Rare-earth-based donor–acceptor metal–organic frameworks with low thermal quenching and dual emission mechanisms for high-temperature sensing

Abstract

Rare-earth-based metal–organic frameworks (RE-MOFs) hold significant promise for temperature sensing applications but face challenges due to the common thermal quenching (TQ) effect. In this study to address this limitation, we designed and synthesized a novel class of RE-based donor–acceptor MOFs (RE-DA-MOFs, termed DZU-500⊃PAH) with enhanced thermal stability and highly tunable luminescence, via integrating a phenazine-based electron-deficient ligand (dppz), RE ions (Eu³⁺, Sm³⁺, Gd³⁺, Tb³⁺, Dy³⁺), and polycyclic aromatic hydrocarbon (PAH) guests. Due to their host–guest architectures that are stabilized by the hydrogen bonds among the triple-fold metal chain structures and π–π stacking interactions between the donor and acceptor units, non-radiative decay of the framework can be effectively suppressed at elevated temperatures. Thus, these RE-DA-MOFs exhibit TQ-resistant through-space charge transfer (TSCT) fluorescence properties (298–473 K), which can be well modulated in the visible light range (493–584 nm) through the changing of PAH molecules. Specifically, the Eu³⁺-based MOFs, [DZU-500(Eu)⊃PAH], not only display TSCT-based emission that is TQ-resistant, but also exhibit characteristic Eu³⁺-centered emission that is TQ-sensitive. Through the difference of the dual emission mechanisms, DZU-500(Eu)⊃PAH can be used as both intensity-ratiometric and colorimetric high-temperature sensing materials. Firstly, the intensity ratio of Eu³⁺- and TSCT-based emission peaks exhibited good polynomial relationships with increasing temperature. Furthermore, by selecting an appropriate PAH guest as the donor, reversible color changes (red to green) in response to temperature variations can be observed in the corresponding MOF. These results highlight the potential of RE-DA-MOFs as low thermal-quenching materials and high-temperature fluorescent thermometers.