N-Heterocyclic carbene formation induced fluorescent and colorimetric sensing of fluoride using perimidinium derivatives

Article abstract of DOI:10.1002/chem.201404806

In this study, two perimidinium derivatives (1 and 2) were designed, synthesized, and developed as efficient fluorescent and colorimetric chemodosisensors for F-in DMSO or more competitive media (DMSO containing 10% water). In the presence of F-, the yell

Full text of DOI:10.1002/chem.201404806

DOI: 10.1002/chem.201404806
Full Paper
&
Fluorescent Sensors
N-Heterocyclic Carbene Formation Induced Fluorescent and
Colorimetric Sensing of Fluoride Using Perimidinium Derivatives
[
a, b]
[a]
[b]
[b]
Dawei Zhang,
Haiqiang Yang, Alexandre Martinez,* Kelsey Jamieson,
[b]
[a]
Jean-Pierre Dutasta, and Guohua Gao*
À
Abstract: In this study, two perimidinium derivatives (1 and
carbene deprotonated by F , which immediately reacted
with water to give a colourless and fluorescent carbinol. In-
terestingly, it was found that this carbinol intermediate was
unstable and further underwent a redox disproportionation
to generate two other optically changed compounds. All the
proposed mechanisms for the sensing process have been
carefully confirmed by experiments.
2
) were designed, synthesized, and developed as efficient
À
fluorescent and colorimetric chemodosisensors for F in
DMSO or more competitive media (DMSO containing 10%
À
water). In the presence of F , the yellow and non-fluorescent
solution of 1/2 became colourless and exhibited strong blue
fluorescence. This unique spectroscopic behaviour of 1/2 to-
À
wards F was attributed to the formation of N-heterocyclic
Introduction
tion of a covalent bond between the anion and the Lewis acid
[3]
centre. For the second class, in most cases the hydrogen-
bond donors of the receptors consist of amide, urea, thiourea,
À
Fluoride anion (F ), bearing a small ionic radius, high charge
[2f,4]
density, and high hydration enthalpy, displays special chemical
and physical properties among the inorganic anions, such as
guanidinium, imidazolium, or pyrrole functionalities.
Hydro-
gen bonds can be considered the beginning of a proton-trans-
fer reaction, and in some cases, it has been demonstrated that
[
1]
its hard Lewis basic nature. It plays a fundamental role in
a number of chemical and biological processes and is com-
monly found in daily life. For example, fluoride is used as addi-
tive in toothpaste to prevent dental caries and enamel demin-
eralization, and it is also found in osteoporosis drugs and
drinking water. Due to its possible toxicity, the development of
synthetic fluorescent sensors for its detection has attracted
considerable attention in the field of modern supramolecular
À
the strong basicity of F can promote the deprotonation of
[5]
the hydrogen-bond donor moieties. This process is also fav-
À
oured by the stability of the HF2 complex and has been ob-
[6]
[7]
served in particular for receptors containing urea, thiourea,
[8]
or amide binding units. For example, Fabbrizzi et al. recently
[
6a]
reported
two fluorogenic ureas containing 2-anthracenyl
À
and 1-pyrenyl moieties as fluorescent sensors for F in DMSO.
Due to the proton transfer and the urea deprotonation of the
[
2]
chemistry.
À
À
Receptors that sense F can be divided into two main
sensor induced by F during the interaction process, an “ON-
À
À
classes: 1) Lewis acidic receptors that can covalently bind F ,
OFF-ON” fluorescent response towards F was displayed. In
+
À
and 2) receptors capable of hydrogen bonding with this
terms of imidazolium-based receptors, the (CÀH) ···X ionic hy-
drogen bond, which formed between the C(2)ÀH of imidazoli-
[
2f]
À
anion. The first class allows F to be detected in water at
low concentration and mainly involves group 13 or 15 Lewis
acids. Gabba ¨ı et al., for example, described the use of cationic
À
um and F , is often proposed to account for the recognition
[9]
properties of the host. Nevertheless, deprotonation of imida-
À
À
borane or stibonium ion for turn-on fluorescent sensing of F
zolium derivatives induced by acid–base reaction with F has
[10]
in water at parts per million concentrations through the forma-
also been observed in very few cases: for example, a tetra-
À
propyl benzobisimidazolium PF6 salt was used as an efficient
fluorescent and colorimetric sensor for CO in CH CN due to
2
3
+
+
[
a] D. Zhang, H. Yang, Prof. G. Gao
À
the carbene formation induced by F reacting with CO2 to
Shanghai Key Laboratory of Green Chemistry and Chemical Processes
Department of Chemistry, East China Normal University
[10a]
form an imidazolium carboxylate.
