Aromatic ring-fused BODIPY-based conjugated polymers exhibiting narrow near-infrared emission bands

Article abstract of DOI:10.1021/ma901449c

Three conjugated copolymers, consisted of alternating p-phenylene- ethynylene and boron di(iso)indomethene units in the backbone, were synthesized via palladium-catalyzed Sonogashira coupling reaction of 1,4-diethynyl-2,5- dihexadecyloxybenzene and three diiodophenyl-fused BODIPY monomers. The structures and properties of the conjugated polymers were characterized by ¹H NMR, ¹¹B NMR, and Fourier transform infrared (FT-IR) spectroscopies, elemental analysis, size exclusion chromatography (SEC), UV-vis absorption spectroscopy, photoluminescence (PL) spectroscopy, and theoretical calculation using density-functional theory (DFT) method. The polymers obtained were fusible and soluble in common organic solvents including THF, benzene, toluene, CHCl₃, and CH₂Cl₂, etc. The incorporation of the indomethene monomers into p-phenylene-ethynylene main chain led to red shifts in UV-absorption and PL spectra by extended π-conjugation of the copolymers in comparison with the monomers. Accordingly, the copolymers emitted in the range from deep-red to near-infrared region with emission spectral maxima at around 691-720 nm and exhibited high quantum yields (Φ_F = 33-49%). The photostabilities of the polymers were examined by monitoring decrease of the PL spectra under continuous UV irradiation using a UV lamp under aerobic conditions. Further, their thermal stabilities were also investigated by TGA measurement.

Full text of DOI:10.1021/ma901449c

Macromolecules 2010, 43, 193–200 193
DOI: 10.1021/ma901449c
Aromatic Ring-Fused BODIPY-Based Conjugated Polymers Exhibiting
Narrow Near-Infrared Emission Bands
Atsushi Nagai and Yoshiki Chujo*
Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Katsura,
Nishikyo-ku, Kyoto 615-8510, Japan
Received July 3, 2009; Revised Manuscript Received November 24, 2009
ABSTRACT: Three conjugated copolymers, consisted of alternating p-phenylene-ethynylene and boron
di(iso)indomethene units in the backbone, were synthesized via palladium-catalyzed Sonogashira coupling
reaction of 1,4-diethynyl-2,5-dihexadecyloxybenzene and three diiodophenyl-fused BODIPY monomers.
The structures and properties of the conjugated polymers were characterized by 1H NMR, 11B NMR, and
Fourier transform infrared (FT-IR) spectroscopies, elemental analysis, size exclusion chromatography
(SEC), UV-vis absorption spectroscopy, photoluminescence (PL) spectroscopy, and theoretical calculation
using density-functional theory (DFT) method. The polymers obtained were fusible and soluble in common
organic solvents including THF, benzene, toluene, CHCl3, and CH2Cl2, etc. The incorporation of the
indomethene monomers into p-phenylene-ethynylene main chain led to red shifts in UV-absorption and PL
spectra by extended π-conjugation of the copolymers in comparison with the monomers. Accordingly, the
copolymers emitted in the range from deep-red to near-infrared region with emission spectral maxima at
around 691-720 nm and exhibited high quantum yields (ΦF = 33-49%). The photostabilities of the
polymers were examined by monitoring decrease of the PL spectra under continuous UV irradiation using a
UV lamp under aerobic conditions. Further, their thermal stabilities were also investigated by TGA
measurement.
Introduction
migration to boron-chelating moieties by extending π-conjuga-
tion along the polymer main chain.
Organoboron dyes with light-emitting ability are of increasing
interest for not only chemistry and material science but also
biological science. Many organoboron dyes have been used as
chemical probes,1 photosensitizers,2 and optical sensing3 due to
large molar extinction coefficients and two-photon absorption
cross sections, high emission quantum yields (ΦF), and sensitivity
to the surrounding medium.4 Recently, the incorporation of
several organoboron dyes into a polymer main chain, side chain,
and initial end is more attractive for application as electrolumi-
nescent devices, organic field-effect transistors, photovoltaics,
4-Difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) deriva-
tives are also one of the organoboron dyes14 and have become the
preferred fluorophores in new fluorescent probes that found
widespread applications in numerous fields of modern medicine
and science.16 This is a result of their valuable characteristics,
such as relatively higher photostability and photoproperties (such
as narrower absorption bands, sharper emission, and higher ΦF,
etc.) relative to fluorescein and other organoboron dyes, e.g.,
boron quinolate and boron diketonate. Although fine-tuning of
their valuable characters containing red shift of absorption and
emission maxima has been carried out by functionalization of the
BODIPY moiety,14a,b most studies have focused on low mole-
cules of BODIPY dyes. Previously, we have reported first paper
describing preparation of highly fluorescent organoboron poly-
mers with supramolecular self-assembled chain and network
structures by incorporating the BODIPY dye into poly( p-ary-
lene-ethynylene) backbones.17 Electronic properties of the poly-
(p-arylene-ethynylene)s displayed higher energy transfer
efficiency from π-conjugated linkers to BODIPY moieties, How-
ever, no red shift of absorption and emission maxima from
extended π-conjugation was observed, because p-arylene-ethy-
nylene moieties were directly attached to boron atoms. Recently,
to improve our defective electroproperties, Liu et al. have
reported synthesis of BODIPY polymeric dyes with emission
maxima at 585-683 nm; i.e., the conjugated polymers showed
significant extension of π-conjugation by attaching directly to
BODIPY cores, with triple-bond18 or fluorene19 connections
between BODIPY cores and aromatic units. These reports encour-
aged us to further extend these investigations to design BODIPY-
based conjugated polymers with longer wavelength emission,
narrower emission band, and higher ΦF, i.e., near-infrared (NIR)
€
etc. For example, Jakle et al. have reported that novel well-
defined organoboron quinolate polymers were synthesized by the
polymeric reaction of 8-hydroxyquinoline and thienyl-substi-
tuted poly(borylstyrene)5 or poly(fluorenylborane)6 and have
further succeeded in synthesis of intriguing coordination poly-
mers with quinolate ligands and boron centers embedded in the
main chain through boron-induced ether cleavage.7 Fraser et al.
have demonstrated synthesis of boron diketonate-end-functio-
nalized polylactides,8 poly(ε-caprolactone),9 and their block
copolymers10 exhibiting interesting phosphorescence by ring-
opening polymerization of lactides or ε-caprolactone using boron
diketonate with a hydroxyl group as an initiator. We have also
reported the synthesis of the π-conjugated polymers integrated
organoboron quinolates,11 aminoquinolate,12 and diketonate13
into polymer backbones such as poly(p-arylene-ethynylene)s,
which are currently one of the most important classes of con-
jugated polymers used as emitting, charge-transporting, conduct-
ing, and sensing materials.14 Their polymers possess similar
properties such as strong fluorescence and efficient energy
*Corresponding author. E-mail: chujo@chujo.synchem.kyoto-u.ac.jp.
r 2009 American Chemical Society
Published on Web 12/04/2009
pubs.acs.org/Macromolecules

194 Macromolecules, Vol. 43, No. 1, 2010
Nagai and Chujo
conjugated polymers (emission maxima >700 nm),20 which is of
great interest to extend the emission wavelength to NIR region to
apply the light-emitting polymers to telecommunications,21 ionic
laser,22 photovoltaic cells,23 and light-emitting devices,24 etc. Here-
in, a candidate approach is the introduction of a BODIPY core
fused aromatic ring, i.e., boron di(iso)indomethene replaced pyr-
role by isoindole (high light emitting at 610-730 nm),25 into a
polymer main chain. In this article, we wish to describe the synthesis
of high NIR emissive π-conjugated polymers with narrow emission
bands by the incorporation of three different aromatic-
fused BODIPY monomers into the poly(p-phenylene-ethynylene)
backbone.
14.8 Hz, Ar-H), 7,24 (t, 2H, J = 8.40 and 18.4 Hz, Ar-H), 7.30
(s, 1H, Ar-H), 7.40 (d, 1H, J = 8.40 Hz, Ar-H), 7.57 (t, 1H,
J = 7.2 and 14.4 Hz, Ar-H), 7.83 (d, 1H, J = 6.4 Hz, Ar-H),
11.25 (s, 1H, 1H, æCdN-NH-(CdO)-), 13.42 ppm (s, 1H, 1H,
-C6H3-OH). HRMS (EI) Calcd for C16H15O3N2 (Mþ): m/z
410.0127. Found: m/z 410.0122.
Synthesis of (Z)-N0-(1-(2-Hydroxy-4-iodophenyl)ethylidene)-
4-methoxybenzohydrazide (3c). 3c was prepared from 4-methox-
ybenzylhydrazine (2c) (2.91 g, 17.5 mmol) in 99% yield (4.71 g,
11.58 mmol) according to the method for 3a.1H NMR (DMSO-
d6): δ = 2.46 (s, 3H, C6H3-(CdN-)-CH3), 3.85(s, 3H,
-NH-(CdO)-C6H4-OCH3), 7.08 (d, 2H, J = 8.80 Hz,
Ar-H), 7.27 (t, 2H, J = 8.4 and 19.6 Hz, Ar-H), 7.39 (d, 1H,
J = 8.00 Hz, Ar-H), 7.94 (d, 2H, J = 8.80 Hz, Ar-H), 11.24 (s,
1H, 1H, æCdN-NH-(CdO)-), 13.66 ppm (s, 1H, 1H,
-C6H3-OH). HRMS (EI) Calcd for C16H15O3N2 (Mþ): m/z
410.0127. Found: m/z 410.0112.
Synthesis of 1-(2-Benzoyl-4-iodophenyl)ethanone (4a). Lead
tetraacetate (6.56 g, 14.8 mmol) was added to a suspension of 3a
(4.64 g, 12.2 mmol) in dry THF (110 mL) in small portions over a
period of 5 min. After stirring at room temperature for 2 h, the
resulting solid was removed by filtration. The filtrate is con-
centrated by rotary evaporator and purified by silica gel chro-
matography using CHCl3 as an eluent. Yield = 93% (3.98 g,
11.4 mmol). 1H NMR (CDCl3): δ = 2.48 (s, 3H, C6H3-
C(dO)-CH3), 7.43 (t, 2H, J = 7.56 and 15.1 Hz, Ar-H),
7.53-7.61 (m, 2H, Ar-H), 7.72 (d, 3H, J = 8.56 Hz, Ar-H),
7.94 ppm (d, 1H, J = 8.0 Hz, Ar-H). HRMS (EI) Calcd for
C15H13O2N2 (Mþ): m/z 349.9804. Found: m/z 349.9801.
Synthesis of 1-(4-Iodo-2-(2-methoxybenzoyl)phenyl)ethanone
(4b). 4b was prepared from 3b (5.0 g, 12.2 mmol) in 95% yield
(4.40 g, 11.6 mmol) according to the method for 4a. 1H NMR
(CDCl3): δ = 2.38 (s, 3H, C6H3-C(dO)-CH3), 3.55 (s, 3H,
-C6H3-OCH3), 6.86 (d, 1H, J = 8.28 Hz, Ar-H), 6.97 (t, 1H,
J = 7.89 and 15.12 Hz, Ar-H), 7.53 (d, 1H, J = 8.04 Hz,
Ar-H), 7.45 (t, 1H, J = 7.08 and 14.16 Hz, Ar-H), 7.59 (d, 1H,
J = 1.48 Hz, Ar-H), 7.68 (dd, J = 1.71 amd 4.03 Hz, Ar-H),
7.78 ppm (dd, 1H, J = 1.72 and 4.04 Hz, Ar-H). HRMS (EI)
Calcd for C16H13O3I (Mþ): m/z 379.9909. Found: m/z 379.9897.
Synthesis of 1-(4-Iodo-2-(4-methoxybenzoyl)phenyl)ethanone
(4c). 4c was prepared from 3c (4.64 g, 11.3 mmol) in 98% yield
(4.21 g, 11.1 mmol) according to the method for 4a. 1H NMR
(CDCl3): δ = 2.54 (s, 3H, C6H3-C(dO)-CH3), 3.56 (s, 3H,
-C6H3-OCH3), 7.12 (d, 2H, J = 8.40 Hz, Ar-H), 7.26 (t, 2H,
J = 8.2 and 19.2 Hz, Ar-H), 7.35 (d, 1H, J = 8.60 Hz, Ar-H),
7.82 ppm (d, 2H, J = 8.20 Hz, Ar-H). HRMS (EI) Calcd for
C16H13O3I (Mþ): m/z 379.9909. Found: m/z 379.9906.
Synthesis of Di(iso)indomethene Ligand (5a). Concentrated
NH4OH (NH3 content 28-30%, 45 mL) was added to a
solution of 4a (3.78 g, 10.8 mmol) in methanol (150 mL) and
acetic acid (75 mL). The mixture was stirred at 50 ꢀC for 2 days,
and the resulting solid is collected by filtration to crude product.
The crude product was purified by silica gel chromatography
with CHCl3 as an eluent to give 5a as a dark blue solid. Yield =
45% (3.15 g, 4.87 mmol). 1H NMR (CDCl3): δ = 7.34-7.45 (m,
6H, Ar-H), 7.52 (s, 1H, Ar-CH=), 7.67 (s, 1H, Ar-H),
7.66-7.82 (m, 3H, Ar-H), 8.22 (s, 1H, Ar-H), 8.21 ppm (s,
2H, Ar-H). HRMS (EI) Calcd for C29H18I2N2 (Mþ): m/z
647.9559. Found: m/z 647.9559.
Experimental Section
1
Instrumentation. H (400 MHz) and 11B (128 MHz) NMR
spectra were recorded on a JEOL JNM-EX400 spectrometer. 1H
NMR spectra used tetramethylsilane (TMS) as an internal
standard in CHC12, DMSO-d6, and 11B NMR spectra were
referenced externally to BF3 OEt2 (sealed capillary). Number-
3
average molecular weight (Mn) and molecular weight distribu-
tion [weight-average molecular weight/number-average molec-
ular weight (Mw/Mn)] values of all polymers were estimated
by size exclusion chromatography (SEC) with a TOSOH
8020 series [a dual pump system (DP-8020), a column oven
(CO-8020), and a degasser (SD-8020)] equipped with three
consecutive polystyrene gel columns [TOSOH gels: R-4000]
and a refractive-index (RI-8020) and an ultraviolet detector
(UV-8020) at 40 ꢀC. The system was operated at a flow rate of
1.0 mL/min with chloroform as an eluent. Polystyrene standards
were employed for calibration. Fourier transform infrared
(FT-IR) spectra were recorded as KBr pellets on a Shimadzu
IRrestige-21 spectrometer. UV-vis absorption spectra were
recorded on a Shimadzu UV-3600 spectrophotometer, fluores-
cence emission spectra were measured on a HORIBA Jobin
Yvon Fluoromax-4 spectrofluorometer, and fluorescence
micrograph on an Olympus IX71 fluorescence microscope.
Materials. 2-Hydroxy-4-iodoacetophenone26 and 1,4-diethy-
nyl-2,5-dihexadecyloxybenzene13 were prepared according to
the literature. 9,9-Dioctylfluorene-2,7-diboronic acid (Aldrich
Chemical Co., 96%), lead(IV) acetate (Wako Chemical Co.,
90%), boron trifloride diethyl etherate (BF3 OEt2, Aldrich
3
Chemical Co.), benzoylhydrazine (Tokyo Kasei Kogyo Co.,
>98%), 4-methoxybenzoylhydrazine (Tokyo Kasei Kogyo
Co., >98%), and 2-methoxybenzoylhydrazine (Aldrich Che-
mical Co., >98%) were used as received. Tetrahydrofuran
(THF) and triethylamine (NEt3) were purified using a two-
column solid-state purification system (Glass Coutour System,
Joerg Meyer, Irvine, CA).
Synthesis of (Z)-N0-(1-(2-Hydroxy-4-iodophenyl)ethylidene)-
benzohydrazide (3a). A solution of 1-(2-hydroxy-4-iodophe-
nyl)ethanone (1) (4.0 g, 15.3 mmol) and benzylhydrazine (2a)
(3.15 g, 23.1 mmol) in 1-propanol (20 mL) was stirred at 110 ꢀC
for 12 h. After cooling to room temperature, the resulting solid is
collected by filtration, washed with 1-propanol, and then dried
to give 3a (5.63 g, 14.8 mmol). The obtained 3a was used for next
reaction without purification. Yield = 97%. 1H NMR (DMSO-
d6): δ = 2.47 (s, 3H, C6H3-(CdN-)-CH3), 7.26 (d, 1H, J =
8.28 Hz, Ar-H), 7.31 (s, 1H, Ar-H), 7.40 (d, 1H, J = 8.32 Hz,
Ar-H), 7.55 (t, 2H, J = 7.32 and 14.6 Hz, Ar-H), 7.63 (t, 1H,
J = 7.32 and 14.6 Hz, Ar-H), 7.94 (d, 2H, J = 7.32 Hz, Ar-H),
11.41 (s, 1H, æCdN-NH-(CdO)-), 13.61 ppm (s, 1H,
-C6H3-OH). HRMS (EI) Calcd for C15H13O2N2 (Mþ): m/z
380.0022. Found: m/z 380.0012.
Synthesis of (Z)-N0-(1-(2-Hydroxy-4-iodophenyl)ethylidene)-
2-methoxybenzohydrazide (3b). 3b was prepared from 2-meth-
oxybenzylhydrazine (2b) (3.84 g, 23.1 mmol) in 97% (6.10 g,
14.9 mmol) yield according to the method for 3a. 1H NMR
(DMSO-d6): δ = 2.40 (s, 3H, C6H3-(CdN-)-CH3), 3.97 (s,
3H, -NH-(CdO)-C6H4-OCH3), 7.12 (t, 1H, J = 7.60 and
Synthesis of 5b. 5b was prepared from 4b (4.11 g, 10.8 mmol)
in 20% yield (1.51 g, 2.13 mmol) according to the method for 5a.
1H NMR (CDCl3): δ = 3.76 (s, 6H, -OCHH3), 7.05 (d, 2H, J =
8.0 Hz, Ar-H), 7.12 (t, 2H, J = 7.2 and 8.4 Hz, Ar-H), 7.41 (t,
2H, J = 7.6 and 15.2 Hz, Ar-H), 7.51 (s, 1H, Ar-CH=), 7.63
(dd, 4H, J = 8.4 and 36.0 Hz, Ar-H), 7.86 (d, 3H, J = 7.6 Hz,
Ar-H), 8.20 ppm (s, 1H, Ar-H). HRMS (EI) Calcd for
C31H22O2N2I2 (Mþ): m/z 707.9771. Found: m/z 707.9776.
Synthesis of 5c. 5c was prepared from 4c (4.11 g, 10.8 mmol) in
28% yield (2.12 g, 2.99 mmol) according to the method for 5a.
1H NMR (CDCl3): δ = 3.93 (s, 6H, -OCHH3), 7.09 (d, 4H,

Article
Macromolecules, Vol. 43, No. 1, 2010 195
Scheme 1. Synthetic Route to Boron Di(iso)indomethene-Based Conjugated Polymers
J = 8.8 Hz, Ar-H), 7.40 (s, 1H, Ar-CH=), 7.60 (dd, 4H, J =
8.4 and 21.6 Hz, Ar-H), 7.90 (d, 4H, J = 8.8 Hz, Ar-H), 8.31
ppm (s, 1H, Ar-H). HRMS (EI) Calcd for C31H22I2N2O2 (Mþ):
m/z 707.9771. Found: m/z 707.9767.
Synthesis of Boron Di(iso)indomethene Dyes (6a). Dry triethyl-
amine (1.20 mL, 12.3 mmol) was added to a solution of 5a (0.80 g,
1.23 mmol) in CH2Cl2 (500 mL), followed by addition of
Synthesis of 6c. 6c was prepared from 5c (0.18 g, 0.23 mmol) in
71% yield (deep purple solid, 123 mg, 0.16 mmol) according to
the method for 6a. 1H NMR (CDCl3): δ = 3.89 (s, 6H,
-C6H3-OCH3), 7.04 (d, 4H, J = 6.80 Hz, aromatic proton),
7.61 (s, 1H, Ar-CH=), 7.63 (s, 1H, Ar-H), 7.67-7.69 (m, 2H,
Ar-H), 7.71 (s, 1H, Ar-H), 7.76 (d, 4H, J = 8.80 Hz, Ar-H),
7.98 ppm (s, 2H, Ar-H). 13C NMR (CDCl3): δ = 55.3, 89.7,
114.1, 120.5, 122.8, 127.8, 131.8, 132.4, 132.6, 132.7, 137.3,
150.9, 160.9 ppm. 11B NMR (CDCl3): δ = 1.56 ppm (t, J =
37.5 and 62.5 Hz). HRMS (EI) Calcd for C31H21O2F2N2BI2
(Mþ): m/z 755.9754. Found: m/z 755.9750. Anal. Calcd for
C31H21O2N2F2BI2: C, 49.24; H, 2.80; N, 3.70; I, 33.57. Found:
C, 49.21; H, 2.68; N, 3.46; I, 33.51.
BF3 OEt2 (3.00 mL, 24.6 mmol). After the reaction mixture
3
was stirred at 50 ꢀC for 12 h, it is washed with water. The organic
layer is separated, dried over anhydrous magnesium sulfate, and
concentrated by rotary evaporator to give a blue solid. The crude
product was purified by silica gel chromatography with CHCl3 as
an eluent to give 6a as a deep green solid. Yield = 35% (0.30 g,
0.43 mmol). 1H NMR (CDCl3): δ = 7.48-7.53 (m, 6H, Ar-H),
7.63 (s, 1H, Ar-CH=), 7.67 (s, 1H, Ar-H), 7.71-7.78 (m, 3H,
Ar-H), 7.80 (s, 1H, Ar-H), 7.96 ppm (s, 2H, Ar-H). 13C NMR
(CDCl3): δ = 90.2, 120.5, 125.1, 128.2, 128.6, 129.0, 129.1, 129.2,
130.0, 131.8, 132.5, 137.6 ppm. 11B NMR (CDCl3): δ = 1.47 ppm
(t, J = 25.0 and 62.5 Hz). HRMS (EI) Calcd for C29H17N2F2B I2
(Mþ): m/z 695.9542. Found: m/z 695.9547. Anal. Calcd for
C29H17N2F2B I2: C, 50.04; H, 2.46; N, 4.02; I, 36.46. Found: C,
50.13; H, 2.75; N, 3.72; I, 36.44.
Synthesis of Polymer 7a. Triethylamine (0.75 mL) was added
to a solution of 6a (52.2 mg, 0.075 mmol), 1,4-diethynyl-2,5-
dihexadecyloxybenzene (45.5 mg, 0.075 mmol), Pd(PPh3)4
(4.33 mg, 3.75 μmol), and CuI (0.71 mg, 3.75 μmol) in THF
(1.5 mL) at 50 ꢀC under a nitrogen atmosphere. After the
mixture was stirred at 50 ꢀC for 48 h, the solvent was evapo-
rated out in vacuo. The residue was extracted with CHCl3,
washed with 10% ammonia-water and then water, and dried
over MgSO4; the volatile products were evaporated. The
residue was dissolved in a small amount of CHCl3 and poured
into a large excess of methanol to precipitate a polymer. The
polymer was collected by filtration with suction, further
washed with acetone, and then dried under vacuum at 60 ꢀC
for 12 h. 7a was obtained as a deep green blue solid. Yield =
Synthesis of 6b. 6b was prepared from 5b (1.50 g, 2.11 mmol)
in 76% yield (deep blue solid, 1.22 g, 1.61 mmol) according to
the method for 6a. 1H NMR (CDCl3): δ = 3.70 and 3.78 (s ꢀ 2,
6H, -C6H3-OCH3 ꢀ 2), 6.97-7.08 (m, 3H, Ar-H), 7.43-7.48
(m, 3H, Ar-H), 7.59-7.75 ppm (m, 8H, Ar-CH= and Ar-H).
13C NMR (CDCl3): δ = 55.6, 55.8, 89.1, 111.1, 115.4, 119.3,
120.4, 127.5, 131.4, 131.9, 132.3, 132.8, 133.0, 137.1, 157.7 ppm.
11B NMR (CDCl3): δ = 1.17 ppm (t, J = 25.0 and 50.0 Hz).
HRMS (EI) Calcd for C31H21O2N2F2BI2 (Mþ): m/z 755.9754.
Found: m/z 755.9744. Anal. Calcd for C31H21O2N2F2BI2: C,
49.24; H, 2.80; N, 3.70; I, 33.57. Found: C, 48.90; H, 2.73; N,
3.50; I, 33.69.
1
46% (72.0 mg, 68.8 μmol). Mn = 8200, Mw/Mn = 1.94. H
NMR (CDCl3): δ = 0.62-0.85 (6H, CH3 ꢀ 2), 0.85-1.35
(48H, -CH2- ꢀ 24), 1.36-1.60 (4H, -CH2- ꢀ 2), 1.63-1.89
(4H, -CH2- ꢀ 2), 3.77-4.03 (4H, -OCHH2- ꢀ 2), 6.68-7.96
ppm (19H, Ar-H). 13C NMR (CDCl3): δ = 14.1, 22.7, 25.9,
29.4, 29.7, 29.7, 31.9, 69.3, 86.5, 95.1, 113.9, 115.2, 118.9, 120.5,
127.4, 128.3, 129.9, 130.2, 130.5, 131.9, 132.5, 133.0, 137.5,

196 Macromolecules, Vol. 43, No. 1, 2010
Nagai and Chujo
Figure 1. X-ray crystal structures of 6a (a) top view and (b) side view with thermal ellipisoids drawn to the 50% probability level.
152.6, 153.7 ppm. 11B NMR (CDCl3): δ = 1.56 ppm. IR (KBr):
ν = 3439, 2922. 2850, 1618, 1589, 1560, 1541, 1508, 1458, 1389,
1263, 1204, 1157, 1107 cm-1. Anal. Calcd for (C71H85O2-
N2F2BF2)n: C, 81.43; H, 8.18; N, 2.67. Found: C, 79.55; H,
8.03; N, 2.67.
Results and Discussion
Synthesis and Characterization. The synthetic route to-
ward the BODIPY monomers fused bis-iodophenyl groups,
and the polymers are outlined in Scheme 1. A variety of aryl
groups, phenyl, o-methoxyphenyl, and p-methoxyphenyl
groups were introduced to boron di(iso)indomethene mono-
mers at the position adjacent to nitrogen atoms in the pyrrole
ring to extend further conjugation length of the monomers.
First, the di(iso)indomethene ligands 5a-c were prepared via
the condensation of ammonia and substituted 2-acetophe-
nones 4a-c, which were obtained from 2-hydroxy-4-iodo-
acetophenone and various hydrazines. These were treated
with boron trifluoride to give boron di(iso)indomethene-
based monomers 6a-c in satisfactory yields. Further, a
single crystal of 6a was obtained by recrystallization from
a mixed solvent of CH2Cl2/hexane. X-ray analysis indicated
that 6a forms tetracoordination state on the central boron
atom (Figure 1a and Table S1) and has high planarity of the
boron-coordinated ligand moiety (Figure 1b). The structures
of all the intermediates and the final monomers were con-
Synthesis of Polymer 7b. 7b was prepared from 6b with 1,
4-diethynyl-2,5-dihexadecyloxybenzene in 43% yield (72.0 mg,
65.0 μmol), according to the method for polymer 7a. Mn
=
7600, Mw/Mn = 2.12. 1H NMR (CDCl3): δ = 0.74-0.86 (6H,
CH3 ꢀ 2), 0.98-1.34 (48H, -CH2- ꢀ 24), 1.34-1.62 (4H,
-CH2- ꢀ 2), 1.63-1.85 (4H, -CH2- ꢀ 2), 3.58-3.66 and
3.68-3.73 (6H, -OCHH3 ꢀ 2), 3.84-3.99 (4H, -OCHH2- ꢀ
2), 6.79-7.08 (6H, Ar-H), 7.30-7.87 ppm (11H, Ar-H). 13C
NMR (CDCl3): δ = 14.1, 22.7, 25.9, 29.3, 29.4, 29.6, 29.7, 31.9,
55.7, 56.1, 69.6, 85.8, 95.7, 111.0, 115.4, 116.8, 117.9, 118.8,
119.6, 120.4, 127.4, 127.6, 131.2, 131.9, 132.4, 132.7, 153.6, 157.8
ppm. 11B NMR (CDCl3): δ = 1.27 ppm. IR (KBr): ν = 3442,
2924, 2852, 2814, 1614, 1589, 1562, 1502, 1266, 1203, 1155, 1102
cm-1. Anal. Calcd for (C71H89O2N2F2BF2)n: C, 79.18; H, 8.10;
N, 2.53. Found: C, 78.23; H, 7.89; N, 2.22.
Synthesis of Polymer 7c. 7c was prepared from 6c with 1,
4-diethynyl-2,5-dihexadecyloxybenzene in 45% yield (75.0 mg,
1
firmed by H NMR, 13C NMR, 11B NMR, and electron
67.7 μmol), according to the method for polymer 7a. Mn
=
ionization mass spectroscopies or elemental analysis.
8100, Mw/Mn = 2.32. 1H NMR (CDCl3): δ = 0.74-0.94 (6H,
CH3 ꢀ 2), 0.97-1.41 (48H, -CH2- ꢀ 24), 1.42-1.64 (4H,
-CH2- ꢀ 2), 1.70-1.93 (4H, -CH2- ꢀ 2), 3.81-3.93 (6H,
-OCHH3 ꢀ 2), 3.93-4.10 (4H, -OCHH2- ꢀ 2), 6.72-7.15
(6H, Ar-H), 7.43-8 ppm (11H, Ar-H). 13C NMR (CDCl3):
δ = 14.1, 22.7, 26.0, 29.4, 29.4, 29.7, 31.9, 55.3, 69.6, 86.2, 96.2,
113.9, 116.8, 118.9, 120.2, 123.0, 124.1, 127.8, 128.4, 130.4,
131.9, 132.1, 132.9, 152.5, 153.8, 160.9 ppm. 11B NMR
(CDCl3): δ = 1.66 ppm. IR (KBr): ν = 3412, 2924, 2853,
1611, 1598, 1504, 1454, 1439, 1395, 1255, 1206, 1159, 1139, 1107
cm-1. Anal. Calcd for (C71H89O2N2F2BF2)n: C, 79.18; H, 8.10;
N, 2.53. Found: C, 75.68; H, 7.97; N, 2.11.
The polymerization was accomplished by palladium-cat-
alyzed Sonogashira reaction of 6a-c and 1,4-diethynyl-2,5-
dihexadecyloxybenzene in a mixed solvent of THF/NEt3 in
the presence of Pd(PPh3)4 and Cu(I)I. After 48 h at 50 ꢀC, the
polymers were precipitated into methanol and further ace-
tone in 43-46% yields. All polymers synthesized were
fusible and soluble in common organic solvents including
THF, benzene, toluene, CHCl3, and CH2Cl2, etc. The size-
exclusion chromatography (SEC) in CHCl3 toward poly-
styrene standards revealed the number-average molecular
weights (Mn) and the molecular distribution (Mw/Mn) of

Article
Macromolecules, Vol. 43, No. 1, 2010 197
Figure 2. 1H NMR spectra of 6c and 7c in CDCl3.
8200 and 1.94, 7900 and 2.12, and 8100 and 2.32 (7a, 7b, and
7c, respectively). The degrees of polymerization (DPs), esti-
mated by Mn from SEC, of the polymers were 7.1-7.8. The
strong S0 f S1 (π f π*) transition at around 670-702 nm
and weaker broad bands at a shorter wavelength around
375 nm ascribed to the S0 f S2 (π f π*) transition. The
absorption maximum (λab) of monomer 6c was shifted to
longer wavelength than those of 6a and 6b due to extension
of conjugation length by p-methoxyphenyl group as elec-
tron-donating group. In contrast, the absorption maximum
of 6b with o-methoxyphenyl group was blue-shifted com-
pared with that of 6a, probably causing no extension of
conjugation length due to rectangular state between o-meth-
oxyphenyl groups and ligand core in 6b by steric hindrance
(discussion later). However, the molar absorption coefficient
(ε) of 6b was higher than those of 6a and 6c. The absorptions
of the polymers were observed at strong π f π* transition at
around 691-720 nm and weaker bands at shorter wave-
length at around 440 nm attributable to πfπ* transition of
the p-phenylene-ethynylene segments. Introduction of the
monomers 6a-c into the poly(p-phenylene-ethynylene) seg-
ments led to red shifts of the UV absorption (7a: 24 nm; 7b:
24 nm; 7c: 27 nm). The red-shifted absorptions of the
polymers in the order were 7c > 7a > 7b as well as the
results of the monomers. Moreover, the absorption peaks of
the polymers become broader than the monomers as a result
of the extended π-conjugation. In the PL spectra (Figure 3b),
the maxima (excited at λab) of 6a-c were 673-702 nm; that
is, they emit in the range from deep-red to NIR region. In
contrast, the polymers 7a-c exhibit obvious bathochromic
shifts of the PL maxima relative to monomers (7a: 22 nm; 7b:
1
chemical structures of the polymers were confirmed by H
NMR, 11B NMR, and IR spectroscopies, besides elemental
analysis. All the purified polymerization products gave
satisfactory spectroscopic data corresponding to their ex-
1
pected molecular structures. A typical example of the H
NMR spectra of 6c and 7c is shown in Figure 2, which
sufficiently supports the structure of the products by the
assignments of the signals as described in the Experimental
1
Section. As expected, the resonance peaks in the H NMR
spectra of polymers are broader than those of monomers due
to part to their longer rotational correlation times, indicating
that the monomers had been polymerized successfully.
Further, in the 1H NMR spectra of 6b and 7b the two signals
assignable to o-methoxyphenyl groups in 6b and 7b were
observed at around 3.70-4.00 ppm, whereas ligand 5b is
only one signal assigned to o-methoxyphenyl groups at 3.76
ppm, meaning the presence of isomers originating from steric
hindrance between two fluoride atoms and two o-methoxy-
phenyl groups.
UV-vis Absorption and Photoluminescence. The UV-vis
absorption and photoluminescence (PL) properties of the
monomers 6a-c and polymers 7a-c are presented in
Table 1. Figure 3a shows the absorption spectra of the
monomers and polymers in CHCl3 solution (1.0 ꢀ 10-5 M).
The absorptions of the monomers are characterized by

198 Macromolecules, Vol. 43, No. 1, 2010
Nagai and Chujo
18 nm; 7c: 18 nm), indicating efficient extension of π-
conjugation along the p-phenylene-ethynylene linker.
Although absolute quantum yields (ΦF) of the polymers
decreased in comparison with those of the monomers, their
F was enough high in the range from deep-red to NIR region
(ΦF = 33-49%). Further, the molar absorption coefficients
of the polymers were very large.
Molecular Orbital Calculations. To confirm assignments
of the absorption bands for the polymers 7a-c, especially
relationship between 7a and 7b, we performed the theoretical
calculation of the model compounds 8a-c, which were
designed by the Gaussian 03 suit of programs,27 using the
density-functional theory (DFT) method at the B3LYP/
6-31G(d,p)//B3LYP/6-31G(d,p) level of theory. Figure 4
displays the lowest unoccupied molecular orbital (LUMO)
and the highest occupied molecular orbital (HOMO) of
8a-c. The LUMO of the model compounds is mainly
located on the boron di(iso)indomethene ligand, and the
HOMO is localized not only on the ligand but also on the
p-phenylene-ethynylene moieties. However, the LUMO and
HOMO of 8b are not almost on the whole of o-methoxyphe-
nyl groups in the ligand due to orthogonal situation between
o-methoxyphenyl groups and ligand by steric hindrance,
meaning lower extended π-conjugation of monomer 6b
and 7b relative to other monomers and polymers. Further,
the HOMO-LUMO band gap of 8b is wider than that
Table 1. UV-vis Absorption and Photoluminescence Data for
Monomers 6a-c and Polymers 7a-c in CHCl3 Solutiona
compound
λ
ab (nm) ε (ꢀ105 M-1 cm-1
)
λemb (nm) ΦFc (%)
6a
6b
6c
7a
7b
7c
653
638
667
677
662
694
1.55
2.09
2.05
1.42
2.02
2.14
683
673
702
705
691
720
56
62
72
33
49
38
a CHCl3 (1.0 ꢀ 10-5 M). b Excited at absorption maxima (λab). c ΦF =
absolute quantum yield (excited at λab).
Figure 3. (a) UV-vis absorption spectra and (b) normalized photoluminescence spectra of 6a-c and 7a-c in CHCl3 (1.0 ꢀ 10-5 mol/L).
Figure 4. Structures and molecular orbital diagrams for the LUMO and HOMO of designed model compounds 8a-c (B3LYP/6-31G(d,p)//B3LYP/
6-31G(d,p)).

Article
Macromolecules, Vol. 43, No. 1, 2010 199
Conclusion
Through the use of palladium-catalyzed Sonogashira cou-
plings, three light-emitting conjugated copolymers with alternat-
ing p-phenylene-ethynylene and boron di(iso)indomethene units
were successfully prepared. The introduction of the boron
di(iso)indomethene skeleton into the polymer backbone was
confirmed by chemical and photophysical characterizations.
The incorporation of the indomethene monomers into p-pheny-
lene-ethynylene main chain led to red shifts in UV-absorption
and PL spectra by extended π-conjugation of the copolymers in
comparison with indomethene monomers. Consequentially,
three conjugated copolymers emitted intensely in the range from
deep-red to NIR region (ΦF = 33-49%). The photostabilities of
the polymers were examined by monitoring decrease of the PL
spectra under continuous UV irradiation using a UV lamp under
aerobic conditions. As far as we know, this is the first finding of
the synthesis of aromatic ring-fused BODIPY-based conjugated
polymers with both intense NIR luminescence and the narrow
emission bands. Currently, further studies are underway to design
NIR luminescence conjugated polymer sharing both intense
NIR-emitting monomers with longer wavelength such as boron
azadipyrromethene (aza-BODIPY) and conjugated linker skele-
ton with narrower band gap.
Figure 5. Photoluminescence spectra of (a) 7a, (b) 7b, and (c) 7c under
continuous UV irradiation (254 nm) in 1,2-dichloropropane (c = 1.0 ꢀ
10-5 M) and (d) TGA profiles of 7a-c.
Supporting Information Available: CIF file and Table S1 of
monomer 6a. This material is available free of change via the
Internet at http://pubs.acs.org.
of 8a and 8c, meaning higher bathochromic shift of 7a
relative to that of 7b. Accordingly, the order of the absorp-
tion maxima of the polymers 7a-c is excellently identical to
that of the band gaps of the designed model compounds;
i.e., the λab is in the order 7c > 7a > 7b, and the band gaps
are in the order 8c < 8a < 8b.
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