Tri-(2-picolyl)amine-modificated triarylborane: Synthesis, photophysical properties and distinguish for cyanide and fluoride anions in aqueous solution

Article abstract of DOI:10.1016/j.saa.2019.03.116

We designed and synthesized a tri-(2-picolyl) amine (TPA) functionalized triarylborane, 1-(6-(4-(dimesitylboryl)phenyl)pyridin-2-yl)-N,N-bis(pyridin-2-ylmethyl)methanamine (PB2). The photophysical properties of PB2 were thoroughly explored. Moreover, PB2

Full text of DOI:10.1016/j.saa.2019.03.116

Accepted Manuscript
Tri-(2-picolyl)amine-modificated
triarylborane:
Synthesis,
photophysical properties and distinguish for cyanide and fluoride
anions in aqueous solution
Yufeng Zhang, Xianchao Du, Long Chen, Zixiu Li, Wenji Wang,
Tianbao Li, Mao-Sen Yuan
PII:
DOI:
Reference:
S1386-1425(19)30370-1
https://doi.org/10.1016/j.saa.2019.03.116
SAA 17006
Spectrochimica Acta Part A: Molecular and Biomolecular
Spectroscopy
To appear in:
Received date: 22 December 2018
Revised date:
Accepted
date:
30 March 2019
30 March 2019
Please cite this article as: Y. Zhang, X. Du, L. Chen, et al., Tri-(2-picolyl)amine-
modificated triarylborane: Synthesis, photophysical properties and distinguish for cyanide
and fluoride anions in aqueous solution, Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy, https://doi.org/10.1016/j.saa.2019.03.116
This is a PDF file of an unedited manuscript that has been accepted for publication. As
a service to our customers we are providing this early version of the manuscript. The
manuscript will undergo copyediting, typesetting, and review of the resulting proof before
it is published in its final form. Please note that during the production process errors may
be discovered which could affect the content, and all legal disclaimers that apply to the
journal pertain.

ACCEPTED MANUSCRIPT
Tri-(2-picolyl)amine-modificated triarylborane: synthesis,
photophysical properties and distinguish for cyanide and fluoride
anions in aqueous solution
Yufeng Zhang‡, Xianchao Du‡, Long Chen, Zixiu Li, Wenji Wang*, Tianbao Li* and Mao-Sen Yuan*
Corresponding author:
College of Chemistry & Pharmacy, Northwest A&F University, Yangling, Shaanxi 712100, P. R.
China. E-mail: wjwang@nwsuaf.edu.cn; litianbao@nwsuaf.edu.cn; yuanms@nwsuaf.edu.cn
‡ These two authors contributed equally to this work.
1

ACCEPTED MANUSCRIPT
ABSTRACT
We designed and synthesized a tri-(2-picolyl)amine (TPA) functionalized triarylborane, 1-(6-(4-
(dimesitylboryl)phenyl)pyridin-2-yl)-N,N-bis(pyridin-2-ylmethyl)methanamine (PB2). The
photophysical properties of PB2 were thoroughly explored. Moreover, PB2 can capture CN- and F- in
aqueous solution through strong chelation induced by the synergy of a boron atom and metal ion
gripped by TPA to display entirely different fluorogenic responses such as fluorescence enhancement for
CN- and fluorescence quenching for F-. The results of TOF-MS-EI analysis and theoretical calculations
indicate that the complexing of PB2 with CN- formed a 2-to-2 adduct with a stabilized configuration,
resulting in strong emission. The complexing of PB2 with F- formed a 1-to-1 adduct with a loose
configuration, resulting in weak emission. In pure water, the detection limit of PB2 for CN- is 0.79 μM,
and in H2O/THF (1:9 v/v) system, the detection limits of PB2 for CN- and F- can reach 0.39 and 2.12
μM, respectively, indicating its potential application for effective detection and discrimination of CN-
and F-.
KEYWORDS
Cyanide anions; Fluoride anions; Triarylborane; Fluorescent probe; Chalation
2

ACCEPTED MANUSCRIPT
1. Introduction
The cyanide anion, whose toxic attack is rapid and low-dose, is known as highly poisonous anion
for both biological systems as well as the environment. Cyanide anions mainly come from mining,
electroplating, tanning industries, and synthetic fiber production [1]. Cyanide can bind to a heme unit of
cytochrome c to inhibit cell respiration which leads to vomiting, twitch, coma, loss of consciousness ,
and even death [2]. Fluorine, an essential element in our body, is usually added to toothpaste for
protecting teeth [3]. In addition, fluorine-containing pesticides and rubbers have also been widely used,
and the fluoride from the decomposition of these materials will infiltrate into the soil and underground
water [4]. Ultimately, people ingest fluorine from crops and drinking water. However, an excessive
intake of fluorine will lead to dental and gastric disorders, skeletal fluorosis, urolithiasis, and even death
[5]. Therefore, developing a simple and effective detection strategy for on-site detection of trace
amounts of cyanide and fluoride anions is highly desirable and significant.
At present, the usual methods to detect these two anions include selective electrode methods, ion
chromatography, and chromatography-mass spectrometry (GC-MS) [6]. These traditional detection
methods have their own advantages, but the drawbacks, such as the high detection limit and complex
sample preparation, are also extremely obvious [7]. In comparison with instrumental analysis, systems
based on chromogenic and fluorogenic methods are much simpler and easier to operate [7,8]. Borane-
based organic compounds have attracted much attention because of their intriguing photophysical
properties and they have been exploited as fluorescent, colorimetric, or ratiometric probes for certain
nucleophilic anions. This is attribute to the vacant p orbital and inherent Lewis acidic nature of trivalent
organoboron [9]. In particular, triarylboranes containing two mesityl groups are widely explored as
chemosensors for cyanide and fluoride anions. Their utility is ascribed to their moisture-stability and to
their high steric hindrance which prevents large anions from approaching boron [10].
However, the design and development of organoboron-based water-tolerance fluorescence sensors
for cyanide and fluoride is very challenging because of three counts: the poor solubility of triarylboranes
3

