Synthesis and photophysical properties of dinaphtho[2,3-b:2′,3′-i]dihydrophenazine derivatives

Article abstract of DOI:10.1016/j.tetlet.2019.03.035

A dinaphtho[2,3-b:2′,3′-i]dihydrophenazine (DNP) derivative was synthesized by Buchwald-Hartwig cross-coupling, and its electronic spectrum was compared with that of dinaphtho[b,i]dihydrophenazine-5,18-dione (DNP-dione) as an anthraquinone analog. An absorption band of DNP is attributed to extension of π-conjugation over the entire molecule via the N atom. DNP-dione showed a broad absorption band in the range 450–490 nm due to intramolecular charge-transfer interactions. Additionally, the absolute fluorescence quantum yield of DNP was larger than that of DNP-dione. DNP-dione exhibited reversible oxidation peaks and a similar oxidation potential to DNP, since there are very weak electronic interactions between the anthracene and anthraquinone units across the N atoms with the 4-octyloxyphenyl substituent.

Full text of DOI:10.1016/j.tetlet.2019.03.035

Accepted Manuscript
Synthesis and photophysical properties of dinaphtho[2,3-b:2’,3’-i]-dihydrophe-
nazine derivatives
Tetsuo Iwanaga, Naoto Asano, Haruo Yamada, Shinji Toyota
PII:
S0040-4039(19)30241-2
https://doi.org/10.1016/j.tetlet.2019.03.035
TETL 50676
DOI:
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
5 February 2019
8 March 2019
12 March 2019
Please cite this article as: Iwanaga, T., Asano, N., Yamada, H., Toyota, S., Synthesis and photophysical properties
of dinaphtho[2,3-b:2’,3’-i]-dihydrophenazine derivatives, Tetrahedron Letters (2019), doi: https://doi.org/10.1016/
j.tetlet.2019.03.035
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Synthesis and Photophysical Properties of
Dinaphtho[2,3-b:2’,3’-i]dihydrophenazine
Derivatives
Leave this area blank for abstract info.
Tetsuo Iwanaga,* Naoto Asano, Haruo Yamada, Shinji Toyota
R
N
O
O
R
R
N
NH
Anthraquinone
Anthracene
N
R
NH
R
N
R
Extended π-conjugation
Intramolecular Charge-Transfer

