Aminoanthraquinone-based chemosensors: Colorimetric molecular logic mimicking molecular trafficking and a set-reset memorized device

Article abstract of DOI:10.1039/c2dt12201d

The synthesis, photophysical properties, protonation and metal-ion coordination features of a family of four (3-6) anthraquinone-based schiff base derivatives are reported. The outstanding UV-vis absorption properties of the 1-aminoanthraquinone chromopho

Full text of DOI:10.1039/c2dt12201d

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PAPER
Aminoanthraquinone-based chemosensors: colorimetric molecular logic
mimicking molecular trafficking and a set–reset memorized device†
Navneet Kaur*a and Subodh Kumarb
Received 17th November 2011, Accepted 8th February 2012
DOI: 10.1039/c2dt12201d
The synthesis, photophysical properties, protonation and metal–ion coordination features of a family of
four (3–6) anthraquinone-based schiff base derivatives are reported. The outstanding UV-vis absorption
properties of the 1-aminoanthraquinone chromophore allowed the efficient visual detection and
quantification of Cu2+ and/or Ni2+ in buffered aqueous solution. Analysis of spectrophotometric data with
SPECFIT yielded the macroscopic and microscopic stability constants of the complexes. Furthermore, the
different optical output signals (i.e. absorbance) observed with addition of various metal ions to a solution
of 6 can be used for mimicking the operation of a traffic signal and “Set–Reset” molecular level
information processing device.
related to the integration and processing of binary data of con-
Introduction
ventional microprocessor systems.12 Conventional silicon based
Recently, the development of new artificial chemosensors for the
recognition of physiologically and environmentally important
analytes has attracted considerable attention.1–3 Among the
various detection methods available, UV-vis and fluorescence
spectroscopy still remain the most frequently used modes due to
their high sensitivity and easy operational use. More recently, a
new chemosensor design concept of “single sensor for multiple
analytes” has emerged, that is the analysis of more than one
analyte by one receptor using a single detection method or an
array of detection methods.4–7 There are mainly two methods to
realize this concept. One method is by combination of multichro-
mogenic units into a single receptor,8 and the other one is by
using a variety of detection methods such as UV-vis and
fluorescence.4,9
devices have the limitation that they can only be miniaturized
down to the nanoscale.13 Therefore, the development of
materials for information storage and retrieval at the molecular
level is a promising choice to overcome this limitation.14 The
sequential integration of molecular logic gates is an important
step for the realization of information storage processes (memory
devices).15 Sequential logic circuits, which are functions of both
past and present inputs, operate through a feedback loop in
which one of the outputs of the device operates as an input and
is memorized as a “memory function”. Van der Boom et al.16
reported molecular level random access memory (RAM) using
“Set–Reset”/“Flip–Flop” functions based on surface-confined
osmium polypyridyl complexes using chemical reagents as
inputs. Chemical devices such as molecular keypad locks,17 set–
Recently, the development of molecular logic gates10 and
photonic devices11 based on the optical sensing of specific ana-
lytes has emerged an attractive research area for unconventional
computing. The chemically encoded information was converted
into fluorescent signals as the output, which results in develop-
ment of molecular level logic gates such as AND, OR, NOR,
INHIBIT, XOR, YES, NOT, and XNOR logic gates. The inte-
gration of these molecular logic gates at molecular level is
19
reset logic devices15,16,18 and molecular trafficking have been
mimicked by sequential integration of molecular logic gates.
Recently, Pischel18c highlighted the importance of sequential
logic circuits with memory function in molecular computing.
Thus, intelligent molecules which are capable of producing
sequential logic operations are extremely interesting. However
there are only
a few reports about “set–reset” logic
devices15,16,18 where the memorized unit20 has been mimicked
by sequential integration of molecular logic gates.
