Synthesis and characterization of luminescent polystyrene derivatives with sterically protected fluorenyl- and carbazolylborane moieties

Article abstract of DOI:10.1021/ma200358s

Polystyrene was functionalized with luminescent fluorenyl- and carbazolylborane pendant moieties. Because of an interaction of the empty p orbital on boron with the extended π-systems of fluorene or carbazole, the resulting polymeric materials exhibit int

Full text of DOI:10.1021/ma200358s

ARTICLE
pubs.acs.org/Macromolecules
Synthesis and Characterization of Luminescent Polystyrene
Derivatives with Sterically Protected Fluorenyl- and
Carbazolylborane Moieties
Kshitij Parab, Ami Doshi, Fei Cheng, and Frieder J€akle*
Department of Chemistry, Rutgers University—Newark, 73 Warren Street, Newark, New Jersey 07102, United States
S Supporting Information
b
ABSTRACT: Polystyrene was functionalized with luminescent fluorenyl- and
carbazolylborane pendant moieties. Because of an interaction of the empty p
orbital on boron with the extended π-systems of fluorene or carbazole, the
resulting polymeric materials exhibit intense blue emission with maxima in the
range 390À420 nm. The solution quantum yields were 65% for the fluorene
derivative and 68 and 11% for two different carbazole derivatives, respectively.
The stability of the borylated polymers was enhanced by attachment of a bulky
triisopropylphenyl group to each of the boron centers. Thus, the polymers were
found to be stable for a period of over 1 month. Thermal stability up to ca. 250 °C
was confirmed by thermogravimetric analysis.
’ INTRODUCTION
which leads to quenching or a change of the emission color that
results in turn-on of fluorescence. We also demonstrated that
with ferrocene as one of the pendent organoborane substituents,
polymers that show interesting redox behavior can be obtained.12
In the course of these studies it became apparent that the stability
of these boron-containing polymers to oxygen and moisture can
be significantly enhanced by replacing 2,4,6-trimethylphenyl
(Mes) groups with more sterically demanding 2,4,6-triisopro-
pylphenyl (Tip) groups.13 Here we report the synthesis and
characterization of a new class of triarylborane polymers with
improved stability and favorable luminescence characteristics, as
a result of boron substitution with fluorene or carbazole deriva-
tives as chromophores and the presence of sterically demanding
Tip groups as protective groups.
Interaction of the empty boron-centered p-orbital in tricoor-
dinate organoboranes with a conjugated π-system is known to
give rise to interesting optical and electronic properties.1 Various
research groups have explored this pÀπ interaction in organo-
boranes with respect to its potential for applications, for instance,
as emissive materials for OLEDs, in linear and nonlinear optics,
and as sensors for nucleophiles.2 Polymeric materials have also
attracted much interest in recent years.3,4 Following the pioneer-
ing work by Chujo and co-workers,5 a broad range of main-chain
type luminescent organoborane polymers have been developed
over the past decade.6 The attachment of organoborane chro-
mophores as pendent or terminal groups to polyolefins and other
chain growth polymers has more recently attracted interest since
well-defined and more complex polymer architectures can more
easily be realized.4,7 For instance, Fraser and co-workers demon-
strated that functionalization of poly(lactic acid) (PLA) with
boron diketonate chromophores leads to room temperature
phosphorescent materials that are useful for tumor imaging,8
Chujo and co-workers reported on the functionalization of block
copolymers with highly emissive BODIPY functionalities,9 and
our group introduced amphiphilic block copolymers with orga-
noboron quinolato moieties that form micellar solutions in
water.10 In all these cases, the boron center is tetracoordinate
and the emissive properties are dominated by the organic
chromophore.
’ RESULTS AND DISCUSSION
A postpolymerization modification strategy similar to the one
introduced earlier for the preparation of ferrocenylborane-sub-
stituted polymers12 was chosen for the functionalization of
polystyrene with the desired chromophoric triarylborane moi-
eties. Polystyrene was decorated with BBr2 groups using a
siliconÀboron exchange protocol as previously reported.14
Then, one of the bromines on each of the BBr2 groups in PSBBr2
was replaced by reaction with a trimethylstannyl-substituted
fluorene or carbazole derivative (Scheme 1). The second bro-
mine was then exchanged for a methoxy group by reaction with
Me3SiOMe, and the resulting polymer species PSB(Ar)OMe
were treated with TipMgBr, leading to formation of the desired
In earlier work, we showed that attachment of tricoordinate
bithiophene(mesityl)borane chromophores to polystyrene re-
sults in fluorescent polymers with substitution-dependent ab-
sorption and emission characteristics.11 Moreover, the presence
of the tricoordinate organoborane moieties can be exploited for
the fluorescent detection of fluoride and cyanide, the binding of
Received: February 15, 2011
Revised:
June 24, 2011
Published: July 15, 2011
r
2011 American Chemical Society
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Scheme 1. Synthesis of Polymers with Pendent Fluorescent
Organoborane Moieties (Tip = 2,4,6-Triisopropylphenyl)
Figure 2. 13C NMR overlay of PSBTipCzSi and MBTipCzSi. Key: (a)
aliphatic region; (b) aromatic region.
Figure 1. Comparison of 11B NMR spectra of polymers and model
compounds.
triarylborane groups in PSBTipAr. Similar methods were used to
synthesize molecular model compounds MBTipAr that mimic
one of the polymer repeat unit (Scheme 1). The model com-
pounds and polymers were purified by column chromatography,
and the polymer solutions were subsequently precipitated first
into methanol and then from toluene into ethanol.
