Synthesis and electrochemical and in situ spectroelectrochemical characterization of manganese, vanadyl, and cobalt phthalocyanines with 2-naphthoxy substituents

Article abstract of DOI:10.1016/j.electacta.2011.03.069

Metallo (Mn, Co, VO) phthalocyanines bearing peripheral 2-naphthoxy groups were synthesized by cyclotetramerisation of the corresponding phthalonitrile derivative. The phthalocyanine compounds were characterized by elemental analyses, mass, FT-IR and UV-v

Full text of DOI:10.1016/j.electacta.2011.03.069

Electrochimica Acta 56 (2011) 5102–5114
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Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
Synthesis and electrochemical and in situ spectroelectrochemical
characterization of manganese, vanadyl, and cobalt phthalocyanines with
2-naphthoxy substituents
a
Ibrahim Özc¸ es¸ meci , Atıf Kocab,∗, Ahmet Güla,∗∗
˙
a Technical University of Istanbul, Department of Chemistry, Istanbul, Turkey
b Marmara University, Department of Chemical Engineering, Faculty of Engineering, Istanbul, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Metallo (Mn, Co, VO) phthalocyanines bearing peripheral 2-naphthoxy groups were synthesized by
cyclotetramerisation of the corresponding phthalonitrile derivative. The phthalocyanine compounds
were characterized by elemental analyses, mass, FT-IR and UV–vis spectral data. Three intense bands
in the electronic spectra clearly indicate the absorptions resulting from naphthyl groups along with
the Q and B bands of the phthalocyanines. Electrochemical and spectroelectrochemical measurements
exhibit that incorporation of redox active metal ions, CoII and MnIII, into the phthalocyanine core extends
the redox capabilities of the Pc ring including the metal-based reduction and oxidation couples of the
metal. Presence of molecular oxygen in the electrolyte system affects the voltammetric and spectroelec-
trochemical responses of the cobalt and manganese phthalocyanines due to the interaction between the
complexes and molecular oxygen. Interaction reaction of oxygen with CoPc occurs via an “inner sphere”
Received 8 December 2010
Received in revised form 15 March 2011
Accepted 17 March 2011
Available online 25 March 2011
Keywords:
Phthalocyanine
Manganese
Electrochemistry
Spectroelectrochemistry
Electrocolorimetry
−
2−
,
chemical catalysis process. While CoPc gives the intermediates [O2−–CoIIPc−2
]
and [O22–CoIIPc−2
]
MnPc forms ␮-oxo MnPc species. An in situ electrocolorimetric method has been applied to investigate the
color of the electro-generated anionic and cationic forms of the complexes for possible electrochromatic
applications.
© 2011 Elsevier Ltd. All rights reserved.
1. Introduction
sensors under homogenous and heterogeneous conditions [1,2,9].
Vanadylphthalocyanine (VOPc) has been investigated extensively
Phthalocyanines (Pcs) are 18 ␲-electron macrocyclic conjugated
systems which attract great interest due to their diverse appli-
cations in medicinal and materials chemistry [1]. A number of
modifications can be made in the macrocycle either by introduc-
tion of different central ions or by substitution of various groups
at the peripheral sites of the ring [2]. The addition of substituents
to the peripheral positions of the phthalocyanine ring is expected
to give enhanced solubility in numerous organic solvents [3,4] and
affect the electronic spectra depending on their properties and sol-
vents may also lead to changes in photochemical and photophysical
behavior of phthalocyanines [5].
Over the years metallophthalocyanines (MPcs) have been the
active site of many applications in areas such as catalysis [6], sen-
sors [7] and photodynamic therapy (PDT) [8]. MPcs containing
redox active transition metal ions such as Co2+, Fe3+ and Mn3+
are known to be effective electrocatalysts and electrochemical
as a photosensitive reagent in photo-electrophoresis, xerographic
imaging techniques, and optical recording materials [10] and have
been employed for polymerisation of ethylene in the presence of
methyl-aluminoxane (MAO) as a co-catalyst [11]. The electrochem-
ical properties of manganese phthalocyanine (MnPc) complexes
have also generated considerable attention [12]. MnPc complexes
show interesting electrochemical behavior with oxidation states
of the central manganese ion ranging from MnI to MnIV [13], thus
enhancing detection of various analytes involving multi-electron
transfer processes.
The present paper reports the synthesis and characterization
of metallo (Mn, Co, VO) phthalocyanines containing 2-naphthol
moieties at the periphery, since the interest in MPcs having redox
active metal centers which are easily reduced and/or oxidized
is of importance since these complexes are well-known electro-
chromophores and electro-catalysts for many reactions such as
electrocatalytic reduction of molecular oxygen for fuel cell appli-
cations [14–18]. The electrocatalytic mechanisms of MPcs for
oxygen reduction reaction (ORR) in aqueous solution are well
known [14–18]. Although ORR mechanisms in the aprotic sol-
vents such as acetonitrile (CH3CN), dimethylsulfoxide (DMSO) and
∗
Corresponding author. Tel.: +90 216 3480292; fax: +90 216 3450126.
Corresponding author. Tel.: +90 212 2856827; fax: +90 212 2856386.
E-mail addresses: akoca@marmara.edu.tr (A. Koca), ahmetg@itu.edu.tr (A. Gül).
∗∗
0013-4686/$ – see front matter © 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.electacta.2011.03.069

