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A new principle for selective sensing cyanide anions based on 2-hydroxy-naphthaldeazine compound
Sensors and Actuators B 177 (2013) 322–326
Contents lists available at SciVerse ScienceDirect
Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb
A new principle for selective sensing cyanide anions based on 2-hydroxy-naphthaldeazine compound Wei-Tao Gong ∗ , Qing-Lan Zhang, Li Shang, Bei Gao, Gui-Ling Ning ∗ State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, P.O. Box 43, Comprehensive Building, No. 2 Ling Gong Road, High Technology Zone, Dalian 116024, PR China
a r t i c l e
i n f o
Article history: Received 12 July 2012 Received in revised form 3 November 2012 Accepted 6 November 2012 Available online 19 November 2012 Keywords: “Turn-on” fluorescence 2-Hydroxy-naphthaldeazine Cyanide anions Hydrogen bonds Aggregation-induced emission
a b s t r a c t 2-Hydroxy-naphthaldeazine (HNA), synthesized readily via one-step condensation from 3-hydroxy2-naphthaldehyde and hydrazine monohydrate, behaves as “turn-on” fluorescent sensing of CN− selectively. The sensing mechanism was ascribed to the dual influence of hydrogen bonds and aggregation-induced emission, coming from the interactions of HNA and CN− . The speculation was partially supported by fluorescence emission spectra, UV–vis spectrum, 1 H NMR titration experiments and further particle size analysis. © 2012 Elsevier B.V. All rights reserved.
1. Introduction During the past decades, considerable attention has been focused on the design of artificial receptors that can recognize and sense anions selectively [1–4] due to the important roles and potential applications anions play in biological, environmental and supramolecular sciences [5–8]. Among these anions, cyanide (CN− ) is highly toxic and dangerous for biology and environment, owing to its ability to suppress the transport of oxygen [9–14]. In this sense, easy and affordable detection methods are in great demand for sensing CN− . Up to now, a variety of analytical methods such as titrimetric [15], voltammetric [16], chromatographic methods [17], electrochemical devices [18,19], colorimetric [20–22] and fluorimetric [23–31] have been developed for cyanide determination. Among the various reported methods, fluorescent sensors present many appealing advantages, including high sensitivity and selectivity, low cost, easy detection, and especially suitability as a diagnostic tool for biological concern [32]. While some “turn-on” fluorescent anion chemosensors for selective CN− detection have been reported so far [33–37], all these probes require complicated synthesis steps and few of them are capable of displaying high selectivity over other anions with similar basicity. Therefore,
easy to synthesis and higher selectivity “turn-on” fluorescent CN− chemosensors are still appealing. In this paper, we report a simple-structured molecule 2hydroxy-naphthaldeazine (HNA) synthesized readily via one step condensation from 3-hydroxy-2-naphthaldehyde and hydrazine monohydrate (Scheme 1), which exhibits “turn-on” fluorescent sensing of CN− selectively. The sensing mechanism was ascribed to the influence of the hydrogen bonds and aggregation-induced emission, coming from the interactions of HNA and CN− . 2. Experimental 2.1. Reagent and apparatus All chemical reagents and solvents used were purchased from commercial suppliers and were used without further purification. Elemental analysis was performed on a Perkin-Elmer 2400 CHN Elemental Analyzer. Mass spectra were measured on a Agilent 6310 MS spectrometer and a Q-TOF MS spectrometer. 1 H NMR and 13 C NMR spectra were obtained on a Bruker AVANCE-400 spectrometer. The photoluminescence (PL) studies were conducted with a JASCO FP-6300 spectrofluorimeter. 2.2. Synthesis of receptor HNA
∗ Corresponding authors. Tel.: +86 411 84986067; fax: +86 411 84986067. E-mail addresses: [email protected] (W.-T. Gong), [email protected] (G.-L. Ning). 0925-4005/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.snb.2012.11.009
The synthesis of receptor HNA was easily achieved according to previously reported procedure [38]. A solution of 3-hydroxy2-naphthaldehyde (1.72 g, 10 mmol) and hydrazine monohydrate
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323
Scheme 1. Synthesis of receptor HNA.
