Hypsochromically‐shifted Emission of Metal‐organic Frameworks Generated through Post‐synthetic Ligand Reduction

Abstract

Luminescent materials with tunable emission are becoming increasingly desirable as we move towards needing efficient Light Emitting Diodes (LEDs) for displays. Key to developing better displays is the advancement of strategies for rationally designing emissive materials that are tunable and efficient. We report a series of emissive metal-organic frameworks (MOFs) generated using BUT-10 (BUT: Beijing University of Technology) that emits green light with λ max at 525 nm. Post-synthetic reduction of the ketone on the fluorenone ligand in BUT-10 generates new materials, BUT-10-M and BUT-10-R. The emission for BUT-10-R is hypsochromically-shifted by 113 nm. Multivariate BUT-10-M structures demonstrate emission with two maxima corresponding to the emission of both fluorenol and fluorenone moieties present in their structures. Our study represents a novel post-synthetic ligand reduction strategy for producing emissive MOFs with tunable emission ranging from green, white-blue to deep blue.

Multivariate metal–organic frameworks generated through post-synthetic modification: impact and future directions

“…They created a MOF with aldehyde groups as tags, which were then replaced with other groups under mild conditions. 19 Various other methodologies have been employed, including azide–alkyne click reactions, 21,26 diazotization, 3,27 Schiff base conversion of amino to aldehyde, 3,28 reduction 15 and more. 29 This method has proven effective in modifying the photochemistry of MOFs.…”

“…By reducing the ketone to an alcohol, resulting in the generation of fluorenol, we were able to achieve a hypsochromic shift in the MOF's emission. 15 MTV-MOFs were then achieved by adjusting the duration of the reduction process, allowing us to generate structures with mixtures of ketone and alcohol-functionalized ligands.…”

“…3). 15 Considering the synergistic potential, one can envision combining effective strategies of both PSM and MTV-MOFs to create novel materials. For example, the Cohen group has described a covalent modification of UMCM-1-(OBnNO 2 ), where an ether group was replaced with an alcohol group, drawing inspiration from the removal of organic protecting groups.…”

“…14 Our research group has shown that modifying organic ligands through PSM is an effective strategy for tuning the emission of MOFs, suggesting its potential for MOFs as optical devices. 15 In this article we focus on PSM because it offers two major advantages: bypassing de novo synthesis and introducing new ligands into MOFs while retaining the crystal structure both of which can lead to improved performance of the MTV-MOF.…”