Cruciform alkynylated anthanthrene derivatives: A structure-properties relationship case study

Article abstract of DOI:10.1021/jo402674m

An efficient and versatile synthetic strategy toward cruciform anthanthrene compounds using Sonogashira couplings steps was developed. Acetylenic linkers were used to effectively extend the π-conjugation of polycyclic anthanthrone and anthanthrene compounds and tune their optoelectronic properties. Structure-property relationships supported by DFT calculations indicated more effective π-conjugation along the 6,12 axis than along the 4,10 axis. These molecules displayed strong J-aggregation both in solution and in the solid state and proved to be highly photostable with reversible redox processes, which are properties of interest in materials sciences.

Full text of DOI:10.1021/jo402674m

Article
pubs.acs.org/joc
Cruciform Alkynylated Anthanthrene Derivatives: A Structure−
Properties Relationship Case Study
Jean-Benoît Giguere, Joel Boismenu-Lavoie, and Jean-Franco
̧
is Morin*
̀
̈
Dep
Queb
́
artement de Chimie and Centre de Recherche sur les Mater
ec, Canada G1V 0A6
́
iaux Avances
́
́ ́
(CERMA), Universite Laval, 1045 Ave de la Medecine,
́
S
* Supporting Information
ABSTRACT: An efficient and versatile synthetic strategy
toward cruciform anthanthrene compounds using Sonogashira
couplings steps was developed. Acetylenic linkers were used to
effectively extend the π-conjugation of polycyclic anthanthrone
and anthanthrene compounds and tune their optoelectronic
properties. Structure−property relationships supported by
DFT calculations indicated more effective π-conjugation
along the 6,12 axis than along the 4,10 axis. These molecules
displayed strong J-aggregation both in solution and in the solid
state and proved to be highly photostable with reversible redox
processes, which are properties of interest in materials
sciences.
active materials in both solar cells and OFET applications with
power conversion efficiencies (PCEs) and mobilities reaching
4.84% and 0.15 cm2 V−1 s−1, respectively.9 It is worth
mentioning that a PCE of 2.0% was obtained for a simple
TIPS-appended anthanthrene derivative.10
We recently undertook the derivatization of the commer-
cially available hexacyclic pigment 4,10-dibromoanthanthrone
(VAT Orange 3, compound 1 in Scheme 2) and were able to
tune its optoelectronic properties through functionalization at
the 4 and 10 positions and the 6 and 12 positions on either
quinoidal or fully aromatic anthanthrene derivatives.11,12 The
nature of the linker between the polycyclic core and the
appended moiety appeared to be of the utmost importance,
mainly because of steric constraints. We were therefore drawn
to study the effect of freely rotating acetylenic linkers in order
to extend the π-conjugation of anthanthrone and anthanthrene
derivatives.
A second point of order was to assess the contribution of the
conjugation axis on the resulting properties. Conjugation
pathways in polycyclic aromatic molecules are nontrivial, as
many parameters, such as the resonance energy, must be taken
into account.12,13 The two conjugation axes studied are
depicted in Figure 1: the lengthwise 4,10 axis is depicted in
blue, whereas the 6,12 axis along the width is represented in
red. Although 4,10-dibromoanthanthrone presents a versatile
structure, its chemical functionalization is not always
straightforward, so special attention was paid to the synthetic
aspects with respect to practical considerations. Herein we
report the synthesis of 4,10-arylethynylanthanthrone and
INTRODUCTION
■
The fascination of chemists for aromatic molecules has never
weakened, from the earlier studies of aromaticity with Huckel’s1
and Clar’s2 rules to the more recent developments of semi-
conducting π-conjugated molecules for organic electronics.3,4
Fused aromatic compounds, especially acenes, have attracted a lot
of attention because of their performance as semiconductors in
organic field-effect transistors (OFETs). Among others, pentacene
and its derivatives such as TIPS-pentacene exhibit excellent
charge-carrier properties, and mobilities of over 1 cm2 V−1 s−1 are
routinely achieved under optimized conditions. Some limitations
of acene derivatives are their poor photostability, sensitivity to
oxidation, and rather complex synthesis.5,6 A strategy to tackle
these obstacles that limit their use in organic electronics is precise
control of the frontier molecular orbitals, namely, the highest
occupied molecular orbital (HOMO) and lowest unoccupied
molecular orbital (LUMO).7 The manipulation of the HOMO
and LUMO energy levels is particularly important in organic
photovoltaics (OPVs), in which the absorption of photons and
the electron transfer between the donor and acceptor materials are
governed by the positions of the frontier orbitals. For polycyclic
aromatic molecules, primarily three strategies have been used to
tune the optoelectronic properties: heteroatom (N, O, S, Se)
replacement, core substitution (halogens, cyano), and side-chain
engineering.5,8 Electron-withdrawing substituents such as fluoride
and imines are often introduced to lower the HOMO and LUMO
levels and, consequently, to improve the stability toward oxidation
and reach an n-type or ambipolar character. At the opposite
extreme, thienoacenes have been extensively used to obtain p-type
mobility.
Relevant to the present work, the Choi group went in a
different direction and used X-shaped anthracene derivatives as
Received: December 3, 2013
Published: February 25, 2014
© 2014 American Chemical Society
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the reaction was performed with lithium triisopropylsilylacetylide,
the desired compound 9 was isolated in a moderate 48% yield. It
was possible to perform the same reaction with trimethylsilyla-
cetylene (TMSA), but the solubility of the resulting product was
much lower. The major difference between the two substrates lies
in the electronic character of the acetylenic unit. Because of the
poor reliability and difficult analysis of side products, we decided
not to investigate this reaction further, instead proceeding with
TIPS-appended compound 9 because of its versatility and ease of
preparation.
From a synthetic perspective and following our objective of
studying the effect of the acetylenic linker, we were interested
in preparing 4,6,10,12-thienyl-appended compound 11. Con-
trary to arylethynyl compounds, 2-thiophenyllithium proved to
be a suitable reagent for the preparation of compound 11 (39%
yield) from compound 10 (Scheme 4).11 The stronger
nucleophilic character of the 2-thiophenyllithium might be
responsible for this improved reactivity.
Figure 1. Numbering of anthanthrene positions and depiction of the
4,10 and 6,12 conjugation axes (shown in blue and red, respectively).
4,6,10,12-tetrasubstituted anthanthrene derivatives along with a
structure−property relationship analysis of their optoelectronic
properties.
In order to properly establish the effect of the acetylenic
linkage on the optoelectronic properties, we prepared
compounds 16 and 18 with thiophene units at the 4, 6, 10,
and 12 positions but with different linkers (Scheme 5). Starting
from compound 9, we performed a twofold Sonogashira
coupling with compound 4 under standard conditions to
provide compound 15 in 74% yield. Subsequent deprotection
of the alkyne using tetrabutylammonium fluoride (TBAF)
afforded the terminal alkyne in excellent yield. Although the
TBAF-mediated deprotection of alkynes is a seemingly
straightforward step, it proved to be crucial to use water as
the proton source for both TMS and TIPS deprotection to
obtain the desired products in good yields with minimal
formation of side products. The use of methanol as an additive
proved to be unsuitable. The following step consisted of a
second twofold Sonogashira coupling with 2-bromo-5-octylth-
iophene. For this particularly demanding coupling reaction of a
bisacetylenic compound, it was important to use a Pd(0) source
since the reduction of the Pd(II) species would consume 2
equiv of alkyne, which would greatly affect the yield in this case
as the alkyne was the limiting reagent and could not be used in
excess.16 Therefore, we used a combination of Pd2(dba)3 and
tBu3PHBF4 as a precatalyst for the coupling of electron-rich
bromoarenes. Using these optimal conditions, we obtained
compound 16 in an excellent 80% yield. Compound 18 with
thiophenes directly attached at the 4 and 10 positions was
prepared using the same strategy, but the first reaction step
consisted of a Stille coupling using an in situ-prepared stannyl
compound. Compound 17 proved to be insoluble in THF, so
the deprotection reaction was performed in CH2Cl2, followed
by the twofold Sonogashira coupling with the bromothiophene
to afford compound 18 in excellent yield.
In order to assess the presence of intramolecular charge
transfer through donor−acceptor interactions, we prepared
electron-donating thiothiophene derivative 13 and electron-
withdrawing sulfonylthiophene derivative 14. The sulfonylth-
ienyl group has been used in high-performance polymers for
solar cells17,18 and was chosen because the electroactive group is
located linearly with the conjugation axis, thus leading to a greater
impact on the properties. As depicted in Scheme 6, thiophene was
lithiated using n-BuLi and added to elemental sulfur to form the
thiolate, which was alkylated using 2-ethylhexylbromide to afford
compound 12 in good yield. Subsequent bromination using NBS
afforded compound 13 almost quantitatively, and the thioether
was oxidized with m-CPBA to give sulfone 14.
RESULTS AND DISCUSSION
■
Synthesis. The targets are depicted in Figure 2, and the
rationale and synthesis is described herein. As first synthetic
targets, we chose to study anthanthrones functionalized at the 4
and 10 positions with arylethynyl moieties (as opposed to the
previously reported nonconjugated ethynyltriisopropylsilyl
moiety11) to assess the effect of the acetylenic linker on the
optoelectronic properties of quinoidal anthanthrone and
aromatic anthanthrene scaffolds. We previously functionalized
4,10-dibromoanthanthrone through Sonogashira coupling, so
we followed this efficient strategy for the introduction of
alkynes onto the anthanthrone/anthanthrene scaffold.11 To
obtain good solubility and film-forming properties, we chose
compounds 2 (Scheme 2)14 and 4 (Scheme 1) with hexyl and
octyl alkyl chains, respectively. Compound 4 was prepared by
coupling of 2-bromo-4-octylthiophene and 2-methylbut-3-yn-2-
ol using a highly active catalyst derived from PdCl2(MeCN)2
and tBu3PHBF4.15 Free alkyne 4 was obtained using KOH-
promoted deacetonative deprotection in hot toluene. A
protecting group bearing a polar alcohol group was chosen to
ease the purification by column chromatography.