(90%) (0.5 mL, 10 mmol) in 50 mL of ethanol was refluxed for 3 h. After completion of the reaction, the obtained yellow precipitate was filtered and washed several times with cold ethanol to give HNA as pure yellowish solid in 85% yield. HRMS: m/z 339 (M−H+ ). 1 H NMR (400 Hz, DMSO-d ), ı: 11.3315 (s, 2H, OH), 8.797 (s, 6 2H, N CH), 8.260 (s, 2H, Ar CH), 7.880 (d, J = 8.4 Hz, 2H, Ar CH), 7.760 (d, J = 8.4 Hz, 2H, Ar CH), 7.501 (m, 2H, Ar CH), 7.344 (m, 2H, Ar CH), 7.305 (s, 2H, Ar CH). 2.3. General procedure for anions detection A stock solution of probe HNA (2.5 × 10−4 mol L−1 ) was prepared by dissolving the requisite amount of HNA in DMSO, and solutions of various inorganic anions were prepared by dissolving as their tetra-n-butyl ammonium salts in CH3 CN. All measurements were made according to the following procedure. In a small cell, an appropriate volume of the stock solution of HNA and an appropriate volume of various inorganic anions solution were mixed, then the fluorescence sensing of different metal ions was run. 3. Results and discussion The anion sensing properties of receptor HNA was first investigated by fluorescence spectra. Based on the time-dependent fluorescence intensity changes of HNA upon addition of CN− , the response time was set to 30 min (Supplementary data, Fig. S4). Fig. 1 showed the changes of emission spectra of HNA (10 M) upon addition of various inorganic anions (F− , Cl− , Br− , I− , H2 PO4 − , NO3 − , AcO− , OH− and CN− , as their tetra-n-butyl ammonium salts). It can be seen that in the absence of any anions, HNA exhibits a characteristic emission band centered at 462 nm. Upon addition of anions, only CN− induced an apparent bathochromic shift of fluorescence emission centered at 504 nm with increasing intensity and gave rise to a strong green fluorescence. Other anions did not show any apparent spectral changes. These results indicated that HNA could behave as a “turn-on” fluorescence sensor for selectively sensing CN− over other investigated anions. It must be noted that the changes in fluorescence spectra induced by CN− are unaffected in the presence of other background anions (Fig. 2), indicating the prior selectivity of HNA toward CN− even in the presence of competing anions.
Fig. 2. Changes in fluorescence spectra (ex = 405 nm) of receptor HNA (10 M) upon addition 20 equiv. of CN− (as a n-bu4 N+ salt) with various respective anions in CH3 CN.
To validate the selectivity of sensor HNA in aqueous solution, fluorescence spectral change of HNA upon addition of various anions in CH3 CN with 5% H2 O were measured (see Supplementary data, Fig. S5). Upon addition of various anions mentioned above to the CH3 CN with 5% H2 O solution of HNA, only CN− induced a dramatic fluorescence enhancement. Although HNA could not be used to detect CN− in 100% H2 O, the possibility of HNA to be used in CH3 CN with 5% H2 O implies that HNA is strong enough to use the sensing mechanism to detect CN− also in more polar environments. In order to know more about the interactions between HNA and CN− , fluorescence titration was carried out. When there is no CN− , HNA showed very week fluorescence intensity with emission band centered at 462 nm (Fig. 3). Upon addition of CN− increasing from 0 to 100 equiv., a new obvious emission peak centered at 504 nm was observed and obviously enhanced with the increase of CN− . By fluorescence titration, the binding constant between HNA and CN− was determined to be about (4.571 ± 0.1) × 103 M−1 and the detection limit of HNA toward CN− was obtained as 4.4 × 10−6 mol L−1 (Supplementary data, Fig. S6), which is sufficiently low for the detection of the CN− found in many chemical systems. And from the mass data for HNA–CN− conjugate, the 1:1 stoichiometry ratio between HNA and CN− was proposed (supporting information Fig. S7). To explore the sensing mechanism between HNA and CN− , the interaction between HNA and OH− was also investigated. Fluorescence emission spectral change of HNA upon addition of OH− was quite different compared with that of upon addition of CN− , which partially excluded the deprotonation between HNA and CN− (Fig. 4). In this case, the changes of -conjugation and internal
FluorescenceIntensity
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100 equiv. of CN -
200 150 100
0 equiv. of CN-
50 0 450
Fig. 1. Changes in fluorescence spectra (ex = 405 nm) of receptor HNA (10 M) in CH3 CN upon addition 100 equiv. of respective anions (as their n-bu4 N+ salts).
