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.
Synthetic accesses to formylated photochromic 3,3-diphenyl-[3H]-naphthopyrans (or 2H-benzochromenes) are developed through classical cyclization between appropriate hydroxynaphthaldehydes and 1,1-diphenylpropyne-1-ol and also via substituent transformations on the naphthopyran skeleton including bromine/lithium exchange and the oxidation of an hydroxymethyl group. Examples of formyl group reactivity (Wittig and Knoevenagel reactions, imine formation) from these compounds are given, showing their interest in the subsequent preparation of supramolecular systems involving a photoreactive entity. (C) 1999 Elsevier Science Ltd. All rights reserved.