Multi-channel receptors based on thiopyrylium functionalised with macrocyclic receptors for the recognition of transition metal cations and anions

Article abstract of DOI:10.1039/b921486k

We report herein the synthesis and characterization of a family of ligands containing different cation binding sites covalently connected to a thiopyrylium signalling reporter. The receptors L¹-L⁶ are able to signal the presence of c

Full text of DOI:10.1039/b921486k

View Article Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/dalton | Dalton Transactions
Multi-channel receptors based on thiopyrylium functionalised with
macrocyclic receptors for the recognition of transition metal cations
and anions
a,b,c
D. Jime´nez,b M. Moragues,a,b,c S. Royo,a,b,c R. Mart´ınez-Ma´n˜ez,*a,b,c F. Sanceno´n,a,b,c
´
T. Abalos,
J. Soto,a,b A. M. Costero,*a,d M. Parraa,d and S. Gila,d
Received 14th October 2009, Accepted 4th January 2010
First published as an Advance Article on the web 5th February 2010
DOI: 10.1039/b921486k
We report herein the synthesis and characterization of a family of ligands containing different cation
binding sites covalently connected to a thiopyrylium signalling reporter. The receptors L1–L6 are able to
signal the presence of certain metal cations via three different channels; i.e. electrochemically,
fluorogenically and chromogenically. An acetonitrile solution of L1–L6 shows a bright blue colour due
to a charge-transfer band in the 575–585 nm region. The colour variation in acetonitrile of L1–L6 in the
presence of the metal cations Ag+, Cd2+, Cu2+, Fe3+, Hg2+, Ni2+, Pb2+ and Zn2+ has been studied. A
selective hypsochromic shift of the blue band was found for the systems L4-Pb2+ and L5-Hg2+.
Additionally, L1–L6 are poorly fluorescent but coordination with certain metal cations induces an
enhancement of the fluorescence at ca 500 nm. For instance, the presence of Cu2+ and Fe3+ induced a
remarkable 42-fold and 45-fold enhancement in the emission intensity of L1 centred at 500 nm,
respectively. Also remarkable was the 18-fold enhancement observed for L4 and L5 in the presence of
Fe3+ and Cu2+, respectively. The electrochemical behaviour of receptors L1–L6 was studied in
acetonitrile using platinum as a working electrode and [Bu4N][BF4] as a supporting electrolyte. This
family of receptors showed a one-electron reversible redox process at ca. -0.46 V versus sce attributed to
the reduction of the thiopyrylium group. A moderate anodic shift in the presence of certain metal
cations was observed. The effect in the UV-visible spectra of acetonitrile solutions of receptor L1–L6 in
the presence of anions was also studied. A remarkable bleaching was found in the presence of cyanide.
to several basic protocols for the development of chemosensors.
Introduction
The most commonly used is the so-called ‘binding site-signalling
subunit,2,3 in which both subunits are connected through covalent
bonds. A closely related approach relies on the formation of an
ensemble between the binding site and the signalling subunit that
is characterized by the absence of any covalent link between the
two units.6 In this case, the coordination platform incorporates an
external indicator, and the overall signalling functions as a colori-
metric displacement assay. Finally, the so-called ‘chemodosimeter’
approach made use of specific chemical reactions induced by the
target species coupled with changes in certain physical properties.7
The coupling of these three main approaches with the three
types of signalling subunits (fluorescence groups, organic dyes,
and redox-active groups) has lead in recent years to a myriad
of selective receptors for a number of chemical species including
anions, cations and neutral guests. Additionally, the versatility
of these protocols has resulted in the development of differential
receptors that respond rather unspecifically, yet differently, to a
group of similar guests.8
One appealing research area within the field of supramolecular
chemistry is the development of chemical sensors1 that are
generally composed of two subunits; namely the binding site
and the signalling subunit.2 The binding site carries out selective
coordination with a certain target guest and is usually designed
bearing in mind coordination and supramolecular chemistry
principles in order to achieve a high degree of complementarity.
The coordination event modulates the spectroscopic properties of
the signalling unit, therefore transducing host–guest recognition
into an easily measurable signal. Three main systems have been
extensively employed as reporter units: fluorescent groups,3 dyes,4
and redox-active moieties5 that transform the recognition event
through changes in fluorescence emission, colour, and redox-
potential shifts, respectively.
These two basic components, i.e. signalling and coordination
subunits, could be spatially preorganised in different styles leading
aInstituto de Reconocimiento Molecular y Desarrollo Tecnolo´gico, Centro
Mixto Universidad Polite´cnica de Valencia-Universidad de Valencia, Valen-
cia, Spain
However, anddespite the developmentofindividual fluorogenic,
chromogenic, and electrochemical molecular sensors, there are few
examples of receptors capable of displaying two or more output
signals upon guest binding. Moreover, in the past decade some
groups have become increasingly interested in including more
than one chemically addressable group in chemosensors.9,10 These
have been used as dual-responsive dyes, and also in the design
bDepartamento de Qu´ımica, Universidad Polite´cnica de Valencia, Camino de
Vera s/n, 46022, Valencia, Spain. E-mail: rmaez@qim.upv.es
cCIBER de Bioingenier´ıa, Biomateriales y Nanomedicina (CIBER-BBN)
dDepartamento de Qu´ımica Orga´nica, Facultad de Ciencias Qu´ımicas,
Universidad de Valencia, 46100, Burjassot, Valencia, Spain. E-mail:
ana.costero@uv.es
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 3449–3459 | 3449
©

View Article Online
of molecular logic gates, ion-pair signalling, and cooperative
recognition.
In relation to chemosensing, an easy mode for preparing multi-
channel receptors is the functionalisation of certain binding
sites with two different signalling subunits. Recent examples
of this class of poly-functionalised ligands include the works
of Delavaux-Nicot,11 Beer,12 Shimidzu and Lehn,13 Mart´ınez-
Ma´n˜ez,14 Molina,15-17 and Ghosh.18
The second class of multi-channel chemosensors are those that
are functionalised with only one subunit capable of displaying
two or more observable events upon addition of certain guests.
Although examples showing both fluorescence and colour changes
are not uncommon in intrinsic chemosensors,19,20,21 paradigms dis-
playing fluorescence or colour modulations and electrochemical
responses are rare,22 while chemosensors exhibiting three or more
signalling channels are unusual.23
Because of our experience in the design of molecular probes24
for various analytes and our background in functionalised
chromophores we became interested in developing new multi-
channel chemosensors able to detect the presence of metal cations
via chromogenic, fluorogenic, and electrochemical signals. In
this context we report herein the synthesis, characterisation,
binding behaviour, and signalling properties of a new family
of chemosensors containing different crown ether cation bind-
ing sites anchored to a 4-aminophenyl-2,6-diphenylthiopyrylium
scaffolding. The 4-aminophenyl-2,6-diphenylthiopyrylium group
is simultaneously a redox-active group, showing reduction pro-
cesses at moderately modest potentials, and a chromo-fluorogenic
signalling reporter. Additionally, the thiopyrylium moiety has
been barely used as a signalling subunit in the development
of chemical sensors–except for a recent example that used the
pyrylium-to-thiopyrylium transformation for the development of
a probe for sulfide anion detection in aqueous solution.25 We have
recently published a preliminary communication of part of this
work.26
Scheme 1 Synthetic procedure and chemical structures of receptors
L1–L6.
The 1H-NMR spectra of receptors L2–L4 showed the methylene
protons of the macrocycle located near nitrogen and oxygen atoms
in the 3.4–3.8 range whereas for receptors L5 and L6 the macrocycle
protons appear split into two clearly defined zones: (i) methylene
protons adjacent to the sulfur atoms at d 2.6 to 2.9 ppm; and (ii)
methylene protons located near nitrogen or oxygen atoms found in
the 3.5–3.8 ppm range. The aromatic part of the spectrum was very
similar for all the receptors synthesised showing a typical singlet
centred at ca. 8.45 ppm from the aromatic 2,4,6-trisubstituted
thiopyrylium ring. Also the presence of two doublets centred at ca.
6.90 and 8.15 was indicative of the presence of one p-disubstituted
benzene derivative. The appended monosubstituted benzene rings
show two broad multiplets centred at ca. 7.60 and 7.85 ppm. The
13C-NMR showed the same well defined zones (see experimental
section).
This family of receptors contains an extended p-conjugated
system involving one donor anilino nitrogen atom and the acceptor
thiopyrylium ring. The lowest-energy absorption bands for com-
pounds L1–L6 are broad, structureless, and centred at ca. 580 nm
in acetonitrile. This charge transfer band is responsible for the
deep blue colour of the solutions.30 L2–L6 are functionalised with
macrocyclic subunits of different sizes and containing different
types of heteroatoms that could coordinate with transition metal
Results and discussion
Synthesis and characterization
Receptors L2–L6 contain macrocyclic binding sites (of dif-
ferent sizes and also containing different heteroatoms such
as nitrogen, oxygen and sulfur) and a 4-aminophenyl-2,6-
diphenylthiopyrylium salt as a signalling reporter (see Scheme 1).