500 550 Wavelength/nm
600
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Fig. 3. Changes in fluorescence titration spectra (ex = 405 nm) of HNA (10 M) upon addition of various amounts of CN− (0, 0.5, 1, 2, 3, 5, 10, 15, 20, 30, 50, and 100 equiv.) at an excitation of 405 nm in CH3 CN.
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Fluorescence Intensity
250
CN -
200 150 100 50
OH -
0 450
500
550
600
650
Wavelength/nm Fig. 4. Changes in the emission spectrum of receptor HNA (10 M) in CH3 CN upon addition of CN− anions and OH− in TBA form at an excitation of 405 nm. Fig. 6. Effect of water volume fraction on the AIEE of HNA–CN− in H2 O/CH3 CN (from 0 to 9:1, v/v). Excitation was performed at 405 nm.
100
Distribution %
80
Fig. 5. Changes in 1 H NMR spectra of receptor HNA upon addition of 0.5, 1 equiv. and 15 equiv. of CN− (TBA salts) in DMSO-d6 .
charge distribution induced by the hydrogen bonds between CN− and HNA could be responsible for the “turn-on” fluorescence and the red-shift of emission peak from 462 nm to 504 nm. Absorption spectral changes of HNA in the presence of various anions provided further evidence to above speculation. Upon addition of CN− , the absorption band at 350 nm diminished, while a new red-shifted absorption band appeared at 450 nm (Supplementary data, Figs. S8 and S9). Furthermore, the interaction of HNA to CN− was also investigated 1 H NMR titration experiments. As shown in Fig. 5, upon addition of CN− , the OH signal of HNA disappeared completely, indicating the presence of hydrogen bonds between CN− and naphthol OH protons. In contrast, other H signals on the naphthaldehyde rings shifted upfield due to the increasing of electron density around them. As a contrast, there was no new peaks observed, which excluded the nucleophilic addition of cyanide to the imine. More interestingly, upon addition of some water to the system of HNA with 50 equiv. of CN− in acetonitrile/water solvents (from 0 to 1:9, v/v), the emission intensity of 504 nm did not decrease instead to increase gradually. As shown in Fig. 6, in a good solvent of
90% Water D=208nm
60 40 20 0 0
100
200 300 Particle size/nm
400
500
Fig. 7. Size distributions of nanoparticles of HNA–CN− in acetonitrile–water mixture containing 90% water.
CH3 CN, complex was well dispersed and displayed relative weaker fluorescence intensity of their “solution” state. With water volume fraction increasing from 0 to 90%, the emission intensity of about 504 nm enhanced gradually exhibiting typical AIEE characters. As a contrast, only HNA without addition of CN− did not show any AIEE effect (Supplementary data, Fig. S10). This AIEE effect could be explained by the blocking of the nonradiative intramolecular rotation decay of excited molecules through the formation of HNA–CN− complex. The blue shift of the emission band with the increasing of water volume fraction indicated the H-aggregates [39,40]. Such kind of phenomenon was also found in other salicylaldehyde Schiff base compound [40,41]. To provide further evidence, particle size analysis was performed and the result indicated the formation of nano-scaled aggregates with an average particle diameter
Scheme 2. Proposed binding mode of receptor HNA with CN− .
