Tetraalkoxyphenanthrene-Fused Thiadiazoloquinoxalines: Synthesis, Electronic, Optical, and Electrochemical Properties, and Self-Assembly

Article abstract of DOI:10.1021/acs.joc.7b00084

π-Extended thiadiazoloquinoxaline (TQ) derivatives 1a,b-3a,b, in which a tetraalkoxyphenanthrene moiety is annulated with the TQ core and benzene rings are incorporated via the ethynylene spacer, were synthesized. They display absorption bands reaching in

Full text of DOI:10.1021/acs.joc.7b00084

Subscriber access provided by University of Newcastle, Australia
Article
Tetraalkoxyphenanthrene-Fused Thiadiazoloquinoxalines: Synthesis,
Electronic, Optical, and Electrochemical Properties, and Self-Assembly
Shin-ichiro Kato, Keitaro Watanabe, Misaki Tamura, Masahiko Ueno, Masashi Nitani,
Yutaka Ie, Yoshio Aso, Takeshi Yamanobe, Hiroki Uehara, and Yosuke Nakamura
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.7b00084 • Publication Date (Web): 22 Feb 2017
Downloaded from http://pubs.acs.org on February 23, 2017
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a free service to the research community to expedite the
dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts
appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been
fully peer reviewed, but should not be considered the official version of record. They are accessible to all
readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered
to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published
in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just
Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor
changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers
and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors
or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
The Journal of Organic Chemistry is published by the American Chemical Society.
1155 Sixteenth Street N.W., Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the
course of their duties.

Page 1 of 43
The Journal of Organic Chemistry
1
2
3
4
5
6
Tetraalkoxyphenanthrene-Fused Thiadiazoloquinoxalines: Synthesis,
Electronic, Optical, and Electrochemical Properties, and Self-Assembly
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Shin-ichiro Kato,† Keitaro Watanabe,† Misaki Tamura,† Masahiko Ueno,† Masashi Nitani,‡
Yutaka Ie,‡ Yoshio Aso,‡ Takeshi Yamanobe,† Hiroki Uehara,† and Yosuke Nakamura*,†
†
Division of Molecular Science, Faculty of Science and Technology
Gunma University
1-5-1 Tenjin-cho, Kiryu, Gunma 376-8515, Japan
Tel: +81-277-30-1311
Fax: +81-277-30-1314
E-mail: nakamura@gunma-u.ac.jp
The Institute of Scientific and Industrial Research (ISIR)
Osaka University
‡
______________________
Table of Contents/Abstract Graphic:
Abstract: π-Extended thiadiazoloquinoxaline (TQ) derivatives 1a,b‒3a,b, in which a
tetraalkoxyphenanthrene moiety is annulated with the TQ core and benzene rings are incorporated
via the ethynylene spacer, were synthesized. They display absorption bands reaching into 750 nm
1
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 2 of 43
1
2
3
4
5
6
7
8
9
and possess the electron-affinity comparable to [60]fullerene. The CF3- and OMe-substituents on
the benzene rings have moderate effects on modulation of the HOMO and LUMO levels.
Tetraalkoxyphenanthrene-fused TQs 1a,b‒3a,b aggregate in the solid state and assemble in solution
through π‒π stacking interactions. The self-assembly of 1a,b‒3a,b into 1D superstructures was
confirmed, and the difference in the alkoxy groups and the solvents for self-assembly proved to
change their morphology. Comparison of the properties of 1a and those of reference compounds 4
and 5 clarified the effects of both the fusion of the phenanthrene moiety and the introduction of
ethynylene spacers on the properties.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Keywords: thiadiazoloquinoxaline ∙ π‒π interactions ∙ self-assembly ∙ alkyne ∙ phenanthrene
_____________________
Introduction
The field of π-conjugated materials has recently gained significant importance because of their
potential utility in future-generation electronic devices such as organic photovoltaics (OPVs), organic
light-emitting diodes (OLEDs), and organic field-effect transistors (OFETs).1 In the molecular
design, it is important to control both the electronic structure and the solid-state structure of
π-conjugated molecules appropriately to achieve optimal function of the above mentioned devices.2
As a consequence, polycyclic aromatic hydrocarbons (PAHs) were extensively studied over the
years,3 because they tend to show intriguing photophysical and electrochemical properties (e.g.
strong fluorescence and multistep redox behavior) and form a dense molecular packing due to their
planar and rigid π-frameworks. Among PAHs, oligoacenes with linearly annulated benzene units,
in particular, pentacene and its derivatives have constituted important class of π-electron-rich
materials.4 Although acenes are inherently susceptible to oxidative degradation,5 the incorporation
2
ACS Paragon Plus Environment

