7,14-Diaryl-substituted zethrene diimides as stable far-red dyes with tunable photophysical properties

Article abstract of DOI:10.1021/jo401061g

Synthesis and physical characterizations of a series of 7,14-diaryl-substituted zethrene diimides (ZDIs) bearing different substituents (alkyl chain, oligoethyleneglycol ether chain, and aryl group) at the imide sites as well as at the bay regions are described in this study. The synthesis takes advantage of Pd-catalyzed cyclodimerization reaction that allows construction of zethrene core and substitution at the bay region in one single step. The partially cyclized ZDI is also separated as a minor product. The carboxylic acid group is introduced to the bay region for the purpose of further bioconjugation. The photophysical properties, electrochemical properties, and photostability of these ZDI dyes are investigated with UV/vis spectroscopic measurements, cyclic voltammetry measurements, and photoirradiation tests. These dyes exhibit tunable photophysical properties in the far-red spectral region with moderate fluorescent quantum yields and good stability. The enhanced stability as compared to the parent zethrene and the 7,14-substituted zethrenes can be attributed to the electron-withdrawing effect of the imide groups and the kinetic blocking of the most reactive sites at the bay region.

Full text of DOI:10.1021/jo401061g

Subscriber access provided by Otterbein University
Article
7,14-Diaryl-substituted Zethrene Diimides as Stable
Far-red Dyes with Tunable Photophysical Properties
Zhe Sun, and Jishan Wu
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/jo401061g • Publication Date (Web): 28 Aug 2013
Downloaded from http://pubs.acs.org on September 2, 2013
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 29
The Journal of Organic Chemistry
1
2
3
4
7,14-Diaryl-substituted Zethrene Diimides as Stable Far-red Dyes
5
6
7
8
9
with Tunable Photophysical Properties
Zhe Sun[a] and Jishan Wu*[a, 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
[a] Department of Chemistry, National University of Singapore, 3 Science Drive 3, 117543, Singapore, chmwuj@nus.edu.sg
[b] Institute of Materials Research and Engineering, A*STAR, 3 Research Link, 117602, Singapore
TOC Graphic
ABSTRACT: Synthesis and physical characterizations of
a
series of
7,14-diaryl-substituted zethrene diimides (ZDIs) bearing different substituents (alkyl
chain, oligoethyleneglycol ether chain and aryl group) at the imide sites as well as at
the bay regions are described in this study. The synthesis takes advantage of
Pd-catalyzed cyclodimerization reaction that allows construction of zethrene core and
substitution at the bay region in one single step. The partially cyclized ZDI is also
separated as a minor product. The carboxylic acid group is introduced to the bay
region for the purpose of further bio-conjugation. The photo-physical properties,
electrochemical properties and photo-stability of these ZDI dyes are investigated with
UV/Vis spectroscopic measurements, cyclic voltammetry measurements and
photo-irradiation tests. These dyes exhibit tunable photophysical properties in the
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 2 of 29
1
2
3
4
5
6
7
8
9
far-red spectral region with moderate fluorescent quantum yields and good stability.
The enhanced stability compared to the parent zethrene and the 7,14-substituted
zethrenes can be attributed to the electron-withdrawing effect of the imide groups and
the kinetic blocking of the most reactive sites at the bay region.
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
INTRODUCTION
Zethrene refers to a type of Z-shaped polycyclic hydrocarbon where two terminal
naphthalene units are bridged by one or more butadiene moiety (Figure 1). Based on
the number of the butadiene moieties (n) or the number of the six-membered rings (m),
the molecule is called zethrene (n = 1, m = 6), heptazethrene (n = 2, m = 7),
octazethrene (n = 3, m = 8), and so on. This family of π-conjugated hydrocarbon has
long been fascinating to both theoretical chemists and synthetic chemists due to its
unique structure and physical properties.[1] Structurally, it represents a rare type of
polycyclic hydrocarbon with fixed double bonds in the central part, which makes the
central six-membered rings lack of aromaticity.[2] Our recent research demonstrated
the significant butadiene character of the two bridging double bonds in the smallest
member of this family, zethrene, where the two central benzenoid rings undergo
electrophilic addition instead of electrophilic substitution.[3] The higher order
zethrenes such as heptazethrene and octazethrene are better regarded as a structure
where the two naphthalene units are bridged by a p-quinodimethane and a
2,6-naphthaquinodimethane, respectively. A large singlet biradical character was
theoretically predicted for them due to the recovery of aromaticity of the central
ACS Paragon Plus Environment

Page 3 of 29
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
benzene and naphthalene moiety upon resonance from a closed-shell quinoidal form
to an open-shell biradical form.[4] As a result, these higher order zethrene molecules
are highly reactive, which has limited their synthesis for a long time.
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
R1
R1
O
N
O
imide site
O
N
O
R2
R2
R2
bay region
R2
n
n
R2
R2
O
N
O
n = 1, Zethrene
n = 2, Heptazethrene
n = 3, Octazethrene
O
N
O
R1
R1
ZDI
n = 0, PDI
n = 1, TDI
Figure 1. Structures of zethrenes, perylene diimide (PDI), terrylene diimide (TDI) and zethrene
diimide (ZDI).
The first pursuit of zethrene was reported by Clar in 1955.[5] Since then, a number
of synthetic approaches have been developed to access zethrene family including: (a)
transannular cyclizations from dehydroannulene species,[6] (b) Pd-catalyzed
cyclodimerization,[7] and (c) nucleophilic addition of the corresponding diketone
precursor followed by reduction.[8] During the synthesis, thermodynamic stabilization
by electron-withdrawing substituents (e.g. dicarboximide) and kinetic stabilization by
blocking the most reactive sites are necessary to obtain relatively stable zethrene
derivatives. Through these strategies, 7,14-disubstituted zethrenes,[7],[9] kinetically
blocked heptazethrene and octazethrene,[8] as well as zethrene diimide (ZDI)[3] and
heptazethrene diimide (HZ-DI) compounds[10] have been successfully prepared which
allows the experimental examination of many theoretical predictions, such as their
large singlet biradical character and their unique third-order non-linear optical
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 4 of 29
1
2
3
4
5
6
7
8
9
response. Driven by the fast development of the synthetic chemistry of zethrenes,
another task seems inevitable: how to make use of these molecules for practical
applications? Theoretical works have pointed out a number of possibilities for
zethrenes as organic ambipolar semiconductors,[11] nonlinear optical materials[4],[12]
and near-infrared dyes.[13] However, the study on this area is still in its early stage and
many obstacles need to be overcome, such as low material stability, lack of
functionality and low scalability. Among all possible applications of zethrenes, one
promising direction is to use it as a fluorescent dye in biological systems.
Fluorophores based on polycyclic aromatic hydrocarbon (PAH) usually enjoy better
photo-stability compared to commercially available fluorescent dyes (e.g. cyanine
dyes),[14] and their performance in biological systems can be optimized once the
following criteria are met: (a) water solubility, (b) high photo-/chemical stability, (c)
high fluorescence intensities, (d) absorption and emission maxima above 600 nm to
minimize self-absorption of the bio-molecules, (e) presence of functional groups for
attachment onto the bio-molecules and (f) scalable synthesis.[15] One representative
example of PAH-based fluorescent dye is the rylene compound.[16] Currently, many
works have been dedicated to perylene diimide (PDI) dyes and a few water soluble
PDIs have been prepared by attaching hydrophilic groups[17] or charged groups[18]
onto either the imide sites or the bay regions (Figure 1). The photophysical
properties of these dyes have been systematically studied[19] and they have been
successfully employed in the field of bio-imaging and bio-labeling.[20] However, the
absorption spectral region of PDI dyes still falls below 600 nm and up to now, only
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
ACS Paragon Plus Environment

