Fluorescent Molecular Sensors
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2H), 4.40 (s, 4H), 4.15 (s, 4H), 4.14–4.10 (m, 8H), 1.24–1.20 ppm (m,
12H).
129.0, 127.0, 125.7, 111.1, 103.6, 60.6, 55.9, 55.8, 41.3, 41.2 ppm; HRMS
(ES+): m/z: calcd: 630.2888 [M+H+]; found: 630.2880.
Sensor AS3: Sensor AS3 was obtained as a light-yellow solid (79%).
M.p. 148.3–149.58C; 1H NMR (400 MHz, D2O, 25 8C): d=7.82 (d, J=
8.4 Hz, 2H), 7.50 (d, J=8.4 Hz, 2H), 7.31 (s, 1H), 7.29 (s, 1H), 4.20 (s,
4H), 4.12 (s, 4H), 3.55–3.50 (m, 8H), 3.30–3.25 ppm (m, 8H); 13C NMR
(100 MHz, D2O, 25 8C): d=172.5, 160.8, 147.1, 142.4, 141.0, 136.2, 132.6,
129.4, 126.8, 118.6, 112.9, 111.7, 103.8, 59.9, 55.7, 41.3, 41.2 ppm; HRMS
(ES+): m/z: calcd [M+Na+]: 677.2659; found: 677.2657.
Compound 3: Compound 2 (1 g, 1.7 mmol) was dissolved in dry THF
(100 mL) containing Pd/C (1 g, 5%) and cyclohexene (20 mL), and the
mixture was stirred and refluxed under nitrogen for 2 h. Then the Pd/C
was removed by filtration and the filtrate was concentrated under
vacuum. The product was purified by flash chromatography using
hexane/ethyl acetate (7:3) as the eluent, affording 3 (0.81 g, 1.63 mmol,
96%) as a red oil. 1H NMR (400 MHz, CDCl3, 258C): d=10.72 (s, 1H),
7.83 (s, 1H), 6.55 (s, 1H), 4.47 (s, 4H), 4.20–4.11 (overlapped, 12H),
1.27–1.23 ppm (m, 12H).
Compound 4: Compound 3 (0.6 g, 1.21 mmol) was dissolved in dichloro-
methane (5 mL) and acetic acid (50 mL). Zn powder (4 g, 62.5 mmol)
was added to this solution and the mixture was stirred at room tempera-
ture for 5 min. The unreacted Zn was removed by filtration and the fil-
trate was poured into dichloromethane (200 mL). The organic solution
was extracted three times with water (200 mL) to remove the acetic acid
and dried over sodium sulfate for 5 min. Note: product 4 was not charac-
terized because of its easy oxidation and was used directly in the follow-
ing reaction.
Acknowledgements
This work was supported by the National Natural Science Foundation of
China and the National Key Project for Basic Research
(2003CB 114400). We thank the referees for their smart and pertinent
comments; some discussions originate from their comments. We also
thank Dr. A. Wu and Dr. K. Bathula for valuable discussions.
Compound 5: 4-Dimethylaminobenzaldehyde (0.3 g, 2 mmol) was added
[1] For a recent book and reviews on fluorescent molecular sensors see:
a) B. Valeur, Molecular Fluorescence: Principles and Applications,
Wiley-VCH, Weinheim, 2001; b) A. P. de Silva, H. Q. N. Gunaratne,
T. Gunnlaugsson, A. J. M. Huxley, C. P. McCoy, J. T. Rademacher,
T. E. Rice, Chem. Rev. 1997, 97, 1515; c) D. T. McQuade, A. E.
Pullen, T. M. Swager, Chem. Rev. 2000, 100, 2537; d) R. Martínez-
MµÇez, F. Sancenón, Chem. Rev. 2003, 103, 4419; e) L. Pu, Chem.
Rev. 2004, 104, 1687.
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Chem. Soc. 2005, 127, 10197; b) E. Sasaki, H. Kojima, H. Nishimat-
su, Y. Urano, K. Kikuchi, Y. Hirata, T. Nagano, J. Am. Chem. Soc.