Both the polymers as well as model compounds were char-
acterized by multinuclear NMR spectroscopy. The 11B NMR
shifts for the model compounds were in the expected range for
triarylboron containing compounds with a very broad peak at
∼70 ppm (Figure 1). A significant upfield shift to ∼50 ppm and
narrowing of the signals was evident for the polymers, which may
be due to relaxation phenomena and shielding effects of neigh-
boring groups in the polymer chain, as suggested by our previous
studies on related triarylborane polymers.11,12 The presence of
small shoulder peaks in the 11B NMR spectra of the polymers
around 30À40 ppm was observed in some cases, possibly due to
the presence of a small amount of boronic acid (ArB(OH)2) or
borinic acid (Ar2BOH) functionalities as a result of incomplete
substitution with the functional aryl groups (Figure 1). The peaks
in the 1H NMR spectra of the polymers were broad and not very
informative, but integration of the protons in the aromatic and
aliphatic regions was close to the calculated number of protons
for each repeat unit of the polymer. Also, the 13C NMR spectra of
the polymers matched well with those of the model compounds,
thus supporting a structure in which the fluorene or carbazole
Figure 3. Thermogravimetric analysis (TGA) plots of polymers
PSBTipAr.
aryl groups as well as the 2,4,6-triisopropylphenyl moieties are
attached to boron (Figure 2).
The molecular weights from GPC-RI analysis in THF relative
to PS standards were higher than that of the silylated precursor
(Mn = 21100, Mw = 23800, PDI = Mw/Mn = 1.13), but in the
range expected considering the presence of much larger side
groups (PSBTipFl, Mw = 42800, Mn = 36900, PDI = 1.16; PSB-
TipCzSi, Mn = 38300, Mw = 44000, PDI = 1.15; PSBTipCzBr,
Mn = 32500, Mw = 37200, PDI = 1.14). The polydispersity
increased only slightly; however, a small high molecular weight
shoulder (%Area = 5À20) was observed in all cases, which
corresponds to about twice the molecular weight of the main
peak (%Area = 80À95), indicating that homocoupling at the end
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Table 1. Comparison of Photophysical Data of Polymers and
Model Compounds in Solution and as Thin Films
polymer
PSBTipFl
PSBTipCzSi
PSBTipCzBr
λabs [nm]a
λem [nm]b
332 (sh), 345
422
0.65e
285, 305, 345
271, 306, 342
392
0.11e
397
0.68
345
392
c
ΦF
λ
λ
abs film [nm]d
em film [nm]b,d
332, 346
396
312, 340
387
model
MBTipFl
MBTipCzSi
MBTipCzBr
λabs [nm]a
λem [nm]b
330 (sh), 341
390
286, 304, 344
410
269, 305, 341
391
0.12e
c
ΦF
0.80
0.72
a Data were acquired in CH2Cl2 solution unless noted otherwise.
b Excited at the longest wavelength absorption maxima. c Anthracene
used as a standard. d Thin film cast from toluene. e Measured in THF.
groups may have occurred to a small extent. An alternative
explanation is that substitution of the boron centers during the
attachment of the bulky Tip group was incomplete. As men-
tioned above, the presence of small shoulder peaks in the 11B
NMR spectra could be due to boronic acid (ArB(OH)2) or
borinic acid (Ar2BOH) functionalities, which might lead to the
formation of chemical cross-links giving rise to a small fraction of
higher molecular weight polymers.
Thermogravimetric analysis (TGA) data indicated that the
polymers are thermally stable up to ∼250 °C, above which
multistep decomposition was observed. The residual weights at
750 °C were 7À9% for PSBTipFl and PSBTipCzSi, while the
polymer PSBTipCzBr showed a residual weight of 23%
(Figure 3). The thermal stability and the residual ceramic yields
of the polymers are comparable to those of the previously
reported (bithiophene)mesitylborane-substituted polymers,11
thus indicating that the presence of the bulkier Tip group has
little to no effect on the thermal stability of the newly synthesized
fluorene and carbazole containing polymer.
However, the new polymers and the corresponding model
compounds show muchimproved stabilityto oxygen and moisture
in both solution as well as the solid state. For example, in C6D6 or
CDCl3, the model compound MBTipCzSi and polymer
PSBTipCzSi are stable for a period of ca. 1 month and in the
solid state they are stable toward both oxygen and moisture for
over 3 months. A similar trend is observed for the other model
compounds and polymers, thus indicating that the presence of a
more sterically demanding Tip group and a chromophore like the
fluorene or carbazole moiety significantly enhances the stability in
comparison to polymers11 that contain bithiophenes as the
chromophore and mesityl groups for steric protection.
The longest wavelength absorption maxima of the polymers in
CH2Cl2 solution are found in a narrow range from ca. 340 to
345 nm (Table 1, Figure 4). The spectrum of PSBTipFl shows a
single absorption maximum at 345 nm with a high-energy
shoulder at 332 nm, whereas for PSBTipCzSi we find multiple
bands at 285, 305, 345 nm and for PSBTipCzBr at 271, 306,
342 nm. The polymer spectra generally resemble those of the
respective model compounds. For example, PSBTipFl and
MBTipFl display absorption maxima at 345 and 341 nm, respec-
tively. Thin film absorption data also show very similar features to
those of the polymer solutions in CH2Cl2 (Figure S1, Supporting
Information).
Figure 4. Comparison of the normalized absorption and emission
spectra of (top) MBTipFl and PSBTipFl, (middle) MBTipCzSi and
PSBTipCzSi, and (bottom) MBTipCzBr and PSBTipCzBr in CH2Cl2
Solution.
