The synthesis and photovoltaic properties of A-D-A-type small molecules containing diketopyrrolopyrrole terminal units

Article abstract of DOI:10.1039/c2nj40963a

A series of novel A-D-A structured small molecule photovoltaic (PV) materials [CZ(TDPP)₂, DPA(TDPP)₂, PTZ(TDPP)₂ and FL(TDPP)₂] with diketopyrrolopyrrole (DPP) as an electron-withdrawing group were synthesized and characterized. These small molecular donors exhibit excellent solubility in common organic solvents. The density functional theory (DFT) calculations demonstrated the intramolecular charge transfer (ICT) behavior of the synthesized PV materials and an efficient charge separation was observed by a fluorescence quenching experiment. In addition, their photophysical and electrochemical properties show that they harvest sunlight over the entire visible spectrum range and keep appropriate energy levels to satisfy the requirement of solution-processable OSCs. Therefore, we explored the PV properties of the synthesized donors by fabricating BHJ solar cells with a typical structure of ITO/PEDOT:PSS/Donors: PC₆₁BM/LiF/Al. Among them, CZ(TDPP)₂ revealed a promising performance in PV devices with a power conversion efficiency (PCE) of 1.50%, along with an open-circuit voltage (V_OC) of 0.66 V, a short-circuit current density (J_SC) of 4.12 mA cm^-2, and a fill factor (FF) of 0.44, under an illumination of AM 1.5G (80 mW cm^-2).

Full text of DOI:10.1039/c2nj40963a

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The synthesis and photovoltaic properties of
A–D–A-type small molecules containing
Cite this: DOI: 10.1039/c2nj40963a
diketopyrrolopyrrole terminal units†
Ling Zhang,a Shaohang Zeng,a Lunxiang Yin,a Changyan Ji,ab Kechang Li,b
Yanqin Li*a and Yue Wangb
A series of novel A–D–A structured small molecule photovoltaic (PV) materials [CZ(TDPP)2, DPA(TDPP)2,
PTZ(TDPP)2 and FL(TDPP)2] with diketopyrrolopyrrole (DPP) as an electron-withdrawing group were
synthesized and characterized. These small molecular donors exhibit excellent solubility in common
organic solvents. The density functional theory (DFT) calculations demonstrated the intramolecular
charge transfer (ICT) behavior of the synthesized PV materials and an efficient charge separation was
observed by a fluorescence quenching experiment. In addition, their photophysical and electrochemical
properties show that they harvest sunlight over the entire visible spectrum range and keep appropriate
energy levels to satisfy the requirement of solution-processable OSCs. Therefore, we explored the
PV properties of the synthesized donors by fabricating BHJ solar cells with a typical structure of
ITO/PEDOT:PSS/Donors:PC61BM/LiF/Al. Among them, CZ(TDPP)2 revealed a promising performance in
Received (in Montpellier, France)
22nd October 2012,
Accepted 28th November 2012
PV devices with a power conversion efficiency (PCE) of 1.50%, along with an open-circuit voltage (VOC
)
DOI: 10.1039/c2nj40963a
of 0.66 V, a short-circuit current density (JSC) of 4.12 mA cmꢀ2, and a fill factor (FF) of 0.44, under an
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illumination of AM 1.5G (80 mW cmꢀ2).
novel small molecular semiconductors is of great value for pre-
paring high performance solution-processable OSCs.
Introduction
Organic semiconductors for photovoltaic devices have attracted
tremendous investigation due to their advantages of easy-
synthesis, flexibility, light-weight and large-scale fabrication.1
For solution-processable bulk-heterojunction organic solar cells
(BHJ OSCs), polymers exhibit outstanding PV properties with PCEs
over 8%.2 Meanwhile, in order to overcome the short comings of
semiconducting polymers, such as batch-to-batch variation, broad
molecular weight distributions and difficult purification,
p-conjugated small molecules have become attractive due to their
well-defined structure, high purity and reproducibility. Currently,
prominent efficiencies with 6–7% have been achieved for small
molecule BHJ OSCs.3 Significantly, Zhou et al. recently reported a
record PCE of 7.38% for small molecular donor based OSCs,4
which demonstrated that small-molecule solar cells are compar-
able with polymeric counterparts. Therefore, the exploration of
To extend the absorption range to longer wavelengths, small
molecular PV materials were typically composed of p-bridged
electron-donating (D) and electron-withdrawing (A) groups,
because ICT transitions in this structure can effectively reduce
the molecular band gap.5 Meanwhile, the energy levels of this
push–pull structure are adjustable by incorporating different
functional groups.6 Ideal donors for the active components of
BHJ OSCs should possess a low-lying highest occupied molecular
orbital (HOMO) to guarantee a high VOC of the devices, and own a
lowest unoccupied molecular orbital (LUMO) which is at least
0.3 eV7 higher than that of the acceptors to form a downhill
driving force for electron separation. Rational energy level control
of the p-type materials will result in desirable HOMO and LUMO
compared with those of PC61BM, a soluble fullerene derivative
which has been widely used as an acceptor in OSCs.
