Signal processing at the molecular level [26]

Full text of DOI:10.1021/ja005699n

J. Am. Chem. Soc. 2001, 123, 4651-4652
Signal Processing at the Molecular Level
4651
Fran c¸ isco M. Raymo* and Silvia Giordani
Center for Supramolecular Science
Department of Chemistry, UniVersity of Miami
301 Memorial DriVe, Coral Gables Florida 33146-0431
1
ReceiVed October 16, 2000
ReVised Manuscript ReceiVed February 6, 2001
Human sensory receptors transduce chemical, light, mechanical,
and thermal stimulations into nerve impulses, which are transmit-
1
ted to the brain. This sequence of events involves a concatenation
of processes at the molecular level. At each step, input signals of
one form are converted into output signals of another. This
complex mechanism is related conceptually to the manipulation
2
of binary data in microprocessor systems. The data introduced
into a computer are elaborated through a sequence of logic
operations and converted in a specific output. In modern
microprocessor systems, logic circuits are built integrating
electronic devices. However, they could be fabricated combining
mechanical, pneumatic, or other types of devices, including
Figure 1. The switching cycle associated with the three states SP, ME,
and MEH.
3
molecular-sized switches.
Molecules able to perform simple logic operations are known.4-6
Reliable and efficient methods to integrate organic compounds
into simple circuits are starting to be developed.7-10 The fabrica-
tion of nanoscaled logic circuits incorporating sequences of
molecular switches can be envisaged. The resulting artificial
systems will be able to reproduce the functions of their natural
counterparts by detecting, elaborating, and transmitting signals
at the molecular level. Their development requires first a
fundamental understanding of the behavior of individual molecules
in response to environmental stimulations. It is necessary to
(
1) Wasserman, P. D. Neural Computing: Theory and Practice; Van
Nostrand Reinhold: New York, 1989.
2) Mitchell, R. J. Microprocessor Systems: An Introduction; Macmillan:
(
London, 1995.
(
3) Special issue on “Photochromism: Memories and Switches”, Chem.
ReV. 2000, 100, 1683-1890.
-
4
Figure 2. The absorption spectra of (a) a solution of SP (1.0 × 10 M,
(
4) (a) de Silva, A. P.; Gunaratne, H. Q. N.; McCoy, C. P. Nature 1993,
3
64, 42-44. (b) de Silva, A. P.; Gunaratne, H. Q. N.; McCoy, C. P. J. Am.
MeCN, 25 °C) and of the same solution after the consecutive (b)
Chem. Soc. 1997, 119, 7891-7892. (c) de Silva, A. P.; Dixon, I. M.;
Gunaratne, H. Q. N.; Gunnlaugsson, T.; Maxwell, P. R. S.; Rice, T. E. J. Am.
Chem. Soc. 1999, 121, 1393-1394. (d) de Silva, A. P.; McClenaghan, N. D.
J. Am. Chem. Soc. 2000, 122, 3965-3966.
irradiation with ultraviolet light, (c) addition of 1 equiv of CF
3 2
CO H,
and (d) irradiation with visible light.
(5) (a) Asakawa, M.; Ashton, P. R.; Balzani, V.; Credi, A.; Mattersteig,
establish how (1) ultraminiaturized switches can be addressed
precisely from the macroscopic level, (2) they can elaborate such
input signals, and (3) they can transmit their response in the shape
of measurable output signals. We have designed, synthesized, and
investigated a three-state molecular switch. This relatively simple
system combines light and chemical stimuli transducing them into
optical outputs through a complex sequence of logic operations.
The spiropyran derivative SP was synthesized in three steps,
starting from 2,3,3-trimethyl-3H-indole. Light and chemical
stimulations induce the switching of SP (Figure 1) to the
merocyanine forms ME and MEH. The differences in the
absorption and emission properties of the three states can be
exploited to follow anticlockwise (Figure 2) and clockwise (Figure
3) switching cycles starting and ending with SP.
G.; Matthews, O. A.; Montalti, M.; Spencer, N.; Stoddart, J. F.; Venturi, M.
Chem. Eur. J. 1997, 3, 1992-1996. (b) Credi, A.; Balzani, V.; Langford, S.
J.; Stoddart, J. F. J. Am. Chem. Soc. 1997, 119, 2679-2681.
(6) (a) Pina, F.; Roque, A.; Melo, M. J.; Maestri, I.; Belladelli, L.; Balzani,
V. Chem. Eur. J. 1998, 4, 1184-1191. (b) Pina, F.; Maestri, M.; Balzani, V.
Chem. Commun. 1999, 107-114. (b) Roque, A.; Pina, F.; Alves, S.; Ballardini,
R.; Maestri, M.; Balzani, V. J. Mater. Chem. 1999, 9, 2265-2269. (i) Pina,
F.; Melo, M. J.; Maestri, M.; Passaniti, P.; Balzani, V. J. Am. Chem Soc.