Upon excitation at the longest wavelength absorption maxima,
the polymers and their respective model compounds emit bright
blue light in solution as well as in the thin film state (Figure 4,
Figure S1, Supporting Information). The emission of thin films
of PSBTipCzBr is similar to that of polymer solutions in CH2Cl2,
and both are almost unchanged in comparison to that of the
molecular model compound MBTipCzBr. This suggests that the
chromophore units act independently and excimer formation is
not favorable. In contrast, the emission spectra of the other
polymers and model compounds show some interesting trends.
While the emission maximum for the polymer PSBTipFl in
CH2Cl2 is red-shifted by ca. 30 nm relative to that of the model
compound MBTipFl, upon casting a thin film the emission shifts
back to higher energy giving rise to a profile similar to that of the
molecular species MBTipFl. These observations are attributed to
the generation of excimer states for PSBTipFl that result from
attachment of planar π-conjugated side groups to the atactic
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suggest that these compounds could be of interest for OLED
applications as well as in the recognition of anions on the basis of
changes in the fluorescence characteristics upon anion binding.
’ EXPERIMENTAL SECTION
Materials and Methods. n-BuLi (1.6 M in hexanes) and BBr3
(99.9%) were purchased from Acros, Me3SiOMe (98%) from Aldrich,
and Me3SnCl (98%) from Strem Chemicals. BBr3 was further purified by
vacuum distillation. Caution! BBr3 is toxic and highly corrosive and should be
handled appropriately with great care. Fluorinated grease was used for ground
glass joints in all reactions involving boron tribromide. The compounds
2,4,6-triisopropylphenylmagnesium bromide,16 2,7-dibromo-9,9-dihexyl-
fluorene,17 2-bromo-7-trimethylsilyl-9,9-dimethylfluorene,18 2-trimethyl-
stannyl-7-trimethylsilyl-9,9-dimethylfluorene, 2-trimethylstannyl-7-trimethyl-
silyl-9,9-dihexylfluorene, 3-bromo-6-trimethylsilyl-9-n-butylcarbazole,19
and 3,6-dibromo-9-(4-tert-butylphenyl)carbazole20 were synthesized ac-
cording to literature procedures. Poly(4-trimethylsilylstyrene) (PSSi) of
Mn = 21 100; Mw = 23 800; PDI = 1.13 (GPC-RI) was prepared as
previously reported.14 All reactions were carried out under inert atmosphere
using Schlenk techniques or a glovebox (Innovative Technologies). Ether
solvents were distilled from Na/benzophenone prior to use. Hydrocarbon
and chlorinated solvents were purified using a solvent purification system
(Innovative Technologies; alumina/copper columns for hydrocarbon
solvents), and the chlorinated solvents were subsequently distilled from
CaH2 and degassed via several freezeÀpumpÀthaw cycles.
Figure 5. Photographs illustrating the blue emission of a CH2Cl2
solution and of a thin film of PSBTipCzSi on a glass slide (excited with
a hand-held UV lamp at λmax = 365 nm).
polymer backbone. Formation of multiple excimer states has,
for example, been reported for poly(N-vinylcarbazole) and
poly(vinylnaphthalene).15 Packing effects in thin films of
PSBTipFl may lead to orientations of the side groups that
prevent effective formation of these excimer states, resulting in
the observed blue-shift of the emission. For the trimethylsilyl-
functionalized carbazole compounds, PSBTipCzSi and
MBTipCzSi, a different behavior was observed in that the
polymer emission (λem = 397 nm) is blue-shifted by ∼13 nm
in comparison to that of the model compound (λem = 410 nm)
and the emission of a polymer thin film (λem = 392 nm) is further
blue-shifted by ∼5 nm. The blue-shift of the emission of the
polymer PSBTipCzSi relative to its model system could also be a
result of the particular orientation of neighboring carbazole
groups in the polymer chain. Another possibility is that steric
effects of the polymer chains prevent optimal overlap of the
boron-centered empty p-orbital with the organic π-system,
leading to a less conjugated system.
Instrumentation. All 499.9 MHz 1H, 125.7 MHz 13C, 160.4 MHz
11B NMR, 99.3 MHz 29Si, and 186.4 MHz 119Sn NMR spectra were
recorded on a Varian INOVA spectrometer equipped with a boron-free
5 mm dual broadband gradient probe (Nalorac, Varian Inc., Martinez,
CA). Solution 1H and 13C NMR spectra were referenced internally to
solvent signals. 11B NMR spectra were referenced externally to BF3
3
Et2O(δ=0),119Sn NMR spectra were referenced to SnMe4 in C6D6 (δ=0)
and 29Si NMR spectra were referenced to SiMe4 in C6D6 (δ = 0). 11
B
NMR spectra were acquired with boron-free quartz NMR tubes. All
NMR spectra were recorded at ambient temperature unless noted
otherwise. The abbreviations Ph (phenyl), Hex (n-hexyl), Cz
t
(carbazolyl), Me (methyl), Bu (n-butyl), BuPh (4-tert-butylphenyl),
The fluorene and silylcarbazole polymers and model com-
pounds emit light with very high quantum yields of ca. 65À80%
(Table 1, see also Figure 5). These values are comparable to
those of the bithiopheneborane derivatives reported previously
(∼75% for the models and ∼66% for the polymers11). The
significantly lower quantum yield of PSBTipFl in comparison to
MBTipFl might be due to randomly distributed traps in the
polymer chains. PSBTipCzBr and the model MBTipCzBr show
comparatively much lower quantum yields of ca. 11À12%. The
lower quantum yields are attributed to the presence of the
bromine atoms, which induce quenching of fluorescence due
to heavy atom effects.
and Tip (2,4,6-triisopropylphenyl) are used for the peak assignments
and the labeling scheme shown here was applied.
