Chinese Chemical Letters  2015, Vol.26 Issue (05):580-584   PDF    
A highly selective turn-on colorimetric and luminescence sensor based on a triphenylamine-appended ruthenium(II) dye for detecting mercury ion
Su-Hua Fana, Jie Shena, Hai Wua, Ke-Zhi Wangbb , An-Guo Zhangc    
a School of Chemical and Materials Engineering, Fuyang Normal College, Fuyang 236037, China;
b College of Chemistry, Beijing Normal University, Beijing 100875, China;
c College of Materials and Chemistry & Chemical Engineering, Chengdu University of Technology, Chengdu 610059, China
Abstract: A dual colorimetric and luminescent sensor based on a heteroleptic ruthenium dye [Ru(Hipdpa)(Hdcbpy)(NCS)2]-·0.5H+0.5[N(C4H9)4]+ Ru(Hipdpa) {where Hdcbpy = monodeprotonted-4,4'-dicarboxy-2,2'- bipyridine and Hipdpa = 4-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)-N,N-diphenylaniline} for selective detection of Hg2+ is presented. The results of spectrophotometric titrations revealed an evident luminescence intensity enhancement (I/I0 = 11) and a considerable blue shift in visible absorption and luminescence maxima with the addition of Hg2+. The sensitive response of the optical sensor on Hg2+ was attributed to the binding of the electron-deficient Hg2+ to the electron-rich sulfur atom of the thiocyanate (NCS) ligand in the Ru(Hipdpa), which led to an increase in the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). Accordingly, the blue shift in the absorption spectrum of Ru(Hipdpa) due to the binding of Hg2+ was obtained. Ru(Hipdpa) was found to have decreased Hg2+ detection limit and improved linear region as compared to di(tetrabutylammonium) cis-bis(isothiocyanato)bis(2,2'-bipyridine-4-carboxylic acid-4'- carboxylate)ruthenium(II) N719. Moreover, a dramatic color change from pink to yellow was observed, which allowed simple monitoring of Hg2+ by either naked eyes or a simple colorimetric reader. Therefore, the proposed sensor can provide potential applications for Hg2+ detection.
Key words: Ruthenium dye     Mercury     Colorimetric sensor     Luminescence sensor    
1. Introduction

Mercury,one of the most toxic elements,causes serious environmental and public health problems [1]. Mercury is generated by many sources such as coal and gold mining,solid waste incineration,wood pulping,fossil fuel combustion,and chemical manufacturing [2]. It is readily absorbed by the human gastrointestinal tract,crosses the blood-brain barrier and targets the central nervous system,causing prenatal brain damages, cognitive and motion disorders,and the Minamata disease [3, 4]. Consequently,it is of great significance for the development of a low-cost,rapid and facile detection and quantification of mercury in environmental and biological samples.

Traditional quantitative approaches of Hg2+ detection include atomic absorption spectroscopy,electrochemical devices,and gas/ liquid chromatography [5, 6]. However,they often require sophisticated instrumentation,skilled operators,and complicated sample preparation. Optical spectroscopy techniques,such as colorimetric and luminescence detection systems are the most convenient methods due to their simplicity,speed,and low limit of detection [7, 8]. To date,a large number of Hg2+ sensors based on colorimetric and luminescent reporting units have been developed. Among reported luminescence ‘‘turn-on’’ [9, 10, 11, 12, 13] and ‘‘turnoff’’ [14, 15, 16, 17] sensors,the former sensors are preferable because they can lessen or eliminate false reports and are more amenable to multiplexing. Moreover,the luminescence ‘‘turn-on’’ sensors remain a great challenge due to the fact that the luminescence in most cases is quenched rather than enhanced by heavy metal ions such as Ag+ ,Pb2+ ,and Hg2+ [18, 19]. Therefore,the ‘‘turn-on’’ luminescence sensors for Hg2+ were much less frequently reported than ‘‘turn-off’’ types.

