Synthesis and characterization of a series of annelated benzotriazole based polymers with variable bandgap

Article abstract of DOI:10.1021/jo301281d

Here we report the synthesis and characterization of a series of annelated benzotriazole based polymers with variable bandgap. Benzobistriazole monomers reported by us previously were desymmetrized using partial reduction ring opening followed by ring closure to produce a wide range of annelated benzotriazole based monomers. These monomers were co-polymerized with a fluorene moiety to give polymers with bandgaps ranging from 1.16 to 2.41 eV.

Full text of DOI:10.1021/jo301281d

Article
pubs.acs.org/joc
Synthesis and Characterization of a Series of Annelated
Benzotriazole Based Polymers with Variable Bandgap
Teck Lip Dexter Tam,†,‡ Wanting Ye,† Hong Hup Ronnie Tan,† Feng Zhou,† Haibin Su,†
Subodh G. Mhaisalkar,†,‡ and Andrew C. Grimsdale*,†,‡
†School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798
‡Energy Research Institute @NTU (ERI@N), Nanyang Technological University, 50 Nanyang Drive, Singapore 637553
S
* Supporting Information
ABSTRACT: Here we report the synthesis and characterization of a
series of annelated benzotriazole based polymers with variable bandgap.
Benzobistriazole monomers reported by us previously were desymme-
trized using partial reduction ring opening followed by ring closure to
produce a wide range of annelated benzotriazole based monomers. These
monomers were co-polymerized with a fluorene moiety to give polymers
with bandgaps ranging from 1.16 to 2.41 eV.
diamine.21 However, reductions of BBTa and its derivatives are
to the best of our knowledge unreported to date.
INTRODUCTION
■
Benzotriazole based polymers have been recently attracting
attention as active materials for use in organic photovoltaics
(OPV), organic electrochromics (OEC), and organic light
RESULTS AND DISCUSSION
■
emitting diodes (OLED) due to the easy synthesis and
modification of the triazole moiety.1−12 As our interest is to
expand the variety of functional materials available for such
application, we have sought to exploit the benzo[1,2-d;4,5-
d′]bistriazole (BBTa) monomer units reported by us
previously13 by co-polymerizing them with a fluorene moiety.
The relatively high combined overall yield of the 2,6- and 1,6-
dialkylated BBTa monomers also led us to investigate possible
desymmetrization by selective reduction of the BBTa core, as
we have previously demonstrated in the case of benzo[1,2-c;4,5-
c′]bis[1,2,5]thiadiazole (BBT),14 so as to test the synthetic
versatility of using them as starting materials for other
annelated benzotriazole based materials. Such materials,
especially donor−acceptor co-polymers containing such units,
are of great interest as possible active components in
applications such as LEDs15 or solar cells16 where the tuning
of the optical bandgaps and/or orbital energies is an important
aspect in designing materials with optimal device performance.
Reduction of benzotriazole (BTa) has been reported by
several groups using different reducing agents such as sodium in
liquid ammonia,17 and N-substituted benzotriazoles can be
reduced with sodium in butanol18 or zinc19 or polaro-
graphically20 to give N-substituted o-phenylenediamines.
Reduction of 3,4,5,6-tetrachlorobenzotriazole was also reported
by using zinc with hydrochloric acid to give the corresponding
BBTa26 and BBTa16 were synthesized as previously
reported.13 Treatment of the BBTa derivatives with iron in
acetic acid yielded no reaction, unlike BBT, which underwent
reduction of one heterocyclic ring under these conditions.22
Instead, treatment with zinc gave rise to reductive ring opening
at one of the triazole rings in the BBTa core. By contrast this
reagent reduces both heterocyclic rings in BBT,22 thus
demonstrating the greater resistance of the triazole over the
thiadiazole ring toward reduction. Interestingly, reductive ring
opening involves the expulsion of a 2-position nitrogen in both
BBTa26 and BBTa16, which leads to the diamines 1a and 1b,
respectively (Scheme 1). Both 1a and 1b appear to be unstable
as their colors darken rapidly upon standing.23
The partial reduction of BBTa26 provides an alternate route
to the synthesis of the diamine 1a, which we have previously
obtained in a five-step synthesis with an overall yield of 7.6%
(Scheme 2).24 This alternate route takes one less step starting
from tetraaminobenzene tetrahydrobromide, requires less
forceful conditions, and produces potentially higher overall
yield (for isolatable shorter alkyl chains).
Syntheses of SBTa, SeBTa, TaQ1, and TaQ2 here were
analogous to that reported by us earlier24 except that the
diamine was not purified due to its instability. To synthesize
Received: July 17, 2012
Published: October 23, 2012
© 2012 American Chemical Society
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Scheme 1. Reduction of BBTa26 and BBTa16 Using Zinc
and Acetic Acid
Scheme 3. Ring Closure of 1a
Scheme 2. Synthesis of the C6 Analogue of 1a According to
the Literature; Overall Yield = 7.6%
a five-membered ring by incorporating sulfur/selenium, it is
possible to form an aromatic five-member imidazole ring by
adding a carbon atom. Thus H-ImBTa and CF3-ImBTa were
synthesized via an one-pot reductive ring opening of BBTa16
using the procedure above followed by ring closure using
formic acid or trifluoroacetic acid, respectively (Scheme 4).
