVENTION

[0007] An object of the present disclosure is to provide a method of converting 2D COFs into quasi 3D COFs.

[0008] Another objective of the present disclosure is to provide a 3D COFs without loss of crystallinity and with improved electronic conductivity.

[0009] Another objective of the present disclosure is to provide a clear well- controlled route for converting 2D COF into 3D COF by covalently knitting the organic layers of the 2D COF using polymer chains.

[0010] Another objective of the present disclosure is to provide a controlled route to covalently knitting the layers of 2D or layered polymer by conjugated polymeric chainsleading to new out-of-plane conduction pathway. Increased degree of conjugation in the overall 3D system.

[0011] Another objective of the present disclosure is to convert 2D non-conducting COF into highly conjugated 3D conducting COF.

[0012] Yet another objective of the present disclosure is to provide a process for connecting organic COF layers covalently through polypyrrole chains or covalently linking polypyrrole chains to the 2D COF layers to generate a 3D architecture with high degree of crystallinity and simultaneously creating a new out-of-plane or cross-linking conduction pathway.SUMMARY OF THE INVENTION

[0013] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in Detailed Description section. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0014] The present invention relates to a process for synthesizing a cross-linked COF in which polypyrrole chains connect the two-dimensional (2D) COF layers through covalent bonds via post-synthetic modifications to form quasi-three-dimensional (qua-si-3D) COF with improved electronic conductivity and the structural robustness of covalent organic frameworks (COFs).

[0015] An aspect of the present invention is directed to a process of converting two dimensional covalent organic frameworks (2D COFs) into a quasi three dimensional covalent organic frameworks (3D COFs) having out-of-plane, covalently cross-linking conduction pathway comprising the steps of: a) reacting 0.15mmol to Imol 2D COFs (COF20-NH2) having free amine groups with a solvent in the presence of 10 mol % catalyst by refluxing under N2atmosphere for 6 h to 12 h to obtain COFs wherein the free amine groups are selectively converted into pyrrole units (COF20-Pyr) and COF20-Pyr is obtained in a crystalline form; b) filtering the COF20-Pyr product of step (a) obtained as a dark brown powder;(c) washing the filtered COF20-Pyr product of step (b) with acetone, methanol and tetrahydrofuran(THF) ;d) drying the washed product of step (c) in air under a temperature ranging from 23 °C to 28°C, and e) subjecting the dried 2D COF20-Pyr obtained in step (d) to conversion to 3D COFs in the presence of an oxidizing agent and a solvent at a temperature in the range from 23°C to -20°C for a time period in the range from 24 h to 120 h to obtain the polypyrrole pillared or knitted 3D COFs (COF20-Ppy).

[0016] In another aspect of the present invention, the solvent in step (a) of the process is selected from a group consisting of water, tetrahydrofuran, ethylacetate, ethanol, acetonitrile, dichloromethane and combinations thereof.

[0017] In another aspect of the present invention, the solvent in step (a) is 0.45 mmol to 3 mol of 2,5 -dimethoxy tetrahydrofuran in acetonitrile.

[0018] In another aspect of the present invention, the process in step (a) is carried out at a temperature in the range from 40°C to 100°C.

[0019] In another aspect of the present invention, the process of step (a) is carried out in acetonitrile at 60°C for a time period in the range from 2 h to 6 h to obtain a 2D COF20-Pyr.

[0020] In another aspect of the present invention, the catalyst in step (a) of the process is selected from a group consisting of CuC12.2H2O, AuC13.hydrate, RuC13.hydrate and combinations thereof.

[0021] In another aspect of the present invention, the solvent in step (e) of the process is hexane or acetonitrile.

[0022] In another aspect of the present invention, the conversion of step (e) of the process is carried out at -16°C for a time period of 12 h to obtain the polypyrrole pillared or knitted 3D COFs (COF20-PPy).

[0023] In another aspect of the present invention, the oxidizing agent in step (e) of the process is selected from a group consisting of iodine, ammonium persulfate, ferric chloride and combinations thereof.

[0024] In another aspect of the present invention, the oxidizing agent in step (e) of the process is present in an amount ranging from 0. 1 mmol to 1 mmol.

[0025] In another aspect of the present invention, the 3D COFs obtained in step (e) of the process have electronic conductivity in a range from 10° Sm'1to 10'4Sm'1.

