Quinoxaline derivatives with broadened absorption patterns

Article abstract of DOI:10.1039/c3ob41059e

Quinoxaline-based semiconducting materials are currently of high interest in the field of organic photovoltaics. The number of structural variations employed has been, however, quite limited to date. In this paper we report on the synthesis of a series of quinoxaline monomers and triads with improved optical features. This was achieved by using conjugated linkers, i.e. ethenyl, butadienyl and/or aryl groups, to graft the solubilizing alkyl side chains onto the central quinoxaline core. The influence of the appended groups on the light-harvesting properties of the materials is briefly discussed.

Full text of DOI:10.1039/c3ob41059e

Organic &
Biomolecular Chemistry
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Quinoxaline derivatives with broadened absorption
patterns†
Cite this: Org. Biomol. Chem., 2013, 11,
5866
Lidia Marin,a,b Laurence Lutsen,b Dirk Vanderzandea,b and Wouter Maes*a,b
Quinoxaline-based semiconducting materials are currently of high interest in the field of organic photo-
voltaics. The number of structural variations employed has been, however, quite limited to date. In this
paper we report on the synthesis of a series of quinoxaline monomers and triads with improved optical
features. This was achieved by using conjugated linkers, i.e. ethenyl, butadienyl and/or aryl groups, to
graft the solubilizing alkyl side chains onto the central quinoxaline core. The influence of the appended
groups on the light-harvesting properties of the materials is briefly discussed.
Received 22nd May 2013,
Accepted 15th July 2013
DOI: 10.1039/c3ob41059e
www.rsc.org/obc
Nowadays, a variety of printing techniques are available for
roll-to-roll processing of large area solar cell modules.4 As a
Introduction
The number of studies on the design and synthesis of organic result, there is increased interest in solution-processable small
light-harvesting materials applicable in optoelectronic devices molecules as active light-harvesting donor and acceptor
such as light-emitting diodes (OLEDs), field-effect transistors materials for OPV applications.5
(OFETs), and photovoltaics (OPVs) has increased almost expo-
To encompass the strong π–π intermolecular interactions in
nentially over the last decade. For optimal performance and conjugated (polymer) materials and to allow solution proces-
depending on the targeted device architecture and function, sing of such compounds, solubilizing side chains need to be
these photoactive materials need to fulfil specific criteria. In introduced. Most often, these are linear or branched alkyl
OLEDs for instance, materials with high electroluminescence groups, connected to the (hetero)aromatic unit by C–C or C–O
quantum efficiencies that emit light in the visible range of the single bonds. The side chains are not only used for solvation
solar spectrum are required.1 For OFETs, organic semiconduc- of the materials, at the same time simplifying the synthetic
tors with high charge carrier mobilities are desirable, the uni- protocols and purification, but also they have a huge impact
directional charge transport being facilitated by high degrees on the degree of order and molecular interactions within the
of crystallinity and a tendency to self-assemble.2 For organic system.6 As a rule of thumb, linear substituents enhance the
solar cells, high extinction coefficients and a broad coverage of degree of order (crystallinity), while branched chains induce
the solar spectrum, ideally extended to the low energy side disorder. As a result, linear groups generally confer lower solu-
where the photon flux is most abundant, are additionally bility compared to branched ones. Additionally, the side
required.3 In all cases, either individual or a combination of chains can be used as a tool for fine tuning the optical pro-
conjugated (hetero)aromatic building blocks – in small mole- perties of the photoactive species. The introduction of conju-
cule or semiconducting polymer structures – has been applied gated spacers (e.g., C–C double or triple bonds) between the
successfully. For OPV devices, polymer active layer materials central chromophore and the side chains is a common
are almost exclusively processed from solution, whereas small approach to extend the conjugated system. This generally
molecules were traditionally processed by vacuum deposition affords
a broadening of the absorption window, which
techniques. Solution processing is preferred due to consequently increases the light-harvesting abilities of the
reduced energy consumption and lower manufacturing costs. materials.7
Electron deficient quinoxaline heterocycles have been
selected on numerous occasions as interesting candidates for
the development of new materials for organic electronics.8,9 In
aDesign & Synthesis of Organic Semiconductors (DSOS), Institute for Materials
the OPV field, a number of donor–acceptor (D–A) low band
gap copolymers incorporating quinoxaline units as the elec-
tron poor components have appeared, showing modest to very
high solar cell efficiencies.9 In this paper, we present a series
of quinoxaline derivatives with broadened absorption
patterns specifically designed for optoelectronic applications.
Research (IMO), Hasselt University, Agoralaan 1 – Building D, 3590 Diepenbeek,
Belgium. E-mail: wouter.maes@uhasselt.be
bIMEC, IMOMEC Ass. Lab., Universitaire Campus – Wetenschapspark 1, 3590
Diepenbeek, Belgium
†Electronic supplementary information (ESI) available: 1H and 13C NMR spectra
of all novel compounds, and additional information on their UV-Vis absorption
(solution and film) and emission properties. See DOI: 10.1039/c3ob41059e
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The solubilizing side chains are attached via C–C double system, further on served as reference compounds in the evalu-
bonds (i.e. ethenyl or butadienyl spacers) to the quinoxaline ation of the optical properties of the derivatives bearing
core. Some of the derivatives were also applied in cross-coup- ethenyl or butadienyl spacers between the side chains and the
ling reactions to afford a range of donor–acceptor–donor (D– quinoxaline unit (vide infra). The UV-Vis spectra of derivatives
A–D) type small molecules. In these triads, the conjugation is Q2–Q4 (Fig. 1, Table S1†) showed a bathochromic shift upon
extended in both the horizontal and vertical directions, which going from phenyl to thienyl and 5-(2-ethylhexyl)thienyl. This
makes these compounds promising light-harvesting (precur- trend is in accordance with the electron donor strength of the
sor) materials. For comparison purpose, some derivatives in side chain substituents. For Q3 and Q4, the enhanced conju-
which the side chains are directly attached to the quinoxaline gation led to an extension of the absorption window towards
core by C–C single bonds were also synthesized. The influence the visible region, additionally covering the 400–450 nm range.
of the side chains on the absorption features of the materials The solid-state spectra showed similar features (Fig. S39†).
is discussed.
Compound Q1, bearing bromomethyl groups in positions
2 and 3, served as a key precursor for the synthesis of all
materials with conjugated side chains (Scheme 2). Treatment
of Q1 with triethyl phosphite led to the generation of phospho-
nate groups (Arbuzov reaction). Further basic treatment and
condensation in the presence of an (alkenyl)aldehyde A1–A6
(Horner–Wadsworth–Emmons reaction) afforded quinoxaline
monomers M1–M6 in 56–80% yield. M1 and M2 again served
as reference compounds and were not used in further trans-
formations due to the likelihood of solubility issues.