Ring closure with benzoic acid did not yield the corresponding
ImBTa but gave a complex mixture of unidentified products. A
conventional route via benzotriazole would suggest the diamine
1a as the likely intermediate, followed by ring closure using the
appropriate acids and then alkylation. This would take a total of
Scheme 4. Synthesis of H-ImBTa and CF3-ImBTa via
BBTa16 (Five Steps in Total Starting from
Tetraaminobenzene Tetrahydrobromide) versus via
Benzotriazole (7 Steps in Total)
SBTa and SeBTa, BBTa26 was reduced, and the reaction
mixture was extracted. The crude 1a was then treated with N-
thionylaniline and TMSCl in pyridine or SeO2 in ethanol to
give SBTa and SeBTa ,respectively (Scheme 3). For TaQ1 and
TaQ2, after reduction of BBTa26, the reaction mixture was
filtered, and 1,2-diketone 2 or 3 was reacted with the filtrate to
give TaQ1 and TaQ2, respectively (Scheme 3). The yields
obtained via reduction of BBTa26 were all higher than by our
previous synthesis despite the instability of 1a (SBTa, 12.3% vs
lit. 6.4%; SeBTa, 10.8% vs lit. 6.6%; TaQ1, 14.4% vs lit. 6.2%;
TaQ2, 15.3% vs lit. 5.8%), suggesting this is a viable alternative
synthesis.
Though the alkyl amine on 1b does not allow aromatic
cyclization to form a six-membered ring using 1,2-diketones or
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Scheme 5. Synthesis of the Annelated Benzotriazole Based Polymers
a
Table 1. Characterization of P1−P7
HOMO (eV)
LUMO (eV)
CV Eg (eV)
solution opt Eg (eV)
thin film opt Eg (eV)
Mw × 10−4
PDI
b
P1
P2
P3
P4
P5
P6
P7
−5.04
−5.38
−5.09
−5.02
−5.22
−5.18
−5.35
−3.45
−3.27
1.59
2.11
1.36
1.16
1.52
1.37
1.51
2.04
1.22
1.10
1.36
1.23
2.32
2.53
2.15
0.88
0.83
0.77
0.84
0.91
2.93
2.87
1.87
1.95
1.79
1.52
1.66
b
b
b
b
b
−3.64 (−3.73)
−3.74 (−3.86)
−3.71 (−3.71)
−3.82 (−3.81)
1.45
1.28
1.51
1.36
b
−2.94
2.41
b
a
Electrochemical and photophysical properties were measured in chloroform. Determined from HOMO and optical bandgap.
Figure 1. (a) Solution (chloroform) and (b) thin film UV−vis−NIR absorption of P1−P7.
seven steps, versus five steps via tetraaminobenzene tetrahy-
drobromide with BBTa16 as intermediate.
polymers using the HOMO values from the oxidation onsets
and the optical bandgap. For polymers P3−P6 these values
match closely those we obtained from our best estimate of the
reduction onsets. Polymer P3 with a different alkyl chain has
recently been reported by another group, with properties
almost identical to those reported here by us.25 This polymer
has been used as an electron donor in a BHJ solar cell with a
promising efficiency of 2.56%.
Table 1 shows the series of annelated benzotriazole based
polymers with optical bandgap ranging from 1.16 to 2.41 eV
that can be achieved by simply changing the annelated ring in
the benzotriazole core. The increase in the bandgaps is in
accordance with the decreasing electron-accepting ability of the
The annelated benzotriazole based monomers, with the
exception of CF3-ImBTa because of its low yield, were
brominated using NBS, and the resultant dibromo derivatives
were Suzuki co-polymerized with fluorene diboronic acid
pinacol ester to yield the polymers P1−P7 (Scheme 5).
These polymers were characterized using UV−vis−NIR
absorption spectroscopy and cyclic voltammetry, the results
of which are shown in Table 1 and Figure 1. The reduction
onsets for polymers P1, P2, and P7 could not be detected,
while those for P3−P6 could not be determined unambigu-
ously. We therefore estimated the LUMO values for these
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Figure 2. DFT calculation of 6a−g via geometry optimization using B3LYP 6-31G+2(d,p) for 6a,b13 and 6e−g, 6-31G+2(3d,3p) for 6c,13 and 6-31+
+(3df,3pd) for 6d. The large alkyl groups were reduced to methyl groups for simplicity.
cores, and this can be taken with referral to previously studied
benzazoles and quinoxaline systems (ring 2 and 3).11,26 The
lowest bandgap was observed for P3 and P4, which seems to be
due to the hypervalent sulfur and selenium in the diazole
ring.27−29 A thorough study by Schanze et al. has shown that
these systems are better described by a three-center-four-
electron bond in which the central sulfur/selenium atom is
expected to have a +1 charge.30 This condition produces an
electron deficiency in these systems, which reduces the energy
of the LUMO. The selenium analogue P4 has lower bandgap
than the sulfur analogue P3 due to larger polarizability (as
shown by a larger contribution to the LUMO of 6d in Figure 2)
and electrochemical amphotericity of selenium.11 This is
followed by P5 and P6, which have the electron-accepting
pyrazine ring. P5 shows higher bandgap than P6 because the
biphenyls on the triazoloquinoxaline are less conjugated than
the bithienyls, leading to lower/less LUMO contribution/
stabilization. These trends are similar to those observed for
thiadiazoloquinoxalines reported by us previously.31,32 Replace-
ment of sulfur/selenium in P3/P4 with nitrogen resulted in a
higher bandgap P1 due to the significantly smaller contribution
from the nitrogen to the LUMO. According to the theoretical
calculations reported by us previously, changing the position of
the alkyl chain from the 2- to the 1-position from BBTa26 to
BBTa16 results to a large dihedral angle between the core and
thiophene on one side of the latter.13 This reduced conjugation
in BBTa16 is expected to repeat in the polymer backbone, and
thus P2 has a higher bandgap than P1. Replacement of the 2-
azo-nitrogen in the annelated triazole ring of P2 with carbon in
P7 results in a weaker electron-accepting imidazole ring. Thus
bandgap of P7 is expected to be higher than that of P2.
