Molecular logic gates based on 2-tyrylquinoline derivatives

Article abstract of DOI:10.1007/s11172-008-0372-5

Various logical operations can be performed by molecular logic gates (MLG) based on 2-styrylquinoline derivatives using irradiation with light and protonation as input signals and absorbance (optical density) as output signal. The MLG operation type ("INH

Full text of DOI:10.1007/s11172-008-0372-5

Russian Chemical Bulletin, International Edition, Vol. 57, No. 12, pp. 2586—2591, December, 2008
2586
Molecular logic gates based on 2ꢀstyrylquinoline derivatives*
M. F. Budyka, N. I. Potashova, T. N. Gavrishova, and V. M. Lee
Institute of Problems of Chemical Physics, Russian Academy of Sciences,
1 prosp. Akad. Semenova, 142432 Chernogolovka, Moscow Region, Russian Federation.
Fax: +7 (496) 514 3244. Eꢀmail: budyka@icp.ac.ru
Various logical operations can be performed by molecular logic gates (MLG) based on
2ꢀstyrylquinoline derivatives using irradiation with light and protonation as input signals and
absorbance (optical density) as output signal. The MLG operation type ("INH", "OR", "AND")
depends on the observation wavelength.
Key words: diarylethylene, photoisomerization, absorption spectrum, molecular logic gate.
Scheme 1
Currently, the possibility of performing logical operaꢀ
tions on the molecular level in order to design molecular
logic gates (MLG) for information technologies has been
studied intensively.2—8 Most often, the role of input sigꢀ
nals for MLG is played by some chemical impact or irradiꢀ
ation with light, while the output signal is the optical denꢀ
sity or luminescence.
Styrylquinolines represent azaꢀsubstituted diarylethylꢀ
enes (azaꢀDAE) containing a central double bond and an
endocyclic (quinoline) nitrogen atom, which can undergo
reversible transformations (photoisomerization and proꢀ
tonation, respectively). This makes azaꢀDAE convenient
systems for studying the principles of the design and operꢀ
ation of MLG including controllable switches, logic gates,
etc. One can switch between the cisꢀ and transꢀstates of
azaꢀDAE using a photoisomerization reaction controlled
by protonation of the aza function. Therefore, there are
four stable states (forms) in this system including neutral
cisꢀ and transꢀisomers and protonated cisꢀ and transꢀisoꢀ
mers. Switching between them occurs in two steps and
involves irradiation with light and protonation.
Scheme 1 presents different states of azaꢀDAE and
possible types of transitions between them taking the
sꢀtransꢀconformer of 2ꢀstyrylquinoline (1) as an example.
Compared to other styrylquinolines, both the neutral and
protonated forms of 1 are characterized by high quantum
yields of cis—transꢀ and trans—cisꢀphotoisomerizations;
this compound also is not involved in side reactions (with
respect to photoisomerization), such as photocyclization
and oxidation to fused aromatic compounds.9,10 Thereꢀ
fore, the cycle of reactions with participation of compound
1 is fully reversible. An important factor is also the thermal
stability of all four forms of compound 1 (see Scheme 1).
In the present work, we studied 2ꢀstyrylquinoline (1)
and its paraꢀsubstituted derivatives 2—5 and showed that
these compounds can serve as a basis for various MLG
where the role of input signals is played by irradiation with
light and protonation while the output signal is the optical
density at a specified wavelength. The output signal can
take values equal to 0 or 1 depending on whether the optiꢀ
cal density is below or above than a particular threshold
value. Combining two input signals allows one to produce
various output signals and thus perform logical operations.
R = H (1), F (2), Cl (3), EtO (4), NO2 (5)
Experimental
* Preliminary results were reported at the "Nanophotonics" Symꢀ
posium (Chernogolovka, Moscow Region, Russian Federation,
September 18—22, 2007), see Ref. 1.
The synthesis of styrylquinolines 1—5 was reported earliꢀ
er.10,11 Hydrochlorides were obtained in situ by adding HCl soluꢀ
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2535—2540, December, 2008.
1066ꢀ5285/08/5712ꢀ2586 © 2008 Springer Science+Business Media, Inc.

