A Nature-Inspired Conjugated Polymer for High Performance Transistors and Solar Cells

Article abstract of DOI:10.1021/acs.macromol.5b00542

A novel, highly soluble chromophore for use in organic electronics based on an indigoid structure is reported. Copolymerization with thiophene affords an extremely narrow band gap polymer with a maximum absorption at ～800 nm. The novel polymer exhibits high crystallinity and high ambipolar transport in OFET devices of 0.23 cm² V^-1 s^-1 for holes and 0.48 cm² V^-1 s^-1 for electrons. OPV device efficiencies up to 2.35% with light absorbance up to 950 nm demonstrate the potential for this novel chromophore in near-IR photovoltaics.

Full text of DOI:10.1021/acs.macromol.5b00542

Article
pubs.acs.org/Macromolecules
A Nature-Inspired Conjugated Polymer for High Performance
Transistors and Solar Cells
Kealan J. Fallon,† Nilushi Wijeyasinghe,‡ Nir Yaacobi-Gross,‡ Raja S. Ashraf,‡ David M. E. Freeman,†
Robert G. Palgrave,† Mohammed Al-Hashimi,§ Tobin J. Marks,∥ Iain McCulloch,‡
Thomas D. Anthopoulos,‡ and Hugo Bronstein*,†
†Department of Chemistry, University College London, Christopher Ingold Building, London WC1H 0AJ, U.K.
‡Centre for Plastic Electronics, Imperial College London, London SW7 2AZ, U.K.
§Department of Chemistry, Texas A&M University at Qatar, P.O. Box 23874, Doha, Qatar
∥Department of Chemistry, Materials Research Center, and Argonne-Northwestern Solar Energy Research Center, Northwestern
University, 2145 Sheridan Road, Evanston, Illinois 60208, United States
S
* Supporting Information
ABSTRACT: A novel, highly soluble chromophore for use in
organic electronics based on an indigoid structure is reported.
Copolymerization with thiophene affords an extremely narrow
band gap polymer with a maximum absorption at ∼800 nm.
The novel polymer exhibits high crystallinity and high
ambipolar transport in OFET devices of 0.23 cm2 V−1 s−1
for holes and 0.48 cm2 V−1 s−1 for electrons. OPV device
efficiencies up to 2.35% with light absorbance up to 950 nm
demonstrate the potential for this novel chromophore in near-IR photovoltaics.
INTRODUCTION
■
The development of novel organic conjugated polymers has
gained momentum in recent times due to their possible
applications in organic photovoltaic (OPV) and organic field-
effect transistor (OFET) devices where their lower cost, light
weight, and mechanical flexibility are all attractive properties.
Current high performance polymers have enabled OFET
devices with mobilities in excess of 2 cm2 V−1 s−1 and OPV
devices with power conversion efficiencies (PCEs) of over
8%.1−3 Ultra-narrow band gap conjugated polymers are of great
interest due to the ease of charge injection when incorporated
into ambipolar OFETs and also their near-IR optical absorption
for use in both tandem and transparent OPV devices.4
Considerable interest has focused on planar bis-lactam
containing polymers such as diketopyrrolopyrrole (DPP, 1)5
Figure 1. Bis-lactam containing compounds and polymer building
and isoindigo (2).6 The electron withdrawing nature of the
blocks.
lactam core alongside its planarity has enabled DPP and
isoindigo containing conjugated polymers to reach both OPV
PCEs and OFET mobilities.