An anthraquinone chromophoric system may be important as
a chemosensor because its optical properties can be significantly
perturbed by chemical stimuli. It is also important to note that
the carbonyl group of 9,10-anthraquinone ligands is known to
interact with various metal ions to cause a pronounced color
change.21,22 Also, different anthraquinones bearing electron-rich
coordinating sites at 1/1,8 or 1,4 positions have been investigated
by our group for their metal-sensor behavior through color
change. In all the chemosensors, Cu2+-induced deprotonation of
the amine NH of anthracene-9,10-dione has been observed,
aDepartment of Chemistry, Panjab University, Chandigarh, 160 014
Punjab, India. E-mail: neet_chem@yahoo.co.in; Fax: +91 172
2545074; Tel: +91 172 2541435
bDepartment of Chemistry, Guru Nanak Dev University, Amritsar, 143
005 Punjab, India. E-mail: subodh_gndu@yahoo.co.in; Fax: +91 183
2258820; Tel: +91 183 2258802-09 Ext. 3206
†Electronic supplementary information (ESI) available: Changes in
absorption spectrum of chemosensors 3, 5 and 6 upon addition of
various metal ions, absorption curves for molecular scale implemen-
tation of “traffic on”, “traffic off” and “Set–Reset” with addition of
different inputs. See DOI: 10.1039/c2dt12201d
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 5217–5224 | 5217

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which was responsible for the drastic color changes.23 However,
in anthraquinone based derivatives having Schiff base linkages,
π-electron delocalization and alcohol deprotonation are mainly
responsible for the signal generation as a consequence of cation
binding events. Herein, we report different anthraquinone based
Schiff base derivatives that can detect Cu2+ and Ni2+ differen-
tially by visible color changes. The diverse photometric
responses i.e. regulation of Cu2+ (input 2) and Ni2+ (input 3) at
variable pH range (input 1) observed in the case of chemosensor
6 mimics the trafficking mechanism (vide infra). Molecular
trafficking represents a phenomenon in which the information is
processed and transmitted with signals in a specific manner at
the molecular level. The synthetic systems in which the infor-
mation is processed and transmitted in a specific manner are
helpful in rationalizing intricate aspects of inter- and intracellular
metal trafficking. In addition to this, encoding binary digits of
logic conventions, we have proposed a logic circuit for designing
a molecular traffic signal with incorporation of an R–S (Reset–
Set) latch16a circuit i.e. a circuit comprising cross coupled NOR
logic gates which responds to a sequence of input pulses. Nearly
all digital electronic devices (microprocessors, digital clocks,
mobile phones, cordless telephones, electronic calculators, etc.)
are designed on such sequential circuits. Thus, the significant
role played by trafficking in day to day life and the application
of latch circuits raised our interest in the development of a mol-
ecular system mimicking the trafficking mechanism.
Scheme 1 Synthesis of chemosensors 3–5
Results and discussion
The photophysical studies of chemosensor 2 have already been
discussed in ref. 23e. However, in order to study the role of
extended π-conjugation and the presence of other hetero atoms
(N) in the azo-methine unit, the chemosensors 3–6 were syn-
thesized.
Scheme 2 Synthesis of chemosensor 6
resulted in a ∼100 nm bathochromic shift (from λmax = 500 nm
to λmax = 600 nm) of the absorption band (Fig. S1a, ESI†) along
with color change of the solution from red to blue. This red shift
has been attributed to Cu2+ induced deprotonation of amine NH
of anthracene-9,10-dione moioety.23 Simulation of the spectral
data shows the formation of ML (log β 7.0 0.5) and M2L3 (log
β 25.0 0.8) species. The addition of Ni2+ to the solution of
chemosensor 3 resulted in deprotonation of the NH of both the
anthracene-9,10-dione moiety and the –OH group by which two
new bands appeared at λmax 700 nm and 445 nm, repectively.23e
Simultaneously, the absorption bands lying at λmax 500 nm and
415 nm decreased (Fig. S1b, ESI†). The spectral changes with
addition of Cu2+ and Ni2+ are similar to those obtained in the
case of chemosensor 2.23e The presence of other heavy metal
ions, alkali and alkaline earth metal ions caused nominal
changes in the absorption spectra of 3.
However, the UV-Vis spectrum of 4 exhibited absorption
bands at λmax 485 nm due to anthraquinone moiety and at λmax
435 nm due to hydroxyquinoline moiety. Addition of Cu2+ to
the solution of 4 (50 μM; CH3OH : H2O 4 : 1; pH 7.0 0.1;
10 mM HEPES) resulted in a ∼100 nm bathochromic shift of
the absorption band along with color change of the solution
from red to blue. Simulation of the spectral data shows the for-
mation of ML (log β 7.1 0.5) and M2L (log β 11.9 0.5)
species. However, addition of Ni2+, Co2+ and Zn2+ to a solution
of 4 resulted in a hypsochromic shift of the 435 nm absorption
band to 410 nm (Fig. 1) but the 485 nm band due to the
Synthesis of chemosensors 3–5
Stirring 1-(2-Aminoethylamino)anthracene-9,10-dione (1a)23a
with different aromatic aldehydes in ethanol resulted in the for-
mation of azo-methine derivatives 3–5, dark red solids
(Scheme 1).