The Ru(II) polypyridyl complexes have attracted ever-increasing interest for luminescence intensity and lifetime based recognizing and sensing of Hg2+ due to their excellent photophysical and photochemical properties,visible absorption and emission spectra as well as good thermodynamic and dynamic stability [20, 21, 22, 23]. The dye-sensitized solar cell Ru(II) dyes of di(tetrabutylammonium) cis-bis(isothiocyanato)bis(2,2' -bipyridine-4-carboxylic acid-4' -carboxylate)ruthenium(II) (N719) and analogs in fluid solution or adsorbed on nanocrystalline mesoporous TiO2films were reported to exhibit colorimetric sensing for Hg2+ [20, 22]. In order to further improve Hg2+ sensing properties of this interesting family of the Ru(II) dyes,we have designed and synthesized a Ru(II) solar cell sensitizer [Ru(Hipdpa)(Hdcbpy)(NCS)2]- ·0.5H+ 0.5[N(C4H9)4]+ (denoted as Ru(Hipdpa) {where Hdcbpy = monodeprotonted-4,40 -dicarboxy-2,2' -bipyridine and Hipdpa = 4-(1H-imidazo[4, 5, f][1, 10]phenanthrolin-2-yl)-N,Ndiphenylaniline} [24],which have been comparatively investigated for their sensing properties for Hg2+ with N719. The molecular structures of Ru(Hipdpa) and N719 are shown in Scheme 1.

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Scheme 1.The molecular structures of Ru(Hipdpa) and N719.
2. Experimental

Ru(Hipdpa) was synthesized by a one-pot reaction according to a previous study [24]. Firstly,the mononuclear Ru(II) complex was obtained by the reaction of Ru-dimer with Hipdpa,then 2,2' -bipyridyl-4,4'-dicarboxylic acid (H2dcbpy) was added into the reaction mixture. Finally,excessive ammonium thiocyanate was added and Ru(Hipdpa) was obtained. Ethanol was distilled from Mg and I2. Other chemicals were of analytical grade and used as received.

UV-visible (UV-vis) absorption spectra were measured on a GBC Cintra 10e UV-vis spectrophotometer using 1.0 cm path length quartz cells. Luminescence spectra were obtained with a Varian Cary Eclipse luminescence spectrophotometer. The FTinfrared (FT-IR) spectra were obtained using a Nicolet Avtar 360 FT-IR spectrometer with 2 cm-1 resolution.

For spectroscopic titration experiments,the aliquots of the metal ions in ethanol (1.0×10-3 mol L-1 )ofHg2+ ,Ca2+ ,Mg2+ ,Ba2+ , Zn2+ ,Ni2+ ,Cu2+ ,andFe2+ as perchlorate salts were successively injected into a quartz cuvettes containing the complex (3 mL, 2.0×10-5 mol L-1 ) in ethanol. The competition experiments were conducted by adding 4.0×10-5 mol L-1 of Hg2+ to the stock solution of the Ru complex with one other metal ion added (2.0×10-4 mol L-1 ). All the optical measurements were conducted at room temperature (298 K).