Page 5 of 29
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
few terrylene diimide (TDI) dyes can absorb and emit above 600 nm while maintain
significant fluorescence.[21] On the other hand, zethrene diimide dyes reported by us[3]
provide an alternative choice due to the structural similarity to rylene diimides, with
both the imide sites and the bay region available for chemical modifications (Figure
1). In addition, ZDIs generally display emission spectra above 650 nm (far-red region)
with moderate fluorescence quantum yield,[3] which is desirable for bio-related
applications. However, the challenges lie in the stability, the water solubility, the
attachment of functional groups and above all, the suitable synthetic method.
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
Method 1:
Method 2:
R
N
R
N
R
N
R
O
O
O
O
O
O
O
N
O
R
O
N
O
[Pd]
Ar
Stille
Trannsannular
cyclization
Ar
Br Br
+
cyclodimerization
coupling
Br
Bu3Sn
SnBu3
Ar
O
N
R
O
O
N
R
O
O
N
R
O
Scheme 1. Two synthetic methods of ZDIs.
In the course of seeking for stable and soluble ZDI dyes, we previously reported
their synthesis by transannular cyclization reactions via a tetradehydro[10]annulene
intermediate (Method 1, Scheme 1). Unfortunately, this method does not allow further
substitution on the bay region as the attempted bromination on the 7,14-positions ends
up with oxidized diketone product due to the butadiene character of the central
bridge.[3] The stability of the obtained ZDI is not sufficient for practical applications.
To further improve the chemical and photo-stability and to introduce functionality, we
expect that the 7,14-diaryl-substituted zethrene diimide should be much more stable
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 6 of 29
1
2
3
4
5
6
7
8
9
due to the attachment of electron-withdrawing imide groups and the kinetic blocking
of the most reactive 7,14-positions with high HOMO coefficient. The synthesis can be
fulfilled by using Pd-catalyzed cyclodimerization approach[6] (Method 2, Scheme 1)
which allows construction of ZDI core and substitution at the bay region in one step.
Therefore, a series of ZDI2-ZDI4 with different substituents in the imide sites are
prepared which show tunable photophyscial properties and a large enhancement in
stability compared to ZDI1 (Figure 2). The different substituents were chosen to serve
different purposes, for example, the oligoethyleneglycol ether chains can increase the
solubility in polar solvent while the 2,6-diisopropylphenyl groups are known to be
effective for suppressing dye aggregation, thus preventing fluorescence quenching.
Moreover, carboxylic acid groups are attached at the bay region to afford ZDI5 for
the purpose of further conjugation with bio-molecules. The partially cyclized ZDI6 is
also obtained as a minor product (Figure 2). Herein, the synthesis, structure,
photophysical properties, electrochemical properties and photo-stability test of these
novel 7,14-diaryl-substituted ZDI far-red dyes are investigated in detail.
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
ACS Paragon Plus Environment

Page 7 of 29
The Journal of Organic Chemistry
1
2
3
4
R
5
O
N
O
O
N
O
6
7
8
ZDI2: R =
ZDI3: R =
O
O
O
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
ZDI4: R =
O
N
O
O
N
R
O
ZDI1
O
N
O
O
N
O
HOOC
HOOC
COOH
COOH
O
N
O
O
N
O
ZDI5
ZDI6
Figure 2. Structures of ZDI derivatives ZDI1-ZDI6
RESULTS AND DISCUSSION
Synthesis: The synthesis of all target compounds is outlined in Scheme 2, starting
from 1,8-dibromonaphthoic anhydride 2 previously reported by us.[3] Imidization of 2
with 3,7-dimethyloctan-1-amine and 2-(2-(2-methoxyethoxy)ethoxy)ethanamine in
toluene/ethanol mixed solvent under reflux afforded 3 in 80% yield and 4 in 65%
yield, respectively. Compound
5
was obtained by reacting
2
with
2,6-diisopropylaniline in refluxing acetic acid. The obtained monoimide intermediates
3-5 were then subjected to one fold Sonogashira coupling reaction by treating with 1
equivalent phenylacetylene in THF/triethylamine mixed solvents in presence of
Pd(PPh)2Cl2/CuI. The reaction carried on smoothly at room temperature and gave the
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 8 of 29
1
2
3
4
5
6
7
8
9
mono-substituted products 6-8 in 62-70% yield. However, the reaction time must be
strictly controlled within 30 minutes since the two-fold coupling by-products will
make the separation extremely difficult, especially for compound 7 with
oligoethyleneglycol ether substituents. Although the two-fold coupling by-products
for 7 and 8 cannot be excluded completely, the crude material can be used for the next
step directly. Then, the precursors 6-8 were heated up to 130 oC in degassed o-xylene
using Pd(OAc)2/P(furyl)3 as catalyst and Ag2CO3 as base to provide the desired
ZDI2-ZDI4 as blue solids in 30-35% yield.[22] The structures of ZDI2-ZDI4 were
identified by NMR spectroscopy and high-resolution mass spectrometry (Supporting
Information (SI)).
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 efforts were also made to attach carboxylic acid groups at the bay region as
functional sites for future bio-conjugation. The 2,6-diisopropylphenyl group was
chosen as the substituent at the imide site to suppress dye aggregation. As shown in
Scheme 2, compound 5 was treated with tert-butyl-4-ethynylbenzoate under
Sonogashira coupling condition to afford precursor 9 in 75% yield, which was further
subjected to similar cyclodimerization condition to give 10 in 28% yield. A partially
cyclized product 11 was also isolated as a minor product in 5% yield by silica gel
column chromatography, whose polarity was slightly lower than 10. Similar partially
cyclized products were also obtained in the cases of ZDI2 and ZDI4, but the amount
was quite small. However, in the case of ZDI3, no such by-product was observed. The
NMR spectrum of 11 is quite complicated due to the loss in symmetry; however, the
structure can be determined with the help of 2D-COSY NMR spectrum and
ACS Paragon Plus Environment

