Boric-Acid-Functional Lanthanide Metal–Organic Frameworks for Selective Ratiometric Fluorescence Detection of Fluoride Ions

Abstract

Here, we report that boric acid is used to tune the optical properties of lanthanide metal-organic frameworks (LMOFs) for dual-fluorescence emission and improves the selectivity of LMOFs for the determination of F ions. The LMOFs are prepared with 5-boronoisophthalic acid (5-bop) and Eu ions as the precursors. Emission mechanism study indicates that 5-bop is excited with UV photons to produce its triplet state, which then excites Eu ions for their red emission. This is the general story of the antenna effect, but electron-deficient boric acid decreases the energy transfer efficiency from the triplet state of 5-bop to Eu ions, so dual emission from both 5-bop and Eu ions is efficiently excited at the single excitation of 275 nm. Moreover, boric acid is used to identify fluoride specifically as a free accessible site. The ratiometric fluorescent detection of F ions is validated with the dual emission at single excitation. The LMOFs are very monodisperse, so the determination of aqueous F ions is easily achieved with high selectivity and a low detection limit (2 μM). For the first time, we reveal that rational selection of functional ligands can improve the sensing efficiency of LMOFs through tuning their optical property and enhancing the selectivity toward targets.

Fluorescent “Turn‐on” Sensing Based on Metal–Organic Frameworks (MOFs)

“…In ar ecent report by Yina nd co-workers, boronic acid functionalized MOF was employedf or the recognition of fluoride ion. [14] In this report, Eu-based MOF,n amely Eu-MOF 1w as synthesized from boronic acid appended linker (5-boronoisophthalic acid (5bop)) ( Figure 2a). Upon excitation at 275 nm, Eu-MOF 1 showedd ual emission at 366 and 625 nm along with antenna effect.…”

“…(a) Structural representation of the two-dimensional( 2D) sheet of MOF;( b) Fluorescences pectra (l ex :275 nm) of 0.2 mg mL À1 Eu-MOF 1u pon incremental addition of fluoride ion. Reproduced from ref [14]. with the permissionoft he American Chemical Society.…”

Ratiometric fluorescent detection of Cu2+ based on dual‐emission ZIF‐8@rhodamine‐B nanocomposites

“…Therefore, the construction of ratiometric fluorescence sensors is of great significance. Yin and coworkers have developed some excellent ratiometric fluorescence sensors based on MOFs . For example, Ru@MIL‐101(Al)‐NH 2 was used for the detection of water.…”

A π‐Conjugated Chromophore Dye and Its Functional Paper Strips for Visually On‐Site Sensing F− and Its Reaction Mechanism

“…For fluoride ion (F − ), the smallest size and highest charge density, any chronic deficiency of F − will lead to gastric and kidney disorder or osteoporosis, while excess F − would induce dental and skeletal fluorosis and other serious diseases including collagen breakdown, bone disorders and immune system disruption . Great efforts have been devoted for F − detection, such as chromatography, electrochemistry, photoluminescence, mass spectrometry,, fluorescent spectrophotometry and colorimetric spectrophotometry . For example, Bhosale, et al .…”