Colorimetric Naphthalene-Based Thiosemicarbazide Anion Chemosensors with an Internal Charge Transfer Mechanism

Article abstract of DOI:10.1002/ejoc.201600509

A series of thiosemicarbazide anion chemosensors substituted with naphthalene and 4-nitrophenyl or phenyl units were synthesized. The molecules were characterized by using¹H,¹³C DEPT and¹⁵N NMR spectroscopy. The anion bind

Full text of DOI:10.1002/ejoc.201600509

DOI: 10.1002/ejoc.201600509
Full Paper
Anion Chemosensors
Colorimetric Naphthalene-Based Thiosemicarbazide Anion
Chemosensors with an Internal Charge Transfer Mechanism
Kristina N. Farrugia,[a] Damjan Makuc,[b,c] Agnieszka Podborska,[d] Konrad Szaciłowski,[e]
Janez Plavec,[b,c] and David C. Magri*[a]
Abstract: A series of thiosemicarbazide anion chemosensors an internal charge-transfer mechanism. 1H/13C/15N NMR titra-
substituted with naphthalene and 4-nitrophenyl or phenyl units tion studies and DFT and charge distribution calculations sup-
were synthesized. The molecules were characterized by using port a mechanism involving deprotonation of the central N–
1H,13C DEPT and 15N NMR spectroscopy. The anion binding H bond. Compound 4 with a methylene spacer between the
properties of compounds 1–4 were investigated by UV/Vis ab- naphthalene and thiosemicarbazide moieties was deliberately
sorption and fluorescence spectroscopy in DMSO, DMSO/H2O designed as a fluorescent photoinduced electron-transfer anion
(9:1 v/v), and acetonitrile with hydroxide, fluoride, acetate, (PET) sensor. However, the methylene spacer did not prevent
hypophosphate, and chloride anions. Striking color changes delocalization of the HOMO orbital between the planar aro-
were observed with nitro-containing chemosensors 2–4 with all matic ring and the thiosemicarbazide unit as expected on the
anions, with the exception of chloride, which was attributed to basis of the “fluorophore–spacer–receptor” PET model.
Introduction
action on the basis of these techniques alone often results in
ambiguous or erroneous conclusions. Some groups have re-
sorted to solid-state single-crystal X-ray crystallography, such as
the Gale group with pyrrolylamidothioureas[12] and the Gunn-
laugsson group with thiosemicarbazides,[13] to gain further in-
sight into the mechanism of action. However, obtaining crystals
of suitable quality for X-ray crystallography is not always possi-
ble. With the assistance of two-dimensional 1H/13C/15N NMR
correlation spectroscopic techniques and corroborated by den-
sity functional theory (DFT), we recently showed for the first
time in solution, rather than in the solid state, that the mecha-
nism of action of thiosemicarbazides involves deprotonation of
the central thiourea N–H proton.[18] Our conclusions contradict
an earlier report based solely on 1H NMR and UV/Vis absorption
spectroscopy.[17]
The development of chemosensors for the detection of anions
is an area of active research within the realm of supramolecular
chemistry.[1–3] Anions are ubiquitous species in nature that play
important roles in biological and environmental ecosystems.[4,5]
Standard approaches employed in anion chemosensor design
include attachment of a receptor unit electronically coupled to
a chromophore for sensing by an internal charge-transfer (ICT)
mechanism or the linking of a lumophore to a receptor unit
decoupled by a hydrocarbon spacer for sensing by a photo-
induced electron-transfer (PET) mechanism.[6] An assortment of
anion chemosensors with neutral receptors have been reported,
including conjugated ureas,[7] thioureas,[8] benzamidothio-
ureas,[9] squaramides,[10] thiosemicarbazones,[11] and thiosemi-
carbazides.[12–18] Typically, these studies involve monitoring the
interaction of various anions with the receptor unit by a combi-
nation of 1H NMR, UV/Vis absorption, and/or fluorescence emis-
sion spectroscopy. However, elucidation of the mechanism of
In this study, we report the anion recognition properties of
a series of four naphthalene-containing thiosemicarbazide
chemosensors 1–4 in the aprotic solvents DMSO and aceto-
nitrile as well as in DMSO/H2O (9:1 v/v). Naphthalene was intro-
duced as a potential fluorophore to explore the anion recogni-
tion by fluorescence spectroscopy in addition to UV/Vis absorp-
tion spectroscopy. Compounds 2 and 3 were designed with a
purposely integrated electron-withdrawing 4-nitrophenyl sub-
stituent, whereas 1 is a model compound devoid of a nitro
moiety. Moreover, compound 4 was deliberately designed with
an intervening methylene spacer between the naphthalene
chromophore and the thiosemicarbazide unit according to a
“fluorophore–spacer–receptor” format,[19] which should facili-
tate fluorescence switching by a PET mechanism. DFT calcula-
tions and two-dimensional 1H,15N NMR correlation spectro-
scopy provide further insight into the physiochemical proper-
ties of these compounds.
[a] Department of Chemistry, Faculty of Science, University of Malta,
Msida, MSD 2080, Malta
E-mail: david.magri@um.edu.mt
https://www.um.edu.mt/profile/davidmagri
[b] Slovenian NMR Centre, National Institute of Chemistry,
Hajdrihova 19, 1000 Ljubljana, Slovenia
[c] EN→FIST Centre of Excellence,
Trg Osvobodilne fronte 13, 1000 Ljubljana, Slovenia
[d] AGH University of Science and Technology, Faculty of Non-Ferrous Metals,
al. Mickiewicza 30, 30-059 Kraków, Poland
[e] Academic Centre of Materials and Nanotechnology, AGH University of
Science and Technology,
al. Mickiewicza 30, 30-059 Kraków, Poland
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/ejoc.201600509.
Eur. J. Org. Chem. 0000, 0–0
1
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
Results and Discussion
reflux in dichloromethane/acetonitrile (4:1). Thiosemicarbazides
1–4 were fully characterized by 1H NMR, 13C NMR, 15N NMR,
and IR spectroscopy in addition to HRMS (see the Experimental
Section for details).
