Direct arylation as a versatile tool towards thiazolo[5,4-d]thiazole-based semiconducting materials

Article abstract of DOI:10.1039/c4ob00360h

A series of thiazolo[5,4-d]thiazole-based small molecule organic optoelectronic materials is synthesized via a straightforward microwave-activated Pd-catalyzed C-H arylation protocol. The procedure allows us to obtain extended 2,5-dithienylthiazolo[5,4-d]thiazole chromophores with tailor-made energy levels and absorption patterns, depending on the introduced (het)aryl moieties and the molecular (a)symmetry, by shortened sequences without organometallic intermediates. The synthesized materials can be applied as either electron donor or electron acceptor light-harvesting materials in molecular bulk heterojunction organic solar cells. This journal is

Full text of DOI:10.1039/c4ob00360h

Organic &
Biomolecular Chemistry
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Direct arylation as a versatile tool towards thiazolo-
[5,4-d]thiazole-based semiconducting materials†
Cite this: Org. Biomol. Chem., 2014,
12, 4663
Julija Kudrjasova,a,b Roald Herckens,a,b Huguette Penxten,a,b Peter Adriaensens,a,b
Laurence Lutsen,a,b Dirk Vanderzandea,b and Wouter Maes*a,b
A series of thiazolo[5,4-d]thiazole-based small molecule organic optoelectronic materials is synthesized
via a straightforward microwave-activated Pd-catalyzed C–H arylation protocol. The procedure allows us
to obtain extended 2,5-dithienylthiazolo[5,4-d]thiazole chromophores with tailor-made energy levels and
absorption patterns, depending on the introduced (het)aryl moieties and the molecular (a)symmetry, by
shortened sequences without organometallic intermediates. The synthesized materials can be applied as
either electron donor or electron acceptor light-harvesting materials in molecular bulk heterojunction
organic solar cells.
Received 17th February 2014,
Accepted 6th May 2014
DOI: 10.1039/c4ob00360h
www.rsc.org/obc
been quite limited until recently, when the high potential of
these molecules was more widely recognized, notably in the
Introduction
Optoelectronic devices based on organic semiconductors – field of solution-processed organic photovoltaics (OPVs).6–8
organic solar cells, transistors, light-emitting diodes and Despite the strong rise in interest in these molecules, the syn-
related applications – are steadily entering the market as thetic chemistry behind TzTz-based materials has only been
organic components allow development of very thin and flexi- developed to a minor extent, and there is certainly room for
ble large area devices with tunable color and transparency at a improvement and broadening of the material scope.2
low cost using solution-based deposition techniques such as
roll-to-roll printing. The optoelectronic properties of the active substituted
In previous work, we have synthesized a number of 5′-aryl-
2,5-bis(3′-hexylthiophen-2′-yl)thiazolo[5,4-d]thia-
materials can readily be optimized through versatile organic zole derivatives via Suzuki and Stille cross-coupling reactions
synthesis protocols. In the design of potent organic semicon- and these expanded semiconductors were investigated as
ductors, careful consideration of molecular properties such as active materials for solution-processable organic field-effect
oxidation potentials, electron affinities, light-harvesting/emit- transistors (OFETs).9 On the other hand, it was shown that
ting and/or charge transport features, solubility and intermole- charge transfer (in the weak driving force limit) occurs in
cular π–π interactions is of crucial importance. Oligothiophene blends of dithienyl-TzTzs and MDMO-PPV (poly[2-methoxy-5-
structures have been shown to possess excellent semiconduc- (3′,7′-dimethyloctyloxy)-1,4-phenylene vinylene]) towards fuller-
tor characteristics and a wide range of heterocycles has been ene-free OPV devices with high open-circuit voltages (Voc).10
introduced into thiophene-based π-conjugated small molecule Fullerenes till now have turned out to be the superior electron
materials to optimize particular properties.1 The thiazolo[5,4-d]- acceptors in organic solar cells. The promises of more generic
thiazole (TzTz) fused biheterocyclic system possesses
a
and versatile low-cost non-fullerene small molecules as accep-
number of features – a rigid planar structure, strong electron tors in solution-processed bulk heterojunction (BHJ) organic
deficient character, high oxidative stability, and high charge solar cells have not been fulfilled so far, with maximum
mobility – that render TzTz derivatives particularly attractive efficiencies around 4% (and routinely below 2%).11 It has
for organic electronics.2–5 Nevertheless, their application has recently been calculated though that the cumulative energy
demand (CED) required to produce BHJ OPVs, although on
average 50% less than for conventional inorganic photo-
voltaics, is strongly affected by the presence of fullerenes, com-
prising 18–30% of the CED, despite being present in small
quantities.12 On the other hand, recent progress in the field of
solution-processed molecular OPVs, based on small molecule
electron donor materials and fullerene acceptors, has afforded
power conversion efficiencies in the same range as the best
polymer BHJ OPV systems.1b,13 In this line of thought, we now
aDesign & Synthesis of Organic Semiconductors (DSOS), Institute for Materials
Research (IMO-IMOMEC), Hasselt University, Agoralaan 1 – Building D, B-3590
Diepenbeek, Belgium
bIMOMEC Assoc. Lab., IMEC, Universitaire Campus – Wetenschapspark 1, B-3590
Diepenbeek, Belgium. E-mail: wouter.maes@uhasselt.be; Fax: +32 11268299;
Tel: +32 11268312
†Electronic supplementary information (ESI) available: 1H and 13C NMR spectra
and CV traces for the novel TzTz materials. See DOI: 10.1039/c4ob00360h
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report on a series of TzTz-based small molecules, synthesized optimized for the combination of TzTz 1 and methyl 4-bromo-
via microwave-activated direct arylation reactions, which allow benzoate (2d) (Table 1), in particular aiming at selective mono-
tuning of the energy levels and light absorption towards appli- arylation as this provides access to unprecedented
cations in OPVs, either as small molecule electron donor asymmetrically substituted TzTz materials. For that purpose,
materials or alternative electron acceptors.
1.1 equivalents of 2d were used and the reaction time was
varied between 4 and 7 hours, whereas the reaction tempera-
ture was gradually increased from 100 to 180 °C. The highest
yield was achieved at 180 °C (64% 3d, 34% 4d), although the
selectivity was still modest. It should be mentioned here that
the yield of the disubstituted product 4d is based on the
amount of TzTz 1 (a minority of 0.55 equiv. with respect to 2d)
and might therefore look somewhat overestimated. In this
respect, the isolated product amount (as mentioned in the
Experimental section) might be more illustrative for the reac-
tion selectivity (mono- vs. disubstitution). At lower tempera-
tures, quite some starting material (TzTz 1) remained.
Running the reaction at 100 °C for a longer time (7 h) did not
significantly change the reaction outcome. Addition of an
extra portion of fresh catalyst (2 mol%)18 after 4 hours of reac-
tion at 100 °C (and stirring for another 3 h at the same temp-
erature) did not cause any significant increase in the yield of
3d and 4d (49 and 7%, respectively) either.
Results and discussion
Direct arylation reactions, in which the Pd-catalyzed coupling
occurs directly between a (hetero)aryl bromide and a (hetero)-
aryl compound with activated C–H groups, have a number of
advantages over traditional cross-coupling techniques, i.e.
fewer synthetic operations and potentially higher yields, lower
catalyst loadings, and, most importantly, no need for (high
purity) organometallic intermediates (resulting in toxic bypro-
ducts, e.g. trialkyltin compounds), making them an ideal strat-
egy for the synthesis of advanced materials for organic
electronics.14 C–H arylation procedures are often conducted in
combination with microwave activation to speed up the reac-
tions. Direct arylation protocols have recently been employed
for the synthesis of low bandgap small molecules15 and
polymer materials16 for organic solar cells, but they have not
been applied on TzTz materials so far. In this work, we have
used a C–H arylation strategy to synthesize a series of TzTz-
based semiconductors with varying electron affinities to be
applied in organic solar cells, with a particular emphasis on
monosubstitution, enabling us to obtain asymmetrical push–
pull derivatives to broaden the absorption window.
