Synthesis and characterization of perylene-bithiophene-triphenylamine triads: Studies on the effect of alkyl-substitution in p-type NiO based photocathodes

Article abstract of DOI:10.1039/c2jm16847b

We report the synthesis of new donor-π-acceptor (D-π-A) dyes and their application in dye-sensitized solar cells (DSCs) with nickel(ii) oxide (NiO)-based photocathodes. These D-π-A sensitizers incorporate a triphenylamine donor, a bithiophene π-bridge, and a perylenemonoimide (PMI) acceptor group. Two carboxylate groups attached to the triphenylamine afford strong anchoring to the NiO surface. The dyes in this series were varied firstly by the inclusion of an ethynyl linker between bithiophene and the triphenylamine moieties (1vs. 2), thereby increasing the length of the conjugated bridge. Despite very similar optoelectronic properties, the ethynyl-containing dye 2 showed a ～25% improvement in power conversion efficiency in p-DSCs compared to 1, mostly attributed to the increased current density. Contrary to initial expectations, there was no major influence of the distance between the PMI unit of the dye and the NiO surface on the photoinduced dye anion lifetime, as measured by nanosecond transient absorption spectroscopy (TAS). Furthermore, altering the position of the alkyl chains on the bridging bithiophene in 3 and 4 resulted in a modest red shift in the dye absorption on account of increased charge delocalisation between the PMI and the π-bridge, owing to a reduced torsion angle between the PMI and the adjacent thiophene unit. Quantum-chemical DFT calculations were performed in order to evaluate these torsion angles and to study their influence on the electron density distribution in the relevant molecular orbitals. These changes of the molecular structure of the isomeric dyes 3 and 4 did not translate into improved photovoltaic performance, which is primarily attributed to lower charge photogeneration rates probed by transient absorption spectroscopy. While for p-type DSCs impressive overall solar-to-electric conversion efficiency of 0.04-0.10% under full sun illumination (simulated AM1.5G sunlight, 100 mW cm^-2) and a broad incident photon to current efficiency (IPCE) response (350-700 nm) is demonstrated for these new dyes, the study clearly shows the need for judicious design rules for p-type sensitizers for application in photocathodic DSCs.

Full text of DOI:10.1039/c2jm16847b

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PAPER
Synthesis and characterization of perylene–bithiophene–triphenylamine
triads: studies on the effect of alkyl-substitution in p-type NiO based
photocathodes†
a
a
Martin Weidelener, Amaresh Mishra, Andrew Nattestad,bd Satvasheel Powar,c Attila J. Mozer,d
*
b
a
b
Elena Mena-Osteritz, Yi-Bing Cheng, Udo Bach and Peter Bauerle
a
*
*
€
Received 26th December 2011, Accepted 6th February 2012
DOI: 10.1039/c2jm16847b
We report the synthesis of new donor–p–acceptor (D–p–A) dyes and their application in dye-sensitized
solar cells (DSCs) with nickel(II) oxide (NiO)-based photocathodes. These D–p–A sensitizers
incorporate a triphenylamine donor, a bithiophene p-bridge, and a perylenemonoimide (PMI) acceptor
group. Two carboxylate groups attached to the triphenylamine afford strong anchoring to the NiO
surface. The dyes in this series were varied firstly by the inclusion of an ethynyl linker between
bithiophene and the triphenylamine moieties (1 vs. 2), thereby increasing the length of the conjugated
bridge. Despite very similar optoelectronic properties, the ethynyl-containing dye 2 showed a ꢀ25%
improvement in power conversion efficiency in p-DSCs compared to 1, mostly attributed to the
increased current density. Contrary to initial expectations, there was no major influence of the distance
between the PMI unit of the dye and the NiO surface on the photoinduced dye anion lifetime, as
measured by nanosecond transient absorption spectroscopy (TAS). Furthermore, altering the position
of the alkyl chains on the bridging bithiophene in 3 and 4 resulted in a modest red shift in the dye
absorption on account of increased charge delocalisation between the PMI and the p-bridge, owing to
a reduced torsion angle between the PMI and the adjacent thiophene unit. Quantum-chemical DFT
calculations were performed in order to evaluate these torsion angles and to study their influence on the
electron density distribution in the relevant molecular orbitals. These changes of the molecular
structure of the isomeric dyes 3 and 4 did not translate into improved photovoltaic performance, which
is primarily attributed to lower charge photogeneration rates probed by transient absorption
spectroscopy. While for p-type DSCs impressive overall solar-to-electric conversion efficiency of 0.04–
0.10% under full sun illumination (simulated AM1.5G sunlight, 100 mW cmꢁ2) and a broad incident
photon to current efficiency (IPCE) response (350–700 nm) is demonstrated for these new dyes, the
study clearly shows the need for judicious design rules for p-type sensitizers for application in
photocathodic DSCs.
in coming years. In this context, n-type dye-sensitized solar cells
Introduction
(n-DSCs) have attracted considerable attention with state-of-the-
art DSCs displaying overall power conversion efficiencies (h) in
excess of 12%.1–5 These devices utilise Ru(II)-polypyridyl
complexes or metal-free organic dyes as the photoactive material
which are adsorbed onto a high surface area mesoporous n-type
titanium dioxide (TiO2) along with a catalytic cathode typically
from platinum.6,7 In this case, photocurrent results from electron
injection from a photoexcited dye into the n-type semiconductor.
In contrast, dye-sensitized photocathodic solar cells (p-DSCs)
operate in an inverse mode with the transfer of a hole from
a photoexcited dye to the valence band of a p-type semi-
conductor such as NiO. Although some organic dyes such as
erythrosin B,8 coumarin9–12 and perylene derivatives13 have been
used as sensitizers for p-DSCs, recent studies have shown that for
The direct conversion of solar energy to electricity is expected to
provide a significant contribution to the renewable energy sector
aInstitute for Organic Chemistry II and Advanced Materials, University of
Ulm, Albert-Einstein-Allee 11, 89081 Ulm, Germany. E-mail: amaresh.
mishra@uni-ulm.de; peter.baeuerle@uni-ulm.de
bARC Centre of Excellence for Electromaterials Science, Department of
Materials Engineering, Monash University, Clayton, Victoria, Australia.
E-mail: udo.bach@monash.edu
cARC Centre of Excellence for Electromaterials Science, School of
Chemistry, Monash University, Clayton, Victoria, 3800 Australia
dARC Centre of Excellence for Electromaterials Science, Intelligent
Polymer Research Institute, AIIM Facility, Innovation Campus,
University of Wollongong, New South Wales, 2522, Australia
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c2jm16847b
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efficient p-type NiO-based photocathodic sensitizers it is
important that the anchoring groups are attached to the electron
donor part of the dye molecule and that the acceptor unit should
be spatially removed from the semiconductor surface.6,13–15
Due to good chemical and photostability, as well as reasonable
transparency, NiO represents to date the most successful p-type
semiconductor used for construction of dye-sensitized photo-
cathodes and of tandem np-DSCs, in which both electrodes are
photoactive,8,12,13 although other metal oxide semiconductors
have also been used.16,17 Photocurrent matching is an essential
prerequisite for the realization of highly efficient tandem pn-
DSCs. Recently, we demonstrated a judicious design of D–p–A
dyes which led to record efficiencies in p-DSCs and tandem np-
DSCs.18 p-DSCs with peak incident photon to current efficiency
(IPCE) values as high as 62% and overall efficiencies of up to
0.41% were observed using the perylenemonoimide–oligothio-
phene–triphenylamine (PMI–nT–TPA) triads. In tandem
np-DSC devices record efficiencies of up to 2.42% were demon-
strated. While these efficiencies constitute the best reported for
p-type DSCs to date, photocurrent matching of efficient np-
DSCs requires p-type sensitizers demonstrating high quantum
efficiency over a spectral range complementary to their n-type
counterparts. Due to intensive research efforts over the last two
decades, the number of available efficient n-type sensitizers is
very broad.6 Furthermore, there is a fairly well understood set of
criteria governing charge injection, charge recombination and
charge regeneration reactions in n-type DSCs.6,19 In contrast,
p-type DSCs are still in their infancy with only a few reports
highlighting the correlations between the molecular structure and
their solar cell performance.13,18,20–23
dye 1 to 3), however, results in steric hindrance between the tri-
phenylamine and the bithiophene bridge, which was further
reduced by the inclusion of an ethynyl unit in dye 4. This series of
dyes facilitates investigation into the effect of steric hindrances
within sensitizing molecules for p-DSCs. The insertion of a rigid
triple bond in dyes 2 and 4 increases the distance between the
acceptor and the NiO surface. It was anticipated that this extra
distance may affect the recombination kinetics between the
photoinjected holes on NiO and electrons primarily located on
the perylene unit of the photoreduced dye.
Results and discussions
Synthesis
Synthesis of triphenylamine building block 11 was achieved
according to Scheme 1. 4-Bromo benzoic acid 5 was suspended in
thionyl chloride and then stirred under reflux for 1 hour. After
removal of the excess of thionyl chloride the intermediate 4-
bromo benzoic acid chloride 5a was reacted with potassium tert-
butylate dissolved in THF at 0 ꢂC to afford 4-bromo benzoic acid
tert-butyl ester 6 in an overall 87% yield after bulb-to-bulb
distillation.24 Reaction of 1.5 eq. of aniline with 4-bromo benzoic
acid tert-butyl ester 6 in a Pd0-catalyzed amination by using
Herein, we present a further structural fine tuning of D–p–A
dye 1 as a model for the series of PMI–nT–TPA. In derivative 2
an additional ethynylene unit is incorporated between the
bridging bithiophene unit and the triphenylamine donor. D–p–A
dyes 3 and 4 represent regioisomers to 1 and 2, respectively, and
bear the hexyl side chain at the other b-position in each thio-
phene ring of the bithiophene bridge. Instead of creating
a distortion of the PMI and the adjacent 3-hexylthiophene unit in
dyes 1 and 2, in isomers 3 and 4 the steric repulsion is released
(Chart 1). This was further confirmed by quantum-chemical
DFT calculations. By shifting the alkyl chain position, the
torsion angle between the perylene and thiophene units in 3
decreases, resulting in a more planar dye with red-shifted
absorption. Changing the position of the alkyl chain (going from
Scheme 1 Synthesis of triphenylamine building block 11. Reagents and
conditions: (a) SOCl2, reflux; (b) KOtBu, THF, 0 ꢂC; (c) Pd2dba3,
[HP(tBu)3]BF4, KOtBu, toluene, rt; (d) ICl, Zn(OAc)2, dioxane, rt; (e)
trimethylsilylacetylene, CuI, Pd(PPh3)2Cl2, piperidine, 60 ꢂC; and (f)
CsF, THF, methanol, rt.
Chart 1 Structures of D–p–A dyes 1–4.
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2.25 eq. of potassium tert-butylate in toluene at room tempera-
ture yielded 78% of diphenylamine 7 after recrystallization.
Under similar conditions, diphenylamine 7 was reacted with 1.2
eq. of aryl bromide 6 to give corresponding triphenylamine 8 in
93% yield after column chromatography. Triphenylamine 8 was
iodinated in dioxane using 2 eq. of iodine monochloride which
had been activated by zinc acetate as Lewis acid.25 Iodinated
triphenylamine 9 was obtained in 90% yield after recrystalliza-
tion. Ethynyl-triphenylamine building block 10 was synthesized
by Pd0-catalyzed Sonogashira reaction of iodinated triphenyl-
amine 9 and 1.5 eq. of trimethylsilylacetylene in piperidine. The
reaction mixture was stirred at 60 ꢂC for 3 hours and triarylamine
10 was obtained in 92% yield after chromatographic work-up.
