Record-high near-band-edge optical nonlinearities and two-level model correction of poled polymers by spectroscopic electromodulation and ellipsometry

The determination of nonlinearities near the band edge of organic and polymeric electro-optic(EO)materials is important from the viewpoint of molecular nonlinear optics(NLO)and photonic device applications.Based on transmission-mode Stark effect electromodulation(EM)spectroscopy,we study the electric-field-induced changes in optical absorption and refraction of newly developed EO polymers from the visible to near-infrared(NIR)wavelengths and report record-high near-band-edge complex EO effects from poled thin films.Values ofΔn andΔk up to 10^-3 and 10^-2 are found at an applied electric field of 2.0×10⁵-3.0×10⁵V/cm.The study of linear optical properties of poled films by spectroscopic ellipsometry shows large polinginduced birefringence and a nearly two-fold increase in the extinction coefficients at the extraordinary polarization.Through the Kramers-Kronig analysis,we obtained the real and imaginary second-order nonlinear coefficients up to~3,500 and~5,600 pm/V,respectively,which are believed to be the highest NLO coefficients of poled polymers through the resonance enhancement.Our approach goes beyond the previous works,applicable only to several discrete wavelengths,to a full-spectral analysis with independent verification of slab waveguide measurements.By considering both the electroabsorption and electrorefraction effects,our study overcomes the limitation of the classic qualitative two-level model and provides a quantitative understanding of near-resonance optical nonlinearities of organic EO materials.It can inspire the exploration of high-speed,absorptive,or phase-shifting light-modulators using EO polymers for on-chip applications.     

Ageratum conyzoides L. and Its Secondary Metabolites in the Management of Different Fungal Pathogens

Ageratum conyzoides L. (Family—Asteraceae) is an annual aromatic invasive herb, mainly distributed over the tropical and subtropical regions of the world. It owns a reputed history of indigenous remedial uses, including as a wound dressing, an antimicrobial, and mouthwash as well as in treatment of dysentery, diarrhea, skin diseases, etc. In this review, the core idea is to present the antifungal potential of the selected medicinal plant and its secondary metabolites against different fungal pathogens. Additionally, toxicological studies (safety profile) conducted on the amazing plant A. conyzoides L. are discussed for the possible clinical development of this medicinal herb. Articles available from 2000 to 2020 were reviewed in detail to exhibit recent appraisals of the antifungal properties of A. conyzoides. Efforts were aimed at delivering evidences for the medicinal application of A. conyzoides by using globally recognized scientific search engines and databases so that an efficient approach for filling the lacunae in the research and development of antifungal drugs can be adopted. After analyzing the literature, it can be reported that the selected medicinal plant effectively suppressed the growth of numerous fungal species, such as Aspergillus, Alternaria, Candida, Fusarium, Phytophthora, and Pythium, owing to the presence of various secondary metabolites, particularly chromenes, terpenoids, flavonoids and coumarins. The possible mechanism of action of different secondary metabolites of the plant against fungal pathogens is also discussed briefly. However, it was found that only a few studies have been performed to demonstrate the plant’s dosage and safety profile in humans. Considered all together, A. conyzoides extract and its constituents may act as a promising biosource for the development of effective antifungal formulations for clinical use. However, in order to establish safety and efficacy, additional scientific research is required to explore chronic toxicological effects of ageratum, to determine the probability of interactions when used with different herbs, and to identify safe dosage. The particulars presented here not only bridge this gap but also furnish future research strategies for the investigators in microbiology, ethno-pharmacology, and drug discovery.     

Investigation and optimization of the recovery of coal fines using oil agglomeration process: Use of waste oils from different sectors

The high cost of the bridging liquid subdues the implementation and commercialization of oil agglomeration process. To overcome this problem, waste oils from different sectors were used in this present study. The performance of the process was assessed based on the responses like ash rejection and organic matter recovery. The aim of the present study was to investigate the usage of waste oils from different sectors and to optimize and analyze the behavioral pattern showcased by different variables (pulp density, oil dosage, agglomeration time and oil type) using response surface methodology (Box-Behnken design). Experimental investigation shows that the optimum pulp density, oil dosage, agglomeration time and oil type condition obtained as 3%, 15%, 15?min and waste engine oil, respectively. At optimum condition, the % ash rejection and % organic matter recovery obtained as 63.94% and 81.8%, respectively.     

