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Differential recognition of anions with ZnO based urea-coupled sensors
Materials Letters 107 (2013) 154–157
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Differential recognition of anions with ZnO based urea-coupled sensors Simanpreet Kaur a, Vimal K. Bharadwaj b, Amanpreet Kaur a, Narinder Singh b, Navneet Kaur a,n a b
Centre for Nanoscience and Nanotechnology (UIEAST), Panjab University, Chandigarh 160014, India Department of Chemistry, Indian Institute of Technology Ropar (IIT Ropar), Rupnagar, Panjab 140001, India
art ic l e i nf o
a b s t r a c t
Article history: Received 20 May 2013 Accepted 28 May 2013 Available online 5 June 2013
With the emergence of nanoparticles as a class of attractive probes for selective sensors, a need arise for the development of nanoparticles based multifunctional sensors. Herein, a simple strategy is explored for the differential recognition of two different anions. The anion receptors have been coated on the surface of ZnO and the product was characterized with SEM, XRD, EDX, UV–vis absorption and fluorescence spectroscopy. A comparison of anion recognition properties of pure host and the same host coated on ZnO revealed magnificent change in the recognition properties. The fluoride binding leads to red shift in the absorption spectrum of receptor and SO42− binding causes blue shift. These results demonstrated that our design strategy offers an effective way to develop an excellent differential sensor for anions. & 2013 Elsevier B.V. All rights reserved.
Keywords: ZnO Sensors Recognition Nanoparticles Surfaces Semiconductors
1. Introduction With the development of sensors, the research on anion recognition has become more significant due to diverse role of anions in environment and biomedical research [1]. Among various types of methods, the chromogenic receptors provide simple and reliable solution for anion estimation [2]. The various types of chromogenic sensors are available in literature including azo dye, nanoparticles, nitro compounds and various other organic dyes [3]. The chromogenic sensors are generally relay with urea moiety, which is provided in conjugation with p-nitrophenyl group [3]. These sensors convey the signal on the concept that when anion coordinates to the sensor within the cleft of sensor, the UV–vis absorption spectra of sensor is changed [4]. These sensors are generally selective for one particular anion and most likely this anion is fluoride due to the high charge density of fluoride [5]. On the other hand, the substituted urea moiety may offer binding affinity with other anion depending upon the coordination sphere of receptor. In this intension, we coated the anion receptor on the surface of ZnO, so that assembly can bind with more than one anion and it must bind with different coordination sphere. This strategy will authenticate the use of assembly for the recognition of two anions. The ZnO is selected as platform because of its biocompatible nature and secondly the grain boundaries affect the physical properties of ZnO, which can
n
Corresponding author. Tel.: +91 172 253 4464. E-mail addresses: [email protected], [email protected] (N. Kaur).
0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.05.130
be modulated by coating of organic ligand on its surface and thus desirable property can be achieved [6]. 2. Results and discussion The receptor 1 (Fig. 1A) was synthesized with the condensation reaction between salicylaldehyde and propylamine and the corresponding imine linkage was reduced with NaBH4. The product with reduced imine linkage was treated with 4-nitrophenylisocyanate and a yellow colored product (1) separated out. The product was characterized with spectroscopic methods such as the 1 H NMR (400 MHz, CDCl3) of compound 1 confirmed its formation: δ 7.2 (s, 1H, ArH), 8.2 (d, 2H, ArH), 8.1 (d, 2H, ArH), 7.2 (d, 1H, ArH), 6.8 (m, 2H, –CH2), 4.4 (s, 2H, Ar-CH2), 3.3 (t, 2H, –N-CH2), 2.3 (m, 2H, –CH2), 1.0 (t, 3H, –CH3). The 13C NMR (400 MHz, CDCl3) spectrum further confirms the formation of compound 1 through signals at: δ 155.97, 155.48, 153.37, 