Deprotection of 10 using 3 eq. of caesium fluoride in a THF/
methanol mixture afforded acetylene 11 in quantitative yield.
5-Bromo-30,4-dihexyl-2,20-bithiophene26 12 was lithiated with
n-butyllithium (n-BuLi) in THF at ꢁ78 ꢂC and successively
quenched with trimethylsilyl (TMS) chloride to afford TMS-
protected bithiophene 13 in 83% yield (Scheme 2). Lithiation of
ꢂ
bithiophene 13 with n-BuLi in THF at ꢁ78 C and subsequent
addition of pinacol isopropyl borate led to boronic ester 14 in
87% yield (GC-purity: 90%), which was used for the next step
without further purification. Perylenyl-bithiophene dyad 16 was
synthesized by Pd0-catalyzed Suzuki-type cross-coupling reac-
tion of brominated perylenemonoimide 15 and boronic ester 14
in THF at 60 ꢂC and successive in situ deprotection of the TMS
group using tetrabutylammonium fluoride. After column chro-
matography perylenyl-bithiophene 16 was obtained in an overall
yield of 92%. Dyad 16 was iodinated using an effective mercury-
mediated iodination procedure26 to afford iodinated perylenyl-
bithiophene 18 in 92% yield after column chromatography.
Regioisomeric perylenyl-bithiophene building blocks 17
(ref. 26) and 18 were reacted with freshly deprotected triphe-
nylamine 11 in a Pd0-catalyzed Sonogashira reaction to afford
corresponding triads 19 and 20 in 60 and 87% yield, respectively,
after column chromatography (Scheme 3). The hydrolysis of the
ester group in the case of 2 and 4 under acidic conditions using
trifluoroacetic acid (TFA) was not successful. Therefore, the
ester groups were saponified with lithium hydroxide in methanol
Scheme 3 Synthesis of perylenyl-oligothiophene–triphenylamines 2 and
4. Reagents and conditions: (a) for 19: CuI, Pd2dba3, [HP(tBu)3]BF4,
piperidine, rt; for 20: CuI, Pd(PPh3)2Cl2, diisopropylamine, toluene, rt
and (b) LiOH, MeOH, THF, 70 ꢂC.
ꢂ
at 70 C to give free acids 2 and 4 in 60 and 88% yields, respec-
tively, after acidification with hydrochloric acid and filtration
over a short column.
PMI–2T–TPA triad 3, which is regioisomeric to parent dye 1,
was built up from bithiophene–triphenylamine dyad 22, which
was obtained by Pd0-catalyzed Suzuki-type coupling reaction of
bromobithiophene 12 and triphenylamine boronic ester 21 in
87% yield after chromatographic work-up. Bromination of 22 at
the free a-position of the terminal thiophene unit was carried out
with N-bromosuccinimide (NBS) in DMF at ꢁ10 ꢂC (Scheme 4).
After column chromatography brominated dyad 23 was
obtained in 80% yield.
Borylation of dyad 23 was obtained in a yield of about 50%
(confirmed by 1H-NMR) via magnesium–bromine exchange
using isopropylmagnesium chloride and lithium chloride in THF
at ꢁ10 ꢂC and subsequent quenching with pinacol isopropyl
borate. It was used for the next step without further purification.
Pd0-catalyzed Suzuki-type reaction of bromoperylenemonoimide
15 and boronic ester 24 afforded PMI–2T–TPA triad 25 in 86%
yield after chromatographic work-up. Triad 25 was hydrolyzed
using TFA in dichloromethane at room temperature to give free
acid 3 in quantitative yield after precipitation from n-hexane.
Optical properties
The UV-Vis absorption spectra of PMI–2T–TPA triads 1–4
showed an intense absorption band positioned at 520 to 530 nm
(Table 1 and Fig. 1). The elongation of the donor part by a triple
bond in 2 and 4 did not change the maximum of the low energy
absorption band compared to triads 1 and 3.27,28 However, the
high energy absorption band, which corresponds to the donor
Scheme 2 Synthesis of perylenylbithiophene building block 18. Reagents
and conditions: (a) (1) n-BuLi, THF, ꢁ78 ꢂC, (2) Me3SiCl; (b) (1) n-BuLi,
THF, ꢁ78 ꢂC, and (2) pinacol isopropyl borate; (c) (1) Pd(PPh3)4,
K3PO4, DME, 80 ꢂC and (2) Bu4NF; and (d) (1) Hg(OCp)2, dichloro-
methane, rt and (2) I2.
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Fig. 1b shows the optical absorption of dyes 1–4 adsorbed
onto the surface of transparent 0.9 mm thick NiO films with the
absorption of the blank NiO film subtracted. Compared to
solution spectra, dyes anchored at the NiO surface show blue-
shifts of ꢀ10 to 20 nm for the low energy absorption band, along
with a spectral broadening. As a result of this broadening the
onset of absorption onto the NiO film is extended to wavelengths
of 650–670 nm. A spectral broadening is also commonly
observed in the absorption of organic dyes adsorbed onto the
surface of n-type TiO2, which is ascribed to the electronic inter-
actions of the dye with the semiconductor and adjacent dye
molecules.29,30 The red shift in the low energy absorption band
between the dyes in solution and attached to NiO is nearly
identical for all dyes. The red shift associated with change in the
hexyl chain position in regioisomer dyes 3 and 4 is also clearly
observed on NiO making these dyes better light absorbers for
p-type DSCs. The similar spectral shifts for each dye, as
compared to solution, suggest there is no major difference in the
orientation or packing of dye molecules on the NiO surface.
Electrochemical properties
Oxidation and reduction potentials of triads 1–4 were measured
by cyclic voltammetry in dichloromethane and tetrabuty-
lammonium hexafluorophosphate (n-Bu4NPF6) as a supporting
electrolyte (Fig. 2). Redox potentials as well as electrochemically
determined band gaps (DECV) are summarized in Table 1. In the
oxidative regime, one oxidation process can be attributed to
the perylene unit (Eꢂox3) while the remaining ones originate from
the oxidation of the combined bithiophene and triarylamine
donor. It is interesting to note that the first and second oxidation
potentials (Eꢂox1 and Eꢂox2) of the ethynyl-containing dyes 2 and
4 are positively shifted compared to non-ethynylated counter-
parts 1 and 3. This can be ascribed to the presence of the electron-
withdrawing ethynylene group at the molecular backbone or by
a conformational change of the thiophene and triphenylamine
unit along the triple bond.28,31 The perylene oxidation of 2
(Eꢂ ¼ 1.10 V) and 4 (Eꢂ ¼ 1.04) is favoured over that of 1
Scheme
4 Synthesis of perylenyl-oligothiophene–triphenylamine 3.
Reagents and conditions: (a) Pd(OAc)2, PPh3, K3PO4, THF, reflux; (b)
NBS, DMF, ꢁ10 ꢂC; (c) (1) isopropylmagnesium chloride, LiCl,
THF, ꢁ10 ꢂC and (2) pinacol isopropyl borate; (d) Pd(PPh3)4, K3PO4,
THF, reflux; and (e) TFA, dichloromethane, rt.
unit (labs ¼ ꢀ360 nm), is slightly broadened towards the lower
energy region.
In comparison to the triads 1 and 2 the change of the hexyl
positions in dyes 3 and 4 led to a red shift of about 10 nm and
a broadening of the low energy absorption band. This might be
due to a partial decoupling between the perylene and bithiophene
p-orbitals, caused by a stronger twist between the perylene and
bithiophene units in 1 and 2, as a result of the hexyl chain close to
the perylene unit. This assumption was supported by the
observed low energy absorption band showing only one red-
shifted maximum (lmax ¼ ꢀ528 nm) for 3 and 4, while one
ox
ox
(Eꢂ ¼ 1.15 V) and 3 (Eꢂ ¼ 1.12). The results demonstrated
ox
ox
that the dications of ethynyl-containing dyes 2 and 4, which are
formed prior to the perylene oxidation, withdraw less electron
density from the adjacent perylene than the donor dications of
ethynyl-free dyes 1 and 3. On the other hand, all triads showed
maximum and an additional shoulder (lmax ¼ 518 nm, lmax, sh
498 nm) in the case of 1 and 2.
¼
Table 1 Optical and electrochemical properties of the perylenyl-bithiophene–triphenylamine triads 1–4 in dichloromethane
labs sol.a /nm 3/L molꢁ1 cmꢁ1
l
abs film /nm Eꢂ c/V Eꢂ c/V Eꢂ c/V Eꢂ c/V Eꢂ c/V EHOMOd/eV ELUMOd/eV DECVe/eV
ox1 ox2 ox3 red1 red2
1
2
361 (57 200)
498 (41 600)b
518 (45 000)
362 (61 800)
498 (39 200)b
519 (41 500)
358 (53 800)
528 (43 100)
362 (59 700)
530 (46 000)
358, 502
0.51
0.69
1.15
ꢁ1.41
ꢁ1.88
ꢁ5.54
ꢁ5.64
ꢁ3.80
ꢁ3.84
1.74
1.80
358, 502
0.62
0.75
1.10
ꢁ1.42
ꢁ1.87
3
4
353, 521
358, 521
0.48
0.60
0.67
0.77
1.12
1.04
ꢁ1.42
ꢁ1.37
ꢁ1.86
ꢁ1.76
ꢁ5.57
ꢁ5.47
ꢁ3.76
ꢁ3.82
1.81
1.65
a
b
c
d
c ¼ 5 ꢃ 10ꢁ5 mol Lꢁ1
.
Shoulder. In dichloromethane/nBu4NPF6 (0.1 M) vs. Fc/Fc+ at 100 mV sꢁ1
.
Taken from the onset and related to the
.
e
Fc/Fc+-couple with a calculated absolute energy of ꢁ5.1 eV. Band gap calculated to DE ¼ ELUMO ꢁ EHOMO
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Fig. 1 (a) UV-Vis spectra of 1–4 in dichloromethane. (b) Absorption spectra of the sensitizers on a NiO film (NiO absorption subtracted).
Fig. 3 Schematic representation of energy level diagram for electron
transfer processes in p-type DSCs. The charge regeneration process is
shown with green arrows and the charge recombination process with
a red arrow.
Fig. 2 Cyclic voltammograms of perylenyl-bithiophene–triphenylamines
1–4 in dichloromethane/nBu4NPF6 (0.1 M) vs. Fc/Fc+ at 100 mV sꢁ1
.
nearly identical electrochemical behaviour in the reductive
regime, which corresponds to the two step reduction of the
perylene unit at around ꢁ1.41 V and ꢁ1.87 V, respectively.
The HOMO levels of the triads calculated from electro-
chemical measurements were sufficiently lower than the valance
band edge of NiO (ꢀ ꢁ5.0 eV vs. vacuum or 0.5 V vs. NHE)
enabling sufficient driving force for hole injection from the dye to
the p-type semiconductor in DSCs. Equally, the LUMO energies
of 1–4 are sufficiently above the redox potential of the iodide–
triiodide redox couple, which should facilitate dye regeneration
(Fig. 3).
Density functional theory (DFT) calculations with a B3LYP
hybrid base (6-31G+(d,p)) were performed in order to evaluate
the distortion between the perylene and the adjacent hexylth-
iophene unit and to analyse the electron distribution of the
frontier orbitals. The HOMO–LUMO distribution of all dyes is
shown in Fig. 4. The HOMO orbital distribution in dyes 3 and 4
is slightly more localized on the thiophene and TPA units,
whereas in dyes 1 and 2 a more pronounced distribution on the
PMI compared to the TPA part is observed. The differences in
Fig. 4 Frontier orbitals distribution of dyes 1–4 calculated using the
B3LYP (6-31G+(dp)) DFT method (carbons in gray, nitrogens in blue,
oxygens in red, sulfurs in yellow and hydrogens in white). In order to
accelerate the convergence of optimizations the long hexyl chains were
replaced with ethyl substituents.
