Poly(1,10-phenanthroline-3,8-diyl) and its derivatives. Preparation, optical and electrochemical properties, solid structure, and their metal complexes

Article abstract of DOI:10.1021/ma0302659

π-Conjugated poly(1,10-phenanthroline-3,8-diyl), PPhen, and its 5,6-dialkoxy derivatives. PPhen(5,6-OR)s, have been synthesized by using an organometallic polycondensation with a zerovalent nickel complex. They have average molecular weights of 4300-6800. PPhen had a stiff structure, as revealed by a light scattering method, and exhibited a strong dichroism in UV-vis absorption and photoluminescence. PPhen(5,6-OR)s formed an end-to-end packing assembly assisted by the side chain crystallization of the OR groups. PPhen and PPhen(5,6-OR)s were susceptible to chemical and electrochemical reduction, and the reduced state showed certain stability toward oxygen in air. The π-conjugated polymers underwent quantitative complex formation with [Ru(bpy)₂]²⁺. Introduction of two more imine nitrogens in the repeating unit of PPhen enhanced much the electron accepting property of PPhen, and n-doping of the obtained polymer took place at E_pc of -1.38 V vs Ag⁺/Ag.

Full text of DOI:10.1021/ma0302659

6722
Macromolecules 2003, 36, 6722-6729
Poly(1,10-phenanthroline-3,8-diyl) and Its Derivatives. Preparation,
Optical and Electrochemical Properties, Solid Structure, and Their
Metal Complexes
Ta k a k a zu Ya m a m oto,*,† Yu ta k a Sa itoh ,† Ka zu sh ige An za i,† Hir ok i F u k u m oto,†
Ta k u m a Ya su d a ,† Yosh ik i F u jiw a r a ,† Byou n g-Ki Ch oi,† Ken ji Ku bota ,‡ a n d
Ta k a yu k i Miya m a e§
Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku,
Yokohama 226-8503, J apan, Faculty of Engineering, Gunma University, Tenjincho,
Kiryu 376-8515, J apan, and Institute of Molecular Science, Okazaki 444-8585, J apan
Received May 9, 2003; Revised Manuscript Received J une 29, 2003
ABSTRACT: π-Conjugated poly(1,10-phenanthroline-3,8-diyl), PPhen, and its 5,6-dialkoxy derivatives,
PPhen(5,6-OR)s, have been synthesized by using an organometallic polycondensation with a zerovalent
nickel complex. They had average molecular weights of 4300-6800. PPhen had a stiff structure, as revealed
by a light scattering method, and exhibited a strong dichroism in UV-vis absorption and photolumines-
cence. PPhen(5,6-OR)s formed an end-to-end packing assembly assisted by the side chain crystallization
of the OR groups. PPhen and PPhen(5,6-OR)s were susceptible to chemical and electrochemical reduction,
and the reduced state showed certain stability toward oxygen in air. The π-conjugated polymers underwent
quantitative complex formation with [Ru(bpy)2]2+. Introduction of two more imine nitrogens in the
repeating unit of PPhen enhanced much the electron accepting property of PPhen, and n-doping of the
obtained polymer took place at Epc of -1.38 V vs Ag+/Ag.
In tr od u ction
π-Conjugated polymers1 constituted of chelating ligands
such as 2,2′-bipyridyl (PBPy),2 2,2′-bipyrimidine
(PBPym),3 and 1,5-naphthyridine4 are the subject of
recent interest.2-5 The chemical and optical properties
of their metal complexes2-6 have vigorously been
investigated.2-7 The chemical and physical properties
of metal complexes of π-conjugated oligomeric ligands
have also been investigated, for example, by Schanze.8
1,10-Phenanthroline is an attractive π-conjugated
ligand, and its function to form molecular archi-
tectures5a,9-14 (e.g. catenanes prepared by Sauvage9) has
been pursued. However, π-conjugated polymers consti-
tuted of 1,10-phenanthroline have not received much
attention. Herein we report the preparation, chemical
properties, and functions of π-conjugated polymers
consisting of the 1,10-phenanthroline unit. 1,10-Phenan-
throline has considerably stronger (by 1 or 2 orders of
magnitude) coordinating ability toward transition met-
als than 2,2′-bipyridyl,15a,b presumably due to its fixed
cis-chelating structure in contrast to the case of 2,2′-
bipyridyl, which takes a s-trans conformation.15c,d
The polycondensation proceeded smoothly, and good
yields were attained.
Poly(1,10-phenanthroline-3,8-diyl), PPhen, was soluble
in formic acid and partially soluble in sulfuric acid;
however, it was not soluble in common organic solvents.
PPhen had a weight average molecular weight, Mw, of
6800, as determined by light scattering analysis17a-c in
formic acid, the Mw value corresponding to a degree of
polymerization (n in eq 1) of 38. PPhen showed no
content of Br in the elemental analysis, indicating that
the formed polymer had a polymer-Ni terminal group
and this terminal group was converted into a poly-
mer-H group during workup, similar to the case of
polypyridine.2b
Resu lts a n d Discu ssion
P r ep a r a tion . Organometallic dehalogenative poly-
condensation using a zerovalent nickel complex1,16 gave
the following π-conjugated poly(1,10-phenanthroline)s.
† Tokyo Institute of Technology.
‡ Gunma University.
PPhen gave an intrinsic viscosity, [η], of 0.40 dL g-1
in formic acid. This [η] value corresponds to a molecular
§ Institute of Molecular Science (Present affiliation: National
Institute of Advanced Industrial Science and Technology).
