Synthesis and electrochemical properties of a series of novel tetra(4-benzoyl)phenoxyphthalocyanine derivatives

Article abstract of DOI:10.1007/s11426-012-4675-x

A novel phthalocyanine, 2,9(10),16(17),23(24)-tetra(4-benzoyl) phenoxyphthalocyanine, and its complexes with Zn(II), Cu(II), Co(II), and Ni(II) have been synthesized and characterized by a combination of elemental analysis, IR, ¹H NMR, UV-vis spectroscopy and mass spectrometry. All of the materials are very soluble in common organic solvents such as dichloromethane, chloroform, tetrahydrofuran, N,N-dimethylformamide and dimethyl sulfoxide. The Q band wavelengths of the complexes decrease in the order: Zn > Cu > Ni > Co. Redox processes were observed at -1.06, -0.74, 0.51 and 0.98 V for the free phthalocyanine, at -0.72 and 1.04 V for the Co(II) complex, at -1.24, -0.77, -0.24, 0.61 and 0.91 V for the Cu(II) complex, and at -0.74 and 1.20 V for the Ni(II) complex. The cyclic voltammograms of the phthalocyanine ring of the four species are similar, with reduction and oxidation couples each involving a one-electron transfer process. Science China Press and Springer-Verlag Berlin Heidelberg 2012.

Full text of DOI:10.1007/s11426-012-4675-x

SCIENCE CHINA
Chemistry
September 2012 Vol.55 No.9: 1872–1880
doi: 10.1007/s11426-012-4675-x
• ARTICLES •
Synthesis and electrochemical properties of a series of novel
tetra(4-benzoyl)phenoxyphthalocyanine derivatives
WANG Kun, FU Qiang*, MA JiCheng, LI WeiLi, LI WenJu, HOU Yang,
CHEN LiLi & ZHAO BaoZhong
Faculty of Chemistry, Northeast Normal University, Changchun 130024, China
Received July 11, 2011; accepted November 3, 2011; published online June 29, 2012
A novel phthalocyanine, 2,9(10),16(17),23(24)-tetra(4-benzoyl)phenoxyphthalocyanine, and its complexes with Zn(II), Cu(II),
1
Co(II), and Ni(II) have been synthesized and characterized by a combination of elemental analysis, IR, H NMR, UV–vis
spectroscopy and mass spectrometry. All of the materials are very soluble in common organic solvents such as dichloro-
methane, chloroform, tetrahydrofuran, N,N-dimethylformamide and dimethyl sulfoxide. The Q band wavelengths of the com-
plexes decrease in the order: Zn > Cu > Ni > Co. Redox processes were observed at 1.06, 0.74, 0.51 and 0.98 V for the free
phthalocyanine, at 0.72 and 1.04 V for the Co(II) complex, at 1.24, 0.77, 0.24, 0.61 and 0.91 V for the Cu(II) complex,
and at 0.74 and 1.20 V for the Ni(II) complex. The cyclic voltammograms of the phthalocyanine ring of the four species are
similar, with reduction and oxidation couples each involving a one-electron transfer process.
synthesis, electrochemical, (4-benzoyl)phenoxy, phthalocyanine
bstituted analogues [12].
1 Introduction
The molecular architecture of a phthalocyanine also
plays a significant role in its binding to metal ions. The
point of attachment of the substituents to the ring and their
relative orientation in space should influence the ease of
metal chelation because of the differences in intersubstitu-
ent distances [13]. Also, peripheral substitution can be used
to change the aggregation behavior. A number of studies of
the preparation and properties of phthalocyanine aggregates
have been carried out [14, 15]. Aromatic systems with
strong electron-donor and -acceptor substituent groups often
exhibit solvent-dependent emission properties due to inter-
nal charge-transfer processes in the excited state [16].
Phthalocyanines can exhibit electron donating properties
and their covalent linking with suitable electron acceptors
may offer some interesting possibilities for electronic inter-
action and modification.
Phthalocyanines have a number of applications, such as in
chemical sensors, liquid crystals, organic semiconductors,
non-linear optical materials, photodynamic therapy, and
photovoltaic devices [1–6], due to their good stability, ar-
chitectural flexibility, diverse coordination properties and
useful spectroscopic characteristics [1, 7]. However, their
poor solubility in common organic solvents limits their ap-
plications. Introducing bulky substituents or long chain
groups, such as alkyl or alkoxy groups, on the periphery of
the phthalocyanine framework can enhance their solubility
[8]. The introduction of sulfonyl [9], carboxyl [10], pyridine
or amino groups [11] gives water-soluble phthalocyanines.
Generally, tetrasubstituted phthalocyanines are more soluble
than symmetrically octasubstituted ones due to the for-
mation of four positional isomers in the case of the tetrasu-
The electrochemical properties of phthalocyanines are
very useful in applications as these macrocycles are known
to have remarkable properties [1]. In particular, metal-
*Corresponding author (email: fqiang@nenu.edu.cn)
© Science China Press and Springer-Verlag Berlin Heidelberg 2012
chem.scichina.com www.springerlink.com