[0026] In another aspect of the present invention, the 3D COFs obtained in step (e) of the process is crystalline having a degree of crystallinity, lattice fringes indexed to the crystallographic planes and ordered, well-defined spots indexed in Selected Area Electron Diffraction (SAED) pattern.

[0027] Another aspect of the present invention provides a method of obtaining 3D COFs from 2D COFs without loss of crystallinity and with improved electronic conductivity compared to the 2D COFs.

[0028] Other aspects of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learnt by the practice of the invention.BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure. The IISERP-COF20- NH2, IISERP-COF20-Pyr, and IISERP-COF20-Ppy are denoted as COF20-NH2, COF20-Pyr, and COF20-Ppy, respectively, in the figures provided below and the accompanying drawings.

[0030] FIGURE 1 is a schematic representation of the synthesis of the 3D COF (IISERP- COF20-Ppy; Ppy = polypyrrole) from 2D COFs according to an embodiment of the present invention.

[0031] FIGURE 2 is a crystallographic modeled structure of IISERP-COF20-Ppy showing a unit cell and lattice parameters of the optimized structure according to an embodiment of the present invention. The color code is: N- blue, C- grey, O- red, and H-white.

[0032] FIGURE 3 illustrates a view along the b-axis showing the cross-linking of the IISERP-COF20-Pyr layers by the covalently linked polypyrrole chains according to an embodiment of the present invention. The Ppy chains are represented in green and orangespace fill.

[0033] FIGURE 4 provides a comparative PXRD pattern of the three phases of the COFs, according to an embodiment of the present invention.

[0034] FIGURE 5 provides the solid state 13C CP-MAS NMR spectra of the IISERP- COF20-NH2, IISERP-COF20-Pyr, and IISERP-COF20-Ppy, according to an embodiment of the present invention.

[0035] FIGURE 6 provides a comparison of the FTIR spectra of the IISERP-COF20-NH2, IISERP-COF20-Pyr, and IISERP-COF20-Ppy COFs, according to an embodiment of the present invention.

[0036] FIGURE 7 provides a comparison of the nitrogen sorption isotherms of the IISERP- COF20-NH2, IISERP-COF20-Pyr, and IISERP-COF20-Ppy COFs measured at 77 K, according to an embodiment of the present invention.

[0037] FIGURE 8 provides a comparison of the I-V plots for the IISERP-COF20-NH2, IISERP-COF20-Pyr, and IISERP-COF20-Ppy COFs, according to an embodiment of the present invention.

[0038] FIGURE 9 provides a comparison of the morphology and crystallinity from the FESEM and HRTEM images of the IISERP-COF20-NH2, IISERP-COF20-Pyr, and IISERP- COF20-Ppy COFs, according to an embodiment of the present invention.

[0039] FIGURE 10 provides HRTEM images of the IISERP-COF20-Ppy showing the high degree of crystallinity and the ordered structure of the COF flakes which give well defined lattice fringes indexed to the crystallographic planes and the SAED gives extremely well- defined spots that have been indexed, according to an embodiment of the present invention.DETAIEED DESCRIPTION OF THE INVENTION

[0040] The following is a detailed description of embodiments of the disclosure. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the present disclosure.

[0041] All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to beincorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.

[0042] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0043] In some embodiments, numbers have been used for quantifying weights, percentages, ratios, and so forth, to describe certain embodiments of the invention and are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable. The numerical values presented in some embodiments of the invention may contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

[0044] Various terms as used herein are shown below. To the extent a term used is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.

[0045] As used in the description herein that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.

[0046] Unless the context requires otherwise, throughout the specification which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense that is as “including, but not limited to.”

[0047] As used in the description herein, the IISERP-COF20-NH2, a 2D COF having amine group is also denoted as COF2O-NH2. Both the notations / terms have the same meaning and are used interchangeably throughout the specification including the drawings.

[0048] As used in the description herein, the IISERP-COF20-Pyr, having pyrrole group / unit is also denoted as COF20-Pyr. Both the notations / terms have the same meaning and are used interchangeably throughout the specification including the drawings.

[0049] As used in the description herein, the IISERP-COF20-Ppy, a 3D COF having polypyrrole group / unit is also denoted as COF20-Ppy. Both the notations / terms have the same meaning and are used interchangeably throughout the specification including the drawings.

[0050] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein.

[0051] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention.

[0052] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and / or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified.

[0053] The description that follows, and the embodiments described therein, is provided by way of illustration of an example, or examples, of particular embodiments of the principles and aspects of the present disclosure. These examples are provided for the purposes of explanation, and not of limitation, of those principles and of the disclosure.

