Tailoring exciton and excimer emission in an exfoliated ultrathin 2D metal-organic framework

Abstract

Two-dimensional (2D) metal–organic frameworks have exhibited a range of fascinating attributes, of interest to numerous fields. Here, a calcium-based metal-organic framework with a 2D layered structure has been designed. Dual emissions relating to intralayer excimers and interlayer trapped excitons are produced, showing excitation-dependent shifting tendency, characteristic of a low dimensional semiconductor nature. Furthermore, the layer stacking by weak van der Waals forces among dynamically coordinated DMF molecules enables exfoliation and morphology transformation, which can be achieved by ultrasound in different ratios of DMF/H2O solvents, or grinding under appropriate humidity conditions, leading to nano samples including ultrathin nanosheets with single or few coordination layers. The cutting down of layer numbers engenders suppression of interlayer exciton-related emission, resulting in modulation of the overall emitting color and optical memory states. This provides a rare prototypical model with switchable dual-channel emissions based on 2D-MOFs, in which the interlayer excitation channel can be reversibly tuned on/off by top-down exfoliation and morphology transformation.

Temperature-dependent interchromophoric interaction in a fluorescent pyrene-based metal–organic framework

“…This arises from the fact that in many instances, the usefulness of MOF materials stems from their fluorescence emission, which in turn is heavily dependent on the interactions between the chromophores. Excimer emission of MOF materials due to interchromophoric interactions have been observed in several cases 3a,b,20. In particular, the extent of the interchromophoric interaction in several MOFs was found to be topology-dependent as each MOF displayed different concentration, distance, and mutual orientation of the ligands 7c,d.…”

CO2 controls the oriented growth of metal-organic framework with highly accessible active sites

“…Up to now, the methods for synthesizing 2D MOFs can be classified into two groups: top-down and bottomup strategies. The top-down exfoliation approach relies on the disintegration of 3D layered MOF solid 11,[16][17][18][19] , usually suffering from high-energy consumption, fragmentation and morphological damage and low yields (typically < 15%) 9,20 . For the bottomup strategy, 2D MOFs are synthesized directly from starting materials by solvothermal route using additives (e.g., surfactant, capping molecules, template) to control the oriented MOF growth [21][22][23][24][25] .…”

Zr‐Metal‐Organic Framework Catalysts for Oxidative Desulfurization and Their Improvement by Postsynthetic Ligand Exchange

“…[20,21] Therefore, obtaining a suitable heterogeneous catalyst remains important.Metal-organic frameworks (MOFs) are a class of hybrid materials formed by connecting organic linkers with inorganic nodes. Their porosity, high surface area, accessible open metal sites, and easy functionalization enable MOFs to be used in various applications in adsorption, [22] separation, [23,24] sensing, [25][26][27] lighting and optics, [28,29] and catalysis. [30,31] In ODS processes, studies have focused on employing MOFs as the support for POM catalysts, making full use of the MOFs' high stability, porosity, and heterogeneity to improve the POM's catalytic activity, even without using any inherent activity of the MOF lattice.…”