Near-infrared emissive BODIPY polymeric and copolymeric dyes

Article abstract of DOI:10.1016/j.polymer.2010.09.029

Novel near-Infrared emissive BODIPY polymeric dyes (polymers A and B) were prepared by Sonogashira cross-coupling reaction of 2,6-diiodo BODIPY dyes bearing one and two styryl groups at 3,5 positions (5, 6) with 2,6-diethynyl BODIPY dye, respectively. The

Full text of DOI:10.1016/j.polymer.2010.09.029

Polymer 51 (2010) 5359e5368
Contents lists available at ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
Near-infrared emissive BODIPY polymeric and copolymeric dyes
*
Venkat R. Donuru, Shilei Zhu, Sarah Green, Haiying Liu
Department of Chemistry, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel near-Infrared emissive BODIPY polymeric dyes (polymers A and B) were prepared by Sonogashira
cross-coupling reaction of 2,6-diiodo BODIPY dyes bearing one and two styryl groups at 3,5 positions (5,
6) with 2,6-diethynyl BODIPY dye, respectively. These polymeric dyes (A and B) display absorption
maxima at 697 and 738 nm, and emission maxima at 715 and 760 nm, respectively. These polymeric dyes
Received 17 June 2010
Received in revised form
10 September 2010
Accepted 11 September 2010
Available online 18 September 2010
exhibit significant red shifts in absorption and emission maxima due to their extended
p-conjugation
systems compared with their BODIPY monomeric dyes. The thin films of polymers A and B display
further red shift with emission maxima 764 and 810 nm, respectively. Near-infrared BODIPY copolymeric
dye (C) was prepared by Sonogashira polymerization of 2,6-diiodo BODIPY dye bearing two styryl groups
with 2,5-diethynyl-3-decylthiophene. For comparison in optical properties, deep-red and red emissive
BODIPY copolymeric dyes (D and E) were prepared by Sonogashira polymerization of 2,6-diiodo BODIPY
dye bearing monostyryl group and 2,6-diiodo BODIPY dye with 2,5-diethynyl-3-decylthiothene,
respectively. These polymers display their absorption maxima at 649 nm and 634 nm, and emission
maxima at 694 nm and 669 nm, respectively. All the polymers displayed good thermal stability and
solubility in dichloromethane, and their lifetimes ranged from 0.7 to 3.4 ns.
Keywords:
Conjugated polymers
BODIPY dyes
BODIPY polymeric dyes
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
from 691 to 720 nm by palladium-catalyzed Sonogashira polymeri-
zation of 1,4-diethynyl-2,5-dihexadecyloxybenzene with diiodo-
BODIPY (4,40-difluoro-4-bora-3a,4a-diaza-s-indacene) dyes have
been well studied because of many distinctive and desirable prop-
erties such as high absorption coefficients, narrow absorption and
emission bands, sharp emissions, high fluorescence quantum yields,
and excellent chemical and photostabilities [1e3]. They have prom-
ising applications in supramolecular fluorescent gels [4], solar cells
[5], sensing [6e8] and imaging [9]. The extended conjugation of
BODIPY units with aromatic, ethynyl, aryl substituents leads to
significant red shifts [1e3]. Recently, some near-infrared emissive
BODIPY dyes have been prepared for emerging and more challenging
biotechnology and biomedical applications [1e3]. Very recently,
a few BODIPY-based conjugated oligomers, polymers and copoly-
mers have been reported that combine the unique properties of both
BODIPY dyes and conjugated polymers into one package for a variety
of potential applications in electronic and biotechnology industry
[10e13]. However, most BODIPY-based conjugated oligomers, poly-
mers and copolymers emit from yellow to deep-red emission with
wavelength ranges from 580 nm to 698 nm [10e15]. Only one paper
has reported BODIPY-based copolymers with near-infrared emission
phenyl-fused BODIPY monomers [15].
Our hypothesis is that significant extension of
p-conjugation of
BODIPY core with one, two styryl groups at 3,5 positions will help
tune BODIPY polymeric dyes to the near-infrared region. In this
article, we report near-infrared emissive BODIPY polymeric and
copolymeric dyes with emission wavelength range from 715 nm to
760 nm. These polymers were synthesized by palladium-catalyzed
Sonogashira coupling reaction of 2,6-diiodo BODIPY derivatives
(5,6) with 2,6-diethynyl BODIPY dye (7) (Scheme 1). For compar-
ison of optical properties, deep-red and red emissive BODIPY
copolymeric dyes were prepared by palladium-catalyzed Sonoga-
shira of 2,6-diiodo BODIPY dye bearing one styryl group (5) with
2,5-diethynyl-3-decylthiophene (9) and 2,6-diethynyl BODIPY
derivative (7) with 2,5-diiodo-3-decylthiophene (8) respectively.
Tridodecyloxy groups were introduced to BODIPY monomer (7) at
the meso-position to enhance solubility of BODIPY polymers in
organic solvents while ethyl esters were introduced to BODIPY
monomers at 3,5 positions in order to facilitate easy separation of
BODIPY monomers bearing one or two styryl groups (5, 6) and
provide a future potential use of the ester-functionalized side
chains as cell-trappable biosensors [12]. These BODIPY polymeric
and copolymeric dyes have been characterized for optical and
thermal properties.
* Corresponding author.
E-mail address: hyliu@mtu.edu (H. Liu).
