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nm as showed in the inset (curve c) of Fig. 1A.§ This can
substantially increase the spectral overlap between the excimer
emission band of bis-pyrene and the absorption band of the ME-
pyrene 2) can “read out” three kinds of binary inputs: I1 (UV),
I2 (Zn2 or Mn or Ce ) and I3 (visible light), and “write” a
specific binary output: O1 (excimer emission at 478 nm). Based
on the above result, the truth table is constructed (see Fig. 2).
For example, when both I1 and I2 are on, and I3 is off, the input
string is 110. Under these condition, the excimer fluorescence
intensity of bis-pyrene 2 was reduced to ca. 47% of the initial
value at 478 nm. Thus the output signal is off and the digit is 0.
The entries in the truth table where I1 and I3 are 1 imply that the
sample is irradiated simultaneously with UV and visible light.
The corresponding combinational logic circuit incorporating
two logic gates is illustrated in Fig. 2.
+
2+
3+
2+
Zn complex. As a result, the energy transfer from excimer to
ME-Zn2+ complex would occur more efficiently, and the
excimer fluorescence would be quenched to some extent. This
assumption is confirmed by similar experiments with the
mixture solution of spiropyan 1 and bis-pyrene 2. As for the
pure solution of spiropyan 1, the absorption spectrum of the
mixture solution, formed by UV light irradiation followed by
2+
addition of 20 equiv. of Zn , is blue-shifted (see curve c, Fig.
A) in the range of 400–700 nm. As a result of this spectral
1
hypsochromic shift, the excimer fluorescence intensity of bis-
pyrene 2 is reduced to ca. 47% of the initial value at 478 nm
while the fluorescence intensities of the bands with maxima
shorter than 400 nm remain nearly constant (curve c, Fig. 1B).
Thus, the addition of Zn2 ion leads to opening up an efficient
pathway for the mutual interaction between pyrene excimer and
the ME form of spiropyan. When the above solution is treated
by visible light irradiation, the ME-Zn2 complex and pure ME
form are rapidly switched back to the SP form (Scheme 2). The
absorption spectrum of the mixture solution is restored (not
shown). Concomitantly, the fluorescence intensity in all
spectral region recovers to its initial value (not shown).
Therefore, the pyrene excimer fluorescence can be reversibly
switched on (ca. 100%) or off (ca. 47%) consecutively in such
a way. As an example, Fig. 2 shows several reversible cycles of
the excimer fluorescence intensity alteration at 478 nm
In summary, by taking advantage of the fact that suitable
metal ions can induce hypsochromic shift of the absorption
spectrum of ME form, the efficient energy transfer (and
intermolecular mutual communication) is realized for the
solution containing spiropyan 1 and bis-pyrene 2 together with
+
metal ion (e.g. Zn2 or Mn or Ce ) under UV light
irradiation. Consequently, the excimer fluorescnce of bis pyrene
2 can be reversibly switched on or off in the presence of
spiropyan 1 by light and metal ions.
+
2+
3+
+
Besides, the present results also demonstrate that the extent of
the excimer fluorescence quenching is dependent on what kind
of metal ions are used. Thus, the present system may be useful
in construction of new metal ion sensors in future.
The present research was financially supported by NSFC
(90101025), Chinese Academy of Sciences and State Key Basic
Research Program (G2000077505). D.-Q Zhang thanks Na-
tional Science Fund for Distinguished Young Scholars.
2+
regulated by ultraviolet light, visible light and Zn ion. Even in
the dark, the conversion of the ME-Zn2 complex and pure ME
form to the SP form can take place. Inset curve in Fig. 1B shows
the gradual intensity change of excimer fluorescence at 478 nm
of the mixture, which was first treated by UV light and then kept
in the dark.
+
Notes and references
† Spiropyran 1: d (CDCl ) 1.22 (s, 3H), 1.33 (s, 3H), 2.78 (s, 3H), 5.88 (d,
H
3
1H), 6.48 (d, 1H), 6.60 (d, 1H), 6.92 (m, 2H), 7.13 (d, 1H), 7.24 (t, 1H), 8.05
(m, 2 H). Elemental analysis: calc. for C19H18N O : H, 5.63; C, 70.79; N,
2+
Similar experiments with other metal ions including Mn ,
2 3
3
+
2+
2+
2+
3+
H 3
8.69. Found: H, 5.74; C, 70.50; N, 8.62%. Bis-pyrene 2: d (CDCl )
Ce , Ca , Ba , Cd and La reduce the excimer fluores-
cence intensity of bis-pyrene 2 to 65%, 64%, 82%, 80%, 85%,
and 87% of the initial value at 478 nm, respectively. Obviously,
1
8
.22–1.38 (m, 12H), 1.68 (m, 4H), 3.64 (t, 4H), 5.25 (s, 4H), 8.08 (m, 10H),
.20 (m, 6H), 8.42 (d, 2H). Elemental analysis: calc. for C44 : H, 7.02;
42 2
H O
C, 87.67.Found: H, 7.14; C, 87.52%.
