Preparation and chemical properties of π-conjugated poly(1,10- phenanthroline-3,8-diyl)s with crown ether subunits

Article abstract of DOI:10.1016/j.reactfunctpolym.2014.05.002

π-Conjugated polymers consisting of 1,10-phenanthroline units and crown ether subunits (Poly-1, Poly-2, and Poly-3) were prepared by dehalogenation polycondensation of the corresponding dibromo monomers using a zero-valent nickel complex as a condensing agent. They were characterized by elemental analysis, ¹H NMR and UV-Vis spectroscopies, and cyclic voltammetry (CV). They were partly soluble in CHCl₃, and the number average molecular weight of the soluble part of Poly-2, which had 15-crown-5 subunits, was estimated to be 5300. The polymers exhibited UV-Vis peaks at approximately λ_max = 360 nm, which was reasonable. Complexation with [Ru(bpy)₂]²⁺ and alkaline metal ions made the polymer soluble in organic solvents. The complexation of [Ru(bpy)₂] ²⁺ to the 1,10-phenanthroline unit proceeded quantitatively, and the [Ru(bpy)₂]²⁺ complexes exhibited CV curves characteristic of [Ru(N-N)₃]²⁺ complexes.

Full text of DOI:10.1016/j.reactfunctpolym.2014.05.002

Reactive & Functional Polymers 82 (2014) 9–16
Contents lists available at ScienceDirect
Reactive & Functional Polymers
journal homepage: www.elsevier.com/locate/react
Preparation and chemical properties of p-conjugated
poly(1,10-phenanthroline-3,8-diyl)s with crown ether subunits
⇑
Hiroki Fukumoto, Yumiko Kase, Take-aki Koizumi, Takakazu Yamamoto
Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
p
-Conjugated polymers consisting of 1,10-phenanthroline units and crown ether subunits (Poly-1, Poly-
Received 6 February 2014
Received in revised form 9 May 2014
Accepted 12 May 2014
2, and Poly-3) were prepared by dehalogenation polycondensation of the corresponding dibromo mono-
mers using a zero-valent nickel complex as a condensing agent. They were characterized by elemental
analysis, 1H NMR and UV–Vis spectroscopies, and cyclic voltammetry (CV). They were partly soluble in
CHCl3, and the number average molecular weight of the soluble part of Poly-2, which had 15-crown-5
Available online 17 May 2014
subunits, was estimated to be 5300. The polymers exhibited UV–Vis peaks at approximately kmax
=
Keywords:
360 nm, which was reasonable. Complexation with [Ru(bpy)2]2+ and alkaline metal ions made the
polymer soluble in organic solvents. The complexation of [Ru(bpy)2]2+ to the 1,10-phenanthroline unit
proceeded quantitatively, and the [Ru(bpy)2]2+ complexes exhibited CV curves characteristic of
[Ru(N-N)3]2+ complexes.
p-Conjugated polymers
Poly(1,10-phenanthroline)
Crown ether
Alkaline metal ions
Ru complex
Ó 2014 Elsevier Ltd. All rights reserved.
Organometallic polymerization
1. Introduction
synthesized [9,27,29–35]. These polymers exhibit interesting elec-
tronic and optical properties and functionalities, such as electrical
p
-Conjugated polymers have been the focus of numerous
conductivity and light-emitting properties. However, the synthesis
of -conjugated poly(1,10-phenanthroline-3,8-diyl)s with crown
ether subunits has not been performed to our knowledge. [35] In
Poly-1, Poly-2, and Poly-3, both the crown ether and Phen units
can react with metal species, and elucidating the chemical reactiv-
ity of these polymers toward metal species will provide further
studies because of their attractive chemical and physical properties
[1–8], and they have been functionalized by introducing reactive
subunits.
In particular, crown ether groups have been introduced into
conjugated polymers [9–26]. Chart 1 shows a schematic drawing of
p
p-
two typical types of
groups.
p-conjugated polymers with crown ether
understanding of
subunits.
p-conjugated polymers with crown ether
These crown-ether-functionalized,
exhibit interesting electrical conductivity and optical properties
and can be employed as metal sensors.
We report the synthesis and basic chemical properties (e.g.,
UV–Vis absorption, electrochemical response, and reactivity
toward metals) of the new A-type 1,10-phenanthroline polymers,
Poly-1, Poly-2, and Poly-3, shown in the lower part of Chart 1.
These polymers were prepared by organometallic dehalogenation
polycondensation of the corresponding dihalogenated monomers
using a zero-valent nickel complex as a condensing agent [27,28].
p
-conjugated polymers
The reactions of low-molecular-weight crown-ether-function-
alized 1,10-phenanthrolines (especially with metal species) have
been reported by Yam and Zu [36,37], Yu [38] and Neumann
[39]. However, the chemical and physical properties of these
crown-ether-functionalized
p-conjugated poly(1,10-phenanthro-
line)s have not been studied. Polymeric materials are interesting
materials not only because of their chemical and physical function-
alities, but also because of their potential for use in films or solids.
