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Exploiting Solvate Ionic Liquids for Amine Gas Analysis on a Quartz Crystal Microbalance Hsin-Yi Li, and Yen-Ho Chu Anal. Chem., Just Accepted Manuscript • Publication Date (Web): 20 Apr 2017 Downloaded from http://pubs.acs.org on April 22, 2017

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Analytical Chemistry

Graphical Abstract

Exploiting Solvate Ionic Liquids for Amine Gas Analysis on a Quartz Crystal Microbalance

Hsin-Yi Li and Yen-Ho Chu*

1

ACS Paragon Plus Environment

Analytical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Exploiting Solvate Ionic Liquids for Amine Gas Analysis on a Quartz Crystal Microbalance

Hsin-Yi Li and Yen-Ho Chu*

Department of Chemistry and Biochemistry, National Chung Cheng University, 168 University Road, Minhsiung, Chiayi 62102, Taiwan, Republic of China

*

Corresponding

author.

Tel:

886

52729139;

fax:

[email protected]

2


886

52721040;

e-mail:

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Abstract We demonstrated in this work the usefulness of solvate ionic liquids, SIL 3 and SIL 4, for chemoselective detection of amine gases on a quartz crystal microbalance. This detection of gaseous amines was achieved by nucleophilic aromatic addition reactions with super electrophilic SIL 3 or SIL 4 thin-coated on quartz chips. Starting with inexpensive reagents, functional SIL 3 and SIL 4 could be readily synthesized in two short steps with high isolated yield (81% and 77%, respectively). The QCM platform developed in this work is readily applicable and highly sensitive to low molecular weight amine gases: for propylamine gas at 10 Hz decrease in resonance frequency, the sensitivity of detection using SIL 4 was 5.4 ppb. This simple and convenient assembly of neutral ligands (e.g., 1a and 1b) with Li+ ion to afford room temperature ionic liquids should be of great importance for a myriad of applications. To the best of our knowledge, no example to date of reports based on nucleophilic aromatic addition reactions demonstrating sensitive amine gas detection in solvate ionic liquids on a QCM has been reported. Furthermore, because of the high color intensity of the Meisenheimer complexes formed, our preliminary result showed that SIL 4 loaded on copier paper can be used not only as a portable amine gas sensor but also as a potential invisible ink that is only revealed by amine vapor.

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This work describes a new application of solvate ionic liquids1-3 tailored for label-free detection of small molecular-weight amine gases by quartz crystal microbalance (QCM)4 in real time and at ambient temperature. This chemoselective detection of gaseous amines was achieved by nucleophilic aromatic addition reactions to furnish the Meisenheimer complexes5,6 with solvate ionic liquids SIL 1-6 (Figure 1) thin-coated on quartz chips. O O

O

O

NTf2

Li O

O

O

Li O

NTf2

O

SIL 1

SIL 2 O

O

O

O

Li

NO2

O

O

O

Li

NTf2 O

O

NO2

O2N

O2N NO2

NO2

SIL 3

SIL 4 O

O O

O

Li O

NTf2

O

NTf2

O

O

O

Li O

NO2

NTf2 NO2

NO2

SIL 5

SIL 6

Figure 1. Structures of solvate ionic liquids, SIL 1-6.

It has been comprehensively studied by Watanabe, Henderson, Angell and others that lithium bis(trifluoromethanesulfonyl)amide (LiNTf2) tightly associates with triglyme and tetraglyme to form long-lived,7 thermally stable (up to 200 oC),8 and highly conductive8 but non-covalent 1:1 complexes (i.e., SIL 1 and SIL 2).

These complexes are called

solvate ionic liquids (SILs).1-3 Also, the coordination number of Li+ ion in SILs has been 4


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determined to be in the range of 4-6. The SIL 1 and SIL 2 show negligible vapor pressure, are nonflammable and liquideous at room temperature, and have been favorable for use as electrolytes in lithium batteries.9 With these intriguing ionic liquid properties in mind, the development of new applications for SILs is highly desirable. Among potential applications, we envisioned that functional SILs such as SIL 3 and SIL 4 embedded with 2,4,-6-trinitrophenyl (TNP) group on a QCM would be of excellent candidates for use in analysis of amine gases.

