luminescent molecules that only respond to defined levels
of multiple inputs.3 These elementary logic operations,
central to the functioning of electronic circuitry, can be
performed by cleverly designed organic molecules, and can
access areas inaccessible by even the smallest electronics.
Instead of using voltage inputs and outputs, molecular logic
is based on chemical inputs and a fluorescence output. A
range of fluorescent molecular logic gates (i.e., AND,
INHIBIT etc) have now been prepared with a variety of
different input types.4 However, to the best of our knowledge,
there have been no reports of fluorescent AND logic gates
with Na+ and K+ inputs that can also function as a single
ion Na+ sensor. Both Na+ and K+ are important blood
electrolytes, and their plasma concentration must be main-
tained at defined levels for normal physiological functioning.5
Fluctuations in plasma levels of Na+ and K+ (hypo-,
hypernatremia and hypo-, hyperkalemia) can be potentially
fatal if left untreated.6 Although there are many single-ion
sensors available for both Na+ and K+,7 probes that can
monitor both of these ions simultaneously are rare. Here,
we design a multifunctional tripodal Schiff base fluorescent
sensor that not only is capable of monitoring Na+ levels (at
λmax ) 355 nm) but also functions as a two-input AND logic
gate using inputs of Na+ and K+ and an emission output at
λmax ) 445 nm.
synthesis, characterization, and photophysical properties of
control compound 4 have been detailed by us in a previous
communication.8
The fluorescence spectrum of 3 was recorded in THF/H2O
(9:1) HEPES (pH 7.0) buffered solution and displayed two
main peaks with λmax ) 310 and 355 nm when excited at
270 nm (Figure 1b). The effects of cations on the fluores-
The sensor 3, a tripodal Schiff base, was formed in three
steps as shown in Scheme 1. Compound 1 was obtained from
Scheme 1. Synthesis of 3
Figure 1. (a) Bar chart reflecting changes in the relative intensity
(∆I/Io) of 3 (20 µM) at 355 nm upon the addition of metal ions
(100 µM). (b) Emission spectra of 3 (20 µM) upon addition of
increasing amounts of Na+. Solvent ) THF/H2O (9:1,v/v) HEPES
buffer solution (pH 7.0 ( 0.1). Concentrations (µM) of Na+ are
shown in the inset.
cence properties of 3were investigated by the addition of a
variety of physiological and environmentally relevant ions
as their chloride salts. A substantial fluorescence enhance-
ment was observed for sodium (Figure 1) with only minor
changes observed for the other ions. Figure 1b shows the
(4) (a) de Silva, A. P.; Vance, T. P.; West, M. E. S.; Wright, G. D.
Org. Biomol. Chem. 2008, 6, 2468–2480. (b) de Silva, A. P.; Uchiyama, S.
Nature Nanotechnol. 2007, 2, 399–410. (c) Raymo, F. M.; Giordani, S.
J. Am. Chem. Soc. 2002, 124, 2004–2007. (d) Raymo, F. M.; Alvarado,
R. J.; Giordani, S.; Cejas, M. A. J. Am. Chem. Soc. 2003, 125, 2361–2364.
(e) Tian, H.; Quin, B.; Yao, R. X.; Zhao, X. L.; Yang, S. J. AdV. Mater.
2003, 15, 2104–2107. (f) Wang, H. M.; Zhang, D. Q.; Guo, X. F.; Zhu,
L. Y.; Shuai, Z. G.; Zhu, D. B. Chem Commun. 2004, 670–671. (g)
Uchiyama, S.; Mc Clean, G. D.; Iwai, K.; de Silva, A. P. J. Am. Chem.
Soc. 2005, 127, 8920–8921. (h) Liu, Y.; Jiang, W.; Zhang, H. Y.; Li, C. J.
J. Phys. Chem. B. 2006, 110, 14231–14235. (i) de Silva, A. P.; McClena-
ghan, N. J. Am. Chem. Soc. 2000, 122, 3965–3966. (j) Andre´asson, J.; Kodis,
J.; Terazono, Y.; Liddell, P. A.; Bandyopadhyay, S.; Mitchell, R. H.; Moore,
T. A.; Moore, A. L.; Gust, D. J. Am. Chem. Soc. 2004, 126, 15926–15927.
(k) Uchiyama, S.; Kawai, N.; de Silva, A. P.; Iwai, K. J. Am. Chem. Soc.
2004, 126, 3032–3033. (l) Magri, D. C.; Brown, G. J.; McClean, G. D.; de
Silva, A. P. J. Am. Chem. Soc. 2006, 128, 4950–4951.
mesitylene after reaction with formaldehyde and a HBr/
AcOH mixture in the presence of ZnBr2. Compound 1 was
then reacted with 2-mercaptoaniline under basic conditions
to produce the amine 2, which, after a condensation reaction
with 2-hydroxynapthaldehyde gave the target compound 3
in 38.2% yield (see the Supporting Information). The
(3) deSilva, A. P.; Gunaratne, H. Q. N.; McCoy, C. P. Nature 1993,
364, 42–44.
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Org. Lett., Vol. 11, No. 11, 2009