Synthesis, characterization and some properties of novel bis(pentafluorophenyl)methoxyl substituted metal free and metallophthalocyanines

Article abstract of DOI:10.1016/j.poly.2006.07.011

The preparation of some new tetrakis[bis(pentafluorophenyl)methoxyl] substituted metal free and metallophthalocyanine (MPcs) complexes were achieved by the tetramerization of 4-[bis(pentafluorophenyl)methoxy]phthalonitrile with Li metal in pentan-1-ol or

Full text of DOI:10.1016/j.poly.2006.07.011

Polyhedron 25 (2006) 3593–3602
www.elsevier.com/locate/poly
Synthesis, characterization and some properties of novel
bis(pentafluorophenyl)methoxyl substituted metal free and
metallophthalocyanines
a
b
a
a
a,
*
¨
¨
¨
Metin Ozer , Ahmet Altındal , Ali Rıza Ozkaya , Mustafa Bulut , Ozer Bekarog˘lu
a
Department of Chemistry, Marmara University, Faculty of Art and Science, 34722 Go¨ztepe, Istanbul, Turkey
Department of Physics, Marmara University, Faculty of Art and Science, 34722 Go¨ztepe, Istanbul, Turkey
b
Received 26 June 2006; accepted 6 July 2006
Available online 25 July 2006
Abstract
The preparation of some new tetrakis[bis(pentafluorophenyl)methoxyl] substituted metal free and metallophthalocyanine (MPcs)
complexes were achieved by the tetramerization of 4-[bis(pentafluorophenyl)methoxy]phthalonitrile with Li metal in pentan-1-ol or metal
[Co(II) or Zn(II)] acetates in DMAE, respectively. The structures of the target compounds were confirmed by elemental analysis, IR,
1
UV–vis, H NMR, 19F NMR and mass spectroscopic methods. MPcs are soluble only in strong and medium polar solvents while the
metal free one is soluble in weakly, medium and strong polar solvents. The temperature and frequency dependence of the electrical con-
ductivities were studied on spin coated films of the compounds using dc and impedance spectroscopy techniques in the frequency range
from 40 to 105 Hz and within the temperature range from 290 to 440 K. The temperature dependence of the exponent s and conductivity,
rac, were completely in agreement with the prediction of the hopping model. The redox properties of the complexes were determined by
cyclic voltammetry. The nature of the redox processes was also confirmed using spectroelectrochemical measurements.
ꢀ 2006 Elsevier Ltd. All rights reserved.
Keywords: Phthalocyanine; Synthesis; Bis(pentafluorophenyl)methoxyl; UV–vis spectra; Cyclic voltammetry; Spectroelectrochemistry; Impedance spectra
1. Introduction
alkoxy, phenoxy and macrocylic groups at the peripheral
and axial positions of the Pc ring [1–3].
For many years phthalocyanine (Pc) compounds have
been widely used as organic pigments and dyestuffs.
Besides the application in such traditional areas, phthalo-
cyanines (Pcs) have been extensively studied due to their
spectroscopic, electrochemical, electrical and photoelectric
properties. The solubility of Pcs is very important for the
investigation of their chemical and physical characteristics.
The solubility of Pc can be increased by introducing differ-
ent kinds of solubility-enhancing substituents such as alkyl,
Introducing electron donor and acceptor groups into the
Pc ring also strongly affects the electrical properties of the
molecule. From the viewpoint of organic semiconductors,
it is known that substitution of electron donor and accep-
tor groups leads to p-type and n-type characteristics of the
Pc ring, respectively [4,5].
Fluorinated MPcs are currently receiving a great deal of
attention due to their interesting electron-transporting
characteristics [6,7]. Although many studies on the chemis-
try of MPcs in solution, which have been limited to Pc with
electron-donating substituents, have been carried out,
those with electron-attracting groups, especially containing
fluorine atoms, have not been extensively studied [8–11].
Recently, several workers reported on the syntheses and
*
Corresponding author. Present address: Bilim Sokak, Kardesler Apt.,
No 6/9, Erenko¨y, Istanbul, Turkey. Tel.: +90 216 359 01 30; fax: +90 216
386 08 24.
E-mail address: obekaroglu@marmara.edu.tr (O. Bekarog
¨
˘lu).
0277-5387/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2006.07.011

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M. Ozer et al. / Polyhedron 25 (2006) 3593–3602
3594
properties of some fluoro-substituted Pcs. In the case of
electron-withdrawing peripheral fluorine substituents, Pcs
can be dissolved even in polar aprotic solvents and become
good electron donors for use as chemical sensors [9,10,12].
