Phthalocyanine-based fluorescent chemosensor for the sensing of Zn (II) in dimethyl sulfoxide-acetonitrile

Article abstract of DOI:10.1007/s10847-011-0012-9

A tetra-substituted phthalocyanine based on 4-[2-(4-nitrophenoxy)ethoxy] phthalonitrile carrying nitrophenyl group for the sensing of Zn²⁺ has been prepared and characterized by elemental analysis, FT-IR, ¹H and ¹³C0020NMR, and MS spectral data. The sensing of Zn²⁺ is based on the fluorescence quenching of Pc. Both absorbance and fluorescence spectra of ZnPc exhibit distinct changes in visible region in response to treatment with Zn²⁺ ion in dimethyl sulfoxide. The fluorescence spectrum of the ligand showed quenching in the intensity of the signal at 688 nm for Zn²⁺. The complex composition of ZnPc was found 1:1 by means of spectrophotometric and spectrofluorimetric titration data. The spectrofluorimetric method showed good sensitivity for Zn2⁺ with linear range and detection limit of 4.0 9 10^-6-4.4 9 10^-5 and 2.49 10^-7 M, respectively.

Full text of DOI:10.1007/s10847-011-0012-9

J Incl Phenom Macrocycl Chem (2012) 72:443–447
DOI 10.1007/s10847-011-0012-9
ORIGINAL ARTICLE
Phthalocyanine-based fluorescent chemosensor for the sensing
of Zn (II) in dimethyl sulfoxide-acetonitrile
•
•
˘
˘
Yasemin C¸ aglar Nurhan Gu¨mru¨kc¸u¨oglu
•
Ece Tugba Saka Mirac¸ Ocak Halit Kantekin
•
•
˘
¨
Ummu¨han Ocak
Received: 5 January 2011 / Accepted: 29 June 2011 / Published online: 23 July 2011
Ó Springer Science+Business Media B.V. 2011
Abstract A tetra-substituted phthalocyanine based on
4-[2-(4-nitrophenoxy)ethoxy]phthalonitrile carrying nitro-
phenyl group for the sensing of Zn2? has been prepared
containing extended p-electron delocalisation. Most syn-
thetic organic pigments in the blue to green color range are
Pc derivatives. They also show some properties such as low
solubility, high thermal stability and electrochromism,
which allow them to be utilized in technological applica-
tions [2–5], such as optical data storage, nonlinear optics,
gas sensor, laser technology, catalysis and photodynamic
therapy [6, 7].
and characterized by elemental analysis, FT-IR, 1H and 13
C
NMR, and MS spectral data. The sensing of Zn2? is based
on the fluorescence quenching of Pc. Both absorbance and
fluorescence spectra of ZnPc exhibit distinct changes in
visible region in response to treatment with Zn2? ion in
dimethyl sulfoxide. The fluorescence spectrum of the
ligand showed quenching in the intensity of the signal at
688 nm for Zn2?. The complex composition of ZnPc was
found 1:1 by means of spectrophotometric and spectroflu-
orimetric titration data. The spectrofluorimetric method
showed good sensitivity for Zn2? with linear range
and detection limit of 4.0 9 10-6–4.4 9 10-5 and 2.49
10-7 M, respectively.
It is well known that phthalocyanines and complexes
strongly absorb light in the red portion of the visible
spectrum, thus characteristically these dyes are blue or
greenish [8, 9]. Phthalocyanines have two absorption
bands, a strong Q band in the red region (600–700 nm) and
a medium strength Soret band in UV region (350 nm). Due
to the attractive property of high fluorescence efficiency in
red wavelength region, phthalocyanines are potentially
useful as wavelength transfer devices absorbing the short
wavelength and emitting longer red wavelengths.
Keywords Phthalocyanine Á Fluorescence spectroscopy Á
Complex composition Á Zn2? ion Á Chemosensor
Phthalocyanines are suitable materials for the develop-
ment of chemical sensors, such as electronic conductance
sensors, mass-sensitive sensors, surface acoustic-wave
(SAW) sensors, and optical sensors. Gas sensitivity of some
metal phthalocyanines is known well [10, 11]. Recently,
functional phthalocyanines have been of particular interest
because of their capability of binding multiple metal ions
and hence providing metal sensing in solution [12–14].
