A General Model of Sensitized Luminescence in Lanthanide-Based Coordination Polymers and Metal–Organic Framework Materials

Abstract

Luminescent lanthanides containing coordination polymers and metal-organic frameworks hold great potential in many applications due to their distinctive spectroscopic properties. While the ability to design coordination polymers for specific functions is often mentioned as a major benefit bestowed on these compounds, the lack of a meaningful understanding of the luminescence in lanthanide coordination polymers remains a significant challenge toward functional design. Currently, the study of these compounds is based on the antenna effect as derived from molecular systems, where organic antennae are used to facilitate lanthanide-centered luminescence. This molecular-based approach does not take into account the unique features of extended network solids, particularly the formation of band structure. While guidelines for the antenna effect are well established, they require modification before being applied to coordination polymers. A series of nine coordination polymers with varying topologies and organic linkers were studied to investigate the accuracy of the antenna effect in coordination polymer systems. By comparing a molecular-based approach to a band-based one, it was determined that the band structure that occurs in aggregated organic solids needs to be considered when evaluating the luminescence of lanthanide coordination polymers.

Organically pillared layer framework of [Eu(NH2–BDC)(ox)(H3O)]

“…This may be attributed to a proton-induced fluorescence-quenching mechanism facilitated by the presence of H 3 O + in close proximity to the phenyl ring of NH 2 -BDC 2À (Tobita & Shizuka, 1980;Shizuka & Tobita, 1982). The quenching consequently hinders the sensitization, which is important according to the antenna model (Einkauf et al, 2017). The simplified two-and three-dimensional topologies of I.…”

A selective detection of nanomolar-range noxious anions in water by a luminescent metal–organic framework

“…Detection of these anions is already attempted by a number of pure lanthanide-based MOF 38,39 but the detection of these anions through the naked eye with superior sensitivity is not yet explored as the pure lanthanide-based MOFs undergo self-quenching phenomena. [40][41][42] Minimization of self-quenching can be performed by making the separation between two adjacent emissive lanthanide centers and this can be done by using a very little amount of emissive lanthanide centers. 41,43,44 Moreover, Ln MOFs that are doped with inert lanthanides have acquired immense interest.…”

A series of two-dimensional lanthanide coordination polymers: synthesis, structures, magnetism and selective luminescence detection for heavy metal ions and toxic solvents

“…Ln-MOFs possess unique luminescence properties arising from their 4f electrons (f-f or f-d transitions) (Yan, 2017;Schmitt et al, 2015;Rocha et al, 2011), which is tuned by suitable adjacent organic chromophores of ligands. Specifically speaking, the lanthanide emission is usually sensitized by organic antenna chromophores (antenna effect) due to the spin-and parity-forbidden nature of the f-f transitions causing direct photo-excitation of lanthanide to be difficult (Cui et al, 2018;Lustig et al, 2017;Einkauf et al, 2017). Owing to their unique luminescence properties resulting from f-f transitions generated via the antenna effect, Ln-MOFs have potential applications as fluorescent probes.…”