Systematic structure-property investigations on a series of alternating carbazole-thiophene oligomers

Article abstract of DOI:10.1021/jo402416f

A series of alternating carbazole-thiophene oligomers, namely 2,7-linked carbazole-thiophene oligomers 1, 3, 5, 7, and 9 and 3,6-linked ones 2, 4, 6, 8, and 10, in which the molecular length was systematically elongated, were synthesized by Suzuki-Miyaura coupling reactions. The effects of the conjugation connectivity between the carbazole and thiophene moieties and the molecular length on the electronic, photophysical, and electrochemical properties of 1-10 were comprehensively investigated. In the present oligomer architectures, the connection with thiophene at the 2,7-positions of carbazole ensures p-conjugation to a high extent and high fluorescence quantum yields, while that at the 3,6-positions enhances the donor ability. The increase in the molecular length of the 2,7-linked oligomers effectively extends p-conjugation. The relationship between structural variations and photophysical properties was examined by fluorescence lifetime measurements in detail. The X-ray crystal structure of 6 was also disclosed.

Full text of DOI:10.1021/jo402416f

Article
pubs.acs.org/joc
Systematic Structure−Property Investigations on a Series of
Alternating Carbazole−Thiophene Oligomers
Shin-ichiro Kato, Satoru Shimizu, Atsushi Kobayashi, Toshitada Yoshihara, Seiji Tobita,
and Yosuke Nakamura*
Division of Molecular Science, Faculty of Science and Technology, Gunma University, 1-5-1 Tenjin-cho, Kiryu, Gunma 376-8515,
Japan
S
* Supporting Information
ABSTRACT: A series of alternating carbazole−thiophene
oligomers, namely 2,7-linked carbazole−thiophene oligomers
1, 3, 5, 7, and 9 and 3,6-linked ones 2, 4, 6, 8, and 10, in which
the molecular length was systematically elongated, were
synthesized by Suzuki−Miyaura coupling reactions. The effects
of the conjugation connectivity between the carbazole and
thiophene moieties and the molecular length on the electronic,
photophysical, and electrochemical properties of 1−10 were comprehensively investigated. In the present oligomer architectures,
the connection with thiophene at the 2,7-positions of carbazole ensures π-conjugation to a high extent and high fluorescence
quantum yields, while that at the 3,6-positions enhances the donor ability. The increase in the molecular length of the 2,7-linked
oligomers effectively extends π-conjugation. The relationship between structural variations and photophysical properties was
examined by fluorescence lifetime measurements in detail. The X-ray crystal structure of 6 was also disclosed.
disclosed.6c,9,10 In this context, carbazole can be regarded as an
important scaffold for the construction of π-functional materials
due to its rich diversity in structural modification. Oligothio-
phenes, in particular, α-oligothiophenes, are among the most
INTRODUCTION
■
π-Conjugated oligomers and polymers have attracted much
attention in recent decades due to their potential uses as
semiconductors and electroactive materials in diverse organic
electronic devices such as organic field-effect transistors
intensively investigated organic compounds for a variety of
materials applications,11 and hence mixed π-conjugated
(OFETs), organic light-emitting diodes (OLEDs), organic
oligomers composed of carbazole and thiophene moieties
solar cells (OSCs), and nonlinear optical devices.1,2 In
have recently attracted considerable attention from the
particular, the development of conjugated oligomers with
extended π-electron delocalization is important,3 because the
systematic study on monodisperse oligomers with a precisely
defined length and constitution allows the elucidation of
various properties, which are dependent on the molecular
viewpoint of their potential as the active component of organic
electronics and synthetic accessibility. Various carbazole−
thiophene hybrid oligomers as functional materials through
the use of their fluorescence and donor properties were
reported;12 in particular a large number of derivatives
length and chemical structures, and sheds light on the
properties of polymers.4 π-Conjugated oligomers have the
advantage in the fine-tuning of the electronic, photophysical,
and electrochemical properties by rational structural modifica-
tion to achieve high device performance. Moreover, π-
possessing the anchoring and acceptor group used for OSCs
have been recently synthesized since the pioneering work by
Koumura, Hara, and co-workers.13,14 However, less attention
was paid to the clarification of the structure−property
relationships in the carbazole−thiophene-based π-systems,
conjugated oligomers with sophisticated functionality are now
key components in molecular electronics.5
which are indispensable for materials design.
We have recently synthesized a large series of thienyl-
Carbazole has fine optical properties, a low redox potential,
and high chemical stability, and thereby oligo-/polycarbazoles
have been representative benchmark materials in OFETs,
substituted carbazole derivatives (thienylcarbazoles) including 1
and 2 shown in Chart 1 and investigated the effects of the
OLEDs, and OSCs.6−8 Poly(3,6-carbazole)s and 3,6-function-
conjugation connectivity between the carbazole and thiophene
moieties on the photophysical and electrochemical properties.8a
alized carbazoles have been extensively studied over the past
few decades, because carbazole can be easily functionalized by
electrophilic substitution at its 3,6-positions (para positions
from the nitrogen atom) with high electron density. The recent
It was shown that 1 displays the red-shifted longest absorption
maximum (λmaxabs) and a high fluorescence quantum yield
compared to 2, while 2 has a lower oxidation potential than 1.
These findings indicate that the thienyl substituents at the 2,7-
development in carbazole chemistry has also established the
efficient synthetic pathways to 1,8- and 2,7-functionalized
carbazoles, and their peculiar properties which are apparently
Received: October 29, 2013
different from those of 3,6-carbazole derivatives have been
© XXXX American Chemical Society
A
dx.doi.org/10.1021/jo402416f | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
Chart 1. Linear 2,7- and 3,6-Linked Carbazole−Thiophene Oligomers 1−10
positions of carbazole effectively extend π-conjugation and
enhance fluorescence efficiency, while those at the 3,6-positions
increase the donor ability. On the basis of this study, we
became interested in the following two questions: Does the
effect of the conjugation connectivity between the carbazole
and thiophene moieties on the properties found in
thienylcarbazole π-systems generally apply to extended π-
systems, namely conjugated oligomeric structures? Does the
gradual increase in the thienylcarbazole unit extend the π-
conjugation and consequently enhance the fluorescence
efficiency and donor potency? To approach these questions,
we undertook the design and synthesis of alternating
carbazole−thiophene oligomers, namely 2,7-linked carbazole−
thiophene oligomers 3, 5, 7, and 9 and 3,6-linked ones 4, 6, 8,
and 10 (Chart 1).15 A large series of oligomers 1−10, in which
the molecular length varies systematically, allow us to study the
relevant structure−property relationships in carbazole−thio-
phene hybrid oligomers. Herein, we report the synthesis and
properties, such as the structural features and the electronic,
photophysical, and electrochemical properties, of 3−10
together with 1 and 2 based on X-ray diffraction analysis,
UV−vis and fluorescence spectral measurements, fluorescence
lifetime measurements, cyclic voltammetry (CV), and theoreti-
cal calculations.
RESULTS AND DISCUSSION
■
Synthesis. In our molecular design, ethyl groups were
introduced on the nitrogen atoms in 1−8, while the solubilizing
hexyl groups were introduced in 9 and 10 to alleviate the
anticipated solubility problems. Compounds 1−10 were
synthesized by Suzuki−Miyaura cross-coupling reactions as
key steps as described below.16 For all the reactions,
[Pd(PPh3)4] was used as the catalyst. As shown in Scheme 1,
the cross-coupling reactions were performed on either bromide
11 or 12 with 2,5-bis-thiopheneboronic acid pinacol ester (13)
to give 3 and 4 in 59% and 25% yields, respectively.
The syntheses of 5 and 6 were achieved by sequential
Suzuki−Miyaura cross-coupling reactions from dibromides 14
and 15, respectively (Scheme 2). Thus, the reaction of 14 and
2-thiopheneboronic acid pinacol ester (16) gave monothienyl-
substituted carbazole 17, which was allowed to react with 13 to
furnish 5 in 33% yield. In a similar manner, 6 was prepared in
two steps from 15.
The synthesis of 7 and 8 was outlined in Scheme 3. The
lithium−bromine exchange between 14 and n-BuLi followed by
the successive addition of trimethoxyborane and aqueous HCl
gave diboronic acid 19, which was converted to diboronic acid
pinacol ester 20 in 18% yield in two steps. Likewise, 11 was
converted to boronic acid pinacol ester 22 via boronic acid 21.
Bromide 24 was prepared by the coupling reaction of 22 and 3
equiv of 2,5-dibromothiophene (23) in 20% yield and then was
B
dx.doi.org/10.1021/jo402416f | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
To gain insight into the molecular structure of 6, we
optimized the ground-state structure of 6′, in which the ethyl
groups in 6 were replaced with the methyl groups, by density
functional theory (DFT) calculations at the B3LYP/6-31G(d)
level of theory by the Gaussian 09 program.18,19 The selected
geometrical parameters of 6′ are given in Table S1 in the
Supporting Information and compared with the crystallo-
graphic dihedral angles and bond lengths for 6. As for the bond
lengths, there is good agreement between the experiment and
theory in general. The differences in carbon−carbon bond
lengths and carbon−nitrogen bond lengths are within 0.026 Å.
The large deviation occurs for the carbon−sulfur bond lengths,
with the DFT results providing longer bond lengths of 0.025−
0.046 Å than the X-ray results. The dihedral angles between the
carbazole and thiophene moieties are calculated to be 27°−29°,
and hence the DFT results provided larger angles than those in
the X-ray results by ca. 10°−15°. This finding implies the
contribution of the crystal packing force to the observed high
planarity of 6 in the solid state.20
Scheme 1. Synthesis of 3 and 4
subjected to the coupling reaction with 20 to furnish 7 in 63%
yield. Compound 8 was synthesized following a two-step
transformation from 2. Thus, the bromination of 2 with NBS
was carried out, and then the cross-coupling reaction of
dibromide 25 with 26 afforded the desired 8 in 64% yield.
