Elongation of the π-system of phthalocyanines by introduction of thienyl substituents at the peripheral β positions. Synthesis and characterization

Article abstract of DOI:10.1021/jo010384r

1,4,8,11,15,18,22,25-Octabutoxyphthalocyanines ((OBu)₈Pcs) having eight 2-thienyl (1) and [2,2′-bithiophene]-5-yl (2) groups at β positions and their zinc(II) and cobalt(II) derivatives were prepared from 2-thienyl- (3) or [2,2′-bithiophene]-5-yl (4)-substituted phthalonitriles in moderate to good yields. The electronic absorption spectra of the Pcs showed red-shifted Q-bands relative to β-unsubstituted (OBu)₈Pcs. The longer substituent, the [2,2′-bithiophene]-5-yl group, is more effective than the 2-thienyl group in enlarging the π-conjugated system of the Pcs. The ring oxidation potential obtained by cyclic voltammetry shifted cathodically with increasing chain length, indicating destabilization of the HOMOs. Due to the shift of the Q-band, 2-thienyl- and [2,2′-bithiophene]-5-yl-substituted Pcs exhibit a remarkable color change from the original green color.

Full text of DOI:10.1021/jo010384r

J . Org. Chem. 2001, 66, 6109-6115
6109
Elon ga tion of th e π-System of P h th a locya n in es by In tr od u ction of
Th ien yl Su bstitu en ts a t th e P er ip h er a l â P osition s. Syn th esis a n d
Ch a r a cter iza tion
Tsuyoshi Muto, Tetsuji Temma, Mutsumi Kimura, Kenji Hanabusa, and Hirofusa Shirai*
Department of Functional Polymer Science, Faculty of Textile Science and Technology,
Shinshu University, Tokida 3-15-1, Ueda 385-8567, J apan
hshirai@giptc.shinshu-u.ac.jp
Received April 16, 2001
1,4,8,11,15,18,22,25-Octabutoxyphthalocyanines ((OBu)8Pcs) having eight 2-thienyl (1) and [2,2′-
bithiophene]-5-yl (2) groups at â positions and their zinc(II) and cobalt(II) derivatives were prepared
from 2-thienyl- (3) or [2,2′-bithiophene]-5-yl (4)-substituted phthalonitriles in moderate to good
yields. The electronic absorption spectra of the Pcs showed red-shifted Q-bands relative to
â-unsubstituted (OBu)8Pcs. The longer substituent, the [2,2′-bithiophene]-5-yl group, is more
effective than the 2-thienyl group in enlarging the π-conjugated system of the Pcs. The ring oxidation
potential obtained by cyclic voltammetry shifted cathodically with increasing chain length, indicating
destabilization of the HOMOs. Due to the shift of the Q-band, 2-thienyl- and [2,2′-bithiophene]-5-
yl-substituted Pcs exhibit a remarkable color change from the original green color.
In tr od u ction
and another is to substitute the rings with electron
donors, thereby shifting the Q- and B-bands.16,17 Fur-
thermore, direct attachment of the Pc ring systems with
other chromophores through π-conjugated bridges tends
to alter the electronic structures.18-21 In such cases, the
Q-band of the Pcs undergoes a shift toward the near-
infrared (NIR) direction, which has been attributed to
the extension of the π-conjugation system, with concomi-
tant splitting or broadening of the Q-band.
Phthalocyanines (Pcs) are macrocyclic molecules whose
π-electron system provides their unique photophysical,
electronic, and electrical conducting properties.1,2 Re-
cently, the compounds have gained importance in opto-
electronic industry, as exemplified by their potential use
in electrophotography3,4 and optical data storage materi-
als.5,6 In addition, their properties have been considered
to have potential applications to photovoltaic cells,7,8 gas-
sensing materials,9,10 and the photodynamic therapy
(PDT) of cancer.11,12 Undoubtedly, these properties are
derived from the stability and delocalized electronic
nature of the Pc ring systems. Most of the modern uses
of Pcs are focused on the electronic properties of the
π-electron system of the macrocycles. The diversity of the
properties of Pcs has led us to develop extended Pc
derivatives. One approach to extension of the π-system
of the Pc ring is to benzoannulate the Pc molecules13-15
Much less effort has been focused on the preparation
of the Pc systems having π-conjugated groups at â
positions, such as with aromatic groups22-25 or nonaro-
matic groups.26,27 In preliminary studies by us,28 the
Q-band of a â-heteroaromatic-substituted Pc, 2,3,9,10,-
16,17,23,24-octa(2-thienyl)phthalocyanine, underwent a
red shift of about 20 nm relative to those of tetra-tert-
butylphthalocyanine. This phenomenon is considered to
be a result of a strong interaction between the π-electrons
(15) Aoudia, M.; Cheng, G.; Kennedy, V. O.; Kenny, M. E.; Rodgers,
M. A. J . J . Am. Chem. Soc. 1997, 119, 6029-6039.
(16) Kobayashi, N.; Sasaki, N.; Higashi, Y.; Osa, T. Inorg. Chem.
1995, 34, 1636-1637.
(1) Leznoff, C. C.; Lever, A. B. P. Phthalocyanines-Properties and
Applications; VCH Publishers (LSK) Ltd.: Cambridge, 1989, 1993,
1996; Vols. 1-4.
(2) Mckeown, N. B. Phthalocyanine Materials-Synthesis, Structure
and Function; Cambridge University Press: Cambridge, 1998.
(3) Law, K.-Y. Chem. Rev. 1993, 93, 449-486.
(17) Cook, M. J .; Dunn, A. J .; Howe, S. D.; Thomson, A. J . J . Chem.
Soc., Perkin Trans. 1 1988, 2453-2458.
(18) Kobayashi, N.; Higashi, Y.; Osa, T. Chem. Lett. 1994, 1813-
1816.
(4) Gregory, P. High-Technology Applications of Organic Colorants,
Plenum: New York, 1991.
(5) Emmerius, M.; Pawlowski, G.; Vollmann, H. W. Angew. Chem.,
Int. Ed. Engl. 1989, 28, 1445-1470.
(6) Ao, R.; Ku¨lmmerl, L.; Haarer, D. Adv. Mater. 1995, 7, 495-499.
(7) Whitelock, J . B.; Panayotatos, P.; Sharma, G. D.; Cox, M. D.;
Sauers, R. R.; Bird, G. R. Opt. Eng. 1993, 32, 1921-1934.
(8) Eichhorn, H. J . Porphyrins Phthalocyanines 2000, 4, 88-102.
(9) Snow, A. W.; Barger, W. R. Phthalocyanines-Properties Applica-
tions; Lever, A. B. P.; Leznoff, C. C., Eds.; VCH: New York, 1989; Vol.
