Unsymmetrical phthalocyanines with alkynyl substituents

Article abstract of DOI:10.1016/j.poly.2004.09.021

We report on the synthesis and characterisation of unsymmetrical metallophthalocyanines (M = Zn, Ni, Co) which carry two peripheral hexylthio substituents on each of three of the benzenoid groups, while the fourth one carries two phenylethynyl groups. The

Full text of DOI:10.1016/j.poly.2004.09.021

Polyhedron 23 (2004) 3155–3162
www.elsevier.com/locate/poly
Unsymmetrical phthalocyanines with alkynyl substituents
a
Ayfer Kalkan , Atıf Koca , Zehra Altuntas Bayır
b
a,
*
ß
Department of Chemistry, ITU Fen-Edebiya Fakultesi Kimya bolumu, Technical University of Istanbul, Maslak 34469, Istanbul, Turkey
a
b
Department of Chemical Engineering, Faculty of Engineering, Marmara University, Goztepe 34722, Istanbul, Turkey
Received 30 June 2004; accepted 30 September 2004
Available online 5 November 2004
Abstract
The synthesis of unsymmetrically substituted metallophthalocyanines (M = Zn, Ni, Co) bearing two phenylethyl moieties and six
alkythio substituents was achieved by co-cyclotetramerization of two different phthalonitrile derivatives, namely 4,5-di(hexyl-
thio)phthalonitrile and 4,5-di(phenylethynyl)phthalonitrile in the presence of zinc, cobalt or nickel salts. In contrast to the totally
alkyne substituted phthalocyanines, these partially alkyne-containing derivatives are more soluble and their Q band absorptions are
red-shifted when compared with all alkylthio phthalocyanines. Electrochemical properties of the phthalocyanines were studied by
cyclic voltammetry.
ꢀ 2004 Elsevier Ltd. All rights reserved.
Keywords: Phthalocyanine; Unsymmetrical; Phenylacetylene; Cyclic voltammetry
1. Introduction
substitution with bulky or long-chain groups in the
peripheral positions of the macrocycle, these com-
pounds can be made soluble in common organic sol-
vents, thus increasing the field of possible applications
[3–8].
Phthalocyanines are traditionally used as dyes and
pigments. Phthalocyanine derivatives displaying photo-
physical properties, electron transfer ability and oxido-
reduction capabilities are studied for applications in
electrophotography, optical date-recording systems,
electronic devices, photovoltaic cells, fuel cells and
electrochromic displays. They are also promising mate-
rials for applications in gas sensors, nonlinear optical
and optical limiting devices [1,2]. These properties are
influenced both by the nature of the substituents (elec-
tron donating or electron withdrawing) on the ligand
and by the nature of the metal ion in the core of the
ligand.
There has been a growing interest in unsymmetrical
phthalocyanines which possess interesting properties in
various areas like second order nonlinear optics [9],
photodynamic therapy of cancer [10,11], liquid crystals
[12] and Langmuir–Blodgett film formation [13]. Despite
the variety of synthetic routes developed to prepare sym-
metrically substituted phthalocyanines, relatively few
methods can be applied for preparing unsymmetrical
ones [14]. The most simple approach to the preparation
of phthalocyanines bearing different substituents is a
mixed cyclization of two precursors with different sub-
stituents. The main problem with this method is the iso-
lation of the desired phthalocyanines from a product
mixture made up of components with similar physical
and chemical properties. The second method is synthesis
on a polymeric support developed by Leznoff and Hall
[15], which consists in attaching a diiminoisoindoline
In the synthesis and purification steps and also inves-
tigation of various properties, solubility of the phthalo-
cyanines is of fundamental importance. By appropriate
*
Corresponding author. Tel.: +90 212 285 3223; fax: +90 212 285
6386.
E-mail address: bayir@itu.edu.tr (Z.A. Bayır).
0277-5387/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2004.09.021

3156
A. Kalkan et al. / Polyhedron 23 (2004) 3155–3162
or phthalonitrile to an insoluble polymer, making it re-
act with a different diiminoisoindoline and, after re-
moval of the symmetric phthalocyanine, releasing the
unsymmetrical phthalocyanine from the polymer sup-
port. A third method has been described by Kobayashi
and co-workers [16,17] and involves the ring expansion
of a subphthalocyanine to a phthalocyanine using a pht-
halonitrile unit which bears a different type of substitu-
ent to that on the subphthalocyanine.