The direct arylation of TzTz 1 was then extended to
different types of aryl bromides 2a–g using the same protocol
(180 °C, 4 h) (Scheme 1, Table 2). The amount of (hetero)aryl
bromide was adjusted for either mono- (1.1 equiv.) or diaryla-
tion (2.1 equiv.). Whenever separation and purification of the
mono- and disubstituted compounds proved difficult, prepara-
As the activated C–H part we have chosen 2,5-bis(3′-hexyl-
thiophen-2′-yl)thiazolo[5,4-d]thiazole (1) (Scheme 1), which
was prepared in a straightforward way (in 60% yield) via a con-
densation reaction at an elevated temperature (130 °C)
between dithiooxamide and 3-hexylthiophene-2-carbaldehyde
in nitrobenzene, according to a modified literature pro-
cedure.17 It is worth mentioning that in this method only a
stoichiometric amount of aldehyde (vs. the 6 equiv. used
before9,17) has to be used. Dithienyl-TzTz 1 was then combined
with different (hetero)aryl bromides 2a–g (Scheme 1), chosen
as such to generate a family of compounds with varying elec-
tron affinities. The reaction conditions (PdOAc2, PCy3HBF4,
pivalic acid, K2CO3, toluene, microwave heating)14b were first
Table 1 Optimization (of the reaction time and temperature) for the
direct arylation of TzTz 1 and methyl 4-bromobenzoate (2d) (1.1 equiv.)
T (°C)
Time
3d
4da
100
120
140
160
180
100
4 h
4 h
4 h
4 h
4 h
7 h
43
41
57
60
64
46
8b
30b
33b
33
34
4b
a Reaction yields for the disubstituted product 4d might be somewhat
misleading as they are based on the reaction partner in minority (TzTz
1). b The remaining of the crude reaction mixture is mainly the starting
material (TzTz 1).
Scheme 1 Synthesis of 5’-mono- (3a–g) and diarylated (4a–g) 2,5-bis(3’-hexylthiophen-2’-yl)thiazolo[5,4-d]thiazole derivatives via C–H arylation.
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visible region (λmax 400–470 nm), attributed to the π–π* elec-
tronic transition and intramolecular charge transfer, respect-
ively.19 As expected, the difunctionalized TzTzs show a more
red-shifted (10–28 nm) absorption. In addition, they have
broader absorption spectra and higher molar absorptivities.
Optical HOMO–LUMO gaps were determined from the onset
(λonset) of the absorption spectra in solution. The optical
HOMO–LUMO gaps are between 2.32 and 2.72 eV (Table 3),
hence still rather high for OPV applications. The electron
donating character of the triphenylamine substituent (3g/4g),
together with the extended conjugation length, results in a
broad and red-shifted absorption with the smallest HOMO–
LUMO gap. Basic electrochemical properties were investigated
by cyclic voltammetry (CV) and the derived frontier orbital
energy levels are depicted in Table 3. The presence of electron
withdrawing substituents such as cyano, fluoro and trifluoro-
methyl groups endows the molecules with deeper LUMO levels
(as derived from the reduction onset by CV or calculated from
the HOMO level, as derived from the oxidation onset, and the
optical HOMO–LUMO gap), rendering them possible candi-
dates for n-type acceptor materials for organic solar cells. As is
known from our previous work,10 dithienyl-TzTz semiconduct-
ing molecules with electron accepting substituents can be
combined with a donor polymer (in this case MDMO-PPV) to
afford photoinduced charge transfer (CT) in the resulting
blends. The CT efficiencies were shown to be strongly corre-
lated with increasing acceptor strength. Some of the new com-
pounds (notably 3a/4a) have lower LUMO values as compared
to the published TzTz materials, which could possibly improve
the CT efficiency and the final solar cell performance (consid-
ering also other potential loss mechanisms and sufficient elec-
tron mobility), increasing the very low efficiency of 0.1%
previously observed.10 Fig. 2 gives an overview of the energy
Table 2 Overview of the (isolated) yields and selectivities for the reac-
tions between TzTz 1 and (hetero)aryl bromides 2a–g
Yields
(Hetero)Ar–Br
2a–g
1.1 equiv.
2.1 equiv.
3
4b
3
4b
a
b
49
35
49a
33
58a
64
69
28
50
44
34
52
27
30a
69a
36a
20
c
27a
58a
42a
34
d
e
f
6
92
27
34
32
46
50
70b
38b
64b
38b
g
a These reactions were run for 7 h (instead of the standard 4 h).
b Reaction yields for the disubstituted products might be somewhat
misleading as they are based on the reaction partner in minority (TzTz 1).
tive size exclusion chromatography (SEC) was applied (see the
Experimental section). In general, good overall yields were
achieved, but selectivities remained rather modest (with some
notable exceptions, see Table 2). From the results obtained, it
is difficult to detect clear trends in either yields or selectivities
considering electronic substituent effects.
All TzTz derivatives were completely characterized by 1H
and 13C NMR and HRMS. UV-Vis absorption spectra of the
functionalized TzTz molecules were collected to evaluate their
light-harvesting properties, and the corresponding data (λmax
and ε) are gathered in Table 3. The (normalized) absorption
spectra of all mono- and disubstituted TzTzs in chloroform
solution are depicted in Fig. 1. All UV-Vis spectra show two dis-
tinct absorption bands in the UV (λmax 250–320 nm) and
Table 3 Optical and electrochemical properties of the synthesized TzTzs (and some reference materials)
λmax b (nm) (log ε)c
ΔEopt
E
(V)
HOMOg (eV)
E
(V)
onset
LUMOi (eV)
ΔEec
LUMOcalc k (eV)
d
ox
onset
red
j
TzTz
3a
4a
3b
4b
3c
4c
3d
4d
3e
4e
3f
4f
3g
4g
5
6
427 (4.54)
451 (4.70)
406 (4.55)
421 (4.58)
400 (4.60)
410 (4.69)
417 (4.40)
445 (4.45)
416 (4.58)
440 (4.65)
418 (4.65)
442 (4.80)
440 (4.70)
469 (4.88)
473 (4.66)
449 (4.73)
—
2.49
2.40
2.70
2.59
2.72
2.66
2.61
2.46
2.65
2.51
2.62
2.47
2.46
2.32
2.26
2.40
1.72
1.88
2.12
1.04e
1.06e
1.00f
1.04f
1.00f
1.03e
0.92f
0.88e
0.91f
0.85e
0.67e
0.77e
0.57e
0.53e
0.56e
0.56e
1.26
−5.89
−5.91
−5.85
−5.88
−5.84
−5.87
−5.77
−5.73
−5.75
−5.70
−5.52
−5.62
−5.41
−5.38
−5.41
−5.40
−6.12
−5.10
−5.21
−1.46e
−1.41e
−1.79f
−1.72f
−1.75h
−1.75f
−1.78e
−1.79h
−1.76f
−1.73e
−1.91e
−1.89e
−1.89e
−1.81e
−1.51e
−1.80e
−0.83
−3.38
−3.43
−3.05
−3.12
−3.10
−3.10
−3.06
−3.06
−3.09
−3.12
−2.94
−2.96
−2.96
−3.04
−3.34
−3.05
−4.03
−2.87
−2.93
2.50
2.47
2.80
2.76
2.75
2.78
2.71
2.67
2.66
2.58
2.58
2.66
2.45
2.34
2.07
2.35
2.09
2.22
2.28
−3.40
−3.51
−3.15
−3.29
−3.12
−3.21
−3.16
−3.27
−3.10
−3.19
−2.90
−3.15
−2.95
−3.06
−3.15
−3.00
−4.40
−3.22
−3.09
PCBM
P3HTa
MDMO-PPVa
—
—
0.13
0.24
−2.09
−2.03
a CV data in films. b Measured in CHCl3 solution. c Molar extinction coefficient ε, determined at λmax in CHCl3 solution. d Optical HOMO–LUMO
gap, ΔEopt = 1240/(λonset). e Reversible. f Quasi-reversible. g Determined from the oxidation onset. h Irreversible. i Determined from the reduction
onset. j Electrochemical HOMO–LUMO gap. k LUMOcalc = ΔEopt + HOMO.
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levels obtained for all materials, together with prototype elec-
tron donor polymers (MDMO-PPV and P3HT or poly(3-hexyl-
thiophene)) and the most used acceptor PCBM ([6,6]-phenyl-
C61-butyric acid methyl ester). Whereas previously only
MDMO-PPV could be applied as a donor material for the bis-
(4-cyanophenyl)-substituted dithienyl-TzTz acceptor (HOMO
−5.76 eV and LUMO −3.25 eV),10a the LUMO levels of some of
the novel materials (notably 4a) are sufficiently low to enable
combination with more effective low bandgap polymers such
as PCPDT-DTTzTz7f (poly{[4-(2′-ethylhexyl)-4-octyl-4H-cyclo-
penta[2,1-b:3,4-b′]dithiophene-2,6-diyl]-alt-[2,5-di(3′-hexylthio-
phen-2′-yl)thiazolo[5,4-d]thiazole-5′,5′′-diyl]}), also containing
TzTz as the electron deficient part.
