Fotosensibilisierte Ausbleichung von Azomethinfarbstoffen

Abstract

Fotosensitized Fading of Azomethine DyesThe quantum yields of photofading of the azomethine dyes 1a—h were determined in the presence of the sensitizers benzophenone (B), michler's ketone (MK) and anthracen (A), in isopropanol and benzene. In isopropanol, excluding oxygen, the leuco dyes 5 are formed by benzophenone in high quantum yield (Φ = 0.4). Photofading also takes place using Michler's ketone (Φ ≅ 3 · 10−3) and anthracene (Φ ≅ 1 · 10−4), but 5 was not found. With benzophenone (Φ ≅ 7 · 10−3), Micher's ketone (Φ ≅ 1 · 10−3) and anthracene (Φ ≅ 1 · 10−4) as sensitizers the chromophore of 1a—h were destroyed, when oxygen was present. The photofading with benzophenone and Michler's ketone is a result of radicalic processes.Radical scavangers 8 and 9, therefore, give a strong decrease of the quantum yield of photofading. The photofading in benzene corresponds to the results in isopropanol considering the lower potential of this solvent for photoreduction processes.