The synthesis of 9 started from dibromide 27 which was
allowed to react with 0.5 equiv of 16 to give 28 (Scheme 4).
The transformation of a bromo group in 28 into an iodo group
was performed with excess amounts of CuI/LiI in DMSO to
give 29. Subsequent cross-coupling of iodide 29 with 30 gave
bromo-substituted thienylcarbazole 31, which was further
subjected to the coupling reaction with 32 to afford 9 in 24%
yield. Bromination of 33 with 1 equiv of NBS afforded
monobromide 34. By the cross-coupling reaction of 34 with 35,
compound 10 which was the final member of this series of
oligomers was obtained in 23% yield. All the compounds were
fully characterized by various spectroscopic methods, such as
1H NMR, 13C NMR, and mass spectroscopy and/or elemental
analysis.
Crystal Structure of 6. The single crystal of 6 suitable for
X-ray diffraction analysis was obtained by vapor diffusion of
hexane into CH2Cl2 solution (Figure 1a,b). The molecule
adopts an all s-trans conformation between the carbazole and
thiophene moieties.17 The solid-state structure of 6 is quasi-
planar with torsion angles between the carbazole and thiophene
moieties of 9.0°−19.7°. Compound 6 forms the stacked dimer
structure by effective π−π interactions, and the dimer is again
packed in a herringbone fashion by CH−π interactions; no
noticeable π−π interaction is observed between the neighbor-
ing dimers (Figure S1 in the Supporting Information).
Electronic Absorption Spectroscopy. We measured the
UV−vis absorption spectra of oligomers 1−10 in CH2Cl2
abs
solutions (Figure 2a,b), and the λmax values for discussion
on the extension of π-conjugation are summarized in Table 1.
abs
As expected from our recent finding that the longest λmax
value of 1 (353 nm) is red-shifted relative to that of 2 (314
abs
nm), the longest λmax
values of 2,7-linked carbazole−
thiophene oligomers 3, 5, 7, and 9 are apparently red-shifted
as compared to those of the corresponding 3,6-linked oligomers
4, 6, 8, and 10. Thus, it can be reasonably concluded that the
connection with thiophene at the 2,7-positions of carbazole in
general extends π-conjugation effectively relative to that at the
3,6-positions in the oligomer architectures. Noticeably, the
abs
molar extinction coefficients (ε) at the longest λmax of 2,7-
linked oligomers 1, 3, 5, 7, and 9 are larger than those of the
corresponding 3,6-linked oligomers 2, 4, 6, 8, and 10.
In the series of the 2,7-linked oligomers, clear red shifts of
abs
the longest λmax values were observed from 1, 3, 5, 7, to 9,
indicative of the effective extension of π-conjugation upon
increasing the molecular length (Figure 2a). It seems that 9
does not reach the effective conjugation length for this system
abs
and longer oligomers exhibit further red-shifted longest λmax
values. Oligomers 1, 3, 5, 7, and 9 feature similar absorption
curves to each other in the low-energy region, and their ε values
abs
at the λmax
steadily increase with the number of
heteroaromatic rings.
In sharp contrast to the series of oligomers 1, 3, 5, 7, and 9,
abs
no pronounced red shift of the longest λmax values was
Scheme 2. Synthesis of 5 and 6
C
dx.doi.org/10.1021/jo402416f | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
Scheme 3. Synthesis of 7 and 8
Scheme 4. Synthesis of 9 and 10
observed in the series of 3,6-linked oligomers 2, 4, 6, 8, and 10
upon increasing the molecular length (Figure 2b). For example,
the terminal thienyl functionality in 6 and 10 results in the
and 10 possess almost the same effective conjugation length
and/or the increase in the molecular length in this series
decreases the planarity of the π-conjugated backbone as
predicted by theoretical calculations (vide infra).21
abs
marginal or almost no red shift of the longest λmax values as
compared to those of 4 and 8, respectively (354 nm (4), 362
nm (6), 380 nm (8), 380 nm (10)). The spectral change and
the red shift of the absorption band in the low-energy region
were hardly observed with increase in the molecular length by
reversing the thiophene and carbazole moieties from 6 to 8,
whereas the significant spectral change and the clear red shift of
the absorption onset were observed from 2 to 4. These findings
suggest that 3,6-linked carbazole−thiophene oligomers 4, 6, 8,
Fluorescence Spectroscopy. All of the carbazole−
thiophene oligomers 1−10 are fluorescent. The fluorescence
spectra of 2,7-linked oligomers 1, 3, 5, 7, and 9 and 3,6-linked
ones 2, 4, 6, 8, and 10 in CH2Cl2 (10−5−10−6 mol L−1) are
shown in Figure 3a and 3b, respectively, and the spectral data
are summarized in Table 2.22 The color of the fluorescence of
1−10 ranges from violet, blue, to light green. The two well-
defined vibronic maxima were observed in the fluorescence
D
dx.doi.org/10.1021/jo402416f | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
Table 1. UV−vis Spectroscopic Data and Calculated Lowest
a b
,
Excitation Energies of 1−10
abs
λmax
calcd λmax
b
b
[nm]
[nm] (f)
composition of band
H → L, 97%
c
1
2
269, 290,
353
352 (1.114)
256, 267,
314
328 (0.336)
H − 1 → L, 8%; H → L + 1, 90%
3
4
5
6
7
264, 372
311, 354
269, 401
315, 362
375 (1.597)
359 (0.792)
411 (2.366)
373 (0.814)
421 (2.760)
H → L, 99%
H → L, 95%; H → L + 2, 2%
H → L, 98%
H − 1 → L + 3, 2%; H → L, 96%
H − 1 → L + 1, 2%; H → L, 96%
c
c
265, 325,
407
8
9
314, 349,
384 (0.584)
H − 1 → L + 1, 3%; H → L, 94%
c
380
Figure 1. X-ray crystal structure of 6. (a) Top view and (b) side view.
Displacement ellipsoids are shown at the 50% probability level.
Hydrogen atoms are omitted for clarity.
d
d
270, 340,
416
−
−
d
d
10 321, 358,
−
−
c
380
a
b
Measured in CH2Cl2. TD-DFT (TD/B3LYP/6-31G(d)) calcu-
lations were carried out with the use of optimized structures of 1′−8′,
where the Et groups in 1−8 were replaced with the Me groups, at the
c
B3LYP/6-31G(d) level of theory; H = HOMO, L = LUMO. Peak as
d
shoulder. Not calculated due to the large molecular size.
Figure 2. Electronic absorption spectra of (a) 1, 3, 5, 7, and 9 and (b)
2, 4, 6, 8, and 10 in CH2Cl2 at 298 K.
spectra of 1−10. The fluorescence spectra of 2,7-linked
oligomers 1, 3, 5, 7, and 9 do not seem to be the mirror
image of the absorption spectra. The broad absorption band in
the low energy region and the vibronic fine structure in the
fluorescence spectra of 1, 3, 5, 7, and 9 suggest the contribution
of a more rigid structure in the excited state, namely the
quinoid state, than the ground state.23 The fluorescence
maxima (λmaxfl) of the series of 1, 3, 5, 7, and 9 are gradually
red-shifted upon increasing the molecular length. Similar to the
Figure 3. Fluorescence spectra of (a) 1, 3, 5, 7, and 9 and (b) 2, 4, 6,
8, and 10 on 300-nm excitation in CH2Cl2 at 298 K.
We determined the absolute fluorescence quantum yields
(Φf) of 1−10 by using an integrating sphere system (Table 2).
The 2,7-linked oligomers 1, 3, 5, 7, and 9 display moderate to
high Φf values of 0.44−0.74. It is remarkable that 7 and 9 with
the extensively long π-conjugated backbone display high Φf
values of 0.74 and 0.68, respectively. Thus, they are good
emitters due to a combination of high Φf and large ε values. In
the series of 3,6-linked oligomers, compound 2 exhibits an
exceptionally low Φf value of 0.036. Compounds 4 and 6 show
high Φf values of 0.78 and 0.67, respectively. The Φf values of 8
abs
fl
change of the longest λmax values, the red shift of the λmax
values from 1 to 9 is noticeably large as compared to that from
2 to 10 (391 nm (1), 392 nm (2), 464 nm (9), 429 nm (10)).
The Stokes shifts for 2, 4, 6, 8, and 10 are essentially larger than
those for the corresponding 1, 3, 5, 7, and 9, indicating a
somewhat large structural change and/or electronic distribution
change, which should facilitate the nonradiative process, in the
former rather than the latter.