10.1021/ma0302659 CCC: $25.00 © 2003 American Chemical Society
Published on Web 08/09/2003

Macromolecules, Vol. 36, No. 18, 2003
Poly(1,10-phenanthroline-3,8-diyl) 6723
poly(methyl methacrylate) standards), respectively.
PPhen(5,6-OPen), PPhen(5,6-OOct), and PPhen(5,6-
ODod) did not contain Br; on the other hand, PPhen-
(5,6-OHexd) contained Br in 0.5 wt % (cf. Experimental
Section). This negligible or small content of Br supports
a view that PPhen(5,6-OR)s have mainly an H-termi-
1
nated Phen group. H NMR spectra of PPhen(5,6-OR)s
exhibited a small peak assigned to the 3-H proton in
the terminal PPhen unit, as shown in Figure 1, and the
peak area of the 3-H proton gave Mn of 6000, 4300, 5600,
and 6100 for PPhen(5,6-OPen), PPhen(5,6-OOct), PPhen-
(5,6-ODod), and PPhen(5,6-OHexd), respectively. The
larger Mn value of 17 000 estimated from the GPC
analysis for PPhen(5,6-OPen) may be due to a stiff
structure of PPhen(5,6-Pen), since a stiff polymer is
considered to have a larger effective volume than that
of the random-coil type poly(methyl methacrylate) used
as the standard for the GPC analysis. The 1H NMR peak
area ratio between the aromatic-H and aliphatic-H
agreed with the structure of PPhen(5,6-OR).
IR spectra of the polymers agreed with the structures
shown in eqs 1 and 2. They showed peaks originated
from the monomers, except for the ν(C-Br) peaks at
about 1100 cm-1 (cf. the Supporting Information).
UV-vis Da ta . The UV-vis absorption peak of 1,10-
phenanthroline at 277 nm in formic acid was shifted to
382 nm in PPhen due to the expansion of the π-conjuga-
tion system, the peak position being located near those
of poly(pyridine-2,5-diyl) (374 nm) and poly(2,2′-bipyri-
dine-5,5′-diyl) (373 nm).2 For monomeric 1,10-phenan-
throline itself, its UV-vis absorption peak was shifted
from 265 nm in diethyl ether to 277 nm in formic acid.
The absorption band of PPhen at 382 nm was sharp
with a half-width of about 45 nm, and nonprotonated
PPhen was considered to give the UV-vis band at
somewhat shorter wavelength.
F igu r e 1. 1H NMR spectra of (a) PPhen(5,6-ODod) and (b)
PPhen(5,6-OPen) in CDC13.
weight of 79 000 for polystyrene.17d The light scattering
analysis of PPhen gave a degree of depolarization, Fv,
of 0.15. The Fv value can be taken as a measure for
stiffness of polymers,17a-c and the obtained Fv value is
comparable to that of a stiff all aromatic polyamide,
poly(1,4-phenylene terephthalamide) or Kevlar, in sul-
furic acid; poly(1,4-phenylene terephthalamide) shows
Fv values of 0.175 and 0.11 at Mw values of 4500 and
35 000, respectively.17c The IR spectrum, 1H NMR
spectrum of PPhen in formic acid-d2, and CP-MAS solid
13C NMR spectrum of PPhen are given in the Support-
ing Information.
PPhen 5,6-dialkoxy derivative, PPhen(5,6-OR), type
polymers were soluble in chloroform; however, they
showed lower solubility in THF and DMF. Gel perme-
ation chromatography (GPC) using chloroform as an
eluent was not suited for determination of the molecular
weight of the polymer due to strong interaction between
the polymer and the column. One of the polymers,
PPhen(5,6-OPen), was soluble in hexafluoroisopropanol,
which had been used for GPC analysis of π-conjugated
N-containing heteroaromatic polymers,18 and the GPC
analysis using the solvent gave a number average
molecular weight, Mn, of 17 000 and Mw of 33 000 (vs
PPhen(5,6-OR)s also gave the UV-vis peak (λmax
)
353-359 nm (ꢀ ) (2.1-2.4) × 104 M-1 cm-1 on the basis
of the repeating unit; cf. Table 1) near the λmax position
of PPhen; the λmax position was shifted to a longer
wavelength by 61-68 nm from that of the corresponding
monomers. As shown in Table 1, the UV-vis absorption
peak of PPhen(5,6-OR)s is shifted to a longer wave-
length by 10-20 nm in the film, and this suggests the
presence of intermolecular electronic interaction such
as π-π interaction due to formation of a π-stacked
structure.19-21
Align m en t of P P h en in a Str etch ed P VA F ilm .
Due to the stiff structure of PPhen, it exhibited align-
ment in a stretched PVA (poly(vinyl alcohol)) film.
