Hydroxythiophene-bearing benzothiazole: Selective and sensitive detection of periodate and its application as security ink

Article abstract of DOI:10.1016/j.dyepig.2018.11.026

A hydroxythiophene-bearing benzothiazole (HB) in phosphate buffer solution showed strong yellow fluorescence emission, which selectively and sensitively decreased by addition of IO₄ ^?. The reaction between HB and IO₄ ^? dramatically accelerated by UV irradiation. The fluorescence emission of HB was gradually recovered upon thermal heating of the IO₄ ^?-adducted product, indicating IO₄ ^? release. Using these properties, the solution containing HB and IO₄ ^? has been used as a fluorescence-based security ink.

Full text of DOI:10.1016/j.dyepig.2018.11.026

Accepted Manuscript
Hydroxythiophene-bearing benzothiazole: Selective and sensitive detection of
periodate and its application as security ink
Kyeong-Im Hong, Woo Hyeok Choi, Woo-Dong Jang
PII:
S0143-7208(18)32238-1
https://doi.org/10.1016/j.dyepig.2018.11.026
DYPI 7170
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 9 October 2018
Revised Date: 12 November 2018
Accepted Date: 12 November 2018
Please cite this article as: Hong K-I, Choi WH, Jang W-D, Hydroxythiophene-bearing benzothiazole:
Selective and sensitive detection of periodate and its application as security ink, Dyes and Pigments
(2018), doi: https://doi.org/10.1016/j.dyepig.2018.11.026.
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Hydroxythiophene-bearing Benzothiazole: Selective and Sensitive
Detection of Periodate and Its Application as Security Ink
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Kyeong-Im Hong, Woo Hyeok Choi, and Woo-Dong Jang*
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Department of Chemistry, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Korea
*Corresponding author. E-mail: wdjang@yonsei.ac.kr (W.-D. Jang)
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Abstract
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A hydroxythiophene-bearing benzothiazole (HB) in phosphate buffer solution showed strong yellow
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fluorescence emission, which selectively and sensitively decreased by addition of IO4 . The reaction between
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HB and IO4 dramatically accelerated by UV irradiation. The fluorescence emission of HB was gradually
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recovered upon thermal heating of the IO4 -adducted product, indicating IO4– release. Using these properties, the
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solution containing HB and IO4 has been used as a fluorescence-based security ink.
Keywords: Thiophene, Periodate, ESIPT, Fluorescent probe, Security ink
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1. Introduction
Anions play important roles in many chemical and biological processes.[1-4] A variety of fluorescent
probes has been developed for the selective and sensitive detection of anion species.[5-10] Among
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various anionic species, periodate ion (IO4 ) can be used as a mild oxidant for several chemical species
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including diols and amino alcohols.[11-15] For example, sodium periodate treatment of carbohydrates
has been used for the preparation of biocompatible and biodegradable materials used as scaffolds for
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tissue engineering and drug delivery vehicles.[16-19] Moreover, in the past few decades, several IO4 -
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mediated organic reactions, such as the oxidative dimerization of pyrene, oxidation of aromatic
hydrocarbons, hydrolysis of the epoxide ring, and oxidative cleavage of heterocyclic compounds, have
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been developed.[15, 20, 21] The IO4 -mediated oxidation is an important process in several biological
assays.[22-24] However, the recent researches showed that the periodate ions could cause thyroid
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dysfunction when high concentration uptake of them were taken in mammals.[25-29] Furthermore, IO4
is a potentially hazardous contaminant in the environment and food.[25, 26] Therefore, a method for the
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selective and sensitive detection of IO4 would be useful in the fields of molecular biology,
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environmental monitoring, food science, and clinical diagnosis. However, only limited examples of IO4
-sensitive fluorescent probes have been developed.[26, 30] In this study, hydroxythiophene-bearing
