Synthesis and study of the absorption and luminescence properties of polymers containing Ru(BpyMe2)32+ chromophores and coumarin laser dyes

Article abstract of DOI:10.1021/ma020265t

Polymers containing coumarin and Ru(BpyMe₂)₃²⁺ chromophores were synthesized using a grafting approach and also a copolymerization approach. It was found that the solubility of polymers made from Ru-containing monomers was

Full text of DOI:10.1021/ma020265t

5396
Macromolecules 2002, 35, 5396-5404
Synthesis and Study of the Absorption and Luminescence Properties of
2+
Polymers Containing Ru(BpyMe2)3 Chromophores and Coumarin
Laser Dyes
J a son Ser in ,† Xa vier Sch u ltze,† Alex Ad r on ov,‡ a n d J ea n M. J . F r e´ch et*,†
Department of Chemistry, University of California, Berkeley, 718 Latimer Hall,
Berkeley, California 94720-1460; and Department of Chemistry, McMaster University,
Hamilton, Ontario, Canada L8S 4M1
Received February 19, 2002; Revised Manuscript Received May 2, 2002
2+
ABSTRACT: Polymers containing coumarin and Ru(BpyMe2)3 chromophores were synthesized using
a grafting approach and also a copolymerization approach. It was found that the solubility of polymers
made from Ru-containing monomers was higher than that observed for comparable polymers obtained
by grafting of Ru complexes onto bpy-containing prepolymers. The resulting bichromophoric macromol-
2+
ecules exhibited enhanced absorption and luminescence properties compared to the single Ru(BpyMe2)3
complexes due to a very efficient (>95%) energy transfer between the coumarin donor dyes and the
ruthenium chromophores. In addition, a novel system in which two different donor dyes are present
together with the Ru complex was synthesized and also found to deliver efficient energy transfer to the
ruthenium complexes.
In tr od u ction
meric systems that bear some resemblance to the light-
harvesting dendrimers.15 Although these polymers did
not achieve the level of performance of true dendrimers,
they indeed functioned as light-harvesting antennae
affording relatively high energy transfer efficiencies,
depending on the incorporation ratios of the dye-labeled
monomers.
Solar irradiation on the earth’s surface provides
several times the energy needed by its population.1
Considering the rapid and widespread depletion of fossil
fuels, the utilization of this abundant source of energy
is clearly important. Among the artificial systems
capable of harvesting and using solar energy, ruthenium
complexes have been the center of extensive research
due to their unique photophysical and electrochemical
properties.2-5 In particular, ruthenium polypyridine
complexes have attracted much interest due to their
ability to oxidize or reduce a wide range of substrates
under visible light irradiation, leading to systems
capable of photocatalytic decomposition of water6-8 and
applications such as the sensitization of wide band-gap
semiconductors.9-11 The quenching of excited-state ru-
thenium has also been used in pH, temperature and
pressure sensors as well as for the production of singlet
molecular oxygen.12 However, ruthenium(II) complexes
display relatively low extinction coefficients in the
visible (<14 000 M-1‚cm-1), as well as low quantum
yields of luminescence.13
Our lab has recently developed several light-harvest-
ing dendrimers exhibiting very efficient Fo¨rster-type
energy transfer from laser dyes at the periphery of the
molecule toward a single chromophore at the focal
point.14 The luminescence of the acceptor dye is thus
greatly enhanced due to energy transfer from the
numerous donor dyes that act as an efficient light-
harvesting antenna. Although the energy transfer ef-
ficiencies within our dendrimers are extremely high,
their widespread use as functional materials may be
limited to high added value applications due to the
relative complexity of their preparation. To explore the
applicability of more readily addressed architectures,
we have also explored certain dye-functionalized poly-
Recently, the synthesis of metal-containing polymers
has attracted considerable attention due to their nu-
merous applications in the fields of catalysis, conducting
and photoresponsive materials, as well as in supramo-
lecular chemistry.16 Particularly noteworthy are the
works of Fraser17 and Meyer18 concerning the synthesis
of linear and star-shaped polymeric ruthenium com-
plexes from bipyridine-functionalized polymers. Along
similar lines, we have shown that polymers containing
ruthenium complexes in combination with a single type
of coumarin chromophore also undergo energy transfer
and function as light-harvesting antennae.19 In an
attempt to improve the light-harvesting and conversion
efficiencies, and expand the spectral range of absorption
within these structures, we now report an extensive
study of the synthesis and characterization of polymeric
complexes of ruthenium tris(dimethylbipyridine) (Ru-
(BpyMe2)32+) in combination with multiple laser dyes.
These new polymer systems display very high energy
transfer efficiencies and are therefore potentially inter-
esting for applications in photovoltaics, luminescence-
based sensors, and catalytic systems.
20
Initially, the grafting of Ru(BpyMe2)2Cl2 onto co-
polymers with pendant bipyridine groups having vari-
ous linkers was studied. In addition, polymerization of
a ruthenium-functionalized monomer was attempted
and found to be a better alternative. This strategy
enabled us to synthesize a terpolymer containing the
(Ru(BpyMe2)32+) complex and two different coumarin
donor chromophores, effectively demonstrating an ef-
ficient energy transfer system in which excitation
energy is passed from the two types of donors to the
acceptor chromophore either in a stepwise cascade
fashion or by direct energy transfer.
* Corresponding author. Telephone: (510) 643-3077. Fax: 643-
3079. E-mail: frechet@cchem.berkeley.edu.
† University of California, Berkeley.
‡ McMaster University. Telephone: (905) 525-9140 ext. 23514.
Fax: (905) 522-2509. E-mail: adronov@mcmaster.ca.
10.1021/ma020265t CCC: $22.00 © 2002 American Chemical Society
Published on Web 06/04/2002

Macromolecules, Vol. 35, No. 14, 2002
Absorption and Luminescence Properties of Polymers 5397
Sch em e 1
Resu lts a n d Discu ssion
determined from the quenching of the coumarin-2
emission in Figure 2. On the basis of our earlier work
with similar chromophores,14,15 we believe this to be a
through-space Fo¨rster type energy transfer2d,22 made
possible by the overlap of the emission spectrum of the
A series of coumarin-2/Ru(BpyMe2)32+ copolymers was
prepared through the polymerization of coumarin-2- and
bipyridine-functionalized monomers followed by com-
plexation of Ru(BpyMe2)2(MeOH)22+‚2PF6- (Scheme 1).