ACCEPTED MANUSCRIPT
in aqueous solution, the high hydration enthalpy of fluoride, and the difficulty in distinguishing between
cyanide and fluoride [11]. Successful examples demonstrating that fluorescence sensors can respectively
identify cyanide and fluoride in aqueous solution remain exceedingly rare. In the past few years, the
Gabbaï group developed a series of cationic boranes that can bind fluoride anions in organic or protic
solvents including water [12]. They utilized boranes decorated with peripheral ammonium,
phosphonium, sulfonium, stibonium, or telluronium groups to form onium, which has promoted Lewis
acidity and complexing capacity to capture fluoride in aqueous solution [10b,12b,13]. Among them, two
structural
isomers,
4-[bis(2,4,6-trimethylphenyl)boranyl]-N,N,N-trimethylaniline
([p-
(Mes2B)C6H4(NMe3)]+ and 2-[bis(2,4,6-trimethylphenyl)boranyl]-N,N,N-trimethylaniline ([o-(Mes2-
C6H4(NMe3)]+, exhibited the ability to identify CN- and F- respectively in aqueous solution
(H2O/DMSO 95:5 vol.) [14]. The Wang group designed a bipy functionalized dimesitylboron molecule,
5,5-bis(BMes2)-2,2-bipy, to enhance the electron accepting ability of boron via π-conjugation with
bipy and metal chelation, and this compound can form a 1:1 adduct with F- in the presence of methanol
[15]. Enlightened by the above work, in this paper, tri-(2-picolyl)amine (TPA), a pyridine-based ligand
that can bind to a variety of metal ions with high affinity, was chosen to functionalize PhB(Mes2). One
purpose of such a design is to improve the water solubility of the fluorescence probe via the multiple
pyridyl rings and the chelate metal ion. In addition, the conterminous pyridyl group of PhB(Mes2) will
be a plus factor in enhancing the Lewis acidity of boron due to the electronegative nitrogen atoms
[11b,16]. Furthermore, TPA was anticipated to be powerful for further promoting the electron-accepting
ability of the boron center by metal chelation [10]. Above all, we designed the bifunctional borane/TPA
molecule with the expectation that it can trap fluoride between the boron atom and the TPA-binding
metal ion via synergy between the Coulombic effect and Lewis acidity, thus making it compatible with
aqueous environments.
Herein, two structural isomers of triarylboranes, 1-(6-(3-
(dimesitylboryl)phenyl)pyridin-2-yl)-N,N-bis(pyridin-2-ylmethyl)methanamine (PB1) and 1-(6-(4-
(dimesitylboryl)phenyl)pyridin-2-yl)-N,N-bis(pyridin-2-ylmethyl)methanamine (PB2), were synthesized.
4

ACCEPTED MANUSCRIPT
PB2 exhibited gratifyingly ability for identifying fluoride and cyanide anions in aqueous medium with
different colorimetric responses.
2. Experimental section
2.1 Synthesis and characterizations of the subject compounds
Solvents for reactions and spectral measurements were dried and distilled before use. The reagents used
1
for reactions were purchased from J&K Scientific Ltd. HNMR spectra were recorded at 25 ˚C on
Bruker Avance 500 MHz spectrometer using CDCl3 as solvent. 13CNMR spectra were recorded at 25 ˚C
on Bruker Avance 125 MHz spectrometer using CDCl3 as solvent. Element analyses (C, H and N) were
performed using a PE 2400 autoanalyser. Mass spectrometry analyses were performed by a Bruker
Biflex III matrix assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometer.
Synthesis
of
1-(6-(3-(dimesitylboryl)phenyl)pyridin-2-yl)-N,N-bis(pyridin-2-
The mixture of 1-(6-bromopyridin-2-yl)-N,N-bis(pyridin-2-
ylmethyl)methanamine (PB1).
ylmethyl)methanamine (4) (0.20 g, 0.48 mmol), 2-(3-(dimesitylboryl)phenyl)-4,4,5,5-tetramethyl-1,3,2-
dioxaborolane (6) (0.204 g, 0.48 mmol), Pd(PPh3)4 (6 mg, 0.005 mmol), toluene (6 mL), ethanol (2 mL)
and 1 M K2CO3 aqueous solution (1 mL) in the round-bottom flask were heated to 80 ˚C, and constantly
stirred under an argon atmosphere for 8 h. The mixture was then cooled to room temperature and poured
into water (100 mL). After extraction with DCM, the organic phase was dried over Na2SO4. Purification
by column chromatography on silica gel and elution with dichloromethane-methanol (20:1, v/v) yielded
1
PB1 (0.216 g, 73.2%). H NMR (500 MHz, CDCl3) δ 8.58 (d, J = 4.6 Hz, 2H), 8.30 – 8.27 (m, 1H),
8.07 (s, 1H), 7.73 – 7.64 (m, 5H), 7.59 (d, J = 7.4 Hz, 1H), 7.51 (td, J = 7.3, 3.3 Hz, 3H), 7.18 (ddd, J =
6.7, 4.9, 1.9 Hz, 2H), 6.86 (s, 4H), 3.98 (s, 6H), 2.34 (s, 6H), 2.06 (s, 12H). 13C NMR (126 MHz, CDCl3)
δ 159.64, 159.15, 156.89, 149.10, 140.90, 139.18, 138.71, 137.05, 136.97, 136.41, 134.40, 130.97,
128.62, 128.25, 123.00, 121.97, 121.22, 118.99, 60.23, 60.05, 23.56, 21.26. TOF-MS-EI: m/z 614.3643
[M]+.
Synthesis
of
1-(6-(4-(dimesitylboryl)phenyl)pyridin-2-yl)-N,N-bis(pyridin-2-
5