2005, 127, 3284.
[3] C. J. Chang, J. Jaworski, E. M. Nolan, M. Sheng, S. J. Lippard, Proc.
Natl. Acad. Sci. USA 2004, 101, 1129.
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Fahrni, Proc. Natl. Acad. Sci. USA 2005, 102, 11179.
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Cornelissen, A. E. Rowan, R. J. M. Nolte, Chem. Rev. 2005, 105,
1445.
[6] Y. Wan, H. Yang, D. Zhao, Acc. Chem. Res. 2006, 39, 423.
[7] Very recently, surfactants have been exploited in fluorescent molec-
ular sensing: a) K. Niikura, E. V. Anslyn, J. Org. Chem. 2003, 68,
10156; b) A. Mallick, M. C. Mandal, B. Haldar, A. Chakrabarty, P.
Das, N. Chattopadhyay, J. Am. Chem. Soc. 2006, 128, 3126; c) Y.
Zhao, Z. Zhong, Org. Lett. 2006, 8, 4715.
to the above dichloromethane solution (70 mL) of compound
4
(ꢁ0.4 mmol). The solvent was evaporated under vacuum to obtain a
brown oil and dry benzene (50 mL) was added. The solution was refluxed
under
a nitrogen atmosphere for 20 min. After this time, BaMnO4
(0.31 g, 1.2 mmol) was added after slight cooling and the solution was re-
fluxed again for another 20 min, cooled, and concentrated under vacuum.
The residue was purified by flash chromatography by using hexane/ethyl
acetate (7:3) as the eluent, affording 5 (0.12 g, 0.19 mmol, 48%) as a
light-yellow solid. M.p. 78.2–79.68C; 1H NMR (400 MHz, CDCl3, 258C):
d=8.03 (d, J=8.8 Hz, 1H), 7.39 (s, 1H), 7.28 (s, 1H), 6.76 (d, J=8.8 Hz,
2H), 4.37 (s, 4H), 4.31 (s, 4H), 4.14–4.09 (m, 8H), 3.06 (s, 6H), 1.19 ppm
(t, J=5.6 Hz, 12H); 13C NMR (100 MHz, CDCl3, 258C): d=170.9, 164.0,
152.1, 147.0, 139.7, 139.6, 138.2, 128.7, 114.7, 111.6, 111.4, 103.3, 60.6,
60.5, 53.2, 40.1, 14.2, 14.1 ppm.
Compound 6: Compound 6 was obtained as a light-yellow solid (52%).
M.p. 73.1–74.88C; 1H NMR (400 MHz, CDCl3, 258C): d=8.18–8.16 (m,
2H), 7.50–7.49 (m, 3H), 7.47 (s, 1H), 7.34 (s, 1H), 4.39 (s, 4H), 4.33 (s,
4H), 4.15–4.09 (m, 8H), 1.22 ppm (t, J=5.6 Hz, 12H); 13C NMR
(100 MHz, CDCl3, 258C): d=170.8, 170.7, 162.5, 147.3, 140.9, 140.1,
137.7, 131.0, 128.8, 127.4, 127.2, 112.2, 103.6, 60.6, 60.5, 53.2, 53.1, 14.2,
14.1 ppm.
Compound 7: Compound 7 was obtained as a yellow solid (57%). M.p.
89.6–90.58C; 1H NMR (400 MHz, CDCl3, 258C): d=8.26 (d, J=8.2 Hz,
2H), 7.78 (d, J=8.2 Hz, 2H), 7.50 (s, 1H), 7.34 (s, 1H), 4.41 (s, 4H), 4.34
(s, 4H), 4.15–4.10 (m, 8H), 1.21 ppm (t, J=7.0 Hz, 12H); 13C NMR
(100 MHz, CDCl3, 258C): d=171.3, 161.2, 148.2, 142.7, 141.2, 138.1,
133.3, 132.0, 128.1, 118.9, 114.7, 113.3, 104.2, 61.4, 61.3, 53.7, 14.8 ppm.
