Solution processable donor-acceptor oligothiophenes for bulk-heterojunction solar cells

Article abstract of DOI:10.1039/b926203b

Novel p-type and low bandgap penta- and hexa-thiophenes asymmetrically endcapped with solubilizing triarylamine or triarylamino-substituted carbazole dendron and dicyanovinyl groups, namely, PhNOF-OT(n)-DCN and G ₂-OT(n)-DCN, respectively where n = 5-6 for solution-processable photovoltaic applications have been synthesized and investigated. With the incorporation of a solubilizing electron-donating group, the highly extended oligothiophenes are highly soluble in common organic solvents and solution-processable. Upon extending the oligothiophene backbone, there is a strong increase in the absorption around 420 nm in addition to the intramolecular charge-transfer absorption (520 nm) which results in a strong spectral broadening. The optical band-gap of these donor-acceptor oligothiophene thin-films greatly reduces to 1.85 eV. The solution-processed bulk heterojunction PV cells fabricated from these materials blended with PCBM as an acceptor showed a PCE up to 1.72% with V_oc = 0.79 V in an as-fabricated device. Our findings also suggest that highly extended donor-acceptor oligomers can be useful for a p-type, low-bandgap semiconductor for solution-processable bulk heterojunction PV cells.

Full text of DOI:10.1039/b926203b

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PAPER
www.rsc.org/materials | Journal of Materials Chemistry
Solution processable donor–acceptor oligothiophenes for bulk-heterojunction
solar cells†
a
Weifeng Zhang, Shing Chi Tse, Jianping Lu, Ye Tao and Man Shing Wong
b
b
b
a
*
*
Received 14th December 2009, Accepted 24th December 2009
First published as an Advance Article on the web 2nd February 2010
DOI: 10.1039/b926203b
Novel p-type and low bandgap penta- and hexa-thiophenes asymmetrically endcapped with
solubilizing triarylamine or triarylamino-substituted carbazole dendron and dicyanovinyl groups,
namely, PhNOF-OT(n)-DCN and G2-OT(n)-DCN, respectively where n ¼ 5–6 for solution-processable
photovoltaic applications have been synthesized and investigated. With the incorporation of
a solubilizing electron-donating group, the highly extended oligothiophenes are highly soluble in
common organic solvents and solution-processable. Upon extending the oligothiophene backbone,
there is a strong increase in the absorption around 420 nm in addition to the intramolecular charge-
transfer absorption (520 nm) which results in a strong spectral broadening. The optical band-gap of
these donor–acceptor oligothiophene thin-films greatly reduces to 1.85 eV. The solution-processed bulk
heterojunction PV cells fabricated from these materials blended with PCBM as an acceptor showed
a PCE up to 1.72% with Voc ¼ 0.79 V in an as-fabricated device. Our findings also suggest that highly
extended donor–acceptor oligomers can be useful for a p-type, low-bandgap semiconductor for
solution-processable bulk heterojunction PV cells.
a small molecule PV cell based on the blend of a benzothiadiazole
Introduction
derivative and C61-PCBM showed a PCE of 2.4% in the annealed
device.7 A high PCE of 3.0% has very recently been demon-
strated based on an oligothiophene-diketopyrrolepyrrole and
C71-PCBM blend.8 To achieve a high efficiency heterojunction
PV cell, it is fundamentally important to develop new p-type p-
conjugated small molecules with a narrow energy bandgap to
harvest more solar radiation and a high charge carrier mobility
to transport the photogenerated charges to the electrodes.9
Oligothiophenes endcapped with triarylamino and dicyano-
vinyl or tricyanovinyl groups, which exhibit low optical gap
absorption and possess a large enough LUMO level offset with
the PCBM acceptors for efficient exciton dissociation, have been
shown to be useful for a high performance bilayer heterojunction
photovoltaic cell.10 Nevertheless, these molecules were not suit-
able for solution-processable bulk heterojunction PV cells. For
application in solution-processable bulk heterojunction PV cells,
the materials need to have good solubility and thin-film forming
properties.8 To promote the solution-processable properties of
small molecule donors, we have developed a novel series of
highly extended oligothiophenes asymmetrically endcapped with
a solubilizing triarylamine or triarylamino-substituted dendron
and a dicyanovinyl group as a p-type, low-optical-gap semi-
conductor for solution-processable bulk heterojunction PV cells.
The use of a highly extended p-conjugated system not only
lowers the optical bandgap and promotes strong p–p stacking of
conjugated backbones but also increases the absorption and
broadens the absorption spectrum as compared to the lower
homologues.
