Synthesis and Characterization of Electron-Deficient Asymmetrically Substituted Diarylindenotetracenes

Article abstract of DOI:10.1021/acs.joc.7b02756

Electron-deficient asymmetrically substituted diarylindenotetracenes were prepared via a series of Friedel-Crafts acylations, aryl-aryl cross-couplings, and an intramolecular oxidative cyclization to form the indene ring. Single-crystal X-ray experiments showed good π-π overlap with π-π distances ranging from 3.26 to 3.76 ?. Both thermogravimetric analysis and differential scanning calorimetry indicated that asymmetrically substituted indenotetracenes (ASIs) are stable at elevated temperatures. From cyclic voltammetry experiments, HOMO/LUMO energy levels of ASI derivatives were determined to be near -5.4/-4.0 eV. UV/visible absorption spectra showed strong absorption of light between 400 and 650 nm with molar attenuation coefficients from 10⁴ to 10⁵ M^-1 cm^-1. ASIs were also found to have very low fluorescence quantum yields, less than 4%. Using the solid-state packing determined from the single-crystal X-ray experiments, computational modeling indicated that ASI molecules should favor electron transport.

Full text of DOI:10.1021/acs.joc.7b02756

Subscriber access provided by UNIV OF DURHAM
Article
Synthesis and Characterization of Electron Deficient
Asymmetrically Substituted Diarylindenotetracenes
Lafe J. Purvis, Xingxian Gu, Soumen Ghosh, Zhuoran
Zhang, Christopher J. Cramer, and Christopher J. Douglas
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.7b02756 • Publication Date (Web): 23 Jan 2018
Downloaded from http://pubs.acs.org on January 23, 2018
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 48
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
Synthesis and Characterization of Electron Deficient
Asymmetrically Substituted Diarylindenotetracenes
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
Lafe J. Purvis, Xingxian Gu†, Soumen Ghosh, Zhuoran Zhang, Christopher J. Cramer*, and
Christopher J. Douglas*
Department of Chemistry, Chemical Theory Center, and Supercomputing Institute, University of
Minnesota, Minneapolis, MN, 55455
Graphical abstract
Abstract
Electron deficient asymmetrically substituted diarylindenotetracenes were prepared via a series
of FriedelꢀCrafts acylation’s, arylꢀaryl crossꢀcouplings, and an intramolecular oxidative
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 2 of 48
1
2
3
4
5
6
7
8
9
cyclization to form the indene ring. Single crystal Xꢀray experiments showed good π–π overlap
with π–π distances ranging from 3.26 to 3.76 Å. Both thermogravimetric analysis and differential
scanning calorimetry indicated that ASIs are stable at elevated temperatures. From Cyclic
voltammetry experiments HOMO/LUMO energy levels of ASI derivatives were determined to
be near ꢀ5.4/ꢀ4.0 eV. UV/ visible absorption spectra showed strong absorption of light between
400ꢀ650 nm with molar attenuation coefficients from 10ꢀ4 to 10ꢀ5 Mꢀ1cmꢀ1. ASI were also found
to have very low fluorescence quantum yields, less than 4%. Using the solidꢀstate packing
determined from the single crystal Xꢀray experiments, computational modeling indicated that
ASI molecules should favor electron transport.
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
Over the past decades the demand for cheaper, faster, and smaller electronic devices has
driven chemists to discover a large number of new smallꢀmolecule, electronꢀdonor, pꢀtype
materials. Over the same period, however, there has been significantly less development of novel
smallꢀmolecule, electronꢀacceptor, nꢀtype materials, especially for use in organic solar cells.1 To
date, the benchmark electron acceptor material for organic photovoltaics has been the fullerene
C60, owing to its high electron affinity and efficient, isotropic charge transport.
However, despite having good solidꢀstate properties that allow for efficient electron
transport, fullerenes are not ideal materials for OPVs. The several drawbacks of fullerenes
include poor solubility in organic solvents, limited stability, and relatively high cost. Another
drawback of fullerenes is their poor absorption of light in the visible region. In OPVs, this
relative transparency necessitates a thick absorber layer in order to produce sufficient lightꢀ
generated charge carriers (excitons). Although the thicker absorber layer does result in greater
ACS Paragon Plus Environment

Page 3 of 48
The Journal of Organic Chemistry
1
2
3
4
5
6
exciton generation, it also decreases charge separation efficiency of the device due to the short
diffusion length of excitons in the organic material.2ꢀ5
7
8
Recently, efforts to overcome the inherent deficiencies of fullerenes led to the
9
development of several novel, nonꢀfullerene electron acceptors.6ꢀ13 Nonꢀfullerene electron
acceptors have the potential to greatly improve OPV performance through design of materials
with strong light absorption, tuned highest occupied molecular orbital (HOMO)/lowest
unoccupied molecular orbital (LUMO) levels, and improved processability and photostability.14ꢀ
16 Among these novel electron acceptors, indeneꢀfused aromatic compounds have shown promise
as possible replacements for fullerenes in OPVs. 17ꢀ19
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 intrinsic electron deficiency of indeneꢀcontaining molecules originates from electron
accepting ability of the conjugated five membered ring. The drive towards aromaticity (4n+2)
makes materials containing indenes good electron acceptors. The Plunkett group and Haley
group have independently developed new organic nꢀtype materials based on the indene scaffold
for use in OPVs.8,20,21 Corannulenes may also replace fullerenes as the electron transport layer.22
The cyclopentaneꢀfused polycyclic aromatic hydrocarbons and indacene materials demonstrate
LUMOs below ꢀ3.5 eV and HOMOs below ꢀ5.5 eV, allowing for nꢀtype behavior. These
materials also have good solubility in organic solvents and can be readily derivatized.
Extending the range of indeneꢀbased materials as new nꢀtype acceptors, we have prepared
and studied diarylindenotetracenes. Previously, our group reported on the development of
symmetrically substituted indenotetracenes.23 In this article, we report a divergent synthetic
strategy allowing for rapid diversification and structure–function relationship studies of the
indenotetracene core. Our new synthetic strategy enabled us to prepare several asymmetrically
substituted indenotetracene (ASI) derivatives. Beyond the syntheses, we have examined and
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 4 of 48
1
2
3
4
5
6
modeled their electronic and physical properties to evaluate their potential for use as nꢀtype
materials in organic photovoltaics.24
7
8
RESULTS AND DISCUSSION
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
Synthesis
We began by designing the synthesis of ASIs to allow for lateꢀstage diversification and
easy derivatization. This was accomplished via a series of Friedel–Crafts acylations, arylꢀaryl
crossꢀcoupling reactions, and a Scholl oxidative cyclization (Scheme 1).
Starting with commercially available phthalic anhydride (1) and 1ꢀhydroxyl naphthalene
(2), 2ꢀ(1ꢀhydroxyꢀ2ꢀnaphthoyl)benzoic acid, compound (3), was obtained via a Friedel–Crafts
acylation using the Lewis acid boron trioxide. Following treatment of compound (3) with PCl5
and heating in sulfuric acid 6ꢀchlorotetraceneꢀ5,12ꢀdione, compound (4), was obtained in good
yields, 50% over 2 steps.9 Using the above conditions compound (4) was synthesized on 0.1 M
scale, which, was then be used in all subsequent synthesis. The first point of diversification was
achieved by treating naphthacenequinone 4 with substituted aryllithium reagents, producing the
diol intermediates 5a–g as mixtures of syn/anti isomers. Upon reductive aromatization,
compounds 6a-g became a bright orange/red color indicating that the tetracene core had been
successfully formed.25,26
In the key step of our synthesis we envisioned forming the indene ring via an oxidative
cyclization using Scholl reaction conditions.27,28 In previous syntheses of rubicene, and other
indene containing polycyclic aromatic hydrocarbons (PAH), the indene moieties were prepared
via intramolecular palladiumꢀcatalyzed arylꢀaryl crossꢀcoupling or pentannulation. 29,30 Scholl
reaction conditions have been used in the synthesis of several PAH compounds, and recently,
Chi and coworkers synthesized bisindenoꢀannulated pentacene molecules under Scholl reaction
ACS Paragon Plus Environment