Recently, our efforts have been focused on the prepara-
tion, characterization and electrochemical measurements of
peripherally substituted phthalocyanines having some elec-
tron donor or acceptor groups [15]. In this study, we report a
new type of tetra substituted metal-free phthalocyanine and
the photophysical changes upon complexation of the ligand
with Zn?2. Our aim is to disclose the effect of nitrophenyl
groups located peripherally on the phthalocyanine frame on
the fluorescence properties of the metal-free phthalocyanine
Introduction
Metal-free phthalocyanines (H2Pc), have become the focus
of intense research interest due to their interesting prop-
erties for diverse applications [1]. These macrocyclic
ligands have a chromophoric nature due to their structure
¨
˘
Y. C¸ aglar Á E. T. Saka Á M. Ocak Á H. Kantekin Á U. Ocak (&)
Department of Chemistry, Faculty of Sciences, Karadeniz
Technical University, 61080 Trabzon, Turkey
e-mail: ummuhanocak@yahoo.com
˘
N. Gu¨mru¨kc¸u¨oglu
Vocational School of Health Science, Karadeniz Technical
University, 61080 Trabzon, Turkey
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J Incl Phenom Macrocycl Chem (2012) 72:443–447
during complexation. The complex composition and
complex stability constant were determined by using spec-
trophotometric and spectrofluorimetric titration in DMSO-
acetonitrile (1/1).
dissolved in 20 mL DMF under argon atmosphere in a
Schlenk system connected to a vacuum line at room tem-
perature. Dry K2CO3 (5.36 g, 38.88 mmol) was added to this
yellow solution in equal portions for 2 h. The brown solution
was refluxed under argon atmosphere at 50 °C for 72 h. The
reaction mixture was poured on ice (200 g) and this mixture
was stirred at room temperature for 24 h. At the end of this
period, the reaction mixture was filtered and rinsed with
diethyl ether and then with water. The resultant yellow–green
solid was dried in vacuo with P2O5. The yellow solid was
obtained by crystallization via ethyl alcohol. Yield (% 52),
Experimental
Chemicals
DMSO from Merck (spectrometric grade) was the solvent
for absorption and fluorescence measurements. Zinc per-
chlorate purchased from Acros was of the highest quality
available and vacuum dried over blue silica gel before use.
1
M.p: 129–132 °C. H NMR (200 MHz, CDCl3): d = 8.23
(d, 2H, Ar–H), 8.09 (d, 1H, Ar–H), 7.85 (s, 1H, Ar–H), 7.54
(d, 1H, Ar–H), 7.21 (d, 2H, Ar–H), 4.53 (m, 4H,
CH2-O) ppm. 13C NMR (200 MHz, CDCl3): d = 163.35,
161.74, 142.24, 135.56, 126.22, 126.16, 119.94, 119.77,
117.74, 115.78, 115.40, 114.80, 108.15, 67.43, 66.77 ppm.
IR (KBr): m/cm-1 = 3084 (CH aromatic), 2972–2923 (CH2
aliphatic), 2232 (C:N), 1595, 1564, 1509, 1493, 1343,
1298, 1266, 1255, 1178, 1110, 968, 927, 841, 522 cm-1. MS
(FAB?): (m/z) = 309 [M]?. C16H11N3O4 (390): calcd. C
62.14, H 3.58, N 13.58; found C 60.04, H 3.12, N 12.88.
Apparatus
IR spectra were recorded on a Perkin-Elmer 1600 FTIR
spectrophotometer using KBr pellets. 1H and 13C mea-
surements were performed on a Varian 200 A spectrome-
ter, using DMSO-d6 with TMS as the internal reference.
Elemental analysis was performed on Costech 4010 CHNS
instrument. Mass spectra were measured with a Micromass
Quatro LC-MS/MS spectrometer. UV–Vis spectra were
recorded on a Thermo Evolution 60 model spectropho-
tometer with the use of standard 1-cm quartz cell. Fluo-
rescence study was performed on a Photon Technologies
International Quanta Master Spectrofluorimeter.
Synthesis of ligand (4)
The phthalonitrile derivative (3) (250 mg, 0.81 mmol), dry
n-pentyl alcohol (2.0 mL) and three to four drops of DBU
was added in a standard Schlenk tube. The reaction mixture
was degassed and heated at reflux (160 °C) for 18 h. Then,
diethyl ether (2–3 mL) was added into the reaction mix-
ture, which cooled at room temperature. The precipitated
green solid was filtered off and dried. The reaction product
was purified by column chromatography on silica gel
[chloroform/methanol/pyridine (100:10:1)]. The combined
solvents were evaporated and dark green product was
obtained and then dried in vacuo. Yield: 117 mg (47%).