Results and discussion
The main objective of the present study was to introduce con-
jugated spacers on the 2nd and 3rd positions of the quin-
oxaline moiety in a versatile and flexible way, enabling
broadening of the absorption window. 2,3-Disubstituted qui-
noxaline derivatives can be obtained by condensation reac-
tions between diketones and 1,2-phenylenediamines. The
presence of bromine groups in positions 5 and 8 of the aro-
matic core allows further cross-coupling reactions to extend
the conjugation in two dimensions.
The almost overlapping absorption spectra of monomers
M1–M3, bearing ethenyl spacers to the appended thienyl or
alkoxyphenyl (hetero)aromatic moieties, showed an additional
red shift of the absorption maxima. The secondary lower
Bromination could readily be performed at the precursor
stage, in this case on 2,1,3-benzothiadiazole (1), using a
mixture of Br2 and HBr (Scheme 1).10 Sulphur extrusion in the
presence of NaBH4 afforded 3,6-dibromo-o-phenylenediamine
(3).11 By varying the diketone, one can then easily get access to
a variety of 5,8-dibromoquinoxaline derivatives in which the
side chains are directly attached by C–C single bonds to the
2nd and 3rd positions of the quinoxaline core. 5,8-Dibromo-
2,3-bis(bromomethyl)quinoxaline (Q1), 2,3-diphenyl-5,8-di-
bromoquinoxaline
(Q2),
2,3-bis(thien-2-yl)-5,8-dibromo-
quinoxaline (Q3), and 2,3-bis[5-(2-ethylhexyl)thien-2-yl]-5,8-
dibromoquinoxaline (Q4) were synthesized in this way in good
yields (66–95%) by condensation of diamine 3 with 1,4-dibromo-
butane-2,3-dione (D1), 1,2-diphenyl-ethane-1,2-dione (D2), 1,2-
di(2-thienyl)ethane-1,2-dione (D3), and 1,2-bis[5-(2-ethylhexyl)
thien-2-yl]ethane-1,2-dione (D4), respectively (Scheme 1), in
the presence of a catalytic amount of p-TsOH.12 Compounds
Q2–Q4, with aryl moieties directly attached to the quinoxaline
Fig. 1 UV-Vis spectra (normalized, from a chloroform solution) of quinoxaline
derivatives Q1–Q4.
Scheme 1 Synthesis of reference quinoxaline derivatives Q1–Q4.
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displayed a main band in the UV region and only a weak sec-
ondary band extended into the visible range. The butadienyl
spacer in M6 resulted in a red shift of the main and secondary
absorption bands with ∼50 nm with respect to M5.
From all the quinoxaline derivatives and monomers syn-
thesized up to this stage, M4 appeared to be the most promis-
ing material in terms of optical absorption. Due to the
substituted alkylthiophene groups, this compound also
showed excellent solubility in common organic solvents such
as dichloromethane. Monomers M1–M3 and M5–M6 displayed
appealing optical characteristics as well. To guarantee solution
processability of the final semiconducting materials, only
those monomers bearing alkyl chains with a number of
carbon atoms superior to six were further on employed in
various cross-coupling reactions leading to light-harvesting
polymers and/or small molecules.
As a proof of principle and a first step towards light-harvest-
ing user materials, homopolymer P1 was prepared by Ni0-
mediated Yamamoto polycondensation of quinoxaline
monomer M3 (Scheme 3).13 Despite the reasonable degree of
polymerization obtained (Mn = 6.8 × 104 g mol−1, PDI = 6.0),
no major increase in the conjugation length (red shift of the
absorption maxima and/or onset) was observed from the
absorption spectrum, most probably as a result of twisting
along the polymer backbone, which disrupts the conjugation
(Fig. 2).13 Minimization of the steric hindrance between two
neighbouring quinoxaline units, realized by the introduction
of spacers, e.g., vinylene linkers or small aromatic units such
as thiophene,14,15 was hence explored. Enhancing the co-
planarity of the conjugated backbone results in a narrowing of
the band gap for the final semiconducting small molecule
and/or polymer materials.
We have opted for the introduction of thiophene groups to
afford D–A type expanded chromophores, most conveniently
assembled by cross-coupling reactions. An evaluation of the
reactivity of the quinoxaline compounds towards Suzuki reac-
tions was initially performed (before proceeding to push–pull
polymers). To this extent, D–A–D triads T1–T4 were prepared
starting from thiophene-2-boronic acid (4)16 and quinoxaline
monomers M3–M6 (Scheme 4). To promote the transmetalla-
tion, a base is used for the activation of the boronate, often an
aqueous carbonate or phosphate solution. When these con-
ditions are not suitable, for example in the presence of easily
Scheme 2 Synthesis of quinoxaline monomers M1–M6 with conjugated side
chains.
energy band became slightly more intense and was extended
up to 500 and 550 nm in solution and film, respectively (Fig. 2
and Fig. S39, Table S1†). The contribution of the pendant elec-
tron donating alkoxy chains in M2–M3 seemed negligible.
Monomer M4, bearing 5-(2-ethylhexyl)thien-2-yl side chains
connected by ethenyl linkers, displayed the most promising
optical features. The absorption spectrum is characterized by
three maxima located at 350, 415, and 448 nm, and a shoulder
extending beyond 500 nm, affording enhanced coverage of the
solar spectrum. The absorption spectra of derivatives M5 and
M6, decorated with linear undecyl and heptyl groups
connected by ethenyl and butadienyl linkers, respectively,
Fig. 2 UV-Vis spectra (normalized, from a chloroform solution) of quinoxaline
monomers M1–M6 and polymer P1.
Scheme 3 Synthesis of quinoxaline homopolymer P1 by Yamamoto
polycondensation.
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Fig. 3 UV-Vis spectra (normalized, from a chloroform solution) of D–A–D triads
T1–T5.
Scheme 4 Synthesis of D–A–D triads T1–T4 via Suzuki cross-coupling
consequence the spacers, should preferably be accomplished
in the final step of the synthetic protocol, the bromine atoms
being already present at this point. For future integration of
such building blocks in solution-processable polymer
materials, the introduction of extra solubilizing alkyl
groups was also considered. This could smoothly be achieved
by coupling alkylthienyl units in positions 5 and 8 of the quin-
oxaline core. Synthesis of the dibrominated triad bearing
hexyl side chains in position 3 of the thiophene rings was
accomplished starting from 2-bromo-3-hexylthiophene (5)
(Scheme 5).18 Compound 7 was obtained by Suzuki coupling
with 2,1,3-benzothiadiazole-4,7-bis(boronic acid pinacol ester)
(6). Treatment with LiAlH4 resulted in the formation of the
corresponding diamine. Due to its unstable character, the
latter was immediately used further on, as isolated upon
extraction, in the acid-mediated condensation with 1,4-
dibromo-2,3-butanedione (D1), which led to the formation of
derivative 8 in good overall yield (48% over two steps). Sub-
sequent bromination in the presence of N-bromosuccinimide
afforded dibrominated derivative 9. Addition of triethyl phos-
phite, followed by basic treatment and reaction with aldehyde
A4, finally provided thiophene–quinoxaline–thiophene triad
T5 (Scheme 5).
