Building Structures from 2D to 3D MOFs through Ligand–Metal Engineering: Distinct Aggregation-Induced Emission and Self-Enhanced Electrochemiluminescence Behaviors

Abstract A 2D network complex {[Zn(HL1)(H2O)2]·2H2O}n (Complex 1) was synthesized using 5-(1H-pyrazol-4-yl)isophthalic acid (H3L1) as the ligand. Building on this, the pyrazole ring was replaced with a similar triazole ring, and the metal center was changed, resulting in the synthesis of a 3D complex {[Co(L2)(μ-OH2)]·2H2O}n (Complex 2), where H2L2 = 5-(4H-1,2,4-triazol-4-yl)benzene-1,3-dicarboxylic acid. Structural characterization confirmed the formation of both complexes, and their properties were further tested. Thermogravimetric analysis (TGA) reveals that Complex 1 exhibits good thermal stability up to approximately 400 °C, while Complex 2 remains stable below 330 °C. In terms of photophysical behavior, Complex 2 exhibited aggregation-caused quenching (ACQ), while Complex 1 displayed typical aggregation-induced emission (AIE) characteristics. Electrochemiluminescence (ECL) tests revealed that Complex 1 exhibited stable and reproducible ECL signals, whereas Complex 2 demonstrated significant self-enhancement, with its luminescence intensity increasing by approximately three times after 23 consecutive cycles.