[0054] It should also be appreciated that the present disclosure can be implemented in numerous ways, including as a system, a method or a device. In this specification, these implementations, or any other form that the invention may take, may be referred to as processes. In general, the order of the steps of the disclosed processes may be altered within the scope of the invention.

[0055] The headings and abstract of the invention provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.

[0056] The following discussion provides many example embodiments of the inventive subject matter. Although each embodiment represents a single combination of inventive elements, the inventive subject matter is considered to include all possible combinations of the disclosed elements. Thus, if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, then the inventive subject matter is also considered to include other remaining combinations of A, B, C, or D, even if not explicitly disclosed.

[0057] The present inventors have in an ingenious manner achieved a breakthrough in arriving at a process which allows controlled conversion of 2D COF into 3D COFs by covalently knitting the organic layers of the 2D COF using polymer chains without incurring any loss in crystallinity of the resultant 3D COF whilst also achieving higher electronic conductivity of the 3D COFs compared to the 2D COF. The present process provides a controlled route to covalently knitting the layers of 2D COFs or layered polymer by conjugated polymeric chains leading to new out-of-plane conduction pathway with an increased degree of conjugation in the overall 3D COFs system. This in turn converts the 2D non-conducting COF into highly conjugated 3D conducting COF as shown in FIGURE 1. The present inventors have achieved generation of a 3D architecture with high degree of crystallinity and simultaneously creating a new out-of-plane or cross-linking conduction pathway by connecting the organic 2D COF layers covalently through polypyrrole chains or covalently linking polypyrrole chains to the 2D COF layers.

[0058] An embodiment of the present disclosure provides a synthesis a COF pre-coded with a functional group needed for post-synthetic modification. The use of any 1-D ordered conjugated polymer chains to cross-link COF layers without loss of crystallinity and with improved electronics is not obvious in the existing state of the art and the present disclosure is the first such disclosure providing insight into providing a controlled process for obtaining 3D structured COF from 2D COFs.

[0059] An embodiment of the present invention provides a process of converting two dimensional covalent organic frameworks (2D COFs) into a quasi three dimensional covalent organic frameworks (3D COFs) having out-of-plane, covalently cross-linking conduction pathway comprising the steps of: a) reacting 0.15mmol to Imol 2D COFs (COF20-NH2) having free amine groups with a solvent in the presence of 10 mol % catalyst by refluxing under N2atmosphere for 6 h to 12 h to obtain COFs wherein the free amine groups are selectively converted into pyrrole units (COF20-Pyr) and COF20-Pyr is obtained in a crystalline form; b) filtering the COF20-Pyr product of step (a) obtained as a dark brown powder;(c) washing the filtered COF20-Pyr product of step (b) with acetone, methanol and tetrahydrofuran (THF); d) drying the washed product of step (c) in air under a temperature ranging from 23 °C to 28°C; and e) subjecting the dried 2D COF20-Pyr obtained in step (d) to conversion to 3D COFs in the presence of an oxidizing agent and a solvent at a temperature in the range from 23°C to -20°C for a time period in the range from 24 h to 120 h to obtain the polypyrrole pillared or knitted 3D COFs (COF20-Ppy).

[0060] In another embodiment of the invention, the solvent in step (a) of the process is selected from a group consisting of water, tetrahydrofuran, ethylacetate, ethanol, acetonitrile, dichloromethane and combinations thereof.

[0061] In another embodiment of the invention, the solvent in step (a) of the process is in the range from 0.45 mmol to 3 mol of 2,5-dimethoxy tetrahydrofuran in acetonitrile.

[0062] In another embodiment of the invention, the process of step (a) is carried out at a temperature in the range from 40°C to 100°C.

[0063] In another embodiment of the invention, the process of step (a) is carried out in acetonitrile at 60°C for a time period in the range from 2 h to 6 h to obtain a 2D COF20-Pyr.

[0064] In another embodiment of the invention, the catalyst in step (a) of the process is selected from a group consisting of CuC12.2H2O, AuCh .hydrate, RuCh. hydrate and combinations thereof. Preferably, the catalyst is CuC12.2H2O.

[0065] In another embodiment of the invention, the solvent in step (e) of the process is hexane or acetonitrile.

