π-conjugated poly(aryleneethynylene)s consisting of salophen and Ni-salophen units in the π-conjugated main chain: Preparation and chemical properties

Article abstract of DOI:10.1021/ma101800f

π-Conjugated poly(aryleneethynylene)s consisting of N,N′- bis(salicylidene)-1,2-phenylenediamine (salophen) units (Poly-1-Poly-3) and salophen-nickel complex units (Poly-1-Ni) were prepared in high yields by the palladium-catalyzed polycondensation of H-≡

Full text of DOI:10.1021/ma101800f

10366 Macromolecules 2010, 43, 10366–10375
DOI: 10.1021/ma101800f
π-Conjugated Poly(aryleneethynylene)s Consisting of Salophen and
Ni-Salophen Units in the π-Conjugated Main Chain: Preparation
and Chemical Properties
Hiroki Fukumoto,* Kazuto Yamane, Yumiko Kase, and Takakazu Yamamoto*
Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku,
Yokohama 226-8503, Japan
Received August 6, 2010; Revised Manuscript Received November 19, 2010
ABSTRACT: π-Conjugated poly(aryleneethynylene)s consisting of N,N0-bis(salicylidene)-1,2-phenylene-
diamine (salophen) units (Poly-1-Poly-3) and salophen-nickel complex units (Poly-1-Ni) were prepared in
high yields by the palladium-catalyzed polycondensation of H-t-Ar-t-H (Ar = fluorene or 2,5-dialkoxy-
p-phenylene) with dibromo compounds of salophen (Br2-Salophen) and its nickel complex (Br2-Salophen-Ni),
respectively. The Ni-free polymers (Poly-1-Poly-3) showed good solubility in CHCl3 and THF, had high
thermal stability, and exhibited number-average molecular weights (Mn) of 9200-14000 in GPC analysis.
The UV-vis spectra of the polymers showed π-π* transition peaks at about 420 nm, which was comparable
to those of poly(p-phenyleneethynylene)s. The UV-vis spectrum of Poly-1-Ni exhibited additional
intermediate and small peaks at about 480 and 600 nm, which were assigned to a charge-transfer (CT)
electronic transition and a d-d transition, respectively. The complexation of Poly-1 with Ni2þ proceeded
clearly and quantitatively to give Poly-1-Ni, as monitored by UV-vis spectroscopy. Both the Ni-free and
Ni-containing polymers were electrochemically active, and CV (cyclic volammetry) scans of the polymers
showed a reduction peak of the salophene unit at approximately -2.2 V vs Agþ/Ag and an oxidation peak of
the salophene unit at about 0.8 V vs Agþ/Ag.
Introduction
following polythiophenes with salophen-Cu complex side chains by
electrochemical polymerization:5
Metal complexes of π-conjugated polymer ligands (e.g., Ru2þ
complex of poly(2,20-bipyridine-5,50-diyls)s) have been the subject
of many studies.1,2 Since π-conjugated polymers have mobile elec-
trons along the polymer main chain, metal-containing π-conjugated
polymers show interesting chemical and physical properties such
as high catalytic activity,1,2a-2d electrical conductivity,2d-f and
metal-controlled light-emitting1,2g properties.
Bis(salicylidene)ethylenediamine (salen) and salophen shown
in Chart 1 are typical metal-complex-forming ligands and their
metal complexes have long been studied. Some of the metal
complexes of salen and salophen have been used as catalysts for
organic synthesis.3
The synthesis of polymers containing the salen or salophen
unit4a,b or their metal complexes4a,c-k,5 in aromatic main chains
has been reported as shown in Chart 2.
Most of the salen or salophen unit in the reported polymers
is connected at the p-positions of the phenolic groups, and
π-conjugation is not thought to be extended along the polymer
main chain. Actually, UV-vis data of the polymers have shown
no expanded π-conjugated system along the polymer main chain.
When the salophen unit is linked at m-positions of the phenolic
groups, expansion of π-conjugated system become possible;4c
however, examples of expansion of the π-conjugation system
through the salophen unit in polymers are not many.
This polymer possesses a thiophene analogue of the salophene
unit at the center of the terthiophene unit and has extended
π-conjugation along the polymer main chain. To reveal basic
chemical properties of π-conjugated polymers consisting of the
salophen unit or its metal complex, we have synthesized the
following poly(aryleneethynylene)6 polymers (Chart 3) as well as
their dialkoxy-p-phenylene analogues.
We now report results of the synthesis and chemical properties
of the polymers.
Experimental Section
Materials and Measurements. 3,6-Dibromo-1,2-diaminoben-
zene (1),7 2,7-diethynyl-9,9-dioctylfluorene,8 3-bromo-4,5-diamino-
10
toluene,9 and Pd(PPh3)4 were prepared according to the
literature. 1H NMR spectra were recorded on a JEOL EX-400
or a JEOL Lambda-300 spectrometer. UV-vis and photolumi-
nescence (PL) spectra were measured with a Shimadzu UV-
3100PC spectrometer and a Hitachi F-4010 spectrometer, re-
spectively. The quantum yield (Φ) of the PL was calculated
By contrast, connecting salophen at the 3- and 6-positions
(cf. Chart 1) can give a fully π-conjugated poly(p-phenylene) type
polymer. Reynolds and co-workers reported the synthesis of the
using a quinine sulfate standard (Φ = 54.6% at ca. 10-5
M
solution in 0.5 M H2SO4). IR spectra were recorded on a JASCO
FT/IR 460 PLUS spectrometer. High-resolution mass spectra
*Corresponding authors. E-mail: tyamamot@res.titech.ac.jp (T.Y.);
hfukumot@res.titech.ac.jp (H.F.).
pubs.acs.org/Macromolecules
Published on Web 12/03/2010
r 2010 American Chemical Society

Article
Macromolecules, Vol. 43, No. 24, 2010 10367
(HRMS) were obtained with a JEOL JMS-700 analyzer. TGA
curves were taken using a Shimadzu thermometric TGA-50 system.
