A New Compound for Sequential Sensing of Picric Acid and Aliphatic Amines: Physicochemical Details and Construction of Molecular Logic Gates

Article abstract of DOI:10.1002/asia.202100117

Picric acid (PA) at low concentration is a serious water pollutant. Alongside, aliphatic amines (AAs) add to the queue to pollute surface water. Plenty of reports are available to sense PA with an ultralow limit of detection (LOD). However, only a handful of works are testified to detect AAs. A new fluorescent donor-acceptor compound has been synthesized with inherent intramolecular charge transfer (ICT) character that enables selective and sensitive colorimetric quantitative detection of PA and AAs with low LODs in non-aqueous as well as aqueous solutions. The synthesized compound is based on a hemicyanine skeleton containing two pyridenylmethylamino groups at the donor and a benzothiazole moiety at the acceptor ends. The detailed mechanisms and reaction dynamics are explained spectroscopically along with computational support. The fluorescence property of the detecting compound changes due to protonation of its pyridinyl centers by PA leading to quenching of fluorescence and subsequently de-protonation by AAs to revive the signal. We have further designed logic circuits from the acquired optical responses by sequential interactions.

Full text of DOI:10.1002/asia.202100117

DOI: 10.1002/asia.202100117
Full Paper
A New Compound for Sequential Sensing of Picric Acid and
Aliphatic Amines: Physicochemical Details and Construction of
Molecular Logic Gates
[
a]
[a]
[b]
[a]
Ashutosh Ghosh, Sourav Kanti Seth, Arnab Ghosh, Pradip Pattanayak,
[
c]
[a]
Arabinda Mallick,* and Pradipta Purkayastha*
Abstract: Picric acid (PA) at low concentration is a serious
water pollutant. Alongside, aliphatic amines (AAs) add to the
queue to pollute surface water. Plenty of reports are available
to sense PA with an ultralow limit of detection (LOD).
However, only a handful of works are testified to detect AAs.
A new fluorescent donor-acceptor compound has been
synthesized with inherent intramolecular charge transfer (ICT)
character that enables selective and sensitive colorimetric
quantitative detection of PA and AAs with low LODs in non-
aqueous as well as aqueous solutions. The synthesized
compound is based on a hemicyanine skeleton containing
two pyridenylmethylamino groups at the donor and a
benzothiazole moiety at the acceptor ends. The detailed
mechanisms and reaction dynamics are explained spectro-
scopically along with computational support. The
fluorescence property of the detecting compound changes
due to protonation of its pyridinyl centers by PA leading to
quenching of fluorescence and subsequently de-protonation
by AAs to revive the signal. We have further designed logic
circuits from the acquired optical responses by sequential
interactions.
Introduction
report on the use of a Tröger’s base structural motif using a 4-
amino-1,8-naphthalimide incorporated nitrogen-rich Zn(II) coor-
[8]
Picric acid (PA) or trinitrophenol (TNP) is very well known
because of its explosive nature at high concentrations and a
major and notorious surface water pollutant at very low
concentrations. Plenty of works are available to detect PA using
various types of sensors, many of them with extremely low limit
of detection (LOD). One example is the electron-rich oligofluor-
anthene class of strongly fluorescent compounds that detect
electron deficient Fe(III) ions and PA through fluorescence
quenching mechanism via photoinduced electron transfer
dination polymer yielded good results. Host-guest based
competitive binding controlled aggregation-induced emission
[9–17]
(AIE) method came handy in detecting PA.
Even carbon dot-
based polypyrrole nanocomposites and sol-gel methods also
[
18–25]
proved beneficial for PA detection.
Moreover, modern day
and covalent-organic-
[
26–38]
metal-organic-frameworks (MOFs)
[39–41]
frameworks (COFs)
were found to provide good sensor
materials for PA in different solvents. There are numerous small
[
42–56]
molecule sensors as well to detect PA with low LOD.