In this paper, we report the preparation of some new
bis(pentafluorophenyl)methoxyl substituted Pc derivatives,
and their spectral, electrochemical, spectroelectrochemical
and electrical properties (Scheme 1).
literature [13]. Bis(pentafluorophenyl)methanol 1 was
used as supplied commercially. Routine IR and
UV–vis spectra were recorded on a Shimadzu FTIR-
8300 spectrophotometer as KBr pellets and a Shimadzu
UV-1601
UV–vis
spectrophotometer,
respectively.
Elemental analyses were performed by the LECO CHNS
932. Mass spectra of 4-[bis(pentafluorophenyl)meth-
oxy]phthalonitrile 3 and Pc derivatives 4–6 were obtained
by using the Agilent LC/MSD-TOF spectrometer and
Micromass Quattro LC–MS/MS spectrophotometer
respectively. 1H NMR and 19F NMR spectra were
obtained on a Varian Mercury-V · 400 MHz spectropho-
tometer.
2. Experimental
The starting material 4-nitrophthalonitrile
2 was
synthesized by the methods described previously in the
F
F
F
F
F
F
F
F
F
F
CN
O2N
CN
CN
i
H
C
O
CN
H
C
OH
+
F
F
F
F
F
F
F
F
F
F
1
2
3
ii(a-c)
F
F
F
F
F
F
F
F
H
H
F
F
F
C
C
F
F
F
F
O
O
F
F
F
F
F
N
N
N
N
N
M
N
N
F
F
N
F
F
F
F
O
O
F
F
F
F
C
F
C
F
H
H
F
F
F
F
F
F
F
F
4
5
6
M: 2H
Zn
Co
Scheme 1. (i) K2CO3, CH3CN; (ii) a: Li, pentan-1-ol; b: Zn(CH3COO)2 Æ 2H2O, DMAE; c: Co(CH3COO)2 Æ 4H2O, DMAE.

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M. Ozer et al. / Polyhedron 25 (2006) 3593–3602
3595
2.1. Synthesis
2.1.3. Tetrakis[bis(pentafluorophenyl)methoxy]-
phthalocyaninato zinc(II) (5)
2.1.1. 4-[Bis(pentafluorophenyl)methoxy]phthalonitrile (3)
A mixture of bis(pentafluorophenyl)methanol 1 (1.00 g,
2.74 mmol), 4-nitrophthalonitrile 2 (0.47 g, 2.74 mmol)
and K2CO3 (1.14 g, 8.24 mmol) was heated for 24 h,
refluxing in dry acetonitrile (40 mL) under argon. The
cooled reaction mixture was filtered off and the filtrate
evaporated to dryness under vacuum in a rotary evapora-
tor. After being dried under vacuum, the yellowish vis-
cous product was isolated with column chromatography
over silica gel using chloroform as the eluent. The second
fraction, which is targeted, was eluted with CHCl3. On
evaporation of the solvent, a white product was obtained
(Scheme 1). The compound 3 is readily soluble in CHCl3,
CH2Cl2, acetone, THF, MeOH and EtOH. Yield: 0.822 g
(61%), m.p. 128 ꢁC. Anal. Calc. for C21H4F10N2O: C,
51.45; H, 0.82; N, 5.71. Found: C, 51.71; H, 0.81; N,
5.69%. MS (LC/MSD-TOF, APCI), m/z: 490 [M]+, IR
(KBr pellet) m, cmꢀ1: 3090 (Ar–H), 2923–2854 (alkyl
Compound 3 (196 mg, 0.4 mmol) and Zn(CH3COO)2 Æ
2H2O (22 mg, 0.10 mmol) were mixed in dry 2-N-N-dimeth-
ylaminoethanol (DMAE) (1 mL) in a glass tube. After
being degassed with a vacuum, the mixture was sealed,
and heated at 150–160 ꢁC for 5 h to give a symmetrical
substituted Pc (Scheme 1). After being cooled, the reaction
mixture was poured into 100 mL of ethanol and the dark
green precipitate was separated by centrifuging. The prod-
uct was dissolved in DMF and precipitated with a mixture
of CHCl3 and acetone. After filtration, the precipitate was
washed successively with boiling acetic acid, water and
ether, and dried under vacuum. Compound 5 is soluble in
DMSO and DMF, and partly soluble in acetone, MeOH
and EtOH. Yield: 0.065 g (32%). Anal. Calc. for
C84H16F40N8O4Zn: C, 49.79; H, 0.80; N, 5.53. Found: C,
50.56; H, 0.83; N, 5.49%. MS(LC–MS/MS, ES+) m/z:
2026 [M]+, IR (KBr pellet) m, cmꢀ1: 3087 (Ar–H), 2925–
2883 (alkyl ˜CH), 1242 (C–O–C); UV–vis (DMSO) k, nm
1
1
˜CH), 2233 (C„N), 1242 (C–O–C); H NMR (d-CDCl3):
(loge): 698(4.84), 641(4.35), 356(4.78); H NMR (DMSO-
d = 6.94 (s, 1H, ˜CH), 7.24 (d, 1H, Ar–H), 7.33 (d, 1H,
Ar–H), 7.76 (d, 1H, Ar–H). 19F NMR (d-CDCl3): d
(ppm) = ꢀ141.2 (d, o-fluoro), ꢀ149.9 (t, p-fluoro),
ꢀ159.6 (q, m-fluoro).
