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7,8‐Dimethoxy‐3‐methyl‐1,10‐ethylenealloxazinium chloride (1a) was found to be a superior photooxidation catalyst among substituted ethylene‐bridged flavinium salts (R=7,8‐diMeO, 7,8‐OCH2O‐, 7,8‐diMe, H, 7,8‐diCl, 7‐CF3 and 8‐CF3). Selection was carried out based on structure vs catalytic activity and properties relationship investigations. Flavinium salt 1a proved to be robust enough for practical applications in benzylic oxidations/oxygenations, which was demonstrated using a series of substrates with high oxidation potential, i. e. 1‐phenylethanol, ethylbenzene, diphenylmethane and diphenylmethanol derivatives substituted with electron‐withdrawing groups (Cl or CF3). The unique capabilities of 1a can be attributed to its high photostability and participation via a relatively long‐lived singlet excited state, which was confirmed using spectroscopic studies, electrochemical measurements and TD‐DFT calculations. This allows the maximum use of the oxidation power of 1a, which is given by its singlet excited state reduction potential of +2.4 V. 7,8‐Dichloro‐3‐methyl‐1,10‐ethylenealloxazinium chloride (1 h) can be used as an alternative photocatalyst for even more difficult substrates. [ABSTRACT FROM AUTHOR]

Spatially resolved functionalization of 2D materials is highly demanded but very challenging to achieve. The chemical patterning is typically tackled by preventing contact between the reagent and material, which brings various accompanying challenges. Photochemical transformation on the other hand inherently provides remote high spatiotemporal resolution using the cleanest reagent—a photon. Herein, we combine two competing reactions on a graphene substrate to create functionalization patterns on a micrometer scale via the Mitsunobu reaction. The mild reaction conditions allow introduction of covalently dynamic linkages, which can serve as reversible labels for surface‐ or graphene‐enhanced Raman spectroscopy characterization of the patterns prepared. The proposed methodology thus provides a pathway for local introduction of arbitrary functional groups on graphene. Mapping graphene: Patterns of chemical functional groups are grafted onto graphene via photomodulated Mitsunobu reaction. Enhanced Raman spectroscopy employing covalently dynamic linkages provide easy and direct mapping of the structures prepared. Arbitrary patterns with micrometer resolution can be prepared. [ABSTRACT FROM AUTHOR]

Abstract: New photocatalysts from the flavin family were found to mediate the [2+2] photocycloaddition reaction. 3‐Butyl‐10‐methyl‐5‐deazaflavin (3 a) and 1‐butyl‐7,8‐dimethoxy‐3‐methylalloxazine (2 e), if irradiated by visible light, were shown to allow an efficient (Φ≈3–10 %) intramolecular cyclisation of various types of substrates including substituted styrene dienes and bis(aryl enones), considered as electron‐rich and electron‐poor substrates, respectively, without any additional reagent. The versatility of the procedure was demonstrated by the cyclisation of photosensitive cinnamyl (E)‐3‐iodoallyl ether. Structure–activity studies found alloxazine 2 e was more active than 7‐monosubstituted (R=Cl, Br and MeO) alloxazines. The introduction of chlorine and bromine atom on the deazaflavin skeleton did not enhance the catalytic efficiency of 3 a. A detailed electrochemical and spectroscopic study explains the reaction mechanism proceeding through energy transfer from the flavin excited triplet state to the diene followed by its cyclisation. [ABSTRACT FROM AUTHOR]

Keywords: Aerobic oxidation; Electron transfer; Photochemistry; Photoredox catalysis; Spectroscopy EN Aerobic oxidation Electron transfer Photochemistry Photoredox catalysis Spectroscopy 4283 4283 1 09/23/21 20210921 NES 210921 The B front cover picture b , prepared by Dr D. Prukala, illustrates ethylene-bridged 7,8-dimethoxyflavinium salt excited with blue light. Front Cover Picture: Robust Photocatalytic Method Using Ethylene-Bridged Flavinium Salts for the Aerobic Oxidation of Unactivated Benzylic Substrates (Adv. Aerobic oxidation, Electron transfer, Photochemistry, Photoredox catalysis, Spectroscopy. [Extracted from the article]

Two new photocatalytic systems based on flavinium species formed in situ by protonation of riboflavin-tetraacetate or prepared in advance via alloxazine quaternization are used as tools for the title reaction. [ABSTRACT FROM AUTHOR]

Two new artificial photolyase models that recognize pyrimidine dimers in protic and aprotic organic solvents as well as in water through a combination of charge and hydrogen-bonding interactions and use a mimic of the flavine to achieve repair through reductive photoinduced electron transfer are presented. Fluorescence and NMR titration studies show that it forms a 1:1 complex with pyrimidine dimers with binding constants of ∼10³ M-1 in acetonitrile or methanol, while binding constants in water at pH 7.2 are slightly lower. Excitation of the complex with visible light leads to clean and rapid cycloreversion of the pyrimidine dimer through photoinduced electron transfer catalysis. The reaction in water is significantly faster than in organic solvents. The reaction slows down at higher conversions due to product inhibition. [ABSTRACT FROM AUTHOR]

The method is chemoselective, producing sulfoxide without overoxidation to sulfones. [ABSTRACT FROM AUTHOR]

An alloxazine derivative allows the efficient cyclobutane ring formation via intramolecular [2 + 2] cycloaddition of both electron-rich styrene dienes and electron-poor bis(arylenones). [ABSTRACT FROM AUTHOR]