The introduction of solubility-inducing groups in the first
synthetic step was crucial because 4,10-dibromoanthanthrone 1
has very limited solubility, and this was a major criterion when
determining the optimal retrosynthetic pathway. The couplings
between anthanthrone 1 and terminal alkynes 2 and 4 were
performed under classical Sonogashira coupling conditions
using o-dichlorobenzene (o-DCB) as the solvent, which offers a
higher reaction rate and improved reproducibility compared
with THF (Scheme 2). Phenyl-appended 5 was isolated in 58%
yield, but to our surprise, the yield of compound 6 dropped
drastically to 12% for unknown reasons. Double nucleophilic
attack of the lithium acetylide of compound 2 on the quinone
structure followed by reduction with aqueous SnCl2 afforded
anthanthrene 7 in a mere 25% yield. Because of the low
solubility of compound 7 in the eluent used in the purification
process, the yield was unsatisfactory. Because purity is of
utmost importance in organic electronics, we decided to
explore alternative synthetic pathways in order to determine the
most versatile, straightforward, and efficient strategies.
As depicted in Scheme 3, an obvious alternative was to
exchange the order of the two synthetic steps and start with the
alkynylation/reduction sequence. To our surprise, we could isolate
only traces of phenyl-appended compound 8. Alternatively, when
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Figure 2. Structures of π-extended compounds 5, 6, 7, 11, 16, 18, 20, 22, 25, and 27. Donor and acceptor groups are depicted in red and blue,
respectively.
Once again starting with TIPS-appended compound 9, we
introduced TMS-acetylene at the 4 and 10 positions via
standard Sonogashira coupling to afford compound 19 in excellent
yield (Scheme 7). Selective deprotection of the TMS-acetylene
using K2CO3 followed by twofold Sonogashira coupling with a
monobromo-substituted diketopyrrolopyrrole (DPP) reagent19
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Scheme 1. Synthesis of 2-Ethynyl-5-octylthiophene (4)
Scheme 2. Synthesis of Anthanthrones 5 and 6 and Anthanthrene 7
Scheme 3. Synthesis of 6,12-Ethynyl-Appended
4,10-Dibromoanthanthrenes 8 and 9
strategy, we obtained the 4,10-donor-6,12-acceptor-appended
compound 22 from compounds 21 and 14 in excellent yield.
To obtain the opposite substitution pattern (4,10-acceptor-
6,12-donor) for the sake of comparison, we chose to start from
soluble TIPS-appended 2311 and to introduce TMS-acetylene
substituents at the 6 and 12 positions via a one-pot twofold
carbonyl attack/reduction sequence (Scheme 8). Aryl groups
were then introduced at the 6 and 12 positions via selective
deprotection of the TMS-acetylene followed by a coupling step
with the corresponding aryl bromides to afford DPP-appended
compound 25 and thiothiophene-substituted compound 26 in
62% and 94% yield, respectively. Compound 27 was obtained
from 26 and 14 in a lower 31% yield for the last coupling step,
the reasons for which are unclear.
Optical Properties. The UV−vis spectra of the anthan-
throne and anthanthrene compounds were recorded in CH2Cl2
solutions at concentrations of 10−50 μM or in thin films
prepared by drop-casting from CH2Cl2 on glass slides, and
these spectra are presented in Figures 3−7 or in the Supporting
Information. The fluorescence spectra were recorded in
CH2Cl2 and are presented in the Supporting Information.
The optical properties are summarized in Table 1.
afforded the π-extended compound 20 in 49% yield. Alternatively,
electron-rich compound 13 was coupled using the same conditions
to afford compound 21. Following the previously described
Scheme 4. Synthesis of 4,6,10,12-Tetrakis((5-octyl)thien-2-yl)anthanthrene (11)
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Scheme 5. Synthesis of Tetrakis(thienyl)anthanthrene Derivatives 16 and 18 with Different Acetylenic Linkages
Scheme 6. Synthesis of Thiothienyl Compound 13 and Sulfonylthienyl Compound 14
Both of the 4,10-bis(arylethynyl)anthanthrone derivatives
present broad absorption spectra with λmax = 545 and 570 nm
for compounds 5 and 6, respectively (Figure 3), in accordance
with the stronger donating character of the thiophene unit,
which leads to a stronger donor−acceptor interaction with the
accepting quinone. This interaction is especially marked in the
solid state, as the band gap for compound 6 is lowered by 0.32
to 1.66 eV. To measure the effect of the acetylenic linkage, we
can compare compound 6 with previously reported compound
10 (Scheme 4):11 the absorption maximum of compound 6 is
red-shifted by 35 nm, which is indicative of good electronic
communication between the two appended units, reasonably
caused by the reduced torsion angle of the acetylenic linkage.
For the thienyl- and phenyl-appended anthanthrene
compounds, it is clear that the acetylenic linkage at the 6 and
12 positions is necessary for effective conjugation. Ethynyl-free
compound 11 presents the shortest λmax of 465 nm, whereas
introduction of the acetylene linker in compound 18 causes a
large red shift of 68 nm to a maximum of 533 nm (Figure 4).
The relief of the large dihedral angle (calculated value of 90°)
caused by the steric hindrance between the peri positions and
the thiophene ring is the major contributor to the improved
conjugation. Incorporation of acetylenic linkers at the 4 and 10
positions for compound 16 has a much weaker effect on the
absorption, with a slight red shift of 7 nm. Interestingly, phenyl-
appended compound 7 presents a moderately blue-shifted λmax
of 519 nm, which can be attributed to the weaker donating
character of the phenyl unit versus the thienyl unit.
As presented in Figure 5, the thin-film absorption spectra of
compounds 7 and 16 are very similar, with the exception of a
slightly broader peak for compound 7, meaning that in this case
the nature of the appended aromatic unit has a limited effect on
the solid-state absorption profile. Nevertheless, the solid-state
band gap is lowered by 0.39 eV down to 1.91 eV for compound
7. Such a large modulation is indicative of good intermolecular
interaction and orbital overlap, which supports the NMR
aggregation study (vide infra). It is reasonable to think that for
compound 11 the steric hindrance limits close intermolecular
interactions, leading to a large band gap of 2.35 eV. On the
other hand, compound 18 presents the smallest band gap of
1.90 eV, indicating that the presence of thiophene units at the 4
and 10 positions does not limit close intermolecular interactions.
Compound 18 presents the most characteristic features of J-
aggregation, with a large bathochromic shift in going from dilute
solution to the solid state, the narrowest absorption band, and
most intense absorption at its maxima.20 This suggests that the
increased latitude along the 4,10 axis for the acetylenic-substituted
derivatives 11 and 16 might hinder optimal J-aggregation.
The absorption spectra of compounds 22, 26, and 27 with
λmax values of ca. 545 nm (Figure 6) are very similar to that of
compound 16, revealing a lack of intramolecular donor−
acceptor interactions. Moreover, substitution of the electroni-
cally neutral TIPS group in compound 26 by sulfonylthiophene
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Scheme 7. Synthesis of 4,10-DPP-Appended Anthanthrene 20 and Donor−Acceptor-Substituted Compound 22
Scheme 8. Synthesis of 6,12-DPP-Appended Anthanthrene 25 and Donor−Acceptor-Substituted Compound 27
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Table 1. Summary of the Optical and Electrochemical
a
Properties of Selected Compounds
electrochemical
properties
optical properties
λmax
(nm)
Esgoln
(eV)
λfluor
(nm)
Efgilm
(eV)
Vred
(V)
Vox
(V)
Eg
(eV)
compd
5
6
545
570
519
491
465
505
540
501
533
499
588
505
538
498
650
545
547
2.08
1.98
2.30
2.46
2.53
2.37
2.19
2.38
2.23
2.42
1.97
2.37
2.20
2.44
1.76
2.15
2.13
608
654
538
528
495
513
560
516
552
507
627
521
557
505
−
1.83
1.66
1.91
2.12
2.35
2.18
1.91
2.20
1.90
2.34
1.71
2.17
1.88
2.30
1.46
1.79
1.86
−0.50
−0.51
−1.10
−1.06
−1.40
−1.07
−1.05
−1.21
−1.13
−1.09
−1.01
−1.09
−0.93
−1.10
−0.90
−1.05
−0.99
1.47
1.30
0.70
1.08
0.77
0.94
0.66
0.85
0.58
0.97
0.74
0.89
0.91
0.97
0.75
0.65
0.78
1.97
1.81
1.80
2.14
2.17
2.01
1.71
2.06
1.71
2.06
1.75
1.98
1.84
2.07
1.65
1.70
1.77
7
9
11
15
16
17
18
19
20
21
22
24
25
26
27
Figure 4. Solution UV−vis absorption spectra of compounds 7, 11,
16, and 18.
578
595
a
Esgoln and Efgilm were measured at the onset. Vred and Vox were
measured at the current onset in V vs Ag/AgCl at a scan rate of 100
mV s−1. E1/2 for Fc/Fc+ was measured at 0.45 V vs Ag/AgCl.