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Table 2 Photovoltaic parameters for devices made with 1.5 mm thick
mesoporous NiO electrodes, sensitized with dyes 1–4 and sandwiched
together with a platinized counter electrode at full sunlight (AM 1.5G,
100 mW cm2)
the HOMO orbital distribution are most probably due to a larger
twist in the thiophene–PMI bond in dyes 1 and 2 that arises from
the presence of the alkyl side chain close to the PMI unit (torsion
angle ꢀ63ꢂ) compared to 3 and 4 (torsion angle ¼ 54ꢂ). Conse-
quently, a better electronic delocalization between PMI and
thiophene parts can be expected in dyes 3 and 4 as manifested in
the HOMO electronic distribution. In contrast, the LUMO
orbital distribution is very similar for all dyes and localized
almost entirely on the PMI unit.
VOC/mV
JSC/mA cmꢁ2
Fill factor (%)
Efficiency (%)
1
2
3
4
146 ꢄ 1
147 ꢄ 8
122 ꢄ 9
136 ꢄ 4
1.77 ꢄ 0.04
2.24 ꢄ 0.01
1.06 ꢄ 0.09
1.23 ꢄ 0.22
30 ꢄ 1
30 ꢄ 1
29 ꢄ 3
28 ꢄ 1
0.08 ꢄ 0.01
0.10 ꢄ 0.01
0.04 ꢄ 0.01
0.05 ꢄ 0.01
The presence of the alkyl side chain on the TPA site in the case
of dye 3 resulted in a large torsion angle of about 47.4ꢂ between
the thiophene and phenyl units compared to dye 1 with a torsion
angle of only 25ꢂ. The torsion between the TPA and adjacent
thiophene unit was further reduced to planarity by the intro-
duction of a triple bond (improper torsion angle ¼ 0.9ꢂ) in dye 4,
while no significant difference was observed in the device
performance as compared to dye 3 (vide infra).
electrons occupying the dye’s LUMO and holes located in the
semiconductor electrode strongly governs the observable
recombination time constants.18 No change was observed in the
open circuit voltage (VOC) and FF values for dyes 1 and 2. The
device based on ethynyl-containing dye 2 showed the highest
power conversion efficiency (PCE) of 0.10% among the dyes
studied here, which is about 25% higher compared to dye 1. In
comparison to dye 1 device, a decrease in the VOC and JSC values
was seen by changing the position of the hexyl chain in
regioisomer dye 3, thus, lowering the PCE to 0.04%. The intro-
duction of a triple bond in regioisomer dye 4 slightly increases the
JSC value compared to dye 3, and subsequently the overall PCEs
for both dyes are very similar. The comparable performance of
dyes 3 and 4 can be ascribed to the planarization of the perylene–
thiophene units due to the different hexyl substitution pattern
compared to 1 and 2. The result further confirms that the partial
decoupling between the acceptor and donor units appears to be
essential for better device performance. Compared to dyes 1 and
3, the JSC values are increased for ethynyl-containing sensitizers,
2 and 4, which could be ascribed to the improved injection and/or
reduced recombination process.
Photovoltaic performance
For the potential application in DSCs the stability of the dyes is
very important. This series of dyes are found to be highly stable
under acidic and basic conditions. Current density–voltage (J–V)
curves of devices based on dyes 1–4 are shown in Fig. 5 and the
data are summarized in Table 2. The device measurements are
very coherent and the data are reproducible within the given
experimental accuracy. The results presented are repeated 3 times
(different days) and are average over ꢀ4 devices each.
The advantage of the presence of the ethynylene unit in triad 2
is reflected in an increased short circuit current density (JSC
)
value by about 30% compared to parent dye 1, roughly half the
increase seen previously by going from a bithiophene to qua-
terthiophene bridge.18 Absorption data (Fig. 1), however, show
little difference in the light-harvesting properties of dyes 1 and 2.
This improvement in JSC is likely to arise from the retardation of
charge recombination of the photoreduced dyes with holes in the
NiO-photocathode. This assumption was made based on our
previous observation that the tunnelling distance between
IPCE responses of devices constructed using 1–4 are shown in
Fig. 6 and correspond well with the measured JSC values given in
Table 2. Compounds 1 and 2 exhibit broad IPCE spectra ranging
from 350 up to 650 nm region, which is extended to 700 nm for
dyes 3 and 4. The IPCE spectrum of dye 1 showed a maximum of
about 16% at both absorption peaks of 380 and 503 nm. An
increase in the IPCE peak maximum to 22% was observed by the
insertion of an ethynylene group in dye 2. The result is also
consistent with their absorption spectra in thin films, thus,
showing the contribution of absorption bands to the IPCE and
JSC. In contrast, the regioisomeric dye 3 showed an IPCE
Fig. 5 Current–voltage (J–V) characteristics of devices under AM 1.5
simulated solar (100 mW cmꢁ2) illumination (filled symbols) and in the
dark (open symbols) produced using 1.5 mm thick NiO electrodes,
sensitized with dyes 1–4. Electrolyte composition: 0.6 M N-methyl-N-
butyl imidazoliumiodide, 0.5 M 4-tert-butylpyridine, 0.1 M guanidinium
thiocyanate and 30 mM iodine in 85 : 15 acetonitrile/valeronitrile.
Fig. 6 Incident photon to charge carrier conversion efficiencies for
devices constructed using dyes 1–4.
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maximum of only about 8% at 533 nm, which is slightly increased
to 10% for ethynylene-containing regioisomeric dye 4. The
results clearly show the influence of the ethynylene spacer on the
solar cell performance. In addition to the increasing magnitude
of the IPCE response, there is also an observed broadening in the
absorption peak corresponding to high energy absorption (ꢀ400
to 450 nm), which is in agreement with the thin film absorption
spectra seen in Fig. 1b.
component of the recombination kinetics, beyond the time
resolution of our setup (50 ns).
The transient spectra of photoreduced dyes 1 and 3 resemble
that of the electrochemically generated species (Fig. 8a and b as
well as Fig. S2†). We note that the intense absorption peak of the
electrochemically generated anion 3 centred at 625 nm is not
evident in the TA spectrum (Fig. 8b). We attribute this to the
stronger overlap of the red-shifted ground state absorption of 3
and the first absorption peak of the anion, which has not shifted
significantly between 1 and 3. As a result TAS of NiO sensitized
with dye 3 shows a less significant absorption feature in the 600–
650 nm wavelength range than NiO films sensitized with dye 1.
The NiO hole–dye anion recombination kinetics for all dyes in
Fig. 7 are quite similar and can be characterized with a signal
decay half time of around 300 ns for 1 and 2 and around 250 ns
for 3 and 4, which is very similar to our previously reported value
for the dye 1.18 Contrary to our expectation, the elongation of the
p-bridge in dyes 2 and 4 using the ethynyl spacer did not
translate into an improved dye anion lifetime compared to 1 and
3. In our previous study, increasing the number of bithiophene
units resulted in a 7-fold increase for the quaterthiophene and
a further 2 fold increase for the sexithiophene bridge.18 Clearly,
the ethynyl linker is found to be not as effective as the bithio-
phene bridge. A possible explanation for the reduced charge
generation yield in 3 and 4 could be the reduction of the torsion
angle between the PMI and the adjacent thiophene unit, thus
resulting in a faster hole–dye anion recombination rate.
The IPCE responses show that, in spite of the improved light
harvesting, and a similar magnitude of light absorption (Fig. 1b),
lower quantum efficiencies for either charge injection or trans-
port are mostly responsible for the smaller JSC values recorded
for dyes 3 and 4. This might be due to the planarization of the
perylene–thiophene unit. In Fig. 1b it can be seen that in all cases
spectra of the dyes on NiO films show a peak at ꢀ350 to 360 nm
which is higher than the one at ꢀ500 nm. In contrast, the peaks
of the IPCE at both wavelength regions for all devices are nearly
identical. In these p-DSC devices the IPCE response at short
wavelengths is mitigated due to the light harvesting competition
from both the electrolyte and NiO.
Transient absorption spectroscopy
Transient absorption spectroscopy (TAS) experiments of dyes 1–
4 on NiO films in the absence of a redox mediator were per-
formed to investigate the recombination kinetics of the photo-
reduced dye anions with holes in the NiO-photocathode (Fig. 7).
Substantially higher signal magnitudes have been measured for
dyes 1 and 2 compared to the regioisomeric dyes 3 and 4, which
cannot be attributed to differences in the absorbed pump beam
intensity (1–10ꢁad, where ad is the optical density of the films) at
the pump wavelength of 532 nm (see Fig. 1b and S1†), since the
optical densities of the films were nearly identical. Furthermore,
the absorbance of the electrochemically reduced dye species in
DMF solution is also very similar at the probe wavelength of
700 nm (see Fig. S2†). While the electrochemically reduced 3 and
4 absorb less light in the 600–700 nm main anion absorption
band, the anions of 3 and 4 absorb slightly more due to their red-
shifted absorbance band at the 700 nm TA probe wavelength.
Therefore, the reduced TAS signal magnitude in Fig. 7 is not due
to a lower absorption coefficient of the 3 and 4 anions, but rather
originates from reduced hole injection yield and/or a fast
Further work should focus on determining the photophysical
origin of the reduced performance of dyes 3 and 4 using sub-ns
time-resolved photoluminescence and transient absorption
spectroscopy. Furthermore, photoreduced dye anion and NiO
recombination is fast for all four dyes, competing with dye anion
Fig. 8 Transient absorption spectrum of NiO films sensitized with 1 (a)
and 3 (b) after laser excitation at a wavelength of 532 nm (intensity: 90 mJ
cmꢁ2 pulseꢁ1). The green solid line represents scaled absorption of elec-
trochemically reduced (at ꢁ550 mV versus Ag/AgCl) dye anion in DMF.
The thick black line represents scaled and inverted absorption spectrum
of neutral dye in DMF at open circuit.
Fig. 7 Transient absorption decay signals of NiO films sensitized with 1–
4 after laser excitation at a wavelength of 532 nm (intensity: 32 mJ cmꢁ2
pulseꢁ1), probing at 700 nm.
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regeneration occurring on a similar time scale. Extending dye
anion lifetime to the ms to ms time range, similarly to frequently
observed long photooxidized dye–TiO2 lifetimes of most n-type
dye-sensitised photoanodes, will be crucial for photocathodes to
match their performance, a prerequisite for high efficiency
tandem (np-DSC) devices.
SCL-10A equipped with
a
SPD-M10A photodiode array
detector and a SC-10A solvent delivery system using a LiChros-
phor column (Silica 60, 5 mm, Merck). Thin-layer chromatog-
raphy was carried out on Silica Gel 60 F254 aluminium plates
(Merck). Solvents and reagents were purified and dried by usual
methods prior to use and typically used under inert gas atmo-
sphere. The following starting materials were purchased and used
without further purification: p-bromobenzoic acid (Merck), thi-
onyl chloride (Merck), potassium tert-butylate (Merck), iodine
monochloride (Merck), zinc acetate (Merck), bis(pinacolato)
diboron (Lancaster), ethynyl-trimethyl-silane (ABCR), and
Pd(dppf)Cl2 (Aldrich).
Conclusion
Synthesis and characterization of a new series of PMI–2T–TPA
triads have been reported where (1) an ethynyl group was used to
extend the p-bridge length, and/or (2) the positions of the hexyl
chains on the thiophenes that comprise the p-bridge were altered.