Receptor L1, containing an N,N-dimethylamino moiety, was
selected as the model compound. L1 was prepared following
literature procedures.27 For the preparation of the ligands, firstly
2,6-dipheylpyrylium perchlorate (1) was synthesized28 and the
Richman-Atkins procedure was used to synthesise the phenyl-
functionalised macrocyclic subunits 3-7. The experimental details
of the synthesis of these crowns and their spectroscopic char-
acterization were published elsewhere.22,29 Electrophilic aromatic
substitution reaction between N,N-dimethylaniline (2) or the cor-
responding N-phenyl macrocycle (3-7) and 2,6-diphenylpyrylium
perchlorate in dry DMF resulted in formation of the correspond-
ing pyrylium derivatives 8-13. Finally, multi-channel receptors
L1–L6 were prepared by reaction of the pyrylium salts with an
aqueous solution of sodium sulfide and subsequent treatment with
perchloric acid (see Scheme 1).
3450 | Dalton Trans., 2010, 39, 3449–3459
This journal is
The Royal Society of Chemistry 2010
©

View Article Online
Table 1 Abpsortion lmax (nm) for receptors L1–L6 (C
=
1.0 ¥
10-5 mol dm-3) and their variation upon addition of metal cations in
acetonitrile solutions
lmax
Cu2+
Fe3+
Hg2+
Pb2+
a
a
a
a
a
a
a
a
L1
L2
L3
L4
L5
L6
585
584
575
580
575
582
560↓
574↓
575
555↓
554↓
575↓
580↓
555↓
500↓
585
585
584
575
a
a
584↓
575
a
b
580
580
560↓ /400↑
a
a
b
575↓
535↓ /405↑
575
a
560↓
550↓
582
a The downward pointing arrows indicate a significant hypochromic
change in the visible band with respect to that of the free ligand. b The
upward pointing arrows indicate the appearance of a new visible band.
Table 2 Logarithm of constant stability for the formation [M(Ln)]m+ and
[M(Ln)2]m+ in acetonitrile solutions
Mn+ (L:Mn+
)
Fe3+
Cu2+
Hg2+
Pb2+
Fig. 1 UV-visible spectra of L1 in acetonitrile (1.0 ¥ 10-5 mol dm-3) and
L1 in the presence of 10 equivalents of Fe3+ and Cu2+ cations.
L1
L2
(1 : 1)
(1 : 1)
(2 : 1)
(1 : 1)
(1 : 1)
(1 : 1)
(1 : 1)
3.69 0.07 3.57 0.03
4.65 0.02 3.1 0.1
9.94 0.02 8.34 0.05
4.23 0.01
6.01 0.08
—
—
—
—
—
—
—
—
—
to acetonitrile solutions of L2 induced negligible changes in the
visible spectra. For Fe3+, a strong hypochromic effect (10-fold
intensity reduction) together with a moderate hypsochromic shift
of 30 nm was found, whereas for Cu2+ a 1.5-fold decrease in
intensity and a hypsochromic shift of 10 nm was measured. For
L2, the absence of isosbestic points in the UV-visible titrations
with Fe3+ and Cu2+ indicate the formation of 1 : 1 and 1 : 2 metal-
to-ligand complexes. The formation of these species is most likely
due to the large size of Fe3+ (64.5 pm) and Cu2+ (73.0 pm) that
induced a poor fit on the macrocyclic cavity of L2; and resulted
in the formation of 1 : 2 complexes in which the metal cation is
most likely surrounded by two macrocycles in a sandwich-like
structure.32
Receptor L3 is similar to L2 but contains one more oxygen atom
and one more ethylene bridge. Acetonitrile solutions of receptor
L3 show an absorption band at 575 nm. Of all the metal cations
tested, only the addition of Fe3+ clearly induced changes, showing
an intensity decrease of 1.7-fold without any remarkable shift in
the wavelength.
Acetonitrile solutions of L4 showed an absorption band at
580 nm. L4 remains silent in the presence of the tested metal
cations except for Fe3+ and especially Pb2+ (see Fig. 2). The
response upon addition of Fe3+ induced a simple reduction in
the extinction coefficient (3-fold). However, the most remarkable
effect observed for receptor L4 was the selective response in the
presence of the cation Pb2+. Receptor L4 shows a large macrocyclic
cavity ready to coordinate larger cations such as Pb2+ (119.0 pm
of ionic radius). In fact, addition of equimolar quantities of Pb2+
induced the appearance of a new band centred at 400 nm; together
with a 3-fold reduction of the intensity of the band at 580 nm. The
existence of isosbestic points in the titration profiles indicates the
formation of [Pb(L4)]2+ complex.
L3
L4
L5
L6
—
—
—
—
4.01 0.09
—
—
6.98 0.09
4.8 0.1
4.59 0.07 4.72 0.04
cations. Additionally, the presence of a positive charge in this
thiopyrylium ring also determines its electronic properties and
reactivity (vide infra).31
Spectroscopic studies involving metal cations
The chromogenic behaviour of receptors L1–L6 in the presence
of the metal cations Ag+, Cd2+, Cu2+, Fe3+, Hg2+, Ni2+, Pb2+
and Zn2+ was studied in acetonitrile (see Table 1). Additionally,
the logarithm of the stability constants for the formation of
the corresponding complexes is summarised in Table 2. Firstly
coordination studies with receptor L1, which lacks a macrocyclic
subunit, in the presence of these metal cations were carried out.
Acetonitrile solutions of receptor L1 show a visible band centred at
585 nm. Addition of up to 10 equivalents of Ag+, Cd2+, Hg2+, Ni2+,
Pb2+ and Zn2+ induced negligible changes in its visible spectra,
suggesting very weak or no interaction with these metal cations.
In contrast, upon the addition of Cu2+ and Fe3+ a colour change
in the solution of L1 from blue to magenta was observed (see
Fig. 1). In more detail, the presence of 10 equivalents of Cu2+
induced a moderate hypsochromic shift of 30 nm in the visible
band together with a small hypochromic effect. The presence of
defined isosbestic points at 540 nm and at 390 nm suggested the
formation of a single 1 : 1 receptor–cation complex. The addition
of 10 equivalents of Fe3+ to solutions of L1 resulted in a similar
behaviour to that found for Cu2+; i.e. a hypsochromic shift of
45 nm and a hypochromic effect. Again the presence of isosbestic
points indicated the formation of the [Fe(L1)]3+ complex. These
hypsochromic shifts observed upon addition of Cu2+ and Fe3+ are
consistent with a binding of the cations with the aniline group, so
weakening its donor character.
Interestingly, L5 also behaves very differently when compared
with the other receptors. This different behaviour is governed by
the presence in the macrocycle of two S atoms, near the aniline N
atom, that strongly inhibit this site against complexation with
non-thiophilic cations.33d,33i Therefore, L5 shows a remarkable
selectivity for Hg2+ as can be seen in Fig. 3. In fact, it is well-
known that Hg2+ coordination can be achieved by introducing
From the studied N-crowned receptors, L2 contains the smaller
macrocycle. L2 shows a visible band centred at 584 nm. Addition of
Ag+, Cd2+, Hg2+, Ni2+, Pb2+ and Zn2+ metal cations (10 equivalents)
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 3449–3459 | 3451
©

View Article Online
Fig. 3 (Top) UV-visible spectra of L5 in acetonitrile (1.0 ¥ 10-5 mol dm-3)
and L5 in the presence of 10 equivalents of Hg2+ cation. (Bottom) changes
in the visible band centred at 405 nm for receptor L5 upon addition of
increasing quantities of Hg2+ cation.
Fig. 2 (Top) UV-visible spectra of L4 in acetonitrile (2.0 ¥ 10-5 mol dm-3)
and L4 in the presence of 10 equivalents of Fe3+ and Pb2+ cations. (Bottom)
changes in the visible band centred at 400 nm for receptor L4 upon addition
of increasing quantities of Pb2+ cation.
ring instead of thiopyrylium. Although the coordination chemistry
of the MeNPys derivatives is quite complex due to the presence
of two coordination sites (i.e. the aniline and pyridine units) it
is important to remark that MeNPy generally showed stability
constants one order of magnitude greater than those found with
the receptors L1–L6.8e,8f The lower stability constants observed for
the thiopyrylium derivatives are most likely due to the positive
charge located in the structure of the chromophoric system
that leads to some degree of repulsion between the charged
thiopyrylium ring and the metal cation.
sulfur atoms in the macrocyclic ring.33 The addition of equimolar
quantities of Hg2+ in acetonitrile solutions of L5 induced a 5-fold
reduction in the extinction coefficient of the charge-transfer band
centred at 575 nm together with a hypsochromic shift of 40 nm.