benzothiazole (HB) was synthesized as an excited state intramolecular proton transfer (ESIPT)
fluorescent probe, for selective and sensitive fluorescence quenching by addition of IO4 . From 1H NMR
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and FT-IR measurements, a plausible mechanism of the reversible binding of IO4– to HB was proposed.
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In addition to the selective detection of IO4 , we proposed a unique application of HB as a fluorescence-
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based security ink based on the reversible binding mechanism of IO4 to HB
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2. Materials and Methods
2.1. Materials and measurements
All commercially available reagents were reagent grade and were used without further purification.
Tetrahydrofuran (THF) was freshly distilled before use. All anions used for selectivity tests were as the form of
sodium or potassium salts. UV/Vis absorption spectra were recorded on a JASCO model V-660 spectrometer.
Fluorescence spectra were measured by a JASCO FP-6300 spectrophotometer. All spectral measurements were
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carried out using a quartz cuvette with a path length of 1 cm. 1H and 13C NMR spectra were recorded on Bruker
Advance PDX 250 and DPX 400 spectrometers, respectively, at 25 °C in CDCl3. MALDI-TOF-MS was
performed on a BrukerDaltonics LRF20 with dithranol (1,8,9-trihydroxyanthracene) as the matrix.
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2.2. Synthesis
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1: To a solution of 3-methoxythiophene (2 g, 17 mmol) in anhydrous THF (20 mL), 12 mL of n-BuLi (1.6 M in
hexane, 19 mmol) was added dropwise under N2 atmosphere at -78 °C and the mixture solution was further
stirred for 1 hr. Then, N,N-dimethylformamide (DMF, 1.6 mL, 20 mmol) was slowly added to the reaction
mixture, which was allowed to warm to room temperature. The reaction was terminated by adding small amount
of water. The solution was extracted with H2O/CH2Cl2, and the organic layer was concentrated and purified by
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silica column chromatography with 20% ethylacetate (EtOAc)/hexane as an eluent to give 1 (1.43 g, 57%). H
NMR (250 MHz, CDCl3) δ = 9.99 (s, 1 H), 7.65 - 7.63 (d, J = 5 Hz, 1 H), 6.88 - 6.86 (d, J = 5 Hz, 1 H), 3.99
ppm (s, 3 H).
2: To a solution of 2-aminothiophenol (1.4 g, 11.6 mmol) and 1 (1.5 g, 10.5 mmol) in H2O (15 mL), cetyl
trimethylammonium bromide (CTAB; 0.19 g, 0.53 mmol) was added and refluxed for 20 hr. Then, the reaction
mixture was extracted with H2O/EtOAc, and the organic layer was concentrated and purified by recrystallization
with ethanol to give 2 (2 g, 69%). 1H NMR (400 MHz, CDCl3) δ = 8.00 - 7.98 (d, J = 8 Hz, 1 H), 7.87 - 7.85 (d,
J = 8 Hz, 1 H), 7.46 - 7.42 (m, 1 H), 7.41 - 7.40 (d, J = 4 Hz, 1 H), 7.33 - 7.29 (m, 1 H), 6.95 - 6.94 (d, J = 4 Hz,
1 H), 4.09 ppm (s, 3 H); 13C NMR (100 MHz, CDCl3, 25 °C) = 158.18, 152.61, 135.11, 132.07, 128.27, 126.23,
124.44, 122.44, 121.45, 116.23, 115.61, 59.19 ppm; MALDI-TOF-MS m/z: cald. for C12H9NOS2: 247.01 [M]+;
found: 247.76.
2’: To a solution of 2 (0.7 g, 2.8 mmol) in anhydrous CH2Cl2 (10 mL), BBr3 (0.4 mL of 1 M in CH2Cl2, 4.2
mmol) was added dropwise in N2 atmosphere at −78 °C. The reaction mixture was further stirred for 20 hr and a
small amount of H2O was added to terminate the reaction. The solution was extracted with H2O/CH2Cl2, and the
organic layer was concentrated and purified by silica column chromatography with CH2Cl2 to give 2’ (0.42 g,
65%). 1H NMR (400 MHz, CDCl3) δ = 7.93 - 7.91 (d, J = 8 Hz, 1 H), 7.85 - 7.83 (d, J = 8 Hz, 1 H), 7.50 - 7.47
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(t, J = 12 Hz, 1 H), 7.37 - 7.33 (t, J = 16 Hz, 1 H), 7.30 - 7.29 (d, J = 4 Hz, 1 H), 6.87 - 6.86 ppm (d, J = 4 Hz, 1
H); 13C NMR (100 MHz, CDCl3, 25 °C) = 163.80, 159.98, 152.21, 132.17, 127.90, 126.90, 124.91, 121.75,
120.36, 111.43, 108.81 ppm; MALDI-TOF-MS m/z: cald. for C11H7NOS2: 233.00 [M]+; found: 233.72.
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3: To a solution of 2 (0.55 g, 2.2 mmol) in anhydrous CH2Cl2 (30 mL), N-bromosuccinimide (NBS; 0.41 g, 2.3
mmol) was added under N2 atmosphere at 0 °C. The reaction mixture was further stirred for 1 hr and acetone (1
mL) was added to terminate the reaction. The solution was extracted with H2O/CH2Cl2, and the organic layer
was concentrated and purified by silica column chromatography with 50% CH2Cl2/hexane as an eluent to give 3
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(0.39 g, 54%). H NMR (400 MHz, CDCl3) δ = 7.98 - 7.96 (d, J = 8 Hz, 1 H), 7.86 - 7.84 (d, J = 8 Hz, 1 H),
