DOI: 10.1002/chem.201302638

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& Sensors

Highly Sensitive and Selective Detection of Nitrophenolic Explosives by Using Nanospheres of a Tetraphenylethylene Macrocycle Displaying Aggregation-Induced Emission Hai-Tao Feng and Yan-Song Zheng*[a]

Abstract: A tetraphenylethylene (TPE) Schiff-base macrocycle showing an aggregation-induced emission (AIE) effect has been synthesized, which could aggregate into nanospheres and emit yellow fluorescence in aqueous media. By virtue of its AIE effect, the macrocycle showed a sensitive and selective response to 2,4,6-trinitrophenol (TNP) and 2,4dinitrophenol (DNP) among a number of nitroaromatic compounds, which could be used to detect TNP and DNP at nanomolar levels. Moreover, it exhibited a superamplified quenching effect with DNP but not with TNP, providing

a possible means of discriminating these two compounds. In comparison with open-chain TPE Schiff-bases, the cavity of the macrocycle is essential for the selectivity for DNP over TNP. In addition, quantitative analyses of both DNP and TNP in real water samples and qualitative detection of these two analytes in the solid state by the macrocycle have been tested. The reliability of the quantitative analysis has been confirmed by HPLC. Our findings demonstrate that the TPE Schiff-base macrocycle has great potential as an excellent sensor for DNP and TNP.

Introduction

Hence, the development of fast, convenient, and specific analytical methods for TNP and DNP is highly desirable.[8] Recently, a new class of organic molecules has been developed that are non-emissive in solution but emit strong fluorescence upon aggregation, an effect termed aggregationinduced emission (AIE).[9] These organic compounds show great potential, not only in efficient organic light-emitting diodes (OLEDs) but also in highly selective and stable fluorescent sensors for biological and chemical analytes.[10] Tang et al. reported that polymers composed of tetraphenylethylene (TPE) or tetraphenylsilole units with an AIE effect could serve as highly sensitive sensors for TNP, since they showed a superamplification effect in their emission quenching with this substrate.[11] Fang et al. demonstrated that a chitosan film doped with hexaphenylsilole AIE nanoaggregates showed a strong response to TNP but little sensitivity with 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT), phenol, nitrobenzene, and so on.[12] However, to the best of our knowledge, no data on the sensing of DNP using an AIE system have hitherto been reported. If the AIE component is incorporated into a macrocycle, the selectivity for sensing explosives will be greatly enhanced. In this work, a TPE Schiff-base macrocycle with an AIE effect has been synthesized, which showed a sensitive and selective response to TNP and DNP among a number of nitroaromatic compounds. Moreover, it exhibited a superamplified quenching effect with DNP but not with TNP, thus providing a possible means of discriminating between these compounds.

The detection of explosives in surface water or ground water has become an increasingly important and urgent issue in modern society due to its antiterrorism applications in both national security and environmental protection.[1] To date, many real-time analytical methods have been used for the detection of explosives, such as gas chromatography, ion mobility spectrometry, Raman spectroscopy, fluorescence spectroscopy, and so on.[2] Among these techniques, fluorescence sensing of explosives by harnessing organic dyes has attracted the most attention because it is more simple, sensitive, and cost-effective than other methods.[3] However, selective analysis of explosives has rarely been reported, although the determination of their chemical compositions is critical for tracking their source and terrorist provenance.[4] 2,4,6-Trinitrophenol (TNP, picric acid) and 2,4-dinitrophenol (DNP) are often the principal ingredients of explosives.[5] Moreover, TNP and DNP have also been recognized as environmental contaminants that are harmful to wildlife and humans.[6] They arise as pollutants due to their widespread usage in the manufacture of rocket fuels, fireworks, matches, and so on.[7] In particular, DNP has been found in 61 of 1400 priority sites requiring clean-up of industrial waste.