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dichloromethane (DCM) are well known, there is no study on
detailed investigation of electrocatalytic activity of MPcs for ORR
in aprotic solvents. Indeed, the electrochemical reduction of O2 is
an important field of research as it is the main component in alter-
native fuel applications. Therefore, in this study we have performed
voltammetric and in situ spectroelectrochemical characterization
of the newly synthesized MPc complexes and detailed investigation
for the interaction of MPcs with molecular oxygen with voltam-
metric and in situ spectroelectrochemical measurements. We have
also aimed to determine intermediate adducts with in situ spectro-
electrochemical measurements combined with the voltammetric
data.
employed as the reference electrode and separated from the bulk
of the solution by a double bridge. Electrochemical grade tetra-
butylammonium perchlorate (TBAP) in extra pure DMSO and DCM
was employed as the supporting electrolyte at a concentration of
0.10 mol dm−3
.
UV–vis absorption spectra and chromaticity diagrams were
measured by an Ocean Optics QE65000 diode array spec-
trophotometer. In situ spectroelectrochemical measurements were
carried out by utilizing a three-electrode configuration of a quartz
thin-layer spectroelectrochemical cell at 25 ◦C. The working elec-
trode was a Pt gauze semitransparent electrode. 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. In situ electro-colorimetric measurements, under poten-
tiostatic control, were obtained using an Ocean Optics QE65000
diode array spectrophotometer at color measurement emission
mode by utilizing a three-electrode configuration of the thin-layer
quartz spectroelectrochemical cell. The standard illuminant A with
2◦ observer at constant temperature in a light booth designed
to exclude external light was used. CIE standard illuminant A is
intended to represent typical, domestic, tungsten-filament lighting.
Its relative spectral power distribution is that of a Planckian radia-
tor at a temperature of approximately 2856 K. Due to the nature of
the distribution of cones in the eye, the tristimulus values depend
on the observer’s field of view. To eliminate this variable, the CIE
defined the standard (colorimetric) observer. Originally this was
taken to be the chromatic response of the average human viewing
through a 2◦. Thus the CIE 1931 Standard Observer is also known
as the CIE 1931 2◦ Standard Observer. Prior to each set of mea-
surements, background color coordinates (x, y and z values) were
taken at open-circuit using the electrolyte solution without the
complexes under study. During the measurements, readings were
taken as a function of time under kinetic control, however only the
color coordinates at the beginning and final of each redox processes
were reported.
2. Experimental
2.1. Materials and equipment
Dimethyl sulfoxide (DMSO), dichloromethane (DCM), chloro-
form (CHCl3), tetrahydrofuran (THF), methanol (MeOH), 1-
pentanol, n-hexane and toluene were purchased from Merck.
Potassium carbonate, manganese chloride and cobalt chloride
were purchased from Aldrich. 4-Nitrophthalonitrile was syn-
thesized according to published methods [19]. 4-(2-Naphthoxy)
phthalonitrile (1), tetrakis(2-naphthoxy)vanadylphthalocyanine
(2) and tetrakis(2-naphthoxy)cobalt(II)phthalocyanine (3) were
prepared as reported earlier [20,21].
IR spectra were recorded on a Perkin-Elmer Spectrum One
FT-IR (ATR sampling accesory) spectrophotometer, and electronic
spectra were recorded on a Scinco Neosys-2000 double-beam
ultraviolet–visible (UV–vis) spectrophotometer using 1 cm path
length cuvettes at room temperature. Mass spectra were performed
on Ultima Fourier Transform and Varian 711 mass spectropho-
tometer. Elemental analyses were performed by the Instrumental
Analysis Laboratory of the TUBITAK Marmara Research Centre. All
solvents were dried and purified according to the literature [22].
The homogeneity of the products was tested in each step by TLC
(SiO2).
Oxygen interaction experiments are followed in three cases.
Case 1: CV responses of electrolyte system under atmospheric
conditions were recorded. Case 2: CV responses of MPcs in the
electrolyte system purged with nitrogen were recorded. Case 3: CV
responses of MPcs in the electrolyte system bubbled gradually with
oxygen were recorded.
2.2. 2(3),9(10),16(17),23(24)-Tetrakis-(2-naphthoxy)
phthalocyaninato manganese(III) chloride (4)
A mixture of compound 1 (1.00 mmol, 0.270 g) and anhy-
drous MnCl2 (0.25 mmol, 0.032 g) in 2.0 mL of DMF was fused in
a glass tube. The mixture was heated and stirred at 145 ◦C for
24 h under N2. The resulting brown suspension was cooled to
ambient temperature and the crude product was precipitated by
addition of ethanol–water and then it was filtered off. The pre-
cipitate was washed first with water, cold ethanol, cold acetone,
and hexane and then dried in vacuo. Finally, pure phthalocya-
nine complex was obtained by chromatography on silica gel
using dichloromethane/ethanol (25:1) mixture as eluent. The
yield was 40.10% (115 mg). Melting point: >200 ◦C. Anal. Calc. for
C72H40ClMnN8O4: C, 73.82; H, 3.44; N, 9.56. Found: C, 73.69; H,
3.61; N, 9.75; IR (cm−1): 3054 (Ar–H), 1610–1597 (Ar C C), 1461,
1246 (Ar–O–Ar), 1120, 964, 741; MS: m/z 1171.25 [M+1]+, 1135.55
[M−Cl]+.
3. Results and discussion
3.1. Synthesis and characterization
As used in the preparation of a variety of ether or thioether-
substituted phthalonitriles, the principle reaction to obtain
4-(2-naphthoxy)phthalonitrile (1) was
matic nitro displacement of 4-nitrophthalonitrile with 2-naphthol
[23–25]. The base of choice in this reaction was K2CO3 and dry
DMSO was preferred as the solvent.
Conversion of 4-(2-naphthoxy)phthalonitrile into the corre-
sponding metallo phthalocyanines (2–4) was accomplished in
a high-boiling point solvents (DMF) in the presence of corre-
sponding metal salts (MnCl2, VO(SO4), CoCl2). Produced MPc
products were extremely soluble in various solvents such as
chloroform, dichloromethane, tetrahydrofuran, and acetone and
they were purified by column chromatography on silica gel with
dichloromethane/ethanol (25:1) as the eluent. All compounds
were identified through various spectroscopic techniques such
as 1H NMR, FT-IR, UV–vis, mass spectra, and elemental analy-
sis. The results obtained were in agreement with the predicted
structures given in Scheme 1. Naturally, the phthalocyanine prod-
ucts synthesized during this work are a mixture of positional
a base-catalysed aro-
2.3. Electrochemical in situ spectroelectrochemical and in situ
electrocolorimetric measurements
The cyclic voltammetry (CV) and square wave voltammetry
(SWV) measurements were carried out with Gamry Reference 600
potentiostat/galvanostat controlled by an external PC and utiliz-
ing a three-electrode configuration at 25 ◦C. The working electrode
was a Pt disc with a surface area of 0.071 cm2. A Pt wire served
as the counter electrode. Saturated calomel electrode (SCE) was