At the same time, a new band centred at 405 nm grew in intensity.
These changes in the visible zone of the spectrum were reflected
in colour modulations; i.e. from bright blue for L5 to faint yellow
upon the addition of Hg2+.
The observed behaviour is consistent with a strong Hg2+
coordination with the macrocyclic subunit, and the engagement of
the lone electron pair of the aniline N atom leading to a reduction
of the push-pull character. The issue of selectivity was additionally
confirmed by noting that the addition of other metal cations to
acetonitrile solutions of L5 resulted in negligible changes in the
position and in the intensity of the visible band.
On changing from L5 to L6, in which the two sulfur atoms were
located far from the nitrogen atom (separated by two oxygen atoms
and two ethylene bridges), the selectivity towards Hg2+ cation was
severely diminished. In fact, L6 shows a hypsochromic shift and a
significant decrease of the intensity band at 582 nm in the presence
of the metal cations Hg2+, Cu2+ and Fe3+.
In recent research we have prepared a family of N-crowned 4-(p-
aminophenyl)-2,6-diphenylpyridines (MeNPys).8e,8f These com-
pounds are similar to the L1–L6 family but containing a pyridine
Fluorescence studies involving metal cations
From the emission viewpoint the compounds 2,4,6-
triphenylpyrylium (TPP) and 2,4,6-triphenylthiopyrylium
(TPTP) are both emissive (quantum yields of 0.60 and 0.12,
respectively in acetonitrile)34 the former being extensively used as
a photosensitizer in a wide range of photochemical reactions.35
However, in contrast, acetonitrile solutions of receptors L1–L6 are
poorly fluorescent. This absence of any remarkable emission band
may be ascribed to the presence of non-radiative deactivation
pathways due to the existence of a nitrogen atom in the structure
of the receptors directly attached to the TPTP chromophore.
In order to study the effect that coordination on the nitrogen
has on the emission behaviour of the thiopyrylium derivatives,
3452 | Dalton Trans., 2010, 39, 3449–3459
This journal is
The Royal Society of Chemistry 2010
©

View Article Online
the model compound L1 was selected and its emission behaviour
in acetonitrile studied in the presence of increasing quantities of
protons (using acetonitrile solutions of perchloric acid). Whereas
L1 is not emissive, addition of protons resulted in the appearance
of a broad intense emission band centred at 500 nm (lex = 410
nm). This emission band reaches its highest intensity (305-fold
enhancement) upon addition of 50 equivalents of protons, as
can be seen in Fig. 4. This proton-induced switch-on response is
most likely due to the inhibition of the non-radiative deactivation
mechanism via nitrogen coordination that restores the emissive
properties of the 2,4,6-triphenylthiopyrylium group.36
Fig. 5 Fluorescence enhancements observed upon addition of 10 equiv-
alents of the corresponding metal cations to acetonitrile solutions of
receptor L1 (1.0 ¥ 10-5 mol dm-3, lexc = 410 nm).
behaviour for a certain cation is a sum of the contribution of the
emission enhancement, due to the suppression of the non-radiative
deactivation pathways upon metal coordination (and regeneration
of the TPTP emission) and deactivation paths from the excited
state due to the presence of a certain metal cation (for instance
open-shell paramagnetic, or easily reducible metal cations).37
On changing to L4, the highest enhancement in the emission
intensity, upon excitation at 410 nm was observed upon addition
of 10 equivalents of Fe3+ (17.6-fold). In general, the emission
enhancements in this case are lesser than those observed with
L1 and the same cation. The addition of 10 equivalents of
Hg2+ and Cu2+ induced a 4-fold enhancement in the emission
intensity. Perhaps the most remarkable fact of the fluorescent
behaviour of receptor L4 was the absence of any significant
response in the presence of Pb2+ (only a 1.1-fold enhancement)
that greatly contrasts with the response obtained in UV-visible
titration experiences (vide ante).38 Whereas coordination of Pb2+
with the macrocycle in L4 would induce the suppression of the
non-radiative deactivation pathways thus leading to an increase
in the emission intensity, the presence of a non-emissive decay
pathway arising from a heavy atom effect would, in the opposite
direction, deactivate the emission with the net effect of a very low
fluorescence enhancement.
Upon excitation at 410 nm acetonitrile solutions of receptor L5
showed a poor emission in the 430–600 nm range. However, the
addition of increasing quantities of Hg2+ induced the development
of an emission band centred at ca. 500 nm which reached a
6.2-fold enhancement upon addition of 10 equivalents of the
cation.39 The addition of the trivalent Fe3+ cation induced a
3.2-fold enhancement. However, the most remarkable emission
change was obtained with Cu2+ that induced a 17.6-fold increase
in the emission intensity (see Fig. 6). The fluorescent behaviour
of L5 in the presence of metal cations clearly contrasts with that
observed in the UV-visible experiences (the most important shifts
were obtained with Hg2+ cation). This fact may be related to a
heavy atom effect that is more effective for Hg2+. In the case of
Cu2+ the strength of coordination with the macrocycle of L5, when
compared with Hg2+, is less effective and leads to moderate changes
in the visible band (only a slight hypochromic effect) whereas
Fig. 4 Emission enhancement observed upon addition of 50 equivalents
of protons to acetonitrile solutions of L1 (1.0 ¥ 10-5 mol dm-3, lexc
=
410 nm).
Intrigued by the high enhancement of the emission intensity
observed in the presence of protons we carried out fluorescence
studies with receptors L1, L4 and L5 in the presence of target
metal cations and using 410 nm as the excitation wavelength in
all cases. The results are summarized in Table 3. The addition of
10 equivalents of Fe3+ to acetonitrile solutions of L1 induced a
remarkable 45-fold enhancement in the emission intensity centred
at 500 nm. Nearly the same level of emission enhancement was
observed in the presence of Cu2+ cation (41-fold, see Fig. 5). This
large emission enhancement is remarkable bearing in mind that
the usual behaviour with fluorogenic receptors in the presence
of metal cations is an emission quenching upon complexation.
Smaller enhancements in the emission intensity of 6- and 1.8-
fold were measured for Hg2+ and Pb2+ cations respectively. It
is also noteworthy that the enhancement observed with metal
cations for L1 is lower than that found in the presence of protons.
This might be explained bearing in mind that the final observed
Table 3 Fluorescence emission intensity variation (as % of the receptor
alone) obtained for L1, L4 and L5 (C = 1.0 ¥ 10-5 mol dm-3) upon addition
of 10 equivalents of metal cations in acetonitrile
Cu2+
Fe3+
Hg2+
Pb2+
L1a
L4a
L5a
4000↑
300↑
4400↑
1660↑
220↑
500↑
300↑
520↑
80↑
11↑
5<
1660↑
a Excitation wavelength 410 nm. b The upward pointing arrows indicate an
increase in emission intensity.
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 3449–3459 | 3453
©

View Article Online
Table 4 Electrochemical data for L1, L4 and L5 complexes in acetonitrile
solution (0.1 M [Bu4N][BF4]) at 298 Ka
Reduction E1/2/mVb
L1
L4
L5
-0.47
-0.45
-0.48
a Working electrode, platinum. b E1/2 = (Epa + Epc)/2; Epa and Epc are peak
anodic and peak cathodic potentials, respectively.
Table 5 Values of DE (mV) afor receptors L1, L4 and L5 (C = 1.0 ¥
10-3 mol dm-3) in the presence of metal cations
DE(L1)a
DE(L4)a
DE(L5)a
Cu2+
Fe3+
Hg2+
Pb2+
11
18
24
—
—
25
—
24
12
28
31
—
Fig. 6 Fluorescence enhancements observed upon addition of 10 equiv-
alents of the corresponding metal cations to acetonitrile solutions of
receptor L5 (1.0 ¥ 10-5 mol dm-3, lexc = 410 nm).
a DE(Ln) = E(Ln + Mn+) - E(Ln) (DE in mV)
the emission of the 2,4,6-triphenylthiopyrylium moiety is restored
more efficiently.
response, whereas the remaining cations gave no redox potential
shifts (DE < 5 mV).
The selectivity trend observed in the fluorescence measurement
for L5 was clearly different from that observed in the UV-titration
experiences. Thus, L5 provides an example of sensing modulation
by appropriate selection of the measurement technique; i.e.
acetonitrile solutions of receptor L5 change colour selectively from
blue to yellow in the presence of Hg2+ cation, whereas L5 shows
in the presence of Cu2+ the greatest emission enhancement of the
band centred at 500 nm.
