A series of π-extended thiadiazoles fused with electron-donating heteroaromatic moieties: Synthesis, properties, and polymorphic crystals

Article abstract of DOI:10.1002/chem.201405478

π-Extended thiadiazoles 4-8 fused with various electron-donating heteroaromatic moieties have been designed and synthesized. Just like thiadiazoles 1-3 synthesized previously, 4-8 exhibit intramolecular charge-transfer (CT) interactions, moderate-to-good fluorescence quantum yields of up to 0.78, and electrochemical amphoterism. In comparison with 1-3, the benzannulation in thiadiazoles 4-7 moderately extends the p conjugation and significantly increases the stability of the cationic species formed upon electrochemical oxidation. The fluorescence quantum yields increase remarkably from 3 to 6 and 7 due to the efficient suppression of nonradiative intersystem crossing resulting from the benzannulation. The properties of 4-8 strongly reflect the different species annulated to the pyrrole rings, namely benzothiophene, naphthalene, and benzofuran. Eleven crystals, including poly- and pseudopolymorphic crystals of 1 (1-Crys.(Y ) and 1-Crys.(G)), 2 (2-Crys.(O) and 2-Crys.(G)), 4 (4-Crys.(O) and 4-Crys. (G)), and 6 (6-Crys.(O) and 6-Crys.(G)), were obtained and characterized by X-ray crystallography. The fluorescence colors and efficiencies are distinct for each poly- and pseudopolymorph of 1, 2, 4, and 6. It has been suggested that both the extent of the electronic interactions in the π-stacked dimers and the presence of excitonic interactions originating in the 1D face-to-face slipped columns affect the fluorescence wavelengths of the poly- and pseudopolymorphs.

Full text of DOI:10.1002/chem.201405478

DOI: 10.1002/chem.201405478
Full Paper
&
Donor–Acceptor Systems
A Series of p-Extended Thiadiazoles Fused with Electron-Donating
Heteroaromatic Moieties: Synthesis, Properties, and Polymorphic
Crystals
[
a]
[a]
[b]
[a]
[b]
Shin-ichiro Kato, Takayuki Furuya, Masashi Nitani, Naoya Hasebe, Yutaka Ie,
[b]
[a]
[a]
[a]
Yoshio Aso, Toshitada Yoshihara, Seiji Tobita, and Yosuke Nakamura*
Abstract: p-Extended thiadiazoles 4–8 fused with various
electron-donating heteroaromatic moieties have been
designed and synthesized. Just like thiadiazoles 1–3 synthe-
sized previously, 4–8 exhibit intramolecular charge-transfer
reflect the different species annulated to the pyrrole rings,
namely benzothiophene, naphthalene, and benzofuran.
Eleven crystals, including poly- and pseudopolymorphic
crystals of 1 (1-Crys.(Y) and 1-Crys.(G)), 2 (2-Crys.(O) and 2-
Crys.(G)), 4 (4-Crys.(O) and 4-Crys.(G)), and 6 (6-Crys.(O)
and 6-Crys.(G)), were obtained and characterized by X-ray
crystallography. The fluorescence colors and efficiencies are
distinct for each poly- and pseudopolymorph of 1, 2, 4, and
6. It has been suggested that both the extent of the elec-
tronic interactions in the p-stacked dimers and the presence
of excitonic interactions originating in the 1D face-to-face
slipped columns affect the fluorescence wavelengths of the
poly- and pseudopolymorphs.
(CT) interactions, moderate-to-good fluorescence quantum
yields of up to 0.78, and electrochemical amphoterism. In
comparison with 1–3, the benzannulation in thiadiazoles 4–
7
moderately extends the p conjugation and significantly in-
creases the stability of the cationic species formed upon
electrochemical oxidation. The fluorescence quantum yields
increase remarkably from 3 to 6 and 7 due to the efficient
suppression of nonradiative intersystem crossing resulting
from the benzannulation. The properties of 4–8 strongly
[
5]
Introduction
jugated frameworks, are of special interest because their rigid
co-planar structures promise enhanced p-conjugation and
allow the formation of dense molecular packing in the solid
state, leading to intriguing properties such as strong
fluorescence and high carrier mobility.
Flat and rigid p-conjugated organic molecules are endowed
with characteristic electronic, photophysical, and electro-
chemical properties by virtue of the delocalized electrons and
thereby are key components in organic and molecular elec-
Polarized p-conjugated chromophores consisting of strong
electron donors (D) and acceptors (A) connected by a p spacer
and thus featuring intramolecular charge-transfer (CT) interac-
tions are promising materials for diverse optoelectronic appli-
[
1]
tronics. Research into functional organic materials is con-
stantly evolving in order to fine-tune the electronic structures
of p-conjugated molecules and control their solid-state struc-
tures to obtain proper intermolecular interactions. In particular,
the latter issue is of importance because the electronic proper-
ties of p-conjugated molecules in the bulk state significantly
depend on their molecular-packing patterns. Along these lines,
p-conjugated molecules with fully ring-fused polycyclic skele-
[6,7]
cations. Recently, the intermolecular interactions in these D–
A-substituted compounds have attracted attention as a valid
force for inducing the growth of well-ordered organic nano-
and microstructures. For example, Zhang and co-workers
elegantly prepared single-crystal microtubes with rectangular
cross-sections from a D–A chromophore containing dicyano-
[2,3]
tons, such as polycyclic aromatic hydrocarbons (PAHs),
[
4]
[8]
heteroacenes, and ladder compounds with annulated p-con-
vinyl and N,N-dimethylanilino groups. Liu and co-workers
also synthesized various D–A chromophores and demonstrated
[
9]
[
a] Dr. S.-i. Kato, T. Furuya, N. Hasebe, Dr. T. Yoshihara, Prof. S. Tobita,
Prof. Y. Nakamura
Division of Molecular Science
Faculty of Science and Technology, Gunma University
that they formed hierarchically self-assembled structures. On
the other hand, we envisioned that the fusion of electron-do-
nating and -accepting heteroaromatics in ring-fused polycyclic
skeletons leads not only to the intramolecular CT interactions
characteristic of D–A-substituted compounds but also to
efficient intermolecular p–p stacking interactions in the solid
state. On this basis we recently designed and synthesized
1
-5-1 Tenjin-cho, Kiryu, Gunma 376-8515 (Japan)
E-mail: nakamura@gunma-u.ac.jp
[
b] Dr. M. Nitani, Prof. Y. Ie, Prof. Y. Aso
The Institute of Scientific and Industrial Research (ISIR)
Osaka University
[10]
six-ring fused thiadiazoles 1–3
in which highly electron-
8
-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan)
donating thienopyrrole or indole moieties are annulated to an
electron-accepting benzothiadiazole (BTD) unit to form a new
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201405478.
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[
11–16]
class of D–A-fused chromophores.
We demonstrated that
Results and Discussion
thiadiazoles 1–3 display fluorescence solvatochromism and
electrochemical amphoterism as well as forming dense p-
stacking structures. These results motivated us to synthesize
new thiadiazole congeners with further extended p systems
through benzannulation, which was expected to not only
enrich the structural scope of thiadiazole p systems, but also
create novel properties.
Synthesis
The strategy used for the synthesis of 4–8 is outlined in
Scheme 1. Just like thiadiazoles 1–3, compounds 4–8 were
synthesized from the known benzothiadiazole derivative 9 in
three steps. We first subjected 9 to Migita–Kosugi–Stille
coupling reactions with tributyl(aryl)tin derivatives to prepare
[18]
10–14 in yields of 73–89%. The double-reductive cyclization of
1
0–14 with PPh in o-dichlorobenzene (o-DCB) was carried out
3
[19]
to give the corresponding 15–19 in yields of 60–87%. It is
worth noting that 18 was obtained as the sole product by
using 13 as precursor. The observed regioselectivity of cycliza-
tion reflects the higher electron density of the carbon atom at
the 1-position of naphthalene compared with at the 2-position.
Compounds 4–8 were finally obtained by the reaction of 15–
19 with iodoethane in the presence of NaH as a base in THF.
The low yield of 5 is ascribed to the poor solubility of the
monoethylated intermediate, some of which precipitated as an
orange solid during the reaction at reflux in THF. Unfortunately,
in our hands, we were unable to obtain tributyl(3-benzo[b]fur-
[20]
yl)tin (see Scheme S1 in the Supporting Information), which
is a key reagent in the synthesis of the isomer of 8. All the
compounds were fully characterized by various spectroscopic
methods. Although the solubility of 5 is poor, compounds 4, 6,
7
, and 8 are reasonably soluble in common organic solvents
such as toluene, CH Cl , CHCl , and acetone.
2
2
3
Photophysical properties in solution
The absorption and fluorescence spectra of 4–8 were recorded
in various solvents to investigate their photophysical proper-
ties in detail, and the relevant data for discussion are summar-
ized in Table 1. We recently found that the longest absorption
abs
max
fl
max
maxima (l ) and the fluorescence maxima (l ) are increas-
ingly redshifted from 3 to 2 to 1, and not only the nature of
the aromatic rings fused with the pyrrole rings, but also their
[10]
orientation affect the photophysical properties.
Therefore
the photophysical data for 4–8 are chiefly discussed from the
viewpoint of the effects of 1) the extension of multifused
p-frameworks compared with 1–3, that is, benzannulation,
2) the nature of the aromatic rings annulated to the pyrrole
rings, that is, benzothiophene, naphthalene, and benzofuran,
and 3) their orientation.
In this study we have designed and synthesized eight-ring
fused thiadiazoles 4–7, which are dibenzo-annulated analogues
of 1–3, and 8, in which the sulfur atoms in 4 are replaced by
[
17]
oxygen atoms. By comparing the properties of 1–8, we eluci-
dated the structure–property relationships in p-extended thia-
diazoles fused with electron-donating heteroaromatic moieties.
During the course of this study we found that the compounds
presented herein, with the exception of 5, afford single crystals
that exhibit remarkable fluorescence, and that 1, 2, 4, and 6
form poly- and pseudopolymorphic crystals that show distinct
photophysical properties depending on the molecular arrange-
ment. We report herein in detail the synthesis, structural
features, and electronic, photophysical, and electrochemical
properties of 1–8 in solution, as well as their solid-state photo-
physical properties.