2
000, 122, 4496-4498.
7) Bard, A. J. Integrated Chemical Systems: a Chemical Approach to
Nanotechnology; Wiley: New York, 1994.
8) (a) Metzger, R. M.; Chen, B.; Hopfner, U.; Lakshmikantham, M. V.;
(
(
Vuillaume, D.; Kawai, T.; Wu, X.; Tachibana, H.; Hughes, T. V.; Sakurai,
H.; Baldwin, J. W.; Hosch, C.; Cava, M. P.; Brehmer, L.; Ashwell, G. J. J.
Am. Chem. Soc. 1997, 119, 10455-10466. (b) Metzger, R. M. Acc. Chem.
Res. 1999, 32, 950-957. (c) Metzger, R. M. J. Mater. Chem. 1999, 9, 2027-
2
036. (d) Metzger, R. M. J. Mater. Chem. 2000, 10, 55-62.
(
9) (a) Zhou, C.; Deshpande, M. R.; Reed, M. A.; Jones, L., II; Tour, J.
The absorption spectrum of a colorless solution of SP (Figure
M. Appl. Phys. Lett. 1997, 71, 611-613. (b) Reed, M. A.; Zhou, C.; Muller,
C. J.; Burgin, T. P.; Tour, J. M. Science 1997, 278, 252-254. (c) Chen, J.;
Reed, M. A.; Rawlett, A. M.; Tour, J. M. Science 1999, 286, 1550-1552.
2a) does not show bands at wavelengths greater than 400 nm.
Upon irradiation of this solution with ultraviolet light, the colorless
(10) (a) Collier, C. P.; Wong, E. W.; Belohradsky, M.; Raymo, F. M.;
11
SP switches to the purple ME. The appearance of an absorption
Stoddart, J. F.; Kuekes, P. J.; Williams, R. S.; Heath, J. R. Science 1999,
85, 391-394. (b) Asakawa, M.; Higuchi, M.; Mattersteig, G.; Nakamura,
T.; Pease, A. R.; Raymo, F. M.; Shimizu, T.; Stoddart, J. F. AdV. Mater. 2000,
2, 1099-1102. (c) Wong, E. W.; Collier, C. P.; Belohradsky, M.; Raymo,
F. M.; Stoddart, J. F.; Heath, J. R. J. Am. Chem. Soc. 2000, 122, 5831-5840.
d) Collier, C. P.; Mattersteig, G.; Wong, E. W.; Beverly, K.; Sampaio, J.;
Raymo, F. M.; Stoddart, J. F.; Heath, J. R. Science 2000, 289, 1172-1175.
band at 563 nm (Figure 2b) and an emission band at 647 nm
2
accompanies this process.12 Upon addition of 1 equiv of
1
3 2
CF CO H, the purple ME switches completely to the yellow-
green MEH. Consistently, the absorption band at 563 nm and
the emission band at 647 nm disappear. An absorption band at
(
1
0.1021/ja005699n CCC: $20.00 © 2001 American Chemical Society
Published on Web 04/24/2001

4652 J. Am. Chem. Soc., Vol. 123, No. 19, 2001
Communications to the Editor
Table 1. Truth Table for the Three-State Molecular Switch Where
a 0 Indicates That the Corresponding Signal Is Off and a 1 That It
Is On
-
5
Figure 3. The emission spectra of (a) a solution of SP (1.0 × 10 M,
MeCN, 25 °C, λexc. ) 563 nm) and of the same solution after the
consecutive (b) addition of 1 equiv of CF
3 2
CO H, (c) treatment with
K
2
CO , and (d) irradiation with visible light.
3
4
01 nm is observed instead (Figure 2c). This band disappears
Figure 2d) when the solution is irradiated with visible light,13 as
MEH switches completely to SP closing the anticlockwise cycle.
Upon addition of 1 equiv of CF CO H to a colorless solution
(
Figure 4. The logic circuit equivalent to the three-state molecular switch
transduces the inputs I1-I3 into the outputs O1 and O2 through AND,
NOT, and OR operations.
3
2
of SP maintained in the dark, SP switches to the yellow-green
MEH. The appearance of a band at 401 nm in the absorption
spectrum accompanies this process. However, no emission bands
are detected before and after acidification (Figure 3a and b).
