Synthesis and characterization, novel across adjacent ring formed phthalocyanine

Article abstract of DOI:10.1039/c0dt01163k

Novel mononuclear Zn(ii) 4, Co(ii) 5 and Cu(ii) 6 metallophthalocyanines have been synthesized from 4,4′(ethane-1,1-p-phenol-2,2-p-phenoxy) phthalonitrile 3, which can be obtained by the reaction of 4-nitrophthalonitrile 1 with 1,1,2,2-tetrakis(p-hydroxy-

Full text of DOI:10.1039/c0dt01163k

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PAPER
Synthesis and characterization, novel across adjacent ring formed
phthalocyanine
a
b
c
d
e
¨
¨
Dilek Elmalı, Ahmet Altındal, Ali Rıza Ozkaya, Bekir Salih and Ozer Bekarog˘lu*
Received 3rd September 2010, Accepted 1st October 2010
DOI: 10.1039/c0dt01163k
Novel mononuclear Zn(II) 4, Co(II) 5 and Cu(II) 6 metallophthalocyanines have been synthesized from
4,4¢(ethane-1,1-p-phenol-2,2-p-phenoxy)phthalonitrile 3, which can be obtained by the reaction of
4-nitrophthalonitrile 1 with 1,1,2,2-tetrakis(p-hydroxy-phenyl)-ethane 2. The target water-soluble
derivatives of 7–9 were acquired from a boiling suspension of the compounds in aqueous 20% KOH
solution. The synthesized complexes have been characterized by UV-vis, IR, 1H NMR and
MALDI-TOF-mass spectroscopies. In addition, the geometric and electronic structures of 2–6 were
investigated by ab initio/DFT quantum mechanical calculations using the Gaussian 03 program with
HF theory at the B3LYP/3-21G level. The redox properties of the complexes 4–6 were examined by
cyclic voltammetry on platinum in DMSO/TBAP. These complexes displayed one-electron
metallophthalocyanine-based and multi-electron hydroxyphenyl-based redox processes. The effect of
temperature on the d.c. conductivity and impedance spectra of spin coated films of compounds were
investigated at the temperatures between 300–452 K and in the frequency range of 40–105 Hz.
Thermally activated conductivity dependence on temperature was observed for all compounds. A.c.
results indicated that conduction mechanism can be explained by classical hopping barriers mechanism
for all films.
homo or hetero metals showed intrinsic electrochemical, electrical,
gas sensing, non-linear optical and catalytic properties.3,4 In one
of our previous studies, pentaerythritol was employed to obtain
ball-type Pcs. Firstly, two of four hydroxyl groups were protected
by forming two monoacetyls before replacement reaction with 5-
nitrophthalonitril. After separation of the ball-type Pc with four
pentaerythritol bridging units, acetyl groups were removed by
a known procedure, in order to obtain ball-type Pc with eight
free hydroxyl groups. Further reactions of functional hydroxyl
groups allowed us to prepare various novel ball-type Pcs, which
showed interesting physical properties.3,4,6 Therefore, it would be
worthwhile to design and synthesize ball-type Pcs using distinct
bridged molecules carrying four or more hydroxyl groups. In this
regard, 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane 2 was the choice
as an interesting bridged compound in this study. The reaction
of 4,4¢(ethane-1,1-p-phenol-2,2-p-phenoxy)phthalo-nitrile 3 with
zinc, cobalt and copper in pentanol gave the relevant mononuclear
metal Pcs. In our continuing efforts, we changed the experimental
conditions to the “heating of the solid phase” method with the
aim of the synthesizing novel ball-type Pcs. However, the products
were the same mononuclear Pcs synthesized in pentanol, due to
remarkable guest selectivity of ligand 2 with strong affinity towards
one guest.7 Thus, we report here in detail the synthesis and charac-
terization of mononuclear Pcs and their water-soluble derivatives.
Density functional theory (DFT) is one of the most successful
and widely used powerful theoretical tools in the computational
quantum chemistry, as an approximation method for ab initio
Introduction
Phthalocyanines (Pcs) and their metal complexes forms are the
most studied class of functional organic materials. The functions
of these compounds arise mainly from their conjugated 18p-
electron system having rich electron transfer ability, which depends
on the kind and number of metal centres and substituents. A great
dealofattentionhasbeenpaidtothepropertiesandapplications of
phthalocyanine (Pc) compounds, including electrodichroism, op-
tical disks, laser dyes, liquid crystals, catalysis and electrocatalysis,
non-linear optics, photoelectrochemistry, gas sensors, jet printing
inks, display devices, data storage, chemical sensors, solar cells and
photonic devices.1 In addition to traditional applications, in the
field of cancer treatment, using phthalocyanines for photodynamic
therapy (PDT) in is a new technique.2
We have published a number of papers on ball-type Pcs and in re-
cent years a new class of Pcs has appeared in the literature.3,5 These
compounds, with various bridging units, two co-facial Pc rings and
aDepartment of Chemistry, Anadolu University, 26470, Eskis¸ehir, Turkey.