Zinc
[1]
(
PET). Such polymer and PET-based mechanism was also used
oxide nanomaterials and fluorescent quantum dots were also
[57,58]
to detect PA using donor-acceptor type polymer films, con-
jugated microporous polymers, lanthanide coordination poly-
mers, azo-linked covalent organic polymers and polymer
helpful in PA detection.
The fluorescent outputs due to the
sensing mechanisms were effectively used to prepare logic
[59,60]
based devices in some cases.
[2–7]
nanoparticles.
Additionally, supramolecular materials were
Similarly, there are reports on the detection of aliphatic
amines (AAs) with low LODs in various samples using different
techniques. Self-stabilized micelles of fluorescent block copoly-
effectively used to detect PA with appreciable LODs. A recent
[61]
mers were used to detect AA in surface water. An inter-
penetrated zinc-based coordination polymer could measure it
[
a] Dr. A. Ghosh, Dr. S. K. Seth, P. Pattanayak, Prof. P. Purkayastha
Department of Chemical Sciences
[62]
in all the states of matter, and various polymer matrices were
Indian Institute of Science Education and Research (IISER) Kolkata
WB 741262 Mohanpur, (India)
E-mail: ppurkayastha@iiserkol.ac.in
[63]
used to detect volatile AA. An armory of small molecules was
also effectively used in AA sensing. Ranging from BODIPY
[
[
b] A. Ghosh
Department of Materials Science
Indian Association for the Cultivation of Science
[64]
[65]
fluorophores, zinc-based Schiff base complex, trifluoroace-
[66]
[67]
tophenone-based dyes, certain diarylethenes, aminonaph-
thalene anhydrides,
distyrylbenzenes
algae were used to detect AA efficiently.
[68]
[69]
700032 Jadavpur, Kolkata (India)
perylene derivatives,
extended
c] Dr. A. Mallick
Department of Chemistry
[70]
to bio-inspired diatoms derived from
[71]
Kazi Nazrul University
Kalla Bypass More, WB 713340 Burdwan, (India)
E-mail: ampcju@yahoo.co.in
In this flurry of works to detect PA and AA in different types
of samples under various circumstances, a prominent lacuna is
observed in using the same system to detect both of them
sequentially. Moreover, very few of these reports have
described the dynamics of PET or intramolecular charge transfer
Supporting information for this article is available on the WWW under
https://doi.org/10.1002/asia.202100117
This manuscript is part of a special collection celebrating the 15 Anniver-
th
sary of IISER Inception.
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Full Paper
(ICT) elaborately to obtain a clear and deeper insight into the Results and Discussion
sensing mechanism. Since, the fundamental concept behind
the detection of PA is exploiting its very strong acidic character
and the strong basicity of the AAs, we could conceive an idea
of synthesizing a sensitive organic compound bearing (i) donor-
acceptor property to exhibit ICT for fluorescence signaling, (ii)
suitable prototropic centers to accept proton based on the pKa
values and (iii) good enough protonated form to allow a strong
base to extract proton/s. Such a compound could be obtained
from the hemicyanine family elaborately reported by Kabatc
Selective sensing of PA by 1c
The possible selectivity of 1c toward TNP or PA over the other
nitro compounds mentioned above, was examined from the
changes in the spectroscopic signals of the probe due to
titration with the additives (Figures S2 and S3). The absorption
spectrum of 1c shows a clear change in character from an
unstructured to a structured spectrum with an appreciable
hypsochromic shift (Figure S2A). This indicates conversion of
one form of 1c to another on interaction with PA (0–40 μM) in
acetonitrile solution. The other nitro compounds practically do
not affect the spectrum (Figures S2B–E). The fluorescence of 1c
gets remarkably quenched due to this process with a blue shift
(Figure S3A) with no appreciable effect by the other nitro-
analytes. We have presented several situations of selective
effect of PA on 1c in acetonitrile solution in Figure 1. The
figures demonstrate noticeable quenching of 1c on addition of
PA under various circumstances of the other nitroanalyte
mixtures.
[72,73]
[74]
et al.
