Accepted Manuscript

Novel indole based dual responsive “turn-on” chemosensor for fluoride ion de-tection

Dharmaraj Jeyanthi, Murugan Iniya, Karuppiah Krishnaveni, DuraisamyChellappa

PII: S1386-1425(14)01509-1DOI: http://dx.doi.org/10.1016/j.saa.2014.10.013Reference: SAA 12827

To appear in: Spectrochimica Acta Part A: Molecular and Biomo-lecular Spectroscopy

Received Date: 26 June 2014Revised Date: 25 July 2014Accepted Date: 8 October 2014

Please cite this article as: D. Jeyanthi, M. Iniya, K. Krishnaveni, D. Chellappa, Novel indole based dual responsive“turn-on” chemosensor for fluoride ion detection, Spectrochimica Acta Part A: Molecular and BiomolecularSpectroscopy (2014), doi: http://dx.doi.org/10.1016/j.saa.2014.10.013

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customerswe are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, andreview of the resulting proof before it is published in its final form. Please note that during the production processerrors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Novel indole based dual responsive “turn-on” chemosensor for fluoride

ion detection

Dharmaraj Jeyanthi a, Murugan Iniya a, Karuppiah Krishnaveni a and Duraisamy

Chellappa*a

a School of Chemistry, Madurai Kamaraj University, Madurai, TamilNadu-625021, India.

*Corresponding author. Tel: +91 452 2456614; Fax: +91 452 2459181.

E-mail address: dcmku123@gmail.com

Abstract

An efficient new dual channel chemosensor 2,3-bis((E)-(1H-indole-3-

yl)methyleneamino)maleonitrile (DN) which exhibits selective sensing of F- ions in DMSO, was

synthesized by a facile one step condensation reaction of indole-3-carboxaldehyde with

diaminomaleonitrile. The probe DN was characterized by elemental analysis, 1H, 13C-NMR, ESI-

MS and IR spectral techniques. Upon addition of F-, DN induces remarkable changes in both

absorption and fluorescence spectra on the basis of charge transfer mechanism. The receptor DN

serves for highly selective, sensitive detection of F- without the interference of other relevant

anions. The Job’s plot analysis indicates the binding stoichiometry to be 1:1 (host/guest).

Keywords: Dual channel; ICT mechanism; colorimetric changes

1. Introduction

Recent years witness burgeoning interest on the development of new chemosensors for

the selective recognition of anions[1-5], cations[6-10] or neutral molecules due to its crucial and

potential application in the biological, chemical, environmental, industrial and pathological

processes[11-14]. Fluoride ion is drawing a unique attention among anions because of its small

size, good basicity, high electronegativity, and tendency to form strongest H-bond with –NH or –

OH groups[15]. Fluoride ions are widely used in dental care[16] as it has ability to prevent

Osteoporosis[17], demineralization[18].

Fluorosis, arising due to over-accumulation of fluoride in the bones[19-21], has been

linked with high levels of fluoride in drinking water. High concentration of fluoride in human

body resulted in number of diseases such as urolithasis, gastric and kidney disorders[22],

Alzeimer’s disease[23], neurotransmitter biosynthesis inhibition[24]. Apart from the biological

significance, it can also act as prospective catalyst in organic and inorganic synthesis[25] and

involved in the detection of chemical warfare agents[26]. These features of fluoride have made its

detection at very low levels is of crucial importance. Among methods available anion receptors

with chromogenic and fluorogenic perturbations have several advantages due to their high

sensitivity, spectificity[27,28], low detection limit[29]; besides require no expensive

equipment[30].

Anion-selective receptors based on indoles[31], bisindole[32], carbazole[33],

nitrophenyl[34], quinine[35] and nitrobenzene/azo groups[36] moieties have been reported to

recognize the anions via H-bonding or deprotonation of protons on the receptor[37,38]. The

receptors containing the N-H fragment as the binding site for fluoride ion are frequently reported

in the literature[39,40]. Recently reported Indole-based receptors exhibited high selectivity in

their anions binding capability[41-47].