E-mail: angelnew2000@yahoo.com
bDepartment of Physics, Marmara University, 34722, Go¨ztepe-Istanbul,
Turkey. E-mail: aaltindal@marmara.edu.tr; Fax: +90216347878
cDepartment of Chemisry, Marmara University, 34722, Go¨ztepe-Istanbul,
Turkey. E-mail: aliozkaya@marmara.edu.tr; Tel: +902163478783
dDepartment of Chemistry, Hacettepe University, 06532, Ankara, Turkey.
E-mail: bekir@hacettepe.edu.tr; Fax: +90 3122992163
eDepartment of Chemistry, Technical University of Istanbul, 34469, Maslak-
Istanbul, Turkey. E-mail: obek@itu.edu.tr; Fax: +90 216 3860824
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Scheme 1 (i) 24 h, K2CO3, DMF, (ii) 1-pentanol, reflux, 24 h, a: Zn(CH3COO)2·2H2O, b: Co(CH3COO)2·4H2O, c: Cu(CH3COO)2. H2O, DBU, (iii) %20
KOH.
calculation of electronic structures of many-particle systems.8 It
could be helpful in the devise and syntheses of new molecules
since the calculation of the energy levels of the frontier orbitals
help to explain the reactivity and physicochemical properties of
the molecules. Thus, DFT was employed to calculate the steric
energies and heat of formations of 2–6. The electrochemical and
electrical properties of metallophthalocyanines (MPcs) 4–6 were
also investigated.
OH peak at 3400 cm-1 indicated the presence of hydroxyl groups,
which do not attend in the formation reaction of compound 3. The
formation of compound 3 was also confirmed by the signals for
the aromatic ring protons (in the region ca. 6.66 and 7.69 ppm),
methyl protons (at ca. 4.65 ppm) and hydroxyl protons (at ca. 5.11
ppm) in its1H NMR spectrum.
Compound 3 was converted into the corresponding MPcs 4–
6 in good yields (69.2–74.3%). Elemental analysis results for the
compounds were good. Examination of the spectroscopic data for
4–6 indicated that 1H NMR spectroscopy, coupled with IR, UV-
vis and MALDI-TOF-mass spectroscopy, was potentially the best
analytical technique to provide confirmatory structural evidence
for their formation. The IR spectra of compounds 4, 5 and 6
showed Ar–O–Ar peaks at 1230–1234 cm-1, C C (in phenyl and
naphthalene rings) peaks at 1616 cm-1, C N peak at 1717 cm-1,
Ar–CH peak at 2925 cm-1 and the C–OH peak at 3400 cm-1. The
absence of (C N) stretches in the IR spectra of 4–6 is indicative
of the completion of the reactions for the formation of these
complexes.
The UV-vis spectra of 4–6 in DMSO showed typical absorptions
between 672 and 682 nm in the Q band region (Fig. 1). The Q band
absorptions of the complexes refer to the p → p* transition from
the highest occupied molecular orbital (HOMO) to the lowest
unoccupied molecular orbital (LUMO) of the Pc ring. The B band
absorptions of the complexes were observed within the UV region
between 300 and 330 nm, due to the transitions from the deeper
p levels to the LUMO. The ground state electronic absorption
spectra of 4–6 showed monomeric behaviour evidenced by a single
narrow Q-band, typical of MPc complexes (Fig. 1). Aggregation is
usually depicted as a co-planar association and is dependent on the
concentration.10 In the aggregated state, the electronic structure of
Results and discussion
Syntheses and characterization
4-nitrophthalonitrile 1 was converted to 3 by the reaction of
1,1,2,2-tetrakis(p-hydroxy-phenyl)-ethane 2 in dry DMF as the
solvent and K2CO3 as the base with the method described
previously in the literature.8 Compound 3 was obtained in good
yield (62%). For the synthesis of MPcs in this work, we modified
the method described in the literature.9 The MPcs 4, 5 and 6 were
synthesized by the reaction of compound 3 with Zn(OAc)2·2H2O,
Co(OAc)2·4H2O and Cu(OAc)2·H2O, respectively, in penthanol
in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) at
190 ◦C. Water-soluble Pcs 7, 8 and 9 were obtained by boiling
the suspensions of 4, 5 or 6, respectively, in aqueous KOH (20%)
(Scheme 1).
The structures of compounds 4, 5 and 6 were deduced from
their IR, MALDI-TOF-mass and UV-vis spectroscopic data
and elemental analysis. Compound 3 has satisfactory elemental
analysis results. The IR spectrum of 3 displayed peaks of 3427 cm-1
(OH), 3072 cm-1 (Ar–C–H), 2232 cm-1 (C N) and 1280 cm-1 (Ar–
O–Ar) which confirms the formation of the compound. The C–
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Fig. 1 UV-vis spectra of 4–6 in DMSO.
the complexed Pc rings is perturbed resulting in alternation of
the ground and excited state electronic structures.11 This causes
the broadening or the split of the absorption bands, especially at
high concentrations. Fig. 2a shows the spectra of 4 in DMSO,
7 in DMSO and 7 in water to compare the differences of Pc and
potassium phenolate Pc. The spectra of the structure taken in water
and DMSO are clearly not similar because of the aggregation.