0032-3861/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2010.09.029

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V.R. Donuru et al. / Polymer 51 (2010) 5359e5368
OCH3
OCH3
O
OCH3
O
O
O
O
O
N
N
B
F
N
N
B
F
N
N
n
N
N
B
F
N
N
S
n
n
B
B
F
F
F
F
F
F
F
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
Polymer A
Polymer C
Polymer B
OCH3
O
O
O
S
N
N
B
F
S
n
N
N
n
F
B
F
F
O
O
O
O
O
O
Polymer D
Polymer E
Scheme 1. Chemical structures of near-infrared, deep-red, red emissive BODIPY polymeric and copolymeric dyes.
2. Experimental
2.1. Instrumentation
254 nm and a Waters Model 2410 refractive index detector.
Molecular weights were measured relative to polystyrene
standards.
1H NMR and 13C NMR spectra were collected on a 400 MHz
Varian Unity Inova spectrophotometer instrument. 1H and 13C NMR
2.2. Materials
spectra were recorded in CDCl3, and chemical shifts (d) are given in
Unless otherwise indicated, all reagents and solvents were
obtained from commercial suppliers (Aldrich, Sigma, Fluka, Acros
Organics, Fisher Scientific, Lancaster) and were used without
further purification. Air- and moisture-sensitive reactions were
conducted in oven-dried glassware using a standard Schlenk line or
drybox techniques under an inert atmosphere of dry nitrogen.
4,4-Difluoro-8-(4-methoxyphenyl)-1,3,5,7-tetramethyl-4-bora-3a,
4a-diaza-s-indacene (2), aldehyde derivative (4), 2,6-diethynyl
BODIPY derivative (7) and 2,5-diiodo-3-decylthiophene (8) were
prepared according to the reported procedure [10e12].
ppm relative to solvent peaks (at 7.24 ppm for 1H spectra and at
77.3 for 13C spectra) as internal standard. UV spectra were taken on
a HewlettePackard 8452A Diode Array UVevisible spectropho-
tometer. Fluorescence spectra were recorded on a Spex Fluorolog
16810.22 m steady-state fluorometer. Fluorescence quantum yields
of BODIPY dyes and polymeric dyes were measured in methylene
chloride and calculated by using fluorescein excited at 490 nm in
0.1 N NaOH as the reference (quantum efficiency 85%) [16e19].
Fluorescence lifetimes were measured on a GL-3300 Nitrogen Laser
laserstrobe PTI instrument and analyzed using FeliX32 software.
The solid state films of BODIPY polymeric and copolymeric dyes
were prepared by spin-casting methylene chloride solutions of the
polymers onto quartz discs [12]. Molecular weights of the polymers
were determined by size exclusion chromatography (SEC) by using
a Waters Associates Model 6000A liquid chromatograph. Three
American Polymer Standards Corp. Ultrastyragel columns in series
with porosity indices of 103, 104, and 105 Å were used and housed in
an oven thermostated at 30 ꢀC. Mobile phase, HPLC grade THF was
2.3. 4,4-Difluoro-8-(4-methoxyphenyl)-2,6-diiodo-1,3,5,7-
tetramethyl-4-bora-3a,4a-diaza-s-indacene (3)
Iodic acid (11.26 mmol, 1.98 g) in 4 mL of water was added
dropwise to the ethanol solution (50 mL) containing BODIPY dye (2)
(5.63 mmol 2.0 g) and iodine (6.19 mmol 1.57 g) over 30 min, and
stirred for 3 h. The mixture was concentrated under reduced pres-
sure, dissolved in CH2Cl2, and washed twice with water and satu-
rated sodium chloride solution. The organic layer was collected,
dried over anhydrous Na2SO4, and concentrated under reduced
filtered and degassed by vacuum filtration through a 0.5 mm fluo-
ropore filter prior to use. The polymers were detected by a Waters
Model 440 ultraviolet absorbance detector at a wavelength of

V.R. Donuru et al. / Polymer 51 (2010) 5359e5368
5361
H
O
O
OCH3
OCH3
O
O
O
OCH3
OCH3
OCH3
OCH3
O
O
4
I
I
I
I
N
H
+
N
N
B
F
N
N
B
F
DIEA, BF3-OEt2
CH2Cl2
I2, HIO3
DDQ
F
F
I
I
N HN
N
N
B
F
TFA
CH2Cl2
N
N
B
F
EtOH, H2O
Piperidine, AcOH
Benzene
CHO
F
CH2Cl2
F
O
O
O
Dean-Stark,
1
O
O
3
2
O
O
O
O
O
O
O
O
O
O
O
O
O
5
6
Scheme 2. Synthetic route to BODIPY dyes bearing monostyryl and distyryl groups.
pressure. The crude product was purified according to a reported
procedure to yield compound 3 as red crystals (3.2 g, 94%).
