Low-molecular weight organic dyes with metallic colors are highly desirable because of their light weight and non-conductive nature, especially as paints for large vehicles and electronic devices. To this end, Yukishige Kondo and co-workers at Tokyo University of Science, Japan, have synthesized an azobenzene that reflects gold color upon recrystallization, namely bis[4-(3-methylbutoxy)phenyl]diazene (DC-azo).
Made in three steps via azo coupling and alkylation from p-aminophenol, this compound bears symmetric alkoxy groups at para positions (see figure). Its crystals show a specular reflectance profile very similar to that of gold thin films. The gold coloration, likely as a result from the interplay of absorption by the azo group and molecular packing orientation, is stable against high temperature, UV light, and drying.
Greatly advantageous over other azo dyes that suffer from gradual decoloration, it has therefore become a promising candidate for alternatives to traditional metal-based gold-color paints.
- Gold-Colored Organic Crystals of an Azobenzene Derivative,
Y. Kondo, A. Matsumoto , K. Fukuyasu , K. Nakajima , Y. Takahashi,