Fig. 2b shows the spectra of 7 within the concentration range
from 4.6 ¥ 10-5 to 5.5 ¥ 10-4 M in water as an example. As the
concentration was increased, the intensity of absorption of the
Q-band also increased linearly and there were no new blue shifted
bands due to the aggregated species.
Fig. 3 (a) Fluorescence excitation spectra of 4 at different concentrations
within the range of 5.8 ¥ 10-6-5.8 ¥ 10-5 M in DMSO. (b) The correlation
between time and fluorescence emission intensity of 4 at 693.94 nm in
DMSO.
in DMSO (UF = 0.20).12 It was also observed that the fluorescence
emission of the compound decreased with time (Fig. 3b).
The optimized structure of 5, determined according to the
molecular mechanics calculation is shown in Fig. 4. The molecular
mechanics calculation of 2 and 3 were also carried out to
understand the effect of their conformations on those of 4–6.
The steric energies and heat of formations for 2–6 are listed in
Table 1. Conformers 2 and 3 within the ten optimized ones have
minimum steric hindrances and the lowest heat of formations,
compared to the other conformers. Calculated steric energies
of stable (-0.875 kcal mol-1) and unstable (-1.62 kcal mol-1)
conformers of molecule 2 with HF theory at the B3LYP/3-21G
level are in accordance with literature.7 These results suggest that
a central symmetrical conformation for 2 is in the formation of the
compound 3 and trans conformation for 3 is in the formation of
MPcs. The structure calculations indicated that the conformation
Fig. 2 UV-vis spectra of 4 in DMSO (black), 7 in DMSO (red) and 7 in
water (blue) (a), 7 at different concentrations within the range from 4.6 ¥
10-5 to 5.5 ¥ 10-4M in water (b).
Fig. 3a shows the fluorescence spectra of 4 in DMSO
at different concentrations within the range from 5.8
¥
10-6 to 5.8 ¥ 10-5 M. Fluorescence emission peak was observed at
693.94 nm. The proximity of the wavelength of the component of
the Q-band absorption to the Q-band maxima of the fluorescence
spectra for the complex suggests that the nuclear configurations
of the ground and excited states are similar and not affected
by excitation.12 The intensity of the fluorescence emission of 4
is directly proportional to its concentration. The fluorescence
quantum yield (UF) value of 4 was found 0.19 in DMSO. This
value is slightly lower than that of unsubstituted ZnPc standard
Fig. 4 The optimized conformer of 5, determined with HF theory at the
B3LYP/3-21G level.
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Table 1 Steric energies and heat of formations of 2–6, determined by HF
theory at the B3LYP/3-21G level
Molecule
Steric energy/kcal mol-1
Heat of formation/kcal mol-1
2
3
4
5
6
-0.875
73.46
-2.741
151.52
432.21
402.89
402.97
-80.287
-96.106
-85.862
of 4, 5 and 6 are not planar as shown in Fig. 4. The side groups
diverge from linearity although the MPc rings seem nearly planar.
The MALDI-MS spectra of 4–6, recorded in a-cyano-4-
hydroxycinnamic acid, are shown in Fig. 5–8. For the high
resolution spectra, reasonable peak intensities could not be
obtained because of the short life times of the ions in reflection
mode mass spectrometer. However, the complexes were more
stable under the laser and MALDI-MS conditions in linear mode
mass spectrometer. Thus, in linear mode positive ion mass spectra,
reasonable resolution (about 1500) was obtained for 5 and 6.
This allowed us to observe their resolved peaks resulted from
isotopic distribution of the elemental composition of the elements
existing in these complexes. Experimental and theoretical isotopic
distributions of 5 and 6 matched properly each others. For 6, first
isotopic peak mass started at 1367.35 and finished at 1373.37 Da
in its theoretical isotopic mass distribution (Fig. 5 and 6). In the
experimental data, first 6 peaks were observed in the similar masses
but last one could not be observed because of the low intensity
of the complex. For 5, all theoretical isotopic mass distributions
Fig. 7 Positive ion and linear mode MALDI-TOF-MS spectrum of 4 in
a-cyano-4-hydroxycinnamic acid MALDI matrix using nitrogen laser (at
337 nm wavelength) accumulating 50 laser shots. Inset spectrum shows
expanded molecular mass region of the complex.
Fig.
