Redox Photochromism Involving Near Infrared Absorption Maximum
trans-4,4′-Vinylenebis (1-benzylpyridinium) dichlorides and 1,1′-ethylene-2,2′-bipyridinium dibromides in a poly(N-vinyl-2-pyrrolidone) matrix film exhibited reversible absorption maxima in the near IR(ca. 800 nm) upon UV irradiation. The thermal stability of the absorption maximum thus developed was influenced by the surroundings as well as the kind of compound.