[0066] In another embodiment of the invention, the conversion of step (e) of the process is carried out at -16°C for a time period of 12 h to obtain the polypyrrole pillared or knitted 3D COFs (COF20-Ppy or IISER-COF20-Ppy).

[0067] In another embodiment of the invention, the oxidizing agent in step (e) of the process is selected from a group consisting of iodine, ammonium persulfate, ferric chloride and combinations thereof.

[0068] In another embodiment of the invention, the oxidizing agent in step (e) of the process is present in an amount ranging from 0.1 mmol to 1 mmol.

[0069] In another embodiment of the invention, the 3D COFs obtained in step (e) of the process have electronic conductivity in a range from 10° Sm'1to 10'4Sm'1.

[0070] In another embodiment of the invention, the 3D COFs obtained in step (e) of the process is crystalline having a degree of crystallinity, lattice fringes indexed to the crystallographic planes and ordered, well-defined spots indexed in Selected Area Electron Diffraction (SAED) pattern.

[0071] A crystallographic modeled structure of IISERP-COF20-Ppy showing a unit cell and lattice parameters of the optimized structure is shown in FIGURE 2. A view along the b-axis showing the cross-linking of the IISERP-COF20-Pyr layers by the covalently linked polypyrrole chains is also provided. The Ppy chains are represented in green and orangespace fill as shown in FIGURE 3.

[0072] A comparative PXRD pattern of the three phases of the COFs is given in FIGURE 4. A solid state 13C CP-MAS NMR spectra of IISERP-COF20-NH2, IISERP-COF20-Pyr, IISERP-COF20-Ppy as depicted in FIGURE 5. A comparison of the FTIR spectra of the COFs is shown in FIGURE 6.

[0073] FIGURE 7 provides a comparison of the nitrogen sorption isotherms of the COFs measured at 77 K. The pore-sizes were estimated using the Non-local density functional theory (NLDFT) methods. A comparison of the I-V plots for the IISERP-COF2O-NH2 vs. IISERP-COF20-Ppy showing the marked improvement in electronic conductivity from 10'9S / m to 10'2S / m, respectively, is shown in FIGURE 8.

[0074] A comparison of the morphology and crystallinity from the FESEM and HRTEM images of the COFs is provided in FIGURE 9. The HRTEM images of FIGURE 10 of IISERP-COF20-Ppy, the 3D COF obtained from the conversion of the 2D COFs is demonstrated to have a high degree of crystallinity and the ordered structure of the COF flakes give well defined lattice fringes indexed to the crystallographic planes, and the SAED gives extremely well-defined spots that have been indexed, emphasizing the crystallinity of the 3D COF. The electronic measurements confirmed that the final 3D COF structure drastically improved electronic conductivity. Where it was 10'9S / m for the parent 2D COF, it was 10'2S / m for the 3D polypyrrole -linked COF.

[0075] The ingenious design and synthesis of a cross-linked COF in which polypyrrole chains connect the two-dimensional COF layers through covalent bonds via post-synthetic modifications to form quasi-three-dimensional (qua-si-3D) COF by the present inventors has led to the modified COF displaying remarkable improvement of crystallinity evidenced through SEAD (Selected area electron diffraction) pattern and lattice fringes in high- resolution transmission electron microscopy (HRTEM). This transformation improves electronic conductivity dramatically from 10'9to 10'2S m'1. Evidently, with interlayer crosslinking improve the layer alignment leading to a decrease in the band gap and an increase in inter-layer charge mobility or electronic conductivity.

[0076] While the foregoing describes various embodiments of the disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use theinvention when combined with information and knowledge available to the person having ordinary skill in the art.EXAMPLES

[0077] The present invention is further explained in the form of following examples. However, it is to be understood that the following examples are merely illustrative and are not to be taken as limitations upon the scope of the invention.

[0078] Example 1 Preparation of the 3D COF

[0079] The process is also shown schematically in FIGURE 1 of the accompanying drawings. 100mg-3g free amine group-bearing 2D COFs (IISERP-COF2O-NH2 or COF2O-NH2) of 0.15 mmol to 1 mol was reacted with a solution of 100pl-3mL 2,5- dimethoxy tetrahydrofuran 0.45 mmol to 3 mol in 3-15 mb acetonitrile at 60°C, in the presence of a copper catalyst, CUQ2.2H2O of 10 mol%. The reaction was carried out by refluxing under N2 atmosphere for about 6-12 h.