1,
(19) Garc´ıa-Frutos, E. M.; Ferna´ndi-La´zaro, F.; Maya, E. M.;
Va´zquez, P.; Torres, T. J . Org. Chem. 2000, 65, 6841-6846.
(20) Maya, E. M.; Va´zquez, P.; Torres, T.; Gobbi, L.; Diederich, F.;
Pyo, S.; Echegoyen, L. J . Org. Chem. 2000, 65, 823-830.
(21) Li, J .; Lindsey, J . S. J . Org. Chem. 1999, 64, 9101-9108.
(22) Trominko, G. M.; Berezin, B. D. Zh. Neorg. Khim. 1993, 38,
1048-1052.
(23) J ian, Y.; van de Mark, M. J . Heterocycl. Chem. 1995, 32, 1521-
1524.
(24) Humberstone, P.; Clarkson, G. J .; Mckeown, N. B.; Treacher,
K. E. J . Mater. Chem. 1996, 6, 315-322.
(25) Tian, M.; Wada, T.; Kimura-Suda, H.; Sasabe, H. J . Mater.
Chem. 1997, 7, 861-863.
(10) Dogo, S.; Germain, J . P.; Maleysson, C.; Pauly, A. Thin Solid
Films 1992, 219, 244-250.
(11) Rosenthal, I. Photochem. Photobiol. 1991, 53, 859-870.
(12) Ali, H.; van Lier, J . Chem. Rev. 1999, 99, 2379-2450.
(13) Kobayashi, N.; Nakajima, S.; Osa, T. Inorg. Chim. Acta 1993,
210, 131-133.
(26) Leznoff, C. C.; Li, Z.; Isago, H.; D’ascanio, A. M.; Terekhov, D.
S. J . Porphyrins Phthalocyanines 1999, 3, 406-416.
(27) Beck, A.; Hanack, M. Chem. Ber. 1993, 126, 1493-1494.
(28) Muto, T.; Temma, T.; Kimura, M.; Hanabusa, K.; Shirai, H.
Chem. Commun. 2000, 1649-1650.
(14) Bedworth, P. V.; Perry, J . W.; Marder, S. R. Chem. Commun.
1997, 1353-1354.
10.1021/jo010384r CCC: $20.00 © 2001 American Chemical Society
Published on Web 08/08/2001

6110 J . Org. Chem., Vol. 66, No. 18, 2001
Muto et al.
solution of tetra-n-butylammonium hexafluorophosphate (Bu4-
NPF6, Aldrich) in CH2Cl2 or a 0.3 M tetra-n-butylammonium
perchlorate (Bu4NClO4, Nakalai Tesque) in o-dichlorobenzene
containing 1.0 mM of sample was purged with nitrogen for 20
min; then the voltammograms were recorded at ambient
temperature under dark. Potential was referenced to Ag/Ag+
in MeCN.
4,5-Dibromo3,6-dibutoxyphthalonitrile,31 2-(tri-n-buthyl)-
stannylthiophene,33 2-(tri-n-butyl)stannyl-5,2′-bithiophene,34
(OBu)8ZnPc,17 and (OBu)8CoPc35 were prepared according to
the literature methods or their slight modification. We syn-
thesized six types of new Pcs (1, 2, 1-Zn , 1-Co, 2-Zn , and 2-Co)
in this work (Scheme 1). All the synthesis of the Pcs was
started from 4,5-dibromo-3,6-dibutoxyphthalonitrile.31 The
transformation of this compound into thiophene-substituted
phthalonitriles involves palladium-catalyzed cross-coupling29,34
between the starting material and the appropriate tri-n-
butylstannane of the thiophene. The Pcs obtained in our study
have high solubility (>10-3 M) in common organic solvents
such as CH2Cl2, THF, or toluene, but not in acetonitrile. The
thiophene-substituted (OBu)8Pcs, particularly the free-bases
and zinc derivatives, are acid sensitive. It is advantageous to
base-wash the glassware and the quartz cell prior to use for
the Pcs.
of the Pc ring and the thiophene moieties. From these
results, we noticed the reformation of the π-system of Pc
by â-thienyl substitution which has the potential for
synthetic flexibility compared to other methodologies.
Oligothiophenes are a frequently investigated class of
π-conjugated moieties due to their stability and the fact
that their synthetic chemistry has been well-defined.29
In addition, their structural planarity permits strong
electronic conjugation within the structure. For these
reasons, substitution of thienyl and bithienyl groups at
the â positions of the Pc ring could result in the extension
and refinement of the π-systems.
In this paper, we describe the preparation and elec-
tronic condition of â-octa(2-thienyl)- and ([2,2′-bithiophene]-
5-yl)-1,4,8,11,15,18,22,25-octabutoxyphthalocyanines ((O-
Bu)8MPc, M ) H2, Zn, and Co). The electronic states of
the Pcs are discussed by means of photophysical studies
as well as by electrochemical studies. The (OR)8Pcs
generally are stable compounds that have an intense
Q-band in the red to deep-red region.17,30 This implies
that they have potential to exhibit intense Q-absorption
in the NIR region by the introduction of π-conjugated
moieties to the Pc ring through a σ-bond and are useful
in modern applications as a new class of Pcs.
3,6-Dibu toxy-4,5-d i(2-th ien yl)p h th a lon itr ile (3). 4,5-
Dibromo-3,6-dibutoxyphthalonitrile (1.0 g, 2.33 mmol) and
2-(tri-n-butyl)stannylthiophene (3.9 g, 10.0 mmol) were dis-
solved in 50 mL of dry DMF. The reaction mixture was added
by catalytic amount (ca. 0.1 mol % for the substrates) of bis-
(triphenylphosphine)palladium(II) dichrolide, [Pd(II)(PPh3)2-
Cl2], and then heated at 60-70 °C for 36 h under nitrogen
atmosphere. The reaction mixture was concentrated in a
vacuum and chromatographed on a silica gel column (n-
hexane/CH2Cl2 ) 1/1 v/v as an eluent) to give a light yellow
solid. Recrystallization of the solid from ethanol gave 0.84 g
(1.92 mmol; 83.4% yield) of 3 as a pale-yellow needle. TLC
(SiO2; n-hexane/CH2Cl2 ) 1/1 v/v): Rf ) 0.75. UV/Vis (CH2-
Cl2): λmax (log ꢀ/M-1 cm-1) ) 272 (4.17), 346 nm (4.08). 1H NMR
(400 MHz, CDCl3, TMS): δ ) 0.77-0.87 (m, 6H, CH3), 1.23-
1.32 (m, 4H, CH2), 1.52-1.59 (m, 4H, CH2), 3.74-3.77 (m, 4H,
OCH2), 6.90-6.91 (m, 2H, 3-ArH), 6.95-6.97 (m, 2H, 4-ArH),
7.38-7.39 (m, 2H, 5-ArH). Elemental analysis calcd for
Exp er im en ta l Section
Dichloromethane (CH2Cl2) used for photophysical and elec-
trochemical studies was predried by stirring with CaCl2 and
then distilled from P2O5. Toluene used for photophysical
measurements was dried over P2O5 and distilled. o-Dichlo-
robenzene used in electrochemical studies was shaken with
concentrated H2SO4, washed with water, predried with CaCl2,
and distilled from CaH2 under reduced pressure. Pyridine used
for photophysical studies was dried over KOH and distilled.