Synthesis
The syntheses of thiosemicarbazide compounds 1–3 are shown
in Scheme 1. They were synthesized in 30–83 % yield by a one-
step reaction by heating the appropriate combination of com-
mercially available hydrazine and isothiocyanate at reflux in
acetonitrile. The synthesis of 4 required two reaction steps, as
shown in Scheme 2. 1-Naphthylmethylamine was treated with
thiophosgene in dichloromethane under a nitrogen atmos-
phere at room temperature to yield the naphthalenemethyl iso-
cyanate as a yellow oil in 77 % yield.[20] Product 4 was subse-
quently synthesized in 53 % yield by heating freshly prepared 1-
naphthylmethyl isothiocyanate with 4-nitrophenylhydrazine at
UV/Vis Absorption Spectrophotometric Studies
The photophysical properties of 1–4 were studied by naked-
eye observations and UV/Vis absorption spectroscopy in the
absence and presence of the selected anions, namely, HO–, F–,
–
AcO–, H2PO4 , and Cl–. Studies were first performed in competi-
tive media of DMSO/H2O (9:1 v/v) with the sodium salts of all
anions. Additional experiments were conducted with 3 and 4
in DMSO and 4 in acetonitrile by using tetrabutylammonium
salts. Table 1 summarizes the UV/Vis spectroscopic data.
Compound 1 exhibits a broad band that tails out to 350 nm
in DMSO/H2O (9:1 v/v) solution (Figure S1, Supporting Informa-
Scheme 1. Synthetic scheme for compounds (a) 1 and 2 and (b) 3 with atomic
numbering of the three N–H groups in yields of 66, 83, and 30 %, respectively.
Figure 1. Solutions of 27 μ
M (a) 1, (b) 2, (c) 3, and (d) 4 in DMSO/H2O
Scheme 2. Synthetic scheme for compound 4 with reaction yields of 70 and
53 % for steps 1 and 2, respectively.
(9:1 v/v) and (e) 4 in acetonitrile in the presence of 4 equiv. of HO–, F–,
AcO–, Cl–, and H2PO4
.
–
Table 1. UV/Vis absorption spectroscopic data for compounds 1–4 in the absence and presence of anions in various solvents.[a]
[d,e]
[d,f]
Solvent
λmax [nm] (log εmax
)
λmax [nm] (log εmax
)
Δλmax [nm][g]
Isosbestic points
[h]
[i]
[j]
1
2
2
3
4
4
4
DMSO/H2O (9:1)[b]
DMSO/H2O (9:1)[b]
DMSO[c]
–
NI[i]
–
–
370 (4.27)
370 (4.28)
321 (4.29)
370 (4.17)
371 (4.15)
341 (4.11)
519 (4.48)
525 (4.45)
387 (4.39)
540[k]
545 (4.33)
522 (4.34)
149
155
66
170
175
81
331, 417
333, 418
283, 350
320, 423
322, 423
305, 394
DMSO/H2O (9:1)[b]
DMSO/H2O (9:1)[b]
DMSO[c]
MeCN[c]
[a] The HO–, F–, AcO–, H2PO4–, and Cl– ions were investigated. No change was observed with Cl–. [b] Anions were added as sodium salts. [c] Anions were
added as tetrabutylammonium salts. [d] The λmax (log εmax) value of the most intense peak at titration plateau. [e] In the absence of any anion. [f] In the
presence of anion. [g] Δλmax = λmax (anion added) – λmax (no anion added). [h] No absorption band observed within 280–700 nm. [i] The band is a shoulder
and does not allow for accurate identification (NI: not identified). [j] No isosbestic points present. [k] Peak intensity is anion dependent: log εmax 4.19 (HO–),
3.76 (F–), 4.21 (AcO–). Almost no change with 70 equiv. of H2PO4
.
–
Eur. J. Org. Chem. 0000, 0–0
www.eurjoc.org
2
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
Table 2. Dissociation constants (log ꢀA–) of compounds 1–4.[a]
Anion
1
2
3
4
2
4
4
DMSO/H2O (9:1)[b]
DMSO[c]
MeCN[c]
HO–
F–
3.8( 0.3)
4.0( 0.2)
NI[d]
4.9( 0.1)
4.9( 0.1)
4.9( 0.1)
3.6( 0.2)
5.2( 0.2)
5.0( 0.1)
5.1( 0.1)
4.8( 0.3)
4.1( 0.2)
4.3( 0.1)
2.6( 0.2)
5.4( 0.2)
5.3( 0.2)
5.4( 0.2)
5.1( 0.2)
4.8( 0.2)
4.9( 0.1)
4.9( 0.2)
4.0( 0.1)
5.1( 0.2)
5.3( 0.1)
5.0( 0.1)
4.4( 0.1)
AcO–
H2PO4
–
[e]
[f]
–
–
[a] Determined by UV/Vis absorption titration technique by the equation –log X = log ꢀA– + log [(Amax – A)/(A – Amin)], where A is the absorbance and X is the
molar anion concentration. Least-squares analysis resulted in linear fits with R2 > 0.99. Estimated errors are reported as the range from at least two titration
experiments. Titrations with Cl– resulted in no significant changes. [b] Sodium salts were used. [c] Tetrabutylammonium salts were
used. [d] The band is a shoulder and does not allow for accurate identification (NI: not identified). [e] A broad shoulder, which prevents determination of
log ꢀH PO . [f] No anion–receptor interaction observed.
–
2
4
tion). The addition of HO– yields a broad shoulder at ca. 300 nm. of 1–4 with the various anions; these values are reproducible
A slight increase is observed upon the addition of F– accompa- within an error of 0.2.
nied by a color change from colorless to faint yellow (Figure 1,
a). Dissociation constants (log ꢀA–) of 3.8 and 4.0 were deter-
mined for hydroxide and fluoride, respectively (Table 2). How-
ever, no new bands are observed in the absorption spectra with
–
either H2PO4 or Cl–, which indicates that the thiosemi-
carbazide moiety does not interact appreciably with these two
weakly basic anions. In DMSO/H2O (9:1 v/v), 2 exhibits an in-
tense absorption band at 370 nm and a weaker band at
519 nm. The addition of HO–, F–, AcO–, and H2PO4– results in an
instantaneous color change from faint yellow to intense purple,
whereas no change is observed with Cl– (Figure 1, b). As the
concentration of the basic anion increases, the absorption band
at 370 nm decreases with a concomitant increase in the ICT
absorption band at 519 nm, which is accompanied by two isos-
bestic points at 331 and 417 nm (Figure 2). Similar results are
observed in DMSO (Figure S2). The UV/Vis absorption titration
profiles of 2 in DMSO/H2O (9:1 v/v) are shown in Figure 3. A
plateau is reached with 2 mol equivalents of HO– and F– and
3 mol equivalents of AcO–. By contrast, 70 equivalents of
Figure 3. UV/Vis titration profiles of 27 μM of 2 at (a) 519 nm in DMSO/H2O
(9:1), (b) 525 nm in DMSO with 0 → 4 equiv. of HO– (blue), F– (magenta),
AcO– (red), and H2PO4 (green).