ACCEPTED MANUSCRIPT
ylmethyl)methanamine (PB2). A similar synthetic and purification procedure as for PB2 was followed
for PB1 using 2-(4-(dimesitylboryl)phenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (2) as the
precursor. PB2 (0.231 g, 78.4%).1H NMR (500 MHz, CDCl3) δ 8.58 (d, J = 4.8 Hz, 2H), 8.04 (d, J =
8.2 Hz, 2H), 7.77 (d, J = 7.7 Hz, 1H), 7.68 (ddd, J = 19.1, 9.3, 5.0 Hz, 7H), 7.57 (d, J = 7.5 Hz, 1H),
13
7.19 (dd, J = 5.2, 3.0 Hz, 2H), 6.88 (s, 4H), 4.00 (s, 6H), 2.36 (s, 6H), 2.07 (s, 12H). C NMR (126
MHz, CDCl3) δ 159.57, 159.39, 156.38, 149.12, 142.42, 140.89, 138.72, 137.14, 136.79, 136.46,
128.21, 126.93, 126.44, 122.98, 122.01, 121.72, 119.20, 60.25, 60.17, 24.90, 23.51, 21.26. TOF-MS-EI:
m/z 614.3654 [M]+.
2.2 Photophysical properties measurement
UV-vis absorption spectra for the solutions and the solid-state were recorded with a Shimadzu UV-2550
spectrophotometer. Photoluminescence (PL) spectra were recorded using a Shimadzu RF-5301PC
spectrofluorimeter. The fluorescence quantum yield (Φ) in solution was determined using rhodamine B
in ethanol as a reference according to a previously reported method. Steady-state fluorescence spectra
and decay curves were obtained using an Edinburgh FLS920 fluorescence spectrometer equipped with a
time-correlated single photon counting (TCSPC) card. Reconvolution fits of the decay profiles were
performed with F900 analysis software to obtain the lifetime values.
2.3 Theoretical calculation
By using the Gaussian 09 program, the Time-Dependent Density Functional Theory (TD-DFT) and the
B3LYP scheme in conjunction with the 6-31G(d) basis set has been used to carry out the study of
compounds PB2, [K]+[PB2·F]- and [K2]2+[2PB2·(CN)2]2-. The molecular geometries of PB2,
[K]+[PB2·F]- and [K2]2+[2PB2·(CN)2]2- for electronic structure calculation was obtained by DFT-
B3LYP/6-31G(d) optimization. To include the solvent effects of THF, the Polarizable Continuum
Model (PCM) was used.
3. Results and discussion
6

ACCEPTED MANUSCRIPT
3.1 Synthesis
The probe molecules PB1 and PB2 were prepared according to the synthetic routes shown in
Scheme 1. The 1,4-dibromobenzene and 1,3-dibromobenzene were used as the starting materials. After
respective single-boronation of them with Mes2BF followed by borylation of Mes2BPhBr with
bis(pinacolato)diboron, the corresponding Mes2BPhB(OR)2 (2 and 6) were obtained. 2-Bromo-6-
(bromomethyl)pyridine (3) was prepared via bromomethylation of 2-bromo-6-methylpyridine. A
subsequent reaction of 3 with di-(2-picolyl)amine afforded 1-(6-bromopyridin-2-yl)-N,N-bis(pyridin-2-
ylmethyl)methanamine (4). The final products PB1 and PB2 were readily synthesized through a
conventional Suzuki reaction by reacting compound 4 with corresponding 6 and 2. All of the
compounds are stable in ambient air and H2O, in both solution and in the solid state. Details of the
1
synthesis, and purification processes, along with H and 13C NMR spectroscopy data and HR-MS
results, can be found in the ESI.
3.2 Photophysical properties
The UV-visible absorption and PL spectra of PB1 and PB2 are shown in Figure 1. PB1 exhibited
two UV-visible absorption bands at 295 and 325 nm in THF solution. These bands can be assigned to
the π–π* intramolecular charge transfer (ICT) from TPA location to a benzene ring and π–pπ(B) ICT
from TPA to the dimesitylboryl group, respectively. Different from PB1, PB2 showed only one major
UV-visible absorption band at 330 nm with a higher extinction coefficient. This indicated a greater
degree of ICT from TPA to the dimesitylboryl group in comparison with PB1. The meso-position
substitution of TPA in PB1 lead to a rough ICT path from TPA to boron, resulting in a doublet-band
absorption feature of PB1. Contrary to the absorption spectra, the PL spectra of PB1 displayed a single-
band emission at 389 nm with a quantum efficiency Φ of 0.21, and PB2 displayed a doublet-band
emission at 397 and 415 nm with a quantum efficiency Φ of 0.28. We think that the emission at 389 and
397 nm should be attributed to the short-distance ICT from TPA to benzene, and the emission at 415 nm
7

