Effects of Boronic Acid on the Fluoride-selective Chemosignaling Behavior of a Merocyanine Dye

Abstract

The effects of boronic acid on the fluoride-selective chemosignaling behavior of a merocyanine dye were investigated. In the presence of phenylboronic acid (PBA), N-methylquinolinium-based merocyanine dye displayed fluoride-selective chromogenic signaling behavior over other commonly coexisting anions in the micromolar concentration range. Signaling is produced by a fluoride-induced displacement of the dye from its complex with PBA, resulting in a significant chromogenic signal for the fluoride ion. This signaling was successfully analyzed using a ratiometric analysis of the UV-vis absorption in response to changes in fluoride ion concentration. A PBA substituted with an electron withdrawing group was found to exhibit a more pronounced signal. Polymer-bound PBA also exhibited useful fluoride-selective signaling behavior.

Fluorescence and Colorimetric Chemosensors for Fluoride-Ion Detection

“…The fluoride-selective chemosignaling system consisting of a mixture of the merocyanine dye 34 and phenylboronic acids (PBA−Rs) (Figure 16) was investigated by Cha et al 68 The mechanistic basis for the operation of this sensor involves fluoride-induced displacement of the dye from a complex formed between it and the PBA−Rs in association with the formation of a chromogenic signal. In CH 3 CN, the stabilities of the complexes of PBA−Rs with 34 were found to be in the following order: PBA−CHO > PBA−NO 2 > PBA−CHO-4 > PBA−H > PBA−OCH 3 .…”

Anionic chromogenic chemosensors highly selective for cyanide based on the interaction of phenyl boronic acid and solvatochromic dyes

“…The study of the system in the presence of small amounts of water provided titration curves for the reactions of the dye-PBA with CN − for which the sigmoidal shape is absent, suggesting that water interacts with the dye and PBA through hydrogen bonding, preventing the formation of hydrogenbonded dye-PBA complexes. The strategy reported herein could, in principle, be used in the development of efficient supramolecular devices for the detection of CN − , F − , and diols, such as sugars, in organic and even aqueous systems, with the use of other signalizing units [50], which can be anchored on polymeric matrices [50,75]. …”

“…With the addition of F − to the medium the original color of the solution is restored because the anion reacts with the boron center displacing 2 [35]. In other related study, Cha et al developed a chromogenic chemosensor for F − based on a displacement assay using a merocyanine as the signalizing unit and PBA [50]. Although boronic acids have been utilized as recognition units in optical chemosensors for the detection of CN − [48,49,[51][52][53], this anion was not studied in the previous reports that make use of PBA-merocyanine displacement assays.…”