Wang K, et al. Sci China Chem September (2012) Vol.55 No.9
1873
lophthalocyanine complexes containing large conjugated
substituents often show complicated electrochemistry in-
volving the central metal, the phthalocyanine ring, and the
substituents, and hence elucidation of the electrochemical
behavior of the large conjugated substituents is of interest
[17]. In this regard, the external connection of benzene rings
and the presence of electron-withdrawing groups in the pe-
riphery should enhance the performance and function of a
phthalocyanine, in addition to giving better solubility. Thus,
in this work we report the synthesis, characterization, and
structural investigation of a metal-free phthalocyanine
(H2Pc) tetrasubstituted at the peripheral positions with
(4-benzoyl)phenoxy groups, and its complexes with differ-
ent metal ions. The nature of the UV-vis spectra and elec-
trochemical properties of the materials are discussed in de-
tail. The materials reported are: 2,9(10),16(17),23(24)-
tetra(4-benzoyl)phenoxyphthalocyanine (3a H2Pc), 2,9(10),
16(17),23(24)-tetra(4-benzoyl)phenoxyphthalocyanine zinc
(II) (3b ZnPc), 2,9(10),16(17),23(24)-tetra(4-benzoyl)phe-
noxyphthalocyanine copper(II) (3c CuPc), 2,9(10),16(17),
23(24)-tetra(4-benzoyl)phenoxyphthalocyanine cobalt(II)
(3d CoPc), and 2,9(10),16(17),23(24)-tetra(4-benzoyl)
phenoxyphthalocyanine nickel(II) (3e NiPc).
used without further purification (unless otherwise stated).
All reactions were carried out under a nitrogen atmosphere.
IR spectra were recorded on a Magna 560 FT-IR spectro-
photometer using KBr pellets. Electronic absorption spectra
were recorded on a Cary 500 UV-vis-NIR spectrophotome-
1
ter. H NMR spectra were recorded on a Varian XL-500
NMR spectrometer in DMSO-d6. Mass spectra (MS) were
recorded on a MALDI-TOF mass spectrometer. Cyclic
voltammetry (CV) and square wave voltammetry (SWV)
experiments were performed on a CHI 1120 A electro-
chemical analysis tester.
2.2 Synthesis of compound 2
(4-Benzoyl)phenoxyphthalonitrile (2) was prepared accord-
ing to the method of Leznoff [1820] (Scheme 1).
4-Nitrophthalonitrile (1) (10 mmol, 1.73 g) was dissolved in
60 mL of dimethyl sulfoxide (DMSO) under a N2 atmos-
phere and then 4-hydroxybenzophenone (10 mmol, 1.98 g)
was added to the solution. After stirring for 15 min, finely
ground anhydrous LiOH (25 mmol, 0.60 g) was added por-
tionwise over 2 h with efficient stirring. The reaction mix-
ture was stirred at room temperature for 3 days. Then the
solution was poured into 300 mL of NaCl solution (10%),
and stirring continued for another 1 h at room temperature.
The resulting precipitate was collected by filtration and
washed with water, dried and finally recrystallized from
ethanol to give a pure white solid powder (2.69 g). The
compound was soluble in DMSO, N,N-dimethylformamide
2 Experimental
2.1 Materials and apparatus
All reagents and solvents were commercially available and
Scheme 1 Synthesis of the tetrasubstituted phthalocyanine derivatives.