Diketopyrrolopyrrole is one exceptional chromophore with a
strong fluorescence performance and broad light absorption,
as well as possessing excellent photochemical, mechanical, and
thermal stability.8 Consequently, DPP-based materials have
been widely investigated for pigments, organic light-emitting diodes,
organic field-effect transistors, dye-sensitized solar cells, and so on.9
a School of Chemistry, Dalian University of Technology, Dalian, China.
E-mail: liyanqin@dlut.edu.cn; Fax: +86-411-84986040; Tel: +86-411-84986040
b State Key Laboratory of Supramolecular Structure and Materails,
College of Chemistry, Jilin University, Changchun, China
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
c2nj40963a
c
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Nguyen et al. firstly applied D–A–D-type materials containing DPP All these donor units are extensively utilized in polymeric
as an electron-withdrawing group in BHJ solar cells, achieving an donor materials because of their electron rich structure.13
absorption that extended to 820 nm in a film, and a PCE up These small molecular donors exhibit excellent solubility in
to 2.3%.10 Afterward, a series of DPP-based materials were syn- common organic solvents. In addition, their photophysical and
thesized and utilized as donors or acceptors for OSCs, which electrochemical properties show that they harvest sunlight
obtained a PCE as high as 4.4%.11 Moreover, Marks and coworkers across the entire visible spectrum range and keep appropriate
developed the first A–D–A DPP-based materials, with naphtho- energy levels to satisfy the requirement of solution-processable
dithiophene groups at the centre for efficient organic photo- OSCs. Therefore, we explored the PV properties of the
voltaics, exhibiting a maximum PCE of 4.1%.12 Thus, DPP- synthesized donors by fabricating BHJ solar cells with a
based materials functionalized with a D–A structure will have typical structure of ITO/PEDOT:PSS/Donors:PC61BM/LiF/Al.
an even greater potential in high performance solar cells.
The PCEs of the devices based on CZ(TDPP)2, DPA(TDPP)2,
To examine the effect of novel aromatic donor units on the PTZ(TDPP)2 and FL(TDPP)2 are 1.50%, 0.53%, 0.75% and
properties of DPP-based molecules, we successfully synthesized 0.78%, respectively.
a series of A–D–A structured small molecular donors, all of
which contain thiophene-ended DPP as an arm and include an
alkylated carbazole, diphenylamine, phenothiazine and fluorene
centre, respectively (see Scheme 1 for their molecular structures).
Results and discussion
Synthesis and measurement
The synthetic route for the small molecules is shown in
Scheme 2. The Miyaura borylation reactions of the dibromo-
substituted centre donating groups and bis(pinacolato)-
diborane (B2Pin2) were carried out using KOAc as a base and
Pd(PPh3)2Cl2 as the catalyst in toluene, resulting in compounds
D1–D4. Afterward, CZ(TDPP)2, DPA(TDPP)2, PTZ(TDPP)2 and
FL(TDPP)2 were prepared by the Pd(PPh3)4-assisted Suzuki
coupling reaction in yields of 81%, 81%, 37% and 74%,
respectively. The chemical structures of the small molecules
1
were identified by H-NMR, 13C-NMR and MALDI-TOF HRMS
(see ESI† for detailed spectra). At room temperature, these
synthesized small molecules exhibit excellent solubility in
common organic solvents, such as chloroform, chlorobenzene,
dichlorobenzene, because of the alkyl groups substituted on
the DPP and donor units.
Theoretical calculations
To estimate the ground-state geometries, electronic structures
and energies of the frontier orbitals for the small molecules,
DFT calculations were accomplished by Gaussian 09 software at
the Becke’s three-parameter gradient-corrected functional (B3LYP)
Scheme 1 The molecular structures of CZ(TDPP)2, DPA(TDPP)2, PTZ(TDPP)2
and FL(TDPP)2.
Scheme 2 The synthetic route of CZ(TDPP)2, DPA(TDPP)2, PTZ(TDPP)2 and FL(TDPP)2.
c
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Fig. 1 The geometry and the HOMO and LUMO surface plots for CZ(TDPP)2,
DPA(TDPP)2, PTZ(TDPP)2, and FL(TDPP)2.
with a polarized 6-31G(d) basis. The electron-density distribu-
tions of the HOMO and LUMO at the optimized ground-state
configurations are illustrated in Fig. 1. The DFT calculated
HOMO and LUMO values are summarized in Table 1. The
theoretical calculation results demonstrated that the electronic
density of the HOMO is distributed over the entire molecule,
while that of the LUMO is partly migrated to the DPP moieties
on the arms, as shown in the Fig. 1. Under the assumption that
the long wavelength transitions are predominantly determined
by the HOMO–LUMO transition, the excitation leads to an
intramolecular charge transfer. When an electron is excited
from the HOMO to the LUMO energy level, a charge transfer
occurs in all of the small molecules from the centre donating
group to the DPP units. Notably, there is a consistent trend
between the theoretically calculated energy levels and the
experimentally determined maximum absorption wavelength
of these molecules in solution (see Fig. 2). This relationship
shows that, despite the error in the calculated absolute values,
theoretical calculations can serve as a valuable tool to guide the
synthesis of future designed materials.