UV/Vis spectra
The electronic absorption spectra of 1, 2, 4, 5, and 8 and of 3,
6, and 7 in CH Cl are shown in Figure 1a and b, respectively.
2
2
Similarly to 1–3, compounds 4–8 feature broad, intramolecular
abs
CT bands with the longest l between 429 and 452 nm. The
max
abs
max
longest l values for 4 and 5 are redshifted relative to those
for 1 and 2, respectively (436 (1), 425 (2), 443 (4), and 450 nm
(5)), which has been attributed to the extension of the p con-
jugation resulting from the extension of the multifused p
abs
max
frameworks. Likewise, the longest l
values for 6 and 7 are
&
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Scheme 1. Synthesis of p-extended thiadiazoles 4–8 fused with electron-donating heteroaromatic moieties. Reagents and conditions: a) [Pd(PPh
butyl(2-benzo[b]thienyl)tin for 10, tributyl(3-benzo[b]thienyl)tin for 11, tributyl(1-naphthyl)tin for 12, tributyl(2-naphthyl)tin for 13, tributyl(2-benzo[b]furyl)tin
for 14, THF or methoxycyclopentane, reflux; b) PPh , o-dichlorobenzene (o-DCB), 1808C; c) iodoethane, NaH, THF, reflux.
3 4
) ], tri-
3
redshifted compared with that for 3 (420 nm (3), 434 nm (6),
29 nm (7)). Compounds 4 and 5 or 6 and 7 differ in not only
[
a]
Table 1. Photophysical data for 1–8 in solution.
4
abs
abs
max
fl
max
[d]
Solv.
l
[nm
l
t
f
F
f
k
r
k
nr
their longest l values, but also in the shape of the absorp-
max
[
b]
[c]
7
ꢀ
[e]
7
ꢀ
[f]
(
eV)]
[nm]
[ns]
[10 s ]
[10 s ]
tion spectra, which suggests that their electronic structures are
1
2
3
4
5
6
7
8
toluene 432 (2.88)
523
565
508
565
470
497
522
565
535
575
498
526
493
525
535
582
19.4
16.6
13.0
16.6
0.97 0.07 6.9
1.00 0.04 4.3
0.73 3.8
0.33 2.0
0.45 3.5
0.33 2.0
1.3
4.0
4.2
4.0
96
substantially dependent upon the orientation of the annulated
abs
CH Cl 436 (2.85)
toluene 423 (2.94)
CH Cl 425 (2.92)
toluene 420 (2.96)
2
2
moieties with respect to the pyrrole rings. The longest l
max
value for 8 is redshifted compared with that for 4 by 9 nm,
2
2
abs
[
g]
g]
and hence the trend of increasing l
values in the order
max
[
CH
toluene 440 (2.81)
CH Cl 443 (2.80)
toluene 447 (2.77)
CH Cl 450 (2.75)
toluene 435 (2.85)
CH Cl 434 (2.86)
toluene 428 (2.90)
CH Cl 429 (2.89)
toluene 447 (2.77)
CH Cl 452 (2.75)
2
Cl
2
420 (2.96)
95
naphthalene<benzothiophene<benzofuran holds for 4–8.
10.8
0.78 7.2
0.47 2.9
0.56 3.7
0.26 1.6
2.0
3.3
2.9
4.6
11
9.7
16
9.8
2.6
4.0
2
2
16.3
15.0
16.1
5.16 0.42 8.1
9.17 0.11 1.2
3.91 0.37 9.5
8.09 0.21 2.6
DFT calculations
2
2
To obtain further insight into the electronic properties, we con-
2
2
ducted density functional theory calculations on 4–8 as well as
[21]
on 1–3 by using the Gaussian 09 suit of programs. The fron-
2
2
tier molecular orbital (FMO) plots were obtained by performing
single-point calculations at the B3LYP/6-311G**//B3LYP/6-31G*
level of theory (Figure 2). The HOMOs of 4–8 are almost delo-
calized over the whole of the p system except for the sulfur
atom in the thiadiazole moiety, just like those of 1–3 (see Fig-
ure S20 in the Supporting Information), and thus the peripher-
al benzene rings in 4–8 contribute significantly to the HOMOs.
10.9
14.8
0.72 6.6
0.41 2.8
2
2
[
[
a] Complete data for 1–8 are included in the Supporting Information.
b] Only the longest absorption maxima are shown. [c] Fluorescence
lifetime. [d] Absolute fluorescence quantum yields were determined by
using an integrating sphere system. [e] Radiative decay constant.
[f] Nonradiative decay constant. [g] Shoulder.
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This finding again indicates the effective extension of the p
conjugation in 4–8 compared with in 1–3 by benzannulation.
In all cases, the LUMOs are mainly localized on the electron-ac-
cepting BTD moieties, and hence the peripheral benzene rings
make only marginal contributions to the LUMOs of 4–8. Intri-
guingly, the electron density distribution in the HOMOs of
compounds 4 and 5 or 6 and 7 differ depending on the orien-
tation of the annulated moieties with respect to the pyrrole
rings, which leads to the differences in their photophysical and
[22]
electrochemical properties (see below).
We performed time-dependent (TD) DFT calculations on 1–8
at the TD-B3LYP/6-31G*//B3LYP/6-31G* level of theory to eluci-
date their optical absorption properties (see Tables S6–S10 in
the Supporting Information). The absorption maxima in the
low-energy region of 4–8 can be predominantly attributed to
the HOMO–LUMO transitions as is the case with 1–3. The im-
abs
max
portant findings in relation to the calculated l values, which
are generally consistent with the absorption spectra, can be
summarized as follows. 1) Extension of the multifused p sys-
tems leads to redshifted absorptions except in the cases of
1
and 4 (458 nm (1), 454 nm (4)). 2) The difference in the orien-
tation of the annulated moieties with respect to the pyrrole
Figure 1. UV/Vis absorption spectra of a) 1, 2, 4, 5, and 8 and b) 3, 6, and 7
in CH Cl at room temperature. The data for 5 are plotted with arbitrary
intensity due to its low solubility.
rings in 4 and 5 or 6 and 7 causes distinct differences in the
2
2
abs
calculated longest l
(454 nm (4), 484 nm (5), 466 nm (6),
max
444 nm (7)). 3) The replacement of sulfur atoms by oxygen
atoms in the electron-donating heteroaromatic moieties results
abs
max
in a moderate redshift of the calculated longest l
(454 nm
(
4), 466 nm (8)).
Fluorescence spectra
Figure 3 shows the fluorescence spectra of 1–8 in CH Cl . Simi-
2
2
abs
larly to the change in the longest l values for 1–8 described
max
fl
max
above, the l values are generally redshifted by benzannula-
fl
max
tion. Thus, 5–7 display redshifted l
values relative to the
corresponding 2 and 3 by about 20–30 nm, although 1 and 4
fl
accidentally show identical values of l of 565 nm. Moreover,
max
abs
max
fl
max
as is the case with the longest l values, the l values for
4
–8 are redshifted by changing the moieties annulated to the
pyrrole rings from naphthalene, benzothiophene, to benzofur-
fl
max
an: The l values for 4, 6, and 8 in CH Cl are 565, 526, and
2
2
5
82 nm. Consequently, compound 8 has the longest observed
fl
l
among all the compounds in this study.
max
Notably, pronounced positive fluorescence solvatochromism
is observed for 4–8, whereas the absorption spectra of 4–8
show only slight changes between those recorded in nonpolar
[23]
toluene and polar DMF (Table 1).
The solvent-dependent
spectral changes observed for 4–8 are essentially identical to
those observed for 1–3 previously. Figure 4 shows the fluores-
fl
max
cence spectra of 4 in different solvents. The l values are re-
markably redshifted upon increasing the solvent polarity from
toluene to DMF (522 nm in toluene, 570 nm in DMF), and the
color of the fluorescence changes from green to yellow (see
Figure S9 in the Supporting Information). This clearly indicates
that 4–8 have a more polar electronic structure in the excited
state, namely an intramolecular CT state, than in the ground
state.
Figure 2. Molecular orbital plots (B3LYP/6-311G**//B3LYP/6-31G*) for a) 4,
b) 5, c) 6, d) 7, and e) 8. The lower plots represent the HOMOs, the upper
plots represent the LUMOs.
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3
. The extension of the multifused p frameworks from 1 and 2
to 4 and 5 results in marginal changes in the F values; 4 and
f
5
exhibit F values of 0.47–0.78 and 0.26–0.63, respectively
f
(
see Table S2 in the Supporting Information for the complete
data). Unexpectedly, 6 and 7 display very high F values (0.11–
f
0.43 for 6 and 0.21–0.42 for 7) compared with 3. Nevertheless,
the annulation of benzothiophene moieties to the pyrrole
rings is likely to yield higher F values than the annulation of
f
naphthalene moieties. Comparing 4 and 8, the replacement of
sulfur atoms by oxygen atoms has almost no effect on the
fluorescence efficiency; the F values for 8 (0.34–0.72) are
f
comparable to those of 4.
To obtain further insight into the photophysical properties
of 1–8, we determined their fluorescence lifetimes (t ) by using
f
the time-correlated single-photon counting method and calcu-
lated the radiative (k ) and nonradiative (k ) decay rate con-
r
nr
stants from the singlet excited state according to k =F /t and
r
f
f
k =(1ꢀF )/t (Table 1). No pronounced differences in the t
nr
f
f
f
values are observable upon extension of the multifused p
frameworks from 1 and 2 to 4 and 5, respectively; the tf
Figure 3. Fluorescence spectra of a) 1, 2, 4, 5, and 8 (lex =370, 380, 390, 400,
and 400 nm, respectively) and b) 3, 6, and 7 (lex =370, 390, and 400 nm,
values for 4 (10.8–16.6 ns) are slightly shorter than those for
respectively) in CH
dentally overlap.