Unfortunately, both the
3
663 North Zhongshan Road, Shanghai 200062 (China)
absorption and emission of this sensor were below the visible
[10b]
E-mail: ghgao@chem.ecnu.edu.cn
region of the electronic spectra. Fabrizzi and co-workers
+
[
b] D. Zhang, Dr. A. Martinez, K. Jamieson, Dr. J.-P. Dutasta
also described the deprotonation of a benzimidazolium unit
Laboratoire de Chimie, ꢀcole Normale Supꢁrieure de Lyon
À
by F in which the UV changes during titration experiments
4
6, Allꢁe d’Italie, 69364 Lyon (France)
were fully consistent with the formation of a carbene species.
However, this UV change (below 320 nm) does not allow the
E-mail: alexandre.martinez@ens-lyon.fr
+
[
] These authors contributed equally to this work.
À
naked-eye to detect F and the fluorescence was not involved
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201404806.
in this sensor.
Chem. Eur. J. 2014, 20, 17161 – 17167
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In this research we hypothesized that a receptor combining
an imidazolium-like unit with an appropriate optically respon-
sive fragment should provide an original visible optical sensor
tion in CH OH and CH OH/H O, respectively. As shown in
3
3
2
Scheme 1, the acidic C(2)ÀH of perimidiniums in both 1 and 2
À
À
form strong hydrogen bonds with the counterions Cl and Br ,
respectively (2.37 and 2.59 ꢁ), in the solid state, indicating
their possible deprotonated behaviour in the presence of the
À
À
for F by F -deprotonated carbene formation. The imidazolium
analogues, perimidinium derivatives (Scheme 1), appear as
ideal candidates since: 1) like the imidazolium unit, the C(2)ÀH
À
basic F in solution.
À
of perimidinium is easily deprotonated by F to form a carbine
due to its inborn acidity, 2) the relatively high degree of p-con-
jugation of the aromatic rings could give rise to a visible pho-
tophysical property, and 3) more importantly, the anion-bind-
ing site directly embedded into the fluorophore should make
the signalling response of the sensor more sensitive to both
Fluorescence and absorption sensing properties
The anion-binding performance of chemodosisensors 1 and 2
À
towards F was first evaluated by the fluorescent changes of
5 mm chemodosisensor upon addition of the tetrabutylammo-
[11]
À
the anion interaction and also to the carbene formation.
nium (TBA) F salt in DMSO. As shown in Figure 1a, upon addi-
À
Herein, we report the synthesis of two perimidinium-based
tion of F , a drastic fluorescence enhancement of chemodosi-
À
chemodosisensors 1 and 2 for the detection of F . The interac-
sensor 1 at about 400 nm was observed and continued to in-
À
tion mechanism was carefully investigated and it was shown
crease until 3 equiv of F was added. The solution of chemo-
À
that a deprotonation reaction occurred between F and the
dosisensor 1 also exhibited a vivid blue fluorescent colour
À
perimidinium of 1/2, leading to the carbene species. This spe-
cies then reacted quickly with water to give an optically
changed compound, which immediately elicited a colorimetric
under UV lamp after adding F . Based on the titration curve,
À
the actual detection limit of 1 towards F was lower than
1.0 mm in DMSO. The fluorescent changes of chemodosisensor
À
À
À
À
À
À
and turn-on fluorescent response of F .
1 induced by other anions such as Cl , Br , I , H PO , AcO ,
2 4
À
À
HSO4 and ClO4 were less obvi-
ous or even negligible (Figure S1
in the Supporting Information).
Similar to chemodosisensor 1,
À
the addition of F to the chemo-
dosisensor 2 also led to the
most significant fluorescence en-
hancement at 402 nm among all
the tested anions with an actual
detection limit of 5.0 mm (Fig-
ure S2B in the Supporting Infor-
mation). It is interesting to note
that although the basicity of
À
AcO is a little stronger than
À [12]
that of F , the fluorescent in-
À
crease induced by F for both of
the two chemodosisensors was
much larger than that induced
À
by the same equivalent of AcO .