and emission maximum at 631 nm in CH2Cl2 solution; BODIPY dye
bearing distyryl group (6): 1H NMR (400 MHz, CDCl3):
8.04 (d,
d
J ¼ 16.8 Hz, 2H), 7.51 (d, J ¼ 16.4 Hz, 2H), 7.23 (d, J ¼ 9.2 Hz, 2H), 7.17
(d, J ¼ 8.4 Hz, 2H), 7.10 (s, 2H), 7.01 (d, J ¼ 8.4 Hz, 2H), 6.89 (d,
J ¼ 8.4 Hz, 2H), 4.15e4.05 (m, 16H), 3.85 (s, 3H), 2.55e2.51 (m, 8H),
2.16e2.09 (m, 8H), 1.46 (s, 6H), 1.27e1.20 (m, 12H) ppm. 13C NMR
2.4. 2,6-Diiodo BODIPY dye bearing monostyryl and distyryl groups
(5, 6)
(100 MHz, CDCl3):
d 173.4, 173.3, 160.7, 150.5, 149.1, 145.9, 139.4,
Piperidine (2.88 mL) and acetic acid (2.44 mL) were added to
a solution of benzene (120 mL) containing 2,6-diiodo BODIPY dye
(3) (1.32 mmol, 800 mg) and aldehyde derivative (4) (5.28 mmol,
1.93 g) in a 250-mL flask. After the mixture was stirred and refluxed
by using a Dean Stark trap for 4 h, it was cooled to room temper-
ature and concentrated under reduced pressure. The crude product
was dissolved in ethyl acetate and washed twice with water. The
organic phase was collected, dried over Na2SO4, and filtered. After
the filtrate was concentrated, the residue was purified by silica gel
column chromatography using hexane/EtOAc (5/1 to 3/1, v/v) to
afford dark blue solid compound 5 (540 mg, 43%), dark green solid
compound 6 (410 mg, 24%). BODIPY dye bearing monostyryl group
138.9, 133.6, 130.5, 129.8, 127.4, 121.7, 117.3, 115.0, 114.0, 113.7, 83.3,
68.5, 68.2, 60.6, 60.5, 55.6, 30.9, 24.9, 24.8,17.9,14.4 ppm. IR (cmꢁ1):
2978, 2933,1726, 1595, 1509, 1431, 1354,1244,1170,1094, 1010, 770,
708. ESI-MS: Mþ (C62H76BF2I2N2O13 þ Na) Calcd: m/z ¼ 1382.0,
Found: m/z ¼ 1381.8. The compound displays absorption maximum
at 665 nm and emission maximum at 701 nm in CH2Cl2 solution.
2.5. Polymer A
BODIPY dye bearing monostyryl groups (5) (0.15 mmol,150 mg),
2,6-diethynyl BODIPY dye (7) (0.18 mmol, 169 mg), and CuI (3 mg)
were added to a 100-mL three-neck flask under a nitrogen atmo-
sphere. Pd(PPh3)4 (6 mg) was added to the flask in a glove box
under a nitrogen atmosphere. When degassed anhydrous THF
(40 mL) and diisopropylamine (40 mL) were added to the flask
under a nitrogen atmosphere, the resulting mixture was stirred
under reflux for 24 h. After removal of the solvent, the residue was
dissolved in 250 mL of methylene chloride and washed with water
three times. After the organic layer was collected, dried over
anhydrous MgSO4, and filtered, the filtrate was concentrated under
reduced pressure and added to 250 mL of ethanol to precipitate the
polymer. The precipitated solid was collected, washed with ethanol
(5): 1H NMR (400 MHz, CDCl3):
d
8.05 (d, J ¼ 16.8 Hz, 1H), 7.49 (d,
J ¼ 16.8 Hz, 1H), 7.26 (d, J ¼ 8.4 Hz, 1H), 7.14 (m, 2H), 7.02 (d,
J ¼ 8.0 Hz, 2H), 6.88 (d, J ¼ 8.0 Hz, 1H), 4.18e4.06 (m, 8H), 3.87 (s,
3H), 2.68 (s, 3H), 2.59e2.53 (m, 4H), 2.18e2.13 (m, 4H), 1.48 (s, 3H),
1.44 (s, 3H), 1.26 (t, J ¼ 7.0 Hz, 6H). 13C NMR (100 MHz, CDCl3):
d
173.4, 173.3, 160.7, 156.8, 150.5, 149.2, 146.3, 145.2, 140.5, 139.2,
132.8,132.5, 130.4, 129.9, 129.5, 127.1, 121.9, 117.2, 115.1, 113.9, 113.2,
86.3, 82.6, 68.5, 68.2, 60.6, 55.6, 30.9, 24.9, 24.8, 17.9, 17.4, 16.4, 14.5.
IR (cmꢁ1): 2924, 1728, 1511, 1468, 1346, 1246, 1164, 1109, 995, 706.
ESI-MS: Mþ (C41H48BF2I2N2O7) Calcd: m/z ¼ 983.0, Found: m/
z ¼ 980.3. The compound shows absorption maximum at 597 nm
Pd(PPh3)4, CuI
O
OCH3
O
OCH3
O
O
O
O
O
Diisopropylamine
O
O
THF
Reflux for 24 hours
Compound
5
H
H
N
N
N
N
B
F
N
N
n
N
N
B
F
N
N
n
B
Pd(PPh3)4, CuI
B
B
Compound
6
F
F
F
F
F
F
F
F
Diisopropylamine
THF
7
O
O
O
Reflux for 24 hours
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
Polymer A
Polymer B
Scheme 3. Synthetic route to near-infrared emissive BODIPY polymeric dyes.