–
By contrast, 3 exhibits spectral characteristics that are differ-
ent from those of both 1 and 2 with peaks at 321 and 387 nm
and a broad absorption band out to 700 nm in DMSO/H2O
(9:1 v/v) solution (Figure 4). Upon the addition of HO–, F–,
–
AcO–, and H2PO4 , the absorption band at 321 nm decreases,
whereas new bands at 387 and 540 nm emerge, the latter as a
broad shoulder. Isosbestic points are observed at 283 and
350 nm. A wavelength shift of 66 nm is manifested by a color
change to orange-brown (Figure 1, c). Similar to 2, no change
is observed in the presence of Cl–. For the three more basic
–
H2PO4 are required to complete the titration. In all cases, the
most dramatic changes occur upon the addition of the first
equivalent of the anion. Table 2 summarizes the log ꢀA– values
Figure 2. UV/Vis absorption spectra of 27 μ
M
of 2 in DMSO/H2O (9:1) upon the
Figure 4. UV/Vis absorption spectra of 27 μM of 3 in DMSO/H2O (9:1 v/v)
addition of (a) 0 → 4 equiv. of HO–, (b) 0 → 8 equiv. of F–, (c) 0 → 20 equiv.
upon the addition of (a) 0 → 4 equiv. of HO–, (b) 0 → 4 equiv. of F–,
of AcO–, and (d) 0 → 70 equiv. of H2PO4
.
(c) 0 → 4 equiv. of AcO–, and (d) 0 → 50 equiv. of H2PO4
.
–
–
Eur. J. Org. Chem. 0000, 0–0
www.eurjoc.org
3
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
anions, the titration curves reach a plateau after the addition of but with the absence of an isosbestic point. Most noticeably,
–
2 equivalents of HO–, F–, and AcO–. Three equivalents of H2PO4
whereas 2 equivalents of HO– are required to reach the plateau,
are required to complete the titration. The log ꢀ values reported over 700 equivalents of AcO– are needed. Consequently, the
in Table 2 are comparable to those of 2.
log ꢀA– values of 4 in DMSO/water (9:1 v/v) are significantly
lower than those for 2 and 3 in the same solvent (Table 2). A
comparison of the titration profiles of 4 in the three solvents is
shown in Figure 6.
The ground-state properties of 4 were examined in DMSO,
DMSO/H2O (9:1 v/v), and acetonitrile. In DMSO, an intense ICT
band is observed at 371 nm. The addition of HO–, F–, AcO–, and
–
H2PO4 is accompanied by a decrease in the band at 371 nm
and a concomitant increase in the band at 545 nm with two
clear isosbestic points at 322 and 423 nm, as observed similarly
with 2 (Figure S3). The titration curves yield a plateau upon the
addition of 1 equivalent of HO–, 2 equivalents of F– and AcO–,
–
and 30 equivalents of H2PO4 . Comparably in acetonitrile, 4 has
absorption transitions at 341 and 282 nm (Figure S4). Upon
adding HO–, F–, AcO–, and H2PO4– as tetrabutylammonium salts,
a decrease in the 341 nm band and a notable increase in the
522 nm band are observed. A distinct color change occurs from
pale yellow to purple (Figure 1, e). The main differences in
acetonitrile are blueshifted isosbestic points at 305 and 394 nm,
a considerably smaller shift in the λmax of 81 nm upon the addi-
tion of anions (see Table 1), and the fact that only 5 equivalents
–
(rather than 30 equiv.) of H2PO4 are needed to complete the
titration.
In DMSO/H2O (9:1 v/v), 4 similarly has a peak maximum at
370 nm, which upon the addition of HO– and AcO– results in a
decrease in the band at 370 nm with an accompanying increase
in the band at 540 nm (Figure 5). Similarly, two isosbestic points
are situated at 320 and 423 nm with HO– and AcO–. With
Figure 6. Titration profile of 27 μM of 4 at (a) 540 nm in DMSO/H2O (9:1 v/v),
(b) 545 nm in DMSO, and (c) 522 nm in acetonitrile with 0 → 4 equiv. of
anion HO– (blue), F– (magenta), AcO– (red), and H2PO4 (green).
–
–
H2PO4 and Cl–, only a minimal effect is observed, which does
Compound 4 displays greater selectivity in DMSO/H2O (9:1
v/v) solution than in DMSO or acetonitrile. Titration of 4 with
not allow for the determination of log ꢀA–. In the case of F–,
similar spectral changes are initially observed, but considerably
more of the anion is required, which results in absorbances at
540 nm that are lower than those in the HO– and AcO– titration
profiles. These spectral changes result in a solution color
change from pale yellow to purple, which is most intense with
HO– (Figure 1, d). Furthermore, beyond the addition of
10 equivalents of F–, the absorption spectra generally increase,
HO–, F–, AcO–, and H2PO4 results in slightly different spectral
–
profiles for each anion, which can be used advantageously to
differentiate the anions. Spectral changes with AcO– are only
observed at high excess concentrations (700 equiv.). Titration
with F– results in an increase in the baseline absorbance, possi-
bly as a result of aggregation.[21] These UV/Vis absorption char-
acteristics of 4 with F– and AcO– may suggest that a competi-
tion occurs between deprotonation and hydrogen bonding,
whereas with H2PO4– hydrogen bonding is prevalent.[9] The dif-
ferent reactivities can be attributed to the incorporation of the
methylene spacer unit.
Compounds 1–3 were tested for the possibility of fluores-
–
cence sensing with HO–, F–, AcO–, and H2PO4 . All three chemo-
sensors are essentially non-fluorescent, both in the absence and
presence of anions, independent of the solvent conditions. This
observation is attributed to the overriding effect of the ICT
mechanism. As a consequence, 4 was synthesized on a PET
sensor design by introducing a methylene spacer between the
naphthalene and thiosemicarbazide moieties.[19] The free en-
ergy for electron transfer (ΔGet) from the naphthalene unit to
the nitrophenyl moiety is predicted to be feasible by
–138 kJ mol–1 using the Weller equation.[22] We were surprised
to find that 4 does not behave as a PET fluorescent switch. Our
first intuition was to suggest that the absence of fluorescence
switching could be due to spectral overlap between the
naphthalene emission spectrum (λmax = 335 nm) with the ab-
sorption spectrum of the 4-nitrophenyl moiety (λmax = 402 nm),
Figure 5. UV/Vis absorption spectra of 27 μ
M of 4 in DMSO/H2O (9:1 v/v)
upon the addition of (a) 0 → 4 equiv. of HO–, (b) 0 → 10 equiv. of F– (inset:
10 → 80 equiv. of F–), (c) 0 → 700 equiv. of AcO–, and (d) 0 → 700 equiv. of
–
H2PO4
.
