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did not change. However, the fluorescence emission intensities of 1
displayed about twofold increase after the addition of 2 equiv of
Zn2+ (perchlorate salt) and 40 equiv of each cation (Fig. S4). There-
fore, 1 can selectively detect Zn2+ ion in the presence of excess al-
kali metal ions under physiological conditions. The selectivity for
Zn2+ is due to the high affinity of Zn2+ for three nitrogen atoms
of the Dpa unit.
In conclusion, we have developed naphthalimide-based fluores-
cent chemosensors 1–3 which exhibit fluorescence enhancement
upon binding with Zn2+ ions in 10 mM HEPES buffer (pH 7.4) at
25 °C. Chemosensors 1–3 exhibited a different fluorescence emis-
sion response according to the length of the spacer between the
donor (nitrogen lone pair electrons of the Dpa moiety) and accep-
tor (naphthalimide); the longer the linker length of chemosensors
is, the less efficient the PET process becomes. As a result, 1 (n = 1)
shows the highest PET efficiency, high selectivity, and sensitivity
for Zn2+ over other transition metal ions and alkali metal ions in
water.
8. (a) Ramachandram, B.; Saroja, G.; Sankaran, N.; Samanta, A. J. Phys. Chem. B
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H.-Y.; Guo, Q.-X. Chin. J. Chem. 2006, 24, 1230–1237. In the above papers, the
highest PET efficiency was observed for systems where the fluorophore and the
metal ion binding moiety are separated by two methylene groups..
9. Wang, J.; Xiao, Y.; Zhang, Z.; Qian, X.; Yang, Y.; Xu, Q. J. Mater. Chem. 2005, 15,
2836–2839.
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Gusella, J. F.; Beyreuther, K.; Masters, C. L.; Tanzi, R. E. Science 1994, 265, 1464–
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2002, 124, 10650–10651; (b) Kiyose, K.; Kojima, H.; Urano, Y.; Nagano, T. J. Am.
Chem. Soc. 2006, 128, 6548–6549; (c) Woodroofe, C. C.; Lippard, S. J. J. Am.
Chem. Soc. 2003, 125, 11458–11459; (d) Nolan, E. M.; Ryu, J. W.; Jaworski, J.;
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5758.
16. NIEDPA (1) To a solution of compound 6 (300 mg, 0.99 mmol) in MeCN were
added successively Cs2CO3 (355 mg, 1.09 mmol), KI (181 mg, 1.09 mmol), and
di-2-picolylamine (217 mg, 1.09 mmol). The reaction mixture was stirred at
40 °C overnight, and then all the volatile components were evaporated. The
residue was partitioned between CH2Cl2 and brine (Â2). The combined organic
phase was washed with water, and then dried in anhydrous Na2SO4. Flash
Acknowledgments
This work was supported by the KRF (2008-312-C00206) and
Seoul R&BD. S.Y.K. is grateful to the Ministry of Education for the
award of the BK 21 fellowship.
chromatographic purification (CH2Cl2 to CH2Cl2/MeOH = 20:1) yielded
1
(220 mg, 53% yield). 1H NMR (300 MHz, acetone-d6): d 2.89 (t, J = 6 Hz, 2H),
3.84 (s, 4H), 4.37 (t, J = 6 Hz, 2H), 7.02 (t, J = 5.4 Hz, 2H), 7.27 (t, J = 7.3 Hz, 2H),
7.35 (d, J = 7.7 Hz, 2H), 7.87 (t, J = 7.7 Hz, 2H), 8.33 (d, J = 4.3 Hz, 2H), 8.42–8.49
(m, 4H). 13C NMR (75 MHz, acetone-d6): d 37.48, 51.53, 60.07, 121.61, 122.51,
122.90, 127.04, 128.01, 130.66, 131.84, 133.95, 135.70, 148.61, 159.86, 163.54.
HRMS (FAB): m/e calcd for C26H22N4O2 [M+H]+: 423.1821, found: 423.1821.
NIPDPA (2) 2 was similarly prepared using the same procedure as used in the
synthesis of 1 (56% yield). 1H NMR (300 MHz, acetone-d6): d 1.98 (t, J = 7.0 Hz,
2H), 2.67 (t, J = 6.9 Hz, 2H), 3.83 (s, 4H), 4.18 (t, J = 7.6 Hz, 2H), 7.13 (t,
J = 11.7 Hz, 2H), 7.62–7.70 (m, 4H), 7.80 (t, J = 7.8 Hz, 2H), 8.34 (d, J = 8.2 Hz,
2H), 8.41 (d, J = 4.7 Hz, 2H), 8.46 (d, J = 7.3 Hz, 2H). 13C NMR (75 MHz, acetone-
Supplementary data
Supplementary data (synthesis, 1H NMR, 13C NMR and HRMS
data for chemosensors 1–3, fluorescence emission spectra of 2, 3
for various transition metal ions, I/I0 ratios and FE values of 1–3,
competition experiments for excess alkali metal ions, Job’s plot)
associated with this article can be found, in the online version, at
d6):
130.56, 131.73, 133.89, 136.07, 148.89, 159.97, 163.51. HRMS (FAB): m/e calcd
for C26H22N4O2 [M+H]+: 423.1821, found: 423.1821. NIBDPA (3)
was
d 25.50, 38.32, 51.46, 59.87, 121.76, 122.72, 122.84, 126.95, 127.87,
3
References and notes
similarly prepared using the same procedure as used in the synthesis of 1
(53% yield). 1H NMR (300 MHz, acetone-d6): d 1.67–1.79 (m, 4H), 2.06 (t,
J = 4.3 Hz, 2H), 3.83 (s, 4H), 4.12 (t, J = 7.1 Hz, 2H), 7.17 (t, J = 5.7 Hz, 2H), 7.62–
7.73 (m, 4H), 7.86 (t, J = 7.8 Hz, 2H), 8.39–8.45 (m, 4H), 8.53 (d, J = 7.2 Hz, 2H).
13C NMR (75 MHz, acetone-d6): d 24.76, 25.71, 39.77, 53.92, 60.24, 121.79,
122.63, 122.69, 126.93, 127.79, 130.56, 131.65, 133.87, 136.19, 148.70, 160.11,
163.48. HRMS (FAB): m/e calcd for C27H24N4O2 [M+H]+: 437.1978, found:
437.1972.
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