5362
V.R. Donuru et al. / Polymer 51 (2010) 5359e5368
Pd(PPh3)4, CuI
H
Si(CH3)3
OCH3
Diisopropylamine
THF
Pd(PPh3)4, CuI
Diisopropylamine
THF
Reflux for 24 hours
Tetrabutylamine floride
I
I
(CH3)3Si
Si(CH3)3
H
H
S
S
o
S
N
N
B
F
Reflux for 24 hours
n
S
THF, - 70
C
Compound
6
F
10
9
8
O
O
O
O
O
O
O
Compound
5
O
O
OCH3
Pd(PPh3)4, CuI
O
O
Diisopropylamine
THF
O
N
N
B
F
S
n
Reflux for 24 hours
F
Polymer C
O
O
O
O
O
O
Polymer D
Scheme 4. Synthetic rout to near-infrared and deep-red emissive BODIPY copolymeric dyes (polymers C and D).
and hexane, and dried under vacuum for 24 h at room temperature
to obtain dark-violet solid (0.202 g). 1H NMR (400 MHz, CDCl3):
3.99 (br. m, 2H), 3.87 (br. m, 7H), 2.66 (br. s, 6H), 2.57e2.52 (br. m,
8H), 2.18e2.14 (m, 8H), 1.76 (br. m, 6H), 1.66 (br. s, 12H), 1.56e1.23
(br. m, 66H), 0.86e0.85 (br. m, 9H) ppm. 13C NMR (100 MHz, CDCl3):
d
8.19 (br. d, 1H), 7.56 (br. d, 1H), 7.16e7.10 (br. m, 4H), 7.02e7.00 (br.
m, 2H), 6.84 (br. d, 1H), 6.42 (br. s, 2H), 4.14e4.06 (br. m, 8H), 3.98
(br. m, 2H), 3.86 (br. m, 7H), 2.68e2.64 (br. m, 9H), 2.57e2.52 (br. m,
4H), 2.18e2.13 (br. m, 4H), 1.76 (br. m, 6H), 1.66 (br. s, 6H), 1.54e1.23
(br. m, 66H), 0.86e0.85(br. m, 9H). IR (cmꢁ1): 2922, 2852, 1734,
1509, 1313, 1228, 1164, 1086, 1000, 759. SEC (THF, polystyrene
standard), Mn: 35.5 ꢂ 103 g/mol; polydispersity: 2.3. The polymer
shows absorption maximum at 697 nm and emission maximum at
715 nm in CH2Cl2 solution.
d 173.4, 173.3, 160.7, 154.5, 152.3, 150.7, 149.2, 144.6, 143.4,
139.1, 133.5, 131.5, 130.4, 125.2, 122.1, 117.4, 114.9, 113.9, 113.2,
106.3, 94.6, 91.5, 74.0, 69.8, 68.6, 68.2, 60.6, 60.5, 55.5, 32.1, 31.8, 30.9,
30.5, 29.9, 29.8, 29.5, 26.4, 26.2, 24.9, 24.8, 23.6, 22.9,14.4,14.3 ppm.
IR (cmꢁ1): 2921, 2852, 1733, 1506, 1313, 1238, 1179, 1082, 1004, 758,
709. SEC (THF, polystyrene standard), Mn: 45.1 ꢂ 103 g/mol; poly-
dispersity: 2.4. The polymer shows absorption maximum at 738 nm
and emission maximum at 760 nm in CH2Cl2 solution.
2.6. Polymer B
2.7. Compound 9
2,6-Diiodo BODIPY dye bearing distyryl groups (6) (0.11 mmol,
150 mg), 2,6-diethynyl BODIPY dye (7) (0.13 mmol,122 mg), and CuI
(3 mg) were added to a 100-mL three-neck flask under a nitrogen
atmosphere. Pd(PPh3)4 (6 mg) was added to the flask in the glove
box under a nitrogen atmosphere. After degassed anhydrous THF
(40 mL) and diisopropylamine (40 mL) wereadded tothe flask under
a nitrogen atmosphere, the mixture was stirred under reflux for
24 h. Polymer B was purified by using the procedure for polymer Ato
2,5-Diiodo-3-decylthiophene (8) (4.20 mmol, 2 g), CuI (4 mg),
and Pd(PPh3)2Cl2 (10 mg) were added to a 100-mL three-neck flask
under a nitrogen atmosphere. After degassing anhydrous THF
(20 mL), diisopropylamine (20 mL), and trimethylsilylacetylene
(12.6 mmol, 1.2 g) were added to the flask under a nitrogen atmo-
sphere, the mixture was stirred at room temperature for 12 h. The
mixture was concentrated, dissolved in 50 mL of CH2Cl2 and washed
twice with water and saturated saline solution. When the organic
layer was collected, dried over anhydrous MgSO4, and filtered, the
filtrate was concentrated under reduced pressure. The product was
purified by silica gel column chromatography using hexane/EtOAc
obtain dark-violet solid (0.182 g). 1H NMR (400 MHz, CDCl3):
d 8.20
(br. d, 2H), 7.63 (br. d, 2H), 7.16e7.10 (br. m, 4H), 7.03 (br. s, 2H), 7.02
(br. d, 2H), 6.88 (br. d, 2H), 6.43 (br. s, 2H), 4.15e4.08 (br. m, 16H),
O
O
O
O
Pd(PPh3)4, CuI
O
O
Diisopropylamine
THF
S
H
H
I
I
+
N
N
N
N
S
n
B
B
Reflux for 24 hours
F
F
F
F
8
7
Polymer E
Scheme 5. Synthetic route to red emissive BODIPY copolymeric dye.

V.R. Donuru et al. / Polymer 51 (2010) 5359e5368
5363
Fig. 1. 1H NMR spectra of BODIPY monomeric dyes (5, 7) and polymeric dye (polymer A) in CDCl3 solution.

5364
V.R. Donuru et al. / Polymer 51 (2010) 5359e5368
Fig. 2. 1H NMR spectra of BODIPY monomeric dyes (6, 7) and polymeric dye (polymer B) in CDCl3 solution.