A second particular goal was to prepare asymmetrical
donor–TzTz–acceptor molecules with broadened absorption
profiles by sequential direct coupling reactions, as these com-
pounds are of high appeal as photoactive (electron donor)
materials for OPV. The few literature examples of asymmetri-
cally extended TzTz derivatives were prepared via traditional
Suzuki cross-coupling reactions in moderate yields.8e,20 Push–
pull TzTz compounds 5 and 6 were synthesized from monoary-
lated derivatives 3g and 3c in 85 and 88% yield, respectively
(Scheme 2). The UV-Vis absorption spectra of these materials
(Fig. 1) indeed show extended absorption (up to λmax 473 nm
for 5).
Scheme 2 Synthesis of asymmetrically substituted TzTz derivatives 5
and 6 via stepwise C–H arylation.
Fig. 1 Normalized UV-Vis absorption spectra of the synthesized TzTzs
in CHCl3 solution.
Fig. 2 HOMO–LUMO energy level diagram for the functionalized TzTzs (data from Table 3; LUMOcalc).
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wire dipped in a solution of 0.01 M AgNO3 and 0.1 M NBu4PF6
in anhydrous MeCN). Samples were prepared in anhydrous
Conclusions
A facile and versatile microwave-assisted procedure is develo- CH2Cl2 containing 0.1 M NBu4PF6, and ferrocene was used as
ped for the direct arylation of 2,5-dithienylthiazolo[5,4-d]thia- an internal standard. The respective TzTz products were dis-
zoles with various electron rich and poor (hetero)aryl solved in the electrolyte solution, which was degassed with Ar
bromides towards a variety of molecular chromophores with prior to each measurement. To prevent air from entering the
an extended conjugated backbone. Unsymmetrical derivatives system, the experiments were carried out under Ar. Cyclic vol-
were readily obtained by
a
sequential direct arylation tammograms were recorded at a scan rate of 50 mV s−1. The
approach. These materials are designed to be applied as solu- HOMO–LUMO energy levels of the products were determined
tion-processable solar photon-harvesting materials for bulk using CV data and spectroscopic absorption data. For the con-
heterojunction organic photovoltaics, either as small molecule version of V to eV, the onset potentials of the first oxidation/
electron donor or acceptor constituents. Efforts in this direc- reduction peaks were used and referenced to ferrocene/ferroce-
tion are currently ongoing within our group. In a more general nium, which has an ionization potential of −4.98 eV vs.
sense, the synthetic chemistry developed in this work can vacuum. This correction factor is based on a value of 0.31 eV
stimulate further progress in the development of controllable for Fc/Fc+ vs. SCE21a and a value of 4.68 eV for SCE vs.
Ag/AgNO3
direct arylation protocols as powerful ‘atom-economic’ reac- vacuum:21b EHOMO/LUMO (eV) = −4.98 − E
(V) +
onset ox/red
Ag/AgNO3
tions towards advanced organic materials for printable
E
(V). The HOMO energy levels of the TzTz products
onset Fc/Fc+
electronics.
were determined from the CV data. The LUMO energy levels
were either determined from the CV data or calculated as the
difference between the HOMO values and the optical HOMO–
LUMO gaps. To estimate the optical HOMO–LUMO gap, the
wavelength at the intersection of the tangent line drawn at the
low energy side of the (solution) absorption spectrum with the
Experimental section
General experimental methods
Unless stated otherwise, all reagents and chemicals were x-axis was used (Eg (eV) = 1240/(wavelength in nm)).
obtained from commercial sources and used without further 2,5-Bis(3′-hexylthiophen-2′-yl)thiazolo[5,4-d]thiazole
(1).
purification. Toluene was dried using an MBraun solvent puri- TzTz 1 was prepared by adding 3-hexylthiophene-2-carbalde-
fication system (model MB-SPS 800) equipped with alumina hyde (1.96 g, 0.02 mol, 2 equiv.) and dithiooxamide (2.39 g,
drying columns. Microwave reactions were carried out in a 0.01 mol, 1 equiv.) to nitrobenzene (20 mL) and heating the
CEM Discovery microwave at the given temperature by varying reaction mixture for 24 h at 130 °C under a nitrogen atmos-
the irradiation power. A thick-walled pyrex reaction vessel phere. Nitrobenzene was removed by vacuum distillation. The
(10 mL) with a teflon septum was used for the microwave reac- black solid residue was evaporated on silica gel and conse-
tions. NMR chemical shifts (δ) were determined relative to the quently purified via column chromatography (eluent hexanes–
residual CHCl3 absorption (7.26 ppm) or the 13C resonance EtOAc 95/5). The tubes containing yellow/brown TLC spots (Rf
shift of CDCl3 (77.16 ppm) or C6D5Cl (134.19 ppm). 13C signals 0.5) were evaporated. The product was then crystallized from a
split up by J-coupling with 19F are indicated by their chemical MeOH–EtOAc mixture (2/1) to afford TzTz 1 (1.40 g, 60%) as a
shifts. High resolution electrospray ionization mass spec- yellow crystalline powder. The material identity and purity
trometry (ESI-MS) analysis of the samples was performed were checked via 1H NMR and HRMS and were found to be
using an LTQ Orbitrap Velos Pro mass spectrometer (Thermo- identical to literature data.9,17
Fischer Scientific) equipped with an atmospheric pressure
ionization source operating in the nebulizer assisted electro-
General procedure for the direct arylation reactions
spray mode. The instrument was calibrated in the m/z range 2,5-Bis(3′-hexylthiophen-2′-yl)thiazolo[5,4-d]thiazole (1) (119 mg,
220–2000 using a standard solution containing caffeine, MRFA 0.25 mmol, 1 equiv.), K2CO3 (52 mg, 0.375 mmol 1.5 equiv.),
and Ultramark 1621. UV-Vis absorption spectra were recorded Pd(OAc)2 (1.1 mg, 5 μmol, 2 mol%), PCy3HBF4 (3.7 mg,
with an Agilent Cary 500 Scan UV-Vis-NIR spectrometer in a 10.0 μmol, 4 mol%) and pivalic acid (7.7 mg, 0.075 mmol,
continuous run from 200 to 800 nm at a scan rate of 600 nm 30 mol%) were weighed in air and placed in a microwave vial
min−1. Infrared spectra were collected with a resolution of (10 mL) equipped with a magnetic stirring bar. The solid aryl
4 cm−1 (16 scans) using films drop-casted on a NaCl disk from bromides (2a,d,f,g) were added at this point (1.1 or 2.1 equiv.).
CHCl3 solution. Preparative size exclusion chromatography The vial was purged with Ar and dry toluene (1 mL; 0.25 M
(SEC) was performed on JAIGEL 1H and 2H columns attached final concentration of TzTz 1) was added. The liquid aryl bro-
to an LC system equipped with a UV detector (path 0.5 mm) mides (2b,c,e) were added at this point (1.1 or 2.1 equiv.). The
and a switch for recycling and collecting the eluent (CHCl3: reaction mixture was vigorously stirred under microwave
flow rate 3.5 mL min−1, injection volume 2.5 mL). Electroche- irradiation at 180 °C for 4 h. The solution was then cooled
mical measurements were performed with an Eco Chemie down to room temperature and diluted with CH2Cl2 and H2O.
Autolab PGSTAT 30 potentiostat/galvanostat using a three-elec- The aqueous phase was extracted with CH2Cl2. The organic
trode microcell equipped with a Pt wire working electrode, a Pt fractions were combined and dried over MgSO4, filtered, and
wire counter electrode and a Ag/AgNO3 reference electrode (Ag evaporated under reduced pressure. The obtained product
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mixture was separated by column chromatography or prepara- (2b) (65 µL, 0.525 mmol, 2.1 equiv.); the reaction was run for
tive SEC to afford the pure mono- (3a–g) and disubstituted 7 h; the mixture was purified by column chromatography
(4a–g) TzTzs.
