Exploring aggregation-induced emission through tuning of ligand structure for picomolar detection of pyrene

Article abstract of DOI:10.1002/jmr.2771

Tuning of ligand structures through controlled variation of ring number in fused-ring aromatic moiety appended to antipyrine allows detection of 7.8?×?10^?12?M pyrene via aggregation-induced emission (AIE) associated with 101-fold fluorescence e

Full text of DOI:10.1002/jmr.2771

Received: 22 August 2018
DOI: 10.1002/jmr.2771
Revised: 9 October 2018
Accepted: 26 October 2018
R E S E A R C H A R T I C L E
Exploring aggregation‐induced emission through tuning of
ligand structure for picomolar detection of pyrene
Milan Ghosh1 Sabyasachi Ta1 Sisir Lohar2 Sudipta Das3 Paula Brando4 Vitor Felix4
Debasis Das1
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1 Department of Chemistry, The University of
Abstract
Burdwan, Bardhaman, India
2 Department of Chemistry, T. D. B. College,
Raniganj, Bardhaman, India
Tuning of ligand structures through controlled variation of ring number in fused‐ring
aromatic moiety appended to antipyrine allows detection of 7.8 × 10−12 M pyrene
via aggregation‐induced emission (AIE) associated with 101‐fold fluorescence
enhancement. In one case, antipyrine unit is replaced by pyridine to derive
bis‐methylanthracenyl picolyl amine. The structures of four molecules have been
confirmed by single crystal X‐ray diffraction analysis. Among them, pyrene‐
antipyrine conjugate (L) undergoes pyrene triggered inhibition of photo‐induced
electron transfer (PET) leading to water‐assisted AIE.
3 Department of Chemistry, Raina Swami
Bholananda Vidyayatan, Bardhaman, India
4 Department of Chemistry, CICECO–Aveiro
Institute of Materials, University of Aveiro,
Aveiro, Portugal
Correspondence
Debasis Das, Department of Chemistry, The
University of Burdwan, Bardhaman 713104,
India.
Email: ddas100in@yahoo.com
KEYWORDS
AIE, pyrene, SC‐XRD, sensor, SPE
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1
INTRODUCTION
immense importance of trace level selective detection and estimation
pyrene, which is difficult because of similar properties PAHs.18,19 It is
The design and development of appropriate fluorescence probe for
selective detection and monitoring of toxic molecules have been a
subject of interest in the modern research area.1 Polycyclic aromatic
hydrocarbons (PAHs) are widely distributed and relocated in the envi-
ronment as a result of incomplete combustion of organic matter.2
Reactive PAHs belong to 10 most toxic classes of organic compounds
(by Centre for Disease Control in 2011)3-7 for cell damaging, cytotox-
icity, mutagenicity, damage of nervous system, chemical modification
of protein, and nucleic acid. Pyrene imparts toxicity in living organisms
from bacteria to plants and animals. Its epoxides are highly toxic,
mutagenic and/or carcinogenic to microorganisms and higher systems
including humans.8 Several pyrene derivatives causes skin, lung, blad-
der, liver, and stomach cancers. Being hydrophobic, it easily permeates
cell membrane and accumulates in lipid tissues.9-12 The benzopyrene,
a metabolites of pyrene binds to DNA to cause lung cancer.13 More-
over, relatively high water solubility of pyrene over higher PAHs
allows to spread in living systems through grains, fruits, vegetables,
drinking water, and meat14. Inhalation of combustion products and
coal tar linings15 and dry cleaning of garments are also responsible
for pyrene poisoning.16,17 The above discussion clearly indicates the
to be noted that most of the PAHs, including pyrene, are prone to
aggregation (monomer to excimer) in solution, the main obstacle for
their selective recognition. The literature suggests that the present
optical probe is the first of its kind that selectively recognizes pyrene
through PET‐AIE mechanism.20-25 Additionally, high‐florescence life-
time and quantum yield of pyrene excimer may be useful for solar
energy storage system.26
The present probe, a pyrene–antipyrine conjugate (L) undergoes
pyrene‐induced AIE through π‐π stacking. L is characterized by
1HNMR, UV–Vis, steady state and time‐resolved fluorescence,
fourier‐transform infrared spectroscopy (FTIR), ESI‐MS spectroscopy,
and single‐crystal XRD analysis (Figure S1‐S20, ESI). Density func-
tional theory (DFT) studies support the experimental facts. The devel-
oped method is applied for the determination pyrene2 in water from
Gomti river (India). Solid phase extractive separation of pyrene has
been achieved.