Elemental analysis was carried out using a LECO CHNS-932
analyzer and a Yanako YS-10 SX-Elements microanalyzer. Gel
permeation chromatography (GPC) was performed with a Toso
HLC-8120 system using THF as the eluent, and molecular weights
were estimated using polystyrene standards. The microanalysis
of Ni in Poly-1-Ni was carried out using a Shimadzu ICPS-8100
sequential plasma spectrometer at the Center for Advanced
Materials Analysis (Suzukakedai), Technical Department, Tokyo
Institute of Technology. Poly-1-Ni was decomposed in fuming
nitric acid, and an aqueous solution for Ni analysis was obtained.
Cyclic voltammetry (CV) was performed with a Toyo Technica
Solartron SI-1287 electrochemical interface. Spectro-electrochemical
measurements were carried out using a polymer film-coated ITO
(indium-tin-oxide) working electrode, a Pt counter electrode,
and an Agþ/Ag reference electrode; the measuring system was
controlled by using a Hokuto Denko HSV-100 electrochemical
interface and the spectroscopic changes were followed with a
Shimadzu UV-3100PC spectrometer.
Synthesis of Monomers (cf. Scheme 1). Br2-Salophen. To an
ethanol solution (10 mL) of 1 (2.00 g, 7.5 mmol) salicylaldehyde
(1.85 g, 15.1 mmol) was added at 70 °C, and the mixture was
stirred at 80 °C for 2 h. After cooling to room temperature (rt),
a yellow precipitate was collected by filtration and dried under
reduced pressure to give a precursor compound 2 for Br2-
Salophen. Yield =2.38 g (86%). 1H NMR (400 MHz, CDCl3): δ
12.29 (s, 1H, OH), 8.56 (s, 1H, -CHdN-), 7.45 (ddd, 1H, J=
7.8, 7.3, and 1.5 Hz), 7.39 (dd, 1H, J=7.8 and 1.5 Hz), 7.15 (d,
1H, J=8.3 Hz), 7.07 (dd, 1H, J=7.8 and 1.1 Hz), 6.99 (ddd, 1H,
J = 7.8, 7.3, and 1.1 Hz), 6.92 (d, 1H, J = 8.3 Hz), 4.24 (s, 2H,
NH2). Anal. Calcd for C13H10Br2N2O: C, 42.20; H, 2.72; Br,
43.19; N, 7.57. Found: C, 42.31; H, 2.69; Br, 43.59; N, 7.60.
HRMS calcd for C13H10Br2N2O: 368.9238 (M þ Hþ). Found:
368.9229 (M þ Hþ). FT-IR (KBr): 3484, 3385, 1624, 1457, 1269,
1151, 1054, 916, 755 cm-1
.
Salicylaldehyde (1.22 g, 10.0 mmol) was added to an ethanol
solution (10 mL) of 2 (1.86 g, 5.0 mmol) at 90 °C, and the mixture
was stirred at 90 °C for 1 h. After cooling to room temperature,
a yellow precipitate was separated by filtration and recrystallized
from chloroform-methanol at 0 °C to afford a bright yellow
solid of Br2-Salophen (1.54 g, 65%). 1H NMR (400 MHz,
DMSO-d6): δ 11.68 (s, 2H, OH), 8.75 (s, 2H, -CHdN-), 7.56
(dd, 2H, J=7.8 and 1.5 Hz), 7.52 (s, 2H), 7.39 (ddd, 2H, J=8.3,
7.8, and 1.5 Hz), 6.91 (dt, 2H, J=7.8 and 1.0 Hz), 6.90 (dd, 2H,
J=8.3 and 1.0 Hz). Anal. Calcd for C20H14Br2N2O2: C, 50.66;
H, 2.98; Br, 33.70; N, 5.91. Found: C, 50.45; H, 3.12; Br, 34.05;
Chart 1. Salen and Salophen
N, 5.94. FT-IR (KBr): 1618, 1270, 907, 750 cm-1
Br2-Salophen-Ni. To an ethanol solution (10 mL) of Ni(OAc)2
.
Chart 2. Reported Polymers of Salen and Salophen
3
4H2O (0.262 g, 1.1 mmol) a THF (2 mL) solution of Br2-
Salophen (0.430 g, 0.91 mmol) was added at 70 °C, and the reac-
tion mixture was stirred at 70 °C for 10 min. Cooling to room
temperature gave dark green microcrystals. They were collected
by filtration and dried under reduced pressure. Yield = 0.46 g
(96%). 1H NMR (400 MHz, CDCl3): δ 9.04 (s, 2H, -CHdN-),
7.32 (ddd, 2H, J=8.8, 7.8, and 2.0 Hz), 7.28 (dd, 2H, J=7.8 and
2.0 Hz), 7.24 (s, 2H), 7.11 (dd, 2H, J = 8.8 and 1.0 Hz), 6.63
(dt, 2H, J=7.8 and 1.0 Hz). Anal. Calcd for C20H12Br2N2NiO2:
C, 45.25; H, 2.28; Br, 30.11; N, 5.28. Found: C, 45.10; H, 2.46;
Br, 29.62; N, 5.33. FT-IR (KBr): 1606, 1517, 1443, 1189, 1153,
Chart 3. Synthesized π-Conjugated Salophen Polymers
956, 567, 463 cm-1
.
The one-pot reaction of salicylaldehyde (2.83 g, 23.2 mmol),
1 (2.98 g, 11.2 mmol), and Ni(OAc)2 4H2O (3.04 g, 12.2 mmol) in
ethanol (10 mL) at 70 °C for 40 min also gave Br2-Salophen-Ni
3
1
in 90% (5.3 g) yield. H NMR data of Br2-Salophen-Ni pre-
pared by this one-pot reaction agreed with that of the Ni complex
obtained by the reaction of Br2-Salophen and Ni(OAc)2 4H2O.