functionalized indigoids have been investigated, and the
mobility can be slightly enhanced to 1.3 × 10−2 cm2 V−1 s−1
using 5,5′-dichloroindigo.11 Crucially, the use of naturally
occurring compounds as building blocks for materials in
organic electronics can begin to address the issues of
sustainability associated with them. As an example, Cibalackrot
(7,14-diphenyldiindolo[3,2,1-de:3′,2′,1′-ij][1,5]naphthyridine-
6,13-dione, INDP) is an indigo derivative first synthesized in
Indigo (3) is the most produced natural dye worldwide and
has a highly planar structure arising from intramolecular
hydrogen bonding between the oxygen and the amide protons
of the indol-3-one units.7 Upon photoexcitation, rotation about
the central carbon−carbon bond can effect trans−cis isomer-
ization8 as well as either single or double proton transfer,
resulting in rapid energy loss through internal conversion,
thereby negating any potential for OPV devices.9 As a
semiconductor in OFET devices, indigo has shown hole
mobilities up to 1 × 10−2 cm2 V−1 s−1.10 More recently,
Received: March 13, 2015
Revised: July 1, 2015
© XXXX American Chemical Society
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Scheme 1. Synthetic Route to the Novel INDT Monomer
Table 1. Physical and Optical Properties of INDT-T
a
a
a
b
c
d
e
c
f
soln
film
Mn
15700
Mw
49400
PDI
3.15
λ
(nm)
λ
(nm)
max
HOMO (eV)
LUMO (eV)
Eg (eV)
Ecgalc (eV)
max
797
790
c
−4.24
−3.02
d
1.22
e
1.32
a
b
Determined by SEC(PS) using PhCl as eluent. PhCl solution. Spin-coated from PhCl 5 mg/mL. Determined by XPS. HOMO + optical energy
gap. Determined by TD-DFT using B3LYP/6-31g*.
f
1914 by condensation of indigo and phenylacetyl chloride.12
Importantly, the molecule is locked in a highly planar rigid
conformation where proton transfer and trans−cis isomer-
ization are not possible. This highly conjugated compound has
similar functionality to compounds containing the popular bis-
lactam system, and hence polymers based on this structure
display interesting electronic properties. Remarkably, however,
there are almost no reports of IND implementation in organic
electronics. Glowacki et al. reported the use of the parent small
molecule in OFET devices to obtain reasonable OFET
mobilities,13 and very recently He et al. demonstrated its use
as a comonomer to achieve high field effect mobilities when
copolymerized with solubilizing comonomers.14 We were
interested in developing soluble IND derivatives which would
not require copolymerization with complex comonomers, and
here we report the first synthesis of such materials and their
potential for use in organic electronics. By demonstrating the
use of conjugated polymers containing naturally occurring and
potentially biosustainable building blocks, we believe that we
are taking important steps toward addressing the issue of
sustainability in organic electronics.
RESULTS AND DISCUSSION
■
The synthesis (Scheme 1) begins with protection of
commercially available 5-hydroxy-2-nitrobenzaldehyde (4)
with 3,4-dihydro-2H-pyran, followed by an aldol condensation
to give (E)-5,5′-bis((tetrahydro-2H-pyran-2-yl)oxy)-[2,2′-biin-
dolinylidene]-3,3′-dione (6). A subsequent condensation
reaction and concurrent deprotection of the tetrahydropyranyl
groups affords the 2,9-dihydroxy-7,14-di(thiophen-2-yl)-
diindolo[3,2,1-de:3′,2′,1′-ij][1,5]naphthyridine-6,13-dione
(INDT) compound 7. This compound was then alkylated with
2-octyldodecyl chains to improve solubility and then
subsequently brominated with N-bromosuccinimide to afford
our novel INDT monomer 9. Copolymerization via Stille
coupling of monomer 9 with simple bis(trimethylstannyl)-
thiophene affords polymer INDT-T, which was purified by
Soxhlet extraction using acetone, then hexane, to remove low
molecular weight oligomers, and finally chloroform. The dark
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green polymeric product is soluble in common organic solvents
such as chloroform and chlorobenzene.