Subsequently, steric hindrances within the dye were investigated.
Optical, electrochemical and device results showed the benefit of
an ethynyl linker, although this was much more pronounced for
dye 2 compared to 1 than for 4 compared to 3. There were also
clearly observed differences for the regioisomeric dyes 3 and 4
compared to dyes 1 and 2. Quantum-chemical DFT calculations
showed the planarization of the perylene–thiophene linkage for
compounds 3 and 4, resulting in a beneficial red shift (greater
light harvesting ability), however, this was outweighed by
a decreased charge generation and/or collection, suggesting that
torsion between the acceptor and donor may be necessary for
high quantum efficiencies. A broad IPCE spectrum is observed
for these dyes in the spectral region between 350 and 700 nm,
which increases by insertion of an acetylene unit leading to an
increased p-conjugation length. Using 1.5 mm thick mesoporous
NiO films, power conversion efficiencies in the range from 0.04 to
0.10% under full sun illumination (simulated AM 1.5G sunlight,
100 mW cmꢁ2) were observed, which give valuable insight into
the construction principles of dyes for NiO-photocathodes useful
for p-DSCs. It should be noted that with dye 2 comprising an
ethynylene spacer the power conversion efficiency of the original
PMI–2T–TPA 1 has been increased from 0.08 to 0.10%, i.e.
a 25% improvement. Furthermore, to develop high performance
tandem devices it is also crucial to develop p-type sensitizers that
match the performance of their n-type counterpart and should
have complementary absorption, work towards this direction is
in progress.
Optical and cyclic voltammetric measurements
UV-Vis spectra in dichloromethane solution were taken on
a Perkin-Elmer Lambda 19 spectrometer. Thin film spectra were
taken using a Varian Cary 5000 spectrometer with integrating
sphere attachment (Varian Internal DRA 2500). Cyclic voltam-
metry experiments were performed with a computer-controlled
EG&G PAR 273 potentiostat in a three-electrode single-
compartment cell (5 mL). The platinum working electrode con-
sisted of a platinum wire sealed in a soft glass tube with a surface
of A ¼ 0.785 mm2, which was polished down to 0.5 mm with
Buehler polishing paste prior to use in order to obtain repro-
ducible surfaces. The counter electrode consisted of a platinum
wire and the reference electrode was an Ag/AgCl reference
electrode. All potentials were internally referenced to the ferro-
cene/ferricenium couple. For the measurements concentrations
of 10ꢁ3 mol Lꢁ1 of the electroactive species were used in freshly
distilled and deaerated dichloromethane (Lichrosolv, Merck) and
0.1 M tetrabutylammonium hexafluorophosphate (TBAPF6,
Fluka) which was twice recrystallized from ethanol and dried
under vacuum prior to use.
Quantum-chemical calculations
Density functional theory was employed with the hybrid func-
tionals B3LYP and the basis set 6-31G+ including d and p diffuse
functions from the Gaussian 09 package. The long hexyl chains,
which have no significant impact on the frontier orbitals of the
chromophores, were replaced with ethyl substituents in order to
accelerate the convergence of optimizations.
Experimental
General procedures
Device fabrication
1H NMR spectra were recorded in CDCl3 and d6-DMSO on
a Bruker AMX 400 at 400 MHz. 13C NMR spectra were recorded
in CDCl3 and d6-DMSO on a Bruker AMX 400 at 100 MHz.
Chemical shifts are denoted by a d unit (ppm). The splitting
patterns are designated as follows: s (singlet), d (doublet), t
(triplet), dt (double triplet), quin (quintet), hep (heptet) and m
(multiplet) and the assignments are Pery (perylene), TPA (tri-
4 ꢃ 4 mm NiO films were screen printed onto F:SnO2 glass
(Nippon Sheet Glass) using a paste produced by grinding 15 g of
NiO (Inframat) in ethanol, added in small aliquots. 50 mL of
a 10 wt% ethyl cellulose solution in ethanol and 100 mL terpineol
were then added and after mixing ethanol was evaporated to
leave a terpineol based paste. These were sintered for 30 minutes
at 400 ꢂC, then 10 minutes at 550 ꢂC, before being immersed into
dye solutions (0.2 mM in DMF) for 2 hours. Films were then
removed from this dye solution and rinsed subsequently in DMF
and ethanol before being allowed to dry. Counter electrodes were
produced by applying one drop of H2PtCl6 (10 mM in ethanol) to
F:SnO2 glass and thermally decomposing by firing at 400 ꢂC for
15 minutes under a gentle flow of air. Counter and working
electrodes were sandwiched together with a 25 mm Surlyn
1
phenylamine), Ph (phenyl), and Th (thiophene) for H NMR.
Mass spectra were recorded with a Varian Saturn 2000 GC-MS
and with a MALDI-TOF MS Bruker Reflex 2 (dithranol as the
generally used matrix and 2,5-dihydroxybenzoic acid for the free
€
acids). Melting points were determined with a Buchi B-545
melting point apparatus and are not corrected. Gas chroma-
tography was carried out using a Varian CP-3800 gas chro-
matograph. HPLC analyses were performed on a Shimadzu
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(Dupont) spacer, and heated to ꢀ120 ꢂC for ꢀ30 seconds in
order to create a seal. The electrolyte solution was introduced
through a pre-drilled hole in the counter electrode, which was
subsequently sealed with another piece of Surlyn and a micro-
scope cover slip.
131.06, 131.50, 128.00, 81.84, 28.74; MS (EI) m/z: [M]+ calcd for
C11H13BrO2, 256; found, 257.
4-(N-Phenylamino)benzoic acid tert-butyl ester (7). Aniline
(1.4 g, 15 mmol) and ester 6 (2.6 g, 10 mmol) were dissolved in
50 mL dry toluene. After the solution was degassed potassium
tert-butylate (2.5 g, 22.5 mmol) and the catalyst (Pd2dba3
[104 mg, 0.1 mmol] and [HP(t-Bu3)]BF4 [46 mg, 0.16 mmol]) were
added. Next, the resulting suspension was degassed and stirred
for 2 hours at room temperature. After the reaction was
completed it was poured into water and the aqueous phase was
acidified with hydrochloric acid. The water phase was extracted
with dichloromethane and the organic phase was dried with
magnesium sulfate. After the solvent was removed by rotary
evaporation the residue was dissolved in dichloromethane and
was filtered over a short silica column to remove the catalytic
residues. The solvent was evaporated and the crude product was
dissolved in 5 mL hot chloroform. After addition of 50 mL hot n-
hexane the product was allowed to crystallize. The white crystals
of 7 (2.1 g, 78%) were filtered off and dried in vacuum. M.p.:
Current–voltage characterisation
Solar cells were tested using simulated sunlight (AM1.5, 1000 W
mꢁ2) provided by an Oriel solar simulator with an AM1.5 filter.
Current–voltage characteristics were measured using a Keithley
2400 source meter. Cells were biased from high to low, with
10 mV steps and a 250 ms settling time between the application of
a bias and current measurement.
Incident photon to current efficiency characterisation
IPCE was measured with the cell held under short circuit
conditions and illuminated by monochromatic light. A Corner-
stone 260 monochromator was used in conjunction with an
optical fibre, Keithly 2400 source meter and 150 W Oriel Xe
lamp. Prior to testing a 30 second ‘rest’ period was introduced to
ensure the dark current dropped to zero when the cell was short
circuited. Additionally, 200 ms settling time was applied between
the monochromator switching to a wavelength and measurement
commencing, which was followed by an averaged reading over
a 1 second period.
1
115 ꢂC; H NMR (400 MHz, CDCl3): d ¼ 7.89–7.85 (m, 2H,
(t-Bu)OOC-Ph-2H,6H), 7.35–7.28 (m, 2H, Ph-2H,6H), 7.17–7.13
(m, 2H, (t-Bu)OOC-Ph-3H,5H), 7.04 (d, J ¼ 7.4 Hz, 1H, Ph-4H),
7.00–6.95 (m, 2H, Ph-3H,5H), 5.99 (s, 1H, -NH), 1.58 (s, 9H, C-
(CH3)3); 13C NMR (100 MHz, CDCl3): d ¼ 165.75, 147.54,
141.18, 131.27, 129.48, 123.28, 122.83, 120.06, 114.75, 80.25,
28.31; MS (EI) m/z: [M]+ calcd for C17H19NO2, 269; found, 269.
Elemental analysis: calcd (%) for C17H19NO2: C 75.81, H 7.11, N
5.20; found C 75.85, H 7.00, N 5.19%.
Transient absorption spectroscopy
TAS experiments were performed as previously reported.32
A
N,N-Di(4-benzoic acid tert-butyl ester)phenylamine (8).
Diphenylamine 7 (0.97 g, 3.6 mmol) and ester 6 (1.0 g, 3.9 mmol)
were dissolved in 18 mL dry toluene. After the solution was
degassed potassium tert-butylate (807 mg, 7.5 mmol) and the
catalyst (Pd2dba3 [37 mg, 36 mmol] and [HP(t-Bu3)]BF4 [17 mg,
58 mmol]) were added. Next, the resulting suspension was
degassed and was stirred for 2 hours at room temperature. After
the reaction was completed it was poured into water and the
aqueous phase was acidified with hydrochloric acid (pH ¼ 7).
The water phase was extracted with dichloromethane and the
organic phase was dried with magnesium sulfate. After the
solvent was removed by rotary evaporation the crude product
was purified by column chromatography (SiO2, dichlor-
omethane : petrol ether [2 : 1]) to give 8 (1.5 g, 93%) as a white
solid. M.p.: 63 ꢂC; 1H NMR (400 MHz, CDCl3): d ¼ 7.86 (d, J ¼
8.8 Hz, 4H, (t-Bu)OOC-Ph-2H,6H), 7.32 (d, J ¼ 7.8 Hz, 2H, Ph-
2H,6H), 7.17 (d, J ¼ 7.3 Hz, 1H, Ph-4H), 7.14–7.10 (m, 2H, Ph-
3H,5H), 7.06 (d, J ¼ 8.8 Hz, 4H, (t-Bu)OOC-Ph-3H,5H), 1.58 (s,
18H, C-(CH3)3); 13C NMR (100 MHz, CDCl3): d ¼ 165.40,
150.76, 130.80, 129.75, 126.31, 126.10, 122.43, 80.70, 28.26; MS
(CI) m/z: [M]+ calcd for C28H31NO4, 445; found, 445. Elemental
analysis: calcd (%) for C28H31NO4: C 75.48, H 7.01, N 3.14;
found C 75.40, H 7.03, N 3.05%.
532 nm pump was used (Nd-YAG, INDI-40-10, Spectra-
Physics), operating in Q-switch mode (6 ns pulse) at a 10 Hz
repetition rate. A 1000 W Xe lamp (Edinburgh Instruments) was
used for the probe, employing a 700 nm bandpass filter with an
FWHM of 40 nm. The signal was passed through a mono-
chromator to a Si detector (Femto), and a signal recorded by
a Tektronix 4054 oscilloscope.
Synthesis
4-Bromo-benzoic acid tert-butyl ester (6).24 4-Bromobenzoic
acid 5 (10.1 g, 50 mmol) was added to 25 mL thionyl chloride.
After three drops of DMF were added to the suspension it was
stirred under reflux for one hour. When the reaction was
completed the excess of thionyl chloride was removed in vacuum.
