Electropolymerization of bithienyl-appended cerium(III) triple decker porphyrin complex

Article abstract of DOI:10.1246/cl.2003.264

A cerium(III) triple decker porphyrin complex bearing bithienyl substituents (1) at the peripheral meso-positions was synthesized. Electrochemical polymerization of the triple decker porphyrin gave a unique polymer film on the ITO electrode surface without decomposition.

Full text of DOI:10.1246/cl.2003.264

264
Chemistry Letters Vol.32, No.3 (2003)
Electropolymerization of Bithienyl-appended Cerium(III) Triple Decker Porphyrin Complex
Kousei Yamashita, Masato Ikeda, Masayuki Takeuchi,ꢀ and Seiji Shinkaiꢀ
Department of Chemistry and Biochemistry, Graduate School of Engineering, Kyushu University, 6-10-1 Hakozaki, Higashi-ku,
Fukuoka 812-8581
(Received December 16, 2002; CL-021065)
A cerium(III) triple decker porphyrin complex bearing
bithienyl substituents (1) at the peripheral meso-positions was
synthesized. Electrochemical polymerization of the triple decker
porphyrin gave a unique polymer film on the ITO electrode
surface without decomposition.
Electropolymerization of metal complexes has attracted
much attention for applications to electroluminescent devices,
sensors, andelectrochromic coatings.1 Since thiophene andoligo-
thiophene derivatives can be easily oxidized because of their
a; a0-coupling reactions, their electropolymerization has fre-
quently been investigated.2 Several groups have recently ex-
plored the electropolymerization of metal complexes
incorporating oligothienyl substituents. Shimidzu et al. have
investigated the electropolymerization of phosphorus(V) por-
phyrin bearing an axial oligothienylalkoxy ligand and metallo-
porphyrin bearing oligothienyl substituents at the meso-
positions.3 Swager et al. have electropolymerized a number of
metal-salen complexes bearing oligothienyl substituents.4 Shirai
et al. and Swager et al. independently reported metallophthalo-
cyanine bearing oligothiophenyl substituents.5 Our current
interest is focused on the construction of supramolecular
architectures based on lanthanoid metal double and triple decker
porphyrin complexes, which are now considered to be a potential
function unit for the construction of a multibit information storage
system.6;7 Lanthanoid metal porphyrin complexes adopt double
decker or triple decker type structures and possess multiple redox
potentials.8{11 Introduction of the lanthanoid metal porphyrin
complexes to polymer architectures will, therefore, impart a
variety of functions to the resultant polymers. Since these
porphyrin units in the lanthanoid metal porphyrin complex would
act as rotating pillars, one may expect that the resultant polymer
matrixes should show the very unique superstructures as well as
the redox potentials. Here we describe an electrochemical
construction of a new triple decker porphyrin polymer film on
the ITO glass electrode utilizing oxidative couplings between the
bithienyl substituents, as a preliminary step toward constructing
such a multibit information storage system.
The synthetic route of 1 is shown in Scheme 1. Bromination
of 3-hexylthiophene using NBS in CHCl3–AcOH gave 2-bromo-
3-hexylthiophene in 97% yield. The Grignard reagent prepared
from 2-bromo-3-hexylthiophene was used for the subsequent
coupling reaction with 2-bromo-3-hexylthiophene in the pre-
sence of Ni(dppp)Cl2 as a catalyst to obtain 3,30-dihexyl-2,20-
bithiophene (overall yield: 63%). Monoformylation of 3,30-
dihexyl-2,20-bithiophene using POCl3/DMF (Vilsmeier reagent)
gave 3,30-dihexyl-5-formyl-2,20-bithiophene in 71% yield.12
5,10-Bis(3,30-dihexyl-2,20-bithieno-5-yl)porphyrin was obtained
from 3,30-dihexyl-5-formylbithiophene and dipyrromethane
using the method (TFA as an acid-catalyst and DDQ as an
Scheme 1. (i) NBS, CHCl3–AcOH, 97%, (ii) Mg/C2H4Br2, Et2O, (iii)
2-bromo-3-hexylthiophene, Ni(dppp)Cl2, Et2O, 63%, (iv) POCl3/
DMF, CH2ClCH2Cl, then NaHCO3, 71%, (v) TFA, CH2Cl2, then
DDQ, 28%, (vi) Ce(acac)3Á3H2O, 1,2,4-trichlorobenzene, 15%.
oxidant) described previously.13 Refluxing of the porphyrin
ligand in 1,2,4-trichlorobenzene with Ce(acac)3Á3H2O afforded a
cerium(III) triple decker porphyrin 1 in 15% yield.8;11 Analyti-
cally pure 1 was obtained as a green solid by column
chromatography (silica gel, eluent:chloroform and Bio-beads
SX-3) and characterized by MALDI TOF MS, FAB-MS, and
elemental analysis.14
The compound 1 was soluble in organic solvents such as
CH2Cl2, CHCl3, and hexane. The absorption spectrum of 1 in
CH2Cl2 shows a p-pꢀ absorption band of bithienyl moieties at
334.0nm, a Soret band at 405.0nm, which was blue-shifted about
12.0nm from that of free-base porphyrin (417.0nm), and Q bands
at 548.0and 594.0nm. The shape of the absorption spectrum was
consistent with that of cerium (III) triple decker porphyrin
reported previously.8;11 These spectral results indicate that there
is no significant electronic interaction between porphyrin rings
and bithienyl moieties in 1 at their ground states.
The cyclic voltammogram (CV) of 1 in CH2Cl2 revealed
three separated redox waves (0.59, 0.89, and 1.20 V vs. Ag/Agþ)
in the first scan as shown in Figure 1 (bold line). The oxidation
waves at 0.59 V and 1.20 V are assignable to the oxidation of
cerium (III) triple decker porphyrin.8 The potential peak at 0.89 V
is assigned to the oxidation of bithienyl moieties because this
value is consistent with that for 5,10-bis(3,30-dihexyl-2,20-
bithieno-5-yl)porphyrinato zinc(II) (0.82 V). Compound 1 was
oxidatively polymerized (plain line in Figure 1) when the
potential of the electrode was cycled between 0and 1.4 V versus
Copyright Ó 2003 The Chemical Society of Japan

