Luminescence response mode and chemical sensing mechanism for lanthanide-functionalized metal–organic framework hybrids

Abstract

The luminescence response application in chemical sensing by metal–organic frameworks (MOFs) and their hybrid materials has been reported extensively in recent years. However, the reviews on this topic are mainly focused on the sensing materials (MOFs and their functionalized hybrid materials) and analytes (all types of species). In this comprehensive review, the luminescence response mode and chemical sensing mechanism for lanthanide-functionalized MOF hybrids (abbreviated as LnFMOFH) are systematically summarized. Specifically, ten sections are subdivided, and importantly involve three main topics. Firstly, LnFMOFH and the luminescence responsive chemical sensing for these hybrids are introduced. Secondly, three single luminescence response modes, including “Turn-Off”, “Turn-On” “Turn–Off–On” and dual mode, as ratiometric luminescence (RL) for chemical sensing in LnFMOFH materials are summarized. Thirdly, some types of chemical sensing mechanisms observed in LnFMOFH materials are outlined, which involve the ligand–metal energy transfer (LMET) for the luminescence response in chemical sensing of enhanced or weakened analytes; the fluorescence (Förster) resonance energy transfer (FRET) and photo-induced electronic transfer (PET) mechanism depending on the energy match between the probe and analyte; and some special chemical interactions for their luminescence response upon chemical sensing, such as hydrogen bonding interaction, coordination interaction and other reactions. Finally, the conclusion and prospects are given for this topic. It needs to be noted that pure lanthanide MOFs (lanthanide ions as the framework metal, including mixed lanthanide MOFs) are not the topic of this review and are only mentioned for background knowledge. Herein, LnFMOFH materials in which the lanthanide ions behave only as photoactive species to functionalize MOF units via post-synthetic modification (PSM) by researchers are the emphasis of this review.