Among many reactions available to chemists engaged in synthesis and mechanism studies, nucleophilic aromatic substitution (SNAr) is fundamental and has been used to functionalize aromatic molecules in both conventional molecular solvents and ionic liquids.10,11 For addition-elimination mechanisms, Meisenheimer complexes are common intermediates in SNAr reactions. They are formed by the addition of nucleophiles to highly electron-deficient aromatic moieties such as TNP group. Subsequently, this intermediate, if unstable or short-lived, proceeds forward by rearomatization to afford the substituted product. Ionic liquids are known to accelerate SNAr reactions10,11 and TNP-containing arenes can sufficiently stabilize the resulting build-up of negative charge during Meisenheimer complex formation. Moreover, many stable Meisenheimer complexes have been isolated and reported in literature.5 Based specifically on SNAr reaction, this work reports concise synthesis of solvate ionic liquids SIL 1-4 and demonstrates their value in amine gases detection on QCM.

EXPERIMENTAL SECTION Synthesis of Solvate Ionic Liquids, SIL 1-6. Both SIL 1 and SIL 2 obtained as colorless 5



liquid were prepared following a modified protocol originally developed by Watanabe and coworkers.3 Detailed experimental procedures of SIL 1-6 syntheses were given in the Supporting Information. SIL 1: colorless liquid; 1H NMR (400 MHz, CDCl3) δ 3.46 (s, 6H, 2 × CH3), 3.60-3.65 (m, 4H, 2 × CH3OCH2), 3.67-3.77 (m, 4H, 2 × CH3OCCH2), 3.71 (s, 4H, 2 × CH2); 13C NMR (100 MHz, CDCl3) δ 58.92, 67.95, 68.36, 70.39, 119.60 (q, JCF = 319 Hz, CF3); ESI-HRMS m/z [M]+ calcd for C8H18LiO4 185.1365, found 185.1362. SIL 2: colorless liquid; 1H NMR (400 MHz, CDCl3) δ 3.42 (s, 6H, 2 × CH3), 3.58-3.64 (m, 4H, 2 × CH3OCH2), 3.67-3.77 (m, 12H, 6 × OCH2); 13C NMR (100 MHz, CDCl3) δ 58.92, 68.41, 68.55, 68.93, 70.49, 119.69 (q, JCF = 319 Hz, CF3); ESI-HRMS m/z [M]+ calcd for C10H22LiO5 229.1627, found 229.1624. SIL 3: yellow liquid; 1H NMR (400 MHz, CDCl3) δ 3.44 (s, 3H, CH3), 3.59-3.65 (m, 2H, CH3OCH2), 3.67-3.74 (m, 4H, 2 × CH2), 3.74-3.81 (m, 2H, ArOCCOCH2), 3.96 (t, J = 4.2 Hz, 2H, ArOCCH2), 4.48 (t, J = 4.2 Hz, 2H, ArOCH2), 8.92 (s, 2H, aryl H); 13C NMR (100 MHz, CDCl3) δ 59.01, 68.62, 68.78, 69.39, 69.68, 70.02, 77.30, 119.23 (q, JCF = 318 Hz, CF3), 124.59, 141.77, 144.82, 150.97; ESI-HRMS m/z [M]+ calcd for C13H17LiN3O10 382.1074, found 382.1073. SIL 4: yellow liquid; 1H NMR (400 MHz, CDCl3) δ 3.41 (s, 3H, CH3), 3.55-3.65 (m, 2H, CH3OCH2), 3.65-3.84 (m, 10H, 5 × CH2), 3.93 (t, J = 4.2 Hz, 2H, ArOCCH2), 4.46 (t, J = 4.2 Hz, 2H, ArOCH2), 8.91 (s, 2H, aryl H); 13C NMR (100 MHz, CDCl3) δ 58.92, 68.15, 68.28, 68.40, 68.84, 69.50, 69.50, 70.33, 76.92, 119.39 (q, JCF = 318 Hz, CF3), 124.52, 141.71, 144.74, 151.03; ESI-HRMS m/z [M]+ calcd for C15H21LiN3O11 426.1336, found 426.1334. SIL 5: yellowish liquid; 1H NMR (400 MHz, CDCl3) δ 3.41 (s, 3H, CH3), 3.63-3.56 (m, 6