[0080] Upon completion of the reaction, the free amine groups in the COFs are selectively converted into pyrrole units, and denoted as IISERP-COF20-Pyr or COF20- Pyr. The IISERP-COF20-Pyr was obtained as dark brown powder, which was isolated by filtering and washed with acetone, methanol and tetrahydrofuran solvents.

[0081] The washed IISERP-COF20-Pyr was then dried at an ambient temperature ranging from 23°C to 28°C. The washed and dried IISERP-COF20-Pyr was characterized by solid-state NMR analysis and IR analysis. The IISERP-COF20-Pyr obtained is a 2D COF with a crystalline form. It was observed that the organic transformation of the amine group into pyrrole rendered the IISERP-COF20-Pyr in its crystalline form.

[0082] The pyrrole functional group in the IISERP-COF20-Pyr 2D COF was further subjected to a post-synthetic modification and converted to polypyrrole.

[0083] 2D IISERP-COF20-Pyr is further reacted in the presence of 20mg to 200mg oxidizing agent 0.1 mmol to 1 mmol in hexane or acetonitrile solvent at a temperature of - 16°C for a period of 72 hrs to obtain the polypyrrole pillared or knitted 3D COF or IISER-COF20-Ppy. This IISER-COF20-Ppy, a 3D COF was synthesized as a poly crystalline powder with a yield of about 65%.

[0084] The final material, IISER-COF20-Ppy, formed as a polycrystalline powder was thoroughly characterized. Its structure was modeled using atomic-level crystallographic computation. The final structure was a typical 2D layered COF having layers pi-stacked to form a three-dimensional (3D) ordering. The layers were shifted, giving a staggered configuration with respect to each other, causing the porosity to be very limited, as seen in a schematic representation provided in FIGURE 1.

[0085] Example 2: Characterization of the 2D and 3D COFs

[0086] The IISERP-COF20-NH2, IISERP-COF20-Pyr, and IISERP-COF20-Ppy, obtained as insoluble polycrystalline powders in Example 1 were characterized using the following techniques.

[0087] Powder X-ray diffraction: Powder XRDs were carried out using a full-fledged Bruker D8 Advance instrument and Rigaku MiniFlex 600 benchtop powder X-ray diffraction (XRD) instrument. The data analysis was performed using the Reflex module of Materials Studio V6.

[0088] Infra-Red Spectroscopy: IR spectra were obtained using a Nicolet ID5 attenuated total reflectance IR spectrometer operating at ambient temperature. The solid-state IR spectra were recorded using KBr pellets as background.

[0089] Field Emission-Scanning Electron Microscopy (FESEM): Electron Microscope with integral charge compensator and embedded EsB and AsB detectors. Oxford X-max instruments 80mm2. (Carl Zeiss NTS, Gmbh), Imaging conditions: 2kV, WD= 2mm, 200kX, Inlens detector. For SEM images, as an initial preparation, the samples were ground thoroughly, soaked in EtOH for 30 min. and were sonicated for 2 hrs. These well-dispersed samples were drop-casted on a silicon wafer and dried under vacuum for at least 12 hrs.

[0090] High Resolution Transmission Electron Microscopy (HRTEM): Transmission electron microscopy (TEM) was performed using a JEM 2200FS TEM microscope operating at an accelerating voltage of 200 kV). The diffractograms were recorded at a scanning rate of 1° min-1 between 20° and 80°. The samples were drop-casted on holey carbon Cu-grids from ethanol immediately prior to the imaging.

[0091] Adsorption study: Adsorption studies were carried out using a Micromeritics 3-FLEX pore and surface area analyzer. Samples were evacuated under 10-4-10-5 Torr vacuum at 150°C for 12 hrs to 24 hrs.

[0092] EPR Measurements: The electron spin resonance (ESR) spectra were measured by a JEOL JES-FA200 ESR spectrometer, the data of electron was collected at scanning frequency: 9229.871 MHz; scanning power, 0.998 mW; central field, 329.4 mT; scanning width, 50 G; scanning temperature: 298 K.

[0093] Ultraviolet photoelectron spectroscopy (UPS): Ultraviolet photoemission valance band spectrum (UPS) was performed on Thermo ESCALAB XI+ with Helium light source (hv=21.2 eV) and a bias voltage of -10 V. Applying a negative bias to the sample can help analyze the work function of the material and enhance the electron count rate, especially the secondary electron part.