Painting the PVA film with the formic acid solution of
PPhen and drying up the film under vacuum gave the
Ta ble 1. Syn th etic a n d Op tica l Da ta of P olyp h en a n th r olin es
molecular weighta UV-vis peak,c nm
PL peak,c,d nm
no.
polymer
PPhen
yield, %
Mn
Mw
[η],b dL g-1
in solution
film
in solution
film
1
2
81
84
6800(L)
33000(G)
0.40
382(F)
359(C)
380
369
413(F)
504(C)
535
530
PPhen(5,6-OPen)
17000(G)
6000(N)
4300(N)
5600(N)
6100(N)
3000(G)f
3
4
5
6
PPhen(5,6-OOct)
PPhen(5,6-ODod)
PPhen(5,6-OHexd)
PDPypd
63
74
86
70
356(C)
359(C)
353(C)
370(F)e
435(D)e,f
368
380
371
370
485(C)
478(C)
468(C)
500(F)
500(D)
518
517
520
a
Mn ) number average molecular weight. Mw ) weight average molecular weight. L, determined by light scattering; G, determined by
GPC; N, determined from 1H NMR data. Intrinsic viscosity. dL ) 100 mL. c F, in formic acid; C, in chloroform; D, in N,N-
b
dimethylformamide (DMF). PL ) photoluminescence. e An additional weak peak at about 440 nm is observed. f For a DMF soluble part.
d

6724 Yamamoto et al.
Macromolecules, Vol. 36, No. 18, 2003
of the excimer-like adduct is considered to be enhanced.
For PPhen(5,6-OPen), even the PL peak (504 nm)
observed in the chloroform solution is deviated to a
longer wavelength from the onset position (about 410
nm) of the UV-vis absorption band, as shown by curves
c and d in Figure 3. These results indicate that PPhen-
(5,6-OPen) has a strong tendency to form the stabilized
excimer-like adduct even in the chloroform solution at
an order of 10-5-10-4 M (molarity is based on the 1,10-
phenanthroline unit). Assistance of the side OPen
groups to form the excimer-like adduct is conceivable,
since long alkyl side chains of π-conjugated polymers,
as in head-to-tail type poly(3-alkylthiophene),19-21 often
assist self-assembly of the polymers. In the film, the PL
peak of PPhen(5,6-OPen) shifts further to a longer
wavelength, as depicted by curve e in Figure 3, presum-
ably due to enhancement of the formation of the
excimer-like adduct. PPhen(5,6-OR)s showed a quantum
efficiency of about 4% for PL in the chloroform solution.
P h otolu m in escen ce of P P h en in th e Str etch ed
P VA F ilm . Since PPhen molecules were oriented along
the direction of the stretching in the stretched PVA film,
a unique PL response was observed with the stretched
PVA film containing PPhen.
F igu r e 2. Dichroism of the stretched PVA film containing
PPhen. At 385 nm. Dichroic ratio ) Abs(|)/Abs( ); Abs(|) and
Abs( ) are absorbances observed on irradiation with light with
the oscillating electric field parallel and perpendicular, re-
spectively, to the direction of the stretching of the PVA film.
For the stretching ratio, cf. the Supporting Information.
When nonpolarized light was used to irradiate the
stretched (stretching ratio ) 13.6) PVA film containing
PPhen, PL light with a peak at 505 nm was emitted,
and the emitted light was found to be polarized. The |
(the direction of the oscillating electric field of the
emitted light is parallel to the direction of the stretching
of the film) component of the emitted light was about 6
times stronger than the component. Irradiation with
| polarized light of the film led to emission of | polarized
light; however, irradiation with polarized light caused
a very weak emission of light. These results indicate
that both absorption and emission of light take place
along the direction of the main chain of the stiff PPhen
molecule.
F igu r e 3. UV-vis and photoluminescence (PL) spectra of
PPhen (s) and PPhen(5,6-OPen) (- - -): (a) PL of PPhen in
formic acid at 10-6 M of the monomer units; (b) PL of a PPhen
cast film; (c) UV-vis of PPhen(5,6-OPen) in chloroform; (d)
PL of PPhen(5,6-OPen) in chloroform; (e) PL of a PPhen(5,6-
OPen) cast film.
Electr on -Accep tin g P r op er ties. 1,10-Phenanthro-
line is a typical electron-accepting ligand and stabilizes
low valent transition metal complexes.
PVA film containing PPhen molecules in the surface
region, and the film showed the UV-vis peak of PPhen
at λmax ) 385 nm. Stretching of the PVA film caused
alignment of the PPhen molecules along the direction
of the stretching, which was seen from dichroism
observed for the film. As shown in Figure 2, the dichroic
ratio [)(absorbance at a parallel mode)/(absorbance at
a perpendicular mode)] increases with increase in the
stretching ratio of the PVA film. These results support
the stiff linear structure of PPhen.
The π-conjugated 1,10-phenanthroline polymers were
inert against electrochemical oxidation. However, their
cast films on a Pt electrode were susceptible to electro-
chemical reduction (or n-doping),14 for example,
P h otolu m in escen ce. Figure 3 exhibits photolumi-
nescence (PL) spectra of PPhen and PPhen(5,6-OPen).
Other PPhen(5,6-OR)s gave essentially the same PL
spectra as PPhen(5,6-OPen).