The molecular mass of INDT-T was determined by
SEC(PS) to be Mn ∼ 15.7 kDa and Mw ∼ 49.4 kDa which,
although is perhaps lower than optimal, is sufficient to evaluate
the promise of this material in organic electronic devices. Figure
2a shows the solution (chlorobenzene) and thin film (spin-
coated from a 5 mg/mL solution in chlorobenzene) UV−vis
absorption spectra of INDT-T. Both spectra show a broad
featureless absorption in the near-IR with λmax ∼790 nm. The
spectrum becomes somewhat broadened on going from
solution to thin films which is attributed to solid state packing
effects, often observed in similar materials. The optical band
gap in the film can be estimated to be ∼1.22 eV, demonstrating
the effectiveness of the IND core at creating near-IR-absorbing
materials. The HOMO and LUMO energy levels were
determined by XPS, and the optical energy gaps are found to
be −4.24 and −3.02 eV, respectively. Both values are in a
similar range to typical DPP and isoindigo polymers, thus
showing that the IND containing polymers are an important
addition to the bis-lactam containing conjugated polymer
family.
The influence of annealing temperature on the molecular
packing in INDT-T thin films was studied by X-ray diffraction
(Figure 2b). Drop-cast polymer thin films (5 mg/mL solution
in chlorobenzene) show a Bragg reflection at 2θ = 3.8°,
corresponding to the (100) reflection and indicative of a typical
lamellar packing distance of 2.3 nm. Annealing at 100 °C for 10
min leads to a substantial increase in thin film crystallinity as
observed by the increased intensity of the (100) peak, though
we note that this improvement may not necessarily arise from
increased ordering of the π−π stacking in the thin film.15 The
appearance of the corresponding (200) reflection also indicates
increased long-range order. No noticeable changes in the film
crystallinity are observed after annealing at higher temperatures.
To investigate the electronic structure of the new polymer,
DFT calculations were carried out on model trimers with
methoxy substituents. The calculated energy gap is found to be
1.32 eV, in good agreement with experiment. Figure 3 shows
the HOMO and LUMO distributions of the geometry
optimized structure of INDT-T using Gaussian 09 (DFT,
B3LYP/6-31G*). The backbone displays a high degree of
Figure 2. (a) Normalized UV−vis absorption spectra of INDT-T.
Solution spectra were recorded in chlorobenzene, and thin films were
spun from a 5 mg/mL solution of INDT-T in chlorobenzene. (b) X-
ray diffraction of a drop-cast INDT-T film from a 5 mg/mL solution of
INDT-T in chlorobenzene.
Figure 3. (a) HOMO and (b) LUMO distributions of the geometry-optimized structure of INDT-T using Gaussian 09 (DFT, B3LYP/6-31G*).
C
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coplanarity indicating that charge transport in this material
should be efficient. Both the HOMO and LUMO are
delocalized well over both the thiophenes and the central bis-
lactam core. However, while there is little contribution to the
HOMO from the peripheral phenyl groups, there is substantial
delocalization of the LUMO onto these sites. This indicates
that further substitutions at these positions will enable
independent manipulation of the LUMO level without
disruption of the HOMO.
OFETs with top gate−bottom contact architecture were
fabricated using the novel polymer on glass substrates with
CYTOP dielectric. Al + Au bilayer (20 nm + 20 nm) electrodes
for ambipolar charge transport were used. The organic
semiconductor layer was spin-coated on top of the substrates
from a chlorobenzene solution (10 mg/mL). Finally, CYTOP
dielectric was spin-coated on top followed by a thermally
evaporated Al gate electrode. Representative transfer and
output characteristics are shown in Figure 4, and data are
determined from the best fit of the second derivative of transfer
curve saturation regime with the peak value measured being
0.52 cm2 V−1 s−1. The best-fit value for the electron mobility is
0.48 cm2 V−1 s−1 with a remarkable peak mobility of 1.2 cm2
V−1 s−1; however, we note that there was a significant amount
of noise present in the second-derivative mobility extraction
plot. As was shown in XRD experiments, we believe that the
improved OFET characteristics are due to the increased
ordering of the INDT-T polymer with annealing.