Compared to triads T1–T4, this novel (macro)monomer dis-
played slightly blue-shifted values for the absorption/emission
maxima and optical band gap (Fig. 3, Table S1 and Fig. S40†),
presumably due to torsional strains induced by the hexyl
groups on the brominated thiophenes. However, its intense
and broad absorption from 300–500 nm still makes it an
attractive unit to be incorporated into low band gap polymer
materials the properties of which can be further tuned by
varying the comonomer. Additionally, starting from building
block 9 and simply varying the aldehyde and thereby the solu-
bilizing side chains, one can quickly get access to a variety of
dibrominated triads in which the optical and organizational
features can be easily fine-tuned.
reactions.
hydrolysable functionalities or substrates with a limited solu-
bility, water-free Suzuki conditions can be employed.17 Due to
the poor solubility of M3 in a biphasic solvent system
(toluene : water) and its tendency to precipitate, we turned to
such conditions (CsF as a base in DME) for the synthesis of
triad T1 (Scheme 4). These conditions were then also
employed for the synthesis of the remaining triads T2–T4.
Even when using a three-fold excess of the boronic acid
(6 equiv.), the products were obtained in average yields
(41–78%). The modest efficiency of the coupling reaction
could be due to the low reactivity of the quinoxaline mono-
mers towards such transformations or the non-optimized
water-free Suzuki conditions.
Compared to the corresponding monomers M3–M6, the
presence of additional thiophene groups led to an improve-
ment of the optical properties for the D–A–D small molecules
(Fig. 3, Table S1†). The main absorption bands were broadened
and slightly red shifted, the absorption onset being extended
towards 600 nm in the solid state. Once more, the derivative
with 5-(2-ethylhexyl)thien-2-yl side chains (T2) showed the
most promising absorption profile.
At this point it became clear that a future transformation of
the synthesized quinoxaline monomers M3–M6 by Suzuki
polycondensation reactions (towards quinoxaline-containing
polymers applicable in OPV), for which an efficient coupling
of the monomers using a precise 1 : 1 feed ratio is required,
was not viable by this approach. It was additionally envisaged
that dibrominated triads, rather than quinoxalines, would be
more reactive coupling partners. To exploit this possibility, a
new synthetic pathway was required, as the presence of the
conjugated linkers burdened direct bromination of triads
T1–T4. The introduction of the quinoxaline side chains, and in
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Scheme 5 Synthesis of dibrominated D–A–D triad T5.
spectrometry (GC-MS) analyses were carried out applying
Chrompack Cpsil5CB or Cpsil8CB capillary columns. Electro-
Conclusions
In this paper we have reported on the synthesis of a series of spray ionization mass spectrometry (ESI-MS) analyses were
novel conjugated quinoxaline derivatives with an absorption carried out using a Thermo Finnigan LCQ Advantage appar-
window extended into the visible range of the solar spectrum. atus. High resolution ESI-MS of the samples was performed
This was accomplished by the introduction of ethenyl or buta- using an LTQ Orbitrap Velos Pro mass spectrometer (Thermo-
dienyl spacers, inducing
a vertical conjugation pathway Fischer Scientific) equipped with an atmospheric pressure
between the solubilizing alkyl side chains and the quinoxaline ionization source operating in the nebulizer assisted electro-
core. The presence of electron rich substituents led to a broad- spray mode. The instrument was calibrated in the m/z range
ening of the absorption window by approximately a factor of 220–2000 using a standard solution containing caffeine, MRFA
two. In an attempt to extend the conjugation in the horizontal and Ultramark 1621. Polymer molecular weights and mole-
direction as well, synthetic protocols towards thiophene–quin- cular weight distributions were determined relative to
oxaline–thiophene triads were explored. The developed polystyrene standards (Polymer Labs) by size exclusion chrom-
alternative route leading to dibrominated triads (Scheme 5) atography (SEC). Chromatograms were recorded using
a
showed several advantages: (i) higher efficiency of the Suzuki Spectra Series P100 (Spectra Physics) equipped with two
cross-coupling reaction, in terms of yield and ratio of the reac- mixed-B columns (10 µm, 0.75 cm × 30 cm, Polymer Labs) and
tants; (ii) the requested boronate is commercially available or a refractive index detector (Shodex) at 40 °C. THF was used as
can be synthesized in one step; (iii) one common precursor (9) the eluent at a flow rate of 1.0 mL min−1. Solution UV-Vis
provides access to a library of dibrominated triads. The syn- absorption measurements were performed with a scan rate of
thesis of low band gap polymers incorporating the novel quin- 600 nm min−1 in a continuous run from 200 to 800 nm. Films
oxaline building blocks and the evaluation of these materials were drop-cast from CHCl3 solutions. Fluorescence measure-
in bulk heterojunction organic solar cells are currently ments (of CHCl3 solutions) were performed on a Fluorolog
ongoing and will be reported in a forthcoming paper.
Tau-3 Lifetime System from Horiba Jobin Yvon. Unless stated
otherwise, all reagents and chemicals were obtained from
commercial sources and used without further purification.
Diethyl ether and THF were dried prior to use by distil-
lation from Na/benzophenone. 2,1,3-Benzothiadiazole-4,7-bis-
(boronic acid pinacol ester) (95%) (6), 1,4-dibromobutane-2,3-
dione (D1), 1,2-diphenylethane-1,2-dione (D2), and 1,2-di-
(2-thienyl)ethane-1,2-dione (D3) were obtained from commercial
sources and were used without further purification.
Experimental section
Materials and methods
NMR chemical shifts (δ, in ppm) were determined relative to
the residual CHCl3 absorption (7.26 ppm) or the 13C resonance
shift of CDCl3 (77.16 ppm). Gas chromatography-mass
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Synthesis
1,2-Bis[5-(2-ethylhexyl)thiophen-2-yl]ethane-1,2-dione (D4)
4,7-Dibromo-2,1,3-benzothiadiazole (2),10 3,6-dibromo-o-phenyl- Oxalyl chloride (0.283 g, 2.24 mmol) in 1,2-dichloroethane
enediamine (3),19 thiophene-2-boronic acid (4),16 2,3-diphenyl- (1 mL) was added dropwise to a solution of AlCl3 (1.331 g,
5,8-dibromoquinoxaline (Q2),20 and 4-dodecyloxybenzaldehyde 9.94 mmol) in 1,2-dichloroethane (5 mL) cooled to −20 °C, fol-
(A3)21 were synthesized according to literature procedures. lowed by the addition of a mixture of 2-(2-ethylhexyl)thiophene
Material identity and purity were confirmed by GC-MS and (0.950 g, 4.84 mmol) and pyridine (0.346 g, 4.39 mmol) in 1,2-
1H NMR.