Solution UVÀvisible measurements were performed in CH2Cl2
using a Varian Cary 500 scan UVÀvis-NIR spectrophotometer with a
1 cm quartz cuvette. The fluorescence data were measured on a Varian
Cary Eclipse fluorescence spectrophotometer using optically dilute
solutions (A < 0.1). Anthracene was used as the standard for determina-
tion of quantum yields (ϕ = 0.30)21 using a relative method that is
generally assumed to be accurate to (10%. An SCS|G3P-8 Spin Coat
System from Specialty Coating Systems Inc. was used to spin-cast thin
films from toluene on 1 cm Â1 cm glass slides from Fisher Scientific at
3000 rpm.
Gel permeation chromatography (GPC) analyses (THF, 1 mL/min)
were performed using a Waters Empower system equipped with a
717plus autosampler, a 1525 binary HPLC pump, a 2998 photodiode
array detector, and a 2414 refractive index detector. A series of styragel
columns (Polymer Laboratories; two 5 μm Mix-C columns in series),
’ CONCLUSIONS
In summary, we have prepared new organoborane polymers
that feature fluorene or carbazole moieties as the chromophores,
while steric protection of the boron centers is provided by bulky
Tip groups. The presence of the Tip groups imparts good
stability, to a much greater extent than what was observed
previously for related mesityl-substituted polymers. The poly-
mers are well soluble in common organic solvents such as
CH2Cl2, THF, and toluene. Both, polymers as well as model
compounds emit in the blue region of the spectrum and show
high quantum yields, except for the compounds that have a
bromo substituent attached to the chromophore. Our results
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which were kept in a column heater at 35 °C, were used for separation.
The columns were calibrated with narrow PS standards (Polymer
Laboratories). Thermogravimetric analyses (TGA) were performed
under N2 atmosphere using a Perkin-Elmer Pyris 1 system with ca.
5 mg of polymer at a heating rate of 10 °C/min from 50 to 750 °C.
GC-MS spectra were acquired on a Hewlett-Packard HP 6890 Series
GC system equipped with a series 5973 mass selective detector and a
series 7683 injector. A temperature profile with a heating rate of
20 °C/min from 50 to 300 °C was used. High resolution mass spectral
data for the complexes were obtained on an Apex-ultra 70 Hybrid FT-MS
(Bruker Daltonics) using electrospray ionization. Elemental analyses were
obtained from Quantitative Technologies Inc. Whitehouse, NJ.
mixture turned light green. The mixture was allowed to stir for 20 h at room
temperature, Me3SiOMe (0.55 mL, 3.99 mmol) was added neat, and the
solution was stirred for another 24 h. All volatile components were
removed under high vacuum. The greenish solid residue was taken up
into THF (10 mL), a solution of TipMgBr (0.35 M in THF, 7.2 mL,
2.5 mmol) was added, and the mixture was allowed to react for 1 h at room
temperature and then kept at reflux for 5 days. The polymer solution was
passed through a short alumina column using toluene as the eluent to
remove the magnesium salts. The solution was then concentrated to ca.
1.5 mL and precipitated into methanol (50 mL), followed by precipitation
from toluene into ethanol (50 mL). The product was dried, taken up into
benzene, and obtained as white powdery material upon freeze-drying from
benzene (0.15 g, 17%). For PSBTipFl, data are as follows. 11B NMR
Synthesis of 3-Trimethylstannyl-6-trimethylsilyl-9-n-bu-
tylcarbazole. A solution of nBuLi (1.6 M in hexanes, 10.2 mL, 16.3
mmol) was added dropwise over a period of 90 min to a solution of
3-bromo-6-trimethylsilyl-9-n-butylcarbazole (6.10 g, 16.3 mmol) in
diethyl ether (350 mL) at À78 °C. The mixture was stirred for 25
min and then allowed to slowly warm up to 0 °C. After cooling the
reaction mixture back down to À78 °C, a solution of Me3SnCl (3.40 g,
17.1 mmol) in ether (20 mL) was added dropwise. The mixture was
stirred at À78 °C for 3 h and then for an additional 12 h at ambient
temperature. Aqueous NH4Cl solution was added, and the organic layer
was extracted with ether. A yellowish-brown oily material was obtained
upon evaporation of the solvents. Crystallization from hot methanol
gave the pure product as a white crystalline solid (5.69 g, 76%). 1H NMR
(499.893 MHz, CDCl3): δ = 8.29 (s, 1H, Cz-4), 8.26 (s, 1H, Cz-5), 7.61
(d, 3J = 8.0 Hz, 1H, Cz-7), 7.54 (d, 3J = 8.5 Hz, 1H, Cz-2), 7.43 (d, 3J =
8.0 Hz, 1H, Cz-8), 7.29 (d, 3J = 8.0 Hz, 1H, Cz-1), 4.28 (t, 2H, 3J = 7.0 Hz,
Bu), 1.84 (m, 2H, Bu), 1.39 (m, 2H, Bu), 0.95 (t, 3H, 3J = 7.0 Hz, Bu),
1
(160.41 MHz, CDCl3): δ = 51 (w1/2 = 1000 Hz). H NMR (499.893
MHz, CDCl3): δ = 8.00À7.45 (br, 8H, Pho, Phm, Fl), 7.30À6.00 (very br,
4H, Phm, Tipm), 2.80 (very br, 1H, p-CHMe2), 2.37 (very br, 2H,
o-CHMe2), 1.90À0.50 (br m, 47H, o-CHMe2, p-CHMe2, polymer back-
bone, Hex), 0.29 (br, 9H, SiMe3); 13C NMR (125.69 MHz, CDCl3): δ =
151.8 (Fl), 149.0 (Tipo), 148.2 (Tipp), 141.6 (Fl), 138.0 (Fl), 137.0 (br,
Pho), 131.5 (Fl), 127.6 (br, Fl, Phm), 119.9 (Fl, Tipm), 40.3 (polymer
backbone), 35.3 (o-CHMe2), 34.3 (p-CHMe2), 31.5 (Hex), 29.7 (Hex),
24.3 (o-CHMe2, p-CHMe2), 22.6 (Hex), 14.1 (Hex), À0.7 (Me3Si), not
observed Phi/Tipi/Fli. GPCÀRI (THF vs PS standards): Mn = 36 900,
Mw = 42 800, PDI = 1.16, high molecular weight shoulder: Mn = 91800,
Mw = 99800, PDI = 1.08 (%Area = 78:22). TGA (10 °C/min; N2): 51%
weight loss between 215 and 280 °C; 20% weight loss between 315 and
400 °C; 10% weight loss between 437 and 570 °C; 7% residual mass at
800 °C. Anal. Calcd: C, 84.72; H, 9.90. Found: C, 80.12; H, 9.22.