4-{4-Hexyl-5-[5-(3-hexylthiophen-2-yl)thiazolo[5,4-d]thiazol-2- separation was not possible by column chromatography, the
yl]thiophen-2-yl}isophthalonitrile (3a). 4-Bromoisophthalo- compounds were additionally purified by preparative SEC to
(eluent gradient petroleum ether–CHCl3 9/1–3/2). Since fine
nitrile (2a) (57 mg, 0.275 mmol, 1.1 equiv.); the mixture was afford 3b and 4b in 30 and 69% yield (49 and 140 mg), respect-
1
purified by column chromatography (eluent gradient pet- ively; yellow solid; Mp 158–159 °C; H NMR (300 MHz, CDCl3)
roleum ether–CHCl3 4/1–1/1) to afford 3a (74 mg, 49%) and 4a δ 7.43 (s, 2H), 3.05–2.96 (m, 4H), 1.83–1.69 (m, 4H), 1.52–1.43
1
(41 mg, 44%); red solid; Mp 110–111 °C; H NMR (300 MHz, (m, 4H), 1.40–1.30 (m, 8H), 0.91 (t, J = 7.0 Hz, 6H); 13C NMR
1
CDCl3) δ 8.02 (d, J = 1.1 Hz, 1H), 7.86 (dd, J = 8.3, 1.1 Hz, 1H), (75 MHz, C6D5Cl) δ 160.8, 151.1, 145.9, 144.2 (d, J = 250 Hz),
7.78 (d, J = 8.3 Hz, 1H), 7.73 (s, 1H), 7.37 (d, J = 5.1 Hz, 1H), 143.1, 140.1 (d, 1J = 250 Hz), 138.0 (d, 1J = 250 Hz), 134.6,
7.00 (d, J = 5.1 Hz, 1H), 3.09–2.89 (m, 4H), 1.87–1.64 (m, 4H), 133.7, 109.6 (m), 31.8, 30.3, 30.0, 29.5, 22.8, 14.1. (Due to the
1.55–1.41 (m, 4H), 1.40–1.26 (m, 8H), 0.99–0.83 (m, 6H); poor compound solubility in CDCl3, C6D5Cl was used for the
13C NMR (75 MHz, CDCl3) δ 162.8, 159.7, 151.0, 150.4, 144.2, 13C NMR measurement. The solvent peaks obscure 4 signals
143.8, 140.4, 138.1, 138.0, 136.0, 135.9, 132.7, 131.8, 131.1, between 133 and 124 ppm.) HRMS (ESI) m/z calcd for
130.0, 128.0, 117.1, 116.7, 112.0, 110.7, 31.8, 31.7, 30.5, 30.4, C36H29F10N2S4 [M + H]+ 807.1025; found 807.1054; UV-Vis
30.1, 30.0, 29.47, 29.45, 22.8 14.3; IR (NaCl) νmax 2953/2928/ (CHCl3) λmax (log ε) 421 nm (4.58).
2857 (saturated C–H), 2223 cm−1 (CN); HRMS (ESI) m/z calcd
for C32H33N4S4 [M + H]+ 601.1510; found 601.1564; UV-Vis (3-hexylthiophen-2-yl)thiazolo[5,4-d]thiazole
(CHCl3) λmax (log ε) 427 nm (4.54). 2,4-bis(trifluoromethyl)benzene (2c) (46 µL, 0.275 mmol,
2-{5-[2,4-Bis(trifluoromethyl)phenyl]-3-hexylthiophen-2-yl}-5-
(3c). 1-Bromo-
4,4′-[Thiazolo[5,4-d]thiazole-2,5-diyl-bis(4-hexylthiophene-5,2- 1.1 equiv.); the reaction was run for 7 h; the mixture was puri-
diyl)]diisophthalonitrile (4a). 4-Bromoisophthalonitrile (2a) fied by column chromatography (eluent gradient petroleum
(109 mg, 0.525 mmol, 2.1 equiv.); the mixture was purified by ether–CHCl3 9/1–6/1). Since fine separation was not possible
column chromatography (eluent gradient petroleum ether– by column chromatography, the compounds were additionally
CHCl3 4/1–1/1) to afford 3a and 4a in 34 and 52% yield (96 and purified by preparative SEC to afford 3c and 4c in 58 and 42%
52 mg), respectively; red solid; Mp 285–286 °C; 1H NMR yield (99 and 47 mg), respectively; yellow solid; Mp 77–78 °C;
(400 MHz, CDCl3) δ 8.04 (d, J = 1.7 Hz, 2H), 7.88 (dd, J = 8.2, 1H NMR (300 MHz, CDCl3) δ 8.04 (s, 1H), 7.85 (d, J = 8.1 Hz,
1.7 Hz, 2H), 7.81 (d, J = 8.2 Hz, 2H), 7.74 (s, 2H), 3.06–2.98 (m, 1H), 7.71 (d, J = 8.1 Hz, 1H), 7.36 (d, J = 5.1 Hz, 1H), 7.07 (s,
4H), 1.85–1.72 (m, 4H), 1.55–1.44 (m, 4H), 1.42–1.31 (m, 8H), 1H), 6.99 (d, J = 5.1 Hz, 1H), 3.07–2.88 (m, 4H), 1.84–1.62 (m,
0.91 (t, J = 6.8 Hz, 6H); 13C NMR (100 MHz, CDCl3) δ 160.8, 4H), 1.56–1.41 (m, 4H), 1.39–1.28 (m, 8H), 0.98–0.82 (m, 6H);
151.3, 144.7, 140.4, 138.5, 138.1, 136.1, 135.7, 132.8, 130.1, 13C NMR (75 MHz, CDCl3) δ 162.2, 160.6, 150.5, 150.2, 143.5,
117.0, 116.7, 112.2, 110.9, 31.8, 30.6, 30.0, 29.4, 22.8, 14.2; IR 143.1, 139.3, 136.8, 133.9, 133.6, 132.3 (q, 3J = 3 Hz), 131.9,
2
2
3
(NaCl) νmax 2950/2927/2856 (saturated C–H), 2220 cm−1 (CN); 131.0 (q, J = 34 Hz) 129.8 (q, J = 32 Hz) 128.5 (q, J = 3 Hz),
HRMS (ESI) m/z calcd for C40H35N6S4 [M + H]+ 727.1728; found 127.7, 125.2, 124.1, 123.4 (q, 1J = 273 Hz), 123.3 (q, 1J = 273
727.1773; UV-Vis (CHCl3) λmax (log ε) 451 nm (4.70).
2-[3-Hexyl-5-(perfluorophenyl)thiophen-2-yl]-5-(3-hexylthio- HRMS (ESI) m/z calcd for C32H33F6N2S4 [M + H]+ 686.3530;
phen-2-yl)thiazolo[5,4-d]thiazole (3b). 1-Bromo-2,3,4,5,6- found 686.1429; UV-Vis (CHCl3) λmax (log ε) 400 nm (4.60).
pentafluorobenzene (2b) (33 µL, 0.275 mmol, 1.1 equiv.); the 2,5-Bis{5-[2,4-bis(trifluoromethyl)phenyl]-3-hexylthiophen-2-
reaction was run for 7 h; the mixture was purified by column yl}thiazolo[5,4-d]thiazole (4c). 1-Bromo-2,4-bis(trifluoro-
Hz), 31.8 (2Cs), 30.4, 30.3, 30.1, 29.9, 29.5, 29.3, 22.8, 14.2;
chromatography (eluent gradient petroleum ether–CHCl3 methyl)benzene (2c) (89 µL, 0.525 mmol, 2.1 equiv.); the reac-
9/1–3/2). Since fine separation was not possible by column tion was run for 7 h; the mixture was purified by column
chromatography, the compounds were additionally purified by chromatography (eluent gradient petroleum ether–CHCl3
preparative SEC to afford 3b and 4b in 49 and 36% yield (78 9/1–6/1). Since fine separation was not possible by column
1
and 36 mg), respectively; yellow solid; Mp 84–85 °C; H NMR chromatography, the compounds were additionally purified by
(300 MHz, CDCl3) δ 7.40 (s, 1H), 7.36 (d, J = 5.2 Hz, 1H), 6.98 preparative SEC to afford 3c and 4c in 27 and 58% yield
1
(d, J = 5.2 Hz, 1H), 3.05–2.87 (m, 4H), 1.84–1.64 (m, 4H), (23 and 131 mg), respectively; yellow solid; Mp 152–153 °C; H
1.57–1.41 (m, 4H), 1.41–1.30 (m, 8H), 0.96–0.86 (m, 6H); NMR (400 MHz, CDCl3) δ 8.05 (s, 2H), 7.86 (d, J = 8.1 Hz, 2H),
13C NMR (75 MHz, CDCl3) δ 162.3, 160.2, 150.7, 150.4, 144.3 7.72 (d, J = 8.1 Hz, 2H), 7.08 (s, 2H), 3.04–2.93 (m, 4H),
1
1
(d, J = 250 Hz), 143.6, 142.7, 140.3 (d, J = 250 Hz), 138.2 (d, 1.82–1.70 (m, 4H), 1.53–1.42 (m, 4H), 1.38–1.31 (m, 8H), 0.91
1J = 250 Hz), 134.4 (t, J = 4.1 Hz), 133.7 (d, J = 5.8 Hz), 131.8, (t, J = 7.0 Hz, 6H); 13C NMR (75 MHz, CDCl3) δ 161.1, 150.6,
3
2
131.0, 127.8 (m), 127.7, 109.5 (dt, 2J = 14.9 Hz; 3J = 4.3 Hz), 143.3, 139.5, 136.8, 133.8, 133.6, 132.4 (q, J = 3 Hz), 130.9 (q,
3
31.8, 30.3, 30.0, 29.5, 22.8, 14.2; HRMS (ESI) m/z calcd for 2J = 33 Hz), 129.9 (q, 2J = 34 Hz), 128.6 (q, 3J = 3 Hz), 124.1,
C30H30F5N2S4 [M + H]+ 641.1212; found 641.1212; UV-Vis 123.4 (q, J = 273 Hz), 123.3 (q, J = 273 Hz), 31.8, 30.4, 30.0,
1
1
(CHCl3) λmax (log ε) 406 nm (4.55).