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of 208 nm in a 90% CH3 CN aqueous solution (Fig. 7). In this case, chemosensor HNA has the ability to detect CN− in aqueous solution. From the fluorescence emission spectrum, UV–vis, 1 H NMR titrations spectra and particle size analysis studies, possible binding model of receptors HNA with CN− was proposed (as shown in Scheme 2). Upon binding of CN− anions, the formation of hydrogen bonds between CN− and HNA, and further aggregation of HNA–CN− complex restrict the free rotation of N N single bonds. So the nonradiative intramolecular rotation decay can be suppressed during the formation of hydrogen bonds and aggregation process, which were responsible for the fluorescence emissions change. 4. Conclusion In summary, the new chemosensor HNA, prepared readily, exhibits fluorescent “turn-on” sensing for CN− selectively. The sensing mechanism is novel and ascribed to hydrogen bonds and the aggregation-induced emission, coming from the interactions of HNA and CN− . Further studies on such kind of new sensing principle are underway. Acknowledgments This work was supported by the National Natural Science Foundation of China (No. 21206016) and the Fundamental Research Funds for the Central Universities (DUT11LK13). Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.snb.2012.11.009. References [1] P.A. Gale, Anion receptor chemistry: highlights from 2008 and 2009, Chemical Society Reviews 39 (2010) 3746–3771. [2] C. Caltagirone, P.A. Gale, Anion receptor chemistry: highlights from 2007, Chemical Society Reviews 38 (2009) 520–563. [3] S. Kubik, Anion recognition in water, Chemical Society Reviews 39 (2010) 3648–3663. [4] P.A. Gale, From anion receptors to transporters, Accounts of Chemical Research 44 (2011) 216–226. [5] Z. Szijgyarto, A. Garedew, C. Azevedo, A. Saiardi, Influence of inositol pyrophosphates on cellular energy dynamics, Science 334 (2011) 802–805. [6] P. Li, T. Xie, N. Fan, K. Li, B. Tang, Ratiometric fluorescence imaging for distinguishing chloride concentration between normal and ischemic ventricular myocytes, Chemical Communications 48 (2012) 2077–2079. [7] O.A. Bozdemir, F. Sozmen, O. Buyukcakir, R. Guliyev, Y. Cakmak, E.U. Akkaya, Reaction-based sensing of fluoride ions using built-in triggers for intramolecular charge transfer and photoinduced electron transfer, Organic Letters 12 (2010) 1400–1403. [8] P.D. Beer, P.A. Gale, Anion recognition and sensing the state of the art and future perspectives, Angewandte Chemie International Edition 40 (2001) 486–516. [9] J. Isaada, F. Salaünb, Functionalized poly (vinyl alcohol) polymer as chemodosimeter material for the colorimetric sensing of cyanide in pure water, Sensors and Actuators B 157 (2011) 26–33. [10] N. Kumari, S. Jha, S. Bhattacharya, Colorimetric probes based on anthraimidazolediones for selective sensing of fluoride and cyanide ion via intramolecular charge transfer, Journal of Organic Chemistry 76 (2011) 8215–8222. [11] G.-J. Kim, H.-J. Kim, Doubly activated coumarin as a colorimetric and fluorescent chemodosimeter for cyanide, Tetrahedron Letters 51 (2010) 185–187. [12] L. Shang, L. Zhang, S. Dong, Turn-on fluorescent cyanide sensor based on copper ion-modified CdTe quantum dots, Analyst 134 (2009) 107–113. [13] M.H. Kim, S. Kim, H.H. Jang, S. Yi, S.H. Seo, M.S. Han, A gold nanoparticle-based colorimetric sensing ensemble for the colorimetric detection of cyanide ions in aqueous solution, Tetrahedron Letters 51 (2010) 4712–4716. [14] C.R. Maldonado, A. Touceda-Varela, A.C. Jones, J.C. Mareque-Rivas, A turn-on fluorescence sensor for cyanide from mechanochemical reactions between quantum dots and copper complexes, Chemical Communications 47 (2011) 11700–11702. [15] P.J. Anzenbacher, D.S. Tyson, K. Jursikova, F.N. Castellano, Luminescence lifetime-based sensor for cyanide and related anions, Journal of the American Chemical Society 124 (2002) 6232–6233.
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Biographies Wei-Tao Gong received his PhD from Dalian University of Technology in 2006. He is working in Dalian University of Technology as an associate professor now. His
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current interests include the design of sensors, assembly and characterization of functional supramolecules.
Bei Gao is currently a master in Dalian University of Technology. Her main research fields are fluorescent probes design and chemical sensors.
Qing-Lan Zhang is currently a master in Dalian University of Technology. Her main research fields are fluorescent probes design and chemical sensors.
Gui-Ling Ning received her PhD in organic chemistry from Kinki University in Japan in 1999. She is working in Dalian University of Technology college of chemistry as a professor now. Her current interests include assembly and characterization of functional supramolecules.
Li Shang is currently a master in Dalian University of Technology. Her main research fields are fluorescent probes design and chemical sensors.