The residual yellowish solid 5a was dissolved in 10 mL dry THF
and the resulting solution was cooled down to 0 ꢂC. Next, under
constant stirring a solution of potassium tert-butylate (6.7 g,
60 mL) dissolved in 50 mL dry THF was added slowly over
a period of one hour while the temperature was not allowed to
ꢂ
exceed 5 C. The resulting suspension was poured into 250 mL
water and was extracted with diethylether. The organic phase
was washed with a saturated sodium hydrogen carbonate solu-
tion and was dried with magnesium sulfate. After the solvent was
removed by rotary evaporation the crude product was purified
by bulb-to-bulb distillation to afford ester 6 (11.2 g, 87%) as
a colorless liquid. 1H NMR (400 MHz, CDCl3): d ¼ 7.84 (d, J ¼
8.6 Hz, 2H, Ph-2H,6H), 7.54 (d, J ¼ 8.6 Hz, 2H, Ph-3H,5H), 1.59
(s, 9H, C-(CH3)3); 13C NMR (100 MHz, CDCl3): 165.38, 132.03,
N,N-Di(4-benzoic acid tert-butyl ester)-4-iodo-phenylamine (9).
Iodine chloride (413 mg, 2.46 mmol) and zinc acetate (270 mg,
1.23 mmol) were added to 3 mL dioxane and was stirred for
15 min at room temperature. Next, diphenylamine 8 (550 mg,
1.23 mmol) dissolved in 2 mL dioxane was added slowly and the
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resulting brownish solution was stirred at room temperature for
3 hours. After the reaction was completed the reaction mixture
was poured into 20 mL of a 1 molar sodium thiosulfate solution.
The water phase was extracted with dichloromethane and the
organic phase was dried with magnesium sulfate. After the
solvent was removed by rotary evaporation the crude product
was dissolved in 3 mL hot chloroform. After addition of 30 mL
hot methanol the product was allowed to crystallize. The white
crystals of 9 (635 mg, 90%) were filtered off and dried in vacuum.
M.p.: 172–173 ꢂC; 1H NMR (400 MHz, CDCl3): d ¼ 7.87 (d, J ¼
8.8 Hz, 4H, (t-Bu)OOC-Ph-2H,6H), 7.60 (d, J ¼ 8.8 Hz, 2H, Ph-
3H,5H), 7.05 (d, J ¼ 8.8 Hz, 4H, (t-Bu)OOC-Ph-3H,5H), 6.87 (d,
J1 ¼ 8.8 Hz, 2H, Ph-2H,6H), 1.58 (s, 18H, C-(CH3)3); 13C NMR
(100 MHz, CDCl3): d ¼ 126.26, 150.23, 138.72, 130.92, 127.57,
126.64, 122.78, 80.86, 28.23; MS (MALDI-TOF) m/z: [M]+ calcd
for C28H30INO4, 571; found [M + H]+, 572. Elemental analysis:
calcd (%) for C28H30INO4: C 58.85, H 5.29, N 2.45; found C
58.92, H 5.32, N 2.37%.
146.94, 133.63, 131.07, 127.01, 125.00, 123.30, 117.93, 107.90,
83.40, 81.02, 28.38; 165.26, 150.25, 146.43, 133.32, 130.89,
126.72, 124.86, 123.06, 118.89, 104.60, 94.41, 80.84, 28.22; MS
(CI) m/z: [M]+ calcd for C30H31NO4, 469; found [M + H]+, 470.
5-Trimethylsilyl-4,30-dihexyl-2,20-bithiophene (13). n-Butyl-
lithium (0.39 mL, 0.62 mmol) was added dropwise to a solution
of bromo-bithiophene 12 (250 mg, 0.60 mmol) in 3 mL dry THF
at ꢁ78 ꢂC. After the addition the solution was stirred for 15 min
at ꢁ78 ꢂC. Trimethylsilyl chloride was added, subsequently. The
cooling bath was removed and the reaction was stirred until it
had warmed up to room temperature. Then the mixture was
poured into water and the organic layer was separated and the
aqueous phase was extracted with diethylether. The combined
organic phases were washed with brine and dried over sodium
sulfate and the solvent was removed by rotary evaporation. The
crude product was purified by column chromatography (SiO2/n-
1
hexane) to give 13 (203 mg, 83%) as a yellow oil. H NMR
(400 MHz, CDCl3): d ¼ 7.13 (d, J ¼ 5.2 Hz, 1H, 50-H), 7.03 (s,
1H, 3-H), 6.91 (d, J ¼ 5.2 Hz, 40-H), 2.75 (t, J ¼ 7.9 Hz, 2H, a0-
CH2), 2.64 (t, J ¼ 7.9 Hz, 2H, a-CH2), 1.66–1.57 (m, 4H, b-CH2,
b0-CH2), 1.41–1.26 (m, 12H, -CH2-), 0.90 (t, J ¼ 6.8 Hz, 3H, Th0-
CH3), 0.88 (t, J ¼ 6.7, 3H, Th-CH3), 0.35 (s, 9H, Si-CH3); 13C
NMR (100 MHz, CDCl3): d ¼ 150.672, 140.044, 139.164,
132.879, 130.974, 129.921, 129.133, 123.293, 31.761, 31.721,
31.639, 31.451, 30.629, 29.398, 29.183, 22.623, 14.097, 0.401; MS
(EI) m/z: [M]+ calcd for C23H38S2Si, 406; found, 406. Elemental
analysis: calcd (%) for C23H38S2Si: C 67.91, H 9.42, S 15.77;
found C 68.18, H 9.40, S 15.56%.
N,N-Di(4-benzoic acid tert-butyl ester)-4-trimethylsilanyle-
thynyl-phenylamine (10). Triphenylamine 9 (115 mg, 0.2 mmol),
ethynyl-trimethylsilane (30 mg, 0.3 mmol), Pd(PPh3)2Cl2
(7.0 mg, 0.01 mmol) and CuI (3.8 mg, 0.02 mmol) were added to
0.5 mL piperidine. The reaction mixture was carefully degassed
ꢂ
and was stirred at 60 C for 3–4 hours. After the reaction was
completed the mixture was poured into water (20 mL) and was
acidified with concentrated hydrochloric acid (pH ¼ 1). The
organic layer was taken off while the water phase was extracted
with dichloromethane. The combined organic phases were dried
with magnesium sulfate and the solvent was removed by rotary
evaporation. The crude product was purified by column chro-
matography (SiO2/dichloromethane : petrol ether [2 : 1]) to give
5-(4,30-Dihexyl-50-trimethylsilyl-2,20-bithien-5-yl)-4,4,5,5-tetra-
methyl-[1,3,2]dioxaborolane (14). n-Butyllithium (0.14 mL, 0.35
mmol) was added dropwise to a solution of trimethysilyl-
bithiophene 13 (130 mg, 0.32 mmol) in 1.5 mL dry THF
at ꢁ78 ꢂC. After the addition the solution was stirred for 15 min
at ꢁ78 ꢂC. Trimethylsilyl chloride was added, subsequently. The
cooling bath was removed and the reaction was stirred until it
had warmed up to room temperature. Then the mixture was
poured into water and the organic layer was separated and the
aqueous phase was extracted with diethylether. The combined
organic phases were washed with brine and dried over sodium
sulfate and the solvent was removed by rotary evaporation.
Boronic ester 14 was obtained as a yellow oil (165 mg, 92%) with
a purity of 95% (GC). It was used without further purification.
1H NMR (400 MHz, CDCl3): d ¼ 7.44 (s, 1H, 4-H), 7.10 (s, 1H,
30-H), 2.75 (t, J ¼ 7.9 Hz, 2H, a0-CH2), 2.64 (t, J ¼ 7.9 Hz, 2H, a-
CH2), 1.66–1.57 (m, 4H, b-CH2, b0-CH2), 1.41–1.26 (m, 12H,
-CH2-), 0.90 (t, J ¼ 6.8 Hz, 3H, Th0-CH3), 0.88 (t, J ¼ 6.7, 3H,
Th-CH3), 0.35 (s, 9H, Si-CH3); MS (EI) m/z: [M]+ calcd for
C29H49BO2S2Si, 532; found, 533.
ꢂ
1
10 (100 mg, 92%) as a white solid. M.p.: 150–151 C; H NMR
(400 MHz, CDCl3): d ¼ 7.87 (d, J ¼ 8.6 Hz, 4H, (t-Bu)OOC-Ph-
2H,6H), 7.39 (d, J ¼ 8.6 Hz, 2H, Ph-3H,5H), 7.07 (d, J ¼ 8.6 Hz,
4H, (t-Bu)OOC-Ph-3H,5H), 7.02 (d, J ¼ 8.6 Hz, 2H, Ph-2H,6H),
1.58 (s, 18H, C-(CH3)3), 0.25 (s, 9H, Si-(CH3)3); 13C NMR
(100 MHz, CDCl3): d ¼ 165.26, 150.25, 146.43, 133.32, 130.89,
126.72, 124.86, 123.06, 118.89, 104.60, 94.41, 80.84, 28.22; MS
(MALDI-TOF) m/z: [M]+ calcd for C33H39NO4Si, 541; found [M
+ H]+, 542. Elemental analysis: calcd (%) for C33H39NO4Si: C
73.16, H 7.26, N 2.59; found C 72.89, H 7.17, N 2.39%.
N,N-Di(4-benzoic acid tert-butyl ester)-4-ethynyl-phenylamine
(11). To a solution of diphenylamine 10 (65 mg, 0.12 mmol) in
1 mL THF was added caesium fluoride (54 mg, 0.36 mmol dis-
solved in 0.36 mL methanol). The resulting solution was stirred
for 1 hour at room temperature. After the reaction was
completed the mixture was poured into water and the organic
layer was taken off while the water phase was extracted with
dichloromethane. The combined organic phases were washed
with water three times and were dried with magnesium sulfate.