ACCEPTED MANUSCRIPT
originates from the long-distance ICT from TPA to dimesitylboryl group [17].
3.3 Sensing and differentiating F- and CN-
To examine our design concept and to assess the detection performance of PB1 and PB2 for F- and CN-,
we firstly inspected whether they can work well for capturing and discriminating CN- and F- in a
THF/H2O system. Titration experiments were carried out in an aqueous solution of H2O/THF (1:9 v/v)
by using KCN and KF as the cyanide or fluoride anion source, respectively. The changes in the
fluorescent spectra of PB1 and PB2 upon the addition of KCN and KF are shown in Figure 2. Very
weak fluorescent quenching was observed for PB1 upon the titration of CN- even up to six equivalents
(Figure 2a). And for the titration of F-, the fluorescent spectra of PB1 hardly changed, indicating the
poor complexation ability of PB1 to F- and CN- in a water-containing system. However, it is worth
noting that the addition of KCN to PB2 caused a significant enhancement of the fluorescence peak at
389 nm, and the PL intensity of PB2 became saturation when the concentration of KCN reached 2.5×10-
5 M (2.5 equivalents) with a quantum efficiency Φ of 0.59. In contrast, the incremental addition of KF to
PB2 displayed a gradual decease of the fluorescence intensity, and the fluorescence was almost entirely
quenched (Φ = 0.03) when the accumulated quantity of F- reached 2.5 equivalents of PB2 (Figure 2d).
We found that whether enhancement for CN- or decline of the fluorescent intensity for F-, the spectral
shape of PB2 behaved the same and changed from doublet-band (397 and 415 nm) to a single-band (397
nm). The disappearance of the fluorescent band at 415 nm indicated the termination of the long-distance
ICT from TPA to the dimesitylboryl group due to the F- → B coordination, saturating the electron
acceptor. In addition, visual fluorescent decline or enhancement of the PB2 solution can be readily
observed by the naked eye upon the addition of F- and CN-, respectively. The vivid fluorescent changes
suggest that PB2 can be used as a colorimetric sensor for F- and CN-.
The UV-visible absorption spectra of PB2 exhibited a very similar change for CN- and F-, as shown
in Figures S1 and S3 in SI. With the addition of incremental amounts of CN- or F-, the absorption of
8

ACCEPTED MANUSCRIPT
PB2 at 330 nm gradually decreased until it finally disappeared, and in the meantime, a new absorption
band at 300 nm arose, which further indicated that the π–pπ(B) charge transfer was interrupted after B
bound with these anions. Binding constants (K) of PB2 with KCN and KF in H2O/THF (1:9 v/v) were
determined based on the absorbance titration to be approximately 2.6 × 104 M−1 and 5.5 × 103 M−1
(Figures S2 and S4 in SI), respectively. The detection limits of probe QB for KCN and KF were
estimated to be 0.39 and 2.12 μM, respectively, based on a signal-to-noise ratio (S/N) of 3 under the test
conditions. We also investigated the selectivity of PB2 for CN- and F- by measuring the changes in the
-
PL spectra upon addition of an excess amount of various other anions, such as Cl-, Br-, NO3 , AcO-,
-
-
-
H2PO4 , ClO4 , HSO4 and HS-. As shown in Figure 3, PB2 did not show any affinity toward these
anions, indicating the highly selectivity and distinguishing ability of PB2 for CN- and F-. The
competitive experiments in the presence of CN- and F- were also carried out. The results manifested that
fluoride anion did not interfere with the sensitivity of the probe PB2 towards cyanide anion. However,
the cyanide anion seriously interfered with the sensitivity of the probe PB2 towards fluoride anion
(Figure S10 in SI). On the other hand, the effect of pH on the sensing of PB2 for CN- and F- in
H2O/THF (1:9 vol.) solutions has also been explored (see Figure S11 in SI). The probe PB2 can be used
to detect CN- and F- in a wide range of pH values (5.5‒12).
Motivated by these favorable results, we then investigated the capturing ability of PB2 for CN- and F-
when increasing concentration of water (Figure S11 in SI). As shown in Figure 4, in pure water, the
emission band at 389 nm was gradually enhanced upon adding KCN to PB2 solution and reached
saturation at 3.0 equivalents of PB2, with a binding constant of 4.6 × 104 M−1 and detection limit of 0.79
μM (Figures S6 and S9). However, no obvious changes in the PL spectra can be observed even upon the
addition of 10 equivalents of fluoride anions to PB2. This suggests the inadequate capacity of PB2 to
complex fluoride in pure water because of the high hydration of the fluoride anion. But for all that, PB2
clearly exhibited the excellent ability for sensing and discriminating CN- and F- in aqueous solution. As
shown as Table 1, The low detection limits of PB2 for these two anions in aqueous solution are
9