Organic photovoltaic (PV) cells, which directly convert sunlight
into electricity, have drawn considerable attention from both
academia and industry because of their promise as low-cost,
lightweight, renewable energy sources.1 Heterojunction PV cells
based on solution-processable conjugated p-type semiconducting
materials blended with a soluble fullerene derivative, [6,6]-phenyl
C61-butyric acid methyl ester (PCBM) offer advantages of facile
and large-area fabrication on flexible substrates by various
printing or coating techniques or a roll-to-roll process2 affording
high power conversion efficiencies (PCE) of greater than 6%
recently.3 However, the structural characteristics including
molecular weight, polydispersity, and regioregularity as well as
the purity of the polymer greatly affect its functional properties,
the performance and the stability4 of the resulting devices. In
addition to polymers, p-conjugated small molecules have been
found attractive as alternative solution-processable p-type donor
materials because of monodispersity, ease of obtaining in high
purity and reproducible properties. Nevertheless, the use of
solution-processable small molecules for PV applications has
drawn considerable attention.5 Recently, a PCE of 1.17% was
obtained from a solution-processed BHJ solar cell using an
anthracene-core donor and C61-PCBM acceptor.6 In addition,
aDepartment of Chemistry and Centre for Advanced Luminescence
Materials, Hong Kong Baptist University, Kowloon Tong, Hong Kong,
SAR, China. E-mail: mswong@hkbu.edu.hk
bInstitute for Microstructural Sciences (IMS), National Research Council
of Canada (NRC), 1200 Montreal Road, Ottawa, ON K1A 0R6, Canada.
E-mail: Ye.Tao@nrc-cnrc.gc.ca
We report herein the synthesis and molecular properties of
novel p-type and low bandgap penta- and hexa-thiophenes
asymmetrically endcapped with solubilizing triarylamine or tri-
arylamino-substituted carbazole dendron and dicyanovinyl
† Electronic supplementary information (ESI) available: Physical
characterization and spectra of new compounds. See DOI:
10.1039/b926203b
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Scheme 1 Synthesis of triarylamine dicyanovinyl asymmetrically disubstituted oligothiophenes, PhNOF-OT(n)-DCN, n ¼ 5 or 6.
groups, namely, PhNOF-OT(n)-DCN and G2-OT(n)-DCN,
respectively where n ¼ 5–6 for solution-processable photovoltaic
applications. With the incorporation of a solubilizing electron-
donating group, the highly extended oligothiophenes are highly
soluble in common organic solvents and solution-processable.
The optical band-gap of these donor–acceptor oligothiophene
thin-films greatly reduces to 1.85 eV. The solution-processed
bulk heterojunction PV cells fabricated from these materials
blended with PCBM as acceptors showed a PCE up to 1.72%
with Voc ¼ 0.79 V in an as-fabricated device. Our findings also
suggest that highly extended donor–acceptor oligomers can be
used as a p-type, low-bandgap semiconductor for solution-
processable bulk heterojunction PV cells.
Results and discussion
The synthesis of novel triarylamine and dicyanovinyl asymmet-
rically disubstituted oligothiophenes is outlined in Scheme 1. By
adapting the convergent approach used previously,10 the palla-
dium-catalyzed Suzuki cross-coupling of 7-diphenylamino-9,9-
di-n-decylfluorenyl-2-boronic acid 1 and iodobithiophene 2 in
the presence of Pd(PPh3)4 as a catalyst afforded the desired
Scheme 2 Synthesis of triarylamino-substituted carbazole dendron and dicyanovinyl asymmetrically disubstituted oligothiophenes G2-OT(n)-DCN, n
¼ 5 or 6.
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diphenylaminofluorenyl-substituted bithiophene 3 in 73% yield.
Lithiation of 3 at ꢀ78 ꢁC followed by quenching with trime-
thylborate and subsequently acid hydrolysis afforded the corre-
sponding boronic acid 4 in a good yield. The palladium catalyzed
Suzuki cross-coupling of 7-diphenylamino-9,9-di-n-decyl-
fluorenyl-50-bithiophene-5-boronic acid 4 with iodoter- or iodo-
quater-thiophenecarboxaldehyde 5a or 5b afforded the desired
diphenylaminofluorenyl-substituted penta- and hexa-thio-
phenecarboxaldehydes, 6a and 6b, respectively in good yields
(78–80%). Condensation of these aldehydes 6a or 6b, with
malononitrile in the presence of pyridine in refluxing chloroform
afforded the desired donor–acceptor oligothiophenes PhNOF-
OT(n)-DCN, n ¼ 5 or 6 in excellent yields. Furthermore, the
synthesis of novel triarylamine-substituted carbazole dendron
and dicyanovinyl asymmetrically disubstituted oligothiophenes
is outlined in Scheme 2. 5-{3,6-Bis[4-(diphenylamino)-1-phe-
nyl]carbazol-9-yl}-2-bithiophene-boronic acid, 7 was prepared
according to the previously published protocol.5f The palladium
catalyzed Suzuki cross-coupling of boronic acid 7 with iodoter-
or iodoquater-thiophenecarboxaldehyde 5a or 5b afforded the
desired triarylamine-substituted dendritic penta- and hexa-thio-
phenecarboxaldehydes, 8a and 8b, respectively in good yields
(80–83%). Similarly, subsequent condensation of 8a or 8b with
malononitrile afforded the triarylamine-substituted carbazole
dendron and dicyanovinyl asymmetrically disubstituted oligo-
thiophenes G2-OT(n)-DCN, n ¼ 5 or 6 in 89–91% yields. All the
newly synthesized donor–acceptor oligothiophenes were fully
characterized with 1H NMR, 13C NMR, MALDI-TOF MS, and
elemental analysis and found to be in good agreement with their
structures.
