We have designed a molecular switch based on the photoinduced opening and thermal closing of an oxazine ring. Ultraviolet excitation of this molecule induces the cleavage of a [CO] bond to form ap-nitrophenolate chromophore in less than 10 ns with a quantum yield of ca. 0.1. The photogenerated isomer reverts thermally to the original oxazine within 50 ns. Our photochromic switch survives more than 3000 excitation cycles without decomposing, ...