Over the past few years, palladium catalysed cross-
coupling reactions provide a further and important
means of functionalising the phthalocyanine ring with
interesting grouping. This has produced various deriva-
tives that include alkynyl and alkenyl functionalised
phthalocyanines including some unsymmetrical phthalo-
cyanines. Examples of some of these compounds and re-
lated structures have interesting NLO effects [18,19].
We have previously reported peripherally substituted
symmetrical and unsymmetrical phthalocyanines [20–
22]. The incorporation of macrocyclic groups such as
dioxadiaza and triaza-macrocycles has enhanced the sol-
ubility of these compounds [23,24]. A consequence of
incorporating a sulfanyl function on the periphery has
been a shift of the Q-band absorption to longer wave-
lengths [25]. This is preferred for a number of applica-
tions such as with IR absorbers and photosensitizers.
In the present work, we report on the synthesis and
characterization of unsymmetrical metallophthalocya-
nines which carry two peripheral hexylthio substituents
on each of three of the benzenoid groups while the
fourth one carries two phenylethynyl groups.
mel electrode (SCE) was employed as the reference elec-
trode. The working electrode was a Pt plate with an area
of 1.0 cm2. Electrochemical grade tetrabutylammonium-
perchlorate (TBAP) in extra pure DCM was employed
as the supporting electrolyte at a concentration of
0.1 mol dmꢀ3. High purity N2 was used for deaeration
and to maintain a nitrogen blanket for at least 15 min
prior to each run. For controlled potential coulometric
(CPC) studies, a Pt gauze working electrode (10.5 cm2
surface area), a Pt gauze counter electrode separated
with a double bridge, a saturated calomel reference elec-
trode (SCE) and a model 377/12 Synchronous stirrer
were used. The potential of the working electrode was
set to the Ep value obtained in the CV experiments.
Then the solution was electrolysed with efficient stirring.
2.1. 4,5-Di(phenylethynyl)phthalonitrile (3)
To a solution of 1 g (5.10 mmol) of 1 dissolved in
100 ml of triethylamine was added 0.20 g (0.30 mmol)
of bis(triphenylphosphine)palladium(II)chloride, 0.04 g
(0.20 mmol)of copper(I)iodide and then 3.34 ml (30.45
mmol) of phenylacetylene. The reaction mixture was
heated to 90 ꢁC for 24 h under N2. As the reaction pro-
ceeded, a dark brown precipitate was formed. The
resulting suspension was filtered off and the brown solid
collected was washed with hexane. The yellow product
was obtained by column chromatography with silica
gel using CHCl3/hexane (50:1) as eluent. Yield: 0.67 g,
40%; m.p. 190 ꢁC. IR (KBr), m (cmꢀ1): 3080 (Ar–H),
2238(C„N), 2212 (C„C), 1600, 1523, 1446, 911, 782,
706 cmꢀ1 1H NMR (CDCl3):d: 7.92 (s, 2H, Ar–H),
;
7.59 (d, 4H, Ar–H), 7.42 (m, 6H, Ar–H); UV–Vis kmax
(nm) (log e) in CHCl3: 279 (4.62), 307 (4.70), 349
(4.34). Anal. Calc. for C24H12N2: C, 87.79; H, 3.68; N,
8.53. Found: C, 87.07, H, 3.66; N, 8.33%.
2. Experimental
IR spectra were recorded on a Mattison 1000 FTIR
spectrophotometer using KBr pellets, electronic spectra
on a Unicam UV2 spectrophotometer. Elemental analy-
ses were performed by the Instrumental Analysis Labo-
ratory of the TUBITAK Marmara Research Centre.
1H NMR spectra were recorded on a Bruker 250 MHz
spectrometer using TMS as an internal reference. All
reagents and solvents were of reagent grade quality ob-
tained from commercial suppliers. The homogeneity of
the products was tested in each step by TLC. 4,5-Dich-
lorophthalonitrile (1) [26] and 4,5-di(hexylthio)phthalo-
nitrile (2) [27] were synthesized according to published
methods.