Figure 5. Thin-film UV−vis absorption spectra of compounds 7, 11,
16, and 18.
meaning that the conjugation between the two units is quite
limited. The introduction of DPP units at the 6 and 12
positions in compound 25 causes a red shift of λmax by 62 nm
(vs compound 20) to 650 nm, indicating more effective
conjugation. A small band gap of 1.46 eV was obtained for thin
films of compound 25, indicating good intermolecular
interactions in the solid state.
Photostability. All of the synthesized anthanthrene
compounds proved to be highly stable under standard
laboratory conditions, which is a significant advantage over
linearly fused acenes such as anthracene and pentacene
derivatives that suffer from photooxidation.22 To assess the
stability of the anthanthrene scaffold, compound 16 was studied
as a representative example. A 10 μM solution of 16 in CH2Cl2
was irradiated in a glass vial in air for 60 min under a 500 W
halogen lamp and compared against a sample kept in the dark.
Illumination under the high-power white light had a negligible
effect on the absorption profile (Figure 8). We attribute this
improved photostability to the absence of a reactive diene and
Figure 3. UV−vis absorption spectra of compounds 5 and 6 in
CH2Cl2 solution (solid lines) and thin films (dashed lines).
units in compound 27 has a negligible effect on the absorption
spectra, analogous to cross-conjugated systems.21 The poorly
defined thin-film absorption profiles of the three molecules could
be indicative of weak intermolecular interactions even in the solid
state. Interestingly, thiothienyl-appended compound 26 has the
smallest band gap at 1.79 eV, which could indicate that the bulkier
sulfonyl group hinders close intermolecular interactions.
Comparison of DPP-appended compounds 20 and 25 allows
for the unambiguous determination of whether the 4,10 axis or
the 6,12 axis is the most effective conjugation axis. In the
solution absorption spectrum of 4,10-DPP-appended com-
pound 20 (Figure 7), there is a sharp peak at 507 nm that can
be assigned to the absorption profile of the tetrakis(ethynyl)-
anthanthrene (see Figure S8 in the Supporting Information),
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Figure 6. Solution (solid lines) and thin-film (dashed lines) UV−vis
absorption spectra of compounds 22, 26, and 27.
Figure 8. Photostability of compound 16 under illumination with
white light from a halogen lamp.
values determined for a polycyclic hexabenzocoronene (HBC-
C12) (Ka = 484 M−1)26 and phenylacetylene macrocycles
(PAMs) (Ka = 39 M−1),25 which suggests that the intermolecular
interactions are surprisingly strong for a carbon-rich, heteroatom-
free molecule. It is reasonable to think that such interactions
could lead to liquid-crystalline properties in the solid state with
appropriate side chains, although studies in this direction have
not yet been undertaken.
Electrochemistry. In order to determine the redox
potentials and the positions of the frontier orbitals, we
performed cyclic voltammetry in CH2Cl2 with Bu4NPF6 as
the electrolyte, a Ag/AgCl reference electrode, and a platinum
wire working electrode. The potentials were measured at the
current onset and are reported in Table 1.
As presented in Figure 10, both of the anthanthrone
derivatives 5 and 6 present two reversible and well-defined
reduction peaks typical of anthanthrone compounds11 with very
similar potentials of −0.50 and −0.87 V. The major difference
between the two compounds lies in the lower oxidation potential
of compound 6: substitution of the phenyl group by the electron-
rich thiophene moiety lowers Vox by 0.17 V down to 1.30 eV,
which is indicative of good electronic communication between the
two moieties and corroborates the optical data.
Among the anthanthrene compounds presented in Figure 11,
ethynyl-free compound 11 presents the highest oxidation and
reduction potentials (0.77 and −1.40 V, respectively).
Introduction of the ethynyl linker at the 6 and 12 positions in
compound 18 drastically lowers both Vred by 0.26 V to −1.13 V
and Vox by 0.19 V to 0.58 V. This proves that acetylenic linker is
effective at extending the conjugation along the 6,12 axis and
stabilizing both the negative and positive charges with highly
reversible redox processes. Introduction of the acetylenic linker at
the 4 and 10 positions shifts the HOMO−LUMO frontier orbitals
down by 0.08 eV for compound 16. Substitution of the thiophene
units by phenyl ones in compound 7 increases both Vred and Vox
by ca. 0.05 V compared with compound 16, corroborating the
higher optical band gap.
Figure 7. Solution (solid lines) and thin-film (dashed lines) UV−vis
absorption spectra of DPP-appended compounds 20 and 25.
the more rigid structure of the fused polycyclic core as opposed
to linearly fused acene.22
Solution Aggregation Study. The absorption red shift of
compound 7 prompted us to study its solution aggregation
1
behavior, and we chose to perform this study via H NMR
spectroscopy in CHCl3 at different concentrations. The NMR
spectra of the aromatic region at concentrations ranging from
0.8 to 35 mg/mL are presented in Figure 9. The singlet resonance
labeled with a red dot is assigned to the anthanthrene protons at
the 5 and 11 positions and is strongly shifted upfield by up to
0.57 ppm with increasing concentration. The resonances for the
other anthanthrene aromatic protons (peaks just above 8.2 ppm for
the 0.8 mg/mL spectrum) are also shifted to a similar extent,
whereas the chemical shifts of the signals associated with the phenyl
groups are less influenced. Upfield shifts are generally indicative of
face-to-face interactions in aromatic systems.23 Using a monomer−
dimer model,24,25 we were able to determine an association
constant of 84 M−1 (Figure S12 in the Supporting Information).
Although a direct comparison of the association constants with
those of the parent structures is difficult, this value lies between the
Analysis of the cyclic voltammograms of compounds 22, 26,
and 27 presented in Figure 12 allows the effects of donor and
acceptor groups on the redox potentials to be ascertained. 6,12-
Sulfonylthiophene-appended compound 22 presents the lowest
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1
Figure 9. H NMR spectra of ethynylphenyl-appended compound 7 at different concentrations in CDCl3 at 23 °C.
Figure 10. Cyclic voltammograms of anthanthrone compounds 5
and 6.
Figure 11. Cyclic voltammograms of anthanthrenes 7, 11, 16, and 18.
behavior are not well understood at this time. The electro-
chemical band gap of compound 25 is 1.65 V, which is lowered
by 0.10 V compared with that of compound 20, indicative of
the better conjugation along the 6,12 axis. This result
corroborates the lower optical band gap observed for the
extended conjugation along the 6,12 axis.
To obtain the vacuum levels from the cyclic voltammetry
data, the potentials were corrected against an external ferrocene
standard measured at 0.45 V vs Ag/AgCl and fixed at 5.1 eV
against vacuum. The results are reported in Figure 14.27
DFT Calculations. We performed calculations of the
frontier orbitals using the commonly used B3LYP/6-31G*
level of theory28 for representative compounds 6, 11, 16, and
18. The optimized structure of anthanthrone 6 is highly planar
reduction potential at −0.93 V, whereas compound 27 has a
higher reduction potential at −0.99 V, indicating that the
electron-withdrawing group is more effective at stabilizing a
negative charge when installed at the 6 and 12 positions. The
same trend is observed when the oxidation potentials are
compared: 6,12-thiothienyl-appended compound 27 is oxidized
at a much lower potential than compound 22 (0.78 vs 0.91 V,
respectively). Surprisingly, substitution of the TIPS groups
in compound 26 with the sulfonylthiophene in compound
27 increases Vox by 0.13 V, whereas Vred is lowered by only
−0.06 V and appears to be less reversible.
The two DPP-appended compounds 20 and 25 (Figure 13)
present multiple oxidation processes, and the reasons for this
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Figure 15. Calculated frontier orbitals for compounds 6 and 11.
LUMO is concentrated on the anthanthrone core along the
quinoidal axis as expected (Figure 15). The HOMO and LUMO
of compound 11 are mostly localized over the anthanthrene
moiety, and the large dihedral angle of 90° between the aromatic
planes and the thiophenes at the 6 and 12 positions limit all
delocalization beyond the anthanthrene. At the 4 and 10
positions, the smaller but significant calculated dihedral angle of
53° allows limited delocalization over the thiophene.
Figure 12. Cyclic voltammograms of compounds 22, 26, and 27.
The distributions of the HOMO and LUMO in compounds
16 and 18 are mostly delocalized over the 6,12 axis (Figure 16),
supporting the experiments showing improved conjugation
along that axis. The frontier orbitals are hardly delocalized
beyond the acetylenic bond at the 4 and 10 positions, once
again supporting the negligible effect of appending electroactive
units at these positions.
CONCLUSION
■
Acetylic linkers were successfully used to tune the optoelec-
tronic properties of anthanthrone and anthanthrene derivatives.
From a synthetic standpoint, Sonogashira coupling proved to
be a highly versatile and efficient tool to attach different
electroactive aromatic units, whereas direct nucleophilic attack
of lithiated reagents followed by reduction proved to be highly
susceptible to electronic effects on both the reagents and
reactants. The simple thiophene-appended anthanthrone
Figure 13. Cyclic voltammograms of DPP-appended compounds 20
and 25.
with a HOMO that is homogeneously distributed lengthwise
over the whole molecule along the 4,10 axis, whereas the
Figure 14. Electrochemically determined (bottom) HOMO and (top) LUMO energy levels for selected compounds.
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Computational Methods. DFT calculations were carried out with
the Gaussian 09 program suite28 at the B3LYP/6-31G* level of theory,
and the orbital plots are reported at an isovalue of 0.02.