Page 5 of 48
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
conditions using FeCl3 as the oxidizing agent.31,32 Using two different Scholl reaction conditions,
compounds 7a–b were formed via oxidative cyclization using AlCl3 in nitrobenzene while
compounds 7c–g were obtained from a solution of chloroform and methanesulfonic acid in the
presence of 2,3ꢀdichloroꢀ5,6ꢀdicyanoꢀ1,4ꢀbenzoquinone (DDQ), with yields ranging from 40 to
86%.33,34 The formation of compounds 7a-g resulted in another color change, from the
orange/red color of compounds 6a-g, to a purple/black color. Interestingly, the regiochemsitry of
compounds 7a-g was found to be very specific. Oxidative cyclization was only observed to occur
at the C12 of the tetracene core and never at the C10. We attributed this high regionꢀselectivity to
stericꢀrepulsion between the C5 chloride and the C6 phenyl group. This stericꢀrepulsion pushes
carbons 5 and 6 away from each other, which, in turn pushes the C11 phenyl group closer to the
C12 hydrogen.
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
From compounds 7a–g, we performed the final lateꢀstage diversification using Kumadaꢀ
Corriu crossꢀcoupling conditions previously developed in our lab to produce compounds 8a–m
in yields between 40 and 92%.23,35,36 We found that, in most cases, the primary impurities in the
crude reaction mixtures were the unreacted starting material and dehalogenated compound (7).
These impurities were readily separable from the desired product by either column
chromatography and/or recrystallization, the only exception being compound 8d. 37 We were
unable to find purification conditions which separated unreacted starting material 7d from
product 8d. In order to obtain pure 8d the reaction had to be driven to completion then
recrystallization could be performed to remove any additional impurities.
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 6 of 48
1
2
3
HO
O
O
O
Cl
R1
Br
OH
O
O
OH
4
5
6
7
8
9
1) B2O3, 180 °C, 4 h
1) PCl5, 160 °C, 1.5 h
R1 = H,
+
O
+
2) H2O, reflux, 1 h
65–67%
Me, nPr, Et,
OMe, CF3, F
2) H2SO4, 60 °C, 1 h
45–56%
O
1
2
3
4
nBuLi, THF
–78 °C–rt
R1
R1
R1
R1
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
DDQ/MeSO3H
CHCl3, rt, 20 min
56–80%
Ar
Cl
Cl
Cl
SnCl2, BF3•Et2O
dioxane, 105 °C, 0.5 h
OH
Ar–MgBr
PEPPSITM–iPr
toluene
or nitrobenzene
AlCl3, 60 °C, 4 h
81–86%
or
SnCl2, HCl, THF,
54–56%, 2 steps
OH
or THF, 65 °C
Ar, see Table 1
25–92%
R1
8a-m
R1
R1
R1
7a-g
6a-g
5a-g
Scheme 1: Synthesis of asymmetric indenotetracenes 8a–m
Table 1: Functional groups at R1 and Ar and the yield of three key steps, preparation of 6–8.
Entry
R1
H
H
H
H
H
6, % yield 7, % yield
6a, 80 a
Ar
8, % yield
Ph c
pꢀC6H4F c
pꢀtol c
8a, 60
8h, 51
8i, 67
8j, 45
8k, 47
8l, 88
8b, 40
8m, 67
8n, 25
8c, 90
8d, 92
8e, 54
8f, 74
8g, 74
1
2
3
4
5
7a, 81
1ꢀnaphthyl c
4ꢀNMe2C6H4
4ꢀOMeC6H4
Ph c
c
c
6
7
8
H
Me
Me
6b, 88 a
7b, 86
4ꢀNMe2C6H4
pꢀC6H4F c
Ph c
c
9
Me
F
CF3
OMe
Et
10
11
12
13
14
6c, 53 b
6d, 46 b
6e, 65 b
6f, 73 a
6g, 80 a
7c, 81
7d, 40
7e, 69
7f, 67
7g, 47
Ph d
Ph c
Ph c
nPr
Ph c
a Reduction using SnCl2 in THF, 1M HCl at room temperature 1 hour. b Reduction using SnCl2 in
dioxane, BF3•Et2O at 105 °C for 20 minutes. c Palladium catalyzed crossꢀcoupling using PEPPSIꢀ
iPr™ THF at 65 °C. d Palladium catalyzed crossꢀcoupling using PEPPSIꢀiPr™ in toluene at 65
°C.
MATERIAL CHARACTERIZATION
Crystal structure
ACS Paragon Plus Environment

Page 7 of 48
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
In small molecule based OPVs exciton dissociation and electron transport generally
occurs via Dexter energy transfer.38 For Dexter energy transfer to occur, tight packing and good
orbital overlap is required between neighboring molecules in the solid state. Therefore,
determining the packing in the solid state is critical to understand how a material will function as
an organic semiconductor. To examine the solid state packing of ASIs single crystals were
grown for Xꢀray diffraction experiments. Single crystals of ASIs were grown as small, purple,
plateꢀlike crystals via either vacuum sublimation or physical vapor transport using argon as the
carrier gas.
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
Three packing motifs were observed with ASIs: monoclinic C2/c or P21/c, and
orthorhombic Pbca.39 The parent, symmetric compound 8a packed in the monoclinic C2/c space
group.23 Substitution of hydrogens with isosteric fluorines, as in 8c and 8h, also resulted in the
same C2/c space group. When larger functional groups were introduced, however, the crystal
packing changed to monoclinic P21/c for 8d and 8e, and orthorhombic Pbca for 8b.40 A range of
close contact distances between neighboring molecules was observed in all ASIs due to a slight
twisting of the indenotetracene core ranging from 0.70˚ in 8e, to 9.67˚ in compound 8h. Average
π–stacking distances were determined by generating a plane through the ASI molecule using the
atoms of the indene ring, supporting information (SI) Section S3, and then measuring the
distances between neighboring planes. The monoclinic C2/c crystals showed a slipped 1ꢀD
packing, Figure 1a, with good overlap of the indenotetracene core and small π–π close contacts
averaging around 3.4 Å, (8a, 8c, and 8h, Table 2) which would allow for efficient electron
transport.41 In the solid state compound 8b (orthorhombic Pbca) was observed to pack in a πꢀ
stacked herringbone motif, Figure 1b. Again, we observed good overlap of the indenotetracene
cores with π–π distances that averaged 3.46 Å and a closest contact measuring 3.36 Å. In the
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 8 of 48
1
2
3
4
5
6
7
8
9
monoclinic P21/c systems, compound 8e showed little overlap of the indenotetracene core due to
a horizontal displacement along the indenotetracene backbone; compound 8d, however,
demonstrated good overlap, SI Section S3. Compound 8d was also unique in that it contained
two molecules in the asymmetric unit giving two different π–π close contacts, 3.28 and 3.26 Å.
Compounds for which we obtained single crystal Xꢀray data were further studied for their
electrochemical, optical, and physical 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
Figure 1: a) C2/c slipped 1ꢀD πꢀstack in 8c b) Pbca πꢀstacked herringbone in 8b Table 2: Single
crystal packing motifs for compound 8a–e, h, and corresponding tetracene backbone π–π
distances.
Crystal system Packing Motif
Compound
πꢀspacing Å
C2/c
C2/c
C2/c
P21/c
P21/c
Pbca
3.42
3.42
3.37
8a
8c
8h
8d
8e
8b
Monoclinic
3.26/3.28a
3.76
Orthorhombic
3.46
a Compound 8d contains two molecules in the asymmetric unit with different π–π distances
Thermal Stability
To determine thermal stability and decomposition temperatures, we submitted
compounds 8a-e, h to thermogravimetric analysis (TGA) studies. Shown in Table S2,
ACS Paragon Plus Environment

