Photochromism of Salicylidene Aniline

Photochromic properties of two crystalline forms of salicylidene aniline have been investigated, emphasizing properties not previously evaluated. A broad band with maximum absorbance at 480 mmu is induced by near uv radiation; 380 mmu is most effective. Occurring spontaneously, the reverse change is accelerated by visible radiation; 480 mmu is most effective. The two crystalline forms require similar energy for inducing the 480-mmu band, but differ markedly in energy for the reverse change and in the kinetics of spontaneous fading. For thin films, maximum absorbance change divided by thickness is about 0.5mu(-1). The compound resists fatigue excellently when cycled by radiation most effective for photochromic changes.