The solvent was removed in vacuum to give 11 (56 mg, quanti-
tative) as a brownish, viscous oil which was used without further
purification. 1H NMR (400 MHz, CDCl3): d ¼7.87 (d, J ¼
8.6 Hz, 4H, (t-Bu)OOC-Ph-2H,6H), 7.41 (d, J ¼ 8.6 Hz, 2H, Ph-
3H,5H), 7.07 (d, J ¼ 8.6 Hz, 4H, (t-Bu)OOC-Ph-3H,5H), 7.04 (d,
J ¼ 8.6 Hz, 2H, Ph-2H,6H), 3.07 (s, 1H, C^CH), 1.58 (s, 18H,
C-(CH3)3); 13C NMR (100 MHz, CDCl3): d ¼ 165.41, 150.39,
5-([N-(2,6-Diisopropylphenyl)]-9-perylenyl-3,4-dicarboximide)-
3,40-dihexyl-2,20-bithiophene (16). Bromoperylene 15 (187 mg,
0.32 mmol) and bithiophene boronic ester 14 (226 mg,
0.38 mmol) were dissolved in 3 mL DME. The resulting solution
was carefully degassed and the catalyst (Pd(PPh3)4 (4 mol%)
and the base (2 M aqueous potassium phosphate solution
(0.48 mL, 3 eq.)) were added. Next, the reaction mixture was
carefully degassed and stirred at 80 ꢂC for 1.5 h. Then
This journal is ª The Royal Society of Chemistry 2012
J. Mater. Chem., 2012, 22, 7366–7379 | 7375

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tetrabutylammonium fluoride (400 mg, 1.27 mmol) was added
and the reaction mixture was stirred for a further 2.5 h. After the
reaction was completed the mixture was poured into water
(15 mL) and the organic layer was separated while the aqueous
phase was extracted with dichloromethane. The combined
organic phases were dried over sodium sulfate and the solvent
was removed by rotary evaporation. The crude product was
Di-tert-butyl
4,40-[(4-({50-([N-(2,6-diisopropylphenyl)]-9-per-
ylenyl-3,4-dicarboximide)-30,4-dihexyl-2,20-bithien-5-yl}ethynyl)
phenyl)imino]dibenzoate (19). Iodinated perylenyl-bithiophene 17
(45 mg, 48 mmol), triphenylamine 11 (27 mg, 57 mmol) and CuI
(10 mol%) were dissolved in 1.5 mL toluene. The solution was
carefully degassed and the catalyst (Pd(PPh3)2Cl2 (4 mol%)) and
0.9 mL diisopropylamine were added. The resulting solution was
degassed carefully and stirred at room temperature for 4 h. After
the reaction was completed the mixture was poured into water
(7 mL) and the organic layer was separated while the aqueous
phase was extracted with dichloromethane. The combined
organic phases were dried over sodium sulfate and the solvent
was removed by rotary evaporation. The crude product was
purified by column chromatography (SiO2/n-hexane : ethyl
acetate [5 : 1]) to give 19 (37 mg, 60%) as a dark red solid. M.p.:
170–171 ꢂC; 1H NMR (400 MHz, CDCl3): d ¼ 8.68–8.65 (m, 2H,
Pery-1H,6H), 8.52–8.43 (m, 5H, Pery-2H,5H,7H,8H,12H), 7.90
(d, J ¼ 8.7 Hz, 4H (t-Bu)OOC-Ph-2H,6H), 7.74 (d, J ¼ 7.8 Hz,
1H, Pery-10H), 7.69(t, J ¼ 8.0 Hz, 1H, Ph-4H), 7.50–7.44 (m,
3H, Pery-11H, Ph-3H,5H), 7.35 (d, J ¼ 7.8 Hz, 2H, Ph-3H,5H),
7.19 (s, 1H, Th-3H), 7.12–7.09 (m, 6H, (t-Bu)OOC-Ph-3H,5H,
TPA-Ph-2H,6H), 7.03 (s, 1H, Th0-4H), 2.89 (t, J ¼ 7.8 Hz, 2H,
Th0-a-CH2), 2.84–2.74 (m, 2H, Ph-CH-(CH3)2, Th-a-CH2), 1.80–
1.69 (m, 4H, Th-b-CH2, Th0-b-CH2), 1.60 (s, 18H, tBu-CH3),
1.50–1.28 (m, 12H, -CH2-), 1.20 (d, J ¼ 6.8 Hz, 12H, Ph-CH-
(CH3)2) 0.92 (t, J ¼ 7.2 Hz, 3H, Th0-CH3), 0.90 (t, J ¼ 7.0 Hz, 3H,
Th-CH3); 13C NMR (100 MHz, CDCl3): d ¼ 165.28, 163.96,
150.28, 148.34, 146.34, 145.75, 140.69, 138.95, 137.57, 137.25,
135.79, 135.20, 132.61, 132.53, 132.17, 132.07, 131.54, 131.09,
130.95, 130.55, 129.51, 128.99, 128.96, 128.60, 127.44, 127.06,
126.90, 126.87, 125.04, 124.15, 124.02, 123.40, 123.16, 121.09,
121.07, 120.47, 120.30, 118.96, 118.48, 96.34, 82.55, 80.89, 31.71,
31.68, 30.66, 30.21, 29.72, 29.68, 29.34, 29.18, 29.00, 28.26, 24.03,
22.68, 22.64, 14.13, 14.11; MS (MALDI-TOF) m/z: [M]+ calcd
for C84H84N2O6S2, 1281; found [M + H]+, 1282. Elemental
analysis: calcd (%) for C84H84N2O6S2: C 78.72, H 6.61, N 2.19;
found C 78.86, H 6.72, N 2.23%.
purified
by
column
chromatography
(SiO2/dichlor-
omethane : n-hexane [2 : 1]) to give 16 (238 mg, 92%) as a red
ꢂ
1
solid. M.p.: 94–96 C; H NMR (400 MHz, CDCl3): d ¼ 8.65–
8.62 (m, 2H, Pery-1H,6H), 8.49–8.36 (m, 5H, Pery-
2H,5H,7H,8H,12H), 7.71 (d, J ¼ 7.9 Hz, Pery-10H), 7.64 (t, J ¼
8.0 Hz, 1H, Pery-11H), 7.49 (t, J ¼ 7.7 Hz, 1H, Ph-4H), 7.36
(d, J ¼ 7.8 Hz, 2H, Ph-3H,5H), 7.18 (s, 1H, Th-4H), 7.07 (d, J ¼
0.9, 1H, Th0-5H), 6.96 (d, J ¼ 0.9, 1H, Th0-3H), 2.87 (t, J ¼ 7.7
Hz, 2H, Th-a0-CH2), 2.84–2.74 (m, 2H, Ph-CH-(CH3)2), 2.65 (t, J
¼ 7.6 Hz, 2H, Th-a0-CH2), 1.79–1.64 (m, 4H, Th-b-CH2, Th-b0-
CH2), 1.49–1.29 (m, 12H, -CH2-), 1.20 (d, J ¼ 6.8 Hz, 12H, Ph-
CH-(CH3)2), 0.91 (t, J ¼ 7.0 Hz, 6H, Th-CH3, Th0-CH3); 13C
NMR (100 MHz, CDCl3): d ¼ 163.92, 145.64, 143.80, 139.98,
138.33, 137.49, 137.18, 135.37, 135.21, 132.76, 132.36, 131.98,
131.28, 131.01, 130.43, 129.42, 129.29, 129.07, 128.80, 128.64,
128.44, 127.51, 127.26, 126.74, 124.04, 124.00, 123.36, 120.88,
120.82, 120.40, 120.28, 120.10, 31.69, 30.71, 30.51, 30.41, 29.43,
29.30, 29.14, 29.02, 24.02, 22.66, 14.11; MS (MALDI-TOF) m/z:
[M]+ calcd for C54H55NO2S2, 813; found [M + H]+, 814.
Elemental analysis: calcd (%) for C54H55NO2S2: C 79.66, H 6.81,
N 1.72; found C 79.66, H 6.61, N 1.80%.
5-([N-(2,6-Diisopropylphenyl)]-9-perylenyl-3,4-dicarboximide)-
3,40-dihexyl-50-iodo-2,20-bithiophene (18). To a solution of per-
ylenyl-bithiophene 16 (230 mg, 0.28 mmol) in dry dichloro-
methane was added mercury caproate (122 mg, 0.28 mmol). The
resulting suspension was stirred at room temperature for 24 h
until the mercury compound was completely dissolved. Next,
iodine (1.1 equivalents) was added and the mixture was stirred
for another 6 h. Then the solution was filtered over basic
aluminium oxide and the filtrate was concentrated in vacuum.
Upon addition of methanol the product was allowed to
precipitate, filtered and dried in vacuum to give 17 (245 mg,
92%) as a red solid. M.p.: 98–100 ꢂC; 1H NMR (400 MHz,
CDCl3): d ¼ 8.68–8.65 (m, 2H, Pery-1H,6H), 8.53–8.44 (m, 5H,
Pery-2H,5H,7H,8H,12H), 7.73 (d, J ¼ 7.8 Hz, Pery-10H), 7.69
(t, J ¼ 8.0 Hz, 1H, Pery-11H), 7.49 (t, J ¼ 7.8 Hz, 1H, Ph-4H),
7.35 (d, J ¼ 7.8 Hz, 2H, Ph-3H,5H), 7.18 (s, 1H, Th-4H), 6.87 (s,
1H, Th0-3H), 2.85–2.75 (m, 5H, Th0-a-CH2, Ph-CH-(CH3)2),
2.58 (t, J ¼ 7.7 Hz, 2H, Th-a-CH2), 1.77–1.59 (m, 4H, Th-b-
CH2, Th0-b-CH2), 1.49–1.28 (m, 12H, -CH2-), 1.19 (d, J ¼
6.9 Hz, 12H, Ph-CH-(CH3)2), 0.91 (t, J ¼ 6.9 Hz, 6H, Th-CH3,
Th0-CH3); 13C NMR (100 MHz, CDCl3): d ¼ 163.96, 147.79,
145.73, 140.58, 140.23, 139.00, 137.58, 137.27, 135.20, 132.54,
132.07, 131.83, 131.25, 131.06, 130.55, 129.52, 129.42, 129.03,
129.00, 128.96, 128.60, 127.43, 126.92, 126.79, 124.15, 124.00,
123.39, 121.09, 120.47, 120.30, 74.46, 32.38, 31.66, 30.70, 29.98,
29.45, 29.26, 29.16, 28.92, 24.01, 22.65, 22.62, 14.09; MS
(MALDI-TOF) m/z: [M]+ calcd for C54H54INO2S2, 939;
found [M + H]+, 940. Elemental analysis: calcd (%) for
C54H54INO2S2: C 69.00, H 5.74, N 1.49; found C 69.18, H 5.64,
N 1.63%.
Di-tert-butyl 4,40-[(4-({50-([N-(2,6-diisopropylphenyl)]-9-peryl-
enyl-3,4-dicarboximide)-30,4-dihexyl-2,20-bithien-5-yl}ethynyl)
phenyl)imino]dibenzoate (20). Iodinated perylenyl-bithiophene 18
(94 mg, 0.1 mmol), triphenylamine 11 (56 mg, 0.12 mmol) and
CuI (10 mol%) were dissolved in 1 mL piperidine. The solution
was carefully degassed and the catalyst (Pd2(dba)3 [2.5 mol%]
and [HP(t-Bu)3]BF4 [10 mol%]) were added. The resulting solu-
tion was degassed carefully and stirred at room temperature for
24 h. After the reaction was completed the mixture was poured
into water and the organic layer was separated while the aqueous
phase was extracted with dichloromethane. The combined
organic phases were dried over magnesium sulfate and the
solvent was removed by rotary evaporation. The crude product
was purified by column chromatography (SiO2/petrol ether :
ethyl acetate [5 : 1]) to give 20 (110 mg, 85%) as a dark red solid.
M.p.: 183–184 ꢂC; 1H NMR (400 MHz, CDCl3): d ¼ 8.67 (d, J ¼
8.1 Hz, 2H, Pery-1H,6H), 8.52–8.46 (m, 4H, Pery-
2H,5H,7H,12H), 7.98 (d, J ¼ 8.4 Hz, 1H, Pery-8H), 7.79
(approx. d, J ¼ 8.6 Hz, 4H, (t-Bu)OOC-Ph-2H,6H), 7.69 (d, J ¼
7.8 Hz, 1H, Pery-10H), 7.64 (t, J ¼ 7.9 Hz, 1H, Pery-11H),
7.49 (t, J ¼ 7.7 Hz, 1H, Ph-4H), 7.44 (d, J ¼ 8.6 Hz, 2H,
7376 | J. Mater. Chem., 2012, 22, 7366–7379
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TPA-Ph-3H,5H), 7.35 (d, J ¼ 7.8 Hz, 2H, Ph-3H,5H), 7.15 (m,
2H, Th-3H, Th0-4H), 7.12–7.06 (m, 6H, (t-Bu)OOC-Ph-3H,5H,
TPA-Ph-2H,6H), 2.75–2.65 (m, 4H, Th-a0-CH2, Ph-CH-(CH3)2),
2.44 (t, J ¼ 7.6 Hz, 2H, Th-a-CH2), 1.70 (quin, J ¼ 6.8 Hz, 2H,
Th-b0-CH2), 1.59 (s, 18H, C-(CH3)3), 1.55 (quin, J ¼ 6.8 Hz, 2H,
Th-b-CH2), 1.45–1.40 (m, 2H, Th-g0-CH2), 1.39–1.30 (m, 4H, Th-
CH2-), 1.20–1.10 (m, 6H, Th-CH2-), 1.19 (d, J ¼ 6.8 Hz, 12H, Ph-
CH-(CH3)2), 0.89 (t, J ¼ 6.8 Hz, 3H, Th0-CH3), 0.77 (t, J ¼ 6.9
Hz, 3H, Th-CH3); 13C NMR (100 MHz, CDCl3): d ¼ 165.27,
163.97, 150.23, 146.42, 145.70, 142.05, 139.53, 137.53, 137.25,
135.34, 134.97, 134.71, 134.49, 133.86, 132.69, 132.43, 132.11,
132.07, 131.01, 130.51, 130.39, 129.47, 128.26, 127.66, 127.37,
126.91, 126.83, 124.89, 124.03, 123.20, 123.12, 121.15, 120.89,
120.39, 118.53, 93.72, 82.99, 80.78, 31.68, 31.47, 30.48, 30.45,
29.38, 29.20, 29.15, 28.99, 28.90, 28.23, 24.03, 22.63, 22.49, 14.12,
14.02; HRMS (MALDI-TOF) m/z: [M]+ calcd for C84H84N2O6S2,
1280.577; found, [M + H]+ 1281.578.