dichloroethane (2 mL). The reaction was run for 20 min at this
temperature. After warming up to 0 °C, the mixture was
poured over ice and extracted with CH2Cl2. The organic
extracts were dried over MgSO4, filtered and concentrated by
evaporation in vacuo. The residue was purified by column
chromatography (silica, eluent 10% ethyl acetate in hexanes)
to afford a yellow oil (0.740 g, 74%). GC-MS (EI) m/z 446 [M+];
HRMS (ESI) calcd for C26H38O2NaS2 [M + Na]+ 469.2211; found
5,8-Dibromo-2,3-bis(bromomethyl)quinoxaline (Q1): general
procedure 1
A mixture of 3,6-dibromo-o-phenylenediamine (3) (0.778 g,
2.92 mmol), 1,4-dibromobutane-2,3-dione (D1) (0.713 g,
2.92 mmol), and a catalytic amount of p-toluenesulfonic acid
(0.055 g, 10 mol%) in methanol (15 mL) was reacted at reflux
temperature for 3 h. The resulting mixture was allowed to cool
to rt and the yellow precipitate was filtered off and washed
with methanol. Column chromatographic purification (silica,
eluent 30% CHCl3 in hexanes) afforded Q1 as amber crystals
(1.251 g, 91%). Material identity and purity were confirmed by
GC-MS and 1H NMR.14
1
m/z 469.2205; found m/z 469.2212; H NMR (300 MHz, CDCl3)
δ 7.86 (d, J = 3.9 Hz, 2H), 6.86 (d, J = 3.9 Hz, 2H), 2.81 (d, J =
6.6 Hz, 4H), 1.67–1.61 (m, 2H), 1.38–1.23 (br m, 16H),
0.91–0.86 (m, 12H); 13C NMR (75 MHz, CDCl3) δ 182.7 (CO),
159.0, 137.8, 136.9, 127.5, 41.7, 34.9, 32.5, 28.9, 25.6, 23.0,
14.2, 10.9.
5,8-Dibromo-2,3-bis[5-(2-ethylhexyl)thiophen-2-yl]quinoxaline
(Q4)
5,8-Dibromo-2,3-bis(thiophen-2-yl)quinoxaline (Q3)
According to general procedure 1: 3 (0.236 g, 0.89 mmol), 1,2-
bis[5-(2-ethylhexyl)thien-2-yl]ethane-1,2-dione (D4) (0.396 g,
0.89 mmol), p-TsOH (0.015 g, 10 mol%), methanol (20 mL),
eluent 10% CHCl3 in hexanes, yellow-green solid (0.401 g,
66%). MS (CI) m/z 675/677/679 [MH+]; HRMS (ESI) calcd for
C32H40Br2N2NaS2 [M + Na]+ 697.0892; found m/z 697.0884;
1H NMR (300 MHz, CDCl3) δ 7.78 (s, 2H), 7.40 (d, J = 2.7 Hz,
2H), 6.70 (d, J = 2.7 Hz, 2H), 2.80 (d, J = 5.1 Hz, 4H), 1.70–1.64
(m, 2H), 1.43–1.24 (m, 16H), 0.94–0.89 (m, 12H); 13C NMR
(75 MHz, CDCl3) δ 150.9, 147.4, 138.6, 132.7, 130.5, 126.1,
123.0, 1.6, 34.6, 32.5, 29.0, 25.7, 23.2, 14.3, 11.0; UV-Vis
(CHCl3, nm) λmax (log ε) 270 (4.068), 324 (4.314), 420 (4.100);
mp 99–100 °C.
According to general procedure 1: 3 (0.800 g, 3.00 mmol), 1,2-
di(thiophen-2-yl)ethane-1,2-dione (D3) (0.670 g, 3.00 mmol),
p-TsOH (0.057 g, 10 mol%), methanol (40 mL), eluent 30%
CHCl3 in hexanes, yellow-green solid (1.159 g, 85%). GC-MS
(EI) m/z 450/452/454 [M+]; HRMS (ESI) calcd for C16H9Br2N2S2
[M + H]+ 450.8496; found m/z 450.8542; 1H NMR (300 MHz,
CDCl3) δ 7.84 (s, 2H), 7.56 (dd, J = 0.9/3.6 Hz, 2H), 7.48 (dd, J =
0.9/2.7 Hz, 2H), 7.05 (dd, J = 2.7/3.6 Hz, 2H); 13C NMR
(75 MHz, CDCl3) δ 147.4, 141.0, 138.9, 133.2 (CH), 130.6 (CH),
130.3 (CH), 127.9 (CH), 123.2; UV-Vis (CHCl3, nm) λmax (log ε)
262 (4.238), 316 (4.355), 401 (4.085); mp 188–191 °C.
2-(2-Ethylhexyl)thiophene
5,8-Dibromo-2,3-bis[(E)-2-(thien-2-yl)vinyl]quinoxaline (M1):
general procedure 2
n-BuLi (2.5 M in n-hexane, 50 mL) was added dropwise to a
THF (50 mL) solution of thiophene (10.50 g, 125 mmol) cooled
to −40 °C. The mixture was allowed to react at this temperature Q1 (1.000 g, 2.11 mmol) was dissolved in triethyl phosphite
for 1 h and then stirred for 1 h at rt. 2-Ethylhexyl bromide (5 mL) and the mixture was reacted at 165 °C for 2 h. The
(22.14 g, 125 mmol) was added dropwise and the reaction was excess of triethyl phosphite was then removed under reduced
continued overnight. The mixture was poured in cold water pressure and the residue (orange solid) was subsequently dis-
(100 mL) and extracted with hexanes. The organic extracts were solved in THF (10 mL). The mixture was cooled to 0 °C and a
dried over MgSO4, filtered and concentrated by evaporation solution of MeMgBr (3.0 M in diethyl ether, 1.5 mL) was added
in vacuo. The residue was purified by vacuum distillation dropwise. The mixture was allowed to react for 30 min at rt,
(92 °C, 2.0 mbar) to afford a colourless oil (8.543 g, 58%). and then a solution of thiophene-2-carbaldehyde (A1) (0.515 g,
GC-MS (EI) m/z 196 [M+]; HRMS (ESI) calcd for C12H20NaS [M + 4.60 mmol) in THF (100 mL) was added and the mixture was
Na]+ 219.1178; found m/z 219.1761; 1H NMR (300 MHz, CDCl3) reacted at rt overnight. The reaction was quenched by the
δ 7.11 (dd, J = 1.2/5.1 Hz, 1H), 6.92 (dd, J = 3.3/5.1 Hz, 1H), addition of a saturated NH4Cl solution and the mixture was
6.76 (dd, J = 1.2/3.3 Hz, 1H), 2.76 (d, J = 6.6 Hz, 2H), 1.62–1.55 extracted with CHCl3. The organic extracts were dried over
(m, 1H), 1.39–1.29 (m, 8H), 0.89 (t, J = 7.2 Hz, 6H); 13C NMR MgSO4, filtered and concentrated by evaporation in vacuo. The
(75 MHz, CDCl3) δ 144.5, 126.7 (CH), 125.1 (CH), 123.0 (CH), residue was purified by column chromatography (silica, eluent
41.6 (CH), 34.0 (CH2), 32.5 (CH2), 29.0 (CH2), 25.6 (CH2), 23.2 30% CHCl3 in hexanes) to afford a light-green solid (0.639 g,
(CH2), 14.3 (CH3), 11.0 (CH3).