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7.47 - 7.43 (m, 1 H), 7.34 - 7.30 (m, 1 H), 6.96 (s, 1 H), 4.06 ppm (s, 3 H); MALDI-TOF-MS m/z: cald. for
C12H8BrNOS2: 324.92 [M]+; found: 325.68.
4: To a solution of 3 (104 mg, 0.32 mmol) and 2-tributylstannylthiophene (100 mg, 0.27 mmol) in anhydrous
toluene (15 mL), Pd(PPh3)4 (9 mg, 0.008 mmol) was added and refluxed for 10 hr under N2 atmosphere. Then,
the reaction mixture was extracted with H2O/EtOAc, and organic layer was concentrated and purified by silica
column chromatography 30% CH2Cl2/hexane as an eluent to give 4 (80 mg, 91%). 1H NMR (400 MHz, CDCl3)
δ = 7.99 - 7.97 (d, J = 8 Hz, 1 H), 7.86 - 7.84 (d, J = 8 Hz, 1 H), 7.46 - 7.42 (m, 1 H), 7.33 - 7.30 (m, 3 H), 7.08
- 7.05 (m, 1 H), 7.01 (s, 1 H), 4.12 ppm (s, 3 H); 13C NMR (100 MHz, CDCl3, 25 °C) = 158.88, 157.93, 152.67,
139.30, 137.06, 135.17, 133.45, 128.47, 126.28, 126.04, 124.97, 124.35, 122.33, 121.31, 112.15, 59.3 ppm;
MALDI-TOF-MS m/z: cald. for C16H11NOS3: 329.00 [M]+; found: 329.79.
5: To a solution of 4 (0.2 g, 0.6 mmol) in anhydrous CH2Cl2 (20 mL), N-bromosuccinimide (NBS; 0.1 g, 0.6
mmol) was added under N2 atmosphere at 0 °C. The reaction mixture was further stirred for 1 hr and acetone (1
mL) was added to terminate the reaction. The solution was extracted with H2O/CH2Cl2, and the organic layer
was concentrated and purified by silica column chromatography with 50% CH2Cl2/hexane as an eluent to give 5
(0.2 g, 81%). 1H NMR (400 MHz, CDCl3) δ =8.00 - 7.98 (d, J = 8 Hz, 1 H), 7.87 - 7.85 (d, J = 8 Hz, 1 H), 7.47
- 7.44 (t, J = 12 Hz, 1 H), 7.34 - 7.31 (t, J = 12 Hz, 1 H), 7.06 - 7.05 (d, J = 4 Hz, 1 H), 7.03 - 7.02 (d, J = 4 Hz,
1 H), 6.94 (s, 1 H), 4.12 (s, 3 H). MALDI-TOF-MS m/z: cald. for C16H10BrNOS3: 408.91 [M]+; found: 409.76.
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6: To a solution of 5 (0.2 g, 0.49 mmol) in anhydrous CH2Cl2 (25 mL), BBr3 (0.09 mL of 1 M in CH2Cl2, 0.98
mmol) was added dropwise in N2 atmosphere at −78 °C. The reaction mixture was further stirred for 20 hr and a
small amount of H2O was added to terminate the reaction. The solution was extracted with H2O/CH2Cl2, and the
organic layer was concentrated and purified by silica column chromatography with CH2Cl2 to give 6 (0.17 g,
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88%). H NMR (400 MHz, CDCl3) δ = 8.07 - 8.05 (d, J = 8 Hz, 1 H), 7.90 - 7.89 (d, J = 4 Hz, 1 H), 7.50 -
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7.46(m, J = 16 Hz, 1 H), 7.38 - 7.34 (m, J = 16 Hz, 2 H), 7.30 - 7.29 (d, J = 4 Hz, 1 H), 6.98 ppm (s, 1 H);
MALDI-TOF-MS m/z: cald. for C15H8BrNOS3: 394.89 [M+H]+; found: 395.8.
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7: To a solution of polyethylene glycol monomethyl ether (Mw=550; 5.0 g, 9 mmol) in anhydrous toluene (10
mL), NaOH (0.72 g, 18 mmol) and propargyl bormide (2.4 g, 18 mmol) was added in N2 atmosphere at 0 °C.
The reaction mixture was further stirred for 20 hr and extracted with H2O /CH2Cl2. The organic layer was
washed with aqueous saturation NaHCO3, and concentrated to give 7 (4.7 g, 89%). 1H NMR (400 MHz, CDCl3)
δ = 3.97 (s, 2 H), 3.42 - 3.31 (s, broad, 48 H), 3.15 (s, 3 H), 2.34 ppm (s, 1 H); MALDI-TOF-MS m/z:
found:444.73, 488.76, 532.79, 76.82, 620.86, 664.86 708.94, 752.98, 797.015, 841.057.
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HB: To a solution of 6 (0.32 g, 0.8 mmol) and 7 (0.30 g, 0.5 mmol) in anhydrous THF (10 mL), AsPh3 (0.34 g,
1.0 mmol) and Pd2(dba)2 (0.25 g, 0.27 mmol) was added in N2 atmosphere. And then, triethylamine (TEA; 10
mL) was added to the reaction mixture and further stirred for 20 hr. After then, the reaction mixture was
extracted with H2O/CH2Cl2 and the organic layer was concentrated and purified by silica column
chromatography with 3% MeOH/CH2Cl2 as an eluent to give HB (0.3 g, 64%). 1H NMR (400 MHz, CDCl3) δ =
7.85 - 7.83 (d, J = 8 Hz, 1 H), 7.79 - 7.77 (t, J = 8 Hz, 1 H), 7.44 - 7.40 (t, J = 16 Hz, 1 H), 7.30 – 7.26 (t, J = 16
Hz, 1 H), 7.08 ( s, 2 H), 6.86 (s, 1 H), 4.42 (s, 2H), 3.64 - 3.61 (m, broad, 48 H), 3.34 ppm (s, 3 H); 13C NMR
(100 MHz, CDCl3, 25 °C) = 162.57, 159.52, 152.03, 137.93, 133.54, 133.16, 126.81, 124.77, 124.53, 122.91,
121.61, 121.40, 116.36, 108.27, 91.29, 71.96, 70.59, 69.40 ppm;
3. Results and Discussion
The synthesis of HB was outlined in Scheme 1. Oxidative cycloaddition of aldehyde-containing
methoxythiophene units to form 2-aminobenzenethiol and successive deprotection of the methoxy
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group were carried out to get HB. Briefly, a formyl group was introduced to 3-methoxythiophene to
obtain compound
of compound . Subsequently, bromination was performed using