The threshold voltage for electrons is in the range of ∼20−
50 V which is comparable to values measured in DPP and
isoindigo-based OFETs. However, the large threshold voltages
for holes indicate an injection barrier. We attribute this to
nonoptimized matching of the electrodes and the polymer
HOMO. To overcome this, OFETs with UV-O3-treated Au
electrodes with an Al adhesion layer (40 + 5 nm) for optimized
hole injection due to a deeper work function were fabricated.
The results are shown in Table 3.
Only p-type transport is observed for these devices; however,
it is clear that both the measured hole mobility and threshold
voltage are significantly improved relative to the equivalent
devices presented in Table 2. This indicates that the larger
threshold voltages observed in the initial device data are likely
due to improper work function matching or suboptimal metal−
polymer contact. Bottom gate−bottom contact OFET devices
were also fabricated, but these suffered from significant
hysteresis and lower mobilities.
Conventional and inverted bulk-heterojunction OPV devices
were fabricated using a 1:2 blend of INDT-T:PC71BM as the
active layer spin-coated from a 4:1 CHCl3:ODCB solution (10
mg/mL). The J−V curves and EQE are shown in Figure 5, and
the data are presented in Table 4. The conventional OPV
device provides a PCE of 2.25%, with a short circuit current
(Jsc) of 6.27 mA cm−2, an open circuit voltage (Voc) of 0.62 V,
and a fill factor (FF) of 0.58. The relatively high open circuit
voltage is impressive considering the extremely narrow band
gap of INDT-T, and the devices all have relatively good fill
factors, indicating good charge extraction at low fields. The
inverted devices show similar overall efficiencies of 2.35% but
have slightly increased short circuit currents (Jsc = 6.88 mA
cm−2) and lower open circuit voltages (Voc = 0.59 V). Similar
variations between conventional and inverted OPV devices
have been shown before in DPP-based conjugated polymers.
The EQE shows that the majority of the photocurrent
originates from the fullerene absorption, but there remains an
appreciable contribution from the extremely near-IR absorbing
INDT-T polymer up to 950 nm. Despite the modest overall
efficiencies, these devices represent some of the highest
efficiencies from such ultranarrow band gap materials.16 We
believe that the lower contribution to the photocurrent is
predominantly due to insufficient energetic offset of the
polymer with respect to the fullerene.17 More importantly,
we demonstrate the first functioning OPV devices of this very
novel chromophore, indicating that it is well-suited for further
development in this field.
Figure 4. Transfer and output characteristics of an OFET devices of
INDT-T annealed at 200 °C.
CONCLUSION
compiled in Tables 2 and 3. The 100 °C annealed film
maximum hole and electron mobilities extracted from the
saturation regime of the transfer curves are both approximately
0.08 cm2 V−1 s−1, demonstrating good balanced ambipolar
behavior and negligible hysteresis. Annealing the devices at 200
°C leads to significant improvement in both the hole and
electron mobility. A high hole mobility of 0.23 cm2 V−1 s−1 is
■
We report the synthesis of a novel soluble monomer INDT for
use in conjugated polymers based on naturally occurring indigo.
Incorporation of this novel unit in a conjugated polymer,
INDT-T, results in an extremely narrow band gap material with
high crystallinity. This polymer exhibits high ambipolar
transport in OFET devices, with holes and electrons exhibiting
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Table 2. OFET Characteristics of INDT-T
ab
ab
,
c
,
annealing temp
channel length
μhole (peak value)
Ion/Ioff for
μelectron (peak value)
(cm2 V−1 s−1
Vth,electron
(V)
Ion/Ioff for
c
c
c
(°C)
(μm)
(cm2 V−1 s−1
)
Vth,hole (V)
holes
)
electrons
d
100
40
50
0.04 0.003
−120
−23
8
104
105
105
103
0.075 0.01
(0.11 0.03)
0.075
43
22
29
52
5
105
106
106
106
(0.046 0.002)
0.076
(0.09)
(0.094)
100
50
0.048
−90
0.079
(0.069)
(0.13)
e
200
0.23 0.01
−131
2
0.48
0
3
(0.52 0.08)
(1.2 0.05)
a
b
μhole and μelectron refer to the highest effective mobilities measured in the saturation regime for a gate-voltage range of 20 V. Peak values for
c
saturation regime mobility are given in parentheses next to the best-fit values because the second-derivative plots are noisier. The threshold voltages
(Vth) and the on-to-off ratios (Ion/Ioff) were extracted from the linear regime (Vd = −30 V (all devices) except for 200 °C annealed (−90 V) for holes
d
e
and Vd = 30 V (all devices) except for 40 μm device (60 V) for electrons). Average of four devices. Average of two devices.