Eur. J. Org. Chem. 0000, 0–0
www.eurjoc.org
4
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
which would allow for an energy-transfer quenching mecha-
In the 13C NMR spectra of 1–3, 15 resonances corresponding
nism. However, upon performing DFT calculations we found to 17 carbon atoms are observed. Because of the methylene
that the methylene unit does not act as an effective spacer unit spacer, 16 signals are observed for 4 corresponding to 18
(see below).
carbon atoms. In [D6]DMSO, the thiourea carbonyl consistently
appears at ca. δ = 182 ppm. The other aromatic carbon signals
are found between δ = 106 and 154 ppm. The carbon reso-
nance assignments for 1–4 are supported by DEPT experiments
(see the characterization data). The 13C signals due to carbon
atoms with no protons attached disappear, whereas the signal
from the methylene group in 4 at δ = 47 ppm is inverted.
1H NMR titration experiments with AcO– were performed
with 2. The stacked 1H NMR titration spectra of 2 upon the
addition of AcO– in [D6]DMSO/0.5 % water are given in Figure 7.
A striking observation is that the thiourea H3 proton is drasti-
cally shielded from 10.19 to 7.48 ppm (ΔδH3 = 2.71 ppm). This
assignment was aided by 1H,13C HSQC and HMBC as well as
1H,15N HSQC correlation spectra of 2 upon the addition of acet-
ate (Figures S18–S20). By contrast, the aromatic N–H resonance
NMR Titration Studies
1
The H NMR and 13C NMR resonances of 1–4 were assigned on
the basis of the analysis of the 1D proton, 1D carbon, and
carbon DEPT spectra. The resonances of 1–4 were further ana-
lyzed by 1H,13C and 1H,15N HSQC and HMBC experiments.[18]
Table 3 provides a summary of the diagnostic 1H NMR, 13C NMR,
and 15N NMR chemical shifts, whereas the complete NMR data
is reported in the Experimental Section. The 1H NMR and 1H,15N
HSQC spectra of 1–4 are provided in Figures S5–S8 and S9–S12,
respectively.[23] The 1H,15N HMBC spectrum of 4 is also included
(Figure S13). In addition, the 1H,13C HSQC and HMBC spectra of
2 and 4 are presented in Figures S14–S17.
of H1 undergoes a chemical shift from 9.38 to 9.84 ppm (ΔδH1
=
The unequivocal assignment of the three N–H nitrogen and
hydrogen atoms was performed by analysis of both the 1H NMR
1
and H,15N NMR spectra, for which correlation signals are ob-
served for directly bonded N–H atoms as well as multibond
couplings.[24,25] The aryl protons are observed within a chemical
shift range of δ = 6.7–8.4 ppm for 1–4 (Table 3). The aromatic
N–H proton (H1) is observed in the range of δ = 8.2–9.4 ppm,
whereas the two thiourea protons (H2 and H3) are observed
further downfield at δ = 9.7–10.3 and 10.0–10.3 ppm, respec-
tively. An exception is observed with 4, for which the H3 proton
exhibits a more deshielded resonance at δ = 8.8 ppm. This ap-
parent anomaly can be explained by the methylene spacer,
which prevents delocalization of the nitrogen lone pair of elec-
trons into the naphthalene system; this results in shielding of
the proton resonance. The chemical shifts are consistently in
the order of δH3 > δH2 > δH1 for 1–3.[12]
The 15N NMR chemical shifts for the three thiourea N–H
1
nitrogen atoms were determined indirectly by 2D H,15N NMR
spectroscopy experiments. The aromatic N–H nitrogen atoms
(N1) are observed between δ = 96 and 106 ppm, whereas the
two thiourea N–H nitrogen atoms (N2 and N3) are observed in
the δ = 127–137 and 112–127 ppm regions, respectively. The
15N NMR chemical shifts show only minor variations as a result
of the structural differences in the molecules. The chemical shift
of the nitrogen atom of the nitro group in 4 is observed at
372 ppm.[18] The nitro group is not observed for either 2 or 3
in the 1H,15N HMBC spectra, whereas compound 1 lacks the
nitro moiety. Refer to Table 3 for specific 15N NMR chemical
shift data.
Figure 7. 1H NMR spectra of 0.01
M
2 upon increasing the addition of AcO–
in [D6]DMSO/0.5 % water at 298 K. Numbers on the left correspond to the
number of equivalents of anion added. The asterisk * marks the resonance
at 11.95 ppm due to the protonation of AcO–. The unassigned signals are
attributed to the naphthalene moiety.
Table 3. 1H NMR, 13C NMR, and 15N NMR chemical shifts of compounds 1–4 in [D6]DMSO.
δ(1H) [ppm]
δ(13C) [ppm]
δ(15N)[a] [ppm]
H1
H2
H3
Ar–H
C=S
Ar–C
N1
N2
N3
NO2
[b]
1
2
3
4
8.21
9.38
8.75
9.12
9.77
10.03
10.19
10.34
8.79
6.79–8.01
6.92–8.20
6.77–8.36
6.73–8.20
183.1
183.2
180.9
182.5
112.9–148.1
111.4–154.2
106.0–145.7
111.4–154.2
96
106
96
133
129
137
127
118
121
127
112
–
–
–
[c]
10.03
10.23
9.76
[c]
104
372
[a] 15N NMR chemical shifts determined by 1H,15N HMBC and HSQC correlation experiments. [b] The nitro substituent is absent. [c] No correlation signals were
observed for the nitro group in the 1H,15N HMBC spectra.
Eur. J. Org. Chem. 0000, 0–0
www.eurjoc.org
5
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
0.46 ppm). The appearance of a broad signal at 11.95 ppm is proton throughout the series of four compounds (Table 4, Fig-
attributed to the formation of acetic acid, which results from ure S21). The H–N bond lengths in 1–4 are nearly identical with
deprotonation of the H2 proton in the thiosemicarbazide recep- an average calculated length of 1.012(2) Å.
tor upon the addition of up to 0.6 mol equivalents of acetate
Table 4. Mulliken charges on the N–H1, N–H2, and N–H3 hydrogen atoms
and the H–N1, H–N2, and H–N3 nitrogen atoms in chemosensors 1–4 calcu-
(Figure 7). At 1 mol equivalent of acetate, no further changes
are observed, which marks the plateau of the titration. The ef-
lated at the B3LYP/6-311++G(d,p) level of theory with tight convergence cri-
teria.[30]
fect on the N3 atom is significant with shielding from 121 to
114 ppm and the N1 shifts downfield from 106 to 160 ppm
(ΔδN3 = 7 and ΔδN1 = 54 ppm). This substantial deshielding of
the N1 atom is attributed to deprotonation of the central
N2–H bond.[26]
Mulliken charge [au]
N–H1
H–N1
N–H2
H–N2
N–H3
H–N3
1
2
3
4
0.258
0.292
0.291
0.278
–0.304
–0.503
0.065
0.345
0.345
0.327
0.321
0.182
0.300
–0.138
0.169
0.336
0.336
0.308
0.319
0.020
0.000
0.017
0.091
0.341
DFT Studies
The frontier molecular orbitals of anion sensors 1–4 are de-
picted in Figure 8. The highest occupied molecular orbitals
(HOMOs) of 1 are localized on the phenyl and thiourea moie-
ties. By contrast, the HOMOs of 2–4 reside primarily on the
naphthalene chromophore and the thiourea subunits, although
the orbitals of 2 appear diffused into the nitrophenyl moiety.