d6): d = 7.94–7.63 (m, 3H, Ar–H), 6.81 (s, 1H, ˜CH). 19F
NMR (DMSO-d6): d(ppm) = ꢀ143.2 (d, o-fluoro), ꢀ156.5
(t, p-fluoro), ꢀ163.2 (q, m-fluoro).
2.1.4. Tetrakis[bis(pentafluorophenyl)methoxy]-
phthalocyaninato cobalt(II) (6)
2.1.2. Tetrakis[bis(pentafluorophenyl)methoxy]-2H-
phthalocyanine (4)
A mixture of compound 3 (0.089 g, 0.18), Co(CH3-
COO)2 Æ 4H2O (0.011 g, 0.045 mmol) and DMAE
(0.5 mL) was heated and stirred at 150–160 ꢁC for 6 h in
a sealed glass tube under argon to afford symmetrical Pc
(Scheme 1). After cooling to room temperature, the reac-
tion mixture was treated with ethanol and a dark blue
precipitate was separated by centrifuging. The product
was dissolved in DMF and precipitated with a mixture of
CHCl3 and acetone. After filtration, the precipitate was
washed several times with boiling AcOH, water and EtOH
to obtain the targeted Pc. The dark blue product was dried
under vacuum. Compound 6 is soluble in DMSO and
DMF. Yield: 0.014 g (16%). Anal. Calc. for C84H16F40-
N8O4Co: C, 49.95; H, 0.80; N, 5.55. Found: C, 49.08; H,
0.83; N, 5.62%. MS(LC–MS/MS, ES+) m/z: 2021
[M + 1]+, IR (KBr pellet) m, cmꢀ1: 3085 (Ar–H), 2927–
2884 (alkyl ˜CH), 1244 (C–O–C); UV–vis (DMSO) k, nm
(loge): 675(4.77), 320(4.99).
Compound 3 (0.245g, 0.5 mmol) was added to 5 mL
pentan-1-ol and heated to dissolve. An excess of Li wire
was subsequently added to the solution. As the Li was
added, a large quantity of gas was evolved and the reac-
tion mixture turned to dark green. The mixture was
heated at reflux under nitrogen for 5 h [10]. On cooling,
30 mL of AcOH/H2O (1:1-v/v) was added to the mixture
and stirred for 20 min at the room temperature. The
resulting waxy green Pc phase was separated from the
mixture. The Pc product which remained in the flask
was washed with water three times, and the residue was
dried under vacuum to give tarry green Pc (Scheme 1).
The crude Pc 4 was treated with three portions of
30 mL of (CHCl3/H2O – 3:1) (v/v) mixture. After the sep-
aration of the CHCl3 phases, the CHCl3 extracts were
then combined, dried with anhydrous Na2SO4, and the
total volume was evaporated to dryness using a rotary
evaporator. The purification of the aimed Pc was carried
out on silica gel column with CHCl3. Compound 4 is sol-
uble in CHCl3, CH2Cl2, THF, EtOH, MeOH, DMSO and
DMF. Yield: 0.085 g (34%). Anal. Calc. for
C84H18F40N8O4: C, 51.39; H, 0.92; N, 5.71. Found: C,
52.02; H, 0.89; N, 5.83%. MS(LC–MS/MS, ES+) m/z:
1963 [M]+, IR (KBr pellet) m, cmꢀ1: 3297 (NH), 3073
(Ar–H), 2948–2893 (alkyl ˜CH), 1236 (C–O–C). UV–vis
2.2. Electrochemical and spectroelectrochemical
measurements
The cyclic voltammetry (CV) and controlled potential
coulometry (CPC) measurements were carried out with a
Princeton Applied Research Model VersaStat II potentio-
stat/galvanostat controlled by an external PC and utilizing
a three-electrode configuration at 25 ꢁC. The working elec-
trode was a Pt plate with a surface area of 0.10 cm2. The
surface of the working electrode was polished with a H2O
(DMSO)
k,
nm
(loge):
700(4.72),
674(4.75),
650(4.67), 326(5.03); 1H NMR (d-CDCl3) d: 7.41–7.96
(m, 3H, Ar–H), 6.99 (s,1H, ˜CH), ꢀ8.2 (br s, 2H,
NH).