Fig. 2 Normalized UV-vis absorption spectra of CZ(TDPP)2, DPA(TDPP)2, PTZ(TDPP)2
and FL(TDPP)2 in chloroform and in film.
compounds from CZ(TDPP)2 to FL(TDPP)2 indicated an
enhanced ICT transition band, resulting in the extension of
the absorption spectral range. The thin films exhibited similar
absorption spectra to those in solution, but the lmax of
the small molecules were red-shifted and the peaks were
broadened, suggesting p–p intermolecular interactions in the
solid state. For the UV-vis spectra in film, all small molecules
displayed strong absorptions, almost covering the entire range
of visible light, and presented extrapolated absorption edges
from 671 nm for FL(TDPP)2 up to 738 nm for PTZ(TDPP)2.
Optical properties
Electrochemical characteristics
The normalized UV-vis absorption spectra of the studied small In order to determine the HOMO and LUMO of the synthesized
molecules in chloroform and in film are shown in Fig. 2, and molecules, cyclic voltammetry (CV) was employed in 0.1 M
the corresponding maximum absorption wavelengths (lmax
)
tetrabutylammonium tetrafluoroborate (Bu4NBF4) solution of
and optical band gaps (Eogpt) are listed in Table 1. The lmax of dichloromethane as the supporting electrolyte at a scan rate of
CZ(TDPP)2, DPA(TDPP)2, PTZ(TDPP)2 and FL(TDPP)2 in 100 mV sꢀ1 under a nitrogen atmosphere at room temperature.
solution were observed at 588 nm, 595 nm, 594 nm and Using the ferrocene–ferrocenium (Fc/Fc+) couple as an internal
599 nm, respectively, owing to the ICT transition between the standard, the HOMO energy levels, LUMO energy levels and
donating and withdrawing groups, while that of compound A the electrochemical band gaps (Eegc) of the four molecules
was at 560 nm (Fig. 1 in the ESI†). The increased lmax of were calculated from the onset oxidation potentials (Eox) and
Table 1 Optical, electrochemical and DFT calculated properties of CZ(TDPP)2, DPA(TDPP)2, PTZ(TDPP)2 and FL(TDPP)2
UV-vis absorption spectra
Cyclic voltammetry
DFT calculation
HOMO (eV)
lsmoalx (nm)
lfmilamx (nm)
Eogpt (eV)
HOMO (eV)
LUMO (eV)
Eegc (eV)
LUMO (eV)
EDg FT (eV)
Compound
CZ(TDPP)2
DPA(TDPP)2
PTZ(TDPP)2
FL(TDPP)2
588
595
594
599
644
618
626
618
1.78
1.80
1.69
1.85
ꢀ5.03
ꢀ5.01
ꢀ5.04
ꢀ5.16
ꢀ3.32
ꢀ3.33
ꢀ3.34
ꢀ3.36
1.71
1.68
1.70
1.80
ꢀ4.70
ꢀ4.67
ꢀ4.72
ꢀ4.78
ꢀ2.47
ꢀ2.53
ꢀ2.53
ꢀ2.65
2.23
2.14
2.19
2.13
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onset reduction potentials (Ered) according to the following On the anodic scan, the four molecules showed onset oxidation
equations:14
potentials of 0.28 V for CZ(TDPP)2, 0.26 V for DPA(TDPP)2,
0.29 V for PTZ(TDPP)2 and 0.41 V for FL(TDPP)2. In contrast,
the cathodic scan exhibited onset reduction potentials of
ꢀ1.43 V for CZ(TDPP)2, ꢀ1.42 V for DPA(TDPP)2, ꢀ1.41 V for
PTZ(TDPP)2 and ꢀ1.39 V for FL(TDPP)2. The corresponding
band gaps (Ecgv) of the four compounds were estimated to be
about 1.71 eV, 1.68 eV, 1.70 eV and 1.80 eV for CZ(TDPP)2,
DPA(TDPP)2, PTZ(TDPP)2 and FL(TDPP)2, respectively. The data
imply that the electrochemical band gaps of these compounds
were similar, except for FL(TDPP)2, where the Eegc was broader
than for the others. The HOMO and LUMO energy levels of the
four molecules showed that they were suitable for donors in
solution-processable BHJ solar cells with PC61BM as the
acceptor.
ferrocene
1/2
HOMO = ꢀ(Eox ꢀE
+ 4.8) eV
+ 4.8) eV
ferrocene
LUMO = ꢀ (Ered ꢀ E
1/2
Eegc = LUMO ꢀ HOMO
where Eox and Ered are the measured onset potentials relative to
ferrocene
1/2
Ag/Ag+. E
= 0.05 V versus Ag/Ag+.