Electrochemical techniques were carried out with a
Princeton Applied Research Model 273 potentiostat/gal-
vanostat controlled by an external PC using the compu-
ter program HEADSTRT and utilising a three-electrode
configuration at 25 1 ꢁC. An Origin 6.0 graph pro-
gram was used to evaluate Headstrt software data, to
draw voltammograms, and to analyse them. A Pt spiral
wire served as the counter electrode. A saturated calo-
2.2. 2,3,9,10,16,17-Hexakis(hexylthio)-23,24-bis(pheny-
lethynyl)-29H, 31H-phthalocyaninato zinc (II) (4)
A mixture of 0.16 g of 2 (0.49 mmol), 0.53 g of 3 (1.46
mmol), 0.09 g of anhydrous Zn(CH3COO)2 (0.49
mmol), 32 ll of DBU and 5 ml of anhydrous n-pentanol
was refluxed with stirring for 24 h under N2. The dark
green mixture was cooled to room temperature and then
diluted with ethanol until the crude product precipi-
tated. The precipitate was filtered off and washed several
times with hot ethanol and methanol to remove unre-
acted materials. Finally, the green precipitate was chro-
matographed on silica gel and eluted with CHCl3/
CH3OH (50:1). Yield: 0.10 g, 14%; m.p. > 200 ꢁC. IR
(KBr), m (cmꢀ1): 3080 (H–Ar), 2987–2870 (alkyl CH),
2212 (C„C) 1600, 1523, 1421, 1395, 1089, 987, 757,
1
706 cmꢀ1; H NMR (CDCl3): d: 0.94 (t, 18H, CH3),
1.62 (m, 36H, CCH2C), 1.88 (qnt, 12H, SCCH2), 3.18
(t, 12H, SCH2),7.42–7.90 (m, 18H, Ar–H); UV–Vis kmax

A. Kalkan et al. / Polyhedron 23 (2004) 3155–3162
3157
(nm) (log e) in CHCl3: 277 (4.68), 329 (4.80), 727 (4.93).
Anal. Calc. for C84H96N8S6Zn: C, 68.41; H, 6.51; N,
7.60. Found: C, 68.28; H, 6.49; N, 7.47%.
noisoindolines. Statistical considerations predict that
reaction of two different phthalonitriles of the same
reactivity in a 3:1 ratio will afford a mixture of products
in the following percentages: A4 (33%), A3B (44%),
other cross-condensation products (23%) [14]. Using
phthalonitriles with different solubility characteristics
may permit separation of the unsymmetrical phthalocy-
anines by virtue of the different solubilities of the com-
pounds present in the resulting statistical mixture. The
attachment of alkylthio groups at the peripheral posi-
tions of one of the starting compounds facilitates the
isolation of the A3B product, as this substituent confers
solubility in organic solvents and disfavours aggregation
of the macrocycles [28].
4,5-Di(hexylthio) phthalonitrile (2) and 4,5-di(phe-
nylethynyl)phthalonitrile (3) were chosen as starting
materials for this study. 2 was prepared from 4,5-dichlor-
ophthalonitrile and hexanethiol in DMF. K2CO3 was
used as the base for this nucleophilic aromatic displace-
ment [27]. Leznoff and Suchozak [29] have reported the
synthesis of 3 from 4,5-diiodophthalonitrile. In the pre-
sent work, 3 was synthesised from 4,5-dichlorophthalo-
nitrile which is easily obtained from commercially
available 4,5-dichloro-1,2-benzenedicarboxylic acid in
four steps [26]. Under typical Sonogashira reaction con-
ditions [30], the cross-coupling reaction between an ex-
cess of phenylacetylene and 4,5-dichlorophthalonitrile
in triethylamine with bis(triphenylphosphine)palladi-
um(II)chlorideand copper(I)iodide as catalysts at 90 ꢁC
under nitrogen atmosphere produced 3 in 40% yield.