Table 3. Hole Optimized OFET Characteristics of INDT-T
mobilities of 0.23 and 0.48 cm2 V−1 s−1, respectively.
Conventional and inverted OPV devices give efficiencies of
up to 2.35% with photocurrent generated up to 950 nm,
demonstrating the potential of this novel monomer unit for
implementation in near-IR OPV devices.
channel
ab
,
annealing
length
μhole (peak value)
Ion/I
off c
c
temp (°C)
(μm)
(cm2 V−1 s−1
)
Vth,hole (V)
for holes
104
d
100
30
0.1 0.01
(0.13 0.015)
−14 0.5
a
EXPERIMENTAL SECTION
μhole refers to the highest effective mobilities measured in the
■
b
Characterization. 1H NMR spectra were recorded at 400 MHz on
a Bruker Avance 400 spectrometer, at 500 MHz on a Bruker Avance
500 spectrometer, or at 600 MHz on a Bruker Avance 600
spectrometer in the stated solvent using residual protic solvent
CHCl3 (δ = 7.26 ppm, s) or DMSO (δ = 2.56 ppm, qn) as the internal
standard. 13C NMR spectra were recorded at 125 MHz on a Bruker
Avance 500 spectrometer or at 150 MHz on a Bruker Avance 600
spectrometer in the stated solvent using the central reference of
CHCl3 (δ = 77.0 ppm, t) or DMSO (δ = 39.52 ppm, septet) as the
internal standard. Mass spectra were obtained using either a VG70-SE
or MAT 900XP spectrometer at the Department of Chemistry,
University College London. X-ray diffraction (XRD) measurements
were carried out with a Bruker D4 Endeavor diffractometer equipped
with a nickel-filtered Cu Kα1 beam and a scintillation counter detector
and postsample graphite monochromator, using a current of 30 mA
and an accelerating voltage of 40 kV. UV−vis spectra were recorded on
a PerkinElmer Lambda 950 spectrophotometer.
saturation regime for a gate-voltage range of 20 V. Peak values for
saturation regime mobility are given in parentheses next to the best-fit
values because the second-derivative plots are noisier. The threshold
voltages (Vth) and the on-to-off ratios (Ion/Ioff) were extracted from
c
d
the linear regime (Vd = −30 V) for holes. Average of two devices.
Synthesis. 2-Nitro-5-((tetrahydro-2H-pyran-2-yl)oxy)-
benzaldehyde. 5-Hydroxy-2-nitrobenzaldehyde (5.09 g, 31 mmol)
and 3,4-dihydro-2H-pyran (13.7 mL, 0.15 mol) were dissolved in a 4:1
solution of dichloromethane:hexane (61 mL). p-Toluenesulfonic acid
(58 mg, 1 mol %) was suspended in dichloromethane (15 mL), and a
few drops of pyridine were added. The acidic mixture was then added
in one portion, and the reaction was stirred for 12 h. Solvent and
unreacted 3,4-dihydro-2H-pyran were then removed in vacuo to give a
brown oil which was purified by flash chromatography on silica gel
(4:1, PET:EtOAc, RF = 0.3) to give the product as a yellow oil (7.66 g,
100%). 1H NMR (400 MHz, CDCl3) δ: 10.49 (s, 1H), 8.17 (d, J = 9.0
Hz, 1H), 7.51 (d, J = 2.8 Hz, 1H), 7.33 (dd, J = 9.0, 2.8 Hz, 1H), 5.62
(t, J = 2.8 Hz, 1H), 3.84−3.74 (m, 1H), 3.71−3.63 (m, 1H), 1.96−
1.90 (m, 2H), 1.80−1.69 (m, 2H), 1.68−1.62 (m, 2H). LRMS (CI+)
m/z 252 [MH]+.