60%). GC-MS (EI) m/z 502/504/506 [M+]; HRMS (ESI) calcd for
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C20H12Br2N2NaS2 [M + Na]+ 524.8701; found m/z 524.8669; H −78 °C and the mixture was reacted at rt overnight. The reac-
NMR (300 MHz, CDCl3) δ 8.33 (d, J = 15.3 Hz, 2H), 7.81 (s, 2H), tion was quenched by the addition of HCl (2.0 M) and
7.44–7.38 (m, 6H), 7.12–7.09 (m, 2H); 13C NMR (75 MHz, extracted with CH2Cl2. The organic extracts were dried over
CDCl3) δ 149.5, 142.0, 139.8, 132.8, 132.6, 130.1, 128.3, 127.5, MgSO4, filtered and concentrated by evaporation in vacuo. The
123.5, 120.2; UV-Vis (CHCl3, nm) λmax (log ε) 292 (4.382), 341 residue was purified by column chromatography (silica, eluent
(4.857), 431 (4.528); mp 238–239 °C.
10% ethyl acetate in hexanes) to afford a yellow oil (3.679 g,
82%). GC-MS (EI) m/z 224 [M+]; HRMS (ESI) calcd for
5,8-Dibromo-2,3-bis[(E)-4-methoxystyryl]quinoxaline (M2)
1
C13H20ONaS [M + Na]+ 247.1127; found m/z 247.1103; H NMR
According to general procedure 2: Q1 (4.500 g, 9.50 mmol), (300 MHz, CDCl3) δ 9.81 (s, 1H), 7.60 (d, J = 3.9 Hz, 1H), 6.88
triethyl phosphite (20 mL), THF (100 mL), MeMgBr (3.0 M in (d, J = 3.9 Hz, 1H), 2.80 (d, J = 6.7 Hz, 2H), 1.66–1.61 (m, 2H),
diethyl ether, 6.4 mL), p-anisaldehyde (A2) (2.723 g, 1.35–1.22 (m, 8H), 0.91–0.86 (m, 6H); 13C NMR (75 MHz,
20.0 mmol), eluent CHCl3, light-orange solid (4.210 g, 80%). CDCl3) δ 182.3 (CHO), 156.2, 141.7, 136.9, 126.7, 41.3, 34.6,
MS (EI) m/z 552/554/556 [M+]; HRMS (ESI) calcd for 32.2, 28.6, 25.4, 22.8, 14.0, 10.6.
C26H20Br2N2NaO2 [M + Na]+ 572.9784; found m/z 572.9780;
5,8-Dibromo-2,3-bis[(E)-2-(5-(2-ethylhexyl)thien-2-yl)vinyl]-
1H NMR (300 MHz, CDCl3) δ 8.18 (d, J = 15.3 Hz, 2H), 7.80 (s,
quinoxaline (M4)
2H), 7.68 (d, J = 8.9 Hz, 4H), 7.53 (d, J = 15.3 Hz, 2H), 6.97 (d,
J = 8.9 Hz, 4H), 3.88 (s, 6H); 13C NMR (75 MHz, CDCl3) δ 160.9, According to general procedure 3: Q1 (2.188 g, 4.62 mmol),
150.3, 139.8 (CH), 139.7, 132.3 (CH), 129.6 (CH), 129.3, 123.5, triethyl phosphite (10 mL), THF (50 mL), NaH (0.374 g,
119.1 (CH), 114.5 (CH), 55.6 (CH3); UV-Vis (CHCl3, nm) 9.36 mmol), THF (50 mL), 5-(2-ethylhexyl)thiophene-2-carb-
λmax (log ε) 290 (4.300), 336 (4.661), 428 (4.331); mp aldehyde (A4) (2.100 g, 9.36 mmol), THF (50 mL), eluent 30%
229–230 °C.
CHCl3 in hexanes, orange oil (1.891 g, 56%). MS (EI) m/z
726/728/730 [M+]; HRMS (ESI) calcd for C36H44Br2N2NaS2
5,8-Dibromo-2,3-bis[(E)-4-dodecyloxystyryl]quinoxaline (M3):
general procedure 3
1
[M + Na]+ 749.1205; found m/z 749.1187; H NMR (300 MHz,
CDCl3) δ 8.27 (d, J = 15.1 Hz, 2H), 7.76 (s, 2H), 7.27 (d, J =
Q1 (4.998 g, 10.6 mmol) was dissolved in triethyl phosphite 15.1 Hz, 2H), 7.18 (d, J = 3.6 Hz, 2H), 6.76 (d, J = 3.6 Hz, 2H),
(20 mL) and the mixture was reacted at 165 °C for 2 h. The 2.80 (d, J = 3.1 Hz, 4H), 1.69–1.61 (m, 2H) 1.44–1.25 (br m,
excess of triethyl phosphite was then removed under reduced 16H), 0.95–0.90 (m, 12H); 13C NMR (75 MHz, CDCl3) δ 149.8,
pressure. The residue (orange solid) was dissolved in THF 147.9, 139.9, 139.6, 133.2, 132.3, 130.6, 126.6, 123.4, 118.8,
(100 mL) and transferred using a cannula to a suspension of 41.6, 34.8, 32.5, 29.0, 25.7, 23.2, 14.3, 11.0; UV-Vis (CHCl3, nm)
NaH (0.885 g, 22.2 mmol) in THF (50 mL), cooled at 0 °C.22 λmax (log ε) 296 (3.782), 345 (4.091), 415 (3.949).
