Multi‐Responsive Afterglows from Aqueous Processable Amorphous Polysaccharide Films

Abstract Polymer‐based room‐temperature phosphorescence (RTP) materials, especially polysaccharide‐based RTP materials, earn sustained attention in the fields of anti‐counterfeiting, data encryption, and optoelectronics owing to their green regeneration, flexibility, and transparency. However, those with both ultralong phosphorescence lifetime and excitation wavelength‐dependent afterglow are rarely reported. Herein, a kind of amorphous RTP material with ultralong lifetime of up to 2.52 s is fabricated by covalently bonding sodium alginate (SA) with arylboronic acid in the aqueous phase. The resulting polymer film exhibits distinguished RTP performance with excitation‐dependent emissions from cyan to green. Specifically, by co‐doping with other fluorescent dyes, further regulation of the afterglow color from cyan to yellowish‐green and near‐white can be achieved through triplet‐to‐singlet Förster resonance energy transfer. In addition, the water‐sensitive properties of hydrogen bonds endow the RTP property of SA‐based materials with water/heat‐responsive characteristics. On account of the color‐tunable and stimuli‐responsive afterglows, these smart materials are successfully applied in data encryption and anti‐counterfeiting.