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RESULT AND DISCUSSION
Five probes, viz, L, L1, L2, L3, and L4 have been synthesized
(Scheme 1). L displays very weak emission at 475 nm upon excitation
CCDC No: 1562252 (L), 1562217(L1), 1562244 (L3), 1562253 (L4)
J Mol Recognit. 2018;e2771.
wileyonlinelibrary.com/journal/jmr
© 2018 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/jmr.2771

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GHOSH ET AL.
(λEm, 397 nm), perylene (λEm, 285 nm), and picene (λEm, 289 nm)
remain silent (Figure 1). The pyrene‐assisted green emission of L is
very distinct and highly selective. Several model probes have been
synthesized to unveil the underlying sensing mechanism of pyrene.
Subtle tuning of the structure of ligand (L) by varying the appended
unit to antipyrine results, L1 (appended unit is anthracene,
λEx = 340 nm, λEm = 482 nm) and L2 (appended unit is naphthalene,
λEx = 342 nm, λEm = 477 nm). However, neither L1 nor L2 undergo
pyrene assisted significant fluorescence enhancement like
L
(Figure S21–22, ESI). Moreover, L detects pyrene without any inter-
ference from other common PAHs (Figure S23, ESI). On the other
hand, L3 and L4 are unable to detect pyrene. Figures S24 and 25
(ESI) show interference suffered during pyrene detection by L1 and L2.
The emission profiles of L, L1, and L2 (Figure S26, ESI) indicate no
significant change at pH range, 3.0 to 12.0, suggesting their usefulness
at physiological pH. Therefore, entire studies have been performed at
pH 7.4 using HEPES buffered aqueous DMSO (20mM, DMSO/H2O;
4/1, v/v). However, other media like aqueous MeOH (MeOH/H2O;
4/1, v/v), aqueous CH3CN (CH3CN/H2O; 4/1, v/v) and aqueous
DMF (DMF/H2O; 4/1, v/v) have also been tested. Changes in emis-
sion intensity being maximum in aqueous DMSO (DMSO/H2O; 4/1,
v/v) are used for the entire studies.
SCHEME 1 Synthesis of probes
at 384 nm (Figure S4, ESI). Similarly, L1, L2, L3, and L4 exhibit weak
emissions at 396, 376 and 522, 444, and 396 nm upon excitation at
340, 342, 396, and 318 nm, respectively.
Figure 2A represents the changes of emission spectra of L upon
gradual addition of pyrene (DMSO/H2O, 4/1, v/v, pH 7.4). Upon grad-
ual addition of pyrene to L, the emission intensity of the pyrene mono-
mer at 393 nm decreases while that of excimer increases at 498 nm
with an isoemissive point at 460 nm (Figure S27, ESI). This is due to
the π‐π stacking of pyrene unit of L with pyrene analyte. This red shift
of the emission is accompanied by 101‐ and 36.7‐fold enhancement of
Pyrene perturbs steady state emission (λEm, 498 nm) of L at
picomolar level while other tested common PAHs (λEx, 384 nm) viz
naphthalene (λEm, 332 nm), anthracene (λEm, 411 nm), anthanthrene
(λEm, 418 nm), acenaphthene (λEm, 330 nm), acephenanthrene (λEm
,
297 nm), acridine (λEm, 443 nm), phenanthrene (λEm, 289 nm), chrys-
ene (λEm, 303 nm), benzo [a] pyrene (λEm, 414 nm), benzo [g] chrysene
FIGURE 1 Emission spectra of L (20 μM,
DMSO/H2O, 4/1, v/v, 20mM HEPES buffer,
pH 7.4) in presence of common PAHs (λEx
,
384 nm)
FIGURE 2 Changes in (A) emission and (B)
absorption spectra of L (20 μM) in HEPES‐
buffered (20mM, DMSO/H2O, 4/1, v/v,
pH 7.4) solution upon gradual addition of
pyrene (0.0, 0.005, 0.01, 0.05, 0.1, 0.5, 1.0,
2.0, 5.0, 10, 20, 30, 50, 75, 100, 200, 300,
500, 1000, 1500, 2000, 2500, and 3000 μM)
(λEx, 384 nm)

GHOSH ET AL.