Mixed condensation of 4,5-di(phenylethynyl)phthalo-
nitrile with 4,5-di(hexylthio) phthalonitrile in the pres-
ence of the corresponding metal(II) salt afforded the
unsymmetrical zinc-, nickel- and cobalt-substituted com-
plexes 4–6. Some experiments with different molar ratios
were carried out to raise the yield of the desired unsym-
metrically substituted phthalocyanines 4–6. A 1:3 ratio
of the two precursors was found to be the most appropri-
ate for dinitriles 2 and 3. The unsymmetrical phthalocya-
nines were separated by column chromatography from
the corresponding totally symmetrical octahexylthiopht-
halocyanine formed in the statistical condensation. The
unsymmetrical phthalocyanines 4–6 show good solubility
in common organic solvents such as dichloromethane,
chloroform and tetrahydrofuran (see Scheme 1).
2.3. 2,3,9,10,16,17-Hexakis(hexylthio)-23,24-bis(pheny-
lethynyl)-29H,31H-phthalocyaninatonickel (II) (5)
A mixture of 0.40 g of 2 (1.22 mmol), 1.32 g of 3 (3.66
mmol), 0.16 g of anhydrous NiCl2 (1.22 mmol) and 80 ll
of DBU was refluxed in 13 ml of anhydrous n-hexanol
with stirring for 36 h under N2. The resulting suspension
was cooled to room temperature and the crude product
was precipitated by addition of ethanol. It was filtered
off and washed first with hot ethanol, then with metha-
nol. The green product was isolated on a silica gel col-
umn first with hexane/THF (5:1) and then with THF/
DMF (5:1) as eluent. Yield 0.09 g, 5%. Melting
point > 200 ꢁC. IR (KBr), m (cmꢀ1): 3080 (H–Ar),
2987–2870 (alkyl CH), 2212 (C„C) 1600, 1523, 1421,
1
1395, 1089, 989, 756, 706 cmꢀ1; H NMR (CDCl3 250
MHz): 0.97 (t, 18H, CH3), 1.66 (m, 36H, CCH2C),
1.93 (qnt, 12H, SCCH2), 3.22 (t, 12H, SCH2), 7.38–
7.91 (m, 18H, Ar–H), 7.78 (s, 2H); UV–Vis kmax (nm)
(log e) in CHCl3: 322 (4.89), 703 (4.83). Anal. Calc. for
C84H96N8S6Ni: C, 68.72; H, 6.54; N, 7.63. Found: C,
68.53; H, 6.41; N, 7.33%.
2.4. 2,3,9,10,16,17-Hexakis(hexylthio)-23,24-bis(pheny-
lethynyl)-29H,31H-phthalocyaninatocobalt (II) (6)
A mixture of 0.30 g of 2 (0.92 mmol), 0.99 g of 3 (2.75
mmol), 0.12 g of anhydrous CoCl2 (0.92 mmol) was ref-
luxed in 10 ml anhydrous n-pentanol in the presence of
60 ll of DBU under N2 with stirring for 24 h. The reac-
tion mixture was cooled and the crude product was pre-
cipitated by addition of ethanol. It was filtered off and
washed several times with hot ethanol and acetone.
The green product was chromatographed on silica gel
with hexane/THF (2:1) as eluent. Yield 0.11 g, 8%. Melt-
ing point > 200 ꢁC. IR (KBr), m (cmꢀ1): 3080m (H–Ar),
2987–2870 (alkyl CH), 2212 (C„C) 1600, 1523, 1421,
1395, 1089, 987, 757, 706 cmꢀ1; UV–Vis kmax (nm)
(log e) in CHCl3: 270 (3.98), 329 (4.19), 711 (4.00). Anal.
Calc. for C84H96N8S6Co: C, 68.71; H, 6.54; N, 7.63.
Found: C, 68.35; H, 6.36; N, 7.50%.
The spectroscopic characterisation of the newly
synthesised compounds included 1H NMR, IR and
UV–Vis. Spectral investigations and the results are in
accord with the proposed structures. In the IR spectrum
of 3 the intense absorption band at 2238 cmꢀ1, corre-
sponding to C„N vibrations, disappears after its con-
version into the phthalocyanines. The 1H NMR
spectrum of 3 indicates aromatic protons at d 7.92,
7.59 and 7.42 ppm.
