En l'absence de lumikre UV, il s'ktablit un tquilibre acide-base entre la forme spiro et une forme protonee fermke. Par irradiation dans des conditions acides approprites, on peut transformer la forme spiro en une forme cationique ouverte par le biais de la forme merocyanine. I1 s'ttablit un Cquilibre acide-base entre les deux formes ouvertes. A l'exception de la forme protonte fermCe, on a confirme les structures par RMN. Faisant appel 2i la photolyse eclair, on a CtudiC la cinetique de la reaction thermique de fermeture de cycle des deux formes. I1 est dernontre que la reaction de fermeture de cycle se produit uniquement par le biais de la forrne merocyanine. Les valeurs de pK, dCterminees pour les deux equilibres, fournissent les valeurs de pH dans lesquelles le changement de charge moltculaire induit par la lumikre se produit.[Traduit par la redaction] Introduction Recently, the photochromic behaviour of indolinospirooxazine derivatives has been intensively investigated (1-6). This is mainly due to their rapid photoresponsive change of the molecular structure and the better photodurability as compared to the indolinospiropyran derivatives. The photochromism and the acid-base behaviour of indolinospiro compounds is summarized in Scheme 1.By UV irradiation the C-0 bond of the colourless spiroform A is cleaved and the coloured merocyanine form B is formed. The reverse reaction proceeds thermally or photochemically (5-1 1). In the case of spiropyran derivatives it has been established (12-18) that the zwitterionic B-form can be protonated to the cationic C-form. The same is expected for spirooxazine compounds.Due to the different electronic structures and molecular geometries of the A-, the B-, and the C-forms, their physical and chemical properties, such as colour, polarity, charge, and their acidity and basicity are also different. The possibilitv to switch between the various forms and thus the var-
SynopsisAn azo dye, 2-methyl-N, N-bis(2-hydroxyethyl)-4-aminoazobenzene (nonionic dye) and its conjugate acid (cationic dye) are simultaneously adsorbed by the cellulose membranes carrying sulfonic acid groups from a slightly acidic aqueous solution. Sorption equilibria of the nonionic and the cationic dye are described in terms of the Henry's partition and the ionic exchange mechanism, respectively; in the latter case, the ion exchange constants obtained for the membrane with sulfonic acid group content (SAG) =
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