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fluorescence intensity and quantum yield, respectively (λEx, 384 nm;
Φ, 70.27). In presence of pyrene, L1 (λEx, 340 nm) and L2 emit at
482 and 477 nm (λEx, 342 nm, Figure S28, ESI), respectively. Upon
gradual addition of pyrene to L1 or L2, the emission intensity at 388
(L1) and 393 nm (L2) decreases gradually with concominant increase
at 482 (L1) and 477 nm (L2) associated with isoemissive points at
408 (L1) and 449 nm (L2), respectively (Figure S29–30, ESI). This
pyrene‐assisted fluorescence enhancement is attributed to the π‐π
stacking of anthracene and naphthalene moieties (L1 and L2) with
pyrene. Figure 2A and S28 (ESI) clearly indicate that the decrease in
the number of rings of PAH blue shifts the emission band from 498
(L) to 482 (L1) to 475 nm (L2), and at the same time, the emission
intensity decreases significantly. Probably benzene moiety of L3 fails
π‐π stacking with pyrene as no fluorescence enhancement is observed
(Figure S31, ESI). Despite having two anthracene units, L4 also fails to
π‐π stacking and hence, to recognize pyrene. This is because two
anthracene rings lie in different planes that also differ from the pyri-
dine unit, revealed from its single crystal X‐ray structure (Figure S32,
ESI and Scheme 2).
poor for L4 as appended anthracence units being attached to the sp3
N are out of plane and hence extended conjugation is not feasible.
Consequently, π‐π stacking of L4 with pyrene is much less than it
could be for a planar molecule.
It is already mentioned that very weak emission of L is attributed
to the PET process from imine N to the photo‐excited pyrene moiety.
The fluorescence of L at 498 nm enhances in the presence of pyrene
in DMSO medium due to π‐π stacking of pyrene units of L with exter-
nally added pyrene leading to formation of dynamic excimer where
syn‐ and anti‐ forms of L remain in equilibrium. Interestingly, upon
addition of water to the system, hydrogen bonds involving imine N
and water O stabilize the syn‐ forms of L, and consequently, external
pyrene accommodates in between two pyrene units of two L leading
to formation of stable static excimer. Hence, significant fluorescence
enhancement occurs through water‐assisted aggregation involving L
and external pyrene (Scheme 3), termed as AIE. The presence of an
isoemissive point at 460 nm indicates the existence of two different
species at equilibrium (Figure S27, ESI). In the absence of external
pyrene, steric crowding of methyl group attached to antipyrine of L
restricts two pyrene units from two L to come sufficiently closer and
parallel for π‐π stacking (homo) to occur. In the absence of external
pyrene, addition of water even fails to enhance the fluorescence
(Scheme 3). However, upon addition of external pyrene, it
accomodates in between two probes (L) and qualify the distance
required to form π‐π stacking (hetero) with the pyrene units of L
and escapes the steric hindrance mentioned supra. Thus, pyrene
assisted dynamic excimer equilibrium between syn‐ and anti‐ forms
of L turns into static excimer where the syn‐ conformation is stabilized
through water‐assisted intermolecular hydrogen bonding. This kind of
observations are absent for L1 and L2. Although, the anthracene unit
of L1 is capable of π‐π stacking with external pyrene, probably it is
not strong enough to form stable static excimer leading to AIE in the
presence of water. Similarly, L2 containing naphthalene moiety has
further less π‐π stacking efficiency in the series with external pyrene
fails to show water‐assisted AIE.
The plots of emission intensity versus pyrene concentration for L,
L1, and L2 are presented in Figure S33–35 (ESI). The LODs2g, h of L,
L1, and L2 for pyrene are 2 × 10−12 M, 2 × 10−9 M, and 5 × 10−9
M
while respective association constants are 3.81
×
106 M−1
,
7.60 × 105 M−1, and 2.09 × 105 M−1, determined applying the Hill
equation27 (Figure S36–38, ESI). Moreover, the LOD of L for pyrene
is 7.8 × 10−12 M following 3σ/K method2d–f where σ is the standard
deviation of the blank, and K is the slope of the calibration curve
(Figure S33, ESI, inset plot). Thus, L is effective for detection of pyrene
in river and tap water samples.2 The Job's plot28 indicate 1:1 (mole
ratio) interaction between probe and pyrene (Figure S39–41, ESI).
In the presence of pyrene, the very weak absorption of L is blue
shifted from 406 to 403 nm and increases gradually with increasing
pyrene concentration (Figure 2B). Besides, two new absorption bands
that appear at 246 and 293 nm also increase gradually. On the other
hand, two new absorption bands that appear at 373 and 325 nm upon
addition of pyrene to L1 and L2 also increase gradually with increasing
pyrene concentration. In the presence of pyrene, the gradual blue shift
of absorption band from 403 (L) to 373 (L1) to 325 nm (L2) is probably
due to lesser π‐π stacking between the probe and pyrene (Figure S42,
ESI). This notion is obvious because with increasing conjugation of the
probe with increasing number of appended aromatic nucleus enhances
π‐π stacking between the probe and pyrene. Thus, for L3, it is less
(Figure S43, ESI) while little better for L4 (Figure S44, ESI) as reflected
from the absorption spectrum. However, the π‐π stacking is relatively
FTIR spectra29 of L, L1, and L2 and their pyrene adduct support
their interactions (Figure S45‐S47, ESI).
