Decoding the Morphological Diversity in Two Dimensional Crystalline Porous Polymers by Core Planarity Modulation

Abstract

Tw on ew chemically stable triazine-and phenylcore-based crystalline porous polymers (CPPs) have been synthesized using as ingle-step template-free solvothermal route.U nique morphological diversities were observed for these CPPs [2,3-DhaTta (ribbon) and 2,3-DhaTab (hollow sphere)] by simply altering the linker planarity.Adetailed time-dependent study established as ignificant correlation between the molecular level structures of building blocks with the morphology of CPPs.M oreover,aDFT study was done for calculating the interlayer stacking energy,w hich revealed that the extent of stacking efficiency is responsible for governing the morphological diversity in these CPPs.Twodimensionalcrystallineporouspolymers(CPPs),including covalent organic frameworks (COFs) [1] and covalent triazine frameworks (CTFs), [2] are porous materials constructed by covalently linked light elements,such as C, N, O, H, B, and Si. These materials have triggered substantial research interest because of their extensive applications in molecular storage, [3] catalysis, [4] sensing, [5] and opto-electronics.[6] However,the overall properties of such porous materials do not rely only on their composition, structure,and porosity, but also on their nanoscale morphologies.[7] Therefore,a n explicit understanding of the morphology-modulation with respect to their constituents is required.[8] To achieve such am olecular level understanding, herein we report two CPPs that self-assemble to ribbon and hollow spherical [9] morphologies upon crystallization in as ingle step without any templating agents.Hollow spherical structures are considered to be ah ighly important morphology in polymeric materials owing to several potential applications.H owever,t heir existence is extremely rare and often require the usage of templating agents.[10] Thei ntermediates responsible for producing these above morphologies were prepared at different time intervals to understand the mechanism for the formation of the final morphology (at 72 h).TheC PPs reported here show high crystallinity as revealed from their PXRD patterns (Figure 1). Ahigh intense peak at 2.88 8 (2q)f or 2,3-DhaTta and 2,3-DhaTab (Figure 1e and 1f,r espectively) appear owing to the strong reflections from the 100 planes.2,3-DhaTta and 2,3-DhaTab show other minor peaks at 4.9, 5.7, 7.5, and 9.98 8 (2q)o wing to the reflections from the 110, 200, 120, and 220 planes,r espectively.P eaks at 268 8 (2,3-DhaTta) and 25.88 8 (2,3-DhaTab) correspond to their 001 plane reflections.T he d-spacing values between the 001 planes were used to calculate the p-p stacking distances between vertically stacked CPP layers [3.3 and 3.4 inthe respected CPPs].The high crystallinity of these CPPs is attributed to the presence of strong intramolecular OÀH···N hydrogen bonding [11] interactions between the imine nitrogen and the hydroxy functionality of the aldehyde core,w hich is influential in keeping the phenyl rings in one plane and increases stacking interactions within adjacent CPP layers.T og et an overview...

A Hollow Microtubular Triazine‐ and Benzobisoxazole‐Based Covalent Organic Framework Presenting Sponge‐Like Shells That Functions as a High‐Performance Supercapacitor

“…The TEM images of the synthesized COF confirmed its hollow nature and sponge‐like surface of tubules. In Figures d–e, the tubule's center appears as a bright area and its outer surface as a dark area‐a basic characteristic feature of a hollow structure; the nanowires on the outer surface were responsible for the formation of the sponge‐like structure . Statistical analysis of the TEM images provided average values for the outer and inner diameters of the tubules of 0.90 and 0.53 μm, respectively.…”

2D-Covalent Organic Frameworks with Interlayer Hydrogen Bonding Oriented through Designed Nonplanarity

“…including room temperature FT-IR analysis and solvent stability tests under harsh conditions have been previously reported to characterize interlayer hydrogen bonding in COFs, 12,[17][18][19] direct observation can still be challenging. We expected that the presence of strong hydrogen bonding interactions would lead to significant frequency shifts in IR spectrum of the functional groups directly involved in the hydrogen-bonded bridges.…”

“…There are only a few examples of hydrazone 17,18 or urea 12 containing COFs where interlayer hydrogen bonding is observed or predicted, reported in literature. Several COFs have been reported that have interlayer C-H⋯O, and C-H⋯N hydrogen bonding through sidechain interactions, 13,14,19 however, more canonical N-H⋯O hydrogen bonding interactions similar to those found between amide groups found in Nature, or in synthetic polymers such as Kevlar or Nylon, are much rarer.…”

Covalent Organic Frameworks: From Materials Design to Biomedical Application

“…Similarly, Banerjee and co-workers constructed flower-like COFs and the sheet-like structures were also prepared by using π-π stacking of COF layers [ 99 ]. They also synthesized hollow spherical COFs (COF-DhaTab) through an Ostwald ripening process, as shown in Figure 8 b [ 116 , 239 ]. The formed COF-DhaTab showed rod-shaped morphology at first and then were aggregated.…”