Contents lists available at SciVerse ScienceDirect
Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb
A new principle for selective sensing cyanide anions based on 2-hydroxy-naphthaldeazine compound Wei-Tao Gong ∗ , Qing-Lan Zhang, Li Shang, Bei Gao, Gui-Ling Ning ∗ State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, P.O. Box 43, Comprehensive Building, No. 2 Ling Gong Road, High Technology Zone, Dalian 116024, PR China
a r t i c l e
i n f o
Article history: Received 12 July 2012 Received in revised form 3 November 2012 Accepted 6 November 2012 Available online 19 November 2012 Keywords: “Turn-on” fluorescence 2-Hydroxy-naphthaldeazine Cyanide anions Hydrogen bonds Aggregation-induced emission
a b s t r a c t 2-Hydroxy-naphthaldeazine (HNA), synthesized readily via one-step condensation from 3-hydroxy2-naphthaldehyde and hydrazine monohydrate, behaves as “turn-on” fluorescent sensing of CN− selectively. The sensing mechanism was ascribed to the dual influence of hydrogen bonds and aggregation-induced emission, coming from the interactions of HNA and CN− . The speculation was partially supported by fluorescence emission spectra, UV–vis spectrum, 1 H NMR titration experiments and further particle size analysis. © 2012 Elsevier B.V. All rights reserved.
1. Introduction During the past decades, considerable attention has been focused on the design of artificial receptors that can recognize and sense anions selectively [1–4] due to the important roles and potential applications anions play in biological, environmental and supramolecular sciences [5–8]. Among these anions, cyanide (CN− ) is highly toxic and dangerous for biology and environment, owing to its ability to suppress the transport of oxygen [9–14]. In this sense, easy and affordable detection methods are in great demand for sensing CN− . Up to now, a variety of analytical methods such as titrimetric [15], voltammetric [16], chromatographic methods [17], electrochemical devices [18,19], colorimetric [20–22] and fluorimetric [23–31] have been developed for cyanide determination. Among the various reported methods, fluorescent sensors present many appealing advantages, including high sensitivity and selectivity, low cost, easy detection, and especially suitability as a diagnostic tool for biological concern [32]. While some “turn-on” fluorescent anion chemosensors for selective CN− detection have been reported so far [33–37], all these probes require complicated synthesis steps and few of them are capable of displaying high selectivity over other anions with similar basicity. Therefore,
easy to synthesis and higher selectivity “turn-on” fluorescent CN− chemosensors are still appealing. In this paper, we report a simple-structured molecule 2hydroxy-naphthaldeazine (HNA) synthesized readily via one step condensation from 3-hydroxy-2-naphthaldehyde and hydrazine monohydrate (Scheme 1), which exhibits “turn-on” fluorescent sensing of CN− selectively. The sensing mechanism was ascribed to the influence of the hydrogen bonds and aggregation-induced emission, coming from the interactions of HNA and CN− . 2. Experimental 2.1. Reagent and apparatus All chemical reagents and solvents used were purchased from commercial suppliers and were used without further purification. Elemental analysis was performed on a Perkin-Elmer 2400 CHN Elemental Analyzer. Mass spectra were measured on a Agilent 6310 MS spectrometer and a Q-TOF MS spectrometer. 1 H NMR and 13 C NMR spectra were obtained on a Bruker AVANCE-400 spectrometer. The photoluminescence (PL) studies were conducted with a JASCO FP-6300 spectrofluorimeter. 2.2. Synthesis of receptor HNA
∗ Corresponding authors. Tel.: +86 411 84986067; fax: +86 411 84986067. E-mail addresses: [email protected] (W.-T. Gong), [email protected] (G.-L. Ning). 0925-4005/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.snb.2012.11.009
The synthesis of receptor HNA was easily achieved according to previously reported procedure [38]. A solution of 3-hydroxy2-naphthaldehyde (1.72 g, 10 mmol) and hydrazine monohydrate
W.-T. Gong et al. / Sensors and Actuators B 177 (2013) 322–326
323
Scheme 1. Synthesis of receptor HNA.