The dynamic light scattering (DLS) studies also support aggrega-
tion of L in the presence of pyrene. At constant concentration of L
(20 μM) in a particular solvent, increasing pyrene concentration
increases the average particle size (Zav) in solution. The value of Zav
increases from 165 to 240 nm upon increase of pyrene concentration
from 1000 to 1300 μM in DMSO/H2O (4/1, v/v, pH 7.4), indicating
pyrene triggered aggregation of L (20 μM). Moreover, Zav further
SCHEME 2 SCXRD structures of probes

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GHOSH ET AL.
SCHEME 3 Sensing mechanism
increases from 735 to 828 nm with increasing water percentage,
keeping concentration of L and pyrene unaltered. This highlights the
role of water towards AIE (Figure S48, ESI). For L1 and L2, no aggre-
gation is observed.
because of exchange of L molecules between free and aggregated
state (Figure 3).
Effect of added water on the emission characteristics of [L‐
pyrene] system in DMSO have been investigated (Figure S49a, ESI).
The emission intensity of L (λEm, 498 nm) enhances approximately
41‐fold at 60% water (v/v) and 52‐fold at 90% water (v/v). Further
increase of water content intensifies the emission intensity further;
however, turbidity appears, a signature of aggregation ascribed to
AIE process.30 The AIE process is also reflected in absorption spectro-
scopic studies. Gradual increase of water (25‐75%, v/v) to the DMSO
solution of [L‐pyrene] system broadens and red shifts the absorption
peak from 406 to 436 nm (Figure S49b, ESI). On the other hand, this
kind of water‐assisted pyrene‐induced aggregation are absent in L1
and L2. These facts are demonstrated in a snapshot in Figure S50
(ESI) where emission peaks associated with free L, pyrene monomer
(393 nm), excimer (475 nm), and pyrene‐induced water‐assisted AIE
of L (498 nm) are captured altogether. It is to be noted that the ratio
The 1HNMR titration is performed by gradual addition of pyrene
to L (Figure 3). Addition of 0.5 equiv pyrene to L up field shifted alkyl
protons from 3.388 to 3.253 ppm, indicating some sort of interaction.
Addition of 1 equiv pyrene, further shifted those protons up field to
3.179 ppm, indicating stronger interaction. Moreover, addition of 0.5
equiv pyrene to L shifted “a” proton (labeled in Figure S2, ESI) up field
from 9.812 to 9.631 ppm, probably due to hydrogen bonding between
N center of antipyrene moiety (L) with water present in DMSO‐d6.
The aromatic “b” proton also shifted up field. Additionally, all aromatic
protons up field shifted from 7.892 to 7.505 ppm because of
increased electron density in the ring via π‐π interaction with added
pyrene that accommodates itself in between two pyrene units of
two L, forming excimer, a step forward towards aggregation at
higher‐pyrene concentration. At higher‐pyrene concentration, in addi-
tion to up field shift of the protons, peak broadening occurs, probably
of emission intensity (EI), viz, EI
at 498 nm/EI
at
[pyrene]
[L‐pyrene]
475 nm is 15.3 (DMSO/H2O, 2/3, v/v, pH 7.4).
FIGURE 3 1HNMR spectra of L in absence
and presence of pyrene in DMSO‐d6: (1) L; (2)
L + 0.5 equiv pyrene; (3) L + 1.0 equiv pyrene

GHOSH ET AL.
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The fluorescence lifetime data corroborates the proposed sensing
laser‐based time‐correlated single‐photon counting (TCSPC) spec-
trometer (IBH, UK, λex = 384 nm) coupled to MCP‐PMT detector
(model FL‐1057). A Systronics digital pH meter (model 335) is used
for pH measurement. 1HNMR spectra are recorded on a Bruker
Avance III HD (400 MHz) spectrometer. Chemical shifts are reported
in parts per million (ppm), and the residual solvent peak is used as an
internal reference: tetramethylsilane (TMS, δ 0.00) is used as a
reference. Multiplicity are indicated as follows: s (singlet), d (doublet),
t (triplet), q (quartet), m (multiplet). Coupling constants are reported
in Hertz (Hz).
mechanism (Figure S51–53, ESI). The average lifetime of L is 0.759 ns
in DMSO. In the presence of pyrene (L: pyrene = 2: 1, mole ratio), the
fluorescence lifetime significantly increases to 5.7258 ns in DMSO.