The lowest occupied molecular orbitals (LUMOs) reside exten-
sively on the nitrophenyl moieties in the cases of 2–4 and on
the naphthalene chromophore of 1. The distinct change in the
location of the HOMOs and LUMOs clearly illustrates the pres-
ence of ICT character. Incorporation of a methylene bridge in
4 as a spacer results in a significant reduction in the HOMO
delocalization. However, the single sp2 carbon atom does not
prevent delocalization of the HOMO orbital between the planar
aromatic ring and the planar thiosemicarbazide unit. Indeed,
the methylene spacer fails to act as an insulator.[27] A similar
observation was reported with squaramide-based fluorescent
sensors containing anthracene.[10c] Charge distribution calcula-
tions indicate that the N–H2 hydrogen atom is the most acidic
Conclusions
We synthesized thiosemicarbazide-based colorimetric chemo-
sensors 1–4 in DMSO, DMSO/H2O (9:1 v/v), and acetonitrile with
anions of varying basicity. The compounds possess acidic prop-
erties suitable for recognition of basic anions by deprotonation
of the thiosemicarbazide functionality. UV/Vis absorption spec-
troscopy revealed that upon the addition of basic anions, a sig-
nificant redshift was observed in the ICT absorption band,
which was accompanied by dramatic color changes visible to
the naked eye for 2–4. 1H,15N NMR spectroscopy allowed for
the correct assignment of the three N–H chemical shifts for
both atoms and confirmed that the mechanism of action was
deprotonation of the central thiourea N–H proton.[18] To our
surprise, no significant fluorescence modulation was observed
for any of the compounds, most notably with 4, despite the
favorable predicted driving force for PET. Insertion of a single
carbon atom (with its two hydrogen atoms) between an elec-
tron donor and a fluorophore has been a dependable strategy
for changing an ICT sensor into a PET sensor.[28] However, we
found that insertion of a CH2 group between the fluorophore
and electron donor, in this case naphthalene and thiosemicar-
bazide, respectively, did not electronically decouple the mod-
ules, as predicted for simple PET model systems.[29]
Experimental Section
General Procedure: A solution of 1-naphthyl isothiocyanate in dry
acetonitrile (10 mL) was added dropwise to a stirred solution of
the hydrazine in dry acetonitrile (10 mL) at room temperature. The
resultant mixture was heated at reflux with magnetic stirring for
5 h. The solution was then cooled in an ice bath, and the resulting
precipitate was collected by suction filtration, washed with dry
chloroform, and dried under vacuum.
2-(Naphthalene-1-yl)-N-phenylhydrazinecarbothioamide
(1):
Phenylhydrazine (254 mg, 2.35 mmol) in dry acetonitrile was heated
at reflux with 1-naphthyl isothiocyanate (434 mg, 2.35 mmol) to
yield, upon cooling, the product as a white powder in 66 % yield.
Rf = 0.58 (hexane/ethyl acetate, 1:1), m.p. 186–188 °C. 1H NMR
(250.1 MHz, [D6]DMSO): δ = 10.03 (s, 1 H, N-H), 9.77 (s, 1 H, N-H),
8.21 (s, 1 H, N-H), 8.01–7.88 (m, 1 H, Ar-H), 7.86–7.71 (m, 2 H, Ar-H),
7.56–7.37 (m, 4 H, Ar-H), 7.29 (t, J = 7.8 Hz, 2 H, Ar-H), 6.95–6.79 (m,
3 H, Ar-H) ppm. 13C NMR (62.9 MHz, [D6]DMSO): δ = (13C DEPT) =
Figure 8. Depiction of the calculated HOMOs and LUMOs for thiosemicarb-
azides 1–4.
Eur. J. Org. Chem. 0000, 0–0
www.eurjoc.org
6
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
183.1 (–), 148.1 (–), 135.5 (–), 133.6 (–), 130.4 (–), 128.9 (↑), 127.9 (↑),
126.5 (↑), 126.1 (↑), 125.8 (↑), 125.7 (↑), 125.3 (↑), 123.1 (↑), 119.6
was extracted with hexane (3 × 20 mL). The organic fractions were
combined, dried with anhydrous sodium sulfate, and concentrated
(↑), 112.9 (↑) ppm. 15N NMR (30 MHz, [D6]DMSO): δ = 96 (1 N, N- under reduced pressure. 1-Naphthylmethyl isothiocyanate was col-
H), 118 (1 N, N-H), 133 (1 N, N-H) ppm. IR (KBr): ν = 3285, 3215, lected in high purity as a viscous orange oil in 70 % yield. Rf =
˜
3169, 1602, 1547, 1516, 1499, 1489, 1475, 1393, 1275, 1256, 1225,
1087, 885, 860, 775, 759, 688 cm–1. UV/Vis (DMSO/H2O, 9:1): no
absorption band observed. HRMS (ESI-TOF): calcd. for C17H15N4O2S
[M + H]+ 294.1082; found 294.1065.
0.60 (hexane/dichloromethane, 5:1). 1H NMR (250.1 MHz, CDCl3): δ =
7.94–7.86 (m, 3 H, Ar-H), 7.65–7.45 (m, 4 H, Ar-H), 5.15 (s, 1 H, CH2)
ppm. 13C NMR (62.9 MHz, CDCl3): δ = (13C DEPT) = 133.4 (–), 130.5
(–), 129.8 (–), 129.4 (↑), 129.0 (↑), 127.0 (↑), 126.3 (↑), 125.9 (↑), 125.4
(↑), 122.5 (↑), 47.1 (↓) ppm.