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Fig. 2. Q bands of compounds 2–4 (10−5 mol dm−3) in different solvents.
solvents [30]. The higher the refractive index of the solvent, the
more red-shifted the Q band of the MPc complex concerned. THF
has a refractive index of 1.406 (at 718 nm), compared to 1.479 for
DMSO (at 733 nm), justifying the red-shift in the Q band of the
complexes in THF, relative to that in DMSO. The B-bands of 2–4
were observed at around 340–350 nm as a single band. An intense
absorption due to the ␲–␲* transition of naphthalene groups
appears for 2–4 in the UV region at about 286 nm (Fig. 1) [31].
Scheme 1. Synthetic route of metallo phthalocyanine derivatives (2–4).
isomers while the phthalonitrile precursor carries a single sub-
stituent but the isomers were hardly separated by chromatography
[26].
In the IR spectra of 4, aromatic C–O–C peak was observed at
1222 cm−1 and characteristic substituted naphthalene peak was
observed at about 758 cm−1. In the mass spectra of 4, the presence
of the characteristic molecular ion peaks at m/z = 1171.25 [M+1]+
and 1135.55 [M−Cl]+ confirmed the proposed structure. 1H-NMR
measurement of the manganese phthalocyanine was precluded
owing to its paramagnetic nature.
The phthalocyanines 2 and 3 show typical electronic spectra
with two strong absorption regions; one of them in the UV region at
about 300–400 nm (B band) arising from the deeper ␲-levels → ␲*
transition and the other in the visible part of the spectrum around
600–700 nm (Q band) attributed to the ␲–␲* transition from the
highest occupied molecular orbital (HOMO) to the lowest unoccu-
pied molecular orbital (LUMO) of the Pc−2 ring. The characteristic
Q band transition of metallophthalocyanines with D4h symmetry is
observed as a single band of high intensity in visible region (Fig. 1)
[27]. The vanadyl phthalocyanine 2 shows the expected Q band as
a single absorption at around 703 nm (Fig. 1). The observation of
near-IR absorption for 2, containing V(IV) central metal, confirms
that near-IR absorption is favored for MPc complexes containing
central metals in a high oxidation state. The red shift is a result of
the lowering of the HOMO–LUMO gap, by either destabilizing the
HOMO or stabilizing the LUMO by the central metal [28].
3.2. Voltammetric characterization
The CVs and SWVs of VOPc (2), CoPc (3), and MnPc (4) were
obtained in deaerated DMSO and DCM/TBAP electrolyte system on
a Pt working electrode. Table 1 lists the assignments of the redox
couples and estimated electrochemical parameters including the
half-wave peak potentials (E1/2), ratio of the anodic to the cathodic
peak currents (Ip,a/Ip,c), peak to peak potential separations (ꢀEp)
and difference between the first oxidation and reduction processes
(ꢀE1/2). ꢀE1/2 reflects the HOMO–LUMO gap for metal free Pcs and
it is related with HOMO–LUMO gap in MPc species having redox
inactive metal center. Peak to peak separations, E1/2 and ꢀE1/2 val-
ues are in agreement with the reported data for redox processes of
the metallophthalocyanine complexes [32–38].
Fig. 3 shows the CV and DPV of VOPc (2). Within the elec-
trochemical window of DMSO/TBAP, the complex 2 illustrates
two one-electron oxidation and two quasi-reversible one-electron
reduction processes. For the first oxidation couple, the anodic to the
cathodic peak separations (ꢀEp) changed from 67 to 130 mV with
the scan rates from 10 to 500 mV s−1 support the quasi-reversible
electron transfer character of the redox process. Reversibility is
illustrated by the similarity in the forward and reverse SWVs
(Fig. 3b) [39]. Unity of the Ipa/Ipc ratio with the scan rate and lin-
ear variation of the Ipc with square root of the scan rates indicated
the purely diffusion controlled electron transfer mechanism of the
processes. Other redox processes have quasi-reversible electron
transfer characters. Assignments of the redox couples are per-
formed by spectroelectrochemical measurements given below.
Fig. 4 shows the CV and DPV of CoPc (3) in DCM/TBAP electrolyte.
Within the electrochemical window of DCM/TBAP, the complex 3
undergoes a one-electron oxidation and two one-electron reduc-
tion processes. For the first reduction couple, ꢀEp values changed
from 61 to 115 mV with the scan rates from 10 to 500 mV s−1 which
supports reversible electron transfer character of the redox pro-
cess. Reversibility is illustrated by the similarity in the forward
and reverse SWVs (Fig. 4b) [39]. While the Ipa/Ipc ratio of first
reduction couple is unity at slow scan rates, it deviates from unity
with increasing scan rates, which indicate existence of a kinetic
control after the first reduction process. A wave (Rx) at −0.68 V
recorded at high scan rates support existence of this kinetic control.
While the Rx process is invisible at slow scan rates, its peak cur-
rent increases more than that of RI with increasing scan rates and
this wave disappeared with dilution. These data indicate aggre-
The Q-band of complex 4 in the UV–vis spectra was red-shifted
(at 718–733 nm) in different solvents (Fig. 2) relative to that of
the other analogs. This observation is characteristic of manganese
phthalocyanine complexes [29]. Positions of the Q bands of MPc
complexes are closely related to the refractive indices of the
Fig. 1. UV–visible spectra of compounds 2 and 3 (5 × 10−6 mol dm−3) in THF.

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Table 1
Voltammetric data of the complexes with the related metallophthalocyanines for comparison.
Complex
Ring oxidations
MIII/MII
MII/MI
Ring reductions
dꢀE1/2
Ref.
VOPc (in DCM)
aE1/2 vs. SCE
bꢀEp (mV)
cIpa/Ipc
1.41e
–
–
0.90
85
0.87
0.80
300
0.98
0.83
105
−0.64
62
0.99
−0.98
655
0.88
−1.83
85
0.85
1.54
tw
tw
tw
tw
CoPc (in DCM)
CoPc (in DMSO)
MnPc (in DCM)
aE1/2 vs. SCE
bꢀEp (mV)
cIpa/Ipc
−0.32
70
0.97
−0.55
75
1.00
−0.95
152
−1.43
1.12
0.82
1.20
130
0.62
aE1/2 vs. SCE
bꢀEp (mV)
cIpa/Ipc
0.27
62
0.78
−0.16
170
−1.49
−2.12e
68
–
–
0.80
1.04
78
0.96
aE1/2 vs. SCE
bꢀEp (mV)
cIpa/Ipc
1.23e
–
–
1.02
1.21
−1.45
220
0.85
0.68
0.76
0.94
0.87
0.97
0.43
0.65
0.99
0.91
0.55
OV[Pc(SC5H11)8]
OV[Pc(OC6H3(t-Bu)2)4]
OV[Pc(C8H17)4]
E1/2 (in DCM)
E1/2 (in DCM)
E1/2 (in DMF)
E1/2 (in DMF)
E1/2 (in DMSO)
E1/2 (in DCM)
E1/2 (in DCM)
E1/2 (in DMSO)
−0.58
−0.62
−0.51
−1.46
−0.98
−0.89
−1.12
−0.97
−1.14
−2.07
−1.94
[32]
[33]
[33]
[34]
[35]
[36]
[37]
[38]
Mn-OAc[Pc(. . .)4]
−0.14
−0.12
1.00
–
−0.69
−0.66
−0.37
−0.39
−0.43
Mn-OAc[Pc(S(CH2)2OH)8]
Co[Pc(S(CH2)2OH)4]
Co[Pc(OC6H4(OC6F5)2)4]
CoPc[Pc(OCH2(C6F5)2)4]
−129
−1.90
−1.39
−1.45
−0.83
0.43
tw: this work.
a
E1/2 = (Epa + Epc)/2 at 0.100 V s−1
.
b
ꢀEp = |Epa − Epc|.
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) = HOMO–LUMO gap for metallophthalocyanines having electro-inactive metal center (metal to ligand (MLCT) or ligand
to metal (LMCT) charge transfer gap for MPc having redox active metal center.).
e
The process is recorded with SWV.
Fig. 4. (a) CVs of CoPc (3) (5.0 × 10−4 mol dm−3) at various scan rates on Pt in
DCM/TBAP (inset: CVs of CoPc recorded at different cathodic switching potentials at
0.100 V s−1 scan rate). (b) SWV of CoPc, SWV parameters: pulse size = 100 mV; step
size: 5 mV; frequency: 25 Hz.
Fig. 3. (a) CVs of VOPc (2) (5.0 × 10−4 mol dm−3) at various scan rates on Pt in
DCM/TBAP. (b) SWV of VOPc, SWV parameters: pulse size = 100 mV; step size: 5 mV;
frequency: 25 Hz.

