Red Room Temperature Phosphorescence from Lignin

Abstract

Materials with red room-temperature phosphorescence (RTP) derived from sustainable resources 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.