The optical bandgaps show that the electron-accepting
strength of the core can be assigned as SeBTa > SBTa > TaQ >
BBTa26 > BBTa16 > H-ImBTa. The results can also be
translated as 1,2,5-selenadiazole >1,2,5-thiadiazole > pyrazine
>2-triazole >1-triazole > imidazole. Instructively, the trend of
the optical bandgaps of these polymers follows the trend of the
theoretical bandgaps of the acceptor unit due to the common
fluorene donor unit.
non-regioregular. Such small shifts would be expected of P2
and P7 since packing of their polymer chains would be
inefficient. On the other hand, P1 is a planar and regioregular
polymer, and thus packing should be efficient, The same goes
for P5 and P6 since their aromatic substituents would provide
stronger π−π interactions. The heavy sulfur and selenium atom
in P3 and P4, respectively, result in stronger aggregation since
there are presence of strong electrostatic effect33 and secondary
bonding interaction.34
CONCLUSION
■
In conclusion, we have demonstrated the reductive ring
opening of BBTa26 and BBTa16 using zinc and acetic acid.
The diamine obtained from the reduction of the former can be
ring closed with the appropriate reagents to yield SBTa, SeBTa,
TaQ1, and TaQ2, by a more convenient and efficient route
than previously reported. The diamine obtained from the
reduction of the latter on the other hand can be ring closed
with formic acid or trifluoroacetic acid to yield H-ImBTa or
CF3-ImBTa, respectively. The annelated benzotriazole based
monomers were co-polymerized with a fluorene moiety, and
the resulting polymers showed bandgaps as low as 1.16 eV to as
high as 2.41 eV. Using this strategy of varying the annelated
ring, a wide variety of benzotriazole based derivatives with
different energy levels and bandgaps can be obtained. These
derivatives may find application in the field of organic
photovoltaics, organic field effect transistors, organic light
emitting diodes, and electrochromic displays where such
electronic properties are important.
EXPERIMENTAL SECTION
■
All reagents were purchased from commercial sources and used
without further purification, unless otherwise stated. Column
chromatography was carried out with silica gel (230−400 mesh),
and thin layer chromatography (TLC) were performed on silica gel 60
Al-backed plates (20 cm × 20 cm). 1H NMR data were obtained on a
400 MHz spectrometer with chemical shifts referenced to CDCl3.
Thin film UV−vis−NIR samples were prepared by spincoating 10 mg/
mL of polymer in chloroform. Cyclic voltammetry measurements were
recorded in ACS grade CHCl3 with 0.1 M tetrabutylammonium
hexafluorophosphate as supporting electrolyte (scan rate of 100 mV
s−1). The electrolyte was bubbled with nitrogen gas for 5 min prior to
measurement. The experiments were performed at room temperature
with a conventional three electrodes configuration consisting of a
platinum wire working electrode, a gold counter electrode, and an Ag/
AgCl in 3 M KCl reference electrode. The measured potentials were
UV−vis−NIR spectra in Figure 1 show a slight bathochromic
shift of the band edge from solution to thin film for P2 and P7,
while larger shifts were observed for P1, P3, P4, P5, and P6.
The amount of bathochromic shift can be viewed as the
amount of aggregation existing in the solid state. P2 and P7 are
the only polymers with highly twisted backbones and are also
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converted to SCE (saturated calomel electrode with reduction
potential of −4.4 eV relative to vacuum).
1.04 (t, 6 H, J = 7.6 Hz), 1.36 (m, 44 H), 1.83 (quintet, 4 H, J = 7.6
Hz), 2.38 (m, 1 H), 4.03 (t, 4 H, J = 6.4 Hz), 4.79 (d, 2 H, J = 6.4),
6.99 (d, 4 H, J = 8.8 Hz), 7.28 (dd, 2 H, J = 4.0, 0.8), 7.63 (m, 10 H),
7.89 (d, 4 H, J = 8.4), 8.96 (dd, 2 H, J = 0.8, 3.6). 13C NMR (CDCl3):
δ [ppm] 14.0, 14.3, 19.4, 22.8, 26.4, 27.1, 29.5, 29.78, 29.82, 30.1, 31.5,
31.7, 32.1, 39.3 57.9, 60.8, 67.9 114.9, 119.3, 126.2, 126.6, 128.2, 130.7,
131.4, 131.8, 132.7, 133.3, 136.0, 136.9, 141.3, 142.1, 151.3, 159.2.
Anal. Calcd for C72H89N5O2S2: C, 77.17; H, 8.00; N, 6.25; O, 2.86; S,
5.72. Found: C, 77.38; H, 8.14; N, 6.13; S, 5.54. MALDI-TOF-MS m/
z: 1117.27; calcd for C72H89N5O2S2 = 1120.64.