[a] H.-T. Feng, Y.-S. Zheng School of Chemistry and Chemical Engineering Huazhong University of Science and Technology Wuhan 430074 (China) Fax: (+ 86) 27-87543632 E-mail: [email protected]

Results and Discussion It is well known that TPE and its derivatives, including 1, have a special AIE effect and have been extensively studied for use

Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201302638. Chem. Eur. J. 2014, 20, 195 – 201

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Full Paper in efficient OLEDs and fluorescent sensors. Therefore, the known compound 1 was used as a building block for constructing the macrocycle. The TPE Schiff-base macrocycle 3 was synthesized according to the synthetic route shown in Scheme 1. Compound 1 was formylated with hexamethylene-

Figure 1. Fluorescence spectra of 2 mm 3 in a mixed solvent of THF/water with different water fractions. Inset: Curve of fluorescence intensity versus water fraction.

A TEM image (Figure 2, top) revealed that the suspension of 3 in a mixed solvent of water/THF (9:1, v/v) was composed of round spherical aggregates of diameters 50–230 nm. An FESEM image of the suspension also revealed round nanosphere structures with diameters of 50–170 nm (Figure 2, bottom), which was consistent with the TEM measurement. The suspension of nanospheres was stable and no precipitate was observed after it had been left to stand for more than one week. Initially, the responses of 3 to TNP and DNP were measured by UV/Vis absorption spectroscopy in a mixed solvent of water/THF (9:1). As shown in Figure 3, the UV/Vis spectrum of compound 3 in THF features absorption bands at 345 and 251 nm. The absorption intensity of a mixture of 3 and DNP was obviously much larger than the sum of the absorption intensities of these two individual compounds, indicating an in-

Scheme 1. Synthesis of fluorescence sensors 3 and 4.

tetramine in trifluoroacetic acid (TFA) to give dialdehyde 2. Following a condensation reaction of the dialdehyde 2 with (1R,2R)-1,2-diaminocyclohexane in ethanol in the presence of acetic acid, the TPE Schiff-base macrocycle 3 was obtained simply by recrystallization from chloroform and methanol in 86 % yield. Open-chain TPE Schiff-base 4 was prepared in the same way in order to compare it with the macrocycle 3. As expected, while a dilute solution of 3 in THF showed almost no fluorescence, as a solid it was yellow light-emitting under a UV lamp. When a poor solvent (water) was added to a solution of 3 in THF, the macrocycle started to aggregate, although the fluorescence intensity showed only a slight increase when the water content was less than 50 %. When the water content exceeded 50 %, however, the solution became obviously turbid and the fluorescence intensity increased rapidly (Figure 1). Due to amorphous aggregation, the intensity did not increase but decreased a little after the addition of more than 80 % water. At 90 % water, the fluorescence intensity of the resultant suspension was more than four times higher than that of the solution in THF. Moreover, a very large Stokes shift of 200 nm was observed (excitation wavelength 350 nm, emission maximum wavelength 550 nm), which would be suitable for practical applications. The above results indicated that macrocycle 3 acted as an AIE compound. In analogous experiments, 4 also displayed an AIE effect (Figure S1). Chem. Eur. J. 2014, 20, 195 – 201

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Figure 2. TEM (top; scale bar 0.2 mm) and FESEM (bottom; scale bar 1 mm) images of a suspension of 3 (0.1 mm) in water/THF (9:1).

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Figure 4. (A) Fluorescence spectra of 2 mm 3 in the presence of different nitroaromatic compounds as well as phenol (30 mm) in H2O/THF (9:1). Excitation at 350 nm. (B) Fluorescence quenching efficiencies ((1 I/I0)  100 %), where I and I0 denote the fluorescence intensity of 3 with and without analyte, respectively) of different analytes (1, blank; 2, TNP; 3, DNP; 4, PNP; 5, phenol; 6, TNT; 7, DNT; 8, PNT; 9, DNB; 10, NB; 11, DNCB; 12, DNBA; 13, NBA).

Figure 3. UV/Vis spectra of 3, TNP (A) or DNP (B), and mixtures thereof in H2O/THF (9:1) ([3] = 5.0  10 6 m, [TNP] = [DNP] = 1.5  10 5 m).