(90%) (0.5 mL, 10 mmol) in 50 mL of ethanol was refluxed for 3 h. After completion of the reaction, the obtained yellow precipitate was filtered and washed several times with cold ethanol to give HNA as pure yellowish solid in 85% yield. HRMS: m/z 339 (M−H+ ). 1 H NMR (400 Hz, DMSO-d ), ı: 11.3315 (s, 2H, OH), 8.797 (s, 6 2H, N CH), 8.260 (s, 2H, Ar CH), 7.880 (d, J = 8.4 Hz, 2H, Ar CH), 7.760 (d, J = 8.4 Hz, 2H, Ar CH), 7.501 (m, 2H, Ar CH), 7.344 (m, 2H, Ar CH), 7.305 (s, 2H, Ar CH). 2.3. General procedure for anions detection A stock solution of probe HNA (2.5 × 10−4 mol L−1 ) was prepared by dissolving the requisite amount of HNA in DMSO, and solutions of various inorganic anions were prepared by dissolving as their tetra-n-butyl ammonium salts in CH3 CN. All measurements were made according to the following procedure. In a small cell, an appropriate volume of the stock solution of HNA and an appropriate volume of various inorganic anions solution were mixed, then the fluorescence sensing of different metal ions was run. 3. Results and discussion The anion sensing properties of receptor HNA was first investigated by fluorescence spectra. Based on the time-dependent fluorescence intensity changes of HNA upon addition of CN− , the response time was set to 30 min (Supplementary data, Fig. S4). Fig. 1 showed the changes of emission spectra of HNA (10 M) upon addition of various inorganic anions (F− , Cl− , Br− , I− , H2 PO4 − , NO3 − , AcO− , OH− and CN− , as their tetra-n-butyl ammonium salts). It can be seen that in the absence of any anions, HNA exhibits a characteristic emission band centered at 462 nm. Upon addition of anions, only CN− induced an apparent bathochromic shift of fluorescence emission centered at 504 nm with increasing intensity and gave rise to a strong green fluorescence. Other anions did not show any apparent spectral changes. These results indicated that HNA could behave as a “turn-on” fluorescence sensor for selectively sensing CN− over other investigated anions. It must be noted that the changes in fluorescence spectra induced by CN− are unaffected in the presence of other background anions (Fig. 2), indicating the prior selectivity of HNA toward CN− even in the presence of competing anions.
Fig. 2. Changes in fluorescence spectra (ex = 405 nm) of receptor HNA (10 M) upon addition 20 equiv. of CN− (as a n-bu4 N+ salt) with various respective anions in CH3 CN.
To validate the selectivity of sensor HNA in aqueous solution, fluorescence spectral change of HNA upon addition of various anions in CH3 CN with 5% H2 O were measured (see Supplementary data, Fig. S5). Upon addition of various anions mentioned above to the CH3 CN with 5% H2 O solution of HNA, only CN− induced a dramatic fluorescence enhancement. Although HNA could not be used to detect CN− in 100% H2 O, the possibility of HNA to be used in CH3 CN with 5% H2 O implies that HNA is strong enough to use the sensing mechanism to detect CN− also in more polar environments. In order to know more about the interactions between HNA and CN− , fluorescence titration was carried out. When there is no CN− , HNA showed very week fluorescence intensity with emission band centered at 462 nm (Fig. 3). Upon addition of CN− increasing from 0 to 100 equiv., a new obvious emission peak centered at 504 nm was observed and obviously enhanced with the increase of CN− . By fluorescence titration, the binding constant between HNA and CN− was determined to be about (4.571 ± 0.1) × 103 M−1 and the detection limit of HNA toward CN− was obtained as 4.4 × 10−6 mol L−1 (Supplementary data, Fig. S6), which is sufficiently low for the detection of the CN− found in many chemical systems. And from the mass data for HNA–CN− conjugate, the 1:1 stoichiometry ratio between HNA and CN− was proposed (supporting information Fig. S7). To explore the sensing mechanism between HNA and CN− , the interaction between HNA and OH− was also investigated. Fluorescence emission spectral change of HNA upon addition of OH− was quite different compared with that of upon addition of CN− , which partially excluded the deprotonation between HNA and CN− (Fig. 4). In this case, the changes of -conjugation and internal
FluorescenceIntensity
250
100 equiv. of CN -
200 150 100
0 equiv. of CN-
50 0 450
Fig. 1. Changes in fluorescence spectra (ex = 405 nm) of receptor HNA (10 M) in CH3 CN upon addition 100 equiv. of respective anions (as their n-bu4 N+ salts).