Atomistic simulation, using density function theory (DFT) at
B3LYP35,36 (which includes the gradient corrected exchange and
correlation functionals along with the exact exchange) method with
double-ζ quality basis functions 6-31G* (augmented with polarized
function for all non-hydrogen atoms) was used to optimize the
geometry of 6d−g molecules. Geometry was fully relaxed, and no
symmetry constraints were imposed during optimization using
Gaussian 09 code3 with a convergence criterion of 10−3 au on the
gradient and displacement and 10−6 auon energy and electron density.
Harmonic vibrational analyses showed no imaginary frequency,
indicating these structures are a local minimum. The obtained
HOMOs and LUMOs were visualized using GaussView 5.0.
TaQ2. The synthetic procedures were exactly the same as TaQ1.
BBTa26 (480 mg, 0.48 mmol) and 1,2-bis(5′-hexyl-2,2′-bithiophen-5-
yl)ethane-1,2-dione (320 mg, 0.58 mmol) were used. Column
chromatography was carried out on silica using hexane to hexane/
dichloromethane (4:1) to yield pure TaQ2 as a black amorphous solid
During reduction of 1a, the reaction mixture changes from red (PL
orange) to yellow (PL blue) upon completion. For 1b, reaction
mixture changes from PL green to PL blue. All reductions were
monitored using thin layered chromatography.
1
(287 mg, 51% overall). H NMR (CDCl3): δ [ppm] 0.92 (m, 12 H),
1.35 (m, 52 H), 1.73 (quintet, 4 H, J = 7.6 Hz), 2.36 (m, 1 H), 2.84 (t,
4 H, J = 7.6 Hz), 4.78 (d, 2 H, J = 6.4 Hz), 6.74 (d, 2 H, J = 3.6 Hz),
7.04 (d, 2 H, J = 4.0 Hz), 7.18 (d, 2 H, J = 3.2 Hz), 7.27 (dd, 2 H, J =
1.2, 4.0), 7.50 (d, 2 H, J = 4.0 Hz), 7.66 (dd, 2 H, J = 0.8, 4.4), 8.87
(dd, 2 H, J = 1.2, 4.0). 13C NMR (CDCl3): δ [ppm] 14.2, 14.3, 22.7,
22.8, 26.4, 28.9, 29.5, 29.79, 29.83, 30.1, 30.4, 31.70, 31.72, 32.1, 39.2,
60.7, 118.8, 123.2, 124.6, 125.1, 126.6, 130.6, 131.8, 131.9, 132.7,
134.6, 135.8, 139.9, 142.3, 142.6, 144.1, 146.6. Anal. Calcd for
C68H89N5S6: C, 69.87; H, 7.67; N, 5.99; S, 16.46. Found: C, 69.98; H,
7.90; N, 5.67; S, 16.45. MALDI-TOF-MS m/z: 1165.13; calcd for
C68H89N5S6 = 1168.86.
H-ImBTa. BBTa16 (0.82 g, 0.82 mmol) and zinc powder (2.15 g,
32.88 mmol) in 40 mL of acetic acid and 20 mL of THF were heated
at 60 °C for 1 day. Ten milliliters of formic acid was added on the
second day, and the reaction was heated to 80 °C for another 1 day.
Water and dichloromethane was added to the reaction mixture, and
the organic layer was washed thoroughly with water. The organic layer
was dried over anhydrous magnesium sulfate, and solvent was
removed. Column chromatography was carried out on silica using
hexane to hexane/dichloromethane (1:1) to yield pure H-ImBTa as a
yellow amorphous solid (50% yield).1H NMR (CDCl3): δ [ppm] 0.90
(m, 12 H), 1.27 (m, 80 H), 1.63 (m, 1 H), 2.32 (m, 1 H), 3.93 (d, 2 H,
J = 7.6 Hz), 4.72 (d, 2 H, J = 6.8), 7.20 (m, 2H), 7.28 (dd, 1 H, J = 1.2
Hz, 4.0 Hz), 7.53 (m, 2 H), 8.00 (s, 1 H), 8.85 (d, 1 H, J = 2.8 Hz).
13C NMR (CDCl3): δ [ppm] 14.2, 22.7, 22,8, 25.3, 25.7, 26.3, 29.4,
29.5, 29.6, 29.66, 29.69, 29.71, 29.74, 29.76, 29.95, 30.02, 30.5, 31.5,
31.7, 32.00, 32.03, 34.7, 38.0, 39.2, 51.5, 60.3, 103.0, 113.8, 126.8,
127.0, 127.2, 127.7, 129.7, 130.1, 133.3, 134.7, 136.7, 138.7, 141.6,
143.6, 149.2. Anal. Calcd for C63H105N5S2: C, 75.92; H, 10.62; N, 7.03;
S, 6.43. Found: C, 76.05; H, 10.67; N, 7.11; S, 6.17. MALDI-TOF-MS
m/z: 996.20; calcd for C63H105N5S2 = 996.67.