M.p. [ 300 °C. 1H NMR (200 MHz, DMSO-d6): d = 7.64
(m, 8H, Ar–H), 7.43 (m, 8H, Ar–H), 7.21 (m, 12H, Ar–H),
4.16 (m, 16H, CH2O) ppm. IR (KBr): m/cm-1 = 3292 (N–
H), 3060 (CH aromatic), 2923–2851 (CH2 aliphatic), 1610
Measurements
Stock solution of the ligand was prepared in DMSO and the
ligand solutions used for all spectrometric and spectroflu-
orometric titrations were prepared from these solutions by
dilution. Any changes in titration experiments were
recorded upon addition of perchlorate of the respective
metals to its DMSO solution, while the ligand concentra-
tion was kept constant (4 9 10-5 M). The solution of the
metal perchlorates was prepared in acetonitrile. The con-
centration of metal perchlorates was between 4 9 10-5
and 9.6 9 10-5 M. Fluorescence emission spectra were
recorded in the range 678–800 nm.
(C=N), 1593–1508–1341 (NO2), 790–751 (C–N) cm-1
.
UV/Vis (Pyridine): kmaks(loge) nm = 317 (5.02), 608
(4.47), 641 (4.55), 668 (4.85), 707 (4.92). MS (FAB?): (m/
z) = 1238 [M]?. C64H46N12O16 (1238): calcd. C 62.04, H
3.74, N 13.56; found C 61.01, H 2.98, N 12.83.
The stoichiometry of the complex and the complex
stability constant were determined according to molar-ratio
method [16] and Valeur’s method [17], respectively.
Synthesis
Results and discussion
Synthesis of (3)
Characterization of compounds 3 and 4
The precursor 2-(4-nitrophenoxy)ethanol (1) was purchased
from Merck. 2-(4-nitrophenoxy)ethanol (2 g, 10.93 mmol)
and 4-nitrophthalonitrile (2) (1.89 g, 10.93 mmol) were
Starting from 2-(4-nitrophenoxy)ethanol (1) and 4-nitropht-
halonitrile (2), the general synthetic route for the synthesis of
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J Incl Phenom Macrocycl Chem (2012) 72:443–447
445
new phthalonitrile (3) is given in Scheme 1. The new pht-
halonitrile 3 was obtained with a yield of 52%. The IR
spectra of the phthalonitrile compound (3) clearly indicate
the presence of C:N group by the intense stretching bands
at 2232 cm-1. Disappearance of the sharp O–H stretching
vibration belonging to compound (1) confirmed formation of
phthalocyanine ring is an N–H stretching at 3292 cm-1
.
The IR spectra of metal-free (4) and phthalonitrile (3) are
very similar, except for these m (NH) vibrations of the inner
phthalocyanine core in the metal-free molecule (4). In the
1H NMR spectrum of (4), the typical shielding of inner core
protons couldn’t be observed due to the probable strong
aggregation of the molecules [18]. The aromatic protons
appear at 7.64 (m, 8H, Ar–H), 7.43 (m, 8H, Ar–H), 7.21 (m,
12H, Ar–H) ppm. In the mass spectra of metal-free phtha-
locyanine (4), the molecular ion peak was observed at m/z
1238 [M]?. The elemental analysis confirmed the presence
of the desired metal-free phthalocyanine (4).
1
the new phthalonitrile (3). The H NMR spectra of pht-
1
halonitrile compound 3 was recorded in CDCl3. In the H
NMR spectrum of compound (3), OH group of 2-(4-nitro-
1
phenoxy)ethanol (1) disappeared as expected. In the H
NMR spectrum of phthalonitrile (3), the aromatic protons
appear at 8.23 (d, 2H, Ar–H), 8.09 (d, 1H, Ar–H), 7.85 (s, 1H,
Ar–H), 7.54 (d, 1H, Ar–H), 7.21 (d, 2H, Ar–H) ppm. The 13
C
NMR spectrum of compound (3) indicates the presence of
nitrile carbon atom at d = 115.78, 115.40 ppm. In the mass
spectra of phthalonitrile compound (3), the molecular ion
peak was observed at m/z 309 [M]?. The elemental analysis
confirmed the presence of the desired compound (3).
Absorption spectra
Figure 1 shows the absorption and emission spectra of the
ligand (4). The absorption spectra of the ligand (4) in
DMSO-acetonitrile (1/1) display two absorption bands, a Q
band in the red region (655 nm) and a Soret band in UV
region (340 nm), which is characteristic to phthalocyanines
[19]. Molar absorption coefficients are 2.5 9 104 and
7.59103 cm-1 M-1 for these wavelengths, respectively.