In a first attempt, 1 and 2 were polymerized in a 3:1
ratio, respectively, in chlorobenzene with AIBN as
initiator.19 A copolymer (3) was obtained with a com-
position reflecting the monomer feed. The Ru(BpyMe2)2-
2+
coumarin dye with the Ru(BpyMe2)3 metal-to-ligand
charge transfer (MLCT) band at 465 nm. An energy
transfer efficiency of 70% was calculated by comparing
the fluorescence of the coumarin-2 chromophore before
and after grafting of the ruthenium complex.19
A
-
(MeOH)22+‚2PF6 intermediate, obtained by refluxing
significant antenna effect was observed, which resulted
in a 5-fold increase of the ruthenium emission at 630
nm when 4 was excited at 350 nm (the coumarin-2
maximum absorption wavelength) relative to 465 nm,
which corresponds to the direct excitation of the ruthe-
nium chromophore (Figure 2, inset).
Ru(BpyMe2)2Cl220 with AgPF6 in methanol overnight,21
was then refluxed with 3 in dimethoxyethane for 48 h.
The UV-vis spectrum of the resulting polymer (4)
exhibited a new absorption band at 465 nm due to the
formation of the ruthenium complex (Figure 1). The
efficiency of Ru incorporation, calculated using the
extinction coefficients of both chromophores and com-
paring the relative absorption of both chromophores
within the polymer, was estimated to be only 30%.
However, a significant energy transfer was observed
between coumarin-2 and the ruthenium complex as
It has previously been observed that the grafting of
Ru(Bpy)2Cl2 on a bipyridine containing poly(acrylate)
was drastically improved when a spacer group was
introduced between the bipyridine and the polymer
backbone.23 Therefore, we synthesized monomer 9 by

5398 Serin et al.
Macromolecules, Vol. 35, No. 14, 2002
Sch em e 2
F igu r e 1. UV-vis spectra of 3 and 4 normalized at the
coumarin-2 maximum absorption.
determined by integrating the methylene protons at the
benzyl positions of both monomers in the 1H NMR
spectrum. The ratio of 9 to 1 in the polymer was found
to be 0.8:3, respectively. The UV-vis spectrum of 10
displays two bands at 290 and 350 nm, characteristic
of the bipyridine and the coumarin-2 units (Figure 3).
Grafting of the Ru(BpyMe2)2(MeOH)22+‚2PF6- complex
was performed (vide supra; Scheme 1) to afford a red
polymer (11) exhibiting the characteristic UV absorption
of the ruthenium MLCT at 465 nm (Figure 3). As
expected, although the ratio of bipyridine to coumarin-2
in 10 is slightly lower than in 7, the introduction of the
aryl ether spacer leads to an improved grafting ef-
ficiency (>95%) of the ruthenium complex (as deter-
mined from the UV-vis spectrum of 11 in Figure 3).
Fluorescence measurements showed an energy-transfer
efficiency of better than 95%, as calculated by comparing
the emission of coumarin-2 at 450 nm in both 10 and
11 when exciting the polymer at 350 nm (Figure 2). At
this excitation wavelength (as opposed to 465 nm), the
emission of the ruthenium chromophore is amplified by
a factor of 3.6 as a result of an antenna effect (Figure
2, inset). This increase of the ruthenium emission is
lower than in the case of 4 as a result of the higher Ru
content and therefore higher Ru(BpyMe2)32+:coumarin-2
ratio in 11.
F igu r e 2. Luminescence spectra of 3, 4, 10, and 11 in the
coumarin-2 emission region. The inset shows the antenna
effect observed in the region where the Ru(BpyMe2)32+ emits.
first deprotonating a single benzylic position of 5 with
lithium diisopropylamide (LDA) followed by anion trap-
ping with trimethylsilyl chloride (TMSCl) to form 6.
Subsequent bromination using 1,2-dibromotetrafluoro-
ethane gave compound 7 in 74% overall yield, which was
previously prepared using a three-step synthesis in 31%
overall yield.24 Compound 7 was then coupled to p-
hydroxybenzaldehyde to form 8. Monomer 9 was syn-
thesized from 8 using a standard Wittig reaction
(Scheme 2). Polymerization of 9 with 1 using a 1:3 ratio
(9:1) in a minimum amount of dichlorobenzene contain-
ing 2% AIBN was then performed (Scheme 1). After two
successive precipitations in Et2O, 10 was obtained as a
white powder. The composition of 10 (Table 1) was
Although these macromolecular complexes display
high energy-transfer efficiencies resulting in an en-
hanced excitation of the ruthenium chromophore, they
are only slightly soluble in common organic solvents.
Therefore, the terpolymerization of monomers 1, 9, and
styrene was performed in order to “dilute” the polymer
with styrene moieties used as solubilizing groups. These
monomers were polymerized to 37% conversion in a feed
ratio of 1:1:10 (1:9:styrene) to produce polymer 12 with
Ta ble 1. Com p osition of th e Stu d ied Cou m a r in /Ru th en iu m P olym er s
monomer feeda polymer compositiona
compound
Mw; PDI
yield (%)
3
1 (0.75); 2 (0.25)
1 (0.75); 9 (0.25)
1 (0.083); 9 (0.083); styrene (0.83)
1 (0.75); 14 (0.25)
1 (0.25); 14 (0.75)
1 (0.75); 2 (0.25)
1 (0.79); 9 (0.21)
1 (0.083); 9 (0.083); styrene (0.83)
1 (0.75); 14 (0.25)
1 (0.36); 14 (0.64)
15400; 1.6
41300; 1.4
33 000; 1.3
ndb
70
76
37
60
20
42
36
10
12
16
17
21
22
ndb
14 (0.2); 1 (0.4); 20 (0.4)
2 (0.2); 1 (0.4); 20 (0.4)
14 (0.41); 1 (0.29); 20 (0.3)
2 (0.42); 1 (0.32); 20 (0.26)
ndb
22800; 1.7
a
b
The number in parentheses represents the mole fraction of the monomer in the feed and in the polymer. nd ) not determined (see
Experimental Section).