¨
M. Ozer et al. / Polyhedron 25 (2006) 3593–3602
3596
suspension of Al2O3 before each run. The last polishing
was done with a particle size of 50 nm. A Pt wire served
as the counter electrode. A saturated calomel electrode
(SCE) was employed as the reference electrode and was
separated from the bulk of the solution by a double bridge.
The ferrocene/ferrocenium couple (Fc/Fc+) was also used
as an internal standard. Electrochemical grade tetrabuty-
lammonium perchlorate (TBAP) in extra pure dimethyl-
sulfoxide (DMSO) was employed as the supporting
electrolyte at a concentration of 0.10 mol dmꢀ3. High pur-
ity N2 was used for deoxygenating the solution for at least
20 min prior to each run and to maintain a nitrogen blan-
ket during the measurements. For controlled potential
chronocoulometry (CPC) studies, a Pt gauze working elec-
trode (10.5 cm2 surface area), Pt wire counter electrode sep-
arated by a glass bridge, and a SCE as a reference electrode
were used. The spectroelectrochemical measurements were
carried out with an Agilent Model 8453 diode array spec-
trophotometer equipped with a potentiostat/galvanostat
and utilizing a three-electrode configuration of a thin layer
quartz spectroelectrochemical cell at 25 ꢁC. The working
electrode was transparent Pt gauze. A Pt wire counter
electrode separated by a glass bridge and a SCE reference
electrode, separated from the bulk of the solution by a dou-
ble bridge, were used.
data acquisition system incorporated into a personal
computer.
3. Results and discussion
3.1. Synthesis
The main precursor, molecule 3, for the synthesis of
bis(pentafluorophenyl)methoxyl substituted Pcs was
obtained by a nitro displacement reaction [3,14] of
4-nitrophthalonitrile (2) and bis(pentafluorophenyl)metha-
nol (1). The peripherally substituted Pc derivatives were
prepared from the phthalonitrile derivative 3 with Li in
pentan-1-ol [10] or with metal acetates [Zn(OAc)2 Æ 2H2O
or Co(OAc)2 Æ 4H2O] in DMAE by a cyclotetramerization
reaction.
The central metal ions and the peripheral substituents
on the Pc ring effect the solubility of the MPcs. Perflu-
oro-substituted compounds have a tendency for high solu-
bility in polar solvents. This situation may be interpreted
with the extreme electronegativity of the fluorine atom.
Both the metal-free 4 and Zn(II) Pc 5 were soluble in strong
and medium polar solvents such as DMSO, DMF, EtOH
and MeOH, while the Co(II)-Pc (6) was soluble only in
strong solvents, e.g. DMSO and DMF. On the contrary
to Pcs 5 and (6), the metal-free one 4 also showed solubility
in less polar solvents such as CHCl3, CH2Cl2 and THF.
The IR spectra were derived from potassium bromide
disks. The existence of C„N groups was apparent from
a single peak at 2233 cmꢀ1 in the spectrum of 3. The forma-
tion of phthalocyanines from the dinitrile derivative was
verified by the disappearance of the C„N stretching vibra-
tion band at 2233 cmꢀ1. The IR spectra of 4–6 showed sim-
ilar characteristics, except for metal-free 4 which showed a
peak at 3297 cmꢀ1, assigned to NH groups of the inner
core.
2.3. Dc and impedance spectral measurements
Spin coated thin films of the compounds were prepared
on a glass substrate fitted with interdigitated (IDT) gold
electrodes for electrical characterization. Before vacuum
evaporation, the glass substrates were thoroughly cleaned
˚
ultrasonically and then coated with 100 A of chromium fol-
˚
lowed by 1200 A of gold in a Leybold Univex 450 coater
system. The film was patterned photolithographically and
etched to provide 10 fingers pairs of electrodes having a
width of 100 lm, spaced 100 lm from the adjacent elec-
trodes. The finger overlap distance was 5 mm. DMF was
used as the solvent. The reason for using DMF as the sol-
vent is the good solubility of the compounds in DMF. The
compounds were dissolved in DMF at concentrations of
5 · 10ꢀ3 M for all compounds. Twenty microlitres of such
solutions were added with a glass pipette onto the IDT
structure held on a spinner (Speciality Coatings Systems
Inc., Model P6700 Series). The substrate was spun at
2000 rpm for 20 s and then the films were dried at 60 ꢁC
under vacuum for 2 h to evaporate the solvent. Dc conduc-
tivity measurements were performed between 290 K and
440 K using a Keithley 617 electrometer. Impedance spec-
troscopy measurements were carried out with a Keithley
3330 LCZ meter in the frequency range 40–105 Hz, and
in the temperature range 290–440 K. A close cycle liquid
helium cryostat was used to allow electrical characteristics
to be measured over a wide temperature range. The tem-
perature of the samples was controlled with a Leybold
LTC 60 temperature controller during the measurements.