Page 9 of 29
The Journal of Organic Chemistry
1
2
3
4
5
6
high-resolution mass spectrometry (see SI). Hydrolysis of the ester groups in 10 and
11 with trifluoroacetic acid (TFA) gave the corresponding acids ZDI5 and ZDI6 in
7
8
9
85-90% yield.
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
R
O
N
O
R
N
O
O
3, 6, ZDI2: R =
4, 7, ZDI3: R =
5, 8, ZDI4: R =
O
O
O
ZDI2, 30%
ZDI3, 35%
ZDI4, 32%
(a), for 3, 4
(b), for 5
(c)
(d)
O
O
O
Br
Br Br
Br Br
6, 67%
7, 62%
8, 70%
3, 80%
4, 65%
5, 29%
2
O
N
O
O
N
O
O
N
O
O
O
O
O
O
N
O
(d)
(e)
+
Br
O
O
O
O
Br Br
O
N
O
O
N
O
5
O
O
9, 75%
10, 28%
11, 5%
(f)
(f)
ZDI5, 90%
ZDI6, 85%
Scheme 2. Synthesis of ZDI2-ZDI6. Synthetic conditions: (a) 3,7-dimethyloctan-1-amine or
2-(2-(2-methoxyethoxy)ethoxy)ethanamine, toluene/ethanol, reflux, 3h; (b) 2,6-diisopropylaniline,
AcOH, reflux, 24h; (c) phenylacetylene, Pd(PPh3)2Cl2, CuI, THF/triethylamine, RT, 30 mins; (d)
Pd(OAc)2, P(2-furyl)3, Ag2CO3, o-xylene, 130 oC, 18h; (e) t-butyl-4-ethynylbenzoate, Pd(PPh3)2Cl2,
CuI, THF/triethylamine, RT, 30 mins; (f) trifluoroacetic acid, DCM, RT, 12h.
Photophysical properties: All the obtained ZDI dyes are soluble in common organic
solvents including dichloromethane (DCM), CHCl3 and tetrahydrofuran (THF) to give
a blue solution, and the solubility is found substituent-dependant in certain solvents.
For example, ZDI1, ZDI2 and ZDI4 are soluble in hexane but not soluble in polar
solvents such as methanol, whereas ZDI3 and ZDI5 are soluble in methanol, DMSO
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 10 of 29
1
2
3
4
5
6
7
8
9
and partially in water due to the presence of hydrophilic groups such as
oligoethyleneglycol ether and carboxylic acid units. The UV/Vis absorption and
fluorescence spectra of ZDI1-ZDI6, recorded in DCM are shown in Figure 3 and the
data are collected in Table 1. All ZDI dyes display well-resolved absorption spectra
with maxima ranging from 600 nm to 650 nm, and molar extinction coefficient (ε) in
the order of 104 M-1cm-1. The absorption wavelength is longer than PDI dyes and is
comparable to TDI dyes, which is suitable for bio-imaging and bio-labeling
applications. Compared to ZDI1, all 7,14-disubstituted ZDI dyes exhibit 18–41 nm
hypsochromic shifts, presumably due to the deviation from planarity induced by the
bay-region substitution. In addition, compared to ZDI5, the partially cyclized ZDI6
displays a hypsochromic shift in absorption, which could be explained by Clar’s
aromatic sextet rule as ZDI6 possesses one more aromatic sextet ring in the backbone
than ZDI5, and similar examples are also reported for other PAHs.[23] On the other
hand, all ZDI dyes are fluorescent in DCM with emission maxima ranging from 626
nm to 704 nm, which is also a desirable window for many bio-related applications.
The photoluminescence quantum yield (Ф) were determined according to an optical
dilute method (optical density A ‹ 0.05) using Rhodamine B as a standard.[24] The 7,
14-diaryl-substituted ZDI dyes show moderate quantum yields and smaller than that
of ZDI1 due to the twisted structure. Moreover, a substituent-dependant phenomenon
was also observed. ZDIs with alkyl chains (ZDI2) or oligoethyleneglycol ether chains
(ZDI3) in the imide sites show significantly lower Ф values than ZDI4 with
2,6-diisopropylphenyl group, which is known to be effective to suppress dye
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
ACS Paragon Plus Environment

Page 11 of 29
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
aggregation. The formation of dye aggregation is also evidenced by the
concentration-dependant fluorescence measurements (SI), ZDI2-ZDI4 exhibit
decrease in the fluorescence intensities with the decrease in solution concentration
from 10-5 M to 10-4 M, together with a hypsochromic shift in the fluorescence maxima.
This observation suggests that the major fluorescence quenching pathway in this
series of dyes is aggregation. It is also worth noting that all 7,14-diaryl-substituted
ZDI dyes exhibit larger Stokes shift (ranging from 60 nm to 74 nm), compared to
ZDI1 (20 nm), arising from the decrease in rigidity of the structure. A large Stokes
shift is one of the crucial requirements for applications in bio-imaging.
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
20000
1.0
(a)
(b)
ZDI1
ZDI2
ZDI3
ZDI4
ZDI1
ZDI2
ZDI3
ZDI4
15000
10000
5000
0
0.8
0.6
0.4
0.2
0.0
300
400
500
600
700
800
600
650
700
750
800
850
900
Wavelength (nm)
Wavelength (nm)
15000
10000
5000
0
1.0
0.8
0.6
0.4
0.2
0.0
(c)
ZDI5
ZDI6
(d)
ZDI5
ZDI6
300
400
500
600
700
800
550
600
650
700
750
800
850
900
Wavelength (nm)
Wavelength (nm)
Figure 3. UV-Vis absorption and fluorescence spectra recorded in DCM solutions: (a) absorption
spectra of ZDI1-ZDI4, (b) normalized fluorescence spectra of ZDI1-ZDI4, (c) absorption spectra of
ZDI5 and ZDI6, and (d) normalized fluorescence spectra of ZDI5 and ZDI6. The excitation
wavelengths for the fluorescence measurements are 590 nm for ZDI1 – ZDI5 and 580 nm for ZDI6.
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 12 of 29
1
2
3
4
Table 1. Photophysical data of ZDI compounds ZDI1-ZDI6 recorded in DCM.
5
6
7
8
9
Compd
λabs
ε
λem
Stokes
Shift
(cm-1)
462
Ф
(nm) (M-1cm-1) (nm)
ZDI1
ZDI2
ZDI3
ZDI4
ZDI5
ZDI6
648,
596
630,
585
630,
585
631,
581
622,
575
607,
562
18600
12100
12300
13700
13400
12900
668
704
695
702
682
626
0.53
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
1669 0.13
1485 0.05
1603 0.24
1414 0.30
500
0.75
Electrochemical properties: The electrochemical properties of ZDI2-ZDI6 were
investigated by cyclic voltammetry (Figure 4) and differential pulse voltommetry (see
SI) measurements, with anodic scan performed in anhydrous DCM and cathodic
sweeping in anhydrous THF. The electrochemical data, including half-wave potentials,
HOMO, LUMO energy levels and energy gaps are listed in Table 2. Electrochemical
data for ZDI1 collected in DCM is also listed for comparison. In general, ZDI1-ZDI4
exhibited one or two quasi-reversible oxidation waves and two to three reversible
reduction waves, suggesting that all these compounds can be reversibly reduced into
corresponding anionic species which can be stabilized by the electron-withdrawing
imide groups. The lowest half-wave oxidation potentials fluctuated from 0.84 to 0.93
V (vs Fc/Fc+), showing an anodic shift compared to the 7,14-disubstituted zethrenes
without imide groups (e.g., 0.29 V for 7,14-bis(phenylethynyl)zethrene) due to the
attachment of electron-withdrawing imide groups. For ZDI5 and ZDI6, only
ACS Paragon Plus Environment

