Cations Functionalized Lanthanide Metal–Organic Frameworks: Tunable Luminescence, Upconversion Luminescence, and Efficient Reactive Oxygen Species Storm Generation for Photodynamic Antibacterial Applications

Abstract

Photodynamic antibacterial activity is an emerging application for lanthanide metal–organic frameworks (Ln-MOFs) that remains in its early stages of development. Herein, we report the solvothermal synthesis of a series of cations functionalized Ln-MOFs (denoted Cl-Ln-MOFs), constructed from 1,3-bis(4-carboxyphenyl)imidazolium chloride (H2L) linkers and Ln(NO3)3·6H2O (Ln = Eu, Tb, Gd) precursors. By fine-tuning the molar ratio of organic linker to metal salt, we successfully isolated a hydrogen-bonded organic framework (Cl-HOF), which assembles into a three-dimensional network stabilized by five distinct types of strong hydrogen-bonding interactions. Systematic photophysical investigations of codoped heterometallic EuxTb(1–x)-MOFs demonstrated that even Eu0.3Tb0.7-MOF, with only 30% Eu(III) content, preserves the characteristic fingerprint luminescence of Eu(III), while the pristine Cl–Eu-MOF displays desirable thermally responsive luminescence quenching behavior. Moreover, Tb0.3Yb0.7-MOFs and Eu0.3Yb0.7-MOFs exhibited efficient upconversion luminescence (UCL) under 980 nm near-infrared excitation, and the UCL process in Tb0.3Yb0.7-MOFs was verified to be a two-photon absorption process. Under low-power light irradiation, Cl–Gd-MOFs triggered a burst of reactive oxygen species (ROS) generation, delivering excellent photodynamic antibacterial activity against both Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli), with average inhibition zone diameters of 3.10 and 4.63 cm, respectively. This work establishes a versatile platform of Ln-MOF-based materials for high-performance photodynamic antibacterial applications.