SBTa. BBTa26 (1.36 g, 1.36 mmol) and zinc powder (3.57 g, 54.53
mmol) in 130 mL of acetic acid and 65 mL of THF were heated at 60
°C for 1 day. Dichloromethane and water were added, and the organic
layer was washed thoroughly with water. The organic layer was dried
over anhydrous magnesium sulfate, and all volatiles were removed to
yield crude 1a. N-Thionylaniline (0.31 mL, 2.76 mmol) followed by
trimethylsilyl chloride (1.73 mL, 13.63 mmol) were added to the crude
1a dissolved in dry pyridine (15 mL) in a round-bottom flask purged
with nitrogen. The mixture was heated at 80 °C for 1 day and cooled
to room temperature. The mixture was poured into dichloromethane
and washed repeatedly with dilute hydrochloric acid. The organic layer
was collected, dried over anhydrous MgSO4, and filtered, and solvent
was removed. Column chromatography was carried out on silica using
hexane to hexane/dichloromethane (4:1) to yield pure SBTa as a
1
purple amorphous solid (379 mg, 41% overall). H NMR (CDCl3): δ
[ppm] 0.89 (t, 3 H, J = 7.2 Hz), 0.90 (t, 3 H, J = 7.2 Hz), 1.34 (m, 40
H), 2.34 (m, 1 H), 4.75 (d, 2 H, J = 6.4), 7.26 (dd, 2 H, J = 3.6, 4.8),
7.58 (dd, 2 H, J = 0.8, 4.8), 8.73 (dd, 2 H, J = 0.8, 3.6). 13C NMR
(CDCl3): δ [ppm] 14.3, 22.82, 22.83, 26.4, 29.5, 29.78, 29.80, 30.0,
31.7, 32.0, 39.3, 61.2, 111.8, 127.6, 129.3, 131.0, 137.3, 142.5, 149.7.
Anal. Calcd for C38H55N5S3: C, 67.31; H, 8.18; N, 10.33; S, 14.19.
Found: C, 67.46; H, 8.46; N, 10.10; S, 13.98. MALDI-TOF-MS m/z:
676.51; calcd for C38H55N5S3 = 678.07.
SeBTa. BBTa26 (0.97 g, 0.972 mmol) was reduced in the similar
manner as above. SeO2 (129 mg, 1.17 mmol) was added to the crude
1a in ethanol (40 mL) in a round-bottom flask purged with nitrogen.
The mixture was refluxed for 1 day and cooled to room temperature.
The ethanol solvent was removed using rotary evaporator, and the
residue was dissolved in dichloromethane and washed repeatedly with
water. The organic layer was collected, dried over anhydrous MgSO4,
and filtered, and solvent was removed. Column chromatography was
carried out on silica using hexane to hexane/dichloromethane (7:3) to
yield pure SeBTa as (253 mg, 36% overall).1H NMR (CDCl3): δ
[ppm] 0.89 (t, 3 H, J = 7.2 Hz), 0.90 (t, 3 H, J = 7.2 Hz), 1.32 (m, 40
H), 2.34 (m, 1 H), 4.70 (d, 2 H, J = 6.8), 7.25 (dd, 2 H, J = 3.6, 1.2),
7.59 (dd, 2 H, J = 0.8, 5.2), 8.75 (dd, 2 H, J = 0.8, 2.8). 13C NMR
(CDCl3): δ [ppm] 14.3, 22.81, 22.82, 26.4, 29.47, 29.48, 29.76, 29.79,
30.0, 31.7, 32.0, 32.1, 39.3, 61.3, 112.1, 127.5, 129.8, 131.2, 138.0,
143.3, 156.0. Anal. Calcd for C38H55N5S2Se: C, 62.96; H, 7.65; N,
9.66; S, 8.85; Se, 10.89. Found: C, 63.16; H, 7.71; N, 9.69; S, 8.87.
MALDI-TOF-MS m/z: 724.40; calcd for C38H55N5S2Se = 724.97.
TaQ1. BBTa26 (0.48 g, 0.48 mmol) was reduced in the similar
manner as above. The reaction mixture was filtered, and 1,2-bis(4′-
butoxybiphenyl-4-yl)ethane-1,2-dione (293 mg, 0.58 mmol) was
added. The reaction flask was purged with nitrogen and heated at
80 °C for 1 day. The reaction mixture was cooled to room temperature
and dichloromethane was added. The organic layer was washed
thoroughly with water, collected, and dried over anhydrous MgSO4,
and solvent was removed. Column chromatography was carried out on
silica using hexane to hexane/dichloromethane (3:1) to yield pure
CF3-ImBTa. The synthetic procedures were exactly the same as H-
ImBTa. BBTa16 (0.62 g, 0.62 mmol) and trifluoroacetic acid (7.5
mL) were used. Column chromatography was carried out on silica
using hexane to hexane/dichloromethane (3:2) to yield pure CF3-
1
ImBTa as a yellow liquid (23% yield). H NMR (CDCl3): δ [ppm]
0.89 (m, 12 H), 1.26 (m, 80 H), 1.57 (m, 1 H), 2.32 (m, 1 H), 4.19 (d,
2 H, J = 7.2 Hz), 4.75 (d, 2 H, J = 6.8), 7.25 (m, 2H), 7.29 (dd, 1 H, J
= 1.2 Hz, 4.0 Hz), 7.58 (m, 2 H), 8.88 (dd, 1 H, J = 1.2, 3.6 Hz). 13C
NMR (CDCl3): δ [ppm] 14.3, 22.8, 26,0, 26.4, 29.45, 29.50, 29.64,
29.70, 29.76, 29.79, 29.81, 29.83, 29.84, 30.5, 31.6, 32.04, 32.07, 37.8,
39.2, 51.1, 60.6, 104.5, 115.9, 119.0 (quartet, CF3, J = 272.3 Hz),
126.9, 127.3, 127.7, 129.0, 130.2, 131.1, 134.3, 134.4, 136.1, 138.5,
139.0, 144.4, 146.04 (quartet, C-2, J = 37.6 Hz). Anal. Calcd for
C64H104F3N5S2: C, 72.20; H, 9.85; F, 5.35; N, 6.58; S, 6.02. Found: C,
72.13; H, 9.99; N, 6.21; S, 6.17. MALDI-TOF-MS m/z: 1063.33; calcd
for C64H104F3N5S = 1064.67.
