Single polymer photosensitizer for Tb3+ and Eu3+ ions: An approach for white light emission based on carboxylic-functionalized poly(m-phenylenevinylene)s

Article abstract of DOI:10.1021/jp9067312

Here, we have demonstrated a facile molecular approach to generate white light emission by combining carboxylic functionalized poly(m-phenylenevinylene)s polymeric architectures with lanthanide ?2-diketonate complexes. The new class of carboxylic function

Full text of DOI:10.1021/jp9067312

14128
J. Phys. Chem. B 2009, 113, 14128–14138
Single Polymer Photosensitizer for Tb3+ and Eu3+ Ions: An Approach for White Light
Emission Based on Carboxylic-Functionalized Poly(m-phenylenevinylene)s
A. Balamurugan,† M. L. P. Reddy,*,† and M. Jayakannan*,‡
Chemical Sciences and Technology DiVision, National Institute for Interdisciplinary Science and Technology,
Council of Scientific & Industrial Research (CSIR), ThiruVananthapuram-695019, Kerala, India, and
Department of Chemistry, Indian Institute of Science Education and Research (IISER), NCL InnoVation Park,
Dr. Homi Bhabha Road, Pune 411008, India
ReceiVed: July 16, 2009; ReVised Manuscript ReceiVed: August 21, 2009
Here, we have demonstrated a facile molecular approach to generate white light emission by combining
carboxylic functionalized poly(m-phenylenevinylene)s polymeric architectures with lanthanide ꢀ-diketonate
complexes. The new class of carboxylic functional conjugated polymeric materials was custom-designed
from phenyl propanoic and acetic acids and structurally characterized by NMR, FT-IR, and MALDI-TOF
spectroscopic techniques. The designed conjugated polymers were employed for the synthesis of lanthanide
complexes in the presence of acetyl acetone (acac) as coligand and investigated their photophysical properties.
For comparison, carboxylic-anchored oligo-phenylenevinylene (OPV) was also designed, characterized, and
utilized for the synthesis of lanthanide complexes in the presence of acetyl acetone as coligand. Investigations
revealed that carboxylic functionalized polymeric material with Eu3+-ꢀ-diketonate complex exhibits unique
magenta emission when excited at 310 nm. On the other hand, carboxylic functionalized polymeric material
with Tb3+-ꢀ-diketonate complex shows bright sky-blue emission. Interestingly, when Eu3+ and Tb3+ were
incorporated into polymer backbone in equimolar ratio along with acetyl acetone as coligand, exhibited a
white emission with CIE 1976 color coordinates x ) 0.28, y ) 0.34. The intrinsic quantum yield and lifetime
of Ln3+ complexes have been evaluated. The singlet and triplet energy levels of the antenna chromophore
ligands have been calculated and the probable energy transfer mechanisms in Ln3+ complexes have also been
discussed. The effect of polymer structure and spacer effect on the photosensitizing of Tb3+ and Eu3+ ions
was also investigated.
Introduction
effect”.7 The mechanism of antenna sensitization can be
approximated by three differing steps, the initial excitation of
the ligand, followed by intersystem crossing to give an excited
triplet state, and then subsequent energy transfer to yield the
metal centered excited state, which emits light. Among a host
of organic ligands, the ꢀ-diketones8 and aromatic carboxylates9
are the most frequently used sensitizing ligands for enhancing
lanthanide luminescence because they can chelate effectively
to lanthanide cations. Interesting luminescent properties featuring
either dual emission or binomial mode emission have been
reported to result from the incorporation of two different
lanthanides into a single molecular scaffold.10 However, many
of the low-molecular-weight lanthanide complexes undergo
decomposition to some extent during film formation by vacuum
deposition. Decomposition of the lanthanide complexes can be
avoided in spin-coated films containing the lanthanide com-
plexes dispersed in polymer matrices.11 A drawback of this
technique is that nonuniform blending or dispersion of the
dopants may result in phase separation and ionic aggregation.12
The use of polymers with the lanthanide complexes covalently
bonded in the main chain or as pendant groups will help to
overcome the above-mentioned problems. Further, energy
transfer in a covalently bound system will be effective due to
the close proximity of the two components. Many studies have
been focused on polymer systems doped or blended with
lanthanide complexes.13 However, blending may not give rise
to uniformly disperse and thermodynamically stable composi-
tions. π-Conjugated polymers or poly(methylmethacrylate)
bearing phenonthroline, bipryridyl, binapthyls, terpyridine,
Polymer light-emitting diodes (PLEDs) have been widely
investigated since the first successful design of a functional diode
using a conjugated polymer as the electroluminescent material
in 1990.1 Conjugated polymers exhibit several unique electrical
and optical properties, easy fabrication as uniform films, and
mechanical flexibility, as compared to inorganic electrolumi-
nescent materials.2 Though the conjugated polymers have been
successfully demonstrated for electroluminescent devices, many
issues such as low luminescence intensity and lifetime, π-stack
induced aggregated quenching, low quantum efficiency, and
poor color purity are some of the unresolved problems.3 The
use of polymers with lanthanide complexes that covalently bond
in the main chain or as pendant groups will help to overcome
the above drawbacks.4 The fascinating optical properties of
lanthanide ions have promoted the use of such complexes in a
wide variety of technological applications ranging from bio-
medical analysis to materials science.5,6 However, since f-f
transitions are forbidden, free luminescent lanthanide cations
have extremely low extinction coefficients and direct lanthanide
excitation results only in modest luminescent intensities. To
obviate this problem, organic ligands with large molar absorption
coefficients can be coordinated to the lanthanide ion, resulting
in sensitized emission by means of the so-called “antenna
* To whom correspondence should be addressed. E-mail: (M.J.)
jayakannan@iiserpune.ac.in; (M.L.P.R.) mlpreddy55@gmail.com.
† National Institute for Interdisciplinary Science and Technology.
‡ Indian Institute of Science Education and Research (IISER).
10.1021/jp9067312 CCC: $40.75  2009 American Chemical Society
Published on Web 09/25/2009

Single Polymer Photosensitizer for Tb3+ and Eu3+ Ions
J. Phys. Chem. B, Vol. 113, No. 43, 2009 14129
Figure 1. Single polymer based photosensitizer for tuning of emission colors in Ln3+ complexes.
N,N′diphenylenamine, polyvinylpyrrolidone, and polyvinylcar-
bazole were reported for lanthanide metal ions.4,14 Recently, a
novel white-light emission has been proposed from a two-
emitting system comprising a blue-emitting dysprosium-chelated
terpyridine-based polymer and a red-emitting ruthenium com-
plex.15 Design of single π-conjugated polymer based highly
selective photosensitizer for one or two lanthanide metal ions
(Eu3+ and Tb3+) is a very attractive approach because (i)
selective photosensitizing to either Tb3+ or Eu3+ can be utilized
for sharp and bright green and red emission, (ii) partial self-
emission of conjugated polymer may be used as a third primary
color for the white emission, and (iii) fundamental understanding
of color tuning and mechanistic aspects of energy transfer
process in single polymeric systems-lanthanide complexes are
not known. To the best of our knowledge, there is no report for
single π-conjugated polymer based photosensitizer for white
light emission from lanthanide ions.