Page 3 of 43
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
of an alkynyl group efficiently enhances the oxidation stability,6 which enables them to be prominent
examples of p-type semiconducting materials for high performance devices. The replacement of
benzene rings with heteroaromatic rings in the acene framework is known to drastically change
electronic properties. Azaacenes, which contain electron-deficient heteroaromatics such as pyridine
or pyrazine rings, possess electron-accepting ability and thus have attracted considerable attention as
promising candidates for n-type semiconducting materials.7
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
[1,2,5]Thiadiazolo[3,4-g]quinoxaline (TQ) is classified as an azaacene molecule with an
o-quinoid structure.8 TQ possesses an outstanding electron-accepting ability due to the presence of
electron-deficient thiadiazole and pyrazine rings,9 and has become one of the most important
building blocks for the construction of π-functional materials.10 For instance, the embedding of
electron-donating units at the 4- and 9-positions of TQ unit has been recognized as the useful
approach to create compounds with low energy gap since the pioneering work by Yamashita and
co-workers.9a Very recently, Salleo, Andersson, and co-workers have synthesized alternating
TQ‒thiophene polymers with the extremely low energy gap of ca. 0.7 eV that is among the lowest
value reported to date and disclosed that these polymers can function as active materials in OFETs
and electrochromic devices.10f Baumgarten and co-workers also reported analogous TQ-based
semiconducting polymers, in which the TQ unit is connected to the thiophene unit via an ethynylene
π-spacer, and demonstrated that the incorporation of the π-spacer allows for high planarity of the
polymer backbone and thereby provokes the strong solid-state packing.10d
The self-association behavior through effective π‒π stacking interaction of π-conjugated
molecules is one of the key factors for achieving their morphological organization and structural
order at mesoscopic length scale by self-assembly.11 In this context, extension of the conjugated
framework by fusing aromatic systems into the TQ scaffold would be a rational design strategy to not
3
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 4 of 43
1
2
3
4
5
6
7
8
9
only modulate electronic structures but also bring about self-association properties in solution
originating from an enlarged π-surface, because π‒π stacking interaction is strongly associated with
the size of the conjugated aromatic surface. Some TQ derivatives with extended fused π-systems
have been synthesized by several research groups so far;12 for instance, TQ derivatives incorporating
triisopropylsilylethynyl groups were reported by Baumgarten and co-workers.12g However, the
elucidation of structure‒property relationships of TQs with extended fused π-systems still remains as
an important issue to give the guideline for the molecular design of TQ-based π-functional
materials.12b In addition, there is no report on self-association in TQs to the best of our knowledge,
although the formation of 1D superstructures of TQs was demonstrated by Lee and co-workers.12c
It is considered that the lack of the self-association property of TQs in solution is mainly attributable
to attached bulky substituents, which prevent the π-surfaces of the polycyclic molecules from
approaching each other to guarantee the solubility.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Here, we present the synthesis of π-extended TQ derivatives 1a,b‒3a,b and their electronic,
optical, and electrochemical properties and self-assembling behavior (Chart 1). Compounds
1a,b‒3a,b possess both large π-surface and high planarity due to the fusion of a
tetraalkoxyphenanthrene moiety with the TQ scaffold and the introduction of ethynylene spacers
between the TQ moiety and the benzene rings.13 We envisaged that tetraalkoxyphenanthrene-fused
TQs 1a,b‒3a,b not only show self-association behavior in solution through π‒π stacking interactions
but also form self-assembled 1D superstructures by the interplay of π‒π stacking interactions and van
der Waals interactions stemming from the attached alkoxy chains.14 The effects of the substituents
on the benzene rings (i.e. H-, CF3-, and OMe-substituents) and the phenanthrene moiety (i.e. linear
decyloxy and branched 2-ethylhexyloxy groups) on the overall properties of 1a,b‒3a,b are disclosed.
We also focused our attention on elucidation of the effects of the fusion of the phenanthrene moiety
4
ACS Paragon Plus Environment

Page 5 of 43
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
and the introduction of ethynylene spacers on the properties of the resulting molecules from the
viewpoint of the structure‒property relationships, and thus the comparison of the properties of 1a
with those of reference compounds 4 and 5 is reported.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Chart 1. π-Extended Thiadiazoloquinoxalines 1a,b–3a,b and Reference Compounds 4 and 5
RO
RO
OR
OR
RO
RO
OR
OR
RO
RO
OR
OR
N
N
N
N
N
N
F3C
CF3
MeO
OMe
N
N
N
N
N
N
S
S
S
1a,b
2a,b
3a,b
RO
RO
OR
OR
RO
RO
OR
OR
N
N
N
N
N
1a–3a, 4, and 5: R = -(CH2)9CH3
1b–3b: R =
C2H5
N
N
N
S
S
C4H9
4
5
Results and Discussion
Synthesis. The synthetic route of π-extended TQs 1a,b‒3a,b is outlined in Scheme 1. First, we
investigated the condensation of 2,3,6,7-tetrakis(decyloxy)-9,10-dihydrophenanthrene-9,10-dione,
which
was
obtained
by
oxidative
cyclization
of
benzil
6a,15
with
4,7-dibromo-2,1,3-benzothiadiazole-5,6-diamine (7)16 in acetic acid under reflux to synthesize TQ 9a
as a key intermediate (Table S1 in the Supporting Information), but the desired 9a was obtained in
only 3% yield; the starting materials were recovered in ca. 90% even after 3 days. We then
examined the alternative synthetic route of 9a. The condensation of 6a with diamine 7 in acetic
acid gave 8a (Scheme 1). Then, the intramolecular oxidative cyclization of 8a by the treatment
5
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 6 of 43
1
2
3
4
5
6
7
8
9
with vanadium (V) oxitrifluoride was carried out in CH2Cl2 at room temperature, and gratifyingly we
obtained 9a in 66% yield in two steps. In a similar manner, 9b was obtained in 46% yield in two
steps from 6b17 via 8b. Such intramolecular cyclization was thought to be challenging because the
electron-accepting TQ moiety would increase the oxidation potential which makes the oxidative
cyclization hard to occur to some extent. The Pd-catalyzed Sonogashira coupling reaction between
9a,b and the corresponding ethynylbenzene derivatives gave 1a,b‒3a,b in 3‒38% yields; the
consideration of the reaction conditions (e.g. Pd catalyst, reaction temperature, and reaction solvent)
did not improve the product yields in our hands. The particularly low yield of 2a is attributed to the
severely low solubility, which leads to the substantial loss of material. During the completion of the
present work, Baumgarten and co-workers reported the efficient synthetic route of ethynylated TQ
derivatives.12g,18 Whereas 1a‒3a having linear decyloxy groups are soluble in only chlorinated
solvents, 1b‒3b having branched 2-ethylhexyloxy groups are readily soluble in various solvents such
as acetone, toluene, and THF. The synthesis of 4 and 5 is shown in Schemes S1 and S2,
respectively, in the Supporting Information.19
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Scheme 1. Synthesis of π-Extended Thiadiazoloquinoxalines 1a,b‒3a,ba
RO
RO
OR
OR
RO
RO
OR
OR
(iii)
(iv)
(v)
1a (15%)
1b (15%)
RO
RO
OR
OR
N
N
N
N
(i)
(ii)
2a (3%)
2b (18%)
Br
Br
Br
Br
O
O
N
N
N
N
3a (29%)
3b (38%)
S
S
a: R = -(CH2)9CH3
9a (66%)
9b (46%)
6a
6b
8a
8b
b: R =
C2H5
C4H9
a Reagents and conditions: (i) 4,7-dibromo-2,1,3-benzothiadiazole-5,6-diamine (7), AcOH, 80 °C; (ii) vanadium (V)
oxitrifluoride, CH2Cl2, RT; (iii) ethynylbenzene, [Pd(PPh3)4], CuI, RT; (iv) 1-ethynyl-4-(trifluoromethyl)benzene,
[Pd(PPh3)4], CuI, RT (for 2a) or 0 °C (for 2b), (v) 1-ethynyl-4-methoxybenzene, [Pd(PPh3)4], CuI, RT (for 3a) or 0 °C
(for 3b).
6
ACS Paragon Plus Environment