Styrylquinolines as logic gates
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 12, December, 2008
2587
tions to styrylquinoline solutions. Electronic absorption spectra
were recorded with a Specord Мꢀ40 spectrophotometer in ethaꢀ
nol. The source of UV light was a DRShꢀ500 mercury lamp; the
313 and 365 nm spectral lines were selected using a set of glass
filters. Photochemical studies were carried out in airꢀsaturated
solutions at room temperature. The concentration of styrylquinꢀ
oline in the solutions was (2—20)•10–5 mol L–1 and the intensity
of incident light was in the range (5—50)•10–10 Einstein cm–2 s–1
(measured by a PPꢀ1 cavity detector or ferrioxalate actinomꢀ
eter). Quartz cells with an optical path length l of 1 cm were used.
(form) of the styrylquinoline molecule. Any form of
styrylquinoline can be chosen as the initial state of the
logic gate (A), because transitions between all forms are
possible in all directions due to full reversibility. Now we
can formulate the requirements for the properties of parꢀ
ticular forms of compound 1, which should be met to
design a MLG. For instance, the operation of a logic gate
performing logic multiplication ("AND") requires (see Taꢀ
ble 1) that the output signal be equal to 1 only for the (1,1)
combination of the input signals and equal to 0 in the other
three cases. From a comparison of Schemes 1 and 2 it
follows that the properties of a form of compound 1 to be
assigned the final state (D) of the MLG should differ from
the properties of the other three forms treated as the initial
and intermediate states (A, B, and C) of the MLG taking
into account the possibility for these three states to exhibit
identical properties.
As an example, Fig. 1 presents the absorption spectra
of the neutral and protonated forms of cisꢀ and transꢀ2ꢀ(4ꢀ
fluorostyryl)quinoline 2, which correspond to four therꢀ
mally stable compounds similar to those shown in Scheme
1. Having assigned each compound to a particular state of
the MLG, the state (A, B, C, or D) of the MLG can be
determined with ease because different forms of styrylquinꢀ
oline exhibit significantly different spectra.
Results and Discussion
A logic gate is a switch whose output signal equal to 0
or 1 depends on the input signal, which also can take two
values, 0 or 1. A logic gate with two inputs and one output
has four states corresponding to four combinations of the
input signals, namely, (0,0), (0,1), (1,0), and (1,1). In
each case, the value of the output signal (0 or 1) depends
on the type of the logic gate and is determined by a
truth table in which each combination of input sigꢀ
nals (logical variables) is assigned a desired value of the
output signal (a logic function in question). Table 1 preꢀ
sents the truth tables for some logic gates whose
functions will then be modeled using the derivatives of
styrylquinoline 1.
Consider the cisꢀisomer as the initial state of the MLG
and irradiation with light and acidification as input signals
(in1 and in2, respectively). Then, different states of the
MLG, created after the impact of input signals are related
to different forms of styrylquinoline as shown in Table 2.
The final state (D) of the MLG corresponds to the protoꢀ
nated transꢀisomer. To perform the logical function "AND"
(see above), one should distinguish between the state D
and the other three states. From Fig. 1 it follows that this
For clarity, in Scheme 2 four different states (A—D) of
the logic gate occupy the vertices of a square. Transitions
between them (responses to some impacts on two inputs,
in1 and in2) are shown by arrows aligned to the edges of
the square.
Scheme 2
ε/L mol–1 cm–1
60000
η (%)
5
6
4
80
60
40
20
40000
20000
A comparison of the Schemes 1 and 2 shows that each
state of the logic gate can be assigned to a particular state
3
2
1
Table 1. Truth tables for different logical functions
Input
in1
Output
INH
250
300
350
λ/nm
in2
AND
OR
Fig. 1. Absorption spectra of cisꢀ (1, 2) and transꢀisomers (3, 4) of
2ꢀ(4ꢀfluorostyryl)quinoline 2 in the neutral (1, 3) and protonated
(2, 4) forms and the content of the cisꢀisomer in the photostaꢀ
tionary mixture (degree of conversion η) plotted vs. irradiation
wavelength for the neutral (5) and protonated (6) forms of 2.
0
1
0
1
0
0
1
1
0
0
0
1
0
1
0
0
0
1
1
1