Page 9 of 48
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
compounds 8a, c, and d demonstrated no more than 1% mass loss below 300 ˚C, due to
sublimation, while 8b, e, and h did not reach 1 % mass loss until above 300 ˚C. All ASIs
demonstrated good thermal stability measuring less than having 5 % mass loss below 325 ˚C and
possessing onset temperatures of greater than 343 ˚C. 6,42,43 With 8a–e, h demonstrating good
thermal stability, we next performed differential scanning calorimetry (DSC) to examine phase
transitions.10,15 Complete DSCs for each compound can be found in supporting information
Section S3. The DSC data for compounds 8a-d, h showed no phase change between 0 to 150 ˚C,
Figure 2. Compound 8e showed a reversible thermal expansion at 115 ˚C, Figure 2. Upon
further heating to 260 ˚C, compounds 8b-e, h showed multiple endothermic events suggesting
the formation of alternative polymorphs at elevated temperatures. The measured thermal stability
of ASIs is adequate to resist decomposition or phase changes at typical OPV device operating
temperatures.
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 10 of 48
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 2: Differential scanning calorimetry results for compounds 8a-e, h
Electrochemical properties
As stated previously indenotetracenes possess an electron deficient πꢀsystem due to the
electronic configuration imposed by the fiveꢀmembered ring. Twoꢀelectron reduction has been
observed in other indeneꢀcontaining molecules.1,8,44,45 The HOMO and LUMO levels of 8a–e, h
were determined via cyclic voltammetry (CV) referenced to ferrocene (4.8 eV versus vacuum),
Figure 3. HOMO/LUMO levels were estimated from the onset of the oxidation and reduction
peaks, Section S5.42
All ASI derivatives showed at least two reversible, or quasiꢀreversible, reduction and one
oxidation red–ox couples. From CV experiments, the energy levels of the LUMO, to which a
first electron is added, were determined to be around ꢀ4.1 eV while addition of the second
electron occurred between ꢀ3.27 and ꢀ3.42 eV, Table 3. The low reduction potentials of ASIs,
ACS Paragon Plus Environment

Page 11 of 48
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
E1/2 = ꢀ0.9 to ꢀ0.6 V, demonstrate the high electron affinities of these molecules. All ASIs
showed at least one oxidation peak near E1/2 = 0.7 V. Estimated HOMO energy levels measured
for ASIs range from ꢀ5.40 to ꢀ5.67 eV. The HOMO/LUMO energies determined for ASIs were
comparable to those determined in other indeneꢀbased electron acceptors. 8,45,46
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
We adjusted the HOMO/LUMO energies of ASIs via substitution around the
indenotetracene core. The addition of an electron donating methoxy group, compound 8e, raised
both the HOMO and LUMO in energy. The increased electron density of the indenotetracene
core raised the HOMO energies to such a degree that a second oxidation peak could now be
observed, Figure 3. Upon addition of CF3 groups, 8d, the measured HOMO energy decreased to
ꢀ5.67 eV while addition of the first and second electron into the LUMO lowered to ꢀ4.25 and ꢀ
3.42 eV respectively. Compound 8d also now shows a third reduction which occurred at ꢀ2.67
eV. The band gaps calculated from the measured HOMO/LUMO energy levels are shown in
Table 3. The energy gaps determined from CV were found to be in good agreement with the
calculated energies, SI Table S16.
The modulation of HOMO/LUMO levels of ASI via substitution with electronꢀdonating
and electronꢀwithdrawing groups can be understood by examining the corresponding orbital
amplitudes (Figure 4) determined from density functional theory (DFT) calculation. Figure 4
shows that rather than being localized to one section of the molecule, e.g. the tetracene unit, both
the HOMO and LUMO are delocalized throughout the entire indenotetracene πꢀsystem. The
HOMO/LUMO energies determined for the ASIs are within the range that would favor electron
accepting or ambipolar character for charge transport.47 The higher LUMO energy levels for
electron injection into indenotetracenes, compared to that measured for C60, ꢀ4.5 eV, would
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 12 of 48
1
2
3
4
5
6
potentially increase the open circuit voltage of an OPV by increasing the difference between the
HOMO of the donor and the LUMO of the acceptor.48,49,50
7
8
9
104
8h
52
0
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
-52
104
8e
52
0
-52
64
32
0
8d
8c
8b
8a
-32
92
46
0
-46
40
20
0
-20
54
27
0
-27
-2
0
2
Potential (V vs Ag/AgCl)
Figure 3: Cyclic voltammogram of compound 8a–e, h, Fc/Fc+ used as standard. Compound 8a,
b, d, e were ran at a scan rate of 0.2 V/s, compound 8c, h at 0.1 V/s
Table 3: Onset potentials, measured HOMO/LUMO energies for compound 8a–e, h, compared
to Fc/Fc+, and energy gap.
Eox/onset
V
1
Ered/onset
V
1
Ered/onset
V
2
HOMO
eV
LUMO
eV
Eg
eV
LUMO 2nd
electron eV
Eg
eV
Compound
ꢀ5.52
ꢀ5.54
ꢀ5.52
ꢀ5.67
ꢀ5.40
ꢀ5.48
ꢀ4.18
ꢀ4.20
ꢀ4.15
ꢀ4.25
ꢀ3.99
ꢀ4.15
1.34
1.34
1.37
1.42
1.41
1.33
ꢀ3.35
ꢀ3.30
ꢀ3.38
ꢀ3.42
ꢀ3.27
ꢀ3.32
2.17
2.24
2.14
2.25
2.13
2.16
8a
8b
8c
8d
8e
8h
0.72
0.74
0.72
0.87
0.60
0.68
ꢀ0.62
ꢀ0.60
ꢀ0.65
ꢀ0.55
ꢀ0.81
ꢀ0.65
ꢀ1.47
ꢀ1.50
ꢀ1.42
ꢀ1.38
ꢀ1.53
ꢀ1.48
ACS Paragon Plus Environment