N,N-Dimethylformamide (DMF) was dried over BaO and
distilled under reduced pressure. These solvents were stored
with molecular sieves 4A under dark and used as soon as
possible. Tetrahydrofuran (THF) was distilled from LiAlH4 and
stored with sodium wire. N,N-Dimethylaminoethanol was
dried over KOH and distilled prior to use. All other reagents
and solvents were purchased and used without further treat-
ment. In addition, we have synthesized 4-(2-thienyl)-3,6-
dibutoxyphthalonitrile (4T(OBu)2Phn) as a structural analogue
of 3 and 4 from 4-bromo-3,6-dibutoxyphthalonitrile.31 Silica
gel (Fuji Silysia, BW-820MH), activated alumina (Wako,
abt.200 mesh), and Bio Beads SX-3 (Bio-Rad) were used for
column chromatography.
All spectroscopic measurements were performed at ambient
temperature. Elemental analysis were carried out with a
Perkin-Elmer 2400II-CHN. Proton and carbon-13 NMR spec-
tra were measured with a Bruker AVANCE 400 spectrometer
with TMS as a standard. Matrix-assisted laser desorption/
ionization time-of-flight (MALDI-TOF) spectra were obtained
on a Perseptive Biosystems Voyager VE-Pro with a dithranol
matrix. UV-Vis-NIR absorption spectra and emission spectra
were taken on a J asco V-570 spectrophotometer and a J asco
FP-750 spectrophotometer, respectively. Fluorescence quan-
tum yields (Φf) of (OBu)8Pcs were obtained using (OBu)8ZnPc
(Φf ) 0.62, in pyridine)16 as a standard.32
C
24H24N2O2S2 (436.5): C, 66.02; H, 5.54; N, 6.42; O, 7.33; S,
14.61, found: C, 66.35; H, 5.50; N, 6.64. IR (KBr): ν ) 2228
cm-1 (m).
3,6-Dibu toxy-4-(2-th ien yl)ph th alon itr ile, 4T(OBu )2P h n .
4-Bromo-3,6-dibutoxyphthalonitrile31 (0.4 g, 0.93 mmol) and
2-(tri-n-butyl)stannylthiophene (2.8 g, 7.2 mmol) were dis-
solved in 30 mL of dry DMF. A catalytic amount of [Pd(II)-
(PPh3)2Cl2] was dissolved in the reaction mixture and then
stirred at 60 °C for 48 h under nitrogen atmosphere. The
reaction mixture was concentrated in a vacuum and passed
through a silica gel column (n-hexane/CH2Cl2 ) 1/1 v/v as an
eluent) to give a light yellow solid. The solid material was
purified by recrystallization from ethanol gave 0.34 g (0.89
mmol; 95.7% yield) of title compound as a pale-yellow needle.
TLC (SiO2; n-hexane/CH2Cl2 ) 1/1 v/v): Rf ) 0.82. UV/Vis
(CH2Cl2): λmax (log ꢀ/M-1 cm-1) ) 318 (4.04), 362 nm (4.22).
1H NMR (400 MHz, CDCl3, TMS): δ ) 0.89-1.05 (m, 6H, CH3),
1.44-1.59(m, 4H, CH2), 1.78-1.89 (m, 4H, CH2), 3.94-3.98
(t, 2H, OCH2), 4.12-4.15 (t, 2H, OCH2), 7.15-7.17 (q, 1H,
4-ArH), 7.34 (s, 1H, PhH), 7.51-7.53 (d, 1H, 3-ArH), 7.57-
7.59 (d, 1H, 5-ArH). Elemental analysis calcd for C20H22N2O2S
(354.5): C, 67.77; H, 6.26; N, 7.90; O, 9.03; S, 9.05, found: C,
67.35; H, 6.30; N, 7.89. IR (KBr): ν ) 2226 cm-1 (m).
3,6-Dibu toxy-4,5-bis([2,2′-bith iop h en e]-5-yl)p h th a lon i-
tr ile (4). A mixture of 2-(tri-n-butyl)stannyl-5,2′-bithiophene
(3.0 g, 6.59 mmol) and 4,5-dibromo-3,6-dibutoxyphthalonitrile
Electrochemical measurements were carried out on an ALS
MODEL 400S voltammetric analyzer. The cell consists of a
platinum working electrode (BAS, 1.6 mm diameter), a plati-
num wire counter electrode, and a BAS RE-5 (Ag/AgNO3)
reference electrode. Typical experimental conditions: a 0.1 M
(29) Tour, J . M.; Wu, R. Macromolecules 1992, 25, 1901-1907.
(30) Rihter, B. D.; Kenny, M.; Ford, W. E.; Rodgers, M. A. J . J . Am.
Chem. Soc. 1990, 112, 8064-8070.
(31) Cook, M. J .; Heeney, M. J . Chem. Eur. J . 2000, 6, 3958-3967.
(32) Dames, J . N.; Crosby, G. A. J . Phys. Chem. 1971, 75, 991-
1024.
(33) Gopinathan, S.; Gopinathan, C.; Gupta, J . Ind. J . Chem. 1974,
12, 623-625.
(34) Zhu, S. S., Swager, T. M. J . Am. Chem. Soc. 1997, 119, 12568-
12577.
(35) Matsuzawa, Y.; Seki, T.; Ichimura, K. Thin Solid Films 1997,
301, 162-168.

Elongation of the π-System of Phthalocyanines
J . Org. Chem., Vol. 66, No. 18, 2001 6111
Sch em e 1
(1.0 g, 2.33 mmol) in 30 mL of dry DMF was added by the
catalytic amount of [Pd(II)(PPh3)2Cl2] and stirred at 60-70 °C
for 56 h under nitrogen atmosphere. The reaction mixture was
concentrated and chromatographed with a silica gel column
(n-hexane/CHCl3 ) 3/1-1/1 v/v) afforded yellow solid. The solid
was purified by recrystallization from 1-propanol/n-hexane
gave 1.23 g (2.05 mmol; 87.9% yield) of 4 as a yellow scale.