2,5-Bis[3-hexyl-5-(perfluorophenyl)thiophen-2-yl]thiazolo- [M + H]+ 899.1413; found 899.1486; UV-Vis (CHCl3) λmax (log ε)
[5,4-d]thiazole (4b). 1-Bromo-2,3,4,5,6-pentafluorobenzene 410 nm (4.69).
29.3, 22.8, 14.2; HRMS (ESI) m/z calcd for C40H35F12N2S4
4668 | Org. Biomol. Chem., 2014, 12, 4663–4672
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Paper
Methyl 4-{4-hexyl-5-[5-(3-hexylthiophen-2-yl)thiazolo[5,4-d]- tive SEC to afford 3e and 4e in 34 and 50% yield (47 and
thiazol-2-yl]thiophen-2-yl}benzoate (3d). Methyl 4-bromo- 78 mg), respectively; red solid; Mp 168–169 °C; 1H NMR
benzoate (2d) (59 mg, 0.275 mmol, 1.1 equiv.); the mixture was (300 MHz, CDCl3) δ 8.59 (d, J = 4.7 Hz, 2H), 7.80–7.60 (m, 4H),
purified by column chromatography (eluent gradient pet- 7.50 (s, 2H), 7.21–7.15 (m, 2H), 3.08–2.87 (m, 4H), 1.85–1.61
roleum ether–CHCl3 12/1–10/1) to afford 3d and 4d in 64 and (m, 4H), 1.57–1.40 (m, 4H), 1.40–1.29 (m, 8H), 0.98–0.85 (m,
34% yield (98 and 32 mg), respectively; red solid; Mp 95–96 °C; 6H); 13C NMR (75 MHz, CDCl3) δ 161.6, 151.8, 150.6, 149.9,
1H NMR (300 MHz, CDCl3) δ 8.05 (d, J = 8.2 Hz, 2H), 7.70 (d, 145.4, 144.4, 136.8, 133.3, 128.2, 122.6, 119.2, 31.8, 30.5, 30.0,
J = 8.2 Hz, 2H), 7.36 (d, J = 5.1 Hz, 1H), 7.31 (s, 1H), 6.99 (d, J = 29.4, 22.8, 14.3; HRMS (ESI) m/z calcd for C34H37N4S4 [M + H]+
5.1 Hz, 1H), 3.92 (s, 3H), 3.04–2.90 (m, 4H), 1.84–1.65 (m, 4H), 629.1901; found 629.1881; UV-Vis (CHCl3) λmax (log ε) 440 nm
1.54–1.41 (m, 4H), 1.40–1.23 (m, 8H), 0.98–0.83 (m, 6H); 13C (4.65).
NMR (75 MHz, CDCl3) δ 166.7, 162.0, 161.0, 150.4, 150.3,
2-[3-Hexyl-5-(4-methoxyphenyl)thiophen-2-yl]-5-(3-hexylthio-
144.3, 144.0, 143.4, 137.8, 132.6, 131.9, 131.0, 130.5, 129.6, phen-2-yl)thiazolo[5,4-d]thiazole (3f). 1-Bromo-4-methoxyben-
128.1, 127.6, 125.6, 52.4, 31.8 (2Cs), 30.6, 30.3, 30.1, 29.5, 22.8 zene (2f) (51 mg, 0.275 mmol, 1.1 equiv.); the mixture was
14.3; IR (NaCl) νmax 2956/2929/2857 (saturated C–H), purified by column chromatography (eluent gradient pet-
1719 cm−1 (COOMe); HRMS (ESI) m/z calcd for C32H37N2O2S4 roleum ether–CHCl3 10/1–7/1). Since fine separation was not
[M + H]+ 609.1738; found 609.1730; UV-Vis (CHCl3) λmax (log ε) possible by column chromatography, the compounds were
417 nm (4.40).
additionally purified by preparative SEC to afford 3f and 4f in
Dimethyl 4,4′-[(thiazolo[5,4-d]thiazole-2,5-diyl)-bis(4-hexyl- 28 and 70% yield (41 and 60 mg), respectively; orange solid;
1
thiophene-5,2-diyl)]dibenzoate (4d). Methyl 4-bromobenzoate Mp 83–84 °C; H NMR (300 MHz, CDCl3) δ 7.56 (d, J = 8.7 Hz,
(2d) (113 mg, 0.525 mmol, 2.1 equiv.); the mixture was purified 2H), 7.33 (d, J = 5.1 Hz, 1H), 7.08 (s, 1H), 6.97 (d, J = 5.1 Hz,
by column chromatography (eluent gradient petroleum ether– 1H), 6.91 (d, J = 8.7 Hz, 2H), 3.85 (s, 3H), 3.01–2.86 (m, 4H),
CHCl3 12/1–10/1) to afford 3d and 4d in 6 and 92% yield (9 1.81–1.61 (m, 4H), 1.53–1.25 (m, 8H), 0.96–0.81 (m, 6H);
1
and 178 mg), respectively; red solid; Mp 211–213 °C; H NMR 13C NMR (75 MHz, CDCl3) δ 161.6, 161.4, 159.9, 150.2,
(300 MHz, CDCl3) δ 8.06 (d, J = 8.2 Hz, 4H), 7.70 (d, J = 8.2 Hz, 149.9, 145.7, 144.3, 143.1, 132.0, 130.9, 130.1, 127.4, 127.2,
4H), 7.24 (s, 2H), 3.92 (s, 3H), 2.96–2.89 (m, 4H), 1.80–1.68 (m, 126.4, 125.7, 114.5, 55.5, 31.8, 30.6, 30.3, 30.1, 30.0, 29.5,
4H), 1.53–1.44 (m, 4H), 1.40–1.32 (m, 8H), 0.92 (t, J = 7.1 Hz, 22.8, 14.3; HRMS (ESI) m/z calcd for C31H37N2OS4 [M + H]+
6H); 13C NMR (75 MHz, CDCl3) δ 166.7, 161.1, 150.5, 144.3, 581.1789; found 581.1765; UV-Vis (CHCl3) λmax (log ε) 418 nm
144.0, 137.7, 132.6, 130.5, 129.5, 128.0, 125.5, 52.4, 31.8, 30.6, (4.65).