Similarly, stirring of 1b23b with 2-hydroxy benzaldehyde in
ethanol gave chemosensor 6 (Scheme 2).
A. Photophysical studies of chemosensors 3–6
A1. Metal ion binding studies of chemosensors 3–6. Chemo-
sensor 3 showed two bands at 500 nm and 415 nm due to the
anthraquinone moiety and the hydroxynaphthalene group,
respectively. Addition of Cu2+ to solution of chemosensor 3
(50 μM; CH3OH : H2O 4 : 1; pH 7.0
0.1; 10 mM HEPES)
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another peak at λmax 385 nm was observed. The intensity of the
new peaks increased gradually with increasing concentration of
Ni2+ up to 25 μM and then a plateau was achieved. However, a
concomitant decrease in absorbance at λmax 530 nm with the
addition of Ni2+ was observed (Fig. S3b, ESI†). All these absor-
bance changes resulted in a visual change in color of the solution
from purple to blackish blue.
The titration fitting of the spectra obtained by titration of 6
(25 μM) with Co2+ or Ni2+ at pH 7.0 0.1 in CH3CN : H2O
(4 : 1) shows the formation of ML and M2L3 species as described
in eqn (1) and (2).
Fig. 1 Effect of different metal ions on UV-vis spectrum of chemosen-
sor 4.
Co2þ
Co2þ
ðCo2þÞ ꢁ 6
Co2þ ꢁ 6 ð1Þ
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ*
)ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ*
6
3 )ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ
2
logβM2L3¼22:6+0:3
logβML¼6:4+0:1
anthraquinone moiety remained unaffected. Therefore, the pres-
ence of an additional binding site i.e. nitrogen in the azo-
methine unit of chemosensor 4 in comparison with 2 leads to
preferable binding of Ni2+ with the 8-hydroxyquinoline unit and
did not cause Ni2+ induced deprotonation of the aryl NH
observed in the case of chemosensors 2 and 3. The presence of
other metal ions did not cause any notable change in the absorp-
tion spectrum of 4.
The absorption spectrum of chemosensor 5 (50 μM), which
lacks an –OH group, showed only nominal changes in its absorp-
tion maxima and absorbance in the visible region on addition of
0.001 M Na+, K+, Ca2+, Mg2+, Ba2+, Co2+, Cd2+, Zn2+ and Ni2+.
However, the addition of Cu2+, even in equimolar quantities to 5
caused switching of the absorption band from λmax 492 nm to
600 nm with a bathochromic shift of ∼100 nm. This resulted in
a visible change in color from red to blue (Fig. S2, ESI†).
Chemosensor 1b, possessing two aminoethylamino appen-
dages, has been found to bind with two Cu2+ ions in a stepwise
manner and on binding with Cu2+ showed emergence of two
new absorbance bands with red shift of nearly 150 and 265 nm,
respectively.23b These bands were associated with different color
changes dependent on the concentration of Cu2+ ions. So,
keeping in view these results, chemosensor 6 with two azo-
methine-ethylamino appendages at the 1 and 8 position of the
anthraquinone moiety was then synthesized, which would be sig-
nificantly more sensitive Cu2+ sensor than 2.23a,b
Ni2þ
Ni2þ
6
ðNi2þÞ ꢁ 6
Ni2þ ꢁ 6
ð2Þ
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ*
)ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ*
3 )ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ
2
logβM2L3¼24:0+0:4
logβML¼7:0+0:2
Contrary to changes observed with the addition of Co2+ and
Ni2+, the addition of Cu2+ to a solution of 6 (25 μM; pH 7.0;
CH3CN : H2O 4 : 1) results in precipitation due to separation of
Cu2+-complex, which did not allow estimation of Cu2+ ions.
Moreover, addition of Cu2+ caused a visual change in color from
red to blue.
The addition of other metal ions (25 μM) viz. Na+, K+, Ca2+,
Mg2+, Ba2+, Sr2+, Cd2+and Zn2+ to the solution of 6 (25 μM; pH
7.0; 10 mM HEPES: CH3CN : H2O 4 : 1) did not show any
visible color change or absorbance changes in the UV-vis
spectra (Fig. 2).