Page 13 of 48
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 4. Orbital pictures for i) HOMO and ii) LUMO for 8a (single point with M06ꢀ2X/6ꢀ
31+G(d,p)). 51
Optical Properties
A major disadvantage of fullerenes is their poor absorptivity of visible light.14 Having
both the donor and acceptor layers being strong absorbers would lead to the creation of more
lightꢀgenerated carriers, increasing short circuit current, improving organic solar cell
performance. 48,49,52
UV/Visible absorption spectroscopy of compounds 8a–e, h showed strong absorbance
over a large range of the visible spectrum, 390 to 650 nm, SI Section S7. All compounds showed
very similar absorbance spectra with minor differences in peak shape, Figure 5. The variations
in peak shape are attributed to the difference in bond vibrational modes/energies and
intermolecular interaction between the ASI derivatives. ASIs demonstrated a strong highꢀenergy
absorption around 299 nm and weaker midꢀrange absorption, 350 to 500 nm, which correspond
to π–π* transitions of the ASI molecules.43,53,54 Absorption from 450 to 650 nm is similar to that
of other reported indene compounds, resulting from the chargeꢀtransfer band, indicating some π–
π interaction between molecules in solution.16,20,46 The molar attenuation coefficient determined
for compounds 8a–e, h, SI Tables S9–S14, is comparable to ruthenium dipyridyl complexes and
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 14 of 48
1
2
3
4
5
6
7
8
9
other materials used in dyeꢀsensitized solar cells, which have molar attenuation coefficients
around 104 Mꢀ1 cmꢀ1 in the visible region.55 The energyꢀgap calculated from the chargeꢀtransfer
band, λonset, Table 4, for 8a–e, h were around 1.9 eV. This agrees with those calculated from CV
measurements, Table 3, and theoretical linearꢀresponse timeꢀdependent density functional theory
(LRꢀTDDFT) calculations, Table S16.
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
Comparing the absorbance of ASIs molecules to symmetrically substituted
indeotetracenes we observed that both have similar molar attenuation coefficients, between 104
and 105 Mꢀ1 cmꢀ1. This is to be expected due to the fact that πꢀconjugation of the indenotetracene
core are same.23
13
8a
8b
12
11
8c
8d
8e
8h
10
9
8
7
6
5
4
3
2
1
0
400
500
600
700
800
Wavelength (nm)
Figure 5: Absorption spectra of compounds 8a-e, h, 10ꢀ5 M
Table 4: λmax and optical band gaps
λmax
(nm)
Compound
Eg (eV)a
ACS Paragon Plus Environment

Page 15 of 48
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
550
553
551
553
555
546
1.98
1.86
1.93
1.96
1.89
1.98
8a
8b
8c
8e
8d
8h
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 Optical band gap was calculated using equation ꢀꢁ = ꢂꢃ where h is Planck’s constant, c is the
speed of light constant, and λ is the absorption onset.
ꢄ
Fluorescence is the most common path for exciton decay in organic materials, and can
decrease OPV efficiency by decreasing exciton (Dexter) energy transfer. Figure 6 shows the
absorbance and corresponding fluorescence spectra of compounds 8a-e, h. Derivatives 8a-e, h
demonstrated weak fluorescence from 600 to 800 nm, which is common for similar, indeneꢀ
containing molecules.8 The fluorescence quantum yields for compounds 8aꢀe and h, Table 5,
were all less than 4 %.
A portion of the very low Φ can be attributed to reꢀabsorbance due to partial overlap of
the absorption and fluorescence spectra. The lack of any significant fluorescence indicates that
nonꢀradiative decay pathways, which may include intersystem crossing and/or intermolecular
charge transfer, are occurring. 6,54,56 If operative, these alternate decay pathways could increase
the efficiency of OPVs in which ASIs are used as the electron accepting layer due to the
possible generation of longer lived excitons as well as faster exciton dissociation.10,15,57
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 16 of 48
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 6: Fluorescence and corresponding absorbance spectra compounds 8a-e, h.
Table 5: Calculated fluorescence quantum yield for compounds 8a-e, h relative to rhodamine b.
Compound
Φ
Rhodamine B
0.7
0.018
0.016
0.042
0.029
0.0015
0.018
8a
8b
8c
8d
8e
8h
Theoretical modeling of electronic structure of ASI and charge transport in the solid state
To understand excitedꢀstate properties of ASIs, LRꢀTDDFT calculations were performed.
As stated presiously, the LRꢀTDDFT calculations for singlet and triplet energies agreed well
with those determined experimentally. Singletꢀtriplet energy gaps in ASIs also suggest the
possibility of singlet fission occurring in these molecules. Singlet fission is a process where one
singlet exciton is converted into two triplet excitons in a spin allowed process. For singlet fission
ACS Paragon Plus Environment

Page 17 of 48
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
to occur, transition from the singlet excited state to the multiexcitonic state with two correlated
triplet excitons must be exoergic or at least isoergic, ꢀꢅ ≥ 2ꢀꢆ. For compound 8a ꢀꢅ − 2ꢀꢆ is
0.1 eV, 0.96 kJ/mol. The same relationship was also found for compounds 8b-e, h, Table S16.58
Singlet fission has been observed in other acenes and is thought to be highly beneficial for
increasing the efficiency of OPVs.59ꢀ61
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 hole and electron reorganization energies were computed for ASI derivatives 8a-e, h
and found to be comparable (see SI).62 For each compound, 8a-d, h, the hole reorganization
energy was found to be slightly smaller than the electron reorganization energy, except for 8e.
The presence of the methoxy group in 8e significantly increased the hole reorganization energy
compared to 8a-d, h, while leaving the electron reorganization energy unchanged.
Hole and electron transfer integrals were computed for compounds 8a–e, h using dimer
models developed from the solved singleꢀcrystal Xꢀray structures of each compound (Table 6;
see SI Section S2 for dimer pictures). For compounds 8a and h, C2/c crystal structures with 1ꢀD
brick packing, the electron transfer integral was determined to be significantly higher than the
hole transfer integral. However, in the case of compound 8c, also C2/c and 1ꢀD brick packing,
the hole and electron transfer integrals were comparable. Compound 8b, with Pbca packing, had
an absolute electron transfer integral significantly higher than the hole transfer integral. The
P21/c crystal system gave two very different results depending on the substitution. Methoxy–
substituted ASI 8e had a hole transfer integral 3 times larger than the electron transfer integral;
however, CF3–substituted ASI 8d had comparable hole and electron transfer integrals.
Calculated electron transfer integrals for perylene diimides, a proven small molecule
electron transport material, range from 10 to 200 meV depending on the functional group and the
model used.63,64 The computed transfer integrals for 8a–d, h were found to be comparable to
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 18 of 48
1
2
3
4
5
6
7
8
9
those observed for perylene diimides. When considering both the reorganization energies and
charge transfer integrals, theoretical calculations predict that compounds 8a–d, h could function
as either an electron transport or ambipolar material allowing them to function as nꢀtype
semiconductors in OPVs.
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 6: Absolute values for effective transfer integral (meV, PBE0/6ꢀ31G(d)) predicted for
compounds 8a-e, h. 65
Transfer integrals
Electron (meV)
Transfer integrals
Hole (meV)
Compounds Crystal Packing
C2/c
Pbca
C2/c
P21/c
32
34
5
4
8a
8b
8c
8d
19
87/53a
28
82/81a
P21/c
C2/c
19
44
57
7
8e
8h
a Compound 8d contains two molecules in the asymmetric unit with slightly different π–π
distances. Transfer integrals were calculated for both distances
Conclusion
In summary, a new class of electron transport material based on the indene scaffold,
asymmetrically substituted indenotetracenes (ASI), have been successfully prepared.
Electrochemical and thermal characterizations demonstrate the potential of ASIs as a novel
electron transport material in OPVs. ASIs were shown to strongly absorb over a broad range of
the visible spectrum, with little to no concomitant fluorescence, potentially increasing short
circuit current. The higher LUMO levels of ASIs relative to C60 should allow for increased open
circuit voltage. ASIs also demonstrated good thermal stability which could improve OPV
lifetime. Single crystal Xꢀray diffraction experiments showed tight πꢀstacking and good
backbone overlap in the solid state, allowing for efficient charge transport in the solid state.
ACS Paragon Plus Environment