TLC (SiO2; CHCl3): Rf ) 0.65. UV/Vis (CH2Cl2): λmax (log ꢀ/M-1
cm-1) ) 316 (4.48), 380 (4.29). 1H NMR (400 MHz, CDCl3,
TMS): δ ) 0.79-0.86 (m, 6H, CH3), 1.30-1.39 (m, 4H), 1.59-
1.66 (m, 4H), 3.83-3.86 (m, 4H), 6.84 (d, J ) 3.52 Hz, 2H,
3-ArH), 6.99-7.02 (m, 2H, 3′-ArH), 7.04 (d, J ) 3.50 Hz, 2H,
4-ArH), 7.13-7.15 (m, 2H, 4′-ArH), 7.22-7.24 (m, 2H, 5′-ArH).
13C{1H} NMR (100 MHz, CDCl3, TMS) δ ) 14.0, 19.2, 32.3,
76.2, 110.4, 113.5, 123.8, 124.7, 125.5, 128.3, 131.7, 132.2,
136.3, 136.9, 141.2, 157.4. Elemental analysis calcd for
NH), 0.83-0.87 (m, 24H, CH3), 1.21-1.30 (m, 16H, CH2), 1.78-
1.85 (m, 16H, CH2), 4.74-4.78 (m, 16H, OCH2), 7.06-7.09 (m,
8H, 4-ArH), 7.19-7.20 (m, 8H, 3-ArH), 7.44-7.45 (m, 8H,
5-ArH). MALDI-TOF-mass spectrum m/z calcd for (C96H98N8-
O8S8) 1748.4, found 1749. Elemental analysis calcd for
C
96H98N8O8S8: C, 65.95; H, 5.65; N, 6.41; O, 7.32; S, 14.67.
found: C, 66.02; H, 5.82; N, 6.30. UV/Vis (in CH2Cl2): λmax
(log ꢀ/M-1 cm-1) ) 778 (5.270), 684 (4.756), 338 nm (4.866).
1,4,8,11,15,18,22,25-Octabu toxy-2,3,9,10,16,17,23,24-octa-
([2,2′-bith iop h en e]-5-yl)p h th a locya n in e (2). Compound 4
(0.27 g, 0.45 mmol) was dissolved in minimum amount of dry
THF at room temperature. This solution was added by 10 mL
of absolute methanol and purged with NH3 gas for 20 min. A
catalytic amount of NaOMe was added to the mixture and
stirred at 50 °C for 6 h under NH3 bubbling. The reaction
mixture was poured into water, and yellow precipitate formed,
5,8-dibutoxy-6,7-di([2,2′-bithiophene]-5-yl)-1,3-dihydro-1,3-di-
iminoisoindole, which was isolated by filtration and dried
under vacuum. The yellow intermediate was suspended in
freshly distilled N,N-dimethylaminoethanol (10 mL) and re-
fluxed for 48 h under N2. The mixture was poured into excess
methanol, and the precipitate formed was filtered off. This
material was purified by column chromatography with acti-
vated alumina (toluene) and then SX-3 (CH2Cl2) to give 2 as
a red powder (47.9 mg, 17.7%). 1H NMR (400 MHz, CDCl3,
TMS): δ ) 0.59 (s, 2H, NH), 0.85-0.89 (m, 24H, CH3), 1.33-
1.42 (m, 16H, CH2), 1.85-1.98 (m, 16H, CH2), 4.80-4.82 (m,
16H, OCH2), 7.04-7.06 (m, 8H, 3′-ArH), 7.09 (d, J ) 3.56 Hz,
8H, 3-ArH), 7.17 (d, J ) 3.60 Hz, 8H, 4-ArH), 7.22-7.25 (m,
16H, 4′-ArH, 5′-ArH). MALDI-TOF-mass spectrum m/z calcd
for (C128H114N8O8S16) 2405.3, found 2404.9. Elemental analysis
calcd for C128H114N8O8S16: C, 63.91; H, 4.78; N, 4.66; O, 5.32;
S, 21.33. found: C, 64.18; H, 4.81; N, 4.82. UV/Vis (in CH2-
Cl2): λmax (log ꢀ/M-1 cm-1) ) 794 (5.316), 705 (4.663), 493
(4.554).
C
32H38N2O2S4 (600.8): C, 63.97; H, 4.70; N, 4.66; O, 5.33; S,
21.35, found: C, 63.67; H, 4.78; N, 4.70. IR (KBr): ν ) 2226
cm-1 (m).
1,4,8,11,15,18,22,25-Octabu toxy-2,3,9,10,16,17,23,24-octa-
(2-th ien yl)p h th a locya n in e (1). Compound 3 (0.2 g, 0.45
mmol) in 10 mL of absolute methanol was purged with NH3
gas for 20 min. A catalytic amount of NaOMe was dissolved
in the mixture and stirred at 50 °Cfor 6 h under NH3
atmosphere. The mixture was poured into water. The precipi-
tate formed, and 5,8-dibutoxy-6,7-di(2-thienyl)-1,3-dihydro-1,3-
diiminoisoindole was filtered off and dried under vacuum. This
material was used for the following reaction without further
purification. 5,8-Dibutoxy-6,7-di(2-thienyl)-1,3-dihydro-1,3-di-
iminoisoindole was suspended in freshly distilled N,N-di-
methylaminoethanol (10 mL) under N2 and heated at refluxed
state for 48 h. After cooling to room temperature, the reaction
mixture was diluted with excess methanol. The green precipi-
tate formed was filtered off and chromatographed on activated
alumina using CH2Cl2/n-hexane ) 1/1 v/v (Rf ) 0.95) and then
SX-3 (CH2Cl2) to give 1 (29.5 mg, yield 15.0%) as a green
powder. 1H NMR (400 MHz, CDCl3, TMS): δ ) 0.52 (s, 2H,
Gen er a l P r oced u r e for th e P r ep a r a tion of 2-Th ien yl-
or ([2,2′-Bith iop h en e]-5-yl)-Su bstitu ted 1,4,8,11,15,18,22,-

6112 J . Org. Chem., Vol. 66, No. 18, 2001
Muto et al.