[0094] X-ray Photoelectron Spectroscopy: XPS measurements were carried out using Thermo Kalpha+ spectrometer equipped with micro-focused and monochromated AlKa radiation with energy 1486.6 eV. The base pressure of the spectrometer was better than 10-8 mbar during the spectral acquisition. The pass energy for the spectral acquisition was kept at 50 eV for individual core-levels. The electron flood gun was utilized for providing charge compensation during data acquisition. The peak fitting of the individual core levels were done using XPS peak software with a Shirley type background.

[0095] Solid-state UV spectroscopy: Diffuse reflectance spectra of the polymer powders in the UV-visible region are recorded using a Shimadzu UV-3600 plus UV-vis-NIR spectrophotometer. Then KubelkaMunk transformation is used for the analysis of diffuse reflectance spectra. It relates the reflectance data with the absorption coefficient as in equation (1): F(R) = a / S = (1-R)2 / 2R (1) where F(R) is the Kubelka-Munk function, R is reflectance, a is absorption coefficient, and S is the scattering factor.

[0096] 13C Solid-State Nuclear Magnetic Resonance (NMR) Spectroscopy: High- resolution solid-state NMR spectrum was recorded at ambient pressure on a Bruker AVANCE III spectrometer using a standard CPTOSS pulse sequence (cross-polarization with total suppression of sidebands) probe with 4 mm (outside diameter) zirconia rotors. Cross- polarization with TOSS was used to acquire 13C data at 100.37 MHz. The 13C ninety-degreepulse widths were 4 ps. The decoupling frequency corresponded to 72 kHz. The TOSS sample-spinning rate was 5 kHz. Recycle delays were 2s.

[0097] Electronic conductivity measurement: The COF powder samples were ground into a homogeneous powder using a mortar and pestle. The powder was added to a 6 mm die and pressed into pellets using a hydraulic press under a pressure of 80kN. The pellet was then connected and mounted to a sample probe. Conductivity was investigated in the four-probe current-applying voltage measurement (V-I) method and the two-probe voltage-applying current measurement (I-V) method by using Keithley 2450 source meter. Moreover, I-V curves were measured to ensure all the contacts were Ohmic contacts. The temperature dependence of the conductivity was measured upon heating in the temperature range from 298 to 333 K.

[0098] Electrochemical Measurements: The acid electrolyte and non-aqueous electrolyte measurement: The constant current charge-discharge measurements were performed using AMETEK galvanostatic-potentiostatic analyzer using VERSA STUDIO (Version 2.52) software. The cyclic voltammetry and potentiostatic electrochemical impedance studies were performed in PARSTAT Multichannel electrochemical workstation.

[0099] Stability tests involving boiling solvents, heating-cooling cycles, steam, and moisture were carried out according to standard methods in the art.

[0100] As evidenced by adsorption measurements and the FIGURES 2-7, the 2D IISER- COF20-NH2and IISER-COF20-Pyr were nominally porous.

[0101] The final structure of IISER-COF20-Ppy modeled using computational crystallographic techniques and refined against the experimental PXRD using Pawley methods demonstrated a good fit with acceptable parameters.

[0102] The final framework (IISER-COF20-Ppy) was crystalline and had the 2D layers covalently knitted by the polypyrrole chains running out-of-plane with respect to the COF layers and connecting them in the third orthogonal direction. This now is a crystalline structure with 3D covalently linked framework.

[0103] As seen in FIGURE 8, the electronic measurements confirmed that the final 3D structure drastically improved electronic conductivity by exhibiting 10'9S m'1for the parent2D COFs, IISER-COF20 NH2and IISER-COF20 Pyr versus 10’2S m1for the 3D polypyrrole-linked COF, IISER-COF20-Ppy. Without wishing to be bound by theory, the present inventors submit that essentially, the polypyrrole not only covalently knits the COF but acts as a “conjugation bridge” that extends the conjugation pathway for charge carrier mobility and also orders the COF layers.

[0104] The IISER-COF20-Ppy retained all the properties of the parent 2D COF in terms of stability, crystallinity and porosity as seen in FIGURES 2-10. The most important evidence for the formation of a robust, highly crystalline framework was from High-resolution transmission electron microscopy (HRTEM) wherein the lattice fringes and the highly ordered SAED pattern from HRTEM confirm the enormously improved crystallinity of the 3D COF, IISER-COF20-Ppy (FIGURE 10).