Page 7 of 43
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
Electronic and Optical Properties. In the electronic absorption spectra in CHCl3 (Figure 1),
1a‒3a displayed broad absorption bands reaching into 750 nm. Compounds 1b‒3b showed almost
the same spectra of the corresponding 1a‒3a (Figure S5 in the Supporting Information).20,21 The
longest absorption maximum (λmaxabs) of 1a is red-shifted relative to those of 4 and 5 by 84 nm and
54 nm, respectively (654 nm (1a), 570 nm (4), 600 nm (5)), clearly indicating that combination of the
fusion of the phenanthrene moiety with the TQ core and the introduction of ethynylene spacers
between the TQ core and the benzene rings effectively extend π-conjugation in 1a. Considering
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
abs
that the λmax and the absorption onset (λonset) of 5 are red-shifted compared to the corresponding
values of 4, the phenanthrene moiety may have a larger effect on the extension of π-conjugation in 1a
abs
than the ethynylene spacers. Whereas the λmax value of 2a is almost the same as that of 1a, the
λmaxabs value of 3a is apparently red-shifted relative to that of 1a (660 nm (2a), 684 nm (3a)).
Figure 1. Electronic absorption spectra of 1a‒3a, 4, and 5 in CHCl3 at RT.
We conducted density functional theory (DFT) calculations of 1’‒5’, where the decyloxy or
2-ethylhexyloxy groups in 1‒5 were replaced with the methoxy groups, at the PBE0/6-31G(d) level
to obtain further insight into the electronic properties.22 The optimized structure of 1’ is highly
planar, and thus the TQ moiety and the benzene rings attached to the TQ moiety via the ethynylene
7
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 8 of 43
1
2
3
4
5
6
7
8
9
spacer lie in the same plane (Figure S1).23 The planarity of 4’ and 5’ is apparently lower than 1’.
Thus, in 4’ the dihedral angle between the dimethoxybenzene ring and the TQ moiety is 34°, and in
5’ the angle between the benzene ring and the TQ moiety is 46° (Figure S1); there exist steric
repulsions between the two dimethoxybenzene rings in 4’ and between the benzene rings and the TQ
moiety in 5’. This finding indicates that the efficient extension of π-conjugation in 1 relative to 4
and 5 observed in the electronic absorption spectra is attributed to the high planarity together with
the large conjugated framework in 1.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 2 shows the HOMOs and LUMOs of 1’‒5’.24 The HOMO of 1’ is delocalized over the
π-conjugated framework, whereas its LUMO is relatively localized in the TQ and ethynylene
moieties. The HOMO of 4’ has almost no contribution from the dimethoxybenzene rings. This
manifests that the fusion of the phenanthrene moiety results in the effective π-conjugation in 1
compared to 4. The ethynylene spacers are found to enable both the HOMO and LUMO to be
delocalized and thus extend π-conjugation in 1 relative to 5.
8
ACS Paragon Plus Environment

Page 9 of 43
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
Figure 2. Molecular orbital plots of (a) 1’,
(b) 2’, (c) 3’, (d) 4’, and (e) 5’ at the
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
PBE0/6-31G(d) level of theory. The left plots
represent the HOMOs, and the right plots
represent the LUMOs.
Compounds 1‒3 and 5 are nonfluorescent, whereas 4 is fluorescent. The fluorescence maximum
(λmaxfl) of 4 is 640 nm in CHCl3 at the diluted regime (Figure S6), and its absolute fluorescence
quantum yield (Φf) is 0.12.25 This result suggests that the fluorescence quenching in 1‒3 and 5 is
attributable to the phenanthrene moiety. Although the reason for the nonfluorescent nature of 1‒3
and
5
is not clear at present, similar fluorescence quenching is observed in
quinoxalinophenanthrophenazine derivatives.26
9
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 10 of 43
1
2
3
4
5
6
7
8
9
Electrochemical Properties. We first performed cyclic voltammetry (CV) experiments on 1–5 in
o-dichlorobenzene (0.1 mol L‒1 nBu4NPF6, standard Fc+/Fc) to investigate their electrochemical
properties (Figure S7). Compounds 1‒5 showed two TQ-centered 1e‒ reduction steps. The first
and second reduction processes of the TQ derivatives are reversible or quasi-reversible in general;
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
the second reduction process of 3a is exceptionally irreversible.
This illustrates that
electrochemically generated anionic species of the present TQs are essentially stable. Whereas 5
showed one reversible 1e– oxidation step, 1–4 displayed irreversible oxidation steps, indicating that
the cationic species of 1‒4 are unstable, and their instability comes from the ethynylene spacers.
We further conducted differential pulse voltammetry (DPV) measurements on 1–5 to determine
their redox potentials, ionization potentials (IP), and electron affinity (EA) (Figure S8); DPV affords
better sensitivity than CV and results in sharper peak onsets due to the sharper current response. As
summarized in Table 1, the first reduction potential (Ered) of 1a is positively shifted as compared to
those of 4 and 5 (–1.13 V (1a), –1.21 V (4), –1.34 V (5)), and the difference of the first Ered values of
1a and 5 is larger than that of 1a and 4. This result demonstrates that both the phenanthrene moiety
and the ethynylene spacers effectively increase the electron-accepting ability, and the latter has the
more marked effect than the former. The oxidation potential (Eox) of 1a is negatively shifted
relative to that of 4 and almost the same as that of 5 (0.63 V (1a), 0.75 V (4), 0.61 V (5)), indicating
that the phenanthrene moiety exclusively increases the donor ability. The electrochemical
HOMO‒LUMO gap (ΔEredox) of 1a is smaller than those of 4 and 5 (1.76 V (1a), 1.96 V (4), 1.95 V
(5)), which is consistent with the finding that the λmaxabs value of 1a is red-shifted relative to those of
4 and 5.
10
ACS Paragon Plus Environment