3. Results and discussion
3.1. Synthesis and characterisation
Different strategies to synthesise unsymmetrically
substituted phthalocyanines (A3B) have been reported,
the most common one being the statistical condensation
reaction between two different phthalonitriles or diimi-
1
The H NMR spectra of the unsymmetrical phthalo-
cyanines 4 and 5 are in excellent agreement with the

3158
A. Kalkan et al. / Polyhedron 23 (2004) 3155–3162
C
NC
NC
SC6H13
SC6H13
NC
NC
C
C
3
+
M
+
C
C6H13
S
SC6H13
SC6H13
C6H13
S
N
M
N
N
N
N
N
N
N
C6H13
S
C
C
C6H13
S
C
C
4
5
6
M
Zn2+
Ni2+
Co2+
Scheme 1.
proposed structures. The dominant features in the NMR
spectra of 4 and 5 are the hexylthio group resonances.
These resonances are shifted downfield by the phthalo-
cyanine ring current relative to the precursor compound
The UV–Vis spectra of 4–6 recorded in chloroform
show the typical pattern of phthalocyaninatometal com-
plexes. They are dominated by the p–p* transitions
within the heteroaromatic 18-p-electron system. The
electronic absorption spectra of 4–6 exhibit a Q band
absorption at 727, 703 and 711 nm, respectively. B
bands of these phthalocyanines appear in the UV region
at about 329 nm. The Q-bands of octakis alkylthio-sub-
stituted phthalocyanines are above 700 nm [27], the
replacement of one of the benzenoid rings by a phenyle-
thynyl ring gives rise to a bathochromic shift. The differ-
ent Q band absorptions of 4–6 are attributable to the
nature of the central metal ion.
1
2 [27]. H NMR spectrum of 4 exhibited the aromatic
protons at around d 7.42–7.90 ppm as multiplets, the
SCH2, SCCH2 protons at d 3.18 and 1.88 ppm as a tri-
plet and a quintet, respectively, and the aliphatic CH3
protons as a triplet at d 0.94 ppm. The ratio of aromatic
to aliphatic protons appears to show that the benzo
groups with two different substituents are present in a
3:1 ratio. The presence of alkylthio side chains in 4
was also confirmed by IR spectroscopy which showed
an intense aliphatic C–H stretching at 2987–2870
cmꢀ1. The 1H NMR spectrum of 5 is similar to that of 4.
In conclusion, unsymmetrical metallophthalocya-
nines 4–6 substituted with one phenylethynyl and three

A. Kalkan et al. / Polyhedron 23 (2004) 3155–3162
3159
hexylthio groups were synthesised by a statistical con-
densation route. Their spectral properties in a given sol-
vent depends strongly on the central metal ion.
and CoII/CoIII (IV), and at 0.327 and ꢀ1.247 V at
0.100 V sꢀ1 scan rate easily attributed to Pc2ꢀ/Pc3ꢀ
(II) and Pc2ꢀ/Pc1ꢀ (III) redox couples, respectively. It
is clearly indicated that first-row transition metallopht-
halocyanines differ from those of the main-group metall-
ophthalocyanines due to the fact that metal ‘‘d’’ orbitals
may be positioned between the HOMO and LUMO of
the phthalocyanine (Pc2ꢀ) ligand. This has been well
established by several papers published by Lever et al.
[1,42–44]. According to these studies, electrochemistry
of metallophthalocyanines containing a redox active me-
tal center such as Mn, Fe and Co can conveniently be
split into two sections, that referring to non-donor sol-
vents, and that referring to donor solvents. For CoPc
complexes, donor solvents or coordinating counter ani-
ons strongly favour Co(III)Pc by coordinating along the
axis to form a six-coordinate L2Co(III)Pc species. If a
donor solvent is not present, such as DCM used in this
study, then oxidation to Co(III)Pc is inhibited and ring
oxidation occurs first. So in this study, it is possible to
assign the first oxidation of the CoPc species at 0.33 V
to the ring oxidation and the second one at 0.64 V to
the metal center. According to this behaviour of CoPc
in DCM, the electron transfer sequence would be
[Co(III)/(II)]Pc(1ꢀ) > Co(II)[Pc(1ꢀ)/(2ꢀ)] > [Co(II)/(I)]
Pc(2ꢀ) > Co(I)[Pc(2ꢀ)/(3ꢀ)].