144.84, 143.99, 142.96, 142.67, 131.42, 130.37, 125.25, 125.02, 48.52, 47.47, 21.04, and 11.46. The product 2 (Fig. 1B) was synthesized by the one pot chemical precipitation method already reported by us [7] and afforded modified ZnO containing receptor 1, i.e., assembly 2. To evaluate the photophysical properties of assembly 2; the solid-state UV–vis absorption and solid-state fluorescence spectra were recorded. The solid-state absorption spectrum of 1 exhibited absorption band at around 345 nm, corresponding to charge transfer transitions. However, the absorption spectrum of 2 has band at around 410 nm due to charge transfer transitions associated with compound 1, which superimpose the band due to ZnO core (Fig. 1C). It is worth mentioning here that the intensity of absorption band of ZnO core is low when
S. Kaur et al. / Materials Letters 107 (2013) 154–157
155
Fig. 1. (A) Chemical structure of compound 1; (B) Chemical structure of compound 2; (C) A comparison of solid-state UV—vis spectra of uncoated ZnO and compound 2 (ZnO coated with compound 1); (D) A comparison of solid-state Fluorescence spectra of uncoated ZnO and compound 2 (ZnO coated with compound 1); (E) EDX analysis of compound 2 (as prepared) showing the coatings of organic molecules on ZnO; and (F) EDX analysis of compound 2 (obtained by heating compound 2 at 500 1C for 2 h) showing the burning of organic molecules from the surface of ZnO. (G) X-ray powder diffractogram of ZnO (obtained by heating compound 2 at 500 1C for 2 h; (H) Distribution of particle size of compound 2 (showing average particle size of 7.5 nm); measured with DLS based particle size analyzer by dissolving the compound in DMSO:H2O (70:30; v/v); (I) SEM image of compound 2, showing a self-assembled structure due to the structure directing nature of compound 1.
compared to intensity of compound 1 and is thus responsible for superimposition of band due to ZnO. Although, the excitation state of ZnO core in assembly 2 could not be resolved from absorption band of compound 1; nevertheless the fluorescence spectra of 2 provided information about its well-defined emission profile; showed green emission at around 480 nm due to the presence of surface defects
(Fig. 1D). The washing of as synthesized assembly 2 with chloroform will remove unreacted organic receptor 1 and only attached with ZnO surface will appear in EDX results. Thus, to realize as if the organic receptor 1 has been attached with ZnO or not, the synthesized assembly was washed with chloroform 4 times and the samples were analyzed with EDX and it shows the presence of organic compound
S. Kaur et al. / Materials Letters 107 (2013) 154–157
along with ZnO (Fig. 1E). However, if we heat the assembly 2 at 500 1C for 2 h, the EDX analysis shows no remnant of organic compound (Fig. 1F). These results show that after heating the assembly at 500 1C, the organic receptor was burnt and further authenticate the attachment of organic receptor 1 on the surface of ZnO. The XRD pattern of 2 (after burning organic receptor) exhibits the scattering angles (2θ) corresponding to the reflection from the 100, 002, 101, 102, 110, 103 and 112 crystal planes, respectively and are in good agreement with literature reports (Fig. 1G). The particle size distribution of compound 2 was measured with DLS based particle size analyzer by dissolving the compound in DMSO:H2O (70:30; v/v); and it was showing average particle size of 7.5 nm (Fig. 1H). The structure directing nature of compound 2 leads to the formation of self-assembled structure of 2 as evident from the SEM image of compound 2 (Fig. 1I). Photophysical studies were performed to study the sensing properties of assembly 2. For anion binding studies of 1, the solution of compound 1 (10 μM) in DMSO:H2O (95:5) was prepared along with anion solution. No selective or differential change in the absorption spectra of 1 was observed upon addition of any anion (F−, Cl−, Br−, I−, CN−, AcO−, NO3−, PO43−, SO42− and ClO4−) (Fig. 2A). For anion binding studies of ZnO nanoparticles coated with compound 1, same types of solutions were prepared as that were prepared for the