(E)-5,5′-Bis(benzyloxy)-[2,2′-biindolinylidene]-3,3′-dione. 2-Nitro-
5-((tetrahydro-2H-pyran-2-yl)oxy)benzaldehyde (2.3 g) was dissolved
in acetone (34.5 mL) and cooled to −10 °C. With vigorous stirring, a
0.2 M solution of potassium hydroxide (4.6 mL) was added dropwise
over 15 min, turning the solution pale yellow. After 30 min the
solution was warmed to 5 °C, and a 0.4 M solution of potassium
hydroxide (34.5 mL) was added dropwise slowly. When half of this
solution was added, the reaction turned deep green; once addition was
complete, the reaction was a dark green/blue color. After addition, the
reaction was covered and allowed to warm to room temperature and
stirred for 24 h. The solid was then collected by vacuum filtration and
washed with methanol until washings ran colorless to give a blue solid
Figure 5. (a) J−V characteristics of INDT-T:PC[70]BM solar cells.
(b) External quantum efficiency of the INDT-T:PC[70]BM solar cell.
Table 4. OPV Device Characteristics of INDT-T-Based Solar
Cells
architecture
Jsc (mA cm−2
)
Voc (V)
FF
PCE (%)
conventional
inverted
6.27
6.88
0.62
0.59
0.58
0.58
2.25
2.35
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(0.72 g, 34%). 1H NMR (600 MHz, CDCl3) δ: 8.76 (s, 2H), 7.42 (d, J
= 2.5 Hz, 2H), 7.22 (dd, J = 8.7, 2.5 Hz, 2H), 6.96 (d, J = 8.7 Hz, 2H),
5.34 (t, J = 3.3 Hz, 2H), 3.97−3.88 (m, 2H), 3.68−3.58 (m, 2H),
2.04−1.94 (m, 4H), 1.92−1.82 (m, 4H), 1.73−1.63 (m, 4H). LRMS
(CI+): m/z 463 [MH]+. HRMS Found (CI+): [MH]+ 463.18632;
C26H27N2O6 requires 463.18691.
7.54 (d, J = 3.9 Hz, 2H), 7.21 (d, J = 3.9 Hz, 2H), 7.07 (dd, J = 8.9, 2.4
Hz, 2H), 3.83 (d, J = 5.7 Hz, 4H), 1.83−1.75 (m, 2H), 1.48−1.41 (m,
4H), 1.41−1.36 (m, 4H), 1.36−1.17 (m, 56H), 0.91−0.83 (m, 12H).
13C NMR (150 MHz, CDCl3) δ: 158.1, 137.6, 136.6, 123.0, 129.2,
129.0, 126.8, 124.4, 122.4, 118.7, 111.0, 72.0, 51.0, 38.0, 32.0, 31.4,
30.2, 29.8, 29.5, 27.0, 22.8, 14.3. HRMS Found (ES−): [M − H]−
1221.4817; C68H91Br2N2O4S2 requires 1221.4787.