In order to avoid the micro-precipitaion caused by addition of
Cu2+, the photophysical studies were performed in THF : H2O
(4 : 1) mixtures. Addition of Cu2+ to a solution of 6 (25 μM;
THF : H2O 4 : 1; pH 7.0 0.1; 0.1 mM HEPES) resulted in a
decrease in absorbance at λmax 530 nm with the appearance of
two new bands at λmax 640 nm and 700 nm along with a color
change of the solution from purple to blue. Addition of Co2+ or
Ni2+ to a solution of 6 (25 μM; THF : H2O 4 : 1; pH 7.0 0.1;
0.1 mM HEPES) resulted in similar effects as those obtained in
the case of CH3CN : H2O mixture (Fig. S4, ESI†). Here, Cu2+
induced deprotonation of only aryl NH, while both Co2+ and
Ni2+ induced deprotonation of both aryl NH and –OH groups as
similar types of absorption curves were obtained in the case of 6
upon addition of Co2+ and Ni2+ (similar association constants,
Table 1).
The absorption spectrum of 6 (25 μM; CH3OH : H2O 4 : 1;
pH 7.0; 10 mM HEPES) showed λmax at 530 nm which on
addition of equimolar quantities of Cu2+, Ni2+ or Co2+ showed a
bathochromic shift of the absorption band, but within a few
minutes precipitation took place. So, due to the poor solubility
of the metal complexes in aqueous-methanol, further photophy-
sical studies were done in either CH3CN : H2O or THF : H2O
mixtures.
Simulation of the spectral data shows the formation of ML
and M2L3 species (Table 1). Significantly, the analysis of UV-vis
With gradual addition of Co2+ to 6 (25 μM; pH 7.0; 10 mM
HEPES: CH3CN : H2O 4 : 1), two new bands at λmax 700 nm
and 365 nm appeared and color of the solution underwent a
visible change from purple to blue. The decrease in absorbance
at λmax 530 nm and increase at λmax 700 nm and 365 nm
achieved their maximum values up to ∼25 μM of Co2+, and
addition of further Co2+ led to only nominal changes in their
absorption spectra (Fig. S3a, ESI†). On the other hand, on
addition of 2.5 μM Ni2+ to a solution of sensor 6 (25 μM; pH
7.0; 10 mM HEPES; CH3CN : H2O 4 : 1), the emergence of a
new broad peak between λmax 700 nm–780 nm along with
Fig. 2 Effect of different metal ions on the absorption spectrum of 6.
Dalton Trans., 2012, 41, 5217–5224 | 5219
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Table 1 log β values of 6–M2+ complexes in THF : H2O 4 : 1 at pH
7.0 0.1
M2+
log βML
log βM2L3
Cu2+
Co2+
Ni2+
6.2 0.1
5.4 0.1
5.2 0.1
21.6 0.3
19.6 0.4
19.7 0.2
spectral data obtained by titration of 6 with Cu2+ [in THF : H2O
(4 : 1)] and Co2+, Ni2+ [both in CH3CN : H2O (4 : 1) and
THF : H2O (4 : 1)] shows the formation of mainly 1 : 1 com-
plexes. All these complexes have log K values at 5.6 0.5. This
situation was quite favorable for estimation of Cu2+ and Co2+ or
Ni2+ in a similar manner as that observed with the help of che-
mosensor 2. However, keeping the solutions of 6–M2+ for more
than 5 h led to precipitation of complexes in the case of Cu2+.
So, the simultaneous estimation of metal ions could not be
performed.
A2. Effect of pH on 3–6 and their metal complexes. In order
to probe the nature of species formed during complexation of
3–6 with M2+, a series of pH and UV-vis titrations were per-
formed and the respective spectral data were analyzed using an
iterative method on multi-wavelength data using the programme
Specfit/32.26 The pKa values of chemosensors 3–6 were deter-
mined by observing the changes in their UV-vis spectra upon
titration of solutions of 3–6 with HCl or NaOH solutions,
separately.
Fig. 3 (a) Effect of pH on absorbance of 6; (b) Plot of absorbance of 6
(25 μM) at λmax 530 nm and 385 nm with change in pH. The points
refer to experimental values and solid line refers to curve fitting.
suggests deprotonation of the aryl amine NH and shows the for-
mation of different complexes as described in eqn (5).
Due to the poor solubility of chemosensor 3 in aqueous
DMSO or CH3OH under acidic and basic conditions, the effect
of pH on 1 : 1 solutions of M2+ − 3 could not be evaluated.
Addition of acid and base to a solution of 4 caused small
changes (∼10%) in absorbance with a ∼15 nm bathochromic
shift in basic medium. However, the absorbance at λmax 400 nm
gradually increased on increasing the pH from 2 to 12, without
causing any change in the color of the solution. Titration fitting
of the data shows the step-wise tri-protonation of 4 to form LH–
LH3 species (eqn (3)). Here, L represents the monoanion formed
by deprotonation of phenolic OH in 4.