Synthesis and structure of a chiral areno-bridged [2.4]metacyclophane

The reductive coupling reaction of 1,4-bis(3-acetyl-5-tert-butyl-2-methoxyphenyl)butane 3 was carried out using TiCl₄-Zn in pyridine followed by a McMurry coupling reaction to afford the compounds anti and syn 1,2-dimethyl[2.4]MCP-1-ene 4. Bromination of 4 with BTMA-Br₃ in dry CH₂Cl₂ afforded the interesting compound 1,2-bis-(bromomethyl)-5,15-di-tert-butyl-8,18-dimethoxy[2.4]MCP-1-ene 6 and consecutive debromination with Zn and AcOH in CH₂Cl₂ solution afforded the stable solid 5,15-di-tert-butyl-8,18-dimethoxy-1,2-dimethylene[2.4]MCP 7 in 89% yield. Compound 7 was conveniently employed in a Diels–Alder reaction with dimethyl acetylenedicarboxylate (DMAD) to provide 2-(3′,6′-dihydrobenzo)-5,15-di-tert-butyl-8,18-dimethoxy[2.4]MCP-4′,5′-dimethylcarboxylate 8 in good yield. Diels–Alder adduct 8 was converted into a novel and inherently chiral areno-bridged compound [2.4]MCP 9 by aromatization. The chirality of the two conformers was characterized by circular dichroism (CD) spectra of the separated enantiomer which are perfect mirror images of each other.     

An Electron-Deficient Triosmium Cluster Containing the Thianthrene Ligand: Synthesis, Structure and Reactivity of [Os3(CO)9(μ3-η2-C12H7S2)(μ-H)]

Reaction of [Os₃(CO)₁₀(CH₃CN)₂] with thianthrene at 80 °C leads to the nonacarbonyl dihydride compound [Os₃(CO)₉(μ-3,4-η²-C₁₂H₆S₂)(μ-H)₂] (1) and the 46-electron monohydride compound [Os₃(CO)₉(μ₃-η²-C₁₂H₇S₂)(μ-H)] (2). Compound 2 reacts reversibly with CO to give the CO adduct [Os₃(CO)₁₀(μ-η²-C₁₂H₇S₂)(μ-H)] (3) whereas with PPh₃ it gives the addition product [Os₃(CO)₉)(PPh₃)(μ-η²-C₁₂H₇S₂)(μ-H)] (4) as well as the substitution product 1,2-[Os₃(CO)₁₀((PPh₃)₂] (5) Compound 2 represents a unique example of an electron-deficient triosmium cluster in which the thianthrene ring is bound to cluster by coordination of the sulfur lone pair and a three-center-two-electron bond with the C(2) carbon which bridges the same edge of the triangle as the hydride. Electrochemical and DFT studies which elucidate the electronic properties of 2 are reported. Dedicated to the memory of a great scientist, F. Albert Cotton.     

Two-Dimensional Supramolecular Polymerization of a Bis-Urea Macrocycle into a Brick-Like Hydrogen-Bonded Network

We report on a dendronized bis-urea macrocycle 1 self-assembling via a cooperative mechanism into two-dimensional (2D) nanosheets formed solely by alternated urea-urea hydrogen bonding interactions. The pure macrocycle self-assembles in bulk into one-dimensional liquid-crystalline columnar phases. In contrast, its self-assembly mode drastically changes in CHCl₃ or tetrachloroethane, leading to 2D hydrogen-bonded networks. Theoretical calculations, complemented by previously reported crystalline structures, indicate that the 2D assembly is formed by a brick-like hydrogen bonding pattern between bis-urea macrocycles. This assembly is promoted by the swelling of the trisdodecyloxyphenyl groups upon solvation, which frustrates, due to steric effects, the formation of the thermodynamically more stable columnar macrocycle stacks. This work proposes a new design strategy to access 2D supramolecular polymers by means of a single non-covalent interaction motif, which is of great interest for materials development.