Density functional theory (DFT) calculations were performed using the Becker’s three parameterized Lee-Yang-Par (B3LYP) exchange correlation functional and 6-31G* basis set as implemented in the Gaussian 03 program package [25]. 3. Results and discussion UV-vis absorption spectra of the complex in ethanol exhibited four bands centered at 300 nm (ε=4.94×104 Lmol-1 cm-1 ), 312 nm (shoulder,ε=4.58×104 mol-1 Lcm-1 ),366 nm (ε=4.39 ×104 mol-1 Lcm-1 ),and 525 nm (ε=1.41×104 Lmol-1 cm-1 ) (Fig. 1a). The two high-energy bands at 300 and 366 nm are assigned to the π-π* transitions dominantly contributed by Hipdpa. The shoulder peak at 312 nm is ascribed to thep-p* transitions of Hdcbpy. The broad absorption band at 525 nmis attributed to a spinallowed metal-to-ligand charge-transfer (MLCT) transition. Changes in the visible absorption spectra of the complex as a function of Hg2+ concentrations in ethanol are shown in Fig. 1b. Upon successive addition of Hg2+ from 6.90×107 mol L-1 to 3.20×10-5 mol L-1 , the MLCT band at~525 nm gradually decreased and a new peak at 485 nm appeared and progressively increased,along with the appearance of a well defined isosbestic point at 505 nm,indicating a strong ground-state interaction between the complex and Hg2+ .By plotting the absorbance ratios at 485 and 525 nm (A485 nm/A525 nm) versusHg2+ concentrations,a linear correlation (inset of Fig. 1b) was obtained in the concentration range from 3.40×107 mol L-1 to 1.51×10-5 mol L-1 .AlthoughHg2+ -induced spectral changes of Ru(Hipdpa) were similar to those of N719 (Figs. S1 and S2 in Supporting information),the detection limit (1.08×107 mol L-1 ) of Ru(Hipdpa) for Hg2+ in ethanol (S/N = 3) [13] was lower than that of 1.50×106 mol L-1 for N719 under the same experimental conditions. It was also worth mentioning that the absorption changes were clearly visible to naked eyes due to the distinct color change of the complex solution from pink to yellow,in sharp contrast to the slightly affected violet colors for the complex in the presence of other cations (bottom panel of Fig. 2). The absorbance ratios of A485 nm/A525 nmfor the complex solution in the presence of the same concentration of Ca2+ ,Mg2+ ,Ba2+ ,Zn2+ ,Ni2+ ,Cu2+ ,orFe2+ cations remained almost unchanged,but obviously changed in the presence of Hg2+ (top panel of Fig. 2).

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Fig. 1. UV-vis spectrum of Ru(Hipdpa) (a) and changes in absorption spectra of Ru(Hipdpa) (2.0×10-5 mol L-1 ) upon additions of Hg2+ from 0 to 3.2×10-5 mol L-1 (b) in ethanol. The inset displays the plot of the absorbance ratios at 485 nm and 525 nm (A485 nm/A525 nm)versus Hg2+ concentrations.

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Fig. 2. The absorbance ratios ofA485 nm/A525 nm (top panel) and color changes (bottom panel) of Ru(Hipdpa) (2.0×10-5 mol L-1 ) in ethanol in the absence and the presence of 2.0×10-5 mol L-1 different metal ions,from left to right: free Ru dye,Ca2+ ,Mg2+ ,Ba2+ ,Hg2+ ,Zn2+ ,Ni2+ ,Cu2+ ,Fe2+ .

To further explore the suitability of Ru(Hipdpa) as a Hg2+ sensor,competition experiments were also conducted and the results are depicted in Fig. S3 in Supporting information. Upon adding 10 equiv. of either Ca2+ ,Mg2+ ,Ba2+ ,Zn2+ ,Ni2+ or Cu2+ ,the UV-vis absorption spectra did not produce significant changes. In contrast,when 2 equiv. of Hg2+ was added to the Ru(Hipdpa) solution containing one of aforementioned metal ions,the metalto-ligand charge-transfer (MLCT) band was hypsochromically shifted from 525 to 485 nm,similarly to the behaviors for the Ru(Hipdpa) solution in the presence of Hg2+ . These results indicate that sensor Ru(Hipdpa) exhibited excellent selectivity toward Hg2+ ,which makes it feasible for practical applications.

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Fig. 3. Changes in luminescence spectra of Ru(Hipdpa) (2×10-5 mol L-1 ) upon additions of Hg2+ (0-3.2×10-5 mol L-1 ) in ethanol. The inset displays the plot of luminescence intensities at 720 nm versusthe concentrations of Hg2+ .