2. Experiments
p
-Conjugated polymers consisting of N-chelating ligand units
(e.g., 2,20-bipyridine (bpy) and 1,10-phenanthroline (Phen) units)
have been the subject of many papers, and various poly(pyridine-
2,5-diyl)s and poly(1,10-phenanthroline-3,8-diyl)s have been
2.1. Materials, general procedures, and measurements
Bis(1,5-cyclooctadiene)nickel [Ni(cod)2] was prepared according
to literature methods [40,41] or used as purchased. 3,8-Dibromo-
1,10-phenanthroline (Br2Phen) and 3,8-dibromo-5,6-dihydroxy-
1,10-phenanthroline were prepared according to literature
methods [33]. Anhydrous solvents (DMF and ethanol) were
⇑
Corresponding author. Tel.: +81 45 924 5961; fax: +81 45 924 5976.
E-mail address: takakazuyamamoto@kir.biglobe.ne.jp (T. Yamamoto).
http://dx.doi.org/10.1016/j.reactfunctpolym.2014.05.002
1381-5148/Ó 2014 Elsevier Ltd. All rights reserved.

10
H. Fukumoto et al. / Reactive & Functional Polymers 82 (2014) 9–16
purchased from Kanto Chemical Co., Inc. (Tokyo, Japan) and stored
under N2. The polymerization was performed using standard
Schlenk techniques under N2 or Ar. 1H NMR spectra were collected
with JEOL Lambda 300, JEOL JNM-EX400, and Brucker ADVANCE III
400 spectrometers. IR spectra were recorded on a JASCO FT/IR 460
PLUS spectrometer. UV–Vis spectra were measured with Shimadzu
UV-2550 and UV-3100PC spectrometers, and photoluminescence
(PL) spectra were recorded using a Hitachi F4500 spectrometer.
The combined extracts were washed with water and dried over
Na2SO4, and the solvent was removed by evaporation. The crude
product was purified by column chromatography on silica (elu-
ent = ethyl acetate) to yield Monomer-1 (0.93 g, 64%) as a white
solid. 1H NMR (CDCl3, 400 MHz) d 9.11 (d, 2H, J = 2.2 Hz, 2,9-H of
the Phen unit), 8.68 (d, 2H, J = 2.2 Hz, 4,7-H of the Phen unit),
4.48 (m, 4H), 4.05 (m, 4H), 3.89 (s, 4H) ppm. IR (KBr) 1606, 1582,
1442, 1420 cmꢀ1. Anal. Calcd. for C18H16Br2N2O4: C, 44.66; H,
3.33; N, 5.79; Br, 33.01%. Found: C, 44.54; H, 3.28; N, 5.69; Br,
32.15%. MS (FAB) m/z = 485 (M + H+).
The PL quantum yield (
U) was calculated using a quinine sulfate
standard (
U
= 54.6% for ca. 10ꢀ5 M solution in 0.5 M H2SO4). 1H
NMR spectra recorded on a Brucker ADVANCE III 400 spectrometer
and a part of the UV–Vis spectra were obtained by one of the authors
(FH) after he moved to Ibaraki University, Japan. Elemental analyses
were performed using LECO CHNS-932 and Yanaco YS-10
SX-Elements microanalyzers. ICP-AES (inductively coupled plasma
atomic emission spectrometry) was performed with a Shimadzu
ICPS-8100 apparatus. FAB mass spectra were obtained with a JEOL
JMS-700 analyzer. ESI-MS data were obtained by Ms. K. Tsutsui of
the Institute for Molecular Science using a Waters Micromass LCT
spectrometer and MassLynx Ver. 4.0. CH3CN solutions of Phen com-
pounds (Br2Phen or the monomer) and M[PF6] (M = Li, Na, or K)
were used for the ESI-MS analysis. TGA (thermogravimetric analy-
sis) curves were obtained using a Shimadzu thermometric TGA-50
system. CV was performed using a Hokuto-Denko (Tokyo, Japan)
HSV-100 electrochemical interface. Gel permeation chromatogra-
phy (GPC) was performed at TOSOH Analysis and Research Center
Co., Ltd. (Yokkaichi, Mie, Japan) using a TOSOH HLC-8220GPC appa-
ratus with 10 mM CF3COONa in hexafluoro-2-propanol as the eluent
and poly(methyl methacrylate) standards.
Monomer-2 and Monomer-3 were prepared using analogous
procedures.
Monomer-2. White solid. 25% yield. 1H NMR (CDCl3, 300 MHz)
d 9.10 (d, 2H, J = 2.4 Hz, 2,9-H of the Phen unit), 8.67 (d, 2H,
J = 2.4 Hz, 4,7-H of the Phen unit), 4.47 (t, 4H, J = 6.2 Hz), 4.09 (t,
4H, J = 6.2 Hz), 3.82 (m, 4H), 3.79 (m, 4H) ppm. IR (KBr) 1607,
1581, 1437, 1420 cmꢀ1. Anal. Calcd. for C20H20Br2N2O5: C, 45.48;
H, 3.82; N, 5.30; Br, 30.26%. Found: C, 45.27; H, 3.72; N, 5.30; Br,
30.35%. MS (FAB) m/z = 529 (M + H+). The molecular structure of
Monomer-2 was confirmed by X-ray crystallography.