25-Octa bu toxyp h th a locya n in a to Com p lexes. A mixture
of phthalonitrile (3 or 4, 0.9 mmol) and corresponding metal
as chloride salt (0.23 mmol) in 2.5 mL of 1-hexanol was heated
to 90 °C under N2, and then 0.16 mL (1.08 mmol) of DBU was
added. The reaction mixture was stirred at 100-120 °C for
18 h under N2. After being cooled to room temperature, the
reaction mixture was poured into excess methanol. The
precipitate formed was filtered off and purified by column
chromatography.
[1,4,8,11,15,18,22,25-Octabu toxy-2,3,9,10,16,17,23,24-octa-
(2-th ien yl)p h th a locya n in a to]zin c(II) (1-Zn ). 65% from 3;
yellow-green powder, purified using an activated alumina
column (CH2Cl2/THF ) 2/1 v/v) (Rf ) 0.85) and SX-3 (CH2-
Cl2). 1H NMR (400 MHz, CDCl3, TMS) δ ) 0.83-0.87 (m, 24H,
CH3), 1.20-1.30 (m, 16H, CH2), 1.78-1.85 (m, 16H, CH2),
4.80-4.83 (m, 16H, OCH2), 7.07-7.09 (m, 8H, 4-ArH), 7.19-
7.20 (m, 8H, 3-ArH), 7.43-7.45 (m, 8H, 5-ArH). 13C{1H} NMR
(100 MHz, CDCl3, TMS) δ ) 14.5, 19.6, 32.6, 77.0, 126.5, 127.1,
130.3, 131.0, 132.9, 138.8, 152.1, 152.8. MALDI-TOF-mass
spectrum m/z calcd for (C96H96N8O8S8Zn) 1811.76, found 1810.
Elemental analysis calcd for C96H96N8O8S8Zn: C, 63.64; H,
5.34; N, 6.18; O, 7.06; S, 14.16; Zn, 3.61. found: C, 63.73; H,
5.51; N, 6.15. UV/Vis (in CH2Cl2): λmax (log ꢀ/M-1 cm-1) ) 758
(5.42), 678 (4.73), 370 nm (4.78).
[1,4,8,11,15,18,22,25-Octabu toxy-2,3,9,10,16,17,23,24-octa-
(2-th ien yl)p h th a locya n in a to] coba lt(II) (1-Co). 20% from
3; yellow-green powder, purified using a silica gel column (CH2-
Cl2/n-hexane ) 1/2 v/v) (Rf ) 0.65) and SX-3 (CH2Cl2). MALDI-
TOF-mass spectrum m/z calcd for (C96H96N8O8S8Co) 1804.3,
found 1805. Elemental analysis calcd for C96H96N8O8S8Co: C,
63.87; H, 5.36; N, 6.21; O, 7.09; S, 14.21; Co, 3.26. found: C,
63.52; H, 5.17; N, 6.12. UV/Vis (in CH2Cl2): λmax (log ꢀ/M-1
cm-1) ) 746 (5.34), 670 (4.71), 304 nm (4.92).
[1,4,8,11,15,18,22,25-Octabu toxy-2,3,9,10,16,17,23,24-octa-
([2,2′-b it h iop h en e]-5-yl) p h t h a locya n in a t o]zin c(II) (2-
Zn ). 54.0% from 4; brown powder, purified using an almina
column (CH2Cl2) (Rf ) 0.98) and SX-3 (CH2Cl2). 1H NMR (400
MHz, TMS) δ ) 0.89-0.93 (m, 24H, CH3), 1.33-1.38 (m, 16H,
CH2), 1.89-1.97 (m, 16H, CH2), 4.86 (m, 16H, OCH2), 7.04-
7.06 (m, 8H, 3′-ArH), 7.09 (d, J ) 3.60 Hz, 8H, 3-ArH), 7.17
(d, J ) 3.80 Hz, 8H, 4-ArH), 7.22-7.25 (m, 16H, 4′-ArH, 5′-
ArH). 13C{1H} NMR (100 MHz, CDCl3, TMS) δ ) 14.6, 19.9,
32.7, 76.9, 123.7, 124.5, 128.2, 131.1, 132.2, 137.8, 138.4, 139.1,
144.3, 148.2, 152.1, 152.9. MALDI-TOF-mass spectrum m/z
calcd for (C128H112N8O8S16Zn) 2468.75, found 2468. Elemental
analysis calcd for C128H112N8O8S16Zn: C, 62.27; H, 4.57; N,
4.54; O, 5.18; S, 20.78; Zn, 2.65. found: C, 62.35; H, 4.56; N,
4.61. UV/Vis (in CH2Cl2): λmax (log ꢀ/M-1 cm-1) ) 768 (5.48),
686 (4.85), 332 nm (5.20).
F igu r e 1. Partial 1H NMR spectra of (A) 4T(OBu)2Phn, (B)
3, (C) 1-Zn , (D) 4, and (E) 2-Zn , respectively, in CDCl3 (400
MHz) at room temperature. Inset in (A) shows structural
formula of 4T(OBu)2Phn.
4-position was observed as a quasi-triplet or multiplet.
On the other hand, the heteroaromatic resonant peaks
of compound 3 and 4 underwent upfield shifting relative
to 4T(OBu)2Phn (Figure 1B and 1D). In both cases, these
shifting are most firmly observed in the resonance of the
3-positions. From these results, the significant shifting
is attributed to the shielding effect caused by the close
proximity of the thiophene moieties. Given the interest-
ing NMR behavior of the precursors, we also examined
the NMR studies for the Pcs under the same conditions.
The proton NMR spectra of 1-Zn and 2-Zn were also well
resolved and showed downfield shifts due to the intense
ring current of the Pc nucleus (Figure 1C and 1E). For
both 1-Zn and 2-Zn , the downfield shifting was most
firmly observed for the eight protons at the 3-positions.
On the other hand, the downfield shifting of the outer
side thiophene rings, the 3′-, 4′-, and 5′-positions, in 2-Zn
was relatively small compared with those of the inner
side protons. This observation also supports the above
explanation of the proton NMR. Due to the high solubility
and rigid structures, the carbon-13 NMR spectra of 1-Zn
and 2-Zn were well resolved and showed 12 carbon
signals for 1-Zn and 16 carbon signals for 2-Zn , respec-
tively.
[1,4,8,11,15,18,22,25-Octabu toxy-2,3,9,10,16,17,23,24-octa-
([2,2′-bith iop h en e]-5-yl)p h th a locya n in a to]coba lt(II) (2-
Co). 52.8% from 4; green-black powder, purified using a silica
gel column (CH2Cl2) (Rf ) 0.95) and Bio Beads SX-3 (CH2Cl2).