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2H, CH3OCH2), 3.66-3.79 (m, 8H, 4 × CH2), 3.80-3.87 (m, 2H, ArOCCOCH2), 3.98 (t, J = 4.6 Hz, 2H, ArOCCH2), 4.27 (t, J = 4.6 Hz, 2H, ArOCH2), 6.99 (d, J = 10.2 Hz, 2H, aryl H) , 8.18 (d, J = 10.2 Hz, 2H, aryl H); 13C NMR (100 MHz, CDCl3) δ 58.92, 67.76, 68.37, 68.44, 68.49, 69.14, 69.36, 69.69, 70.35, 114.54, 119.54 (q, JCF = 319 Hz, CF3), 125.91, 141.74, 163.39; ESI-HRMS m/z [M]+ calcd for C15H23LiNO7 336.1635, found 336.1631. SIL 6: yellow liquid; 1H NMR (400 MHz, CDCl3) δ 3.40 (s, 3H, CH3), 3.56-3.64 (m, 2H, CH3OCH2), 3.66-3.82 (m, 8H, 4 × CH2), 3.84-3.95(m, 2H, ArOCCOCH2), 4.05 (t, J = 4.2 Hz, 2H, ArOCCH2), 4.48 (t, J = 4.2 Hz, 2H, ArOCH2), 7.34 (d, J = 9.6 Hz, 1H, aryl H) , 8.47 (dd, J = 9.6, 2.8 Hz, 1H, aryl H) , 8.75 (d, J = 2.8 Hz, 1H, aryl H); 13C NMR (100 MHz, CDCl3) δ 58.87, 68.11, 68.24, 68.39, 68.78, 68.89, 69.82, 69.99, 70.29, 115.15, 119.48 (q, JCF = 318 Hz, CF3), 121.73, 129.57, 138.50, 140.26, 156.32; ESI-HRMS m/z [M]+ calcd for C15H22LiN2O9 381.1485, found 381.1476. QCM Measurements. A flow PSS QCM system (9 MHz) available from the ANT Technology Co. (Taipei, Taiwan) was operated at room temperature and nitrogen was used as carrier gas. The 9-MHz AT-cut quartz chips deposited with gold electrodes (area 11 mm2) on both sides were also available from ANT Technology. Before use, the gold electrodes on chips were cleaned with NaOH (5 N, 30 min), H2O (5 min), HCl (1 N, 5 min), and H2O (5 min) for two cycles to remove any organic absorbents, and finally rinsed with water thoroughly and dried under nitrogen. Ionic liquid solutions were prepared by dissolving individual SIL (1 µL) in acetonitrile (HPLC grade, 300 µL). The freshly prepared solutions (1 µL) were carefully pipetted onto the cleaned bare gold electrodes (area 11 mm2) situated at the center of quartz chip. The ionic liquid coated chips were placed in an oven (110 oC) for 1 min to remove 7



residual solvent. The quartz sensor chips were then mounted in the gas flow chamber (100 cm3) and nitrogen was used as carrier gas at flow rate of 3 mL/min. Until a stable baseline was obtained, amine gas samples were injected into the chamber. The resonance frequency drops versus time curves were measured and recorded. Amine sample vapors were obtained by gasifying the chemicals in the sealed glass container (1.26 L). Using the PSS QCM apparatus for QCM measurements, a rapid initial non-specific frequency decrease (approximately 0.1 to 0.4 Hz) was typically detected within 5 sec after sample injection, which was totally insignificant with reference to reaction-based frequency drops owing to nucleophilic aromatic addition reactions of SILs with amine gases.

RESULTS AND DISCUSSION Scheme 1 illustrates the synthesis of SIL 3 and SIL 4 of which the amine-reactive TNP elements 1a,b could be conveniently assembled from commercial triethylene glycol monomethyl ether (for 1a) and tetraethylene glycol monomethyl ether (for 1b) with the freshly prepared picryl chloride in the presence of triethylamine. The synthesis was straightforward and, in our hands, the overall isolated yield for this 2-step synthesis of SIL 3 and SIL 4 were 81% and 77%, respectively. The known SIL 1 and SIL 2 were prepared following a modified protocol previously developed by Watanabe and coworkers.3 All SIL 1-4 obtained are liquid at room temperature. Detailed experimental procedures, NMR (1H and 13C) and HR-MS spectra and data of SIL 1-4 are summarized in the Supporting Information.

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Scheme 1 Synthesis of SIL 3 and SIL 4.

The analysis of volatile organic amines is known to be of great importance for food spoilage detection12 and for use as biomarkers in human cancers.13 In addition, bacterial amine volatiles have been suggested to play ecological roles in microbe signaling and defense.14 To selectively detect gaseous amines, we incorporated TNP functional group in SIL 3 and SIL 4 for the reasons that it is an amine-reactive super electrophile15 and has also been studied extensively in SNAr reactions.5,6 Moreover, it was reported10,11 that SNAr reactions proceed with faster reaction rates in ionic liquids than those performed in molecular solvents.