Monomer-3. White solid. 24% yield. 1H NMR (CDCl3, 300 MHz)
d 9.09 (d, 2H, J = 2.4 Hz, 2,9-H of the Phen unit), 8.72 (d, 2H,
J = 2.4 Hz, 4,7-H of the Phen unit), 4.49 (m, 4H), 4.03 (m, 4H),
3.81 (m, 4H), 3.79 (m, 4H), 3.71 (s, 4H) ppm. IR (KBr) 1606, 1582,
1442, 1420 cmꢀ1. Anal. Calcd. for C22H24Br2N2O6: C, 46.18; H,
4.23; N, 4.90; Br, 27.93%. Found: C, 45.99; H, 4.26; N, 4.90; Br,
27.50%. MS (FAB) m/z = 572 (M+). The molecular structure of
Monomer-3 was confirmed by X-ray crystallography.
2.3. Polymer preparation
2.2. Monomer preparation
Poly-1. Monomer-1 (0.48 g, 1.0 mmol) was added to a DMF
(50 mL) solution containing [Ni(cod)2] (0.33 g, 1.2 mmol), 1,5-
cyclooctadiene (0.6 mL, 5 mmol), and bpy (0.19 g, 1.2 mmol), and
the mixture was stirred at 60 °C for 24 h. After removing approxi-
mately half of the solvent by evaporation, the reaction mixture was
poured into aqueous ammonia to obtain a dark brown precipitate.
The precipitate was separated by filtration, and washed with (i) an
aqueous ammonium–methanol solution of dimethylglyoxime and
HCl–acidic methanol alternatively (10 times total), (ii) aqueous
ammonia-basic methanol (twice), and (iii) a water–methanol mix-
ture (once) in succession. The precipitate was dried under vacuum
to obtain Poly-1 (0.15 g, 46%) as a yellow–brown solid. Some of the
polymer seemed to be lost during the work-up, particularly during
repeated washing. 1H NMR (CDCl3, 300 MHz) of the CHCl3-soluble
part: d 9.59 (1.73H, 2,9-H of the inner Phen unit), 9.20 (0.27H, 2,9-
H of the terminal Phen unit), 8.94 (1.73H, 4,7-H of the inner Phen
unit), 8.61 (0.27H, 4,7-H of the terminal Phen unit), 7.71 (0.27H,
3,8-H of the terminal Phen unit), 4.62–4.55 (4H), 4.14 (4H), 3.94
(4H) ppm. IR (KBr) 1614, 1434 cmꢀ1. Anal. Calcd. for (C18H16N2O4-
ꢁ2H2O)n: C, 59.99; H, 5.59; N, 7.77%. Found: C, 59.62; H, 5.28; N,
8.08%. Br was not detected. The polymer appears to be hydrated
similarly to 1,10-phenanthroline and reported polypyridines. It
was difficult to remove the waters of hydration completely. Poly-
2 and Poly-3 were prepared following analogous procedures.
Poly-2. Yellow–brown solid. 41% yield. 1H NMR (CDCl3,
300 MHz) of the CHCl3-soluble part: d 9.60 (1.86H, 2,9-H of the
inner Phen unit), 9.18 (0.14H, 2,9-H of the terminal Phen unit),
8.98 (1.86H, 4,7-H of the inner Phen unit), 8.62 (0.14H, 4,7-H of
the terminal Phen unit), 7.70 (0.14H, 3,8-H of the terminal Phen
unit), 4.63–4.56 (4H), 4.19 (4H), 3.87–3.83 (8H) ppm. IR (KBr)
1610, 1430 cmꢀ1. Anal. Calcd. for (C20H20N2O5ꢁ3H2O)n: C, 56.87;
H, 6.20; N, 6.63%. Found: C, 57.02; H, 5.66; N, 5.59%. Br was not
detected. The discrepancy between the calculated and experimen-
tally determined values might be due to the high thermal stability
of the polymer.
Monomer-1. NaH (0.17 g, 7.1 mmol) was added to a DMF
(50 mL) solution of 3,8-dibromo-5,6-dihydroxy-1,10-phenanthro-
line (1) (1.11 g, 3.0 mmol) at room temperature under N2, and
the reaction mixture was stirred for 30 min to obtain a dark red
mixture. Li2CO3 (0.11 g, 1.5 mmol) was added to the reaction mix-
ture. A DMF (ca. 15 mL) solution of triethylene glycol di-p-tosylate
(1.5 g, 3.3 mmol) was slowly added at room temperature, and the
mixture was stirred at 80 °C for 24 h. After cooling to room temper-
ature, the mixture was extracted with chloroform (three times).
Chart 1. Top: schematic drawing of two typical types of
with the crown ether subunits. A-Type: the crown ether group is directly attached
at the -conjugated polymer main chain. B-Type: the -conjugated polymer has
pendant crown ether subunits. Bottom: newly synthesized A-Type -conjugated
polymers with a 1,10-phenanthroline main chain and crown ether subunits.
p-conjugated polymers
p
p
p

H. Fukumoto et al. / Reactive & Functional Polymers 82 (2014) 9–16
11
Scheme 1. Synthetic routes for monomers and polymers and complexation of the polymers with [Ru(bpy)2]2+. L = neutral ligand such as cod (1,5-cyclooctadiene) or bpy;
a = number of L.
Poly-3. Yellow–brown solid. 38% yield. 1H NMR (CDCl3,
300 MHz) of the CHCl3-soluble part: d 9.61 (1.73H, 2,9-H of the
inner Phen unit), 9.18 (0.27H, 2,9-H of the terminal Phen unit),
9.06 (1.73H, 4,7-H of the inner Phen unit), 8.66 (0.27H, 4,7-H of
the terminal Phen unit), 7.69 (0.27H, 3,8-H of the terminal Phen
unit), 4.64–4.57 (4H), 4.10 (4H), 3.88–3.83 (8H), 3.74 (4H) ppm.