MALDI-TOF-mass spectrum m/z calcd for (C128H112N8O8S16
Co) 2462.30, found 2462. Elemental analysis calcd for C128H112
-
-
N8O8S16Co: C, 62.44; H, 4.58; N, 4.55; O, 5.20; S, 20.84; Co,
2.39. found: C, 62.58; H, 4.45; N, 4.50. UV/Vis (in CH2Cl2):
λmax (log ꢀ/M-1 cm-1) ) 762 (5.43), 680 (4.71), 304 nm (4.92).
Resu lts a n d Discu ssion
From CPK modeling of compounds 3 and 4, each of
thiophene moieties in the phthalonitrile derivatives is in
very close proximity with a neighboring thiophene moi-
ety. The proton NMR observation of compounds 3 and 4
supports this explanation. In the proton NMR spectrum
of 4-(2-thienyl)-3,6-dibutoxyphthalonitrile (4T(OBu)2Phn,
Figure 1A), the asymmetric analogue of 3 and 4, the
heteroaromatic resonance of the 3-, 4-, and 5-positions
were observed at 7.533-7.518, 7.173-7.151, and 7.587-
7.575 ppm, respectively. Each of the resonance of the 3-
and 5-positions was observed as a pair of doublet signals
with the same intensity, while the resonance of the
Table 1 summarizes the photophysical data of (OBu)8-
MPcs and their thiophene-substituted analogues. The
absorption spectra of (OR)8H2Pc have intense Q-bands
with a Q(0,0) maxima at 755-760 nm with a small vibronic
satellite at 734 nm, and the molar extinction coefficient
(ꢀ) of the Q(0,0) band was reported for 135000-138000 M-1

Elongation of the π-System of Phthalocyanines
J . Org. Chem., Vol. 66, No. 18, 2001 6113
Ta ble 1. P h otop h ysica l Da ta for P h th a locya n in es
wavelength, nm
Q
(0-0) (log ꢀ, M-1 cm-1),
λF
b
compd
fwmh, cm-1
(Stokes shift, nm)a Φf
(OBu)8H2Pc
1c
758 (5.13)f, 1055.8g
778 (5.27), 954,5
794 (5.31), 932.0
744 (5.12), 327.0
758 (5.42), 307.8
768 (5.52), 287.7
730 (4.88), 689.5
746 (5.34), 659.3
762 (5.43), 572.6
778 (20)h
808 (30)
818 (24)
769 (25)
778 (19)
794 (26)
-
0.58i
0.81
0.49
0.74
0.69
0.60
-
2c
(OBu)8ZnPcd
1-Zn d
2-Zn d
(OBu)8CoPce
1-Coe
-
-
-
-
2-Coe
a
b
λEX ) 355 nm. Obtained using (OBu)8ZnPc in pyridine (Φf
) 0.62)16 as a standard. c In toluene. In CH2Cl2 containing 0.5
d
vol % pyridine. e In CH2Cl2. f In toluene. From ref 17. g In ethanol.
Taken from: Kaneko, Y.; Arai, T.; Sakuragi, H.; Tokumaru, K.;
Pac, C. J . Photochem. Photobiol. A: Chem. 1996, 97, 155-162.
h
i
In benzene. From ref 30. In THF. From ref 16.
cm-1 in toluene17 and benzene.30 On the other hand, the
â-(2-thienyl)-substituted analogue 1 exhibits a red-shifted
Q(0,0) band at 778 nm with the ꢀ of 187000 M-1 cm-1 in
the same media. The two Q-band feature of bare (OR)8H2-
Pc, a Q(0-0) band and a vibronic satellite, is retained, and
this Q-band shifting is attributed to the electronic
interaction between the Pc ring and 2-thienyl groups. The
red-shifting of the Q-absorption of Pcs often causes
broadening of the band,18,19 while our system maintained
the well-defined absorption structure of the (OR)8H2Pcs.
This spectroscopic behavior is observed not only in the
absorption but also in the emission spectra. The emission
band of 1 which mirrors the Q-absorption also underwent
a red-shift about 20 nm relative to the (OR)8H2Pc. These
results suggested that the introduction of 2-thienyl
groups to â positions of the (OR)8H2Pc ring prolongs the
π-system and preserves the sharpness of the spectra.
Furthermore, [2,2′-bithiophene]-5-yl-substituted 2 dis-
plays an intense Q-band at 794 and fluorescence at 818
nm, respectively. Interestingly, the Q(0-0) band of 1 and
2 with a D2h space group does not clearly split into Qx(0-0)
and Qy(0-0) compared with â-unsubstituted species, and
similar to that of the metal complexes. The full width of
the half-maximum (fwhm) value of the Q(0-0) band of the
free-bases implies that symmetrical â-substitution lowers
the D2 nature of the free-base and intensifies the D4-like
nature of the ring system. This effect is seen to a larger
extent in the longer substituent system. Besides the free-
bases, we undertook spectroscopic consideration of zinc
Pcs, a class of Pc for which spectral assignments are the
most firmly established.16,30 As is observed in bare
(OBu)8ZnPcs, both 1-Zn and 2-Zn also exhibited a
relatively small absorption band near 820 nm in addition
to the intense Q-band at 758-770 nm in pure CH2Cl2.
This longer wavelength component disappears upon the
addition of a very small amount, less than 1.0 vol %, of
pyridine to the solvent.30 Thus we have carried out the
photophysical measurements of the (OBu)8ZnPcs in CH2-
Cl2 containing 0.5 vol % pyridine. The thiophene-
substituted (OBu)8ZnPcs, 1-Zn and 2-Zn , exhibited a
sharper Q-band compared with those of the correspond-
ing free-base and cobalt derivative. The spectral events
upon thiophene substitution to the (OBu)8ZnPc nucleus
were similar to the observation in the free-base system.
Figure 2 shows a comparison of the Q-absorption and
emission of three types of zinc phthalocyanines with
different substituent lengths. The Q-absorption energy
F igu r e 2. Vis-NIR absorption (solid line) and emission
(dashed line, λex ) 355 nm) spectra of (OBu)8ZnPc (top), 1-Zn
(middle), and 2-Zn (bottom), respectively, in CH2Cl2 containing
0.5 vol % pyridine. The emission intensities are normalized
at the absorption intensity and do not reflect actual emission
intensity.