3.2. Electrochemical measurements
The electrochemical properties of metallophthalocya-
nine (MPc) complexes are well known [31–44]. Reduc-
tion and oxidation reactions can occur at either the Pc
ring or central metal or both. Oxidation at the Pc ring
in MPc(ꢀ2) occurs by successive loss of one or two elec-
trons from the highest occupied molecular orbital
(HOMO) resulting in the formation of the [MPc(ꢀ1)]+
or [MPc(0)]+2 cations, respectively. Reduction of the
Pc ring occurs by the successive gain of one to four elec-
trons by the lowest unoccupied molecular orbital
(LUMO) of the MPc complex, resulting in the forma-
tion of MPc(ꢀ3), MPc(ꢀ4), MPc(ꢀ5) and MPc(ꢀ6)
species, as commonly shown to indicate the oxidation
states of the phthalocyanine ligand in the literature re-
lated with the electrochemistry of this compounds
[1,6,31,40–44].
It has been demonstrated that substituents on the
periphery of the phthalocyanine ligand strongly influ-
ence the solution redox chemistry of these materials.
Electron-donating groups lead to a negative shift of
the redox potentials and electron-withdrawing groups
to a positive shift. This has been observed with both re-
dox inactive metals like nickel, copper and zinc and re-
dox active metals like cobalt [1].
The separation between the first reduction and first
oxidation processes (640 mV) of 6, which reflects the
HOMO–LUMO gap of the complexes, is smaller than
that in the reported CoPc papers [1,31–44]. This is not
very surprising since extended p-conjugation of 6 may
cause a decrease in the HOMO–LUMO gap of the com-
plex. This voltammetric data was confirmed by the shift-
ing of the Q band towards a longer wavelength in the
Cyclic voltammograms of CoPc (6) (Fig. 1) show four
well-defined redox couples (I–IV) within the available
potential range of the TBAP/DCM solvent system at
ꢀ0.313 and 0.644 V, easily attributed to CoII/CoI (I)
0.2
0.1
0.0
II
I'
I
III
IV
-0.1
1500
1000
500
0
-500
/ mV vs. SCE
Fig. 1. Cyclic voltammogram of 1.0 · 10ꢀ3 mol dmꢀ3 CoPc (6) in 0.1 mol dm3 TBAP/DCM at 100 mV sꢀ1 scan rate.
-1000
-1500
E

3160
A. Kalkan et al. / Polyhedron 23 (2004) 3155–3162
Table 1
The cyclic voltammetric data of the complexes with the related MPc derivatives reported in the literature
e
Complex
Redox processes
IV
Solvent Reference
III
I
II
aE1/2 bDEp cIpc
(mV) (mV) Ipa
/
aE1/2 bDEp cIpc
(mV) (mV) Ipa
/
aE1/2
(mV)
bDEp cIpc
(mV) Ipa
/
aE1/2
(mV)
bDEp cIpc
(mV) Ipa
/
ZnPc (4)
NiPc (5)
CoPc (6)
814
837
644
98
109
92
0.94
0.97
0.78
633
576
75
87
1.1
ꢀ780 149
ꢀ817 186
ꢀ313 287
ꢀ680
1.2
ꢀ1027
191
154
0.75 DCM
0.93 DCM
0.58 DCM
DMF
tw
tw
tw
45
45
46
31
0.60
0.57
0.98 ꢀ1032
327 147
750
620
1.1
ꢀ1247a 157
ꢀ1050
ꢀ1180
ꢀ1560
ꢀ1150
ꢀ670
ZnPc(SC6H4CH3)8
ZnPc(SC4H9)8
ZnPc(OC6H4C(CH3)3)H7
ꢀ830
DMF
DMF
DCM
550
645
ꢀ1080
ꢀ830
ZnPc(SC6H13)8
CoPc(CH3OC6H13 8
850
730
d
)
ZnPc(SC6H4NH2)4Cl4
ꢀ160
ꢀ490
DMSO 32
DMSO 33
DMSO 33
DMSO 33
d
d
ꢀ713
ꢀ1105
ꢀ1037
ꢀ1210
ꢀ1180
ꢀ1220
CoPc(SC6H4NH2)4Cl4
950
605
ꢀ609
d
NiPc(SC6H4NH2)4Cl4
ZnPc(SC4H9)8
CoPc(SC2H4OH)8
a
ꢀ615
1270
620
ꢀ830
DMF
DCM
34
35
ꢀ340
Cathodic peak potential for reduction, anodic peak potential for oxidation for irreversible processes.