To determine the selectivity of 3 for DNP among nitrophenolic compounds, fluorescence titrations of 3 with TNP, DNP, and PNP were carried out at a host concentration of 2 mm. As shown in Figure 5 A–C, with gradual addition of TNP, DNP, or PNP, the fluorescence intensity of 3 in water/THF (9:1) decreased. After 16 equivalents of DNP had been added, the fluorescence of 3 was almost completely quenched. In the presence of TNP and PNP, however, at the same number of moles as in the case of DNP, the macrocycle 3 still showed obvious emission. The change in the fluorescence intensity ratio (I0/I) with concentration of TNP or DNP was exponential rather than linear. With TNP the fluorescence decrease was slow, but with DNP it was very rapid and this substrate displayed a superamplified quenching effect. Applying an exponential quenching equation (I0/I = Aek[Q] + B),[11a] the quenching constants of 3 with TNP and DNP were calculated as 3.0  104 m 1 and 8.0  104 m 1, respectively, from nonlinear curve-fitting using Origin software. For PNP, however, by carefully checking the change in the intensity ratio I0/I with substrate concentration, it was found that the relationship between the intensity ratio and the concentration was linear, in agreement with the Stern–Volmer equation. By linear curve-fitting with this equation, the quenching constant with PNP was determined as 8.2  103 m 1. Generally speaking, fluorescence quenching that is not in accordance with the Stern–Volmer equation is static quenching, whereby a fluorochrome in the ground state can form a nonemissive bound complex with the quencher.[13, 14] Because TNP and DNP have more electron-withdrawing nitro groups, they

teraction between them. Similarly, the absorption intensity of a mixture of 3 and TNP was also larger than the sum of the absorption intensities of the individual compounds, again showing an interaction between them. Moreover, at the same concentration, although the absorption intensity of DNP was less than that of TNP, the absorption intensity of the 3·DNP complex was much larger than that of the 3·TNP complex, indicating that DNP had a stronger interaction with the macrocycle 3 than TNP. The fluorescence quenching of the suspension of 3 in water/ THF (9:1) was tested using TNP, DNP, para-nitrophenol (PNP), phenol, TNT, DNT, para-nitrotoluene (PNT), 1,3-dinitrobenzene (DNB), nitrobenzene (NB), 2,4-dinitrochlorobenzene (DNCB), 3,5-dinitrobenzoic acid (DNBA), and 4-nitrobenzoic acid (NBA). Among these 11 nitroaromatic compounds plus phenol, only TNP and DNP significantly attenuated the fluorescence intensity. As shown in Figure 4 A, after 15 equivalents of TNP and DNP had been added to a suspension of 3 (2  10 6 m) in water/THF (9:1), the fluorescence intensity at 550 nm decreased from 526 to 169 and 29 a.u., respectively. The quenching efficiencies ((1 I/I0)  100 %) of TNP and DNP were 68 % and 94 %, respectively. For PNP, TNT, DNT, PNT, and NB, quenching efficiencies of less than 8 % were obtained. Upon addition of phenol, DNB, DNCB, DNBA, or NBA, however, the fluorescence intensity of 3 slightly increased, giving rise to a negative quenching efficiency for these analytes. The largest change was observed for NBA, amounting to 16 % (Figure 4 B). Chem. Eur. J. 2014, 20, 195 – 201