Scheme 1. The synthetic routes of chemodosisensors 1 and 2, and their crystal structures. For the crystals, nonaci- This could be attributed to the
dic hydrogen atoms and solvent molecules have been omitted for clarity; dashed lines represent hydrogen bonds
2.37 and 2.59 ꢁ for 1 and 2·H O, respectively).
À
higher stability of the HF spe-
2
(
2
À
cies than H(CH COO)2 , promot-
3
ing the formation of N-heterocy-
[5a]
clic carbene.
À
In terms of the
Results and Discussion
sensing performance towards F , chemodosisensor 1 exhibited
a lower detection limit, but the superior selectivity displayed
by chemodosisensor 2 cannot be neglected (Figures S1 and
S2A in the Supporting Information). The different anion sens-
ing performances of chemodosisensors 1 and 2 result partly
from the consequence of the electronic and steric effects of
the substituents of perimidinium and from the difference of
Synthesis and characterization
The synthetic routes used to obtain chemodosisensors 1 and 2
are illustrated in Scheme 1. Compound 3 was first synthesized
by the reaction of perimidine with benzyl chloride in the pres-
ence of NaH in CH CN, followed by a reaction with another
3
[11e]
1
equiv of benzyl chloride under reflux to afford the desired
the counterions.
It is also worth mentioning that unlike
product 1 with an overall yield of 50%. Chemodosisensor 2
was prepared by similar procedures with 70% overall yield.
Direct evidence for the successful synthesis can be seen in the
X-ray crystal structures of 1 and 2, obtained by slow evapora-
most of the reported turn-on fluorescent sensors, the sensors
developed here showed almost “0” background fluorescence
as no fluorescent colour could be observed when the sensors
were irradiated under UV lamp on their own. The lower signal
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ous media (DMSO/H O=9:1, v/v). As shown in Figures S5 and
2
S6 in the Supporting Information, both of 1 and 2 exhibited
similar fluorescent behaviours (turn-on) and absorption
À
changes towards F as those in pure DMSO. This result implies
that chemodosisensors 1 and 2 have the ability to be fluores-
À
cent and colorimetric sensors of F in a more polar environ-
À
ment. It cannot be ignored that more equivalents of F were
needed to saturate the obvious spectroscopic changes of che-
modosisensors 1 and 2 in the more competitive solvent. This is
because water could form hydrogen bonds with both the peri-
À
midinium of 1/2 and F , inhibiting the interactions between
À
them, and rendering the F -induced deprotonation behaviour
of perimidinium unfavourable.
Investigation of the interaction mechanism
In order to investigate the interaction mechanism between
À
1
chemodosisensor 1/2 and F , H NMR titration experiments
were performed in [D ]DMSO. As shown in Figure 2a, when
6
1
equiv of TBAF was added to chemodosisensor 1, the peak of
the C(2)ÀH shifted upfield from 10.05 to 9.87 ppm, which can
be attributed to anion exchange from Cl to F . Indeed, Hu
À
À
[14]
et al. also observed an upfield shift of the C(2)ÀH for imida-
À
À
zolium salts when the Cl anion was replaced by F . Further
addition of TBAF induced no change in the proton chemical
shift of the spectra. However, a gradual decrease of the signals
of the C(2)ÀH in perimidinium (at 9.87 ppm), methylene pro-
tons (at 5.38 ppm) and some aromatic peaks (6.90–7.72 ppm)
of 1 was observed along with the appearance of a new set of
signals. In particular, an evident peak at about 14.50 ppm cor-
Figure 1. a) Fluorescence titrations of 5 mm chemodosisensor 1 with TBAF
excited at 352 nm in DMSO. Insets: the fluorescence intensity at 400 nm as
a function of added TBAF and fluorescent colour of 1 in the absence and
presence of TBAF under UV lamp excited at 365 nm. b) Absorption titrations
of 50 mm chemodosisensor 1 with TBAF in DMSO. Insets: the absorbance at
353 nm as a function of added TBAF and the solution colour of 1 in the ab-
sence and presence of TBAF.
À
[5a]
responding to HF2 appeared, indicating the deprotonation
of perimidinium. A pure spectrum was obtained at the end of
À
noise of the background is very useful for improving the de-
tection sensitivity and is also convenient for bioimaging.