This has led to design and synthesize a new indole based sensor, 2,3-bis((1H-indol-3-

yl)methyleneamino)maleonitrile [DN] for anion recognition. The receptor was synthesized by a

simple Schiff base condensation reaction between indole-3-carboxaldehyde and

diaminomaleonitrile in good yield(Scheme 1). The receptor was systematically and fully

characterized by 1H, 13C-NMR, ESI-MS, IR and elemental analysis(Fig S1-S5, see

supplementary information). The receptor behaves as both colorimetric and fluorimetric sensor

for fluoride ions with high selectivity through H-bonding interaction between –NH protons and

fluoride anion.

2. Materials and Methods

2.1. Materials

All reagents for synthesis obtained commercially were used without further purification.

In the titration experiments, tetrabutylammonium salts were used as the anion source, stored in a

desiccator under vaccum and used without further purification. Solvents used were of

spectroscopic grade.

2.2. Instrumental methods

The NMR spectra were recorded on a Bruker(Avance) instrument operating at 300MHz

in DMSO-d6 with TMS as an internal reference. Chemical shifts were expressed in ppm and

coupling constants(J) in Hz. UV-visible absorption spectra were recorded on JASCO V-550

spectrophotometer. All fluorescence measurements were made on an F-4500 Hitachi fluorescence

spectrophotometer with slit width 5nm used for both excitation and emission. FT-IR spectra were

recorded on FT-IR spectrophotometer (8400S SHIMADZHU) in the range of 4000-400cm-1 using

KBr discs. Electrospray ionization mass spectrometry (ESI-MS) analysis was performed in the

positive ion as well as negative ion mode on a liquid chromatography-ion trap mass spectrometer

(LCQ fleet, Thermo Fischer Instruments Limited, US). Elemental analysis was carried out in a

Perkin-Elmer 4100 elemental analyzer.

2.3. Synthesis of receptor DN

An ethanolic solution of 1H-Indole-3-carboxaldehyde (1.45g, 10mmol) was added to a

solution of diaminomaleonitrile(1.08g, 10mmol) in ethanol at room temperature. The resulting

solution was heated to reflux for 5h. After the completion of reaction, the reaction mixture was

cooled to room temperature. The precipitated compound was collected, washed with EtOH and

dried. The orange solid obtained was further purified by recrystallizing from EtOH. Yield 80%. 1H NMR(300MHz, DMSO-d6, TMS): δ(ppm)= 12.10(br, 2H), 9.94(s, 2H), 8.46(d, 2H, J=7.8Hz),

8.29(s, 2H), 7.15-8.15(m, 6H); 13C NMR(75MHz, DMSO-d6, TMS): δ(ppm)= 152.9, 138.8,

137.6, 124.7, 124.5, 123.8, 123.3, 122.5, 121.9, 121.2, 118.6; IR(KBr, cm-1): υ(N-H) 3361,

υ(C=N) 1616, υ(CΞN) 2236, υ(C-H) 2925, υ(C=C) 1642; Anal. Calcd for C22H14N6: C, 72.92; H,

3.89; N, 23.19; found: C, 72.32; H, 3.56; N, 23.23; MS(ESI): 363 (M+H)+

2.4. Computational details

Density functional theory (DFT) calculations were carried out with B3LYP-6-31G and

B3LYP/LanL2DZ basis set using Gaussian 03 program package to confirm the UV-visible and

fluorescence changes upon the addition of F- anions. The TD-DFT calculations on the optimized

geometries of DN & DN.F- was performed using the above basis set in order to obtained the

electronic behavior and oscillator strength for the corresponding transitions.

3. Results and Discussion

Scheme 1

The evaluation of recognition behavior of sensor DN with various anions was primarily

investigated by UV-vis spectroscopy, color changes, fluorescence titration and 1H NMR

spectroscopy. The spectrophotometric titrations were performed in DMSO solution having a

series of anions namely AcO-, H2PO4-, HSO4

-, Cl-, Br-, I-, NO3-, SCN- and CN- as n-

tetrabutylammonium (n-Bu4N+) salts. The addition of fluoride causes conspicuous color change

from yellowish orange to red (Fig. 1); other tested anions did not induce any color change. The

UV- vis spectral response upon addition of various anions towards receptor DN was investigated.

Only F- give detectable changes in the absorption spectrum(Fig. S6). However, changes in the

absorption spectrum of DN were not observed with the addition of other anions.

Fig 1.

Fig 2.

As depicted in Fig. 2, the receptor DN exhibited an absorption band at 386nm in DMSO.

