Tailoring Photo- and Radio-luminescence in Metal–Organic Frameworks via Coordination Groups Modulation

Abstract

With a versatile triarylamine core and three directional pyridyl donors, tri(4-pyridylphenyl)amine (TPPA) serves as a multifunctional building unit for applications ranging from optical materials to framework linkers. Nevertheless, its conformational flexibility and the influence of molecular packing complicate the prediction and fine-tuning of its optical behavior. Herein, a series of new metal–organic frameworks (MOFs) based on the triangular TPPA ligand, designated ZJU-813, ZJU-814, ZJU-815, and ZJU-816, were synthesized under solvothermal conditions and shown to be isostructural. The most pronounced structural difference among the four TPPA-based MOFs is the introduction of different groups at the Zn coordination environment via terminal coordination groups modulation (CRM) strategy. By solvent modulation, the terminal coordination of Zn in ZJU-813 and ZJU-814 is ethanol molecules and nitrate anions, while ion modulation yields the coordination of chloride and bromide anions in ZJU-815 and ZJU-816. The CRM strategy effectively modulates the photoluminescence properties of TPPA-based MOFs, leading to a more than tenfold increase in the quantum yield of ZJU-813 relative to the organic fluorophore. This is chiefly attributed to solvent molecules in ZJU-813 that favor conformation fixation of TPPA, thereby suppressing nonradiative transition pathways. Meanwhile, the introduction of extra halogen atoms via the CRM strategy of the ZJU-815 and ZJU-816 enhanced the X-ray absorption and the radiation-stimulated photon emissions. This finding demonstrates the efficacy of the CRM strategy in regulating the properties of TPPA-based MOFs and paves the way for the functional customization of metal–organic frameworks.