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

摘要

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-naphthoxazine] 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 evolution of the bichromophoric molecules were followed spectrophotometrically and by high performance liquid chromatography (HPLC). The photochromic reaction was found to be only partially photoreversible. Massive irradiation with visible light led to degradation. The reaction mechanism for these molecules containing a chromene moiety is characterised by an intermediate, which thermally evolves to different products. The quantum yield of formation and the first-order kinetic constant of the thermal evolution of the intermediate 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 compounds allowed reasonable photoreaction mechanisms to be proposed.