The changes in the absorption spectra of chemodosisensors
titration when 8.0 equiv of F was added. The disappearance
of the initial signals and the presence of new peaks indicate
À
that a chemical reaction induced by F may have occurred.
13
1
and 2 upon addition of TBAF in DMSO were also examined.
Next, two C NMR spectra of chemodosisensor 1 before and
À
As shown in Figure 1b, the chemodosisensor 1 displayed
strong absorption bands at 315 and 329 nm and a weak band
at about 400 nm, which corresponded to the yellow solution.
after the addition of 8.0 equiv of F (the end of titration) were
measured, as shown in Figure 2b. No variation was observed
in the number of carbon (12) in chemodosisensor 1 before and
À
À
Consistent with the fluorescence data, 3 equiv of F led to the
after adding F , indicating that the symmetry of the skeleton
most remarkable changes of the absorption spectra compared
to the other tested anions. A new absorption band centred at
was retained after reaction. However, the position of each
carbon shifted obviously: for example, the C in methylene
groups shifted upfield from 54.6 to 51.6 ppm. Most significant-
ly, the characteristic peak of C(2) at 154.7 ppm in perimidinium
disappeared and a peak at 91.4 ppm corresponding to a satu-
rated carbon was observed instead. Considering the possibility
3
4
53 nm significantly increased while the peaks at 315 and
À
00 nm gradually decreased with the addition of F (Figure 1b
and Figure S3 in the Supporting Information). The appearance
of two well-defined isosbestic points at 332 and 374 nm, indi-
cates the formation of a new species after interaction (Fig-
À
of N-heterocyclic carbene formation generated by F deproto-
[
13]
[10b,11,15]
ure 1b). The colour of the solution also changed from yellow
to colourless, which could be easily observed by the naked
eye. Similar anion-induced absorption behaviour was also ob-
nation and the instability of carbene towards water,
we
[11a,16]
proposed the generation of the carbinol 7a.
The structure
1
of 7a is fully consistent with the NMR data: for the H NMR
À
served for the chemodosisensor 2: F gave rise to the stron-
spectrum at the end of titration, the new proton peak at
gest spectral changes and obvious solution colour change (Fig-
ure S4 in the Supporting Information). All these results show
that both 1 and 2 could be used not only as turn-on fluores-
5.82 ppm is assigned to H ’ in compound 7a, and the signals
a
at 6.27 ppm and in the range of 6.98–7.43 ppm correspond to
the aromatic protons. One particular characteristic feature is
the appearance of methylene protons as a pair of diastereo-
À
cent sensors but also as efficient colorimetric receptors for F .
To broaden the practical applicability, we further investigat-
topic doublets (H ’) at about 4.57 ppm. The peak at about
6.62 ppm, which was quite broad and only appeared during
b
À
ed the sensing of F with chemodosisensors 1 and 2 in aque-
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spectrum of 7a for the same
NMR tube was fully converted to
two other sets of signals with
a 1:1 ratio derived from the inte-
gration of the peak (Figure S8 in
the Supporting Information). We
attempted to separate the two
new products by column chro-
matography and finally isolated
the perimidone 8a and dihydro-
perimidine 9a (yields: 32 and
2
9%, respectively; Scheme 2),
1
which were characterized by H
13
and C NMR spectroscopy and
HR-MS (Figures S9 and S10 in
the Supporting Information). The
structure of 9a was also con-
firmed by its X-ray crystal struc-
ture (Scheme 2). These results in-
dicate that the carbinol 7a was
simultaneously reduced and oxi-
dized to form two different
products, and thus a redox dis-
[16a,17]
proportionation occurred.
It
is interesting to note that the di-
hydroperimidine 9a was colour-
less and non-fluorescent, while
the colourless perimidone 8a
was strongly fluorescent (Fig-
ure S11 in the Supporting Infor-
mation). With the same method,
two similar products 8b and 9b
from the mixture of chemodosi-
sensor 2 and TBAF were also ob-
tained (Figures S12 and S13 in
the Supporting Information).