[0105] Example 3: 3D COFs in supercapacitor

[0106] The IISER-COF20-Ppy of example 1 was fabricated into solid-state devices according to standard methods in the art and evaluated for its efficacy for being employed in supercapacitors. It was observed that there yielded a high areal capacitance of 378 mF cm-2from the converted 3D COF IISER-COF20-Ppy, while the parent 2D COF yielded an areal capacitance of only 61 mF cm-2.

[0107] The foregoing examples are merely illustrative and are not to be taken as limitations upon the scope of the invention. Various changes and modifications to the disclosed embodiments will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the scope of the invention.ADVANTAGES OF THE INVENTION

[0108] The present invention provides a clear, well-demonstrated, controlled route for converting 2D COF into 3D COF by covalently knitting the organic layers of the 2D COF using polymer chains such that there is an increased degree of conjugation in the overall 3D system.

[0109] The present invention provides a controlled route to covalently knit the layers of 2D or layered polymer by conjugated polymeric chains leading to new out-of-plane conduction pathway.

[0110] The present invention provides a process for converting 2D non-conducting COF into highly conjugated 3D conducting COF having a high degree of crystallinity and simultaneously creating a new out-of-plane or cross-linking conduction pathway.[oni] The present process invention for obtaining 3D structured COF from 2D COFs is a very versatile approach adaptable to any COF or related crystalline polymers functionalized with functional groups amenable to be converted to groups resembling the monomer of a well-established polymer.

Claims

We Claim:

1. A process of converting two dimensional covalent organic frameworks (2D COFs) into a quasi three dimensional covalent organic frameworks (3D COFs) having out-of-plane, covalently cross-linking conduction pathway comprising the steps of: a) reacting 0.15mmol to Imol 2D COFs (COF20-NH2) having free amine groups with a solvent in the presence of 10 mol % catalyst by refluxing under N2atmosphere for 6 h to 12 h to obtain COFs wherein the free amine groups are selectively converted into pyrrole units (COF20-Pyr) and COF20-Pyr is obtained in a crystalline form; b) filtering the COF20-Pyr product of step (a) obtained as a dark brown powder;(c) washing the fdtered COF20-Pyr product of step (b) with acetone, methanol and tetrahydrofuran(THF) ; d) drying the washed product of step (c) in air under a temperature ranging from 23 °C to 28°C, and e) subjecting the dried 2D COF20-Pyr obtained in step (d) to conversion to 3D COFs in the presence of an oxidizing agent and a solvent at a temperature in the range from 23°C to -20°C for a time period in the range from 24 h to 120 h to obtain the polypyrrole pillared or knitted 3D COFs (COF20-Ppy).

2. The process as claimed in claim 1, wherein the solvent in step (a) is selected from a group consisting of water, tetrahydrofuran, ethylacetate, ethanol, acetonitrile, dichloromethane and combinations thereof.

3. The process as claimed in claim 1, wherein the solvent in step (a) is 0.45 mmol to 3 mol of 2,5 -dimethoxy tetrahydrofuran in acetonitrile.

4. The process as claimed in claim 1, wherein the step (a) is carried out at a temperature in the range from 40°C to 100°C,5. The process as claimed in claim 1, wherein the step (a) is carried out in acetonitrile at 60°C for a time period in the range from 2 h to 6 h to obtain a 2D COF20-Pyr.

6. The process as claimed in claim 1, wherein the catalyst in step (a) is selected from a group consisting of CUCI2.2H2O, AuCE .hydrate, RuCE .hydrate and combinations thereof.

7. The process as claimed in claim 1, wherein the solvent in step (e) is hexane or acetonitrile.

8. The process as claimed in claim 1, wherein the conversion of step (e) is carried out at - 16°C for a time period of 12 h to obtain the polypyrrole pillared or knitted 3D COFs (COF20-PPy).

9. The process as claimed in claim 1, wherein the oxidizing agent in step (e) is selected from a group consisting of iodine, ammonium persulfate, ferric chloride and combinations thereof.

10. The process as claimed in claim 1 wherein the oxidizing agent in step (e) is present in an amount ranging from 0. 1 mmol to 1 mmol.

11. The process as claimed in claim 1, wherein the 3D COFs obtained in step (e) have electronic conductivity in a range from 10° Sm'1to 10'4Sm'1.

12. The process as claimed in claim 1, wherein the 3D COFs obtained in step (e) is crystalline having a degree of crystallinity, lattice fringes indexed to the crystallographic planes and ordered, well-defined spots indexed in Selected Area Electron Diffraction (SAED) pattern.

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