. The number of thiophene units in the structure was increased by palladium catalyzed
with 2-(tributylstannyl)thiophene. The obtained compound was brominated using NBS
, which was further converted to compound by treatment with BBr3. Finally,
propargyl group-bearing oligo(ethylene glycol) ( ) was prepared and reacted with via Sonogashira
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-bromosuccinimide (NBS) to obtain
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compound 3
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coupling of
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to obtain compound
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coupling to obtain HB
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ε425nm: 1.98 x 104 cm-1mol-1dm3, φfl: 13%), with a number average molecular
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weight of the oligo(ethylene glycol) chain of 550 g mol–1. HB was characterized by H and 13C NMR,
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MALDI-TOF-MS, HR-MS and DLS measurement (Figure S1).
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Scheme 1. Synthesis of HB. Reagents and conditions: (i) DMF, n-BuLi, THF, –78 °C, (ii) cetyl
trimethylammonium bromide, H2O, (iii) BBr3, CH2Cl2, 0 °C, (iv) NBS, CH2Cl2, 0 °C, (v) 2-
(tributylstannyl)thiophene, Pd(PPh3)4, toluene, reflux, (vi) NaOH, propargyl bromide, toluene, (vii)
AsPh3, Pd2(dba)2, THF, Et3N, reflux.
HB possessing intramolecular hydrogen bonding could be behaved via ESIPT process. To prove it, the
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probe was diluted in various organic solvents such as cyclohexane, toluene, CH2Cl2, CHCl3,
tetrahydrofuran (THF), ethyl acetate (EA), 1,4-dioxane, and MeOH. In Figure S2, the absorption of HB
was uniformed in regardless of solvent polarity. However, the emission spectra of HB were dependent
on solvent properties. In polar solvents such as THF, EA, 1,4-dioxane, and MeOH, the maxima of
fluorescence spectra are appeared at 486 nm which was emission from enol tautomer. In contrast, the
fluorescence emission of HB in non-polar solvents showed at 518 nm and 588 nm which was longer
than those in polar solvents, indicating HB is an effective ESIPT probe.
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Figure 1. Absorption and fluorescence emission changes of HB (10 µM) by addition of various anions
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(
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: F-,
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: Cl-,
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: Br-,
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: I-,
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: HCO3 ,
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: HSO4 ,
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: CH3CO2 ,
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: SCN-,
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: NO3 , 10: N3 , 11: CN-, 12: ClO3 ,
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13: BrO3 , 14: IO3 , 15: IO4 ) with exposure to 360 nm light. (a) Absorption and (b) emission spectra, (c)
images under 360 nm light and (d) normalized emission intensity (591 nm) of HB solution containing
various anions
Owing to the hydrophilic oligo(ethylene glycol) chain, HB exhibited high solubility in water.
Absorption bands of HB (10 µM) in 10 mM phosphate buffer solution (PBS; pH 7.4, 150 mM NaCl)
appear at 350 and 426 nm (blue solid line in Figure 1a). The fluorescence emission of HB appears at a
much longer wavelength than its absorption band due to the ESIPT mechanism (blue solid line in Figure
1b). The strong yellow fluorescence emission of HB can be observed by the naked eye under
illumination at 360 nm (Figure 1c).
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We tested the fluorescence response of HB to various anionic species (Figure 1). To a 10 µM solution
of HB in 10 mM PBS, 10 molar equivalents of various anionic species were added and incubated for 10
min at 25 °C in the dark. Most anion containing solutions maintained their original absorption and
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emission except for the IO4 solution. For the IO4 -containing solution, the emission intensity was
slightly decreased along with absorption shifts (Figure S3). Interestingly, the absorption spectrum of
HB greatly changed upon exposure to UV light, indicating the reaction between HB and IO4– was
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accelerated by light irradiation. The fluorescence emission also greatly decreased upon addition of IO4
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and subsequent UV irradiation. After 10 min of UV irradiation using a UV handy lamp (Sankyo