Based on the results above,
a mechanism for the detection
À
of F with chemodosisensor 1/2
1
13
Figure 2. a) H NMR titrations of chemodosisensor 1 (5 mm) with TBAF in [D
6
]DMSO. b) C NMR spectra of chemo-
6
]DMSO.
was proposed. As illustrated in
dosisensor 1 (5 mm) in the absence and presence of 8.0 equiv of TBAF in [D
À
Scheme 2, the counterion Cl of
À
1
is initially exchanged by F
(
process I), followed by deproto-
the titration, could be assigned to the C(2)ÀOH. The new peak
nation to form a carbene (process II), which subsequently
reacts with water to generate the colourless and fluorescent
carbinol 7a (process III), and finally the intermediate 7a under-
goes a redox disproportionation to give the fluorescent 8a
and non-fluorescent 9a (process IV). The insertion reaction and
disproportionation that occur in processes III and IV, respec-
tively, are possible since Pozharskii and co-workers also ob-
served that in the presence of both the base and water, the
perimidinium salt could form a carbinol intermediate to give
13
at 91.4 ppm in the C NMR spectrum can be attributed to the
C(2) of the carbinol 7a. Moreover, the integration of each peak
1
in H NMR spectrum and the position of the signals in the
13
C NMR spectrum are also in good agreement with the pro-
posed product 7a. The solution of carbinol 7a in the NMR
tube was almost colourless, but strong blue fluorescence could
be seen under UV lamp (Figure 2a). Similar titration results of
1
13
H NMR and C NMR spectra for chemodosisensor 2 with TBAF
[16a]
were also observed (Figure S7 in the Supporting Information),
and the product 7b was thus proposed.
However, it was found that compound 7a was unstable
even in the airtight NMR tube, and it gradually decomposed
into two other products monitored by TLC. After 24 h, the
the products of perimidone and dihydroperimidine.
Forma-
tion of 10a after adding TBAF in process V as reported by
[10a]
Yoon et al.
is impossible in this case since, if this occurred,
the peak of H ’ should be split into a doublet with a large cou-
a
[18]
pling constant due to the neighbouring F atom (Figure 2a).
Chem. Eur. J. 2014, 20, 17161 – 17167
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À
Scheme 2. The proposed mechanism for the detection of F with the chemodosisensor 1 and the crystal structure of the product 9a. For the crystal, hydro-
gen atoms have been omitted for clarity. See text for details of processes I–VII.
Further insights into the proposed mechanism were ob-
tained from another set of experiments. Instead of TBAF, AgF,
have also observed the easy dimerization of perimidine car-
bene at room temperature and a series of crystal structures of
the analogues of 11 a have been described. The free carbine
6a was also successfully trapped by elemental sulfur in situ
through a reaction between 6a and sulfur as shown in
Scheme 2 (process VII): addition of 4 mmol sulfur to the mix-
ture of 0.5 mmol 1 and 1 mmol AgF in THF led to the forma-
tion of the thiourea 12a which was isolated by column chro-
matography with a yield of 13% (Figure S15 in the Supporting
Information). This clearly demonstrates the formation of the
À
which is also very soluble in DMSO, was chosen as the F
1
+
source for H NMR titration, since the Ag would precipitate
À
with Cl in solution to demonstrate the “real” anion exchange
À
À
from Cl to F (for detecting the species 5a). Furthermore, the
solid AgF does not contain crystal water. This important fea-
ture may restrain the reaction of carbine 6a with water and fi-
nally result in its dimerization to form the olefin 11 a (process
VI) by the Wanzlick equilibrium reaction, which is often regard-
ed as an undesired side reaction for achieving a stable carbine
[11d,20]
free carbine 6a.
All of these additional experiments un-
[
11b,d,19]
1
À
solution.
Thus, the H NMR titration of chemodosisensor
equivocally confirm the proposed sensing process between F
1
with AgF in [D ]DMSO was performed, as shown in Fig-
and the perimidinium-based chemodosisensor 1/2.