Increasing water enhances the fluorescence lifetime gradually from
51.4773 ns (25%, v/v) to 106.1560 ns (30%, v/v) to 206.1660 ns
(50%, v/v), respectively. At the same time, quantum yield31 (ϕ) also
increases from 3.13% to 27.83% to 37.13%.
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APPLICATION
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5.2
Synthesis of L
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3.1
Real sample analysis and solid phase extractive
removal of pyrene
The probe, L is synthesized by refluxing of equimolar mixture of
1‐pyrenecarboxaldehyde (0.50 g, 2.1 mol) and 4‐aminoantipyrine
(0.43 g, 2.1 mol) in methanol for 7 h at 60°C (Scheme 1). The
brown‐yellow crystals are found after few days by slow evaporation
of the solvent. Yield is 95%. Anal. calcd. (%): C, 80.55; H, 5.55 and
N, 10.06; found: C, 80.83; H, 5.86 and N, 9.95. Single crystal of L,
suitable for X‐ray diffraction is mounted on a Bruker SMART APEX
CCD diffractometer at 296 K and diffracted by Mo‐Kα radiation
(λ = 0.71073 Å). The crystal belongs to P21/n space group. The
crystal parameters and refinement details are listed in Table S1
(ESI). The bond angles and lengths are detailed in Table S2 (ESI).
The QTOF–MS ES+ (Figure S1, ESI): m/z for [M + H]+ found at
419.60 (˜100%), (calcd. 419.18) and [M + Na]+ at 441.76 (˜40%).
The 1HNMR spectra is recorded in DMSO‐d6 at 25°C; δ (ppm)
(Figure S2, ESI): 10.616 (1H, s), 8.907–8.886 (1 H, s), 8.243–7.887
(4H, d, J = 6.8), 7.592–7.282 (m, J = 1.6), δ; 3.203–2.572. The exper-
imental FTIR (cm−1) spectra is shown in Figure S3 (ESI): υ (O‐H),
3714; υ(‐C‐H‐), 2988 and 2874; υ(‐C=N‐), 1616; υ(‐C=C‐), 1578
and 1559; υ(C‐H), 1477; υ(‐C‐O‐), 1313; υ(‐C‐N‐), 1080. The UV–
vis. Spectrum of L (DMSO/H2O, 4/1, v/v, 20mM HEPES, pH 7.4)
have three bands, viz. 240 nm, 288 nm, and 406 nm (Figure S4,
ESI). The intense 240 nm band (ε = 9.85 × 103 M−1 cm−1) is
assigned to π‐π* transition while the weak band at 288 nm
(ε = 1.22 × 102 M−1 cm−1) is due to π‐π* transition at lower energy.
The strong band at 306 nm (ε = 5.22 × 103 M−1 cm−1) is attributed to
n‐π* electron transition from non‐bonding terminal N of imine moiety
to an anti‐bonding orbital of L. The excitation of L at 384 nm resulted
emission at 475 nm (DMSO/H2O, 4/1, v/v, 20mM HEPES, pH 7.4,
Figure S4, ESI).
The developed method has been applied2a–c for pyrene determination
in river and tap water samples following standard addition method
(Table S6, ESI). To evaluate the accuracy of the method, recovery
studies have been performed at different concentration levels. A
known amount of pyrene (Table S6, ESI) is added to water sample
collected from Gomati river (a tributary of the river Ganga, one of
the most polluted rivers in India). Total concentration of pyrene
is determined using the developed method. The L, immobilized on
silica, is highly efficient for SPE removal of pyrene from real samples
(Figure S54 and Table S7, ESI).
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CONCLUSION
A
simple antipyrine–pyrene conjugate (L) has been exploited
for detection of picomolar (7.8 × 10−12 M) pyrene in aqueous‐DMSO
media through generation of green fluorescence via water‐assisted
AIE mechanism. The extent of association between L and pyrene is
determined by the Hill equation (Ka = 3.81 × 106 M−1). The developed
method determines concentration of pyrene in Gomti river water.
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EXPERIMENTAL
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5.1
Materials and equipment
High‐purity buffer HEPES, 1‐pyrenecarboxaldehyde, 9‐anthracene
carboxaldehyde, 1‐naphthaldehyde, benzaldehyde, 2‐picolylamine,
9‐chloromethyl anthracene, and 4‐aminoantipyrene have been
purchased from Sigma−Aldrich (India). The solvents used has spectro-
scopic grade. Other molecules and salts are also purchased from
Merck (India). Other analytical reagent grade chemicals are used with-
out further purification unless specified otherwise. Milli‐Q Millipore
18.2 MΩ cm−1 water is used whenever required. A Shimadzu Multi
Spec 2450 spectrophotometer is used for recording UV–vis spectra.