The sensing features showed by these receptors, namely a
remarkable enhancement of the emission intensity instead of
quenching, led us to carry out prospective studies of the response in
aqueous environments. From these studies it was observed that the
addition of increasing amounts of water (up to 20%) to acetonitrile
solutions of the [Hg(L5)]3+ complex induced a reduction of only 2-
fold in the emission. In contrast, addition of water to other metal
complexes induced a severe decrease of the fluorescence intensity.
The still high level of enhancement observed on adding Hg2+ to
acetonitrile–water solutions of L5 opens the door for the use of
this receptor as a selective fluorescent sensor for this highly toxic
cation in aqueous environments.
Electrochemical studies in the presence of certain metal cations
show, in general, a moderate shift of the redox potential of the
thiopyrylium derivatives with maximum anodic shifts of the redox
wave of 31 mV for the L5-Hg2+ system. This anodic shift is
expected bearing in mind that the coordination of the ligand
with the metal cations would result in highly positively charged
species that should be prone to easier reduction. However, it
is apparent that the transformation of the positively charged
thiopyrylium scaffolding into the corresponding metal cations
complexes does not result in a large decrease in the redox potential.
This observation contrasts with other systems that we have recently
reported where large redox shifts were observed in the presence of
metal cations using similar coordination sites.40
Triple signalling
We have studied above the changes in colour, fluorescence emis-
sion, and redox potential for a family of thiopyrylium derivatives
in the presence of certain metal cations in acetonitrile. An outcome
of this study is that, for a given signalling channel, selectivity can
be achieved via the use of different macrocyclic subunits. Thus
for instance, the development of a new band at ca. 400 nm is
observed selectively for Pb2+ and Hg2+ when using the receptors
L4 and L5, respectively. However, it is also noteworthy that for a
certain ligand the response is somewhat different, depending on
the transduction channel studied (electrochemical, chromogenic
or fluorogenic). For instance, L4 shows a selective chromogenic
response to Pb2+, whereas it is the Fe3+ cation which gives a
greater fluorescence enhancement and both cations induced a
reduction wave shift greater than 20 mV. When using receptor
L5, the electrochemical response is of ca. 30 mV for Hg2+ and Fe3+,
whereas a very remarkable Cu2+ response is found in fluorescence
and a selective response is observed in the chromogenic channel
for Hg2+ (see Table 6).
Electrochemical studies involving metal cations
The electrochemical behaviour of thiopyrylium receptors L1, L4
and L5 was studied in acetonitrile with platinum as the working
electrode and [Bu4N][BF4] as a supporting electrolyte. These
receptors show a one-electron reversible reduction process in the
-0.45, -0.49 V range vs. sce attributed to the reduction of the
thiopyrylium ring (see Table 4).
Additionally, a detailed electrochemical study in the presence
of metal cations was carried out with ligands L1, L4 and L5 for
which a remarkable chromo-fluorogenic behaviour was observed.
In Table 5 the electrochemical responses regarding the difference
between the reduction potential of the free ligand and the
reduction potential in the presence of the corresponding metal
cations is summarised. Only the presence of the metal cations
Cu2+, Fe3+, Hg2+ and Pb2+ resulted in a significant electrochemical
In order to explain this effect, it has to be taken into account that
the specific response observed in each channel strongly depends
on the particularities of each coordination-transduction process.
3454 | Dalton Trans., 2010, 39, 3449–3459
This journal is
The Royal Society of Chemistry 2010
©

View Article Online
Table 6 Different channel response of ligands L1, L4 and L5 to metal
cationsa
l at 400 nm
Emission enhancement > 1000%
DE > 20 mV
L1
L4
L5
—
Cu2+, Fe3+
Fe3+
Hg2+
Pb2+
Hg2+
Fe3+, Pb2+
Fe3+, Hg2+
Cu2+
a The ligand concentrations used for the UV-Vis, fluorescence and elec-
trochemical experiments were 1 ¥ 10-5, 1 ¥ 10-5 and 1 ¥ 10-3 mol dm-3,
respectively.
Thus, for instance, the electrochemical response (changes in the
redox wave of the redox-active groups) is usually governed by
changes in the charge between the ligand and the complex; and by
the existence of chemical (i.e. decomplexation) reactions before,
or after, the electrochemical process. Chromogenic transduction
(hypsochromicshift) willbe expectedwhen there is astrongenough
interaction of a certain metal cation with the anilino nitrogen in
the chromophore. Additionally, the strength in the coordination
and the coordination mode of the metal cations with the different
ligands can also modulate the final signal observed. Thus, it is
expected that the interaction of a given cation with binding sites
(such as the oxygen and sulfur atoms) in the macrocycle, but not
directly with the nitrogen atom, may result in an electrochemical or
flurogenic response, but not in changes in colour. Other variables
such as the strength of the coordination bonding (more covalent
or cation-dipole type), or the interaction with the photo-excited
receptors with metal cations through energy or photo-electron
transfer processes, can also influence the observed final response.
This differential response as a function of the channels selected
has also been found in other multi-channel signalling receptors
and we and other authors have suggested that this behaviour might
open the possibility of using a unique receptor for different sig-
nalling applications and for the development of certain molecular
logic gates.
Fig. 7 Changes in the visible band of acetonitrile solutions of receptor
L1 (1.2 ¥ 10-5 mol dm-3) upon addition of increasing quantities of cyanide
anion up to 1 equivalent.
most likely related to a nucleophilic attack on the electron deficient
thiopyrylium ring. In fact, similar behaviour was observed upon
the addition of the anion OH- (added as a tetrabutylammonium
salt) with L2–L6; i.e. a complete bleaching.
Thiopyrylium, and the parent pyrylium heterocycles, contain
in their structures one positively charged sulfur and oxygen atom
respectively, that induce a certain electrophilic character in the
carbons located in the heterocyclic rings.28 In fact, quantum chem-
ical calculations at semiempirical level44 indicate that the charge
density on atoms C2, C3, and C4 for 2,4,6-triphenylpyrylium
are 0.233, -0.266 and 0.245, respectively. In the case of 2,4,6-
triphenylthiopyrylium, similar calculations lead to values of -0.06,
-0.191, and 0.206. These calculations suggest that the pyrylium
and thiopyrylium rings are prone to suffer nucleophilic attack on
C4 and C2 (see Scheme 2). These calculated charges, together with
the fact that the C–O+ and C–S+ bonds in the ring are polarized
by inductive effects, should account for the reactivity observed.
In order to confirm this possible attack, a detailed study was
Spectroscopic studies involving anions
1
carried out with compound L1 and cyanide. H-NMR studies in
The development of abiotic receptors for anions has been a subject
of growing interest in recent years due to the crucial roles played
by anions in biological and environmental processes.41 In this
section we were interested in studying the interaction of L1–L6
with anions. For instance, it has been reported that the parent
derivatives containing pyrylium rings suffer ring opening/closing
processes in the presence of certain anionic species and this effect
has been used in different signalling applications.42
acetonitrile-d3 showed that two different compounds are clearly
formed upon the addition of one equivalent of CN-. The singlet
at 8.63 ppm for L1 turned into three new singlets at 5.96, 6.17, and
7.26, upon cyanide addition. The singlet at 6.17 ppm was assigned
to the product obtained by cyanide attack on C4 (product II),
whereas the other two signals corresponded to the product formed
by cyanide addition on C2 (product I). From the area of the signals,
a ratio of 75 : 25 for structures I·II was determined. Unfortunately,
attempts to isolate the reaction products were unsuccessful and
chromatographic techniques resulted in decomposition of the
products.
These preliminary results pointed to the possible use of receptor
L1 for the colorimetric detection and quantification of cyanide
anion. Unfortunately, it was also confirmed that the addition of
small quantities of water (less than 5%) to acetonitrile solutions
of receptor 1 inhibited bleaching in the presence of cyanide. We
recently reported a more detailed study that included the signalling
in cyanide with L1 in water using micelles.45
-
-
The addition of 1 equivalent of Cl-, Br-, I-, NO3 , H2PO4 ,
-
HSO4 , AcO-, BzO- and NCS- to acetonitrile solutions of L1
induced negligible changes in the UV-visible spectra or in the
colour of the solutions. The most striking effect was observed
upon the addition of 1 equivalent of cyanide anion because a
complete bleaching of the colour of the solution was produced
(see Fig. 7).43 The same behaviour upon addition of anions was
observed with the crown ether-functionalised L2–L6 receptors,
strongly suggesting that the presence of the macrocyclic subunits
in L2–L6 is not responsible for the observed selectivity. This, in
turn, pointed to an interaction of cyanide anions with the 2,4,6-
triphenylthiopyrylium moiety in a chemodosimeter fashion that is
Nearly the same chromogenic behaviour as that observed for
thiopyrylium derivative L1 was found for acetonitrile solutions of
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 3449–3459 | 3455
©

View Article Online
by the nature of the metal cation and the coordination site.
