Photokinetic behaviour of biphotochromic supramolecular systems - Part 2. A bis-benzo-[2H]-chromene and a spirooxazine-chromene with a (Z-)ethenic bridge between each moiety

The photochromic behaviour of two new bichromophoric molecules (a symmetric one, formed by two 3,3-diphenyl-[3H]-naphtho [2,1-b]pyran moieties, and an asymmetric one, formed by a naphthopyran and a spiro [indoline-naphthoxazi ne] moiety) linked through an ethenic double bond has been studied. A model compound, where the chromene moiety is Linked to a naphthalene group, was also investigated for comparison purpose. The photochemical and thermal evo lution of the bichromophoric molecules were followed spectrophotometrically and by high performance liquid chromatography (HPLC). The photochromic rea ction was found to be only partially photoreversible. Massive irradiation w ith visible light led to degradation. The reaction mechanism for these mole cules containing a chromene moiety is characterised by an intermediate, whi ch thermally evolves to different products. The quantum yield of formation and the first-order kinetic constant of the thermal evolution of the interm ediate were determined. The identification of the photoproducts was helped by information from a parallel NMR study. Comparison of these results with those previously obtained on related monochromophoric and bichromophoric co mpounds allowed reasonable photoreaction mechanisms to be proposed. (C) 200 1 Elsevier Science B.V. All rights reserved.