Macromolecules, Vol. 35, No. 14, 2002
Absorption and Luminescence Properties of Polymers 5399
F igu r e 4. Luminescence spectra of 3, 16, and 17. The inset
shows the antenna effect when exciting the donors (λex ) 350
nm) vs the acceptors (λex ) 465 nm).
F igu r e 3. UV-vis spectra of 10 and 11 normalized at the
clearly seen in the quenching of donor emission (Figure
4). The significant change in solubility of 16 supports
the theory that cross-linking led to the low solubility of
4, 11, and 13. This is particularly clear for terpolymer
13 for which solubility remained low despite the incor-
poration of 83 mol % of styrene.
coumarin-2 maximum absorption.
Sch em e 3
To study the impact of the ruthenium content on the
solubility of the polymer and on the antenna effect, a
different copolymer (17) was prepared from a 3:1 feed
ratio of 14 and 1, respectively, using the same polym-
erization conditions as for 16 (Table 1). The lower
isolated yield (20%) obtained for this copolymerization
was due to product loss during purification of the
copolymer. As incorporation of the ruthenium monomer
into the copolymer increases, so does its solubility in
MeOH. Therefore, a portion of 17 dissolves in MeOH
along with the unreacted monomer 14 during the
purification step. Although more than 50% of this
2+
copolymer is composed of highly ionic Ru(BpyMe2)3
units, the copolymer still remains soluble in solvents of
low polarity (CH2Cl2, CHCl3). For both of these copoly-
mers, a high energy-transfer efficiency from the cou-
marin-2 donors to the Ru-containing acceptors was
observed upon excitation at 350 nm (Figure 4). This
results in an increased emission at 630 nm when
exciting the donor chromophores (λex ) 350 nm) vs the
acceptor chromophores (λex ) 465 nm, Figure 4, inset).
As expected, since the ratio of the donor to acceptor
decreases from 16 to 17, so does the antenna effect. The
emission at 630 nm is amplified by a factor of 2.7 in 16
as opposed to 1.3 in 17 when exciting at 350 nm vs 465
nm.
While polymerization of monomer 1 with 14 proved
successful, all attempts to polymerize 15 with 1 failed.
It is believed that, due to the proximity of the ruthenium
center, the benzylic protons in 15 are more labile
relative to those in monomer 9, thereby encouraging
chain transfer termination pathways.
To further enhance the emission properties of these
ruthenium macromolecular complexes, the introduction
of a third chromophore capable of efficient light har-
vesting and energy transfer was studied. Coumarin-343
exhibits a relatively high extinction coefficient (ꢀ )
4.9 × 104 M-1‚cm-1 at 450 nm) and an intense emission
band between 450 and 500 nm (Φf ) 0.8). Therefore,
this chromophore should be a good energy-donor can-
didate for a ruthenium tris(bipyridine) complex. Model
compound 19 was prepared to study energy transfer
between these two dyes (Scheme 4). Coupling of cou-
a repeat unit composition of 1:1:10 (1:9:styrene) as
determined by H NMR and elemental analysis. Graft-
1
ing of the Ru complex was performed as described above.
Although the resulting terpolymer 13 demonstrated
improved solubility in DMF and DMSO, its solubility
remained low. The energy transfer efficiency and the
Ru(BpyMe2)32+ functionalization in 13 were found to be
ca. 86%, and 60%, respectively.
We believe that the low solubility of 4, 11, and 13
arises from secondary reactions resulting in a partial
cross-linking of the polymers.25 To circumvent this
limitation, we studied the synthesis and polymerization
of two ruthenium-containing monomers. Monomers 14
and 15 were obtained in 95% and 90% yield, respec-
tively, by reaction of the corresponding bipyridine-
functionalized monomers 2 and 9 with Ru(BpyMe2)2Cl2
in MeOH, followed by ion exchange with KPF6 (Scheme
3). Copolymerization of these monomers with 1 was
attempted in DMF with AIBN as the initiator. After 12
h at 90 °C, the reaction mixture was precipitated twice
in Et2O and washed with MeOH to remove the unre-
acted ruthenium monomer. When monomer 14 was
polymerized with 1 in a 1:3 ratio, a red solid (16) was
obtained, which exhibited enhanced solubility properties
in organic solvents (CH2Cl2, DMF) and also displayed
a near quantitative energy-transfer efficiency between
the coumarin-2 and the ruthenium complex. This is

5400 Serin et al.
Macromolecules, Vol. 35, No. 14, 2002
Sch em e 4
marin-343 with 7 in the presence of K2CO3 and 18-
crown-6 afforded 18 in 86% yield. Reaction of this ligand
with Ru(DMSO)4Cl2 produced model compound 19 in
tionalized polymer containing the coumarin-2 and cou-
marin-343 donor dyes (Figure 6) was carried out in order
to obtain a macromolecule with improved light-harvest-
ing properties between 300 and 450 nm.