The thermal behaviour and stability of these donor–acceptor
oligothiophenes were investigated by DSC and TGA analyses,
respectively. The results are summarized in Table 1. The triar-
ylamine-substituted oligothiophenes, PhNOF-OT(n)-DCN
exhibit no apparent glass transition except a melting transition
(Tm) in the range of 199–217 ꢁC; on the other hand, the dendron-
substituted oligothiophenes, G2-OT(n)-DCN show distinct and
ꢁ
high glass transition temperatures with Tg > 144 C suggesting
that these dendrimers can form morphologically stable amor-
phous thin films. All the oligothiophenes exhibiꢁt an excellent
thermal stability with Td in the range of 440–515 C. (Fig. 1)
The absorption spectra of these donor–acceptor oligothio-
phenes measured in chloroform and DMSO as shown in Fig. 2
are composed of three broad and structureless absorption bands,
a weak to strong absorption in the range of 310–330 nm corre-
sponding to the n / p* transition of the arylamine moiety of the
triarylamine-based donating group, a moderate to strong
absorption around 410–420 nm corresponding to the transition
of the extended oligothiophene core, and the long wavelength
abs
absorption (l ) around 520 nm corresponding to the intra-
abs
max
max
molecular charge-transfer (ICT) transition. The l
remains
fairly constant for PhNOF-OT(n)-DCNs and shifts slightly to
a longer wavelength for G2-OT(n)-DCNs when the oligothienyl
core extends from five to six indicating the approach of the
effective conjugation length for the series. It is worth mentioning
that in addition to ICT, the enhancement of the absorption
around 420 nm upon extending the oligothiophene backbone
gives rise to a strong spectral broadening. These oligomers also
exhibit an inverted solvatochromic effect upon an increase in
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Fig. 2 Absorption spectra of PhNOF-OT(n)-DCN and G2-OT(n)-DCN
in (a) chloroform and (b) DMSO.
Fig. 1 (a) DSC traces of G2-OT(n)-DCN. (b) TGA traces of PhNOF-
OT(n)-DCN and G2-OT(n)-DCN.
photovoltaic cells was explored. The bulk heterojunction PV cells
with a device structure of ITO/PEDOT : PSS/oligomer : PCBM/
LiF (1 nm)/Al (120 nm) were fabricated by the spin-casting of
a PEDOT-PSS layer and then a blend of oligomer : PCBM layer
followed by vacuum deposition of LiF and Al as the cathode. The
PV responses of these devices were measured under AM 1.5
simulated solar illumination at an irradiation intensity of
100 mW cmꢀ2. The results of the device performance are
summarized in Table 2. Most of the devices have relatively large
Voc (ꢂ 0.8 V) because of the low-lying HOMO levels of these
oligothiophenes (ꢂ ꢀ5.2 eV) resulting in larger differences to the
LUMO level of PCBM. The devices with a thicker active layer
have better PCEs and fill factors. By increasing the film thickness
from 100 nm to 160 nm, devices fabricated with 1 : 2 G2-OT(6)-
DCN:PCBM ratios exhibit a significant increase in Jsc and PCE
up to 1.12% with Voc of 0.79 V (Fig. 4). It is known that the carrier
mobility of a blended film is greatly influenced by the
donor : acceptor ratio. G2-OT(6)-DCN:PCBM-based devices
with a ratio of 1 : 4 exhibit decreases in Jsc, Voc and thus, PCE. In
sharp contrast, devices fabricated with 1 : 4 PhNOF-OT(5)-
DCN:PCBM ratios exhibit dramatic enhancement in Jsc (to 5.41
mA cmꢀ2) and FF (¼ 0.40) with a PCE up to 1.72% (Fig. 5). The
external quantum efficiency (EQE) measurements show that
the PhNOF-OT(5)-DCN-based device exhibits a very broad
polarity of solvent. There is no observable fluorescence emission
abs
upon irradiating at l
which is attributed to the strong charge-
max
transfer character of these donor–acceptor oligothiophenes.
These oligomers showed pronounced peak broadening and red
shifts of ꢂ40 nm of absorption cutoff upon formation into thin
films which is attributed to the planarization of aryl rings and the
presence of interchain interactions in the solid state, resulting in
the optical band gap reducing to 1.85 eV.
