Magnetic nanoparticle-supported eosin Y salt [SB-DABCO@eosin] as an efficient heterogeneous photocatalyst for the multi-component synthesis of chromeno[4,3-b]chromene in the presence of visible light

Heterogeneous photocatalysts present a favourable procedure to realize green and eco-friendly organic reactions. We have demonstrated an SB-DABCO@eosin catalyst in a green one-pot multi-component protocol for the production of various chromeno[4,3-b]chromenes via condensation of aromatic aldehydes and dimedone under the photo-redox catalyst bearing eosin Y using visible light. The synthesized nanocatalyst was characterized using various physicochemical techniques such as FT-IR, XRD, EDX, UV-vis, SEM, TGA and DRS. The significant advantages of the present methodology include excellent yield, cost-effectiveness, easy work-up, 100% atom economy, broad substrate scope, easy separation and efficient recycling. Furthermore, the evidence showed that the investigated condensation reaction proceeds via a radical mechanism, which proved the need for reactive species such as OH˙ and ˙O₂ ^- in the photocatalytic process. In addition to the improved handling and process control, the yield of products and the rate of reactions have increased considerably in the present strategy. Reproducibility studies also guarantee good reusability and stability of the nanocatalyst for at least five runs.

One-pot multicomponent green LED photoinduced synthesis of chromeno[4,3-b]chromenes catalyzed by a new nanophotocatalyst histaminium tetrachlorozincate

Histaminium tetrachlorozincate nanoparticles are prepared, characterized and applied as an effective and recoverable photocatalyst in the one-pot, green and multi-component synthesis of various chromenes by the reaction of dimedone and/or 1,3-cyclohexanedione, arylaldehyde and 4-hydroxycoumarin in high yields under solventless conditions at ambient temperature. This new catalyst is characterized by FT-IR, XRD, EDX, NMR, SEM and TEM techniques. The incorporation of histaminium ions into the framework of ZnCl₄²⁻ significantly affected the photocatalytic activity of tetrachlorozincate such that good reusability and recyclability are attained. Moreover, reactive species such as ˙O₂⁻ and hydroxyl radicals have proved to be active species in the presented photocatalytic reaction. In addition, the hot filtration test confirms enough stability of the photocatalyst and no significant leaching and destruction of the framework in the course of the reaction. The major advantages of the presented methodology include easy work-up, cost effectiveness, nontoxic nature, broad substrate scope, 100% atom economy, ease of separation, and environment friendly reaction conditions. Finally, the catalyst could be reused many times without significant loss of activity.

(His.)ZnCl₄ nanocatalyst is realized for the preparation of chromenes with a green LED. ˙O₂⁻, OH˙ and h⁺ are reactive species for this reaction. Complementary tests assured good stability and reusability of the nanophotocatalyst.

Tunable terahertz wave generation through a bimodal laser diode and plasmonic photomixer

We demonstrate a compact, robust, and stable terahertz source based on a novel two section digital distributed feedback laser diode and plasmonic photomixer. Terahertz wave generation is achieved through difference frequency generation by pumping the plasmonic photomixer with two output optical beams of the two section digital distributed feedback laser diode. The laser is designed to offer an adjustable terahertz frequency difference between the emitted wavelengths by varying the applied currents to the laser sections. The plasmonic photomixer is comprised of an ultrafast photoconductor with plasmonic contact electrodes integrated with a logarithmic spiral antenna. We demonstrate terahertz wave generation with 0.15-3 THz frequency tunability, 2 MHz linewidth, and less than 5 MHz frequency stability over 1 minute, at useful power levels for practical imaging and sensing applications.

A new method for the preparation of 1,3,5-triarylbenzenes catalyzed by nanoclinoptilolite/HDTMA

An efficient method for the preparation of 1,3,5-triarylbenzenes. Natural surface-modified NCP as a new and reusable catalyst. Using solvent-free conditions.

H6P2W18O62/Nanoclinoptilolite as an efficient nanohybrid catalyst in the cyclotrimerization of aryl methyl ketones under solvent-free conditions

A new natural nanohybrid material HPA/NCP was prepared. An efficient and environmentally benign method for cyclotrimerization of acetophenones is reported. Water was the only by-product.

Switchable scattering meta-surfaces for broadband terahertz modulation

Active tuning and switching of electromagnetic properties of materials is of great importance for controlling their interaction with electromagnetic waves. In spite of their great promise, previously demonstrated reconfigurable metamaterials are limited in their operation bandwidth due to their resonant nature. Here, we demonstrate a new class of meta-surfaces that exhibit electrically-induced switching in their scattering parameters at room temperature and over a broad range of frequencies. Structural configuration of the subwavelength meta-molecules determines their electromagnetic response to an incident electromagnetic radiation. By reconfiguration of the meta-molecule structure, the strength of the induced electric field and magnetic field in the opposite direction to the incident fields are varied and the scattering parameters of the meta-surface are altered, consequently. We demonstrate a custom-designed meta-surface with switchable scattering parameters at a broad range of terahertz frequencies, enabling terahertz intensity modulation with record high modulation depths and modulation bandwidths through a fully integrated, voltage-controlled device platform at room temperature.