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Electrochemical CO2 reduction to valuable chemicals represents a greenand sustainable approach to close the anthropogenic carbon cycle, but hasbeen impeded by low efficiency and high cost of electrocatalysts. Here, acost-effective hybrid catalyst consisting of hemin (chloroprotoporphyrin IXiron(III)), a product recovered from bovine blood, adsorbed onto commercialVulcan carbon is reported. Upon heat treatment, this material shows significantlyimproved activity and selectivity for CO2 reduction in water whileexhibiting good stability for more than 10 h. The heat treatment leads toconsecutive removal of the axial chlorine atom and decomposition of the ironporphyrin ring, restructuring to form atomic Fe sites. The optimized hybridcatalyst obtained at 900 °C shows near-unity selectivity for reduction of CO2to CO at a small overpotential of 310 mV. The insight into transformation ofadsorbed Fe complexes into single Fe atoms upon heat treatment providesguidance for development of single atom catalysts.

Herein we report the photo- and electrochemical characterization of pyrimidopteridine N-oxide-based heterocycles. The potential of their application as organic photoredox catalysts is showcased in the photomediated contra-thermodynamic E→Z isomerization of cinnamic acid derivatives and oxidative cyclization of 2-phenyl benzoic acid to benzocoumarin using molecular oxygen as a mild oxidant. Furthermore, unprecedented intermolecular non-covalent n-π-hole interactions in solid state are discussed based on crystallographic and theoretical data.

Herein we describe the synthesis and photophysical and electrochemical characterization of pyrimidopteridine-based photoredox catalysts. The pyrimidopteridines can be obtained from the corresponding N-oxides through photo-mediated oxygen atom transfer to a sacrificial acceptor molecule on gramscale. The presence of a triplet excited state was evidenced by means of transient absorption spectroscopy. Pyrimidopteridines are potent excited state oxidants with excited state reduction potentials exceeding +2.10 V vs. SCE in MeCN. The catalytic activity is illustrated in the photo-mediated oxidative annulation of 2-phenylbenzoic acid.

Selective aerobic oxidation of benzyl alcohol to benzaldehyde by a (bpy)Cu

The Mizoroki-Heck coupling of 1-bromopyrene with acrylates provides a convenient access to a variety of 3-pyrenylacrylates in very good yields (up to 93%). Their photophysical properties combined with solvatochromic effects were studied. In addition, electrochemical oxidation potentials were determined by DPV (differential pulse voltammetry) measurements. The fine structure of the absorbance spectra obtained from photophysical measurements are compared with the results of theoretical calculations performed by time dependent TD-B3LYP methods using the 6-31G* basis set.

The direct electrochemistry of a HRP–chi–[C 4 mim][BF 4 ] film (where HRP = horseradish peroxidase, chi = chitosan, and [C 4 mim][BF 4 ] = the room temperature ionic liquid (RTIL) 1-butyl-3-methylimidazolium tetrafluoroborate) has been studied by cyclic voltammetry on a glassy carbon electrode. The mechanism for the electrochemical reaction of HRP is suggested to be EC for the reduction, and CE for the following re-oxidation, as the oxidative peak potential remained approximately unchanged across the scan rate range. The half wave potential of HRP reduction was found to be pH dependent, suggesting that a concomitant proton and electron transfer is occurring. Using theoretical simulations of the experimentally obtained peak positions, the standard electron transfer rate constant, k 0 , was found to be 98 (± 16) s − 1 at 295 K in pH 7 phosphate buffer solution, which is very close to the value reported in the absence of ionic liquid. This suggests that the ionic liquid used here in the HRP–chi–[C 4 mim][BF 4 ]/GC electrode does not enhance the rate of electron transfer. k 0 was found to increase systematically with increasing temperature and followed a linear Arrhenius relation, giving an activation energy of 14.20 kJ mol − 1 . The electrode kinetics and activation energies obtained are identical to those reported for HRP films in aqueous media. This leads us to question if the use of RTIL films provide any unique benefits for enzyme/protein voltammetry. Rather the films may likely contain aqueous zones in which the enzymes are located and undergo electron transfer.

Tetrafold Sonogashira reactions of tetrachloropyrazine were investigated to provide a one-step synthesis of various tetraalkynylpyrazines. The reaction conditions were thoroughly optimized using modern catalysts and ligands, and products were generally isolated in good to excellent yields. Furthermore, photophysical and electrochemical properties of selected compounds were studied and compared with those of previously reported tetraalkynylpyridines and benzenes. As a matter of fact, tetraalkynylpyrazines proved to show very promising fluorescence properties due to very high quantum yields reaching up to 0.85.

As a new approach for tuning the electronic properties of pyrene derivatives, we converted 1-bromopyrene into different substituted styrenes using the Mizoroki–Heck reaction. Several 1-(arylalkenyl)pyrenes have been characterized and their electronic properties studied by absorption and emission spectroscopy. The effect of the electronic ambience on the emission spectra of these compounds is discussed. Amongst the intramolecular influences, such as electron donating or withdrawing groups, other influences in the form of solvatochromatism are considered. Electrochemical oxidation potentials determined by DPV (differential pulse voltammetry) are discussed with regard to substituent effects. The fine structure of the absorbance spectra obtained from photophysical measurements is compared with theoretical calculations performed by time dependent B3LYP DFT (TD-DFT) methods using the 6-31G* basis set. In this context, we discuss the calculated potential energy surfaces and geometric structures with regard to the substitution pattern of the pyrenes.

The reaction pathways of bis-(2-phenylpyridinato-)(2,2'-bipyridine)iridium(III)hexafluorophosphate [Ir(ppy)2(bpy)]PF6 within a photocatalytic water reduction system for hydrogen generation based on an iron-catalyst were investigated by employing time-resolved photoluminescence spectroscopy and time-dependent density functional theory. Electron transfer (ET) from the sacrificial reagent to the photoexcited Ir complex has a surprisingly low probability of 0.4% per collision. Hence, this step limits the efficiency of the overall system. The calculations show that ET takes place only for specific encounter geometries. At the same time, the presence of the iron-catalyst represents an energy loss channel due to a triplet-triplet energy transfer of Dexter type. This loss channel is kept small by the employed concentration ratios, thus favoring the reductive ET necessary for the water reduction. The elucidated reaction mechanisms underline the further need to improve the sun light's energy pathway to the catalyst to increase the efficiency of the photocatalytic system.