The CV curves of these materials are shown in Fig. 3 and
the electrochemical energy levels are summarized in Table 1.
Photoinduced charge separation
According to the DFT calculations and electrochemical proper-
ties of the synthesized donor molecules, all the materials have
the potential to generate photoinduced charge separation with
PC61BM, since their LUMO energy levels were higher than that
of PC61BM (ꢀ4.3 eV). The differences in the LUMO energy levels
was also over 0.3 eV,7 which is the requirement to guarantee a
sufficient driving force for efficient charge separation at the
interface of the donor materials and PC61BM. The fluorescence
quenching experiments were carried out in order to investigate
the photoinduced charge separation process and the charac-
teristics are shown in Fig. 4. The emission maximum peaks of
CZ(TDPP)2, DPA(TDPP)2, PTZ(TDPP)2 and FL(TDPP)2 were
revealed at 625 nm, 649 nm, 676 nm and 629 nm, respectively.
The fluorescence of the synthesized materials was gradually
quenched as the concentration of PC61BM was increased in
CHCl3. This phenomenon suggested an efficient photoinduced
charge separation process between the synthesized donor molecules
and the acceptor material PC61BM. Furthermore, at low
Fig. 3 Cyclic voltammetry of CZ(TDPP)2, DPA(TDPP)2, PTZ(TDPP)2 and FL(TDPP)2
in 0.1 M Bu4NBF4/CH2Cl2 solution at a scan rate of 100 mV sꢀ1
.
Fig. 4 (a) Fluorescence emission spectra of CZ(TDPP)2 (SM1), DPA(TDPP)2 (SM2), PTZ(TDPP)2 (SM3) and FL(TDPP)2 (SM4) in CHCl3 (1.0 ꢁ 10ꢀ5 M) with increasing
concentration of PC61BM (ꢁ10ꢀ5 M): 0.0 (0), 2.5 (1), 5.0 (2), 10.0 (3), 15.0 (4), 20.0 (5), 25.0 (6), 30.0 (7). The insets are Stern–Volmer fluorescence-quenching plots for
the compounds. (b) Fluorescence of compounds without and with PC61BM in CHCl3 under UV-irradiation (365 nm).
c
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Table 2 The device properties of CZ(TDPP)2, DPA(TDPP)2, PTZ(TDPP)2 and
FL(TDPP)2 with PC61BM as the acceptor
quencher concentrations, the dependencies of the fluorescence
intensity on the concentration of PC61BM are linear in con-
formity with the Stern–Volmer equation:15
Compound SM/PC61BM (w/w) JSC (mA cmꢀ2) VOC (V) FF PCE (%)
CZ(TDPP)2 1 : 2
DPA(TDPP)2 1 : 2
PTZ(TDPP)2 1 : 2
FL(TDPP)2 1 : 2
4.12
1.95
2.63
3.17
7.50
0.66
0.64
0.65
0.66
0.59
0.44 1.50
0.34 0.53
0.35 0.75
0.30 0.78
0.58 3.21
F0/F = 1 + Ksv[C]
where F0 and F represent the intensity of fluorescence in
the absence and presence of PC61BM, respectively, Ksv is the
quenching constant, and [C] is the concentration of PC61BM.
The Ksv values of CZ(TDPP)2, DPA(TDPP)2, PTZ(TDPP)2 and
FL(TDPP)2 are 2.85 ꢁ 103 Mꢀ1, 1.90 ꢁ 103 Mꢀ1, 1.88 ꢁ 103 Mꢀ1
and 2.02 ꢁ 103 Mꢀ1, respectively. These values suggest that the
photoinduced charge separation process of CZ(TDPP)2 is more
efficient than that of the other three materials. In order to
understand the photoinduced charge separation better, the
mechanism for that of synthesized donor molecules (DSM) with
acceptor PCBM (APCBM) was illustrated in ESI.†7,16
P3HT
1 : 2
p-electron delocalized backbone structure than that of mole-
cules PTZ(TDPP)2 and FL(TDPP)2, which demonstrates that the
promising PV performance of small molecule solar cells could
be obtained through rational molecule design. The preliminary
photovoltaic investigation suggests that optimization of the
device composition, morphology, and annealing are needed,
thus further work is under investigation.
