A "one-stone-two-birds" strategy for enhancing the quantum yield and designing dual-emission AIE MOFs

Enhancing the quantum yield of aggregation-induced emission (AIE) species (AIEgens) and revealing the emission mechanisms are challenging. We designed and prepared metal-organic frameworks (MOFs) with an AIE ligand (2,3,5,6-tetrakis(4-carboxyphenyl)pyrazine) (TCPP) and Zr⁴⁺ metal cluster. The resulting Zr-TCPP exhibited enhanced blue emission, which was attributed to coordination-induced restriction of intramolecular rotation. Salicylalazine (SA) with AIE characteristics was encapsulated within the porous Zr-TCPP host. The restriction effect of channels transformed SA from having colourless to bright-yellow emission. Consequently, encapsulation-induced emission (EIE) was proposed as additional evidence of the AIE mechanism. The EIE strategy increased the quantum yield of SA@Zr-TCPP to 11.62% and introduced a new fluorescence emission site within AIE MOFs. To verify the EIE mechanism, a high concentration of ClO^- was selected as the target analyte, which disrupted the restriction effect of channels and unlocked the molecular rotors of SA. The optical behaviors of dual-emission SA@Zr-TCPP validated the proposed EIE mechanism and realized ratiometric fluorescent detection of ClO^-.