ACCEPTED MANUSCRIPT
inaccessible for most of organic fluorescent probes [18-23].
3.4 Sensing mechanism
PB2 exhibited different fluorescent responses for CN- and F-, enhancement and quenching respectively.
To make certain of the reason and mechanism for the different fluorescent changes of PB2 for CN- and
F-, the reaction mixtures of PB2 with respective KCN and KF were analyzed by using the TOF-MS-EI
technique. The results revealed that a 2-to-2 adduct product including two PB2 and two KCN molecules
formed in the reaction system of PB2 with KCN (Figure 5a), and the reaction of PB2 with KF formed a
1-to-1 adduct confirmed by the molecular ion peak of 672.3267 (Figure 5b), which is consistent with
our previous studies [10a]. For a better understanding of the PL spectral behaviors before and after PB2
is bound to these two anions, theoretical calculations were performed using TD-DFT methods. The
geometry of the 2-to-2 adduct ([K2]2+[PB2·(CN)2]2-) of PB2 with KCN was reasonably surmised based
on our recent research results and was further optimized. We thought that two KCN molecules were
simultaneously or successively captured by two PB2 molecules via teamwork (Figure 6). The KCN was
firmly chelated by boron and TPA, which were respectively affiliated with two individual PB2
molecules. The C-terminal of KCN points towards the boron atom and is bound through the
coordination effect, and the potassium is gripped by TPA segment of another PB2 molecule. Another
single KCN in the 2-to-2 adduct exhibit an identical coordination pattern, but a staggered construction.
The PB2-KCN adduct [K2]2+[PB2·(CN)2]2- showed a very stable molecular configuration and the
intramolecular single-bond rotations and configuration vibrations were deeply restricted to avoid
nonradiative decay, resulting in the strong emission upon being excited. Therefore, PB2 exhibited a
turn-on fluorescence response for KCN. In addition, after complexing CN- with the electron-deficient
boron atom, the intramolecular charge transfer (ICT) from TPA to boron was blocked and the ICT path
from TPA to an adjacent benzene ring was rebuilt (Figure 6), leading to the disappearance of the
fluorescent band at 415 nm and the enhancement of fluorescent band at 397 nm. As for the coordination
10

ACCEPTED MANUSCRIPT
geometry of PB2 with KF, the results of the theoretical calculation indicate that KF is chelated by the
boron and TPA from the same single PB2 molecule (Figure 6), which conformed to our anticipation.
The probe PB2 can capture the KF from the aqueous solution by itself. However, different from the
PB2-KCN adduct [K2]2+[PB2·(CN)2]2-, the PB2-KF adduct [K] +[PB2·F]- behaves a loose molecular
configuration. The coordination of PB2 with KF may aggravate the molecular configuration vibrations
upon being excited to mainly result to the nonradiative decay. Therefore, PB2 exhibited a turn-off
fluorescence response for KF.
4. Conclusion
In conclusion, we successfully designed and synthesized a fluorogenic chemodosimeter PB2 for the
detection and discrimination of CN- and F- in aqueous solution with high sensitivity (3.19 μM for CN-
and 3.19 μM for F-). The probe molecule PB2 is composed of two segments, PhB(Mes2) and tri-(2-
picolyl)amine (TPA). The photophysical properties of PB2 were explored. Moreover, PB2 can capture
KCN and KF through strong chelation induced by the synergy of boron binding anions and TPA binding
metal ion in THF/H2O solution to exhibit entirely different fluorogenic responses, fluorescence
enhancement for KCN and fluorescence quenching for KF. The results of TOF-MS-EI analysis and
theoretical calculations indicate that the complexing of PB2 with KCN formed a 2-to-2 adduct with a
stabilized configuration, resulting in strong emission, and the complexing of PB2 with KF formed a 1-
to-1 adduct with a loose configuration, resulting in weak emission.
Acknowledgments
We gratefully acknowledge the National Natural Science Foundation of China (21202132, 21675126
and 21874108), China Postdoctoral Science Foundation (2016M592837) for funding.
References
[1] (a) R. Koenig, Wildlife deaths are a grim wake-up call in eastern europe, Science 287 (2000) 1737
—1738;
11