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Full Paper complex results in fluorescence quenching. The obvious changes in the UV/Vis spectrum of 3 upon addition of TNP or DNP (Figure 3) confirmed the formation of complexes in the ground state. PNP, on the other hand, is less acidic and cannot form a complex with macrocycle 3 in the ground state. Nevertheless, bimolecular interaction of macrocycle 3 and PNP in the excited state could give rise to quenching, which would be dynamic and consistent with the Stern–Volmer equation. Based on the order of acidity and number of nitro groups of TNP, DNP, and PNP, TNP should show the strongest interaction with Schiff-base macrocycle 3, which would result in the most favorable PIET and highest quenching constant. However, DNP, rather than TNP, exhibited the highest quenching constant of these three nitrophenolic compounds. This result may have been due to the cavity size of the macrocycle 3, which is better suited for binding DNP than TNP. This would account for the higher quenching constant and superamplified quenching effect seen with DNP. To demonstrate the effect of the macrocyclic cavity on the selectivity, open-chain TPE Schiff-base 4 was synthesized and tested with these nitrophenolic compounds. Due to the lower basicity of 4 (only two imine groups) compared to 3 (four imine groups), the fluorescence of 4 was less efficiently quenched by TNP, DNP, and PNP. Moreover, the changes in the fluorescence intensity ratio (I0/I) with the concentrations of TNP, DNP, and PNP were all linear, indicating that the quenching was dynamic and that complexation between 4 and the nitrophenolic molecule in the ground state occurred less readily. By linear curve-fitting using the Stern–Volmer equation, the quenching constants with TNP, DNP, and PNP were determined as 5.7  104 m 1, 3.6  104 m 1, and 1.7  104 m 1, respectively, and were thus in accordance with the order of acidity and the numbers of nitro groups. This confirmed the key role of the macrocyclic cavity in selectively sensing DNP. In order to determine the limits of detection of TNP and DNP by the macrocycle 3, the fluorescence changes of 1 mm 3 with different amounts of TNP or DNP were measured. As shown in Figure 6 A, the fluorescence intensity of 3 decreased with both substrates. Even in the presence of 1 nm (0.2 mg L 1) DNP (Figure 6 A) and 5 nm (1.1 mg L 1) TNP (Figure 6 B), the fluorescence intensity exhibited a significant decrease. Moreover, the linear change in fluorescence intensity versus the logarithm of concentration of DNP or TNP is convenient for quantitative analysis of these substrates in water. Considering the fact that the maximum permissible concentration of such hazardous substances in drinking water stipulated by the European Union is around 10 mg L 1, macrocycle 3 could serve as a promising fluorescent probe for the detection of DNP and TNP. To explore the practical applicability of the fluorescent macrocycle 3 to natural systems, real water samples including tap water were tested. After the distilled water in the mixed solvent of water/THF (9:1) had been replaced by tap water, the fluorescence of 3 could still be clearly quenched by DNP and TNP (Figure 7), whereas other nitroaromatic compounds as well as phenol led only to minor changes in the fluorescence. Even at a low concentration of 5 nm, TNP and DNP produced

Figure 5. Changes in fluorescence spectra of macrocycle 3 (2 mm) with the addition of DNP (A), TNP (B), and PNP (C) in H2O/THF (9:1). Inset: Curves of fluorescence intensity versus concentration of nitrophenolic compound. (D) Comparison of curves of intensity ratio I0/I of 3 or 4 versus concentration of nitrophenolic compound.

are more acidic and can form complexes in the ground state by interaction with the four Schiff-base groups of macrocycle 3, and then photoinduced electron transfer (PIET) within the Chem. Eur. J. 2014, 20, 195 – 201

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Figure 6. Changes in the fluorescence spectra of 1 mm 3 with different concentrations of DNP (A) (blank, 1  10 9 m, 5  10 9 m, 1  10 8 m, 5  10 8 m, 1  10 7 m, 5  10 7 m, 1  10 6 m, 2  10 6 m, 5  10 6 m, 1  10 5 m) and TNP (B) (blank, 5  10 9 m, 1  10 8 m, 5  10 8 m, 1  10 7 m, 5  10 7 m, 1  10 6 m, 2  10 6 m, 5  10 6 m, 8  10 6 m, 1  10 5 m) in H2O/THF (9:1). Inset: Fluorescence intensity versus logarithm of concentration of DNP or TNP.

Figure 8. Fluorescence spectra of 2 mm macrocycle 3 with different concentrations of DNP (A) and TNP (B), which were extracted into H2O/THF (9:1) from soil. Inset: Curves of fluorescence intensity of 3 at 535 nm versus logarithm of concentration of nitrophenolic compound.

