An all-photonic molecule-based parity generator/checker for error detection in data transmission

Article abstract of DOI:10.1021/ja403828z

The function of a parity generator/checker, which is an essential operation for detecting errors in data transmission, has been realized with multiphotochromic switches by taking advantage of a neuron-like fluorescence response and reversible light-induced transformations between the implicated isomers.

Full text of DOI:10.1021/ja403828z

Communication
pubs.acs.org/JACS
An All-Photonic Molecule-Based Parity Generator/Checker for Error
Detection in Data Transmission
Magnus Balter,† Shiming Li,† Jesper R. Nilsson,† Joakim Andreasson,*,† and Uwe Pischel*,‡
́
̈
†Department of Chemical and Biological Engineering, Physical Chemistry, Chalmers University of Technology, SE-412 96 Goteborg,
Sweden
̈
‡CIQSO Center for Research in Sustainable Chemistry and Department of Chemical Engineering, Physical Chemistry, and Organic
Chemistry, University of Huelva, Campus de El Carmen, s/n, E-21071 Huelva, Spain
S
* Supporting Information
Table 1. Truth Table of a 2-Bit Parity Generator
ABSTRACT: The function of a parity generator/checker,
a
entry
inputs
output
∑
which is an essential operation for detecting errors in data
transmission, has been realized with multiphotochromic
switches by taking advantage of a neuron-like fluorescence
response and reversible light-induced transformations
between the implicated isomers.
b
b
c
D1
D2
P
1
2
3
4
0
0
1
1
0
1
0
1
0
1
1
0
0, even
2, even
2, even
2, even
a
b
Number of 1’s in the D1D2P string. 380 nm light (0.5 mW/cm2).
c
he use of chemical processes, including electrochemical
Fluorescence intensity at 630 nm.
T
and photochemical ones, to achieve binary information
processing according to Boolean logic, in short molecular logic,
continues to receive a great deal of attention.1−10 In recent
years the research efforts have divided into two different, yet
complementary directions: (i) the exploitation of relatively
simple logic operations, such as AND, OR, INHIBIT, for
bioinspired applications (delivery/activation of drugs, diagnos-
tics)11−23 or the design of smart materials7,13,14,24−28 and (ii)
the challenging task of integrating more and more complex
functions into purpose-designed molecular and supramolecular
architectures.28−44 The ultimate goal of the latter task is clearly
related to molecular computing, which is also actively pursued
in alternative approaches, such as quantum computing45 and
computing with DNA building blocks.46−50
Scheme 1. Representation of a Parity Generator/Checker
3-bit string, the checker device gives an “alert” in form of a
binary 1 for the output C (parity error check). This occurs if
the number of 1’s in the received string is odd (see Table 2). In
the case of a correct transmission procedure, the number of 1’s
in the string is even, and the output is 0.
Among the various strategies followed for the realization of
molecular logic devices, photoswitches have turned out to be
very promising.9,31,36,40,42−44,51 This is related to the possibility
of (i) all-photonic operation, i.e., exclusively optical signaling
(UV−vis and/or fluorescence) is used to address and read the
system, (ii) spatiotemporal control, (iii) remote operation, and
(iv) the ease by which many excited state processes (e.g.,
electron transfer, energy transfer) can be controlled.31,51,52
A frequently encountered and essential problem in any type
of data transmission is the occurrence of erroneous procedures.
These failures can be detected by parity generation and
checking.53 Typically, a parity bit (P) is generated and added to
the data bits Dn such that the total number of 1’s (∑) in the
transmitted string is even. This device is called an even parity
generator. For example, if two bits of data are to be transmitted,
the parity generator would assign to P the binary value
according to the truth table of an exclusive OR (XOR) gate,
where D1 and D2 are the inputs and P is the output (see Table
1 and Scheme 1). The resulting D1D2P string is transmitted to
the receiver and subsequently analyzed by a parity checker (see
Scheme 1). In the case of an erroneous data transmission of the
Here we report for the first time the molecular
implementation of the above-discussed parity generator/
checker device. For this purpose the photochromic Triads 1
and 2 shown in Scheme 2a were used. The compounds consist
of two different types of photoswitches: a fulgimide (FG) and a
dithienylethene (DTE). Triad 1 contains two identical
fulgimide units and one DTE unit,40 whereas Triad 2 contains
one FG unit and two identical DTE units (see Supporting
Information (SI) for the isomerization scheme, structures, and
spectral properties of the individual FG and DTE models).
Given that each switch may exist in an open (o) and a closed
(c) form and that only triads with the identical FG or DTE
units present in the same form are relevant, four states can be
distinguished: FGo-DTEo, FGc-DTEo, FGc-DTEc, and FGo-
DTEc. However, only the three first isomers are implied in the
complete description (see below) of the logic operations of a
Received: April 17, 2013
© XXXX American Chemical Society
A
dx.doi.org/10.1021/ja403828z | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Communication
nm as output P. For D1 and D2, degenerate 380 nm light inputs
are used, a wavelength which can isomerize both open forms
FGo and DTEo. The input application (one or both active) can
be controlled through the time of irradiation. Starting from the
nonfluorescent FGo-DTEo form (P = 0), irradiation with 380
nm light for a defined time (D1 or D2 equals binary 1) will
enrich the sample in the fluorescent FGc-DTEo form (P = 1);
see Scheme 2b.55 Upon prolonged irradiation (D1 = D2 = 1)
the prevailing isomer will be the nonfluorescent FGc-DTEc
form, corresponding to the output P = 0.
Table 2. Truth Table and Interpretation of a 3-Bit Parity
Checker
inputs
output
b
c
c
d
a
entry
D1
D2
P
C
∑
Interpretation
1
2
3
4
5
6
7
8
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
0
0
1
1
0
1
0
0
0, even
1, odd
1, odd
2, even
1, odd
2, even
2, even
3, odd
ok
error
error
ok
0
0
0
1
1
1
1
error
ok
This notion was confirmed by the experimental observation
of a clear off−on−off fluorescence pattern for both triads (see
Figure 1) with UV light exposure time, which translates into the
ok
1
error
a
b
Number of 1’s in the D1D2P string. 380 nm light (0.5 mW/cm2) for
c
P = 0 and visible light (λ > 540 nm, 30 mW/cm2) for P = 1. 380 nm
d
light (0.5 mW/cm2). Fluorescence intensity at 630 nm.
Scheme 2. (a) Structures of Triads 1 and 2 in the All-Closed
Form and (b) Photoswitching Between the Essential Isomers
Figure 1. Fluorescence of solutions of Triads (a) 1 and (b) 2 at 630
nm as a function of irradiation time with 380 nm UV light. D1 and D2
correspond each to 500 and 250 s irradiation time for Triads 1 and 2,
respectively; see also ref 56.
desired XOR logic gate.31 Here, D1 and D2 correspond each to
380 nm UV exposure (0.5 mW/cm2) for 500 and 250 s for
Triad 1 and 2, respectively.56 The results are presented as bar
graphs in Figure 2; the entries 1−4 correspond to the described
XOR gate. The fluorescence switching is complemented by the
observed changes in the absorption spectra of Triad 1 and 2;
shown in the SI. As a side observation, the prompt rise of the
fluorescence signal noted for Triad 2 reflects a more complex
kinetic situation than expected from the time constants that
were derived from UV−vis measurements (see Table 3 and SI).
The observation of the described neuron-like response of
Triads 1 and 2 is by no means trivial as a series of conditions
must be fulfilled: (i) First of all, only one isomeric form of the
triad should be fluorescent. (ii) The fluorescent isomer should
be part of a serial photoreaction sequence, being formed from a
precursor isomer and subsequently transformed into a final
molecule-based parity generator/checker. The corresponding
photochemical transformations are depicted in Scheme 2b. It is
vital to the understanding of the system to realize that only FGc
is fluorescent (λf,max = 630 nm, τf = 135 ps, Φf = 0.005).40 This
emission, however, is quenched by DTEc in an efficient
resonance energy-transfer process.54 Hence, fluorescence,
which herein is defined as output signal, is exclusively observed
for FGc-DTEo.40
The XOR gate required for the 2-bit parity generator can be
implemented by defining the FGc-DTEo fluorescence at 630
B
dx.doi.org/10.1021/ja403828z | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Communication
function correctly, D1 is visible light (λ > 540 nm, 30 mW/cm2,
30 min exposure time),57 whereas P and D2 are defined as 380
nm UV light (same irradiation conditions as described above
for the XOR gate). For the application of P, D1, and D2 over
the initial form FGo-DTEo, the following chemical processes
occur: Applying P alone (entry 5; Table 2) yields a high
concentration of FGc-DTEo, and fluorescence emission is
observed (C = 1). If this is followed by another dose of UV
light irradiation (P = D2 = 1; entry 6), the nonfluorescent FGc-
DTEc is formed (C = 0). If instead visible light is applied (P =
D1 = 1; entry 7), back isomerization to the initial form FGo-
DTEo is observed; here the fluorescence output is low (C = 0).
Finally, the additional application of UV light (P = D1 = D2 = 1;
entry 8) yields the fluorescent FGc-DTEo state (C = 1).
Noteworthy, accounting for the well-known memory ef-
fects40,42 that are intrinsic for photochromic switching between
thermally stable forms, for P = 1 situations the inputs should be
applied in the order P, D1, D2 (see also SI). The above-
described behavior concludes the function described by the
truth table of an even 3-bit parity checker (see Table 2 and
Figure 2). The system can be quantitatively reset to its initial
state (FGo-DTEo) by visible light irradiation at any point of
operation.
The robustness of the switching and reading processes has
been tested as well. Several switching cycles for the alternate
application of UV and visible light (reversible switching
between FGo-DTEo and FGc-DTEo isomers) and reading of
the FGc fluorescence output were performed, and the operation
can be repeated for at least 10 cycles without loss of
performance (see SI). The high thermal stability of all species
(<10% variation in the absorption spectra of FGc-DTEc after
standing for a week in the dark) makes it possible to read the
output state conveniently after input application.
In conclusion, a new molecule-based logic operation in form
of parity generation/checking was functionally integrated in the
photoswitchable Triads 1 and 2. The fulfillment of a series of
molecular design criteria, including photokinetic considerations,
is vital to the successful realization of the molecular device. In a
proof-of-principle approach it was shown that the switching and
reading of the device can be performed all-photonically, very
robust, and in a reversible manner. This underlines the
potential of all-photonic devices in molecular information
processing and may open new paths for the application of
multiphotochromic switches in molecular logic.
Figure 2. Performance of Triads (a) 1 and (b) 2 as a parity generator/
checker under the application of various input entries from Tables 1
and 2. For signal-to-noise ratios and for reproducibility of the data in
cycling experiments, see Figure 1 and SI. The dotted line is the
threshold used for the assignment of binary 0 (below) and 1 (above).
Table 3. Time Constants and Quantum Yields for
Photoisomerization Reactions
a
b
c
compound
photoisomerization
time constant (s)
Φr
d
FG model
FG model
FGo → FGc
312
40
0.10
0.20
e
FGc → FGo
d
DTE model
DTE model
DTEo → DTEc
730
0.34
e
DTEc → DTEo
150
0.0077
a
b
See structures in SI. 380 nm light (0.5 mW/cm2) and visible light (λ
> 540 nm, 30 mW/cm2) used in the closing and the opening reactions,
respectively. Photoisomerization quantum yield. Photostationary
c
d
state distribution: [FGc]/[FGo] ∼ 100/0, [DTEc]/[DTEo] ∼ 80/20.
e
Photostationary state distribution: [FGo]/[FGc] ∼ 100/0, [DTEo]/
[DTEc] ∼ 100/0.
ASSOCIATED CONTENT
* Supporting Information
Synthesis of Triad 2, additional photophysical and kinetic data,
recycling experiments, data for input application by using a
neutral density filter, discussion of memory effect. This material
is available free of charge via the Internet at http://pubs.acs.org.
product isomer, both nonfluorescent. (iii) There is an upper
limit for the rate of the closing reaction for the DTE
photoswitch. If it occurs too fast, it will suppress the build-up
of the fluorescent isomer FGc-DTEo. (iv) The photostationary
state should contain as much as possible of DTE in its
quenching closed form DTEc, so that the on−off ratio upon
prolonged irradiation (D1 = D2 = 1) is maximized. For Triads 1
and 2, these conditions are clearly fulfilled which is also
supported by the kinetic data (see Table 3 and SI).
After demonstrating the molecular implementation of the
parity generator, the realization of the corresponding parity
checker was attempted. The truth table of this device (Table 2)
can be broken down into two parts. The first one refers to the P
= 0 situations (entries 1−4), which correspond to the XOR
logic described before (now the fluorescence output is referred
to as C). On the other hand, for P = 1 (entries 5−8 of Table 2)
the complementary XNOR function with respect to the data
inputs D1 and D2 is identified. In order to implement this
■
S
AUTHOR INFORMATION
Corresponding Author
uwe.pischel@diq.uhu.es; a-son@chalmers.se
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The financial support by the Spanish Ministry for Economy and
Competitiveness (grant CTQ2011-28390 for U.P.), the Junta
́
de Andalucia (grant P08-FQM-3685 for U.P.), the Swedish
C
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Journal of the American Chemical Society
Communication
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