The synthesis and spectral properties of amber phthalocyanines

Article abstract of DOI:10.1016/j.dyepig.2010.06.007

Novel antimony(V)-phthalocyanine complexes, [Sb(tObpc)(OH) ₂]⁺, [Sb(tppc)(OH)₂]⁺, and [Sb(tppc)Cl₂]⁺ (where tObpc and tppc denote tetra(n-butoxy)phthalocyaninate, C₄₈H₄₈

Full text of DOI:10.1016/j.dyepig.2010.06.007

Dyes and Pigments 88 (2011) 187e194
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
The synthesis and spectral properties of amber phthalocyanines
,
a
a
b
Hiroaki Isago a , Yutaka Kagaya , Harumi Fujita , Tamotsu Sugimori
*
a National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan
b Graduate School of Medicine and Pharmaceutical Sciences, Univ. of Toyama, 2630 Sugitani, Toyama-shi, Toyama 930-0194, Japan
a r t i c l e i n f o
a b s t r a c t
Novel antimony(V)-phthalocyanine complexes, [Sb(tObpc)(OH)2]þ, [Sb(tppc)(OH)2]þ, and [Sb(tppc)Cl2]þ
(where tObpc and tppc denote tetra(n-butoxy)phthalocyaninate, C48H48N8O24ꢀ, and tetrakis(20,60-dime-
thylphenoxy)phthalocyaninate, C64H48N8O24ꢀ, respectively) were synthesized by oxidizing the corre-
sponding antimony(III) derivatives either with tert-butyl perbenzoate or sulfuryl chloride. The compounds
are dissimilar to conventional phthalocyanines in that they are of amber color in solution. Optical prop-
erties were studied by absorption and magnetic circular dichroism spectroscopy. The amber
Article history:
Received 21 April 2010
Received in revised form
3 June 2010
Accepted 11 June 2010
Available online 25 June 2010
color was attributed to a combination of an intense absorption band (Q-band; log(
3
/Mꢀ1 cmꢀ1) ¼ ca. 5) at
Keywords:
Phthalocyanine
Antimony
Amber
Optical absorption
MCD
w735e760 nm, which was red-shifted by w1000e1200 cmꢀ1 compared to conventional phthalocyanines
and a less intense (log(
3
) ¼ ca. 4) but broad band at w400e500 nm, which is not observed for conventional
phthalocyanines. The additional band at w400e500 nm was considered to be a red-shifted Soret band.
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
distorted from planarity owing to steric hindrance between the
neighboring peripheral phenyl groups [8].
Phthalocyanines and their metal complexes (hereafter referred as
Pc’s) are versatile compounds and have attracted much attention
in many industrial and medical fields, such as dyes and pigments,
photovoltaic and solar cells, charge generating material (CGM), optical
data storage, infrared cut-filter, photodynamic cancer therapy,
nonlinear optics, sensors, one-dimensional metal and semiconductor,
and electrochromism [1e3].
The present authors have reported that the presence of an anti-
mony ion in the cavity of a phthalocyanine macrocycle, irrespective of
its oxidation state, gives rise to a significant red-shift of the Q-band
(by ca.1100e1600 cmꢀ1) [9e19]. In addition, it is known that alkoxyl-
and phenoxyl-substituted Pc’s show an extra band at the red-flank of
the Soret band, which has been assigned as a nep
* transition
involving lone pair orbitals of oxygen atoms in the alkoxyl/phenoxyl
groups [20]. Therefore, antimony derivatives of Pc’s bearing alkoxyl
or phenoxyl groups as peripheral substituents, of which the
corresponding phthalonitriles (as the starting material) are easily
prepared or even commercially available, may show a different color.
Nyokong’s group has studied antimony derivatives of octaphenoxyl-
substituted phthalocyanines [21]. Although an extra band w400 nm
was observed for antimony(III) derivatives, little attention has been
paid to this band and the color of the complexes. With respect to
the corresponding antimony(V) derivatives, their spectral data are
available only for the Q-region; nothing has been mentioned about
the presence/absence of such an extra band in their “window” region
probably because they had not isolated the compounds in analyti-
cally pure form at that stage. In this work, we will report syntheses
of a few novel antimony(V)-phthalocyanines bearing alkoxyl or
phenoxyl groups as peripheral substituents (Fig. 1). As is described
below, we have successfully accomplished a new approach to non-
blue/green Pcs with the aforementioned strategy.
Conventional Pc’s are generally blue in color because they
intensely absorb red light (650e700 nm; log (
this being termed a Q-band and assigned to a pep
3
/Mꢀ1 cmꢀ1) ¼ ca. 5,
* (HOMOeLUMO)
transition in character) but are transparent in other parts of the
visible spectrum [4e6]. Some Pc’s also absorb violet light
(380e420 nm; log(3) ¼ ca. 4) and hence they may display a green
color. In any case, the appearance of the main band in 650e700 nm
and the essential transparency in other parts of the spectrum
determine the color of the Pc. Hence, if a Pc has a considerably
red-shifted Q-band and an extra band in other parts of the spectrum,
the Pc should show a non-blue/green color. This possibility was
exemplified by Kobayashi and coworkers, who reported octaphenyl-
substituted Pc’s that exhibit ocher and red colours [7]. In this case,
the Pc’s were unusual in that the macrocycle was significantly
In addition to that, as is described below, the new Pcs absorb
a wide range of visible light. Therefore, these should be of interest
* Corresponding author. Tel.: þ81 29 859 2734; fax: þ81 29 859 2701.
E-mail address: Isago.Hiroaki@nims.go.jp (H. Isago).
0143-7208/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2010.06.007

188
H. Isago et al. / Dyes and Pigments 88 (2011) 187e194
2.1.3. Synthesis of (tetra-n-butoxyphthalocyaninato)antimony(III)
triiodide, [Sb(tObpc)]I3
The antimony(III) complex was synthesized in essentially the
same manner to that described for its tbpc analogue [11]. A mixture of
4-n-butoxyphthalonitrile (0.82 g; 4.0 mmol) and antimony iodide
(1.0 g; 2.0 mmol) was fused in a sealed glass tube at 170 ꢁC for 72 h.
