Electrochemical and spectroelectrochemical properties of novel lutetium(III) mono- and bis-phthalocyanines

Article abstract of DOI:10.1016/j.electacta.2013.09.088

Peripherally and non-peripherally substituted mono and sandwich lutetium(III) phthalocyanines bearing 3,4-(dimethoxyphenylthio) substituents have been synthesized and characterized by elemental analysis, FT-IR, UV-vis spectroscopy and mass spectroscopy. Voltammetric, in-situ spectroelectrochemical, and in-situ electrocolorimetric characterization of the newly synthesized phthalocyanines were performed in solution. Changing the number and the position the substituents altered the reversibility of the electron transfer processes and affected the easy of electron transfer reactions. While the mono phthalocyanines had an oxidation-reduction peak separation (ΔE_1/2) higher that 1.50 V, this value decreased up to 0.36 V due to the π-π interaction of phthalocyanine rings around the lutetium core. Solvent of the electrolytic system also affected the redox behaviors of the complexes considerably. In-situ electrocolorimetric method was applied to investigate the color of the electrogenerated anionic and cationic forms of the complexes for their possible electrochromic applications.

Full text of DOI:10.1016/j.electacta.2013.09.088

Electrochimica Acta 113 (2013) 668–678
Contents lists available at ScienceDirect
Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
Electrochemical and spectroelectrochemical properties of novel
lutetium(III) mono- and bis-phthalocyanines
Mürsel Arıcıa, Ceyda Bozog˘lub, Ali Erdog˘mus¸ c, Ahmet Lütfi Ug˘urd, Atıf Kocab,∗
a Eskisehir Osmangazi University, Faculty of Arts and Sciences, Department of Chemistry, 26480 Eskis¸ehir, Turkey
b Department of Chemical Engineering, Faculty of Engineering, Marmara University, Göztepe, 34722 Istanbul, Turkey
c Department of Chemistry, Yildiz Technical University, Esenler, 34210 Istanbul, Turkey
d Yenice Vocational School, C¸ anakkale 18 March University, Yenice/Canakkale, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 14 May 2013
Received in revised form 26 August 2013
Accepted 11 September 2013
Available online 11 October 2013
Peripherally and non-peripherally substituted mono and sandwich lutetium(III) phthalocyanines bearing
3,4-(dimethoxyphenylthio) substituents have been synthesized and characterized by elemental analysis,
FT-IR, UV–vis spectroscopy and mass spectroscopy. Voltammetric, in-situ spectroelectrochemical, and in-
situ electrocolorimetric characterization of the newly synthesized phthalocyanines were performed in
solution. Changing the number and the position the substituents altered the reversibility of the electron
transfer processes and affected the easy of electron transfer reactions. While the mono phthalocya-
nines had an oxidation–reduction peak separation (ꢀE1/2) higher that 1.50 V, this value decreased up
to 0.36 V due to the ␲–␲ interaction of phthalocyanine rings around the lutetium core. Solvent of the
electrolytic system also affected the redox behaviors of the complexes considerably. In-situ electrocol-
orimetric method was applied to investigate the color of the electrogenerated anionic and cationic forms
of the complexes for their possible electrochromic applications.
Keywords:
Electrochemistry, Lutetium
Bis-phthalocyanines
Spectroelectrochemistry
Electrocolorimetry
Electrochromism
© 2013 Elsevier Ltd. All rights reserved.
1. Introduction
properties is possible by varying the nature of the central metal
ion and the substituents on the phthalocyanine rings. The elec-
For designing new devices for electrochemical applications,
metallophthalocyanines (MPcs) have extensively studied because
of their properties such as electrochromic[1–3], semiconductor[4],
liquid crystal material [5], electrosensor [6–9], and electrocat-
alytic behaviors [10–12]. Among phthalocyanine derivatives, the
syntheses of lanthanide(III) phthalocyanines have attracted great
attention due to their physical, electrical, optical, and electro-
chemical properties originated from their extensive ␲-electron
delocalization and their thermal and chemical stability [13–15].
Lanthanide(III) phthalocyanines, especially lutetium phthalocya-
nines have been investigated owing to their electrochromic and
gas sensing properties and high intrinsic conductivity [1,16–18]. It
is well documented that these properties can be tuned by changing
the electron-donating or electron-withdrawing substituents on the
phthalocyanine ring [15,19–22].
tronic and steric effects of substituents can influence the orbital
and molecular structure of the MPc complexes, and thus affect
intrinsic physicochemical properties. MPcs complexes that are
peripherally or non-peripherally substituted with alkanethiol and
phenylthiol derivatives showed rich electrochemical and photo-
chemical properties [23–25]. Moreover, the presence of electron
donating sulphur groups on Pc caused shifting of the Q-band to
the longer wavelengths, which directly alter the electrochemical
responses [25–27]. In this respect, it needs to understand the elec-
trochemical and spectroelectrochemical properties of the newly
synthesized complexes to open a way to their technological appli-
cations.
It is well known that extent electrochemical properties of
sandwich phthalocyanines determine their possible technolog-
ical applications [15]. Although mono and bis phthalocyanines
have frequently been described, comparison of those bearing
different number of substituents at different positions have
not been extensively studied, especially those bearing tetra
and octa substituents. Thus in this study, we have synthesized
and reported the spectroscopic characterization and voltammet-
ric, in-situ spectroelectrochemical, and in-situ electrocolorimetric
responses of Lu(III) mono- and bis-phthalocyanines bearing
3,4-dimetoxyphenylthio substituents on peripheral and non-
peripheral positions (Schemes 1 and 2). The results of this study
The specific electronic structure, characterized by the pres-
ence of an intramolecular axial interaction between the ligand
␲
systems, allows sandwich complexes to find application
in modern high-technology fields. Structural control of their
∗
Corresponding author. Tel.: +90 2163480292; fax: +90 2163480292.