E
dx.doi.org/10.1021/jo402416f | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
a
Table 2. Summary of Fluorescence Data of 1−10
b
c
d
e
Stokes shifts [cm−1
]
Φf
τf [ns]
kr [107 s−1
]
knr [107 s−1
]
fl
λmax [nm]
1
2
391, 412
392, 411
428, 451
420, 442
448, 476
424, 446
455, 483
426, 448
464, 493
2750
6330
3510
4430
2610
4040
2530
2840
2540
3000
0.44 (0.61)
0.036 (0.06)
0.50 (0.79)
0.78 (0.59)
0.63 (0.63)
0.67 (0.55)
0.74 (0.67)
0.33 (0.24)
2.12
1.68
0.62
0.61
0.74
0.64
0.80
0.70
0.72
0.72
20.8
2.1
26.4
57.4
80.7
36.1
50.0
51.6
32.5
95.7
44.4
97.2
3
80.6
128
85.1
104
92.5
47.1
94.4
41.7
4
5
6
7
8
f
9
0.68 (−)
0.30 (0.25)
10
429, 451
a
b
Measured in CH2Cl2. Absolute quantum yields determined by an integrating sphere system. The values in parentheses are in cyclohexane.
c
d
e
f
Lifetime. Radiative decay constant. Nonradiative decay constant. Not determined due to insolubility.
a
Table 3. Oxidation Potential (Epa) and Onset (Eonset) by Cyclic Voltammetry in CH2Cl2 (0.1 mol L−1 n-Bu4NPF6),
b
Theoretically Calculated HOMO and LUMO Levels and Their Gaps (ΔEHOMO−LUMO), and Optical HOMO−LUMO Gaps
c
(ΔEopt
)
bd
,
b
b
Epa [V]
Eonset [V]
HOMO [eV]
LUMO [eV]
ΔEHOMO−LUMO [eV]
ΔEopt [eV]
f
1
2
3
+0.65
+0.55
+0.43
+0.42
−5.44 (−5.35)
−5.31 (−5.23)
−5.26 (−5.22)
−1.66
−1.21
−1.65
3.78
4.09
3.61
3.51
3.94
3.33
f
+0.54
e
+0.57
f
+0.97
e
4
+0.30
+0.20
−5.02 (−5.00)
−1.20
3.82
3.50
e
+0.64
f
5
6
+0.38
+0.31
+0.22
−5.21 (−5.11)
−5.02 (−5.02)
−1.88
−1.30
3.33
3.72
3.09
3.42
e
+0.30
f
+0.55
f
7
8
9
+0.34
+0.29
+0.18
+0.30
+0.19
−5.13 (−5.09)
−4.91 (−4.98)
−5.12 (−5.10)
−4.92 (−4.99)
−1.86
−1.26
−1.96
−1.30
3.27
3.65
3.16
3.05
3.55
2.98
3.46
f
+0.22
f
+0.35
e
10
+0.25
3.62
a
b
All potentials are given versus the Fc+/Fc couple used as the external standard; scan rate = 100 mV s−1. Calculated by B3LYP/6-311G(d,p)//
c
B3LYP/6-31G(d) for 1′−10′, where the alkyl groups on the nitrogen atoms in 1−10 are replaced with the methyl groups. The values are obtained
d
abs
from the longest λmax
. The values in the parentheses are those deduced from the Eonset values according to the following equation: HOMO =
e f
−(4.8 + Eonset) eV (ref 25). Reversible wave. Irreversible wave.
(0.33) and 10 (0.30) are almost half of those of 4 and 6, and
thus the Φf values of the 3,6-linked oligomers tend to decrease
with the increase from the two to three carbazole moieties,
which contrasts with the trend for the Φf values in the 2,7-
linked oligomers. Overall, it is likely that the connection with
thiophene at the 2,7-positions of carbazole ensures high
fluorescence efficiency relative to that at the 3,6-positions.
To obtain further insight into the photophysical properties of
1−10, we determined the fluorescence lifetimes (τf) with the
time-correlated single-photon counting method (Figures S3−
S12)24 and calculated the radiative (kr) and nonradiative (knr)
decay rate constants from the singlet excited state, based on the
equations kr = Φf/τf and knr = (1 − Φf)/τf. Compounds 1 and 2
with the one carbazole moiety exhibit τf values of 2.12 and 1.68
ns, respectively. Compounds 3−10 with the two or three
carbazole moieties display shorter τf values of 0.61−0.80 ns
than 1 and 2.
(3)). The clear decrease in the knr values is again observable
from 3 and 5 to 7 and 9, although 1 shows the smallest knr
value. Thus, the marked high Φf values of 5, 7, and 9 derive
from a combination of the promotion of the radiative process
and suppression of the nonradiative one by increasing the
molecular length. In the series of 3,6-linked oligomers,
compound 2 displays an exceptionally small kr value of 2.1 ×
107 s−1 (vide infra), while 4 shows a large kr value of 128 × 107
s−1. Upon an increase in the molecular length from 4, 6, 8 to
10, the kr values decrease and the knr values increase, which
stands in sharp contrast to the trend for the values in the 2,7-
linked oligomers. In particular, increasing the number of
carbazole units from 4 and 6 to 8 and 10, that is, from the two
to three units, drastically changes the kr and knr values. As a
consequence, the knr values are larger than the kr values in 8 and
10, and hence the nonradiative processes become preferable to
the radiative ones.
Interestingly, the calculated kr and knr values of 1−10 were
found to be highly dependent on the conjugation connectivity
between the thiophene and carbazole moieties and the
molecular length. With increasing molecular length in the
series of 2,7-linked oligomers 1, 3, 5, 7, and 9, the kr values
increase exclusively, and the increase in the kr values from 1 to
3 is particularly remarkable (20.8 × 107 s−1 (1), 80.6 × 107 s−1
Electrochemistry. In order to elucidate the effects of the
conjugation connectivity between the carbazole and thiophene
units and the elongation of the molecular length on the donor
ability and the electrochemical stability, we performed the CV
for 1−10 in CH2Cl2 containing 0.1 mol L−1 n-Bu4NPF6 as a
supporting electrolyte (Figure S13 in the Supporting
Information). The oxidation potentials (Epa) and onsets (Eonset
)
F
dx.doi.org/10.1021/jo402416f | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
Figure 4. Molecular orbital plots (B3LYP/6-311G(d,p)//B3LYP/6-31G(d)) of (a) 1′, (b) 2′, (c) 3′, (d) 4′, (e) 5′, (f) 6′, (g) 7′, (h) 8′, (i) 9′, and
(j) 10′. The lower plots represent the HOMOs, and the upper plots represent the LUMOs.
versus Fc+/Fc (ferrocenium/ferrocene couple) are listed in
Table 3.
Oligomers 3, 6, and 10 displayed the reversible first oxidation
waves, and 4 experienced the two reversible oxidation waves
(Figure S13e). The irreversible oxidation behavior and/or the
substantial peak amplitude were observed for 1, 2, 5, 7, 8, and
9, indicative of the instability of the cationic species. As a whole,
it seems that the connection with thiophene at the 3,6-positions
of carbazole brings about high electrochemical stability relative
to that at the 2,7-positions, which should result from the
effective resonance stabilization of the cationic species,26 in
addition to high donor ability.
Theoretical Calculations. To obtain further insight into
the electronic properties of 1−10, we performed the geo-
metrical optimization and frontier molecular orbital (FMO)
calculations of 1′−10′, where the ethyl or hexyl groups of 1−10
are replaced with the methyl groups. The FMO plots and the
HOMO and LUMO levels were obtained by the single-point
calculations at the B3LYP/6-311G(d,p)//B3LYP/6-31G(d)
level of theory. The results are summarized in Table 3, and
the HOMOs and LUMOs of 1′−10′ are shown in Figure 4.
The geometrical optimization suggests that the conjugated
backbone of 3,6-linked oligomers 8′ and 10′ presents a
deviation from planarity, while that of 2,7-linked ones 7′ and 9′
shows high planarity (Figures S15 and S16).27 This may be one
of the reasons for the lower extent of π-conjugation of 8 and 10
than 7 and 9, respectively, as found in the UV−vis spectra. All
the HOMOs and LUMOs are roughly delocalized over the
whole π-skeleton; however, both of them seem to become
gradually localized at the central part of the molecules upon an
increase in the molecular length.
As described above, we have recently found that the thienyl
functionalization at the 3,6-positions of carbazole enhances the
donor ability of the resulting molecules as compared to that at
the 2,7-positions. As a typical example, 2 is oxidized at a lower
potential than 1. This finding is reasonably explained by the
substitution pattern of the carbazole moiety. The thienyl
substituents in 1 are located at the meta positions relative to the
nitrogen atoms of the carbazole moiety, while those in 2 are at
the para positions. Noticeably, the effect of the conjugation
connectivity on the donor ability is clearly observable in 3−10.
The first Epa and Eonset values for 3,6-linked oligomers 4, 6, 8,
and 10 are cathodically shifted as compared to those for the
corresponding 2,7-linked oligomers 3, 5, 7, and 9, thus
demonstrating that the connection with thiophene at the 3,6-
positions of carbazole effectively enhances the donor ability
relative to that at the 2,7-positions in the present oligomer
architectures. From 1, 3, 5 to 7, the oxidations occur at
potentials cathodically shifted by ca. 300 mV. Similarly, the
oxidations are facilitated from 2, 4, and 6 to 8. These results
indicate that the increase in the molecular length is substantially
effective for the enhancement of the donor ability. However,
compounds 4 and 6, 7 and 9, or 8 and 10 do not differ much in
the first Epa and Eonset values, suggesting that the terminal
thiophene units in 6, 9, and 10 make almost no contribution to
the enhancement of the donor ability, which is further
supported by the calculations (vide infra).
