Indigo and Tyrian Purple - From Ancient Natural Dyes to Modern Organic Semiconductors

We describe the history of indigo dye and its derivative Tyrian purple, from their roles in the ancient world to recent research showing the semiconducting properties of indigoids. Indigoids are natural dyes that have been produced for centuries, and indigo is currently the most produced dye worldwide. Herein we review the history of these materials, their chemistry and physical properties, and their semiconducting characteristics in the solid state. Due to hydrogen bonding and p-stacking, indigo and Tyrian purple form highly-ordered crystalline thin films. Such films have been used to fabricate high-performance organic field-effect transistors with ambipolar charge transport, as well as complementary-like circuits. Mobility values were found to be in the range of 10-20.4 cm2/Vs. With performance on par with the best available organic semiconductors, indigoids demonstrate the potential of sustainable electronics based on biodegradable and biocompatible materials.