8
Positive ion and reflection mode MALDI-TOF-MS spec-
trum of C84H48K4N8O8Zn complex was obtained in 1,8-dihy-
droxy-9(10H)-anthracenone (dithranol) MALDI matrix using nitrogen
laser (at 337 nm wavelength) accumulating 50 laser shots.
matched the experimental data exactly, with isotopic peak masses
starting at 1363.35 and finishing at 1367.37 Da. For 4, only a
single peak with low resolution could be obtained (Fig. 7). This
is because of more isotopic peaks of zinc compared to cobalt
and copper. In the case of 4, experimental molecular ion peak
mass can be assigned to its theoretical average mass. MALDI-MS
results showed that the complexes were synthesized truly in the
experimental route and purified perfectly.
Positive ion and refection mode MALDI-MS spectrum of the
synthesized complex was obtained and is given in Fig. 8. Some
novel MALDI matrices were tried to find intense molecular ion
peak at 1517.13 Da (monoisotopic) and low fragmentation under
the MALDI-MS conditions for this complex. Only dithranol
yielded the best MALDI-MS spectrum for the complex. Beside the
protonated molecular ion peak of the complex, some potassium
removed ion signals also observed. These ions were found to be [M
- K + 2H]+, [M - 2K + 3H]+, [M - 3K + 4H]+ and [M - 4K + 5H]+.
These ions were occurred in acidified matrix solution as a normal
processes in MALDI-MS during the salt analysis. MALDI-MS
spectrum showed that complex was synthesized successfully and
there was no impurity in the complex.
Fig. 5 Positive ion and linear mode MALDI-TOF-MS spectrum of 5 in
a-cyano-4-hydroxycinnamic acid MALDI matrix using nitrogen laser (at
337 nm wavelength) accumulating 50 laser shots. Inset spectrum shows
expanded molecular mass region of the complex.
Electrochemistry
The redox properties of the complexes 4–6 were examined by cyclic
voltammetry on platinum in DMSO/TBAP. The voltammetric
dataissummarizedinTable2. Thelinearvariationofpeakcurrents
Fig. 6 Positive ion and linear mode MALDI-TOF-MS spectrum of 6 in
a-cyano-4-hydroxycinnamic acid MALDI matrix using nitrogen laser (at
337 nm wavelength) accumulating 50 laser shots.
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Table 2 Voltammetric data for 3–5 on Pt in DMSO/TBAP
c
Complex
ZnPc 4
CoPc 5
Redox process
E1/2 a/V (vs.SCE)
DEp b/V
Ipa/Ipc
R1
R2
O1
R1
R2
R1
-0.66
-1.14
0.29
-0.51
-0.98
-0.54
0.10
0.24
0.12
0.06
0.18
0.12
1.00
2.50
1.00
1.00
2.85
1.00
CuPc 6
a E1/2 values were measured by cyclic voltammetry [E1/2 = (Epa + Epc)/2].
b DEp = Epa+ Epc at 0.050 V s-1. c
pa/Ipc for reduction, Ipc/Ipa for oxidation
processes at 0.050 V s-1 scan rate.
I
with potential scan rate within the range of 0.010–0.500 V s-1 for all
redox processes of 4–6 showed that they are diffusion-controlled.
Complexes 4 and 6 displayed two reduction processes (Table 2).
Fig. 9 shows typical cyclic voltammograms of 4 at 0.050 V s-1 scan
rate. It is clear from well-known redox properties of mononuclear
MPcs and redox-inactive nature of Zn(II) and Cu(II) metal centers
in Pc cavity that these redox processes are Pc-ring based.13
Cyclic voltammetric data and controlled-potential coulometry
measurements suggested that the first reduction couples of 4
and 6 are one-electron quasi-reversible processes with anodic to
cathodic peak separations of 0.100 V and 0.120 V, respectively.
The cathodic peak currents of the second reduction processes
of these complexes were much higher than those of the first
reduction couples, as shown in Fig. 9 for 4. This implies that
the second reduction processes of these complexes correspond to
the reduction of 1,1,2,2-tetrakis(p-hydroxy-phenyl)-ethane-based
peripheral hydroxy-phenyl groups. With the aim of clarifying
this comment, we also examined the voltammetric behaviour
of 1,1,2,2-tetrakis(p-hydroxy-phenyl)-ethane, 2 (Fig. 10). This
compound displays an irreversible reduction signal at -1.70 V vs.
SCE at the end of available potential window in DMSO/TBAP,
providing support for the assignment of the second reduction
processes of 4 and 6 to 1,1,2,2-tetrakis(p-hydroxy-phenyl)-ethane-
based peripheral hydroxy-phenyl groups. The reduction of 2 occurs
at relatively high negative potentials, compared to the second redox
processes of 4 and 6. This can be attributed to the strong electronic
Fig. 10 Cyclic voltammogram of 2 at 0.050 V s-1 scan rate on Pt in
DMSO/TBAP.
coupling between the Pc ring and peripheral 1,1,2,2-tetrakis(p-
hydroxy-phenyl)-ethane-based peripheral moieties in 4 and 6. The
appearance of the second reduction potential of 5 at relatively less
negative potentials, compared to the reduction potential of 2 was
also observed (Table 2 and Fig. 10).