26
35% yield. The normalized luminescence spectra of 18
and 19 are shown in Figure 5. As can be seen in this
figure, the emission of 18 at 470 nm (λex ) 400 nm) is
completely quenched after complexation with Ru-
(DMSO)4Cl2. Furthermore, a 5.8-fold increase in the
ruthenium emission at 630 nm is observed when 19 is
excited at 400 nm as opposed to 480 nm. Since the
absorbance of the Ru(BpyMe2)32+ complex in 19 at 480
nm is slightly lower than at 465 nm (A480/A465 ) 0.9),
extrapolation of the data at 465 nm suggests that the
antenna effect provided by the coumarin-343 dyes
results in a 5.2-fold increase of the ruthenium emission
when excited at its maximum absorption (assuming that
the luminescence quantum yield remains constant
between 465 and 480 nm). Both the quenching of the
coumarin emission and the resulting antenna effect
confirm that this dye is an excellent energy donor for
the ruthenium tris(bipyridine) complex. As a result of
this model study, the synthesis of a ruthenium-func-
Terpolymerization of 1 and 14 along with a styrenic
coumarin-343 monomer15 (20) in a ratio of 2:1:2, respec-
tively, gave terpolymer 21 (Scheme 5). In addition,
model terpolymer 22 was also synthesized from a
mixture of 1, 2, and 20 (2:1:2) in order to determine the
energy transfer efficiency of the two coumarin dyes in
the ruthenium-containing polymer. The UV-vis spectra
of both polymers are shown in Figure 7. The presence
of the ruthenium MLCT band accounts for the broaden-
ing of the coumarin-343 absorption band between 400
and 500 nm. Monomers 2 and 14 are readily incorpo-
rated to the same extent in 22 and 21, respectively,
suggesting that the introduction of ruthenium does not
affect significantly the reactivity of the vinyl group. The
emission spectrum of model polymer 22 (Figure 8) shows
a nearly quantitative quenching of the coumarin-2
fluorescence and the appearance of the coumarin-343
F igu r e 5. Luminescence spectra of 18 and 19. The inset
shows the antenna effect when exciting the ruthenium center
through the donor chromophore (λex ) 400 nm).
F igu r e 6. Graphic representation of the light-harvesting
system containing two-donor chromophores.

Macromolecules, Vol. 35, No. 14, 2002
Absorption and Luminescence Properties of Polymers 5401
Sch em e 5
fluorescence band at 480 nm, as well as a broad band
between 510 and 700 nm resulting from excimer forma-
tion due to the lack of an appropriate acceptor.15
Significant attenuation of these two bands is observed
for 21 as a result of energy transfer between the two
coumarin dyes and the ruthenium complex. The ef-
ficiency of this process is above 95% for both laser dyes.
Extrapolating from the values obtained at 480 nm
excitation (Figure 8), the antenna effect observed when
exciting 21 at 350 and 400 nm is 1.5× and 3.1×,
respectively, when compared to direct excitation at 465
nm. As a result of the efficient transfer of the additional
energy absorbed by the coumarin dyes between 300 and
450 nm, the macromolecular complex 21 exhibits highly
enhanced absorption and luminescence properties.
Con clu sion
Polymers containing coumarin laser dyes (energy
2+
donors) and a Ru(BpyMe2)3
chromophore (energy
acceptor) have been synthesized. These macromolecules
efficiently concentrate absorbed energy through energy
transfer at the acceptor and display a significant
antenna effect. A grafting approach led to polymers that
displayed low solubility, which could not be improved
F igu r e 8. Luminescence spectra of 21 and 22 showing the
quenching of the coumarin-2 and coumarin-343 donor emission
and the resulting antenna effect when exciting 21 at 350 and
400 nm.
F igu r e 7. UV-vis spectra of polymer 21 and 22 normalized
to the coumarin-2 maximum absorption.

5402 Serin et al.
Macromolecules, Vol. 35, No. 14, 2002
was stirred for 10 min. A saturated aqueous solution of sodium
bicarbonate (50 mL) was added, and the mixture turned yellow
upon formation of a precipitate. The mixture including the
precipitate was poured into a separatory funnel and extracted
with ethyl acetate (3 × 200 mL). The organic layers were
combined, dried over Na2SO4, filtered, and evaporated to
dryness to yield a yellow solid (6) (2.79 g, 99%). This product
was used without further purification. 1H NMR (400 MHz,
CDCl3, TMS): δ ) 2.17 (s, 2), 2.39 (s, 3), 6.90 (d, J ) 5 Hz, 1),
7.08 (d, J ) 5 Hz, 1), 8.02 (s, 1), 8.19 (s, 1), 8.44 (d, J ) 5 Hz,
1), 8.49 (d, J ) 5 Hz, 1).
To a mixture of the crude product (2.00 g, 780 mmol) and
dibromotetrafluoroethane (2.00 mL, 167 mmol, 2.1 equiv) in
100 mL of DMF was added CsF (3.15 g, 207 mmol, 2.7 equiv).
The suspension was stirred at room temperature for 3 h and
then poured into a separatory funnel containing 200 mL of
H2O. The mixture was extracted with ethyl acetate (3 × 200
mL), and the organic layers were combined, washed with brine
(3 × 200 mL), dried over Na2SO4, filtered, and evaporated to
dryness to yield a clear, colorless oil, which solidified overnight
under vacuum (1.55 g, 75%). 1H NMR (400 MHz, CDCl3,
TMS): δ ) 2.44 (s, 3), 4.48 (s, 2), 7.15 (d, J ) 4 Hz, 1), 7.33 (d,
J ) 4 Hz, 1), 8.24 (s, 1), 8.42 (s, 1), 8.54 (d, J ) 4 Hz, 1), 8.65
(d, J ) 4 Hz, 1). 13C NMR (100 MHz, CDCl3, TMS): δ ) 21.09,
30.66, 120.87, 121.95, 123.40, 124.89, 147.07, 148.14, 148.92,
149.55, 155.21, 156.85. UV (CHCl3): λmax ) 285 nm. HRMS
(EI): calcd for C12H11N279Br1 m/z ) 262.0117, found m/z )
262.0105; calcd for C12H11N281Br1 m/z ) 264.0087, found
m/z ) 264.0085.
Syn th esis of 4-Meth yl-4′-(p-ben za ld eh yd e)m eth yl-2,2′-
bip yr id in e Eth er (8). A solution of 7 (1.06 g, 4.03 mmol) in
10 mL of acetone was treated with p-hydroxybenzaldehyde
(541 mg, 4.43 mmol), K2CO3 (1.11 g, 8.06 mmol), and 18-
crown-6 (106 mg, 0.443 mmol). The solution was stirred at
reflux for 7 h. The resulting pink solution was concentrated,
redissolved in a minimum of CH2Cl2, and filtered through
Celite. The product was concentrated, dissolved in a minimum
of CH2Cl2, and purified by column chromatography on silica
gel first passivated with 9:1 hexanes:Et3N using first 7:3
hexanes:EtOAc and then 7:3 CH2Cl2:EtOAc as the eluents to
yield 1.15 g of a white solid (94%). 1H NMR (400 MHz, CDCl3,
TMS): δ ) 2.43 (s, 3), 5.23 (s, 2), 7.08 (d, J ) 9 Hz, 2), 7.15 (d,
J ) 5 Hz, 1), 7.37 (d, J ) 5 Hz, 1), 7.84 (d, J ) 8 Hz, 2), 8.24
(s, 1), 8.44 (s, 1), 8.53 (d, J ) 5 Hz, 1), 8.68 (d, J ) 5 Hz, 1),
9.88 (s, 1). 13C NMR (100 MHz, CDCl3, TMS): δ ) 21.11, 68.49,
115.04, 118.80, 121.24, 122.00, 124.92, 130.40, 131.95, 146.07,
148.21, 148.92, 149.49, 155.35, 156.65, 163.00, 190.61. UV
(CHCl3): λmax ) 283 nm. mp 95-96 °C. MS (EI): m/z ) 304
(M+), 183. Anal. Calcd for C19H16N2O2: C, 74.98; H, 5.30; N,
9.20. Found: C, 74.69; H, 5.33; N, 8.81.
Syn th esis of 4-Meth yl-4′-(p-vin yla r yl eth er )m eth yl-
2,2′-bip yr id in e (9). To a flame-dried flask charged with argon
was added Ph3PCH3I (173 mg, 427 µmol) and 1 mL of THF.
The solution was cooled to 0 °C, and n-BuLi (23 mg, 3.6 × 102
µmol, 1.1 equiv) was added with a syringe while stirring. The
resulting bright yellow-orange solution was warmed to room
temperature, allowed to equilibrate for 40 min, and again
cooled to 0 °C. To another flame-dried flask charged with argon
was added 8 (100 mg, 281 µmol) and 1 mL of THF. This
solution was added to the first flask via cannula. The mixture
was stirred at room temperature for 2.5 h, and 1 mL of MeOH
was added to quench the reaction. A saturated aqueous
NaHCO3 (10 mL) solution was added, and the solution was
poured into a separatory funnel containing 10 mL of H2O. The
mixture was extracted with ethyl acetate (3 × 30 mL). The
combined organic layers were washed with brine (50 mL),
dried over Na2SO4, and evaporated to dryness. The product
was then taken up in a minimum of CH2Cl2 and purified by
column chromatography on silica gel first passivated with 9:1
CH2Cl2:Et3N using 7:3 CH2Cl2:EtOAc as the eluent, to yield
64 mg of a white solid (64%). 1H NMR (400 MHz, CDCl3,
TMS): δ ) 2.43 (s, 3), 5.13 (d, J ) 12 Hz, 1), 5.15 (s, 2), 5.61
(d, J ) 18 Hz, 1), 6.61-6.68 (dd, J ) 12, 18 Hz, 1), 6.92 (d, J
) 8 Hz, 2), 7.13 (d, J ) 5 Hz, 1), 7.34 (d, J ) 9 Hz, 2), 7.39 (d,
J ) 5 Hz, 1), 8.25 (s, 1), 8.43 (s, 1), 8.54 (d, J ) 5 Hz, 1), 8.66
by either the addition of styrene into the polymer
backbone or the placement of a spacer between the
backbone and the acceptor chromophore. However, the
solubility was improved by copolymerizing the donor
2+
monomer(s) with a Ru(BpyMe2)3 acceptor monomer.
The antenna effect observed in these systems was easily
tuned by changing the ratio of donor to acceptor within
the copolymer. The absorption and luminescence prop-
erties of these macromolecular compounds were further
improved by introducing a second coumarin dye. In light
of these findings, the application of these metallopoly-
mers to photonic27 and photovoltaic devices as well as
ruthenium-promoted photoreactions is of continuing
interest.
Exp er im en ta l Section
THF was dried over Na/benzophenone before use. All
solvents used for absorption and luminescence measurements
were spectroscopic grade. All the other solvents were anhy-
drous and reagent grade. Absorption spectra were recorded
on a Cary 50 UV-vis spectrometer in chloroform. Emission
and excitation spectra were obtained using an ISA/SPEX
Fluorolog 3.22 equipped with a 450W Xe lamp, double excita-
tion and double emission monochromators, and a digital
photon-counting photomultiplier. Samples for luminescence
experiments were dissolved in chloroform or in DMF in
standard 1 cm quartz cells. The optical density was kept below
0.1, and the samples were degassed by bubbling argon for 5
min before each measurement. All measurements were per-
formed at room temperature. The compositions of the polymers
in Table 1 were determined by elemental analysis and/or by
UV-vis spectroscopy using the extinction coefficients of mono-
mers 1 (ꢀ ) 1.5 × 104 M-1‚cm-1 at 350 nm), 20 (ꢀ ) 4.9 × 104
M-1‚cm-1 at 450 nm), and 14 (ꢀ ) 1.4 × 104 M-1‚cm-1 at 465
nm) to determine the relative concentrations of each monomer
within the copolymers or terpolymers. The molecular weights
of 3, 10, 12, and 22 were determined by GPC in DMF at a
flow rate of 1 mL/min using a 2690 XE Alliance separation
module (Waters) equipped with a column set comprising two
300 × 7.5 mm i.d. 103 and 105 Å Polymer Labs gel columns
thermostated at 55 °C. Unfortunately, the GPC method could
not be applied to the ruthenium-containing polymers 4, 11,
13, 16, 17, and 21. Similar problems have already been
reported in the literature28 and arise from the strong interac-
tion of ruthenium with the stationary phase used in the GPC
columns. However, it should be mentioned that several
examples for the successful GPC characterization of metal-
containing polymers have been reported.29 Attempts at char-
acterizing the polymer through MALDI-TOF MS using a
variety of matrices were also unsuccessful. Monomers 1, 2, 14,
and 20 were synthesized as previously described in the
literature.15,19,30 The composition, molecular weight, polydis-
persity, and yield of the various polymerizations are reported
in Table 1. High-resolution mass spectra (HRMS) were ob-
tained on a Micromass ProSpec using electron impact (EI) and
a Micromass LCT using electrospray (ES). Matrix-assisted
laser desorption ionization time-of-flight (MALDI-TOF) mass
spectrometry was performed on a PerSeptive Biosystems
Voyager-DE spectrometer using a delayed extraction mode and
with an acceleration voltage of 20 keV. Samples were prepared
from a solution of DMF using 2-(4-hydroxyphenylazo)benzoic
acid (HABA) as the matrix.
Syn th esis of 4-Br om om eth yl-4′-m eth yl-2,2′-bip yr id in e
(7). A solution of 1.80 mL of diisopropylamine (128 mmol, 1.18
equiv) in 20 mL of THF at 0 °C was treated with 4.80 mL of
2.28 M n-BuLi (hexane solution, 109 mmol, 1.00 equiv), and
the mixture was stirred for 30 min under Ar. A solution of 5
(2.00 g, 109 mmol) in 75 mL of THF was quickly added to the
reaction mixture, and the dark brown solution was allowed to
warm to room temperature and stirred for 2 h. It was then
cooled to -78 °C, and 1.5 mL of chlorotrimethylsilane (118
mmol, 1.09 equiv) was quickly injected. After 30 s, 5 mL of
ethanol was injected to quench the reaction and the mixture

Macromolecules, Vol. 35, No. 14, 2002
Absorption and Luminescence Properties of Polymers 5403
(d, J ) 5 Hz, 1). 13C NMR (100 MHz, CDCl3, TMS): δ ) 21.05,
68.02, 111.98, 112.78, 117.85, 121.38, 121.99, 124.90, 127.43,
130.92, 134.01, 147.13, 148.16, 148.87, 149.39, 155.61, 156.48,
157.82. UV (CHCl3): λmax ) 266 nm. mp 117-121 °C. MS
(EI): m/z ) 302 (M+), 277, 201, 183, 152, 77. Anal. Calcd for
precipitated twice in 20 mL of Et2O, filtered and washed with
100 mL of MeOH giving 337 mg of a white powder (10) (76%).
Mw: 41 300 Da. PDI: 1.43. 1H NMR (400 MHz, CDCl3, TMS):
δ ) 0.84 (br s, -CH2CH3), 1.32-1.60 (br m, -CH2- &
-CH-), 2.26-2.38 (br m, aromatic -CH3), 2.85 (br s, N-CH2-
CH3), 3.98 (br s, N-CH2-, 3), 4.95 (br s, O-CH2-, 0.8), 6.03
(br s, aromatics), 6.12-7.15 (br m, aromatics), 7.17-7.35 (br
m, aromatics), 8.12-8.55 (br m, aromatics). Anal. Calcd for
79H82N5O6: N, 5.85. Found: N, 5.68. Mw: 15 400 Da. PDI:
1.6.
The same procedure was used for 3, 12, 16, 17, 21, and 22
except that 16, 17, 21, and 22 were obtained in DMF and
further purified by overnight trituration in MeOH to remove
the unreacted ruthenium monomers.
Gr a ftin g P r oced u r e. In a general procedure, 75 mg of 10
was added to 38 mL of a solution of Ru(5)2(MeOH)2 (PF6)2 (94
mg, 1.14 mmol) in dimethoxyethane (60 mL, 3.1 mM). The
reaction vessel was fitted with a reflux condenser and a
mechanical stirrer, heated at reflux for ca. 48 h, and cooled to
room temperature. The mixture was filtered, diluted with
dichloromethane, and washed with water to remove the
unreacted ruthenium complex. The dichloromethane solution
was then concentrated and precipitated in ether to afford 96
mg of a dark red powder (79%). 1H NMR (500 MHz, DMF-d7):
δ ) 1.04, 1.26, 1.44, 1.77, 2.14, 2.59, 2.75, 3.90, 3.92, 6.85, 7.30,
7.62, 8.00, 8.38, 8.45, 9.00.
C
20H18N2O: C, 79.44; H, 6.00; N, 9.26. Found: C, 79.08; H,
5.91; N, 9.21.
Syn th esis of Ru th en iu m Bis(4,4′-d im eth yl-2,2′-bip yr i-
d in e) 4-Meth yl-4′-(p-vin yla r yl eth er )m eth yl-2,2′-bip yr i-
d in e (15). To a solution of 9 (100 mg, 330 µmol) dissolved in
16 mL of MeOH was added Ru(4,4′-dimethyl-2,2′-bipyridine)2Cl2
(162 mg, 300 µmol), and the solution was stirred at reflux for
12 h. The solution was concentrated, dissolved in a minimum
amount of H2O, and added to 20 mL of a saturated solution of
KPF6. The resulting precipitate was filtered, washed with H2O,
and dried under vacuum to yield 285 mg of a red solid (90%).
1H NMR (400 MHz, DMF-d7): δ ) 2.45-2.56 (m, 15), 5.14 (m,
1), 5.39 (m, 2), 5.73 (m, 1), 6.73 (m, 1), 7.09 (d, J ) 7 Hz, 2),
7.32-7.49 (m, 8), 7.67 (s, 1), 7.84 (m, 4), 8.56 (s, 1), 8.72 (s, 1),
8.81 (s, 3), 8.90 (s, 1), 9.02 (s, 1). 13C NMR (100 MHz, DMF-
d7): δ ) 19.41, 19.43, 66.74, 110.64, 110.92, 114.13, 114.16,
121.31, 124.25, 126.72, 126.76, 127.64, 127. 83, 130.40, 135.38,
C
147.69, 149.01, 150.09, 150.89, 155.87, 156.02, 157.17. MS
-
(ES): m/z ) 917 (M2+ - PF6-)+, 385 (M2+ - 2PF6
)
2+. Anal.
Calcd for C44H42F12N6OP2Ru: C, 49.77; H, 3.99; N, 7.91.
Found: C, 49.92; H, 4.14; N, 7.72.
The same procedure was used for 4 and 13.
Syn t h esis of Cou m a r in -343-F u n ct ion a lized 4,4′-Di-
m eth yl-2,2′-bip yr id in e (18). A mixture of coumarin-343 (215
mg, 754 µmol), 7 (125 mg, 503 µmol), K2CO3 (380 mg, 2.74
mmol), and 18-crown-6 (28.0 mg, 114 µmol) was refluxed in
11 mL CH3CN. After 3 h, the solution was cooled to room
temperature, poured into a separatory funnel containing 300
mL of H2O, and extracted with CH2Cl2 (3 × 200 mL). The
organic layers were combined, washed with brine (200 mL),
dried over Na2SO4, and evaporated to dryness. The resulting
solid was then taken up in a minimum of CH2Cl2, and the
product was isolated by column chromatography on silica gel,
first passivated with 9:1 hexanes:Et3N, using 9:1 CH2Cl2:CH3-
OH as the eluent, to yield 190 mg of a dark yellow solid (86%).
1H NMR (400 MHz, CDCl3, TMS): δ ) 1.96-1.99 (m, 4), 2.45
(s, 3), 2.75-2.77 (m, 2), 2.87-2.91 (m, 2), 3.32-3.37 (m, 4),
5.44 (s, 2), 6.96 (s, 1), 7.14 (d, J ) 4 Hz, 1), 7.53 (d, J ) 4 Hz,
1), 8.24 (s, 1), 8.40 (s, 1), 8.41 (s, 1), 8.54 (d, J ) 4 Hz, 1), 8.68
(d, J ) 4 Hz, 1). 13C NMR (100 MHz, CDCl3, TMS): δ ) 8.56,
19.87, 19.95, 20.92, 21.07, 27.24, 45.95, 49.77, 50.17, 64.60,
70.44, 110.39, 119.16, 119.30, 121.82, 121.93, 124.72, 127.07,
144.96, 148.84, 149.39, 149.54. Anal. Calcd for C28H29N3O6‚
2H2O: C, 66.79; H, 5.80; N, 8.34. Found: C, 66.51; H, 5.87; N,
8.23.
Ack n ow led gm en t. Financial support of this re-
search comes from the AFOSR (No. FDF-49620-01-1-
0167) program and the Office of Naval Research (No.
N00014-98-F-0402) through the U.S. Department of
Energy (No. DE-AC03-76SF00098). A graduate fellow-
ship from the Eastman Kodak Co. (A.A.) is gratefully
acknowledged.
Refer en ces a n d Notes
(1) Merrigan, J . A. Prospects for solar energy conversion by
photovoltaics; MIT press: Cambridge, MA, 1975.
(2) (a) Sauvage, J . P.; Collin, J . P.; Chambron, J . C.; Guillerez,
S.; Coudret, C.; Balzani, V.; Barigelotti, F.; Cola, L.; Flamigni,
L. Chem. Rev. 1994, 94, 993. (b) Plevoets, M.; Vo¨gtle, F.; De
Cola, L.; Balzani, V. New. J . Chem. 1999, 1, 63. (c) Vo¨gtle,
F.; Plevoets, M.; Nieger, M.; Azzellini, G. C.; Credi, A.; De
Cola, L.; De Marchis, V.; Venturi, M.; Balzani, V. J . Am.
Chem. Soc. 1999, 121, 6290. (d) Zhou, X.; Tyson, D. S.;
Castellano, F. N. Angew. Chem., Int. Ed. 2000, 39, 4301.
(3) Newkome, G. R.; He, E.; Godinez, L. A.; Baker, G. R. J . Am.
Chem. Soc. 2000, 122, 9993.
Syn th esis of Ru (Bp y-C343)3(P F 6)2 (19). A solution of 18
(4) Newkome, G. R.; He, E.; Moorefield, C. N. Chem. Rev. 1999,
99, 1689.
26
(60.0 mg, 128 µmol) and Ru(DMSO)4Cl2 (20 mg, 41 µmol) in
5 mL of ethanol was stirred at reflux for 4 days. The reaction
mixture was then concentrated, dissolved in a minimum
amount of H2O, and added dropwise to 20 mL of a saturated
solution of KPF6 in H2O. The precipitate was filtered and
washed with 200 mL of H2O. The resulting solid was dissolved
in a minimum amount of CH2Cl2 and precipitated into 20 mL
of Et2O twice. It was then stirred in 20 mL of MeOH at room
temperature for 24 h. The mixture was filtered, washed with
200 mL of MeOH, and dried under reduced pressure to yield
26 mg of a yellow solid (35%). 1H NMR (400 MHz, CDCl3,
TMS): δ ) 1.97 (s, 12), 2.59 (s, 9), 2.77 (m, 6), 2.87 (m, 6),
3.35 (s, 12), 5.50 (s, 6), 7.06 (m, 3), 7.3 (m, 3), 7.52-7.68 (m,
9), 8.31 (s, 3), 8.47 (m, 3), 8.69 (s, 3). No 13C NMR data could
be obtained due to the low solubility of 5. UV/vis (CHCl3):
(5) Zhou, M.; Roovers, J . Macromolecules 2001, 34, 244.
(6) Kirch, M.; Lehn, J . M.; Sauvage, J . P. Helv. Chem. Acta 1979,
62, 1345.
(7) Seddon, E. A.; Seddon, K. R. In The Chemistry of ruthenium;
Clark, R. J . H., Ed.; Elsevier: Amsterdam, 1984; Chapter 15,
p 1221.
(8) Suzuki, M.; Kobayashi, S.; Uchida, S.; Kimura, M.; Hanabusa,
K.; Shirai, H. Polymer 1998, 39, 1539.
(9) Fendler, J . H. In Nanoparticles and Nanostructured Films;
Fendler, J . H., Ed.; Fendler; Wiley: 1998; Chapter 9, p 207.
(10) Hagfeldt, A.; Gra¨tzel, M. Chem. Rev. 1995, 95, 49.
(11) O’Regan, B.; Gra¨tzel, M. Nature (London) 1991, 353, 737.
(12) (a) Suzuki, M.; Bartels, O.; Gerdes, R.; Schneider, G.; Wo¨hrle,
D.; Schulz-Ekloff, G.; Kimura, M.; Hanabusa, K.; Shirai, H.
Phys. Chem. Chem. Phys. 2000, 2, 109. (b) Bourdelande, J .
L.; Font, J .; Marques, G.; Abdel-Shafi, A. A.; Wilkinson, F.;
Worrall, D. R. J . Photochem. Photobiol. A: Chem. 2001, 138,
65.
(13) (a) Nazeeruddin, M. K.; Kay, A.; Radicio, I.; Humphry-Baker,
R.; Mu¨ller, E.; Liska, P.; Vlachopoulos, N.; Gra¨tzel, M. J . Am.
Chem. Soc. 1993, 115, 6382. (b) J uris, A.; Balzani, V.;
Barigelletti, F.; Campagna, S.; Belser, P.; Von Zelewsky, A.
Coord. Chem. Rev. 1988, 84, 85.
λmax ) 283, 447 nm. MS (MALDI): m/z ) 1504.3 (M2+
-
2PF6 - H+)+, 1649.9 (M2+ - PF6-)+, calcd m/z ) 1502.63,
-
1648.61. MS (ES): calcd for m/z ) 751.7296 (M2+ - 2H+
-
2e- - 2PF6-); found m/z ) 751.7155.
P olym er iza tion . In a typical experiment, 1 (331 mg, 990
µmol), 9 (100 mg, 330 µmol), and AIBN (0.87 mL of a 3 × 10-2
M solution in chlorobenzene) were placed in a 2 mL flask. The
solution was degassed (freeze-thawed) twice, purged with
argon, and heated at 90 °C for 14 h. The solution was then
(14) (a) Adronov, A.; Gilat, S. L.; Fre´chet, J . M. J .; Ohta, K.;
Neuwahl, F. V. R.; Fleming, G. R. J . Am. Chem. Soc. 2000,

5404 Serin et al.
Macromolecules, Vol. 35, No. 14, 2002
122, 1175. (b) Gilat, S. L.; Adronov, A.; Fre´chet, J . M. J .
Angew. Chem., Int. Ed. Engl. 1999, 38, 1422.
(23) Yoshinaga, K.; Toyofuku, I.; Yamashita, K.; Kanehara, H.;
Ohkubo, K. Colloid Polym. Sci. 2000, 278, 481.
(15) Adronov, A.; Robello, D. R.; Fre´chet, J . M. J . J . Polym. Sci.,
Part A: Polym. Chem. 2001, 39, 1366.
(16) (a) Sauvage, J . P. Transition Metals in Supramolecular
Chemistry; Perspectives in Supramolecular Chemistry Series;
Wiley: New York, 1999; Vol VI. (b) Pickup, P. G. J . Mater.
Chem. 1999, 9, 1641.
(17) (a) Wu, X.; Collins, J . E.; McAlvin, J . E.; Cutts, R. W.; Fraser,
C. L. Macromolecules 2001, 34, 2812. (b) Corbin, P. S.; Webb,
M. P.; McAlvin, J . E.; Fraser, C. L. Biomacromolecules 2001,
2, 223.
(18) (a) Strouse, G. F.; Worl, L. A.; Younathan, J . N.; Meyer, T. J .
J . Am. Chem. Soc. 1989, 111, 9101. (b) Friesen, D. A.; Kajita,
T.; Danielson, E.; Meyer, T. J . Inorg. Chem. 1998, 37, 2756.
(c) Fleming, C. N.; Maxwell, K. A.; DeSimone, J . M.; Meyer,
T. J .; Papanikolas, J . M. J . Am. Chem. Soc. 2001, 123, 10336.
(19) Schultze, X.; Serin, J .; Adronov, A.; Fre´chet, J . M. J . Chem.
Commun. 2001, 1160.
(24) Ciana, L. D.; Hamachi, I.; Meyer, T. J . J . Org. Chem. 1989,
54, 1731.
(25) Trouillet, L.; De Nicola, A.; Guillerez, S. Chem. Mater. 2000,
12, 1611.
(26) Treadway, J . A.; Meyer, T. J . Inorg. Chem. 1999, 38, 2267.
(27) (a) Yu, G.; Gao, J .; Hummelen, J . C.; Wudl, F.; Heeger, A. J .
Science 1995, 270, 1789. (b) Kocher, M.; Da¨ubler, T. K.;
Harth, E.; Scherf, U.; Gu¨gel, A.; Neher, D. Appl. Phys. Lett.
1998, 72, 650. (c) Nierengarten, J . F. Mater. Tod. 2001, 4,
16.
(28) (a) Lee, J . K.; Yoo, D.; Rubner, M. F. Chem. Mater. 1997, 9,
1710. (b) Laguitton-Pasquier, H.; Martre, A.; Deronzier, A.
J . Phys. Chem. B. 2001, 105, 4801.
(29) (a) Chujo, Y.; Sada, K.; Saegusa, T. Macromolecules 1993,
26, 6320. (b) Heller, M.; Schubert, U. S. Macromol. Rapid
Commun. 2001, 22, 1358.
(30) (a) Wo¨rner, M.; Greiner, G.; Rau, H. J . Phys. Chem. 1995,
99, 14161.(b) Ghosh, P. K.; Spiro, T. G. J . Am. Chem. Soc.
1980, 102, 5543.
(20) J ones, W. E.; Smith, R. A.; Abramo, M. T.; Williams, M. D.;
Houten, J . V. Inorg. Chem. 1989, 28, 2281.
(21) Wu, X.; Fraser, C. Macromolecules 2000, 33, 4053.
(22) (a) Fo¨rster, T. Ann. Phys. 1948, 2, 55; (b) Fo¨rster, T. Z.
Naturforsch. 1949, 4, 321.
MA020265T