V.R. Donuru et al. / Polymer 51 (2010) 5359e5368
5365
2.67e2.63 (br. m,10H), 2.16e2.09 (br. m, 8H),1.58 (br. t, 2H),1.46 (br.
s, 6H), 1.30e1.20 (br. m, 26H), 0.87 (br. t, 3H) ppm. IR (cmꢁ1): 2921,
2852, 1732, 1509, 1457, 1262, 1249, 1175, 1135, 1044, 958, 750, 723.
SEC (THF, polystyrene standard), Mn: 32.1 ꢂ 103 g/mol; poly-
dispersity: 2.2. The polymer C shows absorption maximum at
713 nm and emission maximum at 758 nm in CH2Cl2 solution.
2.10. Polymer D
2,5-Diiodo BODIPY dye bearing monostyryl group (5)
(0.10 mmol, 100 mg), diethynyl-3-decylthiophene (10) (0.12 mmol,
34 mg), and CuI (3 mg) were added to a 100-mL three-neck flask
under a nitrogen atmosphere. Pd(PPh3)4 (6 mg) was added to the
flask in the glove box under a nitrogen atmosphere. Degassed
anhydrous THF (40 mL) and anhydrous diisopropylamine (40 mL)
were added to the flask under a nitrogen atmosphere, and the
mixture was stirred under reflux for 24 h. The polymer D was
purified by using the same procedure for polymer C to afford dark-
violet solid (0.082 g). 1H NMR (400 MHz, CDCl3):
d 8.17 (br. d, 1H),
7.54 (br. d, 1H), 7.15e7.08 (br. m, 4H), 7.02e6.98 (br.m, 3H), 6.82 (br.
d, 1H), 4.12e4.03 (br. m, 8H), 3.87 (br.s, 3H), 2.67e2.63 (br. m, 5H),
2.58e2.51 (br. m, 4H), 2.16e2.13 (br. m, 4H), 1.58 (br. t, 2H),
1.48e1.24 (br. m, 26H), 0.88 (br. t, 3H) ppm. IR (cmꢁ1): 2921, 2851,
1732, 1509, 1403, 1247, 1178, 1022, 1007, 835. SEC (THF, polystyrene
standard), Mn: 22.4 ꢂ 103 g/mol; polydispersity: 2.1. The polymer D
shows absorption maximum at 649 nm and emission maximum at
694 nm in CH2Cl2 solution (Scheme 5).
Fig. 3. Absorption spectra of BODIPY dyes (2, 3, 5, 6 and 7) and polymeric dyes
(polymers A and B), their thin films.
(98/2 v/v) to yield viscous liquid (1.46 g, 84%). 1H NMR (400 MHz,
CDCl3):
d
6.94 (s, 1H), 2.59 (t, J ¼ 7.6 Hz, 2H), 1.56 (t, J ¼ 6.8 Hz, 2H),
1.31e1.26 (m,14H), 0.87 (t, J ¼ 6.8 Hz, 3H), 0.19 (s,18H) ppm.13C NMR
(100 MHz, CDCl3):
d 148.6, 133.6, 122.9, 120.1, 101.9, 99.6, 97.6, 97.1,
32.1, 30.1, 29.8, 29.7, 29.5, 29.3, 22.9, 14.3, 0.09 ppm.
2.11. Polymer E
2.8. 2,5-Diethynyl-3-decylthiophene (10)
2,6-Diethynyl BODIPY dye (7) (0.14 mmol, 150 mg), 2,5-diiodo-
3-decylthiophene (8) (0.12 mmol, 60 mg), and CuI (3 mg) were
added to a 100-mL three-neck flask under a nitrogen atmosphere.
Pd(PPh3)4 (6 mg) was added to the flask in the glove box under
a nitrogen atmosphere. Anhydrous THF (40 mL) and diisopropyl-
amine (40 mL) were added to the flask in a nitrogen atmosphere.
After stirring under reflux for 24 h, the reaction mixture was added
dropwise to 500 mL of ethanol to precipitate the polymer. The
precipitated polymer was collected, washed with water, ethanol,
acetone and hexane and dried under vacuum for 24 h at room
temperature to obtain dark-violet solid (0.132 g). 1H NMR
Tetrabutylammonium fluoride (5.63 mmol 2.0 g) was added to
the degassed solution of compound 9 (12.1 mmol, 0.50 g) in dry THF
(50 mL) at ꢁ70 ꢀC through syringe and the resulting mixture was
stirred at room temperature for 2 h. After the reaction was
quenched with dilute acetic acid and 50 mL of dichloromethane
was added to the flask, the mixture was washed twice with water
and saturated saline solution. When the organic layer was
collected, dried over anhydrous MgSO4, and filtered, the filtrate was
concentrated. The residue was purified by column chromatography
using hexane/EtOAc (95/5 v/v) to yield yellow liquid (0.28 g, 87%).
The compound was immediately stored at 4 ꢀC. 1H NMR (400 MHz,
CDCl3):
d
7.00 (s, 1H), 3.42 (d, J ¼ 1.2 Hz, 1H), 3.30 (d, J ¼ 0.8 Hz, 1H),
2.63 (t, J ¼ 7.0 Hz, 2H), 1.58(t, J ¼ 7.0 Hz, 2H), 1.31e1.27 (m, 14H),
0.89 (t, J ¼ 6.4 Hz, 3H) ppm. 13C NMR (100 MHz, CDCl3):
d 148.8,
133.9, 122.3, 119.1, 84.2, 81.9, 76.9, 76.2, 32.2, 30.2, 29.9, 29.8, 29.6,
29.5, 29.4, 22.9, 14.4 ppm.