Fig. 3 shows the luminescence titration profile of Ru(Hipdpa) with Hg2+ . The luminescence spectrum of Ru(Hipdpa) exhibited a broad band centered at 760 nm. The successive additions of Hg2+ resulted in progressive blue shifts to 720 nm. The increment became saturated with a luminescence enhancement factor of 11. That is much smaller than that of 33 (Figs. S4 and S5 in Supporting information) observed for N719,when one equiv. of Hg2+ was added. In contrast,the other metal ions (Ca2+ ,Mg2+ ,Ba2+ , Zn2+ ,Ni2+ ,Cu2+ ,andFe2+ ) at the same concentration level had almost no influence on the luminescence spectra (Fig. 4). The luminescent enhancement and blue-shift resulted from the binding of Hg2+ to Ru(Hipdpa) facilitates the charge transfer between the electron-deficient Hg2+ and the electron-rich sulfur atom of Ru(Hipdpa). Linear luminescent response of Ru(Hipdpa) toward Hg2+ was found to be from 1.33×106 mol L-1 to 2.00×10-5 mol L-1 ,which is much broader than that found for N719 (see inset of Figs. S4 and S5),with a Hg2+ detection limit of 4.2×107 mol L-1 ,also lower than that (1.25 ×106 mol L-1 )of N719 and those for some representative analogous Ru(II) complexes (see Table 1). The results indicated that Ru(Hipdpa) served as a highly selective and sensitive colorimetric and ‘‘turn-on’’ Hg2+ luminescence sensor.

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Fig. 4. The luminescence intensity (lex= 525 nm) ratio of Ru(Hipdpa) (2.0×10-5 mol L-1 ) in ethanol,I andI0represent the luminescence intensity in the presence and the absence of 2.0×10-5 mol L-1 different metal ions

Table 1
The comparison of optical Hg2+ sensing properties of Ru(Hipdpa) with those of previously reported analogous Ru complex-based sensors and typical ‘‘turn-on’’ type of photochemical Hg2+ sensor.

In order to investigate the feasibility of the utility of the present sensor in aqueous solutions,a Hg2+ sensing experiment was carried out in pH 7.0 aqueous solution. As shown in Fig. S6 in Supporting information,the linear concentration range was from 0.423 molL-1 to 4.23×106 mol L-1 (R= 0.9804),which is narrower than that obtained in ethanol solutions. This likely resulted from the dissociation of the carboxylic acid in Ru(Hipdpa) to the negatively charged carboxylate ion in neutral and alkaline aqueous solutions,which could react with Hg2+ through the electrostatic force,decreasing the binding of Hg2+ to sulfur atom of the thiocyanate ligand. But the results presented here indicate that it is possible to detect Hg2+ in aqueous solutions on at micromolar level concentrations using Ru(Hipdpa).

In addition,in order to further evaluate the practicality of Ru(Hipdpa),it was absorbed on TiO2 film (Ru(Hipdpa)/TiO2)to measure the sensing sensitivity of the modified film toward Hg2+ in aqueous solutions. The obvious change of color from red to yellow was observed when (Ru(Hipdpa)/TiO2was dipped into the Hg2+ solution (Fig. S7 in Supporting information). Therefore,it suggests that Ru(Hipdpa) can be applied to the practical detection under proper conditions.

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Fig. 5. The Job’s plot for the binding of Hg2+ to Ru(Hipdpa)

To further investigate the binding properties between Hg2+ and Ru(Hipdpa),the stoichiometry of the Ru(Hipdpa)-Hg2+ complex was ascertained by the Job’s method [26]. Fig. 5 shows the corresponding Job’s plot and the mole fraction was found to be 0.5 at the maximum point,indicating a 1:1 stoichiometry for the formation of the Ru(Hipdpa)-Hg2+ complex. The binding constant (Kb) was derived to be (5.57±0.25)×106 Lmol-1 (the correlation coefficient R2 = 0.997) by a nonlinear least-square fitting of the absorbance (A) at 485 nm as a function of the Hg2+ concentrations according to the following equation [27, 28]:

where A0 and A are the absorbance of the complex in the absence and presence of Hg2+ ,respectively.Alimis the limit of absorbance at saturation level.CRu is the total Ru(Hipdpa) concentration,cMis the concentration of Hg2+ . It can be seen that the kb value of Ru(Hipdpa)-Hg2+ is slightly less than that of (8.25±0.75)×106 Lmol-1 for N719-Hg2+ ,but much greater than that of previously reported for Ru(H2dcbpy)(aphen)(NCS)2-Hg2+ {aphen = 5-amino-1,10-phenanthroline} (8.71×104 Lmol-1 ) [21].

