A simple unimolecular multiplexer/demultiplexer

Article abstract of DOI:10.1002/anie.200802018

Simple but effective! 8-Methoxyquinoline, an unsophisticated fluorophore, displays both 2:1 multiplexer and 1:2 demultiplexer digital functions (see picture). Protonation of the fluorophore results in completely different optical spectral profiles and multiplexing/demultiplexing behavior is obtained by exploiting the proton-driven reversible modulation of two complementary absorption and fluorescence signals. (Figure Presented).

Full text of DOI:10.1002/anie.200802018

Communications
DOI: 10.1002/anie.200802018
Molecular Logic
A Simple Unimolecular Multiplexer/Demultiplexer**
Matteo Amelia, Massimo Baroncini, and Alberto Credi*
In living organisms information is processed, transferred, and
[
1]
stored using molecular or ionic substrates. The design and
construction of molecular systems capable of elaborating
[2]
information could lead to the development of radically new
computing paradigms and, in the long term, to the realization
of useful devices. Leaving aside speculation related to the
construction of a chemical computer, molecular logic systems
could perform relatively simple computing tasks that cannot
be accomplished with silicon-based devices, e.g. in nanoscale
[
3]
[4]
spaces or in vivo.
Molecular switches convert input stimuli into output
[
5]
[6]
signals. Hence, the principles of binary logic can be applied
to signal transduction operated by molecules under appro-
[
7]
priate conditions. Many chemical systems that mimic the
operation of semiconductor logic gates and circuits have been
reported.
[
8–15]
Scheme 1. Operation scheme (top) and combinational logic network
An important function in information technology is signal
multiplexing/demultiplexing. A 2:1 multiplexer (mux) is a
circuit with two data inputs, one address input, and one
output. The mux selects the binary state from one of the data
inputs and directs it to the output; the selected input depends
on the binary state of the address input (Scheme 1a).
Conversely, a 1:2 demultiplexer (demux) is a circuit that
possesses one data input, one address input, and two outputs.
The demux routes the data input to one of the output lines,
and the selected output is determined by the binary state of
the address input (Scheme 1b). Hence a multiplexer allows
the encoding of multiple data streams into a single data line
for transmission, and a demultiplexer can decode entangled
data streams from a single signal (Scheme 1a, b). The
combinational circuits corresponding to a 2:1 multiplexer
and 1:2 demultiplexer are shown in Schemes 1c and d,
respectively.
(bottom) corresponding to a 2:1 multiplexer (a and c) and a 1:2
demultiplexer (b and d).
[
19]
described.
Here we show that the reversible acid/base
switching of the absorption and photoluminescence proper-
ties of a fluorophore as simple as 8-methoxyquinoline in
solution can form the basis for molecular 2:1 multiplexing and
1:2 demultiplexing with a clear-cut digital response.
8-Methoxyquinoline (8-MQ, Scheme 2) is related to the
well-known fluorogenic compound 8-hydroxyquinoline
[
20]
(8-HQ).
The absorption spectrum of 8-MQ in CH CN
3
Molecules that can mimic the function of a 2:1 multi-
[
16]
[17,18]
plexer
or a 1:2 demultiplexer
have recently been
Scheme 2. Acid/base-controlled switching between 8-methoxyquinoline
(8-MQ) and its protonated form (8-MQ-H ).
+
reported. However, these systems either rely on carefully
designed multicomponent species
external optical device, or imply a dependence of the data
input on the binary state of the address input. Demulti-
plexers based on solid-state nanostructures have also been
[
16,17]
and coupling to an
[
17]
[
18]
(Figure 1a) shows a band with l = 301 nm, assigned to a p–
max
[
21]
p* transition.
In contrast with 8-HQ, 8-MQ is strongly
fluorescent (lmax = 388 nm, Figure 1b) because the presence
of the methoxy group prevents the intramolecular proton
transfer process in the excited state responsible for the strong
[
*] Dr. M. Amelia, M. Baroncini, Prof. A. Credi
Dipartimento di Chimica “G. Ciamician”
Università di Bologna
Via Selmi 2, 40126 Bologna (Italy)
Fax: ( +39)051-209-9456
[
21,22]
fluorescence quenching in 8-HQ.
equivalent of triflic acid (CF SO H) to 8-MQ affords the
The addition of one
3
3
+
protonated form 8-MQ-H (Scheme 2), the absorption and
fluorescence spectra of which are markedly different from
E-mail: alberto.credi@unibo.it
[
**] Financial support by the Italian Ministry of University and Research
[
21]
those of 8-MQ. Specifically, the absorbance in the region of
the 8-MQ absorption band (270–320 nm) decreases substan-
tially, and a new absorption band (lmax = 358 nm, Figure 1c) is
observed in a spectral region where 8-MQ does not absorb
light. The fluorescence band of 8-MQ, which has a maximum
(
PRIN 2006034123_003) and the University of Bologna (Progetto
strategico CompReNDe) is gratefully acknowledged. We thank Prof.
V. Balzani and Dr. M. Montalti for discussions.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.200802018.
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Angew. Chem. Int. Ed. 2008, 47, 6240 –6243