recognition properties of 1 and UV–vis absorption profile for each were recorded (Fig. 2B). The results demonstrate that 1 bearing the substituted urea receptors are non-selective; however as expected maximum binding affinity was observed with fluoride. On the other hand, when receptor with substituted urea moieties are provided on the surface of ZnO, the selectivity is shifted toward tetrahedral anion like SO42− in addition to the binding affinity for fluoride. On these lines; it can be proposed that if substituted urea groups are inserted on nano-particle framework; then it may offer coordination modes for spherical anion as well as for tetrahedral anion. To gain more insight about the sensor
0.7
Absorbance
0.6
properties of assembly 2 as a receptor for SO42−, the titrations of SO42− ion were performed with successive addition of SO42− ion (5 mM–265 mM) to the solution of 2 (10 mM) (Fig. 2C). Similarly, the fate of the addition of fluoride ion (5 mM–295 mM) to the solution of 2 (10 mM) was monitored with UV–vis absorption spectroscopy (Fig. 2D). Both the titrations revealed the anion selective binding pattern through the shifts in the absorption profile of 2; blue shift in case of SO42− ion while red shift in case of fluoride ion. To rule out the possibility that the addition of SO42− and fluoride ion may influence the pH of solution, which may modulate the absorption spectra of 2; a pH titration was conducted. There are no unexpected results, demonstrated that the anion is coordinated to the sensor within the cleft of sensor, which is in conjugation with the p-nitrophenyl group (Fig. 3A–B). In order to test the interference of SO42− and fluoride in sensing of each other with assembly 2, competitive experiments were carried out with assembly 2 (10 mM) in the presence of SO42− mixed with fluoride at different concentrations and vice versa. It has been observed that the two anions do not interfere till total analyte concentration of 200 mM. However at higher concentration they hinder the estimation of each other.
3. Conclusion ZnO nanoparticles coated with substituted urea based ligand (compound 1) were prepared through chemical precipitation technique, which were then characterized through various characterization techniques. XRD, NMR, EDX and IR spectroscopy tools confirmed the formation of ZnO nanoparticles coated with substituted urea based ligand. Photophysical characterization (UV–vis studies) revealed that ZnO nanoparticles coated with compound 1 resulted in a differential sensor for SO42− and fluoride ion by undergoing blue and red shifts respectively.
Receptor
Fluoride
0.8
Chloride
Bromide
0.7 0.6
Iodide
Cyanide
0.5
Sulfate
Nitrate
0.4
Acetate
Phosphate
Perchlorate 0.3 0.2
Absorbance
156
Receptor Chloride Iodide Acetate Phosphate Perchlorate
0.5 0.4
Fluoride Bromide Cyanide Nitrate Sulfate
0.3 0.2
0.1
0.1
0
0 260
310
360
410
460
510
560
Wavelength (nm)
270
320
370
420
470
520
570
Wavelength (nm)
0.8
Absorbance
0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 260
310
360
410
460
Wavelength (nm) Fig. 2. Changes in UV—vis absorption spectra of (A) compound 1 (10 mM); (B) Compound 2 (10 μM) upon addition of tetrabutyl ammonium salt of a particular anion in DMSO/H2O (9.5/0.5 ; V/V) solvent system; (C) Changes in UV—Vis absorption spectrum of compound 2 (10 μM)) in the presence of different concentrations of tetrabutyl ammonium sulfate in the DMSO/H2O (9.5/0.5,v/v) solvent system; (D) changes in UV—vis absorption spectrum of compound 2 (10 μM) in the presence of different concentrations of tetrabutyl ammonium fluoride in the DMSO/H2O (9.5/0.5,v/v) solvent system.
S. Kaur et al. / Materials Letters 107 (2013) 154–157
157
0.9 0.7
pH 12.7
0.7
0.6
0.6
0.5
Absorbance
Absorbance
0.8
0.5 0.4
pH 3.25
0.3 0.2
pH 12.7
0.4 0.3 0.2
pH 2.75 0.1
0.1 0 260
310
360
410
460
510
Wavelength (nm)
0 260
310
360
410
460
510
560
Wavelength (nm)
Fig. 3. (A) Effect of pH on the absorption profile of compound 1 (10 μM) recorded in the DMSO/H2O (9.5/0.5,v/v) solvent system; and (B) Effect of pH on the absorption profile of compound 2 (10 μM) recorded in the DMSO/H2O (9.5/0.5,v/v) solvent system.