2588
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 12, December, 2008
Budyka et al.
Table 2. Correspondence between the action on the MLG,
its state (see Scheme 2), and the form of 2ꢀ(4ꢀfluorostyꢀ
ryl)quinoline 2 corresponding to this state (starting form is
the cisꢀisomer)
The absorption spectra of the reaction mixtures in the
four photostationary states created upon irradiation of soꢀ
lutions of neutral styrylquinoline 2 and 2•HCl at λ = 313
and 365 nm are shown in Fig. 2. Compared to the pure
isomers (see Fig. 1), the spectral differences became less
pronounced, but they still allow the state of the system to
be determined unambiguously. If the initial state of the
MLG is the photostationary state PS365 enriched with the
cisꢀisomer (η365 = 90%, see Table 3) and the role of the
input signals is played by the irradiation at 313 nm and
protonation (HCl addition), one gets a fully reversible sysꢀ
tem, which returns to the initial state after neutralization
and irradiation at λ = 365 nm.
Vertical lines in Fig. 2 show the wavelengths 323, 353,
and 373 nm. Signal readout at these wavelengths allows
one to obtain three different MLG ("INH" at 323 nm,
"OR" at 353 nm, and "AND" at 373 nm), which process
the input signals according to Table 2. Using commonly
accepted graphic notations of logic elements, the operaꢀ
tion of the MLG based on 2ꢀstyrylquinoline derivatives is
described by Scheme 3.
Since the output signal is the optical density, for each
MLG one should set a threshold optical density value,
such that if the optical density is below (above) the
threshold value, the output signal has a value of 0 (1).
Table 4 lists all four combinations of the input signals, the
corresponding photostationary states of styrylquinoline 2,
the experimental values of the optical densities at three
wavelengths (A323, A353, and A373), and the threshold opꢀ
tical density values; if A323, A353, or A373 value exceeds
the corresponding threshold, the MLG output signal
is equal to 1.
Action
MLG state
Compound
—
hν
HCl
hν + HCl
A
B
C
D
cisꢀ2
transꢀ2
cisꢀ2•HCl
transꢀ2•HCl
can be done with ease using the optical density in the
region λ > 380 nm, where both neutral forms (states A and
B) do not absorb light and the protonated cisꢀisomer (state
C) absorbs much weaker than the transꢀisomer.
It should be noted that it is impossible to create "pure"
MLG states corresponding to the compounds listed in Taꢀ
ble 2, because reversibility of the photoisomerization reacꢀ
tion precludes a 100% conversion of the cisꢀisomer to the
transꢀisomer upon exposure to light and vice versa. Actualꢀ
ly, irradiation creates a photostationary state PSλ (a mixꢀ
ture of cisꢀ and transꢀisomers whose composition depends
on the irradiation wavelength λ). The composition of the
photostationary state can be expressed through the proꢀ
portion of the cisꢀisomer
ηλ = [cis]ps/([trans]ps + [cis]ps),
where [cis]ps and [trans]ps are the concentrations of the cisꢀ
and transꢀisomers in the mixture, respectively. When using
transꢀisomers formed in the synthesis of styrylquinolines
as starting reactants, the parameter η is the degree of conꢀ
version. Irradiation of all compounds studied in this work
at λ = 313 and 365 nm produced the photostationary states
PS313 and PS365, respectively, with the cisꢀisomer content
listed in Table 3.
A
INH OR AND
Table 3. Compositions of photostationary states (content of
the cisꢀisomer in the mixture ηλ) for neutral and protonated
forms of 2ꢀstyrylquinoline derivatives as functions of the
irradiation wavelength
1.0
4
0.5
Comꢀ
pound
η
η
η
η
λ
λ
max
313
365
min
max
min
2
3
%
nm
1
1
61
51
55
54
46
54
64
55
41
46
93
68
90
66
87
65
86
55
82
69
26
31
23
34
16
31
38
25
30
25
94
84
91
80
86
90
91
75
87
94
245
242
244
256
247
257
237
241
246
248
370
394
368
397
360
423
390
440
385
393
1•HCl
2
2•HCl
3
3•HCl
4
4•HCl
5
5•HCl
250
300
350
400
λ/nm
Fig. 2. Absorption spectra of reaction mixtures in the photoꢀ
stationary states of 2ꢀ(4ꢀfluorostyryl)quinoline 2 (ethanol,
3.87•10–5 mol L–1): neutral form 2 (1, 2), protonated form
2•HCl (3, 4), PS365 (1, 3), and PS313 (2, 4). Vertical lines denote
the wavelengths 323, 353, and 373 nm; readout of the optical
density at these wavelengths makes it possible to create a correꢀ
sponding MLG (see text).