E-mail addresses: erdogmusali@hotmail.com (A. Erdog˘mus¸ ),
akoca@marmara.edu.tr (A. Koca).
0013-4686/$ – see front matter © 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.electacta.2013.09.088

M. Arıcı et al. / Electrochimica Acta 113 (2013) 668–678
669
Scheme 1. Synthetic route of 4-(3,4-(dimethoxy phenylthio))phthalonitrile (1) and its lutetium phthalocyanines (4 and 5).
Scheme 2. Synthetic route of 3-(3,4-(dimethoxy phenylthio)) phthalonitrile (3) and 4,5-bis(3,4-(dimethoxyphenylthio))phthalonitrile (2) and their lutetium phthalocyanines
(6 and 7).

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M. Arıcı et al. / Electrochimica Acta 113 (2013) 668–678
will be used to decide possible technological applications of these
novel complexes especially in electrochromic applications.
2993, 2951, 2930 (aliphatic-CH), 1598, 1584, 1503 (C C), 754
(C–S–C), 1438, 1396, 1313, 1253, 1230, 1177, 1135, (C–O–C),
1023, 907, 877, 806 (Pc skeleton). Elemental analyses data for
C128H96N16O16S8Lu: Required: C, 60.39; H, 3.80; N, 8.80; S, 10.08%.
Found: C, 61.49; H, 3.71; N, 8.74; S, 10.28%. MS (ESI-MS) m/z:
Calc.:2545.7; Found: 2546.4 [M + H]+.
2. Synthesis
2.1. Materials
2.3.2. 2,3,9,10,16,17,23,24-Octakis-[3,4-
4-(3,4-(Dimethoxyphenylthio)) phthalonitrile (1), 4,5-bis[3,4-
(dimethoxyphenylthio]phthalocyaninato lutetium(III) acetate
(6)
(dimethoxyphenylthio)]-phthalonitrile
(2)
and
3-(3,4-
(dimethoxyphenylthio)) phthalonitrile (3) was synthesized
according to procedures in the literatures [25–27]. N,Nꢀ-
dimethylformamide (DMF), dimethyl sulfoxide (DMSO),
chloroform (CHCl3), tetrahydrofuran (THF), methanol (MetOH),
dichloromethane (DCM), 1-pentanol, and n-hexane were pur-
chased from Merck. 3-Nitrophthalonitrile, 4-nitrophthalonitrile,
The procedure for the synthesis of 6 was similar to that used
for 4, except compound 2 (0.32 g, 0.68 mmol) was used instead of
compound 1. The crude product was precipitated, collected by fil-
tration and washed with hot hexane. Compound 6 was purified
with column chromatography using a mixture of CHCl3:THF (3:1
by volume) and CHCl3:Methanol (1:1 by volume) as eluents. Com-
pound 6 was obtained as a major product. Yield = 46 mg (12.74%).
UV–vis in DCM (ꢁmax nm (log ε)): 358 (4.71), 639 (4.28), 708 (4.99).
IR spectrum (cm−1): 3055 (Ar-CH), 2951, 2931, 2833 (aliphatic-CH),
1583, 1501 (C C), 1462, 1400, 1369, 1322, 1252 (C–O–C), 1023, 940,
876, 805 (Pc skeleton), 767, 753 (C–S–C). Elemental analyses data
for C64H48N8O8S4Lu: Required: C, 61.93; H, 3.90; N, 9.03; S, 10.33%.
Found: 62.43; H, 4.00; N, 9.13; S, 10.20%. MS (ESI-MS) m/z: Calc.:
2092.2; Found: 2124.87 [M-Ac+ Cyano + 2H]+.
4,5-dichlorophthalonitrile,
3,4-dimethoxythiophenol,
tetra-
buthylammonium perchlorate (TBAP), 1,8-diazabicyclo[5.4.0]
undec-7-ene (DBU), potassium carbonate, and lutetium(III) acetate
were purchased from Aldrich. Column chromatography was
performed on silica gel 60 (0.04–0.063).
2.2. Equipment
Absorption spectra were recorded on a Shimadzu 2001 UV spec-
trophotometer. FT-IR spectra were recorded on a Perkin Elmer
Spectrum One Spectrometer using KBr. Mass spectra were acquired
in the linear modes with average of 50 shots on a Bruker Dal-
tonics Microflex mass spectrometer (Bremen, Germany) equipped
with a nitrogen UV-Laser operating at 337 nm. 2␣-Cyano-4-
hydroxycinnamic acid (20 mg/ml in THF) matrix for the complexes
was prepared. MALDI samples were prepared by mixing com-
pounds (2 mg/ml in THF) with the matrix solution (1:10, v/v) in
a 0.5 ml eppendorf micro tube. Finally 1 ␮l of this mixture was
deposited on the sample plate, dried at room temperature and then
analyzed.1H NMR spectra were recorded on a Varian 500 MHz spec-
trometer in CDCl3 solutions. Elemental analyses were performed
using a Thermo flash EA 1112 Series. GC-MS spectra were acquired
on a Agilent Technologies including 6890 N network GC system and
5973 inert Mass selective detector.