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Fig. 5. (a) CVs of CoPc (3) (5.0 × 10−4 mol dm−3) at various scan rates on Pt in
DMSO/TBAP. (b) SWV of CoPc, SWV parameters: pulse size = 100 mV; step size: 5 mV;
frequency: 25 Hz.
Fig. 6. (a) CVs of MnPc (4) (5.0 × 10−4 mol dm−3) at various scan rates on Pt in
DMSO/TBAP (inset: CVs of MnPc recorded with different switching potentials at
0.100 V s−1 scan rate). (b) SWV of MnPc, SWV parameters: pulse size = 100 mV; step
size: 5 mV; frequency: 25 Hz.
gation of the complex and aggregated species reduce at −0.68 V.
Aggregation–disaggregation equilibrium is affected with the scan
rate and concentration; whose responses are recorded as changing
the relative peak current ratios of the RI and Rx process. Differenti-
ating the switching potential does not alter the CV responses of the
complex as shown in Fig. 4a (inset). Other redox processes have
quasi-reversible electron transfer characters with respect to ꢀEp
and Ip,a/Ip,c values. Assignments of the redox couples are performed
by spectroelectrochemical measurements given below.
To investigate the effect of the solvent to the electrochemical
properties of the complexes, CV and SWV responses of CoPc (3)
are recorded in DMSO/TBAP electrolyte (Fig. 5).Within the elec-
trochemical window of DMSO/TBAP, the complex 3 gives two
one-electron oxidations and three reversible one-electron reduc-
tions. When DMSO is used instead of DCM as the solvent of
electrolyte, it is obvious that redox processes get more reversible
and aggregation of the complex decreases. This may be due to the
coordinating feature of DMSO. It is known that CoPc complexes
can coordinate with coordinating reagent, e.g. DMSO or TBAP [40].
Extension of the coordination of the cobalt center of the complex
prevents interaction of the monomeric species with each other,
thus diminishes aggregation of the complex. Moreover, redox pro-
cesses of the complex shift to the negative potentials due to the
high electron donating ability of DMSO with respect to DCM. While
ꢀE1/2 value of CoPc is 1.21 V in DCM, it decreases to 0.82 V in DMSO.
This decrease in ꢀE1/2 is resulted from shifting of the oxidation
processes to the negative side in DMSO due to the coordination of
DMSO to the CoIII center of the complex. As discusses in the spec-
troelectrochemical measurement section below, the first oxidation
process of CoPc in DMSO is a metal-based ([CoIIPc−2]/[CoIIIPc−2 1+
]
]
)
)
1+
process, while it is a ligand-based process ([CoIIPc−2]/[CoIIPc−1
in DCM solvent. Due to the wide negative potential window of
DMSO, it could be possible to observe the third reduction process
(RIII) at −2.12 V in addition to the reversible RI process at −0.55 V
and the reversible RII process at −1.49 V. Assignment change of the
redox couples during the oxidation processes cause to shifting of
the oxidation processes to the negative side, thus two oxidation
couples are clearly observed at 0.27 V (OI) and 0.83 V (OII).
As shown in Fig. 6, MnPc (4) displays three well-resolved reduc-
tion processes (RI at −0.16 V, RII at −0.95 V and RIII at −1.45 V)
with CV and SWV measurements in DCM/TBAP electrolyte. Two
oxidation couples are also recorded at 1.04 V (OI) and at 1.23 V
(OII) with both CV and SWV measurements. As shown in Fig. 6a
(inset), altering the cathodic switching potential influences the
peak character of the reduction processes. When the potential
is switched before −1.30 V, the first and second reduction pro-
cesses are quasi-reversible and diffusion controlled with respect
to the peak separation and peak current ratio analyses. However,
when the switching potential passes the third reduction potential,
Ip,a/Ip,c values of the first and second reduction processes deviate
from unity due to the decreasing of the anodic peak current of
these processes. This deviation Ip,a/Ip,c values indicate presence of
a chemical reaction succeeding the third reduction process. This
chemical reaction may be removal of the axial chloride from man-
ganese center of the complex. It is documented that decreasing

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Fig. 7. In situ UV–vis spectral changes of VOPc (2) in DCM/TBAP electrolyte. (a) Eapp = −0.80 V. (b) Eapp = −1.30 V. (c) Eapp = 1.00 V. (d) Chromaticity diagram of VOPc (each
1+
symbol represents the color of electro-generated species; ꢀ: [VIVOPc−2], ꢀ: [VIVOPc−3
]
1−, ꢁ: [VIVOPc −4
]
2−, ଝ: [VIVOPc−1
]
.
the oxidation state of a metal ion favors less coordination espe-
cially for CoPc and MnPc complexes [40]. SWV measurements in
Fig. 6b clearly show effect of the switching potential to the elec-
tron transfer properties of the complex. As shown in this figure,
when the anodic scan starts from −1.30 V (green SWV), two clear
anodic waves for RI and RII processes are recorded. However, new
waves are observed in addition to decreasing of the previous wave,
when SWV scan starts from −1.80 V (blue SWV). These data support
presence of the proposed chemical reaction.
477 and 796 nm. The vibration of the isosbestic point at 613 nm
and unusual change of the band at 590 nm may be due to a confor-
mational change within the complex. As shown in Fig. 6b, under the
applied potential at −1.30 V, the Q band at 702 nm decreases with-
out shift while a new broad band is recorded at 535 nm. At the same
time the band at 882 nm shifts to 917 nm with increasing in inten-
sity. Moreover the bands at 335 and 637 nm decrease in intensity.
These spectral changes are characteristic of the ring-based reduc-
tion of [VIVOPc−3 1− to [VIVOPc−4 2−. Fig. 7c represents the spectral
] ]
changes during the first oxidation process of the complex. During
electrolysis at 1.00 V, decreasing of the Q band without shifting
3.3. In situ spectroelectrochemical measurements
and increasing the bands at 533 and 865 nm indicate a Pc ring-
1+
based process and assigned to [VIVOPc−2]/[VIVOPc−1
]
process
Spectroelectrochemical studies were employed to confirm the
assignments of the electron transfer reactions recorded with CV
and SWV measurements of MPcs. Fig. 7 represents in situ UV–vis
spectral changes and in situ recorded chromaticity diagram of VOPc
(2) in DCM/TBAP. During the first reduction process (Eap = −0.80 V),
while the Q band at 702 nm decreases in intensity, two new bands
enhance in the metal to ligand charge transfer (MLCT) regions at
590 and 882 nm. At the same time, the B band at 342 nm and
the band at 410 nm decrease in intensity. These spectral changes
characterize a ligand-based reduction process and assigned to the
[33,34,41]. Chemical reversibility of the processes under controlled
potential application was checked by applying 0.00 V after each
electron transfer reactions. When 0.0 V was applied to the working
electrode, while initial spectrum of VOPc was regenerated after the
first reduction process, initial spectrum was not obtained after the
second reduction and first oxidation reactions. These data indicate
chemical reversibility of the first reduction process and irreversibil-
ity of other processes
The color change of the solution of the complexes during the
redox processes were recorded using in situ colorimetric mea-
surements. Without any potential application, the solution of
[VIVOPc−2] is green (x = 0.287 and y = 0.372) (Fig. 7d). As the poten-
reduction of [VIVOPc−2] to [VIVOPc−3 1− species (Fig. 7a) [33,34,41].
]
The band at 590 nm starts to decrease under the same potential
application at the end of the first reduction process. This unusual
changes cause to vibration of the isosbestic point at around 613 nm
while the process give clear well-defined isosbestic point at 274,
tial is stepped from 0 to −0.80 V, color of the neutral [VIVOPc−2
]
changes and light blue color (x = 0.288 and y = 0.319) for monoan-

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Fig. 8. In situ UV–vis spectral changes of CoPc (3) in DMSO/TBAP electrolyte. (a) Eapp = −0.40 V. (b) Eapp = −1.30 V. (c) Eapp = 0.40 V. (d) Chromaticity diagram of CoPc (each
1+
symbol represents the color of electro-generated species; ꢀ: [CoIIPc−2], ꢀ: [CoIPc−2
]
1−, ꢁ: [CoIPc−3
]
2−, ଝ: [CoIIIPc−2
]
.
ionic form of [VIVOPc−3
reduction. Similarly color of the dianionic species, [VIVOPc−4
]
was obtained at the end of the first
the metal-based process and assigned to [CoIIPc−2]/[CoIIIPc−2
]
1−
1+
2−
]
,
[41–45]. During the second oxidation process (Eap = 1.00 V), spec-
tral changes assigned to a ring-based process was recorded. Color
changes during the reduction and oxidation processes are repre-
sented in Fig. 8d.
was recorded as dark blue (x = 0.290 and y = 0.295) and monoca-
tionic species, [VIVOPc−1 1+, was recorded as orange (x = 0.362 and
]
y = 0.337).
Fig. 8 represents the in situ UV–vis spectral changes and in situ
recorded chromaticity diagram of CoPc (3) in DMSO/TBAP. Dur-
ing the first reduction process, while the Q band shifts from 661 to
702 nm with increasing, a new band enhances at 469 nm. Moreover
the B band shifts from 324 to 313 nm with increasing in inten-
Fig. 9 represents in situ UV–vis spectral changes and in situ
recorded chromaticity diagram of MnPc (4) in DCM/TBAP. When
the spectral changes (recorded under applied potential at the
redox processes potential) are compared with the MnPc com-
plexes in the literature [34,35,45–47], the first two reduction
processes are easily assigned to the metal-based processes,
1−
sity. These spectral changes characterize formation of [CoIPc−2
]
species under the applied potential at −0.40 V (Fig. 8a) [41–45].
Well-defined isosbestic points are observed at 328, 388, 562, 679,
and 742 nm. These isosbestic points demonstrate that the reduction
proceeds cleanly in deoxygenated DMSO to give a single, reduced
species. This process gives a color changes from light blue (x = 0.261
and y = 0.330) to green (x = 0.351 and y = 0.412) as shown in the
chromaticity diagram (Fig. 8d). The process is chemically reversible,
since approximately 95% of the original spectrum was obtained
when 0.0 V was applied after the first reduction reaction. As shown
in Fig. 8b, the Q band at 702 nm decreases without shift while a
new broad band is recorded at 540 nm under the controlled poten-
tial application at −1.30 V. These spectral changes are characteristic
[Cl–MnIIIPc−2]/[Cl–MnIIPc−2
]
and [Cl–MnIIPc−2]/[Cl–MnIPc−2
]
and the third one is assigned to the ligand-based process,
[Cl–MnIPc−2]/[Cl–MnIPc−3]. Oxidation process of the complexes
is a ring-based process, [Cl–MnIIIPc−2]/[Cl–MnIIIPc−1], according
to the spectral changes. Fig. 9a shows in situ UV–vis spectral
changes observed upon controlled potential reduction of 4 at
−0.30 V. Before any potential application, observation of a band
at 524 nm and the red shifted Q band at 731 nm are characteristic
of MnIIIPc−2 species. During the first reduction process, the Q
band at 731 nm shifts to 682 nm, while the B band at 369 shifts
to 391 nm with increasing. These spectral changes are assigned
1−
to [Cl–MnIIIPc−2]/[Cl–MnIIPc−2
]
process. The formation of
of the ring-based reduction of [CoIPc−2
]
species to [CoIPc−3
]
1−
2−
1−
[Cl–MnIIPc−2
] is characterized by shifting of the Q band to
species. Fig. 8c represents the spectral changes during the first oxi-
dation process of the complex. During 0.40 V potential application,
shifting of the Q band from 661 to 675 nm with increasing indicates
shorter wavelength [34,35,45–47]. To diminish the formation of
␮-oxo MnPc species the solution is purged gently with N2 before
the process and the solution is kept under N2 atmosphere during

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Fig. 9. In situ UV–vis spectral changes of MnPc (4) in DCM/TBAP electrolyte. (a) Eapp = −0.30 V. (b) Eapp = −1.20 V (inset: Eapp = −1.50 V). (c) Eapp = 1.00 V. (d) Chromaticity diagram
of MnPc (each symbol represents the color of electro-generated species; ꢀ: [Cl–MnIIIPc−2], ꢀ: [Cl–MnIIPc−2
]
1−, ꢁ: [Cl–MnIPc−2
]
2−, ꢁ: [Cl–MnIPc−3
]
3−, ଝ: [Cl–MnIIIPc−1
]
1+).
1−
2−
ring-based reduction of [Cl–MnIPc−2
]
to [Cl–MnIPc−3
]
the process. It is well known that ␮-oxo MnPc species give an
absorption band at around 630 nm [34,35,45–47]. There is no
band at around this wavelength during the reduction processes.
Thus, all redox processes are easily assigned to the formation
of electrogenerated MnPc(4) species. Color changes of the com-
plex in solution during the redox processes were recorded by
in situ electrocolorimetric measurements. Without any potential
application, the solution of 4 is yellowish green (x = 0.365 and
y = 0.370) (Fig. 9d). As the potential is stepped from 0 to −0.30 V
color of neutral Cl–MnIIIPc−2 changes to bluish green (x = 0.313 and
y = 0.344). The reduction of MnIIPc−2 species has been a subject
of some controversy, with some reports proposing ring reduction
to the MnIIPc−3 species and others suggesting metal reduction to
the MnIPc−2 species. During the second reduction process of 4,
while two new bands are recorded at 518 and 841 nm, the Q band
and the band at 682 nm decrease in intensity. The band recorded
at 524 nm and decreasing of the Q band can characterize a metal-
a
species (Fig. 9b, inset) [34,41–43]. These two different changes
under the same potential application may be due to removing of
the axial chloride ion during the third reduction process. These
spectral changes are in harmony with the CV responses of the
complex given above. While original spectra were obtained after
the first and second reduction processes, the spectrum did not
return to the original spectra after the third reduction process,
when 0.0 V was applied after these processes. These data indicate
irreversibility of the third reduction process. To confirm the origin
of the oxidation process, OI, in situ UV–vis spectral changes were
recorded under the controlled potential application at 1.20 V
(Fig. 9c). During this process, the Q band decreases in intensity,
while a new band at 832 nm is recorded. At the same time the band
characterizing MnIII metal center increases in intensity. These
spectral changes are characteristics of a ring-based oxidation pro-
cess for MnPc complexes, thus the couple OI is easily assigned to
1−
2−
species
based reduction of [Cl–MnIIPc−2
]
to [Cl–MnIPc−2
]
[Cl–MnIIIPc−2]/[Cl–MnIIIPc−1
]
redox process [34,41–43]. Colors
1+
(Fig. 9b) [34,35,45–47]. During the third reduction of the complex
at −1.50 V potential application, two distinct spectral changes are
recorded. First of all while a broad new band is recorded at around
570 nm, the band at 841 nm shifts to 808 nm. At the same time,
the Q band at 682 nm decreases in intensity. During these changes
the band at 518 nm remains as unchanged. Then the bands at
518 nm and 808 nm decrease slightly while the band at 570 nm
continues to increase. In both of these two different spectral
changes, increasing of the band at around 570 nm can characterize
of the anionic and cationic species were given in the chromaticity
diagram (Fig. 9d).
3.4. Interaction of complexes with molecular oxygen
There are many studies on the redox reaction of O2 in the
protic solvents, but studies in the aprotic solvents are deficient
and the majorities of these are related to the mechanistic inves-
tigation of superoxide and/or peroxide formation from molecular

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while ꢀEp values change from 135 to 250 mV in case 3). (iii) While
ORR couple has only one reverse peak in case 2, a split reverse peak
is recorded with SWV in case 3 (Fig. 10b). Shifting of the ORR cou-
ple to the less negative potentials and increasing reversibility of
the ORR process indicate the electrocatalytic activity of CoPc to the
oxygen reduction reaction.
Presence of O2 in the electrolyte system also influences the elec-
trochemical properties of CoPc. Electrochemical responses of CoPc
in case 3 with increasing O2 concentration are recorded as: (i) both
the anodic and the cathodic waves of RI decrease gradually in cur-
rent intensity, while anodic wave shifts to positive potentials. (ii)
Couple IV shifts to the negative potentials with increasing in cur-
rent intensity. (iii) A new wave is recorded at −0.30 V during the
anodic scans. These voltammetric data indicate that CoPc interacts
with O2 and this interaction affects the voltammetric behaviors of
CoPc as well as O2.
In situ spectroelectrochemical studies were employed to deter-
mine the mechanism of the interaction between CoPc and O2.
Fig. 11 represents in situ UV–vis spectral changes of CoPc in case 3in
DMSO/TBAP electrolyte system. Under the open circuit potential,
spectra of CoPc did not change with time in case 3. This behav-
ior indicates that [CoIIPc−2] does not interact with O2. During the
first reduction process (at −0.50 V), spectral changes assigned to
[CoIIPc−2] to [CoIPc−2
]
reduction reaction are observed in both
case 1 (Fig. 8a) and case 3 (Fig. 11a). However final spectrum in case
3 is not completely turned to the spectrum of [CoIPc−2 1− recorded
in case 1 (Fig. 8a). These spectral changes indicate the interac-
tion of reduced complex [CoIPc−2 1− with the molecular oxygen. In
this interaction, the molecular oxygen may reoxidize the reduced
1−
]
]
[CoIPc−2
] ]
1−, and an equilibrium is established between [CoIIPc−2
and [CoIPc−2
]
1−. Different potential applications between −0.60
and −0.90 V were applied to observe the interaction between
[CoIPc−2 1−and molecular oxygen. During these potential appli-
]
cations, spectra of the complex change considerably and give the
Fig. 10. (a) CVs (inset: CVs of O2 in DMSO/TBAP electrolyte system with increas-
ing amounts of O2) and (b) SWVs of CoPc (3) at 0.100 V s−1 scan rate on Pt with
increasing amounts of O2 in DMSO/TBAP electrolyte system. (SWV parameters:
pulse size = 100 mV; step size: 5 mV; frequency: 25 Hz; Ei = 0.00 V and Ef = −1.70 V
for SWV having cathodic currents; Ei = −1.70 V and Ef = 0.00 V for SWV having anodic
currents).
1−
same spectra of [CoIPc−2
]
recorded at −0.50 V potential applica-
tion in case 1. This change indicates that electron transfer reaction
rate gets dominant at more negative potential application with
respect to reoxidation of the reduced [CoIPc−2
]
1− with oxygen, thus
1−
the final spectrum reflects the [CoIPc−2
]
form of the complex
dominantly (Fig. 11b). To observe the effects of the ORR on the spec-
tra of the complex, spectral changes are recorded under the applied
potential at −1.25 V (ORR potential). While there was no spectral
change in case 1, the spectra starts to return back to the original
spectrum of the neutral CoPc in case 3 (Fig. 11c). These spectral
oxygen. In this study, we have investigated the interaction of MPcs
with O2 to clarify the electrocatalytic O2 reduction mechanism
in the aprotic media with different electrochemical and in situ
spectro-electrochemical techniques. Fig. 10a (inset) gives the CV
responses of O2 dissolved in DMSO/TBAP electrolyte system with-
out MPc (case 2). Early investigations of the oxygen reduction
reaction (ORR) in the aprotic solvents such as acetonitrile (ACN),
dimethyl-sulfoxide (DMSO) and N,N-dimethylformamide (DMF),
showed that O2 reduces via 1 e− to superoxide in the non-aqueous
environment [48,49]. Similarly in this study, clear quasi-reversible
oxygen/superoxide (O2/O2−) couple is recorded at −1.00 V in DMSO
1−
with the reduced
changes indicate the interaction of [CoIPc−2
]
oxygen (superoxide, O2−). This interaction forms an intermediate
in which metal center has CoII oxidation state. At more negative
applied potential, RII process could not be recorded in case 3, which
1−
indicates that interaction of [CoIPc−2
]
with the reduced oxygen
gives an intermediate which does not reduce again until −1.70 V
potential. Applying 0.0 V after reduction reactions did not convert
the spectrum to the original form in case 3, which indicates irre-
versibility of the reduction processes. Color change of the complex
during the redox processes in case 3 is recorded using in situ col-
orimetric measurements. When the chromaticity diagrams of the
complex in case 1 and case 3 (Fig. 11d) are compared, it is obvious
that presence of O2 alters the color of the redox species differently
than those in case 1, which support the interaction of complex with
O2.
at 0.10 mV s−1 scan rate. O2/O2 couple shifts to the negative
−
potentials with increasing of O2 concentration. Interaction of O2
with MPcs was performed by bubbling of the electrolyte with
O2 in which MPcs were dissolved. While VOPc did not interact
with O2, and gives similar complex-based redox processes with
those recorded in case 1 (except ORR process), presence of O2 in
the CoPc and MnPc solution alters electrochemical responses of
both MPcs and O2 considerably. Fig. 10 represents voltammetric
responses of CoPc solution bubbled with O2 gradually. Electro-
chemical responses of O2 recorded in case 3 with increasing O2
concentration are analyzed as: (i) Redox couples of CoPc and O2
are considerably influenced with increasing O2 concentration. (ii)
ORR couple in case 3 shifts ca. 70 mV toward the positive direction
and gets more reversible with respect to those recorded in case 2
(ꢀEp values of ORR couple increase from 410 to 582 mV in case 2,
In summary, according to the results of CV, SWV, and in situ
spectroelectrochemical measurements, these are easily concluded
that (i) under the applied potential at −0.50 V, [CoIIPc−2] species are
1−
which is reoxidized back to [CoIIPc−2] with
reduced to [CoIPc−2
]
1−
]
O2 and form an equilibrium between electrogenerated [CoIPc−2
and reoxidized [CoIIPc−2]. However, the electron transfer reaction
rate constant at the electrode should be bigger than the reoxida-

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Fig. 11. In situ UV–vis spectral changes of CoPc (3) in DMSO/TBAP electrolyte saturated with O2. (a) Eapp = −0.50 V. (b) Eapp = −0.90 V). (c) Eapp = −1.25 V. (d) Chromaticity
diagram of CoPc. (each symbol represents the color of electro-generated species after the potential applications; ꢀ: [CoIIPc−2] under open circuit; ꢀ: −1.25 V; ꢁ: −1.50 V.
tion rate constant of [CoIPc−2
]
1− with O2, because spectra assigned
species if more negative potentials are scanned (Scheme 2, Eq.
(5)) or regenerating the starting form of the catalyst [CoIIPc−2] and
to [CoIPc−2
]
species are dominant at this potential. (ii) Under
1−
2−
the product O2
(Scheme 2, Eq. (6)). According to these results,
the applied potential at −1.25 V in case 3, decreasing of the band
assigned to the CoI species at around 470 nm indicate the inter-
conversion of CoI to CoII due to reoxidation of CoI to CoII species
with superoxide. Under this potential application, the final spec-
it looks like the homogeneous catalytic ORR process occurs via
an “inner sphere” chemical catalysis process. Since the interme-
diates [O2−–CoIIPc−2]−and [O2−2–CoIIPc−2 2− are formed between
]
trum illustrates formation of CoII form of the complex. (iii) Shifting
O2 and active form of the catalyst in the solution phase, so rate con-
of the reverse wave of [CoIIPc−2]/[CoIPc−2
]
and decreasing the
1−
stant of these interactions should affect the catalytic activity of the
complex. Saveant and coworkers [50] reported that homogeneous
peak current of RI couple in the CV and SWV of the complex may
due to the interconversion of [CoIPc−2
]
1−
to the intermediate in
which metal center has CoII state. (iv) Shifting of the ORR process
and increasing reversibility of this process support the coordination
of oxygen to [CoIPc−2 1−and form an equilibrium between O2− and
]
the intermediate. (v) Splitting of anodic wave of ORR reaction sup-
ports coordination of oxygen to [CoIPc−2 1−. According to the CV,
]
SWV, and in situ spectroelectrochemical measurements, a homo-
geneous electrocatalytic ORR mechanism is proposed as given in
Scheme 2. As shown in scheme, initially the active form of the
−
catalyst [CoIPc−2
action of [CoIPc−2
the active form of the catalyst and the substrate O2 produced an
intermediate [O2−–CoIIPc−2 − (Scheme 2, Eq. (2)). The intermediate
is very unstable, regenerating rapidly the starting
] is obtained (Scheme 2, Eq. (1)). Then the inter-
1−
]
with O2 and the electron transfer between
]
[O2−–CoIIPc−2
form of the catalyst [CoIIPc−2] and the product O2 (Scheme 2, Eq.
(3)) or produces the second intermediate [O2−2–CoIIPc−2 2− due to
the electron transfer reaction on the working electrode (Scheme 2,
]
−
−
]
Scheme 2. Proposed homogeneous electrocatalytic mechanism of oxygen reduc-
tion reaction.
Eq. (4)). This second intermediate reduced to [O2−2–CoIIPc−3
3−
]