We adopted the protocol reported by Xu et al. to
synthesize 1a (N,N-bis(pyridin-2-ylmethyl)aniline) and 1b (4-(bis
pyridin-2-ylmethyl)amino)benzaldehyde) and added a benzo-
(
thiazolium moiety to 1b to serve as the acceptor end, thereby
to get the desired compound 1c ((E)-2-(4-(bis(pyridin-2-ylmeth-
yl)amino)styryl)-3-ethylbenzo[d]thiazol-3-ium
iodide)
Scheme 1). The synthetic method and characterization of 1c
Figure S1) are elaborately described in the supporting informa-
(
(
tion. The compound 1c was designed to effectively detect PA
as well as the AAs, using the same platform.
The pyridine moieties of 1c are mildly basic centers
(
pKa 7.2) that would attract proton from the extremely strong
PA induces maximum quenching (about 92%) of the 1c
fluorescence compared to the other nitroanalytes. Feeding the
fluorescence intensities of 1c obtained at 588 nm in absence
(I0) and presence (I) of the various nitroanalytes to the Stern-
Volmer equation: I =I ¼ 1 þ K ½Q�, where K and ½Q� are the
acid 2,4,6-trinitrophenol (TNP) or PA (pKa 0.42) selectively from
a mixture of 2,4-dinitrophenol (DNP, pKa 4.09), 4-nitrophenol
(NP, pKa 7.07), 2,4-dinitrotoluene (DNT, pKa 13.53) and 4-nitro-
toluene (NT, pKa 11.27). Subsequently, the protonated 1c
becomes a good acid for strong bases like the AAs (triethyl-
amine (TEA, pKa 10.21), triisopropylamine (TIPA, pKa 11.06),
diethylamine (DEA, pKa 10.58) diisopropylamine (DIPA, pKa 36)
and methylamine (MA, pKa 10.63). The results were compared
with dimethylaniline (DMA, pKa 5.15) and aniline (AN, pKa 4.6)
bases as control. The sensitivity of 1c is appreciable with low
LODs. We used the most popular colorimetric method of trace
detection and explained the mechanism in detail. The previous
reports greatly lacked the vivid elaboration of the dynamics of
PET/ICT that we have showed here along with computational
calculations supporting the experimental findings. Moreover,
we used the sequential PA and AA detection method of 1c in
developing interesting logic devices that may greatly aid
computational detection. Although the initial experiments were
performed in acetonitrile, we have shown that the tests are
valid for aqueous samples as well. In addition, paper-strips
could also be used to visually detect the color changes due to
the interactions of 1c with PA and AAs.
0
SV
SV
quenching constant and the concentration of the quencher,
respectively, we obtained a non-linear fitting with an upward
offset for PA (Figure 2A). The other analytes produced linear
fittings to the data. The non-linearity for PA indicates simulta-
neous static and dynamic quenching of 1c, which could be due
to hydrogen bonding interaction between 1c and PA before
the dynamic proton transfer. From this non-linear curve fitting,
[
75]
using
the
modified
Stern-Volmer
equation:
Figure 1. Comparison of the photoluminescence (PL) intensity of 1c in
acetonitrile (A) in the presence of PA, DNP, NP. DNT and NT; (B) before and
after the addition of the nitroanalytes (80 μL, 1 mM) separately followed by
the addition of the same amount of TNP: the brown, red and pink bars
represent the PL intensities of 1c, on adding the various nitroanalytes to 1c
and the subsequent addition of PA (80 μL, 1 mM) to the mixture (I. DNP, II.
DNT, III. NP and IV. NT; (C) on gradual addition of the nitroanalytes to 1c.
The samples were excited at 505 nm.
Scheme 1. Structure of (E)-2-(4-(bis(pyridin-2-ylmethyl)amino)styryl)-3-ethyl-
benzo[d]thiazol-3-ium iodide (1c).