ð5Þ
Fig. 3 shows the changes for 6 upon pH titration. Sensor 6 on
variation in pH from 2–12 showed only small changes at λmax
530 nm with a ∼15 nm bathochromic shift in basic region (pH
7–12). However, significant changes in absorbance values at
λmax 385 nm were observed with changes in pH. On lowering
the pH from 12, the absorption band at λmax 385 nm gradually
decreased till pH 9.0 and on further lowering the pH, no change
in spectrum was observed (Fig. 3). However, this change in
absorbance at λmax 385 nm did not lead to any visible color
change in 6. The analysis of these pH induced changes in the
absorbance of 6 through iterative titration fitting shows the step-
wise protonation of 6 (eqn (6)).
Hþ
Hþ
Hþ
4
4Hþ
4H2þ
4H3þ ð3Þ
ƒƒƒƒƒƒƒƒ!
ƒƒƒƒƒƒƒƒ!
ƒƒƒƒƒƒƒ!
log βLH9:0+0:02
log βLH213:9+0:1
log βLH316:1+0:4
The combination of pH and UV-vis titration of 1 : 2 solution
of 4-Cu2+ suggests deprotonation of the aryl amine NH and
shows the formation of M2LH−1 and M2LH−1(OH−) and MLH
species (eqn (4)).
ð6Þ
ð4Þ
Insight into formation of various species during titration of 6
with Co2+ or Ni2+ has been provided by using a combination of
pH and UV-vis titrations of solutions of 6 – M2+ (1 : 1) in
CH3CN : H2O 4 : 1. The evaluation of the spectral data obtained
by pH and UV-vis titration of the solution of 6–Co2+ (1 : 1) (eqn
(7), Fig. 4a) shows that chemosensor 6 at pH 6.5 starts forming
MLH−1 and above pH 10.0 forms MLH−1(OH−). However, in
In the case of chemosensor 5, only a small hypsochromic shift
(∼15 nm) of the λmax was observed in the acidic region. Titration
fitting of these data shows the formation of LH (log β 9.6 0.1),
LH2 (log β 17.4 0.2) and LH3 (log β 20.4 0.2). The combi-
nation of pH and UV-vis titration of 1 : 1 solution of 5 and Cu2+
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different pH values are helpful in mimicking the traffic mechan-
ism. To elaborate molecular trafficking based on Boolean arith-
metic, we envisaged Cu2+, Ni2+ and pH as inputs (pH values
greater than 6 and less than 6 are taken as 0 and 1, respectively);
Table 2 is constructed based on binary logic. Input 1 (pH) is
designated red signal, input 2 (Cu2+) is designated yellow signal,
input 3 (Ni2+) is designated green signal (Fig. 6). As the green
light in a traffic signal indicates permission to move forward and
the red light is a warning signal to stop, so, in a similar way, the
output in the absorption spectrum at 800 nm with high absor-
bance values (> 0.8) correlates with movement of ‘traffic on’ and
low absorbance values (< 0.3) correlates with movement of
‘traffic off’. At high pH values (pH values > 5), in the absence
of any chemical input, 6 shows no absorption peak at 800 nm
i.e. output is “0” (Table 1). By operation of input 3 (Ni2+ ions) to
6 at high pH values (pH values >5), a new absorption band with
an absorbance of 0.11 is observed and the output becomes “1”
Fig. 4 Species distribution of 6 as a function of pH for a system con-
taining (a) 6–Co2+ (1 : 1; 25 μM); (b) 6–Ni2+ (1 : 1; 25 μM).
the acidic region i.e. at pH ≤ 6.0, MLH starts forming and it
remains stable between pH 2 and 6. The 1 : 1 solution of 6–Ni2+
also shows the formation of MLH, MLH−1 and MLH−1(OH−)
species (eqn (8), Fig. 4b).
Fig. 5 Changes in the absorbance spectrum of 6 (25 μM; THF : H2O
4 : 1; pH 7.0 0.1) on addition of different metal ion solutions.
ð7Þ
Table 2 Boolean arithmetic operation on chemosensor 6
In 1
pH
In 2
In 3
Cu2+
Ni2+
Output at λ = 800 nm
ð8Þ
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
0
1
0
0
0
0
0
0
Thus, the combination of pH and UV-vis titrations reveals that
6 forms only 1 : 1 complexes with Co2+, Ni2+ and Cu2+ and, as
initially envisaged, M2L complexes are not formed. This is quite
remarkable that two arms of azomethine amino functionality do
not encapsulate two metal ions.
