Über die spektrale Sensibilisierung von Zinkoxid: II. Anomales Sorptionsverhalten von o, o′‐Dihydroxyazofarbstoffen und Entladungskinetik des damit sensibilisierten Zinkoxids

Abstract

The first acidity constants (pK₁) and the zinc complex formation constants (pK_zn) of 9 dyes of the type 1‐(2‐hydroxy‐4′‐X‐5′‐Y‐phenylazo)‐2‐naphthol 1 were measured potentiometrically. The sorption behaviour of these dyes on zinc oxide in toluene demonstrates that first a Langmuir‐type pseudo‐equilibrium of the dye with a monomolecular edge‐on adsorption (11) can be observed. The more acidic the dyes, the more is this equilibrium disguised by a faster dissolution of zinc ions from the surface to form (practically irreversibly) the polymeric 1:1 zinc‐dye complex 10. This complex is detectable in electron micrographs. The discharge kinetics of dye‐sensitized zinc oxide‐binder layers in the dark and under irradiation by visible light (10 interference filters) was determined. Substituents X and Y have no detectable influence on the intrinsic discharge kinetics; however, they influence the formation of the polymer complex 10 which is contrast to 11 is not a good sensitizer.