Exploring Caffeic Acid and Lignosulfonate as Key Phenolic Ligands for Metal-Phenolic Network Assembly.

Films formed by metals and phenols through a coordinative interaction have been extensively studied in previous years. We report the successful formation of MPN films from the phenolic compounds caffeic acid and lignosulfonate using Fe ions for complexation. The likewise examined -coumaryl alcohol showed some MPN film formation tendency, while for coniferyl alcohol and sinapyl alcohol, no successful film buildup could be observed. These newly formed films were compared to tannic acid-Fe films as a reference. Film growth and degradation were tracked by using UV-vis absorption spectroscopy. The films were degradable under different conditions such as alkaline environments or in the presence of a strong chelator. Small hollow capsules with a diameter of 3 μm and thicknesses in the nanometer range were produced. Additionally, the prepared films showed varying colors and levels of wettability. By utilizing the films' coating properties, we successfully dyed human hair in various colors.