2.9. Polymer C
2,5-Diiodo BODIPY dye bearing distyryl groups (6) (0.11 mmol,
150 mg), 2,5-diethynyl-3-decylthiophene (10) (0.14 mmol, 36 mg),
and CuI (3 mg) were added to a 100-mL three-neck flask under
a nitrogen atmosphere. Pd(PPh3)4 (6 mg) was added to the flask in
the glove box under a nitrogen atmosphere. When degassed anhy-
drous THF (40 mL) and diisopropylamine (40 mL) were added to the
flask under a nitrogen atmosphere, the mixture was stirred under
reflux for 24 h, concentrated and added dropwise to 250 mL of
ethanol under stirring to precipitate the polymer. The precipitated
polymer was collected, washed with water, ethanol, acetone and
hexane and dried under vacuum for 24 h at room temperature to
afford dark-violet solid (0.113 g). 1H NMR (400 MHz, CDCl3):
d 8.22
(br. d, 2H), 7.65 (br. d, 2H), 7.16e7.10 (br. m, 4H), 7.05 (br. s, 2H), 7.02
(br. m, 3H), 6.89 (br. d, 2H), 4.15e4.08 (br. m, 16H), 3.87 (br. s, 3H),
Fig. 4. Fluorescence spectra of BODIPY dyes (2, 3, 5, 6 and 7) and polymeric dyes
(polymers A and B).

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V.R. Donuru et al. / Polymer 51 (2010) 5359e5368
Table 1
Absorption and emission maxima, fluorescence quantum yields and lifetimes of BODIPY monomeric and polymeric dyes in methylene chloride solution.
BODIPY dyes or polymers
2
3
5
6
7
A
B
C
D
E
Absorption maxima (nm)
Emission maxima (nm)
Quantum yield (%)
500
510
80
533
548
5.7
1.7
597
631
2.6
1.7
665
701
4
539
554
52
697
715
11
738
760
13
713
758
1.3
0.52
649
694
1.1
0.69
634
669
1.2
0.41
Fluorescence lifetime (ns)
3.8
2.3
3.0
0.86
0.71
(400 MHz, CDCl3):
d
6.95 (br.s, 1H), 6.45 (br. s, 2H), 4.02 (br. s, 2H),
emissive BODIPY polymeric dyes (polymers A and B) were prepared
by palladium-catalyzed Sonogashira polymerization of monostyryl-
and distyryl-substituted BODIPY dyes (5, 6) with 2,6-diethynyl
BODIPY dye (7), respectively (Scheme 3). Both polymers A and B are
readily soluble in common organic solvents such as dichloro-
methane, chloroform, and THF. However, polymer B has higher
solubility than polymer A because of its distyryl groups. To further
demonstrate the potential tuning of the polymer fluorescence and
synthetic diversity, we incorporated a thiophene unit into the
BODIPY-based polymer backbone and prepared near-infrared and
deep-red emissive BODIPY copolymeric dyes (polymers C and D)
(Scheme 4). 2,5-Diethynyl-3-decylthiophene (10) was prepared by
Sonogashira coupling reaction of 2,5-diiodo-3-decylthiophene (8)
with ethynyltrimethylsilane to give compound 9, and followed by
hydrolysis of compound 9 in the presence of tetrabutylammonium
fluoride inTHF (Scheme 4). The BODIPY copolymeric dyes (polymers
C and D) were prepared by palladium-catalyzed Sonogashira poly-
merization of distyryl- and monostyrul-substituted BODIPY dyes (6,
5) with 2,5-diethynyl-3-decylthiophene (10), respectively. These
BODIPY copolymeric dyes (polymers C and D) have lower solubility
in common organic solvents such as methylene chloride, chloro-
form, and THF than polymers A and B. For comparison in optical
properties, we prepared red emissive BODIPY copolymeric dye
(polymer E) by palladium-catalyzed Sonogashira polymerization of
2,6-diethynyl BODIPY dyes (7) with 2,5-diiodo-3-decylthiophene
(8). Polymer E is highly soluble in solvents such as methylene
chloride, chloroform and THF.
3.91 (br. s, 4H), 2.67 (br. s, 6H), 1.77(br. t, 4H), 1.64 (br.s, 6H),
1.49e1.44 (br. m, 6H), 1.24 (br. m, 72H), 0.85 (br. t, 12H) ppm. 13C
NMR (100 MHz, CDCl3):
d 158.7, 154.6, 147.5, 143.2, 142.5, 139.2,
132.4, 131.5, 115.8, 106.3, 90.2, 88.8, 73.9, 69.7, 32.2, 32.1, 30.5, 30.3,
29.9, 29.8, 29.6, 29.5, 26.3, 26.2, 22.9,14.3,13.9,13.5 ppm. IR (cmꢁ1):
2921, 2852, 1525, 1315, 1229, 1111, 1004, 759, 720. SEC (THF, poly-
styrene standard), Mn: 20.8 ꢂ 103 g/mol; polydispersity: 2.2. The
polymer E shows absorption maximum at 634 nm and emission
maximum at 669 nm in CH2Cl2 solution.