Voltammetric behaviour of 5 is different from those of 4 and
6. A typical voltammogram for 5 is shown in Fig.11. It displays
an oxidation couple in addition to two reduction processes. The
first reduction and the first oxidation couples are one-electron
reversible and quasi-reversible processes with anodic to cathodic
peak separations of 0.060 and 0.120 V, respectively. If the transition
metal ion concerned has no accessible d orbital levels between the
HOMO and the LUMO energies of a Pc species, then its all redox
processes are Pc ring-based. The nickel, copper, zinc and some
other MPcs behave in this fashion, with the M(II) central ion
being unchanged as the MPc unit is either oxidized or reduced.13
However, the metal centre in some MPcs such as CoPc, FePc
and MnPc are redox-active due to the presence of d orbital levels
within the HOMO–LUMO gap of a Pc species. These species vary
their electrochemical behaviour according to their environment in
solution and thus their electrochemistry is split into two sections,
that referring to donor solvents and that referring to non-donor
Fig. 9 Cyclic voltammogram of 2.0 ¥ 10-4 M 4 at 0.050 V s-1 scan rate on
Pt in DMSO/TBAP (The inset shows the R1 process over relatively high
sensitive current scale).
Fig. 11 Cyclic voltammogram of 2.0 ¥ 10-4 M 5 at 0.050 V s-1 scan rate
on Pt in DMSO/TBAP.
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solvents.13 The main difference lies in whether metal or the ring
is oxidized first. Donor solvents strongly favour Co(III)Pc(-2) by
coordinating along the axis to form six coordinate species. If such
donor solvents are absent, then oxidation to Co(III) is inhibited and
ring oxidation occurs first. Thus, the first oxidation and the first
reduction processes of 5 are probably metal-based and correspond
to Co(II)Pc(-2)/[Co(III)Pc(-2)]+ and Co(II)Pc(-2)/[Co(I)Pc(-2)]-,
respectively, since the voltammetric measurements were carried
out in DMSO/TBAP, while the second reduction corresponds to
the reduction of 1,1,2,2-tetrakis(p-hydroxy-phenyl)-ethane-based
peripheral hydroxy-phenyl groups. In order to provide additional
support for the identification of the redox processes of 5, in situ
spectroelectrochemistry of this complex was also studied. Fig. 12A
shows the UV-vis spectral changes during the controlled potential
electrolysis of 5 at a potential a bit more negative than the cathodic
peak potential of R1¢ couple, -0.60 V vs. SCE Upon the first
reduction at -0.60 V vs. SCE, the absorptions of the Q band at
673 nm and vibrational band at 606 nm decreases while two new
bands at 454 and 710 nm appear. These spectral changes have well-
defined isosbestic points at 391, 558 and 700 nm. The formation
of a new band within the range of 400–500 nm and red shifting
of the Q band indicate the formation of [Co(I)Pc(-2)]- species,
confirming that first reduction of 5 occurs at the metal center.14
Fig. 12B shows the spectral changes during the oxidation process
of 5 at 0.50 V vs. SCE. The original Q band absorption at 673 nm
increases and shifts to 686 nm. This spectral change is typical of
metal-based Co(II)Pc(-2)/[Co(III)Pc(-2)]+ redox process.14b,c
Electrical properties
Arrhenius plots of lnsd.c. vs. 1/T were plotted to understand the
d.c. conduction mechanism of compounds 4–6 (Fig. 13). The d.c.
conductivity values for the films of compounds were calculated
from the slopes of the measured I–V characteristics by using the
following equation (eqn (1)),
I
d
sd,c
=
(1)
V (2n−1)1.h
where, I is the measured current, V applied voltage, d distance
between the finger pair, n number of the finger pair, l overlap
length and h thickness of the electrodes. It is well known that,
the electrical conduction processes in Pc compounds depend
on several factors that include the chemical nature of Pcs, the
polymorphic phase of the microcrystallites comprising the film, the
film thickness, the presence of impurities or molecular doping and
the electrode materials. It is clear from the figure that lnsd.c. vs. 1/T
curves are straight lines for all compounds showing the validity
of equation sd.c. = s0exp(-EA/kT) in the present case. Where EA
is the activation energy, T the temperature, k the Boltzmann’s
constant and s0 is the constant of proportionality. The values
of the activation energies which are determined from the slope
of the ln d.c. conductivity vs. 1/T graphs, are EA = 0.68, 0.75
and 0.70 eV for compounds 4, 5 and 6, respectively. The general
trend, for the order of electrical conductivities, observed in the
whole temperature range for these compounds are sdc(6) > sdc(5)
> sdc(4). This result is significant because it strongly suggests
that the central metal atom plays a major role in the electrical
conduction behaviour.
Fig. 13 Temperature dependence of d.c. conductivity for the films of 4–6.