2-Methyl-4-(5-octylthiophen-2-yl)but-3-yn-2-ol (3). A dry
flask under nitrogen was charged with 2-bromo-5-octylthiophene
(1.5 g, 5.72 mmol), dichlorobis(acetonitrile)palladium(II) (14 mg,
0.057 mmol), tri-tert-butylphosphonium tetrafluoroborate (33 mg,
0.114 mmol), and copper(I) iodide (11 mg, 0.057 mmol), and the
flask was flushed three times with a vacuum/nitrogen cycle.
Diisopropylamine (5.7 mL) was deaerated using a continuous flow
of nitrogen for 10 min and transferred via syringe to the reaction flask.
The reaction mixture was heated to 70 °C, and 2-methylbut-3-yn-2-ol
(721 mg, 8.58 mmol) was added dropwise. A white precipitate was
quickly formed, and the reaction mixture was heated for 1 h at this
temperature. Once the mixture cooled, a saturated NH4Cl solution was
added, and the aqueous layer was extracted three times with CH2Cl2.
The organic layer was dried with MgSO4, and the solvent was
evaporated under reduced pressure. The crude product was purified by
silica gel column chromatography (AcOEt/hexanes 5:95 to 10:90 v/v)
1
to afford compound 3 as a colorless oil (1.20 g, 75%). H NMR (400
MHz, CDCl3): δ 6.99 (d, J = 3.7 Hz, 1H), 6.62 (d, J = 3.4 Hz, 1H),
2.76 (t, J = 7.3 Hz, 2H), 2.05 (s, 1H), 1.68−1.58 (m, 9H), 1.37−1.22
(m, 10H), 0.88 (t, J = 7.0 Hz, 3H). 13C NMR (100 MHz, CDCl3): δ
148.1, 132.0, 123.9, 119.8, 96.6, 76.0, 65.7, 31.8, 31.5, 31.3, 30.1, 29.3,
29.2, 29.0, 22.7, 14.1. HRMS (APPI+): calcd for C17H27OS (M + H)+
279.1777, found 279.1782.
Figure 16. Calculated frontier orbitals for compounds 16 and 18.
2-Ethynyl-5-octylthiophene (4). A dry flask equipped with a
reflux condenser under nitrogen was charged with 2-methyl-4-(5-
octylthiophen-2-yl)but-3-yn-2-ol (3) (1.2 g, 4.3 mmol), potassium
hydroxide (724 mg, 12.9 mmol), and anhydrous toluene (65 mL), and
the resulting solution was deaerated with a continuous flow of nitrogen
for 5 min and then heated to a vigorous reflux for 30 min. Once the
mixture was cooled to room temperature, hexanes (65 mL) was added,
and the crude mixture was poured onto a silica gel pad and eluted with
derivative 6 with a low band gap of 1.66 eV and a high electron
affinity with a LUMO energy of −4.14 eV was prepared and
presented potentially attractive properties as an acceptor in
solar cells. We determined that the optoelectronic properties of
anthanthrene compounds are governed by substitution at the 6
and 12 positions rather than the 4 and 10 positions and that the
acetylic linker was essential to relieve the steric strain between
the anthanthrene and the appended aromatic unit. Function-
alization with different aromatic units allowed precise control of
the HOMO and LUMO energy levels. Highly reversible redox
processes were generally observed, and low-band-gap materials
could be obtained with the proper conjugated units. We assume
that the 4 and 10 positions of the anthanthrene unit could be
used as a simple way to fine-tune the solubility and packing
behavior via side-chain engineering. Strong face-to-face
interactions were observed in solution, leading to large red
shifts in the solid state indicative of J-aggregation. Such
intermolecular interactions should lead to good charge
transport properties because of the large intermolecular orbital
overlap.6 The ease of preparation from commercial products,
tailorable properties, excellent photostability, and reversible
redox processes of anthanthrene compounds make them
excellent candidates for low-cost organic electronic applica-
tions. The evaluation of the most promising candidates in
OFETs and OPV applications is currently underway along with
the preparation of polymeric analogues.
1
hexanes to afford compound 4 as a colorless oil (702 mg, 74%). H
NMR (400 MHz, CDCl3): δ 7.09 (d, J = 3.5 Hz, 1H), 6.63 (d, J = 3.1
Hz, 1H), 3.29 (s, 1H), 2.77 (t, J = 7.4 Hz, 2H), 1.69−1.60 (m 2H),
1.39−1.19 (m, 10H), 0.88 (t, J = 5.8 Hz, 3H). 13C NMR (100 MHz,
CDCl3): δ 148.6, 133.1, 123.9, 119.2, 80.4, 77.5, 31.9, 31.6, 30.1, 29.3,
29.2, 29.0, 22.7, 14.1. HRMS (APPI+): calcd for C14H21S (M + H)+
221.1358, found 221.1370.
4,10-Bis((4-hexylphenyl)ethynyl)anthanthrone (5). A dry flask
under nitrogen was charged with 1-ethynyl-4-hexylbenzene (2) (550 mg,
2.77 mmol), 4,10-dibromoanthanthrone (515 mg, 1.11 mmol),
dichlorobis(triphenylphosphine)palladium(II) (39 mg, 0.057 mmol),
and copper(I) iodide (8 mg, 0.044 mmol). The flask was flushed three
times using a vacuum/nitrogen cycle. Diisopropylamine (2 mL) and
o-dichlorobenzene (15 mL) were deaerated with a continuous flow of
nitrogen for 10 min and then transferred via syringe to the reaction
flask. The solution was heated to 90 °C for 3 h. Once cooled, the
reaction mixture was poured into MeOH (100 mL). The precipitate
was recovered via filtration, and the crude residue was purified by silica
gel column chromatography (CHCl3/AcOEt from 100:0 to 95:5 v/v)
to afford compound 5 as a purple solid (400 mg, 53%). Mp: 235−238 °C.
1H NMR (500 MHz, CDCl3): δ 8.69 (m, 4H), 8.47 (s, 2H), 7.87−7.81
(m, 2H), 7.57 (d, J = 7.5 Hz, 4H), 7.91 (d, J = 7.9 Hz, 4H), 2.67 (t, J = 7.8
Hz, 4H), 1.70−1.63 (m, 4H), 1.42−1.29 (m, 12H), 0.92 (t, J = 6.4 Hz,
6H). 13C NMR (125 MHz, CDCl3): δ 182.2, 144.5, 133.8, 133.7, 131.9,
131.2, 129.3, 129.2, 128.7, 128.7, 128.1, 127.4, 126.9, 124.4, 119.7, 98.4,
86.1, 36.1, 31.7, 31.3, 29.0, 22.6, 14.1. HRMS (APPI+): calcd for C50H43O2
(M + H)+ 675.3258, found 675.3266.
4,10-Bis((5-octyl-2-thienyl)ethynyl)anthanthrone (6). A dry
flask under nitrogen was charged with 2-ethynyl-5-octylthiophene (4)
(522 mg, 2.37 mmol), 4,10-dibromoanthanthrone (500 mg, 1.08 mmol),
dichlorobis(triphenylphosphine)palladium(II) (38 mg, 0.054 mmol), and
copper(I) iodide (10 mg, 0.054 mmol), and the flask was flushed three
times using a vacuum/nitrogen cycle. Diisopropylamine (2 mL) and o-
dichlorobenzene (10 mL) were deaerated with a continuous flow of
nitrogen for 10 min and then transferred via syringe to the reaction flask.
The solution was heated to 90 °C for 4 h. Once cooled, the mixture was
EXPERIMENTAL SECTION
■
General Methods. 4,10-Dibromoanthanthrone was provided as a
courtesy by Heubach GmbH as product Monolite Red 316801. High-
resolution mass spectrometry (HRMS) was performed using a time-of-
flight (TOF) LC−MS apparatus equipped with an APPI ion source.
Electrochemical Measurements. All of the cyclic voltammo-
grams were acquired employing a three-electrode potentiostat. The
potential was referenced to a Ag/AgCl-saturated KCl electrode, and Pt
wires were used as the working and counter electrodes. CH2Cl2 with a
supporting electrolyte of Bu4NPF6 (0.1 M) was sparged using argon
5 min prior to electrochemical measurements. For calculation of
vacuum levels, the potentials were calibrated against a ferrocene/
ferrocenium external standard measured at 0.45 V versus the Ag/AgCl
reference electrode.
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poured into MeOH (100 mL). The precipitate was recovered via
filtration, and the crude residue was purified by silica gel column
chromatography (CHCl3) to afford compound 6 as a blue solid (99 mg,
12%). 1H NMR analysis was performed at 50 °C because of peak
broadening and poor solubility at room temperature. Acquisition of the
13C NMR spectrum proved unsuccessful because of the poor solubility and
precipitation of the product during the course of the acquisition. Mp: 165−
170 °C. 1H NMR (500 MHz, 50 °C, CDCl3): δ 8.69 (d, J = 7.0 Hz, 2H),
8.64 (d, J = 8.3 Hz, 2H), 8.50 (s, 2H), 7.89−7.83 (m, 2H), 7.29 (d, J =
3.4 Hz, 2H), 6.78 (d, J = 3.0 Hz, 2H), 2.88 (t, J = 7.8 Hz, 4H), 1.80−1.72
(m, 4H), 1.51−1.28 (m, 24H), 0.93 (t, J = 7.0 Hz, 6H). HRMS (APPI+):
calcd for C50H47O2S2 (M + H)+ 743.3012, found 743.3024.