FTIR spectra are recorded on a Shimadzu FTIR (model IR Prestige
21 CE) spectrophotometer. Mass spectra are recorded using a QTOF
60 Micro YA 263 mass spectrometer in ES positive mode. The steady
state emission and excitation spectra have been recorded with a
Hitachi F‐4500 spectrofluorimeter. Time‐resolved fluorescence life-
time measurements are performed with a picosecond pulsed diode
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5.3
Synthesis of L1
Anthracene‐9‐carbaldehyde (1 g, 6.09 mmol), dissolved in methanol is
added to methanol solution of 4‐aminoantipyrine (1.23 g, 6.09 mmol)
(Scheme 1). The mixture is refluxed for 7 hours at 60°C. Slow evapo-
ration of solvent resulted L1 in 95% yield. The brown–yellow crystals
are observed after slow evaporation of the solvent. Yield is 95%. Anal
calcd (%): C, 79.13; H, 5.58 and N, 11.07; found: C, 79.52; H, 5.50 and
N, 9.97. Single crystal of L1, suitable for X‐ray diffraction is diffracted
as narrated for L. The crystal belongs to P21 space group. The crystal
parameters and refinement data are listed in Table S1 (ESI). The

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GHOSH ET AL.
selected bond angles and lengths are detailed in Table S3 (ESI). The
QTOF–MS ES+ (Figure S5, ESI) shows m/z for [M + Na]+ (approxi-
mately 100%) at 414.14 and 392.15 for [M + H]+ (approximately
35%) (calcd. 392.17) while m/z at 424.15 for [M + CH3OH + H]+
observed after slow evaporation of the solvent. Anal calcd (%): C,
74.20; H, 5.88 and N, 14.42; found: C, 74.36; H, 5.80, and N, 14.33.
Single crystal of L3, suitable for X‐ray diffraction, is analyzed at
296 K as mentioned supra. The crystal belongs to P 21/c space group.
The crystal parameter and refinement details are listed in Table S1
(ESI). The bond angles and lengths are detailed in Table S4 (ESI). The
QTOF–MS ES+ (Figure S13, ESI): m/z for [M + H]+ = 292.33 (calcd
292.35) (˜100%); [M + Na]+ = 314.34 (calcd 314.35) (10%). The
1HNMR (Figure S14, ESI) (CDCl3), δ (ppm): 9.763 (1H, s) refers to
imine proton (‐N=C‐H) denoted as “f”; 7.871 (1H, s) for “a” proton;
7.866 (1H, d, J = 1.6) for “e” proton; 7.499–7.259 (8H, m, J = 9.2)
for aromatic protons; 3.153 and 2.494 for aliphatic protons. The
FTIR (cm−1) spectrum is shown in Figure S15 (ESI): 2912 and 2975,
υ(‐C‐H‐); 1630 υ(‐C=N‐); 1610 and 1565, υ(‐C=C‐); 1395, υ(‐C‐H‐);
1047, υ(‐C‐O‐), and 3367, υ(‐O‐H). The UV–vis spectrum of L3
(Figure S16, ESI, DMSO/H2O, 4/1, v/v, 20mM HEPES, pH 7.4) shows
absorbance at 252 nm (ε = 3.44 × 103 M−1 cm−1), assigned to π‐π*
electron transition. The band at 342 nm (ε = 1.55 × 102 M−1 cm−1) is
due to n‐ π* electron transition from nonbonding terminal N of imine
moiety to an antibonding orbital of L3. The excitation of L3 at 396 nm
leads the emission at 444 nm (DMSO/H2O, 4/1, v/v, 20mM HEPES,
pH 7.4, Figure S16, ESI).
(approximately 15%) (calcd 424.51).
A low abundance peak is
observed at m/z 224.48, probably due to water adduct of the
fragmented anthracene aldehyde. The 1HNMR (Figure S6, ESI)
(CDCl3), δ (ppm): 8.238 (1H, s) for (–N=C‐H) assigned as “j” proton;
7.679 (1H, m) for “e” proton; 7.259–6.831 (11H, m, J = 9.2); 2.835–
2.742 are aliphatic protons. The experimental FTIR (cm−1) spectra is
shown in Figure S7 (ESI); 2958 and 2899, υ(‐C‐H‐); 1616, υ(‐C=N‐);
1407, υ(‐C=C‐); 1313, υ(‐C‐O‐); 1049, υ(‐C‐H‐); 3342, υ(‐O‐H‐). The
absorption spectrum of L1 (Figure S8, ESI) (DMSO/H2O, 4/1, v/v,
20mM HEPES, pH 7.4) shows two bands at 256 nm and 365 nm.