The mixture was allowed to react for 1 h at this temperature
5,8-Dibromo-2,3-di[(E)-tridec-1-en-1-yl]quinoxaline (M5)
and then a solution of 4-dodecyloxybenzaldehyde (A3) (6.428 g,
22.2 mmol) in THF (50 mL) was added dropwise and the According to general procedure 3: Q1 (1.100 g, 2.32 mmol),
mixture was reacted at rt overnight. The reaction was quenched triethyl phosphite (5 mL), THF (50 mL), NaH (0.188 g,
by the addition of a saturated NH4Cl solution and the mixture 4.70 mmol), THF (50 mL), dodecenal (A5) (0.942 g,
was extracted with CHCl3. The organic extracts were dried over 5.10 mmol), THF (50 mL), 30% CHCl3 in hexanes, pale-yellow
MgSO4, filtered and concentrated by evaporation in vacuo. The solid (1.007 g, 67%). GC-MS (EI) m/z 646/648/650 [M+]; HRMS
residue was purified by column chromatography (silica, eluent (ESI) calcd for C34H52Br2N2Na [M + Na]+ 669.2389; found m/z
1
30% CHCl3 in hexanes) to afford a bright-yellow solid (6.417 g, 669.2371; H NMR (300 MHz, CDCl3) δ 7.78 (s, 2H), 7.40–7.30
71%). GC-MS (EI) m/z 858/860/862 [M+]; HRMS (ESI) calcd for (m, 2H), 6.91 (d, J = 15.3 Hz, 2H), 2.43–2.36 (m, 4H), 1.64–1.60
1
C48H64Br2N2NaO2 [M + Na]+ 881.3232; found m/z 881.3215; H (m, 4H), 1.43–1.25 (m, 32H), 0.88 (t, J = 6.9 Hz, 6H); 13C NMR
NMR (300 MHz, CDCl3) δ 8.16 (d, J = 15.3 Hz, 2H), 7.78 (s, 2H), (75 MHz, CDCl3) δ 150.0, 144.5, 139.6, 132.2, 123.9, 123.5,
7.65 (d, J = 8.6 Hz, 4H), 7.52 (d, J = 15.3 Hz, 2H), 6.96 (d, J = 33.7, 32.1, 29.83, 29.80, 29.77, 29.67, 29.58, 29.52, 28.9, 22.8,
8.6 Hz, 4H), 4.02 (t, J = 6.0 Hz, 4H), 1.86–1.70 (m, 4H), 14.3; UV-Vis (CHCl3, nm) λmax (log ε) 284 (4.280), 376 (3.780);
1.51–1.19 (br m, 36H), 0.88 (t, J = 6.3 Hz, 6H); 13C NMR mp 57–58 °C.
(75 MHz, CDCl3) δ 160.5, 150.4, 139.9, 139.6, 132.3, 129.6,
129.0, 123.4, 118.9, 114.9, 68.3, 30.1, 29.8, 29.5, 29.4, 26.2,
22.9, 14.3; UV-Vis (CHCl3, nm) λmax (log ε) 292 (4.271), 338
5,8-Dibromo-2,3-di[(1E,3E)-undeca-1,3-dien-1-yl]quinoxaline
(M6)
(4.636), 431 (4.315); mp 122–123 °C.
According to general procedure 3: Q1 (1.100 g, 2.32 mmol),
triethyl phosphite (5 mL), THF (50 mL), NaH (0.188 g,
4.70 mmol), THF (50 mL), trans-2-decenal (A6) (0.725 g,
5-(2-Ethylhexyl)thiophene-2-carbaldehyde (A4)
To
a
solution of 2-(2-ethylhexyl)thiophene (3.927 g, 4.70 mmol), THF (50 mL), eluent 30% CHCl3 in hexanes,
20.0 mmol) in THF (100 mL), cooled to −78 °C, n-BuLi (2.5 M yellow solid (0.801 g, 59%). GC-MS (EI) m/z 586/588/590 [M+];
in n-hexane, 8.0 mL) was added dropwise and the mixture was HRMS (ESI) calcd for C30H40Br2NaS2 [M + Na]+ 609.1450;
allowed to react for 1 h at this temperature, and then for 1 h at found m/z 609.1438; 1H NMR (300 MHz, CDCl3) δ 7.83–7.75
rt. N-Formylpiperidine (2.263 g, 20 mmol) was then added at (m, 4H), 6.93 (d, J = 15.0 Hz, 2H), 6.44–6.35 (m, 2H), 6.26–6.17
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(m, 2H), 2.26–2.20 (m, 4H), 1.53–1.41 (m, 2H), 1.40–1.20 (br m, eluent 30% CHCl3 in hexanes, recrystallization from
12H), 0.89 (t, J = 6.9 Hz, 6H); 13C NMR (75 MHz, CDCl3) methanol, deep-orange solid (0.124 g, 41%). MS (EI) m/z 736
δ 150.3, 143.0, 140.8, 139.6, 132.2, 130.2, 123.4, 122.5, 33.3, [M+]; HRMS (ESI) calcd for C44H50N2NaS4 [M + Na]+ 757.2749;
1
32.0, 29.3, 29.1, 22.8, 14.3; UV-Vis (CHCl3, nm) λmax (log ε) found m/z 757.2726; H NMR (300 MHz, CDCl3) δ 8.32 (d, J =
319 (4.065), 408 (3.363); mp 88–89 °C.
15.2 Hz, 2H), 8.01 (s, 2H), 7.79 (dd, J = 1.2/3.9 Hz, 2H), 7.54
(dd, J = 1.2/5.1 Hz, 2H), 7.32 (d, J = 15.2 Hz, 2H), 7.21–7.16
(m, 4H), 6.76 (d, J = 3.6 Hz, 2H), 2.81 (d, J = 6.9 Hz, 4H),
Poly[2,3-bis((E)-4-dodecyloxystyryl)quinoxaline-5,8-diyl] (P1)
Ni(cod)2 (0.970 g, 3.48 mmol) and 2,2′-bipyridine (0.543 g, 1.72–1.64 (m, 2H), 1.45–1.26 (br m, 16H), 0.96–0.91 (m, 12H);
3.48 mmol) were placed in a Schlenk tube inside a glove box. 13C NMR (75 MHz, CDCl3) δ 147.8, 147.2, 140.3, 139.0, 137.8,
DMF (5 mL), toluene (5 mL) and 1,5-cyclooctadiene (0.376 g, 132.8, 131.0, 129.8, 128.9, 126.58, 126.52, 126.4, 126.1, 120.0,
3.48 mmol), degassed by bubbling through N2 gas for 20 min, 41.6, 34.8, 32.5, 29.0, 25.7, 23.2, 14.3, 11.0; UV-Vis (CHCl3, nm)
were added and the mixture was vigorously stirred for 20 min λmax (log ε) 310 (3.957), 380 (4.000), 454 (3.708); mp 94–95 °C.
at 60 °C. A solution of M3 (1.248 g, 1.45 mmol) in toluene
5,8-Di(thien-2-yl)-2,3-di[(E)-tridec-1-en-1-yl]quinoxaline (T3)
(22 mL) was then added and the mixture was allowed to react
for 2 days at 75 °C. The polymer was poured into a solution of According to general procedure 4: M5 (0.388 g, 0.60 mmol),
methanol–HCl (1 : 1, v/v), collected by filtration and purified thiophene-2-boronic acid (4) (0.460 g, 3.60 mmol), CsF
by repetitive Soxhlet extraction with methanol, acetone and (0.546 g, 3.60 mmol), DME (10 mL), Pd(dppf)Cl2 (3 mol%),
n-hexane. The final polymer was extracted with chloroform eluent 30% CH2Cl2 in hexanes, deep-orange solid (0.280 g,
and was isolated as yellow fibres upon precipitation in metha- 71%). MS (EI) m/z 654 [M+]; HRMS (ESI) calcd for
nol (0.978 g, 96%); UV-vis (CHCl3, nm) λmax 334, 359, 411; SEC C42H58N2NaS2 [M + Na]+ 677.3934; found m/z 677.3913; 1H
(THF, PS standards) Mn = 6.8 × 104 g mol−1, Mw = 4.1 × 105 g NMR (300 MHz, CDCl3) δ 8.03 (s, 2H), 7.80 (dd, J = 1.3/3.8 Hz,
mol−1, PDI = 6.0.
