Single Chromophore-Based White-Light-Emitting Hydrogel with Tunable Fluorescence and Patternability

Bioluminescence is widespread in nature such as the jellyfish, which inspires scientists to design polymer hydrogels with tunable fluorescence. However, it remains a big challenge to develop white-light-emitting hydrogels with local tunability of the fluorescent behavior. Herein, we report a white fluorescent hydrogel prepared by one-pot micellar copolymerization of hydrophilic acrylamide and hydrophobic single donor-acceptor chromophore monomer, in which the unimer and the dimer of the chromophore coexist and generate high- and low-energy emission, respectively, under excitation. The fluorescent behavior of the hydrogel can be well tuned by phototreatment or heat treatment that induces unimer-to-dimer transformation of the chromophore and thus variation of the fluorescent color from blue to white and then to yellow. The fluorescence can also be reversibly switched off by forming terpyridine-Cu²⁺ chelate complexes and recovered by using chelating agent to extract the Cu²⁺ ions out of the gel matrix. These properties afford patterning the fluorescent hydrogel, which is transparent under daylight yet shows the pattern under ultraviolet light. These patterned fluorescent hydrogels should find applications in protected message display for improved information security.