General Procedures for NBS Bromination. A 0.5 g portion of
the annelated benzotriazole monomer was dissolved in 40 mL of
chloroform (20 mL chloroform + 20 mL acetic acid for 6b and 6g),
and the reaction setup was filled with N2 and cooled in an ice bath.
Two equivalents of NBS was dissolved in 100 mL of chloroform and
was added dropwise. After the addition of NBS, the reaction mixture
was allowed to warm to room temperature and stirred overnight.
1
TaQ1 as a brown amorphous solid (260 mg, 48% overall). H NMR
(CDCl3): δ [ppm] 0.92 (t, 3 H, J = 6.8 Hz), 0.93 (t, 3 H, J = 6.8 Hz),
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Dilute aqueous sodium thiosulphate solution was added and stirred
well. The organic layer was collected, washed with deionized water,
and dried over anhydrous magnesium sulfate. Solvent was removed
from the filtrate, and column chromatography was performed using
gradient elution from pure hexane to hexane/DCM mixture (15%
DCM for 7a, 7c and 7d, 20% DCM for 7b, 7e and 7f, and 30% DCM
for 7g).
29.77, 29.98, 30.04, 30.7, 31.5, 32.0, 38.1, 39.2, 51.6, 61.2, 102.3, 113.2,
114.0, 116.0, 129.7, 129.9, 130.0, 130.4, 133.1, 136.2, 138.2, 138.3,
141.5, 143.3, 149.3. Anal. Calcd for C63H102Br2N5S2: C, 65.54; H, 8.99;
Br, 13.84; N, 6.07; S, 5.55. Found: C, 65.47; H, 9.01; N, 6.16; S, 5.49.
MALDI-TOF-MS m/z: 1153.49 (M+); calcd for C63H102Br2N5S2 =
1154.46.
General Procedures for Suzuki Polymerization. A 0.4 g
portion of the dibromo annelated benzotriazole monomer, 1 equiv of
fluorene diboronic acid pinacol ester, and 8 mol % Pd[PPh3]4 in 20
mL of toluene and 20 mL of 2 M K2CO3 was added into a round-
bottom flask purged with N2. The reaction was allowed to stirred at 80
°C for 2 days. The reaction mixture was extracted using dichloro-
methane and deionized water, and the organic layer was collected and
dried over anhydrous magnesium sulfate. The collected filtrate was
concentrated and precipitated in methanol twice.
1
7a: 85% yield. H NMR (CDCl3): δ [ppm] 0.89 (m, 12 H), 1.25−
1.44 (m, 80 H), 2.31 (m, 2 H), 4.75 (d, 4 H, J = 6.0), 7.19 (d, 2H, J =
4.0 Hz), 8.35 (br, 2 H). 13C NMR (CDCl3): δ [ppm] 14.3, 22.9, 26.5,
29.5, 29.8, 29.9, 30.1, 31.7, 32.1, 39.4, 60.7, 108.9, 116.2, 129.8, 130.5,
139.0, 140.6. Anal. Calcd for C62H102Br2N6S2: C, 64.45; H, 8.90; Br,
13.83; N, 7.27; S, 5.55. Found: C, 64.37; H, 8.99; N, 7.36; S, 5.42.
MALDI-TOF-MS m/z: 1152.24 (M+); calcd for C62H102Br2N6S2 =
1155.45.
1
7b: 91% yield. 1H NMR (CDCl3): δ [ppm] 0.88 (m, 12 H), 1.08−
1.38 (m, 80 H), 1.57 (m, 1 H), 2.31 (m, 1 H), 4.53 (d, 2 H, J = 7.6
Hz), 4.75 (d, 2 H, J = 6.4), 7.01 (d, 1 H, J = 3.6 Hz), 7.20−7.23 (m, 2
H), 8.69 (d, 1 H, J = 4.4 Hz). 13C NMR (CDCl3): δ [ppm] 14.3,
22.79, 22.84, 26.0, 26.3, 29.48, 29.51, 29.6, 29.75, 29.76, 29.79, 29.81,
30.0, 30.1, 30.9, 31.6, 32.1, 38.5, 39.3, 54.4, 61.0, 100.5, 114.2, 114.7,
118.2, 130.0, 130.3, 130.7, 131.2, 132.3, 135.4, 137.3, 138.6, 142.5,
145.3. Anal. Calcd for C62H102Br2N6S2: C, 64.45; H, 8.90; Br, 13.83; N,
7.27; S, 5.55. Found: C, 64.33; H, 9.01; N, 7.33; S, 5.43. MALDI-TOF-
MS m/z: 1154.03 (M+); calcd for C62H102Br2N6S2 = 1155.45.
