Phototropism of ortho-nitrobenzyl derivatives

Abstract

In a study of the phototropic properties of various nitrobenzyl derivatives, no compound was found to be phototropic which did not have a nitro group ortho to a benzyl hydrogen. This structural requirement appears to be necessary but is not sufficient in itself to produce photochromic color under the conditions of our experiments. The results are consistent with the photochemical production of an excited species in which hydrogen is transferred from the methylene carbon to the oxygen of the ortho nitro group, producing a colored aci quinoid structure in equilibrium with its anion. The rate of fading of the colored photochemical product varies greatly with solvent, acidity, and temperature, as well as with the structure of the compounds.