The a.c. electrical conduction behaviour of the films was also
investigated. A.c. measurements were carried out in the frequency
range 40–105 Hz. at temperatures between 300 and 452 K. As a
representative result, the temperature dependence of the measured
a.c. conductivity of 6 as a function of frequency at indicated
temperatures is shown in Fig. 14. In organic and many inorganic
Fig. 12 In situ UV-vis spectral changed during the controlled-potential
electrolysis of 5 at (A) -0.60 V and (B) 0.50 V vs. SCE in TBAP/DMSO.
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effect and interfacial polarization phenomena. So, the impedance
spectra technique enables us to separate the effects due to each
component. At low temperatures, the impedance spectra consist
of a quasi-vertical line. The existence of semicircular shaped curves
in the Nyquist plot means that the impedance becomes capacitive
even at relatively high frequency. The effect of temperature on the
impedance spectra of the films becomes clearly visible with rise
in temperature. On the complex plane plot at high temperatures,
only a depressed semicircle with different radius were observed for
all at higher temperatures, indicating deviation from the Debye
dispersion relation (Fig. 15). In the case of a depressed semicircle
in the impedance spectra, the relaxation time is considered as a
distribution of values, rather than a single relaxation time. The
same type of behaviour was observed for other films.
Fig. 14 The variation of a.c. conductivity with frequency for the film of
6 at different temperatures.
materials, the frequency dependent part of the total conductivity,
s (w), is given by the power law of the form shown in eqn (2):
s
s(w) = Aw
(2)
where A and s are temperature dependent parameters.
Various models such as quantum mechanical tunnelling (QMT)
and correlated barrier hopping (CBH) has been proposed to
explain this type of behaviour. But, it is not easy to decide which
of those mechanisms is responsible for the observed conduction
mechanism. However, the behaviour of the exponent s with
temperature can help in determining the possible conduction
mechanism. The frequency exponent, s, were calculated from
the slope of the lnsa.c. vs. ln f graphs and were generally found
to decrease with increasing temperature. The behaviour of s
with temperature cannot be explained by the QMT model. This
model, which is based on phonon assisted tunnelling of electrons,
predicts temperature independent frequency exponent s with a
constant value around 0.8. According to the CBH model, the
a.c. conductivity which can be expressed in terms of the density
of localized states, the permittivity, the effective relaxation time
and the electronic charge. This model suggests a temperature
dependent s parameter which is given by the following equation
(eqn (3)):
Fig. 15 Impedance spectra of the 4 at different temperatures.
3. Experimental
Syntheses and characterization
Melting points (mp) were determined using a Sanyo Gallenkamp
apparatus and are uncorrected. IR spectra were recorded on a
Perkin Elmer Spectrum 100 FT-IR spectrophotometer as KBr
pellets. Electronic spectra were recorded on a Shimadzu UV-
3150 UV-vis-NIR Spectrophotometer. Fluorescence spectra were
recorded on the Varian Eclipse Fluorescence Spectrophotometer.
Elemental analyses were performed on an Elementar Vario EL III
instrument. 1H NMR spectra were recorded on a Bruker Avance
DPX-400 spectrometer, operating at 400.13 MHz for proton.
1H NMR spectra were measured for ca. 25–30% solutions in
DMSO, unless otherwise indicated and all chemical shifts are
expressed relative to Me4Si. Mass spectra were acquired on a
Voyager-DETM PRO MALDI-TOF-mass spectrometer (Applied
Biosystems, USA), equipped with a nitrogen UV-laser operating
at 337 nm. Spectra were recorded in linear mode (1500 resolution)
with average of 50 shots.
kT
s=1-6
(3)
Wm
where Wm is the optical band gap. Unlike QMT model the
CBH model predicts a temperature dependent s parameter which
decreases with increasing temperature. It was observed that the
calculated s parameters decrease with increasing temperature.
These results are quantitatively consistent with the prediction of
the CBH model.
To get more detailed information about the electrical properties
of the compounds, impedance spectra measurements in the
frequency range of 40 – 105 Hz were also carried out on spin
coated film of the compounds. The measured impedance spectra,
when plotted in a complex plane plot, appears in the form
of a succession of semicircles representing the contributions to
the electrical properties due to bulk material, grain boundary
4,4¢(Ethane-1,1-p-phenol-2,2-p-phenoxy)phthalonitrile
3.
Compound 1 (1.384 g, 8 mmol) and compound 2 (1.593 g,
4 mmol) were dissolved in dry DMF under argon. After stirring
for 15 min, finely ground anhydrous K2CO3 (1.655 g, 12 mmol)
was added portion wise in 15 min with efficient stirring. The
◦
reaction mixture was heated and stirred at 90 C for 24 h under
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argon. After cooling to room temperature, it was treated with
water and the product filtered off and washed with water and
ethanol. This compound is soluble in pyridine.