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Wang K, et al. Sci China Chem September (2012) Vol.55 No.9
(DMF), chloroform (CHCl3), dichloromethane (CH2Cl2),
tetrahydrofuran (THF), and acetone. Yield: 83.02%. IR
[(KBr) νmax (cm1)]: 3098, 3041 (Ar–H), 2229 (C≡N), 1646
672 (0.13), 607 (0.04), 329 (0.09). MS (MALDI–TOF)
(THF), m/z: 1359.8 [M+H]. Complex 3d: Yield: 1.03 g
(61%). IR [(KBr) νmax (cm–1)]: 3056 (Ar–H), 1655 (C=O),
1593 (Ar–H), 1235 (C–O–C). UV-vis λmax (nm) (log ε) in
1
(C=O), 1588 (Ar–H), 1482 (Ar–H), 1249 (C–O–C). H
1
DMF: 664 (2.16), 602 (0.64), 330 (1.90). H NMR (500
NMR (500 MHz, DMSO-d6) δ(ppm): 8.19–8.17 (d, H,
Ar–H), 7.99–7.98 (d, H, Ar–H), 7.87–7.85 (d, 2H, Ar–H),
7.78–7.77 (d, 2H, Ar–H), 7.72–7.69 (t, H, Ar–H), 7.61–7.59
(d, 2H, Ar–H), 7.57 (s, H, Ar–H), 7.33–7.35 (d, 2H, Ar–H).
MHz, DMSO-d6) δ(ppm): 8.33–7.93 (m, 20H, Ar–H),
7.60–7.47 (m, 16H, Ar–H), 7.30–7.22 (m, 12H, Ar–H). MS
(MALDI-TOF) (THF), m/z: 1355.1 [M+H]. Complex 3e:
Yield: 1.02 g (60%). IR [(KBr) νmax (cm–1)]: 3057 (Ar–H),
1656 (C=O), 1593 (Ar–H), 1237 (C–O–C). UV-vis λmax (nm)
(log ε) in DMF: 671 (0.29), 612 (0.20), 333 (0.22). 1H NMR
(500 MHz, DMSO-d6) δ(ppm): 7.93–7.80 (m, 20H, Ar–H),
7.60–7.50 (m, 16H, Ar–H), 7.29–7.20 (m, 12H, Ar–H). MS
(MALDI-TOF) (THF), m/z: 1354.0 [M+H].
2.3 Synthesis of compound 3a
A mixture of compound 2 (5 mmol, 1.62 g) and
1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) (0.40 mmol,
0.70 mL) in 15 mL of dry 1-pentanol was stirred under re-
flux for 8 h in N2. After cooling to room temperature, the
reaction mixture was poured into a mixture of metha-
nol:H2O (5:1) and the solid filtered and washed with H2O.
The dark green precipitate was collected, and evaporated
under reduced pressure. The resulting dark green product
was washed with hot EtOH and dried in vacuum. The com-
pound was soluble in DMSO, DMF, CHCl3, and THF,
slightly soluble in acetone, and insoluble in EtOH, MeOH,
and H2O. Yield: 0.91 g (56%). IR [(KBr) νmax (cm1)]: 3430
(N–H) 3056 (Ar–H), 1656 (C=O), 1594 (Ar–H),
3 Results and discussion
3.1 Synthesis and characterization
Compound 2 was prepared via a base-catalyzed (LiOH)
nucleophilic aromatic displacement reaction of 1 with
4-hydroxybenzophenone. Compounds 3a, 3b, 3c, 3d and 3e
were then prepared by the template reaction of compound 2
with DBU in the presence of the appropriate metal salt pre-
cursor (Scheme 1). Relatively good yields (56%–76%) were
obtained after purification by recrystallization. Compounds
3a–3e were peripherally (β) substituted and soluble in sol-
vents such as CH2Cl2, CHCl3, toluene, THF, DMSO and
DMF.
1
1231(C–O–C). H NMR (500 MHz, DMSO-d6) δ(ppm):
7.94–7.80 (m, 18H, Ar–H), 7.59–7.56 (m, 18H, Ar–H),