hydroxide solution (27 eq.) was added and the resulting solution
was stirred for 8 h at 70 ꢂC. After the reaction was completed the
mixture was poured into water (5 mL) and was acidified with 1 M
HCl (pH ¼ 1). The organic layer was separated while the aqueous
phase was extracted with dichloromethane. The combined
organic phases were dried over sodium sulfate and the solvent was
removed by rotary evaporation. The crude product was purified
by column chromatography (SiO2/dichloromethane : acetic acid
[50 : 1]) and was dried in vacuum to give 4 (20 mg, 60%) as a dark
red solid. M.p.: 218–219 ꢂC; 1H NMR (400 MHz, THF-d8): d ¼
8.72–8.66 (m, 4H, Pery-1H,6H, 2H,5H), 8.62–8.59 (m, 2H, Pery-
7H, 12H), 8.47 (d, J ¼ 8.5 Hz, 1H, Pery-8H) 7.94 (d, J ¼ 8.7 Hz,
4H (t-Bu)OOC-Ph-2H,6H), 7.79 (d, J ¼ 7.8 Hz, 1H, Pery-10H),
7.72 (t, J ¼ 8.0 Hz, 1H, Ph-4H), 7.49 (d, J ¼ 8.6 Hz, 2H, Ph-
3H,5H), 7.41–7.37 (m, Pery-11H) 7.32–7.28 (m, 3H, Ph-3H,5H,
Th0-4H), 7.17–7.13 (m, 7H, Th-3H, (t-Bu)OOC-Ph-3H,5H, TPA-
Ph-2H,6H), 2.93 (t, J ¼ 7.8 Hz, 2H, Th0-a-CH2), 2.84–2.76 (m,
4H, Ph-CH-(CH3)2, Th-a-CH2), 1.83–1.73 (m, 4H, Th-b0-CH2,
Th-b0-CH2), 1.53–1.31 (m, 12H, -CH2-), 1.14 (d, J ¼ 6.8 Hz, 12H,
Ph-CH-(CH3)2), 0.92 (t, J ¼ 7.3 Hz, 3H, Th0-CH3), 0.91 (t, J ¼ 7.4
Hz, 3H, Th-CH3); 13C NMR (100 MHz, THF-d8): d ¼ 166.068,
163.323, 150.426, 148.187, 146.723, 145.847, 140.732, 139.234,
137.315, 136.981, 135.676, 134.773, 132.470, 132.390, 131.776,
131.705, 131.651, 131.475, 131.465, 131.080, 130.407, 129.605,
129.213, 128.908, 128.646, 128.544, 127.441, 127.080, 126.836,
125.896, 125.083, 124.446, 123.682, 123.328, 123.113, 121.392,
120.810, 120.697, 118.743, 118.480, 96.402, 81.792, 31.689,
31.670, 30.593, 30.194, 29.443, 29.278, 29.008, 28.942, 23.308,
22.585, 22.552, 13.474; HRMS (MALDI-TOF) m/z: [M]+ calcd
for C76H68N2O6S2, 1168.452; found, [M + H]+ 1169.456.
4,40-[(4-({50-([N-(2,6-Diisopropylphenyl)]-9-perylenyl-3,4-dicar-
boximide)-30,4-dihexyl-2,20-bithien-5-yl}ethynyl)phenyl)imino]
dibenzoate (2). Triad 20 (37 mg, 29 mmol) was dissolved in 1 mL
THF. To the resulting solution 1 mL of a 1 M methanolic lithium
hydroxide solution (27 eq.) was added and the resulting solution
was stirred for 4 h at 70 ꢂC. After the reaction was completed the
mixture was poured into water and was acidified with 1 M HCl
(pH ¼ 1). The organic layer was separated while the aqueous
phase was extracted with dichloromethane. The combined
organic phases were dried over magnesium sulfate and the solvent
was removed by rotary evaporation. The crude product
was purified by column chromatography (SiO2/dichlor-
omethane : acetic acid [50 : 1]) and was dried in vacuum to give 2
(20 mg, 60%) as a dark red solid. M.p.: 227–228 ꢂC; 1H NMR (400
MHz, CDCl3): d ¼ 8.67 (d, J ¼ 7.8 Hz, 2H, Pery-1H,6H), 8.50–
8.40 (m, 4H, Pery-2H,5H,7H,12H), 8.03 (d, J ¼ 8.6 Hz, 4H,
HOOC-Ph-2H,6H), 7.98 (d, J ¼ 8.3 Hz, 1H, Pery-8H), 7.68 (d, J ¼
7.8 Hz, 1H, Pery-10H), 7.64 (t, J ¼ 7.9 Hz, 1H, Pery-11H), 7.51–
7.45 (m, 3H, Ph-4H, TPA-Ph-3H,5H), 7.35 (d, J ¼ 7.6 Hz, 2H,
Ph-3H,5H), 7.19–7.12 (m, 8H, Th-3H, Th0-4H, HOOC-Ph-
3H,5H, TPA-Ph-2H,6H), 2.85–2.75 (m, 4H, Th-a0-CH2, Ph-CH-
(CH3)2), 2.45 (t, J ¼ 7.3 Hz, 2H, Th-a-CH2), 1.70 (quin, J ¼
7.5 Hz, 2H, Th-b0-CH2), 1.55 (quin, J ¼ 7.1 Hz, 2H, Th-b-CH2),
1.45–1.37 (m, 2H, Th-g0-CH2), 1.37–1.30 (m, 4H, Th-CH2-), 1.20–
1.10 (m, 6H, Th-CH2-), 1.19 (d, J ¼ 6.8 Hz, 12H, Ph-CH-(CH3)2),
0.89 (t, J ¼ 6.8 Hz, 3H, Th0-CH3), 0.77 (t, J ¼ 6.9 Hz, 3H, Th-
CH3); 13C NMR (100 MHz, CDCl3): d ¼ 172.30, 164.93, 152.12,
146.80, 146.63, 142.99, 140.47, 138.45, 138.16, 136.22, 136.04,
135.61, 135.47, 134.75, 133.82, 133.52, 133.02, 132.80, 131.90,
131.42, 131.31, 130.38, 130.33, 129.16, 128.62, 128.27, 127.79,
126.65, 124.96, 124.87, 123.98, 122.03, 121.95, 121.66, 121.38,
121.30, 120.49, 94.43, 84.33, 32.59, 32.40, 31.40, 31.37, 30.30,
30.13, 30.08, 29.91, 29.82, 24.96, 23.55, 23.41, 15.04, 14.93; MS
(MALDI-TOF) m/z: [M]+ calcd for C76H68N2O6S2, 1168; found
[M + H]+, 1169. Elemental analysis: calcd (%) for C76H66N2O6S2:
C 78.05, H 5.86, N 2.40; found C 78.21, H 5.99, N 2.33%.
N,N-Di(4-benzoic acid tert-butyl ester)-4-(4,30dihexyl-2,20-
bithien-5-yl)-phenylamine (22). Bromobithiophene 12 (138 mg,
0.33 mmol) and triphenylamine boronic ester 21 (200 mg, 0.35
mmol) were dissolved in 5 mL THF. The resulting solution was
carefully degassed and the catalyst (Pd(OAc)2 (2.5 mol%), PPh3)
(10 mol%)) and the base (2 M aqueous potassium phosphate
solution (0.5 mL, 3 eq.)) were added. Next, the reaction mixture
ꢂ
was carefully degassed and stirred at 80 C overnight. After the
reaction was completed the mixture was poured into saturated
ammonium chloride solution (15 mL) and the organic layer was
separated while the aqueous phase was extracted with dieth-
ylether. The combined organic phases were washed with brine,
dried over sodium sulfate and the solvent was removed by rotary
evaporation. The crude product was purified by column chro-
matography (SiO2/n-hexane : ethyl acetate [92 : 8]) to give 22
(226 mg, 87%) as a bright yellow oil. 1H NMR (400 MHz,
CDCl3): d ¼ 7.90 (d, J ¼ 8.7 Hz, 4H, (t-Bu)OOC-Ph-2H,6H),
7.39 (d, J ¼ 8.5 Hz, 2H, Ph-3H,5H), 7.16–7.11 (m, 7H, (t-Bu)
OOC-Ph-3H,5H, Ph-2H,6H, Th0-5-H), 6.99 (s, Th-3-H), 6.93 (d,
J ¼ 5.1 Hz, Th0-4-H), 2.79 (t, J ¼ 7.8 Hz, 2H, Th0-a-CH2), 2.67 (t,
J ¼ 7.8 Hz, 2H, Th-a-CH2), 1.69–1.62 (m, 4H, b,b0-CH2) 1.59 (s,
18H, tBu-CH3), 1.41–1.26 (m, 12H, -CH2-), 0.88 (t, J ¼ 6.8 Hz,
6H, Th-CH3, Th0-CH3); 13C NMR (100 MHz, CDCl3): d ¼
165.38, 150.56, 145.37, 139.44, 139.02, 136.87, 134.29, 130.89,
130.76, 130.28, 130.08, 128.46, 126.37, 125.69, 123.46, 122.780,
80.81, 31.72, 31.68, 30.93, 30.72, 29.30, 29.27, 29.20, 28.85, 28.26,
22.66, 22.63, 14.14; HRMS (MALDI-TOF) m/z: [M]+ calcd for
C48H59NO4S2, 777.389; found, [M]+ 777.388.