Photovoltaic properties
Conclusions
In order to investigate the photovoltaic properties of the syn-
thesized donors materials, the bulk-heterojunction PV devices In summary, a series of novel A–D–A-type small molecule PV
were fabricated with a typical structure of ITO/PEDOT:PSS/ materials CZ(TDPP)2, DPA(TDPP)2, PTZ(TDPP)2 and FL(TDPP)2
Donors:PC61BM/LiF/Al. Fig. 5 shows the I–V characteristics of with DPP as an electron-withdrawing group were synthesized
the devices under an illumination of AM 1.5G (80 mW cmꢀ2
)
and characterized. The DFT calculations demonstrated ICT
and the energy levels of the materials utilized in these devices. behavior of the synthesized PV donors and an efficient charge
The short-circuit current density (JSC), open-circuit voltage separation was observed by a fluorescence quenching experi-
(VOC), fill factor (FF) and PCEs for all devices are summarized ment. In addition, their photophysical and electrochemical
in Table 2.
properties revealed that they harvest sunlight across the entire
The PV cells based on CZ(TDPP)2 as the donor exhibited a visible spectrum range and keep appropriate energy levels to
VOC of 0.66 V, a JSC of 4.12 mA cmꢀ2, a FF of 0.44 and a PCE of satisfy the requirement of solution-processable OSCs. The PV
1.50%, while the other three devices, based on DPA(TDPP)2, properties of the synthesized donors were investigated by
PTZ(TDPP)2, and FL(TDPP)2, presented PCE values of 0.53%, fabricating BHJ solar cells with a typical structure of ITO/
0.75% and 0.78%, respectively. Under the same conditions, the PEDOT:PSS/Donors:PC61BM/LiF/Al. Among them, CZ(TDPP)2
P3HT-based reference device gave a PCE value of 3.21% (Fig. 2 revealed a promising performance in PV devices with a PCE
in ESI†). These results are in agreement with the discussion of of 1.50%, along with a VOC of 0.66 V, a JSC of 4.12 mA cmꢀ2, and
the photoinduced charge separation process. The relative a FF of 0.44, which revealed that the promising PV performance
higher PCE of the device based on CZ(TDPP)2 is due to a of small molecules could be achieved through rational mole-
more coplanar structure than that of DPA(TDPP)2 and a more cule design.
Fig. 5 Energy levels (a) and I–V characteristics (b) of the PV devices with the structure of ITO/PEDOT:PSS/Donors:PC61BM/LiF/Al under an illumination of AM 1.5G
(80 mW cmꢀ2).
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Experimental section
Reagent and materials
0.85 (t, J = 6.8 Hz, 3H). 13C-NMR (CDCl3, ppm, 100 MHz) d =
142.72, 132.07, 128.08, 122.88, 108.18, 83.53, 43.12, 31.81,
29.38, 29.16, 28.94, 27.24, 24.99, 22.63, 14.10. MALDI-TOF
HRMS: 531.3669 [M+] (calcd for C32H47NO4B2: 531.3691).
N-Hexyl-bis-[4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
phenyl]amine (D2). N-Hexyl-4,40-dibromodiphenylamine (0.62 g,
1.5 mmol), B2Pin2 (0.83 g, 3.3 mmol), KOAc (0.74 g, 7.5 mmol),
and Pd(PPh3)2Cl2 (21 mg, 0.03 mmol) were used to afford D2
(0.18 g, 24%) as a light-yellow solid. M.p.: 138–142 1C. 1H-NMR
(CDCl3, ppm, 400 MHz) d = 7.70 (d, J = 8.4 Hz, 4H), 7.02 (d, J =
8.4 Hz, 4H), 3.73 (t, J = 7.6 Hz, 2H), 1.33 (s, 24 H), 1.29–1.24
(m, 6H ), 0.88–0.84 (m, 5H). 13C-NMR (CDCl3, ppm, 100 MHz)
d = 149.82, 136.21, 120.14, 83.69, 51.82, 31.74, 27.49, 26.50,
26.46, 25.03, 22.66, 14.18. MALDI-TOF HRMS: 505.3492 [M+]
(calcd for C30H45NO4B2: 505.3535).
All reagents were obtained commercially and used without
further purification unless specified otherwise. Tetrahydrofuran
(THF) and toluene were distilled over Na/benzophenone under
nitrogen. All reactions were carried out under an air atmosphere
unless otherwise stated. The following compounds were syn-
thesized according to the procedures reported in the literature
(see ESI† for details): 3,6-dibromo-9-otcylcarbazole,17 3,7-dibromo-
10-octylphenothiazine,13b N-hexyl-4,40-dibromodiphenylamine,18
2,7-dibromo-9,9-dihexylfluorene13c and 3-(5-bromo-2-thienyl)-
2,5-dioctyl-6-thienylpyrrolo[3,4-c]pyrrole-1,4-dione.12,19
Measurements and characterization
1H-NMR and 13C-NMR spectra were obtained by Bruker
AVANCE II 400-MHz spectrometer with CDCl3 as solvent and
TMS as the internal standard. High-solution mass spectra
(HRMS) were collected using a MALDI Micro MX spectrometer.
UV-vis spectra data were recorded on a HP8453 UV-vis spectro-
photometer at room temperature in chloroform using a quartz
cuvette as a container. For the thin film spectra, the small
molecules were firstly dissolved in chloroform, and then spin-
casted on glass slides. Fluorescence spectra and fluorescence
quenching experiments were performed on a Shimadzu RF-
5301PC spectrofluorometer. Cyclic voltammetry (CV) was carried
out on a CHI 610D electrochemical workstation from CH Instru-
ments, Inc. In the electrochemical analyses, the redox properties
of the molecules were measured in Bu4NBF4/CH2Cl2 solutions.