3
Scheme 1. Synthetic Routes to the Monomersa
a Key: (i) salicylaldehyde (2 equiv), EtOH, 80 °C, 2 h; (ii) salicylaldehyde (2 equiv), EtOH, 90 °C, 1 h; (iii) Ni(OAc)2 4H2O, EtOH, 70 °C, 10 min;
3
(iv) salicylaldehyde (2 equiv), Ni(OAc)2 4H2O, EtOH, 70 °C, 40 min.
3

10368 Macromolecules, Vol. 43, No. 24, 2010
Fukumoto et al.
Scheme 2. Synthetic Routes to Polymersa
a Key: (i) Pd(PPh3)4, CuI, Et3N, THF, 70 °C, 24 h; (ii) Pd(PPh3)4, CuI, Et3N, toluene, 70 °C, 48 h; (iii) Ni(OAc)2 4H2O, EtOH, 70 °C, 10 min. A mono-
3
bromo salophen-Ni group is considered to be a major terminal group (A and B) of Poly-1-Ni (cf. the text).
Synthesis of Polymers (cf. Scheme 2). Poly-1. A mixture of
Br2-Salophen (0.25 g, 0.53 mmol), 2,7-diethynyl-9,9-dioctyl-
fluorene (0.23 g, 0.52 mmol), Pd(PPh3)4 (35 mg, 0.03 mmol), CuI
(5 mg, 0.03 mmol), triethylamine (10 mL), and THF (25 mL) was
stirred at 70 °C for 24 h. The reaction mixture was cooled to room
temperature and poured into methanol to obtain a precipitate,
which was collected by filtration and dissolved in THF. The
THF solution was poured into methanol, and the precipitate was
collected. The precipitate was dissolved in THF again, and the
Synthesis of Polymers Containing Ni. Poly-1-Ni. Toluene
(47 mL) and triethylamine (18 mL) were added to a mixture of
Br2-Salophen-Ni (0.25 g, 0.47 mmol) and 2,7-diethynyl-9,9-
dioctylfluorene (0.21 g, 0.48 mmol), Pd(PPh3)4 (27 mg, 0.023 mmol),
and CuI (4.5 mg, 0.023 mmol), and the reaction mixture was
stirred at 70 °C for 48 h. After cooling to room temperature, the
reaction mixture was poured into methanol to obtain a reddish-
brown precipitate. The product was collected by filtration, washed
with an aqueous solution of EDTA 2Na and acetone repeatedly,
3
THF solution was poured into an aqueous solution of EDTA
and dried under reduced pressure to afford a reddish-brown powder
3
1
2Na (EDTA = ethylenediaminetetraacetate). The brown pre-
cipitate was separated by filtration, washed with acetone re-
peatedly, and dried under reduced pressure to yield a brown
powder of Poly-1 (0.38 g, 96%). 1H NMR (300 MHz, CDCl3): δ
12.77 (2H, OH), 8.95 (2H, -CHdN-), 7.50-6.97 (16H), 1.70
(4H), 1.10 (20 H), 0.81 (6H), 0.49 (4H). Anal. Calcd for
(C53H54N2O2)n: C, 84.76; H, 7.25; N, 3.73. Found: C, 83.33; H,
7.25; N, 4.01; Br, 0.00. FT-IR (KBr): 2924, 2852, 2200, 1616,
1465, 1278, 1183, 1150, 901, 819, 753 cm-1. Mn (number-average
molecular weight) = 14200. PDI (=Mw/Mn; Mw, weight-average
molecular weight) = 3.5. Poly-2 and Poly-3 were prepared
analogously.
of Poly-1-Ni (0.35 g, 92%). H NMR (300 MHz, CDCl3): δ
9.86, 9.77, and 9.08 (2H; for detail, see Figure 3b and the text),
7.71 (2H), 7.54 (2H), 7.49 (2H), 7.35-7.28 (6H), 7.13 (2H), 6.61
(2H), 2.00 (4H), 1.08 (20 H), 0.78 (6H), 0.61 (4H). Anal. Calcd
for Br-C20H12N2NiO2-(C53H52N2NiO2)11-Br: C, 76.93; H,
6.24; Br, 1.70; N, 3.57; Ni, 7.48. Found: C, 75.35; H, 6.38; Br,
1.93; N, 3.57; Ni, 8.0. FT-IR (KBr): 2921, 2849, 2193, 1607, 1578,
1519, 1437, 1375, 1186, 816, 750, 534, 445 cm-1
.
Synthesis of Model Compounds (cf. Scheme 3). Br-MeSalophen.
Salicylaldehyde (1.9 g, 15 mmol) was added to an ethanol solution
(10 mL) of 3-bromo-4,5-diaminotoluene (1.49 g, 7.4 mmol) at room
temperature, and the reaction mixture was stirred at 80 °C for 1 h.
After cooling to room temperature, a yellow precipitate was collected
by filtration and purified by recrystallization from chloroform-
methanol to give a yellow powder of Br-MeSalophen (1.97 g,
Poly-2. Brown solid. 95% yield. 1H NMR (300 MHz, CDCl3):
δ 12.75 (2H, OH), 8.87 (2H, -CHdN-), 7.61-7.3 (6H), 7.09-
6.90 (6H), 3.74 (4H), 1.25 (24 H), 0.89 (6H). Anal. Calcd for
Br-C20H14N2O2-(C46H50N2O4)11-Br: C, 77.82; H, 7.00; N, 4.14;
Br, 1.97. Mn=8120. Found: C, 76.53; H, 7.25; N, 4.03; Br, 1.96.