ACCEPTED MANUSCRIPT
(b) W.C. Lin, S.K. Fang, J.W. Hu, H.Y. Tsai, K.Y. Chen, Ratiometric fluorescent/colorimetric
cyanide-selective sensor based on excited-state intramolecular charge transfer-excited-state
intramolecular proton transfer switching, Anal. Chem. 86 (2014) 4648—4652;
(c) R. Jackson, R.P. Oda, R.K. Bhandari, S.B. Mahon, M. Brenner, G.A. Rockwood, B.A. Logue,
Development of a fluorescence-based sensor for rapid diagnosis of cyanide exposure, Anal. Chem.
86 (2014) 1845—1852.
[2] (a) H.R. Bhat, P.C. Jha, Selective Complexation of cyanide and fluoride ions with ammonium
boranes: a theoretical study on sensing mechanism involving intramolecular charge transfer and
configurational changes, J. Phys. Chem. A 121 (2017) 3757—3767;
(b) Y. Shiraishi, M. Nakamura, N. Hayashi, T. Hirai, Coumarin-spiropyran dyad with a
hydrogenated pyran moiety for rapid, selective, and sensitive fluorometric detection of cyanide
anion, Anal. Chem. 88 (2016) 6805—6811;
(c) S. Goswami, S. Paul, A. Manna, Carbazole based hemicyanine dye for both "naked eye" and
'NIR' fluorescence detection of CN- in aqueous solution: from molecules to low cost devices (TLC
plate sticks), Dalton Trans. 42 (2013) 10682—10686.
[3] M. Kleerekoper, The role of fluoride in the prevention of osteoporosis, Endocrinol. Metab. Clin.
North Am. 27 (1998) 441—452.
[4] L. Xiong, J. Feng, R. Hu, S. Wang, S. Li, Y. Li, G. Yang, Sensing in 15 s for aqueous fluoride
anion by water-insoluble fluorescent probe incorporating hydrogel, Anal. Chem. 85 (2013) 4113—
4119.
[5] (a) C.A.N. Kobayashi, A.D.L. Leite, T.L.D. Silva, L.D.D. Santos, F.C.S. Nogueira, K.S. Santos,
R.C.D. Oliveira, M.S. Palma, G.B. Domont, M.A.R. Buzalaf, Proteomic analysis of urine in rats
chronically exposed to fluoride, J. Biochem. Mol. Toxicol. 25 (2015) 8—14;
(b) J.D. Featherstone, R. Glena, M. Shariati, C.P. Shields, Dependence of in vitro demineralization
of apatite and remineralization of dental enamel on fluoride concentration, J. Dent. Res. 69 (1990)
620—625.
[6] (a) Y. Yang, Q. Zhao, W. Feng, F. Li, Luminescent chemodosimeters for bioimaging, Chem. Rev.
113 (2013) 192—270;
(b) J.P. Hutchinson, C.J. Evenhuis, C. Johns, A.A. Kazarian, M.C. Breadmore, M. Macka, E.F.
Hilder, R.M. Guijt, G.W. Dicinoski, P.R. Haddad, Identification of inorganic improvised explosive
devices by analysis of postblast residues using portable capillary electrophoresis instrumentation
and indirect photometric detection with a light-emitting diode, Anal. Chem. 79 (2007) 7005—
12

ACCEPTED MANUSCRIPT
7013;
(c) Michael C. Breadmore, Anne S. Palmer, Mark Curran, Miroslav Macka, a. Nebojsa Avdalovic,
Paul R. Haddad, On-column ion-exchange preconcentration of inorganic anions in open tubular
capillary electrochromatography with elution using transient-isotachophoretic gradients. 3.
implementation and method development, Anal. Chem. 74 (2002) 2112—2118.
[7] M. Sun, S. Wang, Q. Yang, X. Fei, Y. Li, Y. Li, A new colorimetric fluorescent sensor for
ratiometric detection of cyanide in solution, test strips, and in cells, RSC Adv. 4 (2014) 8295—
8299.
[8] (a) Y. Shen, X. Zhang, Y. Zhang, H. Li, Y. Chen, An ICT-modulated strategy to construct
colorimetric and ratiometric fluorescent sensor for mitochondria-targeted fluoride ion in cell living,
Sens. Actuators B 258 (2018) 544—549;
(b) D. Udhayakumari, Chromogenic and fluorogenic chemosensors for lethal cyanide ion. A
comprehensive review of the year 2016, Sens. Actuators B 259 (2018) 1022—1057;
(c) L.E. Santos-Figueroa, M.E. Moragues, E. Climent, A. Agostini, R. Martinez-Manez, F.
Sancenon, Chromogenic and fluorogenic chemosensors and reagents for anions. A comprehensive
review of the years 2010-2011, Chem. Soc. Rev. 42 (2013) 3489—3613;
(d)Y. Chen, W. Shi, Y. Hui, X. Sun, L. Xu, L. Feng, Z. Xie, A new highly selective fluorescent turn-
on chemosensor for cyanide anion, Talanta 137 (2015) 38—42.
[9] (a) C. Wang, J. Jia, W.N. Zhang, H.Y. Zhang, C.H. Zhao, Triarylboranes with a 2-dimesitylboryl-2'-
(N,N-dimethylamino)biphenyl core unit: structure-property correlations and sensing abilities to
discriminate between F- and CN- ions, Chem. Eur. J. 20 (2014) 16590—16601;
(b) S. Yamaguchi, a. Seiji Akiyama, K. Tamao, Tri-9-anthrylborane and its derivatives:ꢀ new boron-
containing π-electron systems with divergently extended π-conjugation through boron, J. Am.
Chem. Soc. 122 (2000) 6335—6336;
(c) X.Y. Wang, F.D. Zhuang, J.Y. Wang, J. Pei, Incorporation of polycyclic azaborine compounds
into polythiophene-type conjugated polymers for organic field-effect transistors, Chem. Commun.
51 (2015) 17532—17535;
(d) G.R. Kumar, S.K. Sarkar, P. Thilagar, Aggregation-induced emission and sensing characteristics
of triarylborane-oligothiophene-dicyanovinyl triads, Chem. Eur. J. 22 (2016) 17215—17225;
(e) K. Dhanunjayarao, V. Mukundam, K. Venkatasubbaiah, Ratiometric sensing of fluoride anion
through selective cleavage of Si-O bond, Sens. Actuators B 232 (2016) 175—180;
(f) C.D. Entwistle, T.B. Marder, Boron chemistry lights the way: optical properties of molecular and
13