Both PhNOF-OT(n)-DCNs and G2-OT(n)-DCNs exhibit very
similar electrochemical redox behavior. All the oligothiophenes
showed three oxidation waves with Eoxd1 at 0.30–0.35 V, Eoxd2 at
0.39–0.48 V, and Eoxd3 at 0.73–0.86 V (E1/2 (Fc/Fc+) ¼ 0.49 V vs.
SCE) corresponding to the sequential removal of electrons from
the arylamino group(s), the oligothiophene core or the interior
carbazole moieties, and the oligothiophene core, respectively.
(Fig. 3) They also exhibit two reduction waves (Ered1 ¼ ꢀ1.50 V
and Ered2 ¼ ꢀ2.00 V vs. Fc/Fc+) corresponding to the reductions
of dicyanovinyl group and the reduction of oligothiophene core,
respectively. Hence, the HOMO and LUMO levels of these oli-
gothiophenes were estimated to be ꢂꢀ5.2 eV and ꢂꢀ3.3 eV,
respectively based on CV data.
The potential of these highly extended oligothiophenes as hole-
transporting light-absorbing materials in solution-processable
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Fig. 3 CV traces of PhNOF-OT(5)-DCN and G2-OT(6)-DCN.
photoresponse range from 300 nm to 680 nm which corresponds
well to the UV-vis absorption spectra of the films and the
maximum EQE reaches 43% at 424 nm. Our findings highlight the
potential of this class of materials for further device optimization
in high performance PV applications.
Fig. 4 (a) J–V characteristics of G2-OT(6)-DCN : PCBM (1 : 2)-based
PV cells (b) the EQE curves of the corresponding PV cells.
hexa-thiophenes asymmetrically endcapped with a triarylamine
or triarylamino-substituted dendron and dicyanovinyl groups
has been synthesized. A highly extended oligothiophene back-
bone results in strong spectra broadening which is advantageous
Conclusions
In summary, a novel series of solution-processable, p-type,
low-optical-gap semiconductors based on penta- and
Table 2 Summary of PV device performance with a device structure of ITO/PEDOT : PSS/oligomer : PCBM/LiF (0.95 nm)/Al (130 nm)
PCE (%)a b
EQEmax (%)
,
Active layer
Thin thickness/nm
JSC/mA cmꢀ2
VOC/V
FF
PhNOF-OT(5)-DCN : PCBM
(1 : 2)
PhNOF-OT(5)-DCN : PCBM
(1 : 4)
PhNOF-OT(6)-DCN : PCBM
(1 : 2)
G2-OT(5)-DCN : PCBM (1 : 2)
G2-OT(6)-DCN : PCBM (1 : 2)
85
160
106
147
81
102
110
100
160
103
141
2.94
4.97
4.16
5.41
1.78
1.96
4.30
3.90
4.99
3.26
3.68
0.93
0.83
0.79
0.79
0.79
0.75
0.54
0.81
0.79
0.52
0.66
0.17
0.28
0.31
0.40
0.52
0.52
0.32
0.35
0.34
0.33
0.35
0.47
0.97
1.03
1.72
0.73
0.76
0.63
1.11
1.12
0.56
0.84
37
47
40
43
18
17
11
28
25
27
26
G2-OT(6)-DCN : PCBM (1 : 4)
a
Jsc and PCE have been calibrated using external quantum efficiency measurement. b Under simulated AM 1.5 solar irradiation of 100 mW cmꢀ2 for as-
fabricated devices.
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out on a CARLO ERBA 1106 Elemental Analyzer. Thermal
stabilities were determined using a therꢁmal gravimetric analyzer
(PE-TGA6) with a heating rate of 10 C minꢀ1 under N2. The
glass transition and melting transition were extracted from the
second run DSC traces which were determined by differential
scanning calorimeter (PE PYRIS Diamond DSC) with a heating
rate of 10 ꢁC minꢀ1 under N2. All absorption measurements were
performed with a Varian Cary 100-UV-Vis spectrophotometer.
The half-wave potential (E1/2) or peak potential (Ep) vs. FC+/FC
were estimated by a cyclic voltammetric method (Voltammetric
Analyzer CV-50W) using a platinum disc electrode as the
working electrode, a platinum wire as the counter electrode, and
SCE as the reference electrode with an agar bridge connecting to
the oligomer solution dissolved in CH2Cl2 using 0.1 M of
Bu4NPF6 as the supporting electrolyte with a scan rate of
100 mV sꢀ1 and all the potentials were calibrated with ferrocene
as an external standard.