For instance, whereas L1 is not emissive, protonation of the
anilino group resulted in the appearance of a broad intense
emission band centred at 500 nm (lex = 410 nm). Additionally,
the presence of Cu2+ and Fe3+ induced a remarkable 42-fold
and 45-fold enhancement in the emission intensity band centred
at 500 nm of receptor L1. Also remarkable was the 18-fold
enhancement observed for L4 and L5 in the presence of Fe3+ and
Cu2+, respectively. This family of receptors showed a one-electron
reversible redox process at ca. -0.46 V versus sce attributed to
the reduction of the thiopyrylium group. A moderate anodic shift
in the presence of certain metal cations was observed. Finally,
the receptors L1–L6 also show sensing features in the presence of
cyanide, which is able to react with the electron-deficient pyrylium
ring and results in a bleaching of the blue solution.
Experimental
General remarks
All commercially available reagents were used without further
purification. Air/water-sensitive reactions were performed in
flame-dried glassware under argon. Acetonitrile was dried with
CaH2 and distilled prior to use.
Scheme 2 Proposed structures for the products of cyanide attack over
thiopyrylium and pyrylium rings presented by receptors L1 and 8.
Physical measurements
pyrylium salt 8 upon the addition of 1 equivalent of cyanide that
induced the complete disappearance of the charge transfer band
centred at 540 nm. 1H-NMR studies in DMSO-d6 (pyrylium salt 8
does not dissolve in acetonitrile-d3) of 8 in the presence of cyanide
resulted in a complex mixture of, at least, three compounds (III, IV
and V). The major product was identified as coming from an attack
of cyanide on the C4 (product IV) at the pyrylium moiety featuring
a singlet at 5.14 ppm and the protons at the dimethylanilynium ring
at 7.89 and 6.9 ppm. The mixture evolved over time producing a
major product coming from the attack on C2 (product III) and the
opening of the pyrylium ring (product V). In this final product, the
dimethylanilynium protons are now at d 6.26 and 6.71 (overlapped
with the olephynic protons) and the phenyl protons are now de-
shielded.
Metal cations (Ag+, Cd2+, Cu2+, Fe3+, Hg2+, Ni2+, Pb2+ and Zn2+
as perchlorate or triflate salts) and anions (F-, Cl-, Br-, I-,
NO3 , H2PO4 , HSO4 , AcO-, BzO-, NCS- and CN- as tetrabuty-
lammonium salts) were used to obtain acetonitrile solutions of
concentration ca. 1.0 ¥ 10-3 mol dm-3. UV-visible studies were
carried out with a Perkin Elmer Lambda 35 spectrometer. The
concentrations of ligands used in the UV-visible measurements
were ca. 5.0 ¥ 10-5 mol dm-3 in acetonitrile. UV-visible spectra
were recorded in the presence of equimolar quantities of the
corresponding ligand and metal cation or anion. The fluores-
cence behaviour was studied with a FS900CDT Steady State T-
Geometry Fluorimeter, Edinburgh Analytical Instruments. All
solutions for photophysical studies were previously degassed.
The concentrations of ligands were ca. 5.0 ¥ 10-5 mol dm-3 in
acetonitrile. Fluorescence emission spectra were recorded in the
presence of equimolar quantities of ligand and the corresponding
metal cation. Electrochemical data were carried out in dry
acetonitrile solutions previously degassed, with a programmable
function generator Tacussel IMT-1, connected to a Tacussel PJT
120-1 potentiostat. The concentration of ligands and metal ions
were ca. 1.0 ¥ 10-3 mol dm-3 in acetonitrile (the metal ions
were perchlorate or triflate salts of Ag+, Cd2+, Cu2+, Fe3+, Hg2+,
Pb2+ and Zn2+). Electrochemical studies were carried out in the
presence of equimolar quantities of ligand and the corresponding
metal cation. The working electrode was platinum connected with
a saturated calomel reference electrode separated from the test
solution by a salt bridge containing the solvent and the supporting
electrolyte (0.25 mol dm-3 [Bu4N][BF4]). The auxiliary electrode
was a platinum wire. The 1H and 13C NMR spectra were recorded
with a Varian Gemini spectrometer. Chemical shifts are reported
in ppm downfield from TMS signal. Spectra taken in CDCl3 were
referenced to residual CHCl3.
-
-
-
Conclusions
A family of receptors based on functionalised thiopyrylium
moieties have been synthesised and characterised and their
interaction with metal cations studied via optical (colour and
emission fluorescence) and electrochemical changes. The optical
properties of the products reveal that the acceptor thiopyrylium
group and the donor aniline moiety are strongly p-conjugated
and produce intense CT bands at ca. 580 nm. The receptors show
a rich chromogenic response to metal cations modulated by the
nature of the coordination ring. A selective hypsochromic shift of
the CT band was observed for the L4-Pb2+ and L5-Hg2+ systems.
Receptors L1–L6 are poorly fluorescent most likely because of
the presence of non-radiative deactivation pathways due to the
presence of a nitrogen atom directly linked to the chromophoric
system. Moreover, coordination at the anilino moiety resulted in
a very remarkable enhancement of the emission that is modulated
3456 | Dalton Trans., 2010, 39, 3449–3459
This journal is
The Royal Society of Chemistry 2010
©

View Article Online
Synthetic procedures
70.6, 73.6, 114.1, 122.5, 125.6, 127.9, 130.2, 132.8, 133.4, 134.6,
153.8, 157.5, 162.0. HRMScalc. for C33H36NS3O2, 574.1908, found
574.1867.
The synthesis of macrocyclic subunits 10-phenyl-10-aza-1,4,
7-trioxacyclododecane (3), 13-phenyl-13-aza-1,4,7,10-tetraoxa-
cyclopentadecane (4), 16-phenyl-16-aza-1,4,7,10,13-pentaoxa-
cycloheptadecane (5), 10-phenyl-10-aza-1,4-dioxa-7,13-dithiacyc-
lopentadecane (6) and 4-phenyl-4-aza-1,7-dioxa-10,13-dithia-
cyclopentadecane (7) were previously published. The syntheses of
pyrylium-based receptors (8–13) were also previously published.
L6: Yield: 40%, 1H NMR (300 MHz, DMSO-D6): d = 2.72 (4H,
t, O-(CH2)2-S), 2.81 (4H, s, N-(CH2)2-S), 3.70 (4H, t, O-(CH2)2-
O), 3.77 (4H, t, O-(CH2)2-S), 3.85 (4H, t, N-(CH2)2-S), 6.91 (2H,
d, C6H4), 7.58 (6H, m, C6H5), 7.87 (4H, m, C6H5), 8.13 (2H, d,
1
C6H4), 8.43 (2H, s, C5H2S). 13C{ H} NMR (75 MHz, CDCl3):
d = 31.93, 32.96, 51.73, 69.23, 72.16, 115.3, 123.5, 126.4, 128.3,
131.0, 131.6, 132.8, 133.7, 154.3, 158.6, 163.3. HRMS calc. for
C33H36NS3O2, 574.1908, found 574.1987.
General procedure for the synthesis of the thiopyrylium derivatives
(L1–L6)
Acknowledgements
N,N-dimethylaniline (2, 2 mmol) or the corresponding N-phenyl
macrocycle (3–7, 2 mmol) were reacted with 2,6-diphenylpyrylium
perchlorate (1, 4 mmol) in dry DMF (20 mL) at 150◦ C for
three hours. Pyrylium derivatives 8–13 (1 mmol, yield: 50%) were
precipitated from the crude reaction as dark brown solids by
addition of dimethyl ether (25 mL). These pyrylium derivatives
(0.8 mmol) were then dissolved in acetone (50 mL), Na2S (2 mL,
10% water solution) was added and the crude reaction was allowed
to react for 20 min at room temperature. Finally, perchloric acid
(2 mL, 20% water solution) was added and the crude reaction
stirred for another 40 min at the same temperature. The final
thiopyrylium derivatives were isolated as dark blue solids by
vacuum filtration and successive washings with water and diethyl
ether.
The authors wish to express their gratitude to the Spanish
Government for financial support (projects CTQ2006-15456-C04-
01, CTQ2006-15456-C04-02). T. A. is grateful to the Ministerio
de Ciencia e Innovacio´n for the fellowship awarded. The English
revision of this paper was funded by the Universidad Polite´cnica
de Valencia, Spain.
References
1 E. V. Anslyn, J. Org. Chem., 2007, 72, 687.
2 R. Mart´ınez-Ma´n˜ez and F. Sanceno´n, Chem. Rev., 2003, 103,
4419.