PPhen in formic acid shows a PL peak at 413 nm
(curve a in Figure 3), which roughly agrees with the
onset position of the UV-vis absorption band, as usually
observed with aromatic compounds, including aromatic
π-conjugated polymers.1 However, in its cast film, the
PL peak shifts to 535 nm, as exhibited by the curve b
in Figure 3. A similar phenomenon was reported for stiff
poly(pyridine-2,5-diyl),2b and this type of shift of the PL
peak to a longer wavelength seems to be attributable
to formation of a stabilized excimer-like adduct between
photoactivated π-conjugated polymer and polymer in the
ground state. In the solid, the distance between the
neighboring PPhen molecules is short, and formation
In eq 3, the peak cathode and anode potentials versus
Ag+/Ag evaluated from cyclic voltammetry (CV) are
shown. The doping level, x in eq 3, was about 0.5, as
estimated from the n-doping current. According to the
reduction, the color of the film of PPhen changed from
reddish brown to dark purple, as described in eq 3. UV-
vis spectra of a cast film of PPhen on an ITO (indium-
tin oxide) glass plate showed new broad absorption
bands at 850 and 1360 nm at -1.9 V versus Ag+/Ag and
at 1100 and 1360 nm at -2.4 V versus Ag+/Ag, respec-

Macromolecules, Vol. 36, No. 18, 2003
Poly(1,10-phenanthroline-3,8-diyl) 6725
Ta ble 2. Cyclic Volta m m etr y Da ta of th e P olym er F ilm s
in a 0.10 M [Bu 4N]P F 6 CH3CN Solu tion a
to the vd-PTh layer to meet holes in vd-PTh, which is
considered to be a hole-carrying material,24 to emit the
light by the electron-hole coupling.
The IR spectrum of vd-PPhen was essentially identi-
cal to that of the original PPhen, showing main peaks
at the same positions; however, PPhen molecules with
a relatively small degree of polymerization were con-
sidered to be vacuum evaporated preferentially. The IR
data and EL spectrum obtained at 9.0 V and 1.0 A cm-2
are shown in the Supporting Information.
The electron-accepting properties of PPhen are con-
sidered to originate from its containing electron-accept-
ing -CdN- imine nitrogens.1,26 To check the effect of
the imine nitrogen and to enhance the electron-accept-
ing properties of PPhen, we have prepared the following
PDPypy, poly(dipyrido[3,2-c:2′,3′-e]pyridazine-3,8-diyl),
using the zerovalent nickel complex.
polymer
PPhen
PPhen(5,6-OPen)
PPhen(5,6-OOct)
PPhen(5,6-ODod)
PPhen(5,6-OHexd)
PDPypy
Epc/V
Epa/V
E° b/V
-2.24
-2.23
-2.15
-2.17
-2.28
-1.38
-1.98
-1.93
-1.96
-1.95
-1.97
-0.82
-2.11
-2.08
-2.06
-2.06
-2.13
-1.10
a
b
Voltage: vs Ag+/Ag. E° ) (Epc + Epa)/2. Obtained with cast
films on a Pt electrode.
tively; such broad absorption bands in the near-infrared
region were often observed with doped π-conjugated
poly(heteroaromatic)s and assigned to polaron and/or
bipolaron bands.1 PPhen(5,6-OR)s also underwent analo-
gous electrochemical reduction (n-doping) and the cor-
responding n-dedoping, and the CV data of the polymers
are summarized in Table 2.
When [NR4]Y (Y ) PF6, BF4) was used as the
electrolyte, the polymer films afforded CV charts with
good reproducibility in repeated scanning. However,
when Li salts such as Li [CF3SO3] were employed as
the electrolyte, only the reduction peak was observed
in the first scan, and its corresponding oxidation (n-
dedoping) was not observed up to 1.5 V versus Ag+/Ag.
In the second scan, neither the reduction nor oxidation
peaks were observed. These data suggest that a strong
interaction22a of Li+ with the 1,10-phenanthroline unit
stabilizes the reduced state, for example,
Assembled transition metal complexes of heteroaro-
matic ligand(s) with multi-N-coordinating sites are
actively investigated, especially recently,27 and transi-
tion metal complexes of dipyrido[3,2-c:2′,3′-e]pyridazine
have been synthesized.28a-c Dipyrido[3,2-c:2′,3′-e]py-
ridazine is one of the strongest electron-accepting N-
ligands, and MO calculation indicates that it has a
LUMO with about 1 eV lower energy compared with
that of 1,10-phenanthroline.28c
The obtained PDPypy had no Br, either, and was
soluble in formic acid and partly (about 30%) soluble in
DMSO and DMF. GPC analysis of the DMF-soluble part
gave Mn of 3000 with a Mw/Mn value of 1.1. Since both
the DMF-soluble and -insoluble parts showed the same
IR spectrum, the polymer molecules with relatively low
molecular weights were considered to be dissolved in
DMF. PDPypy gave a UV-vis peak at 370 nm in formic
acid. The PL spectrum of PDPypy showed a large Stokes
shift from 370 to 500 nm. This large Stokes shift might
be attributed to stabilization of protonated PDPypy by
releasing a proton after the photoexcitation. Stabiliza-
tion of photoexcited molecules by a shift of hydrogen or
protons and ensuring molecular relaxation are subjects
of recent interest.28d-g
Similar stabilization of a reduced state was previously
reported for a π-conjugated polythiophene with a crown
ether subunit. In this case, trap of alkaline metal by
the crown ether subunit seemed to bring about the
stabilization of the reduced state,22b and the reduced
polymer showed some stability even on exposure of the
reduced polythiophene to air.
Analogously, PPhen reduced by sodium naphthalen-
ide showed certain stability on exposure to air. In the
case of Na-reduced poly(pyridine-2,5-diyl), its exposure
to air caused instant color and IR changes;2b however,
the changes in color and IR observed with the reduced
PPhen were gradual. Potassium-doped PPhen gave a
ultraviolet photoelectron spectrum similar to that of
potassium-doped poly(2,2′-bipyridine-5,5-diyl),23 and the
ultraviolet photoelectron spectrum of PPhen indicated
that PPhen had an ionization potential of about 6 eV.