OPV device fabrication and testing
ITO-coated glass substrates (15 U/,) were patterned by
a conventional wet-etching process using an acid mixture of HCl
(6 N) and HNO3 (0.6 N) as the etchant. The active area of each
solar cell was 5 ꢃ 7 mm2. After patterning, the substrates were
rinsed in deionized water, and then ultrasonicated sequentially in
acetone (20 ꢁC) and 2-propanol (65 ꢁC). Immediately before
device fabrication, the ITO substrate was treated in a UV-ozone
oven for 15 min. Subsequently, a poly(3,4-ethylenedioxy-
thiophene)-poly(styrene sulfonate) (PEDOT-PSS) thin film
(50 nm) was spin-coated at 5000 rpm from its aqueous solution
onto the treated substrate, and then baked at 140 ꢁC under
nitrogen for 30 min. The active layer composed of the blend of
oligomer and PCBM at various ratios was then spin-coated on
top of PEDOT-PSS from chlorobenzene solutions for 60 s. The
thickness of the resulting film was measured with a Dektak III
surface profilometer. The device fabrication was completed by
the vacuum deposition of LiF (1 nm) and Al cathode (120 nm).
The solar cells with no protective encapsulation were subse-
quently tested in air under air mass (AM) 1.5 simulated solar
Fig. 5 (a) J–V characteristics of PhNOF-OT(5)-DCN : PCBM (1 : 4)-
based PV cells (b) the EQE curves of the corresponding PV cells.
to light harvesting. The PhNOF-OT(5)-DCN : PCBM-based
device exhibits a high PCE of 1.72% with Voc ¼ 0.79 V and
EQEmax ¼ 43%. Our findings also suggest that highly extended
donor–acceptor oligomers can be useful as a p-type, low bandgap
semiconductor for solution-processable bulk heterojunction PV
cells. Further device optimization to enhance the efficiency of
these oligomer-based PV cells is still in progress.
illumination (100 mW cmꢀ2
, Sciencetech, Model SF150).
Current–voltage (I–V) characteristics were recorded using
a computer-controlled Keithley 2400 source meter.
2-[9,9-Bis(n-decyl)-2-diphenylamino-7-fluorenyl]-bithiophene
(3). To a 100 mL round bottom flask was added 1.4 g
(2.13 mmol) of boronic acid 1, 5-iodo-2,20-bithiophene 2
(746 mg, 2.56 mmol), 100 mg of Pd(PPh3)4, 5 mL of 2 M K2CO3
and 40 mL of THF. The mixture was heated to 80 ꢁC and stirred
overnight under N2. After cooling to room temperature, the
mixture was poured into water and extracted with DCM (3 ꢃ
20 mL). The combined organic phase was dried over anhydrous
sodium sulfate, filtered and evaporated under reduced pressure.
The crude product was purified by silica gel column chroma-
tography using PE–DCM as eluent affording the desired product
Experimental
General procedures and requirements
All the solvents were dried by the standard methods wherever
needed. 1H NMR spectra were recorded using a Bruker-400
NMR spectrometer and referenced to the residual CHCl3
7.26 ppm. 13C NMR spectra were recorded using a Bruker-400
NMR spectrometer and referenced to the CDCl3 77 ppm. Mass
spectroscopy (MS) measurements were carried using fast atom
bombardment on the API ASTER Pulser I Hybrid Mass Spec-
trometer or matrix-assisted laser desorption ionization-time-of-
flight (MALDI-TOF) technique. Elemental Analysis was carried
1
as a colorless crystalline solid (1.2 g, 73%). Mp: 72–74 ꢁC. H
NMR (400 MHz, CDCl3): d 7.54–7.60 (m, 3 H), 7.49 (d, J ¼ 0.8
Hz, 1 H), 7.20–7.27 (m, 6 H), 7.17 (d, J ¼ 4.0 Hz, 1 H), 7.10–7.12
(m, 5 H), 6.99–7.04 (m, 4 H), 1.80–1.95 (m, 4 H), 1.05–1.27 (m, 28
H), 0.86 (t, J ¼ 2.8 Hz, 6 H), 0.67–0.69 (m, 4 H). 13C NMR
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(100 MHz, CDCl3): d 152.3, 151.4, 147.9, 147.2, 144.0, 140.6,
137.6, 136.1, 135.7, 132.0, 129.1, 127.8, 124.6, 124.5, 124.2, 123.8,
123.5, 123.4, 123.2, 122.5, 120.4, 119.6, 119.4, 119.2, 55.1, 40.2,
31.9, 29.9, 29.7, 29.6, 29.5, 29.3, 23.8, 22.6, 14.1. MS (MALDI-
TOF): m/z 778.1 (M+ + 1).
135.5, 135.2, 134.6, 131.9, 129.2, 127.0, 125.2, 124.8, 124.7, 124.6,
124.5, 124.4, 124.3, 124.1, 123.9, 123.4, 122.5, 120.4, 119.6, 119.5,
119.2, 55.1, 40.2, 31.9, 29.9, 29.6, 29.5, 29.3, 23.8, 22.6,14.1. MS
(MALDI-TOF): m/z 1134.3 (M+ + 1).
