Red room temperature phosphorescence from lignin

Materials with red room‐temperature phosphorescence (RTP) derived from sustainable sources are crucial but rarely reported. Here, we produced red RTP materials from lignin. Lignin was covalently modified with Upy (1‐(6‐isocyanatohexyl)‐3‐(6‐methyl‐4‐oxo‐1,4‐dihydropyrimidin‐2‐yl) urea) to obtain Lig‐Upy. The Upy in the Lig‐Upy promoted the interaction between the aromatic units of lignin and reduced energy gaps of these molecules. As a result, Lig‐Upy exhibited red RTP centered at 625 nm with a lifetime of 24.2 ms. Moreover, the hydrogen bonding interactions in Lig‐Upy varied when embedded into different matrices, such as polyvinyl alcohol (PVA) or sodium montmorillonite (MTM), inducing a change in RTP wavelength and lifetime. Utilizing these properties, Lig‐Upy was used as building blocks for producing materials exhibiting time‐dependent phosphorescent colors (TDPCs). Such TDPCs materials have exhibited great potential for visual decorations, information encryption and anti‐counterfeiting logos for medicine bottles.