Highly Emissive Water-Soluble Polysulfurated Pyrene-Based Chromophores as Dual Mode Sensors of Metal Ions

Article abstract of DOI:10.1002/cplu.202000344

Pyrene-based materials have gained considerable attention as stimuli-responsive chemical sensors. We designed a polysulfurated arene system based on a tetra(phenylthio)pyrene core decorated with four carboxylic acid units. Three different regioisomers, ortho, meta and para were studied in organic and aqueous solution. These systems are soluble in water at pH≥8 due to the deprotonation of carboxylic acids. The addition of metal ions cannot only quench the fluorescence of the central pyrene core, but also control the formation of three-dimensional nanoscopic objects in a dual mode function. Several divalent metal ions were tested and compared. Addition of ethylenediaminetetraacetic acid (EDTA) disassembles the non-emissive supramolecular system and restores the initial fluorescence of the pyrene core.

Full text of DOI:10.1002/cplu.202000344

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Highly Emissive Water-Soluble Polysulfurated Pyrene-Based
Chromophores as Dual Mode Sensors of Metal Ions
Marco Villa,*[a, b] Myriam Roy,*[b] Giacomo Bergamini,[a] Paola Ceroni,[a] and Marc Gingras[b]
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Pyrene-based materials have gained considerable attention as
stimuli-responsive chemical sensors. We designed a polysulfu-
rated arene system based on a tetra(phenylthio)pyrene core
decorated with four carboxylic acid units. Three different
regioisomers, ortho, meta and para were studied in organic and
aqueous solution. These systems are soluble in water at pH�8
due to the deprotonation of carboxylic acids. The addition of
metal ions cannot only quench the fluorescence of the central
pyrene core, but also control the formation of three-dimen-
sional nanoscopic objects in a dual mode function. Several
divalent metal ions were tested and compared. Addition of
ethylenediaminetetraacetic acid (EDTA) disassembles the non-
emissive supramolecular system and restores the initial
fluorescence of the pyrene core.
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Introduction
latter case, an organic co-solvent is needed for increasing
solubility and homogeneity, and not only water.
Stimuli-responsive chemical sensors with luminescent materials
have gained considerable attention because their physical or
chemical properties can change with respect to external stimuli,
such as heat,[1] light,[2,3] conduction,[4] presence of ions,[5] pH,[6]
self-assembly,[7] and tensile strength.[8] In a more advanced
form, these systems could be used in a dual mode sensing[9,10]
of analytes, following changes of two properties, like emission
In this work, we are seeking to develop metal ions sensors
with dual functions in water only, after a rational design of
multivalent ligands able to self-assemble with metal ions
(especially heavy ones). A pyrene core is chosen because of its
exalted photophysical and electrochemical sensitivity to its
environment.[23] Substituents on pyrene are needed, while
keeping high emissivity.[24] Alkynylations[25] or arylations[20] of
pyrene at positions 1,3,6,8 were often reported as anchoring
groups. However, heterofunctionalization is less common,
especially with divalent sulfur atoms. Thus, 1,3,6,8-tetra(phenyl-
thio)pyrenes were selected, because they are highly emissive,
often soluble in solvents, and underused. For instance, we
reported the synthesis and the photophysical properties of a
dendrimer made from a tetrasulfurated pyrene core with
phenylene sulfide dendrons,[26] and a similar core with terpyr-
idine ligands.[27] The latter system behaves as a molecular
antenna in which the peripheral units collect light and transfer
the excitation energy to the central luminescent core. The
addition of metal ions to this system can not only switch the
direction of the intramolecular energy transfer, but also control
the formation of three-dimensional nanoscopic objects in a
dual function. Replacement of coordinating terpyridine groups
by simpler ones, under complete aqueous conditions, was
pursued.