The metal ion interaction induced blue24 and red23,25 shifts in
a chromophore are marked with the respective decrease or
increase in electron-donating abilities of the substituents partici-
pating in interactions. In chemosensors 3–6, the red shift in the
case of Cu2+ and Ni2+ (or Co2+ in the case of chemosensor 6
only) points to aryl NH deprotonation.
B. Elaboration of molecular logic gates using chemosensor 6
The diverse photometric responses observed upon addition of
Cu2+ and Ni2+ to the solution of chemosensor 6 (Fig. 5) at
Fig. 6 Assignment of traffic signal colors to different inputs.
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Table 3 Truth table for the memory unit for two input signals Set (H+)
and Reset (Cu2+
)
Reset
In 1
Set
In 2
H+
Cu2+
Output at λ = 490 nm
0
1
0
1
0
0
1
1
1
0
1
1
Fig. 7 The feedback loop showing reversible logic operations for the
memory element with two inputs (Set and Rest) possessing “write–
Read–Erase–Read” functions with optical output signals.
(Table 2). Thus input 3 corresponds to the green color, which
directs the traffic to move (Fig. S5, ESI†).
By operation of input 2 (Cu2+ ions) to 6 at high pH values
(pH values > 5), no band appears at 800 nm (weak absorption
near 800 nm with an absorabance value of 0.01) i.e. the output
is “0” (Table 2). Input 2 corresponds to the yellow color which
directs the traffic to get prepared to stop and defines the ‘low’
value of absorbance (Fig. S6, ESI†). On sequential addition of
both the inputs, i.e. when input 2 (Cu2+ ions) follows input 3
(Ni2+ ions) at high pH values (pH values > 5), a very small
absorption peak with an absorbance value of 0.02 appears i.e.
the output is “0” (Table 2). Hence input 2 is added afterwards,
which means finally the yellow signal glows, which directs the
traffic to get prepared to stop (Fig. S7, ESI†). At low pH values
(pH values < 5), the absorption intensity of 6 at 800 nm is very
low in the absence or presence of any of the chemical inputs i.e.
at low pH values (pH values < 5) the output is “0” (Table 2).
Thus, the pH value less than 5 corresponds to the red signal,
which directs that traffic must stop (Fig. S8, ESI†).
under strong acidic or basic conditions. However, chemosensors
4 and 5 undergo significant absorption changes when Cu2+ ions
are added, with a small hypsochromic shift (∼25 nm) observed
with the addition of Ni2+, Co2+ and Zn2+ to a solution of 4. On
the other hand, chemosensor 6, possessing two hydroxybenzene
units, gives color and absorption changes with the addition of
Cu2+ or Ni2+ or Co2+. Furthermore, the different optical output
signals (i.e. absorbance) observed with addition of various metal
ions to a solution of 6 can be used for mimicking the operation
of a traffic signal and “Set–Reset” molecular level information
processing device.
Experimental
Also, molecular switching using Cu2+ and H+ as chemical
inputs has been integrated into sequential logic circuits with
memory function in a feedback loop which mimics a “Set–
Reset” molecular level information processing device. Here, In 2
is “0” when the pH value is 7 and In 2 is “1” when the pH value
is less than 4. Without addition of “Set” or “Reset” inputs i.e. In
1 and In 2, the output is “read” out optically as high absorption
intensity at 490 nm. When “Set” input is high (In 2 = 1), the
system “writes” and “reads” “logic state 1” with high absorbance
at 490 nm (Table 3, Fig. S9, ESI†). The stored information was
“erased” by the “Reset input” (In 1 = 1) with low absorption
intensity at 490 nm and system write and save “logic state 0”
(Fig. S9, ESI†). For evaluating the multiple “rewriting” ability of
chemosensor 6, many write–erase cycles were performed which
showed that write–erase cycles could be repeated many times
with the same solution without any appreciable reduction in
intensity in the absorption spectra. These reversible sequences of
“Set–Reset” logic operations in a feedback loop demonstrate the
memorized state of the system with “Write–Read–Erase–Read”
functions with an optical output signal at 490 nm (Fig. 7).
General considerations
Melting points were determined in capillaries and are uncor-
rected. H NMR spectra were recorded on JEOL Al 300 MHz
1
instrument using CDCl3 solution containing tetramethylsilane
(TMS) as an internal standard. The chemical shifts are reported
in δ values relative to TMS and coupling constants (J) are
expressed in Hz. 13C NMR spectra were recorded at 75 MHz
and values are reported relative to CDCl3 signal at δ 77.0.
