NIR-IIb-emitted Er-coordination Polymer for Logic Gates and Optical Anticounterfeiting

The second near-infrared window in a 1 500–1 700 nm region (known as the NIR-IIb region) presents low autofluorescence and a deep penetration depth, enabling a potential technology for effective imaging and anticounterfeiting applications. However, existing NIR-IIb-emitted fluorescence materials remain limited and possess low luminescent properties. In implementing the enhanced ~1 525 nm emission of the Er (III) complex in a nonorganic solvent, an amphiphilic diblock copolymer (PEG₁₁₂–PAA₁₂) was initially synthesized to coordinate with Er (III), and then certain Yb (III) was doped to form the PEG–PAA–Er/Yb complex. The complex shows a dramatic fluorescent enhancement of ~250-fold at ~1 525 nm in D₂O than that in H₂O under 980-nm laser irradiation, which is ascribed to the following factors: (1) The substitution of H₂O by D₂O can suppress the quenching effect of H₂O at ~1 470 nm to achieve the emission of PEG–PAA–Er; (2) the doping of Yb (III) enables the co-luminescence effect to PEG–PAA–Er to improve NIR-IIb emission. Notably, the PEG–PAA–Er/Yb complex can construct molecular logic gates with logic functions and optical anticounterfeiting by using the abovementioned fluorescence changes.