2,9-Dihydroxy-7,14-di(thiophen-2-yl)diindolo[3,2,1-de:3′,2′,1′-ij]-
[1,5]naphthyridine-6,13-dione. (E)-5,5′-Bis((tetrahydro-2H-pyran-2-
yl)oxy)-[2,2′-biindolinylidene]-3,3′-dione (2.2 g, 4.8 mmol), and 2-
(thiophen-2-yl)acetyl chloride (3.6 mL, 29 mmol) were dissolved in
anhydrous xylene (96 mL), and the reaction refluxed at 165 °C for 24
h. The blue reaction turned purple after 1 h. After 24 h the vapors
from the argon flow were no longer acidic. The reaction was
transferred to a 250 mL round-bottomed flask washing with methanol
and chloroform. All solvent was removed in vacuo to give a black
residue. The residue was taken up in methanol, and the yellow
methanol washings carefully decanted off, to leave the black solid in
the flask. After five methanol washings the solid was suspended in
methanol, and with stirring, 5% sodium hydroxide solution (20 mL,
2.5 equiv) was added. The solution immediately turned dark red and
then black and allowed to stir for 12 h. 6 M hydrochloric acid (4.1 mL,
24.8 mmol) was then added to neutralize the reaction. The methanol
and water were then removed in vacuo, and the resulting residue was
washed with a small amount of water which was carefully decanted off
to remove any salts. The solid was then taken up in acetone and
filtered off under reduced pressure. The resulting dark solid was
washed with water, acetone, and then methanol and air-dried to give a
Polymer INDT-T. 7,14-Bis(5-bromothiophen-2-yl)-2,9-bis((2-octyl-
dodecyl)oxy)diindolo[3,2,1-de:3′,2′,1′-ij][1,5]naphthyridine-6,13-
dione (60.1 mg, 49.1 μmol), tris(dibenzylideneacetone)dipalladium(0)
(2.6 mg, 2.8 μmol, 6 mol %), tri(o-tolyl)phosphine (3.47 mg, 11.4
μmol), and 2,5-bis(trimethylstannyl)thiophene (20.15 mg, 49.1 μmol)
were added to a dry 10 mL microwave vial equipped with a stirrer bar
and sealed. Chlorobenzene (2.5 mL) was added via syringe, and the
solution was degassed with argon for 30 min. The vial was then placed
in a microwave reactor and heated as follows: 10 min at 100 °C, 5 min
at 120 °C, 5 min at 140 °C, 5 min at 160 °C, and 20 min at 180 °C.
The vial was then allowed to cool, and the reaction had changed color
from sapphire blue to turquoise. The reaction mixture was added
dropwise slowly into rapidly stirring methanol (70 mL) and allowed to
stir for 2 h, forming fine dark blue fibers. The polymeric material was
then filtered under reduced pressure into a cellulose thimble and
washed with methanol and then acetone. The polymer was purified by
Soxhlet extraction as follows: acetone for 12 h, hexane for 12 h, and
chloroform for 12 h. The chloroform was then concentrated to give a
turquoise plastic-like film on the round-bottomed flask. This film was
dissolved in a minimum volume of hot chlorobenzene (∼2.5 mL) and
then added dropwise slowly into rapidly stirring methanol cooled to 0
°C. Once addition was complete, the methanol was stirred for 30 min,
filtered under vacuum, washed carefully with methanol and then a
small amount of acetone, then allowed to dry, forming a dark blue film.
The polymer was air-dried for 1 h, placed in a vial, and dried under
vacuum for 12 h (49 mg, 87%). GPC (PS): Mn = 15687, Mw = 49381,
PDI = 3.15. UV (PhCl) λmax 797, (thin film) λmax 790.
1
black solid (0.7 g, 29%). H NMR (600 MHz, DMSO) δ: 10.03 (s,
2H), 8.22 (d, J = 8.7 Hz, 2H), 7.96 (d, J = 4.5 Hz, 2H), 7.74 (d, J = 3.6
Hz, 2H), 7.53 (d, J = 2.4 Hz, 2H), 7.35 (dd, J = 4.5, 3.6 Hz, 2H), 7.07
(dd, J = 8.7, 2.4 Hz, 2H). LRMS (ES+) m/z 507 [MH]+. HRMS
Found (ES+): [MH]+ 507.0482; C28H15N2O4S2 requires 507.0473.