The glass-carbon electrode served as the working electrode, and
an Ag/Ag+ electrode (Ag in 0.1 M AgNO3 solution of MeCN) and
platinum wire were chosen as the reference electrode and
the counter electrode, respectively. The ferrocene--ferrocenium
(Fc/Fc+) couple was selected as an internal standard.
10-Octyl-3,7-bis-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
phenothiazine (D3). 3,7-Dibromo-10-octylphenothiazine (0.19 g,
0.40 mmol), B2Pin2 (0.22 g, 0.88 mmol), KOAc (0.20 g,
2.0 mmol), and Pd(PPh3)2Cl2 (6.0 mg, 0.01 mmol) were used
to afford compound D3 (0.20 g, 90%) as a white solid. M.p.:
122–125 1C. 1H-NMR (CDCl3, ppm, 400 MHz) d = 7.55 (d, J =
8.4 Hz, 2H), 7.44 (s, 2H), 7.03 (d, J = 8.0 Hz, 2H), 4.00
(t, J = 6.8 Hz, 2H), 2.82 (s, 2H), 1.85–1.76 (m, 2H), 1.52–1.40
(m, 2H), 1.31 (s, 24H), 1.28–1.24 (m, 5H), 0.87–0.83 (m, 3H).
13C-NMR (CDCl3, ppm, 100 MHz) d = 205.29, 147.36, 134.25,
133.35, 123.53, 115.24, 46.97, 29.40, 28.82, 26.52, 24.35, 13.55.
MALDI-TOF HRMS: 563.3440 [M+] (calcd for C32H47NSO4B2:
563.3412).
10,10-Dihexyl-2,6-bis-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-
2-yl)fluorene (D4). 2,7-Dibromo-9,9-dihexylfluorene(0.49 g, 1.0 mmol),
B2Pin2 (0.56 g, 2.2 mmol), KOAc (0.49 g, 5.0 mmol), and
Pd(PPh3)2Cl2 (14 mg, 0.02 mmol) were used to afford com-
pound D4 (0.42 g, 71%) as a white solid. M.p.: 194–199 1C.
1H-NMR (CDCl3, ppm, 400 MHz) d = 7.80 (d, J = 7.6 Hz, 2H), 7.73
(t, J = 7.6 Hz, 4H), 2.02–1.98 (m, 4H), 1.39 (s, 24H), 1.10–0.99
(m, 12H), 0.76–0.72 (m, 6H), 0.57–0.48 (m, 4H). 13C-NMR
General procedures of Miyaura borylation reaction
A solution of dibromo-D (compound 1–4) (1.0 mmol ratio), (CDCl3, ppm, 100 MHz) d = 150.47, 143.93, 133.67, 128.94,
B2Pin2 (2.2 mmol ratio), KOAc (5.0 mmol ratio), and 119.37, 83.70, 55.17, 40.08, 31.43, 29.62, 24.94, 23.58, 22.55,
Pd(PPh3)2Cl2 (0.02 mmol ratio) in dry toluene (20 mL) was 14.00. MALDI-TOF HRMS: 586.4352 [M+] (calcd for C37H56O4B2:
refluxed at 110 1C under a nitrogen atmosphere for 18 h. After 586.4365).
being cooled to room temperature, the mixture was poured into
water (20 mL) and the organic layer was separated. The aqueous
layer was extracted with dichloromethane (3 ꢁ 10 mL) and the
General procedure of the Suzuki coupling reaction for the
target molecules
combined organic layers were dried over anhydrous Na2SO4. To a solution of D-boronic-ester (D1–D4) (1.0 mmol ratio),
The organic solvent was evaporated to dryness and the crude compound A (2.0 mmol ratio), Pd(PPh3)4 (0.1 mmol ratio) and
product was purified by silica column chromatography, eluting sodium carbonate (16 mmol ratio) in distilled toluene (30 mL),
with petroleum ether (60–90 1C)/ethyl acetate to afford the pure degassed deionized water (8 mL) and ethanol (4 mL) were
products (see Scheme 2 for the synthetic route).
added by syringe under a nitrogen atmosphere, then the
9-Octyl-3,6-bis-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)- mixture was refluxed for 19 h. After being cooled to room
carbazole (D1). 3,6-Dibromo-9-octylcarbazole (1.3 g, 3.0 mmol), temperature, the mixture was poured into 30 mL deionized
B2Pin2 (1.7 g, 6.6 mmol), KOAc (1.5 g, 15 mmol), and water and the organic layer was separated. The aqueous layer
Pd(PPh3)2Cl2 (42 mg, 0.06 mmol) were used to yield com- was extracted with dichloromethane (3 ꢁ 20 mL) and the
pound D1 (1.2 g, 74%) as a white solid. M.p.: 89–95 1C. combined organic layers were dried over anhydrous Na2SO4.