FL10BLB), the fluorescence emission from HB almost completely disappeared (Figure 1b, c and d).
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Figure 2 shows the IO4 concentration-dependent fluorescence emission after 10 min of UV irradiation.
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With increasing IO4 concentration, the fluorescence emission intensity of HB gradually decreased. The
fluorescence emission intensity of HB showed a reciprocally linear correlation with the concentration of
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IO4 until the concentration reached 4.0 µM, indicating HB is a very sensitive fluorescent probe for the
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detection of IO4 with detection limit of 4.8 µM. The emission of HB was also disappeared by IO4 in
the presence of various anions and metals (Figure S4).
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Figure 2. Fluorescence intensity change of HB (10 µM) by addition of IO4 with 360 nm illumination. a)
Emission spectra and b) intensity change at 546 nm. Inset: images of HB solution under 360 nm
illumination.
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Because the IO4 is a mild oxidant for various organic chemicals, we initially expected that the
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fluorescence emission change of HB is caused by oxidation of it. To confirm this hypothesis, HB was
treated with KMnO4 as a reference oxidant. Upon addition of KMnO4, the fluorescence emission of HB
was completely disappeared by the generation of an oxidation product (figure S5b, and d). This
oxidation product would possibly be reduced by treatment of reducing agent. Therefore, we again
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treated with dithiothreitol (DTT) as a reducing agent to both reaction products obtained from IO4 and
KMnO4 treatments, respectively. When DTT was added to the product obtained by KMnO4 treatment,
the fluorescence emission of HB was rapidly recovered. However, the fluorescence emission of HB was
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not recovered at all from the reaction product obtained by IO4 addition (Figure S5a, and c), indicating
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the reaction mechanisms of HB with KMnO4 and IO4 are obviously different.
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To get further insight of the reaction mechanism between HB and IO4 , several experiments were
performed. 1H NMR experiments were conducted. To simplify 1H NMR spectrum, we used 2’
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(Scheme 1), a structural fragment of HB, because 2’ exhibited the same fluorescent response to IO4
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addition as that of HB. The reaction between 2’ and IO4 was performed in a mixture of solvents
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consisting of DMSO-d6 and D2O (v/v = 50%) and subsequent extraction was performed with CDCl3. As
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shown in Figure S6, new set of proton signals were observed upon addition of IO4 to 2’. The intensity
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of the proton signals increased upon irradiation, indicating that light irradiation accelerates the reaction
rate. After 10 min of light irradiation of the reaction mixture, the major product was roughly separated
by silica column chromatography. The retention factor of the major product was significantly smaller
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than that of HB due to the increased polarity by the addition of IO4 . Both 2’ and the major product
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formed after IO4 addition exhibited six proton signals (Figure S7a). Upon addition of IO4 to 2’, the
proton signals of thiophene unit were significantly shifted, caused by the formation of the thiophenone
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structure.[31] In this context, the FT-IR spectrum of the IO4 addition product was measured. A new
peak at 1695 cm-1 appeared in the spectrum of the reaction product, indicating the formation of a
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carbonyl group (Figure S7b). Therefore, we propose the plausible mechanism of the formation of IO4
adduct to HB as shown in Scheme S1.
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Figure 3. Fluorescence emission under 360 nm illumination changed by various treatments such as
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KMnO4, IO4 , DTT, heat, and glucose
