A Colorimetric Chemosensor Based on a Nozoe Azulene That Detects Fluoride in Aqueous/Alcoholic Media

Abstract

Colorimetry is an advantageous method for detecting fluoride in drinking water in a resource-limited context, e. g., in parts of the developing world where excess fluoride intake leads to harmful health effects. Here we report a selective colorimetric chemosensor for fluoride that employs an azulene as the reporter motif and a pinacolborane as the receptor motif. The chemosensor, NAz-6-Bpin, is prepared using the Nozoe azulene synthesis, which allows for its rapid and low-cost synthesis. The chemosensor gives a visually observable response to fluoride both in pure organic solvent and also in water/alcohol binary solvent mixtures.

Advances in fluorescent and colorimetric sensors for anionic species

“…The authors rationalized this behaviour to the occupation of a vacant p-orbital on the boronic ester in 33 by fluoride with rehybridization from sp 2 to sp 3 . This was confirmed using 11 B NMR experiments, and resulted in a change in the degree of conjugation experienced by the sensor [70]. Anion sensing of a series of anions (Fig.…”

“…Lewis, James and co-workers have developed boron-based azulene-based colorimetric probe 33 (Fig. 25a) for fluoride recognition [70]. Addition of different anions (F − , Cl − , Br − , I − ) to the THF solution of probe 33 resulted in colour change in the case of fluoride only which could be observed by the naked eye (Fig.…”

Development of Heterocycle-Substituted and Fused Azulenes in the Last Decade (2010–2020)

“…Since the elevated concentrations of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in living organisms are associated with a variety of diseases including cancer and cardiovascular disease, much attention has been paid to the development of methods to detect these active species in living cells. Lewis et al reported AzuFluor 483-Bpin 157 that exhibits fluorescence upon reaction with ROS and RNS ( Scheme 53 ) [ 74 ]. The synthesis of AzuFluor 483-Bpin 157 is accomplished by the palladium-catalyzed borylation of the corresponding 2-amino-6-bromoazulene.…”

Azulene—A Bright Core for Sensing and Imaging

“…Whilst the azulene core has been incorporated into a wide variety of colorimetric chemical probes (exploiting the vivid colours it is famous for) [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 ], this review will focus on those published probes that exploit the fluorescent nature of azulene. The nature of azulene fluorescence is highly dependent on substitution around the azulene core, which affects whether emission is more dominant from the S 2 or S 1 singlet excited state (a notable exception from this can be found in the work of Zhu et al, who showed that emission of azulene aldehydes can occur from the S 3 or S 2 excited state dependent on the nature of the hydrogen bonding present [ 31 , 32 ]).…”