G
dx.doi.org/10.1021/jo402416f | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
The calculated HOMO energy levels of 1′−10′ are in good
agreement with those deduced from the Eonset values of 1−10
within the range of 0.1 eV (Table 3). The calculated HOMO
levels of 2′, 4′, 6′, 8′, and 10′ are higher than those of the
corresponding 1′, 3′, 5′, 7′, and 9′, which agrees well with the
finding that 3,6-linked oligomers 2, 4, 6, 8, and 10 exclusively
display lower first Epa and Eonset values than 2,7-linked ones 1, 3,
5, 7, and 9, respectively. The enhancement of the donor ability
by the connection with thiophene at the 3,6-positions of
carbazole relative to that at the 2,7-positions is readily
interpreted as the HOMO densities. Thus, the HOMO
densities of 2′, 4′, 6′, 8′, and 10′ have a large contribution
from the electron-rich nitrogen atoms of carbazole, whereas
those of 1′, 3′, 5′, 7′, and 9′are not found on the nitrogen
atoms. An increase in the molecular length from 1′, 3′, 5′ to 7′
and 9′ raises the HOMO levels, as does that from 2′, 4′, and 6′
to 8′ and 10′. The HOMO levels of 6′, 9′, and 10′ are almost
the same as those of 4′, 7′, and 8′, respectively, suggesting that
the terminal thiophene moieties in 6′, 9′, and 10′ have a
marginal contribution to their HOMO densities. These findings
agree well with the results in the CV. It is interesting to note
that the terminal thienyl functionalization in 5′, 6′, 9′, and 10′
results in the lowering of the LUMO levels rather than the
elevation of HOMO levels.
connectivity between the carbazole and thiophene moieties in
thienylcarbazole derivatives are also generally applicable to the
oligomer architectures. In contrast to the 3,6-linked oligomers,
the increase in the molecular length of the 2,7-linked oligomers
extends π-conjugation effectively and increases radiative decay
constants. The experimentally obtained structure−property
relationships are in qualitative agreement with the findings
obtained by DFT calculations. We believe that the present
study provides valuable information for the design of new
carbazole−thiophene-based π-functional oligomers.
EXPERIMENTAL SECTION
■
General Suzuki−Miyaura Cross-Coupling Procedure for
Preparation of Carbazole−Thiophene Oligomers. A mixture of
haloarene (1 equiv) and K2CO3 (1−2 equiv) in DME/water (10:1,
∼0.2 mol L−1) was bubbled with argon with stirring for 30 min.
[Pd(PPh3)4] (ca. 2−3%, per reaction point) and boronic acid pinacol
ester were added to the mixture, and the resulting mixture was refluxed
under an argon atmosphere. The organic phase was separated, and the
aqueous phase was extracted with toluene, CH2Cl2, THF, or CHCl3.
The combined organic phase was washed with water, dried over
anhydrous MgSO4, and concentrated under reduced pressure. The
residue was purified by column chromatography. An analytically pure
material was obtained by recycling GPC eluting with CHCl3 and/or
recrystallization.
We carried out the time-dependent (TD) DFT calculations
for 1′−8′ to study the electronic transitions of 1−8 (Tables
S2−S9); the large molecular size of 9′ and 10′ prevented us
from performing the TD-DFT study. The results for absorption
maxima of 1′−8′ at the TD/B3LYP/6-31G(d)//B3LYP/6-
31G(d) level of theory are summarized in Table 1. The
absorption maxima in the low-energy region of 1′ and 3′−8′
are mainly attributed to the HOMO−LUMO transitions. On
the other hand, the absorption maximum of 2′ is related to the
mixed HOMO−1−LUMO and HOMO−LUMO+1 transi-
tions; thus, it is considered that the absorption tail around
380 nm of 2 is ascribed to the forbidden HOMO−LUMO
transition, which may be one of the reasons for its small kr and
low Φf values (vide supra).28 The calculated HOMO−LUMO
gaps (ΔEHOMO−LUMO) are approximately comparable to the
optical HOMO−LUMO gaps (ΔEopt) estimated from the UV−
vis spectra (Table 3). The calculations qualitatively reproduce
the findings that the ΔEHOMO−LUMO values become smaller
upon increasing the molecular length in 2,7-linked oligomers
1′, 3′, 5′, 7′, and 9′ and 3,6-linked oligomers 2′, 4′, 6′, 8′, and
10′ and the change in the ΔEHOMO−LUMO values in the former is
significantly larger than that in the latter (3.78 eV (1′), 4.09 eV
(2′), 3.16 eV (9′), 3.62 eV (10′)).
Preparation of 3. Compound 11 (0.10 g, 3.65 mmol) was allowed
to react with 13 (37 mg, 0.109 mmol) in the presence of K2CO3 (0.10
g, 0.729 mmol) and [Pd(PPh3)4] (25 mg, 21.9 μmol) for 15 h
according to the general Suzuki−Miyaura cross-coupling procedure.
The crude material was purified by column chromatography (SiO2,
toluene/hexane = 1:3) to give 3 (30 mg, 59%) as yellow solids. Mp
1
233−234 °C; H NMR (300 MHz, CDCl3): δ 8.11 (2H, d, J = 8.0
Hz), 8.10 (2H, d, J = 7.7 Hz), 7.67 (2H, d, J = 1.4 Hz), 7.58 (2H, dd, J
= 8.0 and 1.4 Hz), 7.46−7.49 (2H, m), 7.46 (2H, s), 7.41−7.44 (2H,
m), 7.26 (2H, d, J = 7.7 Hz), 4.45 (4H, q, J = 7.2 Hz), 1.52 (6H, t, J =
7.2 Hz); 13C NMR (150 MHz, CDCl3): δ 140.71, 140.69, 140.5,
132.2, 125.8, 124.1, 122.9, 122.6, 120.9, 120.5, 119.2, 117.3, 108.6,
abs
105.4, 37.7, 14.0; UV−vis (CH2Cl2): λmax (ε) 264 (46 100), 372
(53200) nm; HR-FAB-MS (NBA, positive): m/z calcd for C32H26N2S+
470.1817, found 470.1814 (M+).
Preparation of 4. Compound 12 (0.10 g, 3.65 mmol) was allowed
to react with 13 (37 mg, 0.109 mmol) in the presence of K2CO3 (0.10
g, 0.729 mmol) and [Pd(PPh3)4] (25 mg, 21.9 μmol) for 15 h
according to the general Suzuki−Miyaura cross-coupling procedure.
The crude material was purified by column chromatography (SiO2,
toluene/hexane = 1:3) to give 4 (13 mg, 25%) as yellow solids. Mp
183−185 °C; 1H NMR (300 MHz, CDCl3): δ 8.38 (2H, s), 8.17 (2H,
d, J = 7.8 Hz), 7.80 (2H, d, J = 7.7 Hz), 7.48−7.52 (2H, m), 7.42−7.45
(2H, m), 7.42−7.44 (2H, m), 7.36 (2H, s), 7.28 (2H, d, J = 7.8 Hz),
4.40 (4H, q, J = 7.2 Hz), 1.47 (6H, t, J = 7.2 Hz); 13C NMR (125
MHz, CDCl3): δ 140.4, 139.4, 126.01, 125.90, 123.9, 123.4, 122.98,
122.95, 120.7, 119.1, 117.4, 108.84, 108.79, 108.74, 37.6, 13.9; UV−vis
(CH2Cl2): λmax (ε) 311 (27 100), 354 (37 600) nm; HR-FAB-MS
(NBA, Positive): m/z calcd for C32H26N2S+ 470.1817, found 470.1783
(M+).
Preparation of 17. Compound 14 (1.1 g, 3.09 mmol) was allowed
to react with 16 (0.50 g, 2.38 mmol) in the presence of K2CO3 (0.66 g,
4.76 mmol) and [Pd(PPh3)4] (82 mg, 71.4 μmol) for 15 h according
to the general Suzuki−Miyaura cross-coupling procedure. The crude
material was purified by column chromatography (SiO2, toluene/
hexane = 1:5) to give 17 (0.41 g, 48%) as pale yellow solids. Mp 130−
132 °C; 1H NMR (300 MHz, CDCl3): δ 8.03 (1H, d, J = 8.2 Hz), 7.91
(1H, d, J = 8.2 Hz), 7.59 (1H, s), 7.55 (1H, d, J = 1.4 Hz), 7.52 (1H,
dd, J = 8.2 and 1.4 Hz), 7.42 (1H, dd, J = 3.7 and 1.1 Hz), 7.34 (1H, d,
J = 5.2 and 1.1 Hz), 7.31−7.33 (1H, m), 7.13 (1H, dd, J = 5.2 and 3.7
Hz), 4.35 (2H, q, J = 7.2 Hz), 1.47 (3H, t, J = 7.2 Hz); 13C NMR (125
MHz, CDCl3): δ 145.4, 141.4, 140.6, 132.6, 128.2, 124.9, 123.3, 122.3,
122.0, 121.83, 121.62, 120.9, 119.5, 118.2, 111.7, 106.0, 37.8, 13.9;
CONCLUSION
■
We have synthesized a series of structurally well-defined,
alternating carbazole−thiophene oligomers 1−10 systematically
by means of Suzuki−Miyaura cross-coupling reactions as key
steps. By comparing the electronic, photophysical, and
electrochemical properties between 2,7-linked oligomers 1, 3,
5, 7, and 9 and 3,6-linked oligomers 2, 4, 6, 8, and 10, we have
demonstrated the particular importance of the conjugation
connectivity between the carbazole and thiophene moieties and
the elongation of molecular length in their properties. It was
found that the connection with thiophene at the 2,7-positions
of carbazole causes a high extent of conjugation and high
fluorescence efficiency, while that at the 3,6-positions enhances
the donor ability. It is worth mentioning that our initial findings
about the dependence of the properties on the conjugation
H
dx.doi.org/10.1021/jo402416f | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
UV−vis (CH2Cl2): λmaxabs (relative intensity) 267 (0.935), 332 (1.00)
nm; MALDI-TOF-MS (Dith, positive): m/z 354.59 (M+). Elemental
analysis calcd (%) for C18H14BrNS·0.04CHCl3: C, 60.01; H, 3.92; N,
3.88%. Found: C, 59.92; H, 4.03; N, 3.83%.