The conductivity data were recorded using an IEEE 488
The UV–vis spectra of 4–6 in DMSO show characteris-
tic absorptions between 700 and 675 nm in the Q-band
region. As expected, no splitting of the Q-band in the spec-
tra of the MPcs (M: Zn, Co) was observed while the metal-
free Pc 4 showed the expected Q band splitting. The Q
band observed for all Pc compounds was attributed to
the p ! p* transition from the highest occupied molecular
orbital (HOMO) to the lowest unoccupied molecular orbi-
tal (LUMO) of the Pc ring. The kmax value of the fluori-
nated compounds were slightly shifted to shorter
wavelengths [8–10]. The other bands in the UV region at
326 nm for 4, 356 nm for 5 and 320 nm for 6 were observed
due to transitions from the deeper p levels to the LUMO
(Fig. 1).
1
The H NMR spectra are also consistent with the pro-
1
posed structures. The H NMR spectrum of 3 in d-CDCl3
exhibited signals for the aromatic protons around 7.24–
7.76 ppm as three doublets, and a peak for the ˜CH proton
of the aliphatic group at 6.94 ppm as a singlet. However,
the aromatic and aliphatic protons in Pcs 4 and 5 appeared
as multiplets at 7.96–7.41, 7.94–7.63 ppm, and as singlets at

¨
M. Ozer et al. / Polyhedron 25 (2006) 3593–3602
3597
Table 1
Voltammetric data for 4–6
4
3
2
1
0
4
5
6
Compound Redox couple E1/2 (V) vs. SCE and Fc/Fc+b DEp (V)
a
c
4
5
6
Pc(-2)/Pc(-3)
Pc(-3)/Pc(-4)
Pc(-4)/Pc(-5)
ꢀ0.53 (ꢀ1.03)
ꢀ0.93 (ꢀ1.43)
ꢀ1.89 (ꢀ2.39)
ꢀ0.67 (ꢀ1.17)
ꢀ1.04 (ꢀ1.54)
ꢀ1.94 (ꢀ2.44)
0.43 (ꢀ0.07)
ꢀ0.43 (ꢀ0.93)
ꢀ0.83 (ꢀ1.33)
ꢀ1.39 (ꢀ1.89)
0.30
0.42
0.18
Pc(-2)/Pc(-3)
Pc(-3)/Pc(-4)
Pc(-4)/Pc(-5)
0.30
0.44
0.12
Co(III)/Co(II)
Co(II)/Co(I)
Pc(-2)/Pc(-3)
Pc(-3)/Pc(-4)
0.06
0.30
0.54
0.06
a
b
c
E1/2 = (Epa + Epc)/2 at 0.100 V sꢀ1
.
The values in parenthesis indicate the potentials vs. Fc/Fc+.
300
400
500
600
700
800
900
DEp = Epa ꢀ Epc at 0.100 V sꢀ1
.
Wavelength, nm
Fig. 1. UV–vis spectra of 4–6 in DMSO.
scan rate in order to determine the mode of mass transport.
The peak currents for the processes Ic, IIc and IIIc
increased in direct proportion to the square root of the scan
rate between 0.025 and 1.00 V/s, thus suggesting that the
relevant reactions are controlled by diffusion. Compound
5 shows similar voltammetric behaviour to 4. It also
showed three one-electron, quasi-reversible reduction
6.99, 6.81 ppm, respectively. The internal NH protons of
metal-free Pc 4 were confirmed as a broad signal at
ꢀ8.2 ppm.
A close investigation of the 19F NMR spectra of com-
pounds 3 and 5 confirmed the proposed structures. These
compounds displayed signals due to F2,6, F4 and F3,5 at
d: ꢀ141.2, ꢀ149.9 and ꢀ159.6 ppm, and ꢀ143.2, ꢀ156.5
and ꢀ163.2 ppm, respectively. The F4 signal appeared as
a triplet due to F3,5 coupling, the F2,6 signals appeared as
a doublet and the F3,5 signals as a quartet in both com-
pound. Thus, the 19F NMR measurements provided addi-
tional support for the structures of the fluorinated
compounds 3 and 5 [15].
waves at E1/2 = ꢀ0.67 V, E1/2 = ꢀ1.04 V and E1/2
=
ꢀ1.94 V versus SCE (Fig. 3). These reduction processes
are probably ligand based since zinc is not redox active
in Pc complexes. The first reduction processes of 4 occur
at potentials slightly less negative than those of 5. This
can be attributed to the difference in the polarizing power
of central metal and the hydrogens. The first two ring
reduction processes for main group Pcs are generally sepa-
rated by about 0.4–0.5 V. The third reduction occurs 0.8 V
more negative than the second reduction. The separation
between the second and the third reductions is smaller with
more polarizing ions such as Zn(II) [16]. The redox poten-
tials measured for 4 and 5 are consistent with the general
In addition to these supportive results for the structures,
the mass spectra of compounds 3–6 gave the characteristic
molecular ion peaks at m/z: 490 [M]+, 1963 [M]+, 2026
[M]+ and 2021 [M+1]+, respectively, from which the pro-
posed structures were confirmed.
