The development of stable systems to generate chemical fuels through water splitting by sunlight is a key challenge of modern materials chemistry, one that is driven by increasing energy demands and climate change. The central problems are to design chemically stable light-harvesting antenna molecules and co-factors, and then to assemble these active components into an integrated photosystem. Various substances have been examined as visible-light converters, including metal-organic dyes, [1] inorganic semiconductors, [2] and conjugated polymers. [3] The last are of particular interest, as they are much closer to biological systems in composition and are potentially sustainable, as well as cheap and easily processable. Principally, properties such as the HOMO and LUMO position and the resulting band gap can be precisely chemically engineered by synthesizing the constituents. To date, in spite of the wide availability of conducting polymers developed for photovoltaics, [4] the impact of these polymers on water splitting technology remains minor, because ordinary conducting polymers are usually unstable to visible light irradiation in conjunction with exposure to oxygen and water.A recent study has explored metal-free, polymeric graphitic carbon nitride (g-C 3 N 4 ) for the generation of hydrogen from a protic solution with visible light. [5] This carbon nitride (CN) polymer was not only found to be a stable semiconductor, but also to be capable of achieving both half reactions of water splitting, meaning that the band-gap covers both the water reduction and water oxidation potentials. This is indeed a rare and lucky case. However, the activity of pristine g-C 3 N 4 remains moderate. [5] Several strategies, such as nanostructuring, [6] doping, [7] cocatalyzing, [5,8] and copolymerization, [9] have been exploited to improve the photocatalytic activity and selectivity of carbon nitride. Indeed, it was shown that by copolymerizing simple barbituric acid with the carbon nitride precursor through a Schiff base reaction, the performance of g-C 3 N 4 could be enhanced, which is an effect resulting from extension of the optical absorption of the polymer to cover more of the visible light range. [9] However, in this case the HOMO was decreased in energy, thus lowering the oxidation potential, which is presumably the most difficult step in achieving overall water splitting with organic semiconductors. This is why the design of appropriate comonomers with diverse chemical composition and structure to allow for modification of the band structure and optoelectronic properties of carbon nitride is still a relevant and promising task.Herein, we advance this strategy by employing a variety of new monomer building blocks with the desired compositions and electronic structures for chemical incorporation into the conjugated polymeric network of g-C 3 N 4 . Most precursors of carbon nitride polymers contain cyano groups, amino groups, or both, with the simplest case being cyanamide, which can undergo multiple thermal condensations to ...

Coupling on sunshine: A simple and efficient synthesis of benzoxazoles, benzimidazoles, and benzothiazoles is realized through a one‐pot preparation driven by a photocatalytic cascade reaction. Carbon nitride and visible light are employed to achieve this metal‐free aerobic oxidation of amines to imines (see scheme; mpg‐C3N4=mesoporous graphite carbon nitride).

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Ein echter Sonnenschein: Eine einfache und effiziente Synthese von Benzoxazolen, Benzimidazolen und Benzothiazolen gelingt mithilfe eines Eintopfverfahrens, das durch eine photokatalytische Kaskadenreaktion angetrieben wird. Bei dieser metallfreien aeroben Oxidation von Aminen zu Iminen kommen Kohlenstoffnitrid und sichtbares Licht zum Einsatz (siehe Schema; mpg‐C3N4=mesoporöses graphitisches Kohlenstoffnitrid).

A heptazine‐based polymer network (HMP‐3) with a donor–acceptor (D–A) structure was prepared and tested as catalyst for photocatalytic hydrogen evolution from water. Compared to other heptazine‐based materials, which are typically prepared at high temperatures and have recently received much interest as metal‐free photocatalysts, the low‐temperature protocol applied here allows the defined introduction of organic functional groups within the polymer backbone. The structure of HMP‐3 contains alternating heptazine and benzothiadiazole moieties as electron acceptors connected by aminobenzene bridges as electron donors. The resulting material leads to enhanced hydrogen evolution compared to graphitic carbon nitride materials prepared at high temperatures (>500 °C) most probably because of the stabilization of photogenerated charge carriers in the D–A structure.

In this communication we describe the oxidative CC bond formation of tertiary amines with various nucleophiles under very mild and environmental friendly conditions by using mesoporous graphitic carbon nitride (mpg‐C3N4) semiconductor as a heterogeneous, metal‐free photosensitizer in combination with visible light and oxygen as the terminal oxidation agent. This system can be further combined with proline‐organocatalysis to achieve oxidative tandem photocatalysis, demonstrating a rich cascade of chemical possibilities of the current photosynthesis system.

SummaryThis publication describes a highly selective oxidation of aldehydes to the corresponding acids or esters. The reaction proceeds under metal-free conditions by using N-heterocyclic carbenes as organocatalysts in combination with environmentally friendly oxygen as the terminal oxidation agent.

Within the last couple of years, the photocatalytic, oxidative CC coupling has grown to a well‐established methodology, especially for the modification of aryl‐substituted tetrahydroisoquinoline derivatives. However, until now, this reaction is mainly restricted to the usage of strong nucleophiles like nitroalkanes, cyanides, enamines, phosphonates and malonates. Within this publication we present an extension of such a method towards the application of weaker nucleophiles, namely allylstannanes, allylsilanes and allylboranes. Therefore, a very simple protocol was invented, using heterogeneous mesoporous graphitic carbon nitride (mpg‐C3N4) as catalyst and air as oxidizing agent, leading to high yields for a broad range of substrates.