Page 13 of 29
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
irreversible oxidation waves were observed due to the introduction of additional
electron-withdrawing carboxylic acid groups in the bay regions, which could further
destabilize the cationic species. In both cases two reversible reduction waves were
observed. The HOMO and LUMO energy levels were deduced from the onset
potentials of the first oxidation (Eoxonset) and the first reduction wave (Eredonset), on a
basis of the following equations: HOMO = -(4.8+ Eoxonset) and LUMO = -(4.8+
Eredonset).[26] The HOMO energy levels of all ZDI dyes are ranging from -5.50 eV to
-5.63 eV, which are quite low lying and suggest a good oxidation resistance. Among
them, the HOMO energy levels of 7,14-diaryl-substituted ZDI dyes are slightly lower
than that of ZDI1, indicating that substitution at the bay regions increases the
chemical stability of ZDI dyes. On the other hand, the LUMO energy levels of all ZDI
dyes are ranging from -3.87 eV to -4.05 eV, in which ZDI5 exhibited the lowest
LUMO energy level (-4.05 eV), arising from a high electron affinity resulted from
synergistic electron-withdrawing effect of imide substitution and the acid substitution.
The HOMO-LUMO energy gaps of these ZDI dyes are determined as 1.49 eV to 1.66
eV from electrochemical measurements and 1.81 eV to 1.92 eV from optical
measurements. Compared to ZDI5, ZDI6 showed a larger HOMO-LUMO gap which
is in agreement with blue shifted absorption maximum.
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
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 14 of 29
1
2
3
4
5
6
(a)
7
8
9
(b)
(c)
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
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
Potential (V) vs Fc/Fc+
(d)
(e)
-1.5
-1.0
-0.5
0.0
0.5
1.0
Potential (V) vs Fc/Fc+
Figure 4. Cyclic voltammograms of (a) ZDI2, (b) ZDI3, (c) ZDI4, (d) ZDI5 and (e) ZDI6 in DCM
(for anodic scan) and THF (for cathodic scan) with 0.1M Bu4NPF6 as supporting electrolyte, AgCl/Ag
as reference electrode, Au disk as working electrode, Pt wire as counter electrode, and a scan rate of 50
mVs-1.
Table 2. Electrochemical data of ZDI compounds ZDI1-ZDI6.[a]
1
2
1
2
3
4
EC
Opt
Compt
Eox
Eox
Ered
Ered
Ered
Ered
HOM
O[b]
[eV]
-5.50
-5.53
-5.55
-5.63
-5.54
-5.54
LUM
O[b]
Eg
Eg
[V]
[V]
[V]
[V]
[V]
[V]
[eV][c] [eV] [d]
[eV]
-3.96
-3.87
-3.96
-4.01
-4.05
-3.91
0.93
0.84
0.85
0.90
-
-
-0.84
-1.02
-0.96
-0.95
-0.89
-0.97
-0.99
-1.25
-1.16
-1.21
-1.14
-1.20
-1.30
-
-
1.54
1.66
1.59
1.62
1.49
1.63
1.81
1.84
1.84
1.83
1.85
1.92
ZDI1
ZDI2
ZDI3
ZDI4
ZDI5
ZDI6
1.18
1.17
1.30
-
-
-1.40
-1.28
-
-1.88
-
-
-
-
-
-
[a] The redox potentials are calibrated by Fc/Fc+ [b] HOMO and LUMO energy levels were deduced
ACS Paragon Plus Environment

Page 15 of 29
The Journal of Organic Chemistry
1
2
3
4
from the onset potentials of the first oxidation (Eonset ) and the first reduction wave (Eonset
),
ox
red
5
6
7
EC
according to the following equations: HOMO = -(4.8+ Eonsetox ) and LUMO = -(4.8+ Eonset red ). [c] Eg
8
9
Opt
is the electrochemical band gap deduced from the LUMO-HOMO. [d] Eg is optical band gap
estimated from the lowest energy absorption onset.
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
Photo-stability test: The photo-stability of zethrene derivatives is one of the most
essential factors for their preparation, isolation and application, as zethrene itself is
proven to be air- and light-sensitive.[5] Even the 7,14-diphenyl zethrene can be
completely decomposed in 12 hours upon irradiation with sunlight at room
temperature in air.[7] In contrast, all the ZDI dyes can be stored as solids under
ambient conditions for months, despite their smaller band gaps. In solution, the
7,14-diaryl-substituted ZDIs exhibited better stability than the unsubstituted ZDI1.
The photo-stability of ZDI1, ZDI4 and ZDI5 were tested by irradiation with a UV
lamp (4 W), a white-light bulb (100 W) and ambient light, and the change of optical
intensity at the longest absorption band is plotted against the irradiation time as shown
in Figure 5. All dyes degraded with half-life times (t1/2) less than 1 hour under UV
irradiation. In the case of white-light irradiation, ZDI4 and ZDI5 displayed much
larger enhancement in stability, as ZDI1 degraded 50% in optical intensity in 10 hours
while ZDI4 and ZDI5 degraded less than 10% during same period. Under ambient
condition, ZDI4 and ZDI 5 exhibited a significant improvement compared to ZDI1
due to the blocking in bay regions. In particular, ZDI5 showed degradation with less
than 10% over more than 10 days. This remarkable enhancement of photo-stability
can be attributed to the electron-withdrawing effect caused by imide and acid
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 16 of 29
1
2
3
4
substituents, as well as the kinetic blocking of the 7,14-positions at the bay region.
5
6
7
ZDI1
ZDI5
1.0
ZDI4
8
9
0.8
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
0.6
0.4
0.2
0
10
20
30
40
50
Time (min)
ZDI1
ZDI5
ZDI4
1.0
0.9
0.8
0.7
0.6
0.5
0.4
-5
0
5
10
15
20
25
30
35
40
Time (h)
ZDI1
ZDI5
ZDI4
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0
2
4
6
8
10
12
Time (days)
Figure 5. Photo-stability test of ZDI1, ZDI4 and ZDI5 in CHCl3 upon irradiation with (a) UV lamp
(254 nm, 4W), (b) white light bulb (100 W) and (c) ambient light.
ACS Paragon Plus Environment