Upon stepwise addition of fluoride, a band at 348nm was decreases steadily while a new band

emerging at 456nm increased steadily in its intensity. The two prominent isobestic points at 345,

419nm during the titration indicate that a single component such as anion-receptor complex is

produced. These responses are mainly due to high electronegativity of the fluoride and its small

size than other halide ions. Thus, DN selectively detects F- over other anions colorimetrically.

Fig 3.

Furthermore, fluoride sensing performance of DN with same set of anions was also

carried out in DMSO. The fluorescence color change with F- was given in Fig. 1. As shown in the

Fig. S7, the fluorescence spectrum of DN is also interesting. Upon excitation at 375nm, the

receptor DN displayed a weak emission band at 460nm with a fluorescence quantum yield of фf=

0.021. With an incremental addition of fluoride anions to DN, an intense emission band emerged

at 493nm; Using fluorescein as standard the fluorescence quantum yield of DN in the presence

of 2equiv. of F- was found to be фf= 0.16. As with the UV-vis titrations, the fluorescence spectra

were unaltered upon the addition of other anions(Fig. 3) such as AcO-, H2PO4-, HSO4

-, Cl-, Br-, I-,

NO3-, SCN- and CN-. These experimental results suggest that DN behaves both as colorimetric

and fluorimetric sensor with high selectivity for fluoride (Fig. 4) over other competitive anions.

Fig 4.

The selective utility of the receptor DN as a fluorescent chemosensor towards F- ion was

further ascertained by performing competition experiments in the presence of other anions in

DMSO system(Fig. S8). No interference was observed from competing anions thus revealing that

the strong binding ability of the receptor with F-. From this evidence, we conclude that the

receptor DN can be used as a selective fluorescent chemosensor for F- ion in the presence of all

tested anions.

Fig 5.

To firmly prove the binding ratio of receptor DN with fluoride, continuous-variation

method was performed using fluorescence titration. This plot shows that the fluorescence

intensity reaches maximum when the mole fraction is about 0.5 indicating DN associates with

fluoride anion in 1:1 stoichiometry(Fig. 5). On the basis of Job’s method, the equilibrium

constant Ka, calculated from fluorescence titration(Fig. 6), was found to be 1.77x104M-1[48]

(ESI†) and the limit of detection for fluoride ions was determined to be 2.73x10-7M[49](ESI†).

The 1:1 binding stoichiometry was further confirmed by ESI-MS analysis. The receptor DN

shows m/z at 363 which corresponds to (M+H)+ and DN.F- shows m/z at 381.

Fig 6.

To analyze the hydrogen bonding capability of receptor DN for F-, FT-IR spectral (Fig. S9)

studies were accomplished in solid state. The free receptor exhibits the stretching frequency ν(N-

H) at 3361cm-1.When DN binds with fluoride ion, υ(N-H) shifted to higher frequency at 3417cm-1

thereby revealing the hydrogen bonding between fluoride and indole N-H. The restoration of

original color and spectrum of receptor was observed upon the addition of trace amount of protic

solvents like MeOH/H2O (Fig.7). This opines that fluoride ion prefers to have H-bonding with

polar protic solvents rather than hydrogen bonding with indole N-H and therefore gets detached

from probe DN in the presence of protic solvents.

Fig 7.

Fig 8.

Further the binding of receptor DN with TBAF was evident from the 1H NMR

experiments in DMSO-d6 at room temperature. The 1H NMR spectral changes of receptor DN

with incremental addition of fluoride anions are given in Fig. 8. The signal at 12.10 ppm can be

assigned to the –NH moiety of the probe DN. Upon addition of 0.5 equiv. of F-, the –NH signals

get downfield shift and broadened. The imine protons and aromatic protons shifted downfield

slightly. Further the addition of 1equiv. of F- resulted in the downfield shift of –NH protons with

decreasing intensity. It thus ascertains the interaction of fluoride ion with –NH protons. Based

on the above spectral confirmations, the proposed binding model for the interaction between the

receptor DN and F- is shown in Scheme 2.

Scheme 2.

3.1. DFT calculations

To examine the optical changes of DN upon fluoride ion binding mediated through H-

bonding interaction, we carried out the geometry optimization with Gaussian 03 program package

employing B3LYP-6-31G and B3LYP/LanL2DZ basis set[50]. The transition energies and

relative oscillator strength for the optimized structures(Fig. 9) were achieved at the same

calculation level on the basis of the TD-DFT. The experimentally observed spectroscopic data

can be qualitatively explained from the calculated structures and electronic properties. It revealed

that a F- anion binds with –NH protons of DN which is consistent with experimental results.