Fig. 1. ORTEP drawing of Monomer-2 (CCDC No. 921237). Hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (°): N1AC1 1.375(11), N1AC2
1.342(15), N2AC11 1.327(14), N2AC12 1.316(13), Br1AC3 1.908(10), Br2AC10 1.892(10), O1AC6 1.402(12), O5AC7 1.392(9), C6AO1AC13 116.0(9), C7AO5AC20 113.9(6).

12
H. Fukumoto et al. / Reactive & Functional Polymers 82 (2014) 9–16
Table 1
Polymerization results and optical data for Poly-1–Poly-3.
a
Polymer
Yield (%)
Mna, Mw
kmax (nm)
kPL (nm)
In CHCl3
In HCOOH
Film
In CHCl3
(
Ub (%))
Film
425
Poly-1
Poly-2
Poly-3
46
41
38
8900, 47000
(2300)
317
353
325
375
319
363
478
(8.7)
1400, 15000
(5300)
319
361
330
379
322
377
495
(3.3)
435
424
(2900)
319
357
325
379
319
383
496
(3.7)
a
Determined by GPC; for details see the main text. Mn of the CHCl3-soluble fraction (ca. 25%), which was determined by 1H NMR spectroscopy (cf. the main text), is shown
in the parentheses.
b
PL quantum yield calculated by comparison to a quinine sulfate standard (ca. 10ꢀ5 M solution in 0.5 M H2SO4 with a quantum yield of 54.6%).
O
O
O
O
O
O
O
O
O
O
O
O
m
m
m
HterB
HterC
HterA
HintB
4
7
8
9
3
H
N
N
N
N
N
1
N
2
HintA
n-2
10
terA
terB terC
3
intA
intB
Chart 2. PPhen(5,6-OR) prepared by organometallic polycondensation using
[Ni(0)La] and 3,8-dibromo-1,10-phenanthroline (Br2Phen) for the 1H NMR studies.
(4H) ppm. IR (KBr) 1610, 1445, 842, 556 cmꢀ1. The complexa-
tion of Poly-2 and Poly-3 to [RuCl2(bpy)2] was performed
similarly.
Poly-2-Ru. Yellow–brown solid. Quantitative. 1H NMR (CD3CN,
400 MHz) d 8.8–7.3 (20H, bpy and the Phen unit), 4.5–4.4 (4H), 4.0
10
9
8
7
6
5
4
3
(4H), 3.8 (4H), 3.7 (4H) ppm. IR (KBr) 1609, 1445, 842, 556 cmꢀ1
.
Poly-3-Ru. Yellow–brown solid. 50% yield. 1H NMR (CD3CN,
400 MHz) d 9.0–7.3 (20H, bpy and Phen unit), 4.6–4.5 (4H), 4.0–
Fig. 2. 1H NMR spectra of (a) Poly-1, (b) Poly-2, and (c) Poly-3 in CDCl3. Peaks
indicated with a are spinning side bands.
3.3 (16H) ppm. IR (KBr): 1609, 1445, 841, 556 cmꢀ1
.
ꢂ
2.5. Crystal structure determination
IR (KBr) 1610, 1431 cmꢀ1. Anal. Calcd. for (C22H24N2O6ꢁ2H2O)n: C,
58.92; H, 6.29; N, 6.25%. Found: C, 58.82; H, 5.75; N, 7.16%. Br
was not detected. The discrepancy between the calculated and
experimentally determined values might be due to the high ther-
mal stability of the polymer and partial trapping of the ammonium
ion by the crown ether unit. The ability of crown ethers to trap the
ammonium ion has been reported in the literature [42–44].
Monomer-2 and Monomer-3 crystals were obtained for X-ray
analysis. For each monomer, a suitable crystal was mounted on a
glass fiber. Data collection was performed at ꢀ160 °C on a Riga-
ku/MSC Saturn CCD diffractometer with graphite monochromated
2.4. Preparation of Ru(II) complexes of the polymers
A mixture of Poly-1 (30 mg, 0.10 mmol based on the repeating
unit), cis-bis(2,20-bipyridine)dichloro-ruthenium(II) ([RuCl2(bpy)2];
48.4 mg, 0.10 mmol) and distilled water (10 mL) was stirred under
reflux for 5 days under Ar. During the early stages of the reaction,
Poly-1 particles were observed clearly. As the reaction proceeded,
the particles disappeared gradually, and a seemingly homogeneous
red solution was obtained after 5 days. After cooling the solution
to room temperature, the insoluble part was removed by centrifu-
gation. NH4PF6 (81.1 mg, 0.50 mmol) was added to the separated
soluble part to precipitate a dark red solid. After the solid was sep-
arated by filtration, the precipitate was washed with water
and dried under reduced pressure to yield Poly-1-Ru as
a
dark red solid (68 mg, 77% yield). 1H NMR (CD3CN, 400 MHz) d
8.8–7.3 (20H, bpy and the Phen unit), 4.5–4.4 (4H), 4.0 (4H), 3.9
Fig. 3. UV–Vis spectra of (a) Monomer-2 and (b) Poly-2 in CHCl3.