2.3.3. 1(4),10(13),19(22),28(31)-Tetrakis-[3,4-
(dimethoxyphenylthio)]phthalocyaninato lutetium(III) acetate
(7)
The synthesis of 7 was as outlined for 4, except that compound
3 was used instead of the compound 1. The crude product was
precipitated, collected by filtration and washed with hot hexane.
Compound 7 was purified with the column chromatography using
a mixture of CHCl3:THF (3:1 by volume) and CHCl3:MetOH (1:1
by volume) as eluents. Yield = 130 mg (49.43%). UV–vis in DCM
(ꢁmax nm (log ε)): 336 (4.61), 641 (4.28), 714 (4.98). IR spectrum
(cm−1): 3064, 2999 (Ar-CH), 2956, 2931, 2906 (aliphatic-CH), 1727
(C O), 1584 (C C), 1462, 1438, 1313, 1252, 1230 (C–O–C), 1022,
893, 876, 854 (Pc skeleton), 799, 748 (C–S–C). Elemental analyses
data for C66H51N8O10S4Lu: Required: C, 55.85; H, 3.62; N, 7.89; S,
9.04%. Found: C, 56.35; H, 3.72; N, 7.96; S, 8.94% MS (ESI-MS) m/z:
Calc.: 1419.4; Found: 1549.1 [M-Ac + Cyano]+.
2.3. Synthesis
2.3.1. 2(3), 9(10), 16(17),
2.4. Electrochemical, in-situ spectroelectrochemical, and in-situ
electrocolorimetric measurements
23(24)-Tetrakis-[3,4-(dimethoxyphenylthio)]phthalocyaninato
lutetium(III) acetate (4) and bis-[27(24)-tetrakis-[3,4-(dimethoxy
phenylthio)]phthalocyaninato]lutetium(III) (5)
The electrochemical and spectroelectrochemical measurements
A mixture of compound 1 (0.20 g, 0.68 mmol), lutetium(III)
acetate (0.12 g, 0.34 mmol), and 2 ml of 1-pentanol were refluxed
for 20 h in the presence of 1,8-diazabicyclo[5.4.0] undec-7-ene
(DBU)(0.120 ml, 0.8 mmol)undertheargonatmosphere. Aftercool-
ing to the room temperature, the crude product was precipitated
with n-hexane, collected by filtration, and then washed with hot
hexane. The crude product was further purified by chromatogra-
phy over a silica gel column using CHCl2, a mixture of CHCl3:THF
(3:1 by volume) and a mixture of CHCl3:THF:MetOH (3:1:10 by vol-
ume) as eluents, respectively. After the column chromatography,
two products were obtained. For 4, yield = 42 mg (15.97%). UV–vis
in DCM (ꢁmax nm (log ε)): 354 (4.64), 628 (4.33), 695 (5.05). IR spec-
trum (cm−1): 3055 (Ar-CH), 2992, 2929 (aliphatic-CH), 1728 (C O),
1597, 1583, 1500 (C C), 751 (C–S–C), 1436, 1392, 1319, 1250, 1229,
1176, 1134, 1072 (C–O–C), 1021, 907, 876, 804 (Pc skeleton). Ele-
mental analyses data for C66H51N8O10S4Lu: Required: C, 55.85; H,
3.62; N, 7.89; S, 9.04%. Found: C, 56.61; H, 3.70; N, 7.74; S, 9.11%.
MS (ESI-MS) m/z: Calc.: 1419.4; Found: 1549.2 [M-Ac+ Cyano]+.
For 5, yield = 26 mg (12%). UV–vis in DCM (ꢁmax nm (log ε)): 345
(4.91), 624 (4.40), 686 (4.98). IR spectrum (cm−1): 3055 (Ar-CH),
were carried out with a Gamry Reference 600 potentio-
stat/galvanostat utilizing a three-electrode cell configuration at
25 ◦C. For cyclic voltammetry (CV), and square wave voltammetry
(SWV) measurements, the working electrode was a Pt disc with
a surface area of 0.071 cm2. Surface of the working electrode
was polished with a diamond suspension before each run. A Pt
wire served as the counter electrode. Saturated calomel electrode
(SCE) was employed as the reference electrode and separated from
bulk of the solution by a double bridge. Ferrocene was used as
an internal reference. Tetrabutylammonium perchlorate (TBAP)
in dichloromethane (DCM) and/or dimethylsulfoxide (DMSO) was
employed as the supporting electrolyte at a concentration of
0.10 mol dm−3. High purity N2 was used to remove dissolved O2
for at least 15 min 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 OceanOptics QE65000 diode array spectropho-
tometer. In-situ spectroelectrochemical measurements were car-
ried out by utilizing a three-electrode configuration of a thin-layer

M. Arıcı et al. / Electrochimica Acta 113 (2013) 668–678
671
Fig. 1. UV–vis spectra of compounds 4–7 in DCM.
quartz spectroelectrochemical cell at 25 ◦C. The working electrode
was a Pt semi-transparent electrode. A Pt wire counter electrode
separated by a glass bridge and a SCE reference electrode separated
from bulk of the solution by a double bridge were used.
In-situ electrocolorimetric measurements under potentiostatic
control were obtained using an OceanOptics QE65000 diode
array spectrophotometer at color measurement mode by utilizing
three-electrode configuration of a thin-layer quartz spectroelectro-
chemical cell. The standard illuminant A with 2-degree observer at
constant temperature in a light booth designed to exclude external
light was used. Prior to each set of measurements, background color
coordinates (x, y and z values) were taken at open-circuit, using
the electrolyte solution without MPc under study. During the mea-
surements, readings were taken as a function of time under kinetic
control, however the color coordinates at the beginning and final
of each redox processes were also reported.
Fig. 2. Aggregation behaviours of 5 (a) in DCM and 7 (b) in DMSO at different
concentrations: (2 × 10−6 to 12 × 10−6 mol dm−3).
absorption spectra of the compounds 4–7 indicate the character-
istic intense Q bands at 695, 686, 708, and 714 nm, respectively.
In addition, the intense B bands were observed at 354 nm for 4,
345 nm for 5, 358 nm for 6 and 336 nm for 7 (Fig. 1). For the metal-
lophthalocyanine bearing thioether moieties on the non-periphery,
the Q band is shifted to the longer wavelength as a result of the
electron-donating ability of the thioether substituents as shown
in Fig. 1. The aggregation behaviors of lutetium phthalocyanines
(4–7) were also investigated at different concentration in DMSO.
Aggregation is usually depicted as a coplanar association of rings
progressing from monomer to dimer and higher order complexes
[26]. 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. Beer-Lambert law was
obeyed for the complexes in DMSO in the concentration ranging
from 2 × 10−6 to 10 × 10−6 mol dm−3 (Fig. 2) [26].
3. Results and discussion
3.1. Synthesis and characterization
Schemes 1 and 2 show the synthetic route involved for the for-
mation of the complexes 4–7. The lutetium phthalocyanines (4–7)
were formed by cyclotetramerization of the compounds 1, 2 and 3
in the presence of anhydrous Lu(CH3COO)3. Purification of the com-
plexes was achieved by column chromatography. The compounds
4–7 were soluble in THF, CHCl3, DMF, and DMSO. Moreover, all
compounds were soluble in methanol except the compound 5.
FTIR, UV–vis, and mass spectroscopies, as well as elemental
analysis performed the characterizations of lutetium phthalocya-
nines. All results of the complexes are consistent with the assigned
formulations (Schemes 1 and 2). The characteristic vibrations cor-
responding to C N were observed at 2230 cm−1, 2227 cm−1 and
2231 cm−1 for 1, 2 and 3 in the FTIR spectra, respectively. The ether
(C–O–C) and the thioether (C–S–C) vibrations for compounds 1, 2
and 3 were observed at 1277 cm−1 and 740 cm−1, at 1253 cm−1
and 762 cm−1 and at 1023 cm−1 and 729 cm−1, respectively. The
strong CN vibrations of 1–3 were disappeared after conversion to
the complexes 4–7. In the FTIR spectra of compounds 4–7, weak
bands observed above 3000 cm−1 are due to the aromatic C–H
stretching. The aliphatic C–H stretching vibrations of the synthe-
sized complexes were observed between 2960 and 2850 cm−1. In
all complexes, the characteristic vibrations corresponding to the
thioether groups (C–S–C) were observed at 751 nm (for 4), 754 nm
(for 5), 753 nm (for 6), and 748 nm (for 7).
The mass spectra of 4–7 confirmed the proposed structures. The
molecular ion peaks were observed at m/z 1549.2 (M-Ac + cyano)
for 4 and 7, 2546.4 (M + H) for 5 and 2124.87 (M-Ac + cyano + 2H)
for 6, respectively. Elemental analysis results were also consistent
with the proposed structures of the synthesized phthalonitrile and
phthalocyanine compounds (1–7).
3.2. Electrochemical measurements
Bis phthalocyanine complexes (LuPc2) have a sandwich struc-
ture involving a metal center between two Pc rings. However
monomeric LuPc complexes include the same metal center at the
outer space of Pc ring due to the big size of metal center. The struc-
tural differences between the sandwich complex and the others
are well reflected by their voltammetric behaviors [28]. Thus the
voltammetric analyses of the newly synthesized 4–7 complexes
were studied to clarify the effects of these structural differences to
the electrochemical behavior of the complexes. Solvent effects to
the electrochemistry of the complexes were also studied in DMSO
The best evidence for phthalocyanine systems are given by their
UV–vis spectra in solution. The ground state electronic absorp-
tion spectra of the compounds 4–7 are given in Fig. 1. The UV–vis

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M. Arıcı et al. / Electrochimica Acta 113 (2013) 668–678
Table 1
Voltammetric data of the complexes.
a
Complex
Ring oxidations
O2 O1
0.66
Ring reductions
R1
ꢀE1/2
R2
R3
R4
LuPc (4) in DCM
LuPc (6) in DCM
LuPc (7) in DCM
LuPc (4) in DMSO
LuPc (6) in DMSO
LuPc (7) in DMSO
LuPc2 (5) in DCM
LuPc2 (5) in DMSO
E1/2 vs. SCEb
1.16c
−0.89
62
0.91
−1.33
80
0.23
ꢀEp (mV) vs. SCEd
–
–
62
0.98
1.55
1.57
1.56
e
Ipa/Ipc
E1/2 vs. SCEb
ꢀEp (mV)d
1.30
0.63
−0.94
80
0.85
−1.28
57
0.90
−1.52
120
–
55
0.84
–
–
e
Ipa/Ipc
E1/2 vs. SCEb
ꢀEp (mV)d
1.03
90
0.34
0.58
70
0.98
−0.98
60
0.94
−1.44c
–
0.97
e
Ipa/Ipc
E1/2 vs. SCEb
ꢀEp (mV)d
0.68
60
0.87
−0.80
−0.99
−1.26
−1.47
–
–
–
–
–
–
–
–
148
e
Ipa/Ipc
E1/2 vs. SCEb
ꢀEp (mV)d
–
–
–
0.65
73
0.89
−0.87
61
0.97
−1.01
63
0.54
−125
−1.46
1.52
1.62
85
0.65
–
–
e
Ipa/Ipc
E1/2 vs. SCEb
ꢀEp (mV)d
1.13
–
0.62
85
−1.00
61
0.97
−1.11
63
0.54
−1.36
85
−1.57
–
–
e
Ipa/Ipc
–
0.93
0.65
E1/2 vs. SCEb
ꢀEp (mV)d
1.11c
0.52
0.14
59
1.00
−0.92
65
0.87
−1.21
73
−1.62
75
–
–
–
63
0.96
0.38
0.36
e
Ipa/Ipc
0.85
E1/2 vs. SCEb
ꢀEp (mV)d
–
–
–
0.63
90
0.87
0.27
57
0.98
−0.81
62
0.92
−1.10 (−1.30)
−1.59
80
0.87
120
–
e
Ipa/Ipc
Tw: This work.
a
ꢀE1/2 = E1/2 (first oxidation) − E1/2 (first reduction) = HOMO–LUMO gap.
b
c
E1/2 = (Epa + Epc)/2 at 0.100 V s−1
.
The process is recorded with SWV.
d
e
ꢀEp = |Epa − Epc|.
Ipa/Ipc for reduction, Ipc/Ipa for oxidation processes at 0.100 V s−1 scan rate.
and DCM solvents. Table 1 lists the assignments of the redox couples
and the electrochemical parameters, which included half-wave
peak potentials (E1/2), anodic to cathodic peak potential separation
(ꢀEp), ratio of anodic to cathodic peak currents (Ipa/Ipc), and differ-
ence between the first oxidation and reduction potentials (ꢀE1/2).
All electrochemical analyses were performed in both DCM (non-
polar and noncoordinating solvent) and DMSO solvent media (polar
and coordinating solvent) to investigate the effect of the solvent
to the redox behavior of the complexes. As shown in Fig. 3, all
mono LuPc complexes give very similar voltammetric responses
in DCM/TBAP electrolyte system on a Pt working electrode with
small potential shifts due to the different position and the num-
ber of the substituents. Mono LuPc complexes (4, 6, and 7) give
two reduction and two oxidation couples. ꢀE1/2 values of all mono
LuPcs are between 1.48 and 162 V, which are in harmony with those
of MPc having redox inactive metal center and mono LuPc com-
plexes [29–32]. While the first reduction and the first oxidation
couples of all monomeric LuPc complexes are electrochemically
and chemically reversible, the second oxidation and reductions are
irreversible with respect to ꢀEp and Ip,a/Ip,c values [33]. Comparing
ꢀEp values of them with those of ferrocene were also used to check
the electrochemical reversibilities of the complexes. As shown from
the figure, substituting the complex at the nonperipheral position
(complex 7) instead of the peripheral position (complex 4) shifts
the redox processes approximately 100 mV toward the negative
potential. The reversibility of the complexes gets worse, when LuPc
is substituted on nonperipheral position (complex 7). The redox
processes of octa substituted LuPc (6) shifts approximately 50 mV
toward the negative potentials with respect to the peripheral tetra
substituted LuPc (4) due to the presence of more electron releasing
Fig. 3. (a) CVs of 4, 6, and 7 (5.0 × 10−4 mol dm−3) at 0.10 V s−1 scan rate on Pt in
DCM/TBAP. (b) SWV of 4, 6, and 7, SWV parameters: pulse size = 100 mV; Step Size:
5 mV; Frequency: 25 Hz.

M. Arıcı et al. / Electrochimica Acta 113 (2013) 668–678
673
Fig. 4. (a) CVs of 4, 6, and 7 (5.0 × 10−4 mol dm−3) at 0.10 V s−1 scan rate on Pt in
DMSO/TBAP. (b) SWV of 4, 6, and 7, SWV parameters: pulse size = 100 mV; Step Size:
5 mV; Frequency: 25 Hz.
Fig. 5. (a) CVs and (b) SWV of 5 (5.0 × 10−4 mol dm−3) at 0.10 V s−1 scan rate on Pt
in DCM/TBAP and DCM/TBAP electrolyte systems.
anodic side due to the radical form of the one Pc ring of the complex.
While mono Pcs give the first reduction process at around −0.90 V,
the complex 5 gives the first reduction process at 0.14 V in DCM
and 0.27 V in DMSO. On the other hand, the potential of O1 for 5 is
recorded at less positive potential then those of the mono Pc com-
pounds. The ꢀE1/2 value of 5 decreases to 0.38 V due to the shifting
of peaks, while these values of the mono LuPcs are higher than
1.50 V. The value of ꢀE1/2 reflects the energy separation between
the SOMO and the LUMO of the bis-phthalocyanine neutral forms,
and HOMO and LUMO for the mono LuPcs. In turn, the values of the
potential R2 were estimated to be similar for the R1 of all the mono
Pc complexes.
To investigate the effect of the solvent, CV and SWV of 5 were
also recorded in DMSO/TBAP electrolyte system. When compared
with the CV and SWV of 5 in DCM, it is clear that the redox processes
of the complex interestingly shift to the positive potentials. Because
redox processes generally shifts to the negative potentials in DMSO
with respect to DCM due to the electron donating ability of the polar
DMSO solvent. Another different behavior of the complex in DMSO
is the splitting of the R3 process. This extraordinary behavior is
most probably due to the change the interaction of Pc rings of 5 as
a result of the interaction with DMSO.
The number of transferred electrons for each redox process of
the complexes was determined by CPC measurements at suitable
constant peak potentials. Faraday law was used to derive the num-
ber of electron transferred during the electrolysis of the complex
under constant potential applications. CPC showed that all redox
processes of the complex are one-electron redox couples. CV, SWV
and spectroelectrochemical measurements given below also sup-
port one-electron character of the redox couples. It is well known
that peak current of a process is directly proportional with the
3/2 order of the transferred electrons. Thus it could be proposed
the transferred electrons with comparing the peak current of the
redox processes. Characteristic spectral changes during the in-situ
spectroelectrochemical measurements of a complex could be also
used to determine the transferred electron numbers. For instance,
observation of the spectral changes (which are characteristic for
monoanionic LuPc2 species under 0.0 V potential application) indi-
cated one-electron transfer feature of R1 couple of LuPc2.
dimethoxyphenylthio substituents on the complex 6. Differently
all redox processes of 6 are out of the reversible peak character.
When DMSO (polar and coordinating solvent) was used instead
of DCM (nonpolar and noncoordinating solvent) as the solvent of
the complexes, each reduction reaction of the complexes splits into
two waves (Fig. 4). Thus, while these complexes give two reduc-
tion reactions in DCM, they give four reduction reactions in DMSO.
Due to the splitting of the reduction reactions, peak analyses of the
complexes (especially ꢀEp and Ip,a/Ip,c values) could not be per-
formed. Splitting of the reduction processes may be due to the
coordination of DMSO to the lutetium center of the complexes.
Coordinating of DMSO forms equilibrium between coordinated and
non-coordinated complexes. Coordinated and non-coordinated
complexes can transfer electrons at different potentials. Thus,
DMSO splits the redox processes of the complexes. DCM is not a
coordinating solvent, consequently the splitting behaviors of the
complexes could not be observed in DCM. Coordinating effect of
MPcs with different ligands is well documented in literature and
our results are in agreement with the literature [30]. Another com-
mon difference between the redox behaviors of the complexes in
different solvents is the shifting of the electron transfer processes to
the negative potentials due to the higher polarizing effect of DMSO
than DCM.
The redox properties of LuPc2 complex (5) were studied and
compared with those of the LuPc complexes. The complex 5 gives
four reversible reduction processes, labeled as R1 at 0.15 V, R2 at
−0.92 V, R3 at −1.22 V, and R4 at −1.62 V as well as one reversible
and one irreversible oxidation processes, labeled as O1 at 0.52 V and
O2 at 1.10 V in DCM/TBAP and these redox processes shift to nega-
tive potentials in DMSO/TBAP. Fig. 5 shows the CV and SWV of the
complex in DCM/TBAP and DMSO/TBAP. Table 1 lists the fundamen-
tal electrochemical parameter of the complex. All redox processes
are Pc ring-based, because lutetium metal center is redox inactive
in Pc core [32]. The electrochemical processes are schematically
illustrated in Scheme 3, where the reductions were labeled as R1,
R2, R3, and R4 and the oxidations as O1 and O2. Scheme 4 shows
the origin of these electron transfer reactions, which were indi-
cated on the molecular orbital diagram of LuPc2 [15]. As shown in
Table 1 and Figs. 3–5, the redox potential of R1 of 5 is shifted to the

674
M. Arıcı et al. / Electrochimica Acta 113 (2013) 668–678
Scheme 3. Redox mechanism of the complex 5.
3.3. Spectroelectrochemical studies
decreases without shifting during the Pc based reduction processes
of the metallophthalocyanines bearing redox inactive metal cen-
ter [26,28,38]. But differently the Q bands of mono LuPcs shift to
the higher energy side during the Pc ring reduction process of the
LuPcs. So −w1e can easily assign this process to [AcO-LuIIIPc−2]/[AcO-
It is well known that lanthanide phthalocyanines, especially
sandwich type phthalocyanine metal complexes reveal strong
changes in their electronic absorption spectra from UV up to
near-IR region while undergoing oxidation and reduction, and are
thus promising electrochromic materials [34]. Thus spectroelec-
trochemical analyses of the complexes were performed to perform
assignments of the redox processes and to determine the spectrum
and color of the electrogenerated anionic and cationic form of the
complexes.
LuIIIPc−3
]
reduction.
Fig. 6b illustrates the spectral changes during the second and
third reduction processes. These spectral changes are also consis-
tent with the second and third Pc based reduction processes of
MPcs. Thus we assigned these processes to [AcO-LuIIIPc−3
]
−1/[AcO-
] ]
and [AcO-LuIIIPc−4 −2/[AcO-LuIIIPc−5 −3, respectively
−2
LuIIIPc−4
]
All mono LuPc complexes give very similar spectral changes
during the spectroelectrochemical measurements. While all mono
LuPc complexes give distinct spectral changes in DMSO, the spec-
tral changes in DCM are not easily discerned. The different in-situ
spectroelectrochemical behaviors of the complexes in different
solvent are in harmony with the voltammetric responses of the
complexes in these solvents. Different behaviors of the complexes
in DMSO and DCM were arisen from the different nature of these
solvents. Coordinating and more polarizing nature of DMSO affects
the voltammetric and spectroscopic behavior of the complexes
more than these of noncoordinating DCM solvent.
Fig. 6 illustrates the UV/Vis spectral changes for the complex 4 in
DMSO/TBAP during controlled-potential electrolysis, which reflect
transformation of the neutral phthalocyanine into the electron-
reduced and oxidized forms, respectively [35–37]. As shown in
Fig. 6a, while the Q band at 697 nm decreases in intensity with
slight shifting to 692 nm, a new band is recorded at 584 nm dur-
ing the first reduction reaction. Moreover the B band at 361 nm
decreases in intensity and a new band is observed at 434 nm. During
this electrochemical reduction reaction, well recorded isosbestic
points are observed at 385, 625, 635, and 721 nm, which demon-
strates that reduction gives a single reduced product. The Q band
[5,36–39]. Spectral changes during the first oxidation process are
given in Fig. 6c. As shown in this figure, the Q band decreases in
intensity, while two new bands are recorded at 349 and 848 nm.
These new bands are resulted from the metal to ligand charge
transfer (MLCT) processes. These spectral changes are in agree-
ment with the Pc based oxidation of the MPc complexes. All spectral
changes of the complex are in agreement with the orbital diagrams
of these types’ complexes [15]. The color change of the complexes
during the redox processes were recorded using in-situ colorimet-
ric measurements. Fig. 6d shows the chromaticity diagrams of 4
recorded simultaneously during the spectroelectrochemical mea-
surements. Without any potential application, the solution of 4 is
green (x = 0.3033 and y = 0.3657). As the potential is stepped from
0 to −1.00 V, the color of neutral 4 starts to change and a light
blue color (x = 0.2681 and y = 0.3326) of monoanionic form of the
complex was obtained at the end of the first reduction. Similarly
the color of the dianionic and trianionic species was recorded as
deep blue and monocationic species has yellow color (x = 0.3558
and y = 0.3353). As shown in fig. 6d, electrogenerated forms of the
complex have distinct color changes, which are the desired proper-
ties of a material for electrochromic application. All color changes
are reversible. Application of the potential of the previous process
Scheme 4. Origin of the electron transfer reactions on the molecular orbital diagram of LuPc2 [15].

M. Arıcı et al. / Electrochimica Acta 113 (2013) 668–678
675
Fig. 6. In-situ UV–vis spectral changes of 4 in DMSO/TBAP. (a) Eapp = −1.10 V. (b) Eapp = −1.30 V (inset: Eapp = −1.50 V). (c) Eapp = 0.80 V. (d) Chromaticity diagram of 4. Each
−3
symbol represents the color of electro-generated species; ꢀ: [AcO-LuIIIPc−2], ꢁ:[AcO-LuIIIPc−3
]
−1, ꢁ: [AcO-LuIIIPc−3
]
−2, ꢂ: [AcO-LuIIIPc−4
]
,
: [AcO-LuIIIPc1]+1
.
immediately changed the color to the color of the previous species.
Reversibility of the color changes were tested by applying different
potentials to the working electrode. Approximately similar color
coordinated were recorded during the repetitive switching of the
redox processes.
excitation in the neutral form. During the oxidation and reduction
of the neutral form of 5, new bands appear near the former
position of this band, which are characteristic changes for the
sandwich type Pc complexes [15,39,40]. Under 0.0 V potential
application, while the Q band at 688 nm decreases in intensity, a
new Q band for the reduced species is recorded at 643 nm. The
broad band at around 450 nm and the band at 940 nm, which
are characteristic bands for the radical Pc ring, disappear during
this process (Fig. 8a). These spectral chances are characteristic
changes for the sandwich type−P1c complexes and easily assigned to
redox reaction [39–41]. During
this process, well-defined isosbestic points are recorded at 397,
568, 668, 705, and 765 nm, which demonstrate that the reduction
proceeds cleanly in deoxygenated DCM to give a single reduced
species. Green color of the neutral 5 (x = 0.3241 and y = 0.3811)
changed to greenish blue (x = 0.2842 and y = 0.3605) at the end of
the first reduction (Fig. 8d). When reverse potential was applied,
the original green color was obtained reversibly. Fig. 8b illustrates
in-situ UV–vis spectral changes of 5 during the second and third
redox processes, which indicate the one-electron ring based
reductions of the complex. Distinct spectral changes during these
reduction processes also alter the color of the complex. While blue
color (x = 0.2555 and y = 0.3282) is obtained at the end of the second
reduction process, the blue color changes to purple (x = 0.2868 and
y = 0.2762) at the end of the third reduction process (Fig. 8d). UV–vis
spectra of the complex also change significantly during the oxida-
tion processes (Fig. 8c). While the Q band shifts to 724 nm, the band
at around 470 nm increases in intensity in addition to the enhanced
band at 841 nm during the first oxidation process. These spectral
changes indicate radical form of the both Pc rings of the sandwich
type complex. Since the band at 470 nm characterizing radical form
As shown in Fig. 7, the complex 7 gives very similar spectral
changes with the complex 4 during the spectroelectrochemical
measurements in DMSO. While the Q band shifts from 715 nm to
675 nm, a new band is recorded at 608 nm during the first reduc-
tion process (Fig. 7a). Similarly the Q band at 675 nm decreases
without shifting and a new MLCT band is recorded at 563 nm dur-
ing the second reduction process (Fig. 7b). Fig. 7c illustrates the
spectral changes during the oxidation processes. As shown in this
figure, spectral changes which are consistent with the Pc based oxi-
dation are recorded during the first oxidation process. The Q band
decreases in intensity and two new MLCT bands are recorded at 800
and 882 nm during the first oxidation reaction. These spectroscopic
changes indicate a Pc based oxidation process. The monocationic
species decomposed during the second oxidation process as shown
in Fig. 7c inset. Fig. 7d illustrates the distinct color differences
between the electrogenerated anionic and cationic forms of the
complex.