3 (a) R. Mart´ınez-Ma´n˜ez and F. Sanceno´n, J. Fluoresc., 2005, 15, 267;
(b) T. Gunnlaugsson, H. D. P. Ali, M. Glynn, P. E. Kruger, G. M.
Hussey, F. M. Pfeffer, C. M. G. dos Santos and J. Tierney, J. Fluoresc.,
2005, 15, 287; (c) A. P. de Silva, H. Q. N. Gunaratne, T. Gunnlaugsson,
A. J. M. Huxley, C. P. McCoy, J. T. Rademacher and T. E. Rice, Chem.
Rev., 1997, 97, 1515; (d) S. K. Kim, D. H. Lee, J.–H. Hong and J. Yoon,
Acc. Chem. Res., 2009, 42, 23.
4 (a) R. Mart´ınez-Ma´n˜ez and F. Sanceno´n, Coord. Chem. Rev., 2006, 250,
3081; (b) C. Suksai and T. Tuntulani, Chem. Soc. Rev., 2003, 32, 192;
(c) V. Amendola, D. Esteban-Go´mez, L. Fabbrizzi and M. Licchelli,
Acc. Chem. Res., 2006, 39, 343.
5 See for instance: (a) P. D. Beer, Chem. Commun., 1996, 689; (b) P. D.
Beer, Coord. Chem. Rev., 2000, 205, 131; (c) P. D. Beer, J. Cadman,
J. M. Lloris, R. Mart´ınez-Ma´n˜ez, J. Soto, T. Pardo and M. D. Marcos,
J. Chem. Soc., Dalton Trans., 2000, 1805; (d) J. M. Lloris, R. Mart´ınez-
Ma´n˜ez, M. E. Padilla-Tosta, T. Pardo, J. Soto, P. D. Beer, J. Cadman
and D. K. Smith, J. Chem. Soc., Dalton Trans., 1999, 2359; (e) M. E.
Padilla-Tosta, R. Mart´ınez-Ma´n˜ez, T. Pardo, J. Soto and M. J. Lo´pez-
Tendero, Chem. Commun., 1997, 887.
1
L1: Yield: 50%, H NMR (300 MHz, DMSO-D6): d = 3.16
(6H, s, N-(CH3)2), 6.89 (2H, d, C6H4), 7.60 (6H, m, C6H5), 7.88
1
(4H, m, C6H5), 8.19 (2H, d, C6H4), 8.49 (2H, s, C5H2S). 13C { H}
NMR (75 MHz, CDCl3): d = 40.5, 114.3, 122.2, 124.8, 127.7,
130.1, 132.6, 133.2, 134.5, 154.8, 156.6, 160.9. HRMS calc. for
C25H22NS, 368.1473, found 368.1455.
1
L2: Yield: 45%, H NMR (300 MHz, DMSO-D6): d = 3.66
(8H, s, O–CH2-O), 3.75 (4H, t, N–CH2-O), 3.78 (4H, t, O–CH2-
O), 6.88 (2H, d, C6H4), 7.61 (6H, m, C6H5), 7.89 (4H, m, C6H5),
1
8.20 (2H, d, C6H4), 8.47 (2H, s, C5H2S). 13C { H} NMR (75 MHz,
CDCl3): d = 53.5, 70.0, 70.4, 71.3, 114.2, 122.2, 124.7, 127.9,
130.1, 132.4, 133.2, 134.6, 154.7, 156.6, 161.1. HRMS calc. for
C31H32NSO3, 498.2103, found 498.2095.
1
L3: Yield: 48%, H NMR (300 MHz, DMSO-D6): d = 3.62
6 S. L. Wiskur, H. A¨ıt-Haddou, J. J. Lavigne and E. V. Anslyn, Acc. Chem.
Res., 2001, 34, 963.
(4H, s, O-(CH2)2-O), 3.67-3.78 (16H, m, O-(CH2)2-O, N-(CH2)2-
O), 6.92 (2H, d, C6H4), 7.57 (6H, m, C6H5), 7.86 (4H, m, C6H5),
7 See for example: (a) V. Dujols, F. Ford and A. W. Czarnik, J. Am.
Chem. Soc., 1997, 119, 7386; (b) O. Rusin, N. S. St Luce, R. A. Agbaria,
J. O. Escobedo, S. Jiang, I. M. Warner, F. B. Dawan, K. Lian and
R. M. Strongin, J. Am. Chem. Soc., 2004, 126, 438; (c) M. Tomasulo,
S. Sortino, A. J. P. White and F. M. Raymo, J. Org. Chem., 2006, 71,
744; (d) Y.–K. Yang and J. Tae, Org. Lett., 2006, 8, 5721; (e) S. Y.
Kim and J. I. Hong, Org. Lett., 2007, 9, 3109; (f) M. Comes, M. D.
Marcos, R. Mart´ınez-Ma´n˜ez, M. C. Milla´n, J. V. Ros-Lis, F. Sanceno´n,
J. Soto and L. A. Villaescusa, Chem.–Eur. J., 2006, 12, 2162; (g) S.
Basurto, T. Torroba, M. Comes, R. Mart´ınez-Ma´n˜ez, F. Sanceno´n,
L. A. Villaescusa and P. Amoro´s, Org. Lett., 2005, 7, 5469; (h) A. B.
Descalzo, D. Jime´nez, J. El Haskouri, D. Beltra´n, P. Amoro´s, M. D.
Marcos, R. Mart´ınez-Ma´n˜ez and J. Soto, Chem. Commun., 2002, 562.
8 (a) S. L. Wiskur, P. N. Floriano, E. V. Anslyn and J. T. McDevitt,
Angew. Chem., Int. Ed., 2003, 42, 2070; (b) J. J. Lavigne and E. V.
Anslyn, Angew. Chem., Int. Ed., 2001, 40, 3118; (c) K. J. Albert, N. S.
Lewis, C. L. Schauer, G. A. Sotzing, S. E. Stitzel, T. P. Vaid and D. R.
Walt, Chem. Rev., 2000, 100, 2595; (d) R. Mart´ınez-Ma´n˜ez, J. Soto,
E. Garc´ıa-Breijo, L. Gil, J. Iba´n˜ez and E. Llobet, Sens. Actuators, B,
2005, 104, 302; (e) B. Garc´ıa-Acosta, X. Albiach-Mart´ı, E. Garc´ıa, L.
Gil, R. Mart´ınez-Ma´n˜ez, K. Rurack, F. Sanceno´n and J. Soto, Chem.
1
8.14 (2H, d, C6H4), 8.43 (2H, s, C5H2S). 13C { H} NMR (75 MHz,
CDCl3): d = 53.6, 68.2, 69.9, 70.4, 71.0, 114.5, 122.5, 125.1, 127.8,
130.2, 132.7, 133.2, 134.6, 154.7, 157.0, 161.3. HRMS calc. for
C33H36NSO4, 542.2365, found 542.2377.
1
L4: Yield: 46%, H NMR (300 MHz, DMSO-D6): d = 3.63-
3.77 (24H, m, O-(CH2)2-O, N-(CH2)2-O), 6.95 (2H, d, C6H4), 7.56
(6H, m, C6H5), 7.87 (4H, m, C6H5), 8.14 (2H, d, C6H4), 8.39
1
(2H, s, C5H2S). 13C { H} NMR (75 MHz, CDCl3): d = 51.9, 68.5,
70.6, 70.7, 114.3, 122.2, 124.8, 127.7, 130.1, 132.6, 133.2, 134.5,
154.9, 156.6, 160.9. HRMS calc. for C35H40NSO5, 586.2627, found
586.2709.
L5: Yield: 48%, 1H NMR (300 MHz, DMSO-D6): d = 2.76 (4H,
t, N-(CH2)2-S), 2.93 (4H, t, O-(CH2)2-S), 3.63 (4H, s, O-(CH2)2-O),
3.80 (8H, m, S-(CH2)2-N, O-(CH2)2-S), 6.92 (2H, d, C6H4), 7.57
(6H, m, C6H5), 7.86 (4H, m, C6H5), 8.14 (2H, d, C6H4), 8.43 (2H, s,
1
C5H2S). 13C { H} NMR (75 MHz, CDCl3): d = 30.1, 32.1, 52.7,
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 3449–3459 | 3457
©

View Article Online
Commun., 2004, 773; (f) B. Garc´ıa-Acosta, R. Mart´ınez-Ma´n˜ez, F.
Sanceno´n, J. Soto, K. Rurak, M. Spieles, E. Garc´ıa-Breijo and L. Gil,
Inorg. Chem., 2007, 46, 3123.
