Biomass-based thermally tunable dual afterglow with room temperature daylight visibility

Biomass-derived long-persistent afterglow materials that simultaneously deliver thermally activated delayed fluorescence (TADF) and room-temperature phosphorescence (RTP) are highly sought after but remain challenging to achieve, particularly when daylight-visible RTP and high-temperature-tolerant, color-tunable TADF are required. Herein, we develop a thermally tunable RTP-TADF dual-mode afterglow material featuring thermochromic green-to-blue emission by using boric acid (BA) to covalently crosslink natural ellagic acid (EA) and cellulose (Cell) in situ during a facile air-drying process. The resulting EA@Cell, with B-O-C-rigidified structural network, exhibits long-persistent green RTP that remains visible to the naked eye for up to 8 s under daylight conditions upon ultraviolet excitation. Notably, EA@Cell exhibits thermally enhanced TADF emission across 293–413 K, with a 127-fold increase in afterglow lifetime, and maintains its structural integrity and emissive robustness even at temperatures as high as 453 K. As a practical demonstration of EA@Cell, the solution of EA and BA is formulated into daylight-visible RTP inks and thermochromic afterglow inks, enabling low-cost cellulose-based anti-counterfeiting, high-temperature thermal sensing, and dynamic information encryption. Material with both thermally activated delayed fluorescence and room temperature phosphorescence are challenging to achieve with biobased materials. Here, the authors report the use of boric acid as a crosslinker for ellagic acid and cellulose for the preparation of such materials.