30.0, 29.6, 22.8, 14.3; IR (NaCl) νmax 2950/2925/2853 (saturated
2,5-Bis[3-hexyl-5-(4-methoxyphenyl)thiophen-2-yl]thiazolo-
C–H), 1718 cm−1 (COOMe); HRMS (ESI) m/z calcd for [5,4-d]thiazole (4f). 1-Bromo-4-methoxybenzene (2f) (98 mg,
C32H37N2O2S4 [M + H]+ 743.2106; found 743.2067; UV-Vis 0.525 mmol, 2.1 equiv.); the mixture was purified by column
(CHCl3) λmax (log ε) 445 nm (4.45).
chromatography (eluent gradient petroleum ether–CHCl3
2-[3-Hexyl-5-(pyridin-2-yl)thiophen-2-yl]-5-(3-hexylthiophen-2- 10/1–7/1). Since fine separation was not possible by column
yl)thiazolo[5,4-d]thiazole (3e). 2-Bromopyridine (2e) (26 µL, chromatography, the compounds were additionally purified by
0.275 mmol, 1.1 equiv.); the mixture was purified by column preparative SEC to afford 3f and 4f in 32 and 64% yield (55
1
chromatography (eluent gradient petroleum ether–CHCl3 and 93 mg), respectively; red solid; Mp 166–167 °C; H NMR
10/1–7/1). Since fine separation was not possible by column (300 MHz, CDCl3) δ 7.56 (d, J = 8.8 Hz, 4H), 7.08 (s, 2H), 6.92
chromatography, the compounds were additionally purified by (d, J = 8.8 Hz, 4H), 3.84 (s, 6H), 3.00–2.87 (m, 4H), 1.83–1.65
preparative SEC to afford 3e and 4e in 69 and 27% yield (96 (m, 4H), 1.53–1.40 (m, 4H), 1.40–1.29 (m, 8H), 0.90 (t, J =
and 22 mg), respectively; red solid; Mp 98–99 °C; 1H NMR 6.9 Hz, 6H); 13C NMR (75 MHz, CDCl3) δ 161.3, 159.9, 150.0,
(300 MHz, CDCl3) δ 8.59 (dd, J = 4.7, 0.8 Hz, 1H), 7.75–7.63 (m, 145.6, 144.2, 130.2, 127.2, 126.4, 125.7, 114.5, 55.5, 31.8, 30.7,
2H), 7.54 (s, 1H), 7.34 (d, J = 5.1 Hz, 1H), 7.23–7.15 (m, 1H), 30.0, 29.6, 22.8, 14.3; HRMS (ESI) m/z calcd for C38H43N2O2S4
6.98 (d, J = 5.1 Hz, 1H). 3.05–2.90 (m, 4H), 1.83–1.65 (m, 4H), [M + H]+ 687.2207; found 687.2187; UV-Vis (CHCl3) λmax (log ε)
1.56–1.39 (m, 4H), 1.37–1.29 (m, 8H), 0.98–0.79 (m, 6H); 442 nm (4.80).
13C NMR (75 MHz, CDCl3) δ 161.9, 161.4, 151.6, 150.5, 150.3,
4-{4-Hexyl-5-[5-(3-hexylthiophen-2-yl)thiazolo[5,4-d]thiazol-2-
149.6, 144.8, 144.4, 143.3, 137.2, 133.5, 132.0, 130.9, 128.5, yl]thiophen-2-yl}-N,N-diphenylaniline (3g). 4-Bromo-N,N-diphe-
127.5, 122.6, 119.3, 31.8 (2Cs), 30.5, 30.3, 30.1, 30.0, 29.8, 29.5, nylaniline (2f) (89 mg, 0.275 mmol, 1.1 equiv.); the mixture
22.8, 14.3; HRMS (ESI) m/z calcd for C34H34N3S4 [M + H]+ was purified by column chromatography (eluent gradient pet-
552.1636; found 552.1635; UV-Vis (CHCl3) λmax (log ε) 416 nm roleum ether–CHCl3 10/1–7/1). Since fine separation was not
(4.58).
possible by column chromatography, the compounds were
2,5-Bis[3-hexyl-5-(pyridin-2-yl)thiophen-2-yl]thiazolo[5,4-d]- additionally purified by preparative SEC to afford 3g and 4g in
thiazole (4e). 2-Bromopyridine (2e) (50 µL, 0.525 mmol, 50 and 38% yield (90 and 46 mg), respectively; yellow viscous
1
2.1 equiv.); the mixture was purified by column chromato- oil; H NMR (400 MHz, CDCl3) δ 7.50 (d, J = 8.7 Hz, 2H), 7.34
graphy (eluent gradient petroleum ether–CHCl3 10/1–7/1). (d, J = 5.1 Hz, 1H), 7.32–7.26 (m, 4H), 7.17–7.04 (m, 9H), 6.98
Since fine separation was not possible by column chromato- (d, J = 5.1 Hz, 1H), 3.02–2.87 (m, 4H), 1.81–1.67 (m, 4H),
graphy, the compounds were additionally purified by prepara- 1.54–1.40 (m, 4H), 1.40–1.31 (m, 8H), 0.97–0.82 (m, 6H);
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13C NMR (75 MHz, CDCl3) δ 161.6, 161.4, 150.2, 149.9, 148.2, ether–CHCl3 10/1–6/1). Since fine separation was not possible
147.4, 145.7, 144.4, 143.2, 132.0, 130.9, 130.2, 129.5, 127.4, by column chromatography, the compounds were additionally
127.2, 126.7, 125.8, 124.9, 123.6, 123.2, 31.8, 30.6, 30.3, 30.2, purified by preparative SEC to afford 6 in 88% yield (119 mg);
1
30.0, 29.5 (2Cs), 22.8, 14.3; HRMS (ESI) m/z calcd for red solid; Mp 94–95 °C; H NMR (300 MHz, CDCl3) δ 8.05 (s,
C42H44N3S4 [M + H]+ 718.2340; found 718.2375; UV-Vis (CHCl3) 1H), 7.85 (d, J = 8.2 Hz, 1H), 7.72 (d, J = 8.1 Hz, 1H), 7.50 (d, J =
λmax (log ε) 440 nm (4.70).
4,4′-{5,5′-[Thiazolo[5,4-d]thiazole-2,5-diyl]-bis(4-hexylthio- (m, 4H), 1.87–1.66 (m, 4H), 1.59–1.42 (m, 4H), 1.41–1.30 (m,
phene-5,2-diyl)}-bis(N,N-diphenylaniline)
(4g). 4-Bromo- 8H), 1.01–0.81 (m, 6H); 13C NMR (75 MHz, CDCl3) δ 162.7,
8.7 Hz, 2H), 7.34–7.26 (m, 4H), 7.18–7.02 (m, 10H), 3.09–2.88
N,N-diphenylaniline (2f) (170 mg, 0.525 mmol, 2.1 equiv.); the 160.3, 150.6, 150.0, 148.3, 147.4, 146.0, 144.6, 143.0, 139.2,
mixture was purified by column chromatography (eluent gradi- 136.9, 134.0, 133.6, 132.3 (m), 130.9 (q, 2J = 33 Hz), 130.1,
ent petroleum ether–CHCl3 10/1–7/1). Since fine separation 129.8 (q, 2J = 33 Hz), 129.5, 128.5 (m), 127.1, 126.7, 125.8,
was not possible by column chromatography, the compounds 125.0, 124.1, 123.6, 123.4 (q, 1J = 273 Hz), 123.3 (q, 1J =
were additionally purified by preparative SEC to afford 3g and 273 Hz), 123.2, 31.8, 30.7, 30.4, 30.0 (2Cs), 29.5, 29.3, 22.8,
4g in 46 and 38% yield (83 and 91 mg), respectively; red solid. 14.2; HRMS (ESI) m/z calcd for C50H46F6N3S4 [M + H]+
1
Mp: 89–91 °C; H NMR (300 MHz, CDCl3) δ 7.50 (d, J = 8.6 Hz, 930.2479; found 930.2432; UV-Vis (CHCl3) λmax (log ε) 449 nm
4H), 7.35–7.26 (m, 7H), 7.18–7.01 (m, 19H), 3.05–2.84 (m, 4H), (4.73).
1.85–1.66 (m, 4H), 1.54–1.43 (m, 4H), 1.43–1.29 (m, 8H),
0.96–0.88 (m, 6H); 13C NMR (75 MHz, CDCl3) δ 161.3, 150.1,
148.2, 147.4, 145.6, 144.3, 130.3, 129.5, 127.3, 126.7, 125.8,
Acknowledgements
125.0, 123.6, 123.3, 31.8, 30.6, 30.0, 29.5, 22.8, 14.3; HRMS
(ESI) m/z calcd for C50H57N4S4 [M + H]+ 961.3466; found The reported work is supported by the Interuniversity Attrac-
961.3423; UV-Vis (CHCl3) λmax (log ε) 469 nm (4.88).
tion Poles Programme (P7/05), initiated by the Belgian Science
4-{5-[5-(5-(4-(N,N-Diphenylamino)phenyl)-3-hexylthiophen-2- Policy Office, and the project ORGANEXT (EMR INT4-1.2-2009-
yl)thiazolo[5,4-d]thiazol-2-yl]-4-hexylthiophen-2-yl}isophthalo- 04/054), selected in the frame of the operational program
nitrile (5). Triphenylamine-monosubstituted TzTz 3g (65 mg, INTERREG IV-A Euregio Maas-Rijn. We also acknowledge Her-
0.091 mmol, 1.0 equiv.), 4-bromoisophthalonitrile (2a) cules for providing the funding for the LTQ Orbitrap Velos Pro
(20.6 mg, 0.10 mmol, 1.1 equiv.), K2CO3 (18.7 mg, 0.135 mmol, mass spectrometer.