QCM results shown in Figure 2 clearly demonstrate that, using the same concentration (100 ppb) for all gaseous samples tested, the SIL 3 and SIL 4 reacted selectively only with amines: propylamine (∆F = -126 Hz and -166 Hz, respectively), isopropylamine (∆F = -124 Hz and -132 Hz, respectively), methylamine (∆F = -117 Hz and -112 Hz, respectively), and ethylmethylamine (∆F = -54 Hz and -52 Hz, respectively). In QCM measurements, primary amines are more reactive (and accordingly produce larger ∆F responses) than the sterically hindered secondary amine (e.g., propylamine vs. ethylmethylamine). Among all amines tested, propylamine gas produced the largest ∆F value (-166 Hz) with SIL 4. This SIL-based QCM system worked well and was 9



unreactive to potentially nucleophilic methanol, ethanol, and ethanethiol gases, and, as a result, the frequency drop in this continuous flow measurement was not at all due to any nonspecific physisorption of gas onto ionic liquid (Figure 2C and 2D). It is of note that, in our hand, the reaction-based platform developed was insensitive to moisture (100 ppb, Figure 2; 250 ppb, Figure S1), indicating that any residual water present in the gas stream would not interfere with amine gas analysis. Both SIL 3 and SIL 4 performed equally well in capturing amine gases under our experimental conditions. As the control solvate ionic liquids, SIL 1 and SIL 2 are totally inert to all amines, alcohols, and thiol gases tested (Figure 2A and 2B), clearly demonstrating the chemoselectivity of SIL 3 and SIL 4 toward amine gases.

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(A)

(B) water ethanethiol ethanol methanol

∆F (Hz)

ethylmethylamine methylamine isopropylamine propylamine

SIL 1

SIL 2 (D)

(C)

water ethanethiol ethanol methanol ∆F (Hz)

∆ F = -52 Hz

∆ F = -54 Hz

ethylmethylamine ∆ F = -117 Hz

∆ F = -112 Hz

∆ F = -124 Hz

∆ F = -132 Hz

methylamine isopropylamine ∆ F = -126 Hz

SIL 3 0

1

2

3

4

5

SIL 4 0

time (sec x 103)

1

∆ F = -166 Hz 2

3

4

propylamine

5

time (sec x 103)

Figure 2. Chemoselective detection of ethanethiol, ethanol, methanol, ethylmethylamine, methylamine, isopropylamine, and propylamine gases (100 ppb each) all by a 9 MHz QCM thin-coated with (A) SIL 1, (B) SIL 2, (C) SIL 3, and (D) SIL 4 (3.3 nL, 300 nm thickness). The QCM sensorgrams for ethanethiol, ethanol, methanol, ethylmethylamine, methylamine, and isopropylamine gases were vertically shifted (50 Hz in between) for clarity. Nitrogen was used as the carrier gas with a flow rate of 3 mL/min, and gaseous samples were injected at 500 s. The resonance frequency drop, ∆F, in Hz is the QCM response on the quartz chip surface.

As we successfully developed the TNP-conjugated SIL 3 and SIL 4 for sensitive analysis 11



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of amine gases, we next turned our attention to a detailed quantitative study of SIL 3 and SIL 4 reactions with propylamine gas by QCM and investigated their effectiveness in amine gas analysis based on nucleophilic aromatic addition reactions. Figure 3 provides the results (for all QCM sensorgrams, see Figure S2 in the Supporting Information). It showed an essentially linear QCM frequency response within the range of concentrations tested (0-250 ppb). In our hand, both SIL 3 and SIL 4 are highly sensitive to amine gas: for propylamine gas at 10 Hz decrease in resonance frequency (i.e., ∆F = 10 Hz), the sensitivity of detection using SIL 3 and SIL 4 was 8.0 (10 / 1.256) and 5.4 ppb (10 / 1.856), respectively (blue fitting lines in Figure 3). The QCM responses (∆F) of the control SIL 1 and SIL 2 reactions with propylamine gas (0-250 ppb) were completely negligible (black line in Figure 3). 100 0 -100 -200 -300 -400 -500 0

50

100

150

200

250

Figure 3. Detection sensitivity plot of ∆F (Hz) vs concentration (25, 50, 75, 100, 125, 150, 200, and 250 ppb) of propylamine gas using a 9 MHz QCM thin-coated (3.3 nL, 300 nm thickness) with SIL 1-4. Each data point was taken at t = 6000 s from the resonance frequency drop value of various concentrations of propylamine gas (Figure S1). Linear curve fitting equations for SIL 3 and SIL 4: ∆F = -1.256[propylamine] (R = 0.99554) and ∆F = -1.856[propylamine] (R = 0.99243), respectively.

