Free radical production upon photoinduced electron transfer reactions in the presence of vinyl monomers, effect of water addition

摘要

Free radical fragments produced in the photoinduced electron transfer from triethylamine (TEA) to excited pyrenebutyltrimethylammonium (*PyBu+) lead to 1-vinyl-2-pyrrolidinone (VP) and a-hydroxyethyl methacrylate (HEMA) polymerization, Experiments carried out in water/acetonitrile solvent mixtures showed that the polymerization rate of VP increases upon increasing the water content, whereas the polymerization rate of HEMA follows the opposite trend. These results are; interpreted in terms of the strong dependence on the solvent properties of the photochemical behavior of PyBu+ in the presence of the amine or monomers, Thus, the *PyBu+ quenching by VP is almost negligible in both solvents (water and acetonitrile). Whereas, the "PyBu+ quenching rate constant by HEMA in water is 4 x 10(9) M-1 s(-1) and decreases four orders of magnitude in acetonitrile. The quenching of *PyBu+ by TEA in aqueous solutions is controlled by hydrogen-bonding interactions between water molecules and the amine, Quantum yields of the pyrene radical anion (Phi(Py-)) also strongly depend on the water content, decreasing from 0.28 to 0.015 upon going from acetonitrile to water. [References: 23]