A concise method to prepare linear 2,3-diazaoligoacene derivatives

Article abstract of DOI:10.1016/j.tetlet.2014.06.033

In this Letter, we demonstrate that linear 2,3-diazanaphthalene (1), 2,3-diazaanthracene (2), and 2,3-diazatetracene (3) can be easily prepared through [4+2] cycloaddition reaction between 3,6-diphenyl-1,2,4,5-tetrazine as the diene and arynes as dienophiles, generated in situ from ortho- aminoarylcarboxylic acids. The physical properties and crystal packing of the prepared compounds 1-3 were fully investigated. In addition, the experimental data (e.g., band gap and band position) are further confirmed by theoretical studies.

Full text of DOI:10.1016/j.tetlet.2014.06.033

Tetrahedron Letters 55 (2014) 4346–4349
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
A concise method to prepare linear 2,3-diazaoligoacene derivatives
Junbo Li a, Junkuo Gao b, Wei-Wei Xiong a, Qichun Zhang a,
⇑
a School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore
b College of Materials and Textile, Zhejiang Sci-Tech University, Hangzhou 310018, China
a r t i c l e i n f o
a b s t r a c t
Article history:
In this Letter, we demonstrate that linear 2,3-diazanaphthalene (1), 2,3-diazaanthracene (2), and
2,3-diazatetracene (3) can be easily prepared through [4+2] cycloaddition reaction between 3,6-diphe-
nyl-1,2,4,5-tetrazine as the diene and arynes as dienophiles, generated in situ from ortho-aminoarylcarb-
oxylic acids. The physical properties and crystal packing of the prepared compounds 1–3 were fully
investigated. In addition, the experimental data (e.g., band gap and band position) are further confirmed
by theoretical studies.
Received 22 April 2014
Revised 21 May 2014
Accepted 5 June 2014
Available online 12 June 2014
Keywords:
Azaacene
Ó 2014 Elsevier Ltd. All rights reserved.
Diene
Dienophile
Cycloaddition reaction
Crystal packing
As analogs of oligoacenes,1 oligoazaacenes have attracted
significant attention, not only because of their synthetic
challenges,2 but also because of their potential application in field
effect transistors,3 phototransistors,4 solar cells,5 memory devices,6
and sensing probes.7 Although oligoazaacenes can be synthesized
through SN2 reaction between diamines and dihydroxy (or dihalo)
compounds followed by oxidation, or by condensation between a
diamine (or tetraamine) and a diketone (or tetraketone), these
methods have posed a limitation toward the synthesis of larger
azaacenes (n >6)8 because all these methods involve the formation
of water as a by-product, which could modify the targeted azaac-
enes by changing the hybridization of the N atoms from sp2 to
sp3. Thus, a new method to address this problem to approach large
azaacenes is highly desirable.
Given our successful findings that oligoacenes can be prepared
through [4+2] reactions using arynes as dienophiles,9 we believe
that this type of reaction could be a promising method to construct
larger azaacenes.7a Herein, we demonstrate that three 2,3-diazaac-
enes [2,3-diazanaphthalene (n = 0), 2,3-diazaanthracene (n = 1),
and 2,3-diazatetracene (n = 2)] can be easily prepared through
[4+2] reactions between 3,6-diphenyl-1,2,4,5-tetrazine as the
diene and in situ generated arynes as dienophiles (from precursor
ortho-aminoarylcarboxylic acids) (Scheme 1). These compounds
have been reported in the literature through other methods.10 It
is worth noting that all physical data [e.g., cyclic voltammetry
Scheme 1. The synthetic method toward 2,3-diazaacenes.
(CV), crystal structures, and theoretical studies, except UV–vis
absorption] are reported here for the first time.
1,4-Diphenyl-2,3-diazanaphthalene (1), 1,4-diphenyl-2,3-diaza
anthracene (2), and 1,4,6,11-tetraphenyl-2,3-diazatetracene (3)
(Scheme 2) have been synthesized through [4+2] reactions
between 3,6-diphenyl-1,2,4,5-tetrazine and the corresponding
aryne precursors [2-aminobenzoic acid (for 1, yield 58%),
3-amino-2-naphthoic acid (for 2, yield 63%), and 3-amino-9,10-
diphenylanthracene-2-carboxylic acid11 (for 3, yield 40%)]. The
compounds prepared were fully characterized by 1H NMR, 13C
NMR, and high-resolution mass spectrometry (HRMS). Moreover,
the structures of compounds 1–3 were further confirmed by single
crystal structure analysis (CCDC numbers for 1–3 are 998769,
998770 and 993356, respectively).
The crystal structures and the crystal packing arrangements of
compounds 1–3 are shown in Figure 1. Compound 1 possesses an
orthorhombic space group, Cmc21 (36), and its unit cell data are as
follows: a = 20.1791(10) Å, b = 10.7017(6) Å, c = 8.2409(3) Å,
= 90(0)°. The molecules of compound 1 are stacked with an offset
head-to-head mode due to the spatial hindrance of the phenyl
a = b =
c
⇑
Corresponding author. Tel.: +65 67904705; fax: +65 67909081.
E-mail address: qczhang@ntu.edu.sg (Q. Zhang).
http://dx.doi.org/10.1016/j.tetlet.2014.06.033
0040-4039/Ó 2014 Elsevier Ltd. All rights reserved.

