Mechanistic Insights and Kinetic Analysis for the Oxidative Hydroxylation of Arylboronic Acids by Visible Light Photoredox Catalysis: A Metal-Free Alternative

The photocatalytic hydroxylation of boronic acids with methylene blue as photosensitizer proceeds with high efficiency. Detailed time-resolved studies of the relevant rate constants provide a clear mechanistic understanding of excited-state processes and guided the selection of the photocatalyst and the optimization of experimental conditions

Metal-Free Photocatalytic Radical Trifluoromethylation Utilizing Methylene Blue and Visible Light Irradiation

The use of organofluorine compounds, especially those with an incorporated trifluoromethyl moiety, has increased dramatically in both the pharmaceutical and agrochemical industry. It has therefore become imperative to develop a mild and efficient synthetic technique for the inclusion of trifluoromethyl groups. Herein, we report the first use of methylene blue as a photosensitizer for the catalytic radical trifluoro- and hydrotrifluoromethylation of electron-rich heterocycles as well as terminal alkenes and alkynes under visible light irradiation. These reactions proceed with moderate to good yields at low catalyst concentrations; short irradiation times; and most importantly, without the need for potentially toxic transition-metal catalysts. In this work, considerable emphasis was also placed on understanding the kinetics of the mechanistically key steps through the use of laser flash photolysis techniques to more efficiently optimize the reaction conditions

Photoinduced Carbene Generation from Diazirine Modified Task Specific Phosphonium Salts To Prepare Robust Hydrophobic Coatings

3-Aryl-3-(trifluormethyl)­diazirine functionalized highly fluorinated phosphonium salts (HFPS) were synthesized, characterized, and utilized as photoinduced carbene precursors for covalent attachment of the HFPS onto cotton/paper to impart hydrophobicity to these surfaces. Irradiation of cotton and paper, as proof of concept substrates, treated with the diazirine-HFPS leads to robust hydrophobic cotton and paper surfaces with antiwetting properties, whereas the corresponding control samples absorb water readily. The contact angles of water were determined to be 139° and 137° for cotton and paper, respectively. In contrast, water placed on the untreated or the control samples (those treated with the diazirine-HFPS but not irradiated) is simply absorbed into the surface. Additionaly, the chemically grafted hydrophobic coating showed high durability toward wash cycles and sonication in organic solvents. Because of the mode of activation to covalently tether the hydrophobic coating, it is amenable to photopatterning, which was demonstrated macroscopically