Mn = 9200. PDI = 3.7. FT-IR (KBr): 2924, 2854, 2196, 1617,
1
64%). H NMR (300 MHz, CDCl3): δ 12.79 (s, 1H, OH), 12.48
(s, 1H, OH), 8.66 (s, 1H, -CHdN-), 8.51 (s, 1H, -CHdN-), 7.44
(d, 1H, J= 0.9 Hz), 7.42-7.33 (m, 3H), 7.30 (dd, 1H, J=7.7 and
1.5 Hz), 7.04 (d, 1H, J=7.7 Hz), 6.98 (d, 1H, J=0.9 Hz), 6.97-6.88
(m, 3H), 2.41 (s, 3H). Anal. Calcd for C21H17BrN2O2: C, 61.63; H,
4.19; Br, 19.52; N, 6.84. Found: C, 61.86; H, 4.26; Br, 20.03; N, 6.81.
1508, 1458, 1277, 1216, 1030, 754 cm-1
.
Poly-3. Red solid. 97% yield. 1H NMR (300 MHz, CDCl3): δ
12.67 (2H, OH), 8.67 (2H, -CHdN-), 7.61-7.3 (6H), 7.09-6.90
(6H), 3.59(4H),1.26(40H),0.86(6H).Anal. CalcdforBr-C20H14-
N2O2-(C54H66N2O4)10-Br: C, 78.70; H, 7.95; N, 3.60; Br, 1.89.
Mn = 8540. Found: C, 77.01; H, 8.34; N, 3.42; Br, 2.20. Mn =
9700. PDI=2.9. FT-IR (KBr): 2921, 2851, 2192, 1615, 1506, 1464,
Br-MeSalophen-Ni. A mixture of Ni(OAc)2 4H2O (1.27 g,
3
5.1 mmol), 3-bromo-4,5-diaminotoluene (1.02 g, 5.1 mmol), and
salicylaldehyde (1.31 g, 10.7 mmol) in ethanol (25 mL) was stirred
at 80 °C for 30 min to obtain a red solid. The red precipitate was
collected by filtration and dried under reduced pressure to afford
1277, 1215, 1029, 753 cm-1
.

Article
Macromolecules, Vol. 43, No. 24, 2010 10369
Scheme 3. Synthetic Routes to Model Compoundsa
a Key: (i) salicylaldehyde (2 equiv), EtOH, 80 °C, 1 h; (ii) Pd(PPh3)4, CuI, Et3N, THF, 70 °C, 24 h; (iii) Pd(PPh3)4, CuI, Et3N, toluene, 70 °C, 24 h;
(iv) Ni(OAc)2 4H2O, EtOH, 80 °C, 30 min.
3
Br-MeSalophen-Ni (2.13 g, 90%) as a dark red solid. 1H NMR
(300 MHz, CDCl3): δ 9.21 (s, 1H, -CHdN-), 8.15 (s, 1H,
-CHdN-), 7.48 (s, 1H), 7.27-7.24 (m, 5H), 7.12 (d, 1H, J =
8.4 Hz), 7.11 (d, 1H, J=8.4 Hz), 6.64 (t, 1H, J=7.2 Hz), 6.59 (d,
1H, J=7.2 Hz), 2.32 (s, 3H). Anal. Calcd for C21H15BrN2NiO2:
C, 54.13; H, 3.24; Br, 17.15; N, 6.01. Found: C, 54.22; H, 3.66;
Br, 16.77; N, 5.94. FT-IR (KBr): 1609, 1523, 1449, 1190, 987,
7.58-7.52 (m, 6H), 7.35-7.28 (m, 10H), 7.20 (d, 2H, J = 7.2
Hz), 7.18 (d, 2H, J=7.2 Hz), 6.66 (t, 2H, J=7.2 Hz), 6.64 (t, 2H,
J=7.3 Hz), 2.44 (s, 6H), 2.01 (m, 4H), 1.25-1.00 (m, 20H), 0.78
(t, 6H, J = 7.0 Hz), 0.64 (br, 4H). Anal. Calcd for C75H70-
N4Ni2O4: C, 74.52; H, 5.84; N, 4.64. Found: C, 74.11; H, 5.88;
N, 4.64. FT-IR (KBr): 2923, 2825, 1608, 1524, 1445, 1186, 1147,
841, 822, 748, 734, 547, 417 cm-1
.
750, 563, 437 cm-1
.
Model Compound-1. A mixture of Br-MeSalophen (0.20 g,
0.49 mmol), 2,7-diethynyl-9,9-dioctylfluorene (0.11 g, 0.25 mmol),
Pd(PPh3)4 (60 mg, 0.05 mmol), CuI (20 mg, 0.1 mmol), triethyl-
amine (4 mL), and THF (10 mL) was stirred at 70 °C for 24 h.
After the reaction mixture was cooled to room temperature, the
solvent was removed by evaporation. The crude product was
purified by column chromatography on silica (eluent = ethyl
acetate/chloroform (1/1 in volume)) to yield Model Compound-1
(0.19 g, 71%). 1H NMR (300 MHz, CDCl3): δ 13.11 (s, 2H, OH),
12.83 (s, 2H, OH), 8.86 (s, 2H, -CHdN-), 8.69 (s, 2H,
-CHdN-), 7.42-7.32 (m, 16 H), 7.10 (d, 2H, J = 8.1 Hz),
7.02 (s, 2H), 7.00 (d, 2H, J = 8.1 Hz), 6.94 (t, 4H, J = 7.2 Hz),
2.44 (s, 6H), 2.20-1.70 (m, 4H), 1.30-0.90 (m, 20H), 0.80 (t, 6H,
J = 7.0 Hz), 0.54 (brs, 4H). Anal. Calcd for C75H74N4O4: C,
82.23; H, 6.81; N, 5.12. Found: C, 81.88; H, 6.85; N, 4.92. FT-IR
(KBr): 2924, 2852, 2200, 1614, 1465, 1278, 1186, 1150, 901, 820,
Results and Discussion
Scheme 1 shows the synthetic route to the two types of mono-
mers. The reaction of 3,6-dibromo-1,2-diaminobenzene 17 with
salicylaldehyde in a 1:2 molar ratio at 80 °C gave the mono-
salicylidene compound 2 as the main product (86%) and Br2-Sa-
lophen as the minor product. Br2-Salophen was prepared by
further reaction of isolated 2 with salicylaldehyde. The nickel-
containing monomer, Br2-Salophen-Ni, was synthesized in
96% yield by the addition of Ni(OAc)2 4H2O to Br2-Salophen.