pressure. After the residue was dissolved into CHCl3 (20 mL) and
water (20 mL), the organic phase was separated, and the aqueous
phase was extracted with CHCl3 (5 mL × 5). The combined organic
phase was washed with water (5 mL × 3), dried over anhydrous
MgSO4, and concentrated under reduced pressure. The residue was
purified by column chromatography (SiO2, toluene) to give 20 (45
mg, 18%) as white solids. An analytically pure material was obtained
Preparation of 5. Compound 17 (0.19 g, 0.536 mmol) was
allowed to react with 13 (60 mg, 0.178 mmol) in the presence of
K2CO3 (0.15 g, 1.07 mmol) and [Pd(PPh3)4] (12 mg, 10.7 μmol) for
15 h according to the general Suzuki−Miyaura cross-coupling
procedure. The crude material was purified by column chromatog-
raphy (SiO2, toluene/hexane = 1:1) to give 5 (38 mg, 33%) as yellow
1
by recycling GPC eluting with CHCl3. Mp 280 °C; H NMR (300
MHz, CDCl3): δ 8.13 (2H, d, J = 7.8 Hz), 7.90 (2H, s), 7.68 (2H, d, J
= 7.8 Hz), 4.47 (2H, q, J = 7.0 Hz), 1.46 (3H, t, J = 7.0 Hz), 1.41
(24H, s); 13C NMR (75 MHz, CDCl3): δ 140.0, 125.2, 124.9, 120.2,
115.1, 83.9, 37.5, 25.0, 14.4 (1 signal was missing); MALDI-TOF-MS
(Dith, positive): m/z 447.76 (M+). Anal. Calcd for C26H35B2NO4·
0.12CHCl3 (461.51): C, 67.98; H, 7.67; N, 3.03%. Found: C, 67.97;
H, 7.61; N, 3.14%.
1
solids. Mp 275 °C (Decomp.); H NMR (300 MHz, CDCl3): δ 8.08
(2H, d, J = 8.3 Hz), 8.07 (2H, d, J = 7.5 Hz), 7.66 (2H, s), 7.61 (2H,
s), 7.59 (2H, d, J = 8.3 Hz), 7.53 (2H, d, J = 7.5 Hz), 7.46 (2H, s),
7.43 (2H, dd, J = 3.6 and 1.1 Hz), 7.32 (2H, dd, J = 5.1 and 1.1 Hz),
7.14 (2H, dd, J = 5.1 and 3.6 Hz), 4.47 (4H, q, J = 6.9 Hz), 1.53 (6H,
t, J = 6.9 Hz); 13C NMR (150 MHz, CDCl3): δ 145.7, 144.6, 141.1,
132.38, 132.33, 128.2, 124.7, 124.2, 123.2, 122.4, 120.93, 120.88,
118.0, 117.6, 105.9, 105.5, 37.7, 14.1 (2 signals were missing); UV−vis
Preparation of 24. 2,5-Dibromothiophene (23) (42 μL, 0.374
mmol) was allowed to react with 22 (40 mg, 0.124 mmol) in the
presence of K2CO3 (52 mg, 0.374 mmol) and [Pd(PPh3)4] (4 mg, 3.7
μmol) for 6 h according to the general Suzuki−Miyaura cross-coupling
procedure. The crude material was purified by column chromatog-
raphy (SiO2, toluene/hexane = 1:10) to give 24 (9 mg, 20%) as pale
yellow solids. Mp 107−109 °C; 1H NMR (300 MHz, CDCl3): δ 8.08
(1H, d, J = 7.9 Hz), 8.07 (1H, d, J = 8.0 Hz), 7.50 (1H, s), 7.47 (1H, d,
J = 8.0 Hz), 7.41 (1H, d, J = 7.9 Hz), 7.40 (1H, d, J = 8.0 Hz), 7.23
(1H, d, J = 8.0 Hz), 7.16 (1H, d, J = 3.8 Hz), 7.07 (1H, d, J = 3.8 Hz),
4.40 (2H, q, J = 7.2 Hz), 1.47 (3H, t, J = 7.2 Hz); 13C NMR (125
MHz, CDCl3): δ 147.2, 140.3, 131.3, 131.0, 126.0, 123.2, 122.9, 122.7,
121.0, 120.6, 119.3, 117.2, 111.0, 108.6, 105.5, 37.7, 13.9 (1 signal was
abs
(CH2Cl2): λmax (ε) 269 (66 600), 401 (73 400) nm; HR-FAB-MS
+
(NBA, Positive): m/z calcd for C40H30N2S3 634.1571, found
634.1581 (M+).
Preparation of 18. Compound 15 (0.40 g, 1.13 mmol) was
allowed to react with 16 (0.18 mg, 0.871 mmol) in the presence of
K2CO3 (0.24 mg, 1.74 mmol) and [Pd(PPh3)4] (30 mg, 26.1 μmol)
for 16 h according to the general Suzuki−Miyaura cross-coupling
procedure. The crude material was purified by column chromatog-
raphy (SiO2, toluene/hexane = 1:5) to give 18 (0.16 g, 51%) as pale
yellow solids. Mp 136−137 °C; 1H NMR (600 MHz, CDCl3): δ 8.24
(1H, d, J = 1.8 Hz), 8.23 (1H, d, J = 1.9 Hz), 7.74 (1H, dd, J = 8.5 and
1.8 Hz), 7.55 (1H, dd, J = 8.6 and 1.9 Hz), 7.36 (1H, d, J = 8.5 Hz),
7.34 (1H, dd, J = 3.5 and 1.1 Hz), 7.28 (1H, dd, J = 5.1 and 1.1 Hz),
7.26 (1H, d, J = 8.6 Hz), 7.12 (1H, dd, J = 5.1 and 3.5 Hz), 4.30 (2H,
q, J = 7.2 Hz), 1.41 (3H, t, J = 7.2 Hz); 13C NMR (125 MHz, CDCl3):
δ 145.5, 139.7, 139.0, 128.7, 128.1, 126.2, 125.0, 124.6, 123.9, 123.4,
122.4, 122.2, 118.1, 111.9, 110.1, 109.1, 37.8, 13.9; UV−vis (CH2Cl2):
λmaxabs 304 nm; MALDI-TOF-MS (Dith, positive): m/z 356.57 [(M +
H)+]. Elemental analysis calcd (%) for C18H14BrNS: C, 60.68; H, 3.96;
N, 3.93%. Found: C, 60.51; H, 3.95; N, 3.94%.
abs
missing); UV−vis (CH2Cl2): λmax (relative intensity) 330 (1.00),
267 (0.97) nm; HR-FAB-MS (NBA, positive): m/z calcd for
C18H14BrNS+ 357.0010, found 357.0009 (M+).
Preparation of 7. Compound 24 (20 mg, 56.1 μmol) was allowed
to react with 20 (11 mg, 25.5 μmol) in the presence of K2CO3 (14 mg,
0.102 mmol) and [Pd(PPh3)4] (2 mg, 1.5 μmol) for 9 h according to
the general Suzuki−Miyaura cross-coupling procedure. The crude
material was purified by column chromatography (SiO2, CHCl3/
hexane = 1:1) to give 7 (12 mg, 63%) as yellow solids. Mp 295 °C
1
(Decomp.); H NMR (50 °C, 600 MHz, CDCl3): δ 8.11 (2H, d, J =
Preparation of 6. Compound 18 (0.10 g, 0.281 mmol) was
allowed to react with 13 (31 mg, 93.6 μmol) in the presence of K2CO3
(77 mg, 0.561 mmol) and [Pd(PPh3)4] (6 mg, 5.6 μmol) for 15 h
according to the general Suzuki−Miyaura cross-coupling procedure.
The crude material was purified by column chromatography (SiO2,
toluene/hexane = 1:1) to give 6 (14 mg, 24%) as yellow solids. Mp
8.2 Hz), 8.10 (2H, d, J = 7.3 Hz), 8.09 (2H, d, J = 8.0 Hz), 7.67 (4H,
s), 7.59 (2H, d, J = 8.2 Hz), 7.58 (2H, d, J = 8.0 Hz), 7.41−7.49 (8H,
m), 7.22−7.27 (2H, m), 4.44−4.52 (6H, m), 1.49−1.52 (9H, m); 13C
NMR (50 °C, 150 MHz, CDCl3): δ 145.0, 144.8, 141.3, 140.9, 140.7,
132.59, 132.40, 125.9, 124.26, 124.22, 123.1, 122.87, 122.70, 120.97,
120.93, 120.5, 119.3, 117.8, 117.5, 108.7, 105.6, 37.8, 37.8, 14.1, 14.0
1
abs
274 °C (Decomp.); H NMR (300 MHz, CDCl3): δ 8.42 (2H, d, J =
(1 signal was missing); UV−vis (CH2Cl2): λmax (ε) 407 (75 200),
1.5 Hz), 8.39 (2H, d, J = 1.6 Hz), 7.82 (2H, dd, J = 8.4 and 1.5 Hz),
7.77 (2H, dd, J = 8.4 and 1.6 Hz), 7.44 (2H, d, J = 8.4 Hz), 7.42 (2H,
d, J = 8.4 Hz), 7.39 (2H, s), 7.37−7.39 (2H, m), 7.28 (2H, d, J = 5.4
Hz), 7.14 (2H, dd, J = 5.4 and 3.6 Hz), 4.40 (4H, q, J = 7.2 Hz), 1.49
(6H, t, J = 7.2 Hz); 13C NMR (150 MHz, CDCl3): δ 145.8, 143.8,
140.06, 139.97, 128.1, 126.2, 126.1, 124.7, 124.3, 123.8, 123.5, 123.1,
122.2, 118.2, 117.7, 109.12, 109.09, 37.9, 14.0 (1 signal was missing);
325 (19 600), 265 (57 800) nm; HR-FAB-MS (NBA, positive): m/z
+
calcd for C50H39N3S2 745.2585, found 745.2603 (M+).
