Carbon radicals are reactive species useful in various organic transformations. The C-X bond cleavage of organohalides by photoirradiation is a common method to generate carbon radicals in a controlled fashion. The use of organochloride substrates is still a formidable challenge due to the low reduction potential and the high dissociation energy of the C-Cl bond. In this report, we address these issues by using a nonmetal organic molecule with a relatively simple structure as a photocatalyst. In this catalyst (bis(dimethylamino)carbazole), the amino groups increase both the HOMO and LUMO energy levels, especially in the former. As a result, compared to the parent molecule, the new catalyst shows experimentally red-shifted absorption in the visible region and forms an excited state with better reducing capability. This photocatalyst was used in the reduction of unactivated aryl chlorides and alkyl chlorides in the presence of hydrogen atom donor at room temperature. The catalytic system can also be applied to the coupling of aryl chlorides with electron-rich arene and heteroarenes to affect the C-C bond-forming reactions. Our mechanistic study results support the assumption that carbon radicals are formed from the organochlorides via a single-electron-transfer step.

The increasing CO2 concentration in the atmosphere is an urgent social problem that has to be resolved. Reducing CO2 into compounds useful as energy sources and carbon materials is desirable. For the CO2 reduction reaction (CO2RR) to be operational on a global scale, the catalyst system must: (1) use only renewable energy, (2) be built from abundantly available elements, and (3) not require highenergy reactants. Although light is an alluring energy source, most existing methods utilize electricity. Furthermore, catalyst systems are based on rare heavy metals. Herein, we present a transition-metal-free catalyst system for CO2RR using visible light and containing a carbazole photocatalyst and an organohydride co-catalyst based on benzimidazoline. It produced formate with a turnover number exceeding 8000. No other reduced products such as H2 and CO were generated, confirming the high selectivity of the system. This finding is essential for operating artificial photosynthesis on a useful scale.

Employing a photoremovable protecting group is a useful technique to achieve precise conditional control over a biological function. This Communication reports the development of a photoremovable protecting group for the nitrile moiety. In the process, O-(arylcarbonyl) oxime was photochemically converted into the corresponding nitrile in the presence of a carbazole photosensitizer by means of an electron transfer from the excited carbazole to the arylcarbonyl unit. A variety of alkyl and (hetero) aryl nitriles were generated from the corresponding O-(arylcarbonyl) oximes. Moreover, a self-contained variant, in which O-(arylcarbonyl) oxime and carbazole units were covalently bonded, exhibited photochemical nitrile formation even in a highly diluted aqueous solution (0.1 mM), thus demonstrating that this molecular motif is potentially applicable in biological systems.[a] Prof.

The increasing CO2 concentration in the atmosphere is an urgent social problem that has to be resolved. Reducing CO2 into compounds useful as energy sources and carbon materials is desirable. For the CO2 reduction reaction (CO2RR) to be operational on a global scale, the catalyst system must: (1) use only renewable energy, (2) be built from abundantly available elements, and (3) not require high-energy reactants. Although light is an alluring energy source, most existing methods utilize electricity. Furthermore, catalyst systems are based on rare heavy metals. Herein, we present a transition-metal-free catalyst system for CO2RR using visible light and containing a carbazole photocatalyst and an organohydride co-catalyst based on benzimidazoline. It produced formate with a turnover number exceeding 8000. No other reduced products such as H2 and CO were generated, confirming the high selectivity of the system. This finding is essential for operating artificial photosynthesis on a useful scale.