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the quenched fluorescence of 1c by PA is supposed to be
restored by the AAs as we found and depicted in Figure 3. MA
behaves slightly differently as its sensitivity to the protonated
1
c develops above 36 μM (Figure 3E). The fascination of 1c
towards the AAs over the aromatic ones is remarkable as we
could recover ~90% of the PA-quenched fluorescence (Fig-
ure 3H). The calculated LOD of 1c for the AAs is 27 μM in
acetonitrile. This LOD value is quite comparable to the existing
AA sensing data using various other systems (Table S1B). There
is a clear bathochromic shift of the emission spectrum of the
quenched 1c on interacting with the AAs and hence, the
change in color of the solution is visible by naked eyes
(Figure 4A). Experiment on paper strips is also successful which
helps in making the application handy (Figure 4B). It is note-
Figure 2. (A) Stern-Volmer plots of the quenching of 1c on interaction with
the nitroanalyte quenchers, (B) comparison of the extent of quenching of 1c
fluorescence by the nitro analytes and (C) gradual quenching of 1c by PA
compared to the other nitro analytes.
k½PA�
0:0594½PA�
I =I ¼ Ae
0
þ B ¼ 1:29e
À 0:93, we obtain the static
4 À 1
quenching constant (k) as 5.94 x 10 M that reinforces the
hypothesis of hydrogen bond interaction. Linear fitting to the
Stern-Volmer equation for the other nitroanalytes shows colli-
sional interaction with 1c without any static interaction. 92%
quenching percentage of PA (Figure 2B) signifies absolute
specificity of 1c to PA, which is also observed from Figure 2C.
We calculated the binding constant of PA with 1c using the
[76]
Benesi-Hildebrand equation:
1
1
1
¼
þ
(
1)
and I are the
min
I0 À I KðI À IminÞ½PA� ðI À IminÞ
0
o
where, K is the binding constant and I , I
0
fluorescence intensities of 1c without, at the maximum and
varying PA concentrations, respectively. The plot of 1=ðI À IÞ
0
vs. 1=½PA�gives a linear fit (Figure S4) from where the binding
5
À 1
constant was calculated to be 2.72×10 M that establishes
strong binding between the species.
A
plot of
ðI À IÞ=ðI À I Þ vs. log½PA� (Figure S5) gives a linear fit to
max
max
min
the raw data yielding the LOD of PA by 1c in acetonitrile
[42]
solution from the intercept on the x-axis.
The LOD was
Figure 3. (A–D) Restoration of the PA quenched PL of 1c by AAs (TEA, TIPA,
DEA and DIPA, respectively), (E) MA starts reviving the fluorescence above
9
calculated from, ([PA]×MWPA)/1000 multiplied by 10 to get
the value in ppb), where MWPA is the molecular weight of PA.
The LOD, 363 ppb (equivalent to 1.59 μM), is quite low in this
case. This is very competitive with the existing LOD data in the
literature as provided in Table S1A.
3
6 μM concentration (refer to inset), and (F, G) effects of DMA and AN on
the quenched PL of 1c. The insets show that DMA and AN are insensitive
even up to 72 μM. (H) comparison of percentage recovery of 1c emission by
the amines (up to 36 μM).
Recovery of PA-quenched fluorescence of 1c by the AAs
The protonated form of 1c due to interaction with PA should
be deprotonated by the strong AA bases, such as, TEA, TIPA,
DEA, DIPA and MA, while the aromatic amines, such as, DMA
Figure 4. Visual change of color of 1c on application of PA and TEA in
sequence (A) in acetonitrile solution and (B) on paper strips.
and AN, shall remain undetected due to their low pK . Hence,
a
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worthy to mention here that 1c is insensitive to the AAs in
absence of PA as shown by its practically unchanged
fluorescence intensity (Figure S6).
ICT and the faster component signifies a new non-radiative
channel for electron transfer from 1c to PA, which circum-
stantially caused the reduction of ICT in 1c. The fluorescence
up-conversion measurement is in well accordance with the
substantial quenching of the ICT fluorescence of 1c due to
interaction with PA or, in other words, because of the complex
formation. However, as seen in the steady state fluorescence
study with added TEA to the PA-quenched emission of 1c, the
time-resolved decay components responded alike. The electron
transfer process becomes slower and a new growth component
of 22 ps appears that signifies reasonable back electron transfer
to 1c, thus recovering the quenched fluorescence. The
apparent 39 ps decay of the ICT state gets reinforced by the
back donation of electron (30% contribution) due to the
participation of TEA.