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5112
Fig. 12. (a) CVs and (b) SWVs of MnPc (4) at 0.100 V s−1 scan rate on Pt with
increasing amounts of O2 in DCM/TBAP electrolyte system (SWV parameters: pulse
size = 100 mV; step size: 5 mV; frequency: 25 Hz; Ei = 0.00 V and Ef = −1.30 V for
SWV having cathodic currents; Ei = −1.30 V and Ef = 0.00 V for SWV having anodic
currents).
catalysis of slow and irreversible electrochemical processes may be
carried out along two conceptually different types of mechanisms.
In one case, “redox catalysis”, the active form of the catalyst, gener-
ated at the electrode, exchanges electrons with the reactant in an
outer-sphere manner yielding the reaction products and regenerat-
ing the starting form of the catalyst. On the other hand, “chemical
catalysis” involves the transient formation of an adduct between
the active form of the catalyst and the reactant. The chemical bond
thus formed has to be cleaved successively or after the exchange of
additional electrons for eventually yielding the products and regen-
erating the starting form of the catalyst. The proposed mechanism
given in Scheme 2 and voltammetric and spectroelectrochemical
data are in harmony with the previous reported homogeneous cat-
alytic studies [50–54]. For example, Mho and coworkers reported
the homogeneous interactions of unsubstituted cobaltphthalo-
cyanine with oxygen and proposed a conventional regenerative
catalytic mechanism. They did not determine the intermediates
and just predicted the possible intermediate adducts and proposed
mechanism with respect to with respect to cyclic voltammetric and
chronoamperometric responses of the system [54]. In this paper,
we illustrate the proposed intermediates with voltammetric and
in situ spectroelectrochemical measurements especially by com-
paring the spectroelectrochemical changes of the complexes with
and without the presence of the molecular oxygen in the reaction
media.
Fig. 13. In situ UV–vis spectral changes of MnPc (4) in DCM/TBAP electrolyte
saturated with O2. (a) Eapp = −0.50 V. (b) Eapp = −0.90 V and then Eapp = −1.25 V.
(d) Chromaticity diagram of MPc (each symbol represents the color of electro-
generated species after the potential applications; ꢀ: [Cl–MnIIIPc−2] under open
circuit; ꢀ: −1.3 V.

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5113
Fig. 12 represents the interaction of MnPc with the molecular
oxygen in DCM/TBAP electrolyte system. It is well documented
that MnIIPc−2species reacts with O2 and form ␮-oxo MnPc species,
[PcMnIII–O–MnIIIPc] [55]. As shown in Fig. 12a, while MnPc gives a
quasi-reversible reduction process (RI) at 0.15 V without O2, purg-
ing of the electrolyte system gradually with O2 affects the redox
behavior of RI couple. During this purging process, while the anodic
couple of the peak decreases in the current intensity and disappears
finally; two new cathodic waves are recorded at 0.12 and −0.45 V.
These voltammetric data indicate that MnIIIPc−2 species reduce to
MnIIPc−2 at 0.15 V and MnIIPc−2 reacts immediately with O2 and
form [PcMnIII–O–MnIIIPc] which reduces at 0.12 and −0.45 V. Due
to the reaction between MnIIPc−2and O2, concentration of MnIIPc−2
decreases with increasing oxygen, which causes disappearance of
the anodic peak of RI couple assigned to MnIIPc−2/MnIIIPc−2 pro-
cess. As shown in Fig. 12, ORR couple is overlapped with the RII
couple of the complex so we do not analyze ORR process. How-
ever when we compared the ORR process in case 2 (Fig. 12a, inset)
with that in case 3 (Fig. 12), it is clearly shown that ORR couple in
case 3 shifts ca. 300 mV toward the positive direction and gets more
reversible with respect to those recorded in case 2.
complexes were influenced by the nature of central metal. The
manganese derivatives showed red-shifted Q band relative to the
other analogs due to the MnIII metal center of the complex. Voltam-
metric and spectroelectrochemical studies indicate that while
vanadyl phthalocyanine gives only ring-based, multi-electron, and
reversible/quasi-reversible redox processes, cobalt and manganese
phthalocyanine complexes give both metal and ring-based, dif-
fusion controlled, multi-electron, and reversible/quasi-reversible
reduction processes. Solvent of the electrolyte affects the redox
properties of the complexes which have redox active metal center
due to the coordination ability differences of the solvents. Definite
determination of the colors of the electrogenerated anionic and
cationic form of the complexes with chromaticity measurements
is important to decide the possible electrochromic application of
the complexes. Different color of the electrogenerated species indi-
cates their possible application in the display technologies, e.g.
electrochromic and data storage application. Presence of O2 in the
electrolyte system influences both the ORR and the redox couples
of the complexes due to the interaction between different redox
states of O2 and MPcs having redox active metal center.
In situ spectroelectrochemical studies were employed to sup-
port the interaction between MnPc and O2. Fig. 13 represents in situ
UV–vis spectral changes of MnPc in case 3 in DCM/TBAP electrolyte
system during the potential application at the potentials of the
redox processes. Under the open circuit potential, spectra of MnPc
did not change with time in case 3. This behavior indicates that
[Cl–MnIIIPc−2] do not interact with O2.
Acknowledgement
This work was supported by the Research Fund of Istanbul Tech-
nical University.
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case 1 (Fig. 10a). Spectral change of MnPc is different in case 3
(Fig. 13a). Two distinct spectral changes are observed during the
first reduction process in case 3. First of all, while the Q band at
730 nm decreases in intensity, a new band at 683 nm assigned to
[Cl–MnIIPc−2 1− process is observed. At the same time, the band at
]
519 nm decreases in intensity. These spectral changes characterize
reduction of [Cl–MnIIIPc−2] to [Cl–MnIIPc−2 1−. Then, a new band
]
at 627 nm is recorded, while the band at 683 nm starts to decrease
in intensity at the same time. It is well-known that ␮-oxo MnPc
species give an absorption band at around 630 nm. These spec-
1−
troscopic changes indicate that reduced [Cl–MnIIPc−2
]
species
interacts with oxygen and form ␮-oxo MnPc species, which sup-
port the voltammetric data about the interaction of MnPc with
molecular oxygen. Presence of the band at 683 nm assigned to
[Cl–MnIIPc−2 1−process and the band at 630 nm assigned to ␮-oxo
]
MnPc species ([PcMnIII–O–MnIIIPc]) which indicate existence of an
1−
equilibrium between [Cl–MnIIPc−2
]
and ␮-oxo MnPc species.
During the potential application at −1.40 V, while spectral
2−
changes characterized [Cl–MnIPc−2
]
formation in case 1, any
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spectral changes characterizing further reduction is recorded in
case 3 (Fig. 13b). Only relative intensity of the bands at 630 and
682 nm changes with time. Application of more negative poten-
˙
˙
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˙
tial just affects the relative intensity of these bands which support
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˙
1−
the existence of an equilibrium between [Cl–MnIIPc−2
]
and ␮-
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the reduction processes. When the chromaticity diagrams given
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oxygen with MnPc change the spectral and color responses of the
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