Preparation of 25. To a solution of 2 (0.20 g, 0.556 mmol) in
DMF (20 mL) was added dropwise N-bromosuccinimide (0.20 g, 1.11
mmol) in DMF (20 mL) under light protection, and the resulting
mixture was stirred for 2 h at room temperature. After the reaction was
quenched by adding water (100 mL), the organic phase was separated,
and the aqueous phase was extracted with toluene/EtOAc (1:1, 5 mL
× 4). The combined organic phase was washed with water (5 mL × 3),
dried over anhydrous MgSO4, and concentrated under reduced
pressure. The residue was purified by column chromatography (SiO2,
toluene/hexane = 1:3) to give 26 (0.28 g, 96%) as pale yellow solids.
Mp 172−174 °C; 1H NMR (300 MHz, CDCl3): δ 8.24 (2H, d, J = 1.8
Hz), 7.66 (2H, dd, J = 8.5 and 1.8 Hz), 7.41 (2H, d, J = 8.5 Hz), 7.06−
7.11 (4H, m), 4.38 (2H, q, J = 7.2 Hz), 1.47 (3H, t, J = 7.2 Hz); 13C
NMR (125 MHz, CDCl3): δ 147.1, 140.1, 130.9, 125.4, 124.4, 123.3,
abs
UV−vis (CH2Cl2): λmax (ε) 315 (47 700), 362 (37 100) nm;
MALDI-TOF-MS (Dith, positive): m/z 634.17 [(M + H)+].
Elemental analysis calcd (%) for C40H30N2S3·0.13CHCl3: C, 74.11;
H, 4.67; N, 4.31%. Found: C, 74.15; H, 4.96; N, 4.41%.
Preparation of 20. An n-BuLi hexane solution (2.64 M, 0.73 mL,
1.19 mmol) was added dropwise to a solution of 14 (0.20 mg, 0.566
mmol) in dry THF (20 mL) at −98 °C under an argon atmosphere.
After the mixture was stirred at −98 °C for 1.5 h, trimethoxyborane
(0.15 mL, 1.36 mmol) was added dropwise to the mixture. The
resulting mixture was stirred at room temperature for 18 h. After the
reaction was quenched by adding aqueous HCl (3 M, 40 mL), the
organic phase was separated, and the aqueous phase was extracted with
EtOAc (10 mL × 6). The combined organic phase was washed with
water (10 mL × 3), dried over anhydrous MgSO4, and concentrated
under reduced pressure to give crude diboronic acid 19 (0.14 g) as a
white solid. A mixture of the crude 19 (0.14 g) and anhydrous pinacol
(0.17 g, 1.45 mmol) in THF (25 mL) was heated at the refluxing
temperature for 20 h. The mixture was concentrated under reduced
abs
122.3, 117.9, 110.1, 109.2, 37.9, 14.0; UV−vis (CH2Cl2): λmax
(relative intensity) 317 (1.00), 269 (0.58), 256 (0.55) nm; MALDI-
TOF-MS (Dith, positive): m/z 518.37 [(M + H)+]. Elemental analysis
calcd (%) for C22H15Br2NS2: C, 51.08; H, 2.92; N, 2.71%. Found: C,
51.29; H, 3.03; N, 2.69%.
Preparation of 8. Compound 25 (27 mg, 51.9 μmol) was allowed
to react with 26 (50 mg, 0.156 mmol) in the presence of K2CO3 (24
mg, 0.171 mmol) and [Pd(PPh3)4] (4 mg, 3.1 μmol) for 20 h
according to the general Suzuki−Miyaura cross-coupling procedure.
I
dx.doi.org/10.1021/jo402416f | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
The crude material was purified by column chromatography (SiO2,
toluene/hexane = 1:1) to give 8 (25 mg, 64%) as yellow solids. Mp
290 °C (Decomp.); 1H NMR (500 MHz, CDCl3): δ 8.43 (2H, s), 8.40
(2H, s), 8.18 (2H, d, J = 7.6 Hz), 7.81 (4H, d, J = 8.0 Hz), 7.50 (2H, t,
J = 7.6 Hz), 7.43 (4H, d, J = 8.0 Hz), 7.42−7.44 (2H, m), 7.37−7.41
(4H, m), 7.28 (2H, t, J = 7.6 Hz), 4.39 (6H, q, J = 6.8 Hz), 1.47 (9H, t,
J = 6.8 Hz); 13C NMR (150 MHz, CDCl3): δ 144.0, 143.7, 140.5,
139.9, 139.5, 126.3, 126.08, 126.01, 124.3, 124.0, 123.56, 123.54,
120.7, 123.09, 123.03, 119.1, 117.79, 117.68, 109.1, 108.90, 108.79,
37.8, 14.0 (3 signals were missing); UV−vis (CH2Cl2): λmaxabs (ε) 380
(sh, 56 300), 349 (64 600), 314 (42 500) nm; MALDI-TOF-MS
(Dith, positive): m/z 745.28 (M+). Elemental analysis calcd (%) for
C50H39N3S2·0.24CHCl3: C, 77.89; H, 5.10; N, 5.42%. Found: C,
77.74; H, 5.61; N, 5.24%.
(M+). Elemental analysis calcd (%) for C26H24BrNS2·0.09CHCl3: C,
62.02; H, 4.80; N, 2.77%. Found: C, 62.05; H, 4.84; N, 2.78%.
Preparation of 9. Compound 31 (50 mg, 0.101 mmol) was
allowed to react with 32 (23 mg, 46.0 μmol) in the presence of K2CO3
(32 mg, 0.230 mmol) and [Pd(PPh3)4] (3 mg, 2.7 μmol) for 1 h
according to the general Suzuki−Miyaura cross-coupling procedure.
The yellow precipitate was collected by filtration and successively
washed with EtOAc (10 mL) and CH2Cl2 (5 mL) and recrystallized
from CHCl3/hexane twice to afford 9 (12 mg, 24%) as yellow solids.
1
Mp 269−271 °C; H NMR (80 °C, 600 MHz, 1,1,2,2-tetrachloro-
ethane-d2): δ 8.13 (2H, d, J = 7.7 Hz), 8.11 (2H, d, J = 8.6 Hz), 8.10
(2H, d, J = 8.3 Hz), 7.71 (2H, s), 7.70 (2H, s), 7.66 (2H, s), 7.60−7.64
(4H, m), 7.56 (2H, d, J = 8.3 Hz), 7.46−7.52 (6H, m), 7.37 (2H, d, J =
4.3 Hz), 7.16−7.20 (2H, m), 4.45 (2H, t, J = 7.2 Hz), 4.42 (4H, t, J =
7.3 Hz), 2.05 (2H, tt, J = 7.2 and 7.2 Hz), 2.02 (4H, tt, J = 7.3 and 7.3
Hz), 1.37−1.62 (18H, m), 0.99 (3H, t, J = 7.3 Hz), 0.97 (6H, t, J = 7.1
Hz); 13C NMR (80 °C, 150 MHz, 1,1,2,2-tetrachloroethane-d2): δ
145.6, 144.8, 141.77, 141.71, 132.42, 132.39, 132.36, 128.1, 124.7,
124.2, 123.7, 123.2, 122.45, 122.41, 122.38, 120.75, 120.70, 120.4,
118.1, 117.85, 117.81, 106.2, 105.8, 43.3, 31.5, 29.0, 27.0, 22.5, 14.0 (5
signals ascribed to the aromatic groups were missing due to the low
solubility, and 6 signals ascribed to the alkyl groups were overlapped);
UV−vis (CH2Cl2): λmaxabs (ε) 416 (81 200), 340 (sh, 24 400), 300 (sh,
19 200), 270 (65 500) nm; HR-FAB-MS (NBA, positive): m/z calcd
Preparation of 28. Compound 27 (1.90 g, 4.76 mmol) was
allowed to react with 16 (0.50 g, 2.38 mmol) in the presence of K2CO3
(0.66 g, 4.76 mmol) and [Pd(PPh3)4] (55 mg, 45.6 μmol) for 13 h
according to the general Suzuki−Miyaura cross-coupling procedure.
The crude material was purified by column chromatography (SiO2,
toluene/hexane = 1:10) to afford 28 (0.62 g, 63%) as white solids. Mp
1
118−119 °C; H NMR (300 MHz, CDCl3): δ 8.02 (1H, d, J = 8.1
Hz), 7.80 (1H, d, J = 8.2 Hz), 7.74 (1H, s), 7.57 (1H, s), 7.51 (1H, d, J
= 8.1 Hz), 7.51 (1H, d, J = 8.2 Hz), 7.41 (1H, dd, J = 4.9 and 3.5 Hz),
7.32 (1H, d, J = 4.9 Hz), 7.13 (1H, dd, J = 4.9 and 3.5 Hz), 4.26 (2H,
t, J = 7.2 Hz), 1.88 (2H, tt, J = 7.2 and 7.2 Hz), 1.23−1.48 (6H, m),
0.89 (3H, t, J = 6.7 Hz); 13C NMR (75 MHz, CDCl3): δ 145.4, 141.7,
140.9, 132.4, 128.1, 124.7, 123.2, 122.1, 121.77, 121.60, 121.41, 120.7,
119.3, 118.0, 111.7, 106.0, 43.1, 31.5, 28.8, 26.9, 22.6, 14.1; UV−vis
+
for C70H68N3S4 1078.4296, found 1078.4314 [(M + H)+]. Elemental
analysis calcd (%) for C70H67N3S4·0.43CHCl3: C, 74.87; H, 6.01; N,
3.71%. Found: C, 74.88; H, 6.11; N, 3.90%.