7.54–7.45 (m, 14H, Ar–H, N–H). MS (MALDI-TOF)
(THF), m/z: 1298.2 [M+H].
Compounds 3a–3e were characterized by IR, UV-vis,
and 1H NMR spectroscopy, MS and elemental analysis. The
data confirmed the purity of the materials. In the IR spectra,
the disappearance of bands due to NO2 and OH groups,
along with the appearance of the sharp C–O–C, C≡N, C=O
vibration absorption peaks at 1249, 2229, and 1646 cm–1
respectively, confirmed the formation of 2. The typical ab-
sorption peaks of N–H (3430 cm–1) were observed for 3a
but were absent in the spectra of the metal complexes 3b–3e.
2.4 Synthesis of metal complexes 3b–3e
A
mixture of compound
2
(5 mmol, 1.62 g),
Zn(CH3COO)2·2H2O (1.25 mmol, 0.275 g) and DBU (0.4
mmol, 0.7 mL) in 15 mL of dry 1-pentanol was stirred un-
der reflux for 8 h in N2. After cooling to room temperature,
the reaction mixture was poured into a mixture of metha-
nol:H2O (5:1) and the resulting solid was filtered and
washed with H2O to remove unreacted Zn(CH3COO)2·2H2O.
1
The dark green precipitate was collected, and evaporated
under vacuum. The resulting dark green product was
washed with hot EtOH and dried in vacuum. The compound
was soluble in DMSO, DMF, CHCl3, and THF, slightly
soluble in acetone, and insoluble in EtOH, MeOH, and H2O.
Yield: 1.29 g (76%). IR [(KBr) νmax (cm–1)]: 3056 (Ar–H),
1653 (C=O), 1594 (Ar–H), 1234 (C–O–C). UV-vis λmax (nm)
(log ε) in DMF: 678 (0.98), 609 (0.18), 356 (0.36).1H NMR
(500 MHz, DMSO-d6) δ(ppm): 8.01–7.66 (m, 20H, Ar–H),
7.59–7.56 (m, 16H, Ar–H), 7.54–7.45 (m, 12H, Ar–H). MS
(MALDI-TOF) (DMF), m/z: 1360.7 [M+H].
Complexes 3c3e were prepared following the same
procedure with CuCl2·2H2O, CoCl2·6H2O, and NiCl2·6H2O
precursors, respectively. Complex 3c: Yield: 1.10 g (65%).
IR [(KBr) νmax/cm–1]: 3063 (Ar–H), 1695 (C=O), 1597
(Ar–H), 1235(C–O–C). UV-vis λmax (nm) (log ε) in DMF:
The H NMR spectra of the materials showed peaks be-
tween 8.33 and 7.20 ppm arising from substituent and ring
protons. Although the presence of isomers, as well as Pc
aggregation at the concentrations used for the NMR meas-
urements, leads to broadening of the aromatic signals, the
observed spectra of all the materials were relatively
well-resolved [1, 21]. MS also confirmed the formation of
the desired products.
The addition of the aza-linkages and peripheral fused
benzene rings to form MPc breaks the accidental degenera-
cy of the HOMO level in the unsubstituted phthalocyanine
so that the 1a1u and 1a2u orbitals become widely separated,
resulting in the observation of a Q band near 670 nm and a
B band set near 300 nm [22, 23]. After dissolution in DMF,
the well defined Q band maxima observed at 696 nm (3a),
678 nm (3b), 672 nm (3c), 664 nm (3d) and 671 nm (3e),

