Decoding Excimer Formation in Covalent-Organic Frameworks Induced by Morphology and Ring Torsion.

A thorough and quantitative understanding of the fate of excitons in covalent-organic frameworks (COFs) after photoexcitation is essential for their augmented optoelectronic and photocatalytic applications via precise structure tuning. The synthesis of a library of COFs having identical chemical backbone with impeded conjugation, but varied morphology and surface topography to study the effect of these physical properties on the photophysics of the materials is herein reported. The variation of crystallite size and surface topography substantified different aggregation pattern in the COFs, which leads to disparities in their photoexcitation and relaxation properties. Depending on aggregation, an inverse correlation between bulk luminescence decay time and exciton binding energy of the materials is perceived. Further transient absorption spectroscopic analysis confirms the presence of highly localized, immobile, Frenkel excitons (of diameter 0.3-0.5 nm) via an absence of annihilation at high density, most likely induced by structural torsion of the COF skeletons, which in turn preferentially relaxes via long-lived (nanosecond to microsecond) excimer formation (in femtosecond scale) over direct emission. These insights underpin the importance of structural and topological design of COFs for their targeted use in photocatalysis.

A physicochemical introspection of porous organic polymer photocatalysts for wastewater treatment.

Over the past decade, porous organic polymers (POPs) have emerged as powerful photocatalysts for organic transformations and wastewater decontamination. The surface properties and pore space of POPs have been tailored to find optimal physical dimensions for adsorption and catalysis, whereas playing with the donor-acceptor building units lends them unique prospects for bandgap engineering, beneficial for customized applications including the degradation of simple as well as persistent pollutants. Here in this critical perspective, we focused beyond these generic scenarios and provided a detailed physicochemical explanation for the experimental observations. Considering the invaluable role of excitons, along with mobile electrons and holes, we fundamentally justified the reactivities of POPs with regard to water treatment. Both semiconducting and molecular catalyst approaches have been considered for different types of POPs. Depending on the porosity, structural formation and defects in the POP backbone, the exciton formation, charge separation, charge diffusion, etc. are critically explained, highlighting the influence of the dielectric constant and skeletal polarizability of the material. The translation of this fundamental understanding to various reactive oxygen species generation through charge transfer (e.g., O2˙-) and exciton-exciton annihilation (e.g., 1O2) by proximity-induced FRET or Dexter pathways is discussed. The role of the hydrophilic POP skeleton in overall in-water photochemical applications is also discussed. Finally, the gaps in the current state-of-the-art are considered and the future prospects to mitigate these issues are argued.

Novel rapid room temperature synthesis of conjugated microporous polymer for metal-free photocatalytic degradation of fluoroquinolones.

The existence of Fluoroquinolones (FQs), non-biodegradable pharmacophores, in the natural environment possesses a serious threat. We herein report a novel, rapid, room-temperature synthesis of semiconducting conjugated microporous polymer (CMP) for the decontamination of four second-generation FQs, Norfloxacin, Enrofloxacin, Ciprofloxacin, and Ofloxacin. The CMP demonstrated impressive gas uptake and FQ adsorption ability. Decreased HOMO-LUMO bandgap resulted in enhanced exciton pair generation on visible-light-illumination. Additionally, a high degree of photocurrent response and suitable redox potentials of the material conjointly endorsed its almost quantitative FQ-degradation efficiency. Ofloxacin showed the best removal efficiency with 0.061 and 0.207 min-1 adsorption and degradation rate constants, respectively, one of the highest values reported. The CMP exhibited equipotent activity for other FQs as well. On increasing the concentration of the FQs or decreasing the incident photo-intensity, quantitative removal efficiencies are observed. Changing the pH of the medium from acidic to alkaline did not impart any change in catalytic activity as well. The reactive species involved viz. O2-, 1O2, etc. and their roles in the degradation process were determined through control and trapping experiments. A plausible in-depth mechanistic pathway was assessed from the FQ degradation intermediates, and the reactive catalytic species substantiating step-by-step break down of the antibiotic backbone.

Dataset on the development of palladium nanoparticle decorated colloidal porous organic polymer for photocatalytic Suzuki coupling.

Herein, we report the synthesis and characterization data of visible-light-active colloidal azobenzene-based porous organic polymer (Azo-POP) and its Pd-nanoparticle loaded analog (Pd-Azo-POP). The setup for photocatalytic Suzuki reactions triggered by Pd-Azo-POP under conventional batch reaction mode as well as in a prototypal continuous flow system has also been provided in addition to the detailed catalytic data including 1H and 13C NMR spectra of the obtained products. For further discussions on the materials, their effect on overall catalysis and mechanistic insight, please refer to the associated article "Pd-nanoparticle decorated azobenzene-based colloidal porous organic polymer for visible and natural sunlight-induced Mott-Schottky junction mediated instantaneous Suzuki coupling" (Chakraborty et al., 2019).

Synthesis and characterization of chitosan-based waterborne polyurethane for textile finishes.

Chitosan has gained an increased interest of researchers due to its nontoxic, biodegradable, biocompatible and renewable properties as well as its antimicrobial activity. In this work, a series of chitosan-based waterborne polyurethane (CS-WPU) emulsions were synthesized. The synthesis was accomplished by using a two-step emulsion polymerization process. The pre-polymer was prepared using hexamethylene diisocyanate (HDI) and polyethylene glycol (PEG; MW = 6 kDa). Afterwards, the chain extension step was performed by using different mole ratios of chitosan. Moreover, the effect of chitosan on physicochemical properties of the emulsion was studied. To evaluate textile performances such as tear strength, tensile strength and pilling, the CS-WPU emulsion was applied on different plain weave polyester cotton dyed and printed fabrics by using pad-dry cure techniques. The antimicrobial activity of the treated and untreated fabrics was also evaluated via the agar diffusion method. The results displayed that incorporation of chitosan has prominent effects on tensile tear strength, tear strength and antimicrobial activity of polyester cotton dyed and printed fabrics. Moreover, antimicrobial activity was considerably enhanced as the mole ratio of the chitosan was increased. The results emphasize that CS-WPU based on HDI exhibits a better performance as compared to IPDI.

Metal organic frameworks mimicking natural enzymes: a structural and functional analogy.

In this review, we have portrayed the structure, synthesis and applications of a variety of biomimetic MOFs from an unprecedented angle. Synthetic MOF analogues of five distinct enzymes: phosphotriesterase, hydrogenase, cytochrome P450, chymotrypsin and carbonic anhydrase, have been discussed with their skeletal comparison to actual enzymatic active sites as reference, and an explanation of catalytic pathways from the mechanistic cycle of the corresponding enzymes is depicted. We demonstrated critically each of the five discrete situations by assimilating available benchmark researches in an attempt to provide a concise literature source on the ingenious design strategies and versatile biomimetic applications of this domain of materials.