Chromatography was performed with silica gel 100–200 mesh
and the reactions were monitored by thin layer chromatography
(TLC) with glass plates coated with silica gel HF-254. FAB
mass spectra were recorded as normal ion [MF-Linear]. The pH
of the solutions was maintained by using (N-[2-hydroxyethyl]
piperazine-N′-2-ethanesulphonic acid (HEPES) buffer (10 mM).
Photophysical studies
All the solvents were of analytic grade and were used after distil-
lation. The solutions of metal ions were prepared in distilled
water. All pH measurements were made with an equip-tronics
pH-Meter. UV-vis spectroscopy experiments were carried out on
a Shimadzu UV-1601 PC UV-vis Spectrophotometer by using
slit widths of 1.0 nm and matched quartz cells. In the case of
visible absorption spectra as a function of pH, aliquots of acid or
base were added manually with the help of a micropipette.
Enough time was allowed after the addition of metal ion or acid
or base in order for the pH of the mixture to reach the equili-
brium. All absorption scans were saved as ACSII files and were
Conclusions
In conclusion, we synthesized chemosensors 3–6 based on ami-
noanthraquinone derivatives having schiff base linkages and
evaluated them using absorption (UV-vis) studies. Chemosensor
3 undergoes color and absorption changes with addition of
Cu2+–Ni2+ but has poor solubility in aqueous DMSO or CH3OH
5222 | Dalton Trans., 2012, 41, 5217–5224
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further processed in Excel™ to produce all of the graphs shown.
Solutions of 3–5 were typically 50 μM and that of 6 was 25 μM.
(C), 134.77 (C), 135.47 (CH), 136.38 (CH), 148.10 (C), 151.84
(C), 160.43 (CH), 170.55 (C), 183.23 (C), 185.14 (C); Found C
74.27; H 4.68; N 10.10%. C26H19N3O3 requires C 74.10; H
4.54; N 9.97%.
Synthesis of chemosensor 2
Chemosensor 5. Dark red solid; 72%; m.p. 135 °C; FAB mass
1
M+ m/z 406 (M+ + 1); H NMR (CDCl3): δ 3.80 (q, J = 5.7 Hz,
1-(2-aminoehylamino)anthracene-9,10-dione (1a) (532 mg,
2 mmol) was dissolved in ethanol and then 1-hydroxynaphtha-
lene-2-carbaldehyde (413 mg, 2.4 mmol) was added to the sol-
ution. The reaction mixture was stirred at 60 °C for 7 h. After
completion of the reaction, the solid formed was filtered and
then crystallized from ethanol to give pure 3.
2H, CH2), 4.10 (t, J = 5.7 Hz, 2H, CH2), 7.20 (d, J = 8.1 Hz,
1H, ArH), 7.53–7.62 (m, 3H, ArH), 7.70–7.77 (m, 3H, ArH),
7.86 (d, J = 7.8 Hz, 1H, ArH), 8.11 (d, J = 8.4 Hz, 1H, ArH),
8.21–8.25 (m, 4H, ArH), 8.63 (s, 1H, CH), 10.02 (bs,1H, NH,
exchanges with D2O); 13C NMR (normal/DEPT-135) (CDCl3): δ
43.42 (CH2), 60.23 (CH2), 113.34 (C), 115.8 (CH), 118.00
(CH), 118.48 (CH), 126.64 (CH), 126.74 (CH), 127.54 (CH),
127.71 (CH), 128.83 (C), 129.62 (CH), 129.83 (CH), 132.88
(CH), 132.96 (C), 133.88 (CH), 134.69 (C), 134.96 (C), 135.19
(CH), 136.65 (CH), 147.73 (C), 151.62 (C), 154.40 (C), 164.30
(CH), 183.81 (C), 185.00 (C); Found C 77.17; H 4.68; N
10.26%. C26H19N3O2 requires C 77.02; H 4.72; N 10.36%.
Similarly, the stirring of 1a with different aldehydes in ethanol
gave chemosensors 4–5.