Wang K, et al. Sci China Chem September (2012) Vol.55 No.9
1875
shown in Figure 1, are typical of monomeric phthalocya-
nines [24]. The B bands of 3a–3e are observed at 329, 366,
328, 330 and 333 nm, respectively. The Q and B bands both
arise from →* transitions and can be explained in terms
of a linear combination of transitions from a1u (Q) and a2u
/b2u (B) HOMO orbitals to the doubly degenerate eg (LUMO)
orbitals. The slight broadening of the Q bands for 3a–3e
may be attributed to steric effects of the substituents at the
peripheral positions, which result in a slight deviation of the
Pc skeleton from planarity [24, 25]. Similar behavior can be
found for solutions of 3a–3e in CHCl3 and THF.
In DMF solution, all the compounds have a weak absorp-
tion peak around 610 nm in the vicinity of the Q–band
(Figure 2) and the same result also can be observed in other
solvents. We assign this band to the absorption of the dimer
of Pc, as the absorption peak almost disappeared when the
concentration was reduced. This is consistent with previous
reports [26, 27].
se completely conjugated 18  electron systems [8] in this
region, since they have only twofold symmetry rather than
the fourfold symmetry of 3a [28, 29]. Compared with 3a,
3b–3e exhibit a slightly blue-shifted absorption. The Q band
wavelengths of 3b–3e decrease in the order: Zn > Cu > Ni >
Co, in accordance with previous reports [30]. Coordination
of metallic cations with the four nitrogen atoms of the inner
ring, results in a decrease in the charge density of the inner
ring. This affects the electron density of the whole Pc ring,
leading to an increase in the LUMO energy level of the
MPc. Therefore, the absorption wavelength is blue-shifted.
Metal ions with different numbers of d-electrons have dif-
ferent effects on the Pc conjugated ring, thus affecting the
electronic transition behavior of Pc compounds. The maxi-
mum absorption wavelength moves to longer wavelength as
the number of d-electrons in the metal ions increases.
3.2 Cyclic and square wave voltammetry
As shown in Figure 3, the Q–band for 3a (around 680 nm)
is split into two peaks. However, MPc derivatives 3b–3e
show only a single band due to the →* transition of the-
The CV and SWV 3a, 3c, 3d and 3e were performed in
freshly distilled DMF containing 0.1 M tetrabutylammoni-
um tetrafluoroborate (TBABF4) as supporting electrolyte,
with a bare glassy carbon electrode as the working electrode,
in conjunction with a platinum foil counter electrode and
Ag/AgCl reference electrode at a scan rate of 100 mVs–1.
The half-wave potential values (E1/2), anodic to cathodic
peak separation (∆Ep) and peak current ratios (Ipc/Ipa) are
summarized in Table 1. Figure 4 shows both the CV and
SWV of 3a, 3c, 3d and 3e.
Figure 4 shows the CV and SWV traces of 3a, 3c, 3d and
3e. Within the –1.6 to +1.5 V potential window, 3a exhibits
two irreversible one-electron oxidation steps, a qua-
si-reversible one-electron reduction step and an irreversible
reduction process at 0.98, 0.51 –0.75 and –1.06 V, respec-
tively (versus Ag/AgCl at a 100 mV s–1 scan rate). The first
reduction couple (at –0.75 V) displayed a pair of quasi-
reversible redox peaks with an anodic to cathodic peak sep-
aration (∆Ep) of 113 mV at 100 mV s–1 (the ∆Ep value for
the ferrocene standard was 85 mV) [17]. The second reduc-
tion couple monitored by CV at –1.06 V was clearly ob-
served during the SWV measurements. Irreversible peaks
(the first and second oxidation processes) at 0.51 and 0.98 V
were observed in the positive potential scan respectively.
These results are essentially in agreement with the literature
[3133]. These redox couples are attributed to the Pc ring.
The electrochemical reaction mechanism can be represented
as follows:
Figure 1 UV–vis spectra of 3a–3e in DMF.
e
e
2