Pc, 8 was synthesized using a similar procedure to that as
described above for 7. Yield (8): 0.023 g, 76%. M.p. > 300 ◦C.
Pc, 9 was synthesized using a similar procedure to that as
described above for 7. Yield (9): 0.024 g, 78%. M.p. > 300 ◦C.
Yield: 1.612 g, 62%. Mp: 174 ◦C. Anal. calcd for C42H26N4O4: C
77.53, H 4.03, N 8.61. Found: C 77.57, H 4.08, N 8.66%. IR (KBr
pellet) n/cm-1: 3427 (C–OH), 3072 (Ar–H), 2232 (C N), 1563–
1591 (C C), 1240–1280 (Ar–O–Ar); 1H NMR (DMSO) d/ppm:
7.69 (m, 2 H), 7.27 (m, 4 H), 7.02 (m, 8 H), 6.88 (m, 4 H), 6.66 (m,
4 H), 5.11 (brs, 2 H), 4.65 (m, 2 H).
MALDI sample preparation
MALDI matrix, a-cyano-4-hydroxycinnamic acid (ACCA) was
prepared in ethanol–water mixture in 1 : 1, v/v ratio at a concen-
tration of 10 mg mL-1. MALDI samples were prepared by mixing
sample solutions (2 mg mL-1 in DMSO:ethanol mixture, 1 : 1 v/v
3,9,17,23-Bis(ethane-1,1-p-phenol-2,2-p-phenoxy)phthalo-cya-
R
ratio) with the matrix solution (1 : 10 v/v) in a 0.5 mL Eppendorfꢀ
ninatozinc(II)
phenoxy)phthalocyaninatocobalt(II)] (5) and [3,9,17,23-bis(ethane-
1,1-p-phenol-2,2-p-phenoxy)phthalocyaninato-copper(II)] (6).
(4),
[3,9,17,23-bis(ethane-1,1-p-phenol-2,2-p-
micro tube. Finally 0.5 mL of this mixture was deposited on the
sample plate, dried at room temperature and then analyzed.
A
For molecule
7 MALDI matrix, 1,8-dihydroxy-9(10H)-
mixture of compound 3 (0.325 g, 0.5 mmol), and Zn(OAc)2·2H2O
(0.096 g, 0.6 mmol) in 5 mL of DMF was refluxed in a sealed
tube under Ar for 24 h. After cooling to room temperature the
reaction mixture was treated with water to precipitate the product
and then filtered. The crude product was washed with common
organic solvents. This compound was soluble in pyridine and
DMSO.
anthracenone (dithranol) was prepared in tetrahydrofuran at a
concentration of 10 mg mL-1. MALDI samples were prepared
by mixing sample solutions (1.5 mg mL-1 tetrahydrofuran–water
mixture (1 : 1, v/v)) with the matrix solution (1 : 10 v/v) in a
R
0.5 mL Eppendorfꢀ micro tube. Finally 0.5 mL of this mixture
was deposited on the sample plate, dried at room temperature and
then analyzed.
Yield (4): 0.508 g, 74,3%. Mp: > 300 ◦C. Anal. calcd for
C84H58N8O8Zn: C 73.82, H 3.83, N 8.20. Found: C 73.85, H 3.85, N
8.18%. MS (MALDI-TOF), m/z: 1367 [M + H]+. IR (KBr pellet)
n/cm-1: 3100 (C–OH), 2925 (arom. –CH), 2853–2780 (aliph. –
CH2), 1616 (C C), 1230 (Ar–O– Ar). UV-vis(DMSO) l/nm (log
e): 681 (4.30), 617 (3.74).
Pc, 5 was synthesized using a similar procedure to that as
described above for 4. Compound 5 was soluble in DMSO, ethanol
and methanol.
Theoretical calculations
Geometric and electronic structure of compounds 2–6 were
examined by ab initio/DFT quantum mechanical calculations.
These calculations were performed by the Gaussian 03 program,15
using HF theory at the B3LYP/3-21G level. For complex 4,
including atoms over 150, the smaller basis set was selected.
The molecular structure was energetically optimized to reach the
stable structure using HF/3-21G level theory. After optimization,
we investigated the steric energies and heat of formations of the
compounds.
Yield (5): 0.470 g, 69.20%. Mp: > 300 ◦C. Anal. calcd for
C84H58N8O8Co: C 74.17, H 3.85, N 8.24. Found: C 74.20, H 3.87,
N 8.22%. MS (MALDI-TOF), m/z: 1360 [M + H]+. IR (KBr
pellet) n/cm-1: 3434 (C–OH), 2925 (arom. –CH), 1614 (C C),
1231 (Ar–O–Ar). UV-vis (DMSO) l/nm (log e): 673 (4.40), 606
(3.85).
Electrochemical measurements
Pc, 6 was synthesized using a similar procedure to that as
described above for 4. Compound 6 was soluble in DMSO, ethanol
and methanol.