[8] For microscopic polarity of the SDS micelle see: K. Kano, Y. Ueno,
S. Hashimoto, J. Phys. Chem. 1985, 89, 3161.
[9] S. Uchiyama, G. D. McClean, K. Iwai, A. P. de Silva, J. Am. Chem.
Soc. 2005, 127, 8920.
Sensor AS1: Compound 5 (80 mg, 0.13 mmol) was dissolved in acetoni-
trile (10 mL) and 2-aminoethanol (10 mL) was added. The solution was
refluxed under nitrogen for 2 h, then cooled and concentrated under
vacuum to remove the acetonitrile and 2-aminoethanol separately. The
product was purified by flash chromatography using methanol/ammonia/
dichloromethane (20:2:100) as the eluent, affording AS1 (72 mg,
0.11 mmol, 85%) as a light-yellow solid. M.p. 135.5–136.98C; 1H NMR
(400 MHz, D2O, 25 8C): d=7.60 (d, J=8.8 Hz, 2H), 7.27 (s, 1H), 7.23 (s,
1H), 6.48 (brs, 2H), 4.09 (s, 4H), 4.05 (s, 4H), 3.57–3.52 (m, 8H), 3.28–
3.24 (m, 8H), 2.63 ppm (s, 6H); 13C NMR (100 MHz, D2O, 25 8C): d=
172.5, 164.6, 152.5, 146.8, 140.3, 140.2, 137.1, 128.6, 112.6, 111.7, 110.5,
103.5, 59.9, 56.3, 56.2, 41.3, 41.2, 39.2 ppm; HRMS (ES+): m/z: calcd:
673.3310 [M+H+]; found: 673.3315.
[10] We recently demonstrated that polyamide receptors could selective-
ly bind Hg2+ ions in neutral aqueous solution: a) J. Wang, X. Qian,
Chem. Commun. 2006, 109; b) J. Wang, X. Qian, J. Cui, J. Org.
Chem. 2006, 71, 4308; c) J. Wang, X. Qian, Org. Lett. 2006, 8, 3721.
[11] A closely related FSM with typical D–A–D1 constitution using the
benzothiazole fluorophore has been reported: K. Rurack, A. Kovalꢁ-
chuck, J. L. Bricks, J. L. Slominskii, J. Am. Chem. Soc. 2001, 123,
6205.
[12] Like the parent compound 2-phenylbenzoxazole, in AS1–3 the 2-
phenyl ring should be electronically conjugated and coplanar with
the benzoxazole moiety (energy-minimized molecular structure cal-
culated with the Hyperchem software). This notion is supported by
the 1H NMR spectroscopic studies: Hg2+-ion complexation results
in a significant downfield shift of the aromatic protons of the 2-
phenyl ring (see the Supporting Information): J. C. del Valle, M.
Kasha, J. Catalµn, J. Phys. Chem. A 1997, 101, 3260.
AS2 and AS3 were prepared similarly to AS1.
Sensor AS2: Sensor AS2 was obtained as a light-yellow solid (87%).
M.p. 123.7–124.88C; 1H NMR (400 MHz, D2O, 25 8C): d=7.94 (d, J=
8.4 Hz, 2H), 7.48–7.41 (m, 3H), 7.34 (s, 1H), 7.32 (s, 1H), 4.20 (s, 4H),
4.13 (s, 4H), 3.58–3.53 (m, 8H), 3.33–3.29 ppm (m, 8H); 13C NMR
(100 MHz, D2O, 25 8C): d=172.5, 163.5, 147.1, 141.1, 140.1, 136.5, 131.8,
[13] A D1!A transition is expected to absorb light around 350 nm,
judged from the absorption of the parent chromophore 2-(4’-N,N-di-
methylamino)phenylbenzoxazole: E. M. Vernigor, E. A. Lukyanets,
Chem. Eur. J. 2007, 13, 7543 – 7552
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