Unusual negative photochromism via a short-lived imidazolyl radical of 1,1'-binaphthyl-bridged imidazole dimer.

We have synthesized a new photochromic compound that exhibits unusual negative photochromism, in which the stable colored species photochemically converts into the metastable colorless species via a short-lived radical. This compound has a 1,1'-binaphthyl moiety bridging the two diphenylimidazole units. Its photochemical properties were investigated by nanosecond laser flash photolysis.