Synthesis of PSBTipCzSi. A solution of BBr3 (0.41 g, 1.64 mmol)
in CH2Cl2 (10 mL) was added dropwise to a solution of PSSi (0.25 g,
ca. 1.42 mmol of Me3Si groups) in CH2Cl2 (10 mL) and stirred for
20 h. A solution of 3-trimethylstannyl-6-trimethylsilyl-9-n-butylcarba-
zole (0.93 g, 2.03 mmol) in CH2Cl2 (10 mL) was added dropwise and
the reaction mixture turned light green. The mixture was allowed to stir
for 20 h at room temperature, Me3SiOMe (0.70 mL, 5.08 mmol) was
added neat, and the solution was stirred for another 24 h. All volatile
components were removed under high vacuum. The greenish solid
residue was taken up into THF (10 mL), a solution of TipMgBr (0.50 M
in THF, 9.0 mL, 4.5 mmol) was added, and the mixture was allowed to
react for 1 h at room temperature and then kept at reflux for 5 days. The
polymer solution was passed through a short alumina column using
toluene as the eluent to remove the magnesium salts. The solution
was then concentrated to ca. 1.5 mL and precipitated into methanol
(50 mL), followed by precipitation from toluene into ethanol (50 mL).
The product was dried, taken up into benzene, and obtained as white
powdery material upon freeze-drying from benzene (0.37 g, 43%). For
PSBTipCzSi, data are as follows. 11B NMR (160.386 MHz, CDCl3): δ =
2
0.30 (s/d, J(117/119Sn,H) = 52.5/54.5 Hz, 9H, SnMe3). 13C NMR
(125.69 MHz, CDCl3): 141.1, 141.0, 132.7 (s/d, 3J(117/119Sn, 13C) = 44
Hz), 130.7, 130.2, 129.1, 127.9 (s/d, 2J(117/119Sn, 13C) = 41 Hz), 125.7,
123.3, 122.7, 108.9 (s/d, 2J(117/119Sn, 13C) = 52 Hz), 108.5, 43.0, 31.4,
20.8, 14.1, À0.3, À9.0 (s/d, 1J(117/119Sn, 13C) = 333/347 Hz, SnMe3);
119Sn NMR (186.413 MHz, CDCl3): δ = À23.3; GCÀMS (t = 23.5
min): m/z (%): 459 [M+] (20), 444 [M+ À CH3] (100).
Synthesis of 3-Trimethylstannyl-6-bromo-9-(4-tert-butyl-
phenyl)carbazole. A solution of nBuLi (1.6 M in hexanes, 12.6 mL,
20.2 mmol) was added dropwise over a period of 90 min to a solution of
3,6-dibromo-9-(4-tert-butylphenyl)carbazole (9.40 g, 20.5 mmol) in
THF (350 mL) at À78 °C. The mixture was stirred for 25 min and
then allowed to slowly warm up to 0 °C. After cooling the reaction
mixture back down to À78 °C, a solution of Me3SnCl (4.00 g, 20.1
mmol) in THF (30 mL) was added dropwise. The mixture was stirred at
À78 °C for 3 h and then for an additional 12 h at ambient temperature.
Aqueous NH4Cl solution was added, and the organic layer was extracted
with CHCl3. A white solid was obtained upon evaporation of the
solvents. The product was further purified by crystallization from warm
hexanes (8.2 g, 75%). 1H NMR (499.893 MHz, CDCl3): δ = 8.29 (d,
4J = 2.0 Hz, 1H, Cz-4), 8.22 (s, 1H, Cz-5), 7.62 (d, 3J = 8.5 Hz, 2H, Pho),
7.53 (dd, 3/4J = 7.5/1.0 Hz, 1H, Cz), 7.47 (dd, 3/4J = 8.5/2.0 Hz, 1H,
Cz), 7.44 (d, 3J = 8.5 Hz, 2H, Phm), 7.42 (d, 3J = 8.0 Hz, 1H, Cz), 7.29 (d,
3J = 8.5 Hz, 1H, Cz), 1.44 (s, 9H, CMe3), 0.38 (s/d, 2J(117/119Sn,H) = 52.5/
54.5 Hz, 9H, SnMe3). 13C NMR (125.69 MHz, CDCl3): 151.0, 141.9,
139.7, 134.7, 133.7 (s/d, 3J(117/119Sn,13C) = 43 Hz), 132.1, 128.7, 128.0,
127.1, 126.7, 125.0, 123.2, 122.7, 112.8, 111.6, 110.3 (s/d, 2J(117/119Sn,13C) =
50 Hz), 35.1, 31.6, À9.0 (s/d, 1J(117/119Sn,13C) = 333/348 Hz, SnMe3);
119Sn NMR (186.413 MHz, CDCl3): δ = À22.6. GCÀMS (t = 35.0
min): m/z (%): 541 [M+] (19), 526 [M+ À CH3] (100).