2H), 7.51 (dd, J = 1.3/5.1 Hz, 2H), 7.47–7.37 (m, 2H), 7.18 (dd,
J = 3.8/5.1 Hz, 2H), 6.95 (d, J = 15.3 Hz, 2H), 2.46–2.39 (m, 4H),
1.66–1.57 (m, 4H), 1.47–1.20 (br m, 28H), 0.88 (t, J = 6.9 Hz,
6H); 13C NMR (75 MHz, CDCl3) δ 147.9, 143.6 (CH), 139.1,
2,3-Bis[(E)-4-dodecyloxystyryl]-5,8-di(thien-2-yl)quinoxaline
(T1): general procedure 4
M3 (0.108 g, 0.13 mmol), thiophene-2-boronic acid (4) 137.8, 131.0, 128.8 (CH), 126.6 (CH), 126.3 (CH), 126.1 (CH),
(0.100 g, 0.78 mmol, 6 equiv.), and CsF (0.118 g, 0.78 mmol) 124.6 (CH), 33.7 (CH2), 32.1 (CH2), 29.86 (CH2), 29.83 (CH2),
were placed in a Schlenk tube and dissolved in DME (10 mL). 29.7 (CH2), 29.5 (CH2), 29.2 (CH2), 22.9 (CH2), 14.3 (CH3);
The mixture was degassed by bubbling through N2 gas for UV-Vis (CHCl3, nm) λmax (log ε) 311 (4.463), 410 (3.902); mp
20 min. Pd(dppf)Cl2 (3 mol%) was added, the tube was sealed 66–67 °C.
and the mixture was reacted at 90 °C overnight. After cooling
to rt, water was added and the mixture was extracted with
CHCl3. The organic extracts were dried over MgSO4, filtered
5,8-Di(thien-2-yl)-2,3-di[(1E,3E)-undeca-1,3-dien-1-yl]-
quinoxaline (T4)
and concentrated by evaporation in vacuo. The residue was pur- According to general procedure 4: M6 (0.300 g, 0.51 mmol),
ified by column chromatography (silica, eluent 30% CHCl3 in thiophene-2-boronic acid (4) (0.391 g, 3.06 mmol, 6 equiv.),
hexanes), followed by recrystallization from methanol to afford CsF (0.464 g, 3.06 mmol), DME (10 mL), Pd(dppf)Cl2 (3 mol
a dark-red solid (0.059 g, 52%). MS (EI) m/z 867 [M+]; HRMS %), eluent 30% CHCl3 in hexanes, recrystallization from
(ESI) calcd for C56H70N2NaO2S2 [M + Na]+ 889.4771; found m/z methanol, deep-orange solid (0.169 g, 56%). GC-MS (EI) m/z
889.4753; 1H NMR (300 MHz, CDCl3) δ 8.25 (d, J = 15.5 Hz, 594 [M+]; HRMS (ESI) calcd for C38H46N2NaS2 [M + Na]+
2H), 8.04 (s, 2H), 7.82 (dd, J = 1.1/3.7 Hz, 2H), 7.66 (d, J = 617.2995; found m/z 617.2992; 1H NMR (300 MHz, CDCl3)
8.7 Hz, 4H), 7.56 (d, J = 15.5 Hz, 2H), 7.55 (dd, J = 1.1/5.1 Hz, δ 8.01 (s, 2H), 7.85 (dd, J = 10.8/14.7 Hz, 2H), 7.77 (dd, J =
2H), 7.21 (dd, J = 3.7/5.1 Hz, 2H), 6.97 (d, J = 8.7 Hz, 4H), 4.03 0.9/3.9 Hz, 2H), 7.53 (dd, J = 0.9/5.1 Hz, 2H), 7.18 (dd, J =
(t, J = 6.6 Hz, 4H), 1.87–1.78 (m, 4H), 1.51–1.44 (m, 4H), 3.9/5.1 Hz, 2H), 6.95 (d, J = 14.7 Hz, 2H), 6.42 (dd, J = 14.7/10.8
1.40–1.25 (br m, 32H), 0.89 (t, J = 6.9 Hz, 6H); 13C NMR Hz, 2H), 6.23–6.14 (m, 2H), 2.28–2.21 (m, 4H), 1.54–1.45 (m,
(75 MHz, CDCl3) δ 160.3, 148.4, 139.4 (CH), 139.1, 137.9, 4H), 1.40–1.27 (br m, 16H), 0.90 (t, J = 6.9 Hz, 6H); 13C NMR
131.1, 129.5, 129.3 (CH), 128.9 (CH), 126.6 (CH), 126.5 (CH), (75 MHz, CDCl3) δ 148.2, 141.6, 140.2, 139.1, 137.7, 131.0,
126.2 (CH), 120.0 (CH), 115.0 (CH), 68.3 (CH2), 32.1 (CH2), 130.6, 128.8, 126.5, 126.4, 126.1, 123.6, 33.3, 32.0, 29.42, 29.35,
29.80 (CH2), 29.78 (CH2), 29.58 (CH2), 29.52 (CH2), 29.4 (CH2), 29.2, 22.8, 14.3; UV-Vis (CHCl3, nm) λmax (log ε) 309 (4.384),
26.2 (CH2), 22.9 (CH2), 14.3 (CH3); UV-Vis (CHCl3, nm) 433 (3.622); mp 103–104 °C.
λmax (log ε) 363 (4.304), 442 (3.931); mp 118–119 °C.
4,7-Bis(3-hexylthiophen-2-yl)-2,1,3-benzothiadiazole (7)
2,3-Bis[(E)-2-(5-(2-ethylhexyl)thien-2-yl)vinyl]-5,8-di(thien-2-yl)-
quinoxaline (T2)
2-Bromo-3-hexylthiophene (5) (2.741 g, 11.1 mmol, 2.5 equiv.)
and 2,1,3-benzothiadiazole-4,7-bis(boronic acid pinacol ester)
According to general procedure 4: M4 (0.298 g, 0.41 mmol), (6) (1.718 g, 4.43 mmol) were placed in a Schlenk tube which
thiophene-2-boronic acid (4) (0.316 g, 2.47 mmol, 6 equiv.), was brought under an inert atmosphere. All solvents and basic
CsF (0.375 g, 2.47 mmol), DME (10 mL), Pd(dppf)Cl2 (3 mol%), solutions were previously degassed by bubbling through N2
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gas for 20 min. Toluene (70 mL), K2CO3 (2.0 M, 35 mL), H2O (s, 2H), 4.90 (s, 4H), 2.50 (t, J = 7.5 Hz, 4H), 1.61–1.51 (m, 4H),
(25 mL) and Aliquat HTA (4–5 drops) were added and the 1.25–1.14 (br m, 12H), 0.80 (t, J = 6.9 Hz, 6H); 13C NMR
mixture was vigorously stirred for 10 min at rt. Pd(PPh3)4 (75 MHz, CDCl3) δ 150.4, 142.6, 139.9, 133.8, 133.1, 132.3,
(3 mol%) was then added and the mixture was allowed to react 131.7, 113.1, 44.2, 31.7, 30.6, 29.6, 29.2, 22.7, 14.2.