The reliability of quantitative analysis using the TPE Schiffbase macrocycle was corroborated by HPLC analysis. For the DNP concentration range from 1.0  10 6 m to 5.0  10 5 m in deionized water, a standard curve of fluorescence intensity versus logarithm of DNP concentration was obtained by applying the fluorescence sensor 3 (Figure 9 A). Using the same solution of DNP in deionized water, another standard curve of peak area versus concentration of DNP was obtained by HPLC, but the concentration range was from 1.0  10 5 m to 5.0  10 5 m due to lower sensitivity (Figure 9 B). Both standard curves were linear. In the HPLC trace, tap water showed a peak due to an unknown component (1.85 min), but this did not interfere with the DNP peak (2.54 min) (Figure S3). Likewise, this unknown component in tap water did not affect the fluorescence intensity of 3 at 535 nm. A 1.0  10 5 m solution of DNP in tap water was prepared and this was treated as an unknown sample. By HPLC, the sample concentration was estimated as 1.04  10 5 m, corresponding to an error of + 4.0 %. Applying the macrocycle 3 as a fluorescent sensor, the sample concentration was estimated as 0.966  10 5 m, corresponding to an error of 3.4 %. This result confirmed that the quantitative analysis of dinitrophenol in tap water using macrocycle 3 was reliable. Compared with tap water, the aqueous soil extract was more complex. A large peak due to an unknown component (3.11 min) was seen in the HPLC trace, and this unknown component could react with DNP to give a new peak (Figure S4). Therefore, it was impossible to determine DNP in soil by HPLC analysis because its retention times in deionized water and in

Figure 7. Fluorescence spectra of 2 mm 3 in the presence of various nitroaromatic compounds as well as phenol (1, blank; 2, TNP; 3, DNP; 4, PNP; 5, phenol; 6, TNT; 7, DNT; 8, PNT; 9, DNB; 10, NB; 11, DNCB; 12, DNBA; 13, NBA) in tap H2O/THF (9:1). Inset: The color change in the 2 mm 3 with DNP (blank, 5 mm).

an obvious decrease in the emission. In addition, detection of TNP and DNP in soil was also evaluated. Soil was taken from farmland, and it was mixed with deionized water. After leaving the mixture to stand for several hours, the supernatant was isolated by filtration. TNP or DNP was then added to the supernatant, which was ready for measurement. The fluorescence intensity of 3 decreased with increasing concentration of TNP or DNP in the supernatant, showing a linear dependence on the logarithm of concentration, indicating that this fluorescent probe could be used to quantitatively detect TNP and DNP in soil (Figure 8). Chem. Eur. J. 2014, 20, 195 – 201

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Full Paper by filtration and redissolved in THF. After a few days, vermilion block-shaped crystals were obtained by slow evaporation of the solvent at room temperature (Figure 10 b). This result demonstrated that macrocycle 3 could be used to visualize traces of TNP and DNP, showing great potential as a sensor for these compounds.

Conclusions In conclusion, a TPE Schiff-base macrocycle showing an AIE effect has been synthesized, which displayed a sensitive and selective response to TNP and DNP among a number of nitroaromatic compounds. Moreover, it exhibited a superamplified quenching effect with DNP but not with TNP, providing a possible means of discriminating these compounds. This system shows great potential for the detection of DNP and TNP both in water and in the solid state. The incorporation of an AIE moiety into a macrocyclic ring could improve its selectivity for the detection of explosives, and this could offer a general strategy for the design of sensors for explosives.

Experimental Section Materials: All reagents and solvents were chemically pure (CP) grade or analytical reagent (AR) grade and were used as received unless otherwise indicated. Caution: TNP, TNT, and other nitroaromatic compounds used in the present study are highly explosive and should be handled only in small quantities.