Page 19 of 48
The Journal of Organic Chemistry
1
2
3
4
5
6
Using the solved crystal structure, ASIs were predicted to have either electron transport or
ambipolar character in organic photovoltaic devices.
7
8
9
Our findings demonstrate the potential of asymmetrically substituted indenotetracenes to
function as a novel class of nonꢀfullerene electron transport materials in organic photovoltaics
with the potential to improve device lifetime and efficiency.
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
Materials and reagents
All materials were purchased through commercial sources. THF was distilled from sodium and
benzophenone. Toluene was distilled from CaH2. 2ꢀ(1ꢀhydroxyꢀ2ꢀnaphthoyl)benzoic acid (3) and
6ꢀchlorotetraceneꢀ5,12ꢀdione (4) were synthesized using a previously published procedure.9
Measurements and characterization
Melting temperatures for all compounds were performed on samples precipitated from solution.
The melting temperature is defined as the temperature at which the powder anneals to a film
rather than a freeꢀflowing liquid. Highꢀresolution mass spectrometry (HRMS) using GCꢀMS was
performed on a quadrupole timeꢀofꢀflight mass spectrometer with a solid injection probe.
Method: inlet temperature 250 ˚C, source temperature 280 ˚C. The initial temperature was 80 ˚C
and increased to 325 ˚C over 6 minutes and then held for 2.3 minutes. Highꢀresolution mass
spectrometry (HRMS) using ESI was performed on timeꢀofꢀflight instruments.
1H NMR (300, 400, or 500 MHz), and 13C NMR (75, 100, or 125 MHz), 19F NMR (282 or 470
MHz) spectra were recorded on FT NMR instruments. All NMR spectra were reported as δ
values in ppm referenced to chloroform (7.26 ppm), methylene chloride (5.32 ppm) or
tetramethylsilane (TMS, 0.00 ppm) for 1H, chloroform (77.00 ppm) for 13C, and
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 20 of 48
1
2
3
4
5
hexafluorobenzene (ꢀ163.00 ppm) for 19F NMR. 13C NMR spectra are reported to the nearest
0.01 ppm due to the large number of close signals.
6
7
8
9
Infrared (IR) spectra were obtained as films on NaCl plates using an infrared spectrophotometer
in transmission mode.
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
Xꢀray diffraction experiments were performed via singleꢀcrystal XRD using a diffractometer
with graphite monochromater using CuKα radiation (λ=1.5418) at 123 K ω scans and MoK α
radiation (λ=0.71073) at 298 K ω scans. Crystals of 8a, d, c, and h were grown via physical
vapor transport (PVT) using the following technique: the temperature of the sublimation region
was adjusted for each compound and ranged between 150 and 230 ˚C, depending on the
compound. The crystal growth was held between 140 and 200 ˚C. The thermal gradient in the
crystal growth region was created by wrapping thermal tape at continually wider intervals down
the crystal growth region. Argon was used as the carrier gas. Argon flow rate was set via an oil
bubbler at one bubble in the oil bubbler every 1 to 2 seconds. The crystals were grown in the
PVT chamber over a 1 to 3 day period. Crystals of 8b, c were grown via sublimation between
180 and 200 ˚C over 3 days under high vacuum. In the solid state, compounds 8a-c, and h are
configurationally disordered resulting in having to place the substitutions symmetrically about
the diarylindenotetracene core with 50 % occupancy.
Differential scanning calorimetry experiments were performed by heating compounds 8a-e, h to
150 ˚C at 10 ˚C/ min for two cycles then heating to 260 ˚C in a differential scanning calorimeter.
Thermogravimetric analysis was performed by heating samples from 24 to 550 ˚C at a rate of 10
˚C/ minute in a nitrogen atmosphere.
Cyclic voltammetry measurements were performed at 5 mM in anhydrous tetrahydrofuran
previously degassed with Argon. A silver/silver chloride reference electrode, gold working
ACS Paragon Plus Environment

Page 21 of 48
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
electrode, and platinum ground were used for CV experiments. Tetrabutylammonium perchlorate
was used as the electrolyte and ferrocene as the standard. Cyclic voltamagrams were collected at
varying concentrations and sweep rates with all showing similar Red/Ox character. Ferrocene
oxidation onset was referenced to zero.
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
Absorbance measurements were performed on a UV/Visible spectrometer, scanned from
1000nm to 100nm as follows: indenotetracene compounds 8a-e, h were dissolved in
dichloromethane (10 mL). Serial dilutions were performed in factor of ten increments (10ꢀ3, 10ꢀ4,
10ꢀ5, 10ꢀ6 M) and absorbance was measured. Serial dilutions were performed using a 10 mL
volumetric flask and 1 mL volumetric pipet. Attenuation coefficients (ε) were calculated from
absorbance spectra corrected for dichloromethane.
Fluorescence experiments were performed on a fluorescence spectrophotometer in either ethanol
or dichloromethane. The fluorescence quantum yield was calculated using rhodamine b in
ethanol excited at 510 nm. The quantum yield for rhodamine b under these conditions was
previously reported, Φ = 0.7.66,67 Absorption and fluorescence measurements for compounds 8 aꢀ
e and h were performed at 10ꢀ5 M
Computational Methodology:
Monomer: We optimized monomer geometries for neutral, radical cation, and anion species in
the gas phase using the M06ꢀL exchangeꢀcorrelation and 6ꢀ31+G(d,p) basis set. 51 Vibrational
frequency analyses were done to confirm that all structures are minima. LRꢀTDDFT calculations
are performed on neutral optimized geometries in the gas phase using the M06ꢀ2X exchangeꢀ
correlation functional and 6ꢀ31+G(d,p) basis set.
Dimer: We used dimer models to elucidate the transfer of holes and electrons through the
specific packing arrangements of different diarylindenotetracene derivatives. We extracted dimer
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 22 of 48
1
2
3
4
5
6
7
8
9
models from experimental crystal structures of different diarylindenotetracene derivatives.
Subsequently, we constrained the backbone of the diarylindenotetracene derivatives and
optimized peripheryl aryl groups and the subtituents. It is important to perform these constrained
optimizations as there are often uncertainities in the crystal structures related to the position of
the peripheryl aryl group and the substituents. Constrained optimization of dimers was
peroformed using the PBE functional and 6ꢀ31G(d,p) basis set. 68 Damped dispersion effects
were included with the pairwise D3 correction of Grimme et al. and the damping function of
Becke and Johnson.
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
Optimized dimer geometries were used to calculate charge transfer integrals were
accoplished using PBE0/6ꢀ31G(d) level of theory and the fragment molecular orbital (FMO)
approach. In the FMO approach, a dimer Fock matrix is constructed in the basis of monomer
ꢊ
|
ꢍ
orbitals. Offꢀdiagonal elements of the Fock matrix are ꢇꢈꢉ = ꢋꢈ ℎꢌꢅ|ꢋꢉ , where φi represents
the fragment molecular orbitals and i represents the sites (m or n). For the matrix elements
relevant to the hole (or the electron) transfer integral between the mth and nth sites in a system,
ꢋꢈ and ꢋꢉ are the HOMOs (or LUMOs) of mth and nth site respectively. Here, as we are using a
dimer model, sites represent individual monomers and hKS is the KohnꢀSham Fock operator.
ꢊ |
ꢍ
Diagonal elements of the Fock matrix are site energies, ꢎꢏ = ꢋꢏ ℎꢌꢅ|ꢋꢏ . Smn is the overlap
matrix element between orbital ꢋꢈ and ꢋꢉ. Since the Fock matrix is constructed here by using
ꢐꢑꢑ
ꢈꢉ
nonorthogonal monomer orbital basis, effective transfer integral (ꢇ ) is calculated using the
formula,
1
ꢒ )
ꢎꢈ + ꢎꢉ ꢓꢈꢉ
ꢇꢈꢉ
−
ꢐꢑꢑ
ꢈꢉ
2
ꢒ )
1
ꢇ
=
1 − ꢓꢈꢔ ꢉ
ACS Paragon Plus Environment