The reaction mixture solidified when it was allowed to cool down to
room temperature. The solid was heated at 130 ꢁC under vacuum for
72 h to remove unreacted starting materials and volatile byproducts.
The desired product was extracted by o-dichlorobenzene (50 ml) and
the solvent was evaporated. The residue was washed with 200 ml
of CH2Cl2/hexane (4:46(v/v)) until the washings turned essentially
colorless and the product was then dried 80 ꢁC under vacuum to
obtain a 668 mg of crude product (yield 51% assuming the product is
analytically pure). This product was the desired compound as proven
by ESI-MS (m/z ¼ 921 (121Sb(tObpc))þ and 923 (123Sb(tObpc))þ in
acetonitrile) and absorption spectra (lmax ¼ 771 nm in CH2Cl2).
This compound was used in the next procedure although it is not
sufficiently pure at this stage because much of antimony(III) deriva-
tives are known to be lost during purification procedures [11,14].
Fig. 1. Antimony(V)-phthalocyanine complexes studied in this work, [Sb(tppc)(OH)2]þ
(R ¼ 20,60-dimethylphenoxyl, X ¼ OHꢀ), [Sb(tppc)Cl2]þ (R ¼ 20,60-dimethylphenoxyl,
X ¼ Clꢀ), andv[Sb(tObpc)(OH)2]þ (R ¼ n-butoxyl, X ¼ OHꢀ). The tetra substituted Pcs
are mixtures of four regioisomers based on the position of peripheral substituents.
(For interpretation of the references to color in this figure legend, the reader is referred
to the web version of this article).
to those who work not only with dyes and pigments but also
with solar cells and CGM. It should be noted that antimony(V)
derivatives may be attractive from the viewpoint of their potential
application to chemotherapy of protozoan parasite endemic in
tropical and subtropical regions, such as Leishmaniasis because
problems of clinical resistance to the existing pentavalent anti-
monals in use as the first line drugs have become aggravated
[22e24].
2.1.4. Synthesis of dihydroxo(tetra-n-butoxyphthalocyaninato)
antimony(V) triiodide, [Sb(tObpc)(OH)2]I3
The antimony(V) derivatives bearing axial hydroxyl groups were
prepared in essentially the same manner as that for the tbpc analogue
[16]. 556 mg of the crude [Sb(tObpc)]I3 was dissolved in tert-butyl
perbenzoate (Alfar Aesar; 11 ml) and the ensuing solutionwas heated
at 50 ꢁC with vigorous stirring for 45 min. The reaction was moni-
tored using the absorption spectra of the solution (in CH2Cl2 solu-
tion). After the most prominent band at 771 nm ([Sb(tObpc)]þ)
disappeared and a new band appeared at 741 nm, the mixture was
ice-cooled to quench the reaction. 25 ml of hexane was added to
precipitate the product and the solid was collected by centrifugation.
The solids were further washed with 150 ml of CH2Cl2/hexane (1:4
(v/v)) until the washings turned essentially colorless and then dried
at 80 ꢁC under vacuum (514 mg). This was dissolved into acetone
(14 ml) and the solution was filtered to remove insoluble impurities
and then precipitated by the addition of a 36 ml of water. The solid
was collected by centrifugation and again was dissolved into acetone
and precipitated by the addition of water; these procedures were
repeated (5 times in this case) until a considerable amount of solid
became dispersed in the aqueous phase after centrifugation. The
colloidal solution, after being added a small amount (ca. 4.5 ml) of
aqueous Na2SO4 solution (ca. 1 M), was again centrifuged to remove
the aqueous phase. The solid was dried at 80 ꢁC under vacuum and
then was dissolved into CH2Cl2 (25 ml) and filtered to remove
Na2SO4. The solvent was evaporated out and the desired compound
was recrystallized from CH2Cl2/hexane (6:45 (v/v)), washed with
a 50 ml of CH2Cl2/hexane (1:9 (v/v)), and dried at 80 ꢁC under vacuum
(381 mg; yield 42% assuming that the starting antimony(III) deriva-
tive was analytically pure). This product has been found to be the
desired compound by ESI-MS (m/z ¼ 955 (121Sb(tObpc)(OH)2)þ and
957 (123Sb(tObpc)(OH)2)þ in acetonitrile). Anal. Found: C, 47.78, H,
4.06, N, 9.53%. Calcd for [Sb(tObpc)(OH)2]I3 (C48H50O6N8SbI3): C,
43.11; H, 3.77; N, 8.38%. As triiodide salt was difficult to obtain in
analytically pure form [14], we did not make further efforts to purify
this product and have tried to replace the counter anion with
hexafluorophosphate.
2. Experimental
2.1. Materials
2.1.1. Starting materials
Commercially available 4-(20,60-dimethylphenoxy)phthaloni-
trile and 4-n-butoxyphthalonitrile (Tokyo Kasei) were purified by
firstly passing a silica gel column (CH2Cl2) and then recrystalliza-
tion from ethyl acetate/hexane and benzene/hexane, respectively.
Antimony(III) iodide was purchased from Wako and used as
received.
2.1.2. Synthesis of dihydroxo(tetra-tert-butylphthalocyaninato)
antimony(V) hexafluorophosphate, [Sb(tbpc)(OH)2]PF6$3H2O
The triiodide salt, [Sb(tbpc)(OH)2]I3$2H2O (where tbpc denotes
tetra-tert-butyl-phthalocyaninate, C48H48N28ꢀ), was prepared in
a way described previously [16]. To a dry flask containing 200 ml of
dehydrated acetonitrile in which [Sb(tbpc)(OH)2]I3$2H2O (200 mg;
0.095 mmol) was dissolved, was added a dehydrated acetonitrile
solution (4.0 ml) containing AgPF6 (Aldrich; 1.0 mmol). The ensuing
solution was stirred in the dark at room temperature and the reac-
tion was monitored using absorption spectra. Absorption bands in
the 300e400 nm region, which are characteristic of I-3, disappeared
after 30 min, after which time, an additional acetonitrile solution
(1.0 ml) containing AgPF6 (0.30 mmol) was added. After stirring
for 15 min in the dark, the reaction mixture was filtered to remove
precipitated solid (AgI3) and the filtrate evaporated to reduce
its volume (5 ml). To this solution was added 200 ml of water to
precipitate the desired compound. The solid was collected by
filtration, washed with a small amount of water, and then dried at
80 ꢁC under vacuum (142 mg). A portion (52 mg) of the crude hex-
afluorophosphate was twice recrystallized from benzene/hexane.