P1: H NMR (CDCl3): δ [ppm] 0.80−0.86 (br, -CH3), 1.13−1.63
(br, -CH2), 2.11 (br, fluorene-CH2), 2.48 (br, -CH), 4.96 (br, N-CH2),
7.47−7.80 (br, Ar-H), 8.77 (br, Th-H). Anal. Calcd for
(C91H144N6S2)n: C, 78.84; H, 10.47; N, 6.06; S, 4.63. Found: C,
78.47; H, 10.40; N, 6.16; S, 4.62.
1
P2: H NMR (CDCl3): δ [ppm] 0.80−0.87 (br, -CH3), 1.07−1.39
(br, -CH2), 1.73 (br, -CH), 2.09 (fluorene-CH2), 2.42 (br, -CH), 4.70
(br, N-CH2), 4.84 (br, N-CH2), 7.51−7.85 (br, Ar-H), 9.00 (br, Th-
H). Anal. Calcd for (C91H144N6S2)n: C, 78.84; H, 10.47; N, 6.06; S,
4.63. Found: C, 78.45; H, 10.41; N, 6.20; S, 4.66.
1
1
P3: H NMR (CDCl3): δ [ppm] 0.79 (br, -CH3), 0.87 (br, -CH3),
7c: 82% yield. H NMR (CDCl3): δ [ppm] 0.88 (m, 6 H), 1.23−
1.10−1.46 (br, -CH2), 2.09 (br, fluorene-CH2), 2.43 (br, -CH), 4.89
(br, N-CH2), 7.12−7.77 (br, Ar-H), 8.58 (br, Ar-H), 8.88 (br, Th-H).
Anal. Calcd for (C67H95N5S3)n: C, 75.44; H, 8.98; N, 6.57; S, 9.02.
Found: C, 75.27; H, 8.99; N, 6.61; S, 8.81.
1.40 (m, 40 H), 2.27 (m, 1 H), 4.66 (d, 2 H, J = 6.4), 7.10 (d, 2H, J =
4.0 Hz), 8.26 (d, 2 H, J = 3.2 Hz). 13C NMR (CDCl3): δ [ppm] 14.3,
22.9, 26.4, 29.5, 29.8, 29.9, 30.1, 31.7, 32.1, 39.4, 61.2, 110.8, 117.8,
130.5, 131.1, 138.7, 141.8, 149.0. Anal. Calcd for C38H53Br2N5S3: C,
54.60; H, 6.39; Br, 19.12; N, 8.38; S, 11.51. Found: C, 54.49; H, 6.45;
N, 8.43; S, 11.53. MALDI-TOF-MS m/z: 836.83 (M+); calcd for
C38H53Br2N5S3 = 835.86.
1
P4: H NMR (CDCl3): δ [ppm] 0.79 (br, -CH3), 0.87(br, -CH3),
1.09−1.39 (br, -CH2), 2.07 (br, fluorene-CH2), 2.42 (br, -CH), 4.84
(br, N-CH2), 7.12−7.74 (br, Ar-H), 8.58 (br, Ar-H), 8.88 (br, Th-H).
Anal. Calcd for (C67H95N5S2Se)n: C, 72.26; H, 8.60; N, 6.29; S, 5.76;
Se, 7.09. Found: C, 72.02; H, 8.52; N, 6.38; S, 5.55.
1
7d: 88% yield. H NMR (CDCl3): δ [ppm] 0.88 (m, 6 H), 1.23−
1.38 (m, 40 H), 2.24 (m, 1 H), 4.58 (d, 2 H, J = 6.4), 7.09 (d, 2H, J =
4.0 Hz), 8.23 (d, 2 H, J = 3.6 Hz). 13C NMR (CDCl3): δ [ppm] 14.3,
22.8, 26.4, 29.5, 29.8, 29.9, 30.1, 31.6, 32.1, 39.3, 61.3, 110.9, 118.5,
130.3, 131.2, 139.3, 142.4, 154.9. Anal. Calcd for C38H53Br2N5S2Se: C,
51.70; H, 6.05; Br, 18.10; N, 7.93; S, 7.26; Se, 8.94. Found: C, 51.55;
H, 6.16; N, 8.03; S, 7.33. MALDI-TOF-MS m/z: 884.77 (M+); calcd
for C38H53Br2N5S2Se = 882.76.
1
P5: H NMR (CDCl3): δ [ppm] 0.74 (br, -CH3), 0.86 (br, -CH3),
1.00−1.42 (br, -CH2), 1.81 (br, OCH2-CH2), 2.03(br, fluorene-CH2),
2.37 (br, -CH), 4.02 (br, O-CH2), 4.83 (br, N-CH2), 7.00−8.00 (br,
Ar-H), 8.74 (br, Ar-H), 9.00 (br, Th-H). Anal. Calcd for
(C101H129N5O2S2)n: C, 80.38; H, 8.62; N, 4.64; O, 2.12; S, 4.25.
Found: C, 80.09; H, 8.51; N, 4.74; S, 4.18.