In this work, we report the synthesis, characterization, metal
ion coordination and sensing activities of water-soluble, poly-
sulfurated pyrenes incorporating tetracarboxylic acids ligands,
for making new supramolecular systems with tailor-made
photophysical properties and aggregation states. In short, a
family of tetracarboxylated tetra(phenylthio)pyrenes were syn-
thesized and decorated with four peripheral and regioisomeric
carboxylic acid groups at ortho (1O), meta (1M) or para (1P)
positions (Scheme 1). Carboxylic acids can chelate divalent
metal ions for generating a supramolecular object in water,
with a substantial change in the photophysical response of the
system. It thus represents a new avenue for making a family of
intensity and aggregation, due to the formation of
a
supramolecular polymer. By using divalent metal ions that form
complexes in a 2:1 ligand to metal stoichiometry, it is possible
to generate supramolecular coordination polymers in which the
“monomers” are self-assembled by metal ion binding. It thus
generates changes of the photochemical properties of the
initial “monomeric” state to a “polymeric” state.
In this way, pyrene-based stimuli responsive luminescent
materials remain popular as ion sensors,[11] biological markers,[12]
liquid crystals,[13] light-emitting devices[14] and field-effect
transistors.[15] Recently, much efforts focused on sensors com-
patible with water for the detection of toxic metal ions[16,17] or
biomolecules. Some pyrene-based systems were utilized for the
aqueous detection of trivalent metal ions like Cr(III), Al(III)[9] and
Fe(III)[18] or divalent metal ions like Cd(II) or Zn(II)[19] or in the
sensing of lysine and arginine,[20] but rarely for Pb(II).[21,22] In the
[a] Dr. M. Villa, Prof. G. Bergamini, Prof. P. Ceroni
Department of Chemistry “Giacomo Ciamician”
University of Bologna
Via Selmi, 2, 40126 Bologna (Italy)
E-mail: marco.villa11@unibo.it
[b] Dr. M. Villa, Dr. M. Roy, Prof. M. Gingras
Aix Marseille University, CNRS, CINaM, Marseille, (France)
E-mail: myriam.roy@sorbonne-universite.fr
Supporting information for this article is available on the WWW under
https://doi.org/10.1002/cplu.202000344
This article is part of a Special Collection on “Supramolecular Chemistry:
Young Talents and their Mentors”. More articles can be found under https://
onlinelibrary.wiley.com/doi/toc/10.1002/(ISSN)2192-6506.Supramolecular-
Chemistry.
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ester groups were synthesized by nucleophilic aromatic sub-
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stitutions of 1,3,6,8-tetrabromopyrene with the corresponding
isopropyl mercaptobenzoates 3O (ortho), 3M (meta), 3P (para).
The esters were hydrolyzed to the final regioisomeric tetraacids
1O (ortho), 1M (meta), 1P (para). The description of each step is
reported below. As for 1,3,6,8-tetrabromopyrene, we synthe-
sized it on a multiple-gram scale from the bromination of
pyrene in nitrobenzene.[28,29,30] The regioisomeric isopropyl
mercaptobenzoates 3O, 3M and 3P, were synthesized in two
steps.[31,32] The first one is the esterification of commercial ortho-
, meta- and para-mercaptobenzoic acids by heating them with
thionylchloride and isopropanol. The mixture contained ester-
thiol, mostly ester-disulfides, and to some extent ester-
trisulfides, and other minor components. Without purification,
the next step was the reduction of di- and trisulfides by zinc
powder in warm acetic acid to produce the isomeric isopropyl
mercaptobenzoates (overall reaction yields: 57% for 3O and
>92% for 3M and 3P).[31,32]
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Scheme 1. A general synthetic scheme of carboxylic acids 1O (ortho-isomer),
1M (meta-isomer), and 1P (para-isomer) under study. They arised from the
carboxylic esters 2O, 2M and 2P, which themselves came from reactions of
isopropyl mercaptobenzoate isomers 3O, 3M and 3P with 1,3,6,8-tetrabro-
mopyrene.
The isopropyl esters 2O (ortho), 2M (meta), 2P (para) were
synthesized in good yields (>82%) by nucleophilic aromatic
substitutions of 1,3,6,8-tetrabromopyrene with the mercapto-
benzoate isomers 3O, 3M and 3P in the presence of anhydrous
water-soluble metal ion sensors with dual functions, either
under complete aqueous conditions or in organic solvents.