Page 23 of 48
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
All optimization of monomers and dimers and LRꢀTDDFT calculations were performed using
Gaussian09 software. 69 Transfer integral calculations are performed using a developer version
of NWChem. 70
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
Synthesis
6-Chloro-5,12-diphenyl-5,12-dihydrotetracene-5,12-diol (5a):
To a flameꢀdried 250 mL roundꢀbottom flask, bromobenzene (3.23 mL, 30.8 mmol) and 30 mL
anhydrous tetrahydrofuran (THF) were added under nitrogen. The solution was cooled to –78 °C
and then tertꢀbutyllithium (1.7 M, 36.2 mL, 61.5 mmol) was added dropwise to the stirring
solution. The slurry was stirred at –78 °C for 1 h, then warmed to 0 °C and the resultant
phenyllithium was used inmediately. To a flameꢀdried 500 mL roundꢀbottom flask, 6ꢀchloroꢀ
5,12ꢀnaphthacenequinone 4 (1.50 g, 5.12 mmol) and 150 mL anhydrous THF were added under
nitrogen. The suspension was cooled to ꢀ78 °C and the solution of phenyllithium, prepared
earlier, was added slowly. The suspension turned green and became a homogeneous solution
upon the completion of addition. The solution was stirred at –78 °C for 1 h then warmed to
room temperature and stirred for 14 h. The reaction was quenched with 1 N HCl (100 mL) and
extracted with EtOAc (2 × 50 mL). The organic layers were combined, washed sequentially with
saturated NaHCO3 (50 mL) and brine (20 mL), dried over anhydrous Na2SO4, and concentrated
under vacuum. The crude product was carried forward without further purification.
5-Chloro-6,11-diphenyltetracene (6a):
The resultant residue, compound 5a, was dissolved in 15 mL THF. To the resulting saturated
solution of SnCl2 (6.80 g, 35.9 mmol) in conc. HCl (approximately 10 mL) was added slowly, a
red solid precipitated upon addition. The slurry was stirred for additional 1 h upon complete
addition of SnCl2. The reaction was quenched by pouring the slurry into H2O (200 mL). The red
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 24 of 48
1
2
3
4
solid was collected by vacuum filtration. The filtrate was recrystallized from a hot solution of
5
6
toluene/isopropanol (1:10) to give 6a, a red/orange solid (1.70 g, 4.10 mmol, 80%): mp 188ꢀ189
7
8
1
˚C; H NMR (300 MHz, CDCl3) δ 8.38 (d, J = 9.1 Hz, 1H), 8.32 (s, 1H), 7.75 (d, J = 8.5 Hz,
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
1H), 7.71–7.58 (m, 5H), 7.57–7.50 (m, 5H), 7.50–7.39 (m, 3H), 7.36–7.29 (m, 1H), 7.28–7.22
13
(m, 2H); C NMR (75 MHz, CDCl3) δ 142.1, 139.3, 138.2, 136.0, 131.8, 131.5, 131.4, 130.6,
130.1, 130.0, 129.2, 128.8, 128.6, 127.8, 127.7, 127.4, 127.0, 126.8, 126.5, 125.2, 125.1, 125.0
(Not all carbon signals are resolved); IR (KBr) ν 3040, 1598, 1387, 1361, 1238 cmꢀ1; HRMS
(ESIꢀTOF) m/z: [M]+ Calcd for C30H19Cl 414.1175; found 414.1171.
9-Chloro-10-phenylindeno[1,2,3-fg]tetracene (7a):
To a flameꢀdried 100 mL roundꢀbottom flask, anhydrous aluminum chloride (1.60g, 12.1 mmol)
and 15 mL freshly distilled nitrobenzene was added under nitrogen. The slurry was stirred at 60
°C for ten minutes and formed a clear solution. To the solution, compound 6a (1.00 g, 2.41
mmol) and additional nitrobenzene (5 mL) were added. The reaction turned dark green upon the
completion of addition. The reaction was stirred at 60 °C for 3 to 4 h and allowed to cool to
room temperature. The dark green solution was then poured onto a mixture of ice and 1N HCl
solution, turning purple instantaneously. The mixture was extracted with EtOAc (2 × 50 mL).
The organic layers were combined, filtered and concentrated under vacuum. The remaining
nitrobenzene was subsequently removed by azeotropic distillation with H2O (150 mL). The
residue was collected and recrystallized from hot toluene (first crop) and DCM/MeOH (second
crop) to give 7a, a purple/black solid (811 mg, 1.96 mmol, 81%): mp 262–263 ˚C; 1H NMR (300
MHz, CDCl3) δ 8.87 (dd, J = 8.2, 6.9Hz, 2H), 8.61–8.47 (m, 3H), 7.70 (d, J = 9.1 Hz, 1H), 7.68–
7.59 (m, 2H), 7.58–7.55 (m, 3H), 7.53–7.41 (m, 5H), 7.33 (ddd, J = 1.0, 6.5, 9.2 Hz, 1H); IR
(KBr) ν 3068, 3027, 1597, 1451, 1380, 1276, 1150 cmꢀ1; HRMS (ESIꢀTOF) m/z: [M]+ Calcd for
ACS Paragon Plus Environment