Preparation of 34. To a solution of 33 (0.20 g, 0.481 mmol) in
DMF (20 mL) was added dropwise N-bromosuccinimide (86 mg,
0.481 mmol) in DMF (20 mL) under light protection, and the
resulting mixture was stirred for 4 h at room temperature. The reaction
was quenched by adding water (100 mL). The organic phase was
separated, and the aqueous phase was extracted with toluene/EtOAc
(1:1, 10 mL × 4). The combined organic phase was washed with water
(10 mL × 3), dried over anhydrous MgSO4, and concentrated under
reduced pressure. The residue was purified by column chromatog-
raphy (SiO2, toluene/hexane = 1:20) to afford 34 (0.13 g, 59%) as a
yellow oil. An analytically pure material was obtained by recycling
abs
(CH2Cl2): λmax (relative intensity) 355 (sh, 0.54), 332 (0.93), 267
(1.00) nm; HR-FAB-MS (NBA, positive): m/z calcd for C22H22BrNS+
413.0636, found 413.0645 (M+).
Preparation of 29. A mixture of 28 (38 mg, 0.091 mmol), CuI
(176 mg, 0.091 mmol), and LiI (122 mg, 0.091 mmol) in DMSO (4
mL) was stirred at 150 °C for 24 h. The reaction was quenched by
adding aqueous NaHSO3 (10 mL). The organic phase was separated,
and the aqueous phase was extracted with toluene/EtOAc (1:1, 10 mL
× 4). The combined organic phase was washed with water (20 mL ×
3), dried over anhydrous MgSO4, and concentrated under reduced
pressure to afford 29 (40 mg) as white solids, which contains ca. 10%
of 28 as an inseparable material. The crude 29 was used in the next
reaction without further purification. Mp 120−122 °C; 1H NMR (300
MHz, CDCl3): δ 8.02 (1H, d, J = 8.1 Hz), 7.91 (1H, d, J = 8.2 Hz),
7.58 (1H, s), 7.54 (1H, s), 7.51 (1H, d, J = 8.1 Hz), 7.41 (1H, dd, J =
3.6 and 1.1 Hz), 7.33 (1H, d, J = 8.2 Hz), 7.32 (1H, dd, J = 5.1 and 1.1
Hz), 7.13 (1H, dd, J = 5.1 and 3.6 Hz), 4.27 (2H, t, J = 7.2 Hz), 1.89
(2H, tt, J = 7.2 and 7.2 Hz), 1.23−1.48 (6H, m), 0.89 (3H, t, J = 7.0
Hz); 13C NMR (75 MHz, CDCl3): δ 145.4, 142.0, 140.7, 132.7, 128.2,
127.9, 124.8, 123.3, 122.2, 121.86, 121.79, 120.8, 118.1, 117.8, 106.1,
1
GPC eluting with CHCl3. H NMR (300 MHz, CDCl3): δ 8.32 (1H,
d, J = 1.7 Hz), 8.24 (1H, d, J = 1.8 Hz), 7.75 (1H, dd, J = 8.5 and 1.7
Hz), 7.63 (1H, dd, J = 8.4 and 1.8 Hz), 7.39 (1H, d, J = 8.5 Hz), 7.38
(1H, d, J = 8.4 Hz), 7.36 (1H, dd, J = 3.4 and 1.1 Hz), 7.27 (1H, dd, J
= 5.3 and 1.1 Hz), 7.12 (1H, dd, J = 5.3 and 3.4 Hz), 7.09 (1H, d, J =
3.8 Hz), 7.06 (1H, d, J = 3.8 Hz), 4.29 (2H, t, J = 7.2 Hz), 1.88 (2H, tt,
J = 7.2 and 7.2 Hz), 1.24−1.44 (6H, m), 0.88 (3H, t, J = 6.4 Hz); 13C
NMR (75 MHz, CDCl3): δ 147.2, 145.6, 140.51, 140.38, 130.8, 128.1,
126.0, 125.0, 124.6, 124.0, 123.7, 123.2, 123.0, 122.1, 117.9, 117.6,
109.8, 109.27, 109.26, 43.2, 31.6, 29.0, 27.0, 22.6, 14.1 (1 signal was
missing); UV−vis (CH2Cl2): λmaxabs (relative intensity) 345 (sh, 0.59),
316 (1.00), 268 (0.66), 256 (0.61) nm; MALDI-TOF-MS (Dith,
positive): m/z 494.03 [(M+H)+]. Elemental analysis calcd (%) for
C26H24BrNS2·0.07CHCl3: C, 62.27; H, 4.82; N, 2.78%. Found: C,
62.28; H, 4.75; N, 2.77%.
Preparation of 10. Compound 34 (0.10 g, 0.202 mmol) was
allowed to react with 35 (37 mg, 91.9 μmol) in the presence of K2CO3
(63 mg, 0.460 mmol) and [Pd(PPh3)4] (6 mg, 5.5 μmol) for 18 h
according to the general Suzuki−Miyaura cross-coupling procedure.
The crude material was purified by column chromatography (SiO2,
toluene/hexane = 1:2) to afford 10 (23 mg, 23%) as yellow solids. Mp
290 °C (Decomp); 1H NMR (300 MHz, CDCl3): δ 8.43 (2H, s), 8.42
(2H, s), 8.38 (2H, d, J = 1.6 Hz), 7.81 (4H, dd, J = 8.6 and 1.5 Hz),
7.75 (2H, dd, J = 8.5 and 1.6 Hz), 7.42 (2H, d, J = 8.6 Hz), 7.38−7.41
(8H, m), 7.37 (2H, dd, J = 3.6 and 1.1 Hz), 7.26 (2H, dd, J = 4.7 and
1.1 Hz), 7.11 (2H, dd, J = 4.7 and 3.6 Hz), 4.31 (6H, t, J = 7.2 Hz),
1.91 (6H, tt, J = 7.2 and 7.2 Hz), 1.26−1.46 (18H, m), 0.85−0.93 (9H,
m); 13C NMR (150 MHz, CDCl3): δ 145.8, 143.81, 143.73, 140.50,
140.39, 128.1, 126.20, 126.15, 125.9, 124.6, 124.25, 124.19, 123.7,
123.38, 123.36, 123.34, 123.06, 123.03, 122.1, 118.0, 117.5, 109.29,
109.26, 43.4, 31.7, 29.1, 27.1, 22.7, 14.2 (9 signals were missing); UV−
vis (CH2Cl2): λmaxabs (ε) 380 (sh, 58 500), 358 (65 400), 321 (67 200)
abs
90.4, 43.2, 31.6, 28.9, 27.0, 22.6, 14.1; UV−vis (CH2Cl2): λmax
(relative intensity) 360 (sh, 0.52), 334 (0.98), 267 (1.00) nm;
MALDI-TOF-MS (Dith, positive): m/z 458.96 (M+).
Preparation of 31. Crude compound 29 (40 mg) was allowed to
react with 30 (19 mg, 65.3 μmol) in the presence of K2CO3 (18 mg,
0.131 mmol) and [Pd(PPh3)4] (7 mg, 6.5 μmol) for 2 h according to
the general Suzuki−Miyaura cross-coupling procedure. The crude
material was purified by column chromatography (SiO2, toluene/
hexane = 1:10) to afford 31 (24 mg, 65% in 2 steps) as yellow solids.
Mp 179−181 °C; 1H NMR (300 MHz, CDCl3): δ 8.05 (1H, d, J = 8.1
Hz), 8.04 (1H, d, J = 8.1 Hz), 7.59 (1H, d, J = 1.2 Hz), 7.51 (1H, dd, J
= 8.1 and 1.2 Hz), 7.48 (1H, d, J = 1.5 Hz), 7.42 (1H, dd, J = 3.6 and
1.1 Hz), 7.40 (1H, dd, J = 8.1 and 1.5 Hz), 7.32 (1H, dd, J = 5.1 and
1.1 Hz), 7.15 (1H, d, J = 3.8 Hz), 7.13 (1H, dd, J = 5.1 and 3.6 Hz),
7.08 (1H, d, J = 3.8 Hz), 4.34 (2H, t, J = 7.2 Hz), 1.92 (2H, tt, J = 7.2
and 7.2 Hz), 1.23−1.48 (6H, m), 0.89 (3H, t, J = 7.0 Hz); 13C NMR
(75 MHz, CDCl3): δ 147.2, 145.6, 141.61, 141.46, 132.4, 131.4, 131.0,
128.2, 124.8, 123.2, 122.6, 122.1, 120.91, 120.86, 118.0, 117.4, 111.1,
106.1, 105.8, 43.2, 31.6, 29.0, 27.0, 22.7, 14.2 (1 signal was missing);
abs
UV−vis (CH2Cl2): λmax (relative intensity) 380 (sh, 0.72), 357
(1.00), 270 (0.85) nm; MALDI-TOF-MS (Dith, positive): m/z 492.92
J
dx.doi.org/10.1021/jo402416f | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
nm; MALDI-TOF-MS (Dith, positive): m/z 1078.34 [(M + H)+].
Elemental analysis calcd (%) for C70H67N3S4·0.13CHCl3: C, 76.99; H,
6.18; N, 3.84%. Found: C, 76.97; H, 6.26; N, 3.80%.
(10) Dierschke, F.; Grimsdale, A. C.; Mullen, K. Synthesis 2003, 2470.
̈
(11) (a) Mishra, A.; Ma, C.-Q.; Bauerle, P. Chem. Rev. 2009, 109,
̈
1141. (b) Handbook of Thiophene-based Materials; Perepichka, I. F.,
Perepichka, D. F., Eds.; Wiley-VCH: Weinheim, 2009.