Analysis by time-resolved fluorescence up-conversion
spectroscopy
To have a deeper insight to the phenomenon of selective
sensing, we present the findings from time-resolved ultrafast
fluorescence up-conversion spectroscopy. The excited state
decay dynamics of pristine 1c, 1c with PA and 1c with PA and
TEA (representative AA) were investigated in a much shorter
time scale. All the measurements were carried out with 400 nm
pump beam and the decay traces were probed at the emission
wavelength of 1c, i.e., 588 nm. A comparison of dynamics (at
the emission probe position) for all the samples is shown in
Figure 5. Interestingly, faster decay kinetics is observed for 1c-
PA complex compared to pristine 1c. The decay profile at
Sensing capability of 1c in water
5
88 nm fits well with the single exponential component for 1c,
The same process becomes more beneficial if replicated in
water sample. Since, both the additives, PA or the AAs, are
potential pollutants for surface water, hence we attempted their
selective detection in aqueous medium using the same
technique. 1c is extremely sensitive to the environment pH and
shows distinct phases of spectral shifts due to deprotonation at
higher pH (Figures S7A and B). The shift in the emission
maximum plateaued around pH=7.2 (Figure S7C). This inherent
pH sensitivity of 1c is exploited by PA and AAs in selective
sensing. We dissolved 1c in water using acetonitrile (2%) as co-
solvent and tested with PA and aliphatic amines. The results
were similar to the non-aqueous solutions as depicted in
Figure S8A–E. The LODs for 1c in aqueous medium were 3 and
bi-exponential components for 1c-PA and tri-exponential
components for 1c-PA-TEA (Table 1).
As mentioned earlier, ultrafast ICT controls the excited state
dynamics of 1c which decays within 70 ps. For 1c-PA, the time-
resolved fluorescence data were fitted with a bi-exponential
routine decaying in 1 and 55 ps, respectively. Reduction in
decay time of the longer component suggests decrease in the
4
4 μM, respectively for PA and the AAs.
Computational study
To elucidate the mechanism of interaction of 1c with PA in
more detail, we performed density functional theory (DFT)
based computational studies using the Gaussian 09 program
[77]
package. B3LYP hybrid functional and 6–31G basis set were
used for the calculations. The calculated HOMO-LUMO energy
levels for the various nitroanalytes are shown in Scheme 2A,
which portrays that the quenching efficiency is superior for PA
Figure 5. Femtosecond fluorescence up-conversion decay curves of (A) 1c,
(B) 1c-PA and (C) 1c-PA-TEA (λabs:400 nm and λem: 588 nm).
Table 1. Fitting parameters of femtosecond fluorescence up-conversion
decay of 1c with PA and TEA under different circumstances. The subscript
‘
g’ represents growth component and a
i
’s are the weightage of the
respective components.
Sample [ps]
τ
1
a
1
τ
2
[ps] a
a
2
τ
3g [ps]
3
1
1
1
c
70
55
39
1
0.75
0.62
–
1
2.8
–
0.25
0.08
–
–
22
–
–
0.30
Scheme 2. Calculated energy levels of (A) 1c and the different nitroanalytes
and (B) effect on the energy levels due to the 1c-PA complex formation. The
black and red lines represent the HOMOs and LUMOs of the species.
c-PA
c-PA-TEA
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over the others due to the comfortable positioning of the
LUMO (À 3.51 eV) with respect to that of 1c (À 2.85 eV) making
the PET process lucid. The LUMO energies of the other
nitroanalytes are higher and unsuitable for efficient
fluorescence quenching due to PET. As described earlier, PA
attaches to 1c through strong hydrogen bonding to the
prototropic centers stabilizing the LUMO facilitating PET
(Scheme 2B). The HOMO-LUMO energy gap of 1c and 1c-PA
complex are 2.77 and 3.63 eV, respectively which explains the
hypsochromic shift of 1c upon gradually addition of PA.