Chemosensor 3. Dark red solid; 70%; m.p. 195 °C; FAB mass
M+ m/z 421 (M+ + 1); IR νmax (KBr) 1635 (CvO), 1654
(CvO), 3430 (NH–OH) cm−1; 1H NMR (CDCl3): δ 3.77 (q, J =
6.0 Hz, 2H, CH2), 3.99 (t, J = 6.0 Hz, 2H, CH2), 6.99 (d, J = 9.0
Hz, 1H, ArH), 7.11–7.22 (m, 2H, ArH), 7.28–7.34 (m, 1H,
ArH), 7.54–7.62 (m, 3H, ArH), 7.65–7.74 (m, 3H, ArH), 7.88
(d, J = 7.4 Hz, 1H, ArH), 8.15–8.21 (m, 2H, ArH), 8.94 (s, 1H,
CH), 9.97 (bs,1H, NH, exchanges with D2O); 13C NMR
(normal/DEPT-135) (CDCl3): δ 43.45 (CH2), 54.57 (CH2),
96.13 (C), 113.67 (C), 116.31 (CH), 117.62 (CH), 118.45 (CH),
122.88 (CH), 122.99 (CH), 126.66 (CH), 126.80 (CH), 127.77
(CH), 129.11 (CH), 132.93 (CH), 133.03 (C), 133.23 (C),
133.88 (CH), 134.77 (C), 135.47 (CH), 136.38 (CH), 151.34
(C), 160.43 (CH), 171.55 (C), 183.53 (C), 185.34 (C); Found C
77.27; H 4.9; N 6.46%. C27H20N2O3 requires C 77.13; H 4.79;
N 6.66%.
Synthesis of chemosensor 6
1,8-di(2-aminoehylamino)anthracene-9,10-dione (1b) (648 mg,
2 mmol) was dissolved in ethanol and then 2-hydroxybenzal-
dehde (610 mg, 5 mmol) was added to the solution. The reaction
mixture was stirred for 6–8 h at 60 °C. After completion of the
reaction, the solid was filtered and was crystallized from ethanol
to give pure 6.
Chemosensor 6. Dark purple solid; 75%; m.p. 165 °C
1
(C2H5OH–CHCl3); FAB mass M+ m/z 533 (M+ + 1); H NMR
(CDCl3): δ 3.64 (q, J = 6.0 Hz, 4H, CH2), 3.89 (t, J = 6.0 Hz,
4H, CH2), 6.87 (t, J = 8.1 Hz, 2H, ArH), 6.96 (d, J = 8.1 Hz,
2H, ArH), 7.06 (d, J = 8.4 Hz, 2H, ArH), 7.23 (d, 2H, ArH),
7.32 (t, J = 8.7 Hz, 2H, ArH), 7.48 (t, J = 8.1 Hz, 2H, ArH),
7.53 (t, J = 6.3 Hz, 2H, ArH), 8.39 (s, 2H, CH), 9.77 (bs, 2H,
NH, exchanges with D2O), 13.1 (bs, 2H, OH, exchanges with
D2O); 13C NMR (normal/DEPT-135) (CDCl3): δ 43.34 (CH2),
58.66 (CH2), 115.35 (C), 116.98 (CH), 117.60 (CH), 118.69
(CH), 118.79 (C), 131.51 (CH), 132.43 (CH), 134.27 (CH),
134.68 (CH), 150.89 (C), 160.96 (C), 166.78 (CH), 184.31 (C),
186.24 (C); Found C 72.27; H 5.42; N 10.46%. C32H28N4O4
requires C 72.16, H 5.30; N 10.52%.
Synthesis of 3–Ni complex
Chemosensor 3 (420 mg, 1 mmol) was dissolved in THF and
the aqueous methanol solution of Ni(ClO4)2 (365 mg, 1 mmol)
was added to this with stirring. The pH of the solution was main-
tained at 8.0 and it was allowed to stand at 25 °C for two days.
The solid formed was filtered and washed well with CH3OH–
CH2Cl2. The solid was dried in air to get Ni2+ complex of 3.
Complex 3–Ni2+. Dark green solid; 75%; m.p. 280 °C
(C2H5OH–CHCl3); FAB mass M+ m/z 479 (M+ + 1) H NMR
1
(CDCl3): δ 3.27 (t, J = 6.9 Hz, 2H, CH2), 3.65 (t, J = 6.9 Hz,
2H, CH2), 7.06–7.22 (m, 5H, ArH), 7.39–7.47 (m, 2H, ArH),
7.64 (t, J = 6.9 Hz, 2H, ArH), 7.70–7.77 (m, 2H, ArH), 8.18 (d,
J = 7.8 Hz, 1H, ArH), 8.22 (s, 1H, ArH), 8.31 (d, J = 8.1 Hz,
1H, ArH).
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5224 | Dalton Trans., 2012, 41, 5217–5224
This journal is © The Royal Society of Chemistry 2012