N-(Naphthalene-1-yl)-2-(4-nitrophenyl)hydrazinecarbothio-
amide (2): 4-Nitrophenylhydrazine (254 mg, 2.35 mmol) in dry
acetonitrile was heated at reflux with 1-naphthyl isothiocyanate
(434 mg, 2.35 mmol) to yield, upon cooling, the product as a pale
brown powder in 83 % yield. Rf = 0.47 (hexane/ethyl acetate, 1:1),
m.p. 216–217 °C. 1H NMR (250.1 MHz, [D6]DMSO): δ = 10.19 (s, 1 H,
N-H), 10.03 (s, 1 H, N-H), 9.38 (s, 1 H, N-H), 8.20 (d, J = 8.7 Hz, 2 H,
Ar-H), 7.94 (dd, J = 6.3, 3.4 Hz, 1 H, Ar-H), 7.85 (d, J = 8.3 Hz, 1 H,
Ar-H), 7.77 (br. s, 1 H, Ar-H), 7.60–7.44 (m, 3 H, Ar-H), 7.38 (d, J =
7.0 Hz, 1 H, Ar-H), 6.92 (d, J = 8.7 Hz, 2 H, Ar-H) ppm. 13C NMR
(62.9 MHz, [D6]DMSO): δ = (13C DEPT) = 183.2 (–), 154.2 (–), 138.8
(–), 135.4 (–), 133.7 (–), 130.4 (–), 127.9 (↑), 126.9 (↑), 126.3 (↑), 125.9
(↑), 125.8 (↑), 125.7 (↑), 125.3 (↑), 123.2 (↑), 111.4 (↑) ppm. 15N NMR
(30 MHz, [D6]DMSO): δ = 106 (1 N, N-H), 121 (1 N, N-H), 129 (1 N,
2-(Naphthalene-1-yl)-N-(4-nitrobenzyl)hydrazinecarbothio-
amide (4): To a stirring solution of 4-nitrophenylhydrazine (208 mg,
1.36 mmol) in dry dichloromethane/acetonitrile (3:1, 7 mL) was
added 1-naphthylmethyl isothiocyanate (260 mg, 1.30 mmol) dis-
solved in dry dichloromethane (10 mL). The solution was heated at
reflux with magnetic stirring for 48 h. The solid, which precipitated
upon heating, was collected by suction filtration and was purified
by trituration with chloroform; this resulted in a bright yellow pow-
der in 53 % yield. Rf = 0.56 (hexane/ethyl acetate, 1:1), m.p. 190–
1
194 °C. H NMR (250.1 MHz, [D6]DMSO): δ = 9.76 (s, 1 H, N-H), 9.12
(s, 1 H, N-H), 8.79 (br. s, 1 H, N-H), 8.20–8.08 (m, 3 H, Ar-H), 7.98–
7.88 (m, 1 H, Ar-H), 7.81 (d, J = 7.9 Hz, 1 H, Ar-H), 7.56–7.34 (m, 4
H, Ar-H), 6.80 (d, J = 9.1 Hz, 2 H, Ar-H), 5.17 (d, J = 5.7 Hz, 2 H, CH2)
ppm. 13C NMR (62.9 MHz, [D6]DMSO): δ = (13C DEPT) = 182.5 (–),
154.2 (–), 138.8 (–), 134.2 (–), 133.1 (–), 130.7 (–), 128.4 (↑), 127.2 (↑),
126.1 (↑), 125.7 (↑), 125.6 (↑), 125.2 (↑), 124.7 (↑), 123.3 (↑), 111.4
(↑), 45.0 (↓) ppm. 15N NMR (30 MHz, [D6]DMSO): δ = 104 (1 N, N-
N-H), (the nitro group is unaccounted for) ppm. IR (KBr): ν = 3318,
˜
3170, 3134, 1597, 1504, 1489, 1346, 1248, 1113, 842, 810, 777,
636 cm–1. UV/Vis (DMSO/H2O, 9:1): λmax (ε, cm–1 mol–1 L) = 370 nm
(18800). HRMS (ESI-TOF): calcd. for 339.0912 [M + H]+; found
339.0916.
H), 112 (1 N, N-H), 127 (1 N, N-H), 372 (1 N, NO2) ppm. IR (KBr): ν =
˜
3339, 3316, 3229, 2982, 2940, 1595, 1551, 1508, 1491, 1385, 1335,
1296, 1238, 1200, 1111, 955, 839, 773, 750, 731, 688, 640 cm–1. UV/
Vis (DMSO/H2O, 9:1): λmax (ε, cm–1 mol–1 L) = 370 nm (14200). HRMS
(ESI-TOF): calcd. for 353.1058 [M + H]+; found 353.1072
2-(Naphthalene-1-yl)-N-(4-nitrophenyl)hydrazinecarbothio-
amide (3): A solution of 1-naphthalenyl hydrazine hydrochloride
(251 mg, 1.29 mmol) in dry acetonitrile (6 mL) was mixed with
ethylamine (136 mg, 1.34 mmol) to yield a red/orange solution,
which was filtered. To the filtrate, a solution of 4-nitrophenyl isothio-
cyanate (234 mg, 1.30 mmol) in dry acetonitrile (10 mL) was added
dropwise. The mixture was heated at reflux with stirring for 1 h.
Supporting Information: UV/Vis absorption spectra of 1 in DMSO/
H2O (9:1 v/v), 2 in DMSO, and 4 in acetonitrile in the absence and
presence of anions; 1H NMR and 1H,15N HSQC spectra of 1–4 in
[D6]DMSO; 1H,15N HMBC of 4; and charge-distribution calculations
for 1–4.
Upon cooling to room temperature, 0.5
M hydrochloric acid (20 mL)
was added to the mixture, which was then extracted with diethyl
ether (3 × 20 mL). The organic fractions were combined and dried
with anhydrous sodium sulfate, and the solution was concentrated
under reduced pressure. The product was collected by suction filtra-
tion, washed with dry chloroform, and dried under vacuum to give
3 as a yellow powder in 30 % yield. Rf = 0.70 (hexane/ethyl acetate,
1:1), m.p. 161–163 °C. 1H NMR (250.1 MHz, [D6]DMSO): δ = 10.34 (s,
1 H, N-H), 10.23 (s, 1 H, N-H), 8.75 (s, 1 H, N-H), 8.36–8.09 (m, 3 H,
Ar-H), 8.0 (d, J = 9.1 Hz, 2 H, Ar-H), 7.92–7.79 (m, 1 H, Ar-H), 7.60–
7.45 (m, 2 H, Ar-H), 7.40 (d, J = 3.9 Hz, 2 H, Ar-H), 6.77 (t, J = 4.3 Hz,
1 H, Ar-H) ppm. 13C NMR (62.9 MHz, [D6]DMSO): δ (13C DEPT) =
180.9 (–), 145.7 (–), 143.1 (–), 142.9 (–), 133.7 (–), 127.8 (↑), 126.2 (↑),
125.9 (↑), 124.5 (↑), 124.1 (↑), 123.5 (↑), 122.4 (–), 122.1 (↑), 119.6
(↑), 106.0 (↑) ppm. 15N NMR (30 MHz, [D6]DMSO): δ = 96 (1 N, N-
H), 127 (1 N, N-H), 137 (1 N, N-H), (the nitro group is unaccounted
Acknowledgments
D. C. M. acknowledges financial support from the University of
Malta, the Strategic Educational Pathways Scholarship (STEPS)
in part financed by the European Social Fund (ESF) under Oper-
ational Programme II, and the European Cooperation in Science
and Technology (COST Action CM1005 “Supramolecular Chem-
istry in Water”). Thanks are extended to Prof. Robert M. Borg
for assistance with preliminary acquisition of the NMR data. J.P.