Styrylquinolines as logic gates
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 12, December, 2008
2589
Scheme 3
is 55% (in the reverse sequence, 54%). However, this difꢀ
ference does not go beyond the accepted values of the
threshold optical densities and agrees with the data in the
truth table of the MLG (see Table 4).
Clearly, it is desired that transitions between different
states of the system be induced by irradiation at such
a wavelength that produces a photostationary mixture with
the maximum content of the transꢀ or cisꢀisomer. For irraꢀ
diation at the wavelength λ, the composition of the PSλ is
given by the following equation:
(ϕ ε [trans]ps)λ = ϕ ε [cis]ps,
(1)
tc
t
ct c
where ϕtc and ϕct are the quantum yields of the trans—cisꢀ
and cis—transꢀisomerization reactions, respectively, and
εc and εt are the molar absorption coefficients of the cisꢀ
and transꢀisomers, respectively, at the irradiation waveꢀ
length λ.
From Eq. (1) one gets the dependence of the content of
the cisꢀisomer in the photostationary mixture on the irraꢀ
diation wavelength
For instance, when the signal is read out at 323 nm,
one has A323 = 0.6 for the threshold optical density. Then,
the output signal is 0 at A323 < 0.6 and 1 at A323 > 0.6. From
Table 4 it follows that in this case the output value equal to
1 is attained only at input1 = 1, input2 = 0 (PS313 state),
i.e. the system operates as the "INH" logic gate (see Table 2).
This is clearly seen in Fig. 3, where the optical densities at
these wavelengths are shown as diagrams while the threshꢀ
old optical densities for different logic gates are shown by
horizontal lines. At λ = 323 nm (see Fig. 3, а), only the
optical density in the state PS313 is above the threshꢀ
old line. At λ = 353 nm (see Fig. 3, b), the threshold value
is A353 = 0.3, in this case the optical density is above
the threshold value for three states (PS313, PS365•HCl,
and PS313•HCl) and the system operates as the logic
gate "OR" (see Table 2). At λ = 373 nm (see Fig. 3, c),
the threshold value is A373 = 0.9, here only the optical
density of the state PS313•HCl is above the threshold
value and the system operates as the logic gate "AND"
(see Table 2).
ηλ = [ϕ ε /(ϕ ε + ϕ ε )]λ.
(2)
tc
t
tc
t
ct c
The parameters in Eq. (2) were experimentally meaꢀ
sured and used to calculate the dependence of ηλ on the
irradiation wavelength for the neutral and protonated forms
of styrylquinolines.
Figure 1 (see curves 5 and 6) presents the plots of ηλ vs.
irradiation wavelength for the neutral and protonated
styrylquinoline 2. A comparison of the dependence of the
degree of conversion on λ with the absorption spectra (see
Fig. 1, curves 1—4) shows that the maximum possible
content of the cisꢀisomer in the photostationary mixture
(ηmax) is attained on irradiation at the wavelength (λmax
corresponding to the maximum ratio (εt/εc)λ. For the neuꢀ
tral form of styrylquinoline 2, one has ηmax = 91% at λmax
)
From Table 3 it follows that the final state of the sysꢀ
tem corresponding to signals at both inputs (i.e. irradiation
at λ = 313 nm and protonation) is slightly different deꢀ
pending on the order in which the input signals are apꢀ
plied. If irradiation is followed by acidification of the soluꢀ
tion, the content of the cisꢀisomer in the reaction mixture
=
= 368 nm. Irradiation at λmin = 244 nm corresponding to
the minimum ratio (εt/εc)λ allows one create a photoꢀ
stationary mixture with the minimum content of the
cisꢀisomer (ηmin = 23%) and the maximum content of the
transꢀisomer (77%). The maximum and minimum ηλ valꢀ
Table 4. Truth table for a MLG based on photostationary states of 2ꢀ(4ꢀfluorostyryl)quinoline 2*
Input
Photoꢀ
stationary
state
Output
in1
in2
HCl
INH
A323 (0.6)
OR
A353 (0.3)
AND
hν 313
A373 (0.9)
0
1
0
1
0
0
1
1
PS365
PS313
PS365•HCl
PS313•HCl
0 (0.51)
1 (0.73)
0 (0.35)
0 (0.34)
0 (0.18)
1 (0.45)
1 (0.69)
1 (0.80)
0 (0.02)
0 (0.05)
0 (0.71)
1 (1.08)
* Listed are the threshold and experimental values of the optical densities at the specified wavelengths and the correꢀ
sponding values of the output signals.