Acknowledgment This work was supported with research Grant (SR/FT/CS-97/ 2010(G) from the Department of Science and Technology (DST), Government of India and S. Kaur is thankful to DST, New Delhi for the INSPIRE fellowship. References [1] (a) Gunnlaugsson T, Glynn M, Tocci GM, Kruger PE, Pfeffer FM. Coord Chem Rev 2006;250:3094; (b) Cao Y, Hu X, Wang D, Sun Y, Sun P, Zheng J, et al. Mater Lett 2012;69:45. [2] Cho D-G, Sessler JL. Chem Soc Rev 2009;38:1647.
[3] Suksaia C, Tuntulani T. Chem Soc Rev 2003;32:192. [4] Beer PD, Gale PA. Angew Chem Int Ed 2001;40:486. [5] Kumar V, Kaushik MP, Srivastava AK, Pratap A, Thiruvenkatam V, Row TN. Anal Chim Acta 2010;663:77. [6] (a) Straumal BB, Mazilkin AA, Protasova SG, Myatiev AA, Straumal PB, Schutz G, et al. Phys Rev 2009;79:205; (b) Straumal BB, Myatiev AA, Straumal PB, Mazilkin AA, Protasova SG, Goering E, et al. JETP Lett 2010;92:396; (c) Straumal BB, Mazilkin AA, Protasova SG, Myatiev AA, Straumal PB, Baretzky B. Acta Mater 2008;56:6246; (d) Straumal BB, Mazilkin AA, Protasova SG, Myatiev AA, Straumal PB, Goering E, et al. Thin Solid Films 2011;520:1192. [7] (a) Sharma H, Narang K, Singh N, Kaur N. Mater Lett 2012;84:104; (b) Kaur K, Kaur N, Singh N. Mater Lett 2012;80:78.
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Differential recognition of anions with ZnO based urea-coupled sensors Simanpreet Kaur a, Vimal K. Bharadwaj b, Amanpreet Kaur a, Narinder Singh b, Navneet Kaur a,n a b
Centre for Nanoscience and Nanotechnology (UIEAST), Panjab University, Chandigarh 160014, India Department of Chemistry, Indian Institute of Technology Ropar (IIT Ropar), Rupnagar, Panjab 140001, India
art ic l e i nf o
a b s t r a c t
Article history: Received 20 May 2013 Accepted 28 May 2013 Available online 5 June 2013
With the emergence of nanoparticles as a class of attractive probes for selective sensors, a need arise for the development of nanoparticles based multifunctional sensors. Herein, a simple strategy is explored for the differential recognition of two different anions. The anion receptors have been coated on the surface of ZnO and the product was characterized with SEM, XRD, EDX, UV–vis absorption and fluorescence spectroscopy. A comparison of anion recognition properties of pure host and the same host coated on ZnO revealed magnificent change in the recognition properties. The fluoride binding leads to red shift in the absorption spectrum of receptor and SO42− binding causes blue shift. These results demonstrated that our design strategy offers an effective way to develop an excellent differential sensor for anions. & 2013 Elsevier B.V. All rights reserved.