Hg2+ ,a typical soft Lewis acid,can preferentially interact with sulfur (a soft Lewis base) according to Pearson’s hard-soft acid- base theory [29]. Palomares et al. [20] reported that the coordination of Hg2+ to the sulfur atom of NCS groups in N719 caused a significant color change of N719 ethanolic solutions, which was verified by the single-crystal X-ray crystal structure of N719-HgCl2. To investigate the binding mechanism,Fourier transform infrared spectra of Ru(Hipdpa)-HgCl2powder and free Ru(Hipdpa) were compared and the results are shown in Fig. 6. It can be seen from Fig. 6,the asymmetric stretching vibration of C55O at 1716 cm-1 was almost unaffected in the presence of Hg2+ . However,a strong thiocyanate C=N stretching vibration peak at 2102 cm-1 in free Ru(Hipdpa) became very weak and broad,and split into two peaks at 2107 cm-1 and 2143 cm-1 in Ru(Hipdpa)-HgCl2. This is ascribed to the molecular polarity with the coordination of Hg2+ to the sulfur atom in Ru(Hipdpa). The results clearly showed that the sulfur atom rather than carboxyl oxygen atoms of Ru(Hipdpa) interacted with Hg2+.

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Fig. 1. The FT-IR spectra of Ru(Hipdpa) (a) and Ru(Hipdpa)-Hg2+ (b).

In order to further elaborate the mechanism the binding of Ru(Hipdpa) to Hg2+ ,the structural and electronic properties of Ru(Hipdpa) and Ru(Hipdpa)-Hg2+ were investigated by DFT calculations. The DFT optimized geometries are shown in Fig. 7. The HOMO of Ru(Hipdpa) was found to have a smaller amplitude on the ruthenium metalt2gcharacter,but much larger amplitudes on the thiocyanate (NCS) ligands. More specially,they are primarily located on the sulfur atom. In contrast,the electrons on the LUMO of Ru(Hipdpa) are dominantly localized over the diimine framework of the Hdcbpy ligand with appreciable electron density on the oxygen atoms of the carboxyl groups. The electron density of HOMO for Ru(Hipdpa)-Hg2+ is mainly populated on the triphenylaminly moiety,which is the most significant change for the electronic distribution. However,the LUMO of Ru(Hipdpa)-Hg2+ is similar to that of Ru(Hipdpa). The LUMO and HOMO levels for Ru(Hipdpa) were calculated to be -2.83 eV and-4.49 eV, respectively,which gave a HOMO-LUMO energy gap of 1.66 eV. In comparison,the LUMO and HOMO levels for Ru(Hipdpa)-Hg2+ were-3.18 eV and-5.37 eV,respectively,with an energy gap of 2.19 eV. The increased HOMO-LUMO energy gap is due to the binding of the electron-deficient Hg2+ to the electron-rich sulfur atom of the thiocyanate (NCS) ligand,which significantly lowers the HOMO energy level and has a marginal effect on the LUMO energy level. Consequently,an increase in the HOMO-LUMO energy gap occurred and the blue shift in the absorption spectrum of Ru(Hipdpa) was obtained.

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Fig. 7. Optimized structure of Ru(Hipdpa) and Ru(Hipdpa)-Hg2+ and the energy shifts upon binding to Hg2+ . (DFT/B3LYP/LanL2DZ and 6-31G*).
4. Conclusion