Changes of the IR spectrum of Na-doped PPhen on
exposure to air and ultraviolet photoelectron spectra of
PPhen and K-doped PPhen, which reveal formation of
new electronic state(s), are shown in the Supporting
Information. Due to the electron-accepting properties
of PPhen, it is expected to serve as an electron-carrying
material in electronic devices. For example, an elec-
troluminescence device, ITO glass/vd-PTh (100 Å)/vd-
PPhen (180 Å)/Mg:Ag (ITO ) indium-tin oxide; vd-PTh
) vacuum deposited poly(thiophene-2,5-diyl);24 vd-
PPhen25 ) vacuum deposited PPhen; Mg:Ag ) Mg-Ag
alloy (coevaporated)), showed electroluminescence at
about 600 nm24 from the vd-PTh layer. Electrons
injected from the cathode seem to be able to move in
the vd-PPhen layer, and they are considered to reach
CV data of a cast film of PDPypy in a 0.10 M [NEt4]-
BF4 solution of acetonitrile indicated that its electro-
chemical reduction took place more easily than that of
PPhen, as expected.
The CV curve was reproducible on repeated scanning.
The Epc value indicates that PDPypy has the highest
electron-accepting ability among various N-containing
heteroaromatic π-conjugated polymers.28h

6726 Yamamoto et al.
Macromolecules, Vol. 36, No. 18, 2003
F igu r e 4. XRD patterns of (a) PPhen(5,6-OHexd), (b) PPhen-
(5,6-ODod), (c) PPhen(5,6-OOct), (d) PPhen(5,6-OPen), and (e)
PPhen.
P a ck in g Str u ctu r e of th e P olym er s. Figure 4
shows powder XRD patterns of PPhen and PPhen(5,6-
OR)s. The XRD pattern of PPhen(5,6-OPen) gives three
peaks at d1 ) 18 Å, d2 ) ∼4.5 Å, and d3 ) ∼3.4 Å.
π-Conjugated heteroaromatic polymers with side chains
and a regularly repeated structure often give an XRD
peak at a low angle region (2θ(Cu KR) < 5°), and the d1
value of the peak at the low angle region has been
assigned to the distance between the π-conjugated
polymer chains separated by the side chains.19-21,29
Plots of the d1 values of PPhen(5,6-OR)s versus the
number of carbons in the OR group give a linear line,
as depicted in Figure 5. Since one -CH2- group has a
height of 1.25 Å along the direction of the R chain,30
the larger slope of the linear line, 1.51 Å/carbon,
suggests that PPhen(5,6-OR) takes an end-to-end pack-
ing mode, as depicted in part b of Figure 5.
The XRD chart of PPhen(5,6-OPen) (curve d in Figure
4) shows two overlapped peaks at about d2 ) 4.5 Å and
d3 ) 3.4 Å. The d2 peak can be assigned to a side-to-
side distance between the R chains,30 and the d3
distance of 3.4 Å is reasonable for the π-π stacking
distance of the 1,10-phenanthroline polymer sheets.31
If this d3 peak is assigned to the sheet-to-sheet π-π
stacking distance, it gives a calculated density of 1.23
g cm-3 for PPhen(5,6-OPen).32 This calculated value
agreed with the observed density of 1.23 g cm-3. When
the OR side chain gets longer, the d2 peak becomes
stronger and the d3 peak becomes obscure (curves b and
c in Figure 4). In the case of PPhen(5,6-OHexd), the d3
peak seems to be hidden under the strong d2 peak. As
seen from the XRD data, PPhen(5,6-OR)s are considered
to form a sheet depicted in Figure 5, and the sheets are
considered to form a stacked structure. Although the
CPK molecular model of PPhen(5,6-OR) indicates that
there is some space between the OR groups along the
PPhen(5,6-OR) main chain, penetration of the OR
groups into the space in the neighboring PPhen(5,6-OR)
molecules to form the interdigitation packing (cf. part
b in Figure 5) does not seem possible; on this basis,
PPhen(5,6-OR) is considered to take the end-to-end
F igu r e 5. (a) Plots of the d1 value vs number of carbons in
the OR group of PPhen(5,6-OR). (b) Packing model of PPhen-
(5,6-OR). Only one sheet is shown, and sheets are considered
to form a stacked assembly; the OR groups in the lower layer
are considered to come between the OR groups in the upper
layer to form a well-stacked assembly.
packing mode. PPhen (chart e in Figure 4) and PDPypy
showed analogous broad XRD patterns.
PPhen and PPhen(5,6-OR) were thermally stable at
150 °C, as judged from their TGA and DSC curves (cf.
the Supporting Information), although loss of the hy-
dration water is observed with PPhen at the tempera-
ture. Annealing of the polymers afforded essentially the
same XRD patterns for the polymers as those exhibited
in the Supporting Information. PPhen and PPhen(OR)
were stable under air, and no significant change in their
IR spectra was observed after leaving the polymers for
7 and 1 year, respectively. PDPypy was also stable
under air.
Ru th en iu m (II) Com p lexes. PPhen and PPhen(5,6-
OPen) formed complexes in the reaction with RuCl2-
(bpy)2 under reflux conditions in water. Data from
1
elemental analysis and H NMR spectroscopy indicated
the occurrence of almost quantitative complexation of
the 1,10-phenanthroline unit in 1:1 reactions with
RuCl2(bpy)2. PPhen and PPhen(5,6-OPen) seemed to
have higher reactivity toward Ru2+ than poly(2,2′-
bipyridine-5,5′-diyl) (PBPy),2 reflecting higher coordi-
nating ability of 1,10-phenanthroline than 2,2′-bipyridyl,
as discussed in the Introduction.
PPhen and PPhen(5,6-OPen) became soluble in CH3CN
by the complex formation, and the UV-vis chart of
complex-1 is shown in Figure 6. It gives the π-π*
transition bands originated from the bpy unit and
PPhen at 287 and 353 nm, respectively. In addition, it
gives an MLCT band33,34 characteristic of the Ru2+
complex of electron-accepting N-ligands at about 440

Macromolecules, Vol. 36, No. 18, 2003
Poly(1,10-phenanthroline-3,8-diyl) 6727
to contribute to understanding of 1,10-phenanthroline
and related compounds and to design of future electronic
and optical devices using 1,10-phenanthrolines.
Exp er im en ta l Section
Ma ter ia ls. Solvents were dried, distilled, and stored under
N2. RuCl2(bpy)2,36 Ni(cod)2,37 and 3,8-dibromo-1,10-phenan-
throline14 were prepared according to the literature. Chemicals
were purchased from Aldrich Co. Ltd. and Tokyo Kasei Kogyo
Co. Ltd. Salts used for the cyclic voltammetry were purified
by recrystallization.
Mea su r em en ts. The ultraviolet photoelectron spectra were
measured with an angle-resolving UPS spectrometer at BL8B2
of the UVSOR Facility, Institute for Molecular Science. Mono-
chromatized synchrotron radiation of hv ) 40 eV obtained with
a plane-grating monochromator was used as the light source.
The spectra were measured at the normal emission with the
incidence angle of the light of 45°. The total resolution of the
UPS system was 0.3 eV, as estimated from the Fermi edge of
gold. A thin film of PPhen used for UPS measurements was
nm. Complex-2 also gave analogous UV-vis peaks. The
photochemistry of the [Ru(bpy)2(1,10-phenanthroline)]2+
type complex,33,34 especially that related to biochemistry,
has actively been studied. In the cases of these com-
plexes, they usually do not have absorption bands in
the range 300-400 nm (cf. chart c in Figure 6).
However, the UV-vis spectra of the [Ru(bpy)2]2+ com-
plexes of PPhen and PPhen(5,6-OPen) have a π-π*
absorption band covering the near-UV region, which
may be advantageous for carrying out effective photo-
chemical reactions. It was reported that photoenergy
absorbed by the π-π* band of a π-conjugated polymer
prepared on
a gold coated Si(100) substrate by vacuum
evaporation in the preparation chamber (base pressure 1 ×
10-9 Torr) and was subsequently transferred to the measure-
ment chamber with a base pressure of 5 × 10-10 Torr.
Potassium doping of PPhen was carried out in situ using a
SAES potassium-getter source in the preparation chamber.
The getter was heated with a dc current of 5.8 Å for potassium
evaporation. During the doping, the temperature of the film
was kept at 125 ( 5 °C. The thickness of the deposited PPhen
film was monitored with a quartz thickness monitor. The
thickness of the PPhen film was 10 nm.
was transferred to metal centers such as [Ru(bpy)2]2+ 35
.
CV charts of complexes-1 and -2 in a CH3CN solution
of [NBu4]PF6 showed overlapped broadened peaks,
suggesting the occurrence of electron exchange between
Ru complexes in various oxidation states through the
π-conjugated main chain.
Electroluminescence data were obtained by Mr. T. Inoue in
the R&D Center of TDK Corporation. PL spectra were recorded
on a Hitachi F-4010 fluorescence spectrometer. PL spectra of
solutions were measured under N2. Vacuum evaporation of
PTh and PPhen was carried out in a manner similar to that
previously reported.24 1H NMR spectra were obtained by using
a J EOL EX-400 spectrometer. Cyclic voltammetry was per-
formed with a Toyo Technica Solatoron SI 1287 electrochemi-
cal interface. XRD patterns were recorded on a Rigaku RINT
2100 diffractometer with Cu KR radiation. For the determi-
nation of the degree of depolarization (Fv),17a-c it was used for
the scattering geometry that the vertically polarized incident
beam was irradiated, and the intensities of the vertically (Vv)
and horizontally (Hv) scattered light were detected. To take
account of the angular dependence of the scattered light
intensity, the extrapolated values to zero scattering angle were
used for the analysis of the optical anisotropy of PPhen, Fv )
Hv/Vv.
Con clu sion . π-Conjugated poly(1,10-phenanthro-
line)s have been synthesized and characterized. PPhen
assumes a stiff structure, and PPhen(5,6-OR)s forms a
molecular assembly, assisted by the side chain crystal-
lization. Due to its stiff structure, PPhen exhibits unique
dichroism in UV-vis absorption and photolumines-
cence. The polymers possess an expanded π-conjugated
system and are susceptible to chemical and electro-
chemical reduction. The electron-accepting ability of
PPhen is enhanced by increasing the number of the
imine nitrogens, as in PDPypy. PPhen and PPhen(5,6-
OPen) behave as good ligands and undergo quantitative
complex formation with [Ru(bpy)2]2+, and the light
absorption by the obtained complexes covers a wide
range of the UV-vis region. These results are expected
P r ep a r a t ion of Mon om er s. 3,8-Dibromo-1,10-phen-
anthroline was prepared according to the literature.14 Mono-
mers for PPhen(5,6-OR)s were prepared according to the
following procedure.
(1) 3,8-Dibr om o-5,6-d ia lk oxy-1,10-p h en a n th r olin e. OR
) OP en . A mixture of 3,8-dibromo-1,10-phenamthroline (5.0
g, 14.8 mmol), KBr (2.11 g, 17.8 mmol), and a mixed acid (18
mL of concentrated HNO3 and 36 mL of concentrated H2SO4)
was allowed to react for 3 h under reflux. The reaction mixture
was poured on ice blocks and neutralized with NaOH(aq). The
precipitate was separated by filtration, washed with water,
and dried under vacuum to obtain 4.99 g (91.6%) of bright
yellow 3,8-dibromo-1,10-phenanthroline-5,6-dione. 1H NMR
(CDCl3) δ: 9.14 (d, 2.8 Hz, 2H), 8.61 (d, 2.8 Hz, 2H).
A mixture of 3,8-dibromo-1,10-phenanthroline-5,6-dione
(2.21 g, 6.00 mmol) and dithiooxamide (0.864 g, 7.20 mmol)
was allowed to react in anhydrous ethanol (40 mL) under
reflux for 12 h under N2. After the mixture was cooled to room
temperature, the precipitate was separated by filtration,
washed with anhydrous ethanol (3 times) and argon-bubbled
chloroform (once), and dried under vacuum. Since the obtained
yellow powder of 3,8-dibromo-5,6-dihydroxy-1,10-phenanthro-
line seemed unstable under air, the crude product was used
directly for the next step.
F igu r e 6. UV-vis spectra of (a) complex-1, (b) complex-2, and
(c) [Ru(bpy)2(1,10-phenanthroline)](PF6) in CH3CN.
2

6728 Yamamoto et al.
Macromolecules, Vol. 36, No. 18, 2003
To the above-described solid product were added NaH (346
mg, 14.4 mmol) and 40 mL of anhydrous DMSO under argon.
After stirring at 60 °C for 12 h under argon, 1-iodopentane
(1.88 mL, 14.4 mmol) was added to the red solution, and the
mixture was stirred for 16 h at 60 °C. After the mixture was
cooled to room temperature, an aqueous solution of sodium
thiosulfate was added, and the reaction product was extracted
with hexane (3 times). The combined hexane solution was
washed with water (3 times) and a saturated aqueous solution
of NaCl (once) and dried over MgSO4. After removing hexane
by evaporation, the product (light yellow needles) was isolated
by column chromatography on silica (eluent ) 7:3 mixture of
Other PPhen(5,6-OR)s and PDPypy were prepared analo-
gously.
(3) P P h en (5,6-OOct). Anal. Found: C, 74.29; H, 8.88; N,
6.51; Br, negligible (below the limit of detection). Calcd for
(C28H38N2O2‚H2O)n: C, 74.30; H, 8.91; N, 6.18.
(4) P P h en (5,6-ODod ). Anal. Found: C, 77.75; H, 9.71; N,
5.35; Br, 0. Calcd for (C36H54N2O2‚0.5H2O)n: C, 77.79; H, 9.97;
N, 5.04.
(5) P P h en (5,6-OHexd ). Anal. Found: C, 77.37; H, 10.13;
N, 4.57; Br, 0.50. Calcd for (C44H70N2O2‚H2O)n: C, 78.06; H,
10.72; N, 4.14.
(6) P DP yp y. Anal. Found: C, 52.23; H, 4.19; N, 24.37; Br,
0. Calcd for (C10H4N4‚2.8H2O)n: C, 52.08; H, 4.20; N, 24.30.
P r ep a r a tion of Ru Com p lexes. (1) Com p lex-1. A mix-
ture of PPhen (53.4 mg, 0.25 mmol of the PPhen unit) and
RuCl2(bpy)2 (121 mg, 0.25 mmol) in 50 mL of distilled water
was stirred for 5 days under reflux. Oxygen in the water was
removed by bubbling argon before use, and the reaction was
carried out under argon using a Schlenk tube. The reaction
gave a dark red and almost homogeneous solution. After
removing a small amount of the remaining unreacted PPhen
by centrifugation, NH4PF6 (97.8 mg, 0.60 mmol) was added to
the dark red homogeneous solution to obtain a red precipitate.
The precipitate was separated by filtration and washed with
water repeatedly until the UV-vis spectrum of the filtrate did
not show any sign of RuCl2(bpy)2 (monitored at 484 nm). After
drying under vacuum, 146 mg (64%) of complex-1 was ob-
tained. Anal. Found: C, 42.55; H, 3.26; N, 9.37. Calcd for
(C32H22F12N6P2Ru‚1.7H2O)n: C, 42.13; H, 2.81; N, 9.21.
(2) Com p lex-2 was prepared analogously. Anal. Found: C,
46.31; H, 3.93; N, 8.20. Calcd for (C42H42F12N6P2Ru‚H2O)n: C,
47.01; H, 4.14; N, 7.84.
1
hexane and ethyl acetate); yield ) 46%; mp ) 93-94 °C. H
NMR (CDCl3) δ: 9.09 (d, 2.4 Hz, 2H), 8.68 (d, 2.4 Hz, 2H),
4.23 (t, 7.2 Hz, 4H), 1.90 (quin, 7.2 Hz, 4H), 1.52 (m, 4H), 1.45
(m, 4H), 0.98 (t, 7.2 Hz, 6H). Anal. Found: C, 51.68; H, 4.92;
N, 5.49; Br, 31.46. Calcd for C22H26Br2N2O2: C, 51.78; H, 5.14;
N, 5.49; Br, 31.32.
Other monomers for PPhen(5,6-OR)s were prepared analo-
gously, and their IR and 1H NMR data agreed with their
structures.
(2) OR ) OOct. Light yellow needles (28%); mp ) 53 °C.
Anal. Found: C, 56.38; H, 6.31; N, 4.70; Br, 26.53. Calcd for
C
28H38Br2N2O2: C, 56.58; H, 6.44; N, 4.71; Br, 26.88.
(3) OR ) ODod . White powder (40%); mp ) 71 °C. Anal.
Found: C, 61.23; H, 7.85; N, 4.00; Br, 22.38. Calcd for C36H54
Br2N2O2: C, 61.19; H, 7.70; N, 3.96; Br, 22.62.
-
(4) OR ) OHexd . White powder (39%); mp ) 82 °C. Anal.
Found: C, 64.84; H, 9.01; N, 3.48. Calcd for C44H70Br2N2O2:
C, 64.54; H, 8.62; N, 3.42.
3,8-Dibromodipyrido[3,2-c:2′,3′-e] pyridazine (the monomer
for PDPypy) was synthesized as described below.
A mixture of dipyrido[3,2-c:2′,3′-e]pyridazine (1.57 g, 8.6
mmol),38 concentrated HBr (70 mL), and Br2 (41.4 g, 259 mmol)
was stirred for 12 h at 100 °C. After the mixture was cooled
to room temperature, the precipitate was separated by filtra-
tion and washed with water and ethanol. The precipitate was
purified by column chromatography on silica gel (eluent )
ethyl acetate). Evaporation of the solvent yielded a light yellow
powder of 3,8-dibromodipyrido[3,2-c:2′,3′-e]pyridazine (2.7 g,
92% yield); dp ) 250 °C (color change from yellow to black
started at 250 °C without melting). Anal. Found: C, 35.42; H,
1.44; N, 16.31; Br, 47.27. Calcd for C10H4Br2N4: C, 35.33; H,
Ack n ow led gm en t. We are grateful to Professor K.
Seki of Nagoya University and Professor K. Osakada
of Tokyo Institute of Technology for helpful discussion.
Thanks are due to Mr. T. Inoue of TDK Corp. for
evaluation of the electroluminescence device. This study
was partly supported by a 21st century COE program.
Su p p or tin g In for m a tion Ava ila ble: IR spectra of PPhen
and related compounds, IR spectra of PPhen(5,6-OR)s, 1H and
13C NMR data of PPhen, comparison of ultraviolet photoelec-
tron spectroscopic data of K-doped PPhen and K-doped poly-
(2,2′-bipyridine-5,5′-diyl), definition of the stretching ratio, IR
data of vd-PPhen, EL spectrum, data (IR, CV, and XRD) of
the Ru complex, and XRD patterns of annealed polymers. This
material is available free of charge via the Internet at http://
pubs.acs.org.
1
1.19; N, 16.48; Br, 47.01. H NMR (CDCl3) δ: 9.42 (d, 2.0 Hz,
2H), 9.27 (d, 2.0 Hz, 2H).
P r ep a r a tion of P olym er s. (1) P P h en . A mixture of 3,8-
dibromo-1,10-phenanthroline (470 mg, 1.4 mmol), Ni (cod)2,
(610 mg, 2.2 mmol), bpy (220 mg, 1.4 mmol), and 1,5-
cyclooctadiene (0.8 mL) in 50 mL of dry DMF was stirred at
60 °C for 2 days. The obtained yellow precipitate was separated
by filtration, and workup of polymer, including washing with
an aqueous solution of ethylenediaminetetraacetate, was car-
ried out in a manner similar to those applied for workup of
polypyridines.2b For IR and NMR data, see the Supporting
Information. Anal. Found: C, 74.92; H, 3.56; N, 14.43; Br, O.
Calcd for (C12H6N2‚0.75H2O)n: C, 75.18; H, 3.94; N, 14.61.
PPhen seemed to be hydrated similarly to 1,10-phenanthroline
and polypyridines.2b It was difficult to remove hydrated water
completely.
(2) P P h en (5,6-OP en ). A DMF (20 mL) solution of 3,8-
dibromo-5,6-dipentyloxy-1,10-phenanthroline (1.02 g, 2.0 mmol),
Ni(cod)2 (660 mg, 2.40 mmol), bpy (374 mg, 2.4 mmol), and
1,5-cyclooctadiene (1.2 mL) was stirred for 36 h at 60 °C. The
light yellow precipitate was separated by filtration, and
workup of the polymer was carried out similarly. However,
PPhen(5,6-OR) seemed to have higher coordinating ability
toward nickel compounds, and washing with an aqueous
ammonium solution of dimethylglyoxime and ensuing washing
with an HCl-acidic methanol were necessitated to obtain ash-
free PPhen(5,6-OR). Examples of 1H NMR spectra are shown
in Figure 1. Anal. Found: C, 70.35; H, 7.72; N, 7.56; Br, O.
Calcd for (C22H26N2O2‚1.3H2O)n: C, 70.68; H, 7.71; N, 7.49.
Hydrated water of PPhen(5,6-OR) may exist in the space
formed by the stacking of the polymer molecules; cf. the text.
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