Photochromism of p-Phenylenediaminetetraacetic Acid absorbed in Porous Glass

THE compound p-phenylenediaminetetraacetic acid, p-PTDA (I), can be chemically oxidized to give a blue radical cation (II). We have now found that this reaction can be carried out in a novel photochemical manner. When an aqueous solution of the diamine is absorbed by porous glass and irradiated with ultra-violet light, it gives what appears to be the same blue radical-ion species. On interruption of irradiation, the photo-induced coloration rapidly bleaches. Since photochemical reactions leading to reversible colour changes (photochromism) are of fundamental and practical importance, we have undertaken the following investigation of this system.