F igu r e 3. Relation between the substituent length (n) and
the Q(0-0) absorption energy of the free-base in toluene (M )
2H, 9), zinc derivatives in CH2Cl2 containing 0.5 vol % pyridine
(M ) Zn, b), and cobalt derivatives in CH2Cl2 (M ) Co, 2),
respectively.
of (OBu)8ZnPc is decreased by eight 2-thienyl substitu-
tions to about 179.4 cm-1, or 0.022 eV, and by eight [2,2′-
bithiophene]-5-yl substitutions to about 356.9 cm-1, or
0.035 eV, respectively. The Q-absorption of the Pcs
corresponds to a transition from the highest occupied
molecular orbital (HOMO) to the lowest unoccupied
molecular orbital (LUMO).16,38 Therefore, the red shift
can be explained by a decrease of the HOMO-LUMO
energy gap. Figure 3 shows the relation between the
substituent length and the Q(0-0) energy of the (OBu)8-
(36) Fabian, J .; Nakazumi, H.; Matsuoka, M. Chem. Rev. 1992, 92,
1197-1226.
(37) de la Torre, G.; Mart´ınez-D´ıaz, M. V.; Ashton, P. R.; Torres, T.
J . Org. Chem. 1998, 63, 8888-8893.
(38) Ort´ı, E.; Crespo, R.; Piqueras, M. C.; Toma´s, F. J . Mater. Chem.
1996, 6, 1751-1761.

6114 J . Org. Chem., Vol. 66, No. 18, 2001
Muto et al.
MPcs. The degree of the Q-energy lowering upon the
thienyl substitution is in inverse proportion to the
number of aromatic rings in a substituent. This implies
that the substituents smoothly decrease the HOMO-
LUMO gap by π-elongation in this region. The fwhm
value of the Q(0-0) band of each ZnPc is maintained at
the range of 287-327 cm-1. This fwhm value clearly
suggests conservation of the Q-band sharpness before and
after substitution. In addition, the substitution of
thiophene moieties to the Pc ring system tends to
intensify the ꢀ value of the Q-band, and [2,2′-bithiophene]-
5-yl groups are more effective than the 2-thienyl groups.
This hyperchromic effect also supports the π-system
enlargement in the Pcs.14 In this case, spectral changes
such as splitting or broadening of the Q-band were not
detected. This indicates that the introduction of thiophene
moieties did not affect the D4h symmetry of the Pcs. The
Φf values of the free-bases and zinc Pcs were obtained
using (OBu)8ZnPc16 as a Φf known standard, because
(OBu)8Pcs exhibit their fluorescence at the NIR region.
The Φf values of the (OBu)8Pcs decreased as the π-system
was elongated. This implies that Φf values become
smaller as the HOMO-LUMO energy gap decreases.
However, the magnitude of the Q-band shift was rela-
tively small; the spectroscopic events observed in the Pcs
were similar to those in benzoannulated Pcs such as
naphthalocyanines and anthracocyanines.13-15
F igu r e 4. Cyclic voltammograms of (A) (OBu)8ZnPc, (B) 1-Zn ,
and (C) 2-Zn in 0.3 M NBu4ClO4 in o-dichlorobenzene. Condi-
tions: [Pc] ) 1.0 mM, scan rate ) 50 mV s-1
.
Ta ble 2. Electr och em ica l Da ta for P h th a locya n in es
potential, mV vs. Ag/Ag+ in MeCN (∆E)a
The large Q-band shift of our Pcs was accompanied
with visible color change relative to bare (OBu)8MPcs.
The original green color of (OR)8Pcs originates from their
Q-absorption in the deep-red region. The Q-bands of
thiophene-substituted Pcs, particularly [2,2′-bithiophene]-
5-yl-substituted Pcs, penetrate into the NIR region, and
hence the color of the solution changes from the (OBu)8
MPc’s green to brown (2-Zn ) to red (2). Because of high
stability and strong NIR absorbing nature, the â-thienyl-
substituted (OR)8Pcs have potential for new applications
as NIR-absorbing dyes.36
compd
E1/2 (red2)
E1/2 (red1)
E1/2 (ox1) E1/2 (ox2)
(OBu)8ZnPcb
1-Zn b
-1525 (150) 240 (221) 675 (90)
-1375 (130) 180 (80)
-1350 (140) 220 (80)
668 (120)
2-Zn b
850d
(OBu)8CoPcc -1705 (190)
-455 (90)
530 (120) 718 (150)
1-Coc
2-Coc
-1640 (110)
-604 (243) 352 (107) 710 (119)
-562 (130) 350 (103)
a
b
∆E ) |Ep,c - Ep,a|. Recorded with 0.3 M Bu4NClO4 as an
electrolyte in o-dichlorobenzene with a scan rate of 50 mV s-1
.
c Recorded with 0.1 M Bu4NPF6 as an electrolyte in CH2Cl2 with
a scan rate of 50 mV s-1
.
Irreversible wave.
d
To examine the electronic states of thiophene-substi-
tuted Pcs, we undertook electrochemical studies by
means of cyclic voltammetry (CV). As described by other
groups, the HOMO-LUMO energy gap of the Pc ring
systems is estimated from the difference between the first
oxidation and the first reduction potential obtained from
the electrochemical studies,20,37-39 and this principle is
applicable to the Pcs having a main group atom(s) as a
central ion(s). The electrochemical studies for the
(OR)8ZnPcs40,41 and (OR)8CoPcs42,43 have been reported
by several groups. Figure 4A shows a preliminary CV
experiment using the â-unsubstituted (OBu)8ZnPc in 0.3
M Bu4NClO4 in o-dichlorobenzene under dark conditions.
Above the potential of +1000 mV, the complex shows an
irreversible wave and decomposes immediately. Thus, we
examined the CV studies below +900 mV. The voltam-
mogram under this condition was characterized by an
oxidation couple around +240 mV and a reduction couple
around -1525 mV, respectively. From these potentials,
the HOMO-LUMO gap of (OBu)8ZnPc was calculated at
1765 mV. This value is similar to the value reported for
Pc derivatives.39,41 Because of the anodic shift for reduc-
tion and the cathodic shift for oxidation, the HOMO-
LUMO gap of the thiophene-substituted Pc decreases as
the π-conjugation increases. The HOMO-LUMO gaps
obtained from the thiophene-substituted ZnPcs were
calculated at 1555 mV for 1-Zn and at 1570 mV for 2-Zn ,
respectively. The results of the CV experiments of
(OBu)8ZnPc, 1-Zn , and 2-Zn are summarized in Table
2. The eight 2-thienyl-substituted (OBu)8ZnPc, 1-Zn , and
the [2,2′-bithiophene]-5-yl substituted (OBu)8ZnPc, 2-Zn ,
showed a quasi-reversible first oxidation peak at 180 and
220 mV, respectively. In addition, both of the thiophene-
substituted Pcs showed the second oxidation around
+670 mV. On the other hand, these complexes were
reduced at more positive potentials than the control
experiment with (OBu)8ZnPc. A similar observation, a
decrease of the HOMO-LUMO gap, was reported for the
Pcs by others who attributed these results to π-elongation
of the extended Pcs.20
(39) Leznoff, C. C.; Lever, A. B. P. Phthalocyanines-Properties and
Applications; VCH Publishers (LSK) Ltd.: Cambridge, 1993; Vol. 3.