Figure 9. Standard curves in deionized water of (A) fluorescence intensity versus logarithm of DNP concentration measured by the fluorescence method and (B) peak area versus DNP concentration by HPLC analysis in the range 1.0  10 6 m to 5.0  10 5 m.

the aqueous soil extract were different. This unknown component in soil also partially quenched the fluorescence of macrocycle 3, but did not change the emission maximum wavelength. By deducting the blank effect, DNP could be quantitatively analyzed. When a prepared solution of 1.0  10 5 m DNP in aqueous soil extract was analyzed by the fluorescence method, the measured concentration was 0.92  10 5 m, corresponding to an error of 8.0 %. In addition, detection of TNP and DNP was also evaluated in the solid state. Macrocycle 3 adsorbed on a TLC plate showed strong emission, but became non-emissive when the plate was dipped into a solution of DNP or TNP (1.0  10 4 m). This could be observed under a UV lamp by the naked eye (Figure 10 a). Meanwhile, a solid mixture of macrocycle 3 with DNP or TNP also showed a significant color change. The precipitates from mixtures of 3 with DNP or TNP in H2O/THF (9:1) were collected

General: 1H and 13C NMR spectra were measured on a Bruker AV 400 spectrometer at 298 K from sample solutions in CDCl3. Infrared spectra were recorded on a Bruker Equinox 55 spectrometer. Absorption spectra were recorded on a Hewlett Packard 8453 UV/Vis spectrophotometer. Mass spectra were measured on an IonSpec 4.7 Tesla FTMS instrument. Field-emission scanning electron microscopy (FESEM) images were acquired with an FEI Sirion 200 electron microscope operating at 10 kV. Fluorescence emission spectra were collected on a Shimadzu RF-5301 fluorophotometer at 298 K. The fluorescence spectra for the AIE effect were measured after the addition of water and leaving the mixture to stand for 4 h at 298 K. To measure changes in the fluorescence intensity in the presence of explosives, all mixtures of 3 and explosives were left to stand for 8 h at 298 K before measuring their fluorescence spectra. Absorption spectra were measured in H2O/THF (9:1) without leaving the solutions to stand. HPLC analysis of DNP concentration was conducted on an Agilent 1100 HPLC instrument under the following conditions: 4.6  250 mm Agilent HC-C18 column at 35 8C, detection wavelength 225 nm, mobile phase: acetonitrile/ water 41:59 (v/v) with a flow velocity of 0.8 mL min 1. Aqueous soil extracts were prepared as follows. Soil was taken from farmland and mixed with deionized water. After leaving the mixture to stand for several hours, the supernatant was isolated by filtration and was used as the aqueous soil extract. Synthesis of macrocyclic compound 3: For the preparation of the Schiff-base macrocycle, a general procedure was adopted. (1R,2R)( )-1,2-Diaminocyclohexane (0.066 g, 0.57 mmol) was added under vigorous stirring to a solution of 2 (0.2 g, 0.476 mmol) in ethanol (15 mL). The mixture was allowed to react for 4 h. The yellow precipitate was then collected by filtration, dried under reduced pressure, and characterized as 3 (0.21 g, 87 %). M.p. > 300 8C; 1H NMR

Figure 10. (a) Photographs of TLC plates that were first impregnated with compound 3 and then dipped in DNP or TNP solution, viewed under 365 nm UV light (1  10 4 m). (b) Photographs of solid 3 and of 3 mixed with DNP or TNP, viewed under daylight. Chem. Eur. J. 2014, 20, 195 – 201

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Full Paper (400 MHz, CDCl3): d = 1.42–1.53 (m, 4 H), 1.62–1.65 (m, 4 H), 1.83– 1.91 (m, 8 H), 3.25–3.26 (m, 4 H), 6.61 (d, J = 12 Hz, 4 H), 6.84 (d, 4 H), 6.92 (d, J = 4 Hz, 2 H), 6.94 (d, J = 4 Hz, 2 H), 6.97–7.00 (m, 10 H), 7.04–7.10 (m, 10 H), 8.04 (s, 4 H), 13.21 ppm (s, 4 H); 13C NMR (100 MHz, CDCl3): d = 164.35, 159.69, 143.36, 140.19, 138.97, 134.80, 133.93, 133.91, 130.96, 127.76, 126.24, 118.27, 116.35, 71.43, 32.29, 23.69 ppm; IR (film): n˜ = 3054.8, 3022.5, 2930.2, 2858.2, 1632.1, 1585.3, 1489.4, 1445.1, 1381.3, 1347.5, 1281.8, 1225.9, 1176.7, 1125.1, 1078.2, 1034.3, 977.8, 892.4, 831.0, 698.5 cm 1; HRMS (ESI + ): calcd for [M+H] + : 997.4692; found: 997.4672. Synthesis of open-chain Schiff base 4: Cyclohexylamine (0.057 g, 0.57 mmol) was added under vigorous stirring to a solution of 2 (0.10 g, 0.24 mmol) in ethanol (15 mL). The mixture was allowed to react for 4 h. The yellow precipitate was then collected by filtration, dried under reduced pressure, and characterized as 4 (0.10 g, 0.17 mmol, 73 %). M.p. 243.3–244 8C; 1H NMR (400 MHz, CDCl3): d = 1.26–1.39 (m, 6 H), 1.45–1.54 (m, 4 H), 1.61–1.64 (m, 2 H), 1.77–1.78 (m, 8 H), 3.13–3.18 (m, 2 H), 6.67 (d, J = 8 Hz, 2 H), 6.87 (d, J = 4 Hz, 2 H), 6.95 (d, J = 2 Hz, 1 H), 6.97 (d, J = 2 Hz, 1 H), 7.01–7.03 (m, 4 H), 7.07–7.13 (m, 6 H), 8.07 (s, 2 H), 13.76 ppm (s, 2 H); 13C NMR (100 MHz, CDCl3): d = 173.18, 171.57, 154.97, 150.33, 150.06, 146.49, 145.02, 144.83, 142.27, 138.80, 137.22, 129.19, 127.50, 78.07, 45.19, 36.47, 35.28 ppm; IR (film): n˜ = 3075.1, 3058.1, 2930.1, 2854.5, 1631.2, 1585.7, 1491.4, 1446.5, 1381.9, 1348.1, 1279.6, 1176.7, 1083.6, 971.4, 831.9, 699.0 cm 1; HRMS (ESI + ): calcd for [M+H] + : 583.3324; found: 583.3325.

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[9]

Acknowledgements [10]

This research work was supported by the National Natural Science Foundation of China (No. 21072067) and the Analytical and Testing Centre at Huazhong University of Science and Technology.

[11]