CH2Cl2. The organic layer was dried with MgSO4, and the solvent was
evaporated under reduced pressure. The crude product was purified by
silica gel column chromatography (CH2Cl2/hexanes 10:90 v/v)
followed by recrystallization in hexanes (at ca. −15 °C) to afford
1
compound 11 as a yellow solid (57 mg, 39%). Mp: 145−150 °C. H
NMR (500 MHz, CDCl3): δ 8.68 (d, J = 7.5 Hz, 2H), 8.52 (d, J = 8.3
Hz, 2H), 8.28 (s, 2H), 8.12−8.06 (m, 2H), 7.28−7.26 (m, 4H), 7.19
(d, J = 3.2 Hz, 2H), 7.05 (d, J = 2.6 Hz, 2H), 3.02 (t, J = 7.3 Hz, 4H),
2.93 (t, J = 7.3 Hz, 4H), 1.91−1.77 (m, 8H), 1.56−1.28 (m, 40H),
0.95−0.88 (m, 12H). 13C NMR (125 MHz, CDCl3): δ 147.7, 146.5,
139.6, 136.4, 133.3, 131.8, 130.4, 129.9, 129.7, 128.8, 127.9, 127.4,
125.9, 125.9, 124.2, 124.2, 123.6, 123.1, 121.9, 32.0, 31.9, 31.8, 31.7,
30.4, 30.3, 29.7, 29.4 (3C), 29.3 (2C), 22.7 (2C), 14.2, 14.1. HRMS
(APPI+): calcd for C70H85S4 (M + H)+ 1053.5529, found 1053.5534.
2-(2-Ethylhexylthio)thiophene (12). A dry flask under nitrogen
was charged with thiophene (6.00 g, 71.4 mmol) and anhydrous THF
(45 mL) and cooled to 0 °C. A solution of n-butyllithium in hexanes
(2.5 M, 28.5 mL, 71.4 mmol) was added dropwise over 10 min. After
20 min at this temperature, the reaction mixture was cooled to −78 °C
using a dry ice/acetone bath, and sulfur (2.29 g, 71.4 mmol) was
added in a single portion under a positive nitrogen pressure. After
30 min at −78 °C, the solution was allowed to warm to room temperature
and stirred for 3 h. 2-Ethylhexyl bromide (13.78 g, 71.4 mL) was
added in three portions, and the reaction mixture was stirred overnight
at room temperature. Water and hexanes were added to the reaction
mixture. Diluted HCl was added to break the emulsion, and the
aqueous layer was extracted three times with hexanes. The organic
layer was dried with MgSO4, and the solvent was evaporated under
reduced pressure. The crude product was purified by silica gel column
chromatography (hexanes) to afford compound 12 as a colorless oil
4,6,10,12-Tetrakis((4-hexylphenyl)ethynyl)anthanthrene (7).
A dry flask under nitrogen was charged with 1-ethynyl-4-hexylbenzene
(409 mg, 2.07 mmol) and anhydrous THF (20 mL) and cooled to
0 °C. A solution of n-butyllithium in hexanes (2.5 M, 0.83 mL, 2.07 mmol)
was added dropwise over 5 min. After 20 min at this temperature,
compound 5 (280 mg, 0.414 mmol) was added in a single portion
under a positive nitrogen pressure, and the reaction mixture was
warmed to room temperature overnight. Tin(II) chloride dihydrate
(400 mg, 1.78 mmol) dissolved in aqueous HCl (10% v/v, 4 mL) was
added dropwise to the reaction mixture. After 20 min, the mixture was
poured into MeOH (100 mL). The precipitate was recovered via
filtration, and the crude residue was dissolved in CHCl3 with silica gel
(3 g) and evaporated under reduced pressure. The crude product
adsorbed on silica gel was purified by silica gel column
chromatography (toluene/hexanes 20:80 v/v) to afford compound 7
1
as a purple solid (105 mg, 25%). Mp: 200−204 °C. H NMR (500
MHz, CDCl3): δ 8.86 (d, J = 8.2 Hz, 2H), 8.73 (s, 2H), 8.62 (d, J = 7.0
Hz, 2H), 8.06 (t, J = 7.8 Hz, 2H), 7.76 (d, J = 8.2 Hz, 4H), 7.76 (d, J =
7.8 Hz, 4H), 7.28−7.23 (m, 8H), 2.76−2.68 (m, 8H), 1.76−1.66 (m,
8H), 1.47−1.33 (m, 24H), 0.97−0.92 (m, 12H). 13C NMR (125 MHz,
CDCl3): δ 143.2 (2C), 132.0, 131.9, 130.6, 130.0, 129.8, 129.7, 128.5
(2C), 126.1, 125.7, 124.2, 121.7, 121.4, 121.1, 121.0, 119.7, 116.5,
102.5, 95.0, 87.9, 86.5, 36.2, 36.1, 31.9, 31.8, 31.4 (2C), 29.2, 29.1, 22.7
(2C), 14.2 (2C). HRMS (APPI+): calcd for C78H77 (M + H)+
1013.6020, found 1013.5984.
1
(12.2 g, 80%). H NMR (400 MHz, CDCl3): δ 7.31−7.28 (m, 1H),
7.09−7.06 (m, 1H), 6.96−6.93 (m, 1H), 2.80 (d, J = 6.5 Hz, 2H),
1.56−1.18 (m, 9H), 0.91−0.80 (m, 6H). 13C NMR (100 MHz,
CDCl3): δ 135.9, 132.6, 128.5, 127.4, 43.7, 38.9, 32.0, 28.7, 25.2, 22.9,
14.1, 10.6, 29.3, 29.2, 29.0, 22.7, 14.1. HRMS (APPI+): calcd for
C12H21S2 (M + H)+ 229.1079, found 229.1084.
2-Bromo-5-(2-ethylhexylthio)thiophene (13). A dry flask under
nitrogen was charged with 2-(2-ethylhexylthio)thiophene (4.00 g,
17.5 mmol) and anhydrous DMF (30 mL), and N-bromosuccinimide
(3.10 g, 17.5 mmol) was added portionwise followed by sonication for
10 min. Water and hexanes were added to the reaction mixture, and
the organic layer was washed three times with water. The organic layer
was dried with MgSO4, and the solvent was evaporated under reduced
4,10-Dibromo-6,12-bis((triisopropylsilyl)ethynyl)anthanthrene
(9). A dry flask under nitrogen was charged with (triisopropylsilyl)-
acetylene (1.96 g, 10.77 mmol) and anhydrous THF (45 mL) and
cooled to 0 °C. A solution of n-butyllithium in hexanes (2.4 M, 4.5 mL,
10.77 mmol) was added dropwise over 10 min. After 20 min at this
temperature, 4,10-dibromoanthanthrone (1.00 g, 2.15 mmol) was added in
one portion under a positive nitrogen pressure. The reaction mixture
was allowed to warm to room temperature overnight. A solution of
tin(II) chloride dihydrate (2.8 g, 9.26 mmol) in aqueous HCl (50%
v/v, 2.5 mL) was added dropwise, and the resulting mixture was stirred
for 20 min and then poured into MeOH (100 mL). The precipitate
was recovered via filtration, and the residue was dissolved in warm
CHCl3 and filtered again. The filtrate was evaporated under reduced
pressure, and the crude product was recrystallized from hexanes (at
room temperature) to afford compound 9 as a red solid (830 mg,
48%). Mp: 150−155 °C. 1H NMR (500 MHz, CDCl3): δ 9.21 (s, 2H),
9.18 (d, J = 8.2 Hz, 2H), 8.77 (d, J = 7 Hz, 2H), 8.36−8.31 (m, 2H),
1.44−1.33 (m, 42H). 13C NMR (125 MHz, CDCl3): δ 132.5, 130.7,
130.5, 130.0, 127.4, 127.0, 126.3, 125.5, 122.9, 120.8, 116.9, 105.6,
103.2, 19.0, 11.6. HRMS (APPI+): calcd for C44H51Br2Si2 (M + H)+
793.1891, found 793.1878.
4,6,10,12-Tetrakis(5-octyl-2-thienyl)anthanthrene (11). A dry
flask under nitrogen was charged with 2-octylthiophene (113 mg,
0.58 mmol) and anhydrous THF (3 mL) and cooled to 0 °C. A
solution of n-butyllithium in hexanes (2.5 M, 0.23 mL, 0.58 mmol) was
added dropwise over 5 min. After 20 min at this temperature, this
solution was transferred via cannula to a flask containing 4,10-bis(5-
octyl-2-thienyl)anthanthrone (10) (100 mg, 0.14 mmol) and
anhydrous THF (10 mL) at 0 °C. After 1 h at this temperature, a
solution of tin(II) chloride dihydrate (400 mg, 1.78 mmol) in aqueous
HCl (10% v/v, 4 mL) was added dropwise, and the resulting mixture
was allowed to warm to room temperature over 1 h. Water was added
to the reaction mixture, and the organic layer was extracted twice with
1
pressure to afford compound 13 as a colorless oil (5.17 g, 96%). H
NMR (400 MHz, CDCl3): δ 6.90 (d, J = 3.8 Hz, 1H), 6.87 (d, J = 3.6
Hz, 1H), 2.77 (d, J = 6.2 Hz, 2H), 1.56−1.18 (m, 9H), 0.91−0.80 (m,
6H). 13C NMR (100 MHz, CDCl3) 137.2, 133.6, 130.3, 113.4, 43.8,
38.9, 31.9, 28.6, 25.1, 22.9, 14.1, 10.6. HRMS (APPI+): calcd for
C12H19BrS2 (M + H)+ 306.0106, found 306.0101.