Page 17 of 29
The Journal of Organic Chemistry
1
2
3
4
5
6
CONCLUSION
n summary, a series of 7,14-diaryl-substituted ZDI molecules (ZDI2-ZDI5), together
I
7
8
9
with a partially cyclized ZDI molecule (ZDI6) were synthesized through Pd-catalyzed
cyclodimerization reaction. This synthetic approach allows the bay-region
substitutions for ZDI dyes for the first time. The modifications can be done on both
imide structure and bay region. The solubility, optical properties and electrochemical
properties are tunable by introducing different substituents. The obtained ZDI dyes
are investigated in their photophysical properties, electrochemical properties and
photo-stability. The good photo-stability, moderate fluorescence quantum yield,
favourable absorption/emission envelope and attachment of carboxylic acid as
bio-conjugation sites make them promising candidates for applications in biological
systems. The studies on their applications for bio-imaging and bio-labeling are
currently underway in our laboratories.
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
General: All reagents were purchased from commercial suppliers and used as
received without further purification. Anhydrous DCM was distilled from CaH2 and
anhydrous THF was distilled from sodium. 4,6-dibromo-1,8-naphthalimide 5 and 1,
8-dibromonaphthoic anhydride 2 was prepared according to our previous report.[3]
3,7-Dimethyloctan-1-amine,
2-(2-(2-methoxyethoxy)ethoxy)ethanamine
and
1
t-butyl-4-ethynylbenzoate were prepared according to literature.[26] The H NMR and
13C NMR spectra were recorded in solution of CDCl3 with tetramethylsilane (TMS) as
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 18 of 29
1
2
3
4
5
6
7
8
9
the internal standard. The following abbreviations were used to explain the
multiplicities: s = singlet, d = doublet, t = triplet, m = multiplet. MALDI-TOF mass
spectra (MS) were recorded using anthracene-1,8,9-triol as matrix. The fluorescence
quantum yields were measured by optical dilute method (A < 0.05) using Rhodamine
B (λabs = 543 nm, Φ = 0.7 in ethanol) as reference.[25] The electrochemical
measurements were carried out in anhydrous DCM and anhydrous THF with 0.1M
tetrabutylammonium hexafluorophosphate (Bu4NPF6) as the supporting electrolyte at
a scan rate of 0.05 V/s at room temperature under the protection of nitrogen. A gold
disk was used as working electrode, platinum wire was used as counting electrode,
and Ag/AgCl (3M KCl solution) was used as reference electrode. The potential was
calibrated against the ferrocene/ferrocenium couple.
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
General
synthetic
procedure
for
4,6-dibromo-1,8-naphthalimides:
1,8-Dibromonaphthoic anhydride 2 (1.00 g, 2.83 mmol) was suspended in a mixture
solvent of ethanol (20 mL) and toluene (20 mL). To the suspension was added
corresponding amine (5.66 mmol, 2 equiv.) and the resulted mixture was then stirred
at reflux for 3 hours under argon atmosphere. The solvent was then removed and the
residue was purified by column chromatography.
Compound 3: 3,7-Dimethyloctan-1-amine was used and 3 was obtained by column
chromatography (silica gel, DCM: hexane = 1:3 (v/v)) as white solid (1.12 g) in 80%
1
yield. H NMR (CDCl3, 300 MHz) δ: 8.32 (d, J = 7.9 Hz, 2H), 8.13 (d, J = 7.9 Hz,
2H), 4.13 (m, 2H), 0.83-1.67 (m, 19H) ppm. 13C NMR (CDCl3, 75 MHz) δ: 162.9,
ACS Paragon Plus Environment

Page 19 of 29
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
136.0, 131.3, 131.0, 128.0, 127.5, 123.0, 39.2, 39.1, 37.0, 34.8, 31.2, 27.9, 24.6, 22.7,
22.6, 19.5 ppm. HR-MS (EI): m/z: [M]+, calcd. for C22H25O2NBr2 493.0252; Found
493.0242.
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
Compound 4: 2-(2-(2-methoxyethoxy)ethoxy)ethanamine was used and 4 was
obtained by column chromatography (silica gel, ethyl acetate: hexane = 1:2 (v/v)) as
1
orange solid (915 mg) in 65% yield. H NMR (CDCl3, 300 MHz) δ: 8.37 (d, J = 3.4
Hz, 2H), 8.18 (d, J = 3.4 Hz, 2H), 4.39 (d, J = 1.9 Hz, 2H), 3.43-3.82 (m, 10H), 3.31
(s, 3H) ppm. 13C NMR (CDCl3, 75 MHz) δ: 163.1, 136.1 131.5, 128.1, 123.0, 71.8,
70.6, 70.5, 70.1, 67.7, 59.0, 39.4 ppm. HR-MS (EI): m/z: [M]+, calcd. for
C19H19Br2NO5 498.9630. Found 498.9627.
General synthetic procedure for 4-bromo-5-arylsilylethynyl-1,8-naphthalimides:
4,6-Dibromo-1,8-naphthalimide (1.00 mmol), Pd(PPh3)2Cl2 (0.05 mmol, 5%), CuI
(0.10 mmol, 10%) were dissolved in THF (5 mL) and triethylamine (5 mL) under
argon atmosphere. Aryl acetylene (1.20 mmol, 1.2 equiv.) was added and the mixture
was stirred in room temperature for 30 minutes. The mixture was then poured into
water and extracted with chloroform. The organic layer was washed with water and
brine, each for 3 times and dried over anhydrous Na2SO4. The solvent was removed
and the residue was purified by column chromatography to afford the corresponding
product.
Compound 6: Compound 3 and phenyl acetylene were used as starting materials and
compound 6 was obtained as a yellow solid (345 mg) in 67% yield by column
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 20 of 29
1
2
3
4
5
6
7
8
9
chromatography (silica gel, DCM: hexane = 1:3 (v/v)). 1H NMR (CDCl3, 300 MHz) δ:
8.53 (d, J = 7.7 Hz, 1H), 8.36 (d, J = 8.1 Hz, 1H), 8.08 (d, J = 7.8 Hz, 1H), 8.04 (d, J
= 8.2 Hz, 1H), 7.61 (m, 2H), 7.41 (m, 3H), 4.15 (m, 2H), 0.84-1.73 (m, 19H) ppm.
13C NMR (CDCl3, 125 MHz) δ: 163.3, 163.1, 135.6, 134.6, 131.2, 130.6, 130.0, 129.3,
129.0, 128.6, 127.8, 123.0, 122.6, 103.2, 89.4, 39.3, 39.1, 37.1, 34.9, 31.3, 27.9, 24.6,
22.7, 22.6, 19.5 ppm. HR-MS (EI): m/z: [M]+, calcd. for C30H30O2NBr 515.1460;
Found 515.1458
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
Compound 7: Compound 4 and phenyl acetylene were used as starting materials and
compound 7 was obtained as a yellow solid (323 mg) in 62% yield by column
1
chromatography (silica gel, ethyl acetate: hexane = 1:2 (v/v)). H NMR (CDCl3, 500
MHz) δ: 8.54 (d, J = 7.6 Hz, 1H), 8.36 (d, J = 7.6 Hz, 1H), 8.09 (d, J = 7.6 Hz, 1H),
8.05 (d, J = 7.6 Hz, 1H), 7.62 (m, 2H), 7.42 (m, 3H), 4.41 (m, 2H), 3.31-3.83 (m,
10H), 3.31 (s, 3H) ppm. 13C NMR (CDCl3, 75 MHz) δ: 163.4, 163.2, 135.6, 134.6,
131.7, 131.4, 131.2, 131.1, 131.0, 130.1, 129.3, 129.1, 128.8, 128.6, 128.1, 128.0,
123.0, 122.5, 103.3, 89.3, 71.8, 70.6, 70.5, 70.1, 67.7, 59.0, 39.3, 29.7 ppm. HR-MS
(EI): m/z: [M]+, calcd. for C27H24O5NBr 521.0838; Found 521.0814.
Compound 8: Compound 5 and phenyl acetylene were used as starting materials and
compound 8 was obtained as a yellow solid (375 mg) in 70% yield by column
chromatography (silica gel, DCM: hexane = 1:3 (v/v)). 1H NMR (CDCl3, 500 MHz) δ:
8.65 (d, J = 7.5 Hz, 1H), 8.48 (d, J = 8.2 Hz, 1H), 8.19 (d, J = 8.2 Hz, 1H), 8.16 (d, J
= 7.5 Hz, 1H), 7.67 (m, 2H), 7.49 (t, J = 8.2 Hz, 1H), 7.44 (m, 3H), 7.34 (d, J = 7.7
ACS Paragon Plus Environment