Spectroelectrochemical studies were employed to confirm
the assignments in the CVs of the sandwich type complex 5. The
complex 5 shows different spectral changes in DMSO and in DCM
solvents during reduction processes. Fig. 8 illustrates the in-situ
UV–vis spectral changes of 5 in DCM during the redox processes.
Spectral changes in the NIR region are characteristics for the 5 com-
plexes. As Ishikawa and co-workers [39,40] reported the band at
940 nm is easily assigned to the nondegenerate HOMO–LUMO tran-
sition, which corresponds to the charge resonance HOMO–SOMO
[Pc−1LuIIIPc−2]/[Pc−2LuIIIPc−2
]

676
M. Arıcı et al. / Electrochimica Acta 113 (2013) 668–678
Fig. 7. In-situ UV–vis spectral changes of 7 in DMSO/TBAP. (a) Eapp = −1.10 V. (b) Eapp = −1.30 V. (c) Eapp = −0.70 V (inset: Eapp = −1.30 V). (d) Chromaticity diagram of 7. Each
−2
symbol represents the color of electro-generated species; ꢀ: [AcO-LuIIIPc−2], ꢁ: [AcO-LuIIIPc−3
]
−1, ꢁ: [AcO-LuIIIPc−3
]
,
: [AcO-LuIIIPc1]+1
.
Fig. 8. In-situ UV–vis spectral changes of 5 in DCM/TBAP. (a) Eapp = 0.00 V. (b) Eapp = −1.00 V (inset: Eapp = −1.30 V). (c) Eapp = 0.60 V (inset: Eapp = 1.30 V). (d) Chromaticity diagram
−3
+1
of 5. Each symbol represents the color of electro-generated species; ꢀ: [Pc−1LuIIIPc−2], ꢁ: [Pc−2LuIIIPc−2
]
−1, ꢁ: [Pc−3LuIIIPc−2
]
−2, ꢂ: [Pc−3LuIIIPc−3
]
,
: [Pc−1LuIIIPc−1
] .

M. Arıcı et al. / Electrochimica Acta 113 (2013) 668–678
677
Fig. 9. In-situ UV–vis spectral changes of 5 in DMSO/TBAP. (a) Eapp = 0.00 V. (b) Eapp = −1.00 V (inset: Eapp = −1.20 V. (c) Eapp = 0.70 V. (d) Chromaticity diagram of 5. Each symbol
+1
represents the color of electro-generated species; ꢀ: [Pc−1LuIIIPc−2], ꢁ: [Pc−2LuIIIPc−2
]
−1, ꢂ: [Pc−3LuIIIPc−2
]
−2, ꢃ: [Pc−3LuIIIPc−3
]
−3, ଝ: [Pc−1LuIIIPc−1
]
.
of the one Pc ring of the complex increases in intensity. All bands
decrease in intensity due to the decomposition of the complex
during the second oxidation process as shown in Fig. 8c inset. Color
of the monocationic species was recorded as yellow (x = 0.3854 and
y = 0.376) as shown in Fig. 8d. Measurement of the xyz coordinates
allows quantification of each color of redox species that is very
important to decide their possible electrochromic application.
Fig. 9 illustrates the in-situ UV–vis spectral changes of 5 in
DMSO. The complex 5 gives very similar spectroscopic changes dur-
ing the redox processes in both of DCM and DMSO. During the first
reduction process at 0.0 V, while the Q band at 695 nm decreases in
intensity a new band is recorded at 645 nm. At the same time, the
bands at 480 and 943 nm, which characterize the radical neutral
5, disappear completely (Fig. 9a). During this process, well-defined
isosbestic points are recorded at 405, 560, 668, and 710 nm. Yellow-
ish green color of the neutral 5 (x = 0.3244 and y = 0.383) changed
to light green (x = 0.3105 and y = 0.362) at the end of the first reduc-
tion (Fig. 9d). General trend of the spectral changes during the
further reductions and oxidation processes of the complex in DMSO
are very similar with those in DCM with little change differences
as shown in Fig. 9. Distinct color change of the complex during
the redox processes were recorded using in-situ colorimetric mea-
surements. Fig. 9d gives the chromaticity diagrams of 5 recorded
simultaneously during the spectroelectrochemical measurements.
Measurement of the xyz coordinates of the complex and distinct
differences between the different redox states of the complex indi-
cate possible electrochromic application of the complex in both
DCM and DMSO solvent media.
multi-electron and reversible/quasi-reversible redox processes.
The peak potentials of the redox processes were affected consider-
ably from the position and the number of the substituent. Solvent of
the electrolyte also affected the redox behavior of the complexes.
The first reduction process recorded at around 0.14 V is charac-
teristics for the reduction of the radical Pc ring of the sandwich
phthalocyanine. Definite determination of the colors of the electro-
generated anionic and cationic form of the complexes is important
to decide the possible electrochromic application of the complexes.
Multiple electron transfer reactions at small potentials, reversible
and diffusion controlled character of these processes and the dis-
tinct color differences between the electrogenerated anionic and
cationic forms of the complexes are the desired properties for the
usage of a material in the most of the electrochemical technologies
such as electrosensor, electrocatalytic, and display applications. In
our forthcoming studies electrochromic application of these com-
plexes will be performed.
Acknowledgments
This work is supported by TUBITAK (Project no: 111T179) and
Yıldız Technical University (Project No: 2012-01-02-KAP03).
Appendix A. Supplementary data
Supplementary data associated with this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.electacta.2013.
09.088.
4. Conclusions
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