Ligand Energy Staff Gauge for Antenna Effect Study within Metal-Organic Frameworks

Revealing the structure-optical property relationship of aggregation-induced emission (AIE) species (AIEgens) and achieving the synergy between AIE and antenna effect are challenging. Herein, we study the emission behaviors of three AIE ligands with tetraphenyl structures, 1,2,4,5-tetrakis(4-carboxyphenyl)benzene (L1), 2,3,5,6-tetrakis(4-carboxyphenyl)-pyrazine (L2), and 1,1,2,2-tetrakis(4-carboxyphenyl)ethylene (L3), and find their ladder-shaped emission wavelength. In combination with terephthalic acid (L0), we construct a staff gauge from L0 to L3 to realize different sensitization for Ln3+ from the sensitization of both Eu3+ and Tb3+ to single Eu3+ and then to non-sensitization. We proposed the threshold value of 5000 cm-1 for complete sensitization from the different optical behaviors and energy levels of the lanthanide metal-organic frameworks (Ln-MOFs). Coplanar degree of L1-L3 is proposed to explain their optical behaviors and different sensitization. Thus, we revealed the connection among the energy levels, emission wavelength, and their effect on antenna effect for AIE ligands. L1-Eu MOF exhibits a dual emission with a porous property and is used for ratiometric fluorescent detection and removal of F-.

Automated summary

In this study, the emission behaviors of three AIE ligands with tetraphenyl structures were investigated, and their ladder-shaped emission wavelength was found. By constructing a staff gauge from L0 to L3, different sensitization of Ln3+ ions was achieved, from sensitizing both Eu3+ and Tb3+ to sensitizing only Eu3+ and then to non-sensitization. The threshold value of 5000 cm-1 for complete sensitization was proposed based on the different optical behaviors and energy levels of Ln-MOFs. The coplanar degree of L1-L3 was proposed to explain their optical behaviors and different sensitization. Therefore, the connection among the energy levels, emission wavelength, and their effect on antenna effect for AIE ligands was revealed. L1-Eu MOF exhibited dual emission with a porous property and was used for ratiometric fluorescent detection and removal of F-.