°
Cs2CO3 in DMF at 80 C. The resulting esters were hydrolyzed in
°
good yields (>72%) with LiOH*H2O in ethanol at 75 C to afford
Results and Discussion
the tetraacids 1O, 1M, 1P (Scheme 1).
Synthesis
Photophysical properties
Although a strategy by direct nucleophilic aromatic substitu-
tions with the commercial mercaptobenzoic acid isomers and
1,3,6,8-tetrabromopyrene is simple, we found low yields of 1O,
1M and 1P and a difficult way to get pure tetraacids. The
reactions produced partially substituted pyrenes. We thus
needed to protect the carboxylic acids in their isopropyl ester
form for diminishing some supramolecular interactions and for
increasing solubility. Tetra(phenylthio)pyrene derivatives with
four ortho (2O), meta (2M) or para (2P) substituted isopropyl
The isopropyl esters 2O, 2M and 2P were characterized in THF
and the carboxylic acid derivatives (1O, 1M and 1P) were
studied in both THF and in basic aqueous solution. Compounds
2O, 2M and 2P show a band peaked at 420–430 nm (See
Supporting Information, Figure S23), attributed to electronic
transitions localized on the central pyrene core and a higher
energy band peaked at ca. 300 nm with slight differences in
terms of energy and shape of the absorption bands of the three
Dr. Myriam Roy: After training in total syn-
thesis under the direction of Prof. Richard E.
Taylor at the University of Notre Dame, South
Bend, Indiana, and in radiolabeling with Dr.
Bernard Rousseau at CEA-Sacaly, France, Dr.
Myriam Roy joined Prof. Marc Gingras’ team at
the University of Aix-Marseille as assistant
professor. There, she studied families of chiral
organic molecules (i.e. asterisks, dendrimers
and helicenes) providing smart and responsive
nanomaterials under the direction of Prof.
Gingras. Building her knowledge over the
years, it ultimately led to a close collaboration
and to the present study.
Dr. Marco Villa: Marco Villa completed his
master’s degree in Photochemistry and Molec-
ular Materials at the University of Bologna,
Italy, under the supervision of Prof. Ceroni. He
moved to France at Aix-Marseille Université,
under the supervision of Prof. Gingras for a
doctoral position in a joint agreement with
the University of Bologna under the co-super-
vision of Prof. Ceroni. After obtaining his
doctoral degree, he returned to Italy at the
University of Bologna to work with Prof.
Ceroni with a post-doctoral fellowship. In the
last years, a very efficient international collab-
oration on persulfurated aromatic compounds
has led to several scientific contributions and
the last one is reported in this article. The two
supervisors of Marco Villa helped him to
improve his skills in organic synthesis and in
the photophysical characterization of com-
pounds in solution and in the solid state.
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Table 1. Most relevant photophysical data of 1X and 2X compounds in air-equilibrated THF solution at 298 K (unless otherwise noted).
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absorption
ɛ/104
emission
ϕem
λmax/nm
λmax/nm
τ/ns
kr/108 sÀ 1
knr/108 sÀ 1
MÀ 1 cmÀ 1
1P[a]
1O[a]
1M[a]
1P
1O
1M
2P
427
426
433
429
425
432
430
420
434
1.90
1.96
1.92
3.94
3.00
3.36
3.58
3.49
3.58
463
470
463
462
467
463
454
455
453
0.07
0.09
0.42
0.53
0.49
0.51
0.59
0.57
0.58
0.42
0.65
1.42
2.00
2.00
2.00
1.80
1.80
1.80
1.67
1.38
2.96
2.65
2.45
2.55
3.28
3.17
3.22
22.1
14.0
4.08
2.35
2.55
2.45
2.28
2.39
2.33
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2O
2M
[a] in an aqueous solution at pH=8.