The intense band at 256 nm (ε = 8.48 × 102 M−1 cm−1) is assigned
to π‐π* electron transition while the weak band at 365 nm
(ε = 1.22 × 102 M−1 cm−1) is due to n‐ π* electron transition of non‐
bonding electron on terminal N of imine moiety to anti‐bonding orbital
of L1. The excitation of L1 at 340 nm results emission at 396 nm
(DMSO/H2O, 4/1, v/v, 20mM HEPES, pH 7.4, Figure S8, ESI).
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5.4
Synthesis of L2
Naphthalene‐1‐carboxaldehyde (1 g, 6.40 mmol) is dissolved in 10 mL
methanol and added to 10 mL methanol solution of 4‐aminoantipyrine
(1.29 g, 6.40 mmol) (Scheme 1. The mixture is refluxed for 7 h at 60°C.
Slow evaporation of solvent resulted solid L2 with 95% yield. Anal.
calcd (%): C, 77.40; H, 5.61 and N, 12.31; found: C, 77.62; H, 5.50
and N, 12.25. The MS ES+ (Figure S9, ESI): m/z for [M + H]+ = 342.25
(calcd. 342.41) (˜ 22%); 364.30 (calcd. 364.14) for [M + Na]+ (100%)
and 396.34 (calcd. 396.52) for [M + CH3OH + Na]+. The peak having
35% abundance at 157.09 (calcd. 157.18) indicates the molecular ion
peak of naphthalene‐1‐carboxaldehyde. The 1HNMR (Figure S10, ESI)
(CDCl3), δ (ppm): 10.594 (1H, s) refers to (–N=C‐H) denoted as “h”;
8.888 (1H, d, J = 8.4) for “g” proton; 8.219 (1H, t, J = 6.8) for “a” proton;
7.904–7.864 (2H, q, J = 7.6) for “d” and “e” protons; 7.572–7.259 (m,
J = 2) for aromatic protons; 3.181 and 2.551 for aliphatic protons.
The FTIR (cm−1) spectrum (Figure S11, ESI): 2972, υ(‐C‐H‐); 1645,
υ(‐C=N‐); 1565 and 1477, (‐C=C‐); 1298 υ(‐C‐O‐); 1066, υ(‐C‐H‐).
The absorption spectrum of L2 (Figure S12, ESI) (DMSO/H2O, 4/1,
v/v, 20mM HEPES, pH 7.4) shows the intense band at 282 nm
(ε; 3.44 × 103 M−1 cm−1), assigned to π‐π* electron transition. Another
band at 417 nm (ε = 1.65 × 102 M−1 cm−1) is due to n‐ π* electron tran-
sition from non‐bonding electron on terminal N of imine moiety to the
anti‐bonding orbital of L2. The excitation of L2 at 342 nm leads the
emission at 376 and 522 nm (DMSO/H2O, 4/1, v/v, 20mM HEPES,
pH 7.4, Figure S12, ESI).