3. Results and discussion
3.1. Synthesis of BODIPY monomeric, polymeric and copolymeric
dyes
We have prepared deep-red emissive BODIPY polymeric dyes
with emission maxima of up to 698 nm by palladium-catalyzed
Sonogashira coupling of 2,6-diiodo BODIPY dyes with 2,6-ethynyl
BODIPY dyes [10,12]. In order to tune fluorescence of BOIDPY poly-
meric dyes into the near-infrared region, we extended the
p-
conjugation of BODIPY monomeric dyes by introducing styryl
groups at the 3,5 positions of BODIPY dyes (Scheme 2). Meso-aryl-
substituted BODIPY dye (2) was prepared through the condensation
of 4-methoxybenzaldehyde (1) with 2,4-dimethylpyrrole in the
presence of a catalytic amount of trifluoroacetic acid (TFA), and
followed by oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzo-
quinone (DDQ) and chelation with BF3-etherate in the presence of
N,N-diisopropylethylamine (DIEA). Further iodinization of BODIPY
dye 2 at its 2,6 positions afforded 4,4-difluoro-8-(4-methox-
1H and 13C NMR spectroscopy studies confirm the molecular
structures of polymers A and B (Scheme 1). 1H NMR spectral peaks
of polymers A and B are slightly broader than those of its BODIPY
monomers (5, 6 and 7) (Figs. 1 and 2). All peaks corresponding to
BODIPY monomers are readily observed in the 1H NMR spectra of
the polymers except for the singlet proton at 3.30 ppm
yphenyl)-2,6-diiodo-1,3,5,7-tetramethyl-4-bora-3a,
4a-diaza-s-
indacene (3). Condensation of BODIPY dye 3 bearing methyl
substituents on 3 and 5 positions with aldehyde derivative
(4) afforded BODIPY dyes bearing one, two styryl groups (5, 6)
(Scheme 2). Ethyl esters were introduced to BODIPY monomers at
3,5 positions to facilitate easy separation of BODIPY monomers
bearing one or two styryl groups (5, 6) and provide a future potential
use of the ester-functionalized side chains as cell-trappable
biosensors [12]. Yields of BODIPY monomers bearing one or two
styryl groups (5, 6) can be manipulated by controlling reaction time
and ratio of BODIPY dye 3 to aldehyde derivative (4). Increase of
reaction time (to 5 h) and ratio (1:7) of BODIPY dye 3 to aldehyde
deriviative (4) increases yield (up to 33%) of BODIPY monomer
bearing two styryl groups (6). Tridodecyloxy groups were intro-
duced to BODIPY monomer (7) at the meso-position to enhance
solubility of BODIPY polymers in organic solvents. Near-infrared
Table 2
Absorption and emission maxima of thin films on quartz surface.
BODIPY polymers
Thin film
Thin film
Thin film
polymer A
polymer B
polymer E
Absorption maxima
(nm)
759
784
706
Emission maxima
(nm)
769
810
727
Fig. 5. Absorption and fluorescence spectra of BODIPY copolymeric dyes.

V.R. Donuru et al. / Polymer 51 (2010) 5359e5368
5367
and 84 nm in absorption and emission with maxima of 679 nm and
715 nm respectively. Polymer B displays absorption and emission
maxima at 738 nm and 760 nm with significant red shifts of 73 nm
and 59 nm respectively, compared with its distyryl-substituted
BODIPY monomeric dye (6) (Figs. 3 and 4).
Palladium-catalyzed Sonogashira polymerization of distyryl-
and monostyryl-substituted BODIPY dyes (6, 5) with 2,5-dieth-
ynyl-3-decylthiophene (10) resulted in near-infrared and
deep-red emissive BODIPY copolymeric dyes with emission
maxima of 758 nm and 694 nm (polymers C and D), respectively
(Fig. 5). Palladium-catalyzed Sonogashira polymerization of 2,6-
diethynyl-substituted BODIPY dyes (7) with 2,5-diiodo-3-
decylthiophene (8) resulted in red emissive BODIPY copolymeric
dye with emission maxima of 634 nm and 669 nm (polymer E).
All BODIPY copolymeric dyes display low fluorescence quantum
yields because of heavy sulfur atom effect (Table 1). Lifetimes of
BODIPY polymeric dyes are shorter than their monomeric dyes
(Table 1).
Solid state absorption and emission spectra were collected to
evaluate the effect of polymer aggregation on the optical properties
Fig. 6. TGA curves for the BODIPY-based polymers (A, B, C, D).
as the absorption and emission spectra of the film reflect
pep
stacking effects between polymer backbones. The absorption
spectra of the polymers in thin films became a little broader, and
maximum peaks were obviously red-shifted compared with those
in methylene chloride solutions. The fluorescence spectra of the
polymers in solid state thin films retain most of the spectra features
in solution and exhibit further red shifts of their absorption and
emission maxima compared with those in methylene chloride
solution, indicating the presence of intermolecular electronic
interactions and/or increase in coplanarity of the polymer in the
solid state (Table 2).
corresponding to the ethynyl protons in 2,6-diethynyl BODIPY dye
(7) (Fig. 1), which further confirms Sonogashira polymerization via
the CeC triple bond. A similar result was also observed in 1H NMR
spectrum of polymer B (Fig. 2).