Fig 9.

For the receptor DN, both HOMO and LUMO spread over the whole molecule(Fig. S10).

For DN.F-, the HOMO resides on the whole molecule while the electron density of LUMO is

localized mainly on schiff base moieties. This in turn indicates that the binding of fluoride anion

to DN imparts charge transfer character to HOMO-LUMO transition. Furthermore, the

calculation reveals that HOMO-LUMO energy gap is reduced after fluoride binding(Fig. 10).

This could be attributed to the observed bathochromic shift in the absorption and fluorescence

spectra of DN[51] upon binding to fluoride. Further bond length measurement substantiates the

H-bonding interaction between –NH moiety and F- anions. In free DN, the optimized length of

NH(indole) bond is observed at 1.007Å. Upon binding with F- , NH bond is lengthened to

1.121Å. This in turn shows that the H-bond between –NH and F- is significantly strengthened.

Thus, DN is an excellent candidate for colorimetric and “turn-on” fluorescent chemosensor for F-

anions.

Fig 10.

4. Conclusion

In summary, we have successfully synthesized a new indole based sensor that serves as

highly selective robust dual channel sensor (colorimetric and “turn-on” fluorimetric) for fluoride

ions. The anion binding capability of the receptor DN has been substantiated by

spectrophotometric titrations, 1H NMR titrations as well as by the naked-eye detection. The

properties of DN and DN.F- were confirmed by DFT/TD-DFT calculations.

Acknowledgement

The authors D.J., M.I., K.K., are grateful to UGC-BSR for research fellowship and also

thankful to DST-IRHPA, FIST and PURSE for funding and instrumental facilities.

References

1. A.B. Descalzo, D. Jimenez, J.E. Haskouri, D. Beltran, P. Amoros, M.D. Marcos, R. Martinez-

Manez, J. Soto, Chem. Commun. (2002) 562-563.

2. T. Mizuno, W.H. Wei, L.R. Eller, J.L. Sessler, J. Am. Chem. Soc. 124 (2002) 1134-1135.

3. H. Miyaji, W. Sato, J.L. Sessler, V.M. Lynch, Tetrahedron Lett. 41 (2000) 1369-1373.

4. J.L. Sessler, H. Maeda, T. Mizuno, V.M. Lynch, H. Furuta, Chem. Commun. (2002) 862-863.

5. F. Sancenon, R. Martinez-Manez, M.A. Miranda, M.J. Segui, J. Soto, Angew. Chem. Int. Ed.

42 (2003) 647-650.

6. T. Gunnlaugsson, M. Nieuwenhuyzen, L. Richard, V. Thoss, Tetrahedron Lett. 42 (2001)

4725-4728.

7. T. Gunnlaugsson, J.P. Leonard, J. Chem. Soc. Perkin Trans. 2 (2002) 1980-1985.

8. T. Ghosh, B.G. Maiya, A. Samanta, Dalton Trans. (2006) 795-801.

9.Y. Kubo, S. Tokita, Y. Kojima, Y.T. Osano, T. Matsuzaki, J. Org. Chem. 61 (1996) 3758-3865.

10. Y. Kubo, J. Inclusion Phenom. Mol. Recognit. Chem. 32 (1998) 235-249.

11. H. Sohn, S. Letant, M.J. Sailor, W.C. Trogler, J. Am. Chem. Soc. 122 (2000) 5399-5400.

12. K.L. Kirk, Biochemistry of Halogens and Inorganic Halides, Plenum Press: New York,

(1991) pp.58

13. E. Bianchi, J.K. Bowman, E. Garcia-Espana, Supramolecular Chemistry of Anions, Eds.

Wiley-VCH: New York, 1997

14. R. Martinez-Manez, F. Sancenon, Chem. Rev. 103 (2003) 4419-4476.

15. S.V. Bhosale, M.B. Kalyankar, S.J. Langford, Org. Lett. 11 (2009) 5418-5421.

16. D. Buckland, S.V. Bhosale, S.J. Langford, Tetrahedron Lett. 52 (2011) 1990-1992.

17. a) S. Guha, S. Saha, J. Am. Chem. Soc. 132 (2010) 17674-17677; b) H. Miyaji, W. Sato, J.L.