Page 25 of 48
The Journal of Organic Chemistry
1
2
3
4
5
C30H17Cl 412.1019; found 412.0990. A suitable 13C NMR spectrum could not be obtained due to
poor solubility.
6
7
8
9
9,10-Diphenylindeno[1,2,3-fg]tetracene (8a):
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
To a flameꢀdried 100 mL roundꢀbottom flask, compound 7a (100 mg, 0.242 mmol), PEPPSIꢀIPr
(16.0 mg, 0.0235 mmol) and 10 mL freshly distilled 1,4ꢀdioxane were added. The flask was then
sealed with a septum and placed under a nitrogen atmosphere. The solution was stirred at room
temperature and phenylmagnesium bromide in THF (0.24 M, 10 mL, 2.42 mmol) was added.
The reaction was heated to 60 °C and stirred for 4 h. The reaction was then quenched with 1N
HCl and extracted with EtOAc (2 × 50 mL). The organic layers were combined, dried over
Na2SO4 and concentrated under vacuum. The residue was purified by flash column
chromatography (silica gel, 5% ethyl acetate in hexanes, Rf =0.30) to give 8a (87.5 mg, 0.192
mmol, 80%). In order to obtain the product in a solid form, the product obtained from
chromatography was purified by recrystallization in DCM/MeOH to give 8a, a purple/black solid
1
(65.1 mg, 0.143 mmol, 60%): mp 271–272 ˚C; H NMR (300 MHz, CDCl3) δ 8.93 (d, J = 8.8
Hz, 2H), 8.61 (dd, J = 5.6, 3.2 Hz, 2H), 7.59 (m, 2H), 7.53 (dd, J = 5.6, 2.8 Hz, 2H), 7.36 (d, J =
9.2 Hz, 2H), 7.21 (ddd, J = 7.2, 6.4, 0.8 Hz, 2H), 7.05 (m, 6H), 6.93 (m, 4H); 13C NMR (75
MHz, CDCl3) δ 140.8, 140.2, 139.7, 134.0, 131.6, 131.0, 129.2, 128.9, 128.2, 127.4, 127.2,
126.7, 126.3, 124.4, 124.2, 123.8 (not all carbon signal were resolved); IR (thin film) ν 3055,
1946, 1598, 1552, 1449, 1441, 1396, 1361 cmꢀ1; HRMS (ESIꢀTOF) m/z: [M+H]+ Calcd for
C36H23 455.1800; found 455.1806.
6-Chloro-5,12-di-p-tolyl-5,12-dihydrotetracene-5,12-diol (5b):
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 26 of 48
1
2
3
4
5
6
7
8
6ꢀchloroꢀ5,12ꢀdiꢀpꢀtolylꢀ5,12ꢀdihydrotetraceneꢀ5,12ꢀdiol was synthesized analogously to 6ꢀ
chloroꢀ5,12ꢀdiphenylꢀ5,12ꢀdihydrotetraceneꢀ5,12ꢀdiol, compound 5a. The crude product was
carried to the next step without purification.
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
5-Chloro-6,11-di-p-tolyltetracene (6b):
5ꢀchloroꢀ6,11ꢀdiꢀpꢀtolyltetracene
was
synthesized
analogously
to
5ꢀchloroꢀ6,11ꢀ
diphenyltetracene, compound 6a, to give an red/orange solid (2.00 g, 4.51 mmol, 88%): mp 197–
198 ˚C; 1H NMR (300 MHz, CDCl3) δ 8.39 (d, J = 9.1 Hz, 1H), 8.35 (s, 1H), 7.76 (d, J = 8.1 Hz,
1H), 7.70–7.59 (m, 2H), 7.49–7.37 (m, 5H), 7.35 (s, 4H), 7.30 (d, J = 6.5 Hz, 1H), 7.27–7.24
(dd, J = 5.6, 1.9 Hz, 2H), 2.59 (s, 3H), 2.56 (s, 3H); 13C NMR (75 MHz, CDCl3) δ 139.1, 138.1,
137.4, 136.6, 136.2, 136.0, 132.0, 131.3, 130.5, 130.2, 130.1, 129.3, 128.8, 128.6, 128.4, 127.5,
126.9, 126.9, 126.6, 125.7, 125.3, 125.0, 125.0, 21.5, 21.5 (Not all carbon signals are resolved);
IR (KBr) ν 3043, 3016, 2864, 2857, 1510, 1459, 1387, 1357 cmꢀ1; HRMS (ESIꢀTOF) m/z: [M]+
Calcd for C32H23Cl 442.1488; found 442.1488.
10-Chloro-2-methyl-9-(p-tolyl)indeno[1,2,3-fg]tetracene (7b):
10ꢀchloroꢀ2ꢀmethylꢀ9ꢀ(pꢀtolyl)indeno[1,2,3ꢀfg]tetracene was synthesized analogously to 9ꢀ
chloroꢀ10ꢀphenylindeno[1,2,3ꢀfg]tetracene, compound 7a, to give an purple solid (680 mg, 1.54
1
mmol, 86%): mp 197–198 °C; H NMR (300 MHz, CDCl3) δ 8.39 (d, J = 9.1 Hz, 1H), 8.35 (s,
1H), 7.76 (d, J = 8.4 Hz, 1H), 7.71–7.58 (m, 2H), 7.50–7.37 (m, 5H), 7.35 (s, 3H), 7.30 (d, J =
13
6.5 Hz, 1H), 7.23 (d, J = 3.0 Hz, 1H), 2.59 (s, 3H), 2.56 (s, 3H); C NMR (75 MHz, CDCl3) δ
139.1, 138.1, 137.4, 136.6, 136.2, 136.0, 132.0, 131.3, 130.5, 130.2, 130.1, 129.3, 128.8, 128.6,
128.4, 127.5, 126.9, 126.9, 126.6, 125.7, 125.3, 125.0, 125.0, 21.5, 21.5 (not all carbon signals
are resolved); IR (KBr) ν 3023, 2915, 1686, 1601, 1557, 1511, 1458, 1431, 1392, 1377, 1304
cmꢀ1; HRMS (ESIꢀTOF) m/z: [M]+ Calcd for C32H32Cl 440.1332; found 440.1325.
ACS Paragon Plus Environment