The one-pot reaction of 1 with salicylaldehyde in the presence of
3
Ni(OAc)2 4H2O also afforded Br2-Salophen-Ni in 90% yield.
3
Br2-Salophen-Ni has a coplanar coordination geometry around
Ni as determined by single-crystal X-ray crystallography
(cf. Figure 1), similarly to the case of the reported salophen-nickel
complex.11 However, the plane of the phenolic group is distorted
from that of the dibromophenylene unit, presumably due to the
steric repulsion between bromine and hydrogen of the imine
group.
754 cm-1
.
Model Compound-1-Ni. Pd(PPh3)4 (50 mg, 0.05 mmol), CuI
(9.9 mg, 0.05 mmol), and triethylamine (20 mL) were added to a
toluene (50 mL) solution containing Br-MeSalophen-Ni (0.47 g,
1.00 mmol) and 2,7-diethynyl-9,9-dioctylfluorene (0.12 g, 0.28
mmol), and the mixture was stirred at 70 °C for 24 h. After the
reaction mixture was cooled to room temperature, the mixture
was poured into methanol to obtain a precipitate. The precipi-
tate was collected by filtration and purified by recrystallization
from chloroform to give a red powder of Model Compound-1-Ni
(0.33 g, 97%). 1H NMR (300 MHz, CDCl3): δ 9.95 (s, 2H,
-CHdN-), 8.26 (s, 2H, -CHdN-), 7.74 (d, 2H, J=7.9 Hz),
The synthetic routes to the polymers are outlined in Scheme 2.
Palladium-catalyzed polycondensation6 of 2,7-diethynyl-9,9-di-
octylfluorene with Br2-Salophen and Br2-Salophen-Ni, afforded
Poly-1 and Poly-1-Ni in 96% and 92% yields, respectively. Poly-2
and Poly-3 were also obtained in high yields. Poly-1, Poly-2, and
Poly-3 showed good solubility in organic solvents such as chloro-
form and THF; however, Poly-1-Ni was only partially soluble in
chloroform and THF.

10370 Macromolecules, Vol. 43, No. 24, 2010
Fukumoto et al.
Figure 1. ORTEP drawing of Br2-Salophen-Ni. (a) Front view and (b) side view.
Table 1. Polymerization and Optical and Thermogravimetric Data of the Polymers
max, nm
λ
polymer
yield, %
Mn
Mw
in CHCl3
film
λ
PL, nm [in THF (Φ, %)]d
Td, °Cf
Poly-1
Poly-2
Poly-3
96
95
97
92
14200a
9200a
9300a
9400b
49700a
34000a
27000a
c
419
461
457
428
427
485
494
402
526 (0.5)
518 (1.0)
521 (3.0)
e
369
c
346
431
Poly-1-Ni
a Estimated by GPC (eluent: THF, polystyrene standards). b Determined by 1H NMR spectroscopy (cf. the text). c Not measured. d PL quantum yield
calculated by comparing with the standard of quinine sulfate (ca. 10-5 M solution in 0.5 M H2SO4, having a quantum yield of 54.6%). e Not observed.
f 5 wt % loss temperature obtained by thermogravimetry.
The PAE-type polymers often have a polymer-C-Br group as
the major terminal group, because of patial occurrence of Glaser
coupling and/or higher reactivity of the -CtCH group than that
of the -C-Br group.6d-f However, Poly-1 showed no bromine
content, suggesting that the dehalogenation polycondensation
proceeded smoothly. Poly-1 showed Mn of 14,200 in GPC analysis
(vs polystyrene standards), which corresponded to DP (degree of
polymerization) of 19. Poly-1, Poly-2, and Poly-3 showed uni-
modal GPC curves, and the PDIs (Mw/Mn) were estimated to be
about 3.
GPC analysis of Poly-1-Ni was not possible owing to the low
solubility of the polymer or partial aggregation. Poly-1-Ni
contained a small amount of bromine (1.93%; cf. Experimental
Section). If both polymer ends (A and B in Scheme 2) of Poly-
1-Ni contained Br, the DP of Poly-1-Ni was estimated to be
about 10 from the Br content. This DP of Poly-1-Ni is consistent
with 1H NMR data of the polymer. The nickel content of Poly-
1-Ni (8.0% of Ni) agreed with the calculated value (7.48%)
within experimental error. Poly-2 and Poly-3 contained a small
amount of bromine (ca. 2%). If both the polymer ends have a
bromine group, the DP of Poly-2 and Poly-3 was estimated to be
about 10, which agreed with the GPC Mn data for the polymers.
All the polymers had good thermal stability under N2. For
example, the TGA curves of Poly-1 and Poly-1-Ni exhibited a
5% weight loss at 369 and 431 °C, respectively (Table 1).
To understand the nature of the polymers in detail, the corres-
ponding model compounds depicted in Scheme 3 were also synthe-
sized. 2,7-Diethynyl-9,9-dioctylfluorenes capped with two salophen
terminal units and two nickel complexes, Model Compound-1 and
Model Compound-1-Ni, were synthesized by Pd-catalyzed reac-
tions similar to those shown in Scheme 2. 1H NMR spectra and
data from elemental analyses agreed with their structures.