1.5 equiv.), Pd(OAc)2 (0.4 mg, 2.7 µmol, 2 mol%), PCy3HBF4
(1.3 mg, 3.6 µmol, 4 mol%), pivalic acid (2.7 mg, 0.027 mmol,
30 mol%), toluene (0.4 mL); 180 °C for 4 h; purification by
column chromatography (eluent gradient petroleum ether–
Notes and references
CHCl3 10/1–6/1). Since fine separation was not possible by
column chromatography, the compounds were additionally
purified by preparative SEC to afford TzTz 5 in 85% yield
1 (a) L. Zhang, C.-A. Di, G. Yu and Y. Liu, J. Mater. Chem.,
2010, 20, 7059; (b) A. Mishra and P. Bäuerle, Angew. Chem.,
Int. Ed., 2012, 51, 2020.
2 For a recent review on TzTz synthesis and applications, see:
D. Bevk, L. Lutsen, D. Vanderzande and W. Maes, RSC Adv.,
2013, 3, 11418.
3 (a) S. Ando, J.-I. Nishida, Y. Inoue, S. Tokito and
Y. Yamashita, J. Mater. Chem., 2004, 14, 1787; (b) S. Ando,
J.-I. Nishida, H. Tada, Y. Inoue, S. Tokito and Y. Yamashita,
J. Am. Chem. Soc., 2005, 127, 5336; (c) S. Ando, D. Kumaki,
J.-I. Nishida, H. Tada, Y. Inoue, S. Tokito and Y. Yamashita,
J. Mater. Chem., 2007, 17, 553; (d) M. Mamada, J.-I. Nishida,
D. Kumaki, S. Tokito and Y. Yamashita, Chem. Mater.,
2007, 19, 5404; (e) Y. Fujisaki, M. Mamada, D. Kumaki,
S. Tokito and Y. Yamashita, Jpn. J. Appl. Phys., 2009, 48,
111504.
1
(64 mg); red solid; Mp 172–173 °C; H NMR (300 MHz, CDCl3)
δ 8.02 (d, J = 1.7 Hz, 1H), 7.86 (dd, J = 8.3, 1.7 Hz, 1H), 7.79 (d,
J = 8.3 Hz, 1H), 7.74 (s, 1H), 7.53–7.45 (m, 2H), 7.33–7.26 (m,
4H), 7.17–7.03 (m, 9H), 3.06–2.88 (m, 4H), 1.85–1.65 (m, 4H),
1.56–1.42 (m, 4H), 1.42–1.28 (m, 8H), 1.00–0.81 (m, 6H);
13C NMR (75 MHz, CDCl3) δ 162.7, 159.3, 151.2, 150.2, 148.3,
147.4 (2Cs), 146.3, 145.0, 144.1, 140.5, 138.1, 137.9, 136.1
(2Cs), 132.8, 130.0, 129.9, 129.6 (4Cs), 127.0, 126.7, 125.9,
125.0 (4Cs), 123.7 (2Cs), 123.1 (2Cs), 117.1, 116.7, 112.0, 110.7,
31.8, 31.75, 30.7, 30.5, 30.0, 29.5 (2Cs), 22.8, 14.3; IR (NaCl)
νmax 2955/2925/2855 (saturated C–H), 2232 cm−1 (CN); HRMS
(ESI) m/z calcd for C50H46N5S4 [M + H]+ 844.2558; found
844.2576; UV-Vis (CHCl3) λmax (log ε) 473 nm (4.66).
4-{5-[5-(5-(2,4-Bis(trifluoromethyl)phenyl)-3-hexylthiophen-2-
yl)thiazolo[5,4-d]thiazol-2-yl]-4-hexylthiophen-2-yl}-N,N-diphenyl-
aniline (6). Bis(trifluoromethyl)phenyl-monosubstituted TzTz
3c (100 mg, 0.146 mmol, 1.0 equiv.), 4-bromo-N,N-diphenylani-
line (2g) (51.9 mg, 0.160 mmol, 1.1 equiv.), K2CO3 (30.2 mg,
0.218 mmol, 1.5 equiv.), Pd(OAc)2 (0.6 mg, 2.9 µmol, 2 mol%),
PCy3HBF4 (1.3 mg, 3.6 µmol, 4 mol%), pivalic acid (4.5 mg,
0.044 mmol, 30 mol%), toluene (0.6 mL); 180 °C for 4 h; purifi-
cation by column chromatography (eluent gradient petroleum
4 Naraso and F. Wudl, Macromolecules, 2008, 41, 3169.
5 (a) I. Osaka, G. Sauvé, R. Zhang, T. Kowalewski and
R. D. McCullough, Adv. Mater., 2007, 19, 4160; (b) I. Osaka,
R. Zhang, G. Sauvé, D.-M. Smilgies, T. Kowalewski and
R. D. McCullough, J. Am. Chem. Soc., 2009, 131, 2521;
(c) I. Osaka, R. Zhang, J. Liu, D.-M. Smilgies, T. Kowalewski
and R. D. McCullough, Chem. Mater., 2010, 22, 4191.
6 OPV reviews: (a) C. J. Brabec, S. Gowrisanker, J. J. M. Halls,
D. Laird, S. Jia and S. P. Williams, Adv. Mater., 2010, 22,
4670 | Org. Biomol. Chem., 2014, 12, 4663–4672
This journal is © The Royal Society of Chemistry 2014

View Article Online
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Paper
3839; (b) J. Nelson, Mater. Today, 2011, 14, 462;
(c) P.-L. T. Boudreault, A. Najari and M. Leclerc, Chem.
Mater., 2011, 23, 456; (d) L. J. A. Koster, S. E. Shaheen and
Mierloo, A. Schnegg, P. J. Adriaensens, L. Lutsen,
D. Vanderzande, W. Maes, E. Goovaerts and S. Van Door-
slaer, Phys. Chem. Chem. Phys., 2014, 16, 10032.
J. C. Hummelen, Adv. Energy Mater., 2012, 2, 1246; 11 (a) P. Sonar, J. P. Fong Lim and K. L. Chan, Energy Environ.
(e) P. Kumar and S. Chand, Prog. Photovoltaics Res. Appl.,
2012, 20, 377; (f) I. Gang, Z. Rui and Y. Yang, Nat. Photo-
nics, 2012, 6, 153; (g) M. Jørgensen, K. Norrman,
S. A. Gevorgyan, T. Tromholt, B. Andreasen and F. C. Krebs,
Adv. Mater., 2012, 24, 580; (h) K. Vandewal,
S. Himmelberger and A. Salleo, Macromolecules, 2013, 46,
6379; (i) S. B. Darling and F. You, RSC Adv., 2013, 3, 17633.
7 (a) T. W. Lee, N. S. Kang, J. W. Yu, M. H. Hoang, K. H. Kim,
J.-L. Jin and D. H. Choi, J. Polym. Sci., Part A: Polym. Chem.,
2010, 48, 5921; (b) S. Subramaniyan, H. Xin, F. Sunjoo Kim,
Sci., 2011, 4, 1558; (b) J. E. Anthony, Chem. Mater., 2011,
23, 583; (c) Y. Lin, Y. Li and X. Zhan, Adv. Energy Mater.,
2013, 3, 724; (d) A. F. Eftaiha, J.-P. Sun, I. G. Hill and
G. C. Welch, J. Mater. Chem. A, 2014, 2, 1201; (e) Z. Lu,
B. Jiang, X. Zhang, A. Tang, L. Chen, C. Zhan and J. Yao,
Chem. Mater., 2014, 26, 2907.
12 (a) A. Anctil, C. W. Babbitt, R. P. Raffaelle and B. J. Landi,
Prog. Photovoltaics Res. Appl., 2013, 21, 1541; (b) S. Lizin,
S. Van Passel, E. De Schepper, W. Maes, L. Lutsen, J. Manca
and D. Vanderzande, Energy Environ. Sci., 2013, 6, 3136.