Sessler, Angew. Chem., Int. Ed. 39 (2000) 1777-1780.

18. a) C.R. Wade, A.E.J. Broomsgrove, S. Aldridge, F.P. Gabbai, Chem. Rev. 110 (2010) 3958-

3984; b) J.M. You, H. Jeong, H. Seo, S. Jeon, Sens. Actuators B, 146 (2010) 160-164.

19. J. Shao, M. Yu, H. Lin, H.K. Lin, Specrochim. Acta A. Mol. Biomol. Spectrosc. 70 (2008)

1217-1221.

20. S. Ayoob, A.K. Gupta, Crit. Rev. Environ. Sci. Technol. 36 (2006) 433-487.

21. B. Liu, H. Tian, J. Mater. Chem. 15 (2005) 2681-2686.

22. a) K. Youngmin, FP. Gabbai, J. Am, Chem. Soc. 131 (2009) 3363-3369; b) A.E.J.

Broomsgrove, D.A. Addy, A.D. Paolo, I.R. Morgan, C. Bresner, V. Chislett, I.A. Fallis, A.L.

Thompson, D. Vidovic, S. Aldridge, Inorg. Chem. 49 (2010) 157-173.

23. J.A. Varner, K.F. Jensen, W. Horvath, R.L. Isaacson, Brain Res. 784 (1998) 284-298.

24. Y. Yu, W. Yang, Z. Dong, C. Wan, J. Zhang, J. Liu, K. Xiao, Y. Huang, B. Lu, Fluoride,

41 (2008) 134-138.

25. a) J.A. Kalow, A.G. Doyle, J. Am. Chem. Soc. 132 (2010) 3268-3269; b) M.J. Bayer, S.S.

Jalisatgi, B. Smart, A. Herzog, C.B. Knobler, M.F. Hawthorne, Angew. Chem., Int. Ed. 43

(2004) 1854-1857.

26. H. Sohn, S. Letant, M.J. Sailor, W.C. Trogler, J. Am. Chem. Soc. 122 (2000) 5399-5400.

27. H. Miyaji, J.L. Sessler, Angew. Chem., Int. Ed. 40 (2001) 154-157.

28. a) S.K. Dey, G. Das, Chem. Commun. 47 (2011) 4983-4985; b) S. Yun, H. Ihm, H.G. Kim,

C.W. Lee, B. Indrajit, K.S. Oh, Y.J. Gong, J.W. Lee, J. Yoon, H.C. Lee, K.S. Kim, J. Org.

Chem. 68 (2003) 2467-2470.

29. a) P.D. Gale, Amgew. Chem., Int. Ed. 40 (2001) 486-516; b) F.P. Schmidtchen, M. Berger,

Chem. Rev. 97 (1997) 1609-1646; c) T.S. Snowden, E.V. Anslyn, Chem. Biol. 3 (1999) 740-

746.

30. Y. Wu, M.H. Hu, Y.M. Wu, X.F. Tan, Y.Q. Zhao, Z.J. Ji, Spectrochim. Acta A, 65 (2006)

633-637.

31. a) J.O. Yu, C.S. Browning, D.H. Farrar, Chem. Commun. (2008) 1020-1022; b) C.

Caltagirone, J.R. Hiscock, M.B. Hursthouse, M.E. Light, P.A. Gale, Chem.-Eur. J. 14 (2008)

10236-10243; c) C. Caltagirone, P.A. Gale, J.R. Hiscock, S.J. Brooks, M.B. Hurthouse, M.E.

Light, Chem. Commun. ( 2008) 3007-3009; d) F.M. Pfeffer, K.F. Lim, K.J. Sedguick, J. Org.

Biomol. Chem. 5 (2007) 1795-1798.

32. a) K.J. Chang, B.N. Kang, M.H. Lee, K.S. Jeong, J. Am. Chem. Soc. 127 (2005) 12214-

12215; b) U.I. Kim, J.M. Suk, V.R. Naidu, K.S. Jeong, Chem.-Eur. J. 14 (2008) 11406-

11414; c) V.R. Naidu, M.C. Kim, J.M. Suk, H.J. Kim, M. Lee, E. Sim, K.S. Jeong, Org.