J. Li et al. / Tetrahedron Letters 55 (2014) 4346–4349
4347
Figure 2. UV–vis spectra of compounds 1–3 (1 Â 10À5 M) in CH2Cl2.
Scheme 2. Molecular structures of compounds 1–3.
groups. There are weak
p
–
p
stacking interactions (ꢀ3.75 Å)between
the pyridazine unit and benzene groups. Compound 2 has a mono-
clinic space group, C12/c1 (15), and its unit cell data are:
a = 20.4657(5) Å, b = 10.6386(3) Å, c = 7.6951(2) Å, b = 96.16(0)°.
Being different from compound 1, compound 2 shows an offset
head-to-tail stacking and the distance between the two naphthalene
units is nearly 3.86 Å, indicating a very weak p–p stacking interac-
tions between the molecules. Compound 3 possesses a triclinic space
group, p1 (2), with unit cell data of a = 10.0261(4) Å, b = 13.2546(4) Å,
Figure 3. Fluorescence spectra of compounds 1–3 (1 Â 10À5 M) in CH2Cl2.
Figure 4. Cyclic voltammetry curves of compounds 1–3 in CH2Cl2 solution
containing 0.1 M TBAP electrolyte. Scanning rate: 100 mV/s.
Figure 1. Crystal structures of compounds 1–3 (hydrogen atoms are omitted) and
Crystal packing arrangements.

4348
J. Li et al. / Tetrahedron Letters 55 (2014) 4346–4349
Table 1
Electrochemical data and calculated HOMO–LUMO gaps of compounds 1–3
red
a
ox
a
b
e
f
Compound
E
(V)
E
(V)
onset
Egap (eV)
LUMOc (eV)
HOMOd (eV)
Egap/konset [(eV)/nm]
LUMOf (eV)
HOMOf (eV)
Egap (eV)
onset
1
2
3
À1.76
À1.37
À1.11
1.66
1.40
1.23
3.42
2.77
2.34
À2.64
À3.03
À3.29
À6.06
À5.80
À5.63
3.71/334
3.05/406
2.33/533
À1.78
À2.23
À2.47
À6.07
À5.75
À5.19
4.29
3.52
2.72
a
b
c
d
e
f
Obtained from cyclic voltammograms in CH2Cl2. Reference electrode: Ag/AgCl.
ox
red
Egap = E
À E
.
onset
onset
Calculated from cyclic voltammograms.
Calculated according to the formula EHOMO = ELUMO À Egap
.
Optical band gap, Egap = 1240/konset
.
Obtained from theoretical calculations.
c = 23.7718(8) Å,
a
= 100.86(0)°, b = 99.16(0)°,
c
= 106.94(0)°. There
that inserting N atoms at positions 2 and 3 can strongly quench
the fluorescence, which might be attributed to the intersystem
crossing effect.14
are two different stacking columns in the crystal of compound 3
and both columns show head-to-tail packing. However, as shown
in Figure 1c, the left column shows face-to-face packing with a stack-
The electrochemical properties of compounds 1–3 were investi-
gated by CV in anhydrous CH2Cl2 (Fig. 4 and Table 1). Compound 1
shows one irreversible oxidation peak and one irreversible
reduction peak. The onset oxidative and onset reductive potentials
are at 1.66 V and À1.76 V, respectively. With increasing length of
the azaacene, the onset oxidation potentials were reduced from
1.66 V (for 1) to 1.40 V (for 2) and 1.23 V (for 3), respectively.
Meanwhile, the onset reductive potentials were increased from
À1.76 V (for 1) to À1.37 V (for 2) and À1.11 V (for 3), respectively.
Results show that with increasing length, the prepared compounds
become much easier to oxidize and more difficult to reduce.
The molecular geometries of compounds 1–3 were optimized
using density functional theory (DFT) at the B3LYP/6-31G⁄ level.15
The ground state frontier molecular orbitals of the optimized
molecules were also calculated at the same level. As shown in
Figure 5, for compound 1, the highest occupied molecular orbitals
(HOMO) were mainly localized on the pyridazine ring but the
lowest unoccupied molecular orbitals (LUMO) were localized on
the whole molecule including the phenyl groups. For compounds
2 and 3, the HOMO and LUMO orbitals are mainly localized on
the backbones of the molecules. The calculated HOMO, LUMO,
and band gap values of compounds 1–3 are slightly different to
those obtained by cyclic voltammetry, which maybe because the
simulation was performed in the gas phase (Table 1). However,
the variation tendencies of the calculated results are consistent
with experimental data.
ing distance of 3.92 Å (very weak
column, molecules have a large offset stacking, where the main force
for this type of packing might be induced by the CH- stacking
effect between the phenyl groups and backbone of the tetracenes.
Moreover, all the molecules in the two columns are arranged in a
herringbone motif.
p–p interactions), while in the right
p
Figure 2 shows the UV–vis spectra of 1,4-diphenyl-2,3-diaz-
anaphthalene (1), 1,4-diphenyl-2,3-diazaanthracene (2), and 1,
4-diphenyl-2,3-diazatetracene (3) in CH2Cl2. As the length of the
acene increases, the maximum absorption peak is red-shifted from
293 nm to 362 nm to 506 nm. Moreover, compounds 1–3 display
no (for compound 1) or very weak fluorescence (for compounds
2 and 3) (Fig. 3). The fluorescence quantum yields (Uf) of com-
pounds 2 and 3 were calculated as 0.0075 and 0.0071, respectively,
with 9,10-diphenylanthracene (Uf = 0.95 in ethanol)12 and rubrene
(
Uf = 0.96 in CH2Cl2)13 as the reference standards, which indicates
In summary, using the classical [4+2] cycloaddition reaction
between 3,6-diphenyl-1,2,4,5-tetrazine as the diene and in situ
generated arynes as dienophiles, three oligoazaacenes have been
successfully synthesized. The physical properties and crystal
packing of compounds 1–3 have been studied and compared.
Meanwhile, the data from DFT calculations were in accordance
with experimental results. Our method should offer a useful
strategy to prepare challenging larger oligoazaacenes.
Acknowledgments
Q.Z. acknowledges financial support from AcRF Tier 1 (RG 16/
12) and Tier 2 (ARC 20/12 and ARC 2/13) from MOE, and the CRE-
ATE program (Nanomaterials for Energy and Water Management)
from NRF, Singapore.
Supplementary data
Supplementary data (experimental details, the cif files, NMR,
MALDI-TOF, FTIR, and TGA of compounds 1–3) associated with this
article can be found, in the online version, at http://dx.doi.org/
10.1016/j.tetlet.2014.06.033.
Figure 5. HOMO and LUMO wave functions of compounds 1–3.