gratefully acknowledges financial support from the Slovenian
Research Agency (ARRS program number P1-0242) and EN-FIST
Centre of Excellence. DFT calculations were performed at the
Academic Computer Centre CYFRONET AGH within computa-
tional grant number MEiN/SGI3700/UJ/085/2006.
for) ppm. IR (KBr): ν = 3331, 3292, 3165, 1593, 1550, 1521, 1506,
˜
1485, 1393, 1330, 1269, 1217, 1107, 858, 796, 770, 750, 702 cm–1
.
UV/Vis (DMSO/H2O, 9:1): λmax (ε, cm–1 mol–1 L) = 321 nm (19600).
HRMS (ESI-TOF): calcd. for 339.0917 [M + H]+; found 339.0916
Keywords: Anions · Sensors · Chemosensors · Charge
transfer · Electron transfer
1-Naphthylmethyl Isothiocyanate: Synthesized as described in
the literature.[21] 1-Naphthylmethylamine (1.04 g, 6.62 mmol) was
dissolved in dry dichloromethane (3 mL). Finely crushed sodium
hydroxide (785 mg, 19.0 mmol) was slowly added to a stirred solu-
tion of thiophosgene (0.90 mL, 11.8 mmol) in dichloromethane
(4 mL) at 0 °C. The mixture was left to warm to room temperature
over 4 h and then left stirring at 25 °C for another 2 h. Afterwards,
distilled water (20 mL) was added to the yellowish solution, which
[1] a) J. L. Sessler, P. A. Gale, W.-S. Cho, Anion Receptor Chemistry, Royal Soci-
ety of Chemistry, Cambridge, UK, 2006; b) D.-G. Cho, J. L. Sessler, Chem.
Soc. Rev. 2009, 38, 1647; c) E. A. Kataev, C. Müller, Tetrahedron 2014, 70,
137.
[2] a) P. Gale, N. Busschaert, C. J. E. Haynes, L. E. Karagiannidis, I. L. Kirby,
Chem. Soc. Rev. 2014, 43, 205; b) P. Ballester, Chem. Soc. Rev. 2010, 39,
Eur. J. Org. Chem. 0000, 0–0
www.eurjoc.org
7
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
3810; c) Madhuprasad, M. P. Bhat, H.-Y. Jung, D. Losic, M. D. Kurkuri,
Chem. Eur. J. 2016, 22, 6148; d) N. Busschaert, C. Caltagirone, W. Van Ros-
som, P. A. Gale, Chem. Rev. 2015, 115, 8038.
[16] a) M. Boiocchi, L. Del Boca, D. E. Gꢀmez, L. Fabbrizzi, M. Licchelli, E.
Monzani, J. Am. Chem. Soc. 2004, 126, 16507; b) M. Bonizzoni, L. Fab-
brizzi, A. Taglietti, F. Tiengo, Eur. J. Org. Chem. 2006, 3567; c) V. Amend-
ola, D. Esteban-Gꢀmez, L. Fabbrizzi, M. Licchelli, Acc. Chem. Res. 2006,
39, 343; d) D. Esteban-Gꢀmez, L. Fabbrizzi, M. Licchelli, E. Monzani, Org.
Biomol. Chem. 2005, 3, 1495.
[17] J. Shao, H. Lin, H.-K. Lin, Talanta 2008, 75, 1015.
[18] K. N. Farrugia, D. Makuc, A. Podborska, K. Szaciłowski, J. Plavec, D. C.
Magri, Org. Biomol. Chem. 2015, 13, 1662.
[19] A. P. de Silva, T. S. Moody, G. D. Wright, Analyst 2009, 134, 2385.
[20] S. R. Rajski, J. R. Mays, Wisconsin Alumni Research Foundation, Madison,
WI, US patent US20080312164, 2008.
[21] R. M. Duke, J. E. O'Brien, T. McCabe, T. Gunnlaugsson, Org. Biomol. Chem.
2008, 6, 4089.
[3] a) S. Kubik, Chem. Soc. Rev. 2010, 39, 3648; b) S. Kubik, Chem. Soc. Rev.
2009, 38, 585.
[4] M. A. Tetilla, M. C. Aragoni, M. Arca, C. Caltagirone, C. Bazzicalupi, A.
Bencini, A. Garau, F. Isaia, A. Laguna, V. Lippolis, V. Meli, Chem. Commun.
2011, 47, 3805.
[5] M. T. Albelda, J. C. Frías, E. García-España, H.-J. Schneider, Chem. Soc. Rev.
2012, 41, 3859.
[6] a) R. M. Duke, E. B. Veale, F. M. Pfeffer, P. E. Kruger, T. Gunnlaugsson,
Chem. Rev. 2010, 39, 3936; b) T. Gunnlaugsson, M. Glynn, G. M. Tocci,
P. E. Kruger, R. M. Pfeffer, Coord. Chem. Rev. 2006, 250, 3094.
[7] a) V. Amendola, L. Fabbrizzi, L. Mosca, Chem. Soc. Rev. 2010, 39, 3889; b)
M. Boiochhi, L. Del Boca, D. Esteban-Gꢀmez, L. Fabbrizzi, M. Licchelli, E.
Monzani, Chem. Eur. J. 2005, 11, 3097; c) R. M. Duke, T. Gunnlaugsson,
Tetrahedron Lett. 2010, 51, 5402; d) H. D. Paduka Ali, P. E. Kruger, T. Gunn-
laugsson, New J. Chem. 2008, 32, 1153; e) P. A. Gale, J. R. Hiscock, S. J.
Moore, C. Caltagirone, M. B. Hursthouse, M. E. Light, Chem. Asian J. 2010,
5, 555.
[8] a) T. Gunnlaugsson, A. P. Davis, G. M. Hussey, J. Tierney, M. Glynn, Org.
Biomol. Chem. 2004, 2, 1856; b) A. Misra, M. Shahis, P. Dwivedi, Talanta
2009, 80, 532; c) M. G. Murali, K. A. Vishnumurthy, S. Seethamraju, P. C.