500 550 Wavelength/nm
600
650
Fig. 3. Changes in fluorescence titration spectra (ex = 405 nm) of HNA (10 M) upon addition of various amounts of CN− (0, 0.5, 1, 2, 3, 5, 10, 15, 20, 30, 50, and 100 equiv.) at an excitation of 405 nm in CH3 CN.
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Fluorescence Intensity
250
CN -
200 150 100 50
OH -
0 450
500
550
600
650
Wavelength/nm Fig. 4. Changes in the emission spectrum of receptor HNA (10 M) in CH3 CN upon addition of CN− anions and OH− in TBA form at an excitation of 405 nm. Fig. 6. Effect of water volume fraction on the AIEE of HNA–CN− in H2 O/CH3 CN (from 0 to 9:1, v/v). Excitation was performed at 405 nm.
100
Distribution %
80
Fig. 5. Changes in 1 H NMR spectra of receptor HNA upon addition of 0.5, 1 equiv. and 15 equiv. of CN− (TBA salts) in DMSO-d6 .
charge distribution induced by the hydrogen bonds between CN− and HNA could be responsible for the “turn-on” fluorescence and the red-shift of emission peak from 462 nm to 504 nm. Absorption spectral changes of HNA in the presence of various anions provided further evidence to above speculation. Upon addition of CN− , the absorption band at 350 nm diminished, while a new red-shifted absorption band appeared at 450 nm (Supplementary data, Figs. S8 and S9). Furthermore, the interaction of HNA to CN− was also investigated 1 H NMR titration experiments. As shown in Fig. 5, upon addition of CN− , the OH signal of HNA disappeared completely, indicating the presence of hydrogen bonds between CN− and naphthol OH protons. In contrast, other H signals on the naphthaldehyde rings shifted upfield due to the increasing of electron density around them. As a contrast, there was no new peaks observed, which excluded the nucleophilic addition of cyanide to the imine. More interestingly, upon addition of some water to the system of HNA with 50 equiv. of CN− in acetonitrile/water solvents (from 0 to 1:9, v/v), the emission intensity of 504 nm did not decrease instead to increase gradually. As shown in Fig. 6, in a good solvent of
90% Water D=208nm
60 40 20 0 0
100
200 300 Particle size/nm
400
500
Fig. 7. Size distributions of nanoparticles of HNA–CN− in acetonitrile–water mixture containing 90% water.
CH3 CN, complex was well dispersed and displayed relative weaker fluorescence intensity of their “solution” state. With water volume fraction increasing from 0 to 90%, the emission intensity of about 504 nm enhanced gradually exhibiting typical AIEE characters. As a contrast, only HNA without addition of CN− did not show any AIEE effect (Supplementary data, Fig. S10). This AIEE effect could be explained by the blocking of the nonradiative intramolecular rotation decay of excited molecules through the formation of HNA–CN− complex. The blue shift of the emission band with the increasing of water volume fraction indicated the H-aggregates [39,40]. Such kind of phenomenon was also found in other salicylaldehyde Schiff base compound [40,41]. To provide further evidence, particle size analysis was performed and the result indicated the formation of nano-scaled aggregates with an average particle diameter
Scheme 2. Proposed binding mode of receptor HNA with CN− .