ACCEPTED MANUSCRIPT
polymeric systems, Angew. Chem. Int. Ed 41 (2002) 2927—2931;
(g) Y. Kubo, M. Yamamoto, M. Ikeda, M. Takeuchi, S. Shinkai, S. Yamaguchi, K. Tamao, A
colorimetric and ratiometric fluorescent chemosensor with three emission changes: fluoride ion
sensing by a triarylborane- porphyrin conjugate, Angew. Chem. Int. Ed. 42 (2010) 2036—2040.
[10] (a) M.S. Yuan, X. Du, Z. Liu, T. Li, W. Wang, E.V. Anslyn, J. Wang, Di-(2-picolyl)-N-(2-
quinolinylmethyl)amine-functionalized triarylboron: Lewis acidity enhancement and fluorogenic
discrimination between fluoride and cyanide in aqueous solution, Chem. Eur. J. 24 (2018) 9211—
9216;
(b) C.R. Wade, A.E.J. Broomsgrove, S. Aldridge, F.P. Gabbaï, ChemInform abstract: fluoride ion
complexation and sensing using organoboron compounds, Chem. Rev. 110 (2010) 3958—3984.
[11] (a) V.K. Gupta, N. Mergu, L.K. Kumawat, A.K. Singh, A reversible fluorescence “off–on–off”
sensor for sequential detection of aluminum and acetate/fluoride ions, Talanta 144 (2015) 80—89;
(b) H. Zhao, L.A. Leamer, F.P. Gabbaï, Anion capture and sensing with cationic boranes: on the
synergy of Coulombic effects and onium ion-centred Lewis acidity, Dalton Trans. 42 (2013) 8164
—8178;
(c) D.R. Bai, X.Y. Liu, S. Wang, Charge-transfer emission involving three-coordinate organoboron:
V‐shape versus U‐shape and impact of the spacer on dual emission and fluorescent sensing,
Chem. Eur. J. 13 (2010) 5713—5723.
[12] (a) M. Hirai, F.P. Gabbaï, Lewis acidic stiborafluorenes for the fluorescence turn-on sensing of
fluoride in drinking water at ppm concentrations, Chem. Sci. 5 (2014) 1886—1893;
(b) C.R. Wade, F.P. Gabbaï, Colorimetric turn-on sensing of fluoride ions in H2O/CHCl3 mixtures
by pyridinium boranes, Dalton Trans. (2009) 9169—9175；
(c) C.H. Chen, F.P. Gabbaï, Exploiting the strong hydrogen bond donor properties of a borinic acid
functionality for fluoride anion recognition, Angew. Chem. Int. Ed. 57 (2018) 521—525.
[13] (a) H. Zhao, F.P. Gabbaï, A bidentate Lewis acid with a telluronium ion as an anion-binding site,
Nat. Chem. 2 (2010) 984—990;
(b) Y. Kim, F.P. Gabbaï, Cationic boranes for the complexation of fluoride ions in water below the
4 ppm maximum contaminant level, J. Am. Chem. Soc. 131 (2009) 3363—3369.
[14] T.W. Hudnall, F.P. Gabbaï, Ammonium boranes for the selective complexation of cyanide or
fluoride ions in water, J. Am. Chem. Soc. 129 (2007) 11978—11986.
[15] Y. Sun, N. Ross, S.B. Zhao, K. Huszarik, W.L. Jia, R.Y. Wang, D. Macartney, S. Wang, Enhancing
electron accepting ability of triarylboron via pi-conjugation with 2,2'-bipy and metal chelation:
14