1
Tetrahedron Letters
Synthesis and photophysical properties of dinaphtho[2,3-b:2’,3’-i]-
dihydrophenazine derivatives
Tetsuo Iwanagaa,*, Naoto Asanoa, Haruo Yamadaa and Shinji Toyotab
a Department of Chemistry, Faculty of Science, Okayama University of Science, 1-1 Ridaicho, Kita-ku, Okayama 700-0005, Japan
b Department of Chemistry, School of Science, Tokyo Institute of Technology, 2–12–1 Ookayama, Meguro-ku, Tokyo 152–8551, Japan
Dedicated to Emeritus Prof. Takahiko Inazu in celebration of his 81th birthday.
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
A dinaphtho[2,3-b:2’,3’-i]dihydrophenazine (DNP) derivative was synthesized by Buchwald-
Hartwig cross-coupling, and its electronic spectrum was compared with that of
dinaphtho[b,i]dihydrophenazine-5,18-dione (DNP-dione) as an anthraquinone analog. An
absorption band of DNP is attributed to extension of π-conjugation over the entire molecule via
the N atom. DNP-dione showed a broad absorption band in the range 450–490 nm due to
intramolecular charge-transfer interactions. Additionally, the absolute fluorescence quantum
yield of DNP was larger than that of DNP-dione. DNP-dione exhibited reversible oxidation
peaks and a similar oxidation potential to DNP, since there are very weak electronic interactions
between the anthracene and anthraquinone units across the N atoms with the 4-octyloxyphenyl
substituent.
Available online
Keywords:
Dinaphtho[2,3-b:2’,3’-i]dihydrophenazine
Photophysical property
Electrochemical property
Intramolecular charge-transfer interaction
2009 Elsevier Ltd. All rights reserved.
1. Introduction
anthraquinone analogs have not yet been reported in the
literature.
i]dihydrophenazine
Thus,
we
1
designed
and
dinaphtho[2,3-b:2’,3’-
dinaphtho[2,3-b:2’,3’-
As an electron-sufficient moiety, the phenazine framework
has proven an attractive building unit for the molecular design of
new π-conjugated functional materials.1 Particularly, π-extended
phenazine derivatives, including aza analogs2 of pentacenes and
heptacenes, have been extensively applied to developing new
organic dyes and devices,3 such as organic field-effect
transistors.4 Dibenzo[b,i]dihydrophenazine is also a promising
candidate for constructing different functional molecules,5 while
anthraquinone-based dihydrophenazine derivatives such as
indanthrone have been used as organic dyes.6 Recently,
Shinokubo et al. reported the facile synthesis of π-extended
dinaphtho[a,h]dihydrophenazines with zigzag structure by
oxidation using DDQ.7
i]dihydrophenazine-5,18-dione 2 possessing a anthraquinone
unit, in which the nitrogen atoms derived from 4-octyloxyaniline
function as connecting groups (Figure 1). These derivatives were
diaza analogs of 7,16-diphenylheptacene, which is an extremely
weak photo-oxidation.8 Herein, we report the synthesis and
spectroscopic data of dinaphtho derivative 1 and its quinone
analog 2, and their photophysical and electrochemical properties
are compared to assess the electronic interactions via nitrogen
atoms.
2. Results and Discussion
2.1. Synthesis
OC8H17
OC8H17
O
Br
Br
AlCl3
H2SO4
+
O
O
O
N
N
N
N
O
1) NaBH4, MeOH
2) NaBH4, MeOH
3) conc. HCl aq.
O
Br
Br
Br
Br
OC8H17
OC8H17
2
1
O
4
3
Figure 1. Molecular structures of dinaphtho[2,3-b:2’,3’-i]-
dihydrophenazine derivatives 1 and 2.
Scheme 1. Synthesis of 2,3-dibromoanthraquinone 3 and 2,3-
dibromoanthracene 4.
However, to the best of our knowledge, linear-type
dinaphtho[2,3-b:2’,3’-i]dihydrophenazine derivatives and