2 2
Cl at room temperature. The spectra of 6 and 7 acci-
1
(16.6–24.2 ns) , and the t values for 5 (15.0–17.0 ns) are simi-
f
lar to those for 2 (13.0–16.8 ns). The values of both k and k
r
nr
for 4 are larger than those for 1, whereas the values of k and
r
knr for 5 are comparable to those for 2. The t , k, and k values
f
r
nr
for 8 are similar to those for 4, which demonstrates that the re-
placement of sulfur atoms by oxygen atoms in the electron-
donating heteroaromatic moieties barely affects the radiative
and nonradiative processes. Notably, 6 and 7 show very high tf
values compared with 3 (0.97–1.07 ns (3), 5.16–9.29 ns (6),
3
1
1
.91–8.09 ns (7)). The calculated k values for 6 and 7 ((6.1–
nr
7
ꢀ
5)ꢁ10 s ) are significantly smaller than those for 3 ((89–96)ꢁ
7
ꢀ
0 s ), whereas the k values for 6 and 7 are comparable to
r
those for 3. Time-resolved photoacoustic measurements gave
Fisc values in toluene of 0.61 and 0.67 for 6 and 7, respectively,
which are almost two-thirds the value for 3 (see Figures S10–
[24]
S12 in the Supporting Information). In 6 and 7, as is the case
with 3, the sum of F and F is almost equal to 1, within ex-
f
isc
perimental error, which clearly indicates on the basis of the
Figure 4. Fluorescence spectra of 4 in different solvents upon excitation at
390 nm at room temperature.
equation F +F +F =1, in which F is the quantum yield
f
isc
ic
ic
of internal conversion, that internal conversion in 6 and 7
barely occurs. From these results it can be concluded that
The absolute fluorescence quantum yields (F ) for 1–8 in
higher values of F for 6 and 7 than for 3 derive from the ef-
f
f
various solvents were determined by using an integrating
sphere system (Table 1). We could not find any general
fective suppression of intersystem crossing by benzannulation.
relationship between the solvent polarity and the F values for
f
Electrochemical properties
1
–8. The F values in CH Cl for most compounds seem to be
f 2 2
lower than those in other solvents, although the reason for
this is unclear at present. We recently demonstrated that the
moieties annulated to the pyrrole rings significantly affect the
We performed cyclic voltammetry (CV) experiments on 1–8 in
ꢀ
1
+
o-DCB (0.1 molL nBuNPF , standard Fc /Fc) to investigate
6
[25]
their electrochemical properties (Table 2).
As described
[
10]
fluorescence efficiency. Compounds 1 and 2 display moder-
above, we recently found that 1–3 display amphoteric electro-
chemical behavior due to the presence of the electron-with-
drawing BTD moiety and the electron-donating thienopyrrole
ate-to-high F values of 0.33–0.73 and 0.34–0.51, respectively,
f
whereas 3 displays significantly low F values of 0.04–0.07. The
f
quantum yields (F ) for intersystem crossing in 1, 2, and 3 in
toluene are 0.26, 0.56, and 0.94, respectively. Thus, the ex-
or indole moieties. Compounds 1–3 have similar acceptor
isc
red
abilities; they exhibit almost the same reduction onsets (E ).
onset
tremely fast intersystem crossing to the triplet state in 3 com-
On the other hand, they differ in their donor ability, with 1 and
ox
pared with in 1 and 2 is responsible for the low F values for
2 showing oxidation onsets (E ) cathodically shifted relative
f
onset
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and ꢀ6.23 eV, respectively, at the B3LYP/6-311G**//
Table 2. Oxidation and reduction potentials of 1–8 determined by CV in o-DCB
[26]
ꢀ
1
[a]
[b]
B3LYP/6-31G* level of theory. In the series 4–8, the
(0.1 molL nBuNPF
6
), theoretically calculated HOMO and LUMO levels, and electro-
chemical (DEredox) and optical energy gaps (DEopt).
trend in the electrochemical HOMO–LUMO gaps
ox
(
DEredox) almost corresponds to that of the E
onset
ox
onset
red
onset
E
(Epa
)
E
(Epc
)
HOMO LUMO DEredox
DEopt
values, and a good correlation exists between the
[
c]
[d]
[
V]
[V]
[eV]
[eV]
[V]
[eV]
DEredox values and the optical HOMO–LUMO gaps
[
e]
g]
[f]
1
2
3
4
5
6
7
8
+0.31 (+0.46)
ꢀ2.23 (ꢀ2.42)
ꢀ5.18
ꢀ5.24
ꢀ5.52
ꢀ5.18
ꢀ2.00
ꢀ1.91
ꢀ2.13
ꢀ2.00
ꢀ2.07
ꢀ2.07
ꢀ2.12
ꢀ2.03
2.54
2.65
2.84
2.50
2.48
2.66
2.71
2.42
2.85
2.92
2.96
2.80
2.75
2.86
2.89
2.74
(
DEopt).
[
[f]
+0.40 (+0.59) (+1.12)
ꢀ2.25 (ꢀ2.51)
[
e]
[f]
Compounds 1–8 show quasireversible or reversible
+0.62 (+0.77)
ꢀ2.22 (ꢀ2.39)
[f]
[f]
+0.35 (+0.51) (+1.01)
ꢀ2.15 (ꢀ2.33)
reduction waves, and although the first oxidation
waves for 1–3 are quasireversible or irreversible,
those for 4–8 are reversible. Moreover, in contrast to
1 and 3, which show a large peak amplitude after
the first oxidation, reversible second oxidation waves
are observable for 4, 5, 7, and 8. These results dem-
onstrate that the benzannulation effectively enhances
the stability of the cationic species formed upon
electrochemical oxidation.
[f]
[g]
+0.27 (+0.39) (+0.83)
ꢀ2.21 (ꢀ2.34) ꢀ5.14
[f]
[f]
+0.40 (+0.56) (+1.09)
ꢀ2.26 (ꢀ2.48)
ꢀ5.19
ꢀ5.37
ꢀ5.11
[f]
[f]
+0.50 (+0.65) (+1.34)
ꢀ2.21 (ꢀ2.40)
[f]
[f]
+0.27 (+0.39) (+0.89)
ꢀ2.15 (ꢀ2.31)
+
[
a] All potentials are given versus the Fc /Fc couple used as external standard. Scan
rate: 100 mVs . [b] Calculated at the B3LYP/6-311G**//B3LYP/6-31G* level of theory.
ꢀ1
[
E
c] The electrochemical gap, DEredox, is defined as the potential difference between
ox
red
and E . [d] The optical gap, DEopt, is defined as the energy corresponding to
onset
onset
abs
the l
2 2
in CH Cl . [e] Irreversible wave. [g] Quasireversible wave. [f] Reversible wave.
max
Photoluminescent colors of the crystals
to 3, which apparently reflects the difference in the electron-
donating ability of thiophene and benzene. As expected, 4–8
also show amphoteric electrochemical behavior within the
available potential window (Figure 5).
Organic molecules that exhibit solid-state emissions have at-
tracted considerable attention not only in the fundamental re-
search of their photophysical properties, but also in materials
[
27]
science. It is well known that most organic fluorophores are
almost nonluminescent or only faintly emissive in the solid
state, even if they are highly emissive in solution, owing to the
concentration quenching caused by intermolecular interaction-
[
27a,28]
s.
We obtained 11 single crystals of 1–4 and 6–8 (see Fig-
[29]
ure S5 in the Supporting Information), including poly- and
pseudopolymorphic crystals of 1 (1-Crys.(Y) and 1-Crys.(G)), 2
(
(
2-Crys.(O) and 2-Crys.(G)), 4 (4-Crys.(O) and 4-Crys.(G)), and 6
6-Crys.(O) and 6-Crys.(G)), suitable for X-ray crystallographic
analysis, and found that most of them show remarkable fluo-
rescence (Figures 6 and S6). It is considered that in the thiadia-
zole derivatives presented herein, the energy transfer in the ex-
cited state is substantially inhibited owing to large Stokes
shifts, that is, the small overlap between the UV/Vis and fluo-
rescence spectra, which leads to the observed solid-state fluo-
rescence.
Figure 5. Cyclic voltammograms of a) 4, b) 5, c) 6, d) 7, and e) 8 measured in
ꢀ
1
ꢀ1
o-DCB (0.1 molL nBuNPF
6
) at a scan rate of 100 mVs .
red
onset
No pronounced difference in the E
values (ꢀ2.26 to
ox
ꢀ
2.15 V) was observed for 1–8, but their E
values turned
onset
out to be significantly dependent on the structure. Although
ox
onset
the E
value for 4 is only slightly more anodic than that for
ox
Figure 6. Photographs of a) 1-Crys.(Y), b) 1-Crys.(G), c) 2-Crys.(O), d) 2-
Crys.(G), e) 3-Crys., f) 4-Crys.(G), g) 6-Crys.(O), h) 6-Crys.(G), i) 7-Crys., and
j) 8-Crys. under UV irradiation (365 nm).
1
(+0.31 V (1), +0.35 V (4)), the Eonset value for 5 is more
cathodic than that for 2 (+0.40 V (2), +0.27 V (5)), and the
values for 6 and 7 are also more cathodic than that for 3
(
+0.62 V (3), +0.40 V (6), +0.50 V (7)). This finding indicates
that the benzannulation essentially enhances the donor ability.