b
c
DEp = Epa ꢀ Epc at 0.100 V sꢀ1 scan rate.
Ipa/Ipc for reduction, Ipc/Ipa for oxidation at 0.100 V sꢀ1 scan rate.
Complexes also have extra reduction and oxidation couples.
d
e
For CoPc (6) and study in [35], redox processes; I: M(II)Pc(ꢀ2)/M(I)Pc(ꢀ2), II: M(I)Pc(ꢀ2) M(II)Pc(ꢀ3), III: M(II)Pc(ꢀ2)/M(II)Pc(ꢀ1), IV:
M(II)Pc(ꢀ1)/M(III)Pc(ꢀ1). For CoPc complexes studied in [32,33], redox processes; I: M(II)Pc(ꢀ2)/M(I)Pc(ꢀ2), II: M(I)Pc(ꢀ2)/M(II)Pc(ꢀ3), III:
M(II)Pc(ꢀ2)/M(III)Pc(ꢀ2), IV: M(III)Pc(ꢀ2)/M(III)Pc(ꢀ1). For all ZnPc and NiPc complexes, redox processes;I:M(II)Pc(ꢀ2)/M(II)Pc(ꢀ3), II:
M(II)Pc(ꢀ3)/M(II)Pc(ꢀ4), III: M(II)Pc(ꢀ2)/(II)Pc(ꢀ1), IV: M(II)Pc(ꢀ1)/M(II)Pc(0).
UV–Vis spectrum of the complex. The separation be-
tween the metal based reduction and the ring reduction
was found to be 0.930 V, which is in agreement with the
separation reported for CoPcÕs [31–45]. In Table 1, the
CV data, cathodic to anodic peak separation (DEp)
and peak current ratios (Ipa/Ipc) of 6 are listed together
with those of ZnPc (4), NiPc (5) and MPcÕs containing
a similar metal centre and substituents reported in the
literature.
these processes, the anodic peak currents increased lin-
early with the square root of the scan rates for scan
rates ranging from 10 to 500 mV sꢀ1, indicating that
the electrode reaction is purely diffusion-controlled.
For both the III and IV couple, peak current ratios
(Ipa/Ipc) were smaller than unity at slow scan rates,
but move towards unity by increasing the scan rates,
indicating the complication of the mass transport
mechanism of the complex probably with a proceeding
or succeeding chemical reaction.
The observation of two closely spaced reduction
peaks (I0 and I) has been attributed to the presence
of both the aggregated and unaggregated forms of 6
in solution. At the concentration employed for voltam-
metric studies in this work, aggregation of the CoPc
derivatives is expected and was confirmed by a shoul-
der of the Q band in the UV–Vis spectra of 6 [46].