2
Tetrahedron
OC8H17
(a)
Pd(dba)2
t-BuPHBF4
NaOt-Bu
OC8H17
Br
Br
NH
NH
+
toluene
4
NH2
5
6
OC8H17
Scheme 2. Synthesis of 2,3-diaminoanthracene derivative 6.
4
OC8H17
Pd(dba)2
(b)
t-Bu3PHBF4
NaOt-Bu
1
xylene
NH
NH
3
Pd(t-Bu3P)2
NaOt-Bu
2
xylene
6
OC8H17
Scheme 3. Synthesis of dinaphtho[b,i]dihydrophenazine
derivatives 1 and 2.
To synthesize the target phenazine derivatives, 2,3-
dibromoanthracene 49 was used as a key intermediate for
amination via cross-coupling.10 This precursor was produced
according to Scheme 1. Friedel-Crafts reaction of phthalic
anhydride with 1,2-dibromobenzene in the presence of AlCl3
yielded the adduct, which was then dehydrated with conc. H2SO4
to afford 2,3-dibromoanthraquinone 3 via the known method.11
Reduction of 3 with NaBH4 gave 2,3-dibromoanthracene 4 in a
stepwise manner. Compound 4 was produced in 17% overall
yield from 1,2-dibromobenzene.
Figure 2. X-ray structure (a) and packing diagram (b) of
compound 1 (solvent molecules are included).
by the dihedral angles (θ) between the two planes (+81.1° and
−75.6°). In the crystal packing, intermolecular C–H···π contacts
(2.8 Å) between the anthracene and phenyl groups rather than
π···π contacts (3.5 Å) between the anthracene units are dominant.
The molecules have no significant intermolecular contacts as
they are sterically protected by the two 4-octyloxyphenyl groups.
Because we could not obtain single crystals suitable for X-ray
analysis for 2, the molecular structure of model compound 2’
possessing methoxy groups in place of octyloxy groups was
optimized at the B3LYP/6-31G(d) level (Figure S1). In the
global minimum structures, compound 2’
Conventional Buchwald-Hartwig coupling of 4 with 4-
octyloxyaniline 5 (2 equiv.)12 gave compound 6 as a yellow solid
in 64% yield (Scheme 2). The reaction conditions were
optimized for synthesizing 1 from dibromide 4 and diamine 6
(Scheme 3). We reacted 4 and 6 in the presence of Pd(X-
Phos_G1) in xylene under reflux for 48 h, this reaction gave a
complicated mixture which is not including the target compound.
The reaction with 10 mol% of Pd(t-Bu3P)2 gave the desired
compound in 3% yield. This yield was further increased to 5% by
adding Pd(dba)2 and t-Bu3PHBF4 rather than Pd(t-Bu3P)2; this
tetrafluoroborate salt easily generates fresh Pd(0) catalyst in this
reaction system. Anthraquinone analog 2 was prepared by same
cross coupling using Pd(t-Bu3P)2 catalyst of 2,3-
dibromoanthraquinone 3 and diamine 6 (3% yield).
framework with a large surface area.
16
14
1
12
10
8
2
1-FL
6
4
These compounds showed good stability under ambient
conditions and were reliably characterized by NMR and mass
spectroscopy. Molecular ion peaks of 1 and 2 were observed at
m/z 790.45 (C56H58N2O2) and 820.43 (C56H56N2O4), respectively,
2
0
250
300
350
400
450
500
550
600
1
Wavelength /nm
in the mass spectra. In the H NMR spectrum of 1, two singlets
were observed in the aromatic region at  7.7 and 6.3, while in
the 13C NMR spectrum, compound 2 gave a signal due to
carbonyl carbons at  182.0. Compounds 1 and 2 gave 11 and 17
aromatic carbon signals, respectively, which was consistent with
their molecular symmetry.
Figure 3. UV-vis (solid line) and FL (dotted line) spectra of
compounds 1 and 2 in CH2Cl2.
2.3. Electronic Spectra
The absorption spectra of compounds 1 and 2 were recorded
in CH2Cl2 (Figure 3). The spectroscopic data are summarized in
Table 1. These compounds showed absorptions at λmax 474 nm
(1) and 431 nm (2). An absorption band for 1 is attributed to
extension of π-conjugation over the entire molecule via the N
atom, while compound 2 exhibited a characteristic broad
shoulder band extending to ca. 490 nm in the longest wavelength
2.2. Structures
We obtained a single crystal of compound 1 suitable for X-ray
analysis from a hexane/CH2Cl2 solution (Figure 2).13 As
expected, compound 1 has a planar framework with C2h
symmetry. To avoid steric hindrance, the two 4-octyloxyphenyl
groups are twisted from the naphthophenazine plane as indicated