Ramamurthy, RSC Adv. 2014, 4, 20592; d) S. N. Berry, V. Soto-Cerrato,
E. N. W. Howe, H. J. Clarke, I. Mistry, A. Tavassoli, Y.-T. Chang, R. Pérez-
Tomás, Philip A. Gale, Chem. Sci. 2016, 7, 5069.
[22] A. Weller, Pure Appl. Chem. 1968, 16, 115.
[23] a) D. Makuc, J. R. Hiscock, M. E. Light, P. A. Gale, J. Plavez, Beilstein J. Org.
Chem. 2011, 7, 1205; b) D. Makuc, M. Albrecht, J. Plavec, J. Supramol.
Chem. 2010, 22, 603; c) D. Makuc, Triyanti, M. Albrecht, J. Plavec, K. Rissa-
nen, A. Valkonen, C. A. Schalley, Eur. J. Org. Chem. 2009, 4854; d) D.
Makuc, M. Lenarčič, G. W. Bates, P. A. Gale, J. Plavec, Org. Biomol. Chem.
2009, 7, 3505.
[24] G. J. Martin, M. L. Martin, J.-P. Gouesnard, 15N-NMR Spectroscopy, Springer,
Berlin, 1981.
[25] J. Mason, L. F. Larkworthy, E. A. Moore, Chem. Rev. 2002, 102, 913.
[26] M. Witanowski, L. Stefaniak, G. A. Webb, Annu. Rep. NMR Spectrosc. 1981,
11B, 1.
[27] R. A. Bissell, E. Calle, A. P. de Silva, S. A. de Silva, H. Q. N. Gunaratne, J.-L.
Habib-Jiwan, S. L. A. Peiris, R. A. D. D. Rupasinghe, T. K. S. D. Samaras-
inghe, K. R. A. S. Sandanayake, J.-P. Soumillion, J. Chem. Soc. Perkin Trans.
2 1993, 1559.
[28] D. C. Magri, J. F. Callan, A. P. de Silva, D. B. Fox, N. D. McClenaghan,
K. R. A. S. Sandanayake, J. Fluoresc. 2005, 15, 769.
[9] a) F.-Y. Wu, Z. Li, L. Guo, X. Wang, M.-H. Lin, Y.-F. Zhao, Y.-B. Jiang, Org.
Biomol. Chem. 2006, 4, 624; b) L. Nie, Z. Li, J. Han, X. Zhang, R. Yang, W.-
X. Liu, F.-Y. Wu, J.-W. Xie, Y.-F. Zhao, Y.-B. Jiang, J. Org. Chem. 2004, 69,
6449; c) W.-X. Liu, R. Yang, A.-F. Li, A. Li, Y.-F. Gao, X.-X. Luo, Y.-B. Ruan,
Y.-B. Jiang, Org. Biomol. Chem. 2009, 7, 4021.
[10] a) N. Busschaert, R. B. P. Elmes, D. D. Czech, X. Wu, I. L. Kirby, E. M. Peck,
K. D. Hendzel, S. K. Shaw, B. Chan, B. D. Smith, K. A. Jolliffe, P. A. Gale,
Chem. Sci. 2015, 5, 3617; b) R. B. P. Elmes, N. Busschaert, D. D. Czech,
P. A. Gale, K. A. Jolliffe, Chem. Commun. 2015, 51, 10107; c) R. B. P. Elmes,
P. Turner, K. A. Jolliffe, Org. Lett. 2013, 15, 5638.
[11] a) L. E. Santos-Figueroa, M. E. Moragues, M. M. M. Raposo, R. M. F. Batista,
S. P. G. Costa, R. C. M. Ferreira, F. Sancenón, R. Martínez-Máñez, J. V.
Ros-Lis, J. Soto, Org. Biomol. Chem. 2012, 10, 7418; b) V. Amendola, G.
Bergamaschi, M. Boiocchi, L. Fabbrizzi, M. Milani, Chem. Eur. J. 2010, 16,
4368.
[12] a) L. S. Evans, P. A. Gale, M. E. Light, R. Quesada, New J. Chem. 2006, 30,
1019; b) L. S. Evans, P. A. Gale, M. E. Light, R. Quesada, Chem. Commun.
2006, 965.
[29] A. P. de Silva, H. Q. N. Gunaratne, P. L. M. Lynch, A. J. Patty, G. L. Spence,
J. Chem. Soc., Perkin Trans. 2 1993, 1611.
[30] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R.
Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H. Na-
katsuji, M. Caricato, X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G.
Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hase-
gawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J. A.
Montgomery Jr., J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Broth-
ers, K. N. Kudin, V. N. Staroverov, R. Kobayashi, J. Normand, K. Raghava-
chari, A. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega,
J. M. Millam, M. Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J.
Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi,
C. Pomelli, J. W. Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski,
G. A. Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels, Ö.
Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski, D. J. Fox, Gaussian 09,
revision A.02, Gaussian, Inc., Wallingford, CT, 2009.
[13] a) K. Pandurangan, J. A. Kitchen, T. Gunnlaugsson, Tetrahedron Lett. 2013,
54, 2770; b) K. Pandurangan, J. A. Kitchen, T. McCabe, T. Gunnlaugsson,
CrystEngComm 2013, 15, 1421; c) T. Gunnlaugsson, P. E. Kruger, P. Jensen,
J. Tierney, H. D. Paduka Ali, G. M. Hussey, J. Org. Chem. 2005, 70, 10875.
[14] D. Sharma, A. Moirangthem, R. Kumar, S. K. A. Kumar, A. Kuwar, J. F.
Callan, A. Basu, S. K. Sahoo, RSC Adv. 2015, 5, 50741.
Received: April 24, 2016
[15] Z. Li, F. Y. Wu, L. Guo, A. F. Li, Y. B. Jiang, J. Phys. Chem. B 2008, 112, 7071.
Published Online: ■
Eur. J. Org. Chem. 0000, 0–0
www.eurjoc.org
8
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
Anion Chemosensors
K. N. Farrugia, D. Makuc,
A. Podborska, K. Szaciłowski,
J. Plavec, D. C. Magri* ...................... 1–9
Colorimetric
Naphthalene-Based
Four thiosemicarbazide chemosensors On the basis of DFT calculations, these
are studied in DMSO, DMSO/H2O chemosensors are found to interact
(9:1 v/v), and acetonitrile by UV/Vis ab- with basic anions through a deproto-
sorption, fluorescence, and 1H NMR/ nation mechanism.
Thiosemicarbazide Anion Chemo-
sensors with an Internal Charge
Transfer Mechanism
13C NMR/15N NMR spectroscopy.
DOI: 10.1002/ejoc.201600509
Eur. J. Org. Chem. 0000, 0–0
www.eurjoc.org
9
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim