Synthesis, physicochemical properties and electrochemistry of morpholine-substituted phthalocyanines

Article abstract of DOI:10.1142/S108842461000246X

The synthesis, spectroscopic and electrochemical properties of new phthalocyanines bearing four morpholine and four chloro units is reported. Two-step synthesis involved efficient nucleophilic substitution of 4,5-dichlorophthalonitrile as the key step. Th

Full text of DOI:10.1142/S108842461000246X

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2010; 14: 605–614
DOI: 10.1142/S108842461000246X
Published at http://www.worldscinet.com/jpp/
Synthesis, physicochemical properties and electrochemistry
of morpholine-substituted phthalocyanines
Ayfer K. Burat*a, Atıf Kocab, Jan P. Lewtakc and Daniel T. Gryko*c
a Department of Chemistry, Istanbul Technical University, Maslak , Istanbul, TR34469, Turkey
b Department of Chemical Engineering, Faculty of Engineering, Marmara University, Goztepe, Istanbul,
TR34722, Turkey
c Institute of Organic Chemistry of the Polish Academy of Sciences, Kasprzaka 44/52, Warsaw, 01-224, Poland
Received 26 April 2010
Accepted 22 May 2010
ABSTRACT: The synthesis, spectroscopic and electrochemical properties of new phthalocyanines
bearing four morpholine and four chloro units is reported. Two-step synthesis involved efficient
nucleophilic substitution of 4,5-dichlorophthalonitrile as the key step. The free-base phthalocyanine
1
and its several complexes have been characterized using UV-vis, IR, H NMR, 13C NMR and mass
spectroscopicdata.Voltammetricandspectroelectrochemicalstudiesshowthatwhilecobaltphthalocyanine
gives both metal- and ring-based, diffusion-controlled, multi-electron and reversible/quasi-reversible
redox processes, other complexes give ring-based, multi-electron and reversible/quasi-reversible redox
processes.
KEYWORDS: electrochemistry, morpholine, spectroelectrochemistry, zinc
[9–11]. The application possibilities of these compounds
INTRODUCTION
are dependent on their molecular composition. Factors
Phthalocyanines (Pcs) are functional dyes with an
such as the nature of substituents and type of metal in
extended conjugated network of π-electrons. They differ
the phthalocyanine cavity play a role in this regard. The
from the majority of other dyes in that they possess a cen-
molecular architecture, such as the position of the sub-
tral cavity large enough to coordinate almost every metal
stituents, is also important in controlling some of the Pcs
from the periodic table [1]. Phthalocyanines and their
properties [12, 13].
metal complexes (MPcs) are among the most studied
Because of the intermolecular interactions between the
classes of compounds due to their chemical and thermal
macrocycles, peripherally unsubstituted phthalocyanines
stability as well as various applications. The combina-
are practically insoluble in common organic solvents and
tion of rich coordination chemistry with optical and elec-
aqueous media, thereby excluding certain types of appli-
trochemical properties is responsible for their use in jet
cations [14]. Introducing different types of solubility-
printing inks, catalysts, display devices, chemical sen-
enhancing substituents such as alkyl, alkoxyl, phenoxyl
sors, non-linear optics, data storage and liquid crystalline
and macrocyclic groups on the periphery that increase
charge carriers [2–8]. In addition to the application in
such traditional areas, one of their emerging applications
the distance between the 18-π electron-conjugated sys-
tems of Pcs enhances the solubility of these compounds
is the utilization as photosensitizers for photodynamic
[15–18]. The size and the nature of the substituents are
therapy (PDT), a recent new technique for treating cancer
not the only criteria crucial for the solubility of the sub-
stituted phthalocyanines; the change in symmetry caused
SPP full member in good standing
by these groups on the periphery is also important.
Although the symmetrically octasubstituted (where all
the eight substituents are the same) and tetrasubstituted
phthalocyanines have been frequently encountered, octa-
substituted Pcs prepared from disubstituted phthalonitrile
*Correspondence to: Ayfer K. Burat, email: kalkanayf@itu.
edu.tr, tel: +90 212-2853236, fax: +90 212-2856386 and Daniel
T. Gryko, email: daniel@icho.edu.pl, tel: +48 22-6323221,
fax: +48 22-6326681
Copyright © 2010 World Scientific Publishing Company

606
A.K. BurAt et al.
derivatives with two different substituents in the
4,5-positions are relatively less studied and only
a few well characterized species are known [19].
This new class of substituted Pcs usually exhibit
high solubility [20]. In a sense, these types of
derivatives might be considered as alternatives
to asymmetrically substituted phthalocyanines,
which are getting more and more important for
their nonlinear optical properties, Langmuir-
Blodgett film (LB) formation and mesogenic ten-
dencies [21].
O
NC
NC
Cl
Cl
NC
NC
N
rt
+
HN
O
24 h
Cl
1
2
3
i
ii
4
5 - 7
Scheme 1. Synthesis of Pcs 4–7. (i) DBU, 1-pentanol, 24 h, 145 °C,
(ii) DBU, metal salts, 1-pentanol, 24 h, 145 °C
In this regard, we report herein the synthesis of
octasubstituted metal-free (4) and metallophtha-
locyanine complexes (5–7) carrying four morpholine
and four chloro units at the peripheral positions and their
electrochemical studies.
Reaction of 4,5-dichlorophthalonitrile (1) with both
n-butylamine and morpholine under Buchwald-Hartwig
conditions failed to give any isolable products. Conse-
quently, we turned to classical nucleophilic displacement
reasoning that introduction of a first amino-type substitu-
ent possessing strongly electron-donating character will
deactivate a second chlorine atom. Again, reaction with
n-butylamine led to complex, inseparable mixture of
seven compounds which turned out to be unstable. On
the other hand, the same reaction with morpholine was
RESULT AND DISCUSSION
Synthesis and characterization
more straightforward. Indeed, while using an excess of
morpholine at room temperature, only monosubstituted
product was obtained. Increasing the temperature did not
yield disubstituted product but rather led to substantial
decomposition. 4-chloro-5-morpholinophthalonitrile (3)
was obtained in 93% yield by using an excess amount of
morpholine at room temperature under argon atmosphere
for 24 h (Scheme 1).
The synthesis of substituted phthalonitrile derivatives
is a critical step in phthalocyanine synthesis. Of the vari-
ous precursors, 4-nitrophthalonitrile and 4,5-dichloro-
phthalonitrile are preferred because of the ease with
which they can be converted to alkyl/aryl or thioether
derivatives [22, 23]. The use of 4,5-disubstituted phthalo-
nitriles as starting compounds in the synthesis leads to
peripherally octasubstituted phthalocyanines. Gener-
ally, 4,5-dichlorophthalonitrile (1) are reacted with
O- or S-nucleophiles under basic conditions to form 4,5-
disubstituted phthalonitriles, which are then converted
to octasubstituted phthalocyanines [24]. As far as reac-
tions of 4,5-dichlorophthalonitrile with N-nucleophiles
are concerned, only sulfonamides and some alkylamines
have been successfully applied [25, 26]. Luk’yanets and
co-workers also have reported amino-substituted phthalo-
cyanines from the reaction of corresponding nitro- and
halogen-substituted phthalonitriles with amines [27, 28].
In this project, our aim was to find an effective and eas-
ily implemented process for the replacing of one chlo-
rine atom in that substrate by amine substituent. It was
anticipated that this would result in phthalocyanines con-
taining four chloro and four amino groups at peripheral
positions, leading eventually to enhanced solubility.
Currently, aryl halides can be efficiently coupled
with aryl and alkyl amines under a variety of reaction
conditions. Especially, palladium-catalyzed coupling of
aryl halides and amines has been the subject of numer-
ous studies since the groups of Hartwig and Buchwald
developed efficient synthetic protocols to carry out this
transformation [29, 30].
Reaction of compound
3
with metal salts
(Zn(CH3COO)2·2H2O, CoCl2, CuCl2) and an N-donor
base DBU in 1-pentanol led to formation of metallophtha-
locyanines 5–7, respectively (Scheme 1). The synthesis
of metal-free phthalocyanine (4) was also accomplished
in pentanol in the presence of DBU at 145 °C for 24 h
under argon atmosphere. The newly synthesized phthalo-
cyanines were purified via column chromatography on
silica gel by using dichloromethane: methanol mixture as
eluent. Due to the presence of two different substituents
on 4- and 5-positions of phthalonitrile (3), phthalocya-
nines (4–7) are naturally a mixture of positional isomers
[19, 20, 31]. This situation is common in Pcs chemistry,
exemplified by broad use of 4-tert-butylphthalonitrile
[32]. No attempt was made to separate the isomers of 4–7
(Fig. 1). When symmetrically and unsymmetrically octa-
substituted phthalocyanines have been carefully exam-
ined, unsymmetrically substituted Pcs exhibit usually a
higher solubility than symmetric derivatives. The greater
solubility of these unsymmetric Pcs results not only from
the steric bulk of the substituents preventing aggregation,
but also from the presence of the very similar isomers [19,
20, 26]. It was observed that the morpholine groups in the
peripheral positions of the phthalocyanine impart high
solubility in organic solvents when compared with those
unsubstituted or aromatic group carrying derivatives [12].
The compounds prepared in this study show good
Giventhestrongelectron-withdrawingcharacteroftwo
cyano groups, the replacing of one chlorine atom with an
amine could be in principle achieved both by nucleophilic
aromatic substitution and by Buchwald-Hartwig reaction.
Copyright © 2010 World Scientific Publishing Company
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mOrPhOlIne-SuBStItuteD PhthAlOCyAnIneS
607
Fig. 1. Isomers of phthalocyanines 4–7
solubility in a number of organic solvents, such as chlo-
roform, dichloromethane, tetrahydrofuran, dimethylfor-
mamide, dimethylsulfoxide and toluene.
the aliphatic carbon atoms were observed at 65.82 ppm
for O-CH2 and 50.20 ppm for N-CH2.
Cyclotetramerization of the dinitrile (3) was con-
firmed by the disappearance of the sharp C≡N vibra-
tion at 2225 cm-1 after phthalocyanine formation. The
IR spectra of the phthalocyanines 5–7 are very similar,
except the metal-free (4), which shows an NH stretching
band peak at 3288 cm-1 in the inner core.
Elemental analysis and spectral data (1H NMR, 13C
NMR, IR, UV-vis, EI-MS, ESI-MS, MALDI-TOF)
for all new products are consistent with the proposed
structure.
IntheIRspectrumofcompound3,stretchingvibrations
of C≡N groups at 2225 cm-1, aliphatic groups at 2848–
2986 cm-1 and aromatic groups at 3096 cm-1 appeared at
expected frequencies. In the 1H NMR spectrum of 3, the
aromatic protons appeared at 8.27 and 7.81 ppm as a sin-
glet. The O-CH2 and N-CH2 protons were confirmed at
3.73–3.75 and 3.18–3.20 ppm as triplet, respectively. The
13C NMR spectrum of 3 indicated protonated and unsatu-
rated aromatic carbon atoms at 107.42–152.69 ppm. The
nitrile carbons appeared at 115.44 and 115.28 ppm while
1
The H NMR spectra of compounds 4 and 5 are
1
consistent with the proposed structure. In the H NMR
spectrum of metal-free phthalocyanine (4) in CDCl3,
the aromatic protons appeared as multiplet around
6.87–6.52 ppm. Aliphatic O-CH2 and N-CH2 protons of
morpholine groups were observed as triplet 3.91–3.72
and 3.05–2.95 ppm, respectively. The inner core protons
of free-base phthalocyanine were monitored at around
-7.66 ppm. For compound 5, the aromatic protons of
Copyright © 2010 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2010; 14: 607–614

608
A.K. BurAt et al.
shifted to longer wavelengths when compared with
alkyl-substituted derivatives [22, 31]. For the metal-free
phthalocyanine, a split Q band observed at 680 and
712 nm, while the B band remained at 349 nm [12, 16].
The absorption spectra of representative compounds
(4–7) in THF are shown in Fig. 2. In this study, the aggre-
gation behavior of the complexes 4–7 was examined at
different concentrations in THF (Fig. 3, for complex 5
as an example). As the concentration was increased, the
intensity of absorption of the Q band also increased and
there were no new bands (normally blue-shifted) due
to the aggregated species [1, 35]. The phthalocyanine
derivatives 4–7 did not show aggregation in THF. Beer-
Lambert law was obeyed for all of these compounds in
THF for the concentrations ranging from 4.00 × 10-6 to
14.00 × 10-6 M.
Fig. 2. Electronic absorption spectra of 4–7 in THF. Concentra-
tion = 6.00 × 10-6 M
phthalocyanine core appeared at 6.56–6.97 ppm, and the
O-CH2 and N-CH2 protons at 3.73–3.75 and 2.47–2.51
ppm, respectively. The H NMR spectra of 4 and 5 are
Electrochemical measurements
1
Electrochemical characterizations of the complexes
were performed in DCM/TBAP electrolyte on platinum
electrode using CV and SWV measurements. Table 1
lists the assignments of the redox couples and the elec-
trochemical parameters, including the half-wave peak
potentials (E1/2), anodic to cathodic peak potential sepa-
ration (∆Ep), the ratio of anodic to cathodic peak currents
(Ipa/Ipc), and the difference between the first oxidation and
reduction processes (∆E1/2). Peak-to-peak separations,
E1/2 and ∆E1/2 values are in agreement with the reported
data for redox processes of the phthalocyanine complexes
[36–38]. There is harmony between the electrochemical
responses of MPcs having morpholine groups (4, 5 and
6) and MPcs having four dioctylaminocarbonyl bipheny-
loxy substituents [39]. These two MPc groups give redox
couples at approximately the same potentials, indicating
the morpholine and dioctylaminocarbonyl biphenyloxy
substituents have similar electron-releasing ability. The
only difference is the existence of chemical reactions
somewhat broader than the corresponding signals in the
dinitrile derivative (3).
In addition to the elemental analysis results, mass
spectra will be definitive. The mass spectral studies on
the newly synthesized compounds gave expected masses
as shown in section 2. The molecular ion peaks were
found at m/z = 991.8 [M]+ for complex 4, m/z = 1055.7
[M]+ for 5, m/z = 1049.24 [M]+ for 6 and m/z = 1055.13
[M + H]+ for complex 7, respectively.
The phthalocyanine system is characterized by strong
absorption bands in the UV region at 300–350 nm (the
Soret band) and in the visible region at 600–700 nm
(the Q band); both correlate to π→π* transitions [33,
34]. For the metallophthalocyanines (5–7), the Q band
position is constant at about 669–686 nm, revealing that
morpholine groups do not significantly affect the Q band
position in these complexes. However, for the metal-free
phthalocyanine (4), the Q band position was slightly
Fig. 3. Aggregation behavior of 5 in THF at different concentrations: 14 × 10-6 (A), 12 × 10-6 (B), 10 × 10-6 (C), 8 × 10-6 (D), 6 ×
10-6 (E), 4 × 10-6 (F) M
Copyright © 2010 World Scientific Publishing Company
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mOrPhOlIne-SuBStItuteD PhthAlOCyAnIneS
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Table 1. Voltammetric data of MPcs with the related complexes for comparison
Complex
Ring oxidations
MIII/MII
MII/MI
Ring reductions
d∆E1/2
Reference
H2Pc
aE1/2
b∆Ep (mV)
cIpa/Ipc
1.20e
70
0.85
66
—
—
—
—
—
—
-0.68
60
-0.96
1.53
—
—
tw
—
65
0.56
0.85
0.95
0.92
—
CuPc
ZnPc
CoPc
aE1/2
b∆Ep (mV)
cIpa/Ipc
1.26e
105
0.89
80
—
—
—
—
—
—
-0.86
115
-1.12
75
1.65
—
—
tw
—
0.75
0.92
0.92
0.95
—
aE1/2
b∆Ep (mV)
cIpa/Ipc
1.25e
85
0.81
70
—
—
—
—
—
—
-0.93
65
-1.36
72
1.74
—
—
tw
—
0.74
0.80
0.90
0.88
—
aE1/2
b∆Ep (mV)
cIpa/Ipc
—
—
—
1.28
300
0.70
60
-0.21 (-0.56)
-1.44
150
—
—
—
0.81
—
—
tw
—
97
0.55
1.00
0.80
0.65
—
fCuPc
fZnPc
fCoPc
gCoPc
hCoPc
iZnPc
jZnPc
jCoPc
kCuPc
E1/2 (in DCM)
E1/2 (in DCM)
E1/2 (in DCM)
E1/2 (in DMSO)
E1/2 (in DMSO)
E1/2 (in DCM)
E1/2 (in DCM)
fE1/2 (in DCM)
E1/2 (in DCM)
1.42e
1.51e
—
1.03
0.91
0.75
—
—
—
—
—
-0.62
-0.89 (-0.77)
-1.24
-1.17
-1.15
-1.95
—
—
—
—
—
—
—
—
—
—
45
45
45
46
47
48
44
44
49
1.23
0.45
0.49
—
-0.15
-0.37
-0.36
—
—
-1.28
—
0.99
—
-1.27
-1.83
-1.01
-1.16
—
—
-0.78
—
0.85
—
—
—
-0.75
—
0.45
—
-0.42
—
-1.30
—
—
-0.86
-1.26
a E1/2 = (Epa + Epc)/2 at 0.100 V.s-1. b ∆Ep = Epa - Epc at 0.100 V.s-1. c Ipa/Ipc for reduction, Ipc/Ipa for oxidation processes at 0.100 V.s-1
scan rate. d ∆E1/2 = ∆E1/2 (first oxidation) - ∆E1/2 (first reduction). e The process is recorded with DPV. f Substituted with tetra-(1,1-
g
(dicarbethoxy)-2-(2-methylbenzyl))-ethyl 3,10,17,24-tetra chloro moieties. Substituted with tetrakis-[4-nitro-2-(octyloxy)phe-
h
i
noxy] moieties. Substituted with tetrakis-6-(-thiophene-2-carboxylate)-hexylthio moieties. Substituted with tetrakis-octafluoro
pentoxy moieties. j Substituted with tetrapentafluorobenzyloxy moieties. k Substituted with tetrabutyl moieties. Tw: This work.
after the reduction and oxidation processes of MPcs hav-
ing morpholine substituents. MPcs {(M=2H (4) ZnII (5),
and CuII (6)} illustrated common two Pc ring reduction
and two Pc ring oxidation processes with small potential
shifts due to the presence of different metal centers. Only
the places of the redox processes and aggregation tenden-
cies of the complexes are different between the electro-
chemical responses of 4–6. While the electron transfer
processes of 4 and 5 are complicated with aggregation,
the redox processes of the complex 6 are complicated
with chemical reactions in addition to the aggregation.
Figure 4 illustrates the voltammetric responses of 6 in
solution as a representative of MPcs having redox inac-
tive Pc core. As shown in Fig. 4a, the complex 6 gives
two reduction couples at -0.86 (III) and -1.12 (IV) V at
0.100 V.s-1 scan rate. First reduction couple (III) of the
complex is quasi-reversible, since (i) anodic to cathodic
peak separations (∆Ep) values changed from 85 to 150 mV
with the scan rates from 10 to 500 mV.s-1; (ii) the Ipa/Ipc
ratio deviates from unity; and (iii) cathodic wave of the
couple is very broad. These characters of the couple may
be due to the aggregation of the complex. Splitting of
the cathodic wave (III) and disappearance of the split-
ting with dilution of the complex were recorded by
SVW (Fig. 4b), supporting the aggregation properties
of the complex. Figure 4c gives the effects of switching
potential to the CV response of the complex. When the
potential is switched from -1.10 V, the complex 6 gives
a clear reduction couple at -0.86 V. But when the switch-
ing potential was shifted to negative and repetitive scans
were performed, a new reduction couple at -0.40 V was
recorded. This new couple indicates the existence of a
chemical reaction succeeding the second reduction pro-
cess (IV) and the product of the chemical reaction gives
a redox couple (RP) at -0.40 V. This new process is also
recorded with SWV (Fig. 4b). Upon positive potential
scan, when the potential switched from 1.10 V, the com-
plex gave a clear reduction couple at 0.89 V (II). It gaves
an extra wave (OP) at -0.06 V when the potential was
switched after 1.3 V. These voltammetric responses indi-
cate the presence of a chemical reaction succeeding the
second oxidation process (I).
As shown in Fig. 5, CoPc (7) undergoes two one-
electron oxidation and two one-electron reduction
Copyright © 2010 World Scientific Publishing Company
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610
A.K. BurAt et al.
Fig. 5. CVs and SWV of CoPc (7) in DCM/TBAP electrolyte
on Pt working electrode. (a) CVs at 0.100 V.s-1 scan rate and
SWVs with 100 mV pulse size, 5 mV step size, and 25 Hz fre-
quency, (b) CVs recorded with different switching potentials at
0.100 V.s-1 scan rate
potential of the CV does not affect the redox behavior of
the complex considerably (Fig. 5b). First-row transition
metal Pcs differ from those of the main-group metal Pcs,
because metal “d” orbital’s may be positioned between
HOMO and LUMO of the phthalocyanine ligand. The
first oxidation and first reduction processes occur on the
metal center in the MPc complexes only for Mn, Fe and
Co derivatives in polar solvent such as DMF and DMSO,
while the first reduction and second oxidation processes
are metal-based in non-polar solvents such as DCM [36].
Thus, the first reduction (III) and second oxidation (I)
processes of the complex 7 could be assigned easily both
to the CoII/CoI and CoII/CoIII redox couple respectively
and the remaining processes to the phthalocyanine ring
according to the CV and SWV responses. However, the
spectroelectrochemical measurements, which are given
below, assign to the first oxidation process to CoII/CoIII
redox couple.
Fig. 4. CVs and SWV of CuPc (6) in DCM/TBAP electrolyte on
Pt working electrode. (a) CVs at 0.100 V.s-1 scan rate, (b) SWVs
(inset: SWVs with different concentration) with 100 mV pulse
size, 5 mV step size, and 25 Hz frequency, (c) CVs recorded
with different switching potentials at 0.100 V.s-1 scan rate
couples at 1.28 (I), 0.70 (II), -0.21 (III), and -1.44 (IV) V,
respectively at 0.100 mV.s-1 scan rate during the CV and
SWV measurements within the electrochemical window
of DCM/TBAP. For the first oxidation couple (II) of 7,
the value of Ipa/Ipc is close to unity and does not change
with the scan rate. Anodic to cathodic peak separations
(∆Ep) of the couple changed from 60 to 110 mV with
the scan rates from 0.010 to 0.500 mV.s-1 (∆Ep’s were
changed from 60 to 100 mV for ferrocene), suggesting a
reversible electron transfer [40]. However, the first reduc-
tion process (III) of the complex splits into two waves
due to the existence of an aggregation-disaggregation
equilibrium. Dilution effects and spectroelectrochemical
measurements (given below) support the aggrega-
tion behavior of the complex. Changing the switching
Spectroelectrochemical studies
Spectroelectrochemical studies were employed to
confirm the assignments in the CVs of the complexes.
The complexes H2Pc (4), ZnPc (5), and CuPc (6) have
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mOrPhOlIne-SuBStItuteD PhthAlOCyAnIneS
611
CuPc, these spectroscopic changes are
assigned to the reduction of aggregated
species. Further reduction of the com-
plex at -1.25 V indicated the reduction
of [CuIIPc-3]-1 to the dianionic species,
[CuIIPc-4]-2. After the second reduction
process, when 0.00 V was applied, the
spectrum did not return to the spectrum
of the original complex. This situation
indicates that the reduction processes
are not reversible due to the chemical
reaction succeeding the electron trans-
fer reactions. Under the applied poten-
tial at 1.00 V, new bands are observed
at 543 and 763 nm and the band at 630
nm assigned to the aggregated species
and the band at 687 nm assigned to the
monomeric species decreased in inten-
sity (Fig. 6c). These spectral changes
are characteristic of ring-based oxi-
dation of the aggregated and mono-
meric species at the same potential.
All bands decrease in intensity under
the applied potential at 1.40 V, indicat-
ing the decomposition of the complex
at this potential. The changes in the
Fig. 6. In situ UV-vis spectral changes of CuPc (6) in DCM/TBAP electrolyte.
color of the complex solutions were
recorded using in situ colorimetric
measurements during the redox pro-
cesses. Figure 6d gives the chromatic-
ity diagrams of the complex 6 recorded
(a) Former part of the spectral changes at Eapp = -1.00 V, (b) Later part of the spec-
tral changes at Eapp = -1.00 V, (c) Eapp = 1.00 V, (d) Chromaticity diagram (each
symbol represents the color of electro-generated species; : CuIIPc-2, : CuIIPc-3,
: CuIIPc-4, : CuIIPc-1)
redox inactive metal centers, thus they indicated ring-
based characters for all redox couples. Figure 6 shows
the in situ UV-vis spectral changes of 6 as a represen-
tative MPc having redox inactive metal center. Under
open circuit potential, the spectra of 6 indicate the pres-
ence of aggregated species with monomeric species. The
band at 630 nm is due to the aggregated species, with
the monomer appearing as a shoulder at 687 nm. Dur-
ing the potential application at -1.00 V, there are two dis-
tinct changes in the spectra. First of all, the intensity of
the Q band of monomeric species at 687 nm decreases
without shifting and new bands at 590 and 954 nm in the
MLCT region are observed. During this process, the band
assigned to the aggregated species shifts from 630 nm to
648 nm with an increase in its intensity. These increases
may be due to shifting of the aggregation equilibrium,
which causes the change in the degree of aggregation
from oligomer to trimer or to dimer, etc. These charac-
teristic changes indicate the ring-based redox process of
the monomeric species (Fig. 6a) [38, 41–45]. Then, at the
same potential application, while the Q band of aggre-
gated species at 648 nm and the band at 954 nm decrease
in intensity without shifting, new bands are recorded
at 551, 815, and 893 nm. At the same time, the band at
590 nm shifts to 581 nm (Fig. 6b). Although there is not
much literature on the reduction of aggregated species of
simultaneously during the spectroelectrochemical mea-
surements. It is observed that the color of the solution
6 is bluish green without any potential application (x =
0.271 and y = 0.370). As the potential is stepped from
0 to -1.00 V, the color of the neutral 6 turns to light blue
(x = 0.222 and y = 0.301) at the end of the first reduction.
Similarly, the color of the dianionic species, [CuIIPc-4]-2
was recorded as deep purple (x = 0.246 and y = 0.2127).
At the end of the first oxidation process, a colorless (x =
0.330 and y = 0.332) monocationic solution, [CuIIPc-1]+1,
is obtained. Measurement of the xyz coordinates allows
a quantification of each color of the redox species that is
important when determining their possible electrochro-
mic application.
As shown in Fig. 7a, the original spectrum of the com-
plex CoPc (7) indicates the presence of the aggregation
due to the band at 630 nm assigned to the aggregated
species and the Q band of the monomeric species at
675 nm. When -0.70 V potential is applied to the working
electrode, the Q band at 675 nm decreases immediately,
the band at 630 nm remains unchanged and a new band
is recorded at 463 nm. At the end of the process, the Q
band at 675 nm shifts to 711 nm and the band at 630 nm
shifts to 664 nm. These changes indicate that the mono-
meric species are reduced and then the reduction of the
aggregated ones occurs. The band at 664 nm indicates
Copyright © 2010 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2010; 14: 611–614

612
A.K. BurAt et al.
[CoIIIPc-2]1+ with perchlorate anion may
stabilize the CoIII core of the Pc ring,
thus the complex 7 indicates a metal-
based oxidation process before the ring
reduction. Under the applied potential
at 1.40 V, decreasing intensity of the
Q band without a shift and observation
of new bands at 550 and 835 nm indi-
cate the ring-based processes and are
assigned to [CoIIIPc-2]1+/[CoIIIPc-1]2+
(Fig. 7d inset) [36, 39–47]. Figure 7d
shows the colors of the electrogene-
rated anionic and cationic species.
EXPERIMENTAL
General
All chemicals and reagents were
purchased from major suppliers and
used without any further purification.
1
All reported H NMR and 13C NMR
spectra were recorded on Bruker AM
(500 MHz) or Varian 200 MHz spec-
trometers. Chemical shifts (δ, ppm)
were determined with TMS as the
internal reference. IR spectra were
recorded on a PerkinElmer Spectrum
One FT-IR (ATR sampling accessory)
Fig. 7. In situ UV-vis spectral changes of CoPc (7) in DCM/TBAP electrolyte.
(a) Eapp = -0.50 V, (b) Eapp = -1.50 V, (c) Eapp = 1.00 V (inset: Eapp= 1.40 V), (d) Chro-
maticity diagram (each symbol represents the color of electro-generated species;
: CoIIPc-2, : CoIPc-2, : CoIPc-3, : CoIIIPc-2, : CoIIIPc-1)
spectrophotometer. A a PerkinElmer Lambda 25 UV-vis
spectrophotometer was used for electronic spectra. Mass
spectra were performed via EI, ESI or MALDI-TOF MS.
Low- and high-resolution ESI MS spectra were recorded
on a Finnigan LTQ FT spectrometer. The isotopic pat-
terns for all assigned signals are in agreement with the
calculated natural abundance. Data is given for the most
abundant isotope only. Silica gel (Kieselgel 60, 200–400
mesh) was used in the separation and purification of com-
pounds by column chromatography. The homogeneity of
the products was tested in each step by TLC. The purity
of all new compounds was established based on 1H NMR
spectra and elemental analysis. 4,5-dichlorophthalonitrile
(1) [50] was prepared by reported procedures.
The electrochemical and spectroelectrochemical mea-
surements were carried out with Gamry Reference 600
potentiostat/galvanostat utilizing a three-electrode con-
figuration at 25 °C. For the cyclic voltammetry (CV),
and square wave voltammetry (SWV) measurements
the working electrode was a Pt disc with a surface area
of 0.071 cm2. The surface of the working electrode was
polished with a diamond suspension before each run; a
Pt wire served as the counter electrode. Saturated calo-
mel electrode (SCE) was employed as the reference
electrode and separated from the bulk of the solution
by a double bridge. Ferrocene was used as an internal
reference. Tetrabutylammonium perchlorate (TBAP) in
the presence of aggregated species at the end of the first
reduction process. The characteristic changes of the
bands in the spectra indicate the metal-based reduction
of the complex during the first reduction process. During
the electrochemical reduction, changes of the isosbestic
points at around 680 demonstrate that the reduction pro-
ceeds cleanly in deoxygenated DCM to give a mixture
of reduced species (aggregated and monomeric species).
Distinctive color changes are recorded from light blue
(x = 0.266 and y = 0.347) to light green (x = 0.266 and
y = 0.347) during the first reduction process (Fig. 7d).
Further reduction of 7 at -1.40 V indicates the ligand-
based redox process, as the Q band at 711 nm and its
shoulder at 664 nm decrease in intensity without a shift
and a new broad band is recorded at 540 nm (Fig. 7b).
Well-defined isosbestic points observed at 334, 416, 590
and 752 nm demonstrate that the reduction proceeds
cleanly in deoxygenated DCM to give a single, reduced
species. Figure 7c shows the spectral changes during the
oxidation process of the complex. During 0.85V potential
application, the Q band at 675 nm shifts to 785 nm and a
new band is recorded at 500 nm, which are characteristic
of a metal-based oxidation process of CoPc complexes,
assigned to [CoIIPc-2]/[CoIIIPc-2]1+. As it is reported that
the first oxidation process of CoPcs are ligand based in
non-coordinating solvents, such as DCM [36], this is an
unusual behavior for CoPcs in DCM. Coordinating of
Copyright © 2010 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2010; 14: 612–614

mOrPhOlIne-SuBStItuteD PhthAlOCyAnIneS
613
dichloromethane (DCM) was employed as the supporting
electrolyte at a concentration of 0.10 M. High-purity N2
was used to remove dissolved O2 at least 15 minutes prior
to each run and to maintain a nitrogen blanket during the
measurements. IR compensation was applied to the CV
and SWV scans to minimize the potential control error.
UV-vis absorption spectra and chromaticity diagrams
were measured by an Ocean Optics QE65000 diode array
spectrophotometer. In situ spectroelectrochemical mea-
surements were carried out utilizing a three-electrode
configuration of thin-layer quartz spectroelectrochemical
cell at 25 °C. The working electrode was a Pt gauze elec-
trode. A Pt wire counter electrode separated by a glass
bridge and a SCE reference electrode separated from the
bulk of the solution by a double bridge were used.
metal salt (0.044 g Zn(CH3COO)2 ⋅2H2O, 0.027 g CuCl2,
0.026 g CoCl2) and catalytic amount of DBU (1.8-
diazabicyclo[5.4.0]undec-7-ene] in 1-pentanol (2 mL)
was heated and stirred at 145 °C in a sealed tube for
24 h under argon. After cooling to room temperature the
green suspension was precipitated with methanol, filtered
off and washed with the same solvent and then dried in
vacuo. Finally, pure phthalocyanine derivatives were
obtained by chromatography on silica gel using dichlo-
romethane: methanol (20:1) for zinc phthalocyanine (5),
dichloromethane: methanol (25:1) for copper (6) and
cobalt phthalocyanine (7) as eluent. Synthesis of zinc
phthalocyanine (5). Yield: 0.16 g (76%), mp > 200 °C.
Anal. calcd. for C48H40Cl4N12O4Zn: C, 54.59; H, 3.82; N,
15.92%. Found: C, 5.22; H, 3.70; N, 15.82. IR: νmax, cm-1
3070 (C-H, aromatic), 2820–2953 (C-H, aliphatic), 1107
(C-O-C). UV-vis (THF): λmax, nm (log ε) 362 (4.96), 686
(5.44). 1H NMR (500 MHz; CDCl3; Me4Si): δH, ppm 2.47–
2.51 (16H, t, N-CH2), 3.73–3.75 (16H, t, O-CH2), 6.56–
6.97 (8H, m, Ar-H). MS (MALDI-TOF): m/z 1055.7 [M]+.
Synthesis of copper phthalocyanine (6). Yield: 0.11 g
(52%), mp > 200 °C. Anal. calcd. for C48H40Cl4CuN12O4:
C, 54.68; H, 3.82; N, 15.94%. Found: C, 54.71; H, 3.84;
N, 15.91. IR: νmax, cm-1 3070 (C-H, aromatic), 2853–2954
(C-H, aliphatic), 1105 (C-O-C). UV-vis (THF): λmax, nm
(log ε) 325 (5.07), 669 (5.25). MS (MALDI-TOF): m/z
1055.13 [M + H]+. Synthesis of cobalt phthalocyanine
(7). Yield: 0.10 g (47%), mp > 200 °C. Anal. calcd. for
C48H40Cl4CoN12O4: C, 54.92; H, 3.84; N, 16.01%. Found:
C, 55.02; H, 3.70; N, 16.22. IR: νmax, cm-1 3070 (C-H,
aromatic), 2850–2953 (C-H, aliphatic), 1105 (C-O-C).
UV-vis (THF): λmax, nm (log ε) 346 (4.67), 683 (5.12).
MS (MALDI-TOF): m/z 1049.24 [M]+.
Synthesis
4-chloro-5-morpholinophthalonitrile (3). 4,5-dichloro-
phthalonitrile (2.0 g, 10 mmol) (1) was dissolved in mor-
pholine (20 mL). In an argon atmosphere, the reaction
mixture was stirred at room temperature for 24 h. After
24 h the excess of morpholine was removed in vacuo and
thewhitecompoundwaspurifiedbycolumnchromatogra-
phywithneutralaluminausingdichloromethane:methanol
(98:2) as eluent. Yield: 2.35 g (93%), mp 210 °C. Anal.
calcd. for C21H10ClN3O: C, 58.19; H, 4.07; N, 16.97%.
Found: C, 57.94; H, 4.12; N, 16.83. IR: νmax, cm-1 3096
(C-H, aromatic), 2986–2848 (C-H, aliphatic), 2225
1
(C≡N), 1110 (C-O-C). H NMR (200 MHz; d-DMSO;
Me4Si): δH, ppm 3.18–3.20 (4H, t, N-CH2), 3.73–3.75
(4H, t, O-CH2), 7.81 (1H, s, Ar-H), 8.27 (1H, s, Ar-H).
13C NMR (200 MHz; CDCl3): δC, ppm 50.20 (N-CH2),
65.82 (O-CH2), 107.42 (aromatic C), 114.47 (aromatic
C), 115.28 (C≡N), 115.44 (C≡N), 125.46 (aromatic CH),
131.01 (aromatic C), 135.72 (aromatic CH), 152.69 (aro-
matic C). MS (EI): m/z 270.1 [M + Na]+.
CONCLUSION
The nucleophilic substitution of 4,5-dichlorophthalo-
nitrile with cyclic secondary amine leads selectively
to monosubstituted product as an effect of deactivating
influence of amino group. Prepared phthalonitrile under-
goes cyclocondensation under standard conditions, lead-
ing to the set of phthalocyanines displaying very good
solubility in common solvents. The voltammetric and
spectroelectrochemical properties of newly synthesized
phthalocyanine derivatives have been presented in this
work. Voltammetric and spectroelectrochemical studies
show that while metal-free, copper and zinc phthalo-
cyanine complexes give ring-based, multi-electron
and reversible/quasi-reversible redox processes, cobalt
phthalocyanine complex give both metal- and ring-based,
diffusion-controlled, multi-electron and reversible/quasi-
reversible reduction processes.
Synthesis of metal-free phthalocyanine (4). A solu-
tion of 3 (0.20 g, 0.81 mmol) and catalytic amount of DBU
in 1-pentanol (2 mL) was stirred and heated at 145 °C for
24 h under argon atmosphere. The reaction mixture was
cooled to room temperature and then diluted with meth-
anol until the crude product precipitated. The precipitate
was centrifuged and washed several times with methanol
to remove unreacted materials. Finally, the green com-
pound was chromatographed on silica gel and eluted with
dichloromethane:methanol (20:1). Yield: 0.055 g (28%),
mp > 200 °C. Anal. calcd. for C48H42Cl4N12O4: C, 58.07; H,
4.26; N, 16.93%. Found: C, 57.90; H, 4.44; N, 16.15. IR:
ν
max, cm-1 3288 (N-H), 3070 (C-H, aromatic), 2819–2955
(C-H, aliphatic), 1111 (C-O-C). UV-vis (THF): λmax, nm
1
(log ε) 349 (4.89), 680 (4.92), 712 (4.95). H NMR (500
MHz; CDCl3; Me4Si): δH, ppm -7.66 (2H, br s, NH), 2.95–
3.05 (16H, t, N-CH2), 3.72–3.91 (16H, t, O-CH2), 6.52–
6.87 (8H, m, Ar-H). MS (MALDI-TOF): m/z 991.88 [M]+.
Preparation of metallophthalocyanines (5–7). A
mixture of compound 3 (0.20 g, 0.81 mmol), 0.20 mmol
Acknowledgements
This work was funded by Marie Curie Research Train-
ing Network ‘REVCAT’ (Contract Number: MRTN-CT-
2006-035866).
Copyright © 2010 World Scientific Publishing Company
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614
A.K. BurAt et al.
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J. Porphyrins Phthalocyanines 2010; 14: 614–614