2590
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 12, December, 2008
a
Budyka et al.
parameters of other compounds under study are listed
in Table 3.
A323
1.0
0.8
0.6
0.4
0.2
Irradiation with longꢀwavelength light allows one to
create photostationary states enriched with the cisꢀisomer
(up to 94% for compounds 1 and 5•HCl). Irradiation in
this spectral region can be utilized to return the MLG to
the initial state. Irradiation with shortꢀwavelength light in
the region ~250 nm is also suitable for the operation of
MLG. In this case, the maximum attainable content of
transꢀisomers in the photostationary states is usually at
most 70—80%, only for the neutral chloro derivative 3 it
reaches 84% (η247 = 16%, see Table 3) .
An interesting example is provided by ethoxystyrylquinꢀ
oline 4. From Table 3 it follows that the protonated form
of this compound is characterized by the same composiꢀ
tion of the photostationary state (55%) when irradiated at
λ = 313 and 365 nm. This is due to equality of the ratios of
the molar absorption coefficients of the cisꢀ and transꢀ
isomers at these wavelengths (1.46 and 1.44, respectively).
Therefore, it is impossible to design a MLG based on the
PS313 and PS365 states. However, the compositions of the
photostationary states differ noticeably on irradiation at
λ = 237—241 and 390—440 nm (see Table 3). Ethoxyꢀ
styrylquinoline 4 is a convenient model compound, beꢀ
cause its neutral and protonated forms are characterized
by high quantum yields of trans—cisꢀ and cis—transꢀphoꢀ
toisomerizations (0.5 and more).10 In addition, without
significant changes in spectral characteristics the ethyl
group can be replaced by some other alkyl residue in order
to impart specific properties (e.g., the ability to selfꢀasꢀ
sembly) to the new derivative. It is assumed that selfꢀasꢀ
sembly of individual MLG to supramolecular ensembles
will be a step in the design of complex nanoscale blocks for
molecular nanoelectronics.12
PS365
A353
PS313
PS365•HCl PS313•HCl
b
1.0
0.8
0.6
0.4
0.2
PS365
PS313
PS365•HCl PS313•HCl
A373
c
1.0
0.8
0.6
0.4
0.2
Thus, we showed that 2ꢀstyrylquinoline is suitable for
the design of various MLG using irradiation with light and
protonation as input signals; the type of the logical operaꢀ
tion ("INH", "OR", or "AND") depends on the observaꢀ
tion wavelength.
This work was financially supported by the Presidium
of the Russian Academy of Sciences (Basic Research Proꢀ
gram "Development of Methods for Synthesis of Chemical
Compounds and Design of Novel Materials", Subprogram
"Polyfunctional Materials for Molecular Electronics") and
the Russian Foundation for Basic Research (Project
No. 07ꢀ03ꢀ00891).
PS365
PS313
PS365•HCl PS313•HCl
Fig. 3. Optical density diagrams for reaction mixtures in the
photostationary states PS365 and PS313 of neutral 2ꢀ(4ꢀfluoroꢀ
styryl)quinoline 2 and protonated form 2•HCl at 323 (a), 353 (b)
and 373 nm (c); horizontal lines show the threshold optical denꢀ
sity values for different logic gates including "INH" (a), "OR" (b),
and "AND" (c).
References
1. M. F. Budyka, N. I. Potashova, T. N. Gavrishova, V. M. Li,
Ros. Nanotekhnol., 2007, 2, 89 [Nanotechnologies in Russia,
2007, 2, 89 (Engl. Transl.)].
ues for the protonated form of styrylquinoline 2 and the
corresponding wavelengths, as well as the corresponding
2. A. Credi, V. Balzani, S. J. Langford, J. F. Stoddart, J. Am.
Chem. Soc., 1997, 119, 2679.

Styrylquinolines as logic gates
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 12, December, 2008
2591
3. A. P. de Silva, N. D. McClenaghan, J. Am. Chem. Soc., 2000,
122, 3965.
10. M. F. Budyka, N. I. Potashova, T. N. Gavrishova, V. M. Li,
Khim. Vys. Energii, 2008, 42, 497 [High Energy Chem., 2008,
42, 446 (Engl. Transl.)].
11. M. F. Budyka, N. V. Biktimirova, T. N. Gavrishova, Khimiya
Geterotsikl. Soedinen., 2007, 555 [Chem. Heterocycl. Compd.,
2007, 43, 454 (Engl. Transl.)].
4. F. M. Raymo, Spectrum., 2004, 17, 14.
5. D. Gust, T. A. Moore, A. L. Moore, Chem. Commun.,
2006, 1169.
6. D. H. Qu, F. Y. Ji, Q. C. Wang, H. Tian, Adv. Mater., 2006,
18, 2035.
7. H. Tian, S. Wang, Chem. Commun., 2007, 781.
8. A. P. de Silva, S. Uchiyama, Nature Nanotechnology, 2007,
2, 399.
12. Molecular Nanoelectronics, Eds M. A. Reed, T. Lee, ASP,
California, 2003.
9. G. Galiazzo, P. Bortolus, G. Gennari, Gazz. Chim. Ital., 1990,
120, 581.
Received June 17, 2008