Photoreduction of Nitroaromatic Species

Properties and Reactivity of Excited States

Abstract

Photochemical reduction of nitroaromatic species has been critically reviewed. The photoreaction mechanism of nitroaromatic compounds has been less understood in comparison with that of aromatic carbonyl compounds, because the properties of nitroaromatic excited states are still ambiguously described. At least three different lower electronically excited states are involved in the longest wavelength absorption band. These are L_a (long-axis polarization), L_b (short-axis polarization), and nπ^* states. The relative location of these three states is dependent upon the nature of substituents and solvents, and therefore the characterization of lower excited states of nitrobenzene derivatives are rather difficult.
Since complications due to the secondary process of primary photoproducts are inevitable, an intermolecular photoreduction for nitroaromatic species is practically of minor importance. On the other hand, some intramolecular photoredox reactions involving ο-nitrobenzyl moiety have been used for photosensitive protection of a certain functional group and photoresists.