From 6 and 7, 4 and 5, to 8, the oxidations occur cathodically,
which reflects the differences in the electron-donating ability
of naphthalene, benzothiophene, and benzofuran; the HOMO
levels of these moieties were calculated to be ꢀ6.04, ꢀ6.10,
X-ray crystal structures
We recently reported that the crystallization of 1 and 2 by
vapor diffusion of hexane into CH Cl solutions of the mole-
2
2
&
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cules afforded the crystals 1-Crys.(Y) and 2-Crys.(G), respec-
p-stacked fashion at a distance of 3.34–3.76 ꢂ. In contrast, in
1-Crys.(G) as well as in the crystal of 3 (abbreviated as 3-Crys.),
two neighboring molecules are mutually almost orthogonal,
with the molecules lying in parallel with a combination of p–p
and CH–p interactions between the ethyl groups and the p
planes. In the p-stacked dimer structures described above, the
electron-donating moieties, namely thienopyrrole, indole, ben-
zothienopyrrole, benzindole, or benzofuropyrrole, overlap with
the electron-withdrawing BTD moieties, which suggests the
presence of intermolecular CT interactions; no p-stacked dimer
structure was observed in the crystal of 7 (abbreviated as 7-
Crys.). The polymorphs 1-Crys.(Y) and 1-Crys.(G), 2-Crys.(O)
and 2-Crys.(G), and 6-Crys.(O) and 6-Crys.(G) differ in the
extent of overlap and/or the distance between the two p
planes in their p-stacked dimers, whereas the dimer structure
of pseudopolymorph 4-Crys.(O) is almost identical to that of
4-Crys.(G). The X-ray structures of the poly- and pseudopoly-
morphs of 1, 2, 4, and 6 are discussed further below, mainly
from the viewpoint of their molecular arrangements.
[
10]
tively (Figure 6 a,d); the crystals 1-Crys.(G) and 2-Crys.(O)
Figure 6b,c) were obtained as minor products under the same
crystallization conditions, that is, 1-Crys.(Y) and 1-Crys.(G) or
-Crys.(G) and 2-Crys.(O) were obtained concomitantly. Like-
(
2
wise, vapor diffusion of hexane into a CH Cl2 solution of 6
2
gave 6-Crys.(G) as the major product along with 6-Crys.(O) as
the minor product (Figure 6g,h). We could not find the crystal-
lization conditions for the selective formation of specific poly-
morphs of 1, 2, and 6, even after repeated trials. However, we
were able to isolate the different polymorphs by hand by
using a microscope because of their different colors and
shapes (see Figure S5 in the Supporting Information), which
allowed the polymorphs to be characterized individually. The
selective formation of two polymorphs of 4 was achieved by
changing the solvent of recrystallization. Thus, pseudo-
polymorphs 4-Crys.(O) and 4-Crys.(G) were obtained by vapor
diffusion of hexane into CH Cl2 and toluene solutions of 4,
2
respectively; toluene molecules are included in a 4:1 stoichio-
[
30]
metry in 4-Crys.(G).
Packing structures
p-Stacked dimer structures
Figure 8 shows the packing diagrams for the crystal structures
In 1-Crys.(Y), 2-Crys.(O), 2-Crys.(G), 4-Crys.(O), 4-Crys.(G), 6-
Crys.(O), and 6-Crys.(G) as well as in the crystal of 8 (abbreviat-
of 1, 2, 4, and 6. With the exception of 6-Crys.(G), 1D molecu-
[
31]
ed as 8-Crys.), two neighboring molecules form p-stacked
dimer structures in a head-to-tail arrangement to cancel the
dipole (Figures 7 and S4 in the Supporting Information). In the
dimers, the molecules are arranged longitudinally in a slipped
Figure 8. Molecular packing in crystals of a) 1-Crys.(Y), b) 1-Crys.(G),
c) 2-Crys.(O), d) 2-Crys.(G), e) 4-Crys.(O), f) 4-Crys.(G), g) 6-Crys.(O), and
h) 6-Crys.(G). The solvent molecules in 4-Crys.(G) have been omitted for
clarity. The structures of 1-Crys.(Y) and 2-Crys.(G) have been reported previ-
ously. The packing structures of 3-Crys., 7-Crys., and 8-Crys. are included
in the Supporting Information.
Figure 7. Arrangement of neighboring molecules in the polymorphs of a) 1-
Crys.(Y), b) 1-Crys.(G), c) 2-Crys.(O), d) 2-Crys.(G), e) 4-Crys.(O), f) 4-Crys.(G),
g) 6-Crys.(O), and h) 6-Crys.(G).
[
10]
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lar networks are observed. In 1-Crys.(Y), 2-Crys.(O), 4-Crys.(O),
and 6-Crys.(O), the p-stacked dimers interact with other p-
stacked dimers through p–p stacking interactions to form 1D
face-to-face slipped-column structures (Figure 8a,c,e,g). The
angles (qp-stack) between the p planes and the stacking axes in
1-Crys.(Y), 4-Crys.(O), and 6-Crys.(O) are almost identical,
whereas that in 2-Crys.(O) is significantly larger (qp-stack =318
for 1-Crys.(Y), 698 for 2-Crys.(O), 328 for 4-Crys.(O), and 368
for 6-Crys.(O)). The columns in 1-Crys.(Y) and 6-Crys.(O) as-
semble through weak S–H (2.84 ꢂ for 1-Crys.(Y) and 3.05 ꢂ for
6-Crys.(O)) interactions, whereas the columns in 4-Crys.(O) as-
semble through S–p (3.40 ꢂ) interactions. In 2-Crys.(O), no fa-
vorable interaction between neighboring columns is observed.
The packing motifs of 1-Crys.(G), 2-Crys.(G), 4-Crys.(G), and
6-Crys.(G) are apparently different to those of the correspond-
ing 1-Crys.(Y), 2-Crys.(O), 4-Crys.(O), and 6-Crys.(O). In 1-
Crys.(G), the dimers of 1 form cross-stacked columns along
the c axis, and the columns assemble through weak S–H
(2.99 ꢂ) interactions (Figure 8b). The dimers in 2-Crys.(G) are
packed in a sandwich-herringbone motif with a 1D array along
the b axis as a result of S–S (3.59 ꢂ) and CH–p interactions (Fig-
ure 8d). The dimers in 4-Crys.(G) provide 1D brick-like columns
along the b axis through p–p stacking (3.39 and 3.48 ꢂ) and S–
[
32]
S (3.29 ꢂ) interactions (Figure 8f). In 6-Crys.(G), the dimers
interact with other dimers through CH–p interactions, and typ-
ical edge-to-face herringbone structures are formed (Fig-
ure 8h). The packing motifs of the polymorphs of 1, 2, and 6
may reflect the structural features of the p-stacked dimers,
such as the orientation, the extent of overlap, and the distance
[
33]
between conjugated p planes. The significant differences in
the packing structures of 4-Crys.(O) and 4-Crys.(G) can be
attributed to the fact that molecules of toluene from the
[
34]
recrystallization solvent are included in 4-Crys.(G).
The p-stacked dimers in 3-Crys. form a cross-stacked
column structure as is the case with 2-Crys.(G) (see Figure S1a
in the Supporting Information). On the other hand, the dimers
in 8-Crys. form a 1D face-to-face slipped column structure
(see Figure S1d) as observed in 1-Crys.(Y), 4-Crys.(O), and
6-Crys.(O).
Solid-state photophysical properties
We recorded the fluorescence emission and excitation spectra
of crystalline samples of 1–4 and 6–8 to investigate their solid-
Figure 9. Fluorescence excitation (Ex: dashed lines) and emission (Fl: solid
lines) spectra of the poly- and pseudopolymorphs: a) 1-Crys.(Y) and
1-Crys.(G), b) 2-Crys.(O) and 2-Crys.(G), c) 4-Crys.(O) and 4-Crys.(G), and
d) 6-Crys.(O) and 6-Crys.(G). An excitation wavelength of 390 nm was used
for 1-Crys.(Y), 1-Crys.(G), 2-Crys.(O), and 2-Crys.(G), and of 400 nm for
[35,36]
state photophysical properties (Figure 9 and Table 3).
The
flðsolidÞ
emission maxima (lmax ) of the crystals are redshifted by 13–
flðtolÞ
80 nm relative to the corresponding emission maxima (lmax ) in
toluene, in which the contribution from solvent stabilization
should be less than that from other solvents. The largest differ-
4
-Crys.(O), 4-Crys.(G), 6-Crys.(O), and 6-Crys.(G). The fluorescence excitation
spectra of 1-Crys.(Y), 1-Crys.(G), 2-Crys.(O), 2-Crys.(G), 4-Crys.(O), 4-Crys.(G),
6-Crys.(O), and 6-Crys.(G) were monitored at 630, 620, 580, 580, 600, 580,
610, and 520 nm, respectively.
flðsolidÞ
flðtolÞ
ence between the l
and l
values is found in 6-
max
max
flðsolidÞ
flðtolÞ
Crys.(O) (l
=578 nm, l
=498 nm); the fluorescence
max
max
colors of 6-Crys.(O) and a toluene solution of 6 are orange and
flðsolidÞ
green, respectively (Figure 6g). Accordingly, the lmax value
solid
for 6-Crys.(O) is redshifted compared with those for 4-Crys.(O)
and 4-Crys.(G), although 4 shows a redshifted fluorescence
608 nm (Figure 6j). The fluorescence quantum yields (Ff ) in
the solid state are lower than those in toluene solution. It
flðsolidÞ
maximum relative to 6 in toluene. Of the crystals described
would appear that the substantial redshifts of l
and the
max
flðsolidÞ
solid
here, 8-Crys. exhibits the most redshifted lmax
value of
lower values of Ff observed in the solid-state fluorescence
&
&
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of 1-Crys.(Y), 2-Crys.(O), and 6-Crys.(O) relative to those of 1-
[
a]
Table 3. Photophysical data for the crystalline samples of 1–4 and 6–8.
[40]
Crys.(G), 2-Crys.(G), and 6-Crys.(G). The intermolecular dis-
tances (d) between the center of the BTD moiety and the p
plane of the facing molecule in 2-Crys.(O) and 6-Crys.(O) are
larger than those in the corresponding 2-Crys.(G) and 6-
Crys.(G); the d values in 2-Crys.(O), 2-Crys.(G), 6-Crys.(O), and
flðsolidÞ
ex
max
solid[b]
l
[nm]
l
[nm]
Ff
max
1
1
2
2
3
4
4
6
6
7
8
-Crys.(Y)
-Crys.(G)
-Crys.(O)
-Crys.(G)
-Crys.