Keywords: ZnO Sensors Recognition Nanoparticles Surfaces Semiconductors
1. Introduction With the development of sensors, the research on anion recognition has become more significant due to diverse role of anions in environment and biomedical research [1]. Among various types of methods, the chromogenic receptors provide simple and reliable solution for anion estimation [2]. The various types of chromogenic sensors are available in literature including azo dye, nanoparticles, nitro compounds and various other organic dyes [3]. The chromogenic sensors are generally relay with urea moiety, which is provided in conjugation with p-nitrophenyl group [3]. These sensors convey the signal on the concept that when anion coordinates to the sensor within the cleft of sensor, the UV–vis absorption spectra of sensor is changed [4]. These sensors are generally selective for one particular anion and most likely this anion is fluoride due to the high charge density of fluoride [5]. On the other hand, the substituted urea moiety may offer binding affinity with other anion depending upon the coordination sphere of receptor. In this intension, we coated the anion receptor on the surface of ZnO, so that assembly can bind with more than one anion and it must bind with different coordination sphere. This strategy will authenticate the use of assembly for the recognition of two anions. The ZnO is selected as platform because of its biocompatible nature and secondly the grain boundaries affect the physical properties of ZnO, which can
n
Corresponding author. Tel.: +91 172 253 4464. E-mail addresses: [email protected], [email protected] (N. Kaur).
0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.05.130
be modulated by coating of organic ligand on its surface and thus desirable property can be achieved [6]. 2. Results and discussion The receptor 1 (Fig. 1A) was synthesized with the condensation reaction between salicylaldehyde and propylamine and the corresponding imine linkage was reduced with NaBH4. The product with reduced imine linkage was treated with 4-nitrophenylisocyanate and a yellow colored product (1) separated out. The product was characterized with spectroscopic methods such as the 1 H NMR (400 MHz, CDCl3) of compound 1 confirmed its formation: δ 7.2 (s, 1H, ArH), 8.2 (d, 2H, ArH), 8.1 (d, 2H, ArH), 7.2 (d, 1H, ArH), 6.8 (m, 2H, –CH2), 4.4 (s, 2H, Ar-CH2), 3.3 (t, 2H, –N-CH2), 2.3 (m, 2H, –CH2), 1.0 (t, 3H, –CH3). The 13C NMR (400 MHz, CDCl3) spectrum further confirms the formation of compound 1 through signals at: δ 155.97, 155.48, 153.37, 144.84, 143.99, 142.96, 142.67, 131.42, 130.37, 125.25, 125.02, 48.52, 47.47, 21.04, and 11.46. The product 2 (Fig. 1B) was synthesized by the one pot chemical precipitation method already reported by us [7] and afforded modified ZnO containing receptor 1, i.e., assembly 2. To evaluate the photophysical properties of assembly 2; the solid-state UV–vis absorption and solid-state fluorescence spectra were recorded. The solid-state absorption spectrum of 1 exhibited absorption band at around 345 nm, corresponding to charge transfer transitions. However, the absorption spectrum of 2 has band at around 410 nm due to charge transfer transitions associated with compound 1, which superimpose the band due to ZnO core (Fig. 1C). It is worth mentioning here that the intensity of absorption band of ZnO core is low when
S. Kaur et al. / Materials Letters 107 (2013) 154–157
155
Fig. 1. (A) Chemical structure of compound 1; (B) Chemical structure of compound 2; (C) A comparison of solid-state UV—vis spectra of uncoated ZnO and compound 2 (ZnO coated with compound 1); (D) A comparison of solid-state Fluorescence spectra of uncoated ZnO and compound 2 (ZnO coated with compound 1); (E) EDX analysis of compound 2 (as prepared) showing the coatings of organic molecules on ZnO; and (F) EDX analysis of compound 2 (obtained by heating compound 2 at 500 1C for 2 h) showing the burning of organic molecules from the surface of ZnO. (G) X-ray powder diffractogram of ZnO (obtained by heating compound 2 at 500 1C for 2 h; (H) Distribution of particle size of compound 2 (showing average particle size of 7.5 nm); measured with DLS based particle size analyzer by dissolving the compound in DMSO:H2O (70:30; v/v); (I) SEM image of compound 2, showing a self-assembled structure due to the structure directing nature of compound 1.