4,40-[(4-({50-([N-(2,6-Diisopropylphenyl)]-9-perylenyl-3,4-dicar-
boximide)-30,4-dihexyl-2,20-bithien-5-yl}ethynyl)phenyl)imino]
dibenzoate (4). Triad 19 (37 mg, 29 mmol) was dissolved in 1 mL
THF. To the resulting solution 1 mL of a 1 M methanolic lithium
This journal is ª The Royal Society of Chemistry 2012
J. Mater. Chem., 2012, 22, 7366–7379 | 7377

View Article Online
N,N-Di(4-benzoic
acid
tert-butyl
ester)-4-(50-bromo-
(26 mg, 29 mmol) were dissolved in 3 mL THF. The resulting
solution was carefully degassed and the catalyst (Pd(PPh3)4
(10 mol%)) and the base (2 M aqueous potassium phosphate
solution (0.04 mL, 3 eq.)) were added. Next, the reaction mixture
was carefully degassed and stirred at 80 ꢂC for 2 h. After the
reaction was completed the mixture was poured into water
(10 mL) and the organic layer was separated while the aqueous
phase was extracted with dichloromethane. The combined
organic phases were dried over sodium sulfate and the solvent
was removed by rotary evaporation. The crude product was
purified by column chromatography (SiO2/n-hexane : ethyl
acetate [4 : 1]) to give 25 (30 mg, 88%) as a black solid. M.p.: 179–
4,30dihexyl-2,20-bithien-5-yl)-phenylamine (23). Bithiophene–tri-
phenylamine 22 (92.9 mg, 0.12 mmol) was dissolved in 2 mL dry
ꢂ
DMF and stirred at ꢁ20 C under light protection. N-Bromo-
succinimide (21.2 mg, 0.12 mmol) dissolved in 1 mL dry DMF
was added dropwise in 1 h. Next, the reaction mixture was stirred
overnight at room temperature. After the reaction was completed
the mixture was poured into half saturated ammonium chloride
solution (10 mL) and the organic phase was extracted with
diethylether. The combined organic phases were washed with
brine, dried over sodium sulfate and the solvent was removed by
rotary evaporation. The crude product was purified by column
chromatography (SiO2/n-hexane : ethyl acetate [95 : 5]) to give
1
180 ꢂC; H NMR (400 MHz, CDCl3): d ¼ 8.67–8.64 (m, 2H,
1
23 (86 mg, 80%) as a viscous yellow oil. H NMR (400 MHz,
Pery-1H,6H), 8.51–8.41 (m, 5H, Pery-2H,5H,7H,8H,12H), 7.92
(d, J ¼ 8.6 Hz, 4H (t-Bu)OOC-Ph-2H,6H), 7.74 (d, J ¼ 7.9 Hz,
1H, Pery-10H), 7.68 (t, J ¼ 7.9 Hz, 1H, Ph-4H), 7.51–7.42 (m,
3H, Pery-11H, Ph-3H,5H), 7.35 (d, J ¼ 7.8 Hz, 2H, Ph-3H,5H),
7.02–7.12 (m, 8H, Th-3H, Th0-4H, (t-Bu)OOC-Ph-3H,5H, TPA-
Ph-2H,6H), 2.92 (t, J ¼ 7.8 Hz, 2H, Th0-a-CH2), 2.81–2.78 (m,
2H, Ph-CH-(CH3)2), 2.72 (t, J ¼ 7.8 Hz, 2H, Th-a-CH2), 1.82–
1.65 (m, 4H, Th-b0-CH2, Th-b0-CH2), 1.60 (s, 18H, tBu-CH3),
1.39–1.29 (m, 12H, -CH2-), 1.20 (d, J ¼ 6.8 Hz, 12H, Ph-CH-
(CH3)2) 0.92 (t, J ¼ 6.7 Hz, 3H, Th0-CH3), 0.90 (t, J ¼ 6.6 Hz,
3H, Th-CH3); 13C NMR (100 MHz, CDCl3): d ¼ 165.32, 150.51,
146.54, 145.71, 145.56, 139.26, 132.01, 130.89, 130.27, 126.84,
126.49, 125.63, 123.99, 122.84, 120.94, 120.19, 80.79, 31.70,
31.64, 30.91, 30.70, 29.68, 29.31, 29.16, 28.24, 24.01, 22.65, 22.59,
14.09; HRMS (MALDI-TOF) m/z: [M]+ calcd for
C82H84N2O6S2, 1256.577; found, [M + H]+ 1257.576.
CDCl3): d ¼ 7.82 (d, J ¼ 8.8 Hz, 4H, (t-Bu)OOC-Ph-2H,6H),
7.37 (d, J ¼ 8.6 Hz, 2H, Ph-3H,5H), 7.15–7.11 (m, 6H, (t-Bu)
OOC-Ph-3H,5H, Ph-2H,6H), 6.92 (s, Th-3-H), 6.89 (s, Th0-4-H),
2.72 (t, J ¼ 7.8 Hz, 2H, Th0-a-CH2), 2.67 (t, J ¼ 7.8 Hz, 2H, Th-a-
CH2), 1.69–1.62 (m, 4H, b,b0-CH2) 1.51 (s, 18H, tBu-CH3), 1.38–
1.26 (m, 12H, -CH2-), 0.88 (t, J ¼ 6.8 Hz, 6H, Th-CH3, Th0-CH3);
13C NMR (100 MHz, CDCl3): d ¼ 165.31, 150.47, 145.49, 139.96,
139.05, 137.40, 132.86, 132.63, 132.25, 130.85, 130.52, 130.23,
128.77, 126.39, 125.58, 122.79, 122.75, 110.05, 80.78, 31.60,
30.84, 30.53, 29.17, 29.11, 29.09, 28.74, 28.21, 22.57, 14.07; MS
(MALDI-TOF) m/z: [M]+ calcd for C48H58BrNO4S2, 855; found
[M + H]+, 856.
N,N-Di(4-benzoic acid tert-butyl ester)-4-(50-(4,4,5,5-tetra-
methyl-[1,3,2]dioxoborolane-2-yl)-4,30dihexyl-2,20-bithien-5-yl)-
phenylamine (24). Isopropylmagnesium chloride (0.32 mL, 0.64
mmol, 2 M in THF) was added dropwise to a suspension of
lithium chloride (20 mg, 0.48 mmol) in 1 mL dry THF and stirred
until lithium chloride was completely dissolved. 0.33 mL of the
resulting solution was then added to a solution of brominated
bithiophene–triphenylamine 23 (51 mg, 0.06 mmol) in 1 mL dry
THF at 0 ꢂC. Next, the resulting reaction mixture was stirred for
1 h until it was warmed up to room temperature. Then 2-iso-
propoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane was added at
once and the reaction mixture was stirred overnight. After the
reaction was completed the mixture was poured into saturated
ammonium chloride solution (10 mL) and the organic phase was
extracted with diethylether. The combined organic phases were
washed with brine, dried over sodium sulfate and the solvent was
removed by rotary evaporation. Boronic ester 24 was obtained as
a yellow resin (54 mg, 50%) with a purity of 50% (1H NMR). It
was used without further purification. 1H NMR (400 MHz,
CDCl3): d ¼ 7.89 (d, J ¼ 8.8 Hz, 4H, (t-Bu)OOC-Ph-2H,6H),
7.46 (s, 1H, Th0-4-H), 7.39 (d, J ¼ 8.5 Hz, 2H, Ph-3H,5H), 7.15–
7.12 (m, 6H, (t-Bu)OOC-Ph-3H,5H, Ph-2H,6H), 7.05 (s, Th-3-
H), 2.79 (t, J ¼ 7.8 Hz, 2H, Th0-a-CH2), 2.67 (t, J ¼ 7.8 Hz, 2H,
Th-a-CH2), 1.69–1.62 (m, 4H, b,b0-CH2) 1.51 (s, 18H, tBu-CH3),
1.35–1.28 (m, 12H, -CH2-), 1.27 (s, 12H, B-C-CH3), 0.88 (t, J ¼
6.8 Hz, 6H, Th-CH3, Th0-CH3); MS (MALDI-TOF) m/z: [M]+
calcd for C54H70BNO6S2, 903; found [M + H]+, 904.
N,N-Di(4-benzoic acid)-4-(50-(N-(2,6-diisopropylphenyl)-per-
ylene-3,4-dicarboximide-9-yl)-4,30-dihexyl-2,20-bithien-5-yl)-phe-
nylamine (3). Triad 25 (28 mg, 22 mmol) was dissolved in
0.5 mL dry dichloromethane. To the resulting solution
0.09 mL trifluoroacetic acid (1.1 mmol) was added and the
deep violet solution was stirred for 6 h at room temperature.
After the reaction was completed the solution was concen-
trated and the product was precipitated from n-hexane, filtered
and dried in vacuum to give 3 (25 mg, 99%) as a black solid.
1
M.p.: 210–212 ꢂC; H NMR (400 MHz, THF-d8): d ¼ 8.68–
8.65 (m, 2H, Pery-1H,6H), 8.52–8.43 (m, 5H, Pery-
2H,5H,7H,8H,12H), 8.04 (d, J ¼ 8.6 Hz, 4H HOOC-Ph-
2H,6H), 7.78 (d, J ¼ 7.8 Hz, 1H, Pery-10H), 7.71 (t, J ¼
7.9 Hz, 1H, Ph-4H), 7.50–7.47 (m, 3H, Pery-11H, Ph-3H,5H),
7.35 (d, J ¼ 7.8 Hz, 2H, Ph-3H,5H), 7.26–7.21 (m, 7H, Th-3H,
HOOC-Ph-3H,5H, TPA-Ph-2H,6H), 7.13 (s, 1H, Th0-4H), 2.92
(t, J ¼ 7.8 Hz, 2H, Th0-a-CH2), 2.81–2.71 (m, 4H, Ph-CH-
(CH3)2, Th-a-CH2), 1.82–1.67 (m, 4H, Th-b-CH2, Th-b0-CH2),
1.41–1.29 (m, 12H, -CH2-), 1.19 (d, J ¼ 6.8 Hz, 12H, Ph-CH-
(CH3)2) 0.93–0.88 (m, 6H, Th-CH3, Th0-CH3); 13C NMR
(100 MHz, THF-d8): d ¼ 166.92, 164.10, 151.43, 146.66,
146.59, 140.80, 139.95, 139.39, 138.33, 138.08, 137.74, 135.76,
134.32, 133.12, 133.07, 132.47, 132.31, 132.26, 131.82, 131.31,
131.13, 130.94, 130.28, 129.76, 129.60, 129.47, 129.43, 129.36,
129.27, 128.11, 127.54, 126.45, 126.32, 125.19, 124.48, 124.11,
123.56, 122.07, 122.03, 121.52, 121.38, 32.49, 32.43, 32.33,
31.62, 31.46, 30.16, 30.07, 29.89, 29.78, 29.42, 24.10, 23.37,
23.32, 14.27; HRMS (MALDI-TOF) m/z: [M]+ calcd for
C74H68N2O6S2, 1144.452; found, [M]+ 1145.454.
N,N-Di(4-benzoic acid tert-butyl ester)-4-(50-(N-(2,6-diisopro-
pylphenyl)-perylene-3,4-dicarboximide-9-yl)-4,30-dihexyl-2,20-
bithien-5-yl)-phenylamine (25). Bromoperylene 15 (15 mg,
28 mmol) and bithiophene triphenylamine boronic ester 24
7378 | J. Mater. Chem., 2012, 22, 7366–7379
This journal is ª The Royal Society of Chemistry 2012

View Article Online
12 A. Nattestad, M. Ferguson, R. Kerr, Y.-B. Cheng and U. Bach,
Nanotechnology, 2008, 19, 295304, (9pp).
13 (a) A. Morandeira, J. Fortage, T. Edvinsson, L. Le Pleux, E. Blart,
Acknowledgements
The authors would like to thank the German Federal Ministry
of Education and Research (BMBF) for funding our research on
organic solar cell materials in the frame of a joint project. This
work was also supported by the German Science Foundation
(DFG) in the frame of a Collaborative Research Center (SFB)
569. We would also like to thank the Victorian Consortium for
Organic Solar Cells (VICOSC), the ARC Centre of Excellence
for Electromaterials Science (ACES) and the German Academic
Exchange Service (DAAD-Go8 joint research cooperation
scheme) for financial support. Furthermore we would like to
acknowledge the ARC for providing equipment support
through LIEF, as well as supporting UB and AJM with an
Australian Research Fellowship. Special thanks also to Monash
University for supporting U.B. with a Monash Research
Fellowship.
€
G. Boschloo, A. Hagfeldt, L. Hammarstrom and F. Odobel,
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L. Hammarstrom and F. Odobel, Energy Environ. Sci., 2011, 4, 2075.
14 P. Qin, H. Zhu, T. Edvinsson, G. Boschloo, A. Hagfeldt and L. Sun,
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15 P. Qin, M. Linder, T. Brinck, G. Boschloo, A. Hagfeldt and L. Sun,
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