H Pc(0)
H Pc(1)
H Pc(2)




2
2
2


0.98V
0.51V
e
e

2

H Pc(3)
H Pc(4)



2
2


0.74V
1.06V
The redox properties of metallophthalocyanines have
Figure 2 UV–vis spectra of 3b in DMF at different concentrations.
been studied by many authors [17, 3436]. All of them

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Wang K, et al. Sci China Chem September (2012) Vol.55 No.9
Figure 3 UV–vis spectra of 3a–3e in DMF, CHCl3 and THF. (a) 3a; (b) 3b; (c) 3c; (d) 3d; (e) 3e.
agree that the reduction and oxidation of MPc are due to the
interaction between the phthalocyanine ring and the central
metal. According to these studies, the first oxidation and
first reduction processes occur on the metal center in metal-
lophthalocyanines for Mn, Fe and Co derivatives in polar
solvents such as DMF. For Ni, Cu and Zn metallophthalo-
cyanines, redox processes take place on the phthalocyanine
ring [37, 38]. Thus, redox couples of CuPc (3c) should be
attributed to the Pc ring. Interestingly, the CV of 3c dis-
played a reduction peak (at –0.74 V) on sweeping to nega-
tive potential with two anodic peaks (AP1 and AP2) on the
reverse scan. Ozkaya et al. [33] reported the same phenom-
enon. They proposed that the reduction of CuPc by con-
trolled-potential electrolysis at –0.74 V involves a two-
electron redox process. However, the appearance of two re-
oxidation peaks on the reverse sweep suggests that reduc-
tion of CuPc probably occurs in two successive one-electron
steps. According to this interpretation, the electrochemical

Wang K, et al. Sci China Chem September (2012) Vol.55 No.9
1877
Figure 4 CV (bottom) and SWV (top) of 3a, 3c, 3d and 3e in DMF containing 0.1 M TBABF4. Scan rate 0.1 Vs–1. (a) 3a; (b) 3c; (c) 3d; (d) 3e.

1878
Wang K, et al. Sci China Chem September (2012) Vol.55 No.9
Table 1 Voltammetric data for the materials and relevant materials from the literature
Oxidation 2
Oxidation 1
Reduction 1
Reduction 2
Reduction 3
Ref.
c)
c)
c)
c)
c)
E1/2(V) a) ∆Ep(V) b) Ipc/Ipa E1/2(V) a) ∆Ep(V) b) Ipc/Ipa E1/2(V) a) ∆Ep(V) b) Ipc/Ipa E1/2(V) a) ∆Ep(V) b) Ipc/Ipa E1/2(V) a) ∆Ep(V) b) Ipc/Ipa
3a
3c
0.979
0.906
0.246
0.344
0.505
0.919
0.607
1.204
0.72
0.098
0.250
0.200
–0. 738 0.113
0.66 –1.060
–0.718
Tw
Tw
0.013
0.178
0.134
0.54
3d
–0.243
0.186
–0.770
0.55 –1.242
0.48
Tw
3e
–0.742
Tw
[H2Pc]
[CuPc]
[CoPc]
–0.63
–0.62
–0.36
–0.86
–1.43
–0.88
–1.64
[31]
[44]
[39]
[36]
[45]
1.03
–1.17
0.46
0.095
0.95
0.096
1.00
–1.27
–1.25
–1.64
0.103
0.98
[NiPc] 1.51d)
0.89
–1.65
–2.54
[NiPc]
0.14
Tw = this work. a) E1/2(V) = (Epa+Epc)/2 at 100 mV s–1 scan rate; b) ∆Ep(mV) = Epa–Epc at 100 mV s–1 scan rate; c) Ipa/Ipc values are given for reduction
and Ipc/Ipavalues are given for oxidation processes at 100 mV s–1 scan ratel; d) the processes were recorded using SWV.
reaction mechanism can be represented as follows:
For 3e, all the redox processes are assigned to the ring
since only ring reduction or oxidation has been documented
for NiPc complexes in solution. Within the –1.6 to +1.5 V
potential window, complex 3e exhibits an irreversible
one-electron oxidation and an irreversible one-electron re-
ductions processes at 0.92 and –0.72 V. The electrochemi-
cal reaction mechanism for 3d can be described as follows:
e

Cu(II)Pc(1)
Cu(II)Pc(2)







0.92V
e
e
2

Cu(II)Pc(3)
Cu(II)Pc(4)




0.72V
Within the electrochemical window of TBABF4/DMF,
compound 3d undergoes two irreversible one-electron oxi-
dation steps, a two irreversible one-electron reduction and a
quasi-reversible one-electron reduction at 0.91, 0.61, –0.24,
–0.77 and –1.24 V, respectively, versus Ag/AgCl at a
100 mV s–1 scan rate [39]. SWV of the materials clearly
confirms the recorded redox processes. The first reduction
of 3d occurs at –0.24 V, and the first oxidation at 0.61 V
(Table 1). The difference between the voltammetric behav-
ior of 3a and 3d is due to the fact that metallophthalocya-
nines such as MnPc, CoPc and FePc, having a metal that
possesses energy levels lying between the HOMO and the
LUMO of the phthalocyanine ligand, in general exhibit re-
dox processes centered on the metal [31, 37, 41, 42]. The
separation between the first oxidation and the first reduction
potentials of the metal center for the Co(II) complex, 3d (0.
85 V) agrees with the relevant values in the literature [31,
37, 41, 42], and does not reflect the HOMO–LUMO gap.
The process IV (SWV) is not obvious in CV, and it may
overlap with process III. The first oxidation (at 0.61 V) and
first reduction (at –0.24 V) processes of 3f can be assigned
to the Co(II)/Co(III) and Co(II)/Co(I) redox couples respec-
tively and the remaining processes to the Pc ring. Thus, the
electrochemical reaction mechanism for 3d can be de-
e
e




Ni(III)Pc(2)
Ni(II)Pc(2)
Ni(II)Pc(2)






0.92V
0.72V
In addition, the oxidation couple monitored by CV is split
into two processes during the SWV measurements, espe-
cially for 3a, 3c and 3e. This splitting implies that the elec-
tron transfer process is associated with aggregation–
deaggregation equilibria of these species [43]. The effects
of aggregation will be pronounced for CV due to the high
concentrations (>10–4 M) employed compared to for UV-vis
spectroscopy, where low concentrations (10–5 M) are used
[17]. Reduction of the Pc ligand is associated with the posi-
tion of the LUMO, whereas oxidation of the ligand is asso-
ciated with the position of the HOMO [31]. Thus, the dif-
ference between the potentials of the first oxidation and the
first reduction processes reflects the HOMO–LUMO gap
(∆E1/2) for free-base phthalocyanines and it is closely relat-
ed to the HOMO–LUMO gap in metallophthalocyanine
species involving redox-inactive metal centers. The ∆E1/2
values recorded for 3a (1.25 V), 3c (1.64 V) and 3e (1.94 V)
in our study are in agreement with the values previously
reported [3133, 36, 44].
scribed as follows:
4 Conclusions
e
2



Co(III)Pc(1)
Co(III)Pc(2)



0.91V
We have synthesized a novel soluble phthalocyanine 3a and
four of its metal complexes 3b–3e from 4-nitrophthalonitrile
and 4-hydroxybenzophenone in two steps and characterized
the products by a variety of methods. The results confirm
that all the products are formed in excellent purity and have
the expected structures. The nature of their UV-vis spectra
e
e


Co(II)Pc(  2)
Co(I)Pc(  2)





0.61V
0.24V
e
e
2
3

Co(I)Pc(3)
Co(I)Pc(4)





0.77V
1.24V

Wang K, et al. Sci China Chem September (2012) Vol.55 No.9
1879
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