The solid was collected by filtration and dried at 80 ꢁC under vacuum
(29 mg; yield 49%). Anal. Found: C, 52.38, H, 4.84, N, 10.14%. Calcd
for [Sb(tbpc)(OH)2]PF6·3H2O (C48H56O5N8SbPF6): C, 52.81; H, 5.17; N,
2.1.5. Synthesis of dihydroxo(tetra-n-butoxyphthalocyaninato)
antimony(V) hexafluorophosphate, [Sb(tObpc)(OH)2]PF6
The conversion of the triiodide to hexafluorophosphate was
carried out in essentially the same manner as that for the tbpc
analogue. To 150 ml of dehydrated acetonitrile solution containing
[Sb(tObpc)(OH)2]I3 (104 mg; 0.095 mmol assuming that the triodide
10.26%. IR/cmꢀ1; 844 (
n(PeF)) and 558 (d(F-P-F)).

H. Isago et al. / Dyes and Pigments 88 (2011) 187e194
189
was analytically pure) was added dehydrated acetonitrile (4.5 ml)
containing AgPF6 (3.1 mmol) and the resulting mixture was stirred
in the dark at room temperature. Additional acetonitrile (0.5 ml)
containing AgPF6 (0.34 mmol) was added after 30 min. After stirring
for 30 min in the dark, the reaction mixture was filtered to remove
precipitated solid (AgI3) and the filtrate was evaporated to reduce its
volume (30 ml). Crude hexefluorophosphate (103 mg) was obtained
by pouring the solution into 150 ml of water and then treating in the
same way as that for the tppc analogue. A portion (73 mg) of the
crude hexafluorophosphate was dissolved in nitrobenzene (30 ml)
to which was added 250 ml of benzene. A small amount of
dark brown solid precipitated, which was removed by filtration. To
the filtrate was added 300 ml of hexane to precipitate the desired
product. This procedure was repeated twice. The solid was collected
by filtration and dried at 80 ꢁC under vacuum (31 mg; yield 42%
assuming that the starting triiodide was analytically pure). Anal.
Found: C, 52.58, H, 4.49, N, 10.33%. Calcd for [Sb(tObpc)(OH)2]PF6
a 400 ml of benzene/hexane (1:4 (v/v))and dried at 80 ꢁC under
vacuum (515 mg). The solid was again dissolved in acetone (10 ml)
and precipitated by the addition of water (40 ml); this procedure
was repeated 4 times until a considerable amount of solid became
dispersed in the aqueous phase after centrifugation. The ensuing
colloidal solution, to which 3 ml of aq Na2SO4 solution (w1 M)
had been added, was centrifuged to remove the aqueous phase.
The solid was dried at 80 ꢁC under vacuum and then was dissolved
in CH2Cl2 (25 ml) and filtered to remove Na2SO4. The solvent was
evaporated and the desired compound was recrystallized from
CH2Cl2/hexane (6:45 (v/v)), washed with a 50 ml of CH2Cl2/hexane
(1:9 (v/v)), and dried at 80 ꢁC under vacuum (371 mg; yield 50%
assuming that both the starting antimony(III) derivative and the
product were analytically pure). This product has been found to be
the desired compound by ESI-MS (m/z ¼ 1147 (121Sb(tppc)(OH)2)þ
and 1149 (123Sb(tppc)(OH)2)þ in acetonitrile). Anal. Found: C, 53.92,
H, 3.65, N, 7.85%. Calcd for [Sb(tppc)(OH)2]I3 (C64H50O6N8SbI3): C,
50.25; H, 3.29; N, 7.33%. As is the case for tObpc analogue, we did
not make further efforts to purify this product.
(C48H50O6N8SbPF6): C, 52.33; H, 4.57; N,10.17%. IR/cmꢀ1; 845 (
and 558 ( (F-P-F)).
n(P-F))
d
2.1.6. Synthesis of tetrakis{4-(20,60-dimethylphenoxy)}
phthalocyaninatoantimony(III) triiodide, [Sb(tppc)]I3
2.1.8. Synthesis of dihydroxo[tetrakis{4-(20,60-dimethylphenoxy)}
phthalocyaninato]antimony(V) hexafuluorophosphate,
This complex was synthesized according to previously reported
work [11]. A mixture of 4-(20,60-dimethylphenoxy)phthalonitrile
(1.0 g; 4.0 mmol) and antimony iodide (0.5 g; 1.0 mmol) was fused in
a sealed glass tube at 173 ꢁC for 72 h. The reaction mixture was
heated at 130 ꢁC under vacuum for 72 h as was the case for the tObpc
analogue. The desired product was extracted by CH2Cl2eMeOH
mixed solvent (4:1 (v/v); 250 ml) and the solvent evaporated. The
ensuing residue was washed with a 100 ml of CH2Cl2/hexane (8:42
(v/v)) until the washing turned essentially colorless and dried at
80 ꢁC under vacuum to obtain a 1090 mg of crude product. A portion
(890 mg) of the solid was dissolved in acetone (24 ml), to which was
added 76 ml of water to precipitate the desired compound. The solid
was collected by centrifugation, washed with acetone/water (1:4 v/
v) until the washing turned essentially colorless, and then dried at
80 ꢁC under vacuum. This solid was dissolved in CH2Cl2 (20 ml), and,
after being filtered, the solvent was evaporated. The resulting solid
was recrystallized from CH2Cl2/hexane (10:40 (v/v)), washed with
the same solvent system, and dried at 80 ꢁC under vacuum to obtain
732 mg of crude product, which was found to be the desired
compound using ESI-MS (m/z ¼ 921 (121Sb(tObpc))þ and 923 (123Sb
(tObpc))þ in acetonitrile) and absorption spectra (lmax ¼ 771 nm in
CH2Cl2). Yield; 49% (assuming that this is analytically pure).
Although it is not sufficiently pure at this stage, this compound was
used in the next procedure as is the case for tObpc analogue.
[Sb(tppc)(OH)2]PF6
The conversion of the triiodide to hexafluorophosphate was
carried out using the same method as that recounted for the tObpc
analogue. To 10 ml of a dehydrated acetonitrile solution containing
[Sb(tppc)(OH)2]I3 (460 mg; 0.30 mmol assuming that the triodide
was analytically pure), was added a dehydrated acetonitrile solution
(40 ml) containing AgPF6 (2.0 mmol). The ensuing mixture was
stirred for 42 h in the dark at room temperature and the reaction
mixture was then filtered to remove precipitated solid (AgI3) and the
crude hexefluorophosphate (291 mg) was obtained by pouring the
filtrate into 50 ml of water and then treating in the same way as that
for the tppc and tObpc analogues. The solid was dissolved in 100 ml
of benzene and the solution filtered to remove insoluble solids; this
procedure was repeated (three times in this case) until nothing
remained on the filter. The filtrate was evaporated to reduce its
volume to 20 ml and then 120 ml of hexane was added to precipitate
the desired product, which was collected by filtration and dried at
80 ꢁC under vacuum (167 mg (0.13 mmol); yield 45% assuming that
the starting triiodide was analytically pure). Anal. Found: C, 59.53,
H, 4.16, N, 8.71%. Calcd for [Sb(tppc)(OH)2]PF6 (C64H50O6N8SbPF6):
C, 59.41; H, 3.90; N, 8.66%. IR/cmꢀ1; 847 (
n(P-F)) and 558 (d(F-P-F)).
2.1.9. Synthesis of dichloro[tetrakis{4-(20,60-dimethylphenoxy)}
phthalocyaninato]antimony(V) tetrachloroantimonate(III),
[Sb(tppc)Cl2]SbCl4
2.1.7. Synthesis of dihydroxo[tetrakis{4-(20,60-dimethylphenoxy)}
phthalocyaninato]antimony(V) triiodide, [Sb(tppc)(OH)2]I3
The dichloroantimony(V) derivatives was synthesized according
to previous work [15]. A mixture of 250 mg of crude [Sb(tppc)]I3
(0.17 mmol assuming this material is analytically pure) and a 4.0 ml of
sulfuryl chloride (Wako; 50 mmol) was allowed to react at room
temperature with vigorous stirring for 30 min. The reaction was
monitored by measuring absorption spectra of the reaction mixture
in CH2Cl2. After a sharp band at 757 nm (attributable to the desired
product) appeared and a less sharp band w771 nm (the starting
material) completely disappeared, the reaction was quenched
by precipitating the product by addition of hexane (45 ml) to the
mixture. The precipitate was separated from the solution by centri-
fugation and was twice washed with CH2Cl2/hexane (2:48 v/v) until
the washing turned essentially colorless, and then dried under
vacuum at 80 ꢁC. This solid was dissolved in CH2Cl2 (45 ml) and the
solution was filtered three times until nothing remained on the filter.
The solvent was evaporated to obtain the crude, dark brown product
(238 mg) which was again dissolved in benzene (45 ml) and the
solution was filtered three times until nothing remained on the filter.
The hydroxoantimony(V) derivatives was also synthesized
according to previous work [16]. 730 mg of the crude [Sb(tppc)]I3
(0.49 mmol assuming this material is analytically pure) was dis-
solved in tert-butyl perbenzoate (7.0 ml) and the solution was
heated at 50 ꢁC with vigorous stirring for 30 min. The reaction was
monitored by measuring optical absorption spectra of the solution
(in CH2Cl2 solution). After the most prominent band at 771 nm ([Sb
(tppc)]þ) disappeared and a new band grew at 737 nm, the mixture
was ice-cooled to quench the reaction. 93 ml of hexane was added
to the mixture to precipitate the product. The solid was collected
by centrifugation, washed with 50 ml of CH2Cl2/hexane (1:9 (v/v))
until the washing turned essentially colorless, and then dried
at 80 ꢁC under vacuum (691 mg). This was dissolved in benzene
(40 ml), filtered and, to the filtrate, was added 150 ml of hexane to
precipitate the desired compound (this procedure was repeated
twice). The solid was collected by centrifugation, washed with

190
H. Isago et al. / Dyes and Pigments 88 (2011) 187e194
To the filtrate was added 200 ml of hexane to precipitate the solid
which was collected by filtration, washed with hexane (20 ml), and
dried at 80 ꢁC under vacuum (134 mg; 0.093 mmol. Yield 54%
assuming the starting material was analytically pure). This has been
identified as the desired product by ESI-MS in acetonitrile (the
isotopic pattern was so complicated that readers should see the
Supporting material). Anal. Found: C, 52.92, H, 3.26, N, 7.70%. Calcd
for [Sb(tppc)Cl2]SbCl4 (C64H54O4N8Cl6Sb2): C, 53.04; H, 3.34; N, 7.73%.
Our attempts to prepare the corresponding hexafluorophosphate
in a similar way to that for [Sb(tppc)(OH)2]PF6 were unsuccessful.
Treatments with AgPF6 in acetonitrile just resulted in recovery of the
starting SbClꢀ4 salt.
2.1.10. Synthesis of [tetrakis{4-(20,60-dimethylphenoxy)}
phthalocyaninato]copper(II), [Cu(tppc)]
To a hexanol (3 ml) solution containing a mixture of 4-(20,60-
dimethylphenoxy)phthalonitrile (2.0 mmol) and 1,8-diazabicyclo
[5.4.0]undec-7-ene (DBU; 4.0 mmol), was added 1.3 mmol of CuCl.
The mixture was refluxed at 80 ꢁC with stirring for 64 h. After
the mixture was allowed to cool to room temperature, 50 ml of
ethanol was added to precipitate the product, which was collected
by centrifugation, washed twice with ethanol (50 ml) until the
washing turned essentially colorless, and dried at 80 ꢁC under
vacuum (452 mg). This was dissolved in chloroform and passed
through a silica gel (Merck Silicagel 60) column to remove dark
brown impurities which were strongly adsorbed on silica. This was
further chromatographed over a silica gel column (Merck Silicagel
60; chloroform) and then recrystallized from chloroform/hexane,
and dried at 80 ꢁC under vacuum to obtain a 300 mg (0.28 mmol;
yield 57% vs. phthalonitrile) of the desired compound. MS (MALDI;
2,3-dihydroxybenzoic acid as a matrix); m/z ¼ 1055 (Mþ) Anal.
Found: C, 72.24, H, 4.64, N, 10.40%. Calcd for [Cu(tppc)]
(C64H48O4N8): C, 72.75; H, 4.58; N, 10.60%.
Fig. 2. Spectral changes of [Sb(tppc)]I3 in CH2Cl2 before and after oxidation; before
oxidation (black solid line), after oxidation with perbenzoate (red), and after SO2Cl2-
oxidation (blue). (For interpretation of the references to color in this figure legend, the
reader is referred to the web version of this article).
0.65 T was applied to sample solutions during the measurements.
ESI-MS spectra were measured with a JEOL-JMS-T100LC mass
spectrometer both in the positive and negative modes. MALDI-TOF
mass spectra were recorded on a Bruker-Daltonics-Autoflex mass
spectrometer operating in the positive ion mode.
3. Results and discussion
3.1. Oxidation of antimony
Although both pentavalent and trivalent antimony gives rise to
a significant red-shift of Q-band [9e19], we decided to employ the
former derivatives because antimony ion in the latter is known to be
labile and hence antimony(III) complexes are readily demetallated to
form H2Pc1 [11,14]. The desired [Sb(Pc)X2]þ (X ¼ OHꢀ or Clꢀ)
complexes have been successfully synthesized through oxidative
addition process using organic peroxide (for X ¼ OHꢀ) and sulfuryl
chloride (X ¼ Clꢀ) as the oxidant. Fig. 2 shows typical spectral changes
between before and after the oxidation of [Sb(tppc)]þ with tert-butyl
perbenzoate and SO2Cl2. The broad absorption band at around
770 nm attributable to the starting [Sb(tppc)]þ disappeared and
a new sharp band around 737 nm (for X ¼ OHꢀ) and 755 nm (X ¼ Clꢀ)
grew in intensity. The spectra of the products are characteristic of
antimony(V) derivatives [9,10,12e19,21]. The oxidation with SO2Cl2 is
very rapid and completed within a few minutes even at room
temperature. On the other hand, the reaction with peroxide is rather
slow and it takes 30e40 min at 50 ꢁC to complete. Although heat
accelerates the oxidation, the desired product is considered unstable
in the presence of peroxide [14,16]. Actually when the mixture was
allowed to react at 80 ꢁC, the oxidation more rapidly proceeded, but
the reaction mixture turned colorless within 1 h. Therefore, we made
efforts to keep the reaction temperature around 50 ꢁC or below.
A trace amount of byproducts ([Sb(Pc)(OH)(benzoate)]þ; where
Pc ¼ pc and tbpc, benzoate ¼ C6H5COOꢀ) have been detected in
ESI-MS spectra of crude oxidation products although we obtained
analytically pure dihydroxo species at the final stage [14,16]. This is
the case also for the tppc and tObpc analogues. In particular, in the
case of tObpc derivative, we have obtained different products under
some experimental conditions. Under conditions described in the
2.1.11. Synthesis of tetrakis{4-(20,60-dimethylphenoxy)}
phthalocyanine, H2tppc
A hexanol (5 ml) solution containing a mixture of 4-(20,60-
dimethylphenoxy)phthalonitrile (4.0 mmol) and 1,8-diazabicyclo
[5.4.0]undec-7-ene (DBU; 7.6 mmol) was refluxed at 80 ꢁC with
stirring for 94 h. After the mixture was allowed to cool to room
temperature, 50 ml of ethanol was added to precipitate the product,
which was collected by centrifugation, washed twice with ethanol
(50 ml) until the washing turned essentially colorless, and dried at
80 ꢁC under vacuum (653 mg). This was dissolved into chloroform
and passed through a silica gel (Merck Silicagel 60) column to
remove dark brown impurities which strongly adsorb on silica. This
was further chromatographed over a silica gel column (Merck Sil-
icagel 60; benzene/chloroform (1:1)) and then recrystallized from
chloroform/hexane, and dried at 80 ꢁC under vacuum to obtain
a 260 mg (0.26 mmol; yield 52% vs. phthalonitrile) of the desired
compound. MS (MALDI; no matrix); m/z ¼ 994 (Mþ). Anal. Found:
C, 76.98, H, 5.34, N, 10.97%. Calcd for H2tppc (C64H50O4N8): C, 77.24;
H, 5.06; N, 11.26%.
All the other chemicals were of reagent grade and used without
further purification.
2.2. Measurements
All the measurements of optical absorption spectra were
performed with a Shimadzu UV-160A, a Shimadzu UV-1800, or
a
Hitachi U-3500 spectrophotometer at room temperature
(24 ꢂ 1 ꢁC). Magnetic circular dichroism (MCD) spectra were
recorded on a JASCO J-720 spectropolarimeter equipped with
a JASCO MCD-104 electromagnet, which is capable to generate
magnetic fields of up to 0.8 T. A constant field of a magnitude of
1
When we do not want to specify peripheral substituents on phthalocyanine, we
hereafter refer to the macrocyclic ligand as Pc.

H. Isago et al. / Dyes and Pigments 88 (2011) 187e194
191
experimental section, the oxidation almost exclusively gave [Sb
(tObpc)(OH)2]þ. However, when the starting [Sb(tObpc)]I3 was
not sufficiently purified (in particular, when the sublimation
procedure was skipped), the crude products included not only [Sb
(tObpc)(OH)2]þ but also [Sb(tObpc)(OH)(benzoate)]þ and [Sb(tObpc)
(benzoate)2]þ in comparable ratio (all the species have been detec-
ted by ESI-MS). Under some conditions, the product was exclusively
composed of [Sb(tObpc) (benzoate)2]þ. We could isolate neither
[Sb(tObpc)(OH)(benzoate)]þ nor [Sb(tObpc) (benzoate)2]þ because
of lack of reproducibility of the experiments, but the benzoato
species can be easily distinguished from the desired dihyroxo species
by absorption spectroscopy because the Q-band maximum wave-
lengths of the formers are longer than that of the latter (e.g.,
lmax ¼ 752 nm for [Sb(tObpc) (benzoate)2]þ in CH2Cl2 whereas
741 nm for [Sb(tObpc)(OH)2]þ). We did not make efforts to synthe-
size the di(benzoato) species for the aforementioned reason. It
seems that SbI3 can facilitate acylation of the axial hydroxyl groups.
hence the presence of a weak satellite band at a blue flank of the Q-
band (660e670 nm; assigned as vibronic structures of Q-band [4e6])
makes the Pcs blueish. Careful comparison between the tppc and
tObpc analogues finds that the Q-band of [Sb(tObpc)(OH)2]þ is much
broader (its full width of half maxima is 1027 cmꢀ1) than those of [Sb
(tppc)(OH)2]þ (752 cmꢀ1) and the corresponding pc (497 cmꢀ1) [14]
and tbpc (695 cmꢀ1) [15] analogues. This is probably due to aggre-
gation of [Sb(tObpc)(OH)2]þ. It is well known that aggregation of Pc
macrocycles gives rise to a significant spectral change due to exciton
coupling [4e6]. As the presence of the axial OH ligands in [Sb(tObpc)
(OH)2]þ molecule prevents aggregation in a face-to-face manner (i.e.,
H-aggregation), this species is likely to J-aggregate. This has been
evidenced by the red-shift of the Q-band [32] as shown in Fig. 5, in
which absorption spectra of [Sb(tObpc)(OH)2]PF6 in CH2Cl2 at
various concentrations are compared. The spectra are similar but the
apparent molecular extinction coefficient at around the Q-band
decrease whereas those at the red-flank of the Q-band increase with
an increase in concentration. We have reported that, unlike majority
of Pcs [11,25e31], absorbance at Q-band maxima of antimony(V)
derivatives obey LamberteBeer’s law in the concentration range
where absorption spectra can be monitored by using optical cells
with a path length of 1e10 mm [10,12,14,16]. This is probably because
of steric hindrance due to the presence of axial ligands as well as
electric repulsion due to their positive charge [12]. It is well known
that Pcs bearing long alkyl chains as peripheral substituents behave
as liquid crystals [33]. Likewise, the presence of the four n-butoxyl
groups (though not so long) may allow this species to aggregate more
easily than the tppc and tbpc analogues.
3.2. Colors of the complexes
Fig. 3 shows the optical absorption spectra of [Sb(tppc)(OH)2]þ,
[Sb(tppc)Cl2]þ, and [Sb(tObpc)(OH)2]þ in CH2Cl2 and those of [Cu
(tppc)] and H2tppc for comparison. The spectra of [Cu(tppc)] and
H2tppc are characteristic of normal metal- and metal-free Pcs,
respectively [4e6]. The two species intensely absorb red light
(Q-band) while they are essentially transparent in the window region
as mentioned in the introduction and hence they show a blue color
(Fig. 4). It should be noted that the position of the Q-band does not
change very much depending on the nature of the central metal apart
from some exceptions [4e6]. On the other hand, although the spectra
of antimony(V) derivatives are similar to thatof copperderivative and
hence are characteristic of monomeric metalePc complexes, their
Q-band significantly red-shifts by ca. 1000e1200 cmꢀ1 as is the case
for antimony(V) derivatives [9,10,12e19,21]. In addition to that, an
extra broad band appeared in 400e550 nm region, where normal Pcs
(e.g., [Cu(tppc)] and H2tppc) are essentially transparent. Hence
coloration due to the extra band is outstanding, making the antimony
(V) derivatives to show a non-blue color. The [Sb(tppc)(OH)2]þ and
[Sb(tObpc)(OH)2]þ look more bluish than [Sb(tppc)Cl2]þ because the
Q-band of dihydroxo species is located at a slightly shorter wave-
length than that of the corresponding dichloro species [14e16] and
3.3. Absorption spectra in the Soret and extra band region
Since optical absorption by PFꢀ6 and SbClꢀ4 is negligible in this
region [19,34], we may assume that all the absorption bands observed
are ascribable to the antimony-Pcs. The spectra of [Sb(tObpc)(OH)2]þ,
[Sb(tppc)(OH)2]þ, and [Sb(tppc)Cl2]þ in 250e550 nm region are
similar to each other. All the three species show a broad band at
around 400e550 nm and three bands at around 350, 310, and 270 nm
although the latter one is observed as a shoulder for the tppc deriv-
atives. Each absorption band of [Sb(tppc)Cl2]þ slightly red-shifts as
compared to the corresponding band of [Sb(tppc)(OH)2]þ as is the case
for tbpc analogues [10,15,16]. Absorbance of the two tppc derivatives
in 250e300 nm is higher than that of the tObpc analogue probably
because of the presence of peripheral phenoxyl groups. Gouterman
and his coworkers have expected on their calculation study that some
degenerate pep
* transitions should appear for phthalocyanines in UV
region (B, N, L, and C bands going from lower to higher energy) [4,35].
A few decades later, Stillman and his coworkers have shown that the
lowest energy absorption band in the UV region should be a mixture
of two
pep
* transitions and hence they have argued that this
band should be called as B1 and B2 bands [4,36,37]. We have reported
absorption spectra of [Sb(pc)(OH)2]PF6 and assigned that the
absorption bands observed in near-UV region as such [14]. It should be
noteworthy that these bands, except the B1/B2 bands, are hardly
observed for majority of phthalocyanines in solution because common
organic solvents normally absorb UV light and hence the other bands
are hidden in the solvent absorption. Actually, available spectral data
were limited to those observed in vapor phase, thin film, or Ar matrix
[35e39]. The significant red-shifts of the
pep
* transitions for
antimony(V) derivatives (e.g., red-shifted by ca. 1000e1200 cmꢀ1 for
Q-band as compared to copper analogue) may have allowed us to
observe these transitions in solution phase [16].
Fig. 3. Optical absorption spectra of [Sb(tppc)(OH)2]PF6 (red solid line), [Sb(tppc)Cl2]
SbCl4 (green solid), [Sb(tObpc)(OH)2]PF6 (black solid), [Cu(tppc)] (brown broken), and
H2tppc (blue dot-dash) in CH2Cl2. All the spectra were measured in the concentration
range (below 5 ꢄ 10ꢀ6 M) where absorbance obeyed LamberteBeer’s law and hence
effects of aggregation are negligible. (For interpretation of the references to color in
this figure legend, the reader is referred to the web version of this article).
It is known that some Pcs show one or more extra bands in the
“window” region. For example, one-electron-oxidized Pcs (e.g.
ꢃ
radical cation, pcꢀ ) show a characteristic band around 500 nm,
which makes the Pcs red or orange [40]. However, as

192
H. Isago et al. / Dyes and Pigments 88 (2011) 187e194
Fig. 4. The colors of CH2Cl2 solutions containing H2tppc, [Cu(tppc)], [Sb(tppc)Cl2]SbCl4, [Sb(tppc)(OH)2]PF6, and [Sb(tObpc)(OH)2]PF6,(on going from the leftmost to the rightmost).
(For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article).
electrochemical studies on antimony(V)-Pcs have found that they
are easy to reduce (E1/2(pc2ꢀ/pc3ꢀ) ¼ ca. ꢀ0.2 V vs. ferricinium/
ferrocene) while hard to oxidize (E1/2(pcꢀ/pc2ꢀ) ¼ ca. 1.3 V)
[9,13,15,18,19], it is unlikely that antimony(V) derivatives are
oxidized under such conditions. Some Pcs containing a transition
metal (e.g. manganese(II) [41,42], iron(II) [43], cobalt(I) [25,43e45],
etc) in their cavity are also known to show an extra band around
500 nm [4e6], which has been assigned as a charge transfer (MLCT
or LMCT) band. But this possibility may also be excluded because
antimony(V) belongs to the main group and has a closed shell.
Kobayashi and his coworkers have attributed the appearance of
extra bands for mainegroup complexes of octaphenyl-substituted
derivatives to an enhanced metal-ligand (Pc) interaction due
to a significant deformation of the Pc ligand from planarity [7].
However, such an interaction cannot be expected in this case
because tObpc and tppc ligands are both planar. The possibility that
3.4. MCD (magnetic circular dichroism) study
In order to investigate the origin of the extra band, MCD spectra
of [Sb(tObpc)(OH)2]PF6 and [Sb(tppc)(OH)2]PF6 in CH2Cl2 solution
have been studied as well as the corresponding tetra-tert-butyl and
unsubstituted analogues for comparison (Fig. 6). Both the optical
absorption and MCD spectra for tObpc and tppc complexes are
essentially the same, apart from the broadening of the Q-band for
[Sb(tObpc)(OH)2]þ and slightly higher absorbance for [Sb(tppc)
(OH)2]þ in the 250e300 nm regions as described above. The MCD
spectra of the two species around the Q-band show a distinct
s-shaped curve centered at the absorption maximum wavelength
and hence this signal is dominated a Faraday’s A-term indicating
that this transition is orbitally degenerate [4]. This is also the case for
tbpc and pc analogues. This band is assigned as an electronic tran-
sition from non-degenerate HOMO to doubly degenerate LUMO
[4,36,37]. At the blue flank of the Q-band, are observed two less
intense Gaussian signals of a positive and negative sign with their
peak and valley wavelengths centered at the absorption maximum
wavelengths. These signals are dominated by a Faraday’s B-term
indicating that these transitions are orbitally non-degenerate. These
bands are assigned as vibronic progressions of the Q-band [4]. If the
extra absorption around 500 nm is composed of a single band, the
corresponding MCD spectra should be dominated by either a Fara-
day’s A-term or a B-term. Nevertheless, the spectra around the
400e550 nm are quite complicated, suggesting that this absorption
should be an overlapping of more than one band. It is easily found
that both the absorption and MCD spectra in 250e370 nm region
are close to each other for the four [Sb(Pc)(OH)2]þ complexes; three
weak absorption bands around 350, 310, and 270 nm and three
s-shaped curves centered at the absorption maximum wavelengths.
We have studied optical absorption and MCD spectra of [Sb(pc)
(OH)2]þ and assigned the three bands as degenerate N, L, and C
bands after Gouterman’s nomenclature, going from lower to higher
energy [14]. Therefore, we may likewise assign those bands for the
other three complexes. The absorption band around 400 nm for tbpc
derivative may be assigned as B1/B2 bands based on the analogy
with the unsubstituted derivative. Careful comparison among the
four complexes has found that a broad band around 370e450 nm
region (tentatively assigned as B1/B2 bands above) observed for
the origin of the extra bands can be a nep
* transition (involving
lone pairs in the peripheral substituents) in character will be found
unlikely in the following discussion.
Fig. 5. Optical absorption spectra (around the Q-band) of [Sb(tObpc)(OH)2]PF6 in
CH2Cl2 at various concentrations; 2.28 ꢄ 10ꢀ4 M (black), 1.14 ꢄ 10ꢀ4 M (red), and
1.43 ꢄ 10ꢀ5 M (blue). (For interpretation of the references to color in this figure legend,
the reader is referred to the web version of this article).