In conclusion,complex Ru(Hipdpa) was demonstrated to act as a dual colorimetric and turn-on luminescence sensor for the detection of Hg2+ . In the presence of Hg2+ ,a considerable blue shift in the UV-visible absorption spectrum of Ru(Hipdpa) and a drastic enhancement in luminescence intensity with a hypochromic shift in the emission peak were induced. Furthermore,the dramatic color change from pink to yellow allows for straightforward ‘‘naked-eye’’ detection of the Hg2+ . The Hg2+ -induced changes in UV-vis absorption,emission spectra,and color of Ru(Hipdpa) are in sharp contrast to the behaviors of other cations including Ca2+ , Mg2+ ,Ba2+ ,Zn2+ ,Ni2+ ,Cu2+ ,andFe2+ ,indicating high sensitivity and selectivity of the Ru(Hipdpa) sensor for Hg2+ detection. More importantly,the Hg2+ luminescence detection limitation and linear region were found to be superior to those of N719. The Hg2+ sensing behaviors of Ru(Hipdpa) were attributed to the coordination of Hg2+ to the sulfur atom of the thiocyanate (NCS) ligand,as supported by infrared spectroscopy and DFT calculations.

Acknowledgment

We greatly appreciate the supports of the National Natural Science Foundation of China (Nos. 21201037,21405019 and 21171022),the Natural Science Foundation of Anhui Province (No. 1408085QB39),the Innovation Training Program for the Anhui College students (Nos. AH201310371039 and AH201310371041), Anhui Provincial Key Laboratory for Degradation and Monitoring of the Pollution of the Environment,and the Natural Science Foundation of Sichuan Provincial Department of Education (No. 13ZB0056) and Analytical and Measurements Fund of Beijing Normal University.

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.cclet.2014.11.031.