IR and NMR Spectra. The IR spectra of the polymers
agree with their structures and are shown in Figure 2. The IR
spectrum of Poly-1 shows a ν(CtC) peak of disubstituted
acetylene at 2200 cm-1 (Figure 2c). Absorption peaks due to
ν(CtC) and ν(CtC-H) of terminal acetylenes of 2,7-
diethynyl-9,9-dioctylfluorene at 2100 and 3300 cm-1, respec-
tively, (Figure 2b) are not observed. The peak of Poly-1 at
Figure 2. IR spectra of (a) Br2-Salophen, (b) 2,7-diethynyl-9,9-dioctyl-
fluorene, (c) Poly-1, and (d) Poly-1-Ni.
1616 cm-1 is assigned to a ν(CdN) peak of the imine group in
the salophen unit and is located near that (1618 cm-1) of
Br2-Salophen (Figure 2a). Poly-1-Ni (Figure 2d) gives rise
to an IR spectrum similar to that of Poly-1. The IR spectra
of Poly-2 and Poly-3 also exhibit a ν(CtC) peak at about
2100 cm-1 and a ν(CdN) peak at approximately 1610 cm-1
.
Figure 3 shows the 1H NMR spectra of Poly-1 and Poly-
1-Ni in CDCl3. Hydroxy and imine proton signals of Poly-1 are
clearly observed at δ 12.7 and 8.95, respectively (Figure 3a).
The ratios of the area of these signals to that of aliphatic
signals agree with the structure of Poly-1. Poly-2, and Poly-3
give the hydroxy and imine proton signals at approximately
δ 12.7 and 8.7, respectively.
In the 1H NMR spectrum of Poly-1-Ni, the -OH signal
completely disappears. These 1H NMR data and the Ni
content (see above) of Poly-1-Ni reveal that the nickelated
structure of the salophen unit is maintained during poly-
merization.
Poly-1-Ni gives rise to three 1H NMR peaks in the region
between δ 9.0 and 10.0. The major peak at δ 9.86 is assigned
to an imine -CHdN- proton of inner salophen units

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Macromolecules, Vol. 43, No. 24, 2010 10371
Figure 3. 1H NMR spectra of (a) Poly-1 and (b) Poly-1-Ni in CDCl3. Peaks with / are due to impurities in the solvent (CHCl3 and H2O) and TMS.
Spinning side bands of the impurities and TMS are also marked with /.
(Hint; cf. Figure 3b), and the two small peaks at δ 9.77 and 9.08
in a 1:1 ratio are considered to be due to imine protons of the
terminal salophen-Ni unit as shown in Figure 3b. The mag-
netic deshielding effect of the -CtC- group12 seems to bring
about a shift of the -CHdN- signal to a lower magnetic
field from that of Br2-Salophen-Ni at δ 9.04. The 1H NMR
data of Model Compound-1-Ni also shows a large chemical
shift difference (1.69 ppm, cf. Experimental Section) between
the HterA and HterB peaks. The ratio of the peak area of Hint
to that of HterA (or HterB) is approximately 10:1, which agrees
with the DP (ca.10) estimated from the Br content.
UV-Vis and Photoluminescence (PL) Spectra. Figure 4
shows the UV-vis spectra of Poly-1, Model Compound-1, and
the starting materilas (Br2-Salophen and Br-MeSalophen)
for the synthesis in CHCl3. The UV-vis spectra of Br2-
Salophen (Figure 4b) and Br-MeSalophen (Figure 4a) exhibit
peaks at about λmax=335 nm, which are principally assigned
to the π-π* transition in the salophen unit.13 The λmax of
Model Compound-1 (Figure 4c) shifts to a longer wavelength
by about 20 nm because of the extension of the π-conjugation
system (cf. Scheme 3). Poly-1 (Figure 4d) seems to give over-
lapping π-π* transition peaks at about 350 nm and a new
π-π* absorption peak at about 420 nm.
Poly-1 essentially has a poly(p-phenyleneethynylene) PPE
main chain,6,14 and reported PPEs show λmax (at about 420 nm)
near the λmax of Poly-1. Thus, the new peaks of Poly-1 at
about 420 nm are thought to arise essentially from the π-π*
transition along the polymer main chain.
For the previously reported salen or salophen polymers
shown in Chart 2, the π-π* transition peak shows no distinct
shift from that of the corresponding starting monomers4c-k
because they lack formally extended π-conjugation system
along the polymer chain. By contrast, the large bathochromic
shift (Δλmax = 84 nm) observed between Poly-1 and Br2-
Salophen indicates the presence of an extended π-conjugated
system along the polymer chain. Such large red-shifts of λmax

10372 Macromolecules, Vol. 43, No. 24, 2010
Fukumoto et al.
were also found in the UV-vis spectra of Poly-2 (λmax=461 nm,
Δλmax=126 nm) and Poly-3 (λmax=457 nm, Δλmax=122 nm)
to support the presence of extended π-conjugation systems
along the polymer main chain.
π-conjugated main chain are not significantly affected by the
nickelation of the salophen side chain.