for 3 days at 80 °C. After cooling to rt, the mixture was
5,8-Bis(5-bromo-3-hexylthien-2-yl)-2,3-bis[(E)-2-(5-(2-ethylhexyl)-
thien-2-yl)vinyl]quinoxaline (T5)
extracted with CHCl3. The organic extracts were dried over
MgSO4, filtered and concentrated by evaporation in vacuo. The
residue was purified by column chromatography (silica, eluent
10% CHCl3 in hexanes) to afford an orange oil (1.492 g, 72%).
MS (EI) m/z 468 [M+]; HRMS (ESI) calcd for C26H32N2NaS3
According to general procedure 2: 9 (0.185 g, 0.23 mmol),
triethyl phosphite (5 mL), THF (40 mL), NaH (0.019 g,
0.50 mmol), THF (40 mL), 5-(2-ethylhexyl)thiophene-2-carb-
aldehyde (A4) (0.148 g, 0.66 mmol), THF (25 mL), eluent 10%
CHCl3 in hexanes, orange-red oil (0.110 g, 45%). HRMS (ESI)
calcd for C56H72Br2N2NaS4 [M + Na]+ 1081.2837; found m/z
1
[M + Na]+ 491.1620; found m/z 491.1629; H NMR (300 MHz,
CDCl3) δ 7.65 (s, 2H), 7.44 (d, J = 5.2 Hz, 2H), 7.11 (d, J =
5.2 Hz, 2H), 2.67 (t, J = 7.8 Hz, 4H), 1.67–1.58 (m, 4H),
1.30–1.14 (br m, 12H), 0.82 (t, J = 7.2 Hz, 6H); 13C NMR
(75 MHz, CDCl3) δ 154.4, 141.8, 132.3, 130.0, 129.4, 127.6,
126.0, 31.7, 30.8, 29.5, 29.2, 22.7, 14.2.
1
1081.2816; H NMR (300 MHz, CDCl3) δ 8.32 (d, J = 15.0 Hz,
2H), 7.83 (s, 2H), 7.46 (s, 2H), 7.45 (d, J = 15.0 Hz, 2H), 7.31 (d,
J = 3.3 Hz, 2H), 6.95 (d, J = 3.3 Hz, 2H), 2.99 (d, J = 6.6 Hz, 4H),
2.83 (t, J = 7.5 Hz, 4H), 1.86–1.72 (m, 2H), 1.66–1.32 (br m,
28H), 1.15–0.98 (br m, 18H); 13C NMR (75 MHz, CDCl3)
δ 147.8, 147.3, 141.9, 140.1, 139.4, 134.8, 132.5 (CH), 131.9,
131.4 (CH), 130.2 (CH), 129.9 (CH), 126.5 (CH), 119.5 (CH),
113.0, 41.6 (CH), 34.8 (CH2), 32.5 (CH2), 31.7 (CH2), 30.8 (CH2),
29.7 (CH2), 29.3 (CH2), 29.0 (CH2), 25.7 (CH2), 23.2 (CH2), 22.7
(CH2), 14.3 (CH3), 14.2 (CH3), 11.0 (CH3); UV-Vis (CHCl3, nm)
λmax (log ε) 290 (4.541), 364 (4.357).
2,3-Bis(bromomethyl)-5,8-bis(3-hexylthien-2-yl)quinoxaline (8)
A solution of LiAlH4 (4.0 M in THF, 0.44 mL) was added drop-
wise to a solution of 7 (0.163 g, 0.35 mmol) in THF (50 mL)
and the mixture was reacted at reflux overnight. After cooling
to rt, ethanol (20 mL) and H2O (50 mL) were added and the
mixture was extracted with diethyl ether. The organic extracts
were dried over MgSO4, filtered and concentrated by evapor-
ation in vacuo. The diamine, obtained as a pale-yellow solid,
was directly used in the condensation reaction without further
purification (GC-MS (EI) m/z 440 [M+]). 1,4-Dibromobutane-
2,3-dione (D1) (0.195 g, 0.8 mmol) and a catalytic amount of
p-TsOH (0.007 g, 10 mol%) were then added to a solution of
the diamine in methanol (75 mL) and the mixture was reacted
at reflux for 3 h. After cooling to rt, water was added and the
mixture was extracted with CHCl3. The organic extracts were
dried over MgSO4, filtered and concentrated by evaporation
in vacuo. The residue was purified by column chromatography
(silica, eluent 30% CHCl3 in hexanes) to afford 8 as a yellow oil
(0.108 g, 48%). GC-MS (EI) m/z 646/648/650 [M+]; HRMS (ESI)
calcd for C30H36Br2N2NaS2 [M + Na]+ 669.0579; found m/z
669.0560; 1H NMR (300 MHz, CDCl3) δ 7.82 (s, 2H), 7.43 (d, J =
5.1 Hz, 2H), 7.11 (d, J = 5.1 Hz, 2H), 4.89 (s, 4H), 2.54 (t, J =
7.8 Hz, 4H), 1.64–1.54 (m, 4H), 1.28–1.11 (br m, 12H), 0.80 (t,
J = 6.9 Hz, 6H); 13C NMR (75 MHz) δ 150.4, 141.9, 140.2, 133.9,
132.5, 128.9, 125.8, 31.7, 30.8, 30.7, 29.7, 29.3, 22.7, 14.2.
Acknowledgements
The authors acknowledge Hasselt University for continuous
financial support and BELSPO in the frame of the IAP P6/27
and IAP 7/05 networks. The reported activity was partly sup-
ported by the projects ORGANEXT (EMR, INT4-1.2.-2009-04/
054), selected in the frame of the operational program INTER-
REG IV-A Euregio Maas-Rijn, and ORION (FP7-NMP, grant no.
229036). We also thank the IWT (Institute for the Promotion of
Innovation through Science and Technology in Flanders) for
financial support by means of the SBO project PolySpec
(060843).
Notes and references
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NBS (0.064 g, 0.36 mmol) was added to a solution of 8
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(EI) m/z 802/804/806/808/810 [M+]; HRMS (ESI) calcd
for C30H34Br4N2NaS2 [M
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824.8752;1H NMR (300 MHz, CDCl3) δ 7.77 (s, 2H), 7.06
5874 | Org. Biomol. Chem., 2013, 11, 5866–5876
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