Page 11 of 43
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
Table 1. Oxidation and Reduction Potentials, Ionization Potentials (IP), and Electron Affinity (EA) of
1a–3a, 4, and 5 by DPV in o-Dichlorobenzene (0.1 mol L‒1 nBu4NPF6)a, Theoretically Calculated
HOMO and LUMO Levels,b and Electrochemical (ΔEredox),c Theoretical (ΔEcalcd),d and Optical Gaps
(ΔEopt)e
Eox/V
Ered/V
HOMO/eVb
LUMO/eVb
ΔEredox/V ΔEcalcd/eV ΔEopt/eV
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(IP/eV) (EA/eV)
0.63
–1.13, –1.58 –5.21
–3.11
1.76
1.80
1.63
1.96
1.95
2.10
2.11
2.01
2.29
2.43
1.89
1.87
1.81
2.17
2.06
1a
2a
3a
4
(–5.86) (–4.10)
0.72
–1.08, –1.50 –5.50
–3.39
(–5.95) (–4.15)
0.48
–1.15, –1.62 –4.96
–2.95
(–5.71) (–4.08)
0.75
–1.21, –1.72 –5.23
–2.94
(–5.98) (–4.02)
0.61
–1.34, –1.89 –5.32
–2.89
5
(–5.84) (–3.89)
C60
–1.08, –1.48 –6.33
(–4.15)
–3.30
a All potentials are given versus the Fc+/Fc couple used as external standard. Pulse width of 0.1 s in a period of
0.2 s. IP and EA were determined using a work-function value of –5.23 eV for Fc+/Fc. b Calculated by the
PBE0/6-31G(d) level for 1’–5’, where the decyloxy or 2-ethylhexyloxy groups in 1‒5 were replaced with the
methoxy groups. c Electrochemical gap, ΔEredox, is defined as the potential difference between the first oxidation
potential and the first reduction potential. d Theoretical gap, ΔEcalcd, is defined as the energy difference between
e
the HOMO and the LUMO calculated by the DFT method.
Optical gap, ΔEopt, is defined as the energy
abs
corresponding to the longest λmax
.
The data for 1b–3b are summarized in Table S14 in the Supporting
Information.
When compared to 1a, both the Eox and Ered values of 2a are positively shifted, and the values of
3a are negatively shifted (Table 1), and thus the electron-accepting CF3- and electron-donating
OMe-substituents on the benzene rings were found to alter the redox potentials. The positive shift
of the Eox values from 1a to 2a is roughly similar to that of the first Ered values, while the negative
shift of the Eox values from 1a to 3a is more pronounced than that of the first Ered values. As a
11
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 12 of 43
1
2
3
4
5
6
7
8
9
consequence, the ΔEredox value of 2a becomes almost the same as that of 1a, and the ΔEredox value of
3a becomes moderately smaller than that of 1a (1.80 V (2a), 1.63 V (3a)).27 These phenomena
might be explained by the FMO plots of 2’ and 3’. The CF3-substituents in 2’ have almost no
contribution to both the HOMO and LUMO (Figure 2b), and hence the CF3-substituents are likely to
stabilize the HOMO and LUMO to almost the same degree by the inductive effect. Although the
OMe-substituents in 3’ have also almost no contribution to the LUMO as is the case with 2’, the
noticeable contribution to the HOMO is observed (Figure 2c), and thus the OMe-substituents are
considered to markedly destabilize the HOMO relative to the LUMO by the resonance effect.
A good correlation exists between the optical HOMO‒LUMO gaps (ΔEopt) estimated from the
electronic absorption spectra and the ΔEredox values in 1‒5. Noticeably, the electron affinity of 1‒3
are comparable to that (‒4.15 eV) of [60]fullerene (C60), which is the benchmark of n-type organic
semiconductor materials.28
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Aggregation Properties in the Solid State. We first investigated aggregation properties of 1‒3 in
the solid state by MALDI-TOF mass spectrometry. Besides the molecular ion peaks of 1–3, the
peaks ascribed to their aggregated species were detected (Figures 3 and S9). For example, as
shown in Figure 3, the peaks for 1a were seen at m/z 2326 and 3489, which correspond to the
assemblies of two and three molecules, respectively, in addition to the parent ion (m/z 1163). This
apparently illustrates the aggregation tendency of 1‒3 in the solid state.
12
ACS Paragon Plus Environment

Page 13 of 43
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 3. MALDI-TOF-MS spectrum of 1a (dithranol, positive).
Next, the electronic absorption spectra of the drop-casted films of 1‒3 were measured (Figures 4
and S10). The λmaxabs values of 1‒3 in the solid state are red-shifted compared with those in CHCl3
solution by ca. 30‒70 nm (Table S15), strongly supporting marked structural organization in the film
by intermolecular π‒π stacking interactions. The absorption bands in the region of 400‒600 nm of
1a‒3a are broader than those of the corresponding 1b‒3b, suggesting that the aggregative nature of
1a‒3a is stronger than 1b‒3b, respectively, and thus the linear alkoxy chains in the former enable the
neighboring molecules to come closer resulting in the stronger π‒π stacking interactions than the
branched alkoxy chains in the latter (vide infra).
Figure 4. Electronic absorption spectra of 3a in
CHCl3 (dashed line) and the drop-casted film
(solid line) at RT.
13
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 14 of 43
1
2
3
4
5
6
Self-Association Properties in Solution. We measured 1H NMR spectra of present TQs except for
2a in CDCl3 at various concentrations to investigate their self-association properties; the extremely
7
8
9
1
low solubility of 2a hampered the spectral measurements at a high concentration. The H NMR
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
signals of 1a,b, 2b, 3a,b, and 5 in CDCl3 were concentration dependent, and the aromatic signals
shifted upfield upon increasing the concentration (Figures 5 and S11‒S16); the upfiled shifts of the
phenanthrene protons are particularly remarkable.29,30 Such shifts illustrate that they associate by
π‒π stacking interactions in CDCl3, and thereby the aromatic protons are placed in the shielding
regions produced by the neighboring aromatic rings. On the other hand, the aromatic signals of 4
were independent on concentration, indicating that there is almost no self-association occurring.
The lack of self-association property of 4 should be attributed to its smaller π-plane than 1‒3 and 5
and/or lower planarity than 1‒3.
Figure 5. 1H NMR spectra of 1a in CDCl3 in various
concentrations at RT. The small amount of impurity
included in CDCl3 is labeled with asterisk.
The diffusion constants (D) of 1a proved to be almost independent on concentration by DOSY
NMR experiments (Table S16), suggesting that a monomer‒dimer equilibrium predominantly exists
in a CHCl3 solution of 1a.31 Therefore, we determined association constants (Kdim) of 1a,b, 2b,
3a,b, and 5 on the basis of a monomer‒dimer model by nonlinear least-squares fitting of their
14
ACS Paragon Plus Environment