Characterisation of this couple could not be done as
a result of the splitting of the reduction peak. The
process II recorded at ꢀ1.247 V was quasi-reversible
in that it shows a more enhanced forward (cathodic)
peak compared to the return (anodic) peak and a large
DEp value (200 mV at 100 mV sꢀ1). Peak current ratios
(Ipa/Ipc) of this couple were smaller than unity at slow
scan rates and approached unity with increasing scan
rates. This behaviour of the process indicated the exist-
ence of a chemical reaction following the electron
transfer reaction (EC mechanism) [47–49]. Both of
the oxidation processes (III and IV) of 6 exhibited a
quasi-reversible peak character with moderate DEp val-
ues (157 and 147 mV at 100 mV sꢀ1, respectively). For
Complex 4 and 5 exhibited very similar voltammetric
behaviours. Fig. 2 shows the cyclic voltammograms of4
recorded at 100 mV sꢀ1 scan rate. As shown in the fig-
ure, two well-defined reduction processes, (I and II) at
ꢀ0.780 and ꢀ1.027 V attributed to the Pc2ꢀ/Pc3ꢀ and
Pc3ꢀ/Pcꢀ4 redox couples, and two well-defined oxida-
tion processes, (III and IV) at 0.633 and 0.814 V attrib-
uted to the Pc2ꢀ/Pc1ꢀ and Pc1ꢀ/Pc0 redox couples, are
observed. Since the central Zn(II) metal is redox inac-
tive, all oxidation and reduction processes observed
are ring-based [38]. Ring-based redox potentials of com-
plex 4 are considerably different to those of complex 6.
The potential of the [Pc(2ꢀ)/(1ꢀ)] couple of complex 4
is shifted to positive potentials compared with that of
complex 6. The potential of the [Pc(2ꢀ)/(1ꢀ)] couple
of complex 4 is 0.63 V and the [Pc(2ꢀ)/(1ꢀ)] couple of
6 is 0.33 V. Similar behaviour was observed for the ring
reduction potentials of the complexes. The [Pc(2ꢀ)/(3ꢀ)]
couple of 4 is shifted to a more positive potential com-
pared with that of the 6. The difference between the first

A. Kalkan et al. / Polyhedron 23 (2004) 3155–3162
3161
0.16
0.12
0.08
0.04
0.00
-0.04
-0.08
II
III
I
IV
1500
1000
500
0
-500
E / mV vs. SCE
Fig. 2. Cyclic voltammogram of 1.0 · 10ꢀ3 mol dmꢀ3 ZnPc (4) in 0.1 mol dm3 TBAP/DCM at 100 mV sꢀ1 scan rate.
-1000
-1500
and second reduction processes for 4 is 0.244 V, which is
compatible with the average value for the separation of
the first and second reduction processes of similar metal
phthalocyanine complexes [1]. The potential separation
between the first ring oxidation and the first ring reduc-
tion (DE), which corresponds to the magnitude of the
energy difference between the HOMO and LUMO, is
approximately between 1.5 and 1.8 V [1,31]. However,
the DE value of ꢁ1.413 V for 4 is smaller than the range
reported for similar complexes. Exchange of one hexyl-
thio substituent of ZnPc bearing an octakis(hexylthio)
substituent (DE value = 1.475 V) [31] with the dipheny-
lethynylgroup cause a decrease in the DE value of 4 of
about 62 mV.This is perhaps the result of the decreasing
HOMO–LUMO gap by the effect of the extended p-con-
jugation of the complex. The cyclic voltammograms of 5
also gave two one-electron diffusion controlled quasi-re-
versible reduction processes at ꢀ0.817 and ꢀ1.032 V vs.
SCE, attributed to the Pc2ꢀ/Pc3ꢀ and Pc3ꢀ/Pcꢀ4 redox
couples, and two one-electron diffusion controlled qua-
si-reversible oxidation processes at 0.536 and 0.837 V,
attributed to the Pc2ꢀ/Pc1ꢀ and Pc1ꢀ/Pc0 redox couples.
The difference between the first and second reduction
processes (0.215 V) and the small DE value (1.393 V)
for 5 is compatible with those of 4. Moreover, the indi-
vidual potentials for the first reduction and the first oxi-
dation of 4 and 5 varied remarkably due to the function
of the polarising power of the central metal ion. In gen-
eral the more polarising the central metal ions, the easier
it is to reduce the ring, and the more difficult to oxidise
the ring.
was achieved, and the time integration of the electrolysis
current was recorded. The electroactive species in the
solution were depleted during the electrolysis, and the
charge, Q, at the end of the electrolysis was calculated
using the current–time response of solution. FaradayÕs
law was used to estimate the number of electrons trans-
ferred. The CPC studies indicated that the number of
electrons transferred for all electron transfer reactions
of the compounds studied is one.
Acknowledgement
This work was supported by the Research Fund of
the Technical University of Istanbul.
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