Benzothiazole with a neighbouring aromatic hydroxyl group can form an intramolecular hydrogen
bond, which can be converted into the keto isomer via ESIPT.[32-36] During the ESIPT process of
enol-keto tautomerization in the excited state, the nitrogen and oxygen atoms in HB gain partial positive
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and negative charges, respectively.[34, 37, 38] Therefore, the central carbon atom in benzothiazole
becomes reactive in the excited state due to increased electron deficiency. In this step, oxidative attack
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of IO4 on the central carbon atom proceeds to generate the ring opening product of the benzothiazole
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group. In this manner, the oxidative attack of IO4 can proceed and is even accelerated by phoexcitation.
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When considering the structure of IO4 -adducted HB, IO4 would be readily released because IO4 is a
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very good leaving group. The fluorescence emission of HB was gradually recovered upon thermal
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heating of the IO4 -adducted product (Figure S8), indicating IO4 release. Moreover, the recovery of
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fluorescence emission was faster upon addition of sodium thiosulfate (20 eq.), because IO4 is
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decomposed by the thiosulfate ion.[39]
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Because IO4 is mild oxidant for glucose, the release of IO4 can be accelerated by treatment of glucose
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to the IO4 addition product. Figure 3 shows some logic operations that fluorescence emission of HB
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was by treatments of various stimuli such as KMnO4, IO4 , DTT, heating, and glucose.
Using the fluorescence emission changes of HB by external stimuli, we can propose an additional
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application. Solution containing HB (20 µM) with or without treatment of 10 eq. IO4 was filled into a
fountain pen. Some letters were written on a filter paper using the fountain pen (Figure 4a). When the
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letters were written by the IO4 -treated HB solution, the letters could not be read out (Figure 4b). In
contrast, the characters written by HB solution could be directly read by UV irradiation due to the
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strong fluorescence emission (Figure 4c). The letters written by IO4 -treated HB solution become
readable after heating with an electric iron for 5s. (Figure 4d).
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Figure 4. (a) Writing of the security letters using fountain pen on a filter paper, (b) the security letter
before heating under 360 nm illumination, (c) the letter written using HB solution (20 µM) under 360
nm illumination, (d) the security letter after heating with an electric iron under 360 nm illumination.
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4. Conclusion
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In summary, we prepared HB as a selective and sensitive fluorescent probe for detecting IO4 in
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aqueous solutions. Among various ionic species tested, only IO4 could induce absorption and emission
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changes in HB. These changes were accelerated by UV irradiation. Because the fluorescence emission
change of HB was accelerated by photoexcitation, we can reduce the occurrence of false positives by
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undesirable fluorescence quenching processes for the detection of IO4 . Furthermore, the emission
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intensity of HB containing IO4 could be recovered by heating. Using this property, we demonstrated a
fluorescence-based security ink.
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Acknowledgement
This work was supported by the Mid-Career Researcher Program (2017R1A2A1A17069537) funded by
the National Research Foundation (NRF) of Korea.
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Graphical Abstract
Highlights
-
ò
ò
ò
The probe, HB, have successfully recognized IO4 in various anions, which is accelerated by
UV irradiation.
-
The fluorescence emission of HB was recovered upon thermal heating of the IO4 adducted
product.
-
Using the reversibility through thermal heating, the solution containing HB and IO4 could be
used as a fluorescence-based security ink.