1H-NMR (CDCl3, ppm, 400 MHz) d = 8.66 (s, 2H), 7.90 (dd, J1 = After the solvent was evaporated, the crude product was puri-
1.0 Hz, J2 = 8.2 Hz, 2H), 7.38 (d, J = 8.0 Hz, 2H), 4.30 (t, J = fied by silica column chromatography, eluting with dichloro-
7.2 Hz, 2H), 1.88–1.81 (m, 2H), 1.38 (s, 24H), 1.34–1.21 (m, 8H), methane, to afford the target materials.
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6,60-[5,50-(9-Octyl-carbazole-3,6-diyl)bis(thiophene-5,2-diyl)]- 1H-NMR (CDCl3, ppm, 400 MHz) d = 8.97 (dd, J1 = 4.0 Hz, J2 =
bis{2,5-dioctyl-3-(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4-dione} 23.2 Hz, 4H), 7.73 (dd, J1 = 8.0 Hz, J2 = 22.0 Hz, 4H), 7.63 (d, J =
[CZ(TDPP)2]. Compound D1 (0.16 g, 0.30 mmol), compound A 5.6 Hz, 4H), 7.56 (d, J = 4.0 Hz, 2H), 7.29 (t, J = 4.4 Hz, 2H),
(0.41 g, 0.60 mmol), Pd(PPh3)4 (35 mg, 0.03 mmol) and sodium 4.17–4.08 (m, 8H), 2.08–0.74 (m, 86H). 13C-NMR (CDCl3, ppm,
carbonate (0.51 g, 4.8 mmol) were used to afford CZ(TDPP)2 100 MHz) d = 161.44, 161.26, 152.19, 150.54, 141.28, 139.82,
(0.32 g, 81%) as a purple solid. M.p.: 170–173 1C. 1H-NMR 139.49, 136.82, 135.15, 132.43, 130.50, 129.90, 128.61, 125.55,
(CDCl3, ppm, 400 MHz) d = 8.95 (dd, J1 = 4.0 Hz, J2 = 33.6 Hz, 124.61, 120.65, 120.27, 107.95, 107.86, 55.55, 42.28, 40.31,
4H), 8.41 (s, 2H), 7.79 (d, J = 8.4 Hz, 2H), 7.58 (dd, J1 = 4.8 Hz, 31.82, 31.79, 31.46, 30.02, 29.61, 29.24, 29.22, 26.96, 26.92,
J2 = 25.2 Hz, 4H), 7.41 (d, J = 8.4 Hz, 2H), 7.28 (d, J = 4.4 Hz, 2H), 23.81, 22.65, 22.54, 14.10, 13.99. MALDI-TOF HRMS:
4.31 (t, J = 6.4 Hz, 2H), 4.16–4.06 (m, 8H), 1.91–1.75 (m, 9H), 1379.7424 [M+] (calcd for C85H111N4O4S4: 1379.7488)
1.46–1.26 (m, 50H), 0.88–0.82 (m, 16H). 13C-NMR (CDCl3, ppm,
Fabrication of photovoltaic devices
100 MHz) d = 161.37, 160.99, 151.39, 141.07, 139.97, 138.70,
137.07, 134.86, 130.06, 130.00, 128.47, 127.68, 124.78, 123.55,
123.22, 118.10, 109.47, 107.86, 107.27, 43.38, 42.27, 31.85,
30.02, 29.70, 29.34, 29.27, 29.18, 29.00, 27.28, 26.99, 22.66,
22.60, 14.11, 14.06. MALDI-TOF HRMS: 1324.6764 [M+] (calcd
for C80H102N5O4S4: 1324.6815).
Bulk-heterojunction PV devices were fabricated with a conventional
device configuration of ITO/PEDOT:PSS/Donors:PC61BM(1 : 2, w/w)/
LiF/Al. The conductivity of the ITO-coated glass was 20 O/&
and it was ultrasonicated in detergent, acetone, toluene and
isopropyl alcohol for 30 min, respectively. After being dried
with a nitrogen airflow, the ITO substrates were spin-coated
with a thin layer of poly(3,4-ethylenedioxythiophene):poly(styrene
sulfonate) (PEDOT:PSS, Clevios P VPAI 4083) at 4000 rpm sꢀ1
for 1 min and subsequently baked at 140 1C for 30 min on a
hot plate. The active layer was prepared by spin-coating at
800 rpm sꢀ1 for 1 min with the dichlorobenzene solution of
the blended small molecules and PC61BM (total concentration
of 21 mg mLꢀ1, purchased from Lumtec. Corp.) on the top of
ITO/PEDOT:PSS. Finally, LiF (4 nm) and Al (100 nm) layers were
deposited by thermal evaporation through a shadow mask,
yielding six individual devices with a 0.04 cm2 nominal area.