Lett. 10 (2008) 5373-5376.

33. J.M. Suk, K.S. Jeong, J. Am. Chem. Soc. 130 (2008) 11868-11869; b) J.R. Hiscock, C.

Caltagirone, M.E. Light, M.B. Hursthouse, P.A. Gale, Org. Biomol. Chem. 7 (2009) 1781-

1783; c) M.J. Chmielewski, L.Y. Zhao, A. Brown, D. Curiel, M.R. Sambrook, A.L.

Thompson, S.M. Santos, V. Felix, J.J. Davis, P.D. Beer, Chem. Commun. (2008) 3154-3156;

d) P.V. Piatek, M. Lynch, J.L. Sessler, J. Am. Chem. Soc. 126 (2004) 16073-16076; e) M.J.

Chmielewski, M. Charon, J. Jurczak, Org. Lett. 6 (2004) 3501-3504.

34. a) E.J. Cho, B.J. Ryu, Y.J. Lee, K.C. Nam, Org. Lett. 7 (2005) 2607-2609; b) M. Boiocchi,

L.D. Boca, D. Esteban-Gomez, L. Fabbrizzi, M. Licchelli, E. Monzani, J. Am. Chem. Soc.

126 (2004) 16507-16514; c) J.Y. Kwon, Y.J. Jang, S.K. Kim, K.H. Lee, J.S. Kim, J. Yoon, J.

Org. Chem. 69 (2004) 5155-5157; d) C.B. Black, B. Andrioletti, A.C. Try, C. Ruiperez, J.L.

Sessler, J. Am. Chem. Soc. 121 (1999) 10438-10439.

35. A. Das, B. Ganguly, D.K. Kumar, D.A. Jose, Org. Lett. 6 (2004) 3445-3448; b) D. Jimenez,

R. Martinez-Manez, F. Sancenon, J. Soto, Tetrahedron Lett. 43 (2002) 2823-2825.

36. a) D.H. Lee, J.H. Im, S.V. Son, Y.K. Chung, J.I. Hong, J. Am. Chem. Soc. 125 (2003) 7752-

7753; b) F. Sancenon, R. Martinez-Manez, J. Soto, Angew. Chem., Int. Ed. 41 (2002) 1416-

1418; c) D.H. Lee, K.H. Lee, J.I. Hong, Org. Lett. 3 (2001) 5-8.

37. a) M. Wenzel, J.R. Hiscock, P.A. Gale, Chem. Soc. Rev. 41 (2012) 480-520; b) P.A. Gale,

Chem. Soc. Rev. 39 (2010) 3746-3771; c) C. Caltagirone, P.A. Gale, Chem. Soc. Rev. 38

(2009) 520-563; d) P.A. Gale, S.E. Garcia-Garrido, J. Garric, Chem. Soc. Rev. 37 (2008) 151-

190.

38. a) P.A. Gale, Chem. Commun. 47 (2011) 82-86; b) M. Cametti, K. Rissanen, Chem.

Commun. (2009) 2809-2829.

39. A.F. Li, J.H. Wang, F. Wang, Y.B. Jiang, Chem. Soc. Rev. 39 (2010) 3729-3745.

40. a) S. Devaraj, D. Saravanakumar, M. Kandaswamy, Supramol. Chem. 21 (2009) 717-723; b)

S. Goswami, R. Chakrabarty, Eur. J. Chem. 2 (2011) 410-415; c) X. Bao, Y. Zhou, B. Song,

Sens. Actuat. B, 171 (2012) 550-555.

41. P.A. Gale, Chem. Commun. (2008) 4525-4540.

42. M. Lee, J. Hun Moon, K.M.K. Swamy, Y. Jeong, G. Kim, J. Choi, J. Yong Lee, J. Yoon,

Sens. Actuat. B, 199 (2014) 369-376.

43. Y. Zhou, J. Feng Zhang, J. Yoon, Chem. Rev. 114 (2014) 5511-5571.

44. Z. Guo, N.R. Song, J. Hun Moon, M. Kim, E. Jin Jun, J. Choi, J. Yong Lee, C.W. Bielawski,

J.L. Sessler, J. Yoon, J. Am. Chem. Soc. 134 (2012) 17846-17849.