Page 15 of 43
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
concentration-dependent 1H NMR chemical shifts (Table 2).32 The Kdim value of 1a is significantly
higher than that of 5 (111 ± 2 mol‒1 L (1a), 15 ± 2 mol‒1 L (5)), clearly indicating that the ethynylene
spacers enhance the planarity of the π-conjugated framework and thereby increase the
self-association ability efficiently (vide supra). The lower Kdim value (11 ± 3 mol‒1 L) of 1b than 1a
should derive from the sterically bulky 2-ethylhexyloxy groups in 1b. Although the difference of
the Kdim values among 1b–3b seems insignificant, the higher self-association ability of 2b than 1b
and 3b is supported by the pronounced upfield shifts of the aromatic protons of 2b as compared to 1b
and 3b in the region of 0.006‒3 mmol L‒1 (Figures S12, S13, and S15). This observation implicates
that the CF3-substituents have the electronic and/or steric effects on enhancement of π‒π stacking
interactions.33
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Table 2. Self-Association Constants (Kdim) in CDCl3 at RT Determined by 1H NMR Spectroscopy
Kdim/L mol‒1
111 ± 2
N.D.a
Kdim/L mol‒1
11 ± 3
38 ± 1
22 ± 4
15 ± 2
1a
2a
3a
4
1b
2b
3b
5
138 ± 4
N.D.b
a Not determined due to insolubility. b Almost no self-association.
We measured the electronic absorption spectra of 1a,b, 2b, and 3a,b in CHCl3 at various
concentrations.34 In the absorption spectra of 1a and 3a, upon increasing the concentration the ε
values around 720‒770 nm increased and those around 650‒700 nm decreased with a
quasi-isosbestic point (Figures 6 and S17). The concentration region (ca. 0.05‒2 mmol L‒1) in
which the absorption spectral changes of 1a and 3a arise is almost consistent with that in which the
pronounced chemical shift changes for their aromatic protons occur in the 1H NMR spectra described
15
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 16 of 43
1
2
3
4
5
6
7
8
9
above. Thus, it is reasonable to assume that the observed absorption spectral changes of 1a and 3a
originate in their self-association behavior. Unlike 1a and 3a, the absorption spectra of 1b–3b
proved to be almost independent on the applied concentration. These results are in accordance with
the finding that the Kdim values of 1a and 3a are higher than those of 1b–3b as demonstrated by the
1H NMR spectral measurements.35
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 6. Electronic absorption spectra of 1a in
CHCl3 in various concentrations at RT.
16
ACS Paragon Plus Environment

Page 17 of 43
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
To obtain insight into the structure of the self-assembled dimers of 1‒3 in solution, we performed
the DFT calculations for 1’‒3’. Because 1’‒3’ have the dipole moments of 1.64 D, 2.20 D, and 0.41
D, respectively, from the thiadiazole ring to the pyrazine ring (PBE0/6-31G(d)), they are expected to
form the dimers in an antiparallel manner, where the dipole moment should be canceled out. The
optimization of the self-assembled dimers of 1’‒3’ based on this assumption gave the plausible
structures, in which the TQ moiety is located above the phenanthrene moiety of the adjacent
molecule in an offset arrangement (Figures 7 and S3).36,37 These optimized structures suggest that
the shielding effect for the phenanthrene protons is more pronounced than that for the benzene
protons and thus reasonably explain the fact that the phenanthrene protons show the greater upfield
shifts than the benzene protons in the 1H NMR spectra with increasing the concentration.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 7. (a) Top and (b) side view of
the plausible structure of self-assembled
dimer of 1’ optimized at the
PBE0/6-31G(d) level.
Moreover, we compared the HOMO‒LUMO gaps of the self-assembled dimers of 1’‒3’ with
those of the corresponding monomers by the DFT calculations (PBE0/6-31G(d)) to investigate the
change in the electronic structures upon formation of the dimeric structures (Table S3). The
17
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 18 of 43
1
2
3
4
5
6
7
8
9
estimated HOMO‒LUMO gaps of the dimers of 1’‒3’ are smaller than those of the corresponding
monomers by 0.06‒0.10 eV, which is consistent with the finding that the absorption onset of 1‒3 in
the electronic absorption spectra are red-shifted with increasing the concentration.38 Overall, the
experimental and theoretical results strongly support the formation of the dimers in an antiparallel
manner upon self-association in solution.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Formation of Self-Assembled Structures. Because 1‒3 show assembling properties in both the
solid state and the solution, we expected the fabrication of micro- and nanometer-sized
superstructures of 1‒3 through self-assembly by phase transfer method with a mixed solvent system,
in which the molecules in solution experience solubility change during a slow diffusion of a poor
solvent into the solution, thus initiating the formation of self-assembled clusters.39 To CHCl3
solutions of 1a‒3a, MeOH was slowly added.40 The resulting mixtures were allowed to stand at
0 °C, and purple fibrous materials formed (Figure S19). To investigate the morphology of the
materials obtained, we carried out SEM experiments, which confirmed the construction of
well-defined structures from 1a‒3a with high aspect ratio (Figure 8).41 Compounds 1a and 3a
formed long 1D nanobelts with the length up to 100 μm and the thicknesses of 100‒500 nm (Figure
8a,c). Meanwhile, 2a provided more flexible nanofibers with narrower widths of about 30‒80 nm
(Figure 8b).
18
ACS Paragon Plus Environment

Page 19 of 43
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 8. SEM images of self-assembled clusters
of (a) 1a, (b) 2a, and (c) 3a obtained from
CHCl3/MeOH solvent system.
We also attempted to fabricate self-assembled structures of 1b‒3b in CHCl3/MeOH solvent
system, but higher solubility of 1b‒3b than 1a‒3a hampered the formation of precipitates. On the
basis of the finding that the solubility of 1b‒3b in CH2Cl2 is somewhat lower than that in CHCl3, we
applied CH2Cl2/MeOH solvent system for 1b‒3b, which afforded the purple, fibrous materials.42
The SEM measurements confirmed the significant morphological difference, i.e. shape, size, and
appearance, in the self-assembled clusters between 1a‒3a and 1b‒3b, respectively. Compounds 1b
and 3b produced mictometer-sized 1D whiskers with a rough surface (Figure 9a,c), and the widths of
19
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 20 of 43
1
2
3
4
5
6
7
8
9
these clusters were non-uniform. Compound 2b exhibited flexible globular morphology, which
were entangled into complicated networks, with average widths of around 250 nm (Figure 9b). The
difference of the alkoxy chains is considered to affect the degree and balance of intermolecular
noncovalent interactions, namely π‒π stacking interactions between the π-conjugated frameworks
and van der Waals interactions between the alkoxy chains, as the driving force for self-assembly of
1a,b‒3a,b. Therefore, it is likely that the structural difference of the alkoxy chains in the
phenanthrene moiety between 1a‒3a and 1b‒3b is responsible for the observed morphological
difference, although the effect of the chlorinated solvents used on the morphology cannot be
excluded at all. The result that the morphology of the clusters of 2a,b markedly differed from that
of 1a,b and 3a,b may stem from large hydrophobicity of the CF3-substituents in 2a,b.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
20
ACS Paragon Plus Environment

Page 21 of 43
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 9. SEM images of self-assembled clusters
of (a) 1b, (b) 2b, and (c) 3b obtained from
CH2Cl2/MeOH solvent system.
Solvent is an important factor for molecular self-assembly in the solution-based process. We
performed the fabrication of self-assembled clusters for 1b‒3b by replacement of the good solvent
from CH2Cl2 to acetone; compounds 1a‒3a are almost insoluble in acetone.43 The morphology of
the self-assemblies of 1b‒3b formed in acetone/MeOH proved to be different from that formed in
CH2Cl2/MeOH (Figure 10), and the morphological change was especially pronounced in 2b. Thus,
1b‒3b formed 1D nanowhiskers, whose surfaces are markedly smooth, with widths of 250‒350 nm.
The observed morphological change depending on the solvents used may be associated with the facts
21
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 22 of 43
1
2
3
4
5
that acetone is a hydrophilic solvent, while CH2Cl2 is a hydrophobic one and/or the solubility of
6
7
1b‒3b in acetone is lower than that in CH2Cl2.44
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 10.
SEM images of self-assembled
clusters of (a) 1b, (b) 2b, and (c) 3b obtained from
acetone/MeOH solvent system.
The powder X-ray diffraction (PXRD) patterns of the self-assembled clusters of 1b‒3b obtained
from CH2Cl2/MeOH and acetone/MeOH were recorded to examine the effect of the solvents for
self-assembly on the molecular arrangements in the superstructures (Figure 11).45 There are two
22
ACS Paragon Plus Environment

Page 23 of 43
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
distinct 2θ regions where the characteristic reflection peaks are observable; one is the smaller angle
region (2θ = ca. 4‒7°) and the other is the larger angle region (2θ = ca. 23‒30°). For the latter
larger-2θ region, the corresponding d-spacing values are ranging from 3.0 to 3.8 Å. Considering
that the distance between a pair of π-conjugated frameworks in Figure 7 is estimable to be 3.4 Å,
such larger-2θ region surely contains the peak reflecting the π–π stacking periodicity.46 There are
multiple peaks in this larger-2θ region, but the strong peaks similarly locate around 2θ = ca. 26° for
all the clusters of 1b‒3b, independent of used solvents.47 A desirable agreement between the
calculated d-spacing value and the estimated π–π stacking distance supports our structural
assignment discussed above. Thus, the commonality of the peaks at 2θ = ca. 26° corresponding to
π–π stacking periodicity for 1b‒3b indicates that the interaction between the π-conjugated
frameworks is the key for the self-assembly of TQs prepared in this study.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The other smaller-2θ reflections of the clusters of 1b–3b also give us the valuable information for
the effects of substituents attached to the benzene rings on the packing and stacking arrangement of
the clusters because the peak appearances are characteristic in 1b–3b. The strong peaks around 2θ
= ca. 5° are observable for all the self-assembled clusters of 1b‒3b, independent of the used solvents.
However, the peak shape is quite different, i.e., the single peak for 1b, the two peaks for 2b, and the
other lower-2θ peaks are accompanied for 3b. Among these peak features, the single peak for 1b is
basically understandable because it contains no substituent on the benzene rings.
The
corresponding d-spacing is 18 Å, which is attributable to the lateral dimension of the smallest unit of
the cluster, namely, the self-assembled dimer as shown in Figure 7. The split peaks in 2b and 3b
are likely to be due to the substituent effect. As expected from Figure 7, the substituents on the
benzene rings in 2b and 3b should overlap with the 2-ethylhexyloxy groups on the phenanthrene
moiety. The CF3 group in 2b is bulky and hydrophobic, and hence it is considered that the
23
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 24 of 43
1
2
3
4
5
6
7
8
9
repulsion between the CF3 and 2-ethylhexyloxy groups occurs and partly separates the packing
distance between a lateral pair of the clusters, giving the slight peak shift into the lower-2θ side; a
combination of original peak position and partial peak shift is ascribed to the characteristic peak split
in 2b. In the case of 3b, the similar alkyl families of the OMe and 2-ethylhexyloxy groups are
easily conjugated, which restricts the periodicity of lateral arrangement of the clusters, resulting in
the remarkable intensity decrease of 2θ = ca. 5° peak. In turn, the strong peak newly appears
around the further lower 2θ of ca. 4°, corresponding to d-spacing value of 22 Å. Perhaps, the OMe
groups displace the parallel stacking of the cluster frameworks, and the resulting slip-off separates
the lateral arrangement of the frameworks. The remarkable intensity decrease of the peaks at 2θ =
ca. 5° is coincident with such slip-off arrangement model.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The solvents used remarkably affect the broadness of the above mentioned reflection peaks. The
clusters of 1b‒3b obtained from CH2Cl2/MeOH gave moderately sharp peaks. The diffraction
patterns of the clusters of 1b and 2b obtained from acetone/MeOH presented significantly broader
peaks than those of 1b and 2b obtained from CH2Cl2/MeOH, respectively. This apparently
indicates that the crystallinity of assembled 1b and 2b decreases upon changing a good solvent from
CH2Cl2 to acetone. It is noticeable that unlike in cases of 1b and 2b, the cluster of 3b obtained
from acetone/MeOH displayed the quite similar diffraction pattern to that obtained from
CH2Cl2/MeOH in spite of the drastically different morphology depending on the solvents used.
Thus, the cluster of 3b possesses both uniform morphology and moderate crystallinity, although the
reason for this finding is not clear at present. Overall, it is considered that the substituents on the
benzene rings in 1b–3b dominate the packing and stacking arrangement of the clusters in Å level.
In contrast, the solvents for self-assembly play important roles in control over the crystallinity and
morphology of their clusters in the nanometer scale.48
24
ACS Paragon Plus Environment

Page 25 of 43
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 11. PXRD patterns of superstructures of (a) 1b, (b) 2b, and (c) 3b obtained from CH2Cl2/MeOH
solvent system (black lines) or an acetone/MeOH solvent system (gray lines).
Conclusion
We have designed and synthesized π-extended thiadiazoloquinoxaline (TQ) derivatives 1a,b‒3a,b, in
which the tetraalkoxyphenanthrene moiety is fused with the TQ core and the benzene rings are
introduced via the ethynylene spacer, by oxidative transannular cyclization and Sonogashira coupling
with ethynylarenes as key steps, and demonstrated their intriguing electronic, optical, and
electrochemical properties and self-assembling behavior. The compounds in this work would be of
interest as π-functional materials owing to their appealing properties, such as the light absorption up
to 750 nm, the strong electron-accepting ability comparable to [60]fullerene, and the aggregation and
self-association properties through π‒π stacking interactions. By investigating the properties of 1a
and the reference compounds 4 and 5, it can be concluded that the combination of the fusion of the
phenanthrene moiety and the introduction of ethynylene spacers effectively extends π-conjugation
and enhances the acceptor potency and the self-association ability. The substituents on the benzene
rings proved to modulate the electronic properties moderately. Compounds 1a,b‒3a,b produced
nano- and microscopic 1D self-assembled clusters with high aspect ratios, and the difference in the
alkoxy groups on the TQ moiety and the solvents for self-assembly was found to influence the
25
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 26 of 43
1
2
3
4
5
6
7
morphology of the clusters. We believe that the present study will provide a valuable guideline for
the creation of TQ-based materials in organic electronics.
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Experimental Section
Preparation of 4,7-dibromo-2,1,3-benzothiadiazole-5,6-diamine (7).
To a solution of
4,7-dibromo-5,6-dinitro-2,1,3-benzothiadiazole (10) (1.00 g, 2.60 mmol) in acetic acid (15 mL) was
added in small portions iron powder (1.76 g, 31.5 mmol) at 100 °C. After the mixture was stirred at
100 °C for 1.5 h, EtOH (4.0 mL) was added to the mixture. After the resulting mixture was heated
for another 1.5 h, the precipitate was collected by filtration and washed with MeOH. The residue
was extracted by Soxhlet’s extractor with EtOAc for 3 days, and the extract was concentrated under
reduced pressure to afford 7 (0.42 g, 1.30 mmol, 50%) as brown needles; the original procedure for
1
purification was modified to obtain an analytically pure sample. The H NMR data are in
agreement with those previously reported.16 1H NMR (300 MHz, DMSO-d6): δ 6.39 (4H, s).
Preparation of 9a. A mixture of 6a (260 mg, 0.31 mmol) and 7 (100 mg, 0.31 mmol) in acetic acid
(30 mL) was heated at 80 °C for 22 h. After addition of water (30 mL), the mixture was extracted
with CH2Cl2 (15 mL × 3). The combined organic phase was washed with water (20 mL × 5), dried
over anhydrous MgSO4, and concentrated under reduced pressure. The residue was subjected to
column chromatography (SiO2; toluene/hexane 3:1) to afford crude 8a as red solids containing
inseparable impurities. To a solution of crude 8a (0.31 g) in CH2Cl2 (20 mL) was added vanadium
(V) oxytrifluoride (0.15 g, 1.21 mmol) in two portions in a period of 2 h at room temperature under
an argon atmosphere. After the mixture was stirred at room temperature for 5 h, aqueous citric acid
(10%, 50 mL) was added to the mixture. The organic phase was separated, and the aqueous phase
26
ACS Paragon Plus Environment

Page 27 of 43
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
was extracted with CHCl3 (50 mL × 4). The combined organic phase was washed with water (10
mL × 2), dried over anhydrous MgSO4, and concentrated under reduced pressure. The residue was
subjected to column chromatography (SiO2; CH2Cl2/hexane 1:2), and the collected material was
washed with hexane (20 mL) to afford 9a (0.23 g, 0.21 mmol, 66% in two steps) as brown solids.
An analytically pure sample was obtained by recycling GPC eluting with CHCl3. M.p. 212–214 °C;
1H NMR (500 MHz, CDCl3, 40 °C): δ 7.84 (2H, s), 7.06 (2H, s), 4.12 (4H, t, J = 6.5 Hz), 4.00 (4H, t,
J = 6.3 Hz), 1.97–1.88 (8H, m), 1.63–1.57 (8H, m), 1.52–1.35 (48H, m), 0.93 (6H, t, J = 7.0 Hz),
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
13
0.92 (6H, t, J = 7.0 Hz); C NMR (125 MHz, CDCl3, 40 °C): δ 152.8, 151.3, 149.0, 144.1, 137.7,
127.4, 122.0, 112.6, 109.1, 106.1, 69.4, 68.6, 32.20, 32.18, 30.06, 30.00, 29.97, 29.91, 29.8, 29.65,
abs
29.63, 26.55, 26.52, 22.9, 14.2 (25 signals out of 30 expected); UV‒vis (CHCl3): λmax (ε) 260
(38600), 282 (40000), 310 (50500), 476 (27200), 607 nm (sh, 2300); MALDI-TOF-MS (Dith,
positive): m/z 1121.7 [(M + H)+]; anal. calcd for C60H88Br2N4O4S: C, 64.27; H, 7.91; N, 5.00%,
found: C, 64.09; H, 8.00; N, 4.96%.
Preparation of 9b. A mixture of 6b (0.78 g, 1.08 mmol) and 7 (0.35 g, 1.08 mmol) in acetic acid
(20 mL) was heated at 80 °C for 21 h. After addition of water (50 mL), the mixture was extracted
with CH2Cl2 (20 mL × 3). The combined organic phase was washed with water (20 mL × 5), dried
over anhydrous MgSO4, and concentrated under reduced pressure. The residue was subjected to
column chromatography (SiO2; CH2Cl2/hexane 1:2) to afford crude 8b as red solids containing
inseparable impurities. To a solution of crude 8b (0.84 g) in CH2Cl2 (20 mL) was added vanadium
(V) oxytrifluoride (0.40 g, 3.23 mmol) in two portions in a period of 2 h at room temperature under
an argon atmosphere. After the mixture was further stirred at room temperature for 5 h, aqueous
citric acid (10%, 100 mL) was added to the mixture. The organic phase was separated, and the
27
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 28 of 43
1
2
3
4
5
6
7
8
9
aqueous phase was extracted with CHCl3 (30 mL × 3). The combined organic phase was washed
with water (20 mL × 2), dried over anhydrous MgSO4, and concentrated under reduced pressure.
The residue was purified by column chromatography (SiO2; CH2Cl2/hexane 1:3) and recrystallization
from acetone/MeOH to afford 9b (0.50 g, 0.50 mmol, 46% in two steps) as brown solids. An
analytically pure sample was obtained by recycling GPC eluting with CHCl3. M.p. 206–207 °C; 1H
NMR (400 MHz, CDCl3): δ 8.36 (2H, s), 7.42 (2H, s), 4.17 (4H, d, J = 5.6 Hz), 4.13 (4H, d, J = 5.6
Hz), 1.94–1.91 (4H, m), 1.71–1.39 (32H, m), 1.08 (6H, t, J = 7.6 Hz), 1.06 (6H, t, J = 7.6 Hz), 0.98
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
13
(6H, t, J = 7.0 Hz), 0.97 (6H, t, J = 7.0 Hz); C NMR (75 MHz, CDCl3): δ 153.6, 151.4, 149.5,
144.9, 138.1, 127.9, 122.2, 112.8, 109.4, 106.0, 71.7, 71.3, 39.8, 39.4, 30.93, 30.88, 29.42, 29.39,
abs
24.2, 23.39, 23.30, 14.38, 14.33, 11.6, 11.5 (25 signals out of 26 expected); UV‒vis (CHCl3): λmax
(ε) 261 (40100), 282 (42100), 311 (52700), 480 (28800), 607 nm (sh, 2200); MALDI-TOF-MS (Dith,
positive): m/z 1008.2 (M+); anal. calcd for C52H72Br2N4O4S: C, 61.90; H, 7.19; N, 5.55%, found: C,
61.83; H, 7.02; N, 5.48%.
Preparation of 1a. A suspension of 9a (108 mg, 96.6 μmol) in THF/Et3N (8:1, 90 mL) was
bubbled with argon with stirring for 30 min and 9a was dissolved by heating at ca. 50‒60 °C. The
resulting solution was allowed to cool to room temperature, and ethynylbenzene (30 mg, 0.30 mmol),
CuI (3 mg, 15 μmol), and [Pd(PPh3)4] (18 mg, 15 μmol) were added to the solution. The resulting
mixture was stirred at room temperature for 19 h under an argon atmosphere. CH2Cl2 (45 mL) was
added to the mixture. The resulting mixture was filtered through a bed of silica gel, and the filtrate
was concentrated under reduced pressure. The residue was purified by column chromatography
(SiO2; toluene) to afford 1a (17 mg, 15 μmol, 15%) as purple solids. An analytically pure sample
1
was obtained by recycling GPC eluting with CHCl3. M.p. 201 °C (decomp.); H NMR (600 MHz,
28
ACS Paragon Plus Environment

Page 29 of 43
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
CDCl3): δ 8.81 (2H, s), 7.87–7.86 (4H, m), 7.58 (2H, s), 7.45–7.44 (6H, m), 4.26 (4H, t, J = 5.4 Hz),
4.25 (4H, t, J = 5.1 Hz), 1.99–1.95 (4H, m), 1.92–1.87 (4H, m), 1.60–1.29 (56H, m), 0.90 (6H, t, J =
6.9 Hz), 0.89 (6H, t, J = 6.9 Hz); 13C NMR (150 MHz, CDCl3, 50 °C): δ 153.8, 153.0, 149.5, 144.2,
141.4, 132.3, 128.9, 128.5, 127.8, 124.1, 123.4, 113.1, 109.5, 106.8, 105.2, 86.5, 69.7, 68.8, 32.2,
29.97, 29.94, 29.91, 29.89, 29.84, 29.75, 29.63, 29.61, 26.54, 26.45, 22.9, 14.2 (31 signals out of 36
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
abs
expected); UV‒vis (CHCl3): λmax (ε) 265 (40700), 313 (52500), 323 (52500), 499 (21600), 646
(7100), 654 nm (7800); MALDI-TOF-MS (Dith, positive): m/z 1162.9 (M+); HR-FAB-MS (NBA,
positive): m/z calcd for C76H98N4O4S+ 1162.7309, found 1162.7316 (M+).
Preparation of 1b. A solution of 9b (100 mg, 99.1 μmol) in THF/Et3N (8:1, 30 mL) was bubbled
with argon with stirring for 30 min. Ethynylbenzene (40 mg, 0.40 mmol), CuI (4 mg, 20 μmol), and
[Pd(PPh3)4] (23 mg, 20 μmol) were added to the solution at 0 °C. The resulting mixture was stirred
at room temperature for 9 h under an argon atmosphere. CH2Cl2 (20 mL) was added to the mixture.
The resulting mixture was filtered through a bed of silica gel, and the filtrate was concentrated under
reduced pressure. The residue was purified by column chromatography (SiO2; EtOAc/hexane 1:19)
and recrystallization from acetone/MeOH to afford 1b (15 mg, 15 μmol, 15%) as purple solids. An
analytically pure sample was obtained by recycling GPC eluting with CHCl3. M.p. 155–156 °C; 1H
NMR (600 MHz, CDCl3): δ 8.84 (2H, s), 7.87–7.86 (4H, m), 7.61 (2H, s), 7.46–7.44 (6H, m), 4.18
(4H, d, J = 6.0 Hz), 4.16 (4H, d, J = 5.4 Hz), 1.93–1.89 (2H, m), 1.81–1.77 (2H, m), 1.66–1.30 (32H,
m), 1.03 (6H, t, J = 7.5 Hz), 0.94 (12H, t, J = 7.2 Hz), 0.89 (6H, t, J = 6.9 Hz); 13C NMR (150 MHz,
CDCl3): δ 153.8, 153.5, 149.9, 144.7, 141.4, 132.2, 129.1, 128.6, 128.1, 123.7, 123.2, 113.1, 109.3,
106.3, 105.4, 86.0, 71.8, 70.9, 40.1, 39.8, 30.90, 30.83, 30.81, 29.44, 29.39, 24.18, 24.13, 23.28,
abs
23.22, 14.3, 11.6 (31 signals out of 32 expected); UV‒vis (CHCl3): λmax (ε) 267 (43100), 316
29
ACS Paragon Plus Environment