J–V curves were recorded using a computer-controlled Keithley
2400 Source Measure Unit under AM 1.5G illumination with an
intensity of 80 mW cmꢀ2. A controlled OSC with a configuration
of ITO/PEDOT:PSS/P3HT:PC61BM/LiF/Al was fabricated and
characterized under the same working conditions.
6,60-{5,50-[4,40-(Hexylazanediyl)bis(4,1-pheneylene)]bis(thio-
phene-5,2-diyl)}bis{2,5-dioctyl-3-(thiophen-2-yl)pyrrolo[3,4-c]-
pyrrole-1,4-dione} [DPA(TDPP)2]. Compound D2 (51 mg, 0.10 mmol),
compound A (0.14 g, 0.20 mmol), Pd(PPh3)4 (12 mg, 0.01 mmol)
and sodium carbonate (0.17 g, 1.6 mmol) were used to afford
DPA(TDPP)2 (0.11 g, 81%) as a purple solid. M.p.: 160–162 1C.
1H-NMR (CDCl3, ppm, 400 MHz) d = 9.01 (d, J = 4.4 Hz, 2H), 8.90
(s, 2H), 7.61 (d, J = 8.4 Hz, 6H), 7.40 (s, 2H), 7.28 (t, J = 4.4 Hz,
2H), 7.09 (d, J = 8.4 Hz, 4H), 4.13–4.06 (m, 8H), 3.79 (s, 2H),
1.80–1.72 (m, 10H), 1.45–1.27 (m, 46H), 0.90–0.84 (m, 15H).
13C-NMR (CDCl3, ppm, 100 MHz) d = 161.47, 161.17, 150.22,
147.87, 140.13, 138.99, 137.26, 134.91, 130.26, 129.96, 129.04,
128.81, 128.55, 127.76, 127.66, 127.27, 127.20, 127.00, 126.36,
123.58, 121.16, 107.95, 107.45, 60.38, 53.42, 52.40, 42.26, 31.93,
31.83, 31.79, 31.60, 30.00, 29.70, 29.37, 29.23, 29.22, 27.50,
26.92, 26.74, 22.64, 14.20, 14.11, 14.10, 14.01. MALDI-TOF
HRMS: 1297.6644 [M+] (calcd for C78H99N5O4S4: 1297.6580).
6,60-[5,50-(10-Octyl-phenothiazine-3,7-diyl)bis(thiophene-5,2-
diyl)]bis{2,5-dioctyl-3-(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4-dione}
Acknowledgements
[PTZ(TDPP)2]. Compound D3 (0.11 g, 0.20 mmol), compound A The authors would like to thank the NSFC (21102013,
(0.27 g, 0.40 mmol), Pd(PPh3)4 (23 mg, 0.02 mmol) and sodium 20803030), the Dalian Committee of Science and Technology
carbonate (0.34 g, 3.2 mmol) were used to afford PTZ(TDPP)2 (2011J21DW001), the SRF for ROCS-SEM (no. 201001438, no.
(0.10 g, 37%) as a purple solid. M.p.: 201–205 1C. 1H-NMR 201001439), the Fundamental Funds for the Central Universities
(CDCl3, ppm, 400 MHz) d = 8.96 (d, J = 4.0 Hz, 2H), 8.91 (d, J = (DUT11LK20), and the RFDP (no. 20090041120017) for financial
3.2 Hz, 2H), 7.61 (d, J = 4.8 Hz, 2H), 7.46 (d, J = 8.4 Hz, 2H), 7.40 support.
(s, 2H), 7.36 (d, J = 4.0 Hz, 2H), 7.28 (d, J = 4.0 Hz, 2H), 6.86
(d, J = 8.8Hz, 2H), 4.09 (m, 8H), 3.88 (s, 2H), 1.84–1.74 (m, 9H),
Notes and references
1.45–1.27 (m, 52H), 0.89–0.86 (m, 14H). 13C-NMR (CDCl3, ppm,
100 MHz) d = 161.38, 161.14, 148.85, 144.70, 139.84, 139.18,
136.94, 135.02, 130.34, 129.90, 128.54, 128.04, 127.85, 125.40,
124.59, 124.42, 123.76, 115.50, 107.89, 107.60, 47.89, 42.27,
31.83, 31.79, 30.00, 29.23, 26.92, 26.69, 22.64, 14.09. MALDI-TOF
HRMS: 1356.6575 [M+] (calcd for C80H102N5O4S5: 1356.6535).
6,60-[5,50-(9,9-Dihexyl-fluorene-3,6-diyl)bis(thiophene-5,2-diyl)]-
bis{2,5-dioctyl-3-(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4-dione}
[FL(TDPP)2]. Compound D4 (0.15 g, 0.25 mmol), compound A
(0.34 g, 0.50 mmol), Pd(PPh3)4 (29 mg, 0.025 mmol) and
sodium carbonate (0.42 g, 4.0 mmol) were used to afford
FL(TDPP)2 (0.26 g, 74%) as a purple solid. M.p.: 117–122 1C.
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