These factors have prompted us to design a carboxylic
functionalized poly(m-phenylenevinylene)s (m-PPV) for the
selective color tuning of red, green, and white light emissions,
which is a first of its kind based on a single polymeric
photosensitizer for lanthanide complexes. Novel π-conjugated
materials based on carboxylic functionalized poly(m-phenyle-
nevinylene)s (m-PPV)s and oligo-phenylenevinylene (OPV)
from phenyl propanoic or acetic acid and successfully employed
as a suitable photosensitizer for Eu3+ and Tb3+ ions (see Figure
1). The newly designed conjugated polymer was found very
superior in sensitizing Eu3+ or Tb3+ ions for sharp magenta and
sky blue emissions, respectively, in the presence of acetylacetone
as coligand. The partial self-emission from m-PPV conjugated
backbone (blue) in combination with Eu3+ (magenta) and Tb3+
(sky blue) was cleverly utilized to obtain pure white light
emitting materials. Further, the effect of spacer length between
the metal centers to conjugated backbone and influence of
copolymer on the photoexcitation process were also investigated.
Experimental Methods
Materials. 3-(4-Hydroxyphenyl)propanoicacid, 2-ethylhexy-
lbromide, triethylphosphite, benzaldehyde, terephthaldehyde,
isophthaldehyde, potassium-tert-butoxide, acetylacetone,
Gd(NO3)3 ·6H2O, Tb(NO3)3 ·6H2O, and Eu(NO3)3 ·6H2O were
purchased from Aldrich chemicals. HBr in glacial acetic acid,
paraformaldehyde, and all other reagents and solvents were
purchased locally and purified following the standard procedure.
General Procedures. 1H NMR spectra of the compounds and
the polymers were recorded using 300 and 500 MHz Bruker
NMR spectrophotometer in CDCl3 containing small amount of
TMS as internal standard. Infrared spectra of the polymers and
complexes were recorded using Perkin-Elmer Fourier transform
infrared (FTIR) spectrophotometer. The purity of the monomers,
intermediate compounds, and oligomer were determined by
JEOL JSM600 fast atom bombardment (FAB) high-resolution
spectrometry (HRMS) by dissolving the compound in THF and
suspended in 3-nitrobenzyl alcohol as a matrix for FAB mass
measurements. Elemental analysis was carried out using El-
emental Vario EL-III CHN analyzer. The molecular weight of
the polymer was determined by gel permeation chromatography
(GPC) in tetrahydrofuran using polystyrene as standards. The
flow rate of THF was maintained as 1 mL/min. The polymer
solution was prepared by dissolving 3 mg of the sample in 1
mL of THF, filtered and injected for recording the GPC
chromatograms. The chromatograms are recorded using waters
510 pump and detectors of waters 2487 UV-vis detector and
waters 410 differential RI detector. Three mixed styra-gel
columns in series HT 6E, HR 5E, and HR 4E are employed for
separation. The thermal stability of the polymeric complexes
was determined using TGA-50 Shimadzu thermogravimetric
analyzer at a heating rate of 10 °C/min in nitrogen atmosphere.
The absorption and emission studies were done by a Perkin-
Elmer Lambda 35 UV-visible spectrophotometer and SPEX

14130 J. Phys. Chem. B, Vol. 113, No. 43, 2009
Balamurugan et al.
Fluorolog DM-3000Fspectrofluorimeter with a double-grating
0.22 m Spex1680 monochromator and a 450 W Xe lamp as the
excitation source using front face mode at room temperature.
The solution spectra were recorded in THF and for solid state
spectra polymers thin films were prepared by drop casting THF
on quartz substrates. The concentrations of the polymer and
standard solution were adjusted in such a way to obtain the
absorbance equal to 0.1 at 310 nm. The excitation and emission
spectra of the complexes were corrected at instrumental function.
into ice cold water. The precipitate was filtered and washed
with water to completely remove acid impurities. The precipitate
was dried in vacuum oven at 45 °C. Further the purification
was done by recrystallization from hexane and dichloromethane
mixture and the product was obtained as crystalline solid. Yield
) 9.5 g (60%). H1 NMR (in CDCl3) δ: 7.21 (s, 2H, Ar-H),
4.50 (s, 4H, Ar-CH2-Br), 3.96 (d, 2H, Ar-OCH2), 2.90 (t,
2H, Ar-CH2CH2), 2.67 (t, 2H, -CH2CH2-COOH), 1.84 -0.09
(m, 20H, Aliphatic H).13C NMR (in CDCl3) δ: 178.10, 154.12,
136.70, 132.07 (2C), 132.03 (2C), 77.51 (2C), 40.66, 35.22,
30.15, 29.70, 29.12, 27.64, 23.63, 23.11, 14.12, and 11.28. FT-
IR (cm-1): 2959, 2931, 2873, 2861, 1712, 1470, 1385, 1241,
1213, 1162, 1116, 1001, 916, 879, 585, and 515. HR-MS: MW
) 464.24 and m/z ) 464.20.
Synthesis of 3-(3,5-Bis((diethoxyphosphoryl)methyl)-4-(2-
ethylhexyloxy)phenyl)propanoic acid (4). Compound 3 (9 g,
19.4 mmol) and triethylphosphite (6.5 g, 38.8 mmol) (6.6 mL)
were heated about 120-140 °C about 12 h under N2 atmosphere.
The excess triethylphosphite was removed by vacuum distillation
to obtain the ylide as thick oil. It was purified by silica gel
column chromatography using 20% ethyl acetate in hexane.
Yield ) 11.0 g (98%). H1 NMR (in CDCl3) δ: 7.22 (s, 2H,
Ar-H), 4.02 - 4.13 (q, 8H, -PO(OCH2CH3)2), 3.71 (d, 2H,
Ar-OCH2), 3.16-3.23 (d, 4H, Ar-CH2PO-), 2.85-2.88 (t,
2H, Ar-CH2CH2), 2.59-2.61 (t, 2H, CH2-CH2COOH),
0.92-1.58 ppm (m, 32H, aliphatic H). C13 NMR (in CDCl3) δ:
175.56, 153.98, 136.34, 130.09, 129.96, 124.87, 63.71, 62.51,
62.39, 62.34, 62.19, 61.60, 57.99, 53.43, 40.56, 35.76, 30.33,
30.12, 29.04, 27.16, 26.04, 23.48, 23.06, 20.87, 18.12, 16.29,
and 14.16. FT-IR: 3148, 2964, 2928, 2871, 1728, 1618, 1474,
1396, 1247, 1163, 1022, 966, 880, 856, 781, 727, 622, 571,
534, 526, 500, 481, and 492. HR-MS: MW ) 578.63 and m/z
) 577.80.
