Picosecond and Nanosecond Laser Photolyses of p-Nitrophenylacetate in Aqueous Media. A Photoadiabatic Decarboxylation Process?

Article abstract of DOI:10.1021/j100307a019

Employing UV picosecond (266 nm, 22 ps, ca. 0.5 mJ) and nanosecond (266 nm, 12 ns, 0.5-5 mJ) excitation, we have investigated the dynamics of the photodecarboxylation of p-nitrophenylacetate anions in aqueous solution.In agreement with previous micosecond flash photolysis studies, we believe that the primary decarboxylation products are the p-nitrobenzyl anion and carbon dioxide.It is proposed that the anion is produced in its triplet state following photoadiabatic cleavage of the lowest n,?* triplet state of p-nitrophenylacetate.The triplet state of the anion is observed as an intermediate (λ_max ca. 290 nm) of lifetime 90 ns (pH > 5.0).In methanol/water and acetonitrile/water mixtures, its lifetime is found to increase as the aqueous portion of the solvent is decreased.A reaction mechanism is developed.