1
49 (w1/2 = 1200 Hz). H NMR (499.893 MHz, CDCl3): δ = 8.40
(br, 1H, Cz-5), 8.11 (br, 1H, Cz-4), 7.77 (br, 1H, Cz-7), 7.52 (br, 2H,
Pho), 7.30À6.00 (very br, 7H, Phm, Tipm, Cz-1,2,8), 4.3À3.4 (very br,
2H, Bu), 2.80 (very br, 1H, p-CHMe2), 2.40 (very br, 2H, o-CHMe2),
1.90À0.50 (br m, 18H, o-CHMe2, p-CHMe2, Bu), 0.26 (br, 9H, SiMe3);
13C NMR (125.69 MHz, CDCl3): δ = 149.0 (Tipo), 147.9 (Tipp), 143.0
(Cz), 142.0 (Phi/Tipi), 141.3 (Cz), 137.9 (br, Pho), 136.4 (Cz), 133.3
(Czi), 131.6 (Cz), 129.7 (Cz), 129.6 (Cz), 127.1 (Phm), 125.9 (Cz),
123.6 (Cz), 122.6 (Cz), 120.0 (Tipm), 108.6 (Cz), 107.9 (Cz), 42.7
(Bu), 42À40 (polymer backbone), 35.4 (o-CHMe2), 34.3 (p-CHMe2),
31.2 (Bu), 24.3 (o-CHMe2, p-CHMe2), 20.6 (Bu), 13.9 (Bu), À0.4
(Me3Si); GPCÀRI (THF vs PS standards): Mn = 38300, Mw = 44000,
PDI = 1.15, high molecular weight shoulder: Mn = 79500, Mw = 81600,
PDI = 1.03 (%Area = 95:5). TGA (10 °C/min; N2): 56% weight loss
between 256 and 320 °C; 14% weight loss between 396 and 427 °C; 8%
residual mass at 750 °C. Anal. Calcd: C, 82.46; H, 8.90; N, 2.29. Found:
C, 80.43; H, 8.61; N, 2.32.
Synthesis of PSBTipFl. A solution of BBr3 (0.36 g, 1.44 mmol) in
CH2Cl2 (10 mL) was added dropwise to a solution of PSSi (0.21 g, ca.
1.19 mmol of Me3Si groups) in CH2Cl2 (10 mL) and stirred for 20 h. A
solution of 2-trimethylstannyl-7-trimethylsilyl-9,9-dihexylfluorene (0.99 g,
1.72 mmol) in CH2Cl2 (10 mL) was added dropwise and the reaction
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ARTICLE
Synthesis of PSBTipCzBr. A solution of BBr3 (0.31 g, 1.24 mmol)
in CH2Cl2 (10 mL) was added dropwise to a solution of PSSi (0.18 g, ca.
1.02 mmol of Me3Si groups) in CH2Cl2 (10 mL) and stirred for 20 h. A
solution of 3-trimethylstannyl-6-bromo-9-(4-tert-butylphenyl)carbazole
(0.79 g, 1.46 mmol) in CH2Cl2 (10 mL) was added dropwise, and the
reaction mixture turned light green. The mixture was allowed to stir for
20 h at room temperature, Me3SiOMe (0.45 mL, 3.26 mmol) was added
neat, and the solution was stirred for another 24 h. All volatile
components were removed under high vacuum. The greenish solid
residue was taken up into THF (10 mL), a solution of TipMgBr
(0.50 M in THF, 6.5 mL, 3.25 mmol) was added, and the mixture was
allowed to react for 1 h at room temperature and then kept at reflux for 5
days. The polymer solution was passed through a short alumina column
using toluene as the eluent to remove the magnesium salts. The solution
was then concentrated to ca. 1.5 mL and precipitated into methanol
(50 mL), followed by precipitation from toluene into acetone (50 mL).
After drying the product was obtained as an off-white powdery material
(0.31 g, 44%). For PSBTipCzBr, data are as follows. 11B NMR (160.386
(5 mL) was cooled to ca. À10 °C and added dropwise to a precooled
solution (À10 °C) of 4-tBuC6H4BBr2 (0.15 g, 0.49 mmol) in CH2Cl2
(5 mL). The greenish solution was allowed to warm to room tempera-
ture and then stirred for 1 h. Me3SiOMe (0.12 mL, 0.87 mmol) was
added neat and the resulting faint green reaction mixture was stirred for 1
h. All volatile components were removed under high vacuum. The
residue was taken up into THF (10 mL) and a solution of TipMgBr
(0.50 M in THF, 1.1 mL, 0.55 mmol) was added. The reaction mixture
was stirred at room temperature for 30 min and then heated to 80 °C for
4 days. The solvent was removed under high vacuum to leave behind a
green solid, which was extracted with hexanes. Purification by column
chromatography using alumina as the stationary phase and hexanes as
the eluent gave the product as a white powdery material (0.24 g, 76%).
