Light as a tool in organic photocatalysis : multi-photon excitation and chromoselective reactions

Over the past decades, photoredox catalysis has developed to the big mature field of chemistry. Especially in the field of organic synthesis, more and more sustainable alternatives to conventional synthesis are being developed. Nonetheless, most research activities are focused on the development of new synthetic pathways, utilizing photons as a source of energy for breaking and building of new chemical bonds. Indeed, photons are traceless reagents in the photocatalytic system, however the full power of which is usually overlooked. The intensity and energy of photons are important parameters that regulate the thermodynamic limits of photocatalytic reaction, and therefore control its reactivity and/or selectivity. Herein, we overview light as a powerful instrument in hands of organic chemist and discuss such emerging concepts as wavelength-dependent, multi-photon, and chromoselective organic photocatalytic reactions. We discuss relevant cases, where selection of the irradiation mode, light intensity (one-, two- photons) or wavelength (UV, blue, green) has a crucial role on the outcome of the photocatalytic event. Thus, control over irradiation conditions influence the reaction mechanism and offers an access to highly reactive species that are otherwise hardly available and. This allows for the unique chemical events to happen, such as deep reduction reactions, typical for alkali metals. The principles of these concepts and their applications are reviewed for both homogeneous and heterogeneous photocatalysts

Visible Light Driven Reductive (Cyclo)Dimerization of Chalcones Over Heterogeneous Carbon Nitride Photocatalyst

Single-electron reduction of chalcones to the respective radical anions is a useful technique to activate these molecules toward subsequent transformations. Herein, a metal-free photocatalytic version of chalcones reduction in the presence of triethanolamine as a convenient electron donor and using heterogeneous carbon nitride visible-light photocatalyst is presented. The reaction proceeds via a long-lived radical species of the heterogeneous organic semiconductor. The scope of the reaction was studied, and regioselectivity of the chalcone radicals coupling was investigated. (1) Ten chalcones gave selectively polysubstituted cyclopentanoles with 31–73% isolated yield; (2) Two chalcones bearing electron-donor groups, 4-MeOC6H4 and 2-thienyl, gave selectively the β-ketodienes in 42% and 53% isolated yield, respectively; (3) Pentafluorophenyl substituted chalcone gave exclusively the product of the radicals coupling followed by hydrogen transfer from triethanolamine–hexane-1,6-dione in 65% isolated yield. Reductive cross cyclodimerization of a mixture of two different chalcones proceeded regioselectively with the formation of one product out of four possible. The mechanism was investigated by cyclic voltammetry and linear sweep voltammetry and suggests that the reaction proceeds through proton-coupled electron transfer

Solar reforming of biomass with homogeneous carbon dots

A sunlight-powered process is reported that employs carbon dots (CDs) as light absorber for the conversion of lignocellulose into sustainable H2 fuel and organics. This photocatalytic system operates in pure and untreated sea water using a benign pH (2-8) at ambient temperature and pressure. The CDs can be produced in a scalable synthesis directly from biomass itself and their solubility allows for good interactions with the insoluble biomass substrates. They also display excellent photophysical properties with a high fraction of long-lived charge carriers and the availability of a reductive and an oxidative quenching pathway. The presented CD-based biomass photoconversion system opens new avenues for sustainable, practical, and renewable fuel production through biomass valorization

Enhanced organic photocatalysis in confined flow through a carbon nitride nanotube membrane with conversions in the millisecond regime

Bioinspired nanoconfined catalysis has developed to become an important tool for improving the performance of a wide range of chemical reactions. However, photocatalysis in a nanoconfined environment remains largely unexplored. Here, we report the application of a free-standing and flow-through carbon nitride nanotube (CNN) membrane with pore diameters of 40 nm for confined photocatalytic reactions where reactants are in contact with the catalyst for 5 s–1. Such high rates are otherwise only known for special enzymes and are clearly attributed to the confinement of the studied reactions within the one-dimensional nanochannels of the CNN membrane. Namely, a concave surface maintains the internal electric field induced by the polar surface of the carbon nitride inside the nanotube, which is essential for polarization of reagent molecules and extension of the lifetime of the photogenerated charge carriers. The enhanced flow rate upon confinement provides crucial insight on catalysis in such an environment from a physical chemistry perspective. This confinement strategy is envisioned not only to realize highly efficient reactions but also to gain a fundamental understanding of complex chemical processes

Saving the energy loss in lithium-mediated nitrogen fixation by using highly reactive Li₃N intermediate for C–N coupling reactions

Direct synthesis of N-containing organic compounds from dinitrogen (N2) can make synthetic chemistry more sustainable. Previous bottlenecks in lithium-mediated N2 fixation were resolved by loading Li metal anodes covered with the typical Li+ ion-conducting solid electrolyte interface, which are subsequently allowed to react with N2. The developed strategy allowed us to reach high Faradaic efficiencies toward Li3N. These reactive Li3N were then contacted with acylchlorides. Surface nitride ions are more nucleophilic than amines which direct the two C–N coupling reactions toward formation of imides rather than amides, and an integrated current efficiency of 57~77% could be realized. This study thereby not only provides a feasible electrochemical Li3N synthesis, but also delineates an economical and green synthesis of highly valuable N-containing compounds from N2 under mild conditions, just using commercial spare parts and processes from omnipresent Li battery technology

Chromoselektive Synthese von Sulfonylchloriden und Sulfonamiden mit Kalium-Poly(heptazinimid)-Photokatalysator