2+
2+
3+
only three of the seven metal ions, Zn , Mn and Ce , can
effectively change the pyrene excimer fluorescence intensity. In
other words, these three metal ions have an important effect on
the efficient pathway for intermolecular energy transfer be-
tween the communicating components (the ME form of
spiropyran 1 and bis-pyrene 2) of the solution. Control
experiments were performed by injection of 20 equiv. of each
metal ion (of the seven metal ions) separately into the solution
24
25
‡
A THF solution of 1 (1.1 310 M) and 2 (2.1 310 M), and aqueous
solutions of metal halide salts (ZnCl , MnCl , CeCl , CaCl , BaCl , CdCl
and LaCl ) were prepared for the experiments. For the light irradiation
2
2
3
2
2
2
,
3
experiments, the solutions were treated by 140 W high-pressure mercury
lamp (l = 365 nm) for 2 minutes, and 2 minutes by visible light (l > 460
nm). When the sample was simultaneously irradiated by UV and visible
light, the two light sources were held by the same distance from the
sample.
§
The degree of this spectral blue-shift is dependent on the quantities of
2
5
of pure bis-pyrene 2 (2.3 3 10 M), and the results indicated
that these metal ions had negligible influence on the excimer
fluorescence.
metal ions added to the solution. For the present experiment, in order to
induce large spectral shift 20 equiv. (vs. SP) of metal ion was used.
8
The above result can be interpreted by binary logic. The
1
F. M. Raymo and S. Giordani, J. Am. Chem. Soc., 2001, 123, 4651; J. T.
C. Wojtyk, P. M. Kazmaier and E. Buncel, Chem. Commun., 1998, 1703;
M. Inouye, K. Akamatsu and H. Nakazumi, J. Am. Chem. Soc., 1997, 119,
ensemble of the interacting molecules (spiropyran 1 and bis-
9
2
4
160; J. T. C. Wojtyk, P. M. Kazmaier and E. Buncel, Chem. Mater.,
001, 13, 2547; A. N. Shipway and I. Willner, Acc. Chem. Res., 2001, 34,
21.
2
3
4
J. L. Bahr, G. Kodis, L. de la Garza, S. Lin, A. L. Moore, T. A. Moore and
D. Gust, J. Am. Chem. Soc., 2001, 123, 7124.
F. M. Raymo and S. Giordani, J. Am. Chem. Soc., 2002, 124, 2004; F. M.
Raymo and S. Giordani, Org. Lett., 2001, 3, 1833.
T. Förster and K. Kasper, Z. Phys. Chem. (Frankfurt Main), 1954, 1, 275;
T. Förster, Angew. Chem., 1969, 81, 364; T. Förster, Angew. Chem., Int.
Ed. Engl., 1969, 8, 333.
5
6
T. Saika, T. Iyoda, K. Honda and T. Shimidzu, Chem. Commun., 1992,
5
91.
Other systems using more than two types of external inputs, see: A. P. de
Silva, I. M. Dixon, H. Q. N. Gunaratne, T. Gunnlaugsson, P. R. S.
Maxwell and T. E. Rice, J. Am. Chem. Soc., 1999, 121, 1393; F. Pina, M.
Maestri and V. Balzani, Chem. Commun., 1999, 107.
Fig. 2 Demonstration of the reversible excimer fluorescence intensity
alteration, the truth table and the corresponding logic circuit. I1, I2 and I3
are UV, metal ions and visible light, respectively. The output signal (O1) is
off when the relative emission intensity at 478 nm is ca. 47% of the initial
value, and it is on when the relative intensity is ca. 100% of the initial value.
Because I3 has no influence on O1, the combinational logic circuit includes
only the two inputs: I1 and I2.
7 The fluorescence of the solution is due to bis-pyrene 2 since both SP and
ME forms do not emit in this wavelength range.
8 R. J. Mitchell, Microprocessor Systems: An Introduction; Macmillan,
London, 1995.
CHEM. COMMUN., 2003, 914–915
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