584
557
580
534
505
566
545
578
511
520
608
551
500
526
490
462
517
500
536
478
471
569
0.14
0.10
0.19
0.13
0.03
<0.01
0.17
0.25
0.03
0.11
[
c]
6-Crys.(G) are 3.76, 3.45, 3.54, and 3.39 ꢂ, respectively. This
suggests that the extent of overlap of the p-conjugated planes
has a larger effect on the electronic structures of the dimers
than the intermolecular distances. Overall, it is considered that
the photophysical properties of the crystalline samples mainly
reflect the electronic features of the p-stacked dimers deter-
mined by a delicate balance of the arrangement (orientation,
distance, and extent of overlap) of the p-conjugated planes.
In addition to the electronic coupling of neighboring mole-
-Crys.(O)
[
d]
-Crys.(G)
-Crys.(O)
-Crys.(G)
-Crys.
[
e]
-Crys.
0.11
[
a] The data for powder samples obtained by grinding the crystals are in-
cluded in the Supporting Information. [b] The absolute quantum yields
were determined by using an integrating sphere system. [c] Shoulder.
[41]
[d] (4)
4
·toluene. [e] 8·(CHCl
3
)
2
.
cules, the excitonic coupling interactions of the transition
dipole moments of the molecules, which extend further than
solely the nearest neighbors, affect the solid-state optical and
[37]
[42]
mainly derive from intermolecular p–p-stacking interactions;
photophysical properties. According to the electron distribu-
solid
the reason for the extremely low value of Ff
(<0.01) for
tion in the HOMOs and LUMOs of 1–8 (Figure 2), their transi-
tion dipole moments are oriented along the long axis of the
molecules (Figure 10). The qp-stack values in 1-Crys.(Y), 4-
4
-Crys.(O) is not clear at present.
flðsolidÞ
Intriguingly, both the l
values and the fluorescence ex-
max
ex
max
citation maxima (l ) are different for 1-Crys.(Y) and 1-
Crys.(G), 2-Crys.(O) and 2-Crys.(G), 4-Crys.(O) and 4-Crys.(G),
and 6-Crys.(O) and 6-Crys.(G), with crystals of 1-Crys.(Y), 2-
Crys.(O), 4-Crys.(O), and 6-Crys.(O) exhibiting redshifted fluo-
rescence emission and excitation spectra in comparison with
1-Crys.(G), 2-Crys.(G), 4-Crys.(G), and 6-Crys.(G), respectively,
by 17–67 nm (Table 3). This finding clearly indicates that the
electronic and photophysical properties of crystals of 1, 2, 4,
and 6 depend on the arrangements of the p-conjugated
molecules; effects of the toluene molecules in 4-Crys.(G) on
Figure 10. Schematic representation of the transition dipole moment of 4.
The total transition moment is qualitatively shown by the arrow.
flðsolidÞ
ex
[38]
the l
and l values cannot be excluded.
max
max
To assess the effects of the electronic structures of the p-
stacked dimers, namely the smallest supramolecular units, on
the solid-state emission of the poly- and pseudopolymorphs,
we conducted single-point calculations (B3LYP/6-311G**) on
the isolated monomers and p-stacked dimers of 1, 2, 4, and 6
on the basis of their X-ray crystal structures (see Table S4 in
the Supporting Information). The calculated HOMO–LUMO
gaps (DEH-L) of the dimers of 1, 2, 4, and 6 are all smaller than
those of the corresponding monomers by 0.02–0.25 eV; in gen-
eral the HOMO levels increase and the LUMO levels decrease
Crys.(O), and 6-Crys.(O) (31, 32, and 368, respectively) as well
as that in 8-Crys. (378) are apparently less than the “magic
[43]
angle” of 54.78 of Kasha’s exciton theory. Consequently, it is
likely that the packing modes, namely 1D face-to-face slipped
column structures, in polymorphs 1-Crys.(Y), 4-Crys.(O), and 6-
Crys.(O) as well as 8-Crys. mainly contain the components of
J-type aggregates. The unique properties of the J-aggregates
[
44]
include redshifted fluorescence and narrowed bandwidths,
flðsolidÞ
and thus the redshifted lmax values of 1-Crys.(Y), 4-Crys.(O),
and 6-Crys.(O) compared with those of 1-Crys.(G), 4-Crys.(G),
and 6-Crys.(G), respectively, have in part been attributed to
[
39]
from the monomers to the dimers. The difference (0.02 eV)
between the DEH-L values for the monomer and dimer in 6-
Crys.(G) is particularly small compared with those for other
crystals, which may reflect the relatively small overlap of the
p-conjugated planes in the dimer molecules in 6-Crys.(G) (Fig-
ure 7h). Notably, the DEH-L values of the dimers in 1-Crys.(Y),
the J-aggregate-derived excitonic coupling interactions in the
flðsolidÞ
former. Again, the remarkably redshifted l
of 8-Crys. rela-
max
flðtolÞ
tive to the l
of 8 by 73 nm is thought to be due to the for-
max
mation of J-aggregates in the crystalline state; however, the
CHCl molecules included in 8-Crys. are also likely to affect its
3
flðsolidÞ
[45]
2-Crys.(O), and 6-Crys.(O) are less than those in 1-Crys.(G), 2-
l
value.
The full widths at half-maximum height
max
Crys.(G), and 6-Crys.(G), respectively, by 0.14–0.23 eV, whereas
the DEH-L value of the dimer in 4-Crys.(O) is comparable to
that in 4-Crys.(G). These results suggest that the electronic
coupling interactions in the dimers in 1-Crys.(Y), 2-Crys.(O),
and 6-Crys.(O) are stronger than those in 1-Crys.(G), 2-
Crys.(G), and 6-Crys.(G), respectively, which should be respon-
(FWHMs) of the emission bands of 6-Crys.(O) and 8-Crys. are
apparently narrower than those of 6 and 8 in toluene, respec-
ꢀ
1
tively (FWHM=1470, 1600, 2550, and 2550 cm for 6-Crys.(O),
8-Crys., 6 in toluene, and 8 in toluene, respectively). On the
other hand, the FWHMs of the emission bands of 1-Crys.(Y)
and 4-Crys.(O) are almost comparable to those of 1 and 4 in
toluene, respectively (FWHM=2200, 2290, 2610, and
flðsolidÞ
ex
sible for the pronounced redshifts in the lmax and l values
max
Chem. Eur. J. 2014, 20, 1 – 15
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ꢀ
1
2
560 cm for 1-Crys.(Y), 4-Crys.(O), 1 in toluene, and 4 in tol-
resulting mixture was heated at reflux. The mixture was cooled to
room temperature, and the solvent removed in vacuo. The residue
was subjected to column chromatography.
uene, respectively), which implies moderate excitonic interac-
tions in 1-Crys.(Y) and 4-Crys.(O). Although the molecules in
General procedure for PPh -mediated reductive cyclization
reactions: Argon was bubbled through a mixture of dinitro com-
2
-Crys.(O) also form 1D face-to-face slipped column structures,
3
the slip angle (698) in 2-Crys.(O) is larger than those in 1-
Crys.(Y), 4-Crys.(O), and 6-Crys.(O), and the extent of overlap
of the p planes in 2-Crys.(O) is greater than those in 1-
Crys.(Y), 4-Crys.(O), and 6-Crys.(O). This finding implies that 2-
pounds 10–14 (1 equiv) and PPh (10 equiv) in o-DCB for 15 min
3
with stirring at 1808C. The mixture was cooled to room tempera-
ture, and the solvent removed in vacuo. The residue was subjected
to column chromatography.
Crys.(O) contains many more H-type than J-type aggregates;
General procedure for N-ethylation: A mixture of p-extended
thiadiazoles 15–19 (1 equiv), iodoethane (ca. 6.5 equiv), and
sodium hydride (ca. 34 equiv) in THF were heated at reflux in
a sealed bottle. The mixture was then poured into water, and the
flðsolidÞ
however, it is not clear at present why the lmax
(580 nm) of
flðtolÞ
2
-Crys.(O) is significantly redshifted compared with the l
max
[
46]
(508 nm) of 2.
resulting suspension was extracted with CHCl . The combined
3
organic phases were washed with water, dried over MgSO , and
4
Conclusion
evaporated in vacuo. The residue was subjected to column
chromatography.
We have synthesized new p-extended thiadiazoles 4–8 fused
with electron-donating heteroaromatics by Stille cross-cou-
pling reactions of 9 with the corresponding aryltin derivatives,
Preparation of 10: Compound 9 (150 mg, 0.39 mmol) was allowed
to react with tributyl(2-benzo[b]thienyl)tin (413 mg, 0.98 mmol) in
the presence of [Pd(PPh ) ] (22 mg, 0.020 mmol) in THF (15 mL) for
3
4
followed by PPh -mediated reductive cyclizations as the key
3
19 h according to the general procedure for Migita–Kosugi–Stille
coupling. The crude product was subjected to column chromatog-
raphy (silica gel, toluene/hexane. 1:1), and the collected material
was subsequently washed with hexane to give 10 (171 mg,
steps. By investigating the electronic, photophysical, and elec-
trochemical properties of 1–8 in solution, we have demonstrat-
ed the particular importance of benzannulation on their prop-
erties. The benzannulation extends the p conjugation and in-
creases the stability of the cationic species formed upon elec-
trochemical oxidation. Moreover, the benzannulation remarka-
bly increases the fluorescence efficiencies of 6 and 7 relative to
0
.35 mmol, 89%) as a yellow solid. An analytical sample was ob-
tained by reprecipitation from CHCl /hexane. M.p. >3008C;
3
1
H NMR (600 MHz, CDCl ): d=7.94–7.92 (m, 4H), 7.76 (s, 2H), 7.49–
.45 ppm (m, 4H); C NMR (150 MHz, CDCl ): d=152.48, 139.08,
3
13
7
3
1
29.73, 128.49, 126.51, 126.01, 125.31, 125.14, 122.70, 122.34 ppm
3
due to the efficient suppression of nonradiative intersystem
(
one signal is missing); UV/Vis (CH Cl ): l
(e)=293 (24200),
2
2
max
ꢀ
1
ꢀ1
crossing in 6 and 7. We have also shown that the electronic
and electrochemical properties of 4–8 reflect the differences in
the donor potency of the moieties annulated to the pyrrole
rings, that is, naphthalene, benzothiophene, and benzofuran.