Chemistry Letters Vol.32, No.3 (2003)
265
the Ag/Agþ couple at a scan rate of 50mV/s (condition; working
electrode: ITO glass electrode, counter electrode: Pt wire,
reference electrode: Ag/Agþ, solvent: CH2Cl2, electrolyte:
0.1 mol dmꢁ3 TBAPF6). Poly(1) is highly crosslinked owing to
the presence of the six unsubstituted sites on the terminal
thiophenes that are active toward polymerization. Figure 1 shows
a polymerization trace of 1. The cycling of the electrode
potentials results in the increase of electroactivity, indicating
that insoluble polymer deposition on the electrode surface.
Figure 1 (dashed line) shows the CV of the polymer film
deposited on ITO glass electrode in TBAPF6-CH2Cl2 in the
absence of monomer 1. Three characteristic redox waves (0.34,
0.79, and 1.20 V) were observed, which are attributed to
cerium(III) triple decker porphyrin. These results demonstrate
that the polymer film deposited on ITO glass electrode is
comprised of cerium(III) triple decker porphyrins and has unique
multiple redox potentials.
electrode utilizing electro-oxidative polymerization of dithienyl
substituents in 1. Further investigation into the redox or
photophysical properties of the polymers will lead to more
interesting applications.
References and Notes
1
2
3
a) M. O. Wolf, Adv. Mater., 13, 545 (2001). b) M. O. Wolf and Y. Zhu,
Adv. Mater., 12, 599 (2000). c) R. P. Kingsborough and T. M. Swager,
Prog. Inorg. Chem., 48, 123 (1999). d) A. Deronzier and J. C. Moutet,
Coord. Chem. Rev., 147, 339 (1996)
a) ‘‘Handbook of Conducting Polymers,’’ ed. by T. A. Skotheim, R. L.
Elsenbaumer, and J. R. Reynolds, Marcel Dekker, New York (1998). b)
R. D. McCullough, Adv. Mater., 10, 93 (1998). c) J. Roncali, Chem. Rev.,
92, 711 (1992).
a) H. Segawa, N. Nakayama, and T. Shimidzu, J. Chem. Soc., Chem.
Commun., 1992, 784. b) H. Segawa, F. P. Wu, N. Nakayama, H.
Maruyama, S. Sagisaka, N. Higuchi, M. Fujitsuka, and T. Symidzu,
Synth. Met., 71, 2151 (1995). c) T. Shimidzu, Synth. Met., 81, 235 (1996).
d) T. Shimidzu, H. Segawa, F. Wu, and N. Nakayama, J. Photochem.
Photobiol., A, 92, 121 (1995).
4
5
a) R. P. Kingsborough and T. M. Swager, Adv. Mater., 10, 1100 (1998).
b) R. P. Kingsborough and T. M. Swager, J. Am. Chem. Soc., 121, 8825
(1999).
a) T. Muto, T. Temma, M. Kimura, K. Hanabusa, and H. Shirai, Chem.
Commun., 2000, 1649. b) T. Muto, T. Temma, M. Kimura, K. Hanabusa,
and H. Shirai, J. Org. Chem., 66, 6109 (2001). c) R. P. Kingsborough and
T. M. Swager, Angew. Chem., Int. Ed., 39, 2897 (2000).
6
7
M. Ikeda, A. Sugasaki, Y. Kubo, K. Sugiyasu, M. Takeuchi, and S.
Shinkai, Chem. Lett., 2001, 1266.
a) S. Shinkai, M. Ikeda, A. Sugasaki, and M. Takeuchi, Acc. Chem. Res.,
34, 494 (2001). b) M. Takeuchi, M. Ikeda, A. Sugasaki, and S. Shinkai,
Acc. Chem. Res., 34, 865 (2001). c) M. Takeuchi, T. Imada, and S.
Shinkai, Angew. Chem., Int. Ed. Engl., 37, 2096 (1998). d) M. Takeuchi,
T. Imada, and S. Shinkai, Tetrahedron Lett., 39, 7897 (1998). e) M.
Ikeda, M. Takeuchi, A. Sugasaki, A. Robertson, T. Imada, and S.
Shinkai, Supramol. Chem., 12, 321 (2000). f) M. Ikeda, T. Tanida, M.
Takeuchi, and S. Shinkai, Org. Lett., 2, 1803 (2000). g) A. Sugasaki, M.