isomers, likely due to different symmetry of the peripheral
substituents. The emission bands, lifetimes and emission
quantum yields are similar for the three compounds, as shown
in Table 1. This means that the difference between the three
isomers does not affect much the photophysical properties of
the central pyrene core. These photophysical parameters are
similar to those from previous 1,3,6,8-tetra(phenylthio)pyrene-
cored molecules.[27]
The photophysical properties of the regioisomeric acid 1X
(compound 1M in Figure 1a and comparison of compounds 1O,
1M and 1P See Supporting Information, Figure S24) in THF are
very similar to the properties recorded for the esters. The
emission spectra are analogous for the three isomers, as well as
the emission quantum yields, and lifetimes (Table 1). A compar-
ison with the corresponding esters 2X shows that the emission
quantum yield is 5 to 10% lower, while the lifetime increases
from 1.80 to 2.00 ns.
When the tetraacids 1X are dissolved in basic aqueous
solution (pH=8), carboxylic acids are deprotonated so that
water solubility is attained, without using organic co-solvents.
No significant difference in the shape of the absorption and
emission spectra is observed, compared to THF (Figure 1). On
the other hand, we observe an effect in the emission quantum
yields and lifetimes (Table 1).
The emission quantum yield of 2O decreases from 0.49 to
0.09 as well as the lifetime from 2.00 ns to 0.65 ns. 2P has a
similar behavior and the emission quantum yield decreases
from 0.53 to 0.07 as well as the lifetime from 2.00 ns to 0.42 ns.
The isomer 2M is less affected by the solvent change, the
emission quantum yield slightly decreases from 0.51 to 0.42
and the lifetime decreases from 1.80 ns to 1.42 ns. In water
there is an effect of the substituents from ortho and para to
meta. The deprotonation in aqueous solution has an effect on
the non radiative deactivation of the excited state of the
molecule S1. The value of knr increases in aqueous solution
compared to knr in THF and for 1O and 1P there is an increment
of ten times, while for 1M, only two times. We interpreted this
data by a proton transfer between the solvent and the molecule
in the excited state S1 that occurs only in aqueous solution
where this process is extremally fast if compared to an organic
solvent.[33] A similar effect on the isomeric position of a
carboxylic acid is mentioned in literature, where the weaker
conjugated meta isomer, shows higher lifetime compared to
the para isomer.[34]
Metal ion complexation
Under basic aqueous solution, the carboxylic acids 1X are
deprotonated and can coordinate divalent metal ions to
generate a supramolecular architecture. We investigated the
complexation ability (avidity) of 1M with different metal ions
like Ca(II), Cd(II), Co(II), Cu(II), Fe(II), K(I), Li(I), Mg(II), Mn(II), Na
(I),Ni(II), Pb(II), Zn(II). Complexation takes place for all the
investigated metal salts, except for monovalent metal ions, as
evidenced by the absorption spectral changes: the absorption
band at 430 nm decreases in intensity and a new band appears
at 450 nm. However, in the case of Ca2+ and Mg2+ the
complexation is only partial (50%) meaning a lower association
constant than for other cases.
Upon excitation at the isosbestic point, a complete quench-
ing of the tetra(phenylthio)pyrene is observed with all divalent
metal ions, apart from Ca(II) and Mg(II) in which the decrease of
the emission intensity is ca. 50% because of the above-
mentioned lower binding constants (Figure 2).
Figure 1. Normalized absorption spectra (solid lines) and emission spectra
(dash lines) of 1M in air-equilibrated THF solution (red) and air-equilibrated
aqueous solution at pH=8 (black).
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(II) cations with a high binding constant (2×1018 MÀ 1).[36] The
interaction of Pb(II) with 1M is thus reversible and can be used
for sensing applications in water (See Supporting Information,
Figure S28) with a limit of detection near 0.2 μM.
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Conclusion
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We designed a new family of water-soluble, carboxylated tetra
(phenylthio)pyrene ligands in which divalent metal ion coordi-
nation results in the formation of supramolecular assemblies,
and quenching of the pyrene fluorescence in a dual mode
function. It can occur in water only, without the need for
organic co-solvents. Monovalent ions are distinctly ineffective.