9 (a) A. P. de Silva, D. B. Fox, T. S. Moody and S. M. Weir, Trends
Biotechnol., 2001, 19, 29; (b) A. P. de Silva and N. D. McClenaghan,
Chem.–Eur. J., 2004, 10, 574; (c) A. P. de Silva, Y. Leydet, C. Lincheneau
and N. D. McClenaghan, J. Phys.: Condens. Matter, 2006, 18, S1847;
(d) K. Rurack, A. Koval’chuck, J. L. Bricks and J. L. Slominskii, J. Am.
Chem. Soc., 2001, 123, 6205; (e) A. P. de Silva and N. D. McClenaghan,
Chem. Eur. J., 2002, 8, 4935.
27 R. Wizinger and P. Ulrich, Helv. Chim. Acta, 1956, 39, 207.
28 D. Markovitsi, C. Jallabert, H. Strzelecka and M. Veber, J. Chem. Soc.,
Faraday Trans., 1990, 86, 2819.
29 (a) K. E. Krakowiak, J. S. Bradshaw and D. J. Zamecka-Krakowiak,
Chem. Rev., 1989, 89, 929; (b) J. P. Dix and F. Vo¨gtle, Angew. Chem.,
Int. Ed. Engl., 1978, 17, 857.
30 (a) B. Valeur and I. Leray, Coord. Chem. Rev., 2000, 205, 3; (b) K.
Rurack, Spectrochim. Acta, Part A, 2001, 57, 2161; (c) B. Unger, K.
Rurack, R. Mu¨ller, H. Jancke and U. Resch-Genger, J. Mater. Chem.,
2005, 15, 3069.
10 (a) A. P. de Silva, H. Q. N. Gunaratne and C. P. McCoy, J. Am. Chem.
Soc., 1997, 119, 7891; (b) H.–F. Ji, R. Dabestani and G. M. Brown,
J. Am. Chem. Soc., 2000, 122, 9306; (c) S. A. de Silva, B. Amorelli, D. C.
Isidor, K. C. Loo, K. E. Crooker and Y. E. Pena, Chem. Commun., 2002,
1360; (d) A. P. de Silva, G. D. McClean and S. Pagliari, Chem. Commun.,
2003, 2010; (e) B. Bag and P. K. Bharadwaj, Chem. Commun., 2005,
513; (f) A. M. Costero, J. Sanchis, S. Gil, V. Sanz and J. A. G. Williams,
J. Mater. Chem., 2005, 15, 2848; (g) K. Kubo and A. Mori, J. Mater.
Chem., 2005, 15, 2902; (h) M. D. Lankshear, A. R. Cowley and P. D.
Beer, Chem. Commun., 2006, 612; (i) D. C. Magri, G. J. Brown, G. D.
McClean and A. P. de Silva, J. Am. Chem. Soc., 2006, 128, 4950; (j) M.
de Sousa, B. de Castro, S. Abad, M. A. Miranda and U. Pischel, Chem.
Commun., 2006, 2051.
11 (a) J. Maynadie, B. Delavaux-Nicot, S. Fery-Forgues, D. Lavabre and
R. Mathieu, Inorg. Chem., 2002, 41, 5002; (b) B. Delavaux- Nicot and
S. Fery-Forgues, Eur. J. Inorg. Chem., 1999, 1821.
12 (a) P. D. Beer, A. R. Graydon and L. R. Sutton, Polyhedron, 1996, 15,
2457; (b) P. D. Beer and F. J. Szemes, J. Chem. Soc., Chem. Commun.,
1995, 2245; (c) P. D. Beer, A. R. Graydon, A. O. M. Johnson and D. K.
Smith, Inorg. Chem., 1997, 36, 2112.
31 (a) A. T. Balaban and W. Silhau, Tetrahedron, 1970, 26, 743; (b) C.
Uncuta and A. T. Balaban, J. Chem. Res., 2001, 170.
32 (a) R. M. Izatt, R. E. Terry, L. D. Hansen, A. G. Avondet, J. S.
Bradshaw, N. K. Dalley, T. E. Jensen, J. J. Christensen and B. L.
Haymore, Inorg. Chim. Acta, 1978, 30, 1; (b) J. Massaux and J. F.
Desreux, J. Am. Chem. Soc., 1982, 104, 2967.
33 For optical receptors for Hg2+ recognition functionalised with sulfur-
containing systems see for example: (a) S. Yoon, E. W. Miller, Q. He,
P. H. Do and C. J. Chang, Angew. Chem., Int. Ed., 2007, 46, 6658;
(b) K. Rurack, U. Resch-Genger, J. L. Bricks and M. Spieles, Chem.
Commun., 2000, 2103; (c) P. Pallavicini, Y. A. Diaz-Fernandez, F. Foti,
C. Mangano and S. Patroni, Chem.–Eur. J., 2007, 13, 178; (d) A. B.
Descalzo, R. Mart´ınez-Ma´n˜ez, R. Radeglia, K. Rurack and J. Soto,
J. Am. Chem. Soc., 2003, 125, 3418; (e) S. Yoon, A. E. Albers, A. P.
Wong and C. J. Chang, J. Am. Chem. Soc., 2005, 127, 16030; (f) H. G.
Lee, J.–E. Lee and K. S. Choi, Inorg. Chem. Commun., 2006, 9, 582;
(g) S. H. Kim, K. C. Song, S. Ahn, Y. S. Kang and S.–K. Chang,
Tetrahedron Lett., 2006, 47, 497; (h) J. V. Ros-Lis, M. D. Marcos, R.
Mart´ınez-Ma´n˜ez, K. Rurack and J. Soto, Angew. Chem., Int. Ed., 2005,
44, 4405; (i) J. V. Ros-Lis, R. Mart´ınez-Ma´n˜ez, K. Rurack, F. Sanceno´n,
J. Soto and M. Spieles, Inorg. Chem., 2004, 43, 5183; (j) M. Comes, E.
Aznar, M. Moragues, M. D. Marcos, R. Mart´ınez-Ma´n˜ez, F. Sanceno´n,
J. Soto, L. A. Villaescusa, L. Gil and P. Amoro´s, Chem.–Eur. J., 2009,
15, 9024.
13 (a) T. Saika, T. Iyoda, K. Honda and T. Shimidzu, J. Chem. Soc., Perkin
Trans. 2, 1993, 1181; (b) T. Iyoda, T. Saika, K. Honda and T. Shimidzu,
Tetrahedron Lett., 1989, 30, 5429; (c) T. Shimidzu, T. Iyoda and K.
Honda, Pure Appl. Chem., 1988, 60, 1025; (d) F. P. Funeriu, J. M. Lehn,
K. M. Fromm and D. Fenske, Chem.–Eur. J., 2000, 6, 2103; (e) J. M.
Lehn, Chem.–Eur. J., 2000, 6, 2097.
34 R. Akaba, M. Kamata, A. Koike, K. Mogi, Y. Kuriyama and H.
Sakuragi, J. Phys. Org. Chem., 1997, 10, 861.
14 F. Sanceno´n, A. Benito, F. J. Herna´ndez, J. M. Lloris, R. Mart´ınez-
Ma´n˜ez, T. Pardo and J. Soto, Eur. J. Inorg. Chem., 2002, 866.
15 (a) F. Oto´n, A. Ta´rraga, M. D. Velasco, A. Espinosa and P. Molina,
Chem. Commun., 2004, 1658; (b) F. Oto´n, A. Ta´rraga, A. Espinosa,
M. D. Velasco and P. Molina, J. Org. Chem., 2006, 71, 4590.
16 F. Oto´n, A. Espinosa, A. Ta´rraga, C. Ram´ırez de Arellano and P.
Molina, Chem.–Eur. J., 2007, 13, 5742.
17 F. Zapata, A. Caballero, A. Espinosa, A. Ta´rraga and P. Molina, Org.
Lett., 2008, 10, 41.
18 T. Ghosh, B. G. Maiya and M. W. Wong, J. Phys. Chem. A, 2004, 108,
11249.
19 M. Boiocchi, L. Fabbrizzi, M. Licchelli, D. Sacchi, M. Va´zquez and C.
Zampa, Chem. Commun., 2003, 1812.
20 A. P. de Silva, H. Q. N. Gunaratne and M. Lynch, J. Chem. Soc., Perkin
Trans. 2, 1995, 685.
21 (a) M. Yuan, Y. Li, J. Li, C. Li, X. Liu, J. Lv, J. Xu, H. Li, S. Wang and
D. Zhu, Org. Lett., 2007, 9, 2313; (b) M. Zhu, M. Yuan, X. Liu, J. Xu,
J. Lv, C. Huang, H. Liu, Y. Li, S. Wang and D. Zhu, Org. Lett., 2008,
10, 1481.
22 (a) D. Jime´nez, R. Mart´ınez-Ma´n˜ez, F. Sanceno´n and J. Soto,
Tetrahedron Lett., 2004, 45, 1257; (b) D. Jime´nez, R. Mart´ınez-Ma´n˜ez,
F. Sanceno´n, J. V. Ros-Lis, J. Soto, A. Benito and E. Garc´ıa-Breijo,
Eur. J. Inorg. Chem., 2005, 2393.
