Fossil-like pollen grains for construction of UV-responsive photochromic and fluorogenic dual-functional film

Natural pollen, one of the most fascinating biological materials in existence, exhibits chemical modifications and tunable optical property in the process of fossilization. Herein, we firstly fabricated nature-based fossil-like pollen grains (F-PGs) with UV-responsive optical properties through a facile concentrated H2SO4 treatment. The F-PGs featured incomplete carbonization property while remaining the UV-active alkyl aliphatic groups, which could initiate the carbonylation of F-PGs surface under UV irradiation, thus endowing the distinct UV dosedependent photochromic and fluorogenic dual-function of F-PGs. With the sustainable, easy-preparation and cost-effective advantages, the F-PGs were used to construct dual-functional films. The F-PG films presented high photochromic contrast (Delta E* = 32) to serve as smartphone-readable quick response code-patterned UV sensors, which indicated the highest reported cumulative dose of UV irradiation (108 J cm-2, equivalent to 10 days of exposure to sunlight). In addition, the UV-irradiated F-PG films with the fluorogenic property also showed wide applications in one-step and flexible photo-reduction of various metal ions to nanoparticles. Collectively, the novel fossil-like pollen grains and functional films pave the way for utilization of natural pollen for UVresponsive applications and provide a new insight for transporting the renewable biomass into photochromic and fluorogenic materials in the future.

Automated summary

Nature-based fossil-like pollen grains (F-PGs) with UV-responsive optical properties were fabricated through concentrated H2SO4 treatment, showing incomplete carbonization and UV-active alkyl aliphatic groups which induce photochromic and fluorogenic functionalities under UV irradiation. The F-PGs were used to construct high photochromic contrast films serving as UV sensors and for flexible photo-reduction of metal ions to nanoparticles after UV exposure. The innovative F-PGs pave the way for utilizing natural pollen in UV-responsive applications and converting renewable biomass into functional materials.