Synthesis of Methyl 3-(4-hydroxyphenyl)propanoate (1).
3-(4-Hydroxyphenyl)propanoic acid (20 g, 120 mmol) was
dissolved in dry methanol (100 mL). Concentrated H2SO4 (13
mL) was slowly added into the methanol solution with stirring
and the content was refluxed for 24 h. The solvent was
evaporated and the concentrated solution was poured into water.
It was extracted with dichloromethane and the organic layer
was washed with 5% NaHCO3 solution and then with distilled
water. After drying over Na2SO4, the solvent was evaporated
to get colorless viscous liquid as the product. It was purified
by silica gel column chromatography using 10% ethyl acetate
and hexane. Yield ) 19.6 g (91%).1H NMR (in CDCl3) δ: 7.34
(s, 1H, Ar-OH), 6.99 (d, 2H, Ar-H), 6.76 (d, 2H, Ar-H),
3.64 (s, 3H, -CH2-COOCH3), 2.84 (t, 2H, Ar-CH2CH2), 2.58
(t, 2H, CH2-CH2COOCH3). 13C NMR (in CDCl3) δ: 174.56,
154.48, 131.97, 129.36 (2C), 115.49 (2C), 51.93, 36.12, and
30.08. FT-IR (cm-1): 3393, 3022, 2953, 2863, 2699, 1885, 1738,
1713, 1614, 1597, 1516, 1440, 1363, 1297, 1220, 1211, 1173,
1103, 1028, 987, 952, 904, 830, 734, 551, 534, 497, and 459.
HR-MS: MW ) 180.21 and m/z ) 180.06.
Synthesis of Methyl 3-(4-(2-ethylhexyloxy) phenyl)pro-
panoate (2). Compound 1 (15 g, 83.3 mmol) and anhydrous
K2CO3 (34.5 g, 2.5 mmol) were taken in flask containing dry
DMF (60 mL) and stirred well at 75 °C under nitrogen
atmosphere about 1 h. The catalytic amount of KI and
2-ethylhexyl bromide (17.7 g, 16.3 mL, 91.7 mmol) were added
into the reaction mixture. The reaction was continued about 24 h
at 80 °C under nitrogen atmosphere. The solvent was removed
by vacuum distillation, and the residue was poured into the water
and then extracted with dichloromethane. The organic layer was
washed with 5% NaOH, brine solution, water, and then dried
over Na2SO4. The solvent was evaporated to get yellow liquid
as product. It was purified by passing through silica gel column
using hexane +10% ethyl acetate. Yield ) 16.9 g (70%). H1
NMR (in CDCl3) δ: 6.81 (d, 2H, Ar-H), 7.08 (d, 2H, Ar-H),
3.79 (d, 2H, Ar-OCH2), 3.64 (s, 3H, -CH2-COOCH3), 2.87
(t, 2H, Ar-CH2CH2), 2.58 (t, 2H, CH2-CH2COOCH3),
1.72-0.89 (m, 20H, aliphatic H).13C NMR (in CDCl3) δ:
173.44, 157.92, 132.26, 129.33, 129.14, 114.53, 114.32, 70.44,
51.54, 39.41, 36.04, 30.13, 29.10, 23.83, 23.08, 22.98, 14.1,
and 11.11. FT-IR (cm-1): 2961, 2927, 2874, 2859, 1739, 1613,
1582, 1513, 1463, 1436, 1364, 1296, 1245, 1174, 1107, 1034,
987, 825, and 770. HR-MS: MW ) 292.24 and m/z ) 292.24.
Synthesis of 3-(4-(2-Ethylhexyloxy)-3,5-di(E)-styrylphe-
nyl)propanoic acid (OPV) (5). Compound 4 (3 g, 5.2 mmol)
and benzaldehyde (1.2 g, 11.3 mmol) were dissolved in dry
THF (40 mL) and potassium tert-butoxide (15 mL, 1 M THF)
was added and the contents were stirred under nitrogen
atmosphere for 12 h at room temperature. It was poured into
cold water (the residue was completely soluble in water) and
neutralized with 10% HCl. The white precipitate was filtered
and washed with water, dried in vacuum oven at 40 °C. The
crude product was purified by passing through a silica gel
column using 10% ethyl acetate and hexane (2:10 v/v) as eluent.
1
Yield ) 2.1 g (98%). H NMR (in CDCl3) δ: 7.55-7.06 (m,
16H, Ar-H and vinylic H), 3.71-3.70 (d, 2H Ar-O-CH2),
2.98-2.96 (t, 2H, Ar-CH2CH2), 2.77-2.72 (t, 2H,
CH2-CH2COOH), 1.80-0.85 (m, 32H, aliphatic H).13C NMR
(in CDCl3) δ: 178, 153.66, 137.57, 135.91, 133.77, 131.34 (2C),
130.19, 129.66, 128.70, 128.49 (4C), 127.66 (2C), 126.55 (4C),
125.26 (2C), 123.16 (2C), 40.96, 35.75, 30.82, 30.45, 29.41,
23.83, 23.15, 14.08, 11.39. FT-IR (cm-1): 3431, 3026, 2964,
2934, 2862, 1708, 1597, 1496, 1453, 1442, 1382, 1303, 1256,
1205, 1140, 1074, 968 (CHdCH, trans) 870, (CHdCH, cis)
848, 812, 743, 690, 532, 504. HR-MS MW ) 482.67 and m/z
) 482.71, 505.73 (M+ + Na+).
Synthesis of 3-(3,5-Bis(bromomethyl)-4-(2-ethylhexylox-
y)phenyl)propanoic acid (3). Compound 2 (10 g, 34.2 mmol)
and paraformaldehyde (3.1 g, 122.0 mmol) were taken in flask
containing glacial acetic acid (40 mL). HBr in glacial acetic
acid (8.5 mL, 30-33 wt %) was added dropwise to the above
solution at room temperature and stirred for 0.5 h under N2
atmosphere. It was gradually heated to 80 °C and stirred for
24 h. The reaction mixture was cooled to room temperature
and second batch of paraformaldehyde (3.1 g, 122.0 mmol) and
HBr in glacial acetic acid (8.5 mL, 30-33 wt %) were added.