(12) For selected examples, see: (a) Morin, J.-F.; Drolet, N.; Tao, Y.;
Leclerc, M. Chem. Mater. 2004, 16, 4619. (b) Belletete, B.; Morin, J.-
̆
ASSOCIATED CONTENT
* Supporting Information
General experimental methods, X-ray data including a cif file,
fluorescence lifetime data, electrochemical data, theoretical
data, and 1H and 13C NMR spectra of all new compounds. This
material is available free of charge via the Internet at http://
pubs.acs.org.
■
S
F.; Leclerc, M.; Durocher. J. Phys. Chem. A 2005, 109, 6953. (c) Lu, J.;
Xia, P. F.; Lo, P. K.; Tao, Y.; Wong, M. S. Chem. Mater. 2006, 18,
6194. (d) Melucci, M.; Favaretto, L.; Bettini, C.; Gazzano, M.;
Camaioni, N.; Maccagnani, P.; Ostoja, P.; Monari, M.; Barbarella, G.
Chem.Eur. J. 2007, 13, 10046. (e) Khanasa, T.; Praachumrak, N.;
Rattanawan, R.; Jungsuttiwong, S.; Keawin, T.; Sudyoadsuk, T.;
Tuntulani, T.; Promarak, V. J. Org. Chem. 2013, 78, 6702. (f) Masuda,
K.; Maeda, C. Chem.Eur. J. 2013, 19, 2971.
AUTHOR INFORMATION
Corresponding Author
*E-mail: nakamura@gunma-u.ac.jp.
Notes
■
(13) Koumura, N.; Wang, Z.-S.; Mori, S.; Miyashita, M.; Suzuki, E.;
Hara, K. J. Am. Chem. Soc. 2006, 128, 14256.
(14) For selected examples of dye-sensitized solar cells, see:
(a) Wang, Z.-S.; Koumura, N.; Cui, Y.; Takahashi, M.; Sekiguchi,
H.; Mori, A.; Kubo, T.; Furube, A.; Hara, K. Chem. Mater. 2008, 20,
3993. (b) Koumura, N.; Wang, Z.-S.; Miyashita, M.; Uemura, Y.;
Sekiguchi, H.; Cui, Y.; Mori, A.; Mori, S.; Hara, K. J. Mater. Chem.
2009, 19, 4829. (c) Ooyama, Y.; Shimada, Y.; Inoue, S.; Nagano, T.;
Fujikawa, Y.; Komaguchi, K.; Imae, I.; Harima, Y. New J. Chem. 2011,
35, 111. (d) Lee, W.; Cho, N.; Kwon, J.; Ko, J.; Hong, J.-I. Chem.
Asian J. 2012, 7, 343. (e) Chen, C.; Liao, J.-Y.; Chi, Z.; Xu, B.; Zhang,
X.; Kuang, D.-B.; Zhang, Y.; Liu, S.; Xu, J. J. Mater. Chem. 2012, 22,
8994. (f) Sudyoadsuk, T.; Pansay, S.; Morada, S.; Rattanawan, R.;
Namuangruk, S.; Kaewin, T.; Jungsuttiwong, S.; Promarak, V. Eur. J.
Org. Chem. 2013, 5051. See also a review: (g) Koumura, N.; Hara, K.
Heterocycles 2013, 87, 275.
(15) Some of the 3,6-linked oligomers were reported in a patent:
Qiu, Y.; Li, Y.; Dong, H.; Wang, C. CN 101205227 A 20080625, 2008
(Tsinghua Univ., Beijing Visionox Technology Co., Ltd., Kunshan
Visionox Company) .
(16) (a) Miyaura, N.; Yanagi, T.; Suzuki, A. Synth. Commun. 1981,
11, 513. (b) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457.
(17) In contrast to the previously reported thienylcarbazole
systems,8a the rotational disorder for the thiophene units is not
observed in 6.
(18) All calculations were carried out using: Frisch, M. J.; Trucks, G.
W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.;
Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji,
H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.;
Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.;
Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao,
O.; Nakai, H.; Vreven, T.; Montgomery, Jr., J. A.; Peralta, J. E.;
Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.;
Staroverov, V. N.; Keith, T.; 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 B.01; Gaussian, Inc.: Wallingford, CT, 2010.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was financially supported by Grants-in-Aid for
Scientific Research from MEXT, Japan (No. 24550040). The
authors thank Prof. Soichiro Kyushin (Gunma University) for
generous permission to use an X-ray diffractometer.
REFERENCES
■
(1) (a) Organic Electronics: Materials, Manufacturing and Applications;
Klauk, H., Eds.; Wiley-VCH: Weinheim, 2006. (b) Organic Light
Emitting Devices: Synthesis, Properties and Applications; Mullen, K.,
̈
Scherf, U., Eds.; Wiley-VCH: Weinheim, 2006. (c) Functional Organic
Materials; Muller, T. J. J., Bunz, U. H. F., Eds.; Wiley-VCH: Weinheim,
̈
2007. (d) Organic Electroluminescence; Kakafi, Z. H., Eds.; CRC Press:
New York, 2005. (e) Carbon-Rich Compounds: From Molecules to
Materials; Haley, M. M., Tykwinski, R. R., Eds.; Wiley-VCH:
Weinheim, 2006.
(2) (a) Kelley, T. W.; Baude, P. F.; Gerlach, C.; Ender, D. E.; Muyres,
D.; Haase, M. A.; Vogel, D. E.; Theiss, S. D. Chem. Mater. 2004, 16,
4413. (b) Special issue on Organic Electronics and Optoelectronics:
Forrest, S. R., Thompson, M. E., Eds. Chem. Rev. 2007, 107, 923.
(c) Bendikov, M.; Wudl, F.; Perepichka, D. F. Chem. Rev. 2004, 104,
4891. (d) Shirota, Y.; Kageyama, H. Chem. Rev. 2007, 107, 953.
(e) Wu, W.; Liu, Y.; Zhu, D. Chem. Soc. Rev. 2010, 39, 1489.
(3) Electronic Materials: The Oligomer Approach; Mullen, K., Wegner,
C., Eds.; Wiley-VCH: Weinheim, 1998.
̈
(4) (a) Martin, R. E.; Diederich, F. Angew. Chem., Int. Ed. 1999, 38,
1350. (b) Gierschner, J.; Cornil, J.; Egelhaaf, H.-J. Adv. Mater. 2007,
19, 173.
(5) (a) Tao, N. J. Nat. Nanotechnol. 2006, 1, 173. (b) Cuevas, J. C.;
Scheer, E. Molecular Electronics: An Introduction to Theory and
Experiment; World Scientific: Singapore, 2010.
(6) For reviews, see: (a) Grazulevicius, J. V.; Strohriegl, P.;
Pielichowski, J.; Pielichowski, K. Prog. Polym. Sci. 2003, 28, 1297.
̀
(b) Morin, J.-F.; Leclerc, M.; Ades, D.; Siove, A. Macromol. Rapid
Commun. 2005, 26, 761. (c) Blouin, N.; Leclerc, M. Acc. Chem. Res.
2008, 41, 1110. (d) Boudreault, P.-L. T.; Morin, J.-F.; Leclerc, M. In
Design and Synthesis of Conjugated Polymers; Leclerc, M., Morin, J.-F.,
Eds.; Wiley-VCH; Weinheim, 2010; p 205.
(7) The recent development of carbazole-based π-functional
materials is summarized in ref 8.
(19) For details in the structural optimization, see Figure S2 in the
Supporting Information.
(20) We cannot entirely rule out the possibility that the DFT
calculations underestimate the planarity of 6, because we examined
only the B3LYP method for the calculations.
(21) For the effective conjugation length of 3,6-functionalized
carbazole derivatives, see: (a) Paliulis, O.; Ostrauskaite, J.; Gaidelis, V.;
Jankauskas, V.; Strohriegl, P. Macromol. Chem. Phys. 2003, 204, 1706.
(b) Zhao, Z.; Xu, X.; Wang, H.; Lu, P.; Yu, G.; Liu, Y. J. Org. Chem.
2008, 73, 594.
(22) No characteristic excimer fluorescence was observed.
(23) The interpretation of the fluorescence spectra was kindly
proposed by one of the referees.
(8) (a) Kato, S.-i.; Shimizu, S.; Taguchi, H.; Kobayashi, A.; Tobita, S.;
Nakamura, Y. J. Org. Chem. 2012, 77, 3222. (b) Kato, S.-i.; Noguchi,
H.; Kobayashi, A.; Yoshihara, T.; Tobita, S.; Nakamura, Y. J. Org.
Chem. 2012, 77, 9120.
(9) (a) Michinobu, T.; Osako, H.; Shigehara, K. Macromol. Rapid
Commun. 2008, 29, 111. (b) Michinobu, T.; Osako, H.; Shigehara, K.
Macromolecules 2009, 42, 8172. (c) Michinobu, T.; Osako, H.; Murata,
K.; Shigehara, K. Chem. Lett. 2010, 39, 168.
K
dx.doi.org/10.1021/jo402416f | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
(24) The emission decay profiles were numerically fitted by single
exponential kinetics.
(25) (a) Chi, C.; Wegner, G. Macromol. Rapid Commun. 2005, 26,
1532. (b) Pommerehne, J.; Vestweber, H.; Guss, W.; Mahrt, R. F.;
Bassler, H.; Porsch, M.; Daub, J. Adv. Mater. 1995, 7, 551.
(26) The quinoidal thiophene structure should contribute to the
remarkably high electrochemical stability of the cationic species of 4.
(27) We note that the optimized structures are strongly affected by
the initial structures in general. We did not perform the conformation
search for 1′−10′.
(28) The oscillator strength for the HOMO−LUMO transition of 2′
is calculated to be only 0.006 at 341 nm, and the configuration
interaction coefficient is 90%.
L
dx.doi.org/10.1021/jo402416f | J. Org. Chem. XXXX, XXX, XXX−XXX