45. Z. Xu, N. Jiten Singh, S. Kyung Kim, D.R. Spring, K.S. Kim, J. Yoon, Chem. Eur. J. 17

(2011) 1163-1170.

46. H. Sung Jung, H. Jung Kim, J. Vicens, J. Seung Kim, Tetrahedron Lett. 50 (2009) 983-987.

47. J. Feng Zhang, C. Su Lim, S. Bhuniya, B. Rae Cho, J. Seung Kim, Org. Lett. 13 (2011) 1190-

1193.

48. K.A. Connors, Binding Constants: The measurement of molecular complex stability; Wiley,

New York, (1987) pp. 25-28

49. M. Shortreed, R. Kopelman, M. Kuhn, B. Hoyland, Anal. Chem. 68 (1996) 1414-1418.

50. M.J. Frisch et al., Gaussian, Inc., Wallingford, Ct, 2004.

51. G.Y. Li, G.J. Zhao, Y.H. Liu, K.L. Han, G.Z. He, J. Comput. Chem. 31 (2010) 1759-1765.

Figure captions

Scheme 1. The synthetic route of receptor DN

Fig 1. Color changes(a) and fluorescence responses(b) of the receptor DN in DMSO (1x10-

5M), A=Free receptor, B=receptor with F-

Fig 2. UV-vis titration of receptor DN (10µM) towards various concentrations of F- (0-2

equivalents) in DMSO solution at 298K

Fig 3. Changes of emission spectrum of receptor DN (10µM) in DMSO after the addition of

different anions in TBA salt form (2 equivalents). Excitation was at 375nm. Slit width =

5nm/5nm

Fig 4. Bar diagram indicating the selective recognition of F- (2 equivalents) over other

anions by fluorescence responses

Fig 5. Job’s plot for the reaction between receptor DN & TBAF in DMSO by the continuous

variation method

Fig 6. Plot of changes of fluorescence intensity at 493nm with various concentrations of

fluoride ions

Fig 7. Fluorescence responses of DN to F- and with H2O, MeOH at 25˚C in DMSO system.

Excitation at 375nm (slit: 5nm)

Fig 8. 1H NMR spectra of receptor DN upon the addition of F-(TBA salts) in DMSO-d6

Scheme 2. The proposed host-guest binding mode of sensor DN with fluoride anions

Fig 9. Optimized structures of (a) DN & (b) DN.F-. The red and blue spheres refer to H and

F respectively

Fig 10. Frontier molecular orbitals of receptor DN and DN.F- obtained from DFT

calculations using Gaussian 03 program

Figures

Scheme 1. The synthetic route of receptor DN

Fig 1. Color changes(a) and fluorescence responses(b) of the receptor DN in DMSO (1x10-

5M), A=Free receptor, B=receptor with F-

Fig 2. UV-vis titration of receptor DN (10µM) towards various concentrations of F- (0-2

equivalents) in DMSO solution at 298K

Fig 3. Changes of emission spectrum of receptor DN (10µM) in DMSO after the addition of

different anions in TBA salt form (2 equivalents). Excitation was at 375nm. Slit width =

5nm/5nm

Fig 4. Bar diagram indicating the selective recognition of F- (2 equivalents) over other

anions by fluorescence responses

Fig 5. Job’s plot for the reaction between receptor DN & TBAF in DMSO by the continuous

variation method

Fig 6. Plot of changes of fluorescence intensity at 493nm with various concentrations of

fluoride ions

Fig 7. Fluorescence responses of DN to F-, F- with H2O/MeOH at 25˚C in DMSO system. Excitation at 375nm (slit width: 5nm)

Fig 8. 1H NMR spectra of receptor DN upon the addition of F-(TBA salts) in DMSO-d6

Scheme 2. The proposed host-guest binding mode of sensor DN with fluoride anions

(a) (b)

Fig 9. Optimized structures of (a) DN & (b) DN.F-. The red and blue spheres refer to H and

F respectively

Fig 10. Frontier molecular orbitals of receptor DN and DN.F- obtained from DFT

calculations using Gaussian 03 program

Graphical Abstract

Highlights

• The receptor DN was synthesized by a simple method with high yield

• The detection limit of F- by DN was very low (2.73x10

-7M)

• The reversible behavior of the receptor DN towards F- was studied

• The remarkable red shift fluorescence spectra was further supported by DFT

calculations