The electrochemical measurements were carried out with a
Princeton Applied Research Model VersoStat II potentio-
stat/galvanostat controlled by an external PC and utilizing a three-
electrode configuration at 25 ◦C. A platinum disk, a platinum
spiral wire and a saturated calomel electrode (SCE) served as
the working, the counter and the reference electrodes, for cyclic
voltammetry measurements. The reference electrode was separated
from the bulk of the solution by a double bridge. Electrochemical
grade tetrabutylammonium perchlorate (TBAP) in extra pure
dimethylsulfoxide (DMSO) was employed as the supporting
electrolyte at a concentration of 0.10 M. High purity N2 was used
for deoxygenating the solution at least 20 min prior to each run and
to maintain a nitrogen blanket during the measurements. For con-
trolled potential coulometry studies, Pt gauze working electrode
(10.5 cm2 surface area), Pt wire counter electrode separated by a
glass bridge, and SCE as a reference electrode were used. In situ
spectroelectrochemical measurements were carried out by an
Agilent Model 8453 diode array spectrophotometer equipped with
the potentiostat/galvanostat and utilizing an optically transparent
thin layer (OTTLE) cell with three-electrode configuration at
Yield (6): 0.479 g, 70.40%. Mp: > 300 ◦C. Anal. calcd for
C84H58N8O8Cu: C 73.92, H 3.84, N 8.21. Found: C 73.94, H 3.87,
N 8.20%. MS (MALDI-TOF), m/z: 1363 [M + H]+. IR (KBr
pellet) n/cm-1: 3435 (C–OH), 2927 (arom. –CH), 1615 (C C),
1232 (Ar–O–Ar). UV-vis (DMSO) l/nm (log e): 682 (4.33), 617
(3.89).
3,9,17,23-Bis(ethane-1,1-p-phenol-2,2-p-phenoxy)phthalo-cya-
ninatozinc(II) tetrapotassium (7), 3,9,17,23-bis(ethane-1,1-p-
phenol-2,2-p-phenoxy)phthalocyaninatocobalt(II)] tetrapotassium
(8) and [3,9,17,23-bis(ethane-1,1-p-phenol-2,2-p-phenoxy)phthalo-
cyaninatocopper(II)] tetrapotassium (9). Pc,
4
(0.027 g,
0.02 mmol) was suspended in aqueous KOH solution (20%, 5 mL)
and boiled for 10 min. The solution of the compound 7 was cooled,
and the mixture poured into ethanol (100 mL). The performed
precipitate was filtered off, dissolved in water and re-precipitated
in ethanol several times until the solution was neutral. The product
was then washed with ethanol and diethyl ether, and dried in vacuo.
The compound is soluble in water at room temp. Yield (7): 0.021 g,
70%. M.p. > 300 ◦C.
◦
25 C. The working electrode was transparent Pt gauze. Pt wire
counter electrode and a SCE reference electrode separated from
the bulk of the solution by a double bridge were used.
658 | Dalton Trans., 2011, 40, 651–660
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3.5 Electrical measurements
conduction mechanism can be explained by classical hopping
barriers mechanism for all films.
Spin coated thin film of compounds were prepared on the glass
substrate fitted with interdigitated (IDT) gold electrodes for
the d.c. and a.c. measurements. Prior to vacuum evaporation,
glass substrates were thoroughly cleaned by ultrasonically and
Acknowledgements
Financial assistance from The Scientific and Technological Re-
search Council of Turkey (TUBITAK) (project no: 107T834) and
in part from Turkish Academy of Sciences (TUBA) are gratefully
acknowledged. The authors are also thankful to Dr Zafer Odabas¸
for his skilful collaboration for drawing Scheme 1.
˚
˚
then coated with 100 A of chromium followed by 1200 A of
gold in a Edwards Auto 500 coater system. The film patterned
photolitographically and etched to provide 10 fingers pairs of
electrodes having a width of 100 mm, spaced 100 mm from the
adjacent electrodes. The finger overlap distance was 5 mm. Gold
was selected as the electrode material, since it is well-known that
it forms ohmic contact to the Pc. The film of each compound
was obtained by spin-coating DMF solutions of the compounds
over the electrode arrays to obtain devices suitable for electrical
measurements. The substrate temperature was kept constant at
300 K during deposition of the materials over the electrodes.
D.c. conductivity measurements were performed between 300 K
and 452 K by using a Keithley 617 electrometer. Impedance
spectroscopy measurements were carried out with a Keithley
3330 LCZ meter in the frequency range, 40–105 Hz, and in the
temperature range from 300 K to 452 K. All measurements were
carried out on the same sample to avoid the effect of the film
thickness and substrate on the d.c. and impedance properties of
the Pc films, and performed under vacuum (£10-3 mbar) and in
the dark. Both the d.c. conductivity and impedance data were
recorded using an IEEE-488 data acquisition system incorporated
to a personnel computer.
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660 | Dalton Trans., 2011, 40, 651–660
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©