H. Fukumoto et al. / Reactive & Functional Polymers 82 (2014) 9–16
13
10
9
8
7
6
5
4
3
Fig. 4. 1H NMR spectra of (a) Poly-1-Ru, (b) Poly-2-Ru and (c) Poly-3-Ru in CD3CN.
Mo K
a
radiation (k = 0.7107 Å). The data were collected up to a
structure of Monomer-2, and that of Monomer-3 is illustrated in
Fig. S3a in the SM.
maximum 2h value of 55°. A total of 720 oscillation images were
collected. A data sweep was performed using x scans from ꢀ110°
1,10-Phenanthrolines with crown ether subunits that do not
contain Br (those with 12-crown-4 [46], 15-crown-5 [38], and
18-crown-6 [47] subunits, which correspond to Monomer-1,
Monomer-2, and Monomer-3, respectively) have similar molecu-
lar structures with similar bond distances and angles. An analogue
of Monomer-1 without Br (Phen-12-crown-4) adopts a packed
to 70° in 0.5° steps, at
v = 45.0° and u = 0.0°. The structures were
solved using the Crystal Structure software package [45]. Atomic
scattering factors were obtained from the literature. Refinements
were performed anisotropically for all non-hydrogen atoms using
the full-matrix least-square method. Hydrogen atoms were placed
at the calculated positions and were included in the structure cal-
culation without further parameter refinement. The residual elec-
tron densities were of no chemical significance. The crystal data
and processing parameters are summarized in Table S1 in the
Supplementary Material (SM).
structure due to CH-
However, these CH- interactions and hydrogen bonds are absent
in Monomer-2 and Monomer-3. Phen-12-crown-4 does not exhi-
bit an intermolecular interaction in the solid state. In contrast,
p interactions and hydrogen bonds [46].
p
p–p
this type of interaction is observed for Monomer-2 and appears to
be assisted by halogen bonding between Br and O as shown in
Fig. S3b in the SM.
Poly(1,10-phenanthroline-3,8-diyl)s with crown ether subunits
(Poly-1, Poly-2, and Poly-3) were prepared by organometallic
polycondensation of Monomer-1, Monomer-2, and Monomer-3,
respectively, using a zero-valent nickel complex as a condensing
agent [27]. Poly-1, Poly-2, and Poly-3 were partially (approxi-
mately 1/4) soluble in CHCl3 and insoluble in organic solvents such
as DMF, DMSO and THF. Similarly to poly(pyridine-2,5-diyl)s and
3. Results and discussion
3.1. Monomer and polymer preparation
The synthetic routes for the monomers and polymers and their
reactions with [Ru(bpy)2]2+ are shown in Scheme 1.
The diol compound 1 [33] easily reacted with the bis-tosylate
compounds (Ts = tosyl; m = 1–3) to yield Monomer-1,
Monomer-2, and Monomer-3. The 1H NMR and IR spectra and
elemental analysis data are consistent with their structures (cf.
Section 2 and Figs. S1 (1H NMR) and S2 (IR) in the SM.
previously reported
p-conjugated poly(1,10-phenanthroline-3,8-
diyl)s [32–34,48], they were more soluble in formic acid. Specifi-
cally they were soluble in hot (approximately 60 °C) formic acid;
however, cooling the solution to room temperature caused the
polymer to precipitate. As observed for a poly(pyridine-2,5-diyl)
prepared by a similar organometallic polycondensation, Poly-1,
Poly-2, and Poly-3 did not contain Br, indicating that the
polymer–Ni end groups formed during the polymerization were
The molecular structures of Monomer-2 and Monomer-3 were
revealed by X-ray crystallography. Fig. 1 shows the molecular
3
0
-3
-3
-2
-1
0
1
2
Fig. 6. Cyclic voltammogram of Poly-1-Ru in a 0.1 M [Bu4N]ClO4 solution in CH3CN.
Sweep rate = 50 mV sꢀ1
Fig. 5. UV–Vis spectra of Poly-2-Ru in CH3CN.
.

14
H. Fukumoto et al. / Reactive & Functional Polymers 82 (2014) 9–16
9.4
9.2
9.0
8.8
8.64.6
4.4
4.2
4.0
3.8
3.6
Fig. 7. Changes of 1H NMR spectra of Monomer-1 (a) before and (b–d) after the addition of (b) LiPF6, (c) NaPF6 and (d) KPF6 in CD3CN.
a and b: 2,9-H and 4,7-H of the Phen
unit, respectively. A–C: CH2 groups in the crown ether unit (see Fig. S1b).
transformed into polymer-H end groups during the polymer work-
up, which included treating the crude polymer with acid (poly-
mer ꢀ NiLa + H+ ? polymer-H). The Ni complexes, which might
be trapped by the Phen unit, were removed by dimethylglyoxime
(see Section 2). The number average molecular weights (Mns) of
the chloroform-soluble polymer parts were estimated from the
1H NMR data described below. It is assumed that the CHCl3-
insoluble parts have larger Mns.
Poly-1 and Poly-2 were able to be dissolved in hexafluoro-2-
propanol (HFIP). When HFIP was used as the eluent in the GPC
analysis of Poly-1, a unimodal GPC curve was obtained, and
Poly-1 Mn, Mp (peak molecular weight in the GPC curve), and Mw
(weight average molecular weight) values were 8900, 21,000,
and 47,000 g molꢀ1, respectively. Poly-2 exhibited a multimodal
GPC curve [49], and the total GPC curve gave Mn and Mw of 1400
and 15,000 g molꢀ1, respectively. GPC analysis of Poly-3 was not
possible due to its low solubility in HFIP.