6
ure S14A in the Supporting Information. As expected, upon ad-
dition of AgF, a large amount of precipitate corresponding to
AgCl appeared. In terms of the spectra, the C(2)ÀH of perimidi-
nium displayed an upfield shift up to 4.0 equiv of AgF, sup-
porting the anion-exchange process I. Further addition of AgF
gave rise to the extinction of some initial peaks and the ap-
pearance of a new set of signals. The evident peak at about
Conclusion
In summary, we have designed and synthesized two new mo-
noperimidinium-based anion receptors 1 and 2, which dis-
played excellent fluorescent and colorimetric properties for the
À
sensing of F in DMSO. In particular, a remarkable enhance-
À
[5a]
14.0 ppm corresponding to HF2 was also observed. At the
ment of fluorescence from “0” background signal was ob-
served. An original mechanism was utilized, accounting for the
unique spectroscopic behaviours of chemodosisensors 1 and 2
end of titration (96.0 equiv of AgF), the position and integra-
1
13
tion of each peak in H NMR as well as the C NMR spectrum
À
À
(
Figure S14B in the Supporting Information) were in accord
towards F : F was found to deprotonate the perimidinium
[
11b]
[11d]
with the olefin 11 a. Patrick et al.
and Verlinden et al.
unit, leading to the formation of carbine 6a/b which then re-
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acted with water to give the fluorescent carbinol 7a/b. The in-
termediate compound 7a/b then disproportionated to gener-
ate the fluorescent 8a/b and the non-fluorescent 9a/b. We be-
lieve that these unprecedented findings for perimidinium de-
rivatives may lead to a new class of receptors for anions in the
future, and their applications to organo- or organometallic cat-
alysis involving the N-heterocyclic carbene with a six-mem-
bered ring could also be expected.
tion of the reaction, a large amount of precipitate appeared which
was filtered out and washed thoroughly with CH CN (3ꢂ50 mL)
3
and diethyl ether (3ꢂ50 mL) to give the chemodosisensor 2
1
(
1.80 g, 79%). H NMR (500 MHz, [D ]DMSO): d=0.96 (t, J=10.0 Hz,
6
6
4
1
1
H), 1.42–1.47 (m, 4H), 1.77 (t, J=10.0 Hz, 4H), 3.99 (t, J=10.0 Hz,
H), 7.12 (d, J=10.0 Hz, 2H), 7.51 (t, J=10.0 Hz, 2H), 7.61 (d, J=
13
0.0 Hz, 2H), 9.08 ppm (s, 1H); C NMR (125 MHz, [D ]DMSO): d=
6
53.20, 135.01, 132.18, 128.87, 124.04, 121.79, 108.38, 51.55, 28.28,
+
19.47, 14.04 ppm; HR-MS C H N [MÀBr], calcd 281.2012, found
19
25
2
2
81.2031.
Experimental Section
X-ray structure determination
Materials and instrumentation
X-ray diffraction data from suitable crystals were collected on
a Bruker Apex-II CCD area detector equipped with graphite-mono-
chromated MoKa radiation (l=0.71073 ꢁ). Empirical absorption cor-
All chemicals were purchased from Sinopharm Chemical Reagent
Co. (Shanghai, China) unless specified otherwise. The stock solu-
[21]
À
À
À
rections were applied using SADABS program.
The structures
tions of anions were prepared from TBAX (where X=F , Cl , Br ,
À
À
À
À
À
1
13
were solved by the direct method and refined by the full-matrix
I , ClO , AcO , HSO and H PO ). H NMR and C NMR spectra
4
4
2
4
2
least-squares method on F , with all non-hydrogen atoms refined
were recorded using Me Si as an internal standard on a Bruker
4
[22]
with the anisotropic thermal parameters.
All the hydrogen
Avance DRX 500 FT NMR spectrometer operating at 400/500 MHz
1
13
atoms attached to carbon atoms were placed in calculated posi-
tions and refined using the riding model. All calculations were car-
ried out with the SHELXTL software. A summary of the crystallo-
graphic data and refinement parameters are shown in Table S1 in
the Supporting Information.
for H NMR spectra and 100/125 MHz for C NMR spectra. Fluores-
cence spectra were obtained with a Hitachi F-4500 spectrometer.
UV/Vis spectra were measured on a Varian Cary-100 UV spectro-
photometer. HRMS spectra were acquired using an AB SCIEX 4800
plus MALDI-TOF reflector.
Fluorescence spectroscopic titration
Synthesis and characterization
The solution of chemodosisensor 1/2 (2 mL, 5 mm) was placed in
a cuvette, and then predetermined equivalents of a concentrated
anion solution (0.5 or 5 mm) were added stepwise with a syringe.
As a very small volume of guest solution was added, the final
amount of the solution was almost unchanged (2 mL). The mixed
solution was incubated for 30 s and then irradiated at a specific
wavelength. The corresponding emission values during titration
were then recorded.
