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 (H₂BPDC) 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.