Confirmation of hydrogen bonding interaction of the
analytes with 1c
To consolidate the strong hydrogen bonding interaction of PA
with the dangling pyridine moieties of 1c to form the 1c-PA
complex as predicted before and supported by the theoretical
results, we examined the effect of viscosity and temperature on
the molecular motion and hence the ICT emission of 1c. The
intensity of 1c fluorescence intensifies considerably in the
comparatively rigid medium provided by glycerol and lower
temperature (Figure S9). The apparent rigidity presumably
restricts the CÀ N and CÀ C bond rotations. We confirmed this
1
observation from variable temperature (VT) H-NMR spectro-
scopy. It was observed that upon increasing the temperature
from 25°C to 90°C, the H proton (δ=6.86) is more deshielded
i
1
indicating higher rotational motion of CÀ N bond (Figure 6A).
Figure 6. (A) VT H-NMR spectra (selected region) of 1c (solvent=DMSO-d )
6
1
1
and (B) H-NMR titration of (a) 1c upon gradual addition of (b) 0.5 equiv., (c)
.0 equiv. and (d) 3.0 equiv. PA in DMSO-d
protons of 1c for convenience.
H-NMR titration of 1c illustrated that successive addition of PA
1
6
. The inset shows the assigned
shifts the pyridine protons (H , H , H , H ) and the methylene
e
f
g
h
proton (H ) downfield (Figure 6B). This observation clearly
m
reflects protonation of the pyridine nitrogen atoms. The upfield
shift of the H proton is due to the breaking of the hydrogen
i
bonds between the pyridine nitrogen and the H proton of the
anilinic ring upon gradual addition of PA. No distinct H NMR
signal for the tertiary N-atom indicates that it does not get
protonated in the process and hence, the sensing mechanism
proceeds through 1:2 host-guest binding. We found confirma-
tion for such binding in a Job’s plot that we constructed for the
be utilized as ‘Input B’. The absorption values always remained
above the threshold except for the situation of solitary PA. In
presence of PA only the output response was OFF that
designated the binary value 0. Furthermore, considering the
emission responses at 588 nm another IMPLICATION logic gate
could be designed considering the same device and same
chemical inputs. In this logic designing signal from 10 μM 1c
was coupled to the optimum concentrations of the ‘Input A’
(40 μM) and ‘Input B’ (36 μM), respectively (Figure 7A).
i
1
1
c-PA conjugate formation (Figure S10). The relative change in
absorbance showed a break at mole fraction ~0.65 indicating
:2 host-guest stoichiometry.
1
Construction of logic devices from the acquired results
The exhilaratingly selective sensing capability of PA and the
AAs by 1c tempted us to apply the concept in preparing
molecular logic gates. The optical responses in combination
with the chemical retorts were converted to binary 0 s and 1 s
after application of proper threshold to a particular optical
output channel. A dual input single output IMPLICATION logic
gate was designed on the unimolecular platform of 1c,
considering the absorption values received at the 505 nm
channel (Figure S2A). In the IMPLICATION logic designing, signal
from 40 μM PA addition was considered as ‘Input A’, simulta-
neously any of the amines, TIPA/DIPA/TEA/DEA (36 μM) could
Figure 7. Development of IMPLICATION, TRANSFER and AND logic gates.
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Simultaneously, considering the 440 nm absorption channel
Figure S1A), a TRANSFER logic gate was designed with the
channel, respectively. In the memory unit, chemical input PA
was treated as the RESET key, simultaneously any of the amines,
DIPA/TIPA/DEA/TEA could be employed as the SET key.
Whenever the RESET input was high (R=1), the existing ‘1’ state
would be erased and the ‘0’ state will be written and
memorized. In contrast, the system would write and memorize
the binary state ‘1’ as the SET input was high (S=1). Most
interestingly compared to the previously designed chemical
(
same device and same chemical inputs (Figure 7B). TRANSFER
gate is the combination of one NOT, two AND and one OR gate
in a specific approach. In this logic gate the output channel is
simply the reflection of the binary record of a particular input.
