The early processes in the photochemistry of ortho-nitrobenzyl acetate

The early processes in the de-caging of acetic acid from o-nitrobenzyl acetate (oNBAc) were studied by femtosecond techniques. Solutions of oNBAc in acetonitrile were excited by 260 nm laser pulses and the resulting spectroscopic changes probed by transient absorption and stimulated Raman spectroscopy. Absorption and Raman data give evidence of the formation of an aci-nitro species resulting from an intramolecular hydrogen transfer. The species is formed on the 1 ps and 1 ns time scale in equal amounts. The two processes are attributed to hydrogen transfers via a singlet and a triplet channel. The overall quantum yield of the aci-nitro formation is 0.1 matching the de-caging yield.