For MBTipCzSi, data are as follows: 11B NMR (160.386 MHz, CDCl3):
1
δ = 69 (w1/2 = 2000 Hz). H NMR (499.893 MHz, CDCl3): δ =
8.69 (s, 1H, Cz-5), 8.28 (s, 1H, Cz-4), 7.84 (d, 3J = 8.5 Hz, 1H, Cz-7),
7.79 (d, 3J = 8.0 Hz, 2H, Pho), 7.63 (d, 3J = 8.0 Hz, 1H, Cz-8), 7.51 (d,
3J = 8.0 Hz, 2H, Phm), 7.44 (d, 3J = 8.0 Hz, 1H, Cz-2), 7.40 (d, 3J = 8.0
Hz, 1H, Cz-1), 7.03 (s, 2H, Tipm), 4.32 (t, 3J = 7.0 Hz, 2H, Bu), 2.98 (m,
1H, p-CHMe2), 2.54 (m, 2H, o-CHMe2), 1.89 (m, 2H, Bu), 1.44 (m, 2H,
1
MHz, CDCl3): δ = 50 (w1/2 = 1200 Hz). H NMR (499.893 MHz,
CDCl3): δ = 8.60À8.25 (br, 2H, Cz), 8.20À7.90 (br, 3H, Cz, Pho),
7.78À6.25 (br, 9H, Cz, CzÀPho,m, Phm, Tipm), 2.76 (very br, 1H,
p-CHMe2), 2.31 (very br, 2H, o-CHMe2), 1.90À0.30 (br m, 30H,
o-CHMe2, p-CHMe2, polymer backbone, CMe3). 13C NMR (125.69 MHz,
CDCl3): δ = 150.7 (Php, CzÀPhp), 148.8 (Tipo, Tipp, CzÀPho), 143.7
(Cz), 141.4 (Cz), 139.9 (Cz), 137.8 (Cz), 134.4 (Cz), 126.7 (Cz, Phm,
CzÀPhm), 123.2 (Cz), 122.1 (Cz), 120.0 (Tipm), 113.2 (Cz), 111.6 (Cz),
109.3 (Cz), 42À40 (polymer backbone), 35.0 (CMe3), 34.9 (o-CHMe2),
34.3 (p-CHMe2), 31.6 (CMe3), 24.3 (o-CHMe2, p-CHMe2). GPCÀRI
(THF vs PS standards): Mn = 32 500, Mw = 37 200, PDI = 1.14, high
3
Bu), 1.40 (s, 9H, CMe3), 1.35 (d, J = 7.0 Hz, 6H, p-CHMe2), 0.97
(m, 12H, o-CHMe2), 0.87 (m, 3H, Bu), 0.36 (s, 9H, SiMe3). 13C NMR
(125.69 MHz, CDCl3): δ = 154.4 (Php), 149.0 (Tipo), 148.2 (Tipp),
143.2 (Cz), 142.0 (Phi/Tipi), 141.5 (Cz), 140.7 (Tipi/Phi), 137.9 (Pho),
137.1 (Cz), 133.4 (Czi), 131.3 (Cz), 130.8 (Cz), 130.0 (Cz), 125.9 (Cz),
124.8 (Phm), 123.6 (Cz), 122.7 (Cz), 120.1 (Tipm), 108.8 (Cz), 108.0
(Cz), 43.2 (Bu), 35.5 (o-CHMe2), 35.2 (CMe3), 34.4 (p-CHMe2), 31.5
(CMe3), 31.4 (Bu), 24.5, 24.4, 24.3 (o-CHMe2, p-CHMe2), 20.8 (Bu),
14.1 (Bu), À0.3 (Me3Si). Anal. Calcd: C, 82.34; H, 9.42; N, 2.18. Found:
molecular weight shoulder: Mn = 79700, Mw = 81400, PDI = 1.02 (%Area
=
C, 81.69; H, 9.09; N, 2.14. High-res ESIÀMS (positive mode): m/z =
+ 12
96:4); TGA (10 °C/min; N2): 68% weight loss between 233 and 540 °C;
9% weight loss between 540 and 580 °C; 21% residual mass at 750 °C.
Anal. Calcd: C, 77.81; H, 7.11; N, 2.02. Found: C, 76.08; H, 6.82; N, 2.13.
Synthesis of MBTipFl. A solution of 2-trimethylstannyl-7-tri-
methylsilyl-9,9-dimethylfluorene (0.50 g, 2.09 mmol) in CH2Cl2
(5 mL) was cooled to ca. À10 °C and added dropwise to a precooled
solution (À10 °C) of 4-tBuC6H4BBr2 (0.35 g, 1.15 mmol) in CH2Cl2
(5 mL). The clear colorless reaction mixture was allowed to warm to
room temperature and then stirred for 1 h. Me3SiOMe (0.35 mL, 2.54
mmol) was added neat and the resulting reaction mixture was stirred for
1 h. All volatile components were removed under high vacuum. The
residue was taken up into THF (10 mL) and a solution of TipMgBr
(0.50 M in THF, 2.8 mL, 1.4 mmol) was added. The reaction mixture
was stirred at room temperature for 30 min and then heated to 80 °C for
4 days. The solvent was removed under high vacuum to leave behind a
colorless solid, which was extracted with hexanes. Purification by column
chromatography using alumina as the stationary phase and hexanes
as the eluent gave a white oily material. Extraction with acetonitrile
and drying of the residue under high vacuum gave the product as a
powdery white solid (0.38 g, 54%). For MBTipFl, data are as follows.
11B NMR (160.386 MHz, CDCl3): δ = 71 (w1/2 = 2100 Hz). 1H NMR
(499.893 MHz, CDCl3): δ = 7.84 (s, 1H, Fl), 7.78 (m, 5H, Pho, Fl), 7.60
(s, 1H, Fl), 7.54 (d, 3J = 8.0 Hz, 1H, Fl), 7.49 (d, 3J = 8.0 Hz, 2H, Phm),
7.00 (s, 2H, Tipm), 2.96 (m, 1H, p-CHMe2), 2.44 (m, 2H, o-CHMe2),
1.49 (s, 6H, Fl-Me2), 1.38 (s, 9H, CMe3), 1.34 (d, 3J = 6.5 Hz, 6H, p-
CHMe2), 0.97 (m, 12H, o-CHMe2) 0.33 (s, 9H, SiMe3). 13C NMR
(125.69 MHz, CDCl3): δ = 155.1 (Php), 154.0 (Fl), 153.0 (Fl), 149.0
(Tipo), 148.4 (Tipp), 142.7 (Fl), 142.2 (Phi), 141.2 (Fl), 140.6 (Tipi),
139.8 (Fl), 138.1 (Pho), 137.7 (Fl), 132.3 (Fl), 132.2 (Fl), 127.6 (Fl),
124.8 (Phm), 120.1 (Tipm), 119.4 (Fl), 47.0 (Fl-Me2), 35.6 (o-CHMe2),
35.2 (CMe3), 34.4 (p-CHMe2), 31.5 (CMe3), 27.2, 24.4, 24.3
(o-CHMe2, p-CHMe2), À0.6 (SiMe3).