It was further carried out for 24 h by heating at 80 °C. The
reaction mixture was cooled to room temperature and poured
Synthesis of Poly[3-(4-(2-ethylhexyloxy)phenylenevinylene)-
alt-(1,3-phenylenevinylene)propanoic acid] (m-PPV) (6). Com-
pound 4 (1 g, 0.0017 mol) and isophthaldehyde (0.23 g, 1.73
mmol) were dissolved in dry THF (50 mL). The mixture was
stirred well under nitrogen atmosphere about 15 min at room
temperature. Potassium tert-butoxide (10.4 mL in 1 M THF)
was added dropwise and stirred for further 12 h at room
temperature under nitrogen atmosphere. It was poured into water

Single Polymer Photosensitizer for Tb3+ and Eu3+ Ions
J. Phys. Chem. B, Vol. 113, No. 43, 2009 14131
and neutralized with 10% HCL, the product was washed with
excess of water. The sticky product was purified by washing
with water and methanol. It was dried in a vacuum oven at 40
°C for 5 h prior to further analysis. Yield ) 0.36 g (51%).1H
NMR (in CDCl3) δ: 7.52-7.04 (m, 10H, Ar-H and vinylic
H), 3.69-3.68 (d, 2H -O-CH2), 2.97-2.95 (t, 2H,
Ar-CH2CH2), 2.75-2.72 (t,2H, CH2-CH2COOH), 1.90-0.82
(m, 32H, aliphatic H).13C NMR (in CDCl3) δ: 173.20, 153.65,
133.73, 130.15, 129.09, 128.76, 127.75, 125.36, 124.25, 123.92,
40.01, 29.84, 29.58, 29.31, 28.65, 28.15, 27.83, 26.51, 26.19,
25.93, 25.07, 22.75, 20.89, 15.27,14.17, 13.05, 10.20, and 9.30.
FT-IR (cm-1): 3450, 2959, 2933, 2866, 1721, 1600, 1597, 1463,
1347, 1250, 1216, 1156, 1046, 971 (CHdCH, trans), 856
(CHdCH, cis) 795 and 498. Molecular weight (GPC, in THF):
Mn ) 2700 and Mw ) 3300.
968, 916, 847, 981, 688, and 532. Similar procedure was adopted
for the synthesis of other co-PPV, p-PPV complexes.
Gd(m-PPV)(NO3)2. FT-IR (cm-1): 3392, 2928, 1559, 1451,
1416, 1311, 1256, 1201,1188, 1049, 1075, 1046, 960, 847,
772,788, 694, 617, 569, 526, 504, and 486.
Synthesis of Eu0.5Tb0.5(acac)3(m-PPV). To the THF solution
of m-PPV (0.05 g, 0.123 mmol), NaOH (0.005 g, 0.123 mmol)
solution was added, the mixture was stirred for 5 min. To this
a saturated THF solution, in situ prepared Eu0.5Tb0.5(acac)3 is
added dropwise and the stirred for 12 h. Water is then added
into this mixture and the precipitate thus formed is filtered,
washedwithwater,anddriedundervacuumat50°C.Eu0.5Tb0.5(acac)3(m-
PPV): FT-IR (cm-1), 3426, 2956, 2927, 2857, 1599, 1519, 1404,
1260, 1277, 1157, 1022, 963, 916, 847, 763, 655, 529, and 488.
The 1:1 molar ratios of Eu3+/Tb3+ in Eu0.5Tb0.5(acac)3(m-PPV)
and Eu0.5Tb0.5(acac)3(m-PPV-A) were confirmed by EDS analy-
ses (Figure S12-S13 and Table S1, Supporting Information).
Synthesis of Ln(acac)3(OPV) (Ln ) Eu3+ or Tb3+). To an
ethanolic solution of OPV (0.15 g, 0.31 mmol), NaOH (0.014
g, 0.342 mmol) solution was added, the mixture was stirred for
5 min. To this a saturated ethanolic solution, in situ prepared
Ln(acac)3 is added dropwise and the stirred for 10 h. Water is
then added into this mixture and precipitate thus formed is
filtered, washed with water, and dried. It was further purified
by recrystallization from dichloromethane-ethanol mixture.
Synthesis of Ln(acac)3(H2O) (Ln ) Eu3+ or Tb3+). Acetyl
acetone (0.099 g, 0.99 mmol) was dissolved in dry ethanol (5
mL) and NaOH (0.052 g, 1.30 mmol) in water (2 mL) was added
into the mixture. The whole mixture was stirred well about 1/2
h to become a clear solution at room temperature and then
Ln(NO3)3 ·6H2O (0.15 g, 0.341 mmol) in dry ethanol (3 mL)
was added into the reaction mixture.
Results and Discussions
Synthesis of Polymers and Ln3+ Complexes. The carboxylic
functionalized monomer was designed from commercially
available 3-(4-hydroxyphenyl)propanoic acid and was converted
into required bis-ylide monomer and oligo(phenylenevinylene)
(OPV) model compound as shown in Scheme 1. Methyl-3-(4-
hydroxyphenyl)propanoate (1) was prepared by refluxing 3-(4-
hydroxyphenyl)propanoic acid with methanol and concentrated
H2SO4. 2-Ethylhexyl bromide was reacted with 1 in K2CO3/
DMF under nitrogen atmosphere to get methyl-3-(4-(2-ethyl-
hexyloxy)phenyl)propanoate (2). 2 was bis-bromomethylated
with p-formaldehyde in the presence of HBr/acetic acid to yield
3-(3,5-bis(bromomethyl)-4-(2-ethylhexyloxy)phenyl)propano-
ic acid (3). 3 was converted into bis-ylide 3-(3,5-bis ((diethoxy-
phosphoryl)methyl)-4-(2-ethylhexyloxy)phenyl)propanoic acid
(4). The bis-ylide monomer (3) was polymerized with isoph-
thaldehyde and terephthaldehyde under Wittig-Horner reaction
conditions in the presence of potassium tert-butoxide as the base
to yield poly[3-(4-(2-ethylhexyloxy)phenylenevinylene)-alt-(1,3-
phenylenevinylene)] (m-PPV) and its para counterpart poly[3-
(4-(2-ethylhexyloxy) phenylenevinylene)-alt-(1,4-phenylenev-
inylene)] (p-PPV), respectively (see Scheme 2). A copolymer
(co-PPV) bearing 50:50% of p- and m-content was prepared
by polymerizing 3 with equal mole ratio of terephthaldehyde
and isophthaldehyde under the same conditions. A structurally
identical model compound 3-(4-(2-ethylhexyloxy)-3,5-di(E)-
styrylphenyl)propanoicacid (OPV) was prepared by reacting 3
with two moles of benzaldehyde (see Scheme 1). The structures
of the monomers, OPV, and polymer were characterized by 1H,
13C NMR, FT-IR and FAB-HRMS (Figures S1-S10, Support-
ing Information). The 1H NMR spectra of the m-PPV polymer
and OPV were shown in Figure 2 and different types of protons
in the structure were assigned by alphabets. In Figure 2a, the
OPV has three peaks at 3.70, 3.00, 2.75 ppm corresponding to
Ar-OCH2-, Ar-CH2CH2, and CH2-CH2COOH, respectively.
The multiple of peaks above 7.00 ppm were assigned to aromatic
and vinylene protons that were matching with that of expected
structure as reported earlier. In Figure 2b, the m-PPV polymer
has also almost identical pattern of peaks except peaks for
proton-b at 7.45 ppm with respect to its structure. The FT-IR
spectra of the polymers and OPV (Figure S11, Supporting
Information) showed characteristic peaks at 3450 and 3447 cm-1
for O-H stretching of -COOH group, respectively. The peaks
at 1721 and 1708 cm-1 were assigned to CdO stretching of
carboxylic acid groups in m-PPV and OPV, respectively. All
other peaks at 2930, 1250, 1255 cm-1 (C-O ether linkage),
Eu(acac)3(H2O)(OPV). FT-IR (cm-1): 3460, 2924, 1521,
1498, 1405, 1390, 1254, 1218, 1151, 1079, 1014, 975, 946, 920,
846, 731, 694, 660, 643, and 512. Anal. Calcd. for C48H64O10Eu:
C, 60.50; H, 6.77. Found: C, 60.71; H, 7.26. m/z ) 950.60.
Tb(acac)3(H2O)(OPV). FT-IR (cm-1): 3438, 2964, 2935,
2869, 1605, 1517, 1450, 1318, 1274, 1208, 1172, 1080, 1033,
985, 802, 754, 728, 593, 571, and 543. Anal. Calcd. for
C48H64O10Tb: C, 60.06; H, 6.72. Found: C, 59.65; H, 6.47. m/z
) 956.64.
Synthesis of Gd(OPV)32(H2O). An aqueous solution of
Gd(NO3)3 ·6H2O (0.03 g, 0.067 mmol) was added to a solution
of OPV (0.1 g, 0.21 mmol) in ethanol in the presence of NaOH
(0.02 g, 0.64 mmol). Precipitation took place immediately, and
the reaction mixture was stirred for 10 h at room temperature.
The product was filtered, washed with ethanol, water, and
ethanol, and then dried. The complex was then purified by
recrystallization from dichloromethane-ethanol mixture. FT-
IR (cm-1): 3436, 2970, 2928, 2872, 1596, 1537, 1498, 1454,
1315, 1258, 1208, 1136, 1000, 963, 873, 847, 737, 688, and
529. Anal. Calcd. for C99H85O11Gd: C, 72.45; H, 7.25. Found:
C, 72.05; H, 7.48. m/z ) 1638.33.
Synthesis of Eu(acac)3(m-PPV) and Tb(acac)3(m-PPV)
Complexes. To the THF solution of m-PPV (0.05 g, 0.123
mmol), NaOH (0.005 g, 0.123 mmol) solution was added, the
mixture was stirred for 5 min. To this a saturated THF solution
in situ prepared Ln(acac)3 is added dropwise and the stirred for
12 h. Water is then added into this mixture and precipitate thus
formed is filtered, washed with water, and dried under vacuum
at 50 °C.
Eu(acac)3(m-PPV). FT-IR (cm-1): 3421, 2967, 2917, 1597,
1519, 1466, 1412, 1259, 1194, 1016, 918, 782, 760, 657, 627,
573, 525, and 483.
Tb(acac)3(m-PPV). FT-IR (cm-1): 3420, 2964, 2923, 2859,
1560, 1522, 1446, 1413, 1300, 1254, 1202, 1880, 1166, 1045,

14132 J. Phys. Chem. B, Vol. 113, No. 43, 2009
Balamurugan et al.
SCHEME 1: Synthesis of Monomer and Oligo-Phenylenevinylene
SCHEME 2: Synthesis of Carboxylic Functionalized Poly(m-phenylenevinylene)s
972, 970 cm-1 (trans, HC)CH), and 856, 870 cm-1 (cis
HC)CH) vinylene C-H out-of-plane bending and the values
are matching with that of the expected structure. The molecular
weights were obtained Mn ) 2300-5300 and Mw ) 3300-6900
indicating the formation of moderate molecular weight polymers
with an average of 9-10 repeating units in the polymer chain.
In general, poly(m-phenylenevinylenes) were produced lower
molecular weights due to formation macrocyclic rings and also
low degree of conversion in the bis-ylide Witting polyconden-
sation reactions.3f-j Therefore, the molecular weights of the
polymers reported here were typically accepted for bis-ylide
condensation route. It is well-known that the photophysical
properties of the conjugated polymers were almost invariant for
6-8 repeating units in the polymer chain. The synthesized

Single Polymer Photosensitizer for Tb3+ and Eu3+ Ions
J. Phys. Chem. B, Vol. 113, No. 43, 2009 14133
Figure 2. 1H NMR Spectra of OPV and m-PPV in CDCl3.
polymers have an average of 16-20 aromatic rings in the
backbone, and therefore the carboxylic functionalized polymers
were sufficient enough for studying lanthanide metal ions
complexation.
Newly designed carboxylic functionalized polymers (PPVs)
and OPV were utilized as multidentate polymeric or small
molecular ligands for the syntheses of Ln3+ complexes. Acety-
lacetone was used as coligand and the complexation was carried
out in presence of ethanol using NaOH as base. One mole
equivalence of Ln(NO)3 ·6H2O (Ln ) Eu3+ or Tb3+) was reacted
with three mole equivalents of acac in ethanol to form Ln(acac)3
(in situ preparation). The PPVs and OPV were converted into
its sodium salts by reacting with NaOH in water. The sodium
salt was added to the in situ prepared Ln(acac)3 solution. The
complex [Ln(acac)3(OPV) or Ln(acac)3(PPV)] was precipitated
from the reaction solution and it was filtered then washed with
hot water/ethanol to get pure complexes. In the case of the OPV
complexes, the precipitate was further purified by recrystalli-
zation from dichloromethane/ethanol mixture. The formations
of the complexes were confirmed by FT-IR spectroscopic
techniques (Figure S11, Supporting Information). The carbonyl
stretching frequency at 1723 cm-1(CdO stretching) in m-PPV
vanished and new peaks appeared at 1601 and 1420 cm-1
corresponding to the antisymmetric and symmetric vibration of
the M-CdO carboxylate group. The broad peak around 3400-
3550 cm-1 shows that water molecules are also coordinated to
the polymer complexes. Similarly formation OPV complexes
were confirmed by the absence of carbonyl stretching frequency
of the OPV at 1702 cm-1 and new peaks at 1603 and 1450
cm-1 are corresponding to the antisymmetric and symmetric
vibration were observed. The molecular weights and structures
of the OPV complexes were confirmed by MALDI-TOF
analysis. In Figure 3a,b, the molecular ion peaks at 956.64 and
950.60 were matching with expected molecular weights of
Tb(acac)3(OPV)·H2O and Eu(acac)3(OPV)·H2O, respectively.
Figure 3. MALDI-TOF Spectra of Eu(acac)3OPV · H2O and
Tb(acac)3OPV·H2O complexes.
It is clearly evident that the OPV molecule involved in the
complex formation with Tb(acac)3 or Eu(acac)3. The 1:1 molar
ratios of Eu3+/Tb3+ in Eu0.5Tb0.5(acac)3(m-PPV) (Eu/Tb ) 0.98)
and Eu0.5Tb0.5(acac)3(m-PPV-A) (Eu/Tb ) 1.17) were confirmed
by EDS analyses (Figure S12-S13 and Table S1, Supporting
Information). From the thermogravimetric analysis data, it is
clear that complexes Eu(acac)3(m-PPV), Tb(acac)3(m-PPV), and
Eu0.5Tb0.5 (acac)3(m-PPV) undergo weight loss of 5% up to 250
°C, which corresponds to the elimination of coordinated water
molecules. Further decomposition takes place in two steps and
leaves the final residue of approximately 43%, which corre-
sponds to the lanthanide oxides (Figure S14, Supporting
Information).
Photophysical Properties. The absorption and emission
spectra of OPV and m-PPV were recorded at 298 K for drop

14134 J. Phys. Chem. B, Vol. 113, No. 43, 2009
Balamurugan et al.
levels, are also evident in the excitation spectra of these
complexes.16 However, these transitions are weaker than the
absorptions due to the organic ligands and are overlapped by a
broad excitation band, thus proving that luminescence sensitiza-
tion that arises from excitation of the ligand is considerably
more efficient than the direct excitation of the Eu3+ absorption
level. The emission spectra of Eu3+complexes (Figure 5B)
excited at 310 nm exhibited the characteristic narrow bands
arising from the intraconfigurational 5D0f7FJ (J ) 0-4)
transitions of the Eu3+ ion.16 The PL spectrum of the complexes
dispersed in DMSO has also showed the emission from the metal
center; however, its intensity is relatively less compared to that
of the solid state. It is interesting to note that only a weak
residual emission due to m-PPV is observed in Eu(acac)3(m-
PPV), indicating an efficient ligand-to-metal energy transfer
process. On the other hand, in the case of Eu(acac)3(OPV), the
self-emission of OPV was also present indicating that OPV is
a poor-sensitizer for Eu3+. In the case of Eu(acac)3, only weak
intraconfigurational 5D0f7FJ transitions of the Eu3+ ion is
observed. The five narrow emission peaks centered at 579, 590,
612, 649, and 699 nm, assigned to 5D0f7F0, 5D0f7F1, 5D0f7F2,
5D0f7F3, and 5D0f7F4 transitions, respectively.8a,b,9a,16 Among
Figure 4. Absorption (a) and emission (b) spectra of OPV and m-PPV.
5
the peaks, the emission at 612 nm from the D0f7F2 induced
electronic dipole transition is the strongest, suggesting the
chemical environment around Eu3+ ions does not have an
inversion center.17 The relative energy-transfer efficiency in the
OPV or m-PPV containing the Eu(acac)3 complex is determined
from the ratio of the maximum emission intensity of two
chromophores (I612/I350-560, where I612 is the maximum intensity
of main emission peak of Eu3+ complex at around 612 nm and
I350-560 is the maximum intensity of main emission peak of OPV
or m-PPV in the range of 350-560 nm) (Table 1). As can be
seen from Table 1 and Figure 5B, m-PPV has the highest
energy-transfer efficiency in solid state compared to that of OPV.
Thus the combination of strong red emissions from Eu3+ center
at 612 nm and weak blue emissions in the region 375 to 450
nm due to the residual emission from m-PPV results in an
interesting magenta-colored emission with CIE coordinates 0.33
and 0.17, when Eu(acac)3(m-PPV) is excited at 310 nm.
To understand the energy transfer processes in the synthesized
Eu3+ complexes, it was necessary to determine the singlet and
triplet energy levels of the m-PPV and OPV. The singlet (1π
π*) energy levels of these ligands were estimated by reference
to the wavelengths of the UV-vis absorption edges of ligands.
The relevant values were 395 nm (25 300 cm-1), and 370 nm
(27 000 cm-1) for m-PPV and OPV, respectively (see Figure
4). The triplet energy levels (3ππ*) of the ligands were
calculated by reference to the lower wavelength emission edges
(480 nm, 20800 cm-1 and 448 nm, 22300 cm-1 for m-PPV and
OPV, respectively) from the low-temperature phosphorescence
spectra of the Gd3+ complexes of the pertinent ligands (Figure
S16, Supporting Information). Because there is a large energy
Figure 5. Excitation (A) and emission (B) spectra of Eu3+complexes.
Eu(acac)3 (a); Eu(acac)3(OPV) (b); Eu(acac)3(m-PPV) (c).
casted films (on quartz plate) and are given in Figure 4. The
absorption maximum of the m-PPV noted at 305 nm is attributed
to the π-π* absorption of aromatic phenylene rings. The
emission maximum of m-PPV was obtained as 412 nm. The
absorption and emission peak maxima of OPV is same as that
of m-PPV which provides an opportunity to investigate the effect
of long chain and short oligomeric ligand in Ln3+ complexes
without altering their band gaps. The normalized excitation
spectra of the Eu3+ complexes, which was recorded at 298 K
8
gap (ca. 32 000 cm-1) between the S7/2 ground state and the
6
first P7/2 excited state of the Gd3+ ion, it cannot accept any
energy from the first excited triplet state of the ligand via
intramolecular ligand-to-metal energy transfer.18 Thus the
phosphorescence spectra of Gd3+complexes actually reveal the
triplet energy levels (3ππ*) of m-PPV and OPV in the Ln3+
complexes. It is well recognized that the energy-level match
between the triplet state (3ππ*) of the ligand to the 5D0 state of
the Eu3+ cation is one of the key factors that governs the
luminescence efficiency of Eu3+ complexes.8a,c,g Latva’s empiri-
cal rule states that an optimal ligand-to-metal energy transfer
process for Eu3+ requires ∆E (3ππ*-5D0) ) 2500-4000 cm-1
5
7
and monitored around the intense D0 f F2 transition of the
Eu3+ cation, is shown in Figure 5A. The excitation spectra
recorded for the metal-centered emission of the Eu3+ complex
overlaps with the absorption spectra of ligands (OPV and
m-PPV) in the region 250-400 nm. A series of sharp lines,
which are assigned to transitions between the 7F0,1 and 5L6,5D3-1

Single Polymer Photosensitizer for Tb3+ and Eu3+ Ions
J. Phys. Chem. B, Vol. 113, No. 43, 2009 14135
TABLE 1: Luminescence Intensity Ratio of the Complexes
a
b
complexes
ITb/I350-480
IEu/I350-560
ATb/A350-480
AEu/A350-560
Eu(acac)3 (H2O) (OPV)
Eu(acac)3 (m-PPV)
Tb(acac)3(H2O) (OPV)
Tb(acac)3(m-PPV)
0.52
22.13
0.03
1.99
1.49
0.52
0.23
0.11
a Area of emission peak at 547 nm (corresponding to Tb)/area of the sensitizer from 350-480 nm. b Area of emission peak at 612 nm
(corresponding to Eu)/area of the sensitizer from 350-560 nm.
Figure 7. Emission spectra of (a) Eu0.5Tb0.5(acac)3(m-PPV) and (b)
Eu0.5Tb0.5(acac)3(m-PPV-A) in solid state.
transfer from acac ligand to the central Tb3+ ion. Because of
the superior match of the triplet energy level of acac (23 800
cm-1 21 with that of the 5D4 emitting level of Tb3+ ion efficient
)
energy transfer takes place in Tb(acac)3 complex (∆E )
3ππ*-5D4 ) 3400 cm-1). Because of the emission peaks in
blue (375 to 475 nm of m-PPV polymer) and green (547 nm in
Figure 6. Excitation (A) and emission (B) spectra of Tb3+complexes.
Tb(acac)3 (a); Tb(acac)3(OPV)(b); Tb(acac)3(m-PPV)(c).
view of D4 f F5 transitions of Tb3+) regions, Tb(acac)3(m-
PPV) exhibits interesting sky blue emission (Figure 6B) with
CIE 1976 color coordinates 0.18 and 0.15 (Figure 6) when
excited at 310 nm. On the other hand, Tb(acac)3(OPV) complex
shows blue color when excited at 310 nm essentially due to the
strong blue emission of the OPV in the region 360-475 nm.
The energy transfer efficiency of various ligands in the case of
Tb3+ follows the order acac (∆E ) 3400 cm-1) > OPV (∆E )
1900 cm-1) > m-PPV (∆E ) 400 cm-1), which is also in the
order of ratio (I547/I360-475, where I547 is the maximum intensity
of main emission peak of Tb3+ complex at around 547 nm and
I360-475 is the maximum intensity of main emission peak of OPV
or m-PPV in the range of 360-475 nm) of the maximum
emission intensity peaks.
5
7
for Eu3+ 19
On this basis, it can be concluded that the energy
.
transfer to the Eu3+ cation will be more effective in the case of
m-PPV than that of OPV, since ∆E (3ππ*-5D0) for Eu(acac)3(m-
PPV) and Eu(acac)3(OPV) are 3300 and 4800 cm-1, respec-
tively. According to Reinhoudt’s empirical rule, the intersystem
crossing process becomes effective when ∆E (1ππ*-3ππ*) is
at least 5000 cm-1 20 The energy gaps ∆E (1ππ*-3ππ*) for
.
ligands m-PPV and OPV are 4500 and 4700 cm-1, respectively.
As a consequence, the intersystem crossing processes are
effective for both of these chromophores.
The steady-state excitation and emission spectra of Tb3+
complexes at room temperature are shown in Figure 6. The
excitation spectrum of the Tb3+ complexes monitored around
the peak of the intense D4 f F5 transition of the Tb3+ ion
exhibits a broadband between 250 and 450 nm with a maximum
at approximately 310 nm and a shoulder at 370 nm (Figure 6A).
The peak at 310 nm can be assigned to the 1π-π* transition of
the aromatic ring and the shoulder at 370 nm is attributable to
1π-π* transition of the carbonyl group of the ligand. The room-
temperature emission spectra of the Tb3+ complexes excited at
their maximum excitation wavelengths (λex) 310 nm exhibit the
characteristic emission bands for Tb3+-centered emission at 490,
547, 585, and 620 nm, which result from deactivation of the
White Light Emission. Interestingly, when Eu3+ and Tb3+
were incorporated into m-PPV and m-PPV-A polymer backbone
in equimolar ratio along with acetyl acetone as coligand, excita-
tionoftheresultingEu0.5Tb0.5(acac)3(m-PPV)andEu0.5Tb0.5(acac)3(m-
PPV-A) compounds at 310 nm exhibited a novel white emission
color (see Figure 7) with CIE 1976 color coordinates x ) 0.28,
y ) 0.34 (Figure 8) and m-PPV-A (x ) 0.36, y ) 0.38) (Figure
S17 in Supporting Information). The room-temperature emission
spectra displays sharp emissions in the region at 490, 547, 585,
5
7
5
7
and 620 nm corresponding to D4 f FJ (J ) 6, 5, 4, 3)
5D4 excited state to the corresponding ground state FJ (J ) 6,
transitions of Tb3+ ion and the peaks at 581, 594, 612, 653,
7
5
7
5, 4, 3) of the Tb3+ ion.8b,d,9 The most intense emission is
centered at 547 nm and corresponds to the 5D4 f 7F5 transition.
The spectra of both Tb(acac)3(H2O)(OPV) and Tb(acac)3(m-
PPV) complexes showed a broad emission peak between
360-475 nm with respect to self-emission of the ligand
chromophores. No emission bands from the acac ligand is
observed in Tb(acac)3 complex, thus implying efficient energy
705 corresponding to transition of D0 f FJ ) 0, 1,2,3,4 of Eu3+
ion. In addition to the above sharp emissions, there also exists
a broadband in the blue region (350 to 425 nm) due to the
residual emission from the m-PPV polymer. The photograph
of the Eu0.5Tb0.5(acac)3(m-PPV) was showed in Figure 7 which
directly evident for the white emission in both powder and
solution (dispersed in DMSO) states.

14136 J. Phys. Chem. B, Vol. 113, No. 43, 2009
Balamurugan et al.
5
7
A0,J for each D0 f FJ transition. Assuming that nonradiative
and radiative processes are essentially involved in the depopula-
tion of 5D0 state, the intrinsic quantum yield η can be expressed
as
η ) (ARAD/ARAD+ANR
)
(3)
The parameters ARAD, ANR, and the intrinsic quantum yield
values (η) for the Eu3+ complexes are shown in the Table 2. It
is evident from these values that Eu(acac)3(m-PPV) exhibits
higher 5D0 lifetime and intrinsic quantum yield as compared to
Eu(acac)3(OPV).
Effect of Copolymer and Spacer Effect on the Photosen-
sitization of Ln3+ Ions. The effect of polymer structure on the
photosensitizing of Tb3+ and Eu3+ ions was also investigated
and the results are depicted in Figure S28a, S28b and Table S2
in Supporting Information. The results clearly highlights that
the sensitization efficiency of Ln3+ ion with various polymeric
materials increases in the order p-PPV < co-PPV < m-PPV (see
Figure S28 in Supporting Information). Thus it can be concluded
that m-PPV is a better sensitizer for Eu3+ or Tb3+ due to the
superior match of the triplet energy level with that of emitting
levels of the Ln3+ ions. On the other hand, p-PPV shows poor
sensitization for Ln3+ ions due to its extended conjugation,
which in turn decreases the triplet energy level (19 000 cm-1
)
(see Figure S29 in Supporting Information). Thus the triplet
energy level lies less than the emitting level of 5D4 of Tb3+ and
hence it cannot sensitize Tb3+ ion. In the case of Eu3+, poor
sensitization has been noticed with p-PPV in view of the lower
energy gap (∆E ) 3ππ*-5DJ ) 1500 cm-1), which can facilitate
back energy transfer process. Because of decrease in conjuga-
tion, co-PPV sensitizes Eu3+ better than p-PPV. The triplet
energy level of co-PPV 19 600 cm-1 (see Figure S29 in
Supporting Information) lies well above the emitting level of
5D0 of Eu3+. On the other hand, co-PPV triplet energy level
lies below 5D4 level of Tb3+ and hence it cannot sensitize Tb3+
ion. To study the effect of spacer length between the polymer
backbone to the Ln3+ metal ion center, a new carboxylic acid
functionalized poly(m-phenylenevinylene) bearing shorter spacer
(one carbon atom less) was synthesized starting from 3(4-
hydroxypheny)acetic acid (see Supporting Information for detail
synthesis). This new polymer m-PPV-A (A refers to acetic acid)
was also complexed with Tb3+ and Eu3+ under the identical
conditions. The PL-spectra of the Tb3+ and Eu3+ complexes of
m-PPV-A were recorded by exciting at 310 nm and are shown
in Figures S28c and S28d in Supporting Information. The
photosensitization efficiency of Ln3+ ion with m-PPV-A is found
to be same as that of m-PPV (see Table S3 and Figure S28 in
Supporting Information). This suggests that the reducing the
length of the spacer did not showed any appreciable changes
in the emission properties of these Ln3+ complexes.
Figure 8. CIE color coordinates diagram of Ln3+-m-PPV complexes
in both solution and solid states.
Lifetime and Intrinsic Quantum Yield of Ln3+ Complexes.
In addition to the steady-state emission spectra of
Ln3+complexes, the luminescent lifetimes of these complexes
were measured at room temperature (298 K) from the respective
luminescent decay profiles by fitting with monoexponential
decay curves (Figure 9 and Figure S18 in Supporting Informa-
tion). Collectively, these data indicate the existence of a single
chemical environment around the Ln3+ ion in each case. The
pertinent values are summarized in Table 2.
On the basis of the room-temperature emission spectra and
on the lifetime measurements, we can estimate the intrinsic
5
quantum yield (η) of the D0 Eu3+ ion excited state.22 The
luminescence decay lifetime (τ) is directly related to the radiative
and nonradiative decay rates of the lanthanide ion. The radiative
lifetime (τrad) can be calculated using eq 1, assuming that the
5
7
energy of the D0 f F1 transition (MD) and its oscillator
strength are constant23
ARAD ) 1/τrad)AMD,0n3(Itot/IMD
)
(1)
Conclusion
where, AMD,0 (14.65 s-1) is the spontaneous emission probability
In conclusion, new classes of carboxylic-functionalized
poly(m-phenylenevinylene)s were synthesized and utilized as
photosensitizers for tuning the color of lanthanide complexes.
The present investigation has the following important outcomes:
(i) novel blue light emitting oligo and poly(m-phenylenevi-
nylene)s were developed starting from phenyl propanoic and
phenyl acetic acids via witting polycondensation reactions, (ii)
Eu3+ and Tb3+ lanthanide complexes were successfully prepared
for these conjugated materials and characterized by NMR, FT-
IR and MALDI-TOF, (iii) m-PPV polymer was found efficient
5
7
of the D0 f F1 transition in vacuo, Itot/IMD is the ratio of the
total area of the corrected Eu3+ emission spectrum to the area
5
7
of the D0 f F1 band, and n is the refractive index of the
medium. An average index of refraction equal to 1.5 was
considered.20 Lifetime (τ), radiative (ARAD) and nonradiative
(ANR) transition rates are related to through the following eq 2
where ARAD can be obtained by summing over the radiative rates
1/τobs)AT)ARAD+ANR
(2)

Single Polymer Photosensitizer for Tb3+ and Eu3+ Ions
J. Phys. Chem. B, Vol. 113, No. 43, 2009 14137
Figure 9. Decay profiles of the Ln3+ complexes with m-PPV.
TABLE 2: Photophysical Parameters of the Complexes
τ (ms)
complexes
5D0
5D4
I0,1/I0,2
ARAD (s-1
)
ANR (s-1
)
η (%)
Eu(acac)3 (H2O) (OPV)
Eu(acac)3 (m-PPV)
Tb(acac)3(H2O) (OPV)
Tb(acac)3 (m-PPV)
Eu0.5Tb0.5(acac)3(m-PPV)
Eu0.5Tb0.5(acac)3(m-PPV-A)
0.82 ( 0.07
1.53 ( 0.04
11.00
5.34
298
415
914
240
24
63
1.32 ( 0.06
1.19 ( 0.04
1.17 ( 0.05
1.20 ( 0.04
1.33 ( 0.05
1.12 ( 0.05
photosensitizer for both Eu3+ and Tb3+ ions and produced sharp
magenta and sky blue colors, respectively, whereas its small
oligomer counterpart (m-OPV) failed as sensitizer, (iv) the
partial blue emission of the m-PPV in combination with Tb3+
and Eu3+ ions in a single system produce white emission
exhibited a novel white emission color with CIE 1976 color
coordinates x ) 0.28, y ) 0.34, and (v) the effect of spacer
length between the metal center to conjugated backbone as well
as copolymer constituents were also investigated. The m-PPV
conjugated polymer design provides a new opportunity for
tuning the color of the lanthanide complexes that may find
potential applications in optoelectronics. Currently, the research
work in progress to tune the polymer structures for producing
high molecular weight polymers as well as bright emission
colors. These materials will be tested in collaboration with
device fabrication groups. To summarize, in the present
investigation for the first time a new carboxylic acid function-
alized poly(m-phenylenevinylene)s were synthesized to tune the
red, green, and white colors of the lanthanide complexes in a
single polymeric system and the mechanistic aspects of the
energy transfer process were investigated in detail using
photophysical techniques.
spectra, emission spectrum of Eu(acac)3(m-PPV-A) at multiple
excitation wavelength, and CIE coordinate diagram of m-PPV-A
complexes. This material is available free of charge via the
Internet at http://pubs.acs.org.
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Acknowledgment. We thank Department of Science of
Technology, New Delhi, India under Scheme NSTI Programme-
SR/S5/NM-06/2007 for financial support. M.L.P.R. thanks
CSIR, New Delhi, Indian (CSIR-NWP-010) for the financial
support. A.B. thanks CSIR-New Delhi, India for Junior Research
Fellowship.
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