A new phthalocyanine derivative having peripheral 2-thienyl substituents

Article abstract of DOI:10.1039/b004694i

A phthalocyanine derivative having eight 2-thienyl substituents at the β-position was synthesized and electro-chemical oxidation of the phthalocyanine gave an insoluble polymer film on the electrode surface.

Full text of DOI:10.1039/b004694i

A new phthalocyanine derivative having peripheral 2-thienyl substituents
Tsuyoshi Muto, Tetsuji Temma, Mutsumi Kimura, Kenji Hanabusa and Hirofusa Shirai*
Department of Functional Polymer Science, Faculty of Textile Science and Technology, Shinshu University, Ueda,
Nagano 386-8567, Japan. E-mail: hshirai@giptc.shinshu-u.ac.jp
Received (in Cambridge, UK) 9th June 2000, Accepted 24th July 2000
A phthalocyanine derivative having eight 2-thienyl sub-
stituents at the b-position was synthesized and electro-
chemical oxidation of the phthalocyanine gave an insoluble
polymer film on the electrode surface.
p-Conjugated polymers such as polythiophenes or poly-
phenylenes have been the subject of intensive studies.1 Due to
the high stability of the polymers, they are readily characterized
by chemical or physical methods, making them good candidates
for electronic or photonic devices. Polythiophenes are the type
most frequently investigated because they are easily obtained
from chemical reactions2 or electrochemical couplings of
thiophene derivatives,3 and the monomers or precursors are
readily derived by conventional synthetic methods from
thiophene.4 Recently, several groups reported the design of
novel conducting polymer architectures which alternatively
contain functional moieties and aaA-coupled oligothiophene
moieties.5 The wide range of these studies contributed towards
the application of the polymers as organic semiconductors,
sensory materials or electrocatalysts.6 Our current interest in
this class of materials is motivated by the property of the
attractive characteristics, endowed by functional molecules
embedded in the polymer backbone, for the development of
electronic devices. Phthalocyanines or phthalocyanine metal
Scheme 1 (i) Thiophene-2-boronic acid, Pd(0)(PPh)4, toluene, THF,
complexes are known to have a diversity of functions such as
electrocatalysts or organic electronic devices.7 Therefore,
EtOH, 2 M Na2CO3 aq., reflux under N2, 18 h, 62%; (ii) NaOMe, MeOH,
reflux under NH3 gas, 5 h, 95%; (iii) N,N-dimethylaminoethanol, reflux
under N2, 36 h, 32%.
introduction of phthalocyanine moieties to the new polymer
architectures imparts a variety of functions to the polymers. In
this communication we demonstrate the synthesis, photo- and
The pc derivative 1 was oxidatively polymerized when the
potential of the electrode was swept between 0.0 and +1.1 V vs.
Ag/Ag+ at a scan rate of 100 mV s21. [Working electrode,
indium/tin oxide coated glass (ITO) electrode; Counter elec-
trode, Pt wire; Reference electrode, Ag/Ag+; Solvent, 0.1 M
tetra-n-butylammonium hexafluorophosphate (TBAPF6)–
CH2Cl2]. An anodic polymerization trace of 1 is shown in
Fig. 1. The first oxidative scan is characterized by monomer
electrochemical properties of a new phthalocyanine (pc)
derivative which has thiophene moieties as substituents, and the
electrochemical construction of a pc-based polymer film
deposited on the electrode surface.
The synthetic route to 1 used 4,5-dibromophthalonitrile8 as
starting material which was converted into 4,5-di-2-thienyl-
phthalonitrile with thiophene-2-boronic acid9 in the presence of
Pd(0)(PPh3)4 under basic conditions (Scheme 1). Refluxing of
4,5-di-2-thienylphthalonitrile with NaOMe in MeOH gave
5,6-di-2-thienyl-2,3-dihydro-1,3-diiminoisoindole, and the re-
action of this compound in N,N-dimethylaminoethanol at
140 °C gave 1 as a dark-green solid. Analytically pure 1 was
obtained by column chromatography of the crude product on
silica gel by eluting with CH2Cl2–n-hexane (2/1 v/v). This new
1
pc derivative 1 was characterized by H NMR and MALDI-
TOF mass spectrometry.†
The pc derivative 1 was soluble in common organic solvents
such as CH2Cl2, CHCl3, THF and DMF but not in hexane,
toluene or acetonitrile. The shape of absorption and emission
spectra of 1 in CHCl3 were similar to that of tetrakis(tert-
butyl)phthalocyanine (tBupc) except for a broad absorption
around 430 nm and a weak, structureless emission peak