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tersen, F. Sancenn, M. D. Marcos, J. Soto, C. Guillem, P. Amors, ACS Appl. Mater. Interfaces 2013, 5, 1538 – 1543; f) K. K. Kartha, S. S. Babu, S. Srinivasan, A. Ajayaghosh, J. Am. Chem. Soc. 2012, 134, 4834; g) D. Gopalakrishnan, W. R. Dichtel, J. Am. Chem. Soc. 2013, 135, 8357. a) Y. Che, D. E. Gross, H. Huang, D. Yang, X. Yang, E. Discekici, Z. Xue, H. Zhao, J. S. Moore, L. Zang, J. Am. Chem. Soc. 2012, 134, 4978; b) S. Pramanik, C. Zheng, X. Zhang, T. J. Emge, J. Li, J. Am. Chem. Soc. 2011, 133, 4153; c) Y. Salinas, E. Climent, R. Martnez-MÇez, F. Sancenn, M. D. Marcos, J. Soto, A. M. Costero, S. Gil, M. Parra, A. P. de Diego, Chem. Commun. 2011, 47, 11885. The known sensors are not specific for TNP: a) H. Sohn, R. M. Calhoun, M. J. Sailor, W. C. Trogler, Angew. Chem. 2001, 113, 2162; Angew. Chem. Int. Ed. 2001, 40, 2104; b) A. zer, E. ErÅag˘, R. Apak, Anal. Chim. Acta 2004, 505, 83; c) M. E. Germain, M. J. Knapp, J. Am. Chem. Soc. 2008, 130, 5422; d) E. S. Forzani, D. Lu, M. J. Leright, A. D. Aguilar, F. Tsow, R. A. Iglesias, Q. Zhang, J. Lu, J. Li, N. Tao, J. Am. Chem. Soc. 2009, 131, 1390; e) J. S. Park, F. Le Derf, C. M. Bejger, V. M. Lynch, J. L. Sessler, K. A. Nielsen, C. Johnsen, J. O. Jeppesen, Chem. Eur. J. 2010, 16, 848. J. F. Wyman, M. P. Serve, D. W. Hobson, L. H. Lee, D. E. Uddin, J. Toxicol. Environ. Health Part A 1992, 37, 313. J. Akhavan, The Chemistry of Explosives, Royal Society of Chemistry, Cambridge, 2004. The following references demonstrated sensing of TNP; however, no experiments involving selectivity with respect to other nitroaromatic explosives were described: a) D. R. Shankaran, K. V. Gobi, K. Matsumoto, T. Imato, K. Toko, N. Miura, Sens. Actuators B 2004, 100, 450; b) S.-Z. Tan, Y.-J. Hu, J.-W. Chen, G.-L. Shen, R.-Q. Yu, Sens. Actuators B 2007, 124, 68; c) M. Laurenti, E. Lpez-Cabarcos, F. Garca-Blanco, B. Frick, J. RubioRetama, Langmuir 2009, 25, 9579. a) J.-D. Luo, Z.-L. Xie, J. W. Y. Lam, L. Cheng, H.-Y. Chen, C. F. Quip, H. S. Kwok, X.-W. Zhan, Y.-Q. Liu, D.-B. Zhu, B.-Z. Tang, Chem. Commun. 2001, 1740; b) Y.-N. Hong, J. W. Y. Lam, B.-Z. Tang, Chem. Soc. Rev. 2011, 40, 5361. a) M. Wang, G. Zhang, D. Zhang, D. Zhu, B.-Z. Tang, J. Mater. Chem. 2010, 20, 1858; b) Y.-N. Hong, J. W. Y. Lam, B.-Z. Tang, Chem. Commun. 2009, 4332. a) J.-Z. Liu, Y.-C. Zhong, P. Lu, Y.-N. Hong, J. W. Y. Lam, M. Faisal, Y. Yu, K. S. Wong, B.-Z. Tang, Polym. Chem. 2010, 1, 426; b) W. Z. Yuan, H. Zhao, X. Y. Shen, F. Mahtab, J. W. Y. Lam, J. Z. Sun, B. Z. Tang, Macromolecules 2009, 42, 9400; c) R. Hu, J. L. Maldonado, M. Rodriguez, C. Deng, C. K. W. Jim, J. W. Y. Lam, M. M. F. Yuen, G. Ramos-Ortiz, B. Z. Tang, J. Mater. Chem. 2012, 22, 232; d) A. Qin, J. W. Y. Lam, L. Tang, C. K. W. Jim, H. Zhao, J. Sun, B. Z. Tang, Macromolecules 2009, 42, 1421; e) J. Liu, Y. Zhong, J. W. Y. Lam, P. Lu, Y. Hong, Y. Yu, Y. Yue, M. Faisal, H. H. Y. Sung, I. D. Williams, K. S. Wong, B. Z. Tang, Macromolecules 2010, 43, 4921; f) H. Li, H. Wu, E. Zhao, J. Li, J. Z. Sun, A. Qin, B. Z. Tang, Macromolecules 2013, 46, 3907. G. He, H. Peng, T. Liu, M. Yang, Y. Zhang, Y. Fang, J. Mater. Chem. 2009, 19, 7347. Y.-Y. Long, H.-B. Chen, H.-M. Wang, Z. Peng, Y.-F. Yang, G.-Q. Zhang, N. Li, F. Liu, J. Pei, Anal. Chim. Acta 2012, 744, 82. B. Valeur, Molecular Fluorescence: Principle and Applications, Wiley-VCH, Weinheim, 2002.

Received: July 8, 2013 Revised: September 27, 2013 Published online on November 27, 2013

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Highly sensitive and selective detection of nitrophenolic explosives by using nanospheres of a tetraphenylethylene macrocycle displaying aggregation-induced emission.

A tetraphenylethylene (TPE) Schiff-base macrocycle showing an aggregation-induced emission (AIE) effect has been synthesized, which could aggregate in...
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