J. Li et al. / Tetrahedron Letters 55 (2014) 4346–4349
4349
Qian, X. H.; Bunz, U. H. F. J. Org. Chem. 2012, 77, 7479–7486; (c) Li, J.; Gao, J.;
Xiong, W.; Li, P.; Zhang, H.; Zhao, Y.; Zhang, Q. Chem. Asian J. 2014, 9, 121–125;
(d) Li, G.; Wu, Y.; Gao, J.; Li, J.; Zhao, Y.; Zhang, Q. Chem. Asian. J. 2013, 8, 1574–
1578; (e) Li, G.; Duong, H. M.; Zhang, Z.; Xiao, J.; Liu, L.; Zhao, Y.; Zhang, H.;
Huo, F.; Li, S.; Ma, J.; Wudl, F.; Zhang, Q. Chem. Commun. 2012, 5974–5976.
8. (a) Engelhart, J. U.; Lindner, B. D.; Tverskoy, O.; Schaffroth, M.; Rominger, F.;
Bunz, U. H. F. J. Org. Chem. 2013, 78, 1249–1253; (b) Li, J.; Li, P.; Wu, J.; Gao, J.;
Xiong, W.; Zhang, G.; Zhao, Y. L.; Zhang, Q. J. Org. Chem. 2014, 79, 4438–4442.
9. (a) Xiao, J.; Malliakas, C.-D.; Liu, Y.; Zhou, F.; Li, G.; Su, H.-B.; Kanstzidis, M.-G.;
Wudl, F.; Zhang, Q. Chem. Asian J. 2012, 7, 672–675; (b) Xiao, J.; Duong, H.-M.;
Liu, Y.; Shi, W.; Ji, L.; Li, G.; Li, S.-Z.; Liu, X.; Ma, J.; Wudl, F.; Zhang, Q. Angew.
Chem., Int. Ed. 2012, 51, 6094–6098.
References and notes
1. (a) Anthony, J. E. Angew. Chem., Int. Ed. 2008, 47, 452–483; (b) Qu, H. M.; Chi, C.
Y. Curr. Org. Chem. 2010, 14, 2070–2108.
2. (a) Richards, G. J.; Hill, J. P.; Mori, T.; Ariga, K. Org. Biomol. Chem. 2011, 9, 5005–
5017; (b) Bunz, U. H. F.; Engelhart, J. U.; Lindner, B. D.; Schaffroth, M. Angew.
Chem., Int. Ed. 2013, 52, 3810–3821; (c) Maio, Q. Synlett 2012, 326–336; (d) Li,
G.; Wu, Y. C.; Gao, J.; Wang, C. Y.; Li, J.; Zhang, H.; Zhao, Y.; Zhao, Y. L.; Zhang, Q.
J. Am. Chem. Soc. 2012, 134, 20298–20301.
3. (a) Liu, D. Q.; Xu, X. M.; Su, Y. R.; He, Z. K.; Xu, J. B.; Miao, Q. Angew. Chem., Int.
Ed. 2013, 52, 6222–6227; (b) Miao, Q.; Nguyen, T. Q.; Someya, T.; Blanchet, G.
B.; Nuckolls, C. J. Am. Chem. Soc. 2003, 125, 10284–10287; (c) Liu, Y. Y.; Song, C.
L.; Zeng, W. J.; Zhou, K. G.; Shi, Z. F.; Ma, C. B.; Yang, F.; Zhang, H. L.; Gong, X. J.