Page 27 of 48
The Journal of Organic Chemistry
1
2
3
4
2-Methyl-10-phenyl-9-(p-tolyl)indeno[1,2,3-fg]tetracene (8b)
5
6
7
8
To a flameꢀdried 100 mL roundꢀbottom flask, 7b (400 mg, 0.907 mmol), PEPPSIꢀIPr (31.0 mg,
0.0456 mmol) and 10 mL freshly distilled 1,4ꢀdioxane were added. The flask was then sealed
with a septum and placed under a nitrogen atmosphere. The solution was stirred at room
temperature and phenylmagnesium bromide in THF (0.910 M, 10 mL, 9.10 mmol) was added.
The reaction was heated to 60 °C and stirred for 4 h. The reaction was then quenched with 1N
HCl and extracted with EtOAc (2 × 50 mL). The organic layers were combined, dried over
Na2SO4 and concentrated under vacuum. The residue was purified by flash column
chromatography (silica gel, 5% ethyl acetate in hexanes, Rf =0.40) to give 8b (387 mg, 0.802
mmol, 88%). In order to obtain the product in a solid form, the product obtained from
chromatography was purified by recrystallization from hot toluene/iPrOH (1:10) to give a
purple/black solid, compound 8b (175 mg, 0.363 mmol, 40%): mp 179–180 °C; 1H NMR (300
MHz, CDCl3) δ 8.89 (dd, J = 8.9, 15.9 Hz, 2H), 8.45 (d, J = 7.9 Hz, 1H), 8.40 (s, 1H), 7.62–7.53
(m, 2H), 7.45 (d, J = 9.1 Hz, 1H), 7.34 (dd, J = 11.9, 6.7 Hz, 2H), 7.20 (dd, J = 9.2, 6.4 Hz, 2H),
7.14 (dd, J = 8.3, 6.4 Hz, 1H), 7.03 (t, J = 7.4 Hz, 2H), 6.90 (dd, J = 5.2, 3.1 Hz, 2H), 6.84–6.76
(m, 4H), 2.64 (s, 3H), 2.32 (s, 3H); 13C NMR (75 MHz, CDCl3) δ 140.7, 140.4, 140.1, 137.2,
137.1, 136.4, 135.5, 134.0, 133.9, 131.6, 131.5, 131.1, 129.3, 129.3, 128.8, 128.5, 128.4, 127.8,
127.4, 127.2, 127.2, 127.0, 125.5, 125.2, 124.6, 124.3, 123.9, 123.8, 22.1, 21.2. (Not all carbon
signals are resolved); IR (KBr) ν 3042, 3021, 2912, 2857, 1599, 1558, 1511, 1456, 1434, 1396,
1360, 1294, 1133, 1021 cmꢀ1; HRMS (ESIꢀTOF) m/z: [M]+ Calcd for C38H26 482.2035; found
482.2026.
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
6-Chloro-5,12-bis(4-fluorophenyl)-5,12-dihydrotetracene-5,12-diol (5c):
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 28 of 48
1
2
3
4
5
6
7
8
9
To a flame dried 100 mL 3ꢀneck round bottom flask was added anhydrous THF (50 mL), which
was cooled to –77 ˚C. 1ꢀbromoꢀ4ꢀfluorobenzene (1.965 mL, 3.130 g, 17.89 mmol) was added to
THF at –77 ˚C followed by nꢀbutyllithium (2.5 M in hexane, 6.439 mL, 24.53 mmol). The
mixture was stirred at –77 ˚C for 10 minutes to form 4ꢀfluorophenyllitium. In a flame dried 250
mL 3ꢀneck round bottom flask anhydrous THF (150 mL) and 6ꢀchloroꢀ5,12ꢀnaphthacenequinone
4 were combined and cooled to –77 ˚C. The 4ꢀfluorophenyllitium was transferred into the 250
mL round bottom containing the slurry of THF and 6ꢀchloroꢀ5,12ꢀnaphthacenequinone via
cannula at a constant flow. The mixture was allowed to react at –77 ˚C for 2 hours then allowed
to warm to room temperature and stirred for an additional hour. The reaction was quenched with
water (2 mL). The crude reaction mixture was concentrated to a solid and carried forward
without purification.
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
5-Chloro-6,11-bis(4-fluorophenyl)tetracene (6c):
The crude reaction mixture of compound 5c was dissolved in 100 mL of dioxane and poured into
a 250 mL round bottom flask. Tin (II) chloride (5.652 g, 29.81 mmol) and BF3•OEt2 (2.207 mL,
2.538 g, 17.89 mmol) were added to the 250 mL round bottom. The reaction mixture was heated
to reflux (106 ˚C) and reflux was maintained for 45 minutes. The reaction mixture was then
allowed to cool to room temperature and quenched with saturated aqueous NaHCO3 solution,
followed by addition of solid NaHCO3 until the aqueous portion is basic as indicated by pH
paper. The precipitate that formed was removed via filtration over Celite. The filtered solid was
washed with chloroform (3 × 250 mL). The filtrate and chloroform washes were combined and
washed once with water, once with saturated brine, dried over MgSO4, concentrated and placed
under high vacuum overnight. The crude product was dissolved in boiling chloroform followed
by the addition of room temperature methanol and placed in the refrigerator (5 °C) overnight.
ACS Paragon Plus Environment

Page 29 of 48
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
This gave compound 6c, an orange/red solid (2 steps 1.425 g, 3.160 mmol, 53%): mp 207–208
˚C; 1H NMR (500 MHz CDCl3) δ 8.40 (d, J = 9.1 Hz, 1H), 8.28 (s, 1H), 7.77 (d, J = 8.6 Hz, 1H),
7.66 – 7.60 (m, 1H), 7.60–7.55 (m, 1H), 7.50–7.47 (m, 3H), 7.45–7.34 (m, 6H), 7.30–7.27 (m,
2H), 7.25–7.23 (m, 1H); 13C NMR (126 MHz CDCl3) δ 163.5 (d, J = 21.8 Hz), 161.5 (d, J = 20.7
Hz), 137.8 (d, J = 3.6 Hz), 137. 2, 135.1, 135.0 (d, J = 3.6 Hz), 133.0 (d, J = 7.9 Hz), 132.9 (d, J
= 7.8 Hz), 132.0, 130.8, 130.3, 130.2, 129.4, 128.8, 128.6, 127.3 (d, J = 6.8 Hz), 126.6, 126.3,
125.7, 125.6, 125.5, 125.4, 125.0, 115.8 (d, J = 21.3 Hz), 114.8 (d, J = 21.3 Hz) (not all carbon
signals are resolved); 19F NMR (379 MHz) δ ꢀ115.43– ꢀ115.60 (m) ꢀ116.84 (ddd, J = 14.3, 8.8,
5.6 Hz); IR (Thin Film) ν 3073, 1602, 1509, 1461, 1389 cmꢀ1; HRMS (GCꢀQTOF) m/z: [M]+
Calcd for C30H17ClF2 450.0987, found 450.0972.
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-Chloro-2-fluoro-9-(4-fluorophenyl)indeno[1,2,3-fg]tetracene (7c):
Compound 6c (1.425 g, 3.165 mmol) was dissolved in chloroform (20 mL) and the solution was
purged with nitrogen for 3 minutes. Methanesulfonic acid was then added (80 mL) and the
solution was purged with nitrogen for 5 minutes. 2,3ꢀDichloroꢀ5,6ꢀdicyanoꢀ1,4ꢀbenzoquinone
(DDQ) ( 0.862 g, 3.798 mmol) was added to the mixture of chloroform and methanesulfonic acid
and the solution was again purged with nitrogen for an additional 5 minutes. The reaction was
stirred under nitrogen atmosphere for 3h, wrapped in aluminum foil to shield the mixture from
light. The reaction progress was monitored using 1H NMR and TLC, looking for the
disappearance of fluorescence of the 6c spot. The reaction was quenched by adding saturated
NaHCO3 solution (approximately 100 mL, CAUTION: Gas evolution, exothermic) to the
reaction followed by pouring the reaction mixture into a separatory funnel containing solid
NaHCO3 (at least 10g CAUTION: Gas evolution, exothermic). After allowing to cool to room
temperature, the mixture was extracted with chloroform (3 × 200 mL) and the remaining solid
ACS Paragon Plus Environment