A cast film of Poly-1 and Poly-1-Ni on a quartz glass
showed essentially the same UV-vis spectra as those in
Figure 5, suggesting that there was no significant electronic
interaction between the polymer molecules. Two octyl side
chains in the fluorene unit seem to prevent the intermolecular
electronic interactions from taking place, similarly to the
cases of poly(fluorene)s reported. By contrast, the λmax
values of Poly-2 (485 nm) and Poly-3 (494 nm) in cast films
shift to a longer wavelength by 20-30 nm from those in
CHCl3. These data suggest that the polymers have inter-
molecular electronic interaction in the solid state because of a
weak steric repulsion between the polymer molecules. When
π-conjugated polymers assemble in the solid state, it often
brings about intermolecular electronic interactions and a
shift of the UV-vis peak to a longer wavelength.14,15
The PL spectra of Poly-1, Poly-2, and Poly-3 showed a
weak emission peak at approximately 520 nm in THF with
quantum yields of 0.5-3.0%. OH compounds often show
only a weak PL due to the quenching effect of the OH group16
which is thought to originate from vibronic coupling. Poly-
1-Ni showed no observable PL in either a THF solution or
a film. Such a quenching effect of the transition metal was
reported for some π-conjugated polymer ligands.17
Figure 5 shows the UV-vis spectra of Poly-1-Ni, Br-
MeSalophen-Ni, Br2-Salophen-Ni, and Model Compound-
1-Ni. In addition to the strong π-π* absorption peak, these
Ni complexes show a medium UV-vis peak in the range of
about 460-490 nm. Ni-salen and Ni-salophen complexes13
reportedly show analogous absorption bands, and the con-
tribution of a charge transfer (CT) electronic transition to
the absorption band has been suggested.13 A weak peak at
approximately 600 nm (with ε of about 100 M-1cm-1) is
considered to originate from d-d transition.13b,c Comparison
of UV-vis spectra of Poly-1 and Poly-1-Ni indicates that
the π-π* transitions in the single salophen unit and in the
Nickelation of Poly-1. As described earlier, Poly-1-Ni was
synthesized directly from Br2-Salophen-Ni. A similar Ni(II)
complex can be obtained by the reaction of Poly-1 and
Ni(OAc)2 (cf. Scheme 4). Figures 6 and 7 show changes in
the UV-vis spectra of Model Compound-1 and Poly-1 upon
the addition of Ni(OAc)2 4H2O. As shown in Figure 6, the
3
nickelation of Model Compound-1 proceeds with clear iso-
sbestic points, and changes in the peak intensity of the new
peak at 480 nm vs [Ni2þ]/[Model Compound-1] are shown in
Figure 4. UV-vis spectra of (a) Br-MeSalophen (dashed line),
(b) Br2-Salophen (dotted line), (c) Model Compound-1 (dashed dot
line), and (d) Poly-1 (solid line) (solvent = CHCl3).
Figure 6. Changes in UV-vis spectrum of Model Compound-1 (1.15ꢀ
10-5 M) in CHCl3-MeOH (62.5:1 v/v) at various concentrations of
Ni(OAc)2 4H2O. [Ni] = 0, 2.88ꢀ10-6, 5.77ꢀ10-6, 8.65ꢀ10-6, 1.15ꢀ
3
10-5, 1.44 ꢀ 10-5, 1.73 ꢀ 10-5, 2.02 ꢀ 10-5, 2.31 ꢀ 10-5, 2.60 ꢀ 10-5
,
Figure 5. UV-vis spectra of (a) Poly-1-Ni (solid line), (b) Br-
MeSalophen-Ni (dashed line), (c) Br2-Salophen-Ni (dotted line),
and (d) Model Compound-1-Ni (dashed dot line) in CHCl3.
2.88ꢀ10-5, 3.17ꢀ10-5, 3.46ꢀ10-5, 4.04ꢀ10-5, and 4.61ꢀ10-5 M. The
inset indicates the dependence of the absorbance of the shoulder peak at
480 nm on the addition of Ni(OAc)2 4H2O.
3
Scheme 4. Response to Ni(OAc)2

Article
Macromolecules, Vol. 43, No. 24, 2010 10373
the inset of Figure 6. The absorbance increases smoothly
with the [Ni2þ]/[Model Compound-1] ratio and saturates at a
ratio of 2. Plots of data at 382 nm gave analogous results.
Because Model Compound-1 has two coordination sites,
these data indicate that the nickelation of the salophen unit
proceeds smoothly and quantitatively.
Similar UV-vis changes are observed in the reaction of
Poly-1 with Ni(OAc)2, as shown in Figure 7. Isosbestic
points are observed at 438 and 335 nm, and the absorbance
at 480 nm saturates at a [Ni]/[Poly-1-Ni] ratio of 1 (molarity
of Poly-1-Ni is based on the repeating unit) as shown in
the inset of Figure 7. These data indicate that every salophen
unit in Poly-1 smoothly participates in the reaction with
Electochemical Behavior. CV Data. The salophen polymers
and the Ni-salophen polymer are electrochemically active.
Figure 8 shows CV charts of cast films of the polymers on
Pt plates immersed in a CH3CN solution of [Bu4N]PF6. Poly-1
and Poly-3 show a reduction peak at approximately -2.2 V.
Various poly(aryleneethynylene)-type polymers undergo electro-
chemical reduction (or n-doping) near -2 V vs Agþ/Ag,6,19
and the observed reduction peaks of Poly-1 and Poly-3 are
also assigned to the reduction of the π-conjugated polymer
main chain. However, the reduction peak may contain con-
tribution from the reduction of the salophen unit.20 The films
turn from yellow to black (Poly-1) and red (Poly-3) upon
reduction.
Ni(OAc)2 4H2O to give Poly-1-Ni. It is reported that
Poly-1-Ni gives two reduction peaks at -1.7 and -2.1 V
vs Agþ/Ag. The former peak is considered to contain a con-
tribution from the one-electron reduction of the Ni(II)-
salophen complex. Isee et al.21 and Gosden et al.22 reported
the generation of radical anion species ([Ni(II)L]-•, L =
salophen) of the Ni(II)-salophen complex by electrochemi-
cal reduction at -1.4 V vs SCE (or -1.74 V vs Agþ/Ag).
Isse et al. also revealed that the sequential reduction of
[Ni(II)L]-• gives Ni(I) species [Ni(I)L]2- at -1.9 V vs SCE
(or -2.24 V vs Agþ/Ag). These data support the idea that the
peak at -2.1 V vs Agþ/Ag in Figure 8(c) includes contribu-
tion from the reduction of π-conjugated polymer main chain
and that from the Ni(II) f Ni(I) reduction.
3
nickelation of salophen proceeds smoothly, and the product
has a very large stability constant.18 From the onset (approx-
imately 550 nm) of the UV-vis absorption band of Poly-1,
the band gap (Eg(opt)) of Poly-1 is estimated at 2.3 eV.
