Semiconducting Organic Molecular Materials

This feature article gives an overview of recent advances in development of high performance molecular organic semiconductors for field-effect transistors with emphasis on the structure of molecular materials and requirements for highperformance

The Scavenging of DPPH, Galvinoxyl and ABTS Radicals by Imine Analogs of Resveratrol

Resveratrol (3,5,4′-trihydroxystilbene) is a phytoalexin produced by plants. Resveratrol is known for its anti-cancer, antiviral and antioxidant properties. We prepared imine analogs of resveratrol ((hydroxyphenyliminomethyl)phenols) and tested their antioxidant activity. All prepared resveratrol analogs were able to scavenge 2,2-diphenyl-1-picrylhydrazyl (DPPH), galvinoxyl radical (GOR) and 2,2′-azino-bis(3-ethylbenzothiazoline)-6-sulphonic acid (ABTS) radicals. The antioxidant activity efficiency correlated with the number and position of hydroxyl groups. The most effective antioxidants were resveratrol analogs containing three hydroxyl groups in the benzylidene part of their molecules. These results provide new insights into the relationship between the chemical structure and biological activity of resveratrol analogs

Imine resveratrol analogs (IRAs): The strong antioxidant that can protect lymphocytes from oxidative damage

Imine resveratrol analogs (IRAs) are promising new agents that can have higher positive effects and, simultaneously, lower negative properties than resveratrol. In this study, three imine hydroxy derivatives (2-((4-hydroxyphenylimino) methyl) phenol [IRA1], 3-((4-hydroxyphenylimino) methyl) phenol [IRA2], and 4-((4-hydroxyphenylimino) methyl) phenol [IRA3]) were prepared and tested in several biological assays. They performed superior to resveratrol in several antioxidant and biological assays, showing high antioxidant capacity and low genotoxicity. Ferric reducing antioxidant power assay (FRAP) and hydroxyl radicals scavenging assay revealed good Fe(3+) to Fe(2+) reduction and strong inhibition of hydroxyl radical formation, respectively. High dosage (1 mmol/dm(3) ) of IRA2 and IRA3 did not cause genotoxicity in human lymphocytes. Moreover, lymphocytes pretreated with all three IRAs accumulated only very few DNA breaks induced by H2 O2 than lymphocytes pretreated with resveratrol. Additionally, the number of detected DNA breaks appearing after removal of damaged DNA bases, 8-oxo-7,8-dihydroguanine (8-oxoG), did not dramatically increase in lymphocytes treated with IRA2. Thus, we concluded that IRAs, especially IRA2, are strong antioxidants with the ability to protect lymphocytes from oxidative damage

Synthesis and Free Radical Scavenging Activity of New Hydroxybenzylidene Hydrazines

Hydroxybenzylidene hydrazines exhibit a wide spectrum of biological activities. Here, we report synthesis and free radical scavenging activity of nine new N-(hydroxybenzylidene)-N′-[2,6-dinitro-4-(trifluoromethyl)]phenylhydrazines. The chemical structures of these compounds were confirmed by 1H-NMR, 13C-NMR, 19F-NMR, IR spectroscopy, LC-MS, and elemental analysis. The prepared compounds were tested for their activity to scavenge 2,2-diphenyl-1-picrylhydrazyl (DPPH), galvinoxyl radical (GOR), and 2,2′-azino-bis(3-ethylbenzothiazoline)-6-sulphonic acid (ABTS) radicals. The free radical scavenging activity expressed as SC50 values of these compounds varied in a wide range, from a strong to no radical scavenging effect. The most effective radical scavengers were hydroxybenzylidene hydrazines containing three hydroxyl groups in the benzylidene part of their molecules. The prepared compounds were also tested for their activity to inhibit photosynthetic electron transport in spinach chloroplasts. IC50 values of these compounds varied in wide range, from an intermediate to no inhibitory effect

Photo-Reduction of CO2 by VIS Light on Polythiophene-ZSM-5 Zeolite Hybrid Photo-Catalyst

A new hybrid photo-catalyst based on ZSM-5 zeolite suitable for reduction of carbon dioxide was synthesized. The photo-catalyst was prepared by oxidative polymerization of thiophene with FeCl3 in the presence of ZSM-5 with participation of ultrasound. The synthesized photo-catalyst strongly absorbs light radiation up to approx. 650 nm, with the absorption edge in the NIR region. Reactive radicals were generated by VIS light irradiation in an aqueous suspension consisting of the photo-catalyst with CO2. Formic acid and acetic acid were generated as the main products of the CO2 reduction. EPR spin trapping technique was applied to identify the reactive radical intermediates. In this work, the mechanism of product formation is also discussed

NMR study on reaction processes from aluminum chloride hydroxides to alpha alumina powders

Starting from gelatinous aluminum chloride hydroxide, the transformation process toward α‐Al2O3 was examined using 27Al NMR, both in the liquid and solid states, as a main analytical tool. By increasing the hydrolysis ratio (h, defined as [OH−]/[Al3+]) of the starting aqueous precursor up to h = 2.5, the transition temperature to the final product, α‐Al2O3, decreased to as low as 500°C. In this case, the structural change from amorphous alumina to α‐Al2O3 took place without intermediate transition Al2O3 phases. Examining the process of networking during the transition from aqueous sol–through the state of xerogel–to final anhydrous oxide by nuclear magnetic resonance (NMR) revealed the presence of highly polymeric species mainly ascribed to δ‐[Al2O8Al28(OH)56(H2O)24]18+ (δ‐Al30). δ‐Al30 species were found in the solution phase and became predominant after drying. We conclude that the lower temperature synthesis of α‐Al2O3 became possible due to preformation of polymerized AlO6 construction units in the precursor, reducing the energy barrier for the nucleation of the final α‐Al2O3 phase

7-Dialkylaminocoumarin Oximates: Small Molecule Fluorescent “Turn-On” Chemosensors for Low-Level Water Content in Aprotic Organic Solvents

The water sensing properties of two efficient two-component fluorescent “turn-on” chemo-sensors based on the 7-dialkylaminocoumarin oxime acid-base equilibrium were investigated. Interestingly, although simple frontier orbital analysis predicts an intramolecular photoinduced electron transfer quenching pathway in conjugated oximates, TD-DFT (Time-dependent density functional theory) quantum chemical calculations support non-radiative dark S1 excited state deactivation as a fluorescence quenching mechanism. Due to the acid-base sensing mechanism and sensitive “turn-on” fluorescent response, both studied coumarin aldoxime chemosensors exhibit rapid response to low-level water content in polar aprotic solvents, with detection limits comparable to chemodosimeters or chemosensors based on interpolymer π-stacking aggregation

Front Cover: Enhancing the Potential of Fused Heterocycle‐Based Triarylhydrazone Photoswitches (Chem. Eur. J. 8/2024)

A new class of triarylhydrazone photoswitches has been designed, following an idea to control the strength of a hydrogen bond connecting the photo-active hydrazone part with a heteroaryl substituent. Introducing a benzothiazole moiety results in high thermal stability, absorption above 365 nm, and satisfactory photoconversion rates. High-quality calculations and advanced ultrafast spectroscopy allowed the nature of the electronic transitions to be resolved and the photoisomerization mechanism to be elucidated