centered around 500 nm. The position of both absorption and
emission bands of 1 were red-shifted about 20 nm from that of
t
the corresponding Bupc. These results obtained from the
Fig. 1 Trace of oxidative scan of 1 ([1] = 2 3 1024 M) in 0.1 M TBAPF6–
CH2Cl2 with ITO glass electrode (left) and cyclic voltammogram of poly(1)
film deposited on ITO glass electrode in 0.1 M TBAPF6–CH3CN (right).
Conditions: 0.1 V s21, Pt wire counter electrode; Ag/Ag+ reference
electrode.
photophysical measurements are consistent with the presence of
electronic interaction between the pc ring and 2-thienyl
substituents in a molecule of 1 at their ground and excited
states.
DOI: 10.1039/b004694i
Chem. Commun., 2000, 1649–1650
This journal is © The Royal Society of Chemistry 2000
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From these observations, we assume that poly(1) in the oxidized
state has intermediary effective conjugation length of oxidized
oligothiphenes and oxidized polythiophenes.
In conclusion, we have synthesized a new pc derivative 1 and
constructed a p-conjugated polymer film by electrochemical
oxidation of 1. The p-conjugation length of the polymer was
switched between pc-like and oligothiophene-like by applica-
tion of the appropriate voltage. Since this switching is
accompanied by a color change at the applied potential between
0 and +0.8 V vs. Ag/Ag+, the polymer has potential electro-
chromic material applications.11
This work was supported by a Grant-in-Aid for COE
Research ‘Advanced Fiber/Textile Science and Technology’
(No. 10CE2003) and Scientific Research (No. 11450366) from
the Ministry of Education, Science, Sports, Culture of Japan.
Fig. 2 In situ UV-Vis-NIR absorption spectra of poly(1) on ITO electrode
upon applied potential (top): (a) 0.0 V vs. Ag/Ag+; (b) +0.3 V; (c) +0.5 V;
(d) +0.6 V; (e) +0.7 V; (f) + 0.8 V. Difference spectra obtained from the data
of the in situ spectra (bottom). The neutral-point spectrum (V = 0.0 V) was
used as the reference.
Notes and references
† Selected data for 1: (400 MHz, CDCl3, 298 K, TMS): dH = 6.96 (br, 8H),
7.04 (br, 8H), 7.36 (br, 8H), 8.12 (br, 8H); MALDI-TOF spectrum m/z
calcd. for (C64H34N8S8) 1171.5, found 1172.6. UV/Vis (in CH2Cl2): lmax
(log e)
= 724 (5.018), 692 (5.033), 662 (4.782), 634 (4.585), 364
(4.865).
oxidation at +0.60 and +0.90 V followed by associated
reduction at +0.45 and +0.75 V in the return process. The first
oxidation wave observed in the oxidative trace of 1 is attributed
to the oxidation of free-base pc10 and the second could be
attributed to the oxidation of 2-thienyl substituents at the b-
position. In subsequent potential sweeps, an oxidation wave
grows in around +0.70 V. Applied potential cycling results in
further increased electroactivity of the electrode, indicative of
insoluble polymer deposition on the electrode surface.5 The
cyclic voltammogram (CV) of the electrochemical deposited
polymer (poly(1)) in monomer-free 0.1 M TBAPF6–CH3CN is
shown in Fig. 1. The CV is characterized by the appearance of
an oxidation wave at +0.4 V and a redox couple at +0.70 V. The
observed difference between the redox potentials of monomer 1
and poly(1) is in agreement with the difference in p-conjugation
length elongated in the polymerization and oxidation proc-
esses.
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The in situ electronic absorption measurement of poly(1) film
deposited on the ITO electrode recorded at various doping
levels shows that the transition around 360 nm and pc Q-band
absorption (lmax
= 634, 662, 692, 724 nm) decreases
continuously as doping proceeds while two new absorption
bands appear around 560 and 950 nm (Fig. 2). In the absorption
of poly(1) film at high doping levels, the new lower energy p–
p* transition11 around 950 nm was promoted and grew as
shown in Fig. 2. The optoelectrochemical behavior observed in
our system is assigned to formation of oxidized states of poly(1)
and the effective conjugation paths include a pc ring system and
aaA-bithienyl bridges have been formed. The position of the
lower energy p–p* absorption maximum is close to that
reported for cation radicals of oligothiophenes, but the shape of
the band is broader than that of oligothiophene cation radicals.12
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Chem. Commun., 2000, 1649–1650