Enhanced Long Persistent Luminescence by Multifold Interpenetration in Metal–Organic Frameworks

Abstract

Metal–organic frameworks (MOFs) with long persistent luminescence (LPL) have attracted widespread attention due to potential applications in displays, anticounterfeiting, and so on. However, MOFs often have large pore size, which restricts the formation of efficient inter‐ and intramolecular interactions to realize LPL. Herein, a new approach to achieving LPL in MOFs by multifold interpenetration of discrete frameworks is reported. By comparison between threefold‐ and twofold‐interpenetrating MOFs, it was found that the former, which have higher multiplicity and denser frameworks, can be endowed with enhanced inter‐ and intramolecular interactions, and thus enhanced LPL is obtained. Meanwhile, metal‐cluster and heavy‐halogen effects could also cause variations in LPL duration and color.

Phosphorescent Calcium-Based Metal–Organic Framework with Second-Scale Long Afterglow

“…Afterglow is an intrinsic luminescent process that occurs after removal of the excitation light source, , which generally gives rise to the slow release of photons from energy traps in the materials upon thermal stimulation. , Such characteristics make afterglow luminescence materials have potentially significant applications in optical storage, biosensors/imaging, information security, organic light-emitting diodes, and environmental oxygen content/humidity detection . In the past decades, many substantial afterglow materials have been designed and synthesized, such as rare-earth- or noble-transition-metal-modified inorganics, − organometallic complexes, and pure organic materials .…”

“…In 2016, Yang and Yan reported afterglow of metal–organic frameworks (MOFs) for the first time . Then some other groups also found RTP of different MOFs. , Compared with inorganics and organic RTP materials, MOFs are emerging RTP materials because of their intrinsic structure features,, for example, high-crystallinity and periodic frameworks, various metal cluster units, , strong coordination interactions between metal and organic ligands, − and the controllable formation of dense frameworks . All of them help to accelerate triplet generation and produce phosphorescence.…”

“…In addition, the lifetime at 77 K is longer than that at 298 K, which is close to 1 s (985 ms; Figure c and Table S4). RTP can be further understood from a structural point of view: First, the formation of a 1D metal chain with a Ca 3 cluster in 1 has played a crucial role in achieving long-lived persistent RTP because of the metal center arousing variations in the duration . Second, on the basis of strong coordination interaction, Ca-MOF might have enhanced the rigidity of molecular conformations and confined molecular motions/vibrations, so that nonradiative loss of excitons was reduced and phosphorescence emission was promoted. − The bridged N atom can enhance the rigidity of the framework, stabilize the MOF structure, and strengthen the interactions among the frameworks .…”

Multi‐Mode Color‐Tunable Long Persistent Luminescence in Single‐Component Coordination Polymers

“…Yan and co‐workers used aromatic acid and metal ion of Cd 2+ /Zn 2+ to synthesize a series of different metal‐cored coordination polymers with the single green LPL in recent years [19] . In 2019, our group reported a dynamic MOF and a series of interpenetrating MOFs, all of which show a single LPL emission color [11, 20] . Investigating the reason behind, the monochromatic LPL is ascribed to the phosphorescence mainly produced by the triplet excited state of the single molecular ligand.…”

“…[19] In 2019, our group reported ad ynamic MOF and as eries of interpenetrating MOFs,a ll of which show as ingle LPL emission color. [11,20] Investigating the reason behind, the monochromatic LPL is ascribed to the phosphorescence mainly produced by the triplet excited state of the single molecular ligand. On the other hand, halogen atoms are another well-known class of heavy atoms that can not only promote the intersystem crossing (ISC) to enhance the phosphorescence efficiency,b ut also enlarge Stokes shifts of phosphorescence.M ore importantly,t hey have potential in inducing newborn phosphorescence peak through constructing multiple intermolecular halogen-bonding (XB) interactions such as CÀH…”