1
-Butyl-perimidine (4): Perimidine (1.68 g, 10 mmol) in 20 mL
CH CN was added dropwise to a suspension of NaH (60% in miner-
al oil, 0.80 g, 20 mmol) in 5 mL CH CN at 08C. 1-Bromobutane
3
3
(
1.64 g, 12 mmol) was then added to the suspension. The tempera-
ture of the reaction was maintained at 08C for 1 h and allowed to
warm to ambient conditions over the course of 24 h. After the ad-
dition of 10 mL water, the mixture was stirred for 10 min and ex-
tracted with CHCl (3ꢂ50 mL). The organic phase was washed with
3
water (3ꢂ50 mL), dried with anhydrous Na SO , and evaporated
2
4
under reduced pressure. A brown oil was finally obtained (1.94 g,
1
H NMR spectroscopic titration
1
8
9%). H NMR (400 MHz, [D ]DMSO): d=0.92 (t, J=7.4 Hz, 3H),
6
1
.34–1.39 (m, 2H), 1.58–1.63 (m, 2H), 3.63 (t, J=7.2 Hz, 2H,) 6.32
The solution of chemodosisensor 1/2 (0.5 mL, 5 mm) was placed in
an NMR spectroscopy tube, and then predetermined equivalents
of a concentrated guest solution were added stepwise with a sy-
ringe. As a very small volume of guest solution was added, the
final amount of the solution was almost unchanged (0.5 mL). The
mixed solution was incubated for 30 s and then the measurement
(
7
d, J=7.5 Hz, 1H), 6.64 (d, J=7.2 Hz, 1H), 7.06–7.11 (m, 2H), 7.14–
.21 (m, 2H), 7.47 ppm (s, 1H).
Chemodosisensor 1: Perimidine (0.68 g, 4 mmol) in 20 mL CH CN
was added dropwise to a suspension of NaH (60% in mineral oil,
0
chloride (2.03 g, 16 mmol) was added to the suspension. The tem-
perature of the reaction was maintained at 08C for 1 h and allowed
to warm to ambient conditions. After 24 h, the precipitate was fil-
tered out and the filtrate was heated to 908C for another 24 h
3
.32 g, 8 mmol) in 10 mL CH CN at 08C under N . Then benzyl
3
2
1
of H NMR spectroscopy of the solution was carried out.
Acknowledgements
under N . After the reaction was complete, a large amount of pre-
2
cipitate appeared which was filtered out and washed thoroughly
The authors are grateful for the financial support of the Na-
tional Natural Science Foundation of China (21072061,
21273078) and the Shanghai Leading Academic Discipline Proj-
ect (B409).
with CH CN (3ꢂ50 mL) to give the chemodosisensor 1 (0.77 g,
3
1
5
8
4
1
1
0%). H NMR (400 MHz, [D ]DMSO): d=5.40 (s, 4H), 6.94 (d, J=
6
.0 Hz, 2H), 7.43 (m, 8H), 7.56 (d, J=8.0 Hz, 2H), 7.72 (d, J=8.0 Hz,
13
H), 10.05 ppm (s, 1H); C NMR (100 MHz, [D ]DMSO): d=154.67,
6
34.21, 132.79, 131.47, 128.90, 128.42, 128.10, 127.46, 123.78,
21.33, 108.98, 54.64 ppm; elemental analysis calcd (%) for
Keywords: colorimetric sensors
·
fluorescent sensors
·
C H ClN (384.90): C 78.01, H 5.50, N 7.28; found: C 77.97, H 5.46,
2
5
21
2
fluoride · N-heterocyclic carbine · perimidinium
+
N 7.01; HR-MS C H N [MÀCl], calcd 349.1699, found 349.1693.
2
5
21
2
Chemodosisensor 2: Compound 4 (1.12 g, 5 mmol) was stirred in
0 mL CH CN at 908C under N for 10 min, and then 1-bromobu-
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tane (2.74 g, 20 mmol) in 6 mL CH CN was added in one portion.
3
The mixture was stirred at 908C under N2 for 48 h. After comple-
Chem. Eur. J. 2014, 20, 17161 – 17167
www.chemeurj.org
17166
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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Published online on October 24, 2014
Chem. Eur. J. 2014, 20, 17161 – 17167
www.chemeurj.org
17167
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim