Adsorption equilibria of novel phthalocyaninatomagnesium(II) derivatives with thioethers at the toluene/water interface

Article abstract of DOI:10.1246/bcsj.77.2011

Three novel phthalocyaninatomagnesium(II) derivatives with eight peripheral thioethers (MgPc(SR)₈) such as (2,3,9,10,16,17,23,24-octakis- ethylthiophthalocyaninato)magnesium(II) (MgPc(SEt)₈), (2,3,9,10,16,17,23,24-octakisbenzylthioph

Full text of DOI:10.1246/bcsj.77.2011

ꢀ 2004 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 77, 2011–2020 (2004) 2011
Adsorption Equilibria of Novel Phthalocyaninatomagnesium(II)
Derivatives with Thioethers at the Toluene/Water Interface
ꢀ
Kenta Adachi and Hitoshi Watarai
Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043
Received April 19, 2004; E-mail: watarai@chem.sci.osaka-u.ac.jp
Three novel phthalocyaninatomagnesium(II) derivatives with eight peripheral thioethers (MgPc(SR)8) such as
(2,3,9,10,16,17,23,24-octakis-ethylthiophthalocyaninato)magnesium(II) (MgPc(SEt)8), (2,3,9,10,16,17,23,24-octakis-
benzylthiophthalocyaninato)magnesium(II) (MgPc(SBz)8), and (2,3,9,10,16,17,23,24-octakis-benzhydrylthiophthalo-
cyaninato)magnesium(II) (MgPc(SBh)8) were synthesized. The interfacial adsorption and aggregation behavior of the
three derivatives in a toluene/water system were examined by means of a high-speed stirring (HSS) method and a cen-
trifugal liquid membrane (CLM) method. The interfacial adsorption constant of each MgPc(SR)8 derivative at the tol-
uene/water interface was determined by the HSS measurement. Only in the case of MgPc(SEt)8, the formation of the
trimer was observed at the interface. Moreover, the CLM measurements showed that the interfacial aggregate of
MgPc(SEt)8 had a new broad band (613 nm) at the blue flank of the Q band (702 nm) of MgPc(SEt)8 monomer, which
might be ascribed to H-aggregate. Extended double-dipole (EDD) model calculations suggested a cofacially stacked ar-
rangement of MgPc(SEt)8 molecules in the trimer. The interfacial spectral change indicated that the aggregation of
MgPc(SEt)8 at the toluene/water interface proceeded in a two-step, three-stage (monomer ! dimer ! trimer) forma-
tion.
In the last quarter century, the chemistry and engineering of
phthalocyanine compounds (Pc) with functional substituents
have advanced remarkably, particularly in the application of
these compounds in the development of fuel cells, chemical
sensors, solar cells, electrophotography, and photodynamic
therapy (PDT) of cancer.1–4 For the application of Pc com-
pounds, it is quite important to improve their solubility in com-
mon solvents. Peripheral substitution with bulky groups5 or
long alkyl chains6 made Pc compounds more soluble in com-
mon organic solvents. The introduction of sulfonyl,7 carboxyl,8
or amino9 groups gave water-soluble products. Although the
structures and functions of Pcs and their metallocomplexes
have been extensively studied, only a few reports have been
known on Pc derivatives with eight thioether substituents in
the peripheral benzene rings (MPc(SR)8).10,11 These com-
pounds (MPc(SR)8) have unique spectroscopic and photo-
chemical properties. For example, they absorb longer wave-
length light in comparison with other Pc derivatives without
thioether substituents. This is a very useful feature for applica-
tions in PDT and near-IR absorbers.
Chemical reactions at interfaces between two immiscible
liquids have become an important subject in various fields. Re-
cently, the liquid/liquid interface has been recognized as an ef-
fective nano-reaction field in solvent extraction,12 and as a
model for biomembranes.13 Therefore, it is very important to
investigate the interfacial reactivity of Pc derivatives in evalu-
ating their potential in semiconductivity, photocatalytic effi-
ciency, and their biological significance like a porphyrin in
modern interfacial nano-technology. However, studies on the
reactivity of Pc at the liquid/liquid interface have rarely been
performed. The poor solubility of Pc in common organic sol-
vents might be one of the reasons.
In the present work, we synthesized three novel phthalocia-
ninatomagnesium(II) derivatives substituted with eight thio-
ether groups at the peripheral benzene sites (MgPc(SR)8).
These derivatives showed improved solubility in common or-
ganic solvents, and the interfacial adsorption behavior of these
compounds in a toluene/water system using a high-speed stir-
ring (HSS) method14 and a centrifugal liquid membrane
(CLM) technique.15 We report here the first example of inter-
facial adsorption phenomena of Pcs at the liquid/liquid inter-
face.
1. Experimental
1.1 Material. 1-Butanol, tetrahydrofuran, chloroform, and tol-
uene were purchased from Nacalai Tesque Inc. (Kyoto, Japan). 1-
Butanol and tetrahydrofuran were freshly distilled after drying
over molecular sieves before use. Chloroform was shaken three
times with 2 M (mol dmꢁ3) potassium hydroxide solution, fol-
lowed by shaking three times with water, dried over calcium chlo-
ride, and then fractionally distilled. Toluene was purified accord-
ing to a literature method,16 and then saturated with distilled water
immediately before use. Water was distilled and deionized by a
Milli-Q system (Millipore). All other chemicals were of reagent
grade from Tokyo Kasei Kogyo Co., Ltd (Tokyo, Japan) or Wako
Chemicals (Osaka, Japan), and were used as received without fur-
ther purification.
1.2 Synthesis of Thioether-Derivatised Phthalocyaninato-
magnesium(II) [MgPc(SR)8]. Diphenylmethanethiol [BhSH]:
Diphenylmethanol (30.0 g, 0.325 mol), conc. hydrochloric acid
(250 mL), and thiourea (30.0 g, 0.394 mol) were mixed and re-
fluxed for 18 h under a nitrogen atmosphere. After cooling down
to room temperature, 6 M sodium hydroxide solution was added
dropwise into the mixture, followed by refluxing for 3 h. After
the mixture was acidified with conc. hydrochloric acid, the re-
Published on the web November 11, 2004; DOI 10.1246/bcsj.77.2011

2012 Bull. Chem. Soc. Jpn., 77, No. 11 (2004)
Interfacial Adsorption of MgPc Derivatives
duced oily compound was extracted into diethyl ether, and then
dried over anhydrous sodium sulfate. After removal of the solvent,
the residue was distilled under reduced pressure (20 Torr, 130 ꢂC)
to yield BhSH as a colorless oil. Yield of the compound: 25.0 g
(76.9% on the basis of diphenylmethanol); bp 237–239 ꢂC;
1H NMR (300 MHz, CDCl3) ꢀ 2.34 (d, 1H, –SH), 5.50 (d, 1H,
(Ph)2–CH–SH), 7.29–7.50 (m, 10H, –(Ph)2); 13C NMR (75
MHz, CDCl3) ꢀ 48.1, 127.5, 128.1, 128.9, 143.7.
mixture was refluxed for 6 h under a nitrogen atmosphere. The
solvent was removed under reduced pressure, and the resulting
dark green solid was dissolved in chloroform (25 mL). The result-
ing solution was washed with 25 mL of water four times, dried
over absolute magnesium sulfate, and evaporated in vacuum.
The reduced was treated in a Soxhlet apparatus with acetone until
the solvent turned colorless, and then dried in vacuum. The crude
product was further subjected to silica column chromatography
eluted with a chloroform–methanol (9:1 v/v) mixed solvent, and
pure MgPc(SEt)8 was yielded as a dark green solid. This com-
pound was soluble in chloroform, dichloromethane, toluene,
DMSO, and DMF. Yield of compound: 0.353 g (49.6% on the
basis of Pn(SEt)2); mp > 250 ꢂC; TLC Rf ¼ 0:91 (chloroform:
methanol = 9:1); 1H NMR (300 MHz, DMSO-d6) ꢀ 1.70 (t,
24H, S–C–CH3), 3.51 (d, 16H, S–CH2–C), 8.74 (s, 8H, Ar); FT-
IR (KBr, cmꢁ1) 2968, 2925, 2868, 1592, 1476, 1446, 1403,
1369, 1331, 1262 (C–S–C), 1181, 1066, 943, 777, 747;
MALDI-TOF/MS m=z 1018 (M þ Hþ) [matrix: ꢁ-cyano-4-hy-
droxycinnamic acid (ꢁ-CHCA)]; Anal. Calcd for C48H48MgN8S8:
C, 56.64; H, 4.75; N, 11.01%. Found: C, 56.81; H, 4.74; N,
10.57%.
4,5-Bis(ethylthio)phthalonitrile [Pn(SEt)2]:
Ethanethiol
(1.86 g, 30 mmol) and 4,5-dichlorophthalonitrile (1.97 g, 10
mmol) were dissolved in absolute tetrahydrofuran 70 mL under
a nitrogen atmosphere. After stirring for 30 min, finely ground an-
hydrous potassium carbonate (10 g, 0.43 mol) was added portion-
wise over 90 min with efficient stirring. The reaction mixture was
ꢂ
stirred under a nitrogen atmosphere at around 50 C for 12 h. Ice
water (100 mL) was then added to separate any inorganic residues,
and the aqueous phase was extracted with chloroform (3 times
with 25 mL chloroform). The combined extracts were dried over
anhydrous sodium sulfate. After the removal of the solvent, the
residue was crystallized from methanol to yield Pn(SEt)2 as a pale
white solid. Yield of compound: 1.95 ꢂg (78.4% on the basis of 4,5-
dichlorophthalonitrile); mp 109–111 C; TLC Rf ¼ 0:60 (chloro-
form); 1H NMR (300 MHz, CDCl3) ꢀ 1.37 (t, 6H, S–C–CH3),
2.97–3.00 (m, 4H, S–CH2–C), 7.36 (s, 2H, S–Ar–CN); 13C NMR
(75 MHz, CDCl3) ꢀ 13.4, 27.0, 111.4, 115.8, 128.4, 144.2; FT-IR
(KBr, cmꢁ1) 2974, 2932, 2227 (CꢃN), 1562, 1461, 1431, 1377,
1345, 1229 (C–S–C), 1117, 1050, 961, 928, 895, 528; Anal. Calcd
for C12H12N2S2: C, 58.03; H, 4.87; N, 11.28%. Found: C, 57.97;
H, 4.77; N, 11.52%.
(2,3,9,10,16,17,23,24-Octakis-benzylthiophthalocyaninato)-
magnesium(II) [MgPc(SBz)8]: In a similar manner to that of
MgPc(SEt)8, the cyclotetramerization reaction of Pn(SBz)2 (1.00
g, 2.68 mmol) yielded MgPc(SBz)8 as a dark green solid. This
product was soluble in chloroform, dichloromethane, toluene,
DMSO, and DMF. Yield of compound: 0.586 g (57.8% on the
basis of Pn(SBz)2); mp > 250 ꢂC; TLC Rf ¼ 0:88 (chloroform:
methanol = 9:1); 1H NMR (300 MHz, DMSO-d6) ꢀ 4.78 (s,
16H, S–CH2–Ph), 7.29 (t, 8H, –Ph ), 7.39 (t, 16H, –Ph ),
4,5-Bis(benzylthio)phthalonitrile [Pn(SBz)2]: Using a simi-
lar procedure to that of Pn(SEt)2, the reaction of benzylthiol (3.72
g, 30mmol) with4,5-dichlorophthalonitrile (1.97g, 10 mmol) gave
Pn(SBz)2 as a pale white solid. Yield of compound: 3.01 g (80.9%
ð1Þ
ð2Þ
7.70 (d, 16H, –Ph ); FT-IR (KBr, cmꢁ1) 2922, 2851, 1590,
ð3Þ
1494, 1451, 1402, 1368, 1283 (C–S–C), 1110, 1066, 943, 774,
747, 699; MALDI-TOF/MS m=z 1513 (M þ Hþ) [matrix: ꢁ-cya-
no-4-hydroxycinnamic acid (ꢁ-CHCA)]; Anal. Calcd for
C88H64MgN8S8: C, 68.80; H, 4.26; N, 7.40%. Found: C, 68.97;
H, 4.22; N, 7.26%.
ꢂ
on the basis of 4,5-dichlorophthalonitrile); mp 173–174 C; TLC
Rf ¼ 0:77 (chloroform); 1H NMR (300 MHz, CDCl3) ꢀ 4.22 (s,
2H, Ph–CH2–S), 7.28–7.36 (m, 10H, –Ph), 7.42 (s, 2H, S–Ar–
CN); 13C NMR (75 MHz, CDCl3) ꢀ 36.9, 111.8, 114.6, 128.6,
129.0, 129.4, 133.5, 136.4; FT-IR (KBr, cmꢁ1) 2919, 2851,
2227 (CꢃN), 1564, 1494, 1461, 1346, 1237 (C–S–C), 1115,
1070, 1029, 962, 889, 873, 711, 694, 529; Anal. Calcd for
C22H16N2S2: C, 70.93; H, 4.33; N, 7.52%. Found: C, 70.60; H,
4.23; N, 7.58%.
(2,3,9,10,16,17,23,24-Octakis-benzhydrylthiophthalocyani-
nato)magnesium(II) [MgPc(SBh)8]: The cyclotetramerization
reaction of Pn(SBh)2 (1.00 g, 1.91 mmol) gave MgPc(SBh)8 as
a light green solid. The product was soluble in chloroform, di-
chloromethane, toluene, DMSO, DMF, and acetone. Yield of
compound: 0.535 g (52.8% on the basis of Pn(SBh)2); mp >
250 ꢂC; TLC Rf ¼ 0:79 (chloroform:methanol = 9:1); 1H NMR
(300 MHz, DMSO-d6) ꢀ 4.78 (s, 16H, S–CH2–Ph), 7.29 (t, 8H,
–Ph ), 7.39 (t, 16H, –Ph ), 7.70 (d, 16H, –Ph ); FT-IR (KBr,
4,5-Bis(benzhydrylthio)phthalonitrile [Pn(SBh)2]: Similar
to Pn(SEt)2, the reaction of diphenylmethanethiol (3.00 g, 15
mmol) with 4,5-dichlorophthalonitrile (0.98 g, 5 mmol) afforded
Pn(SBh)2 as a pale white solid. Yield of compound: 2.23 g
(85.1% on the basis of 4,5-dichlorophthalonitrile); mp 143–145
ꢂC; TLC Rf ¼ 0:79 (chloroform); 1H NMR (300 MHz, CDCl3)
ꢀ 5.72 (s, 2H, (Ph)2–CH–S), 7.23–7.37 (m, 20H, –Ph), 7.43 (s,
2H, S–Ar–CN); 13C NMR (75 MHz, CDCl3) ꢀ 56.4, 112.0,
115.3, 128.5, 128.7, 131.3, 138.7, 138.7, 143.8; FT-IR (KBr,
cmꢁ1) 2970, 2922, 2231 (CꢃN), 1566, 1493, 1450, 1341, 1226
(C–S–C), 1110, 1077, 1030, 928, 898, 872, 746, 699, 623; Anal.
Calcd for C34H24N2S2: C, 77.83; H, 4.61; N, 5.34%. Found: C,
77.73; H, 4.58; N, 5.00%.
(2,3,9,10,16,17,23,24-Octakis-ethylthiophthalocyaninato)-
magnesium(II) [MgPc(SEt)8]: In following the procedure of a
classic Linstead macrocyclization.17 Metal magnesium (0.67 g,
12.8 mmol) was dissolved in refluxing 1-butanol (10 mL) during
12 h with the aid of an iodine crystal (ca. 0.1 g) as initiator. To the
resulting magnesium butoxide suspension was added Pn(SEt)2
(0.7 g, 2.8 mmol) as a slurry in 5 mL of 1-butanol. The combined
ð1Þ
ð2Þ
ð3Þ
cmꢁ1) 3024, 2923, 1593, 1486, 1447, 1400, 1368, 1330, 1277
(C–S–C), 1180, 1107, 1066, 942, 775, 747, 699; MALDI-TOF/
MS m=z 2123 (M þ Hþ) [matrix: ꢁ-cyano-4-hydroxycinnamic
acid (ꢁ-CHCA)]; Anal. Calcd for C136H96MgN8S8: C, 76.94; H,
4.56; N, 5.28%. Found: C, 77.35; H, 4.51; N, 5.26%.
UV–vis data of MgPc(SEt)8, MgPc(SBz)8, MgPc(SBh)8, and
unsubstituted MgPc18 are summarized in Table 1.
1.3 High-Speed Stirring Measurement. The interfacial ad-
sorption of MgPc(SR)8 derivatives in the toluene/water system
was measured by using a high-speed stirring (HSS) method. The
principle of HSS method was described elsewhere,14,19 and an
analogous procedure was employed.20–22 Fifty milliliters of the
toluene phase containing MgPc(SR)8 derivatives and the same
volume of the aqueous phase containing 0.033 M sodium sulfate
and acetate buffer (pH 6) were put into a glass stir-cell, which
was thermostated by a water-jacket at 25 ꢄ 0:1 ꢂC. The absorption
spectra of the toluene phase were measured at the stirring rate of

K. Adachi et al.
Bull. Chem. Soc. Jpn., 77, No. 11 (2004) 2013
Table 1. UV–Vis Data of Phthalocyaninatomagnesium(II)
Derivatives
with an integration time of 0.5 s. The thickness of each toluene
phase and the aqueous phase was 77 mm and 128 mm, respectively.
The interfacial area (Si) between the two liquid membrane phases
was calculated to be 19.4 cm2.
Compound
MgPcaÞ
ꢃ
max/nm (log "/L molꢁ1 cmꢁ1
674 (4.94) 644 (sh) 607 (4.12) 347 (4.36)
)
1.5 Other Apparatus. Chromatographic separations were
performed by a column with silica gel (Wako Gel C-200). pH
Measurements were conducted using a HORIBA F-14 pH meter
equipped with a HORIBA 6366-10D glass electrode. 1H and
13C NMR spectra were recorded on a Varian Unity 300 spectrom-
eter. Chemical shifts of 1H NMR spectra were relative to an inter-
nal standard of TMS. Infrared spectra (KBr disk) were measured
using a Nicolet MAGNA-IR 560 FT-IR spectrometer. MALDI-
TOF mass spectra were obtained on a PerSeptive Biosystems
Voyager DE-Pro spectrometer with ꢁ-cyano-4-hydroxycinnamic
acid (ꢁ-CHCA) as a matrix. Elemental analysis was done using
a Perkin-Elmer series II CHNS/O analyzer 2400. UV–visible
spectra were measured using a JASCO V-570 spectrometer. All
melting points were taken in capillary tubes without temperature
correction.
MgPc(SEt)8 702 (5.04) 670 (sh) 632 (4.33) 368 (4.61)
MgPc(SBz)8 708 (5.11) 676 (sh) 638 (4.40) 373 (4.73)
MgPc(SBh)8 714 (5.39) 682 (sh) 640 (4.63) 378 (4.99)
a) In pyridine (Ref. 18), sh ¼ shoulder.
5000 rpm and 200 rpm. The stirring rate was monitored by a speed
controller (Nikko Keisoku Co. Ltd., SC-5). The toluene phase was
continuously separated from the stirred two-phase system by
means of a PTFE phase separator, and circulated through a flow
cell installed in a photodiode-array detector (Shimadzu, SPD-M
6A) at the flow rate of 20 mL minꢁ1 by a pump (Flumax Junior,
Fluid Metering Inc.). Hence, we could determine the interfacial
concentration of MgPc(SR)8 derivatives by evaluating the differ-
ence between the absorbances of the toluene phase under high-
speed stirring (5000 rpm) and low-speed stirring (200 rpm) at
the absorption maximum wavelength.
2. Results and Discussion
The adsorption isotherms were measured from the HSS method
using various concentrations of MgPc(SR)8 derivatives. In the
present system, Langmuir isotherm is given by23
2.1 Synthesis of MgPc(SR)8 Derivatives. Three magnesi-
um complexes of the eight thioether substituted phthalocya-
nines were synthesized starting from 4,5-dichlorophthaloni-
trile, as shown in Scheme 1. The first step of the synthesis
was to prepare a phthalonitrile with two thioethers (Pn(SR)8).
By nucleophilic displacement, 4,5-dichlorophthalonitrile was
converted to Pn(SR)8 compound with an excess of thiol in
the presence of an excess amount of anhydrous potassium car-
bonate in tetrahydrofuran. The yield was quite high (around
80%). This synthetic procedure was previously described by
aK0[MgPc(SR)8]o
a þ K0[MgPc(SR)8]o
[MgPc(SR)8]i ¼
;
ð1Þ
where [MgPc(SR)8]i and [MgPc(SR)8]o denote the concentration
of MgPc(SR)8 adsorbed at the toluene/water interface (mol/
dm2) and in the bulk toluene phase (mol/dm3), respectively. a
is the saturated interfacial concentration (mol/dm2) and K0 is
the interfacial adsorption constant (dm) defined at an infinitely
diluted concentration of MgPc(SR)8,
Wohrle et al.26 and was recently improved by Ozoemena et
¨
al.11 From Pn(SR)8 compound, we could readily synthesize
the corresponding MgPc(SR)8 derivatives according to a cross
cyclotetramerization reaction of Pn(SR)2 under the classical
Linstead conditions (magnesium butoxide/n-butanol).17 A pro-
longed reaction time of up to 6 h resulted in a low yield for
MgPc(SR)8 derivatives (<20%), probably due to the decom-
position of the derivatives formed. Decomposition of the pe-
ripheral thioether substituents could have occurred somewhat
during the cyclotetramerization, but all results from the
NMR spectra, the elemental analysis and MALDI-TOF mass
spectra were in good agreement with the expected ones.
Hence, we concluded that the obtained compounds were the
expected ones, and had a single geometric isomer. All deriva-
tives synthesized exhibited good solubility in common sol-
vents (such as CHCl3, DMF, DMSO, and toluene), especially
in the benzhydrylthio (SBh) substituent. MgPc(SR)8 deriva-
tives were stable in these solvents, and also were stable in
water or acid. No demetallation was observed by contact with
water or conc. hydrochloric acid.
[MgPc(SR)8]i
K0 ¼
:
ð2Þ
[MgPc(SR)8]o
The difference between the absorbances of the bulk toluene phase
under high-speed stirring and low-speed stirring conditions, ꢀA,
and the absorbance of the bulk toluene phase, Ao, under the
high-speed stirring can be described as follows,
Si
ꢀA ¼ "l[MgPc(SR)8]i
;
ð3Þ
ð4Þ
Vo
Ao ¼ "l[MgPc(SR)8]o;
where ", l, Si, and Vo are the molar absorptivity in toluene, the op-
tical path length, the total interfacial area, and the organic phase
volume, respectively. The total interfacial area in the toluene/
water system was reported to be 2:0 ꢅ 102 dm2.24
1.4 Centrifugal Liquid Membrane Measurement. The prin-
ciples of a centrifugal liquid membrane (CLM) method were de-
scribed elsewhere.15 The apparatus for CLM method was essen-
tially the same as the one reported previously.25 A toluene solution
(0.150 mL) of 1:0 ꢅ 10ꢁ6 M MgPc(SR)8 derivatives was intro-
duced into a cylindrical cell, whose height and outer diameter
were 3.3 and 2.1 cm, respectively. When the horizontally placed
cylindrical cell was rotated at around 10000 rpm, an aqueous solu-
tion (0.250 mL) containing 0.033 M sodium sulfate and acetate
buffer (pH 6) was injected into the cell through a 2 mm diameter
hole fabricated in the center of the flat side wall. The sum of the
absorption spectra of the bulk phases and interface was measured
with a UV–vis spectrophotometer (Agilent, 8453) at 1.0 s intervals
2.2 Dimerization of MgPc(SR)8 Derivatives in Toluene.
Figure 1 shows the concentration-dependence of the UV–vis
absorption spectra of MgPc(SR)8 derivatives. These spectra
are similar to each other, as observed in unsubstituted MgPc18
(not shown) with D4h symmetry.1 The absorption maxima of
the main peaks of the Q and B bands in MgPc(SR)8 derivatives
appeared at around 700 and 360 nm. In the case of D4h sym-
ꢀ
metry, the Q band in Pcs was attributed to the ꢂ–ꢂ transition
from the HOMO to the LUMO of the phthalocyanine ring, and

2014 Bull. Chem. Soc. Jpn., 77, No. 11 (2004)
Interfacial Adsorption of MgPc Derivatives
(NH2)CS / HCl
R OH
R SH
KOH
EtSH R = Et
BzSH R = Bz
BhSH R = Bh (76.9%)
RS
RS
CN
CN
K2CO3
THF /
∆
Pn(SEt)2 R = Et (78.4%)
Pn(SBz)2 R = Bz (80.9%)
Pn(SBh)2 R = Bh (85.1%)
Cl
Cl
CN
CN
RS
SR
SR
R :
Ethyl
RS
N
(Et)
(3)
Mg(OBu)2
BuOH
N
N
(2)
Benzyl
(Bz)
Mg
N
N
(1)
N
N
N
RS
SR
SR
Benzhydryl
RS
(3)
(Bh)
MgPc(SEt)8 R = Et (49.6%)
MgPc(SBz)8 R = Bz (57.8%)
MgPc(SBh)8 R = Bh (52.8%)
(2)
(1)
Scheme 1. Reaction routes for the syntheses of phthalocyaninatomagnesium(II) with eight peripheral thioether substituents.
the B band has been attributed to the deeper ꢂ levels–LUMO
transition.1 Both the Q and B bands in MgPc(SR)8 derivatives
shifted to a longer wavelength in the order MgPc(SBh)8 >
MgPc(SBz)8 > MgPc(SEt)8 > MgPc (see Table 1). Such a
red shift implies that the energy gap between the HOMO
and the LUMO, and that between deeper ꢂ levels and LUMO,
become smaller in the same order described above.
dimerization with a ‘‘face-to-face’’ configuration.30 The ab-
sorption bands of the monomer and the dimer are separated
quite well, and the molar absorptivity of the monomer Q band
was obtained from the absorbance in the dilute solution. The
dimerization reaction is defined by,
Kd
2 Monomer ꢀ Dimer
ð5Þ
ð6Þ
It is noted here that the Q band of MgPc(SBh)8 was un-
changed over the whole concentration range (from 5:0 ꢅ
10ꢁ7 to 1:0 ꢅ 10ꢁ5 M). The Lambert–Beer relationship is
shown as an inset for MgPc(SBh)8 in Fig. 1c. According to this
result and other reported results,1,27,28 the branching of the
benzhydryl group and its preferential solvation by toluene
molecules might have prevented the aggregation of
MgPc(SBh)8. On the other hand, the absorption spectra of
MgPc(SEt)8 and MgPc(SBz)8 showed a non-linear concentra-
tion dependence, e.g., the intensities of the Q bands of
MgPc(SEt)8 and MgPc(SBz)8 gradually decreased with an in-
crease in their concentrations, and the absorption spectra
showed discernible shoulders at 655 nm (MgPc(SEt)8) and
659 nm (MgPc(SBz)8) in concentrations higher than 1:0 ꢅ
10ꢁ6 M. The following HSS and CLM measurements were
carried out in concentrations of MgPc(SEt)8 and MgPc(SBz)8
in the bulk toluene less than 1:0 ꢅ 10ꢁ6 M. Isosbestic points
were observed in the visible region of these spectra, indicating
that the spectral changes were governed by an initial and a fi-
nal species with no side reactions.29 These concentration-de-
pendent spectral changes are a typical feature of the dimeriza-
tion known in Pc compounds.30–33 The blue-shifting, broaden-
ing, and lowering in the intensity of the Q band clearly indicate
log CD ¼ log Kd þ 2 log CM
where CM and CD are the concentrations of the complex in the
monomer and dimer, respectively. The dimerization constants,
Kd, for MgPc(SEt)8 and MgPc(SBz)8 in toluene were calculat-
ed from the UV–vis spectra using the approximation method of
West and Pearce,34 assuming that the observed spectrum at
concentration lower than 1:0 ꢅ 10ꢁ6 M was that of the mono-
mer. As shown in Fig. 2, the plots of log CD vs log CM for
MgPc(SEt)8 and MgPc(SBz)8 in toluene gave straight lines,
with a slope of ca. 2. The intercepts afforded the values of
log Kd. The observed values of Kd are summarized in Table 2.
2.3 Interfacial Adsorption Behavior of MgPc(SR)8
Derivatives. The interfacial adsorption of MgPc(SR)8 deriv-
atives in the toluene/water system was measured using a high-
speed stirring (HSS) method. The adsorption isotherms of
MgPc(SEt)8, MgPc(SBz)8, and MgPc(SBh)8 were measured,
as shown in Fig. 3. The interfacial adsorption constants, K0,
of MgPc(SBz)8 and MgPc(SBh)8 were obtained under the
Nernst adsorption condition. The values of K0 are also listed
in Table 2. The saturated interfacial concentration, a, was
not obtained, because the interfacial adsorption concentration
was too low under the present total concentrations. On the oth-

K. Adachi et al.
Bull. Chem. Soc. Jpn., 77, No. 11 (2004) 2015
3
2
1
0
-3
-4
-5
-6
-7
-8
(a)
(b)
(c)
MgPc(SEt)8
1.5
1
1
: MgPc(SEt) 8
: MgPc(SBz) 8
ε
M = 1.10x105
0.5
0
1
2
3
4
5
4
[MgPc(SEt)8]o / 10-5 mol dm-3
0
3
MgPc(SBz)8
1.5
2
1
2
1
0
1
1
ε
M = 1.30x105
0.5
4
0
1
2
3
4
5
-7
-6
-5
-4
[MgPc(SBz)8]o / 10-5 mol dm-3
log CM
0
3
3
Fig. 2. Plots of log CD vs log CM for MgPc(SEt)8 (open cir-
cle) and MgPc(SBz)8 (open triangle) in toluene. The bro-
ken lines are the least-squares fitted ones, which slopes
were close to 2. The correlation coefficient was larger than
0.99 for both plots.
MgPc(SBh)8
1
2
1
0
2
1
0
4
ε
M = 2.51x105
0
0.2 0.4 0.6 0.8
1
[MgPc(SBh)8]o / 10-5 mol dm-3
CT ¼ [MgPc(SEt)8]o þ f[MgPc(SEt)8]i
Si
300
400
500
600
/ nm
700
800
þ n[(MgPc(SEt)8)n]g
:
ð9Þ
Vo
λ
Equations 2, 8, and 9 can be combined to give,
Fig. 1. Concentration dependence of absorption spectrum
of MgPc(SR)8 derivatives in toluene (top: MgPc(SEt)8,
medium: MgPc(SBz)8, bottom: MgPc(SBh)8): 1) 1:0 ꢅ
10ꢁ6 mol/dm3; 2) 5:0 ꢅ 10ꢁ6 mol/dm3; 3) 1:0 ꢅ 10ꢁ5
mol/dm3; 4) 2:0 ꢅ 10ꢁ5 mol/dm3. The insets show
Lambert–Beer law plots for the absorbance at Q band of
MgPc(SR)8 monomer; the slopes of broken lines gave mo-
lar absorptivities of monomers, "M. The arrows indicate
the direction of the absorbance changes with increasing
concentration.
f[MgPc(SEt)8]i þ n[(MgPc(SEt)8)n]ig
¼ KaggK0n[MgPc(SEt)8]on þ nK0[MgPc(SEt)8]o: ð10Þ
The stoichiometric analysis of the experimental data using
Eq. 10 suggested the formation of the trimer (n ¼ 3) of
MgPc(SEt)8 at the toluene/water interface. Interfacial adsorp-
tion and the aggregation parameter of MgPc(SEt)8, K0
(2:57 ꢅ 10ꢁ5 dm) and Kaggðn¼3Þ (2:93 ꢅ 1023 molꢁ2 dm4), are
shown in Table 2.
The stable crystal of the aqua complex, MgPc(H2O), has
been reported, in which magnesium(II) ion is displaced by
er hand, the interfacial adsorption behavior of MgPc(SEt)8 did
not obey the Langmuir isotherm. Therefore, we thought that
there were two steps in the adsorption of MgPc(SEt)8 at the
toluene/water interface. The first step was the adsorption of
MgPc(SEt)8 monomer at the toluene/water interface, and the
second step was the interfacial formation of the aggregate,
(MgPc(SEt)8)n, from the monomer (MgPc(SEt)8) represented
by,
ꢁ
0.496 A from the plane of the Pc ring toward the coordinated
oxygen of the water molecule.35 Thus, it can be expected
that the MgPc(SR)8 derivatives adsorbed at the interface take
the hydrated form of MgPc(SR)8(H2O). The interfacial adsorp-
tivity of MgPc(SR)8 derivatives decreased in the order
MgPc(SEt)8 > MgPc(SBz)8 > MgPc(SBh)8. The decrease in
the interfacial adsorption constant, K0, by the replacement of
the hydrogen atoms of the peripheral benzenes of MgPc with
ethylthio-, benzylthio-, or benzhydrylthio-groups are thus as-
cribable to the enhanced lipophilicity or hydrophobicity. This
was confirmed by the linear relationship between log K0 and
the molar volume of the substituents listed in Table 2 (Figure
is not shown). Thus, the interfacial activity of MgPc(SR)8 de-
rivatives is afforded by the hydrated water and the hydropho-
bic groups.
Kagg
n(MgPc(SEt)8)i ꢀ (MgPc(SEt)8)ni;
ð7Þ
ð8Þ
[(MgPc(SEt)8)n]i
[MgPc(SEt)8]in
Kagg
¼
;
where Kagg and [(MgPc(SR)8)n]i are the aggregation constant
of MgPc(SEt)8 at the toluene/water interface and the concen-
tration of MgPc(SR)8 in the aggregate (mol/dm2), respective-
ly. The subscript or superscript ‘‘n’’ in Eq. 7 or 8 denote the
aggregation number distinguishable from the spectra. Since
the total concentration of MgPc(SEt)8, CT, is
2.4 Absorption Spectrum of Interfacial Aggregate of
MgPc(SEt)8. The adsorption spectrum of the aggregates of
MgPc(SEt)8 at the interface was directly measured by CLM

ꢂ
Table 2. Dimerization, Interfacial Adsorption, and Aggregation Constants of MgPc(SR)8 Derivatives at 25 C
aÞ
bÞ
"M/dm3 molꢁ1 cmꢁ1 (ꢃmax
)
"D/dm3 molꢁ1 cmꢁ1 (ꢃmax
)
Vp/cm3 molꢁ1 cÞ
Kd/molꢁ1 dm3 dÞ
K0/dmeÞ
Kaggðn¼3Þ/molꢁ2 dm4 fÞ
MgPc(SEt)8
MgPc(SBz)8
MgPc(SBh)8
1:10 ꢅ 105 (702 nm)
1:30 ꢅ 105 (708 nm)
2:51 ꢅ 105 (714 nm)
2:49 ꢅ 104 (655 nm)
3:69 ꢅ 104 (659 nm)
—
75.5
119.7
183.6
1:54 ꢅ 105
8:99 ꢅ 104
—
2:57 ꢅ 10ꢁ5
1:12 ꢅ 10ꢁ5
3:50 ꢅ 10ꢁ6
2:93 ꢅ 1023
—
—
a) "M; molar absorptivity of monomer, b) "D; molar absorptivity of dimer (expressed in terms of the monomer), c) Vp; estimated molar volume of one substituent, d) Kd; dimerization
constant in toluene solution, e) K0; interfacial adsorption constant (= [MgPc(SR)8]i/[MgPc(SR)8]o), f) Kaggðn¼3Þ; interfacial aggregation constant.
[MgPc(SEt)8] i +[(MgPc(SEt)8)agg i
]
[MgPc(SBh)8]i / 10-11 mol dm-2
[MgPc(SBz)8]i / 10-11 mol dm-2
/ 10-9 mol dm-2

K. Adachi et al.
Bull. Chem. Soc. Jpn., 77, No. 11 (2004) 2017
0.06
0.04
0.02
0
0.15
5 sec
: 0 sec
(a)
(without interface)
: 2 sec
dimer
max = 655 nm
λ
: 3 sec
monomer
: 4 sec
monomer
702 nm
λ
max = 702 nm
: 5 sec
H-aggregate
: 6 sec
: 7 sec
: 8 sec
dimer
655 nm
0.1
0.05
0
λ
max = 613nm
H-aggregate
613 nm
400
500
600
700
/ nm
800
900
λ
0.15
0.1
0.05
0
(b)
500
600
700
800
: monomer
: dimer
λ
/ nm
: H-aggregate
Fig. 4. The spectral change due to the interfacial aggrega-
tion of MgPc(SEt)8 at the toluene/water interface meas-
ured by CLM technique. The absorption spectra were re-
corded at 1 s intervals until the adsorption equilibrium
was achieved (8 s). The concentration of MgPc(SEt)8
was 1:0 ꢅ 10ꢁ6 M. The arrows indicate the direction of
the spectral changes with the time course.
0
2
4
6
8
10
Therefore, it can be concluded that the dimer was formed at
the initial stage at the interface. The dimer band then decreased
with the reaction time, and the blue-shift became more pro-
nounced. The ꢃmax shifted from 702 to 613 nm after 8 s with-
out an isosbestic point. The rise in the absorbance around 613
nm might be ascribed to another aggregate species (probably
H-aggregate36). Higher aggregates of Pc usually show a new
band in the same region as the dimer Q band, with broader
and lower intensity.37–40 Therefore, the present case may be
a new one in Pc aggregation. In the case of MgPc(SBz)8 and
MgPc(SBh)8, no spectral change was observed in the tol-
uene/water system (Spectra are not shown).
Assuming that the interfacial spectra were composed of
three Gaussian peaks of monomer, dimer and H-aggregate,
the absorbance changes of the three individual peaks were ob-
tained as a function of time. As for the spectra of the monomer,
the most intense peak was used for this analysis. An example
of such an analysis is shown in Fig. 5a. The deconvolution
(minimization of ꢄ2 criterion) exhibited a good fit for all spec-
Time / sec
Fig. 5. (a) Example of deconvolution analysis; (b) time
profile of the maximum absorbances of monomer, dimer,
and H-aggregate.
2.5 The Extended Double-Dipole Model for MgPc(SEt)8
H-Aggregate at the Interface. Kohn et al.41 proposed an ex-
tended dipole (ED) model to account for the blue- and red-
shifts of the dye-aggregates. Moreover, Sakakibara et al. im-
proved it to an extended double-dipole (EDD) model for the
aggregation of phthalocyanine molecules.42 The interaction in-
tegrals between Pc molecules in the aggregate are given by a
series of various parameters, i.e., the number of aggregate
molecules (n), the dipole length (l), the slipping distance (d),
and the interplane distance (h). According to the EDD model,
four charges (ꢄ"=2 with distance l) are distributed at each cor-
ner of a square Pc molecule along L- and M-axis (see Fig. 6a,
hereafter we call a moment along L-axis as L-component). The
electrostatic interaction energy J12 between two paired dipoles
is calculated by summarizing the L–L components and M–M
components,
tra, resulting in three distinct bands having the maxima (ꢃmax1
,
ꢃ
max2, and ꢃmax3) at 702, 655, and 613 nm for monomer, di-
mer, and H-aggregate, respectively. This analysis revealed that
the three bands have different time profiles (Fig. 5b). The plots
in Fig. 5b of each absorbance change suggested the two-step,
three-stage processes. The first rapid adsorption occurred in
the time range of 0–2 s, and the second slow adsorption fol-
lowed in up to 8 s. The integrated dimer band at 2 s gradually
decreased to zero, followed by the increase of the H-aggregate
band. The monomer band decreased up to 6 s, and then kept
constant. As observed by the CLM experiments, the liquid–liq-
uid interface had a strong influence on the aggregation state of
MgPc(SEt)8, which proceeded from monomer to H-aggregate
depending on the total interfacial concentration.
ꢀ
2
ð"=2Þ
1
1
1
1
1
1
1
1
J12
¼
þ
þ
þ
þ
þ
þ
þ
D
r11 r12 r21 r22 r33 r34 r43 r44
ꢁ
1
1
1
1
1
1
1
1
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
; ð11Þ
r13 r14 r23 r24 r31 r32 r41 r42
where D is the dielectric constant around the two dipoles
(D ¼ 2:5 the same value was used with Kohn et al.41), and
rab (a or b ¼ 1{4) is the distance between a point a on one
molecule and a point b on another molecule (see Fig. 6b, c).

2018 Bull. Chem. Soc. Jpn., 77, No. 11 (2004)
Interfacial Adsorption of MgPc Derivatives
3000
2000
1000
0
(a)
(2)
(1)
1
2
1
2
: trimer (n=3)
: dimer (n=2)
l
l
l
ε
ε
ε
ε
-
+
+
-
+
l
2
2
2
2
l
l
l
ε
ε
ε
ε
-
+
-
2
2
2
2
l
3
4
3
4
L-axis
(b)
r22
r11
-1000
1.8
0
5
10
15
Slipping distance d / Angstrom
Fig. 7. The EDD model simulation of energy shift (cmꢁ1
of the two absorption bands shown as a function of slip-
r22
r44
)
L-axis
ꢁ
ping distance (A). The interplane distance (h) and the di-
ꢁ
ꢁ
pole length (l) are fixed at 3.26 A and 4 A, respectively.
The upper lines correspond to M–M components and the
lower lines correspond to L–L components. n is the num-
ber of Pc moleculues.
(c)
h
The transition dipole moment ꢅ (¼ "l) is a constant given
by the experimental data, for which we adopted 1.49 Debye for
a MgPc monomer (this value was calculated from the oscilla-
tor strength (0.90) of the degenerate Q band43). The interplane
d
L-axis
Fig. 6. (a) Extended double-dipole (EDD) model of Pc
molecule of Sakakibara et al.42 Each four charges
(ꢄ"=2) are located at the corners of Pc molecular plane
separated by a distance l. The total moment exists along
the M-axis in (1), and it exists along the L-axis in (2).
(b) rab (a or b ¼ 1{4) are distances between charges locat-
ed on different molecules. (c) The interplane distance (h)
and slipping distance (d) are sketched.
43
ꢁ
distance (h) was set to 3.26 A as reported for a MgPc crystal,
and this value was considered to be a typical van der Waals
distance between Pc planes.44–47 According to the procedure
recommended by Sakakibara,42 the dipole length (l) was fixed
ꢁ
at 4 A, and the slipping distance (d) was allowed to vary.
The calculated values ꢀE0 of L–L and M–M components for
various arrangements are indicated in Fig. 7. In MgPc(SEt)8
dimer at the toluene/water interface, the shift of the B band
was 1615 cmꢁ1 (blue-shift from 368 to 347 nm) and that of
the Q band was 1022 cmꢁ1 (blue-shift from 702 to 655 nm).
From this, the energy shift ꢀE0 of a dimer from a monomer
equals 2J12.
The transition energy, ꢀEagg, of a Pc aggregate is then rep-
resented by the excitation energy of a Pc monomer ꢀEm, and
the interaction integral ꢀE0, approximated by,
ꢁ
Those values were fitted to the slipping distance of 1.8 A
ꢁ
(M–M components) and 1.9 A (L–L components) with n ¼
2, respectively. In the case of a trimer (n ¼ 3), which was
observed in the HSS experiments, the calculated slipping dis-
tance corresponding to the blue-shift of 2068 cmꢁ1 in the
ꢀEagg ¼ ꢀEm ꢄ ꢀE0:
ð12Þ
In the case of the aggregate containing n molecules, the ꢀE0
value between the i-th and (i þ 1)-th Pc molecule with L–L
components and M–M components is given as follows;
ꢁ
Q band (702 ! 613 nm) of an H-aggregate was 1.8 A (L–L
components). These results suggest the existence of a dimer
and trimer with a ‘‘face-to-face’’ arrangement between
MgPc(SEt)8 molecules.
ꢀ
n
2
X
Finally, the proposed mechanism for the interfacial adsorp-
tion and aggregation equlibria of MgPc(SR)8 derivatives in
the toluene/water system is summarized in Scheme 2. The
observed parameters listed in Table 2 suggest that the
MgPc(SR)8 derivative, which tends to dimerize in the toluene
solution, is more adsorbable into the interface and more easily
forms the interfacial aggregate.
2ð"=2Þ
1
1
1
1
ꢀE0 ¼
þ þ þ
D
R11 R12 R21 R22
1
1
1
1
1
1
þ
ꢁ
þ
þ
þ
ꢁ
ꢁ
R33 R34 R43 R44 R13 R14
ꢁ
1
1
1
1
1
1
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
;
ð13Þ
R23 R24 R31 R32 R41 R42
3. Conclusion
where Rab (a or b ¼ 1{4) is the distance between a point a on
the i-th molecule and a point b on the (i þ 1)-th molecule. The
summation is performed over the whole aggregate.
The interfacial adsorption and aggregation of MgPc(SR)8
[R ¼ Et, Bz, Bh] derivatives at the toluene/water interface

K. Adachi et al.
Bull. Chem. Soc. Jpn., 77, No. 11 (2004) 2019
Dimer
(MgPc(SR) )
K
d
MgPc(SR)
(R : Et, Bz, Bh)
8
8 2
Toluene
(R : Et, Bz)
K'
Dimer
Trimer
(MgPc(SR) )
(MgPc(SR) )
8 3
MgPc(SR)
8
(R : Et, Bz, Bh)
8 2
(R : Et)
(R : Et)
Interface
Water
K
agg(n=3)
Scheme 2. Proposed scheme for the interfacial adsorption and aggregation mechanism of MgPc(SR)8 derivatives in the toluene/
water system.
Dalton Trans., 1984, 2107.
was investigated by HSS and CLM methods. It was found that
the interfacial adsorption behavior was affected by the hydro-
phobicity of the peripheral substituents. From the absorption
spectra observed by CLM technique, it was found that the ag-
gregation of MgPc(SEt)8 at the toluene/water interface was a
two-step, three-stage process, and that the final aggregate
might be an eclipsed H-aggregate consisting of trimer units
¨
9 M. Kandaz and O. Bekaroglu, Chem. Ber., 130, 1833
(1997).
˘
¨
10 A. Gurek and O. Bekaroglu, J. Chem. Soc., Dalton. Trans.,
˘
¨
1994, 1419.
11 K. I. Ozoemena and T. Nyokong, Inorg. Chem. Commun.,
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13 ‘‘Liquid Interfaces in Chemical, Biological, and Pharma-
ceutical Appreciations,’’ ed by A. G. Volkov, Marcel Dekker,
New York, USA (1997).
14 H. Watarai, K. Sasaki, K. Takahashi, and J. Murakami,
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15 H. Nagatani and H. Watarai, Anal. Chem., 70, 2860 (1998).
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18 M. Whalley, J. Chem. Soc., 1961, 866.
19 H. Watarai, S. Tsukahara, H. Nagatani, and A. Ohashi,
Bull. Chem. Soc. Jpn., 76, 1471 (2003).
ꢁ
with a slipping distance of ca. 1.8 A. The interfacial adsorption
mechanism of Pc derivatives established in this study should
be extended to novel phthalocyanine coordination chemistry,
such as the interfacial catalytic synthesis with metal–phthalo-
cyanine, and the design of self-assembled interfacial net-
work-materials.
This study was supported by the Scientific Research of Pri-
ority Areas ‘‘Nano-Chemistry at the Liquid-Liquid Interfaces’’
(No. 13129204), the Grant-in-Aid for Scientific Research (S)
(No. 16105002) of the Ministry of Education, Culture, Sports,
Science and Technology and the Office of MORESCO under
the contact education program. The authors thank Dr. Kenji
Chayama of Konan University for his kind support in the syn-
thesis of MgPc(SR)8 derivatives. The author (K.A.) also thanks
Dr. Naohiro Kanematsu of MORESCO (Kobe, Japan) for his
helpful support in an early stage of this work.
20 H. Watarai, K. Takahashi, and J. Murakami, Solvent Extr.
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