Eleven crystals were obtained, including the poly- and pseu-
dopolymorphic crystals of 1, 2, 4, and 6, and the fluorescence
colors and efficiencies of 1-Crys.(Y) and 1-Crys.(G), 2-Crys.(O)
and 2-Crys.(G), 4-Crys.(O) and 4-Crys.(Y), and 6-Crys.(O) and
444 nm (9600m cm ); MS (MALDI-TOF, CHCA, positive): m/z:
+
490.57 [M+H] ; elemental analysis calcd (%) for C22
H N O S : C
10 4 4 3
5
3.87, H 2.05, N 11.42; found: C 53.99, H 2.26, N 11.06.
Preparation of 11: Compound 9 (150 mg, 0.39 mmol) was allowed
to react with tributyl(3-benzo[b]thienyl)tin (423 mg, 1.00 mmol) in
the presence of [Pd(PPh ) ] (22 mg, 0.020 mmol) in THF (15 mL) for
3
4
1
9 h according to the general procedure for Migita–Kosugi–Stille
coupling. The crude product was subjected to column chromatog-
raphy (silica gel, toluene/hexane, 2:3), and the collected material
was subsequently washed with hexane to give 11 (149 mg,
6-Crys.(G) were found to be different. The molecular systems
reported herein are fairly complicated, and so at present it is
not easy to provide quantitative discussions on the correlation
between the molecular arrangement and the photophysical
properties of the crystals. However, extensive X-ray crystallo-
graphic analyses and DFT calculations strongly indicate that
the photophysical properties of the poly- and pseudopoly-
morphs are affected by both the extent of the electronic inter-
actions in the p-stacked dimers and the presence of excitonic
interactions originating in the 1D face-to-face slipped columns.
We believe that this study will provide not only a useful guide-
line for tuning the properties of p-extended thiadiazoles but
also on their ability to act as fluorophores in the crystalline
state. The further derivatization of p-extended thiadiazoles is
underway in our laboratory.
0
.30 mmol, 78%) as orange solids. An analytical sample was ob-
tained by reprecipitation from CHCl /hexane. M.p. 214–2158C;
3
1
H NMR (400 MHz, CDCl ): d=8.00 (d, J=8.0 Hz, 2H), 7.82 (d, J=
3
13
6
1
1
1
.8 Hz, 2H), 7.48–7.36 ppm (m, 6H); C NMR (150 MHz, CDCl ): d=
3
53.11, 153.04, 143.72, 139.91, 137.63, 137.56, 129.78, 129.61,
25.58, 125.27, 125.19, 125.16, 124.78, 124.69, 123.25, 123.22,
22.56, 122.45 ppm (two pairs of signals are observed due to slow
conformational exchange on the NMR timescale); UV/Vis (CH Cl ):
lmax (e)=259 (21200), 291 (13400), 300 (15100), 431 nm
2
2
ꢀ
1
ꢀ1
(4000m cm ); MS (MALDI-TOF, CHCA, positive): m/z: 490.95
+
[M+H] ; elemental analysis calcd (%) for C H N O S : C 53.87, H
2.05, N 11.42; found: C 53.71, H 2.23, N 11.30.
22
10
4
4 3
Preparation of 12: Compound 9 (100 mg, 0.26 mmol) was allowed
to react with tributyl(1-naphthyl)tin (341 mg, 0.82 mmol) in the
presence of [Pd(PPh ) ] (16 mg, 0.014 mmol) in methoxycyclopen-
tane (25 mL) for 14 h according to the general procedure for
Migita–Kosugi–Stille coupling. The crude product was subjected to
column chromatography (silica gel, toluene/hexane, 1:1) and the
collected material was subsequently washed with hexane to give
12 (96 mg, 0.20 mmol, 77%) as an orange solid. An analytical
3 4
Experimental Section
General procedure for the Migita–Kosugi–Stille coupling reac-
tions: Argon was bubbled through a mixture of 9 (1 equiv) and
tributyl(aryl)tin (ca. 3.2 equiv) in THF or methoxycyclopentane for
sample was obtained by reprecipitation from CHCl /hexane. M.p.
274–2768C; H NMR (600 MHz, [D ]DMSO): d=8.17 (d, J=7.2 Hz,
3
1
6
3
0 min. [Pd(PPh ) ] (0.05 equiv) was added to the mixture, and the
2H), 8.09 (d, J=7.8 Hz, 2H), 7.79 (d, J=8.4 Hz, 1H), 7.73–7.69 (m,
3
4
&
&
Chem. Eur. J. 2014, 20, 1 – 15
www.chemeurj.org
10
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
1
3
4
[
1
1
1
H), 7.64–7.61 (m, 3H), 7.54–7.49 ppm (m, 2H); C NMR (150 MHz,
crude product was subjected to column chromatography (silica
gel; toluene/ethyl acetate, 2:1) and the collected material was fur-
ther purified by reprecipitation from THF/hexane to give 16
D ]DMSO): d=152.56, 152.87, 142.43, 142.33, 132.68, 132.66,
6
31.04, 130.74, 129.62, 129.02, 128.86, 128.38, 128.28, 128.06,
27.76, 127.45, 126.77, 126.42, 126.32, 125.99, 125.94, 125.25,
25.21, 124.70, 124.68 ppm (two pairs of signals are observed due
(325 mg, 0.76 mmol, 85%) as an orange solid. M.p. 285–2888C
1
(decomp.); H NMR (600 MHz, [D ]DMSO): d=12.52 (s, 2H), 9.10 (d,
6
to slow conformational exchange on the NMR timescale); UV/Vis
J=7.6 Hz, 2H), 8.03 (d, J=7.6 Hz, 2H), 7.58 (t, J=7.6 Hz, 2H),
13
(
(
CH Cl ):
l
(e)=272 (19900), 284 (19200), 406 nm
7.38 ppm (t, J=7.6 Hz, 2H); C NMR (150 MHz, [D ]DMSO): d=
2
2
max
ꢀ1
6
ꢀ
1
2200m cm ); MS (MALDI-TOF, Dith, positive): m/z: 504.52
147.64, 138.99, 135.97, 131.46, 129.04, 125.01, 124.90, 123.90,
123.83, 123.33, 123.18, 122.28, 122.23, 121.13, 107.17 ppm (two
pairs of signals are observed due to slow conformational exchange
+
[M+Na] ; elemental analysis calcd (%) for C H N O S·0.01CHCl : C
26
14
4
4
3
6
5.13, H 2.94, N 11.68; found: C 65.05, H 3.17, N 11.56.
on the NMR timescale); UV/Vis (CH Cl ): l (relative intensity)=
max
Preparation of 13: Compound 9 (156 mg, 0.41 mmol) was allowed
to react with tributyl(2-naphthyl)tin (506 mg, 1.21 mmol) in the
presence of [Pd(PPh ) ] (23 mg, 0.021 mmol) in methoxycyclopen-
tane (25 mL) for 12 h according to the general procedure for
Migita–Kosugi–Stille coupling. The crude product was subjected to
column chromatography (silica gel, toluene/hexane, 1:1) and the
collected material was subsequently washed with hexane to give
2
2
2
73 (0.71), 293 (0.44), 336 (0.81), 353 (1.0), 430 nm (0.25); MS
+
(MALDI-TOF, Dith, positive): m/z: 426.03 [M] ; elemental analysis
3
4
calcd (%) for C H N S ·0.5THF: C 62.31, H 3.05, N 12.11; found: C
22 10
4 3
6
2.31, H 3.73, N 10.95.
Preparation of 17: Compound 12 (92 mg, 0.19 mmol) was allowed
to react with PPh (510 mg, 1.94 mmol) for 17 h according to the
3
1
3 (142 mg, 0.30 mmol, 73%) as an orange solid. An analytical
general procedure for PPh -mediated reductive cyclization. The
3
sample was obtained by reprecipitation from CHCl /hexane. M.p.
crude product was subjected to column chromatography (silica
gel; toluene/ethyl acetate, 3:1) and the collected material was fur-
3
1
2
8
2
1
1
61–2638C; H NMR (600 MHz, CDCl ): d=8.10 (d, J=1.5 Hz, 2H),
3
.06 (d, J=8.4 Hz, 2H), 7.96 (d, J=8.4 Hz, 2H), 7.94 (d, J=7.8 Hz,
ther purified by reprecipitation from CHCl /hexane to give 17
3
13
1
H), 7.64–7.58 ppm (m, 2H); C NMR (150 MHz, CDCl ): d=155.33,
(69 mg, 0.16 mmol, 87%) as a yellow solid. M.p. >3008C; H NMR
3
42.91, 133.97, 133.06, 129.49, 129.27, 129.10, 128.76, 128.08,
(600 MHz, [D ]DMSO): d=12.44 (s, 2H), 10.76 (d, J=8.0 Hz, 2H),
6
27.94, 127.91, 127.25, 125.90 ppm; UV/Vis (CH Cl ): l (e)=310
max
8.11 (d, J=8.0 Hz, 2H), 8.06 (d, J=9.0 Hz, 2H), 7.98 (d, J=9.0 Hz,
2
2
ꢀ1
ꢀ1
13
(
10900), 399 nm (6200m cm ); MS (MALDI-TOF, Dith, positive):
2H), 7.82 (t, J=8.0 Hz, 2H), 7.59 ppm (t, J=8.0 Hz, 2H); C NMR
+
m/z: 479.20 [M+H] ; elemental analysis calcd (%) for
C H N O S·0.03CHCl : C 64.85, H 2.93, N 11.62; found: C 64.75, H
(150 MHz, [D ]DMSO): d=149.13, 135.32, 129.71, 128.66, 128.57,
6
128.31, 126.56, 126.16, 126.10, 124.03, 118.50, 113.92, 109.31 ppm;
2
6
14
4
4
3
3
.14, N 11.28.