Poly-2 and Poly-3, which are listed in Table 1, were also estimated
from the HintA:HterA intensity ratios. The Mn of the CDCl3-soluble
part of Poly-2 is estimated to be 5300. The 1H NMR spectra of
the polymers in warm formic acid-d2 could not be collected
because the aromatic signals overlapped with the signals of solvent
impurities. All the polymers had good thermal stability under N2.
The TGA results for Poly-1, Poly-2, and Poly-3 (Fig. S4b in the
SM) show that they undergo a weight loss below 100 °C, which is
probably due to the loss of the waters of hydration (see Section 2).
The large weight loss observed between 280 and 450 °C might be
due to the decomposition of the crown ether subunit. Increasing
the temperature above 450 °C appears to result in the decomposi-
tion of the whole polymer including the Phen unit.
Fig. 3 shows the UV–Vis spectrum of Poly-2 in CHCl3. The p–
pꢂ
transition peak of Monomer-2 (kmax = 290 nm) in CHCl3 is red-
shifted (kmax = 361 nm) in Poly-2 because of the expansion of the
p
-conjugation system. This kmax value is similar to those of
PPhen(5,6-OR) (Chart 2) (kmax = 353–359 nm) [33] and is located
somewhat higher than that of -conjugated poly(2-alkyl-1,10-phe-
Table 1 summarizes the polymerization results and optical
properties of Poly-1, Poly-2, and Poly-3.
p
The IR spectra of the polymers shown in Fig. S4a in the SM are
nanthroline-3,8-diyl) (kmax = 330 nm) [51], which might have a
twisted main chain due to the steric effects of the 2-alkyl group.
In formic acid, Poly-1, Poly-2, and Poly-3 exhibit UV–Vis peaks
at approximately 380 nm (Table 1), which is similar to the peak
consistent with the polymer structure. The Phen
(C@C) peaks (or ring vibration peaks) of Poly-1 are observed at
approximately 1600 cmꢀ1. The peak at approximately 1270 cmꢀ1
m(C@N) and
m
is assigned to the
m
(CAO) peak of the crown ether subunit.
position observed for p-conjugated, non-substituted poly(phenan-
Fig. 2 shows the 1H NMR spectra of the Poly-1–Poly-3 chloro-
form-soluble parts in CDCl3. The ratios of the aliphatic and aro-
matic peaks areas are consistent with the molecular structures of
the polymers.
throline-3,8-diyl) in formic acid [33]. The UV–Vis absorption peaks
of Poly-1, Poly-2, and Poly-3 in CHCl3 are slightly red-shifted in
cast films (e.g., from 361 nm to 377 nm for Poly-2). The small shifts
indicate the absence of strong intermolecular electronic interac-
tions between the polymer molecules in the solid state.
Poly-1, Poly-2, and Poly-3 exhibited PL emission peaks in CHCl3
in the range of 475–500 nm with quantum yields of 3.3–8.7%,
which are comparable to that of PPhen(5,6-OR) (ca. 4%). UV–Vis
and PL data obtained under various conditions are shown in
Figs. S5 and S6 and Table S2 in the SM.
As shown in Fig. 2, two major aromatic peaks are observed in a
1:1 ratio at approximately d 9.6 and 9.0 in the 1H NMR spectra.
These peaks are assigned to 2,9-H and 4,7-H of the Phen unit (HintA
and HintB in Fig. 2, respectively). Additional peaks appear in the
spectra at approximately d 9.2, 8.6 and 7.7 in a 1:1:1 ratio. The
peak at d 7.7 appears nearly the same position as that of 3,8-H in
1,10-phenanthroline (d 7.6) [50], and is assigned to the terminal-
H of the polymer (HterC in Fig. 2). Thus, the other peaks at d 9.2
and 8.6 are assigned to 2(or 9)-H and 4(or 7)-H, respectively, of
the terminal Phen unit (HterA and HterB, respectively, in Fig. 2).
Because the polymers did not contain Br (vide ante), the 1:1:1 ratio
for the additional peaks is reasonable. Poly(5,6-dialkoxy-1,10-
phenanthroline-3,8-diyl) (PPhen(5,6-OR); Chart 2), which was
prepared by a similar procedure, also exhibits an HterC peak at d
7.7 [33].
3.2. Formation of [Ru(bpy)2]2+ complexes
Reacting the polymers with [RuCl2(bpy)2] under reflux condi-
tions in water yielded water-soluble polymer complexes (see
Scheme 1). The solubility of the products is likely due to their ionic
structures. The addition of NH4PF6 to the reaction mixtures affor-
ded the water-insoluble precipitates Poly-1-Ru, Poly-2-Ru, and
Poly-3-Ru. Similar solubility and precipitation effects due to coor-
dinated [Ru(bpy)2]2+ and NH4PF6, respectively, were observed for
For Poly-1, the intensity ratio of HintA to HterA is approximately
6:1. From these data, the degree of polymerization is calculated to
be approximately 7, which corresponds to an Mn of 2300 g molꢀ1
(Table 1). It is assumed that the Mn of the rest chloroform-insoluble
part (approximately 3/4 of the polymer) is higher. The Mns of
[Ru(bpy)2]2+ complexes of
p
-conjugated oligo-(2,20-bipyridine-
5,50-diyl) and oligo-(2,20-bipyrimidine-5,50-diyl) [52]. Low-molecu-
lar-weight Phen compounds with crown ether subunits usually
react with transition metal complexes (e.g., Re and Ru complexes)

H. Fukumoto et al. / Reactive & Functional Polymers 82 (2014) 9–16
15
to give products in which transition metals are attached to the
Phen unit and not the crown-ether-unit [36–39,47].