3
Table 1. UV-vis absorption and fluorescence data for compounds 1
and 2 in CH2Cl2.
and calculated energy levels are given in Table 2. Compound 1
gave irreversible reduction potentials, while compound 2 gave
reversible reduction potentials at −1.48 and −1.71 V due to the
formation of a radical anion and a dianion species of the
anthraquinone unit, respectively. The first oxidation peak of 1
was observed at +0.24 V, and that of 2 at a similar potential
(+0.26 V). There are very weak electronic interactions between
the anthracene and anthraquinone units through the N atoms of
the p-alkoxyphenyl substituent. This tendency is consistent with
the calculated HOMO energies given in Table 2.
calcd λmax /nm (f)a
λmax /nm
λem /nm
(ε)
[composition of band ]
443 (0.65)
(ΦF)b
474
1
2
483 (0.72)
(59600)
[H−1−>L, 45%; H−>L+2, 3%]
646 (0.02) [H−>L, 49%]
553 (0.08)
431
N. D. c
(68000)
[H−1−>L, 48%; H−1−>L, 2%]
aTD-DFT calculations (TD/B3LYP/6-31G(d)) were performed by using
optimized structures of compounds 1’ and 2’ at the B3LYP/6-31G(d) level; f
= oscillator strength.
Table 2. Electrochemical data for compounds 1 and 2.
HOMO
level /eV b
−4.52
LUMO
level /eV b
−1.45
E1/2ox /Va
E1/2red /Va
bAbsolute fluorescence quantum yields.
cNot measured due to weak fluorescence.
c
1
2
+0.24
+0.26
−
−1.48, −1.71
−4.74
−2.37
a
Measured in CH2Cl2 (1.00 mmol L−1) with n-Bu4NBF4 (0.10 mol L−1) as the
supporting electrolyte and Ag/Ag+ as the reference electrode.
1’
2’
b
Calculated at the B3LYP/6-31G(d) level for model compounds 1’ and 2’.
c
Only the first redox potential is shown due to irreversible waves.
LUMO(−2.37)
LUMO (−1.45)
20µA
HOMO (−4.52)
HOMO (−4.74)
2
1.5
1
0.5
0
-0.5
-1
-1.5
-2
-2.5
Potential / V vs. Fc/Fc+
Figure 5. Cyclic voltammograms of 1 (black) and 2 (red) in
CH2Cl2 with 0.10 mmol L−1 n-Bu4NPF6 as supporting electrolyte,
Ag/Ag+ as reference electrode, a glass carbon disk as working
electrode, a Pt wire as counter electrode, and a scan rate of 0.10 V
s−1.
HOMO−1 (−4.62)
HOMO−1 (−4.92)
3. Conclusion
Figure 4. Energy levels (eV) and calculated MOs of 1’ and 2’
(octyloxy groups were replaced to methoxy groups) using the
B3LYP/6-31G(d) level of theory.
In conclusion, we synthesized dinaphtho[b,i]dihydrophenazine
derivatives via Buchwald-Hartwig coupling. The X-ray
crystallographic analysis of 1 indicated a planar structure. The
photophysical properties were influenced by nitrogen atoms,
resulting in extended π-conjugation for 1 and intramolecular
donor–acceptor interactions for 2. The oxidation potentials of 1
and 2 were similar due to the independence of the 2,3-
diaminoanthracene unit. Further studies involving the synthesis
of π-extended heteroacene analogs and their application to the
design of efficient hole transport materials are in progress.
region. This broad band of 2 was assigned to the HOMO−1 to
LUMO transition based on TD-DFT calculations using model
compound 2’ as described above. The calculated MOs of 2’
suggested that the HOMO−1 and LUMO levels were mainly
located on the anthracene and anthraquinone units, respectively
(Figure 4). Thus, the shoulder absorption peak of 2 at 450–490
nm is attributed to an intramolecular charge-transfer interaction.
The fluorescence spectra were measured in CH2Cl2 (Figure 3
and Table 1). An emission peak for compound 1 was observed at
483 nm, while compound 2 showed a weak emission. The
absolute fluorescence quantum yield ΦF of 1 was 0.72. The non-
fluorescence of 2 was attributed to efficient photoinduced
intramolecular electron-transfer from anthracene to the
anthraquinone unit.14
Supplementary data
Supplementary data associated with this article is available in
the online version under http://dx.doi.org/##.####.
Acknowledgments
This work was partly supported by JSPS KAKENHI Grant-in-
Aid for Young Scientists (B) (Grant Number 16K17874) and
Grant for Promotion of OUS Research Project (OUS-PR-29-1).
The authors gratefully thank the Research Instruments Center,
2.4. Electrochemical Properties
Finally, the redox properties of 1 and 2 were explored by
cyclic voltammetry in CH2Cl2 (Figure 5). The redox potentials

4
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Highlights
π-Extended phenazine derivatives and its quinone analog were prepared.
An absorption band of phenazine derivatives is attributed to π-extension.
A broad absorption of quinone analog is attributed to intramolecular CT interactions.
Electrochemical properties of these compounds are disclosed.