Our successful development of SIL 3 and SIL 4 for amine gas analysis permitted us to validate the critical need of a super electrophilic TNP group on SILs for carrying out 12


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nucleophilic aromatic addition reactions at ambient temperature. Figure 4 shows the QCM results. We were pleased that SIL 4 rapidly reacted with propylamine gas (216 ppb) to produce the largest ∆F (-374 Hz) on chip and, under identical conditions, greatly outperformed SIL 2 (∆F = 0 Hz), SIL 5 (∆F = 0 Hz) and SIL 6 (∆F = -12 Hz). This result unambiguously demonstrated that the TNP group in SIL 4 is critical and essential for its high reactivity and selectivity with amine gas. In our hand, DNP (2,4-dinitrophenyl) in SIL 6 and MNP (4-nitrophenyl) in SIL 5 were electrophilically insignificant or marginal, if any, in its reactivity to conduct nucleophilic aromatic addition reactions at ambient temperature. This ultrahigh reactivity of TNP toward amines is well documented in literature.5,6 Most significantly, the control ionic liquid SIL 2 was completely inert to propylamine gas (∆F = 0 Hz at 216 ppb, Figure 4). Our result reaffirmed that properties of SILs could be readily altered, structurally engineered and closely controlled to equip affinity ionic liquids with tailored functionalities. It is also worth noting that compound 1b is a solid and, much to our delight, SIL 4 is a liquid at room temperature (Scheme 1). Detailed experimental procedures of SIL 5 and SIL 6 syntheses were given in the Supporting Information.

Figure 4. Chemoselective detection of propylamine gas (216 ppb) by a 9 MHz QCM thin-coated with SIL 2, SIL 4, SIL 5, and SIL 6 (3.3 nL, 300 nm thickness), respectively. 13



The QCM sensorgrams obtained from SIL 2, SIL 5, and SIL 6 were vertically shifted (30 Hz in between) for clarity. Nitrogen was used as the carrier gas with a flow rate of 3 mL/min, and gaseous samples were injected at 500 s. The resonance frequency drop, ∆F, in Hz is the QCM response on the quartz chip surface.

The 1H NMR analysis supported the formation of Meisenheimer complexes of SIL 4 reactions with amine gases on quartz chip: an upfield shifted aryl proton signal at δ 9.027 was experimentally obtained from addition of propylamine to SIL 4 in 1:1 mole ratio where aryl protons of free SIL 4 and 2,4,6-trinitro-N-propylaniline (the SNAr product) appeared at δ 9.051 and 9.046, respectively (Figure 5). This nucleophilic aromatic addition reaction (1 M) was performed in SIL 2 solvent. The fact that a gradual, steady upfield shift of the aryl proton signal of SIL 4 upon titrating with propylamine was observed for the complex implicated that the Meisenheimer complex is in fast equilibrium with the non-complexed molecules, giving rise to the solution its strong red color, and certain TNP species of SIL 4 in SIL 2 solution retain their aromaticity.16 This significant color change due to the formation of Meisenheimer complex is apparent to the naked eyes, as seen for the reaction solution (1 M) inside a capillary of the bottom NMR tube (5 mm) in Figure 5.

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1

H NMR (400 MHz) spectra of the highlighted aryl protons of 2,4,6-trinitro-N-propylaniline (SNAr product, 1 M in SIL 2 inside a capillary; top spectrum) and SIL 4 (1 M in SIL 2 inside a capillary) as well as the Meisenheimer adduct formed from SIL 4 reaction with propylamine in SIL 2 (1 M each inside a capillary, bottom spectrum). Capillaries containing samples were placed in standard NMR tubes (5 mm) filled with CDCl3. The red color capillary seen in the bottom NMR Figure 5.

tube revealed that the color change comes from the formation of Meisenheimer complexes upon reaction of SIL 4 with amine in SIL 2.