UV/Vis (CH Cl ): l
(e)=281 (28700), 296 (29000), 323 (20300),
max
2
2
ꢀ1
ꢀ1
3
40 (28500), 355 (39500), 423 nm (13700m cm ); MS (MALDI-
+
Preparation of 14: Compound 9 (400 mg, 1.04 mmol) was allowed
to react with tributyl(2-benzo[b]furyl)tin (1.07 g, 2.63 mmol) in the
presence of [Pd(PPh ) ] (54 mg, 0.047 mmol) in THF (30 mL) for
TOF, Dith, positive): m/z: 415.25 [M+H] ; elemental analysis calcd
(
%) for C H N S 0.04CHCl : C 74.60, H 3.37, N 13.36; found: C
26 14 4 3
3
4
7
4.39, H 3.58, N 13.23.
2
8 h according to the general procedure for Migita–Kosugi–Stille
coupling. The crude product was subjected to column chromatog-
raphy (silica gel, toluene/hexane, 1:1) and the collected material
was subsequently washed with hexane to give 14 (387 mg,
Preparation of 18: Compound 13 (45 mg, 0.094 mmol) was al-
lowed to react with PPh (251 mg, 0.957 mmol) for 24 h according
3
to the general procedure for PPh -mediated reductive cyclization.
3
0
.84 mmol, 81%) as a brown solid. An analytical sample was ob-
The crude product was subjected to column chromatography
(silica gel; toluene/ethyl acetate, 5:1) and the collected material
tained by reprecipitation from CHCl /hexane. M.p. 266–2688C;
3
1
H NMR (600 MHz, [D ]DMSO): d=8.34 (s, 2H), 7.94 (d, J=7.5 Hz,
was subsequently washed with CH Cl2 to give 18 (34 mg,
6
2
1
2
8
1
H), 7.68 (d, J=8.1 Hz, 2H), 7.52 (t, J=7.5 Hz, 2H), 7.42 ppm (t, J=
0.082 mmol, 87%) as an orange solid. M.p. >3008C; H NMR
1
3
.1 Hz, 2H); C NMR (150 MHz, [D ]DMSO): d=154.82, 150.06,
(600 MHz, [D ]DMSO): d=12.55 (s, 2H), 8.57 (d, J=8.4 Hz, 2H), 8.42
6
6
44.75, 139.03, 127.84, 127.57, 124.32, 122.94, 115.70, 115.37,
(d, J=7.8 Hz, 2H), 8.14 (d, J=7.8 Hz, 2H), 7.88 (d, J=8.4 Hz, 2H),
1
3
111.51 ppm; UV/Vis (CH Cl ): lmax (e)=293 (27200), 445 nm
7.80 (t, J=7.8 Hz, 2H), 7.63 ppm (t, J=7.8 Hz, 2H); C NMR
2
2
ꢀ1
ꢀ1
(
11400m cm ); MS (MALDI-TOF, DHBA, positive): m/z: 458.06
(150 MHz, [D ]DMSO): d=148.95, 132.73, 130.96, 128.98, 127.83,
6
+
[M] ; elemental analysis calcd (%) for C H N O S·0.08CHCl : C
126.48, 125.18, 122.19, 121.51, 120.63, 119.88, 119.65, 108.82 ppm;
22
10
4
6
3
5
6.67, H 2.17, N 11.97; found: C 56.66, H 2.28, N 11.75.
UV/Vis (CH Cl ): l (relative intensity)=282 (0.73), 297 (0.73), 324
2
2
max
(
0.51), 340 (0.72), 356 (1.0), 423 nm (0.35); MS (MALDI-TOF, Dith,
Preparation of 15: Compound 10 (100 mg, 0.20 mmol) was al-
+
positive): m/z: 415.26 [M+H] ; elemental analysis calcd (%) for
C H N S: C 75.34, H 3.40, N 13.52; found: C 75.44, H 3.67, N 13.24.
lowed to react with PPh (543 mg, 2.07 mmol) for 7 h according to
3
the general procedure for PPh -mediated reductive cyclization. The
26 14
4
3
crude product was subjected to column chromatography (silica
gel; toluene/ethyl acetate, 2:1) and the collected material was sub-
sequently washed with CH Cl to give 15 (76 mg, 0.18 mmol, 87%)
Preparation of 19: Compound 14 (150 mg, 0.33 mmol) was al-
lowed to react with PPh (858 mg, 3.27 mmol) for 9 h according to
3
the general procedure for PPh -mediated reductive cyclization. The
2
2
3
1
as an orange solid. M.p. >3008C; H NMR (600 MHz, [D ]DMSO):
crude product was subjected to column chromatography (silica
gel; toluene/ethyl acetate, 3:1) and the collected material was sub-
sequently washed with CH Cl to give 19 (77 mg, 0.19 mmol, 60%)
6
d=12.67 (s, 2H), 8.22 (d, J=7.9 Hz, 2H), 8.10 (d, J=7.7 Hz, 2H),
13
7
.56 (t, J=7.7 Hz, 2H), 7.42 ppm (t, J=7.9 Hz, 2H); C NMR
2
2
1
(
150 MHz, [D ]DMSO): d=147.26, 141.84, 134.88, 129.08, 126.52,
as red needles. M.p. >3008C; H NMR (400 MHz, [D ]DMSO): d=
6
6
1
24.93, 124.57, 124.04, 119.94, 117.96, 107.83 ppm; UV/Vis (CH Cl ):
12.17 (s, 2H), 7.97 (d, J=7.6 Hz, 2H), 7.80 (d, J=8.0 Hz, 2H), 7.44–
2
2
13
lmax (relative intensity)=273 (0.72), 293 (0.44), 336 (0.81), 353 (1.0),
7.36 ppm (m, 4H); C NMR (150 MHz, [D ]DMSO): d=158.98,
6
+
4
;
30 nm (0.25); MS (MALDI-TOF, Dith, positive): m/z: 427.12 [M+H]
146.13, 144.56, 127.27, 123.61, 123.22, 122.77, 118.41, 118.24,
elemental analysis calcd (%) for C H N S : C 61.95, H 2.36, N
112.60, 98.39 ppm; UV/Vis (CH Cl ): l
(relative intensity)=337
22
10
4
3
2
2
max
1
3.14; found: C 61.90, H 2.52, N 12.94.
(1.0), 354 (0.99), 438 nm (0.27); HRMS (FAB, NBA, positive): m/z
+
+
calcd for C H N O S : 394.0524; found 394.0517 [M] .
Preparation of 16: Compound 11 (444 mg, 0.90 mmol) was al-
22 10
4
2
lowed to react with PPh (2.51 g, 9.57 mmol) for 8 h according to
Preparation of 4: Compound 15 (100 mg, 0.23 mmol) was allowed
3
the general procedure for PPh -mediated reductive cyclization. The
to react with iodoethane (770 mg, 4.9 mmol) in the presence of
3
Chem. Eur. J. 2014, 20, 1 – 15
www.chemeurj.org
11
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
+
sodium hydride (60% in oil, 293 mg, 7.1 mmol) for 10 h according
to the general procedure for N-ethylation. The crude product was
purified by column chromatography (silica gel; hexane/toluene,
471.26
[M+H] ;
elemental
analysis
calcd
(%)
for
C H N S·0.17CHCl : C 73.82, H 4.55, N 11.41; found: C 73.74, H
30
22
4
3
4.76, N 11.37.
2
:1) to give 4 (95 mg, 0.20 mmol, 84%) as an orange solid. An ana-
Preparation of 8: Compound 19 (35 mg, 0.089 mmol) was allowed
to react with iodoethane (307 mg, 1.97 mmol) in the presence of
sodium hydride (60% in oil, 109 mg, 2.74 mmol) for 48 h according
to the general procedure for N-ethylation. The crude product was
purified by column chromatography (silica gel; toluene) to give 8
(12 mg, 0.027 mol, 30%) as a red solid. An analytical sample was
obtained by reprecipitation from CH Cl /hexane. M.p. >3008C;
lytical sample was obtained by reprecipitation from CHCl /hexane.
M.p. 279–2818C; H NMR (400 MHz, CDCl ): d=8.06 (d, J=7.6 Hz,
3
1
3
2
7
H), 8.01 (d, J=7.6 Hz, 2H), 7.53 (t, J=7.6 Hz, 2H), 7.40 (t, J=
.6 Hz, 2H), 5.00 (q, J=7.2 Hz, 4H), 1.25 ppm (t, J=7.2 Hz, 6H);
1
3
C NMR (150 MHz, CDCl ): d=148.16, 143.70, 138.25, 132.93,
3
1
1
27.57, 124.98, 124.91, 123.86, 122.71, 119.68, 112.32, 45.75,
2
2
5.48 ppm; UV/Vis (CH Cl ): l (e)=277 (30600), 293 (18900), 341
1
2
2
max
H NMR (400 MHz, CDCl ): d=7.79–7.75 (m, 4H), 7.41–7.35 (m, 4H),
3
ꢀ1
ꢀ1
(
34000) 357 (40500), 443 nm (11800 m cm ); MS (MALDI-TOF,
13
4
.75 (q, J=7.2 Hz, 4H), 1.54 ppm (t, J=7.2 Hz, 6H); C NMR
+
Dith, positive): m/z: 483.23 [M+H] ; elemental analysis calcd (%)
for C H N S ·0.025CHCl : C 64.36, H 3.74, N 11.54; found: C 64.21,
H 3.89, N 11.44.
(
150 MHz, CDCl ): d=160.05, 146.84, 146.67, 130.66, 123.96, 123.42,
3
2
6
18
4
3
3
117.42, 113.47, 103.23, 45.79, 15.85 ppm (two signals are missing);
UV/Vis (CH Cl ): l (e)=257 (27700), 288 (13800), 312 (22100),
2
2
max
ꢀ
1
ꢀ1
3
42 (56900), 360 (66900), 451 nm (15200 m cm ); MS (MALDI-
+
Preparation of 5: Compound 16 (50 mg, 0.12 mmol) was allowed
to react with iodoethane (151 mg, 0.97 mmol) in the presence of
sodium hydride (60% in oil, 61 mg, 1.53 mmol) for 4 days accord-
ing to the general procedure for N-ethylation. The precipitate
formed was collected by filtration and purified by column chroma-
tography (silica gel; toluene) to give 5 (4 mg, 8.3 mmol, 8%) as
a red solid. An analytical sample was obtained by reprecipitation
TOF, Dith, positive): m/z: 450.15 [M] ; elemental analysis calcd (%)
for C H N O S·0.12CH Cl : C 68.10, H 3.99, N 12.16; found: C
26 18
4
2
2
2
6
8.01, H 4.05, N 12.11.
Acknowledgements
1
from CHCl /hexane. M.p. >3008C; H NMR (400 MHz, CDCl ): d=
3
3
9
2
7
.39 (d, J=7.7 Hz, 2H), 7.88 (d, J=7.7 Hz, 2H), 7.62 (t, J=7.7 Hz,
This work was financially supported by Grants-in-Aid for Young
Scientists from MEXT, Japan, and a research grant from the
Kurata Memorial Hitachi Science and Technology Foundation.
This work was performed under the Cooperative Research Pro-
gram of “Network Joint Research Center for Materials and Devi-
ces” (Osaka University and Kyushu University). The authors
thank Mr. Taisuke Matsumoto (Kyushu University) for helpful
assistance in X-ray diffraction analyses, Ms. Yasuko Tokitoh
H), 7.39 (t, J=7.7 Hz, 2H), 4.55 (q, J=7.2 Hz, 4H), 1.66 ppm (t, J=
1
3
.2 Hz, 6H); C NMR: not available due to poor solubility; UV/Vis
(relative intensity)=264 (1.0), 295 (0.60), 363 (0.21),
(
CH Cl ): l
max
2
2
+
4
:
52 nm (0.16); HRMS (FAB, NBA, positive): m/z calcd for C H N S
26 18 4 3
482.0694; found: 482.0688 [M] .
+
Preparation of 6: Compound 17 (30 mg, 0.072 mmol) was allowed
to react with iodoethane (78 mg, 0.50 mmol) in the presence of
sodium hydride (60% in oil, 100 mg, 2.48 mmol) for 26 h according
to the general procedure for N-ethylation. The crude product was
purified by column chromatography (silica gel; hexane/toluene,
(
Kyushu University) for helpful assistance in mass spectroscopic
analyses, and Prof. Soichiro Kyushin (Gunma University) for
generous permission to use the X-ray diffractometer.
1
:4) to give 6 (28 mg, 0.060 mmol, 82%) as an orange solid. An an-
alytical sample was obtained by reprecipitation from CHCl /hexane.
3
1
M.p. 298–3008C; H NMR (600 MHz, CDCl ): d=10.92 (d, J=9.0 Hz,
3
Keywords: electrochemistry
systems · polymorphism · X-ray diffraction
·
fluorescence
·
fused-ring
2
4
1
1
1
H), 8.06 (d, J=7.8 Hz, 2H), 7.98 (d, J=9.0 Hz, 2H), 7.89–7.85 (m,
H), 7.63 (ddd, J=7.8, 6.6, 1.2 Hz, 2H), 4.92 (q, J=7.2 Hz, 4H),
13
.04 ppm (t, J=7.2 Hz, 6H); C NMR (150 MHz, CDCl ): d=149.92,
3
[
1] a) A. C. Grimsdale, K. Mꢃllen, Macromol. Rapid Commun. 2007, 28, 1676;
b) I. F. Perepichka, D. F. Perepichka, Handbook of Thiophene-Based Mate-
rials, Wiley-VCH, Weinheim, 2009; c) P. M. Beaujuge, J. M. J. Frꢄchet, J.
Am. Chem. Soc. 2011, 133, 20009; d) H. Usta, A. Facchetti, T. J. Marks,
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39.53, 131.86, 130.56, 129.44, 128.64, 127.84, 126.98, 126.66,
24.80, 122.35, 114.87, 112.83, 43.83, 14.32 ppm; UV/Vis (CH Cl ):
2
2
lmax (e)=277 (30900), 303 (32300), 343 (29300) 373 (17600),
ꢀ
1
ꢀ1
4
4
34 nm (16100m cm ); MS (MALDI-TOF, Dith, positive): m/z:
+
71.32
[M+H] ;
elemental
analysis
calcd
(%)
for
C H N S·0.02CHCl : C 76.23, H 4.69, N 11.84; found: C 76.26, H
3
0
22
4
3
4
.78, N 11.79.
2
208.
2] a) J. E. Anthony, Angew. Chem. Int. Ed. 2008, 47, 452; Angew. Chem.
008, 120, 460; b) Z. Sun, Q. Ye, C. Chi, J. Wu, Chem. Soc. Rev. 2012, 41,
857.
[
Preparation of 7: Compound 18 (19 mg, 0.046 mmol) was allowed
to react with iodoethane (59 mg, 0.37 mmol) in the presence of
sodium hydride (60% in oil, 36 mg, 0.92 mmol) for 24 h according
to the general procedure for N-ethylation. The crude product was
purified by column chromatography (silica gel; hexane/toluene,
2
7
[
3] For example: a) C. D. Simpson, J. D. Brand, A. J. Berresheim, L. Przybilla,
H. J. Rꢅder, K. Mꢃllen, Chem. Eur. J. 2002, 8, 1424; b) M. M. Payne, S. R.
Parkin, J. E. Anthony, J. Am. Chem. Soc. 2005, 127, 8028; c) D. Chun, Y.
Cheng, F. Wudl, Angew. Chem. Int. Ed. 2008, 47, 8380; Angew. Chem.
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:1) to give 7 (13 mg, 0.028 mmol, 62%) as a yellow solid. An ana-
lytical sample was obtained by reprecipitation from CHCl /hexane.
M.p. 290–2938C; H NMR (600 MHz, CDCl ): d=8.90 (d, J=8.4 Hz,
3
1
3
2
8
6
H), 8.58 (d, J=8.3 Hz, 2H), 8.11 (d, J=8.0 Hz, 2H), 7.95 (d, J=
.4 Hz, 2H), 7.72 (ddd, J=8.3, 6.8, 1.2 Hz, 2H), 7.59 (ddd, J=8.0,
.8, 1.2 Hz, 2H), 5.29 (q, J=7.2 Hz, 4H), 0.91 ppm (t, J=7.2 Hz, 6H);
C NMR (150 MHz, CDCl ): d=149.90, 136.79, 133.91, 132.66,
29.94, 126.30, 125.23, 124.89, 124.71, 123.88, 121.82, 120.92,
1
23, 7151; f) M. Watanabe, Y. J. Chang, S.-W. Liu, T.-H. Chao, K. Goto,
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2
4
13.94, 47.14, 14.01 ppm; UV/Vis (CH Cl ): l
(e)=252 (27900),
2
2
max
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91 (69800), 326 (31200) 339 (36900), 362 (12100), 383 (18700),
29 nm (15500 m cm ); MS (MALDI-TOF, Dith, positive): m/z:
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[23] The E (30) parameters (33.9 kcalmol for toluene, 37.4 kcalmol for
T
ꢀ
1
ꢀ1
ꢀ
THF, 38.1 kcalmol for EtOAc, 40.7 kcalmol for CH Cl , 42.9 kcalmol
2
2
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[
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[
[
[
25] Preliminary p-type OFET performances of 4 and 8 are summarized in
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morphs to be exact, because solvent molecules are included in the
latter.
[
[
[
[
[
[
[
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3
31] In 8-Crys., CHCl molecules from the solvent of recrystallization are in-
cluded in a stoichiometry of 1:2.
[
32] The space between the neighboring columns is occupied by toluene
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Information).
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are observable.
[
[
5484.
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[
35] The crystalline samples were carefully used.
36] Thoroughly ground crystals of 1–4 and 6–8 as powder samples were
also confirmed to be microcrystals by X-ray diffraction (XRD) measure-
ments (see Figure S7 in the Supporting Information).
[
[
37] In the crystal structure of 7, S–p interactions instead of p–p stacking in-
teractions are observed.
38] We performed single-point calculations on 4·toluene complexes based
on the X-ray crystal structure of 4-Crys.(G), and the results suggest that
the proximity of the toluene molecule to the sulfur atom of 4 tends to
decrease the HOMO–LUMO gaps (see Figure S21 in the Supporting In-
formation).
[
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and 6-Crys.(O) are comparable to those in 1-Crys.(G), 2-Crys.(G), 4-
Crys.(G), and 6-Crys.(G), respectively. The differences in the DEH-L values
is at most 0.03 eV (see Table S4 in the Supporting Information), which
may reflect differences in the planarity of the monomers.
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at the PW91/TZP level of theory with the Amsterdam density func-
[
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on the X-ray crystal structure, and the results suggest that the close
proximity of the CHCl molecule to the benzene rings of 8 tends to de-
crease the HOMO–LUMO gaps (see Figure S22 in the Supporting Infor-
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5
[
3
3
3
strated by high-level ab initio calculations: S. Tsuzuki, K. Honda, T. Uchi-
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[46] It has been pointed out by Zhang, Wang, and co-workers that the pack-
Received: October 1, 2014
ing along one distinct direction usually consists of a component of J-
Published online on && &&, 0000
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FULL PAPER
p-Extended thiadiazoles: The photo-
physical and electrochemical properties
of a series of p-extended thiadiazoles
fused with electron-donating hetero-
aromatic moieties are disclosed. These
compounds form poly- and pseudopoly-
morphic crystals, and the fluorescence
properties in the crystalline state are
significantly affected by the molecular
arrangement (see figure).
&
Donor–Acceptor Systems
S.-i. Kato, T. Furuya, M. Nitani, N. Hasebe,
Y. Ie, Y. Aso, T. Yoshihara, S. Tobita,
Y. Nakamura*
&
& – &&
A Series of p-Extended Thiadiazoles
Fused with Electron-Donating
Heteroaromatic Moieties: Synthesis,
Properties, and Polymorphic Crystals
Chem. Eur. J. 2014, 20, 1 – 15
www.chemeurj.org
15
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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These are not the final page numbers! ÞÞ