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 ...