compared to intensity of compound 1 and is thus responsible for superimposition of band due to ZnO. Although, the excitation state of ZnO core in assembly 2 could not be resolved from absorption band of compound 1; nevertheless the fluorescence spectra of 2 provided information about its well-defined emission profile; showed green emission at around 480 nm due to the presence of surface defects
(Fig. 1D). The washing of as synthesized assembly 2 with chloroform will remove unreacted organic receptor 1 and only attached with ZnO surface will appear in EDX results. Thus, to realize as if the organic receptor 1 has been attached with ZnO or not, the synthesized assembly was washed with chloroform 4 times and the samples were analyzed with EDX and it shows the presence of organic compound
S. Kaur et al. / Materials Letters 107 (2013) 154–157
along with ZnO (Fig. 1E). However, if we heat the assembly 2 at 500 1C for 2 h, the EDX analysis shows no remnant of organic compound (Fig. 1F). These results show that after heating the assembly at 500 1C, the organic receptor was burnt and further authenticate the attachment of organic receptor 1 on the surface of ZnO. The XRD pattern of 2 (after burning organic receptor) exhibits the scattering angles (2θ) corresponding to the reflection from the 100, 002, 101, 102, 110, 103 and 112 crystal planes, respectively and are in good agreement with literature reports (Fig. 1G). The particle size distribution of compound 2 was measured with DLS based particle size analyzer by dissolving the compound in DMSO:H2O (70:30; v/v); and it was showing average particle size of 7.5 nm (Fig. 1H). The structure directing nature of compound 2 leads to the formation of self-assembled structure of 2 as evident from the SEM image of compound 2 (Fig. 1I). Photophysical studies were performed to study the sensing properties of assembly 2. For anion binding studies of 1, the solution of compound 1 (10 μM) in DMSO:H2O (95:5) was prepared along with anion solution. No selective or differential change in the absorption spectra of 1 was observed upon addition of any anion (F−, Cl−, Br−, I−, CN−, AcO−, NO3−, PO43−, SO42− and ClO4−) (Fig. 2A). For anion binding studies of ZnO nanoparticles coated with compound 1, same types of solutions were prepared as that were prepared for the recognition properties of 1 and UV–vis absorption profile for each were recorded (Fig. 2B). The results demonstrate that 1 bearing the substituted urea receptors are non-selective; however as expected maximum binding affinity was observed with fluoride. On the other hand, when receptor with substituted urea moieties are provided on the surface of ZnO, the selectivity is shifted toward tetrahedral anion like SO42− in addition to the binding affinity for fluoride. On these lines; it can be proposed that if substituted urea groups are inserted on nano-particle framework; then it may offer coordination modes for spherical anion as well as for tetrahedral anion. To gain more insight about the sensor
0.7
Absorbance
0.6
properties of assembly 2 as a receptor for SO42−, the titrations of SO42− ion were performed with successive addition of SO42− ion (5 mM–265 mM) to the solution of 2 (10 mM) (Fig. 2C). Similarly, the fate of the addition of fluoride ion (5 mM–295 mM) to the solution of 2 (10 mM) was monitored with UV–vis absorption spectroscopy (Fig. 2D). Both the titrations revealed the anion selective binding pattern through the shifts in the absorption profile of 2; blue shift in case of SO42− ion while red shift in case of fluoride ion. To rule out the possibility that the addition of SO42− and fluoride ion may influence the pH of solution, which may modulate the absorption spectra of 2; a pH titration was conducted. There are no unexpected results, demonstrated that the anion is coordinated to the sensor within the cleft of sensor, which is in conjugation with the p-nitrophenyl group (Fig. 3A–B). In order to test the interference of SO42− and fluoride in sensing of each other with assembly 2, competitive experiments were carried out with assembly 2 (10 mM) in the presence of SO42− mixed with fluoride at different concentrations and vice versa. It has been observed that the two anions do not interfere till total analyte concentration of 200 mM. However at higher concentration they hinder the estimation of each other.
3. Conclusion ZnO nanoparticles coated with substituted urea based ligand (compound 1) were prepared through chemical precipitation technique, which were then characterized through various characterization techniques. XRD, NMR, EDX and IR spectroscopy tools confirmed the formation of ZnO nanoparticles coated with substituted urea based ligand. Photophysical characterization (UV–vis studies) revealed that ZnO nanoparticles coated with compound 1 resulted in a differential sensor for SO42− and fluoride ion by undergoing blue and red shifts respectively.