PhNOF-OT(5)-DCN. To a 100 mL round bottom flask con-
taining 210 mg (0.20 mmol) of 6a and 10 mL of CHCl3 was added
0.40 g (6.1 mmol) of malononitrile and 0.8 mL of pyridine at
room temperature. The solution was heated to reflux and stirred
overnight under N2. After cooling to room temperature, the
reaction mixture was poured into water, neutralized with 0.1 M
HCl, and extracted with CHCl3 (3 ꢃ 20 mL). The combined
organic phase was washed with water, dried over anhydrous
sodium sulfate, filtered and evaporated to dryness. The crude
product was purified by silica gel column chromatography using
PE–DCM as eluent and further precipitated by CHCl3–Et2O,
washed with methanol and dried under vacuum affording the
5-[9,9-Bis(n-decyl)-2-diphenylamino-7-fluorenyl]-2-pentathio-
phenecarboxaldehyde (6a). To a dry 100 mL two-neck flask
containing 2.0 g (2.57 mmol) of 3 and 30 mL of dry THF was
dropwise added 2.4 mL (3.9 mmol) of 1.6 M of n-butyl lithium
under N2 at ꢀ78 ꢁC while maintaining a good stirring. After
stirring for 1 h, trimethyl borate (0.45 mL, 4.0 mmol) was added
in one portion. The reaction mixture was then stirred for 1 h at
ꢀ78 ꢁC. When the mixture was naturally warmed to ꢀ30 ꢁC,
water and HCl (3 M) were added. Then the solution mixture was
poured into water and extracted with EA (3 ꢃ 50 mL). The
combined organic phase was dried over anhydrous sodium
ꢁ
1
sulfate, filtered and evaporated to dryness at 35 C. The crude
desired product as a black red solid (204 mg, 93%). H NMR
product was purified by silica gel column chromatography using
DCM and PE–EA as eluent affording the desired product, 5-[9,9-
bis(n-decyl)-2-diphenylamino-7-fluorenyl]-2-bithiopheneboronic
acid (4) as a green solid (1.58 g, 75%). The product was directly
used in the next coupling reaction without further purification.
To a 100 mL round bottom flask was added 300 mg (0.36 mmol)
of boronic acid 4, 100 mg (0.25 mmol) of aldehyde (5a), 50 mg of
Pd(PPh3)4, 2 mL of 2 M K2CO3 and 20 mL of THF. The mixture
was heated to 80 ꢁC and stirred overnight under N2. After
cooling to room temperature, the mixture was poured into water
and extracted with DCM (3 ꢃ 20 mL). The combined organic
phase was dried with anhydrous sodium sulfate, filtered and
evaporated to dryness. The crude product was purified by silica
gel column chromatography using PE–DCM as eluent affording
the desired product as a red solid (205 mg, 78%). Mp: 145–
147 ꢁC. 1H NMR (400 MHz, CDCl3): d 9.86 (s, 1 H), 7.67 (d, J ¼
4.0 Hz, 1 H), 7.54–7.60 (m, 3 H), 7.49 (d, J ¼ 1.2 Hz, 1 H), 7.23–
7.28 (m, 7 H), 7.17 (d, J ¼ 4.0 Hz, 1 H), 7.09–7.14 (m, 10 H),
6.99–7.03 (m, 3 H), 1.81–1.96 (m, 4 H), 1.07–1.25 (m, 28 H), 0.86
(t, J ¼ 2.8 Hz, 6 H), 0.67–0.70 (m, 4 H). 13C NMR (100 MHz,
CDCl3): d 182.4, 152.3, 151.5, 147.9, 147.3, 146.7, 144.5, 141.6,
140.8, 138.8, 137.4, 137.0, 136.9, 135.6, 135.5, 135.2, 135.1, 134.5,
131.8, 129.2, 127.0, 125.2, 124.8, 124.7, 124.6, 124.3, 124.1, 124.0,
123.9, 123.5, 123.4, 122.6, 120.4, 119.6, 119.5, 119.2, 55.1, 40.2,
31.9, 29.9, 29.6, 29.5, 29.3, 23.8, 22.7, 14.1. MS (MALDI-TOF):
m/z 1052.2 (M+ + 1).
(400 MHz, CDCl3): d 7.73 (s, 1 H), 7.54–7.62 (m, 4 H), 7.49 (d, J
¼ 1.2 Hz, 1 H), 7.35 (d, J ¼ 4.0 Hz, 1 H), 7.23–7.29 (m, 6 H),
7.09–7.18 (m, 11 H), 6.99–7.03 (m, 3 H), 1.83–1.94 (m, 4 H),
1.07–1.27 (m, 28 H), 0.86 (t, J ¼ 7.2 Hz, 6 H), 0.67–0.70 (m, 4 H);
13C NMR (100 MHz, CDCl3): d 152.3, 151.5, 149.8, 148.8, 147.9,
147.3, 144.5, 140.9, 140.2, 140.1, 137.5, 137.1, 135.5, 135.4, 135.0,
134.6, 133.5, 133.3, 131.8, 129.2, 128.1, 125.6, 124.8, 124.7, 124.6,
124.3, 124.2, 124.1, 123.9, 123.4, 122.6, 120.4, 119.6, 119.5, 119.1,
114.2, 113.5, 75.9, 55.1, 40.2, 31.9, 29.9, 29.6, 29.5, 29.3, 23.9,
22.6, 14.1. HRMS (MALDI-TOF): calcd: For C69H69N3S5:
1099.4089; Found: 1089.4092. Anal calc. for C69H69N3S5: C
75.30, H 6.32, N 3.82; found: C 75.36, H 6.33, N 3.84.