S. Shoaee, J. R. Durrant and S. A. Jenekhe, Adv. Energy 13 (a) Y. Lin, Y. Li and X. Zhan, Chem. Soc. Rev., 2012, 41,
Mater., 2011, 1, 854; (c) M. Zhang, X. Guo, X. Wang,
H. Wang and Y. Li, Chem. Mater., 2011, 23, 4264;
(d) S. K. Lee, J. M. Cho, W. S. Shin, J.-C. Lee, W.-H. Lee,
I.-N. Kang, H.-K. Shim and S.-J. Moon, Chem. Commun.,
2011, 47, 1791; (e) I. Osaka, M. Saito, T. Koganezawa and
K. Tamikiya, Adv. Mater., 2012, 24, 425; (f) S. Van Mierloo,
J. Kesters, A. Hadipour, M.-J. Spijkman, N. Van den Brande,
J. D’Haen, G. Van Assche, D. M. de Leeuw, T. Aernouts,
J. Manca, L. Lutsen, D. Vanderzande and W. Maes, Chem.
Mater., 2012, 24, 587; (g) J. Kesters, T. Ghoos, H. Penxten,
4245; (b) J. Zhou, Y. Zuo, X. Wan, G. Long, Q. Zhang, W. Ni,
Y. Liu, Z. Li, G. He, C. Li, B. Kan, M. Li and Y. Chen, J. Am.
Chem. Soc., 2013, 135, 8484; (c) A. K. K. Kyaw, D. H. Wang,
D. Wynands, J. Zhang, T.-Q. Nguyen, G. C. Bazan and
A. J. Heeger, Nano Lett., 2013, 13, 3796; (d) Y. Liu, Y. Yang,
C.-C. Chen, Q. Chen, L. Dou, Z. Hong, G. Li and Y. Yang,
Adv. Mater., 2013, 25, 4657; (e) V. S. Gevaerts, E. M. Herzig,
M. Kirkus, K. H. Hendriks, M. M. Wienk, J. Perlich,
P. Müller-Buschbaum and R. A. J. Janssen, Chem. Mater.,
2014, 26, 916.
J. Drijkoningen, T. Vangerven, D. M. Lyons, B. Verreet, 14 (a) B. Liégault, D. Lapointe, L. Caron, A. Vlassova and
T. Aernouts, L. Lutsen, D. Vanderzande, J. Manca and
W. Maes, Adv. Energy Mater., 2013, 3, 1180; (h) S. Shoaee,
S. Subramaniyan, H. Xin, C. Keiderling, P. S. Tuladhar,
F. Jamieson, S. A. Jenekhe and J. R. Durrant, Adv. Funct.
Mater., 2013, 23, 3286; (i) I. Osaka, M. Saito, T. Koganezawa
and K. Takimiya, Adv. Mater., 2014, 26, 331;
( j) W. Vanormelingen, J. Kesters, P. Verstappen,
J. Drijkoningen, J. Kudrjasova, S. Koudjina, V. Liégeois,
B. Champagne, J. Manca, L. Lutsen, D. Vanderzande and
W. Maes, J. Mater. Chem. A, 2014, 2, 7535.
8 (a) Q. Shi, P. Cheng, Y. Li and X. Zhan, Adv. Energy Mater.,
2012, 2, 63; (b) P. Dutta, W. Yang, S. H. Eom and S.-H. Lee,
Org. Electron., 2012, 13, 273; (c) P. Dutta, H. Park,
W.-H. Lee, I.-N. Kang and S.-H. Lee, Org. Electron., 2012, 13,
3183; (d) P. Cheng, Q. Shi, Y. Lin, Y. Li and X. Zhan, Org.
Electron., 2013, 14, 599; (e) A. Dessì, B. G. Consiglio,
M. Calamante and L. Zani, Eur. J. Org. Chem., 2013, 1916.
9 (a) S. Van Mierloo, V. Liégeois, J. Kudrjasova, E. Botek,
L. Lutsen, B. Champagne, D. Vanderzande, P. Adriaensens
and W. Maes, Magn. Reson. Chem., 2012, 50, 379; (b) S. Van
K. Fagnou, J. Org. Chem., 2009, 74, 1826; (b) D. Schipper
and K. Fagnou, Chem. Mater., 2011, 23, 1594;
(c) M. Baghbanzadeh, C. Pilger and C. O. Kappe, J. Org.
Chem., 2011, 76, 8138; (d) M. Durso, C. Bettini, A. Zanelli,
M. Gazzano, M. G. Lobello, F. De Angelis, V. Biondo,
D. Gentili, R. Capelli, M. Cavallini, S. Toffanin, M. Muccini
and M. Melucci, Org. Electron., 2013, 14, 3089;
(e) K. Okamato, J. Zhang, J. B. Housekeeper, S. R. Marder
and C. K. Luscombe, Macromolecules, 2013, 46, 8059.
15 (a) J. Zhang, D.-Y. Kang, S. Barlow and S. R. Marder,
J. Mater. Chem., 2012, 22, 21392; (b) S.-Y. Liu, M.-M. Shi,
J.-C. Huang, Z.-N. Jin, X.-L. Hu, J.-Y. Pan, H.-Y. Li,
A. K. Y. Jen and H.-Z. Chen, J. Mater. Chem. A, 2013, 1,
2795; (c) J. Zhang, W. Chen, A. J. Rojas, E. V. Jucov,
T. V. Timofeeva, T. C. Parker, S. Barlow and S. R. Marder,
J. Am. Chem. Soc., 2013, 135, 16376.
16 (a) Y. Fujinami, J. Kuwabara, W. Lu, H. Hayashi and
T. Kanbara, ACS Macro Lett., 2012, 1, 67; (b) S. Kowalski,
S. Allard and U. Scherf, ACS Macro Lett., 2012, 1, 465;
(c) L. Facchetti, A. Vaccaro and A. Marrocchi, Angew. Chem.,
Int. Ed., 2012, 51, 3520; (d) P. Berrouard, A. Najari, A. Pron,
D. Gendron, P.-O. Morin, J.-R. Pouliot, J. Veilleux and
M. Leclerc, Angew. Chem., Int. Ed., 2012, 51, 2068; (e) J. Jo,
A. Pron, P. Berrouard, W. L. Leong, J. D. Yuen, J. S. Moon,
M. Leclerc and A. J. Heeger, Adv. Energy Mater., 2013, 2,
1397.
Mierloo,
K.
Vasseur,
N.
Van
den
Brande,
A. E. Boyukbayram, B. Ruttens, S. D. Rodriguez, E. Botek,
V. Liégeois, J. D’Haen, P. J. Adriaensens, P. Heremans,
B.
Champagne,
G.
Van
Assche,
L.
Lutsen,
D. J. Vanderzande and W. Maes, ChemPlusChem, 2012, 77,
923.
10 (a) N. Nevil, Y. Ling, S. Van Mierloo, J. Kesters, 17 (a) J. R. Johnson and R. Ketcham, J. Am. Chem. Soc., 1960,
F. Piersimoni, P. Adriaensens, L. Lutsen, D. Vanderzande,
J. Manca, W. Maes, S. Van Doorslaer and E. Goovaerts,
Phys. Chem. Chem. Phys., 2012, 14, 15774; (b) Y. Ling, S. Van
82, 2719; (b) J. R. Johnson, D. H. Rotenberg and
R. Ketcham, J. Am. Chem. Soc., 1970, 92, 4046;
(c) R. C. Knighton, A. J. Hallett, B. M. Kariuki and
This journal is © The Royal Society of Chemistry 2014
Org. Biomol. Chem., 2014, 12, 4663–4672 | 4671

View Article Online
Paper
Organic & Biomolecular Chemistry
S. J. A. Pope, Tetrahedron Lett., 2010, 41, 5419; 19 J. Song, F. Zhang, C. Li, W. Liu, B. Li, Y. Huang and Z. Bo,
(d) R. Ziessel, A. Nano, E. Heyer, T. Bura and P. Retailleau, J. Phys. Chem. C, 2009, 113, 13391.
Chem. – Eur. J., 2013, 19, 2582; (e) A. Dessi, M. Calamante, 20 L. Zani, G. Reginato, A. Mordini, M. Calamante and
A. Mordini, L. Zani, M. Taddei and G. Reginato, RSC Adv.,
2014, 4, 1322.
18 Y. Kawamata, S. Tokuji, H. Yorimitsu and A. Osuka, Angew.
Chem., Int. Ed., 2011, 50, 8867.
M. Bruzzi, Tetrahedron Lett., 2013, 54, 3944.
21 (a) J. Bard and L. R. Faulkner, Electrochemical methods:
fundamentals and applications, Wiley, 2nd edn, 2001;
(b) S. Trasatti, Pure Appl. Chem., 1986, 58, 955.
4672 | Org. Biomol. Chem., 2014, 12, 4663–4672
This journal is © The Royal Society of Chemistry 2014