1
7e: 95% yield. 1H NMR (CDCl3): δ [ppm] 0.90 (m, 6 H), 1.04 (t, 6
H, 7.2 Hz), 1.23−1.30 (m, 40 H), 1.56 (sextet, 4 H, J = 7.2 Hz), 1.84
(quintet, 4 H, J = 6.8 Hz), 2.19 (m, 1 H), 4.04 (t, 4 H, J = 6.4 Hz),
4.54 (d, 2 H, J = 7.0), 7.01 (d, 4 H, J = 8.4 Hz), 7.13 (d, 2H, J = 4.0
Hz), 7.64 (m, 8 H), 7.76, (d, 4 H, J = 8.0 Hz), 8.51 (d, 2 H, J = 4.4
Hz). 13C NMR (CDCl3): δ [ppm] 14.1, 14.3, 19.4, 22.9, 26.3, 29.5,
29.77, 29.81, 29.83, 29.86, 30.1, 31.5, 31.6, 32.1, 39.2, 60.6, 67.9, 115.0,
118.3, 119.5, 126.2, 128.3, 129.4, 131.6, 131.8, 132.5, 132.6, 136.3,
137.3, 141.2, 141.5, 151.6, 159.2. Anal. Calcd for C72H87Br2N5O2S2: C,
67.64; H, 6.86; Br, 12.50; N, 5.48; O, 2.50; S, 5.02. Found: C, 67.53;
H, 6.91; N, 5.50; S, 5.20. MALDI-TOF-MS m/z: 1279.70 (M+); calcd
for C72H87Br2N5O2S2 = 1278.43.
P6: H NMR (CDCl3): δ [ppm] 0.79−0.92 (br, -CH3), 1.09−1.34
(br, -CH2), 1.72 (br, ArCH2-CH2), 2.02 (br, fluorene-CH2), 2.29 (br,
-CH), 2.83 (Th-CH2), 4.75 (br, N-CH2), 6.75−7.94 (br, Ar-H), 8.58
(br, Ar-H), 8.90 (br, Th-H). Anal. Calcd for (C97H129N5S6)n: C, 74.80;
H, 8.35; N, 4.50; S, 12.35. Found: C, 74.67; H, 8.30; N, 4.61; S, 12.18.
1
P7: H NMR (CDCl3): δ [ppm] 0.79−0.88 (br, -CH3), 1.09−1.24
(br, -CH2), 1.63 (br, -CH), 2.04 (fluorene-CH2), 2.31 (br, -CH), 4.00
(br, N-CH2), 4.72 (br, N-CH2), 6.97−8.08 (br, Ar-H), 8.56 (br, Ar-
H), 8.84 (br, Th-H). Anal. Calcd for (C92H145N5S2)n: C, 79.77; H,
10.55; N, 5.06; S, 4.63. Found: C, 79.67; H, 10.49; N, 5.19; S, 4.47.
ASSOCIATED CONTENT
■
7f: 93% yield. 1H NMR (CDCl3): δ [ppm] 0.90 (t, 6 H, J = 6.8 Hz),
0.95 (t, 6 H, 6.4 Hz), 1.22−1.45 (m, 52 H), 1.75 (quintet, 4 H, J = 7.6
Hz), 2.17 (m, 1 H), 2.86 (t, 4 H, J = 7.6 Hz), 4.57 (d, 2 H, J = 6.4 Hz),
6.76 (d, 2 H, J = 3.2 Hz), 7.01 (d, 2 H, J = 4.0 Hz), 7.04 (d, 2 H, J =
4.4 Hz), 7.19 (d, 2H, J = 3.6 Hz), 7.41 (d, 2 H, J = 4.0 Hz), 8.38 (d, 2
H, J = 3.6 Hz). 13C NMR (CDCl3): δ [ppm] 14.28, 14.30, 22.8, 22.9,
26.3, 29.0, 29.6, 29.82, 29.85, 29.89, 30.1, 30.4, 31.6, 31.7, 31.8, 32.1,
39.2, 60.5, 117.7, 119.2, 123.0, 124.7, 125.3, 129.2, 131.7, 131.9, 132.1,
134.7, 137.1, 139.4, 141.3, 142.8, 144.1, 146.7. Anal. Calcd for
C68H87Br2N5S6: C, 61.56; H, 6.61; Br, 12.05; N, 5.28; S, 14.50. Found:
C, 61.44; H, 6.73; N, 5.64; S, 14.55. MALDI-TOF-MS m/z: 1327.58
(M+); calcd for C68H87Br2N5S6 = 1326.65.
S
* Supporting Information
NMR and MALDI-TOF spectra of 6c−6g, CF3-ImBTa, 7a−
7g, and P1−P7; CV plots for P1−P7. This material is available
free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: acgrimsdale@ntu.edu.sg.
Notes
7g: 95% yield. 1H NMR (CDCl3): δ [ppm] 0.90 (m, 12 H), 1.09−
1.36 (m, 81 H), 2.28 (m, 1 H), 3.93 (d, 2 H, J = 7.2 Hz), 4.69 (d, 2 H,
J = 6.4), 6.95 (d, 1 H, J = 3.6 Hz), 7.15 (d, 1 H, J = 3.6 Hz), 7.19 (d, 1
H, J = 4.0 Hz), 7.92 (s, 1 H), 8.56 (d, 1 H, J = 4.0 Hz). 13C NMR
(CDCl3): δ [ppm] 14.2, 22.8, 25.8, 26.3, 29.4, 29.5, 29.6, 29.7, 29.75,
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by Robert Bosch (SEA) Pte. Ltd.
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Mhaisalkar, S. G.; Su, H.; Grimsdale, A. C. J. Mater. Chem. 2011, 21,
17798−17804.
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