|
5.6
Synthesis of L4
Dry DMF solution of 9‐chloromethylanthracene (1 g, 8 mmol) is stirred
with anhydrous K2CO3 for 1 hour followed by addition of 2‐
picoylamine (1.26 g, 8 mmol). The mixture is stirred for 15 hours
followed by reflux for 10 hours at 60°C. The solvent is removed using
rotary evaporator, and the residue is partitioned with ethylacetate and
water. Upon removal of solvent, the target compound L4 (0.8 g
4.76 mmol) is isolated (Scheme 1) and recrystallized as dirty white
crystal from methanol solution. Anal calcd (%): C, 83.26; H, 5.95; and
N, 10.79; found: C, 83.52; H, 5.91 and N, 10.57. Single crystal of L4,
suitable for X‐ray diffraction, is analyzed similarly as described supra
at 100 K. The crystal belongs to P‐1 space group. The crystal
parameter and refinement data are listed in Table S1 (ESI). The bond
angles and lengths are detailed in Table S5 (ESI). The QTOF–MS ES+
(Figure S17, ESI): m/z for [M + H]+ = 489.48 (calcd. 489.58) (approxi-
mately 100%); [M + Na]+ = 511.40 (calcd 511.42) (approximately
25%); the 1HNMR spectrum (Figure S18, ESI) (CDCl3), δ (ppm):
10.998 (1H, s) for (‐N=C‐H‐) denoted as “j”; 8.943 (1H, s) for “a” and
“i” proton; 8.920 (1H, d, J = 1.6); 8.243–8.007 (3H, m, J = 6.8) for
aromatic protons; 7.563–7.282 (8H, m, J = 8.4) for aromatic protons;
3.240 for “n” and 2.853 and 2.636 for aliphatic protons (p, o). The FTIR
(cm−1) spectrum (Figure S19, ESI): 2962 and 2880, υ(‐C‐H‐); 1673
υ(‐C=N‐); 1560 υ(‐C=C‐); 1445, υ(‐C‐H‐); 1035, υ(‐C‐N‐), 3348,
υ(‐O‐H). The UV–vis spectrum of L4 (Figure S20, ESI, DMSO/H2O,
|
4/1, v/v, 20mM HEPES, pH 7.4) has a peak at 257 nm
5.5
Synthesis of L3
(ε = 3.44 × 105 M−1 cm−1), assigned to π‐π* electron transition. The
band at 376 nm (ε = 1.69 × 103 M−1 cm−1) is due to n‐ π* electron
transition from nonbonding electron on terminal imine N to an
antibonding orbital of L4. The excitation of L4 at 318 nm leads the
emission at 396 nm (DMSO/H2O, 4/1, v/v, 20mM HEPES, pH 7.4).
Benzaldehyde (1 g, 9.42 mmol), dissolved in methanol, is added to
methanol solution of 4‐amino‐antipyrine (1.91 g, 9.42 mmol)
(Scheme 1). The mixture is refluxed for 7 hours at 60°C. Slow evapo-
ration of the solvent resulted L3 in 95% yield. The yellow crystals are

GHOSH ET AL.
7 of 8
6. Figueira‐DuarteTM, Müllen K. Pyrene‐based materials for organic elec-
tronics. Chem Rev. 2011;111(11):7260‐7314.
ACKNOWLEDGEMENTS
M.G. sincerely acknowledges CSIR (New Delhi) for fellowship. S.T. and
D.D. thank UGC‐DAE‐Kolkata and Department of Environment, Gov
WB for financial assistance.
7. McCallister MM, Maguire M, Ramesh A, et al. Prenatal exposure to
benzo(a) pyrene impairs later‐life cortical neuronal function. Neuro
Toxicol. 2008;29(5):846‐854.
8. Goldman R, Enewold L, Pellizzari E, et al. Smoking increases carcino-
genic polycyclic aromatic hydrocarbons in human lung tissue. Cancer
Res. 2001;61(17):6367‐6371.
CONFLICT OF INTERESTS
No conflict of interest to report.
9. (a) Zhang J, Chang L, Jin H, et al. Benzopyrene promotes lung cancer
A549 cell migration and invasion through up‐regulating cytokine IL8
and chemokines CCL2 and CCL3 expression. Exp Biol Med.
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polarization and inflammatory mediators after intracerebral hemor-
rhage. Mol Neurobiol. 2017;54(3):1874‐1886.
AUTHORS' CONTRIBUTIONS
M.G. synthesized all the compounds and characterized them. S.T.
solved some single crystal X‐ray structures. S.L. grew some single
crystals of the compounds. S.D. performed some solution phase
experiments. P.B. solved few single crystal X‐ray structures. V.F.
refined and wrote single crystal X‐ray structures. The idea of this
research is the brainchild of D.D., one of the corresponding authors.
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S. Dihydrodiol Dehydrogenases and Polycyclic aromatic hydrocarbon
activation: generation of reactive and redox active o‐Quinones. Chem
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M. Unexpected DNA damage caused by polycyclic aromatic hydrocar-
bons under standard laboratory conditions. Mutat Res. 2008;
650(2):96‐103.
ORCID
11. Senkan S, Castaldi M. Combustion. In: Ullmann's Encyclopedia of Indus-
trial Chemistry. Weinheim: Wiley‐VCH; 2003.
Debasis Das http://orcid.org/0000-0003-0474-0842
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SUPPORTING INFORMATION
Additional supporting information may be found online in the
Supporting Information section at the end of the article.
How to cite this article: Ghosh M, Ta S, Lohar S, et al. Explor-
ing aggregation‐induced emission through tuning of ligand
structure for picomolar detection of pyrene. J Mol Recognit.
2018;e2771. https://doi.org/10.1002/jmr.2771
27. (a) Ghosh M, Ghosh A, Ta S, Matalobos JS, Das D. ESIPT‐based
Nanomolar Zn2+ sensor for human breast Cancer cell (MCF7) imaging.