Micro assembly strategies for enhancing solid-state emission of cellulose nanocrystals and application in photoluminescent inks

Crystalline cellulose exhibits photoluminescent properties, making it ideal for solid-state emission through properly assembling crystal arrays. However, assembling in water or other polar solvents poses structural integrity issues. To address this, a micro-assembly method is proposed. Cellulose nanocrystals (CNCs) are organized within a sub-micrometer-sized ZIF-8 metal-organic framework and coated with TiO2. Notably, the assembly within ZIF-8 improves the CNCs' emission quantum yield to 37.8 %. The bonding between ZIF-8 and CNCs relies on electrostatic interactions and hydrogen bonds, which are sensitive to polar solvents. Yet, the sturdy coordination bonds between TiO2 and ZIF-8 enhance resistance. Solvent-resistance tests confirm that TiO2 prevents CNC assembly breakdown, resulting in only an 8.0 % drop in photoluminescent intensity in an alkaline solution after 24 h, compared to 33 % without the coating. For anti-counterfeiting purposes, TiO2@ZIF-8@CNC is combined with a polymer matrix, allowing information to be revealed under specific wavelengths using screen-printed labels.