1
or 0. Thus, the molecular switch reads a string of three binary
inputs and writes a specific combination of two binary outputs.
For example, when the three stimulations I1-I3 are all off, the
input string is 000. Under these conditions, the molecular switch
is in state SP, which does not have absorption bands at
wavelengths greater than 400 nm. As a result, the two output
signals O1 and O2 are off and the output string is 00. If the
14
2 3
Treatment of a yellow-green solution of MEH with K CO is
followed by the formation of a purple color.15 Under these
conditions, MEH switches completely to ME. An absorption band
at 563 nm and an emission band at 647 nm (Figure 3c) appear.
The purple ME switches completely to the colorless SP, closing
the clockwise cycle, when the solution is either irradiated with
visible light or stored in the dark. The disappearance of the
absorption band at 563 nm and the emission band at 647 nm
stimulations I1 and I3 are on, while I2 is off, the input string is
+
101. Under these conditions (ultraviolet light and H ), the
molecular switch is in state MEH, which shows the absorption
band at 401 nm only. In this case, the output O1 is on, while O2
is off, and the output string is 10. All the possible combinations
of input data and the corresponding output strings are illustrated
in Table 1.
The combinational logic circuit (Figure 4) equivalent to this
truth table illustrates the complexity of the operations executed
by the three-state molecular switch. Nine logic elements are
necessary to reproduce the functions performed by a single
molecule. In this circuit, the three inputs I1-I3 are elaborated
through a series of AND, NOT, and OR operations to produce
the two outputs O1 and O2. The eight possible combinations of
input data are transduced into three of the four potential strings
of output data. The logic circuit excludes the output string 11,
which is never produced. Indeed, the two output signals cannot
be on simultaneously. They correspond to two distinct states of
the molecular switch that cannot coexist in solution.
(
Figure 3d) accompanies this process.16
This three-state molecular switch detects three input signals.
+
They are (I1) ultraviolet light, (I2) visible light and (I3) H . It
responds to these stimulations generating two output signals. They
are (O1) the absorption band at 401 nm of MEH and (O2) that
at 563 nm of ME.1 Each signal can be either on or off and can
be represented by a binary digit, i.e. it can only take two values
7
(11) The solution was irradiated for 5 min at 254 nm using a Mineralight
UVGL-25 lamp. During irradiation, the ratio between SP and ME changed
from the initial 100:0 to a stationary 80:20. These values were derived from
the absorbance measured at 563 nm using the molar extinction coefficient of
the merocyanine form of the parent compound 1′,3′-dihydro-1′,3′,3′-trimethyl-
6
-nitrospiro[2H-1-benzopyran2.2′(2H)-indole]. Sakuragi, M.; Aoki, K.; Ta-
maki, T.; Ichimura, K. Bull. Chem. Soc. Jpn. 1990, 63, 74-79.
12) These absorption and emission bands decrease gradually when the
(
solution is either irradiated with visible light (15 min, 524 nm, Cole-Parmer
Fiber Optic Illuminator 9745-99) or maintained in the dark. Under both
conditions, the purple ME switches completely back to the colorless SP. The
rate constant for the switching from ME to SP in the dark at 25 °C is (41 (
The next step in the development of molecule-based logic
circuits will be the attachment of molecular switches to appropriate
supports. The resulting solid-state devices will be able to elaborate
information by detecting inputs of one form and transducing them
into outputs of another. Ultraminiaturized nanoprocessors formed
by arrays of integrated molecular switches are coming.
-
4
-1
1
)‚10
(
s .
13) This absorption band reappears upon irradiation with ultraviolet light,
as SP switches to MEH through the formation of ME. During this switching
process, the ratio between SP and MEH changes from the initial 100:0 to a
stationary 70:30. These values were derived from the absorbance measured
at 401 nm using the molar extinction coefficient determined in the kinetic
studies described in ref 14.
Acknowledgment. We thank the University of Miami for financial
(
14) The rate constant for the switching from SP to MEH in the dark at
support.
-2 -1 -1
2
5 °C is (8 ( 2)‚10
M ‚s . During this switching process, the ratio between
SP and MEH changes from the initial 100:0 to a stationary 70:30.
Supporting Information Available: Experimental procedures for the
synthesis of SP and for the determination of the rate constants (PDF).
This material is available free of charge via the Internet at http://pubs.acs.org.
(
2 3
15) The solution was filtered through a plug of K CO .
(
16) After treatment with base, the rate constant for the switching from
-4 -1
ME to SP in the dark at 25 °C is (36 ( 3)‚10
s .
(
17) Instead of the absorption band at 563 nm of ME, its emission band at
6
47 nm can be used as output signal O2.
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