Page 21 of 29
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
Hz, 2H), 2.71 (m, 2H), 1.17 (d, J = 5.7 Hz, 12H) ppm. 13C NMR (CDCl3, 75 MHz) δ:
163.5, 163.3, 145.6, 135.7, 134.7, 131.9, 131.3, 131.2, 130.9, 130.4, 129.7, 129.5,
129.4, 129.2, 128.6, 128.4, 124.1, 123.0, 122.7, 122.6, 103.6, 89.4, 29.2, 23.9 ppm.
HR-MS (EI): m/z: [M]+, calcd. for C32H26O2NBr 535.1147; Found 535.1143.
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
Compound 9: Compound 5 and t-butyl-4-ethynylbenzoate were used as starting
materials and compound 9 was obtained as a yellow solid (476 mg) in 75% yield by
column chromatography (silica gel, DCM: hexane = 1:3 (v/v)). 1H NMR (CDCl3, 500
MHz) δ: 8.66 (d, J = 7.6 Hz, 1H), 8.49 (d, J = 7.7 Hz, 1H), 8.19 (d, J = 8.7 Hz, 1H),
8.17 (d, J = 7.6 Hz, 1H), 8.05 (d, J = 8.2 Hz, 2H), 7.70 (d, J = 8.2 Hz, 2H), 7.48 (t, J =
7.6 Hz, 1H), 7.33 (d, J = 7.6 Hz, 2H), 2.7 (m, 2H), 1.69 (s, 9H), 1.16 (dd, 4J = 1.3 Hz,
3J = 6.9 Hz, 12H) ppm. 13C NMR (CDCl3, 125 MHz) δ: 165.0, 163.5, 163.3, 145.6,
136.0, 134.9, 132.5, 132.0, 131.2, 130.9, 130.8, 130.3, 129.7, 129.6, 129.5, 129.0,
12.8, 126.9, 124.1, 123.0, 122.7, 102.5, 91.5, 81.6, 29.2, 28.2, 23.9 ppm. HR-MS (EI):
m/z: [M]+, calcd. for C37H34O4NBr 635.1671; Found 635.1653.
General synthetic procedure for 7,14-diaryl-zethrenebis(dicarboximide)s: The
corresponding 4-bromo-5-arylsilylethynyl-1,8-naphthalimide (0.3 mmol), Pd(OAc)2
(7 mg, 30 ꢀmol), P(2-furyl)3 (10 mg, 45 ꢀmol) and Ag2CO3 (83 mg, 0.3 mmol) were
dissolved in o-xylene (10 mL) and purged with argon for 20 minutes, then the mixture
o
was heated up to 130 C and kept at this temperature for 18 hours. After cooled to
room temperature, the solvent was removed under reduced pressure and the residue
was subjected to column chromatography and then preparative TLC to afford the
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 22 of 29
1
2
3
4
corresponding 7,14-diarylzethrenebis(dicarboximide)s.
5
6
7
8
9
ZDI2: Compound 6 was used as starting material and ZDI2 was obtained as a blue
solid (40 mg) in 30% yield by column chromatography (silica gel, CHCl3).
Analytically pure ZDI2 was obtained by preparative TLC (CHCl3:hexane = 1:1 (v/v)).
1H NMR (CDCl3, 500 MHz) δ: 8.43 (d, J = 7.6 Hz, 1H), 8.09 (d, J = 8.2 Hz, 1H), 7.53
(m, 3H), 7.42 (d, J = 8.2 Hz, 1H), 7.41 (d, J = 8.2 Hz, 1H), 7.30 (m, 2H), 4.17 (m,
2H), 0.85-1.73 (m, 19H) ppm. 13C NMR (CDCl3, 125 MHz) δ: 163.7, 163.5, 140.9,
137.9, 137.8, 136.0, 133.3, 131.2, 131.0, 130.1, 128.8, 127.7, 125.6, 126.3, 122.1,
121.1, 114.1, 39.3, 39.0, 37.1, 35.1, 31.3, 30.0, 28.0, 24.6, 22.7, 22.6, 19.6 ppm.
HR-MS (MALDI-TOF): m/z : [M+H]+, calcd. for C60H61N2O4 873.4626; Found
873.4594.
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
ZDI3: Compound 7 was used as starting material and ZDI3 was obtained as a blue
solid (46 mg) in 35% yield by column chromatography (silica gel, ethyl acetate: DCM
= 1:10 (v/v)). Analytically pure ZDI3 was obtained by preparative TLC (CHCl3: ethyl
acetate = 5:1 (v/v)). 1H NMR (CDCl3, 500 MHz) δ: 8.43 (d, J = 8.2 Hz, 1H), 8.09 (d,
J = 8.2 Hz, 1H), 7.53 (d, J = 6.9 Hz, 2H), 7.42 (d, J = 8.2 Hz, 2H), 7.29-7.31 (m, 3H)
4.42 (t, J = 5.7 Hz, 2H) 3.45-3.83 (m, 10H) 3.33 (s, 3H) ppm. 13C NMR (CDCl3, 75
MHz) δ: 163.7, 163.6, 140.9, 138.0, 137.7, 136.1, 133.3, 131.3, 131.0, 130.9, 130.1,
128.8, 127.8, 126.6, 126.3, 121.9, 120.9, 71.9, 70.6, 70.5, 70.1, 68.0, 59.0, 39.1, 31.9,
31.6, 29.7, 29.3, 22.7, 14.1 ppm. HR-MS (EI): m/z: [M]+, calcd. for C54H48N2O10
884.3309; Found 884.3303.
ACS Paragon Plus Environment