Among external stimuli used to promote a chemical reaction, photocatalysis possesses a unique one—light. Photons are traceless reagents that provide an exclusive opportunity to alter chemoselectivity of the photocatalytic reaction varying the color of incident light. This strategy may be implemented by using a sensitizer capable to activate a specific reaction pathway depending on the excitation light. Herein, we use potassium poly(heptazine imide) (K-PHI), a type of carbon nitride, to generate selectively three different products from S-arylthioacetates simply varying the excitation light and otherwise identical conditions. Namely, arylchlorides are produced under UV/purple, sulfonyl chlorides with blue/white, and diaryldisulfides at green to red light. A combination of the negatively charged polyanion, highly positive potential of the valence band, presence of intraband states, ability to sensitize singlet oxygen, and multi-electron transfer is shown to enable this chromoselective conversion of thioacetates

Green Light Photoelectrocatalysis with Sulfur-Doped Carbon Nitride: Using Triazole-Purpald for Enhanced Benzylamine Oxidation and Oxygen Evolution Reactions

Materials dictate carbon neutral industrial chemical processes. Visible-light photoelectrocatalysts from abundant resources will play a key role in exploiting solar irradiation. Anionic doping via pre-organization of precursors and further co-polymerization creates tuneable semiconductors. Triazole derivative-purpald, an unexplored precursor with sulfur (S) container, combined in different initial ratios with melamine during one solid-state polycondensation with two thermal steps yields hybrid S-doped carbon nitrides (C3N4). The series of S-doped/C3N4-based materials show enhanced optical, electronic, structural, textural, and morphological properties and exhibit higher performance in organic benzylamine photooxidation, oxygen evolution, and similar energy storage (capacitor brief investigation). 50M-50P exhibits the highest photooxidation conversion (84 ± 3%) of benzylamine to imine at 535 nm – green light for 48 h, due to a discrete shoulder (≈700) nm, high sulfur content, preservation of crystal size, new intraband energy states, structural defects by layer distortion, and 10–16 nm pores with arbitrary depth. This work innovates by studying the concomitant relationships between: 1) the precursor decomposition while C3N4 is formed, 2) the insertion of S impurities, 3) the S-doped C3N4 property-activity relationships, and 4) combinatorial surface, bulk, structural, optical, and electronic characterization analysis. This work contributes to the development of disordered long-visible-light photocatalysts for solar energy conversion and storage

Green light photoelectrocatalysis with sulfur-doped carbon nitride : using triazole-purpald for enhanced benzylamine oxidation and oxygen evolution reactions

Novel high performing materials will dictate the pace of reinventing industrial chemical processes to attain desired carbon neutrality targets. Regarding the urgency of exploiting solar irradiation long range visible-light photoelectrocatalysts from abundant resources will play a key role in the aforementioned effort. Anionic doping via co-polymerization and pre-organization of precursors results in tuneable and extrinsic semiconductors, making this a highly attractive methodology. Triazole derivative-purpald, an unexplored precursor but sulfur (S) container, combined with melamine during one solid-state polycondensation reaction with two thermal steps leads to S-doped carbon nitrides (C34). The series of S-doped/CN4-based materials demonstrated enhanced optical, electronic, structural, geometric, textural, and morphological properties and exhibited higher performance in organic benzylamine photooxidation, oxygen evolution, and similar storing energy (capacitor brief investigation) than references. Among the five composites, 50M-50P exhibited the highest photooxidation conversion yield (84±3%) of benzylamine to imine at 535 nm – green light for 48h, due to an extra discrete shoulder reaching ~700 nm, an unusual high sulfur content, preservation of crystal size, new intraband energy states, rare deep structural defects by layer distortion, hydrophobic surface, low porosity, and 10-16 nm pores. An in-depth analysis of S doping was investigated coupling x-ray photoelectron spectroscopy, transmission electron microscope, and elemental analysis, providing insights on bonds, distribution, and surface/bulk content. This work contributes to the development of amorphous photocatalysts with long-visible-light range for solar energy conversion and storage

Green Light Photoelectrocatalysis with Sulfur Doped Carbon Nitride Using Triazole Purpald for Enhanced Benzylamine Oxidation and Oxygen Evolution Reactions

Materials dictate carbon neutral industrial chemical processes. Visible light photoelectrocatalysts from abundant resources will play a key role in exploiting solar irradiation. Anionic doping via pre organization of precursors and further co polymerization creates tuneable semiconductors. Triazole derivative purpald, an unexplored precursor with sulfur S container, combined in different initial ratios with melamine during one solid state polycondensation with two thermal steps yields hybrid S doped carbon nitrides C3N4 . The series of S doped C3N4 based materials show enhanced optical, electronic, structural, textural, and morphological properties and exhibit higher performance in organic benzylamine photooxidation, oxygen evolution, and similar energy storage capacitor brief investigation . 50M 50P exhibits the highest photooxidation conversion 84 3 of benzylamine to imine at 535 nm green light for 48 h, due to a discrete shoulder amp; 8776;700 nm, high sulfur content, preservation of crystal size, new intraband energy states, structural defects by layer distortion, and 10 16 nm pores with arbitrary depth. This work innovates by studying the concomitant relationships between 1 the precursor decomposition while C3N4 is formed, 2 the insertion of S impurities, 3 the S doped C3N4 property activity relationships, and 4 combinatorial surface, bulk, structural, optical, and electronic characterization analysis. This work contributes to the development of disordered long visible light photocatalysts for solar energy conversion and storag