3.2. Electrochemistry and spectroelectrochemistry
Cyclic voltammetry of 4–6 was carried out on a plati-
num working electrode in DMSO. Controlled-potential
coulometry studies showed that the redox processes moni-
tored for these compounds generally involves the transfer
of one electron. Voltammetric data of the compounds are
presented in Table 1. It should be noted that as the third
reductions occurred at very negative potentials, it was not
possible to determine correctly the number of electrons
transferred. However, on the basis of the studies reported
previously for mono Pcs [16], it can be assumed that the
third reduction for each compound involves the transfer
of one electron.
IIIc
5
0
IIc
Ic
IIIa
IIa
Ia
Compound 4 displayed three quasi-reversible reduction
0.0
-0.5
-1.0
-1.5
-2.0
waves at E1/2 = ꢀ0.53 V, E1/2 = ꢀ0.93 V and E1/2
=
E / V vs. SCE
ꢀ1.89 V versus SCE, with considerably high anodic to
cathodic peak separations (Fig. 2). These Pc ring-based
redox processes were examined as a function of potential
Fig. 2. Cyclic voltammogram of 4 at 0.100 V sꢀ1 in DMSO/TBAP
solution.

¨
M. Ozer et al. / Polyhedron 25 (2006) 3593–3602
3598
20
15
10
5
will appear very much like that of a main group Pc species.
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. However, some
species vary their electrochemical behaviour according to
their environment, i.e., the oxidation of Co(II)Pc(-2) can
lead to [Co(III)Pc(-2)]+ or [Co(II)Pc(-1)]+ depending on
whether there are any available suitable coordinating
species that would stabilize the Co(II) center. Such electro-
chemistry, especially of Co(II)Pc(-2) and Fe(II)Pc(-2) is
split into two sections, that referring to donor solvents
and that referring to non-donor solvents. The main differ-
ence lies in whether the metal or the ring is oxidized first.
Donor solvents strongly favor Co(III)Pc(-2) by coordinat-
ing 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 oxi-
dation and the first reduction processes of 6 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, while
the second and third reductions are ring based, since the
voltammetric measurements were carried out in DMSO/
TBAP.
In order to provide additional support for the identifica-
tion of the redox processes of 5 and 6, spectroelectrochem-
istry of these complexes was also studied. Typical
absorption spectra for the neutral 5 and its electrochemi-
cally generated species are shown in Fig. 5. Fig. 6a shows
the UV–vis spectral changes of complex 5 during the con-
trolled potential reduction of the complex at ꢀ0.87 V ver-
sus SCE. Upon reduction, a decrease in the absorption of
the Q band centered at 700 nm and its broadening towards
the red region is observed. This is accompanied by an
increase in absorption at the region, 500–600 nm. Isosbestic
points are observed at 337, 372, 606 and 732 nm. These
spectral changes are characteristic for the formation of
Zn(II)Pc(-3) species [17,18]. The well-defined spectral
IIIc
IIc
Ic
IIIa
0
IIa
Ia
0.0
-0.5
-1.0
-1.5
-2.0
-2.5
E / V vs. SCE
Fig. 3. Cyclic voltammogram of 5 at 0.100 V sꢀ1 in DMSO/TBAP
solution.
redox characteristics reported previously for similar Pcs.
The first ring reduction potentials of 4 and 5 are less nega-
tive as compared with those given for unsubstituted Pcs in
the literature [16]. This positive potential shift can be
attributed to the electron withdrawing effect of the fluorine
atoms in 4 and 5. Therefore, it was possible to observe the
third reductions for 4 and 5, which cannot be monitored
generally. On the other hand, the first oxidation could
not be observed for 4 and 5, probably for the same reason,
positively shifted potentials.
A typical voltammogram for 6 is shown in Fig. 4. The
voltammetric behaviour of 6 is different from those of 4
and 5. It indicates three one-electron reduction processes
at E1/2 = ꢀ0.43 V, E1/2 = ꢀ0.83 V and E1/2 = ꢀ1.39 V ver-
sus SCE, and a one-electron oxidation process at E1/2
= 0.43 V versus SCE. If the transition metal ion concerned
has no accessible d orbital levels lying between the HOMO
and LUMO gap of a Pc species, then its redox chemistry
IIIc
IIc
5
Zn(II)Pc(-2)
Ic
Zn(II)Pc(-3)
Zn(II)Pc(-5)
IVc
0
IIIa
IIa
Ia
IVa
Zn(II)Pc(-4)
-5
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
400
600
800
1000
E / V vs. SCE
Wavelength, nm
Fig. 4. Cyclic voltammogram of 6 at 0.100 V sꢀ1 in DMSO/TBAP
Fig. 5. UV–vis spectra of 5 and its electrochemically generated reduced
solution.
species.