Receptor
Fluoride
0.8
Chloride
Bromide
0.7 0.6
Iodide
Cyanide
0.5
Sulfate
Nitrate
0.4
Acetate
Phosphate
Perchlorate 0.3 0.2
Absorbance
156
Receptor Chloride Iodide Acetate Phosphate Perchlorate
0.5 0.4
Fluoride Bromide Cyanide Nitrate Sulfate
0.3 0.2
0.1
0.1
0
0 260
310
360
410
460
510
560
Wavelength (nm)
270
320
370
420
470
520
570
Wavelength (nm)
0.8
Absorbance
0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 260
310
360
410
460
Wavelength (nm) Fig. 2. Changes in UV—vis absorption spectra of (A) compound 1 (10 mM); (B) Compound 2 (10 μM) upon addition of tetrabutyl ammonium salt of a particular anion in DMSO/H2O (9.5/0.5 ; V/V) solvent system; (C) Changes in UV—Vis absorption spectrum of compound 2 (10 μM)) in the presence of different concentrations of tetrabutyl ammonium sulfate in the DMSO/H2O (9.5/0.5,v/v) solvent system; (D) changes in UV—vis absorption spectrum of compound 2 (10 μM) in the presence of different concentrations of tetrabutyl ammonium fluoride in the DMSO/H2O (9.5/0.5,v/v) solvent system.
S. Kaur et al. / Materials Letters 107 (2013) 154–157
157
0.9 0.7
pH 12.7
0.7
0.6
0.6
0.5
Absorbance
Absorbance
0.8
0.5 0.4
pH 3.25
0.3 0.2
pH 12.7
0.4 0.3 0.2
pH 2.75 0.1
0.1 0 260
310
360
410
460
510
Wavelength (nm)
0 260
310
360
410
460
510
560
Wavelength (nm)
Fig. 3. (A) Effect of pH on the absorption profile of compound 1 (10 μM) recorded in the DMSO/H2O (9.5/0.5,v/v) solvent system; and (B) Effect of pH on the absorption profile of compound 2 (10 μM) recorded in the DMSO/H2O (9.5/0.5,v/v) solvent system.
Acknowledgment This work was supported with research Grant (SR/FT/CS-97/ 2010(G) from the Department of Science and Technology (DST), Government of India and S. Kaur is thankful to DST, New Delhi for the INSPIRE fellowship. References [1] (a) Gunnlaugsson T, Glynn M, Tocci GM, Kruger PE, Pfeffer FM. Coord Chem Rev 2006;250:3094; (b) Cao Y, Hu X, Wang D, Sun Y, Sun P, Zheng J, et al. Mater Lett 2012;69:45. [2] Cho D-G, Sessler JL. Chem Soc Rev 2009;38:1647.
[3] Suksaia C, Tuntulani T. Chem Soc Rev 2003;32:192. [4] Beer PD, Gale PA. Angew Chem Int Ed 2001;40:486. [5] Kumar V, Kaushik MP, Srivastava AK, Pratap A, Thiruvenkatam V, Row TN. Anal Chim Acta 2010;663:77. [6] (a) Straumal BB, Mazilkin AA, Protasova SG, Myatiev AA, Straumal PB, Schutz G, et al. Phys Rev 2009;79:205; (b) Straumal BB, Myatiev AA, Straumal PB, Mazilkin AA, Protasova SG, Goering E, et al. JETP Lett 2010;92:396; (c) Straumal BB, Mazilkin AA, Protasova SG, Myatiev AA, Straumal PB, Baretzky B. Acta Mater 2008;56:6246; (d) Straumal BB, Mazilkin AA, Protasova SG, Myatiev AA, Straumal PB, Goering E, et al. Thin Solid Films 2011;520:1192. [7] (a) Sharma H, Narang K, Singh N, Kaur N. Mater Lett 2012;84:104; (b) Kaur K, Kaur N, Singh N. Mater Lett 2012;80:78.