These sensing systems are based on a highly fluorescent tetra
(phenylthio)pyrene core with four appended carboxylic acid
units. Three different regioisomers of pyrene 1X with ortho (1O),
meta (1M) and para (1P) carboxylic groups were thus synthe-
sized, characterized, and studied either in THF or aqueous
solution, in the presence of various metal ions. The photo-
physical properties of the three isopropyl esters 2O, 2M, 2P and
the carboxylic acids 1O, 1M, 1P in THF are very similar, with a
blue-green fluorescent emission and high emission quantum
yields (0.5–0.6). The systems functionalized with carboxylic acids
1X are soluble in aqueous solution at pH >8 due to
deprotonation of the carboxylic acids, and the fluorescence is
less intense, but still high for the meta isomer 1M, probably due
to a less efficient deactivation of the excited state by proton
transfer. The addition of metal ions to these systems can not
only quench the fluorescence of the pyrene core, reducing the
emission quantum yield to almost zero, but also control the
formation of three-dimensional nanoscopic objects in a dual
mode function. Several divalent metal ions were tested and all
of them show fluorescence quenching. The formation of
supramolecular polymers is reversible, i.e. addition of ethyl-
enediaminetetraacetic acid (EDTA) restores the initial conditions
by scavenging metal ions due to a strong EDTA-metal ion
complex. The coordination polymers disassemble, and
fluorescence of the pyrene core is restored. New avenue for
metal ions sensing in a dual function were developed in water,
especially for sensing heavy metal ions.
Figure 2. Relative emission quantum yields of 1M as 3.0 μM solution in water
at pH=8 upon addition of different metal ions (45 μM for K+, Na+ and Li+,
and 10 μM for all other metal ions).
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All three isomers 1P (See Supporting Information, Fig-
ure S26), 1M (Figure 3) and 1O (See Supporting Information,
Figure S27) show complexation with Pb2+. The normalized
absorption and emission intensities change show a plateau at
2 mol-equivalents of metal ions (e.g. 1M in Figure 3) with a limit
of detection of 0.2 μM. These results indicate a complex with a
1:2 molar ratio of pyrene ligand to Pb2+. No evidence of sulfur-
metal ions interaction is observed in the absorption spectra[35]
so metal ions complexation is led by the carboxylate moieties.
Considering the structure of the ligand, two carboxylic acid
functions are too far from each other to allow an intramolecular
complex, so two pyrene molecules are linked together by metal
ions complexation, thus making a complex structure like [Pb2n
(1)n].
Confirmation of this hypothesis is given by DLS analysis of
an aqueous solution of 1M before and after addition of 2.5 mol-
equivalents of Pb(II) per molecule: after addition of the metal
ions a significant increase of the intensity of the scattered light
is observed. A polydisperse aggregate (PDI 0.47) with a mean
diameter of 180 nm is formed (See Supporting Information,
Figure S30).
The supramolecular polymer formed for 1M and Pb(II) can
be disassembled upon addition of ethylenediaminetetraacetic
acid (EDTA, 5 mol-eq.) as observed from DLS measurements
(See Supporting Information, Figure S31). EDTA complexes Pb
Experimental Section
Instrumentation and materials
All reagents, solvents and chemicals were purchased from Sigma-
Aldrich, Fisher, or Alfa-Aesar and used directly unless otherwise
stated (purity: reagent or analytical grade). Solvents were stored for
several days over freshly activated 3 Å molecular sieves (activation
°
for 3 h at 250 C). All reactions were monitored by TLC or LCMS or
FT-IR (ATR) spectroscopy. Isopropryl mercaptobenzoates were
prepared according to the literature.[31] The experiments were
carried out in air-equilibrated solution at 298 K unless noted
Figure 3. Absorption (left) and fluorescence (right) of a 3.0×10À 6 M solution
of 1M in air-equilibrated water solution (pH=8) upon titration with a
3.73 mM water solution of Pb(NO3)2: red line (0 eq), black line (2 eq). Inset
show the normalized absorption changes at 400 nm (red) and 470 nm
(black) and emission intensity changes at 470 nm (green).