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M. Ozer et al. / Polyhedron 25 (2006) 3593–3602
3599
the potential is held constant at a considerably negative
potential.
a
Fig. 7 represents the UV–vis spectra of the neutral 6
and its electro-generated species. Fig. 8a shows the
UV–vis spectral changes of 6 during its first reduction
at ꢀ0.70 V versus SCE. The Q band absorption at
673 nm and the intensity of the shoulder at 623 nm
decrease, while a new intense band at 480 nm appears
and the absorption at the red region of the Q band
increases during the controlled-potential electrolysis. This
reduction process has well-defined isosbestic points at 393,
568 and 703 nm. The new band at 480 nm is typical
for Co(I)Pc(-2) species, and thus suggests that the first
reduction of 6 occurs at the metal center [19,20]. Upon
reduction at ꢀ1.2 V versus SCE, the Q band absorption
goes on decreasing without shift, and the absorption of
the new band also decreases (Fig. 8b). These spectral
changes are accompanied by an increase in the absorption
at the red region of the Q band with isosbestic point at
396, 570 and 701 nm, which is characteristic for Pc ring
reduction [21]. The spectral changes observed during the
third reduction process corresponding to couple III were
also typical for ring reduction. The final spectra of the
species electrochemically generated after third reduction
is shown in Fig. 7. Although the first and second reduc-
tion, and the first oxidation processes were chemically
reversible, the third reduction process was not reversible
on the spectroelectrochemical timescale, and the original
species could not be obtained upon reoxidation of the tri-
ply reduced species. This is also probably due to decom-
position after reduction. Fig. 8c shows the spectral
changes during oxidation of 6. The original Q band
absorption at 673 nm increases with a clear shift to
683 nm while the absorption of the shoulder at 623 nm
decreases slightly and the absorption in the 500–600 nm
region increases. These spectral changes result in isos-
bestic points at 418, 612 and 728 nm, typical of a
Co(II)Pc(-2)/Co(III)Pc(-2) redox process [20].
300
400
500
600
700
800
900
1000
Wavelength, nm
b
400
600
800
1000
Wavelength, nm
Fig. 6. UV–vis spectral changes during (a) the first reduction; (b) the
second reduction of 5.
changes during the second reduction of 5 with an applied
potential of ꢀ1.40 V versus SCE are shown in Fig. 6b. Sim-
ilar spectral changes continue with the formation of well-
defined isosbestic points at 374, 666 and 730 nm. The
appearance of a new broad absorption band with low
intensity at 544 nm is also characteristic for ring reduction.
The first and second reduction processes were chemically
reversible on the spectroelectrochemical time scale and
the nearly original spectrum of the neutral compound 5
was obtained upon reoxidation. It could be concluded that
the species produced during the first and second reduction
processes remained stable throughout the measurement.
The final spectra obtained after the controlled potential
electrolysis of 5 at ꢀ2.10 V versus SCE is given in Fig. 5.
Unfortunately, the third reduction process was not chemi-
cally reversible on the spectroelectrochemical time scale
although it was quasi-reversible during the cyclic voltam-
metric measurement. Reoxidation of the triply reduced spe-
cies did not generate compound 5 with its original
spectrum. This is probably due to the fact that the third
reduction process occurs at considerably negative poten-
tials, and decomposition of the complex may occur when
Co(III)Pc(-2)
Co(II)Pc(-2)
Co(I)Pc(-2)
Co(I)Pc(-3)
Co(I)Pc(-4)
400
500
600
700
800
900
Wavelength, nm
Fig. 7. UV–vis spectra of 6 and its electrochemically generated reduced
and oxidized species.