solvent, and the results are shown in Fig. S9a in the SM. It is
assumed that the sample solution contains both Monomer-1 and
Li+-coordinated Monomer-1 (Monomer-1-Li). The NMR data
shown in Fig. S9a in the SM indicate rapid chemical exchange
between Monomer-1 and Monomer-1-Li on the NMR time scale
because only one signal is observed for 2,9-H (at approximately d
9.0 without LiPF6) and 4,7-H (at approximately d 8.6 without
LiPF6). The procedures to prepare the NMR samples for the data
collection shown in Fig. S9a are described below the figure.
Fig. S9b shows the dependence of the aromatic 4,7-H chemical
shift on the amount of added LiPF6. A comparison of the 1H NMR
data shown in Fig. S1a and part (a) of Fig. S9a shows that the
Monomer-1 aromatic (4,7-H and 2,9-H) signals appear at similar
positions in CDCl3 (Fig. S1a) and in the 6:1 CDCl3:CD3CN mixture
(Fig. S9a). However, the Monomer-1-Li 4,7-H and 2,9-H signal
positions appear to be affected by the nature of the solvent, as
shown in part (b) of Fig. 7 and part (h) of Fig. S9a.
As mentioned previously, the polymer-[Ru(bpy)2]2+ complexes
were soluble in organic solvents, including CH3CN, acetone, and
DMSO. Fig. 4a shows the 1H NMR spectrum of Poly-1-Ru in CD3CN.
The area ratio of the aromatic to crown ether protons is 1.71:1,
which is consistent with the ratio (20:12 or 1.67:1) calculated
based on full coordination of [Ru(bpy)2]2+ to the polymer ligand.
Poly-2-Ru and Poly-3-Ru (Fig. 4b and c, respectively) have similar
1H NMR spectra, which also support the full coordination of
[Ru(bpy)2]2+ to the polymer ligands. These data indicate that
[Ru(bpy)2]2+ can coordinate to the polymeric compounds quantita-
tively because of the high affinity of [Ru(bpy)2]2+ for 1,10-
phenanthroline.
The ICP-AES results showed that Poly-2-Ru contained 9.5% Ru,
which is also consistent with the full coordination of [Ru(bpy)2]2+
to the polymer ligand (calculated Ru content = 9.4% for
((C20H20N2O5)[Ru(bpy)2]2PF6)n or (C40H36F12N6O5P2Ru)n). The Ni
content was negligible. The IR spectra of Poly-1-Ru–Poly-3-Ru
and Poly-1 are shown in Fig. S7 in the SM. In addition to the poly-
Under the rapid-exchange conditions, the chemical shifts of the
Monomer-1 and Monomer-1-Li peaks are averaged to give one
NMR signal. The position of the newly obtained NMR signal reflects
the ratio of these two chemical species, and the molar ratio of
Monomer-1 to Monomer-1-Li can be calculated from the NMR
peak position. Fig. S9b in the SM shows the change in the shift
mer and bpy aromatic ring and
Poly-1-Ru–Poly-3-Ru IR spectra, characteristic PFꢀ6 peaks appear
at approximately 840 and 560 cmꢀ1
As shown in Fig. 5, a new peak is observed at 431 nm in the
Poly-2-Ru UV–Vis spectrum in addition to the
pꢂ transition
m(CAOAC) vibrations observed in
.
(
D
d) of the chemical shift of the 4,7-H peak as a function of the
amount of LiPF6. As shown in Fig. S9b, d appears to reach a max-
imum of approximately d = 0.12–0.13 as the amount of LiPF6
p
–
D
peaks of bpy and the original polymer at 285 and 359 nm. This
new peak is assigned to MLCT (metal-to-ligand charge transfer).
Poly-1-Ru and Poly-3-Ru exhibit similar UV–Vis spectra, and the
UV–Vis spectroscopic data of the polymer complexes are listed in
Table S3 in the SM. The intensity of the peak at 431 nm is reason-
able for MLCT. The position of the MLCT peak is also typical for
[Ru(NAN)3]2+-type complexes, where NAN is an aromatic chelat-
ing ligand with two N coordination sites (e.g., [Ru(bpy)3]2+ and a
[Ru(bpy)2]2+ complex with oligo-(2,20-bipyridine-5,50-diyl)) [52].
Because the polymer complexes are soluble in CH3CN, their
electrochemical responses can be measured with their solutions.
Fig. 6 shows the CV curve for Poly-1-Ru in a 0.1 M [Bu4N]ClO4
(Bu = butyl) solution in CH3CN. This CV curve is similar to those
D
increases. The data shown in Fig. S9b suggest that the Monomer-
1/Monomer-1-Li ratio is 1 when [LiPF6]/[Monomer-1] = 0.7. At
this Monomer-1/Monomer-1-Li ratio, the Li+ concentration is
estimated to be approximately 0.7 mM, which corresponds to an
association constant K = [Monomer-1-Li]/[Monomer-1][Li+] of
approximately 1400 Mꢀ1 (see the caption of Fig. S9b). The
Monomer-1 UV–Vis spectrum does not change significantly upon
the addition of LiPF6.
The Monomer-1 ESI-MS results obtained in the presence of
M[PF6] (M = Li, Na, K; see Section 2), however, suggest somewhat
different complexation mechanism for the monomers and Br2Phen
with M+, indicating that they behave differently toward MPF6
under the ESI-MS conditions. The ESI-MS data shown in Table S4
and Fig. S10 in the SM suggest that (1) Br2Phen does no form com-
plexes with alkaline metal cations and (2) Monomer-1 has a stron-
ger affinity for Na+ than Li+ under the ESI-MS conditions.
Monomer-2 and Monomer-3 have a strong affinity for Na+ and
K+ under the ESI-MS conditions as shown in Table S4.
As mentioned previously, Poly-1, Poly-2, and Poly-3 exhibited
limited solubility in organic solvents. However, the polymers
became more soluble in CH3CN upon the addition of LiPF6.
Fig. S11 in the SM shows the changes in the Poly-1 1H NMR spec-
trum upon the addition of LiPF6. Specifically, the Phen-H signals
undergo larger shifts than the crown ether-H signals, suggesting
that Li+ mainly coordinates to the Poly-1 Phen unit, as is the case
for Monomer-1.
of [Ru(NAN)3]2+-type complexes such as [Ru(bpy)3]2+ and
a
[Ru(bpy)2]2+ complex with poly(2,20-bipyridine-5,50-diyl) [32,53].
The anodic peak at Epa = 0.98 V vs Ag+/Ag is assigned to the oxida-
tion of Ru(II) to Ru(III). In the reduction region, three peaks at
Epc = ꢀ1.29, ꢀ1.88 and ꢀ2.18 V vs Ag+/Ag are observed, which is
typical for [Ru(NAN)3]2+-type complexes. The CV curve of a
Poly-2 film [54] cast on a Pt plate exhibits a reduction peak at
about Epc = ꢀ2.2 V vs Ag+/Ag, which is similar to that of
PPhen(5,6-OR) (Chart 2).
3.3. Reactivity of the monomers and polymers toward alkaline metal
ions
Fig. 7 shows the changes in Monomer-1 1H NMR spectra upon
addition of excess MPF6 (M = Li, Na, K).
The addition of excess LiPF6 significantly enhances the solubil-
ity of Monomer-1 in CH3CN. As shown in Fig. 7, the Phen peaks
undergo obvious changes upon addition of LiPF6 and NaPF6.
However, the crown ether signals are only slightly shifted, indicat-
ing that Li+ and Na+ coordinate mainly to the Phen unit (not to the
crown ether unit). The addition of LiPF6 and NaPF6 to a CD3CN solu-
tion of 3,8-dibromo-1,10-phenanthroline (Br2Phen, Chart 2) also
leads to large changes in its aromatic signals as shown in Fig. S8
in the SM, verifying that Li+ and Na+ coordinate mainly to Mono-
mer-1 Phen unit. The data shown in Fig. 7 and S8 indicate that
Monomer-1 and Br2Phen do not have a strong affinity for K+.
The effects of the amount of added LiPF6 on the Monomer-1 1H
NMR were determined using a 1:6 (vol/vol) CD3CN:CDCl3 mixed
4. Conclusions
New p-conjugated polymers consisting of the 1,10-phenanthro-
line (Phen) units and the crown ether subunits (Poly-1, Poly-2, and
Poly-3) were prepared, and the molecular structures of the mono-
mers were revealed by X-ray crystallography. A part of the polymer
is soluble in CHCl3, and the Mns of the soluble parts were estimated
to be 2300–5300 based on the 1H NMR data. The Phen unit has a
strong affinity for [Ru(bpy)2]2+, and the complexation of these spe-
cies makes the polymer soluble. The resulting Poly-1-Ru–Poly-3-
Ru complexes are electrochemically active and exhibit a reduction
peak at approximately ꢀ2.1 V vs Ag+/Ag. The Phen unit also
interacts with M+ (M = alkaline metal) [55] and the addition of

16
H. Fukumoto et al. / Reactive & Functional Polymers 82 (2014) 9–16
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LiPF6 increases the solubility of the polymer.
mers with crown ether subunits have attracted much interest from
the research community, and the present results add new
knowledge to the field of p-conjugated polymers and crown ethers.
p-Conjugated poly-
Acknowledgement
We are grateful to Ms. K. Tsutsui of the Institute for the
Molecular Science for the ESI-MS analysis.
[33] T. Yamamoto, Y. Saitoh, K. Anzai, H. Fukumoto, T. Yasuda, Y. Fujiwara, B.-K.
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Appendix A. Supplementary data
(IR, 1H NMR, UV–Vis, PL, ESI-MS and CV data and the molecular
structure of Monomer-3). Supplementary data associated with
this article can be found, in the online version, at http://
dx.doi.org/10.1016/j.reactfunctpolym.2014.05.002.
[38] L.-X. Liu, H.-P. Huang, X. Li, Q.-F. Sun, C.-R. Sun, Y.-Z. Li, S.-Y. Yu, Dalton Trans.
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