The change in the absorption spectra of the ligand (4)
with increasing concentrations of Zn?2 in the range
8 9 10-6 and 1 9 10-4 is shown in Fig. 2. The decrease
in absorbance at 676 nm provided the determination of the
Cyclotetramerization of the phthalonitrile derivative 3 to
the metal-free phthalocyanine (4) was accomplished in
n-pentanol in the presence of a few drops of 1,8-diazabi-
cyclo[5.4.0]undec-7-ene (DBU) as a strong base at 160 °C
in sealed tube and the yield was 47%. Cyclotetramerization
of the dinitrile (3) to the metal-free phthalocyanine (4) was
confirmed by the disappearance of the sharp C:N vibration
at 2232 cm-1. IR band characteristic of the metal-free
Scheme 1 Synthetic pathway
to the new phthalocyanine used
in this study
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J Incl Phenom Macrocycl Chem (2012) 72:443–447
1
0,8
0,6
0,4
0,2
0
1,2
1
0,8
0,6
0,4
0,2
0
0
0,00001
0,00002
0,00003
0,00004
0,00005
255
355
455
555
655
755
Wavelength (nm)
[Zn2+]
Fig. 4 Fluorescence intensity of the ligand (4) versus Zn2? concen-
tration for the spectrofluorimetric titration. Wavelength: 681 nm,
Fig. 1 The absorption spectra of the ligand (4) in DMSO-acetonitrile
(1/1). Ligand concentration is 4.0 9 10-5
M
ligand concentration = 4 9 10-5
M
[M]/][L]
0,2
0,4
0,45
Fluorescence spectra
1
0,35
0,6
0,8
1,0
1,2
1,4
1,6
1,8
2,0
0,25
The complex formation was monitored by the effect of
gradual addition of zinc perchlorate to the solution of the
ligand (4). The change in the fluorescence spectra of
4.0 9 10-5 M of ligand (4) with increasing concentrations
of Zn?2 in the range 8 9 10-6 and 4 9 10-4 M is shown
in Fig. 3. The successive decrease of the emission intensity
with addition of Zn2? was observed for the fluorimetric
titration. Molar ratio plot, which was used to determine the
complex composition for Zn2?, clearly shows the forma-
tion of a 1:1 (M:L) complex for the ligand (4) with Zn2?, as
shown in Fig. 3 (inset above). The values of I at 688 nm
was plotted against the ratio of [M]/[L]. I is the fluores-
cence intensity of the solution involving Zn2? cation. In
order to determine the complex stability constant, the ratio
of Io/(I-Io) was plotted versus 1/[M], as in Fig. 3 (inset
below), which gave a good straight line. The stability
constant was calculated from the ratio of intercept/slope
[16]. The value of Log K was 5.11 for the Zn2?-ligand (4)
complex. The proper data for the stability constant could be
obtained from the change of absorbance at 688 nm.
0,8
0,15
0
1
2
0,6
0,4
0,2
0
[M]/[L]
(4)
2,2
2,4
250
350
450
550
650
750
Wavelength (nm)
Fig. 2 Absorption spectra of (4) complexed with Zn2?. The spectral
changes during the addition of 0–2.4 equivalents of Zn(ClO4)2.
Ligand concentration: 4 9 10-5
M
1,2
0,6
0
1
0,8
0,6
0,4
0,2
0
0
1
2
3
4
5
[M]/[L]
1
0,8
0,6
0,4
30000
50000
1/[M]
Figure 4 shows the regular fluorescence enhancement
depending on increasing Zn2? concentrations with the
ligand (4). A linear response of the fluorescence intensity at
681 nm as a function of Zn2? concentration was observed
from 4.0 9 10-6 to 4.4 9 10-5 M with linearly dependent
coefficient R2 = 0.9700 (Fig. 4). The detection limit cal-
culated as three times the standard deviation of the blank
signal was found to be 2.4 9 10-7 M. A regular change
wasn’t found in the fluorescence spectra of the ligand (4)
with increasing concentrations of Ni2?, Co2? and Cd2?
cations as in the case of absorption spectra. Our results
showed that the phthalocyanine molecule does not prefer
interacting with these metal ions. However, Zn2? is a
preferable ion in complexation with the phthalocyanine (4),
implying that the ligand (4) shows selective complexation
to Zn2? rather than Ni2?, Co2? and Cd2? ions. The
680
690
700
710
Wavelength (nm)
Fig. 3 The variation of the fluorescence (kexc = 674 nm) of the
ligand (4) with increasing amounts of Zn2? ions. [L]:4 9 10-5
M
complex composition of Zn2?-ligand (4). As seen from
Fig. 2 (inset), the inflection point was 1.0 ([M]/[L]), sug-
gesting that the ligand (4) formed a stable 1:1 complex with
Zn2?. A regular change in the absorption spectra of the
ligand (4) wasn’t found with increasing concentrations of
Ni2?, Co2? and Cd2? cations, implying that the phthalo-
cycanine molecule prefers to complex with Zn2? ion in
comparison to these ions.
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reported study may highlight the versatile sensing of Zn2?
ion.
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Acknowledgment This study was supported by the Research Fund
of Karadeniz Technical University.
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