Ikeda, M. Takeuchi, and S. Shinkai, Angew. Chem., Int. Ed. Engl., 39,
3839 (2000). h) A. Sugasaki, K. Sugiyasu, M. Ikeda, M. Takeuchi, and S.
Shinkai, J. Am. Chem. Soc., 123, 10239 (2001). i) M. Ikeda, M. Takeuchi,
S. Shinkai, F. Tani, Y. Naruta, S. Sakamoto, and K. Yamaguchi, Chem.—
Eur. J., 8, 5541 (2002).
Figure 1. Cyclic voltammogram of 1 at the ITO electrode in
0.1 mol dmꢁ3 TBAPF6/CH2Cl2 solutions at a scan rate of 50mV/s
(plain line, the electroactivity of 1 increases during 15 cycles) and
cyclic voltammogram of poly(1) (dashed line).
The absorption spectrum was measured for poly(1) film
deposited on the ITO electrode (Figure 2). A sharp Soret band
(409.0nm) accompanied by a broad Q band (587.0nm), which is
characteristic for cerium (III) triple decker porphyrin, were
observed.8;11 These spectral data firmly established that the
polymer film of cerium(III) triple decker porphyrin (poly(1)) on
ITO glass electrode has been obtained by the oxidative electro-
polymerization without decomposition.
8
9
a) J. W. Buchler, A. De Cian, J. Fischer, M. Kihn-Botulinski, H. Paulus,
and R. Weiss, J. Am. Chem. Soc., 108, 3652 (1986). b) D. K. P. Ng and J.
Jiang, Chem. Soc. Rev., 26, 433 (1997). c) J. W. Buchler and D. K. P. Ng,
in ‘‘The Porphyrin Handbook,’’ ed. by K. M. Kadish, K. M. Smith, and R.
Guilard, Academic Press, San Diego (2000), Vol. 3, Chap. 20 and
references cited therein.
Photo- and redox-driven ligand rotational activities of cerium(IV)
double decker porphyrin complexes have been investigated by Aida et
al.; a) K. Tashiro, K. Konishi, and T. Aida, Angew. Chem., Int. Ed. Engl.,
36, 856 (1997). b) K. Tashiro, T. Fujiwara, K. Konishi, and T. Aida,
Chem. Commun., 1998, 1121. c) K. Tashiro, K. Konishi, and T. Aida, J.
Am. Chem. Soc., 122, 7921 (2000).
In conclusion, wehave demonstrated a new synthetic strategy
for constructing a polymer film of cerium(III) triple decker
porphyrin, which has multiple redox potentials, on the ITO
10a) T. Gross, F. Chevalier, and J. S. Lindsey, Inorg. Chem., 40, 4762
(2001). b) D. Gryko, J. Li, J. R. Diers, K. M. Roth, D. F. Bocian, W. G.
Kuhr, and J. S. Lindsey, J. Mater. Chem., 11, 1162 (2001). c) T. F.
´
Magnera, L. M. Peslherbe, E. Korblova, and J. Michl, J. Organomet.
¨
Chem., 548, 83 (1997).
11 H. Miwa, N. Kobayashi, K. Ban, and K. Ohta, Bull. Chem. Soc. Jpn., 72,
2719 (1999).
12 a) F. Wurthner, M. S. Vollmer, F. Effenberger, P. Emele, D. U. Meyer, H.
¨
Port, and H. C. Wolf, J. Am. Chem. Soc., 117, 8090 (1995). b) M. S.
Vollmer, F. Wurthner, F. Effenberger, P. Emele, D. U. Meyer, T.
¨
¨
Stumpfig, H. Port, and H. C. Wolf, Chem.—Eur. J., 4, 260(1998).
13 Q. M. Wang and D. W. Bruce, Synlett., 1995, 1267.
14 1: Mp; 144.2–148.6 ꢂC, GPC (TSKgel G3000H-TSKgel G4000H,
CHCl3, 0.50 mL/min, monitored at 400 nm) retention time 34.7 min,
MALDI TOF MS (CHCA) m=z 3198.58 ([M+H]þ = 3198.12), FAB MS
m=z 3198.12 ([M+H]þ = 3198.1167), UV-vis (CH2Cl2): lmax (log ")
334.0 (4.80), 405.0 (5.48), 548.0 (0.91), 594.0 (0.91), Calcd. for
Ce2C180H204N12S12Á0.5CHCl3: C, 66.49; H, 6.33; N, 5.16%; Found: C,
66.61; H, 6.63; N, 4.83%.
Figure 2. The absorption spectrum of poly(1) film deposited on the
ITO electrode.