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 λmax 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.

Nanoporous Organic Frameworks as Light-Emitting Diodes: A Review

“…Incomplete reduction would give multivariate MOFs containing both FDC�O and FDC-OH, showing a slightly shifted peak at 505 nm with a lower intensity than that of pristine MOF, in addition to a new peak at 412 nm. 76 As the reaction proceeds, the intensity of the peak at 505 nm continues to decrease, while that of the peak at 412 nm increases. The completely reduced form, BUT-10-R, is eventually formed after 24 h, and it exhibits only one emission peak at 412 nm.…”

“…75 BUT-10, a 3D MOF consisting of 9-fluorenone-2,7dicarboxylic acid (FDC�O) and zirconium nodes, emits green light at 525 nm upon UV irradiation at 325 nm. 76 Postsynthetic modification was performed, during which the ketone functional group of the ligand was reduced to an alcohol (FDC-OH), causing disruption of the π-conjugated system. 76 The reduction process could be monitored by emission studies.…”

“…76 Postsynthetic modification was performed, during which the ketone functional group of the ligand was reduced to an alcohol (FDC-OH), causing disruption of the π-conjugated system. 76 The reduction process could be monitored by emission studies. Incomplete reduction would give multivariate MOFs containing both FDC�O and FDC-OH, showing a slightly shifted peak at 505 nm with a lower intensity than that of pristine MOF, in addition to a new peak at 412 nm.…”

“…The completely reduced form, BUT-10-R, is eventually formed after 24 h, and it exhibits only one emission peak at 412 nm. 76 Three isostructural MOFs (FSD-Cd, FSD-Co, and FSD-Mn) have been synthesized from fluorescein (FSD) as the ligand and Co 2+ , Mn 2+ , and Cd 2+ as the metal ions, respectively. Their emission colors are observed to change when the angle of the plane of polarized light is varied (pleochroism) or when they are subjected to external mechanical stimuli (piezochromism).…”

Truxene-to-Fluorenone Energy Transfer in a Robust Mesoporous Zn-MOF

“…Fluorenone-based metal–organic frameworks (MOFs) were first introduced in 2010 using the ligand 9-fluorenone-2,7-dicarboxylate, and upon varying the metallic node and using other coligands, multiple other examples were reported since. These porous fluorenone-based MOFs exhibit a good adsorption capacity of carbon dioxide and various dyes, for example, − but they are also notorious for being emissive. − Their generally intense luminescence was exploited to design various fluorescence-based sensors − and devices (e.g., thermometers) . In addition, photocatalytic C–H bond activation and photodegradation of organic molecules have also been successfully performed using fluorenone-based MOFs.…”