otherwise. UV-vis absorption spectra were recorded with
a
PerkinElmer l40 spectrophotometer using quartz cells with path
length of 1.0 cm. Luminescence spectra were performed with a
PerkinElmer LS-50 or an Edinburgh FLS920 spectrofluorimeter e-
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quipped with a Hamamatsu R928 phototube. Lifetimes shorter than
10 μs were measured by the above-mentioned Edinburgh FLS920
spectrofluorimeter equipped with a TCC900 card for data acquis-
ition in time-correlated single-photon counting experiments (0.5 ns
time resolution) with a 340 nm pulsed diode and a LDH-P-C405
pulsed diode laser. Longer lifetimes were measured by the
PerkinElmer LS-50. Emission quantum yields were measured
following the method of Demas and Crosby[37] (standard used: [Ru
(bpy)3]2+ in aqueous solution).[38] The estimated experimental errors
are 2 nm on the band maximum, 5% on the molar absorption
coefficient and luminescence lifetime, 10% on the emission
quantum yield in solution. TLC analyses were performed on
precoated silica gel (Alugram® SilG/UV254gel) aluminium plates
from Macherey-Nagel. Compounds were visualized with UV-light
(254 or 365 nm). Flash chromatography was performed over silica
gel 60, Merck type 230–400 mesh (40–63 μm). NMR spectra 1H
(400 MHz) and 13C (100.53MHz) were recorded on JEOL ECX-400
spectrometer signals of the residual protic solvent CHCl3 at
7.26 ppm and DMSO-d6 at 2.50 ppm were used as internal
references, along with TMS. As for 13C NMR spectra, the central
resonance of the triplet for CDCl3 at 77.16 ppm and the signal for
DMSO-d6 at 39.52 ppm were used as internal references.[39] The
yellow solid (1113 mg., 1.13 mmol, 93% yield). 1H NMR
(399.78 MHz, CDCl3, ppm): δ=8.70 (s, 4H), 8.45 (s, 2H), 7.83 (d, 8H,
J=8.3 Hz), 7.10 (d, 8H, J=8.3 Hz), 5.18 (sept, 4H, J=6.3 Hz), 1.30 (d,
24H, J=6.4 Hz). 13C NMR (100.53MHz, CDCl3, ppm): δ=165.52,
143.21, 140.45, 133.53, 130.35, 129.15, 128.72, 127.41, 127.05,
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+
126.05, 68.55, 21.99. HRMS (ESI+) calculated for [C56H50O8S4 +NH4
]: 996.2732 m/z, found [M+ NH4+] 996.2731 m/z, FT- IR (cmÀ 1) ν=
2981, 2926, 1709, 1592, 1270, 1247, 1100, 1014, 922, 874, 850, 815,
759, 689. Elemental analysis (%) : Calculated : 68.69%C 5.15%H
13.10%S Found: 68.42%C 5.05%H 13.02%S.
Tetraisopropyl 2,2’,2’’,2’’’-(pyrene-1,3,6,8-tetrayltetrakis(sulfanedi-
yl))tetrabenzoate (2O): Tetrabromopyrene (1494 mg. 2.88 mmol,
1.00 eq), isopropyl-2-mercaptobenzoate (2908 mg., 14.84 mmol,
5,15 mol-eq.) and dry Cs2CO3 (5632 mg., 17.32 mmol, 6.01 mol-eq.)
were dried under high vacuum for 30 min before being introduced
into an oven-dried sealed tube. Under an argon atmosphere, dry
N,N-dimethylformamide (DMF, 12.0 mL) was added and the mixture
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°
was vigorously stirred at 80 C (oil bath temperature) for 4 days.