H. Isago et al. / Dyes and Pigments 88 (2011) 187e194
193
Fig. 6. Optical absorption (top) and MCD (bottom) spectra of [Sb(tppc)(OH)2]PF6
(green) [Sb(tObpc)(OH)2]PF6 (blue), [Sb(tbpc)(OH)2]PF6 (red), and [Sb(pc)(OH)2]PF6
(black), in CH2Cl2. (For interpretation of the references to color in this figure legend,
the reader is referred to the web version of this article).
Fig. 7. Plots of the peak positions of the extra bands (top) and Q-bands (bottom) of [Sb
(tppc)(OH)2]PF6 (red circles) [Sb(tObpc)(OH)2]PF6 (black), [Sb(tppc)Cl2]SbCl4 (blue) in
various solvents against the refractive indices of the solvents in the form of Onsagar’s
solvent optical polarity function. The numbers (1e14) in the figure denote as follows: 1;
methanol, 2; acetonitrile, 3; acetone, 4; ethanol, 5; ethyl acetate, 6; nitromethane, 7; THF,
8; CH2Cl2, 9; CHCl3,10; C6H6,11; chlorobenzene,12; o-dichlorobenzene,13; nitorbenzene,
14; o-dibromobenzene. (For interpretation of the references to color in this figure legend,
the reader is referred to the web version of this article).
unsubstituted and tert-butyl-substituted derivatives is missing in
the spectra of the tObpc and tppc analogues. Interestingly, MCD
spectra around the extra bands of the tppc and tObpc derivatives are
similar to those around the B1/B2 bands of the other two. Therefore,
both the absorption and MCD spectra of the four species are
essentially the same if we assume that the extra bands for tppc and
tObpc derivatives and the broad bands around 400 nm for [Sb(pc)
(OH)2]þ and [Sb(tbpc)(OH)2]þ have the same origin and that these
bands red-shifted in the same order as that for the Q-band (i.e.,
pc < tbpc < tppc < tObpc). If this is true, it is quite unlikely that the
refractive indices in the form of Onsagar’s solvent polarity function.
Both the complexes show the same tendency in that their Q-band
appears at a longer wavelength in a solvent with a larger refractive
index. We have reported fairly good linear correlations between
Q-band positions of some metalephthalocyanine complexes in
solution and refractive indices of the solvents unless the solvent
induces a chemical reaction involving the phthalocyanines or gives
rise to a specific chemical interaction with the chromophore [12].
This phenomenon can be rationalized in terms of stabilization
of the Franck-Condon excited state of the chromophore by an
interaction between the transition dipole moment in the chromo-
phore and induced dipole moment generated temporarily in the
surrounding solvent molecules [48]. That is, the Q-band position in
a specific solvent is determined by the optical polarizability of the
solvent alone unless chemical interaction is involved [12]. The plots
for [Sb(tppc)(OH)2]þ are considerably deviated from linearity
unlike the case for [Sb(tppc)Cl2]þ. This indicates the presence of
some chemical interaction between the chromophore and the
surrounding solvent molecules through the axial OH groups (e.g.,
hydrogen bonding) [14,16]. The extra bands (Fig. 7 top) similarly
behave in that they appear at a longer wavelength in a solvent with
a large refractive index. This suggests that the extra band should be
extra bands are nep
* transitions in character, because pc and tbpc
do not have a lone pair in their peripheral substituents. Thus, it
seems reasonable to assign the extra bands as their B1/B2 bands
for [Sb(tppc)(OH)2]þ and [Sb(tObpc)(OH)2]þ, as is the case for the pc
and tbpc analogues.
It seems that the intensity of Q-band tends to decrease
(pc > tbpc > tppc > tObpc) as the band red-shifts and at the same
time that of the corresponding Faraday’s A-term lowers in this order.
Similar tendency has been reported elsewhere [46,47] but a clear-cut
explanation to these phenomena has not been given until today.
3.5. Solvent effects
As [Sb(tObpc)(OH)2]þ, [Sb(tppc)(OH)2]þ, and [Sb(tppc)Cl2]þ are
all soluble in many of common organic solvents, solvent-depen-
dence of their absorption spectra have been studied. Both [Sb(tppc)
(OH)2]þ and [Sb(tppc)Cl2]þ show small but non-negligible shifts in
peak positions of their Q-band and the extra band although the
spectra in solutions are essentially the same as that in CH2Cl2
(Fig. 3). In Fig. 7, is shown the solvent-dependence of the extra (top)
and Q-bands (bottom) of the two complexes as a function of
of the same character as that of Q-band (i.e., mainly a
pep
* tran-
sition) and hence support the assignment of this band as the Soret
(B1/B2) band. The poor linear relationship of the extra band than

194
H. Isago et al. / Dyes and Pigments 88 (2011) 187e194
that of Q-band is understandable if the assignment is correct,
because it is known that scattering of plots for Soret band is more
significant than those for Q-band in solvatochromism of metal-free
porphyrins [49]. This is because the Q-band of Pcs is an essentially
pure monoelectonic transition while the Soret band is a mixture of
a few transitions with comparable ratios [4]. In addition to that, we
have reported that the solvent-dependence of B1/B2 bands is much
more significant than that of Q-band for [Sb(pc)(OH)2]þ [14].
The solvatochromic behavior of the n-butoxyl-substituted
derivative is more rigorous than those of the tppc analogues
because of the presence of more or less aggregation effects (as
mentioned above). It is well known that susceptibility to aggrega-
tion depends on the nature of the solvent system [50,51]. The much
more scattered plots for tObpc derivative than the tppc analogues
may be rationalized as follows. Aggregation of Pc macrocycles
generally gives rise to a significant spectral change, like blue-/red-
shift, broadening, or splitting of the absorption band, as mentioned
above. In particular, as the extra band is considerably broadened
unlike the well-isolated Q-band, presence of any small portion of
aggregated species can shift the absorption maximum wavelength.
Eventually, Fig. 7 shows considerably scattered plots for tObpc
derivative with respect to the extra band.
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Supplementary data associated with this article can be found in
the online version, at doi:10.1016/j.dyepig.2010.06.007.