Figure 6 highlights reactions involved in amine gas detection by SIL 4 on a QCM. Nucleophilic addition by amines at the aromatic ring carbon of TNP in SIL 4 disrupts its aromaticity, resulting in significant changes in electronic conjugation of the system. With a view to molecular optical sensors (see Figure S3 for the photographic image in the Supporting Information), it is of particular interest that the solution of SIL 4 and amines (e.g., 0.3 M each) in SIL 2 shows an orange red color that are absent to SIL 2 solutions 15



containing only SIL 4 or amines. The color change comes from the formation of Meisenheimer complexes upon reaction of SIL 4 with amine. This orange red color was stabilized in SIL 2 for long hours (> 10 h) at ambient temperature. This result is in agreement with the conclusions made by Fendler and co-workers that the Meisenheimer complexes are most stable in polar aprotic solvents, including DMSO.17 Moreover, our SIL system likely stabilizes the formation of the Meisenheimer complexes through its interactions with the cation of solvate ionic liquids.18 Overall in our hand, Meisenheimer complexes were formed and stabilized under neat (i.e., QCM experiments) or highly concentrated (1 M in polar aprotic SIL 2 solvent) conditions, but were transiently formed and rapidly converted to afford the SNAr product in dilute (50 mM), less polar CDCl3 solvent (Figure S4 in the Supporting Information).

Figure 6. Plausible reaction mechanism of SIL 4 with amine gases.

Furthermore, gas vapors have long been exploited to uncover invisible ink by inducing color formation.13 Owing to high color intensity of the Meisenheimer complexes formed, we reasoned that it should be attractive to develop SILs for invisible ink that can only be revealed by amine vapor. This SIL-for-invisible-ink system was illustrated by using propylamine vapor as example. A 2 µL acetonitrile solution of SIL 4 (47 µg, 70 nmol) for each letter was homogeneously distributed on copier paper and dried by evaporation to provide a portable invisible ink model. As shown in Figure 7, SIL 4 on copier paper 16


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was almost colorless by naked eyes, but its color intensity increased instantaneously upon exposure to propylamine vapor. This preliminary result demonstrated that SIL 4 loaded on paper can be used as a portable sensor for amine vapor detection (Figure S5 in the Supporting Information) as well as invisible ink visualization with an advantage of simple operation. (a)

(b)

Figure 7. Photos of SIL 4 handwritten “CCU” letter on copier paper (a) before and (b) after exposure to propylamine vapor under daylight.

CONCLUSION We demonstrated here the successful development of a system based on solvate ionic liquids aimed at chemoselective detection of amine gases measured by quartz crystal microbalance. This reaction-based detection of gaseous amines was achieved by the nucleophilic aromatic additions with functional SIL 3 and SIL 4 thin-coated on quartz chips. The facile, short-step and low-cost preparation of SIL 3 and SIL 4 using straightforward synthetic chemistry was more advantageous than those of common imidazolium ionic liquids. Our results hold three significant conclusions: (i) solvate ionic liquids, SIL 3 and SIL 4, developed in this work are superior for the chemoselective detection of amine gases, (ii) the analysis of nucleophilic aromatic addition reactions by 17



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QCM is straightforward and label-free, and (iii) the SIL platform is chemoselective, readily applicable to portable gas analysis and exploitation for revealing invisible ink. To the best of our knowledge, we know of no examples to date of reports based on nucleophilic aromatic addition reactions demonstrating sensitive amine gas detection in solvate ionic liquids on a QCM. Albeit we developed to demonstrate an application of lithium solvate ionic liquids for amine gas analysis, new applications of SILs with other metal ions and ligands are possible. Through a comparison to popular imidazolium ionic liquids, this click assembly of electrically neutral organic ligands to rapidly afford ionic liquids using metal ions should be of great interest and would not be straightforward by traditional synthetic methods. In light of new application of SILs, this research is a proof-of-concept use of a SIL-based platform on QCM for reaction-directed analysis of gas samples. Finally, the functional SILs shall open up new use and research on ionic liquids.

Supporting Information Figures S1-S5; detailed synthetic procedures of SIL 1-6, 1H and

13

C NMR and HRMS

spectra and data of SIL 1-6.

ACKNOWLEDGEMENTS This work was supported by a grant (MOST 103-2113-M-194-002-MY3) from the Ministry of Science and Technology of Taiwan, Republic of China. Professor Masayoshi Watanabe (Yokohama National University, Japan) is thanked for drawing our attention to his fascinating research on solvate ionic liquids. We also thank reviewers for constructive comments. 18


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