Upon completion of the reaction, the mixture was cooled down to
room temperature and diluted with 100 mL of 1M HCl (aq), a
yellow-brown solid precipitated and was filtrated. The solid was
°
triturated while stirring vigorously in ethanol (150 mL) at 40 C to
1
resonance multiplicities in the H NMR spectra are described as “s”
afford a yellow solid. recrystallization in cyclohexane gave a pure
yellow solid (2322 mg., 2.37 mmol, 82% yield). 1H NMR
(399.78 MHz, CDCl3, ppm): δ=8.75 (s, 4H), 8.63 (s, 2H), 8.02 (dd, 4H,
J=7.6, 1.6 Hz), 7.09 (ddd, 4H, J=7.4, 7.4, 1.2 Hz), 7.03 (ddd, 4H, J=
7.9, 7.4, 1.6 Hz), 6.50 (dd, 4H, J=7.9, 1.2 Hz), 5.35 (sept, 4H, J=
6.2 Hz), 1.42 (d, 24H, J=6.3 Hz). 13C NMR (100.53MHz, CDCl3, ppm):
δ=166.07, 143.39, 142.31, 134.89, 132.38, 131.31, 129.77, 127.71,
(singlet), “d” (doublet), “t” (triplet), “q” (quarted), “sept” (septet) “m”
(multiplet) or “b” (broad). High resolution mass spectra were
recorded at the Spectropôle of Marseille (France) in triplicate with
double internal standards. Oligomers of poly(propylene glycol)
were used as internal standards. Ionization was facilitated by some
+
adducts with Ag+, NH4 or Na+ ions. Two spectrometers were
used: a) SYNAPT G2 HDMS (Waters) instrument equipped with an
ESI source and a TOF analyser in a positive mode. b) QStar Elite
(Applied Biosystems SCIEX) instrument equipped with an atmos-
pheric ionization source (API). The samples were ionized under ESI
with an electrospray voltage of 5500 V; orifice voltage: 10 V, and air
pressure of the nebulizer at 20 psi. A TOF analyser was used in a
positive mode. MALDI-TOF-MS analyses were performed on an
Autoflex MALDI-TOF Bruker spectrometer (matrix DCTB), in negative
mode, laser 355 nm. Infrared absorption spectra were directly
recorded on solids or neat liquids on a Perkin-Elmer Spectrum 100
127.62, 127.53, 126.17, 124.63, 69.19, 22.12. HRMS (ESI+) calculated
+
for [C56H50O8S4 +NH4+]: 996.2731 m/z, found [M+ NH4
]
996.2731 m/z, FT-IR (cmÀ 1) ν=2977, 2927, 1703, 1562, 1459, 1269,
1249, 1098, 1039, 1053, 916, 828, 738.
Tetraisopropyl 3,3’,3’’,3’’’-(pyrene-1,3,6,8-tetrayltetrakis(sulfanedi-
yl))tetrabenzoate (2M): Tetrabromopyrene (158 mg, 0.30 mmol,
1.00 mol-eq), isopropyl-3-mercaptobenzoate (320 mg, 1.63 mmol,
5.43 mol-eq) and dry Cs2CO3 (658 mg, 2.00 mmol, 6.67 mol-eq) were
dried under high vacuum for 30 min before being introduced into
an oven-dried sealed tube. Under an argon atmosphere, dry N,N-
dimethylformamide (DMF, 2.0 mL) was added and the mixture was
FT-IR Spectrometer equipped with
a universal ATR accessory
(contact crystal: diamond). The determination of the hydrodynamic
diameter distributions was carried out through Dynamic Light
Scattering measurements employing a Malvern Nano ZS instrumen-
t equipped with a 633 nm laser diode. Samples were housed in
disposable polystyrene cuvettes of 1 cm optical path length, using
water as solvent. PDl (Polydispersion Index) indicates the width of
DLS hydrodynamic diameter distribution. In case of a monomodal
distribution (gaussian) calculated by means of cumulant analysis,
PDl =(σ/Zavg) 2, where σ is the width of the distribution and Zavg is
the average diameter of the particles population respectively
°
vigorously stirred at 80 C (oil bath temperature) for 4 days. Upon
completion of the reaction, the mixture was cooled down to room
temperature and diluted with 50 mL of 1M HCl (aq), a yellow-brown
solid precipitated and was filtrated. The solid was triturated while
°
stirring vigorously in ethanol (20 mL) at 40 C to afford a yellow
solid. Recrystallization in cyclohexane gave a pure yellow solid
1
(250 mg, 0.26 mmol, 87% yield). H NMR (399.78 MHz, CDCl3, ppm):
δ=8.66 (s, 4H), 8.03 (s, 2H), 7.98 (br s, 4H), 7.87–7.81 (m, 4H), 7.25–
7.20 (m, 8H), 5.19 (sept, 4H, J=6.3 Hz), 1.32 (d, 24H, J=6.3 Hz). 13C
NMR (100.53MHz, CDCl3, ppm): δ=165.30, 136.51, 136.43, 134.11,
132.08, 131.58, 131.07, 130.85, 129.40, 128.13, 125.86, 68.85, 21.99.