PhNOF-OT(6)-DCN. The synthetic procedure for PhNOF-
OT(5)-DCN was followed using 226 mg (0.20 mmol) of 6b, 0.40 g
(6.1 mmol) of malononitrile, 0.8 mL of pyridine and 10 mL of
CHCl3. The crude product was purified by silica gel column
chromatography using PE–DCM and precipitated by CHCl3–
Et2O affording the desired product as a black red solid (212 mg,
90%). 1H NMR (400 MHz, CDCl3): d 7.74 (s, 1 H), 7.55–7.63 (m,
4 H), 7.49 (s, 1 H), 7.35 (d, J ¼ 4.0 Hz, 1 H), 7.23–7.29 (m, 6 H),
7.09–7.18 (m, 13 H), 6.99–7.03 (m, 3 H), 1.81–1.95 (m, 4 H),
1.07–1.25 (m, 28 H), 0.86 (t, J ¼ 6.8 Hz, 6 H), 0.67–0.70 (m, 4 H).
13C NMR (100 MHz, CDCl3): d 153.3, 151.5, 149.8, 148.8, 147.9,
147.3, 144.4, 140.8, 140.1, 137.4, 136.8, 136.6, 135.6, 135.5, 135.3,
134.7, 133.5, 133.4, 131.8, 129.2, 128.2, 125.6, 124.9, 124.8, 124.7,
124.6, 124.4, 124.3, 124.1, 123.9, 123.4, 122.6, 120.5, 119.6, 119.5,
119.2, 114.2, 113.5, 75.9, 55.1, 40.2, 31.9, 30.9, 29.9, 29.6, 29.5,
29.3, 23.9, 22.7, 14.1. HRMS (MALDI-TOF): calcd: For
C73H71N3S6: 1181.3966; Found: 1181.4034. Anal calc. for
C73H71N3S6: C 74.13, H 6.05, N 3.55; found: C 74.42, H 6.07, N
3.71.
5-[9,9-Bis(n-decyl)-2-diphenylamino-7-fluorenyl]-2-hex-
athiophenecarboxaldehyde (6b). The synthetic procedure for
compound 6a was followed using 300 mg (0.36 mmol) of boronic
acid 4, 121 mg (0.25 mmol) of aldehyde 5b, 50 mg of Pd(PPh3)4, 2
mL of 2 M K2CO3 and 20 mL of 1,4-dioxane. The crude product
was purified by silica gel column chromatography using PE–
DCM as eluent affording the desired product as a red solid (227
mg, 80%). Mp: 162–164 ꢁC. 1H NMR (400 MHz, CDCl3): d 9.86
(s, 1 H), 7.68 (d, J ¼ 3.6 Hz, 1 H), 7.54–7.60 (m, 3 H), 7.49 (d, J ¼
1.2 Hz, 1 H), 7.23–7.29 (m, 7 H), 7.18 (d, J ¼ 4.0 Hz, 1 H), 7.10–
7.15 (m, 12 H), 6.99–7.03 (m, 3 H), 1.81–1.96 (m, 4 H), 1.07–1.25
(m, 28 H), 0.86 (t, J ¼ 2.8 Hz, 6 H), 0.67–0.70 (m, 4 H). 13C NMR
(100 MHz, CDCl3): d 182.4, 152.3, 151.5, 147.9, 147.3, 146.7,
144.4, 141.6, 140.8, 138.7, 137.4, 137.0, 136.9, 136.7, 136.5, 135.6,
5-{3,6-Bis[4-(diphenylamino)-1-phenyl]carbazol-9-yl}-2-penta-
thiophene-carboxaldehyde (8a). The synthetic procedure for
compound 6a was followed using 430 mg (0.5 mmol) of boronic
acid 7, 161 mg (0.4 mmol) of aldehyde 5a, 40 mg of Pd(PPh3)4,
3 mL of 2 M K2CO3 and 20 mL of THF. The crude product was
purified by silica gel column chromatography using PE–DCM as
eluent affording the desired product as a red solid (362 mg, 83%).
