Synthesis and unexpected photochemical behaviour of biphotochromic systems involving spirooxazines and naphthopyrans linked by an ethylenic bridge

Using the Wittig reaction, six new biphotochromic compounds have been prepared by the coupling of conveniently functionalised spiro[indoline–naphthoxazines] and naphthopyrans. Compared to molecules taken individually, unusual photochromic behaviour has been detected with compounds for which a double bond of Z-configuration links both entities by the 5 or 5′ positions of the naphthalenic parts. Indeed, in this case the thermally stable uncoloured and coloured forms (bistable system) can be photochemically converted acting as photochemical switches.