References
[1] H.H. Harris, I.J. Pickering, G.N. George, The chemical form of mercury in fish, Science 301 (2003) 1203.
[2] M.S. Gustin, M. Coolbaugh, M. Engle, et al., Atmospheric mercury emissions from mine wastes and surrounding geologically enriched terrains, Environ. Geol. 43 (2003) 339-351.
[3] C.M.L. Carvalho, E.H. Chew, S.I. Hashemy, J. Lu, A. Holmgren, Inhibition of the human thioredoxin system: a molecular mechanism of mercury toxicity, J. Biol. Chem. 283 (2008) 11913-11923.
[4] T.W. Clarkson, L. Magos, G.J. Myers, The toxicology of mercury-current exposures and clinical manifestations, N. Engl. J. Med. 349 (2003) 1731-1737.
[5] G.J. Myers, P.W. Davidson, C. Cox, et al., Summary of the seychelles child development study on the relationship of fetal methylmercury exposure to neurodevelopment, Neurotoxicology 16 (1995) 711-716.
[6] M. Harada, Minamata disease: methylmercury poisoning in Japan caused by environmental pollution, Crit. Rev. Toxicol. 25 (1995) 1-24.
[7] H.N. Kim, W.X. Ren, J.S. Kim, J. Yoon, Fluorescent and colorimetric sensors for detection of lead, cadmium, and mercury ions, Chem. Soc. Rev. 41 (2012) 3210- 3244.
[8] J.O. Moon, M.G. Choi, T. Sun, J.I. Choe, S.K. Chang, Synthesis of thionaphthalimides and their dual Hg2+-selective signaling by desulfurization of thioimides, Dyes Pigment 96 (2013) 170-175.
[9] X.J. Jiang, C.L. Wong, P.C. Lo, K.P. Ng Dennis, A highly selective and sensitive BODIPY-based colourimetric and turn-on fluorescent sensor for Hg2+ ions, Dalton Trans. 41 (2012) 1801-1807.
[10] S. Maiti, C. Pezzato, S.G. Martin, L.J. Prins, Multivalent interactions regulate signal transduction in a self-assembled Hg2+ sensor, J. Am. Chem. Soc. 136 (2014) 11288-11291.
[11] J.F. Li, Y.Z. Wu, F.Y. Song, et al., A highly selective and sensitive polymer-based OFF-ON fluorescent sensor for Hg2+ detection incorporating salen and perylenyl moieties, J. Mater. Chem. 22 (2012) 478-482.
[12] Y.C. Chen, C.C. Zhu, Z.H. Yang, et al., A new "turn-on" chemodosimeter for Hg2+: ICT fluorophore formation via Hg2+-induced carbaldehyde recovery from 1,3- dithiane, Chem. Commun. 48 (2012) 5094-5096.
[13] Z.Q. Hu, W.M. Zhuang, M. Li, et al., Highly sensitive and selective turn-on fluorescent chemodosimeter for Hg2+ based on thiorhodamine 6G-amide and its applications for biological imaging, Dyes Pigments 98 (2013) 286-289.
[14] L. Wang, X.J. Zhu, W.Y. Wong, et al., Dipyrrolylquinoxaline-bridged Schiff bases: a new class of fluorescent sensors for mercury(II), Dalton Trans. (19) (2005) 3235- 3240.
[15] Z.K. Wu, Zhang Y.F., J.S. Ma, G.Q. Yang, Ratiometric Zn2+ sensor and strategy for Hg2+ selective recognition by central metal ion replacement, Inorg. Chem. 45 (2006) 3140-3142.
[16] Z. Gu, M. Zhao, Y. Sheng, L.A. Bentolila, Y. Tang, Detection of mercury ion by infrared fluorescent protein and its hydrogel-based paper assay, Anal. Chem. 83 (2011) 2324-2329.
[17] X. Ma, F.Y. Song, L. Wang, Y.X. Cheng, C.J. Zhu, Polymer-based colorimetric and "turn off" fluorescence sensor incorporating benzo[2,1,3]thiadiazole moiety for Hg2+ detection, J. Polym. Sci. Part A: Polym. Chem. 50 (2012) 517-522.
[18] K. Rurack, M. Kollmannsberger, U. Resch-Genger, J. Daub, A selective and sensitive fluoroionophore for HgII, AgI , and CuII with virtually decoupled fluorophore and receptor units, J. Am. Chem. Soc. 122 (2000) 968-969.
[19] X.M. Wang, H. Yan, X.L. Feng, Y. Chen, 1-Pyrenecarboxaldehyde thiosemicarbazone: a novel fluorescent molecular sensor towards mercury (II) ion, Chin. Chem. Lett. 21 (2010) 1124-1128.
[20] E. Coronado, J.R. Galán-Mascarós, C. Martí-Gastaldo, et al., Reversible colorimetric probes for mercury sensing, J. Am. Chem. Soc. 127 (2005) 12351-12356.
[21] A.Reynal, J. Albero, A. Vidal-Ferran, E. Palomares, Diastereoselectivity andmolecular recognition of mercury(II) ions, Inorg. Chem. Commun. 12 (2009) 131-134.
[22] W.C. Yang, S.H. Fan, K.Z. Wang, Optically highly selective sensing of fluoride ion by N3 dye, Acta Phys. Chim. Sin. 24 (2008) 1313-1315.
[23] X.H. Li, X.F. Duan, F.Y. Li, C.H. Huang, Synthesis of new mixed-ligands amphiphilic ruthenium complex and its naked-eye detecable recognition of Hg2+, Chem. J. Chin. Univ. 27 (2006) 419-423.
[24] S.H. Fan, A.G. Zhang, C.C. Ju, L.H. Gao, K.Z. Wang, A triphenylamine-grafted imidazo[4,5-f][1,10]phenanthroline ruthenium(II) complex: acid-base and photoelectric properties, Inorg. Chem. 49 (2010) 3752-3763.
[25] M.J. Frisch, G.W. Trucks, H.B. Schlegel, et al., Gaussian 03, Inc, Pittsburgh, PA, 2003.
[26] P. Job, Formation and stability of inorganic complexes in solution, Ann. Chim. 9 (1928) 113-203.
[27] M. Zhang, M.Y. Li, F.Y. Li, et al., A novel Y-type two-photon active fluorophore: synthesis and appliciation in ratiometric fluorescent sensosr for fluoride anion, Dyes Pigment 77 (2008) 408-414.
[28] D.Q. Shi, H.Y. Wang, X.Y. Li, et al., Novel N,N'-diacylhydrazine-based colorimetric receptors for selective sensing of fluoride and acetate anions, Chin. J. Chem. 25 (2007) 973-976.
[29] R.G. Pearson, Hard and soft acids and bases, J. Am. Chem. Soc. 85 (1963) 3533- 3539.