Mp: 298–300 C.1H NMR (400 MHz, CDCl3): d 9.86 (s, 1 H),
ꢁ
2188 | J. Mater. Chem., 2010, 20, 2182–2189
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9.88 (s, 1 H), 8.32 (d, J ¼ 1.2 Hz, 2 H), 7.67–7.70 (m, 3 H), 7.61 (d,
J ¼ 8.4 Hz, 6 H), 7.24–7.29 (m, 11 H), 7.13–7.16 (m, 18 H), 7.02–
7.05 (m, 4 H). 13C NMR (100 MHz, CDCl3): d 182.4, 147.7,
146.7, 146.6, 141.7, 141.3, 138.6, 137.5, 137.4, 136.7, 136.2, 136.0,
135.8, 135.4, 135.1, 134.7, 134.1, 129.3, 127.9, 126.9, 125.6, 125.3,
125.2, 124.7, 124.67, 124.61, 124.3, 124.2, 124.1, 122.8, 122.5,
118.3, 110.6. MS (MALDI-TOF): m/z 1092.1 (M+ + 1).
137.3, 136.4, 136.0, 135.7, 135.6, 135.0, 134.9, 134.0, 133.6, 133.4,
129.3, 128.1, 127.9, 125.6, 125.2, 124.8, 124.7, 124.5, 124.3, 122.8,
122.4, 118.3, 114.2, 113.5, 110.6, 75.8. HRMS (MALDI-TOF):
calcd: For C76H47N5S6: 1221.2150; Found: 1221.2121. Anal calc.
for C76H47N5S6: C 74.66, H 3.87, N 5.73; found: C 74.77, H 3.99,
N 5.58.
5-{3,6-Bis[4-(diphenylamino)-1-phenyl]carbazol-9-yl}-2-hex-
athiophene-carboxaldehyde (8b). The synthetic procedure for
compound 6b was followed using 430 mg (0.5 mmol) of boronic
acid 7, 145 mg (0.30 mmol) of aldehyde 5b, 3 mL of 2 M K2CO3
and 20 mL of 1,4-dioxane. The crude product was purified by
silica gel column chromatography using PE–DCM as eluent
affording the desired product as a red solid (281 mg, 80%). Mp:
302–305 ꢁC. 1H NMR (400 MHz, CDCl3): d 9.87 (s, 1 H), 8.32 (d,
J ¼ 1.6 Hz, 2 H), 7.68–7.71 (m, 3 H), 7.61 (d, J ¼ 8.4 Hz, 6 H),
Acknowledgements
This work was financially supported by Hong Kong Research
Grant Council, GRF, HKBU 202408.
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PhNOF-OT(5)-DCN was followed using 160 mg (0.146 mmol) of
8a, 400 mg (6.1 mmol) of malononitrile, 0.7 mL of pyridine and
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1
(149 mg, 89%). H NMR (400 MHz, CDCl3): d 8.32 (d, J ¼ 1.2
Hz, 2 H), 7.72 (s, 1 H), 7.69 (dd, J ¼ 8.8 Hz, J ¼ 1.6 Hz 2 H), 7.61
(d, J ¼ 8.4 Hz, 7 H), 7.35 (d, J ¼ 4.0 Hz, 1 H), 7.23–7.29 (m, 10
H), 7.12–7.20 (m, 18 H), 7.05 (t, J ¼ 7.4 Hz, 4 H). 13C NMR
(100 MHz, CDCl3): d 149.9, 148.8, 147.8, 146.8, 141.3, 140.1,
140.0, 137.6, 137.3, 136.4, 135.9, 135.8, 135.1, 135.0, 134.1, 133.7,
133.5, 129.3, 128.2, 127.9, 125.7, 125.4, 125.0, 124.9, 124.8, 124.7,
124.4, 124.3, 124.2, 122.8, 122.6, 118.4, 114.3, 113.5, 110.6, 76.1.
HRMS (MALDI-TOF): calcd: For C72H45N5S5: 1139.2273;
Found: 1139.2288. Anal calc. for C72H45N5S5: C 75.82, H 3.98,
N 6.14; found: C 75.87, H 3.99, N 6.03.
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G2-OT(6)-DCN. The synthetic procedure for compound
PhNOF-OT(5)-DCN was followed using 170 mg (0.144 mmol) of
8b, 400 mg (6.1 mmol) of malononitrile, 0.7 mL of pyridine and
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1
(161 mg, 91%). H NMR (400 MHz, CDCl3): d 8.32 (d, J ¼
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1.2 Hz, 2 H), 7.74 (s, 1 H), 7.70 (dd, J ¼ 8.8 Hz, J ¼ 1.6 Hz, 2 H),
7.59–7.62 (m, 7 H), 7.36 (d, J ¼ 4.0 Hz, 1 H), 7.25–7.30 (m, 10 H),
7.12–7.21 (m, 20 H), 7.02–7.06 (m, 4 H). 13C NMR (100 MHz,
CDCl3): d 149.8, 148.7, 147.7, 146.7, 141.2, 140.1, 140.0, 137.4,
This journal is ª The Royal Society of Chemistry 2010
J. Mater. Chem., 2010, 20, 2182–2189 | 2189