HRMS (ESI+) calculated for [C56H50O8S4 +NH4+]: 996.2732 m/z,
found [M+ NH4+] 996.2728 m/z. FT-IR (cmÀ 1) ν=2977, 2927, 1714,
1702, 1418, 1281, 1261, 1101, 922, 874, 830, 747.
Synthetic procedure and compound data
Tetraisopropyl 4,4’,4’’,4’’’-(pyrene-1,3,6,8-tetrayltetrakis(sulfanedi-
yl))tetrabenzoate (2P): Tetrabromopyrene (630 mg 1.22 mmol,
1.00 mol-eq), isopropyl-3-mercaptobenzoate (1789 mg., 6.38 mmol,
5.23 mol-eq) and dry Cs2CO3 (2510 mg, 7.73 mmol, 6.33 mol-eq)
were dried under high vacuum for 30 min before being introduced
into an oven-dried sealed tube. Under an argon atmosphere, dry
N,N-dimethylformamide (DMF, 6.0 mL) was added and the mixture
3,3’,3’’,3’’’-(pyrene-1,3,6,8-tetrayltetrakis(sulfanediyl))tetrabenzoic
acid (1M): A solution of 2M (60 mg, 0.060 mmol, 1.0 eq) and
LiOH*H2O (85 mg, 2.03 mmol, 33 eq) in absolute ethanol (7 mL) was
°
heated under an argon atmosphere at 70 C (oil bath temperature)
for 37 h. The reaction was monitored by FT-IR until disappearance
of the ester C=O functions. Upon completion of the reaction, the
mixture was cooled down to room temperature and diluted with
60 mL of 1M HCl (aq.). A yellow solid precipitated and provided a
solid suspension. The solid was filtered and dried under vacuum at
°
was vigorously stirred at 80 C (oil bath temperature) for 4 days.
Upon completion of the reaction, the mixture was cooled down to
room temperature and diluted with 100 mL of 1M HCl (aq), a
yellow-brown solid precipitated and was filtrated. The solid was
°
triturated while stirring vigorously in ethanol (50 mL) at 40 C to
°
60 C for 3 days to yield the desired product as a yellow solid
(35 mg, 0.043 mmol, 72% yield). 1H NMR (399.78 MHz, DMSO-d6,
afford a yellow solid. Recrystallization in cyclohexane gave a pure
ChemPlusChem 2020, 85, 1481–1486
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© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
doi.org/10.1002/cplu.202000344
ChemPlusChem
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Acknowledgements
P.C. and M.G. acknowledge a financial support from the French-
Italian University for a doctoral contract to M.V. (Vinci Program), a
°
CNRS PICS N PICS07573 Program for International Scientific
Collaborations (Univ. of Bologna), the University of Bologna, Aix-
Marseille Université, the spectropôle of Marseille, CINaM and CNRS
France. We especially acknowledge a financial support from the
Excellence Initiative of Aix-Marseille University – A*Midex, a French
‘‘Investissements d’Avenir’’ programme (A*Midex Emergence, Pyr-
enex project). We also thank the spectropole of Marseille.
Conflict of Interest
The authors declare no conflict of interest.
Keywords: luminescence · metal ions · pyrenes · sensors ·
supramolecular chemistry
Manuscript received: April 29, 2020
Revised manuscript received: June 16, 2020
ChemPlusChem 2020, 85, 1481–1486
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1486
© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim