Highly near-infrared photoluminescence from aza-borondipyrromethene-based conjugated polymers

Article abstract of DOI:10.1002/pola.24335

Near-infrared (NIR) emissive conjugated polymers were prepared by palladium-catalyzed Sonogashira polymerization of diiodobenzene-functionalized aza-borondipyrromethene (Aza-BODIPY) monomers, which were substituted at 3 and 5 or 1 and 7 positions on the A

Full text of DOI:10.1002/pola.24335

Highly Near-Infrared Photoluminescence from
Aza-Borondipyrromethene-Based Conjugated Polymers
RYOUSUKE YOSHII, ATSUSHI NAGAI, YOSHIKI CHUJO
Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Katsura,
Nishikyo-ku, Kyoto 615-8510, Japan
Received 7 April 2010; accepted 20 August 2010
DOI: 10.1002/pola.24335
Published online 5 October 2010 in Wiley Online Library (wileyonlinelibrary.com).
ABSTRACT: Near-infrared (NIR) emissive conjugated polymers
were prepared by palladium-catalyzed Sonogashira polymer-
ization of diiodobenzene-functionalized aza-borondipyrrome-
thene (Aza-BODIPY) monomers, which were substituted at 3
and 5 or 1 and 7 positions on the Aza-BODIPY core, with 1,4-
diethynyl-2,5-dihexadecyloxybenzene or 3,30-didodecyl-2,20-
diethynyl-5,50-bithiophene. The structures of the polymers were
confirmed by 1H NMR, 13C NMR, 11B NMR, Fourier transform
infrared (FT-IR) spectroscopies, and size exclusion chromatog-
raphy (SEC). The optical properties were then characterized by
UV–vis absorption and photoluminescence (PL) spectroscopies,
and theoretical calculation using density-functional theory
(DFT) method. The polymers were fusible and soluble in com-
mon organic solvents including tetrahydrofuran (THF), o-xy-
lene, toluene, CHCl3, and CH2Cl2, etc. The UV–vis absorption
and PL spectra of the polymers shifted to long wavelength
region in comparison with simple Aza-BODIPY as the counter-
part because of extended p-conjugation of the polymers. The
polymers efficiently emitted NIR light with narrow emission
bands at 713ꢀ777 nm on excitation at each absorption maxi-
mum. Especially, the polymer attached 1,4-diethynyl-2,5-dihex-
adecyloxybenzene to 3,5-position on the core revealed intense
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quantum yields (UF ¼ 24%) in this NIR region (753 nm). 2010
Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48:
5348–5356, 2010
KEYWORDS: Aza-BODIPY; near-infrared emission; conjugated
polymers; copolymerization; luminescence
INTRODUCTION Recently, p-conjugated polymers have
received a great deal of attention from both academia and
industry. The tunable electronic property, low manufacturing
cost, and high degree of processability of p-conjugated poly-
mers, e.g., poly(p-phenylenevinylene), polypyrrole, polythio-
phene, and polyfluorene make them promising candidates as
advanced materials for development of optoelectronic appli-
cations such as organic light emitting diodes,1 photovoltaic
cells,2 field effect transistors,3 switch elements,4 and data-
processors in computing systems.5 Among them, near-infra-
red (NIR) emissive conjugated polymers are more attractive
because of their important applications in telecommunica-
tion,6 ionic laser,7 laser optical recording,8 infrared photogra-
phy, numerous types of sensors and probes.9 However, there
are a very limited number of NIR emissive conjugated poly-
mers without containing rare-earth ions,10 and especially
their polymers with high-fluorescence quantum yields in NIR
region are only a few reports. Typically, it is very difficult to
synthesize high NIR emissive conjugated polymers. Because
NIR emission is easily quenched by nonirradiative transi-
tion.11 Previously, Yang and coworkers have demonstrated
the synthesis of conjugated polymers, composed of 4,7-dise-
lenophen-20-yl-2,1,3-benzoselenadiazole and fluorene, exhib-
iting high NIR emission (734ꢀ790 nm, UPL ¼ 0.01ꢀ0.22).
However, there are problems for toxicity of the selen atom
and the broaden emission band.10(c)
On the other hand, boron dipyrromethene (BODIPY) dyes
possess high fluorescence and photostable, and insensitive to
the solvents’ polarity and pH, and further show so narrow
emission band.12 Typical BODIPY dyes are relatively nonpo-
lar and electronically neutral. They have found widespread
applications as laser dyes,13 molecular probes,14 and sensors
in visible region.15 With the advent of BODIPY dyes with
such unique properties, the incorporation of BODIPY dyes
into conjugated polymer backbone has been recently investi-
gated.16 For example, Donuru and coworkers have synthe-
sized narrow NIR emissive conjugated polymers that intro-
duced the BODIPY core into various conjugated polymer
backbones. However, the fluorescence quantum yields of the
polymers in NIR region were not reported.16(f) Previously,
we have also reported the preparation of high NIR emissive
p-conjugated polymers with narrow emission bands by
incorporation of aromatic-fused BODIPY dyes, boron di(iso)-
indomethene replaced pyrrole by isoindole, into p-conju-
gated polymer main chain.17 The polymers showed near
emission to NIR region (691ꢀ720 nm) by the extension of
p-conjugation along the polymer backbone. However, the
emission of the polymers in further NIR region is difficult
Correspondence to: Y. Chujo (E-mail: yoshii@chujo.synchem.kyoto-u.ac.jp)
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Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 5348–5356 (2010) 2010 Wiley Periodicals, Inc.
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SCHEME 1 Synthetic route to Aza-BODIPY monomers.
because of the fully efficient conjugation length. Therefore, it
is necessary to explore the candidate of BODIPY derivatives
with further NIR emission. Herein, we selected Aza-BODIPY
(aza-borondipyrromethene) dyes as the candidate to possess
more long emission maxima (672 nm) than both typical
BODIPY and boron di(iso)indomethene dyes, and high-fluo-
rescence quantum yields.18 In this article, we report novel
high and narrow NIR emissive polymers containing Aza-
BODIPY cores into two conjugated polymer backbones. Ini-
tially, two kinds of Aza-BODIPY-based monomers bearing p-
iodophenyl groups, which were substituted at 3 and 5 or 1
and 7 positions on the Aza-BODIPY core, were prepared.
Then, the synthesis of the corresponding polymers was con-
ducted by palladium-mediated Sonogashira coupling reaction.
The absorption and fluorescent maxima of each copolymer
in o-xylene solution were significantly red-shifted relative to
simple Aza-BODIPY dye owing to extended p-conjugation of
the obtained polymers. Accordingly, these polymers showed
NIR fluorescence emission with high quantum yields.
tate with 2 and followed by chelation with BF3ꢁOEt2. The
structures of all intermediates were confirmed by 1H NMR
and 13C NMR, or ionization mass spectroscopies. Moreover,
the structures of the final monomers were also characterized
1
by H NMR, 11B NMR, 13C NMR, ionization mass spectroscop-
ies, and element analysis.
The polymerization was accomplished by palladium-cata-
lyzed Sonogashira reaction of 4a and 4b with 1,4-diethynyl-
2,5-dihexadecyloxybenzene and 3,30-didodecyl-2,20-diethynyl-
5,50-bithiophene in the mixed solvent of tetrahydrofuran
(THF)/NEt3 in the presence of Pd(PPh3)4 and CuI (Scheme
2). After 72 h at room temperature, the poly1-4 were pre-
cipitated into acetone and further hexane in 17ꢀ46% yields.
All polymers synthesized were soluble in common organic
solvents including THF, o-xylene, toluene, CHCl3, and CH2Cl2,
etc. The size exclusion chromatography (SEC) in CHCl3 to-
ward polystyrene standards revealed the number-average
molecular weight (Mn) and the molecular weight distribution
(Mw/Mn) of 5700 and 1.4, 4400 and 1.2, 5200 and 1.4, and
4700 and 1.9 (poly1, 2, 3, and 4), respectively. The degree
of polymerizations, estimated by Mn from SEC, of the poly-
mers were 4.0ꢀ5.2. The chemical structures of the polymers
were confirmed by 1H NMR, 13C NMR, 11B NMR, and IR
spectroscopies. All the purified polymerization products gave
satisfactory spectroscopic data corresponding to their
expected molecular structures. Typical examples of 1H NMR
spectra of 4a and poly1 are shown in Figure 1, which suffi-
ciently supports the structures of the products by the assign-
ments of the signals as described in the Experimental sec-
RESULTS AND DISCUSSION
Synthesis and Characterization
The synthetic route toward the Aza-BODIPY monomers is
outlined in Scheme 1. Two kinds of Aza-BODIPY-based mono-
mers bearing p-iodophenyl groups, which were substituted
at 3 and 5 or 1 and 7 positions on the Aza-BODIPY core,
were prepared. First, the substituted (E)-chalcones 1 were
prepared via the aldol condensation of substituted benzalde-
hydes and acetophenones, and the substituted 4-nitro-1,3-
diphenylbutan-1-ones 2 were obtained by treatment with
nitromethane. Furthermore, Aza-BODIPY-based monomers 4
were prepared through the condensation of ammonium ace-
1
tion. As expected, the resonance peaks in H NMR spectra of
polymers were broader than those of monomers because of
part to their longer rotational correlation times, indicating
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SCHEME 2 Palladium-catalyzed Sonogashira reaction of 4a and 4b with diethynyl compounds.
that the monomers underwent efficient Sonogashira reaction
with diethynyl compounds.
or diethynylbithiophene linkers. However, absolute quantum
yields (UF) of the polymers decreased in comparison with
that of Aza-BODIPY. The decreased UF of the polymers in NIR
region are because of increased internal conversion according
to the energy gap law. This states that the nonradiative deacti-
vation probability of S1 ! S0 increases as energy gap of S0 !
S1 decreases.11 Especially, the UF of poly1 was enough high in
NIR region (UF ¼ 24%). Further, poly3 with diethynylbithio-
phene unit in the main chain exhibited NIR emission in the
longest wavelength, originating form charge-transfer interac-
tion by incorporation of donor and acceptor system.
UV-Vis Absorption and Photoluminescence
The UV-vis absorption and photoluminescence (PL) proper-
ties of poly1-4 and Aza-BODIPY as the reference compound
are presented in Table 1. Figure 2(a) shows the absorption
spectra of Aza-BODIPY and poly1-4 in o-xylene solution (1.0
ꢂ 10ꢃ5 mol/L). The absorption spectrum of Aza-BODIPY is
characterized by strong S0 ! S1 (p ! p*) transition at
around 656 nm. The absorptions of polymers were observed
at longer wavelength p ! p* transition at around 680 ꢀ
722 nm and at shorter wavelength around 382 ꢀ 450 nm
attributable to p ! p* transition of 1,4-diethynyl-2,5-dihexa-
decyloxybenzene or 3,30-didodecyl-2,20-diethynyl-5,50-bithio-
phene segments. Introduction of the monomers 4a and 4b
into two p-conjugated polymers led to red-shifts of the UV
absorption (poly1: 53 nm, poly2: 24 nm, poly3: 66 nm,
poly4: 25 nm). The red-shifted absorptions of the polymers
were in the order of poly3 > poly1 > poly4 > poly2. There
is a trend that the polymers (poly1 and poly3) synthesized
from 4a have larger red-shifted absorptions than those of
other polymers synthesized from 4b (poly2 and poly4),
probably depending on substituted position of the conju-
gated linkers in the polymers, that is, different electronic envi-
ronment of the Aza-BODIPY moiety in each polymer.17(b)
Moreover, the absorption peaks of the polymers became
broader than that of Aza-BODIPY as a result of the extended
p-conjugation. In the PL spectra [Fig. 2(b)], the maxima
(exited at kab) of poly1-4 exhibited obvious bathochromic
shifts of the PL maxima relative to Aza-BODIPY (poly1: 74
nm, poly2: 34 nm, poly3: 98 nm, poly4: 61 nm), indicating ef-
ficient extension of p-conjugation along the diethynylbenzene
Molecular Orbital Calculation
To confirm assignments of the absorption bands for the
poly1-4, we performed the theoretical calculation of the
model compound model1-4, which were designed by the
Gaussian 03 suit of programs, using the density-functional
theory (DFT) method at the B3LYP/6-31G (d, p)//B3LYP/6-
31G (d, p) level of theory.19 Figure 3 displays the lowest
unoccupied molecular orbital (LUMO) and the highest occu-
pied molecular orbital (HOMO) of model1-4, respectively.
The LUMO of the model compounds is mainly located on the
Aza-BODIPY unit, and the HOMO is localized not only on the
Aza-BODIPY unit but also on the diethynylbenzene or diethy-
nylbithiophene moieties. Because of strong donor-acceptor
interaction between Aza-BODIPY and bithiophene units, the
HOMO–LUMO band gaps of model3 and 4 with diethynylbi-
thiophene moiety were smaller than those of model1 and 2
with diethynylbenzene moiety. With the exception of poly4,
the order of the absorption maxima of the poly1-3 was
excellently identical to that of the band gaps of the designed
model compounds, that is, the kab was in the order of poly3
> poly1 > poly2 and band gaps were in the order of
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FIGURE 1 1H NMR spectra of (a) 4a
and (b) poly1 in CDCl3.
model3 > model1 > model2. Similar to this discrepancy of
poly4, we predict that the conformation of poly4 disturbs
the conjugation in the polymer backbone.
molecular weight [Mw/Mn]) values of all polymers were esti-
mated by SEC with a TOSOH 8020 series (a dual pump sys-
tem [DP-8020], a column oven [CO-8020], and a degasser
[SD-8020]) equipped with three consecutive polystyrene gel
columns (TOSOH gels: a-4000) and a refractive-index (RI-
8020) and an ultraviolet detector (UV-8020) at 40 ꢄC. The
system was operated at a flow rate of 1.0 mL/min with chlo-
roform as an eluent. Polystyrene standards were used for
calibration. Fourier transform infrared (FT-IR) spectra were
recorded as KBr pellets on a Perkin-Elmer 1600 infrared
spectrometer. UV-vis absorption spectra were recorded on a
SHIMADZU UV-3600 spectrophotometer, fluorescence emis-
sion spectra were measured on a HORIBA JOBIN YVON Fluo-
romax-4 spectrofluorometer.
EXPERIMENTAL
Instrumentation
1H (400 MHz), 13C (100 MHz), and 11B (128 MHz) NMR
spectra were recorded on a JEOL JNM EX400 spectrometer.
1H NMR and 13C NMR spectra used tetramethylsilane (TMS)
as an internal standard in CDCl3, and 11B NMR spectra were
referenced externally to BF3ꢁOEt2 (sealed capillary). Number-
average molecular weight (Mn) and molecular weight distri-
bution (weight-average molecular weight/number-average
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TABLE 1 UV-Vis Absorption and Photoluminescence Data for
Aza-BODIPY and poly1-4 in o-Xylene Solutiona
7.88 (d, 2H, J ¼ 8.35 Hz, ArAH), 7.82 (d, 1H, J ¼ 15.65 Hz,
ArAH) 7.74 (d, 2H, J ¼ 8.47 Hz, ArAH), 7.66–7.63 (m, 2H,
ACH¼¼CHA), 7.47 (d, 1H, J ¼ 15.72, Hz, ArAH) 7.43 (t, 3H, J
¼ 3.11 Hz, ArAH) ppm. HRMS (EI): Calcd for C15H11IO (Mþ),
333.9855; found, m/z 333.9849.
b
c
Compound
kab (nm)
kem (nm)
UF (%)
Aza-BODIPYd
poly1
poly2
poly3
poly4
a
656
709
680
722
681
679
753
713
777
740
77
24
4
1b
1b was prepared from 4-iodobenzaldehyde (7.00 g, 0.03
mol) and acetophenone (3.62 g, 0.03 mol) in 90% yield
(9.00 g, 90%) according to the method for 1a. 1H NMR
(CDCl3): d ¼ 8.01 (d, 2H, J ¼ 7.24 Hz, ArAH), 7.77–7.70 (m,
3H, ArAH), 7.62–7.49 (m, 4H, ArAH and ACH¼¼CHA), 7.37
(d, 2H, J ¼ 8.29, Hz, ArAH) ppm. HRMS (EI): Calcd for
5
2
o-xylene (UV–vis absorption: 1.0 ꢂ 10ꢃ5 mol/L, photoluminescence:
1.0 ꢂ 10ꢃ6 mol/L).
b
Excited at absorption maxima (kab).
UF ¼ absolute quantum yield (excited at kab).
C
15H11IO (Mþ), 333.9855; found, m/z 333.9852.
c
d
The literature data.17(b)
Synthesis of 1-(4-Iodophenyl)-4-Nitro-3-
Phenylbutan-1-One
Materials
1a (26 g, 0.08 mol), nitromethane (95.22 g, 1.56 mol) and
potassium hydroxide (0.90 g, 0.02 mol) were dissolved in
ethanol (90 ml), and the mixture was stirred at reflux tem-
perature for 12 h. After cooling to room temperature, the
solvent was concentrated by rotary evaporator and the oily
residue obtained was dissolved in ethyl acetate and washed
with water (3 ꢂ 100 ml). The combined organic layers were
washed with brain, dried over magnesium sulfate, and con-
centrated by rotary evaporator to give the product 2a as an
orange solid (25.72 g, 83%). The obtained 2a was used for
the next reaction without purification. 1H NMR (CDCl3): d ¼
7.82 (d, 2H, J ¼ 8.35 Hz, ArAH), 7.61 (d, 2H, J ¼ 8.35 Hz,
ArAH) 7.35–7.26 (5H, ArAH), 4.81 (dd, 1H, J ¼ 6.82 Hz,
ACH2A) 4.20 (m, 1H, J ¼ 7.06 Hz, ACHA), 3.46–3.35 (2H,
ACH2A) ppm. 13C NMR (CDCl3): d ¼ 196.59, 138.96, 136.19,
133.39, 128.89, 128.56, 127.85, 127.69, 127.29, 79.45, 41.47,
39.23 ppm.
1,4-Diethynyl-2,5-dihexadecyloxybenzene and 4,40-didodecyl-
2,20-bithiophene were prepared according to the literature.20
4-Iodoacetophenone (Aldrich Chemical Company), acetophe-
none (Wako Chemical Company), 4-iodobenzaldehyde (Wako
Chemical Company), benzaldehyde (Wako Chemical Company),
boron trifluoride diethyl etherate (BF3ꢁOEt2, Aldrich Chemical
Company) were used as received. THF and triethylamine
(NEt3) were purified using a two-column solid-state purifica-
tion system (Glasscoutour System, Joerg Meyer, Irvine, CA).
Synthesis of (E)-1-(4-Iodophenyl)-3-Phenylprop-
2-En-1-One
Benzaldehyde (8.63 g, 0.08 mol), 4-iodoacetophenone (20.00
g, 0.08 mol), and potassium hydroxide (0.46 g, 8.20 mmol)
were dissolved in methanol/H2O (1:1 v/v, 350 ml), and the
mixture was stirred at reflux temperature for 12 h. During
the course of the reaction, the product precipitated from the
reaction mixture. After cooling, the reaction mixture was fil-
tered and washed with methanol to give the product 1a as a
white solid (26.18 g, 96%). The obtained 1a was used for
the next reaction without purification. 1H NMR (CDCl3): d ¼
2b
2b was prepared from 1b (9.00 g, 0.03 mol) in 90% yield
(9.6 g, 90%) according to the method for 2a. 1H NMR
(CDCl3): d ¼ 7.82 (d, 2H, J ¼ 8.35 Hz, ArAH), 7.61 (d, 2H, J
FIGURE 2 (a) UV-vis absorption spectra and (b) normalized photoluminescence spectra of Aza-BODIPY and poly1-4 in o-xylene (1.0
ꢂ 10ꢃ5 and 1.0 ꢂ 10ꢃ6 mol/L, respectively). The inset shows the molecular structure of Aza-BODIPY as the reference compound in
Figure 2a.
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FIGURE 3 Structures and molec-
ular orbital diagrams for LUMO
and HOMO of designed model
compounds model1-4 B3LYP/6-
31G (d, p)//B3LYP/6-31G (d, p).
¼ 8.35 Hz, ArAH) 7.35–7.26 (5H, ArAH), 4.81 (dd, 1H, J ¼
6.82 Hz, ACH2A) 4.20 (m, 1H, J ¼ 7.06 Hz, ACHA), 3.46–
3.35 (2H, ACH2A) ppm. 13C NMR (CDCl3): d ¼ 196.20,
138.64, 137.93, 136.00, 133.52, 129.27, 128.61, 127.81,
93.23, 79.09, 41.18, 38.76 ppm.
Synthesis of Aza-Borondipyrromethene Dyes
3a (6.0 g, 8.56 mmol) was dissolved in dry dichloromethane
(300 ml). Triethylamine (9.5 g, 0.09 mol) was then added to
the reaction mixture, and the resulting mixture was stirred
under nitrogen atmosphere at room temperature for 15 min.
After stirring for 15 min, BF3ꢁOEt2 (19.9 g, 0.13 mol) was
added and stirred under nitrogen atmosphere at 50 ꢄC for
48 h. During the course of the reaction, the product precipi-
tated from the reaction mixture. After cooling to room tem-
perature, the solid was filtered and washed with dichlorome-
thane, methanol, and water. Then, the solid was dissolved in
100 ml of THF and added to 500 ml of methanol to precipi-
tate the product 4a as a metallic brown solid (3.5 g, 55%).
1H NMR (CDCl3): d ¼ 8.05 (d, 4H, J ¼ 6.33 Hz, ArAH), 7.84
(d, 4H, J ¼ 8.29 Hz, ArAH) 7.76 (d, 4H, J ¼ 8.52 Hz, ArAH)
7.47–7.45 (6H, ArAH), 7.01 (s, 2H, ArAH) ppm. 13C NMR
(CDCl3): d ¼ 158.52, 147.09, 144.64, 137.96, 132.08, 130.93,
130.88, 129.76, 129.41, 128.70, 118.89, 98.41 ppm. 11B NMR
(CDCl3): d ¼ 0.49 ppm. HRMS (EI): Calcd for C32H20BF2I2N3
(Mþ), 748.9808; found, m/z 748.9805. Anal. Calcd for
Synthesis of Azadipyrromethene Ligand
A solution of 2a (25.7 g, 0.07 mol) and ammonium acetate
(175.0 g, 2.25 mol) in butanol (1 L) was stirred at reflux
temperature for 24 h. After cooling to room temperature, the
solvent was concentrated to a quarter of its original volume
by rotary evaporator, and filtered. The isolated solid was
washed with ethanol to yield the desired product 3a as a
dark-black solid (6.2 g, 25%). The obtained 3a was used for
the next reaction without purification. 1H NMR (CDCl3): d ¼
8.03 (d, 4H, J ¼ 7.06 Hz, ArAH), 7.88 (d, 4H, J ¼ 8.29 Hz,
ArAH), 7.64 (d, 4H, J ¼ 8.52 Hz, ArAH), 7.45–7.35 (6H,
ArAH), 7.17 (s, 2H, ArAH), 3.82–3.14 (broad, 1H, ANHA)
ppm. HRMS (EI): Calcd for C32H21I2N3 (Mþ), 700.9825;
found, m/z 700.9834.
C32H20BF2I2N3: C,51.30; H,2.69; N,5.61; I,33.88. Found: C,
51.05; H,2.53; N,5.40; I,33.73.
3b
4b
3b was prepared from 2b (9.0 g, 0.02 mol) in 35% yield
(2.8 g, 35%) according to the method for 3a. 1H NMR
(CDCl3): d ¼7.95 (d, 4H, J ¼ 7.15 Hz, ArAH), 7.57–7.47 (m,
14H, ArAH), 7.00 (s, 2H, ArAH), 3.91–3.07 (broad, 1H,
ANHA) ppm. HRMS (EI): Calcd for
700.9825; found, m/z 700.9824.
4b was prepared from 3b (2.5 g, 3.56 mmol) in 66% yield
(1.76 g, 66%) according to the method for 4a. 1H NMR
(CDCl3): d ¼ 8.10–7.90 (4H, ArAH), 7.81 (d, 4H, J ¼ 8.29 Hz,
ArAH), 7.75 (d, 4H, J ¼ 7.43 Hz, ArAH) 7.50–7.40 (6H,
ArAH), 7.02 (s, 2H, ArAH) ppm. 13C NMR (100 MHz, CDCl3):
d ¼ 159.86, 145.41, 142.93, 137.91, 131.67, 131.34, 131.12,
C
32H21I2N3 (Mþ),
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
130.69, 129.61, 128.66, 119.21, 96.35 ppm. 11B NMR
(CDCl3): d ¼ 0.57 ppm. HRMS (EI): Calcd for C32H20BF2I2N3
(Mþ), 748.9808; found, m/z 748.9808. Anal. Calcd for
light and air. 1H NMR (CDCl3): d ¼ 6.90 (s, 2H, ArAH), 3.50
(s, 2H, ACBCH ꢂ 2), 2.65 (t, 4H, J ¼ 7.33 Hz, ACH2A ꢂ 2),
1.69–1.57 (m, 4H, ACH2A ꢂ 2), 1.43–1.18 (36H, A (CH2)9A
ꢂ 2), 0.88 (t, 6H, J ¼ 6.60 Hz, ACH3 ꢂ 2) ppm. HRMS (EI):
Calcd for C36H54S2 (Mþ), 550.3667; found, m/z 550.3660.
C32H20BF2I2N3: C,51.30; H,2.69; N,5.61; I,33.88. Found:
C,51.23; H,2.82; N,5.69; I,33.76.
Synthesis of 2,20-Dibromo-3,30-Didodecyl-5,50-
Synthesis of Poly1
Bithiophene
Triethylamine (1 ml) was added to a solution of 4a (74.9
mg, 0.1 mmol), 1,4-diethynyl-2,5-dihexadecyloxybenzene
(60.7 mg, 0.1 mmol), Pd(PPh3)4 (6.0 mg, 5.0 lmol), and CuI
(1.0 mg, 5.0 lmol) in THF (2 ml). The reaction mixture was
stirred under nitrogen atmosphere at room temperature for
72 h, and then poured into acetone (300 ml) to collect the
polymer by filtration. The residue was dissolved in a small
amount of THF, and further poured into a large excess of ac-
etone and hexane, respectively to precipitate the polymer.
The polymer was dried in vacuum to give poly1 as a dark
solid (31 mg, 28%). Mn ¼ 5700, Mw/Mn ¼ 1.4. 1H NMR
(CDCl3): d ¼ 8.20–7.92 (8H, ArAH), 7.90–7.35 (10H, ArAH),
7.12–6.82 (4H, ArAH), 4.14–3.86 (4H, AOCH2A ꢂ 2), 1.97–
1.82 (4H, ACH2A ꢂ 2), 1.69–1.01 (52H, A (CH2)13A ꢂ 2),
0.96–0.74 (6H, ACH3 ꢂ 2) ppm. 13C NMR (CDCl3): d ¼
155.03, 153.91, 146.07, 144.09, 137.93, 132.25, 131.81,
131.73, 131.03, 130.99, 129.66, 129.41, 128.67, 119.33,
117.69, 116.97, 114.2, 69.69, 31.95, 29.74, 29.69, 29.67,
29.46, 29.39, 29.38, 29.18, 29.11, 26.11, 26.08, 25.98, 25.95,
22.71, 14.13 ppm. 11B NMR (CDCl3): d ¼ 0.68 ppm. IR
(KBr): m ¼ 2924, 2853, 2195, 1599, 1506, 1477, 1431, 1387,
1323, 1296, 1217, 1128, 1096, 1034, 1018, 826, 772, 689
N-Bromosuccinimide (0.74 g, 4.18 mmol) dissolved in dry
DMF (5 ml) was added dropwise over 15 min to a solution
of 4,40-didodecyl-2,20-bithiophene (1.00 g, 1.99 mmol) in dry
DMF (15 ml) under nitrogen atmosphere at 0 ꢄC. The solu-
tion was stirred at room temperature for 12 h. The reaction
mixture was then poured into an equal volume of ice and
was extracted with hexane. The combined organic layers
were washed with 2.5 M NaOH solution, brain, and dried
over magnesium sulfate. After filtration of magnesium sul-
fate, the solution was concentrated by rotary evaporator and
the residue was purified by silica gel chromatography with
hexane as an eluent to give 5 as a pale yellow solid (1.16 g,
1
89%). H NMR (CDCl3): d ¼ 6.77 (s, 2H, ArAH) 2.52 (t, 4H, J
¼ 6.58 Hz, ACH2A ꢂ 2) 1.63–1.2 (40H, A (CH2)10A ꢂ 2),
0.89 (t, 6H, J ¼ 5.75 Hz, ACH3 ꢂ 2) ppm. HRMS (EI): Calcd
for C32H52Br2S2 (Mþ), 658. 1877; found, m/z 658.1877.
Synthesis of 3,30-Didodecyl-2,20-
Bis(Trimethylsilylethynyl)-5,50-Bithiophene
Trimethylsilyl acetylene (4.2 ml, 30.38 mmol) was added to
a solution of 5 (1.00 g, 1.52 mmol), PdCl2(PPh3)2 (0.75 g,
1.06 mmol), and CuI (0.20 g, 1.06 mmol) in diisopropyl-
amine (40 ml) under nitrogen atmosphere. Then, the reac-
tion mixture was stirred at 50 ꢄC for 12 h. After cooling to
room temperature, the reaction mixture was poured into
water and extracted with hexane. The combined organic
layers were washed with water, brain, and dried over magne-
sium sulfate. After filtration of magnesium sulfate, the solu-
tion was concentrated by rotary evaporator, and the residue
was purified by silica gel chromatography with hexane as an
eluent. The product dissolved in hexane was precipitated
from MeOH to give pure 6 as a yellow solid (0.60 g, 57%).
1H NMR (CDCl3): d ¼ 6.87 (s, 2H, ArAH) 2.62 (t, 4H, J ¼
7.33 Hz, ACH2A ꢂ 2) 1.61 (m, 4H, ACH2A ꢂ 2) 1.36–1.20
(36H, A (CH2)9A ꢂ 2), 0.88 (t, 6H, J ¼6.60 Hz, ACH3 ꢂ 2)
0.25(s, 18H, ASi(CH3)3 ꢂ 2) ppm. HRMS (EI): Calcd for
cmꢃ1
.
Poly2
Poly2 was prepared from 4b (74.9 mg, 0.10 mmol) in 20%
yield (22 mg, 20%) according to the method for poly 1. Mn
1
¼ 4400, Mw/Mn ¼ 1.2. H NMR (CDCl3): d ¼ 8.18–7.96 (8H,
ArAH), 7.73–7.56 (4H, ArAH), 7.56–7.38 (6H, ArAH), 7.17–
6.83 (4H, ArAH), 4.12–3.85 (4H, AOCH2A ꢂ 2), 1.94–1.74
(4H, ACH2A ꢂ 2), 1.62–0.98 (52H, A (CH2)13A ꢂ 2), 0.91–
0.76 (6H, ACH3 ꢂ 2) ppm. 13C NMR (CDCl3): d ¼ 154.83,
153.68, 145.95, 145.69, 137.91, 132.17, 131.89, 131.45,
131.11, 130.77, 129.62, 129.13, 128.66, 119.17, 119.01,
117.67, 116.86, 69.78, 31.95, 29.75, 29.70, 29.68, 29.49,
29.39, 29.38, 29.17, 29.11, 26.19, 26.15, 25.99, 25.95, 22.71,
14.13 ppm. 11B NMR (CDCl3): d ¼ 0.49 ppm. IR (KBr): m ¼
2924, 2853, 2195, 1599, 1499, 1470, 1391, 1275, 1217,
C
42H70S2Si2 (Mþ), 694.4457; found, m/z 694.4454.
1128, 1099, 1070, 1030, 997, 826, 822, 772, 719, 691 cmꢃ1
.
Synthesis of 3,30-Didodecyl-2,20-Diethynyl-5,50-
Bithiophene
Synthesis of Poly3
Anhydrous K2CO3 (111 mg, 0.81 mmol) was added to a solu-
tion of 6 (0.5 g, 0.72 mmol) in the mixed solvent of MeOH
and THF (1:2 v/v, 30 ml). The mixture was stirred under
nitrogen atmosphere at room temperature for 2 h. Then, the
reaction mixture was poured into water and extracted with
hexane. The combined organic layers were washed with
water, brain, and dried over magnesium sulfate. After filtra-
tion of magnesium sulfate, the solution was concentrated by
rotary evaporator, and the residue dissolved in hexane was
precipitated from MeOH to give pure 7 as a yellow solid
(0.34 g, 86%), which decomposes gradually on exposure to
Triethylamine (3 ml) was added to a solution of 4a (0.20 g,
0.27 mmol), 3,30-didodecyl-2,20-diethynyl-5,50-bithiophene
(0.15 g, 0.27 mmol), Pd(PPh3)4 (15.7 mg, 13.6 lmol), and
CuI (2.6 mg, 13.6 lmol) in THF (6 ml). The reaction mixture
was stirred under nitrogen atmosphere at room temperature
for 72 h, and then poured into acetone (300 ml) to collect
the polymer by filtration. The residue was dissolved in a
small amount of THF, and further poured into a large excess
of acetone and hexane, respectively to precipitate the poly-
mer. The polymer was dried in vacuum to give poly3 as a
dark green solid (48 mg, 17%). Mn ¼ 5200, Mw/Mn ¼ 1.4.
5354
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
1H NMR (CDCl3): d ¼ 8.17–7.96 (8H, ArAH), 7.68–7.36
(10H, ArAH), 7.13–6.79 (4H, ArAH), 2.85–2.59 (4H, ACH2A
ꢂ 2), 1.82–1.52 (40H, A (CH2)10A ꢂ 2), 0.93–0.74 (6H,
ACH3 ꢂ 2) ppm. 13C NMR (CDCl3): d ¼ 152.03, 149.55,
145.86, 138.86, 137.72, 137.02, 132.02, 131.13, 130.80,
129.53, 129.21, 128.47, 125.66, 125.30, 125.10, 124.78,
119.04, 117.61, 31.91, 30.16, 29.82, 29.68, 29.65, 29.57,
29.44, 29.36, 29.31, 29.18, 22.68, 14.12 ppm. 11B NMR
(CDCl3): d ¼ 0.68 ppm. IR (KBr): m ¼ 3422, 2924, 2853,
2187, 1599, 1503, 1474, 1431, 1296, 1225, 1130, 1099,
4 Kar, A. K. Polym Adv Technol. 2000, 11, 553–559.
5 Wu, P. L.; Feng, X. J.; Tam, H. L.; Wong, M. S.; Cheah, K. W.
J Am Chem Soc 2009, 131, 886–887.
6 (a) Suzuki, H.; Yokoo, A.; Notomi, M. Polym Adv Technol
2004, 15, 75–80; (b) Tessler, N.; Medvedev, V; Kazes, M.; Kan,
S. H.; Banin, U. Science 2002, 295, 1506–1508.
7 Suzuki, H. Appl Phys Lett 2000, 76, 1543–1545.
8 Toriumi, A.; HerrMann, J. M.; Kawata, S. Opt Lett 1997, 22,
555–557.
1034, 1018, 827, 772, 691 cmꢃ1
.
9 (a) Licha, K.; Olbrich, C. Adv Drug Deliv Rev 2005, 57,
1087–1108; (b) Levine, M.; Song, I.; Andrew, L. T.; Kooi, E. S.;
Swager, M. T. J Polym Sci Part A: Polym Chem 2010, 48,
3382–3391.
Poly4
Poly4 was prepared from 4b (0.20 g, 0.27 mmol) in 46%
yield (131 mg, 46 %) according to the method for poly3. Mn
1
¼ 4700, Mw/ Mn ¼ 1.9. H NMR (CDCl3): d ¼ 8.31–7.87 (8H,
10 (a) Thompson, B. C.; Madrigal, L.G.; Pinto, M. R.; Kang, T.;
Schanze, K.S.; Reynolds, J. R. J Polym Sci Part A: Polym Chem
2005, 43, 1417–1431; (b) Sun, M.; Jiang, X.; Wang, L.; He, C.;
Du, B.; Yang, R.; Cao, Y. J Polym Sci Part A: Polym Chem 2008,
46, 3007–3013; (c) Yang, R.; Tian, R; Yang, J.; Hou, Q.; Yang,
W.; Zhang, C.; Cao, Y. Macromolecules 2005, 38, 244–253; (d)
Luo, J.; Hou, Q.; Chen, J.; Cao, Y. Synth Met 2006, 156,
470–475; (e) Li, X.; Zeng, W.; Zhang, Y.; Hou, Q.; Yang, W.;
Cao, Y. Eur Polym J 2005, 41, 2923–2933; (f) Zhang, Y.; Yang,
J.; Hou, Q.; MO, Y.; Peng, J.; Cao, Y. Chin Sci Bull 2005, 50,
957–960 (g) Baigent, D. R.; Hamer, P. J.; Friend, R. H.; Moratti,
S. C.; Holmes, A. B. Synth Met 1995, 71, 2175–2176; (h) Li, K.
C.; Hsu, Y. C.; Lin, J. T.; Yang, C. C.; Wei, K. H.; Lin, H. C. J
Polym Sci Part A: Polym Chem 2009, 47, 2073–2092; (i) Xia, Y.;
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ArAH), 7.66–7.32 (10H, ArAH), 7.09–6.82 (4H, ArAH), 2.83–
2.51 (4H, ACH2A ꢂ 2), 1.94–1.00 (40H, A (CH2)10Aꢂ2),
0.92–0.66 (6H, ACH3 ꢂ 2) ppm. 13C NMR (CDCl3): d ¼
152.05, 149.37, 145.52, 138.28, 137.72, 136.89, 131.56,
131.26, 130.90, 130.58, 129.43, 128.99, 128.47, 125.12,
124.78, 124.23, 118.89, 116.67, 31.91, 30.15, 29.82, 29.69,
29.67, 29.56, 29.43, 29.36, 29.27, 29.18, 22.68, 14.12 ppm.
11B NMR (CDCl3): d ¼ 0.49 ppm. IR (KBr): m ¼ 3422, 2924,
2853, 2187, 1603, 1516, 1485, 1452, 1398, 1258, 1128,
1099, 1030, 1001, 826, 768, 694 cmꢃ1
.
CONCLUSIONS
The conjugated polymers have been successfully synthesized
by palladium-catalyzed Sonogashira polymerization of diio-
dobenzene-functionalized aza-borondipyrromethene (Aza-
BODIPY) monomers, which were substituted at 3 and 5 or 1
and 7 positions on the Aza-BODIPY core, with 1,4-diethynyl-
2,5-dihexadecyloxybenzene or 3,30-didodecyl-2,20-diethynyl-
5,50-bithiophene. Their polymers displayed significantly red-
shifted UV-vis absorption and PL spectra because of effective
extension of p-conjugation relative to the simple Aza-BODIPY,
and exhibited NIR light with narrow emission bands at
713ꢀ777 nm on excitation at each absorption maximum.
Especially, the polymer attached 1,4-diethynyl-2,5-dihexade-
cyloxybenzene to 3,5-position on the core revealed intense
quantum yields (UF ¼ 24%) in this NIR region (753 nm). To
best of our knowledge, this is the first report of the synthe-
sis of Aza-BODIPY-based conjugated polymers. Their promi-
nent optical properties suggest the potential applications of
the Aza-BODIPY-based conjugated polymers in the NIR emis-
sive materials. Further, structural and functional elaboration
of the first-generation polymeric Aza-BODIPY prototype is
currently being pursued in our laboratory to improve the
red-shift and the quantum yield.
11 Lakowicz, J. R. Principles of Fluorescence Spectroscopy;
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