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of 208 nm in a 90% CH3 CN aqueous solution (Fig. 7). In this case, chemosensor HNA has the ability to detect CN− in aqueous solution. From the fluorescence emission spectrum, UV–vis, 1 H NMR titrations spectra and particle size analysis studies, possible binding model of receptors HNA with CN− was proposed (as shown in Scheme 2). Upon binding of CN− anions, the formation of hydrogen bonds between CN− and HNA, and further aggregation of HNA–CN− complex restrict the free rotation of N N single bonds. So the nonradiative intramolecular rotation decay can be suppressed during the formation of hydrogen bonds and aggregation process, which were responsible for the fluorescence emissions change. 4. Conclusion In summary, the new chemosensor HNA, prepared readily, exhibits fluorescent “turn-on” sensing for CN− selectively. The sensing mechanism is novel and ascribed to hydrogen bonds and the aggregation-induced emission, coming from the interactions of HNA and CN− . Further studies on such kind of new sensing principle are underway. Acknowledgments This work was supported by the National Natural Science Foundation of China (No. 21206016) and the Fundamental Research Funds for the Central Universities (DUT11LK13). Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.snb.2012.11.009. References [1] P.A. Gale, Anion receptor chemistry: highlights from 2008 and 2009, Chemical Society Reviews 39 (2010) 3746–3771. [2] C. Caltagirone, P.A. Gale, Anion receptor chemistry: highlights from 2007, Chemical Society Reviews 38 (2009) 520–563. [3] S. Kubik, Anion recognition in water, Chemical Society Reviews 39 (2010) 3648–3663. [4] P.A. Gale, From anion receptors to transporters, Accounts of Chemical Research 44 (2011) 216–226. [5] Z. Szijgyarto, A. Garedew, C. Azevedo, A. Saiardi, Influence of inositol pyrophosphates on cellular energy dynamics, Science 334 (2011) 802–805. [6] P. Li, T. Xie, N. Fan, K. Li, B. Tang, Ratiometric fluorescence imaging for distinguishing chloride concentration between normal and ischemic ventricular myocytes, Chemical Communications 48 (2012) 2077–2079. [7] O.A. Bozdemir, F. Sozmen, O. Buyukcakir, R. Guliyev, Y. Cakmak, E.U. Akkaya, Reaction-based sensing of fluoride ions using built-in triggers for intramolecular charge transfer and photoinduced electron transfer, Organic Letters 12 (2010) 1400–1403. [8] P.D. Beer, P.A. Gale, Anion recognition and sensing the state of the art and future perspectives, Angewandte Chemie International Edition 40 (2001) 486–516. [9] J. Isaada, F. Salaünb, Functionalized poly (vinyl alcohol) polymer as chemodosimeter material for the colorimetric sensing of cyanide in pure water, Sensors and Actuators B 157 (2011) 26–33. [10] N. Kumari, S. Jha, S. Bhattacharya, Colorimetric probes based on anthraimidazolediones for selective sensing of fluoride and cyanide ion via intramolecular charge transfer, Journal of Organic Chemistry 76 (2011) 8215–8222. [11] G.-J. Kim, H.-J. Kim, Doubly activated coumarin as a colorimetric and fluorescent chemodosimeter for cyanide, Tetrahedron Letters 51 (2010) 185–187. [12] L. Shang, L. Zhang, S. Dong, Turn-on fluorescent cyanide sensor based on copper ion-modified CdTe quantum dots, Analyst 134 (2009) 107–113. [13] M.H. Kim, S. Kim, H.H. Jang, S. Yi, S.H. Seo, M.S. Han, A gold nanoparticle-based colorimetric sensing ensemble for the colorimetric detection of cyanide ions in aqueous solution, Tetrahedron Letters 51 (2010) 4712–4716. [14] C.R. Maldonado, A. Touceda-Varela, A.C. Jones, J.C. Mareque-Rivas, A turn-on fluorescence sensor for cyanide from mechanochemical reactions between quantum dots and copper complexes, Chemical Communications 47 (2011) 11700–11702. [15] P.J. Anzenbacher, D.S. Tyson, K. Jursikova, F.N. Castellano, Luminescence lifetime-based sensor for cyanide and related anions, Journal of the American Chemical Society 124 (2002) 6232–6233.
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Biographies Wei-Tao Gong received his PhD from Dalian University of Technology in 2006. He is working in Dalian University of Technology as an associate professor now. His
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current interests include the design of sensors, assembly and characterization of functional supramolecules.
Bei Gao is currently a master in Dalian University of Technology. Her main research fields are fluorescent probes design and chemical sensors.
Qing-Lan Zhang is currently a master in Dalian University of Technology. Her main research fields are fluorescent probes design and chemical sensors.
Gui-Ling Ning received her PhD in organic chemistry from Kinki University in Japan in 1999. She is working in Dalian University of Technology college of chemistry as a professor now. Her current interests include assembly and characterization of functional supramolecules.
Li Shang is currently a master in Dalian University of Technology. Her main research fields are fluorescent probes design and chemical sensors.