2-Bromo-5-(2-ethylhexylsulfonyl)thiophene (14). A dry flask
under nitrogen was charged with 2-bromo-5-(2-ethylhexylthio)-
thiophene (2 g, 6.50 mmol) and anhydrous DMF (80 mL). 3-
Chloroperoxybenzoic acid (77% purity, 3.65 g, 16.27 mmol) was
added in a single portion, and the solution was stirred overnight at
room temperature. Dilute aqueous NaOH, hexanes, and AcOEt were
added to the reaction mixture, and the organic layer was washed three
times with dilute aqueous NaOH. The organic layer was dried with
MgSO4, and the solvent was evaporated under reduced pressure to
1
afford compound 14 as a colorless oil (1.599 g, 72%). H NMR (400
MHz, CDCl3): δ 7.44 (d, J = 4.0 Hz, 1H), 7.13 (d, J = 4.0 Hz, 1H),
3.11 (d, J = 5.8 Hz, 2H), 2.00−1.92 (m, 1H), 1.53−1.37 (m, 4H),
1.30−1.16 (m, 4H), 0.90−0.82 (m, 6H). 13C NMR (100 MHz,
CDCl3) 142.0, 133.9, 130.8, 121.7, 61.3, 34.7, 32.3, 28.1, 25.6, 22.6,
14.0, 10.2, 29.3, 29.2, 29.0, 22.6, 14.1. HRMS (APPI+): calcd for
C12H20BrO2S2 (M + H)+ 339.0083, found 339.0086.
4,10-Bis((5-octyl-2-thienyl)ethynyl)-6,12-bis((triisopropylsilyl)-
ethynyl)anthanthrene (15). A dry flask under nitrogen was charged
with 2-ethynyl-5-octylthiophene (4) (522 mg, 2.37 mmol), compound
9 (200 mg, 0.252 mmol), dichlorobis(triphenylphosphine)palladium-
(II) (8.8 mg, 0.013 mmol), and copper(I) iodide (2.4 mg, 0.013 mmol).
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The flask was flushed three times using a vacuum/nitrogen cycle.
Diisopropylamine (1 mL) and THF (10 mL) were deaerated with a
continuous flow of nitrogen for 10 min and transferred via syringe to the
reaction flask. The solution was heated to 65 °C overnight. Once cooled,
the mixture was poured into MeOH (100 mL). The precipitate
was recovered via filtration and recrystallized from CHCl3 (25 mL at ca.
−15 °C) to afford compound 15 as red needles (199 mg, 74%). Mp:
190−195 °C. 1H NMR (500 MHz, CDCl3): δ 9.15 (d, J = 7.9 Hz, 2H),
9.10 (s, 2H), 8.81 (d, J = 7.1 Hz, 2H), 8.33−8.29 (m, 2H), 7.31 (d, J =
3.6 Hz, 2H), 6.79 (d, J = 3.3 Hz, 2H), 2.88 (t, J = 7.5 Hz, 4H), 1.78−
1.72 (m, 4H), 1.46−1.28 (m, 62H), 0.91 (t, J = 6.5 Hz, 6H). 13C NMR
(125 MHz, CDCl3): δ 149.2, 132.6, 131.9, 131.4, 131.0, 130.1, 127.1,
126.4, 124.7, 124.5, 122.6, 122.4, 121.0, 120.5, 117.3, 105.4, 103.6, 91.1,
88.9, 31.9, 31.6, 30.4, 29.4, 29.3, 29.1, 22.7, 19.0, 14.1, 11.7. HRMS
(APPI+): calcd for C72H89S2Si2 (M + H)+ 1073.5939, found 1073.5947.
General Procedure for TIPS-Acetylene Deprotection with
TBAF (Procedure A). To a solution of the bis(TIPS-acetylene)
compound in THF (5−10 mL) containing water (3 drops) under
nitrogen was added a solution of tetrabutylammonium fluoride in THF
(1 M, 3 equiv). The reaction was monitored using TLC. After 1 h,
MeOH (10−20 mL) was added, and the crude bis(ethynyl) product
was recovered by filtration in over 90% yield and used in the next step
without further purification.
transferred with a syringe. The resulting mixture was heated at 90 °C
overnight. Once cooled, the mixture was poured into MeOH
(100 mL). The precipitate was recovered via filtration, and the
residue was purified by silica gel column chromatography (CH2Cl2/
hexanes 0:100 to 4:96 v/v) followed by recrystallization in hexanes (ca.
15 mL at −15 °C) to afford compound 17 as an orange solid (194 mg,
75%). Mp: 170−173 °C. 1H NMR (500 MHz, CDCl3): δ 9.21 (d, J = 8.14
Hz, 2H), 8.98 (s, 2H), 8.89 (d, J = 7.3 Hz, 2H), 8.30−8.26
(m, 2H), 7.43 (d, J = 3.4 Hz, 2H), 6.99 (d, J = 3.4 Hz, 2H), 2.99 (t,
J = 7.5 Hz, 4H), 1.88−1.81 (m, 4H), 1.54−1.29 (m, 62H), 0.98−0.89
(m, 6H). 13C NMR (125 MHz, CDCl3): δ 146.8, 139.2, 134.4, 132.2,
131.4, 130.4, 128.0, 127.6, 126.8, 125.9, 124.6, 124.4, 122.9, 121.2, 117.3,
104.7, 104.1, 32.0 (2C), 30.4, 29.5, 29.3 (2C), 22.7, 19.1, 14.2, 11.6. HRMS
(APPI+): calcd for C68H89S2Si2 (M + H)+ 1025.5939, found 1025.5951.
4,10-Bis(5-octyl-2-thienyl)-6,12-bis((5-octyl-2-thienyl)-
ethynyl)anthanthrene (18). Compound 17 (170 mg, 0.166 mmol)
was deprotected according to procedure A, except that CH2Cl2
(20 mL) was used instead of THF, to afford the terminal bis(alkyne)
(109 mg, 93%). The Sonogashira coupling was performed according to
procedure B using the crude bis(acetylene) product (90 mg, 0.126
mmol) and 5-bromo-2-octylthiophene (109 mg, 0.393 mmol). The
crude product was purified by silica gel column chromatography
(CH2Cl2/hexanes 10:90 v/v) followed by recrystallization in CH2Cl2/
hexanes to afford compound 18 as a golden solid (122 mg, 87%). Mp:
General Procedure for Twofold Sonogashira Coupling Using
the Pd2(dba)3/tBu3PHBF4 Catalyst (Procedure B). In order to
ensure proper stoichiometry, a mixture of catalysts was prepared by
grinding tris(dibenzylideneacetone)dipalladium(0)/tri-tert-butylphospho-
nium tetrafluoroborate/copper(I) iodide [Pd2(dba)3/tBu3PHBF4/CuI]
in a ratio of 1:4:1 (2 equiv of phosphine per Pd, total MW 2455 g/mol)
in a mortar and pestle and stored in a desiccator.
1
175−180 °C. H NMR (500 MHz, CDCl3): δ 8.86 (d, J = 7.3 Hz,
2H), 8.66 (d, J = 7.3 Hz, 2H), 8.63 (s, 2H), 8.10−8.04 (m, 2H), 7.38
(d, J = 3.3 Hz, 2H), 7.34 (d, J = 3.4 Hz, 2H), 6.97 (d, J = 2.9 Hz, 2H),
6.81 (d, J = 3.2 Hz, 2H), 2.99 (t, J = 7.5 Hz, 4H), 2.90 (t, J = 7.7 Hz,
4H), 1.90−1.74 (m, 8H), 1.57−1.27 (m, 40H), 0.96−0.88 (m, 12H).
13C NMR (125 MHz, CDCl3): δ 149.0, 146.6, 139.4, 133.9, 132.3,
A dry flask under nitrogen was charged with bis(ethynyl)-
anthanthrene compound (100−200 mg, 1 equiv), aryl bromide (2−
3 equiv), and the Pd2(dba)3/tBu3PHBF4/CuI mixture (0.05 equiv
relative to the anthanthrene compound), and the flask was flushed three
times using a vacuum/nitrogen cycle. Diisopropylamine (1 mL) and
toluene (5 mL) were deaerated with a continuous flow of nitrogen for
10 min and transferred via syringe to the reaction flask, and the mixture
was heated to 75 °C overnight. Once cooled, the mixture was poured into
MeOH (100 mL). The precipitate was recovered via filtration and
purified according to the specified procedure for each compound.
4,6,10,12-Tetrakis((5-octyl-2-thienyl)ethynyl)anthanthrene
(16). Compound 15 (170 mg, 0.158 mmol) was deprotected
according to procedure A to afford the terminal alkyne (112 mg,
93%). The Sonogashira coupling was performed according to
procedure B using the crude product (100 mg, 0.131 mmol) and
5-bromo-2-octylthiophene (109 mg, 0.393 mmol). The crude product
was purified by silica gel column chromatography (toluene/hexanes
15:85 to 100:0 v/v) followed by trituration with hot acetone to afford
130.7, 130.4, 130.2, 127.7, 127.7, 126.3, 125.6, 124.5, 124.4, 124.3,
122.4, 121.1, 120.7, 116.5, 95.9, 90.8, 32.0, 31.9 (2C), 31.7, 30.5, 30.4,
29.5, 29.4 (3C), 29.3, 29.2, 22.8, 22.7, 14.2 (2C). HRMS (APPI+):
calcd for C74H85S4 (M + H)+ 1101.5529, found 1101.5557.