Page 23 of 29
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
ZDI4: Compound 8 was used as starting material and ZDI4 was obtained as a blue
solid (44 mg) in 32% yield by column chromatography (silica gel, CHCl3)
Analytically pure ZDI2 was obtained by preparative TLC (CHCl3:hexane = 1:1 (v/v)).
1H NMR (CDCl3, 500 MHz) δ: 8.51 (d, J = 7.6 Hz, 2H), 8.16 (d, J = 8.2 Hz, 2H), 7.58
(m, 5H), 7.52 (d, J = 8.2 Hz, 2H), 7.47 (m, 5H), 7.47 (d, J = 7.9 Hz, 1H), 7.39 (m,
4H), 7.32 (d, J = 7.7 Hz, 4H), 2.72 (m, 4H), 1.15 (d, J = 6.9 Hz, 24H) ppm. 13C NMR
(CDCl3, 125 MHz) δ: 163.6, 145.6, 138.4, 137.7, 136.4, 131.7, 131.0, 130.8, 130.2,
130.1, 129.5, 129.4, 129.1, 126.6, 124.1, 124.0, 122.0, 29.1, 24.0 ppm. HR-MS
(MALDI-TOF): m/z: [M+H]+, calcd. for C64H53N2O4 913.4000; Found 913.3976.
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
10 and 11: Compound 9 was used as starting material, 10 was separated as a blue
solid (47 mg) in 28% yield (silica gel, Rf = 0.32 in CHCl3), and 11 was separated as a
1
blue solid (8 mg) in 5% yield (silica gel, Rf = 0.38 in CHCl3). For compound 10, H
NMR (CDCl3, 500 MHz) δ: 8.50 (d, J = 8.2 Hz, 2H), 8.20 (d, J = 8.2 Hz, 2H), 8.19 (d,
J = 8.2 Hz, 2H), 7.56 (d, J = 8.2 Hz, 2H), 7.47 (t, J = 6.3 Hz, 2H), 7.47 (d, J = 8.2 Hz,
4H), 7.37 (d, J = 7.6 Hz, 2H), 7.33 (d, J = 7.6 Hz, 4H), 2.72 (m, 4H), 1.69 (s, 18H),
4
3
1.16 (dd, J = 3.5 Hz, J = 6.9 Hz, 24H) ppm. 13C NMR (CDCl3, 75 MHz) δ: 165.0,
163.6, 163.4, 145.6, 142.1, 140.2, 137.9, 135.8, 133.3, 132.6, 131.8, 131.2, 131.1,
130.7, 130.3, 129.7, 129.6, 128.4, 126.8, 126.5, 124.0, 122.3, 121.4, 81.9, 29.1, 28.2,
24.0 ppm. HR-MS (MALDI-TOF): m/z: [M+H]+, calcd. for C74H69N2O8 1113.5048;
Found 1113.5097. For 11, 1H NMR (CDCl3, 500 MHz) δ: 10.44 (s, 1H), 10.03 (s, 1H),
9.08 (d, J = 9.5 Hz, 1H), 8.90 (d, J = 8.2 Hz, 1H), 8.87 (d, J = 8.2 Hz, 1H), 8.63 (d, J
= 7.5 Hz, 1H), 8.49 (dd, 4J = 1.3 Hz, 3J = 8.9 Hz, 1H), 8.35 (d, J = 8.2 Hz, 2H), 8.30
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 24 of 29
1
2
3
4
5
6
7
8
9
(d, J = 8.2 Hz, 1H), 8.00 (d, J = 8.1 Hz, 1H), 7.76 (d, J = 8.2 Hz, 1H), 7.50-7.59 (m,
4H), 7.41 (d, J = 7.6 Hz, 2H), 7.37 (d, J = 8.2 Hz, 2H), 2.79-2.88 (m, 4H), 1.75 (s,
9H), 1.73 (s, 9H), 1.20-1.22 (m, 24H) ppm. 13C NMR (CDCl3, 75 MHz) δ: 165.1,
165.0, 164.3, 164.0, 163.7, 145.7, 143.8, 141.3, 136.6, 135.1, 134.9, 131.7, 131.5,
130.9, 130.8, 130.7, 130.6, 130.3, 130.2, 130.1, 129.7, 129.6, 129.3, 129.2, 128.9,
128.8, 128.2, 127.9, 127.0, 126.9, 126.1, 124.7, 124.2, 124.1, 122.2, 122.0, 121.4,
121.2, 82.4, 82.0, 29.7, 28.3, 24.0 ppm. HR-MS (MALDI-TOF): m/z: [M+H]+, calcd.
for C74H67N2O8 1111.4892. Found 1111.4841.
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
Synthesis of ZDI5 and ZDI6: 10 (20 mg, 0.02 mmol) or 11 (10 mg, 0.01 mmol) was
dissolved in DCM and trifluoroacetic acid (1 mL) was added under argon. The
resulted blue solution was stirred at room temperature for 12 h. The solvent was then
removed and ZDI5 was obtained in 90% yield (18 mg) by column chromatography
(silica gel, DCM: ethyl acetate = 5:1 (v/v)). For ZDI6, the low solubility in common
solvent makes the column chromatography very difficult, so crude product was
obtained in 85% yield (8 mg) by washing with hexane.
1
For ZDI5, H NMR (CDCl3, 300 MHz) δ: 8.54 (d, J = 8.0 Hz, 1H), 8.33 (d, J = 8.1
Hz, 2H), 8.19 (d, J = 8.0 Hz, 1H), 7.45-7.57 (m, 4H), 7.40 (d, J = 7.9 Hz, 1H), 7.33 (d,
J = 7.7 Hz, 2H), 7.37 (d, J = 8.1 Hz, 2H), 7.33 (d, J = 7.7 Hz, 2H), 2.67-2.75 (m, 2H),
1.16 (d, J = 6.5 Hz, 12H) ppm. 13C NMR (CDCl3, 125 MHz) δ: 170.8, 169.4, 145.6,
143.3, 140.0, 137.7, 135.7, 133.4, 131.9, 131.4, 130.6, 130.3, 130.2, 129.6, 128.4,
126.9, 126.6, 124.1, 122.4, 121.5, 67.7, 45.7, 29.2, 24.0, 21.8, 21.4 ppm. HR-MS
(MALDI-TOF): m/z: [M+H]+, calcd. for C66H53N2O8 1001.3796; Found 1001.3778
ACS Paragon Plus Environment

Page 25 of 29
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
For ZDI6, due to its poor solubility, only high-resolution mass spectrum was recorded.
HR-MS (MALDI-TOF): m/z: [M+H]+, calcd. for C66H51N2O8 999.3640; Found
999.3606.
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
ACKNOWLEDGEMENTS
This work was financially supported by A*STAR BMRC grant (10/1/21/19/642),
MOE Tier 2 grant (MOE2011-T2-2-130) and IMRE core funding (IMRE/12-1P0902).
Supporting Information
Concentration dependent fluorescence spectra, NMR spectra, HRMS spectra and
differential pulse voltammograms. This material is available free of charge via the
Internet at http://pubs.acs.org.
REFERENCES
[1] Reviews for zethrenes: (a) Clar, E. Polycyclic Hydrocarbons, Vol. I/II, Academic
Press, New York, 1964; (b) Harvey, R. G. Polycyclic Aromatic Hydrocarbons,
Wiley-VCH, Weinheim, 1997; (c) Umeda, R.; Hibi, D.; Miki, K.; Tobe, Y. Pure
Appl. Chem. 2010, 82, 871–878; (d) Sun, Z.; Wu, J. J. Mater. Chem. 2012, 22,
4151–4160; (e) Sun, Z.; Ye, Q.; Chi, C.; Wu, J. Chem. Soc. Rev. 2012, 41,
7857–7889. (f) Sun, Z.; Zeng, Z.; Wu, J. Chem. Asian J. 2013, DOI:
10.1002/asia.201300560.
[2] Clar, E. The Aromatic Sextet, Wiley, New York, 1972.
[3] Sun, Z.; Huang, K.-W.; Wu, J. Org. Lett. 2010, 12, 4690–4693.
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 26 of 29
1
2
3
4
[4] Nakano, M.; Kishi, R.; Takebe, A.; Nate, M.; Takahashi, H.; Kubo, T.; Kamada,
5
6
7
K.; Ohta, K.; Champagne, B.; Botek, E. Comput. Lett. 2007, 3, 333–338.
8
9
[5] Clar, E.; Lang, K. F.; Schulz-Kiesow, H. Chem. Ber. 1955, 88, 1520–1527.
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
[6] (a) Mitchell, R. H.; Sondheimer, F. J. Am. Chem. Soc. 1968, 90, 530–531; (b)
Meinwald, J.; Young, J. W. J. Am. Chem. Soc. 1971, 93, 725–731; (c) Staab, H.
A.; Nissen, A.; Ipaktschi, J. Angew. Chem. Int. Ed. Engl. 1968, 7, 226; (d)
Mitchell, R. H.; Sondheimer, F. Tetrahedron 1970, 26, 2141–2150; (e) Staab, H.
A.; Ipaktschi, J.; Nissen, A. Chem. Ber. 1971, 104, 1182–1186.
[7] Wu, T. C.; Chen, C. H.; Hibi, D.; Shimizu, A.; Tobe, Y.; Wu, Y. T. Angew.
Chem., Int. Ed. 2010, 49, 7059–7062.
[8] Li, Y.; Heng, W.-K.; Lee, B. S.; Aratani, N.; Zafra, J. L.; Bao, N.; Lee, R.; Sung,
Y. M.; Sun, Z.; Huang, K.-W.; Webster, R. D.; López Navarrete, J. T.; Kim,
D.-H.; Osuka, A.; Casado, J.; Ding, J.; Wu, J. J. Am. Chem. Soc. 2012, 134,
14913–14922.
[9] Umeda, R.; Hibi, D.; Miki, K.; Tobe, Y. Org. Lett. 2009, 11, 4104–4106.
10] Sun, Z.; Huang, K.-W.; Wu, J. J. Am. Chem. Soc. 2011, 133, 11896–11899.
[11] Ruiz-Morales, Y. J. Phys. Chem. A 2002, 106, 11283–11308.
[12]Knežević, A.; Maksić, Z. B. New J. Chem. 2006, 30, 215–222.
[13] Désilets, D.; Kazmaier, P. M.; Burt, R. A. Can. J. Chem. 1995, 73, 319–324.
ACS Paragon Plus Environment

Page 27 of 29
The Journal of Organic Chemistry
1
2
3
4
5
6
[14] Haugland, R. P. Handbook of Fluorescent Probes and Research Products, 9th
ed., Molecular Probes, Eugene, 2002.
7
8
9
[15] Kobayashi, H.; Ogawa, M.; Alford, R.; Choyke, P. L.; Urano, Y. Chem. Rev.
2010, 110, 2620–2640.
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
[16]Reviews for rylenes: (a) Weil, T.; Vosch, T.; Hofkens, J.; Peneva, K.; Müllen, K.
Angew. Chem., Int. Ed. 2010, 49, 9068–9093; (b) Herrmann, A.; Müllen, K.
Chem. Lett. 2006, 35, 978–985; (c) Avlasevich, Y.; Li, C.; Müllen, K. J. Mater.
Chem. 2010, 20, 3814–3826.
[17](a) Alvino, A.; Franceschin, M.; Cefaro, C.; Borioni, S.; Ortaggia, G.; Bianco, A.
Tetrahedron 2007, 63, 7858–7865; (b) Backes, C.; Schmidt, C. D.; Hauke, F.;
Böttcher, C.; Hirsch, A. J. Am. Chem. Soc. 2009, 131, 2172–2184; (c) Heek, T.;
Fasting, C.; Rest, C.; Zhang, X.; Würthner, F.; Haag, R. Chem. Commun. 2010,
46, 1884–1886; (d) Schmidt, C. D.; Lang, N.; Jux, N.; Hirsch, A. Chem. Eur. J.
2011, 17, 5289–5299; (e) Boobalan, G.; Imran, P. M.; Nagarajan, S. J. Electron.
Mater. 2011, 40, 2392–2397. (f) Görl, D.; Zhang, X.; Würthner, F. Angew. Chem.
Int. Ed. 2012, 51, 6328–6348.
[18] (a) Rehm, S.; Stepanenko, V.R; Zhang, X.; Rehm, T. H.; Würthner, F. Chem. Eur.
J. 2010, 16, 3372–3382; (b) Schönamsgruber, J.; Schade, B.; Kirschbaum, R.; Li,
J.; Bauer, W.; Böttcher, C.; Drewello, T.; Hirsch, A. Eur. J. Org. Chem. 2012,
6179–6186; (c) Sun, J.; Wang, M.; Xu, P.; Zhang, S.; Shi, Z. Synthetic. Commun.
2012, 42, 1472–1479.
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 28 of 29
1
2
3
4
[19]Kohl, C.; Weil, T.; Qu, J.; Müllen, K. Chem. Eur. J. 2004, 10, 5297–5310.
5
6
7
8
9
[20](a) Qu, J.; Kohl, C.; Pottek, M.; Müllen, K. Angew. Chem., Int. Ed. 2004, 43,
1528–1531; (b) Weil, T.; Abdalla, M. A.; Jatzke, C.; Hengstler, J.; Müllen, K.;
Biomacromolecules 2005, 6, 68–79; (c) Peneva, K.; Mihov, G.; Herrmann, A.;
Zarrabi, N.; Börsch, M.; Duncan, T. M.; Müllen, K. J. Am. Chem. Soc. 2008, 130,
5398–5399; (d) Gao, B.; Li, H.; Liu, H.; Zhang, L.; Bai, Q.; Ba, X. Chem.
Commun. 2011, 47, 3894–3896; (e) Céspedes-Guirao, F. J.; Ropero, A. B.;
Font-Sanchis, E.; Nadal, Á.; Fernández-Lázaro, F.; Sastre-Santos, Á. Chem.
Commun. 2011, 47, 8307–8309; (f) Yang, S. K.; Shi, X.; Park, S.; Doganay, S.;
Ha, T.; Zimmerman, S. C. J. Am. Chem. Soc. 2011, 133, 9964–9967. (g) Wang,
L.; Xu, L.; Neoh, K. G.; Kang, E.-T. J. Mater. Chem. 2011, 21, 6502–6505. (h)
Liu, H.; Wang, Y.; Liu, C.; Li, H.; Gao, B.; Zhang, L.; Bo, F.; Baia, Q.; Ba, X. J.
Mater. Chem. 2012, 22, 6176–6181.
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
[21](a) Peneva, K.; Mihov, G.; Nolde, F.; Rocha, S.; Hotta, J.; Braeckmans, K.
Hofkens, J.; Uji-i, H.; Herrmann, A.; Müllen, K. Angew. Chem., Int. Ed. 2008, 47,
3372–3375; (b) Jung, C.; Müller, B. K.; Lamb, D. C.; Nolde, F.; Müllen, K.;
Bräuchle, C. J. Am. Chem. Soc. 2006, 128, 5283–5291.
[22]In Y.-T. Wu’s report (Ref. 7), the reaction yield can be up to 73%. The decreased
reaction yield could be attributed to lower reactivity of Br compared to I. Also in
Wu’s case, one substrate with Br group did not give the corresponding
cyclodimerization product.
ACS Paragon Plus Environment

Page 29 of 29
The Journal of Organic Chemistry
1
2
3
4
5
6
[23]Li, J.; Jiao, C.; Huang, K.-W.; Wu, J. Chem. Eur. J. 2011, 17, 14672–14680.
[24]López Arbeloa, F.; Ruiz Ojeda, P.; López Arbeloa, I. J. Lumin. 1989, 44, 105112.
7
8
9
[25](a) Pommerehne, J.; Vestweber, H.; Guss, W.; Mahrt, R. F.; Bassler, H.; Porsch,
M.; Daub, J. Adv. Mater. 1995, 7, 551–554; (b) Chi, C.; Wegner, G. Macromol.
Rapid Commun. 2005, 26, 1532–1537.
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
[26](a). Clerc, J; Schellenberg, B.; Groll, M.; Bachmann, A. S.; Huber, R.; Dudler, R.;
Kaiser, M. Eur. J. Org. Chem. 2010, 3991–4003; (b) Taylor, E. C.; Wong, G. S. K.
J. Org. Chem. 1989, 54, 3618-3624.
ACS Paragon Plus Environment