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Supplementary Materials
Figure S1. Characterization of HB (a) MALDI-TOF-MS spectrum, (b) DLS profile of HB (10
and (c) high-resolution mass spectrum of HB.
µM) in 7.4 PBS buffer,
S1

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Figure S2. Absorption and emission spectra of HB (10
under 360 nm illumination.
µM) in various solvents with images of HB (10 µM) solution
Figure S3. Absorption and Fluorescence emission change of HB (10 µM) by addition of various anions under dark
condition. (a) Absorption, (b) emission spectra, (c) fluorescence emission under 360 illumination
S2

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-
Scheme S2. plausible mechanism of fluorescence quenching by addition of IO4 to HB.
-
Figure S4. Competitive experiments of HB (10
µ
M) for IO4 (10 eq.) containing various anions and metals (10 eq.) in
-
-
-
-
7.4 PBS buffer solution (1: F-, 2: Cl-, 3: Br-, 4: I-, 5: HCO3 , 6: HSO-, 7: CH3CO2 ,8: SCN-, 9: NO3 , 10: N3 , 11:
-
-
-
CN-, 12: ClO3 , 13: BrO3-, 14: IO3 , 15: IO4 , 16: Li+, 17: Na+, 18: K+, 19: Mg2+, 20: Fe2+, 21: Hg2+, 22: Al2+, 23:
Ni2+, 24: Co2+) with exposure to 360 nm light. (a) normalized emission intensity (at 591 nm), and (b) images
under 360 nm light of HB solution containing various anions and metals.
S3

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Figure S5. Absorption and fluorescence spectra changes of HB (10 µM) treated with oxidant and reducing agent. a)
-
and c) with IO4 , and DTT, b) and d) with KMnO4, and DTT.
Figure S6. 1H NMR experiment using structural fragment of HB (2’) in CDCl3.
S4

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-
Figure S7. (a) 1H NMR in CDCl3 and (b) FT-IR spectra of 2’ (black) and its IO4 adducted product (red)
-
Figure S8. (a) The emission spectra of HB (10
µ
M) solution containing IO4 (10 eq.) with thiosulfate (20 eq.) at room
temperature (rt), 40 °C, and 80 °C. (b) The changes of emission intensity as a function of heat.
S5

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1H NMR spectrum of 1
1H NMR spectrum of 2
S6

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1H NMR spectrum of 2’
1H NMR spectrum of 3
1H NMR spectrum of 4
S7

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1H NMR spectrum of 5
1H NMR spectrum of 6
S8

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1H NMR spectrum of 7
1H NMR spectrum of HB
S9

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13C NMR spectrum of HB
S10

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Highlights
-
ò
ò
ò
The probe, HB, have successfully recognized IO4 in various anions, which is accelerated by
UV irradiation.
-
The fluorescence emission of HB was recovered upon thermal heating of the IO4 adducted
product.
-
Using the reversibility through thermal heating, the solution containing HB and IO4 could be
used as a fluorescence-based security ink.