Enhanced Fluorescence in a Metal–Organic Framework via Second-Linker-Induced Suppression of π–π Stacking

Metal–organic frameworks (MOFs) demonstrate exceptional optical properties, making them promising candidates for applications such as lasers, displays, and organic light-emitting diodes (OLEDs). However, their practical utility is often compromised by π–π stacking interactions and intramolecular motions, which facilitate nonradiative decay and limit photoluminescence quantum yields (PLQYs). In this work, we synthesized a three-dimensional (3D) zinc-based MOF (Zn-BPDC-TPPA) under solvothermal conditions by incorporating the second linker biphenyl-4,4′-dicarboxylic acid (H 2 BPDC) into a two-dimensional (2D) framework (Zn-TPPA) built solely from the organic chromophore tri(4-(pyridin-4-yl)phenyl)amine (TPPA). Remarkably, this linker-induced suppression of π–π stacking triggers a more than 13-fold enhancement in PLQY for Zn-BPDC-TPPA compared to the amorphous fluorophores and their 2D counterpart. Structural analyses and theoretical calculations reveal that the introduction of a second linker transforms the MOF from a 2D to a 3D framework, effectively suppressing π–π stacking. Furthermore, the steric constraints imposed by the 3D framework enhance rigidity and restrict intramolecular motions, ultimately leading to significantly enhanced emission. This finding not only offers a robust platform for probing structure–property relationships but also provides a foundation for designing high-performance fluorescent materials.