4,10-Bis((trimethylsilyl)ethynyl)-6,12-bis((triisopropylsilyl)-
ethynyl)anthanthrene (19). A dry flask under nitrogen was charged
with compound
9 (400 mg, 0.503 mmol), dichlorobis-
(triphenylphosphine)palladium(II) (18 mg, 0.025 mmol), and copper-
(I) iodide (4.8 mg, 0.025 mmol). The flask was flushed three times
with a vacuum/nitrogen cycle. Diisopropylamine (2 mL) and THF
(10 mL) were deaerated with a continuous flow of nitrogen for 10 min
and transferred via syringe to the reaction flask, and (trimethylsilyl)-
acetylene (198 mg, 2.01 mmol) was added. The mixture was heated to
60 °C overnight. Once the mixture was cooled, a saturated NH4Cl
solution was added, and the aqueous layer was extracted twice with
CH2Cl2. The organic layer was dried with MgSO4, and the solvent was
evaporated under reduced pressure. The crude product was purified by
silica gel column chromatography (CH2Cl2/hexanes 0:100 to 5:95 v/v) to
afford compound 19 as a red solid (380 mg, 91%). Mp: 190−195 °C. 1H
NMR (500 MHz, CDCl3): δ 9.16−9.12 (m, 4H), 8.81 (d, J = 7.40 Hz,
2H), 8.33−8.29 (m, 2H), 1.42−1.25 (m, 42H), 0.43 (s, 18H). 13C NMR
(125 MHz, CDCl3): δ 132.9, 131.8, 130.9, 130.3, 127.1, 126.4, 124.9, 122.5
(2C), 121.1, 117.5, 105.4, 103.6, 103.2, 100.4, 19.0, 11.7, 0.1. HRMS
(APPI+): calcd for C54H69Si4 (M + H)+ 829.4471, found 829.4462.
4,10-Bis((5-(2,5-dioctyl-6-(thiophen-2-yl)-1,4(2H,5H)-
dioxopyrrolo[3,4-c]pyrrol-3-yl)-2-thienyl)ethynyl)-6,12-bis-
((triisopropylsilyl)ethynyl)anthanthrene (20). To a solution of
bis(TMS-acetylene) compound 19 (300 mg, 0.363 mmol) in THF
(10 mL) and MeOH (10 mL) containing water (3 drops) under nitrogen
was added K2CO3 (150 mg, 1.09 mmol). After 1 h, MeOH (20 mL)
was added, and the crude product was recovered via filtration after
washing with 1% aqueous HCl and MeOH to afford the bis(ethynyl)
compound (190 mg, 77% yield), which was used for the synthesis of
compounds 20 and 21. The Sonogashira coupling was performed
according to procedure B using the crude bis(ethynyl) compound
(40 mg, 0.058 mmol) and 3-(5-bromothiophen-2-yl)-2,5-dioctyl-6-
(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (5-Br-DPP)
(70 mg, 0.116 mmol). The crude product was purified by silica gel
column chromatography (CHCl3/AcOEt 100:0 to 99:1 v/v) to afford
1
compound 16 as a black solid (121 mg, 80%). Mp: 144−148 °C. H
NMR (400 MHz, CDCl3): δ 8.73 (d, J = 8.0 Hz, 2H), 8.50 (d, J = 7.6
Hz, 2H), 8.43 (s, 2H), 8.07−8.01 (m, 2H), 8.37 (d, J = 3.4 Hz, 2H),
7.37 (d, J = 3.4 Hz, 2H), 7.31 (d, J = 3.5 Hz, 2H), 6.80 (d, J = 3.2 Hz,
2H), 6.77 (d, J = 3.4 Hz, 2H), 2.93−2.84 (m, 8H), 1.85−1.72 (m,
8H), 1.52−1.23 (m, 40H), 0.95−0.90 (m, 12H). 13C NMR (125 MHz,
CDCl3): δ 148.9, 148.6, 132.5 (2C), 130.2, 129.8 (2C), 129.6, 126.4
(2C), 125.9, 124.5, 124.3, 121.6, 121.5, 121.1, 121.0, 119.9, 116.4,
96.2, 91.5, 90.3, 88.8, 32.0, 31.9, 31.7 (2C), 30.5, 30.4, 29.5 (2C), 29.4,
29.3 (3C), 22.74, 14.18. HRMS (APPI+): calcd for C78H85S4
(M + H)+ 1149.5529, found 1149.5550.
4,10-Bis(5-octyl-2-thienyl)-6,12-bis((triisopropylsilyl)-
ethynyl)anthanthrene (17). A dry flask under nitrogen was charged
2-octylthiophene (198 mg, 1.00 mmol) and dry THF (5 mL). The
mixture was cooled to −78 °C, and n-butyllithium (2.5 M in hexane,
1.72 mL, 4.3 mmol) was added dropwise. The mixture was stirred for
60 min before the addition of Bu3SnCl (352 mg, 1.08 mmol)
dropwise. The mixture was warmed to room temperature over 1 h. A
second dry flask under nitrogen was charged with compound 9
(200 mg, 0.252 mmol), dichlorobis(triphenylphosphine)palladium(II)
(9 mg, 0.013 mmol), and toluene (10 mL). The mixture was degassed
with a flow of nitrogen for 10 min, and the stannyl solution was
1
compound 20 as a dark solid (49 mg, 49%). Mp: >260 °C. H NMR
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Article
(500 MHz, CDCl3): δ 9.01 (d, J = 7.8 Hz, 2H), 8.83 (br s, 4H), 8.65 (d,
J = 7.2 Hz, 2H), 8.56 (s, 2H), 8.35−8.31 (m, 2H), 7.49 (d, J = 4.8 Hz,
2H), 7.35 (d, J = 3.6 Hz, 2H), 7.14 (t, J = 3.8 Hz, 2H), 4.01−3.89 (m, 8H),
1.76−1.25 (m, 90H), 0.94−0.85 (m, 12H). 13C NMR (125 MHz, CDCl3):
δ 160.5 (2C), 139.5, 138.1, 135.7, 135.6, 133.5, 131.9, 131.0, 130.8, 130.6,
130.4, 129.7, 129.1, 128.5 (2C), 128.3, 127.3 (2C), 126.5, 124.4, 121.4,
117.2, 108.0, 107.4, 105.4, 103.5, 96.7, 87.9, 31.9, 31.8, 29.5, 29.4, 29.3
(2C), 27.1, 27.0, 22.7 (2C), 19.2, 14.1 (2C), 11.8. HRMS (APPI+): calcd
for C108H129N4O4S4Si2 (M + H)+ 1730.8469, found 1730.8477.
K2CO3 (150 mg, 1.09 mmol). After 1 h, MeOH (20 mL) was added,
and the crude product was recovered via filtration and washed with 1%
aqueous HCl and MeOH to afford the bis(acetylene) compound
(244 mg, 98% yield), which was used for the synthesis of compounds
25 and 26. The Sonogashira coupling was performed according to
procedure B using the crude bis(acetylene) product (40 mg, 0.058
mmol) and 3-(5-bromothiophen-2-yl)-2,5-dioctyl-6-(thiophen-2-yl)-
pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (5-Br-DPP) (70 mg, 0.116 mmol).
The crude product was purified by silica gel column chromatography
(CHCl3) to afford compound 20 as a blue solid (62 mg, 62%).
Mp: >260 °C. 1H NMR (500 MHz, CDCl3): δ 9.08 (br s, 2H), 8.90 (br
s, 2H), 8.84 (d, J = 7.2 Hz, 2H), 8.45−8.40 (m, 2H), 8.30 (br s, 2H),
8.24−8.17 (m, 2H), 7.59 (d, J = 3.0 Hz, 2H), 7.46 (d, J = 4.4 Hz, 2H),
7.08 (m, 2H), 4.13−3.90 (m, 8H), 1.82−1.20 (m, 90 H), 0.96−0.75 (m,
12H). 13C NMR (125 MHz, CDCl3): δ 160.6 (2C), 139.7, 138.1, 135.8,
135.7, 133.8, 133.7, 131.4, 130.5, 129.9, 129.8, 129.2, 128.5, 128.4, 127.3,
125.8, 125.2 (2C), 122.2, 121.0 (2C), 115.6, 108.4, 107.5, 105.4, 97.2,
96.3, 96.2, 31.9 (2C), 29.5, 29.3 (3C), 27.1, 27.0, 22.7 (2C), 19.1, 14.2,
14.1, 11.7. HRMS (APPI+): calcd for C108H129N4O4S4Si2 (M + H)+
1730.8469, found 1730.8444.
4,10-Bis((5-(2-ethylhexylthio)-2-thienyl)ethynyl)-6,12-bis-
((triisopropylsilyl)ethynyl)anthanthrene (21). The Sonogashira
coupling was performed according to procedure B using the crude
4,10-bis(ethynyl)-6,12-bis((triisopropylsilyl)ethynyl)anthanthrene pre-
pared in the synthesis of compound 20 (80 mg, 0.117 mmol) and
compound 13 (108 mg, 0.350 mmol). The crude product was purified
by silica gel column chromatography (CH2Cl2/hexanes 5:95 v/v) to
afford compound 21 as an orange solid (115 mg, 87%). Acetone was
added during the last evaporation step to obtain a powdery solid. Mp:
1
100−103 °C. H NMR (500 MHz, CDCl3): δ 9.06 (d, J = 8.2 Hz,
2H), 8.90 (s, 2H), 8.75 (d, J = 7.6 Hz, 2H), 8.32−8.26 (m, 2H), 7.31
(d, J = 2.7 Hz, 2H), 7.06 (d, J = 2.5 Hz, 2H), 2.96 (d, J = 5.9 Hz, 4H),
1.70−1.25 (m, 60H), 1.00−0.89 (m, 12H). 13C NMR (125 MHz,
CDCl3): δ 139.2, 132.7, 131.8, 131.6, 131.5, 130.7, 129.7, 127.1, 126.4,
125.4, 124.6, 122.1, 122.1, 120.7, 117.2, 105.3, 103.6, 92.5, 87.9, 43.4,
39.2, 32.1, 28.8, 25.3, 23.0, 19.1, 14.2, 11.7, 10.8. HRMS (APPI+):
calcd for C72H89S4Si2 (M + H)+ 1137.5380, found 1137.5374.