¨
M. Ozer et al. / Polyhedron 25 (2006) 3593–3602
3600
negative polarization as well as an ohmic contact behav-
a
iour were found. The conductivity values of the films were
calculated from the slopes of the measured I–V character-
istics. It was found that the conductivity of the films were
reversible for temperature cycling. The measured dc con-
ductivity data of the prepared films were plotted as lnr(T)
versus 1/T. This plot indicated that the compounds are
semiconducting in nature. A linear relationship in conduc-
tivity variations are observed for 4–6 in the temperature
range 290–440 K. The slopes of these plots are determined
and used to evaluate the activation energies and the data
are presented in Table 2. The general trend, for the order
of electrical conductivities, observed in the whole tempera-
ture range for these compounds are rdc(2H) >
rdc(Co) ꢁ rdc(Zn). The observed electrical conductivities
of the compounds are found to be ꢂ102 times higher com-
pared to their parent Pcs. Differences in the order of the
electrical conductivities in this case are mainly due to the
electron withdrawing effect of fluorine atoms. The electron
withdrawing bis(pentafluorophenyl) substituents decreases
the separation distance between the Pc macrocycles. The
smaller interplanar spacing between the molecules as well
as favorable intermolecular stacking are expected to lead
to greater overlap between the p-electron orbitals of both
macrocycles. This result is significant because it strongly
suggests that the overlap of p-electron orbitals plays a
major role in the electrical conduction behaviour. The
highest conductivity in metal free Pc 4 indicates that the
transport of charge carriers is through the ligands, and
not through the metal ions.
400
400
400
500
500
500
600
700
800
800
800
900
900
900
Wavelength, nm
b
600
700
Wavelength, nm
The trend observed in the ac electrical conductivity was
the same as the dc conductivity (rac(2H) > rac(Co) ꢁ
rac(Zn)). Fig. 9 shows the dependence of ac conductivity
on frequency for the compounds at 350 K. As can be seen
from Fig. 9, the frequency has a pronounced effect on the
measured ac conductivity. The frequency dependence of
the conductivity follow a universal power law for all the
compounds [22],
c
racðxÞ ¼ Axs
ð1Þ
where x is the angular frequency, A and the frequency
exponent s are material dependent constants. In general,
ac conductivities are not equal to dc conductivities. Several
mechanisms can be operative for ac conduction in molecu-
lar materials. In the case of ac conductivity, the measured
conductivity depends not only the conductivity of the
material, but also on capacitance. When the impedance
of the sample becomes purely resistive the ac conductivity
equals the dc conductivity. The interpretation of the
600
700
Wavelength, nm
Fig. 8. UV–vis spectral changes during (a) the first reduction; (b) the
second reduction; (c) the first oxidation of 6.
3.3. Dc and impedance spectral measurements
Table 2
To gain more valuable information on the processes tak-
ing place in the films, the temperature dependence of the
direct current conductivity was examined during heating
and cooling processes. Measurements were carried out in
an ambient vacuum (<10ꢀ3 mbar). In the current–voltage
(I–V) measurements symmetrical currents at positive and
The dc conductivity and activation energy values of the compounds
Compound
rdc290 (S/cm)
rdc400 (S/cm)
Ea (eV)
4
5
6
4.4 · 10ꢀ8
1.6 · 10ꢀ9
1.2 · 10ꢀ9
1.3 · 10ꢀ4
5.1 · 10ꢀ5
4.0 · 10ꢀ5
0.81
0.77
0.78

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M. Ozer et al. / Polyhedron 25 (2006) 3593–3602
3601
1.0E-05
1.0E-06
1.0E-07
1.0E-08
1.0E-09
1.0E-06
1.0E-07
1.0E-08
4
5
6
4
5
6
1.0E-09
290
340
390
440
490
Temperature (K)
1
10
100
1000
10000
100000 1000000
Fig. 10. The temperature dependence of the ac conductivity at a constant
frequency of 15 kHz for 4–6.
ln f (Hz.)
Fig. 9. The dependence of ac conductivity on frequency for 4–6 at 350 K.
slope of the lnrac(x, T) versus T graph should be constant.
Fig. 10 shows the temperature dependence of the measured
ac conductivity at constant frequency (15 kHz). The linear
relationship between rac and T confirms that the charge
carrier transport occurs via hopping processes.
measured ac conductivity data should be focused on the
hopping processes. The hopping model, which was devel-
oped by Eliot, assumes that charge carriers hop between
sites over the potential barrier separating them, rather than
tunnelling through the barrier [23]. This model gives an ac
conductivity which can be expressed to a first-order
approximation as
Acknowledgements
np3N2ee0x
This work was supported partly by the Turkish Acad-
emy of Sciences (TUBA), The Research Fund of Marmara
University (SCIENCE-YYP-290506-0130 and SCIENCE-
107/020603) and Scientific and Technical Research Council
of Turkey (TUBITAK) [TBAG-HD/50 (105T262)].
racðx; TÞ ¼
Rx6
ð2Þ
24
where e is the dielectric constant of the material, e0 that
of free space, N is the spatial density of defect states,
n = 1 for a single electron n = 2 for hopping of two elec-
trons and Rx is the hopping distance. The temperature
dependent frequency exponent s for this model is given
by,
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ð3Þ
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¨
¨
¨
where WM is the optical band gap, kB is the Boltzman’s
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ð4Þ
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