Here, the output adopted binary 1 value (‘ON’ situation) for the
situations where PA (Input A) was present, irrespective the
presence or absence of Input B. Interestingly, the concentration
dependent optical responses of 1c-PA system could be utilized
to mimic the truth table of a AND logic gate (Figure 7C). The
initial emission of 1c at 588 nm turned OFF in presence of PA.
Now considering this 1c-PA system as the initial state, addition
of 36 μM MA left the active state as OFF. Whereas, further
[78,79]
triggered memory units,
the versatility of this memory unit
is expected to be much higher as the switching of ‘ON-OFF’
states of ADBTZ (reversibility cycle) could be repeated so many
times without any performance breakdown (Figure 9).
addition of another 36 μM MA to this mixture (10 μM 1c, 40 μM Conclusion
PA and 36 μM MA), turned the fluorescence ON at 588 nm. So,
considering the 36 μM MA as both the inputs (Input A as well
as Input B) a AND gate could be simply designed. Here, the
output channel only adopted the ‘ON state’ in presence of both
the inputs, i.e., a total 72 μM MA.
We have synthesized a new fluorescent ICT probe for selective
and sensitive colorimetric detection of PA over other nitro-
analytes, as well as AAs over the aromatic ones. Both PA and
the AAs are known to be environmentally hazardous even at
appreciably low concentrations. The synthesized compound
(1c) is capable to efficiently detect both pollutants with low
LODs in non-aqueous as well as aqueous media. The detection
is based on colorimetry and can be observed without any
instrumental aid. The mechanism of sensing PA and AAs by 1c
has been explained in detail spectroscopically. The fluorescence
change of 1c is attributed to ICT/PET due to protonation of its
pyridinyl centres by PA leading to quenching the fluorescence
and subsequently de-protonation by AAs to revive the signal.
We have explained the ultrafast dynamics of the process by
fluorescence up-conversion spectroscopy supported by theoret-
ical calculations. The results ensued us to develop different
logic gates and memory device to incorporate the findings in
suitable applications.
All single input-single output (YES, NOT, PASS 0 and PASS 1)
opto-chemical logic gates could be easily designed based on
the emission responses at 588 nm output channel, during the
sequential interaction of 1c with “PA” and different amines.
Considering 1c as the device and PA as the single chemical
input, we designed a NOT gate. In addition, with the same
device (1c) and same output channel (588 nm) we designed a
PASS 1 logic gate, employing any of the amines as the single
chemical input. Now, considering the 1c-PA chemical mixture
as the initial system and TIPA/DIPA/TEA/DEA as the single
chemical input a YES gate was fabricated. Further, with the
same device (1c-PA) and same output channel (588 nm) a
PASS 0 logic gate was mimicked with DMA/AN/MA as the single
chemical input (Figure 8).
Accompanied with the binary logic function, the reversible
and reproducible toggling of fluorescence ON-OFF states of 1c
successively triggered by PA and different amines could be Acknowledgements
utilized to design a sequential “Erase-Read-Write-Read” type
logic memory unit, ultimately to create molecular memory
devices that are capable for storing and processing information.
In the designing, the ON (1) and OFF (0) states were
represented by the strong and less emission outputs at 588 nm
Financial support of the Science and Engineering Research Board,
Government of Indian through the project (CRG/2018/000555) is
gratefully acknowledged. We thank Professor A. Patra, IACS,
Kolkata and INST, Mohali for allowing us to use the fluorescence
up-conversion set-up.
Figure 8. Construction of All single input-single output (YES, NOT, PASS 0
and PASS 1) opto-chemical logic gates.
Figure 9. Development of memory unit from the “Erase-Read-Write-Read”
mechanism.
Chem Asian J. 2021, 16, 1157–1164
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Conflict of Interest
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Keywords: aliphatic amines · charge transfer · logic gates ·
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