In the oxidation region, Poly-1 shows a peak at 1.33 vs
Agþ/Ag, whereas Poly-3 gives rise to two oxidation peaks at
0.72 and 1.20 vs Agþ/Ag. Poly(aryleneethynylene) under-
goes electrochemical oxidation (or p-doping)23 and the oxi-
dation peak is assigned to oxidation of π-conjugated poly-
mer main chain. The positive charge formed in the polymer
main chain by the oxidation is thought to be delocalized
along the polymer main chain; however, the positive charge
seems to exist mainly at the aromatic units because of
electron-accepting nature of the -CtC- group. Appear-
ance of the two oxidation peaks for Poly-3 may be due to the
presence of two kinds of aromatic units and oxidizable24a
phenolic group in the polymer. For Poly-1, another oxida-
tion peak may be hidden under the somewhat broad peak at
1.33 vs Agþ/Ag. Poly-1-Ni also shows two oxidation peaks
Figure 7. Changes in UV-vis spectrum of Poly-1 [1.14 ꢀ 10-5
M
(repeating unit)] in CHCl3-MeOH (50:1 v/v) at various concentrations
of Ni(OAc)2 4H2O. [Ni] = 0, 2.87ꢀ10-6, 5.75ꢀ10-6, 8.62ꢀ10-6, 1.15
3
ꢀ10-5, 1.44ꢀ10-5, 1.72ꢀ10-5, 2.01ꢀ10-5, 2.30ꢀ10-5, 3.45ꢀ10-5
,
4.11 ꢀ 10-5, and 5.13 ꢀ 10-5 M. The inset indicates the increase in
the absorbance of the shoulder peak at 480 nm on addition of
Ni(OAc)2 4H2O.
3
Figure 8. Cyclic voltammograms of the cast film of polymers on Pt electrode (1 cm ꢀ1 cm) in a CH3CN solution containing [Bu4N]PF6 (0.1 M):
(a) Poly-1; (b) Poly-3; (c) Poly-1-Ni. Sweep rate =50 mV s-1
.

10374 Macromolecules, Vol. 43, No. 24, 2010
Fukumoto et al.
Figure 9. Changes of UV-vis spectra with applied potential (vs Agþ/Ag) for (a) Poly-1, (b) Poly-3, (c) Poly-1-Ni. Polymer films cast on ITO
(indium-tin-oxide) glass electrodes were used. In a CH3CN solution of 0.1 M [Bu4N]PF6. The inset in part b shows a differential spectrum obtained
from curves i and a. Noise from the measuring system is observed at about 360 nm.
at 0.75 and 1.4 V vs Agþ/Ag. The potential of the former
peak corresponds to the oxidation potential of the Ni(II)-
salophen unit,24b,c and the latter larger peak is assigned to the
oxidation of the polymer main chain.
The potential difference between the onset of the oxidation
peak of Poly-1 (approximately 0.7 V vs Agþ/Ag) and that of
the reduction peak of Poly-1 (approximately -1.8 V vs Agþ/Ag)
is estimated to be approximately 2.5 V. This potential dif-
ference may be compared with the above-described optical
band gap of Eg(opt)=2.3 eV of Poly-1, if the oxidation and
reduction of the salophen unit cause changes of the electronic
state of whole Poly-1 molecule. From the onset potential of
the oxidation peak,25 HOMO level of Poly-1 is estimated at
approximately -5.5 eV.
Spectro-Electrochemical Data. Figure 9 shows results of
spectro-electrochemical measurements of the polymers in the
oxidation region. Myrick reported weakening of original
UV-vis peaks of a poly(aryleneethynylene)-type polymer
by electrochemical oxidation,26 and similar phenomena are
observed with Poly-1, Poly-3, and Poly-1-Ni.
The oxidation leads to an increase of the absorption
in the 550;800 nm region, suggesting the formation of
polaronic and bipolaronic states reported by Myrick.26
For Poly-3, the differential spectrum depicted in the inset
of Figure 9b show a peak at approximately 570 nm,
suggesting the formation of the polaronic and/or bipolaro-
nic states; however the peak is not so clear as that previously
reported.26,27 Detailed differential spectroscopic data of the
Poly-3 film depending on the applied potential are shown in
Figure S1 in Supporting Information. The reason for
smaller spectroscopic changes of Poly-1-Ni than those
of Poly-1 is not clear. Oxidized Poly-1-Ni may have new
electronic transition(s) corresponding to the absorption
in the 350;550 nm region. In the reduction region, the
polymer films did not attached to the ITO electrode well
and spectro-electrochemical response was not followed
well.
Conclusion and Scope
New π-conjugated poly(aryleneethynylene)s polymers consist-
ing of salophen (Poly-1-Poly-3) and Ni-salophen (Poly-1-Ni)
units were obtained in high yields by Pd-catalyzed polycondensa-
tion. Model compounds of the polymers were also prepared and
1H NMR and UV-vis data of the polymers were discussed using
the corresponding data from the model compounds. Poly-1
responded to Ni2þ to give a 1:1 Ni complex quantitatively. The
polymers were electrochemically active in both the reduction and
oxidation regions. π-Conjugated polymers with immobilized
salophen-metal complexes will expand the scope of polymer
chemistry and coordination chemistry.
Acknowledgment. The authors are grateful to Prof. Dr. Takeuchi
of our institute for the GPC analysis. This work was partially
supported by a Grant-in-Aid for Young Scientists (B) from the
Japan Society for the Promotion of Science (JSPS).
Supporting Information Available: Crystallographic infor-
mation on Br2Salophen-Ni in CIF format and text giving the
X-ray crystallography procedute, tables of crystal data, and a
figure showing spectro-electrochemical data.This material is
available free of charge via the Internet at http://pubs.acs.org.
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