MOF@COFs with Strong Multiemission for Differentiation and Ratiometric Fluorescence Detection

Abstract

Aggregation-caused quenching (ACQ) is often observed in covalent organic frameworks (COFs) for their low emission. Here, we propose that limited COF layers form on UiO-66 to eliminate the ACQ by the formation of UiO@COF composites. UiO-66 is selected because this metal−organic framework (MOF) is easily prepared in nanosize with Zr 4+ ion and 2-aminoterephthalic acid (BDC-NH 2 ). The high affinity of the Zr 4+ ion to phosphate species improves sensing selectivity. The surface −NH 2 reacts with 2,4,6triformylphloroglucinol (Tp) to integrate COF1 and COF2, which are prepared with Tp and phenylenediamine or tetraamino-tetraphenylethylene, respectively. The hydrogen bond formed between the hydroxyl group in Tp and imine nitrogen realizes excited-state intramolecular proton transfer; therefore, multiemission is observed from the enol and keto states of the COFs and UiO-66 at 360, 470, and 613 nm for UiO@COF1 and at 370, 470, and 572 nm for UiO@COF2. When phosphate ion is added in the composites, the emissions from the COFs keep stable, while that from UiO-66 is enhanced. However, adenosine-5′-triphosphate (ATP) improves the emissions from UiO-66 and COF's enol state, but that from the keto state keeps stable. The differentiation and ratiometric fluorescence detection of ATP and phosphate ion are therefore realized with the multiemission, the affinity of Zr 4+ ions, and the structural selectivity of the COFs. Thus, UiO@COF is a novel strategy to integrate multiemission, affinity, and structural selectivity to improve the sensing performance for differentiation and ratiometric detection.

Construction of Core–Shell MOF@COF Hybrids with Controllable Morphology Adjustment of COF Shell as a Novel Platform for Photocatalytic Cascade Reactions

“…Compared with the FTIR results of Ti‐MOF‐CHO, the characteristic peak of C═O stretching vibration in aldehyde groups at 1704 cm –1 disappeared in all the Ti‐MOF@TpTt hybrids, indicating the successful modification of TpTt shell on Ti‐MOF core through Schiff base reaction. Unlike the previous studies on MOF@COF materials with imine‐linked bonds, [ 17 ] the stretching vibration of C═N at around 1620 cm –1 shows no significant changes on account of the β ‐ketoenamine links in TpTt‐COF. Moreover, red‐shifts of C‐N stretching vibration from 1255 cm –1 at Ti‐MOF‐CHO to 1225 cm –1 at 4 provide further evidence for the covalent connection between Ti‐MOF core and TpTt shell.…”

Rapid Removal of Mercury from Water by Novel MOF/PP Hybrid Membrane

“…As shown in Figure 1a, compared to the FTIR spectra of NWF-g-MAH and UiO-66-NH2@NWF-g-MAH, the new absorption peak at 1103 cm −1 was observed at US-N, which was attributed to the stretching mode of C=S [21]. In Figure 1b, the diffraction peaks of US-N at 7.36 and 8.48° matched with the (111) and (002) crystallographic planes of UiO-66 [22], which indicated that the UiO-66-S layer retained its original crystal structure and underlying topology on the substrate surface. In XPS spectra of US-N, the peak of sulfur appeared at 162 eV compared to that of NWF-g-MAH and UiO-66-NH2@NWF-g-MAH in Figure 1c, and the content of sulfur on US-N was 0.58 (At.%).…”

Hybrid Porous Crystalline Materials from Metal Organic Frameworks and Covalent Organic Frameworks

“…Very recently, Yin and coworkers developed the first MOF/COF hybrid‐based fluorescence probe for differentiation and ratiometric fluorescence sensing of ATP and phosphate ions. [ 95 ] NH 2 ‐UiO‐66 was selected as the MOF core because Zr 4+ ions show a high affinity to phosphate group to ensure sensing selectivity, and 2‐aminoterephthalic acid (BDC‐NH 2 ) provides a surface ‐NH 2 group for initiating the growth of COF shell on the surface of NH 2 ‐UiO‐66 ( Figure 20 a ). Core–shell hybrids of UiO@COF1 and UiO@COF2 were prepared from reacting Tp with Pa and tetraamino‐tetraphenylethylene (TPE) in the presence of NH 2 ‐UiO‐66.…”