35 M. A. Miranda and H. Garc´ıa, Chem. Rev., 1994, 94, 1063.
36 S. Parret, F. Morlet-Savary, J. P. Fouassier, K. Inomata, T. Matsumoto
and F. Heisel, Bull. Chem. Soc. Jpn., 1995, 68, 2791.
37 L. Fabbrizzi, M. Licchelli, P. Pallavicini, L. Parodi, A. Taglietti, in
“Transition metals in Supramolecular Chemistry”, Ed. J. P. Sauvage,
1999, p. 93-134, John Wiley & Sons Ltd.
38 For recent fluorescent Pb2+ sensing systems working in water see:(a) L.
Marbella, B. Serli-Mitasev and P. Basu, Angew. Chem., Int. Ed., 2009,
48, 3996; (b) E. Roussakis, S. A. Pergantis and H. E. Katerinopoulos,
Chem. Commun., 2008, 6221.
39 For recent fluorescent Hg2+ sensing systems working in water see:(a) W.
Shi and H. Ma, Chem. Commun., 2008, 1856; (b) X.–Q. Zhan, Z.–H.
Qian, H. Zheng, B.–Y. Su, Z. Lan and J.–G. Xu, Chem. Commun., 2008,
1859; (c) M.–L. Ho, K.–Y. Chen, L.–C. Wu, J.–Y. Shen, G.–H. Lee,
M.–J. Ko, C.–C. Wang, J.–F. Lee and P.–T. Chou, Chem. Commun.,
2008, 2438; (d) L.–J. Ma, Y. Li, J. Sun, C. Tian and Y. Wu, Chem.
Commun., 2008, 6345; (e) M. Tian and H. Ihmels, Chem. Commun.,
2009, 3175; (f) W. Jiang and W. Wang, Chem. Commun., 2009, 3913;
(g) B. Tang, B. Ding, K. Xu and L. Tong, Chem.–Eur. J., 2009, 15, 3147;
(h) F. Song, S. Watanabe, P. E. Floreancig and K. Koide, J. Am. Chem.
Soc., 2008, 130, 16460; (i) J. Huang, Y. Xu and X. Qian, J. Org. Chem.,
2009, 74, 2167; (j) X. Chen, S.–W. Nam, M. J. Jou, Y. Kim, S.–J. Kim,
S. Park and J. Yoon, Org. Lett., 2008, 10, 5235.
23 M. Schmittel and H.–W. Lin, Angew. Chem., Int. Ed., 2007, 46, 893.
24 See for instance: (a) E. Climent, P. Calero, M. D. Marcos, R. Mart´ınez-
Ma´n˜ez, F. Sanceno´n and J. Soto, Chem.–Eur. J., 2009, 15, 1816;
(b) M. Comes, M. D. Marcos, R. Mart´ınez-Ma´n˜ez, F. Sanceno´n, L. A.
Villaescusa, A. Graefe and G. J. Mohr, J. Mater. Chem., 2008, 18,
5815; (c) E. Climent, R. Casasu´s, M. D. Marcos, R. Mart´ınez-Ma´n˜ez,
F. Sanceno´n and J. Soto, Chem. Commun., 2008, 6531; (d) J. V. Ros-
Lis, R. Mart´ınez-Ma´n˜ez, F. Sanceno´n, J. Soto, M. Spieles and K.
Rurack, Chem.–Eur. J., 2008, 14, 10101; (e) A. Costero, S. Gil, M.
Parra, P. M. E. Mancini, R. Mart´ınez-Ma´n˜ez, F. Sanceno´n and S.
Royo, Chem. Commun., 2008, 6002.
40 R. Mart´ınez-Ma´n˜ez, J. Soto, J. M. Lloris and T. Pardo, Trends Inorg.
Chem., 1998, 5, 183.
41 (a) F. P. Schmidtchen and M. Berger,M., Chem. Rev., 1997, 97, 1609;
(b) P. D. Beer and P. A. Gale, Angew. Chem., Int. Ed., 2001, 40, 486;
(c) See Coord. Chem. Rev., 2006, 250, special issue on anion receptors..
42 (a) M. Comes, M. D. Marcos, R. Mart´ınez-Ma´n˜ez, F. Sanceno´n, J.
Soto, L. A. Villaescusa, P. Amoro´s and D. Beltran, Adv. Mater., 2004,
16, 1783; (b) B. Garc´ıa-Acosta, F. Garc´ıa, J. M. Garc´ıa, R. Mart´ınez-
Ma´n˜ez, F. Sanceno´n, N. San-Jose´ and J. Soto, Org. Lett., 2007, 9, 2429;
(c) F. Sanceno´n, A. B. Descalzo, M. A. Miranda and J. Soto, Angew.
Chem., Int. Ed., 2001, 40, 2640; (d) F. Sanceno´n, R. Mart´ınez-Ma´n˜ez
and J. Soto, Chem. Commun., 2001, 2262; (e) F. Sanceno´n, R. Mart´ınez-
Ma´n˜ez, M. A. Miranda, M.–J. Segu´ı and J. Soto, Angew. Chem., Int.
Ed., 2003, 42, 647.
25 D. Jime´nez, R. Mart´ınez-Ma´n˜ez, F. Sanceno´n, J. V. Ros-Lis, A. Benito
and J. Soto, J. Am. Chem. Soc., 2003, 125, 9000.
´
26 T. Abalos, D. Jime´nez, R. Mart´ınez-Ma´n˜ez, J. V. Ros-Lis, S. Royo, F.
Sanceno´n, J. Soto, A. M. Costero, S. Gil and M. Parra, Tetrahedron
Lett., 2009, 50, 3885.
43 For recent cyanide sensing systems see:(a) X. Lou, L. Zhang, J. Qin
and Z. Li, Chem. Commun., 2008, 5848; (b) S.–J. Hong, J. Yoo, S.–H.
3458 | Dalton Trans., 2010, 39, 3449–3459
This journal is
The Royal Society of Chemistry 2010
©

View Article Online
Kim, J. S. Kim, J. Yoon and C.–H. Lee, Chem. Commun., 2009, 189;
(c) C.–W. Chiu and F. P. Gabba¨ı, Dalton Trans., 2008, 814; (d) P. Kaur,
D. Sareen, S. Kaur and K. Singh, Inorg. Chem. Commun., 2009, 12, 272;
(e) D.–G. Cho, J. H. Kim and J. L. Sessler, J. Am. Chem. Soc., 2008,
130, 12163; (f) H.–T. Niu, D. Su, X. Jiang, W. Yang, Z. Yin, J. He and
J.–P. Cheng, Org. Biomol. Chem., 2008, 6, 3038; (g) Z. Ekmekci, M. D.
Yilmaz and E. U. Akkaya, Org. Lett., 2008, 10, 461; (h) H.–T. Niu, X.
Jiang, J. He and J.–P. Cheng, Tetrahedron Lett., 2008, 49, 6521; (i) Q.
Zeng, P. Cai, Z. Li, J. Qin and B. Z. Tang, Chem. Commun., 2008, 1094;
(j) A. Touceda-Varela, E. I. Stevenson, J. A. Galve-Gasio´n, D. T. F.
Dryden and J. C. Mareque-Rivas, Chem. Commun., 2008, 1998; (k)
S.–Y. Chung, S.–W. Nam, J. Lim, S. Park and J. Yoon, Chem. Commun.,
2009, 2866; (l) M. Jamkratoke, V. Ruangpornvisuti, G. Tumcharern, T.
Tutulani and B. Tomapatanaget, J. Org. Chem., 2009, 74, 3919; (m)
K.–S. Lee, H.–J. Kim, G.–H. Kim, I. Shin and J.–I. Hong, Org. Lett.,
2008, 10, 49; (n) L. Peng, M. Wang, G. Zhang, D. Zhang and D. Zhu,
Org. Lett., 2009, 11, 1943; (o) S. K. Kwon, S. Kou, H. N. Kim, X. Chen,
H. Hwang, S.–W. Nam, S. H. Kim, K. M. K. Swamy, S. Park and J.
Yoon, Tetrahedron Lett., 2008, 49, 4102; (p) J. Jo and D. Lee, J. Am.
Chem. Soc., 2009, 131, 16283.
44 HyperChem 6.03 Molecular Modeling System, Hypercube Inc,
Gainesville, Florida, USA, 2000.
´
45 T. Abalos, S. Royo, R. Mart´ınez-Ma´n˜ez, F. Sanceno´n, J. Soto, A. M.
Costero, S. Gil and M. Parra, New J. Chem., 2009, 33, 1641.
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 3449–3459 | 3459
©