664.4507 (calcd for [M + Na]
C
44
1H6011B14N28Si23Na 664.4488).
Synthesis of MBTipCzBr. A solution of 3-trimethylstannyl-6-
bromo-9-(4-tert-butylphenyl)carbazole (0.64 g, 1.18 mmol) in CH2Cl2
(5 mL) was cooled to ca. À10 °C and added dropwise to a precooled
solution (À10 °C) of 4-tBuC6H4BBr2 (0.31 g, 1.02 mmol) in CH2Cl2
(5 mL). This greenish solution was allowed to warm to room tempera-
ture and then stirred for 1 h. Me3SiOMe (0.35 mL, 2.54 mmol) was
added neat, and the resulting faint green reaction mixture was stirred for
another 1 h. All volatile components were removed under high vacuum.
The residue was taken up into THF (10 mL), and a solution of TipMgBr
(0.50 M in THF, 3.3 mL, 1.65 mmol) was added. The reaction mixture
was stirred at room temperature for 30 min and then heated to 80 °C for
4 days. The solvent was removed under high vacuum to leave behind a
green solid, which was extracted with hexanes. Purification by column
chromatography using alumina as the stationary phase and hexanes as
the eluent gave the pure product as a white powdery material (0.37 g,
50%). For MBTipCzBr, data are as follows. 11B NMR (160.386 MHz,
CDCl3): δ = 70 (w1/2 = 2000 Hz). 1H NMR (499.893 MHz, CDCl3):
δ = 8.61 (s, 1H, Cz-5), 8.25 (s, 1H, Cz-4), 7.85 (d, 3J = 8.0 Hz, 1H, Cz-7),
3
3
7.77 (d, J = 8.0 Hz, 2H, Pho), 7.62 (d, J = 8.5 Hz, 2H, CzÀPho),
7.49 (m, 5H, Phm, CzÀPhm, Cz-8), 7.41 (d, 3J = 8.5 Hz, 1H, Cz-2), 7.31
(d, 3J = 8.5 Hz, 1H, Cz-1), 7.03 (s, 2H, Tipm), 2.97 (m, 1H,
p-CHMe2), 2.51 (m, 2H, o-CHMe2), 1.43 (s, 9H, CzÀPhCMe3), 1.39
3
(s, 9H, CMe3), 1.35 (d, J = 7.0 Hz, 6H, p-CHMe2), 0.98 (m, 12H,
o-CHMe2). 13C NMR (125.69 MHz, CDCl3): δ = 154.6 (Php), 151.3
(CzÀPhp), 149.0 (Tipo), 148.4 (Tipp), 143.9 (Cz), 141.5 (Cz), 140.3
(Cz), 137.8 (Pho), 137.6 (Cz), 134.4 (Cz), 131.6 (Cz), 128.8 (Cz),
127.1 (CzÀPh), 126.7 (CzÀPh), 125.9 (Cz), 124.8 (Phm), 123.4 (Cz),
122.1 (Cz), 120.2 (Tipm), 113.4 (Cz), 111.8 (Cz), 109.5 (Cz), 35.6
(o-CHMe2), 35.2, 35.1 (CMe3/CzÀPhCMe3), 34.4 (p-CHMe2), 31.6,
31.5 (CMe3/CzÀPhCMe3), 24.5, 24.4, 24.3 (o-CHMe2, p-CHMe2), Phi
and Tipi not observed. High-res ESI-MS (positive mode): m/z = 764.3539
(calcd for [M + Na]+
C
1H5511B79Br14N23Na 746.3511). Anal.
12
Synthesis of MBTipCzSi. A solution of 3-trimethylstannyl-6-
trimethylsilyl-9-n-butylcarbazole (0.24 g, 0.52 mmol) in CH2Cl2
47
Calcd: C, 77.90; H, 7.65; N, 1.93. Found: C, 77.57; H, 7.65; N, 1.85.
5966
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Macromolecules
ARTICLE
’ ASSOCIATED CONTENT
C. L. Macromolecules 2009, 42, 3162–3169. Zhang, G.; Evans, R. E.;
Campbell, K. A.; Fraser, C. L. Macromolecules 2009, 42, 8627–8633.
(9) Nagai, A.; Miyake, J.; Kokado, K.; Nagata, Y.; Chujo, Y. J. Am.
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2010, 46, 3717–3719.
S
Supporting Information. UVÀvis and emission spectra
b
for thin films of the polymers. This material is available free of
charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail fjaekle@rutgers.edu.
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’ ACKNOWLEDGMENT
Acknowlegment is made to the National Science Foundation
(CHE-0809642 and MRI 0116066) for support of this research.
F.J. thanks the Alexander von Humboldt Foundation for a
Friedrich Wilhelm Bessel Research Award. We thank Dr. Roman
Brukh for acquisition of ESIÀMS data and Pangkuan Chen for
acquisition of 11B NMR data of MBTipCzSi.
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