3.2. Optical properties of BODIPY polymeric and copolymeric dyes
The photophysical characteristics of BODIPY intermediate,
monomeric, and polymeric dyes were investigated in methylene
chloride. The absorption properties of the BODIPY dye 2 in meth-
ylene chloride solution are characterized by a strong S0 / S1
3.3. Thermal stabilities of the polymers
(
p
e
p*) transition at 502 nm and a weaker broad band at a shorter
wavelength around 356 nm due to the S0 / S2
(pe
p*) transition
Thermal stabilities of BODIPY polymeric and copolymeric dyes
were evaluated by thermogravimetric analysis (TGA) at the heating
rate of 20 ꢀC/min under nitrogen atmosphere. The thermograms
show that polymers A, B and C lost 5% of their weight at 250 ꢀC (the
decomposition temperature (Td) that corresponds to weight loss of
5%), which suggests good thermal stability (Fig. 6). Clear phase
transition in differential scanning calorimetry (DSC) of polymers
was not observed, which may arise because the rigid backbone of
the BODIPY causes transition temperatures greater than its
decomposition temperatures or because the glass transitions are
very broad.
[20] (Fig. 4). The introduction of diiodo substituent to the dipyr-
romethene core (2) results in a significant red shift (up to 33 nm
and 38 nm) of both the absorption and emission maxima of BODIPY
dye 3 corresponding to S0 / S1 (pe
p*) transition (Figs. 3 and 4),
and significantly quenches the fluorescence because of the heavy
atom effect (Table 1). Absorption and fluorescence spectra of 2,6-
diiodo-substituted BODIPY dye 3 exhibit good mirror symmetry
with similar band shapes for the absorption and emission spectra
which was also verified by measuring their full width at half-
maximum (Figs. 3 and 4). Further condensation of 2,6-diiodo
BODIPY dye bearing methyl substituents at 3 and 5 positions (3)
with aldehyde derivative (4) gave longer wavelength absorbing
BODIPY dyes bearing alkoxymonostyryl and alkoxydistyryl groups
4. Conclusion
(5, 6). The extended p-conjugation in these dyes results in signifi-
cant red shifts in both absorption and emission spectra compared
with their precursor BODIPY dye (3). Monostyryl-substituted
BODIPY dye (5) shows absorption and emission maxima at 579 nm
and 631 nm with red shifts of 79 nm and 121 nm in absorption and
emission spectra, respectively, compared with its starting BODIPY
dye (2). Distyryl-substituted BODIPY dye (6) displays further red
shifts of 165 nm and 170 nm in absorption and emission spectra
with absorption and emission maxima of 665 nm and 701 nm,
respectively, compared with its starting BODIPY dye (2) (Table 1).
Both monostyryl and distyryl-substituted BODIPY dyes (5, 6)
exhibit low fluorescence quantum yields because of the heavy atom
effect. Palladium-catalyzed Sonogashira polymerization of BODIPY
dyes (5, 6) with 2,6-diethynyl-substituted BODIPY (7) resulted in
near-infrared emissive BODIPY polymeric dyes (polymers A and B)
We have successfully synthesized new near-infrared emissive
BODIPY polymeric and copolymeric dyes (polymer A, B and C) by
palladium-catalyzed Sonogashira polymerization of BODIPY dyes
substituted with one and two styryl groups (5, 6) with 2,6-dieth-
ynyl-substituted BODIPY (7), and BODIPY dye bearing two styryl
groups (6) with 2,5-diethynyl-3-decylthiophene (9), respectively.
Chemical and photophysical characterizations confirm that BODIPY
units were indeed incorporated into the polymer backbones
through triple-bond connection between BODIPY cores at positions
2 and 6. By analogous synthetic approaches a variety of functional
groups such as cancer-homing peptides and carbohydrates could be
introduced through long flexible oligo(ethylene glycol) tethered
spacers to near-infrared emissive BODIPY polymeric and copoly-
meric dyes at the meso-position of BODIPY cores for near-infrared
imaging biomedical applications. We will report these results in
due course.
with significant extension of
p-conjugation, relative to their
monomeric dye (5). Polymer A shows dramatic red shifts of 100 nm

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V.R. Donuru et al. / Polymer 51 (2010) 5359e5368
[6] Huh JO, Do Y, Lee MH. Organometallics 2008;27(6):1022e5.
Acknowledgements
[7] Hudnall TW, Gabbai FP. Chem Commun 2008;38:4596e7.
[8] Atilgan S, Ozdemir T, Akkaya EU. Org Lett 2008;10(18):4065e7.
[9] Zheng QD, Xu GX, Prasad PN. Chem Eur J 2008;14(19):5812e9.
[10] Donuru VR, Vegesna GK, Velayudham S, Green S, Liu HY. Chem Mater 2009;
21(10):2130e8.
[11] Meng G, Velayudham S, Smith A, Luck R, Liu HY. Macromolecules 2009;
42(6):1995e2001.
[12] Donuru VR, Vegesna GK, Velayudham S, Meng G, Liu HY. J Polym Sci Part A
Polym Chem 2009;47(20):5354e66.
H.Y. Liu acknowledges the Research Excellence Fund of Michigan
Technological University and the 21st Century Jobs Fund of Michi-
gan (contract number: 06-1-P1-0283) for support of the work. This
project was also partially supported by a National Research Initia-
tive Grant no. 2007-35603-17740 from the USDA Cooperative State
Research, Education, and Extension Service - Nanoscale Science and
Engineering for Agriculture and Food Systems.
[13] Cakmak Y, Akkaya EU. Org Lett 2009;11(1):85e8.
[14] Kim B, Ma B, Donuru VR, Liu H, Frechet JMJ. Chem Commun (Camb) 2010;
46(23):4148e50.
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