Am. Chem. Soc. 2010, 132, 16349–16351.
4. Wu, Y. C.; Yin, Z. Y.; Xiao, J. C.; Liu, Y.; Wei, F. X.; Tan, K. J.; Kloc, C.; Huang, L.;
Yan, Q. Y.; Hu, F. Z.; Zhang, H.; Zhang, Q. ACS Appl. Mater. Interfaces 2012, 4,
1883–1886.
5. Zhang, Q.; Xiao, J.; Yin, Z. Y.; Duong, H.-M.; Qiao, F.; Boey, F.; Hu, X.; Zhang, H.;
Wudl, F. Chem. Asian J. 2011, 6, 856–862.
10. (a) Kaban, S. J. Heterocycl. Chem. 1986, 23, 13–16; (b) Robev, S. K. Tetrahedron
Lett. 1981, 22, 345–348; (c) Regen, T. H.; Miller, J. B. J. Org. Chem. 1966, 31,
3053–3055; (d) Haddadin, M. J.; Agha, B. J.; Tabri, R. F. J. Org. Chem. 1979, 44,
494–497.
11. Li, J. B.; Zhang, Q. C. Synlett 2013, 24, 686–696.
12. Morris, J. V.; Mahaney, M. A.; Huber, J. R. J. Phys. Chem. 1976, 80, 969–974.
13. Paraskar, A. S.; Reddy, A. R.; Patra, A.; Wijsboom, Y. H.; Gidron, O.; Shimon, L. J.
W.; Leitus, G.; Bendikov, M. Chem. Eur. J. 2008, 14, 10639–10647.
14. (a) Liu, Y. Q.; Zhang, F.; He, C. Y.; Wu, D. Q.; Zhuang, X. D.; Xue, M. Z.; Liu, Y. G.;
Feng, X. L. Chem. Commun. 2012, 4166–4168; (b) Schmidt, K.; Brovelli, S.;
Coropceanu, V.; Beljonne, D.; Cornil, J.; Bazzinim, C.; Caronna, T.; Tubino, R.;
Meinardi, F.; Shuai, Z. G.; Brénardi, F. J. Phys. Chem. A. 2007, 111, 10490–10499.
15. (a) Hehre, W. J.; Ditchfie, R.; Pople, J. A. J. Chem. Phys. 1972, 56, 2257–2261; (b)
Becke, A. D. J. Chem. Phys. 1993, 98, 5648–5652.
6. (a) Gu, P. Y.; Zhou, F.; Gao, J.; Li, G.; Wang, C.; Xu, Q. F.; Zhang, Q.; Lu, J.-M. J. Am.
Chem. Soc. 2013, 135, 14086–14089; (b) Li, G.; Zheng, K.; Wang, C.; Leck, K. S.;
Hu, F.; Sun, X. W.; Zhang, Q. ACS Appl. Mater. Interfaces 2013, 5, 6458–6462; (c)
Wang, C.; Wang, J.; Li, P.; Gao, J.; Tan, S. Y.; Xiong, W.; Hu, B.; Lee, P. S.; Zhao, Y.;
Zhang, Q. Chem. Asian. J. 2014, 9, 779–783.
7. (a) Li, J.; Gao, J.; Li, G.; Xiong, W.; Zhang, Q. J. Org. Chem. 2013, 78, 12760–
12768; (b) Bryant, J. J.; Zhang, Y. X.; Lindner, B. D.; Davey, E. A.; Appleton, A. L.;