2,9-Bis((2-octyldodecyl)oxy)-7,14-di(thiophen-2-yl)diindolo[3,2,1-
de:3′,2′,1′-ij][1,5]naphthyridine-6,13-dione. 2,9-Dihydroxy-7,14-di-
(thiophen-2-yl)diindolo[3,2,1-de:3′,2′,1′-ij][1,5]naphthyridine-6,13-
dione (0.7 g, 1.4 mmol), potassium carbonate (2.67 g, 19 mmol), and
9-(bromomethyl)nonadecane (1.25 g, 3.5 mmol) were dissolved in
dimethylformamide (28 mL) and heated at 60 °C with stirring for 24
h. The reaction was then cooled and poured into a separating funnel
containing brine and hexane. The organic layer was extracted with
brine (5 × 50 mL), separated, and filtered under reduced pressure to
remove black particulates. The purple organic filtrate was then dried
over magnesium sulfate, filtered, and concentrated in vacuo to give a
purple oil. The crude oil was purified by flash chromatography on silica
gel (9:1, PET: EtOAc, RF = 0.2) to give a pure purple oil (119 mg,
ASSOCIATED CONTENT
* Supporting Information
■
S
Experimental details, characterizations, and NMR spectra. The
Supporting Information is available free of charge on the ACS
Publications website at DOI: 10.1021/acs.macromol.5b00542.
AUTHOR INFORMATION
Corresponding Author
*E-mail: h.bronstein@ucl.ac.uk (H.B.).
■
1
8%). H NMR (600 MHz, CDCl3) δ: 8.40 (d, J = 8.9 Hz, 2H), 7.74
Notes
(dd, J = 3.6, 0.8 Hz, 2H), 7.69 (dd, J = 5.1, 0.8 Hz, 2H), 7.65 (d, J =
2.5 Hz, 2H), 7.27−7.24 (m, 2H), 7.08 (dd, J = 8.9, 2.5 Hz, 2H), 3.81
(d, J = 5.8 Hz, 4H), 1.81−1.73 (m, 2H), 1.47−1.40 (m, 4H), 1.40−
1.35 (m, 4H), 1.35−1.20 (m, 56H), 0.90−0.84 (m, 12H). 13C NMR
(150 MHz, CDCl3) δ: 158.5, 158.0, 138.0, 134.8, 130.3, 130.2, 130.1,
127.1, 126.3, 125.1, 122.5, 118.4, 118.3, 111.0, 71.9, 38.0, 32.0, 31.4,
30.2, 29.8, 29.7, 29.5, 26.9, 22.8, 14.3. LRMS (ES−) m/z 1065 [M −
H]+.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors gratefully acknowledge support of this work from
the Qatar National Research Fund project number: 7-286-1-
046.
7,14-Bis(5-bromothiophen-2-yl)-2,9-bis((2-octyldodecyl)oxy)-
diindolo[3,2,1-de:3′,2′,1′-ij][1,5]naphthyridine-6,13-dione. 2,9-Bis-
((2-octyldodecyl)oxy)-7,14-di(thiophen-2-yl)diindolo[3,2,1-
de:3′,2′,1′-ij][1,5]naphthyridine-6,13-dione (119 mg, 0.11 mmol) was
dissolved in dichloromethane (15 mL), and the solution was cooled to
0 °C. N-Bromosuccinimide (43 mg, 0.24 mmol) was added all at once
to the stirring solution, and the reaction was covered and kept at 0 °C
for 30 min. The ice bath was then removed, and the reaction was
allowed to warm to room temperature and stir for a further 12 h. After
1 h the solution had changed from purple to sapphire blue. After 12 h,
the reaction was diluted with further dichloromethane, washed with
water (2 × 30 mL) and then brine (30 mL), dried over magnesium
sulfate, and concentrated to give a waxy solid. Methanol was added to
the flask and to give a suspension, which was then collected by vacuum
filtration to give a pure blue waxy solid (60 mg, 44%). 1H NMR (600
MHz, CDCl3) δ: 8.34 (d, J = 8.9 Hz, 2H), 7.67 (d, J = 2.4 Hz, 2H),
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