ACCEPTED MANUSCRIPT
5,5'-bis(BMes(2))-2,2'-bipy and its metal complexes, J. Am. Chem. Soc. 129 (2007) 7510—7511.
[16] (a)Y. Deng, Y. Sun, D. Cao, Y. Chen, Z. Liu, Q. Fang, Two-photon excited fluorescence properties
and anions recognition of a trivalent organoboron compound, J. Mol. Struct. 1000 (2011) 145—
149;
(b) S.K. Sarkar, P. Thilagar, A borane-bithiophene-BODIPY triad: intriguing tricolor emission and
selective fluorescence response towards fluoride ions, Chem. Commun. 49 (2013) 8558—8560;
(c) P. Chen, R.A. Lalancette, F. Jäkle, π-Expanded borazine: an ambipolar conjugated B-π-N
macrocycle, Angew. Chem. Int. Ed. 51 (2012) 7994—7998;
(d) X. Yin, K. Liu, Y. Ren, R.A. Lalancette, Y.L. Loo, F. Jäkle, Pyridalthiadiazole acceptor-
functionalized triarylboranes with multi-responsive optoelectronic characteristics, Chem. Sci. 8
(2017) 5497—5505.
[17] J. Lei, F. Qi, Y. Mao-Sen, L. Zhi-Qiang, S. Yu-Xiang, C. Hong-Feng, Switching high two-photon
efficiency: from 3,8,13-substituted triindole derivatives to their 2,7,12-isomers, Org. Lett. 12
(2010) 5192—5195.
[18] J.L. Fillaut, H. Akdas-Kilig, E. Dean, C. Latouche, A. Boucekkine, Switching of reverse charge
transfers for a rational design of an OFF-ON phosphorescent chemodosimeter of cyanide anions,
Inorg. Chem. 52 (2013) 4890—4897.
[19] R. Wang, J. Li, G. Li, C. Hao, Y. Zhang, S. Wang, J. Zhao, Q. Liu, Z. Shi, Synthesis of 1-amino-
12-hydroxyl-perylene tetra-(alkoxycarbonyl) for selective sensing of fluoride, Dyes Pigments 156
(2018) 225—232.
[20] K. Dhanunjayarao, V. Mukundam, K. Venkatasubbaiah, Ratiometric sensing of fluoride anion
through selective cleavage of Si-O bond, Sens. Actuators B 232 (2016) 175—180.
[21] S.K. Padhan, M.B. Podh, P.K. Sahu, S.N. Sahu, Optical discrimination of fluoride and cyanide ions
by coumarin-salicylidene based chromofluorescent probes in organic and aqueous medium, Sens.
Actuators B 255 (2018) 1376—1390.
[22] H. Li, R.A. Lalancette, F. Jakle, Turn-on fluorescence response upon anion binding to
dimesitylboryl-functionalized quaterthiophene, Chem. Commun. 47 (2011) 9378—9380.
[23] L. Wang, L. Li, D. Cao, Dual binding site assisted chromogenic and fluorogenic discrimination of
fluoride and cyanide by boryl functionalized BODIPY, Sens. Actuators B 228 (2016) 347—359.
15

ACCEPTED MANUSCRIPT
Caption for Table
Table 1. Several organic fluorescent probes and their sensing properties for F- and CN-.
Caption for Scheme
Scheme 1. Synthetic routes to PB1 and PB2.a aReaction conditions: (a) 4,4,4',4',5,5,5',5'-octamethyl-
2,2'-bi(1,3,2-dioxaborolane), KOAc, Pd(PPh3)2Cl2, 1,4-dioxane, reflux, 4 h; (b) NBS, AIBN, CCl4,
reflux, 4 h; (c) bis(pyridin-2-ylmethyl)amine, NaOH, DCM, 0 ˚C, overnight; (d) Pd(PPh3)4, toluene,
ethanol, 1 M K2CO3 aqueous solution, 80 ˚C, 8 h.
Captions for Figures
Figure 1. Absorption (a) and normalized PL (b) spectra of PB1 and PB2 in THF (10 μM).
Figure 2. Changes in the fluorescence spectra of PB1 (10 μM) in H2O/THF (1:9 vol) upon addition of
KCN (a) and KF (b); Changes in the fluorescence spectra of PB2 (10 μM) in H2O/THF(1:9 vol) upon
addition of KCN (c) and KF (d). Inset: Plot of emission intensity as a function of the concentrations of
CN- or F-; the visual fluorescence color of probe PB2 upon addition of KCN and KF under a 365nm UV
lamp.
Figure 3. Fluorescence changes of PB2 in H2O/THF (1:9 vol.) solutions (10 μM) upon addition of
various anions (3 equivalents) using their potassium salt as the anions source.
Figure 4. Changes in the fluorescence spectra of PB2 (10 μM) in pure water upon addition of KCN (a)
and KF (b).
Figure 5. TOF-MS-EI of the adducts of PB2 with KCN (a) and KF (b).
Figure 6. Schematic illustration of intramolecular charge-transfer (ICT) before and after PB2 binding
with KCN and KF.
16

ACCEPTED MANUSCRIPT
Sensing
ions
Probes
Response
LODS
Solvents
References
turn on
6 μM
CH2Cl2
CN-
[18]
turn off
turn on
1.18 μM
CH2Cl2
F-
F-
[19]
[20]
no data
DMSO
CH3CN
turn on
turn on
0.72 μM
2.7 μM
F-
[21]
[22]
CH3CN/H2O
(1:1, vol)
CN-
turn on
turn off
no data
THF
F- & CN-
2.96 μM
F-
THF/H2O
(98:2, vol)
[23]
ratio
5.23 μM
2.12 μM
CN-
F-
turn off
THF/H2O
(9:1, vol)
turn on
turn on
0.39 μM
0.79 μM
CN-
CN-
This work
water
Table 1
17

ACCEPTED MANUSCRIPT
Highlights:
> A tri-(2-picolyl)amine-modificated triarylborane was synthesized. > The photophysical properties of
this compound were explored. > The triarylborane can capture and differentiate CN- and F- in aqueous
solution. > It exhibited fluorescent enhancement for CN- and fluorescent quenching for F-. > The sensor
can form 2-to-2 adduct with KCN and 1-to-1 adduct with KF.
18