4,10-Bis((5-(2-ethylhexylthio)-2-thienyl)ethynyl)-6,12-bis((5-
(2-ethylhexylsulfonyl)-2-thienyl)ethynyl)anthanthrene (22).
Compound 21 (75 mg, 0.066 mmol) was deprotected according to
procedure A to afford the bis(acetylene) (52 mg, 96%). The Sonogashira
coupling was performed according to procedure B using the crude
bis(acetylene) product (70 mg, 0.084 mmol) and compound 14 (71 mg,
0.212 mmol). The crude product was purified by silica gel column
chromatography (CH2Cl2/AcOEt 100:0 to 99:1 v/v) followed by
recrystallization in CH2Cl2/hexanes to afford compound 22 as a red
solid (104 mg, 91%). Mp: 235−240 °C. 1H NMR (400 MHz, CDCl3): δ
8.32 (d, J = 8.6 Hz, 2H) 8.23 (d, J = 7.6 Hz, 2H), 7.89−7.81 (m, 4H), 7.67
(d, J = 3.7 Hz, 2H), 7.40 (d, J = 3.9 Hz, 2H), 7.31 (d, J = 3.5 Hz, 2H), 7.06
(d, J = 3.5 Hz, 2H), 3.30 (d, J = 5.7 Hz, 2H), 3.01 (d, J = 6.2 Hz, 2H),
2.21−2.12 (m, 2H), 1.72−1.21 (m, 34H), 1.05−0.78 (m, 24H). 3C NMR
(125 MHz, CDCl3): δ 141.9, 139.7, 133.7, 133.1, 132.1, 131.4, 131.3, 129.1,
128.5, 128.4, 128.3, 126.1, 125.0, 124.8, 124.4, 121.3, 119.8, 118.6, 114.2,
94.1, 93.4, 92.0, 88.6, 61.5, 43.4, 39.2, 34.8, 32.5, 32.2, 28.8, 28.3, 25.8, 25.4,
23.1, 22.9, 14.2 (2C), 10.9, 10.4. HRMS (APPI+): calcd for C78H85O4S8
(M + H)+ 1342.4247, found 1342.4127.
4,10-Bis((triisopropylsilyl)ethynyl)-6,12-bis((5-(2-ethylhex-
ylthio)-2-thienyl)ethynyl)anthanthrene (26). The Sonogashira
coupling was performed according to procedure B using the crude
4,10-bis((triisopropylsilyl)ethynyl)-6,12-bis(ethynyl)anthanthrene pre-
pared in the synthesis of compound 25 (100 mg, 0.146 mmol) and
compound 13 (134 mg, 0.438 mmol). The crude product was purified
by silica gel column chromatography (CH2Cl2/hexanes 5:95 v/v) to
afford compound 26 as a purple solid (147 mg, 94%). Mp: 188−192 °C.
1H NMR (400 MHz, CDCl3): δ 8.77 (d, J = 8.2 Hz, 2H), 8.36−8.32 (m,
4H), 8.08−8.02 (m, 2H), 7.30 (d, J = 3.5 Hz, 2H), 7.02 (d, J = 3.7 Hz,
2H), 1.74−1.21 (m, 60H), 1.03−0.94 (m, 12H). 13C NMR (100 MHz,
CDCl3): δ 139.1, 132.4, 131.6, 131.4, 129.7, 129.3, 126.6, 125.7 (2C),
124.6, 121.7, 121.0, 119.5, 115.9, 105.5, 96.3, 95.5, 91.7, 43.4, 39.1, 32.1,
28.8, 25.3, 23.0, 19.0, 14.1, 11.6, 10.8. HRMS (APPI+): calcd for
C72H89S4Si2 (M + H)+ 1137.5380, found 1137.5372.
4,10-Bis((5-(2-ethylhexylsulfonyl)-2-thienyl)ethynyl)-6,12-
bis((5-(2-ethylhexylthio)-2-thienyl)ethynyl)anthanthrene (27).
Compound 26 (140 mg, 0.123 mmol) was deprotected according to
procedure A to afford the bis(acetylene) (98 mg, 96%). The
Sonogashira coupling was performed according to procedure B using
the crude bis(acetylene) product (90 mg, 0.109 mmol) and compound
14 (111 mg, 0.327 mmol). The crude product was purified by silica gel
column chromatography (CH2Cl2/AcOEt 100:0 to 99:1 v/v) to afford
1
compound 22 as a dark solid (46 mg, 31%). Mp: 205−210 °C. H
NMR (500 MHz, CDCl3): δ 8.24 (d, J = 7.72 Hz, 2H), 8.04 (d, J = 7.1
Hz, 2H), 7.77−7.73 (m, 2H), 7.68 (s, 2H), 7.63 (d, J = 3.6 Hz, 2H),
7.32 (d, J = 3.6 Hz, 2H), 7.28−7.26 (m, 2H), 7.07 (d, J = 3.4 Hz, 2H),
3.32−3.28 (m, 4H), 3.04 (d, J = 6.5 Hz, 4H), 2.20−2.14 (m, 2H),
1.76−1.32 (m, 34H), 1.09−0.90 (m, 24H). 13C NMR (125 MHz,
CDCl3): δ 141.8, 140.0, 133.5, 132.8, 132.3, 131.5 (2C), 130.6 (2C),
128.8, 128.4, 128.3, 126.1, 125.7, 125.0, 123.9, 120.6, 118.8, 116.2,
95.8, 95.6, 91.1, 86.2, 61.5, 43.4, 39.3, 34.8, 32.5, 32.2, 28.8, 28.3, 25.8,
25.4, 23.1, 22.8, 14.2, 14.1, 10.9, 10.3. HRMS (APPI+): calcd for
C78H85O4S8 (M + H)+ 1341.4208, found 1341.4170.
4,10-Bis((triisopropylsilyl)ethynyl)-6,12-bis((trimethylsilyl)-
ethynyl)anthanthrene (24). A dry flask under nitrogen was charged
with (trimethylsilyl)acetylene (736 mg, 7.49 mmol) and anhydrous
THF (15 mL) and cooled to 0 °C. A solution of n-butyllithium in
hexanes (2.5 M, 3.0 mL, 7.49 mmol) was added dropwise over 10 min.
After 20 min at this temperature, 4,10-bis((triisopropylsilyl)ethynyl)-
anthanthrone (23) (500 mg, 0.75 mmol) was added in one portion under
a positive nitrogen pressure. The reaction mixture was allowed to warm to
room temperature overnight. A solution of tin(II) chloride dihydrate (974
mg, 3.22 mmol) in aqueous HCl (50% v/v, 2 mL) was added dropwise,
and the resulting mixture was stirred for 20 min and then poured into
MeOH (100 mL). The precipitate was recovered via filtration, and the
residue was purified by silica gel column chromatography (CH2Cl2/
hexanes 0:100 to 5:95 v/v) to afford compound 24 as a red solid
ASSOCIATED CONTENT
■
S
* Supporting Information
Optical and electrochemical characterizations of selected
compounds, NMR spectra, and calculated coordinates and
total energies. This material is available free of charge via the
Internet at http://pubs.acs.org.
1
(480 mg, 77%). Mp: >260 °C. H NMR (500 MHz, CDCl3): δ 9.11
(d, J = 8.2 Hz, 2H), 9.02 (s, 2H), 8.36 (d, J = 7.4 Hz, 2H), 8.33−8.29 (m,
2H), 1.37−1.26 (m, 42H), 0.53 (s, 18H). 13C NMR (125 MHz, CDCl3):
δ 132.5, 131.7, 130.6, 130.4, 127.1, 126.4, 124.9, 122.9, 122.3, 121.1,
117.0, 108.6, 105.3, 101.8, 97.1, 18.9, 11.5, 0.2. HRMS (APPI+): calcd for
C54H69Si4 (M + H)+ 829.4471, found 829.4443.
4,10-Bis((triisopropylsilyl)ethynyl)-6,12-bis((5-(2,5-dioctyl-6-
(thiophen-2-yl)-1,4(2H,5H)-dioxopyrrolo[3,4-c]pyrrol-3-yl)-2-
thienyl)ethynyl)anthanthrene (25). To a solution of bis(TMS-
acetylene) compound 24 (300 mg, 0.362) in THF (15 mL) and
MeOH (10 mL) containing water (3 drops) under nitrogen was added
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: jean-francois.morin@chm.ulaval.ca.
Notes
The authors declare no competing financial interest.
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The Journal of Organic Chemistry
Article
Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin,
K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.;
Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega,
N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.;
Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.;
Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.;
Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.;
Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.;
Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09,
revision C.01; Gaussian, Inc.: Wallingford, CT, 2010.
ACKNOWLEDGMENTS
■
This work was supported by NSERC through a Discovery
Grant. J.-B.G. thanks the NSERC for a Ph.D. scholarship and
Marc-Andre Courtemanche (ULaval) for assistance with the
́
DFT calculations.
̈
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