(40) Iijima, S.; Mizutani, F.; Asai, M.; Ichimura, K. Denki Kagaku
1989, 57, 1215-1216.
The redox potentials and reaction paths of CoPcs are
well studied and known to be affected by the nature of
the solvents.39,44 The first oxidation and second reduction
(41) Poon, K.-W.; Yan, Y.; Li, X.-Y.; Ng, D. K. P. Organometallics
1999, 18, 3528-3533.
(42) Mizutani, F.; Yabuki, S.; Iijima, S. Anal. Chim. Acta 1995, 300,
59-64.
(43) Mizutani, F.; Yabuki, S.; Iijima, S. Electroanalysis 1995, 7, 706-
709.
(44) Irvine, J . T. S.; Eggins, B. R.; Grimshaw, J . J . Electroanal.
Chem. 1989, 271, 161-172.

Elongation of the π-System of Phthalocyanines
J . Org. Chem., Vol. 66, No. 18, 2001 6115
agreement with the zinc derivatives. In addition, 1-Co
and 2-Co systems clearly exhibit the second reduction
couple at -1705 and -1640 mV, respectively. Since bare
(OBu)8CoPc lacks the second reduction peak, we only
noticed the difference between 1-Co and 2-Co, but the
difference was too small to make a comparison. As
described above, the second reduction wave of CoPcs is
assigned to the reduction peak of the Pc ligand to form
Co(I)Pc(3-).39 A remarkable trend obtained from the CV
of (OBu)8CoPcs is enhancement of the electron-donating
nature of (OBu)8CoPcs by thiophene-substitution, and
this also suggests the destabilization of the HOMOs in
the thiophene-substituted Pcs.
From the electrochemical results, the HOMO-LUMO
gap of the (OBu)8ZnPcs is narrowed about 190 mV by
the introduction of thiophene moieties. However, the
redox processes of (OBu)8Pcs have a slightly irreversible
nature; decrease of the HOMO-LUMO gap upon thio-
phene substitution is mainly ascribed to the destabilized
nature of the HOMOs.
Con clu sion s
F igu r e 5. Cyclic voltammograms of (A) (OBu)8CoPc, (B) 1-Co,
and (C) 2-Co in CH2Cl2 containing 0.1 M NBu4PF6. Condi-
The synthesis of eight 2-thienyl- and ([2,2′-bithiophene]-
5-yl)-substituted Pcs has been achieved starting from
readily available 4,5-dibromo-3,6-dibutoxyphthaloni-
trile.31 The 2-thienyl-substituted (OBu)8Pc derivatives
exhibit a red-shifted Q-band, but the spectral shape is
little influenced. Substitution of eight ([2,2′-bithiophene]-
5-yl) groups to the (OBu)8Pc nucleus further shifts the
Q-absorption to the NIR region, but the spectral features
are still retained. Interestingly, the addition of thiophene
moieties to the nucleus strongly intensifies the ꢀ values,
and the longer substituent, ([2,2′-bithiophene]-5-yl), is
more effective than the 2-thienyl group. The sufficient
Q-band shift from the deep red to the NIR region by
thiophene-substitution implies the decrease of the HO-
MO-LUMO gap by π-elongation. The CV observations
of the Pcs showed that the decrease of the HOMO-
LUMO gap was mainly attributed to the destabilized
nature of their HOMOs and that the influence of the
substituent length on the CV is small. Furthermore, the
Pcs obtained are a stable group of compounds that can
be made by a reliable synthetic procedure in good yields.
These results demonstrate a further diversity in the
effects on the Pc ring system by â-substitution and enable
potential application of the thiophene-substituted Pcs as
attractive NIR-absorbing dyes or superior photosensitiz-
ers having an intense and tunable absorption band in
the far red/NIR region.36
tions: [Pc] ) 1.0 mM, scan rate ) 50 mV s-1
.
peaks of CoPcs generally have been assigned to the ligand
oxidation and the ligand reduction potential, respectively,
in nondonating media.39 These potentials are generally
situated within potential ranges between -2000 and
+1000 mV,20 and this permits the electrochemical con-
sideration of (OBu)8Pcs from E1/2(ox1) and E1/2(red2)
values in Table 2. In addition, the electrochemical process
of the CoPcs generally contains cobaltous-centered reac-
tions.20,44 Because the redox center of this process is
enveloped by the Pc ring, this potential is influenced by
the electron-accepting/donating nature of the Pc ring. A
preliminary CV experiment of bare (OBu)8CoPc was
carried out in CH2Cl2 containing 0.1 M Bu4NPF6 between
+900 and -2000 mV. Under these conditions, (OBu)8CoPc
exhibits three redox couples at +530, +850, and -455
mV, respectively, but lacks the second reduction couple
which is present in a normal CoPc system (Figure 5A).39,44
The second oxidation, E1/2(ox2), and first reduction,
E1/2(red1), couples under these conditions are assigned
to the cobaltous-centered processes Co(II)/Co(III) and
Co(I)/Co(II), respectively.39 To evaluate the electrochemi-
cal stability of the thiophene-substituted CoPcs, we have
carried out the continuous potential sweeping of 1-Co
and 2-Co under the same condition. The electrochemical
results obtained from the cobalt complexes are sum-
marized in Table 2. The CV trace of both 1-Co and 2-Co
did not suffer any potential shift and change on the trace
shape, indicating an electrochemical stability of the Pc
derivatives under these conditions (Figure 5B and 5C).
The cobalt complexes 1-Co and 2-Co display a two-
oxidation and two-reduction couple in this region. Each
of the oxidation couples underwent a large cathodic shift
relative to bare (OBu)8CoPc. This implies the enhance-
ment of the electron-donating nature with increasing
conjugation length. However, the difference between the
1 and 2 system was not clearly detected; this result is in
Ack n ow led gm en t. This work was partially sup-
ported by a Grant-in-Aid for COE Research “Advanced
Fiber/Textiles Science and Technology” from the Min-
istry of Education, Culture, Sports, Science and Tech-
nology of J apan (No. 10CE2003).
Su p p or tin g In for m a tion Ava ila ble: UV-Vis-NIR ab-
sorption (1, 2, 1-Zn , 1-Co, 2-Zn , and 2-Co) and fluorescence
spectra (1, 2, 1-Zn , and 2-Zn ) of the new Pcs. This material is
available free of charge via the Internet at http://pubs.acs.org.
J O010384R