Angewandte
Chemie
Table 1: Truth table for the 2:1 multiplexer function.
Data inputs
In2
Address input
A
[H ]/[8-MQ]
Data output
Out
IF (474 nm)
In1
[
a]
[a]
+
[b]
Iex (285 nm)
Iex (350 nm)
0
1
0
1
0
1
0
1
0
0
1
1
0
0
1
1
0
0
0
0
1
1
1
1
0 (0)
1 (21)
0 (5.1)
1 (26)
0 (0)
0 (9.2)
1 (21)
1 (30)
[
a] Binary state 1 corresponds to irradiation with the excitation lamp of
the spectrofluorimeter; state 0 corresponds to no excitation (lamp off).
b] The values in parentheses indicate the experimental fluorescence
[
intensity values in arbitrary units; the corresponding binary states are
determined by applying a threshold value of I =15 arbitary units.
F
corresponds to that of a 2:1 multiplexer. If the address input is
+
0
(no H added, 8-MQ form), the output reports the state of
data input In , whereas if the address input is 1 (1 equivalent
1
+
+
of H added, 8-MQ-H form), the output mirrors the state of
data input In2.
The system can be easily reconfigured to behave as a 1:2
demultiplexer by changing the optical input and output
channels. In this case, the data input (In) was the incident light
intensity at 262 nm, which is an isosbestic point in the
+
absorption spectra of 8-MQ and 8-MQ-H . The two output
signals were represented by the fluorescence intensity at
Figure 1. Absorption (top) and fluorescence (l =262 nm, bottom)
spectra of 8-MQ (a and b) and 8-MQ-H (c and d). The wavelengths
+
ex
388 nm (lmax for 8-MQ, Out ) and 500 nm (l for 8-MQ-H ,
1
max
+
Out ), respectively. Table 2 shows the fluorescence output
2
of the inputs and outputs signals relevant for the mux/demux binary
À5
À1
functions are indicated. Conditions: 1.5”10 molL , air-equilibrated
MeCN, RT.
Table 2: Truth table for the 1:2 demultiplexer function.
Data input
In
Iex (262 nm)
Address input
A
[H ]/[8-MQ]
Data outputs
Out1
Out2
IF (500 nm)
at 388 nm, is replaced by a weaker emission band with lmax
=
[a]
+
[b]
[b]
IF (388 nm)
5
00 nm (Figure 1d). The unprotonated form can be regen-
erated on addition of one equivalent of tris-n-butylamine
nBu N). The acid/base-controlled switching between 8-MQ
0
1
0
1
0
0
1
1
0 (0)
1 (71)
0 (0)
0 (0)
0 (0.5)
0 (0)
(
3
+
and 8-MQ-H is fully reversible and can be repeated many
times with the same solution without appreciable reduction in
intensity in the absorption and fluorescence spectra. This
particular spectroscopic behavior and the chemical reversi-
bility of the acid/base switching can be used to obtain both 2:1
mux and 1:2 demux functions, using proton concentration as
the address input (A), and excitation and emission optical
signals as the data inputs and outputs, respectively.
0 (2.1)
1 (21)
[
a] Binary state 1 corresponds to irradiation with the excitation lamp of
the spectrofluorimeter; state 0 corresponds to no excitation (lamp off).
b] The values in parentheses indicate the experimental fluorescence
[
intensity values in arbitrary units; the corresponding binary states are
determined by applying a threshold value of I =10 arbitary units.
F
In the case of the 2:1 multiplexer the incident light
intensities at 285 nm (In ) and 350 nm (In ) were used as the
levels measured for a solution of 8-MQ in MeCN under the
conditions corresponding to the four combinations of the
binary data and address inputs. On fixing an appropriate
threshold for the fluorescence output, the truth table of the
1:2 demultiplexer is obtained. If the address input is 0 (8-MQ
1
2
data inputs; these wavelengths were chosen in order to
+
achieve selective excitation of 8-MQ and 8-MQ-H , respec-
tively (Figure 1a–c). The output (Out) was monitored using
the fluorescence intensity at 474 nm, a wavelength at which
form), the binary state of the data input is transmitted to Out ;
1
+
+
both 8-MQ and 8-MQ-H fluoresce (Figure 1b–d). The
conversely, if the address input is 1 (8-MQ-H form), the
fluorescence output levels measured for a solution containing
binary data input is transmitted to Out2.
8
-MQ in MeCN under the conditions corresponding to the
Although the construction of a practical device was not
the overall purpose of this work, we investigated whether the
acid/base switching of the 8-MQ fluorescence observed in
solution could also be obtained in a solid-state environment.
eight combinations of the binary data and address inputs are
listed in Table 1. A threshold value could be easily identified
in order to assign binary output states so that the truth table
Angew. Chem. Int. Ed. 2008, 47, 6240 –6243
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Communications
To this end, we embedded 8-MQ into polystyrene thin films
Keywords: binary logic · luminescence · molecular devices ·
photochemistry · quinolines
.
and recorded the fluorescence spectra of the resulting
materials upon exposure to acidic and basic reagents. The
result of a typical experiment is shown in Figure 2. Upon
[
[
[
[
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ex
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À2
À1
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3
À2
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Received: April 29, 2008
Published online: July 4, 2008
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