Luminescent properties of phenylenediamine derivatives depending on the redox states

Article abstract of DOI:10.1016/j.tetlet.2010.04.028

Phenylenediamines bearing the ethoxycarbonyl groups were synthesized to modulate luminescent properties. Switching of the luminescent properties was achieved by redox change between the phenylenediamine and quinonediimine derivatives.

Full text of DOI:10.1016/j.tetlet.2010.04.028

Tetrahedron Letters 51 (2010) 3190–3192
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Luminescent properties of phenylenediamine derivatives depending
on the redox states
*
*
Satoshi D. Ohmura, Toshiyuki Moriuchi , Toshikazu Hirao
Department of Applied Chemistry, Graduate School of Engineering, Osaka University, Yamada-oka, Suita, Osaka 565-0871, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Phenylenediamines bearing the ethoxycarbonyl groups were synthesized to modulate luminescent prop-
erties. Switching of the luminescent properties was achieved by redox change between the phenylenedi-
amine and quinonediimine derivatives.
Received 15 March 2010
Revised 5 April 2010
Accepted 9 April 2010
Available online 18 April 2010
Ó 2010 Elsevier Ltd. All rights reserved.
Since the last decade,
p
-conjugated compounds with lumines-
cated to participate in intramolecular hydrogen bonding in solu-
tion. The intramolecular hydrogen bonding was also observed in
the case of 1m-red and 1p-red. Furthermore, the OH of 2o-red
was found to participate in intramolecular hydrogen bonding with
the CO moiety as shown in Figure 1.
cent properties have paid much attention because of the applica-
tions to electronic materials such as light-emitting diodes
(LEDs).1 Solution processing is possible with organic materials, per-
mitting the easy and low-cost fabrication of optoelectronic devices.
The emission colors of
to their -conjugated electronic states.
Phenylenediamines are molecular units of polyanilines as
p
-conjugated molecules are closely related
The phenylenediamine 1-red was oxidized into the quinonedii-
mine 1-ox by treatment with lead(IV) acetate as an oxidant.6 The
oxidized form 1-ox could be again reduced to 1-red with hydrazine
monohydrate (Fig. 2).
p
p
-
conjugated polymers. The redox-active phenylenediamine exists
in three redox forms: the reduced phenylenediamine, the partially
oxidized phenylenediamine radical cation, and the oxidized qui-
nonediimine. In previous papers, we have already demonstrated
the redox switching of the emission properties of Ru(II) dipyridyl
complexes bearing the phenylenediamine moieties by changing
the redox states of the phenylenediamine moieties.2 On the other
hand, 2,5-bis(arylamino)terephthalate derivatives have been re-
ported to show luminescent properties.3 The luminescent proper-
ties of the phenylenediamine derivatives are expected to be
regulated by changing their redox states. Herein, we report lumi-
nescent phenylenediamines for redox switching (Fig. 1).
The phenylenediamine derivatives 1-red were synthesized by
the reaction of diethyl 2,5-dioxocyclohexane-1,4-dicarboxylate
with the corresponding anilines.4,5 Phenylaminophenol 2o-red
was also obtained as a byproduct from the synthesis of 1o-red.
The thus-obtained phenylenediamines and phenylaminophenol
are stable under air and light, and were fully characterized by spec-
tral data and elemental analyses.
The crystal structure of diethyl N,N0-diphenyl 2,5-diamino-
terephthalate was reported to show the formation of the intra-
molecular hydrogen bonds between NH and CO at the central
benzene ring.7 The single-crystal X-ray structure determination8
of 1o-red also confirmed the formation of the intramolecular
hydrogen bonds between the NH and CO at the central benzene
ring (Table 1). The anti-conformation of the
p-conjugated moiety
(Fig. 3a) is formed, and another hydrogen bonds were observed be-
tween NH and CO at the terminal benzene rings. The terminal and
central benzene rings are oriented with a dihedral angle of
43.82(8)°. This is probably due to the steric repulsion between
the ortho-hydrogen atoms despite the formation of the intramolec-
ular hydrogen bonds, which might induce a coplanar structure of
the
p-conjugated moiety. The crystal structure of 1o-ox revealed
the anti-conformation with a dihedral angle of 99.22(5)° between
O
OEt
O
OEt
In the 1H NMR spectrum of 1o-red in CD2Cl2 (1.0 ꢀ 10ꢁ2 M), the
NHs of the phenylenediamine moiety were hardly perturbed by the
addition of aliquot DMSO-d6 to CD2Cl2 (CD2Cl2: 10.56 ppm, CD2Cl2-
DMSO-d6 (9:1): 10.51 ppm). The FT-IR spectrum of 1o-red in
CH2Cl2 (1.0 ꢀ 10ꢁ2 M) showed a hydrogen-bonded NH stretching
at 3316 cmꢁ1. From these observations, the NH moieties are indi-
H
N
H
O
EtOOC
N
N
COOEt
H
H
EtO
O
O
OEt
EtO
O
2o-red
1o-red: ortho
1m-red: meta
1p-red: para
* Corresponding authors. Tel.: +81 6 6879 7413; fax: +81 6 6879 7415.
E-mail addresses: moriuchi@chem.eng.osaka-u.ac.jp (T. Moriuchi), hirao@
chem.eng.osaka-u.ac.jp (T. Hirao).
Figure 1. Phenylenediamine and phenylaminophenol derivatives.
0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.04.028

S. D. Ohmura et al. / Tetrahedron Letters 51 (2010) 3190–3192
OEt
3191
O
O
OEt
H
N
EtOOC
EtOOC
N
Pb(OAc)4
NH2NH2 • H2O
N
N
COOEt
COOEt
H
EtO
O
EtO
O
1o-ox:
1m-ox:
1p-ox:
ortho
meta
para
1o-red:
1m-red:
1p-red:
ortho
meta
para
Figure 2. Redox interconversion between the phenylenediamines and quinonediimines.
Table 1
The reduced form 1o-red exhibited strong luminescence at
536 nm (Fig. 4a). On the contrary, weak luminescence was ob-
served with 1o-ox. These findings indicate that redox switching
of the luminescent properties is achieved by changing the redox
Intramolecular hydrogen bonds for 1o-red and 2o-red
Crystal
Donor
Acceptor
D. . .A (Å)
D-H. . .A (°)
1o-reda
N(1)
N(1)
N(1*)
N(1*)
N(1)
N(1)
O(5)
O(1*)
O(3)
O(1)
O(3*)
O(1*)
O(3)
O(1)
2.700(1)
2.713(2)
2.700(1)
2.713(2)
2.760(2)
2.686(2)
2.611(2)
123(2)
129(1)
123(2)
129(1)
120(1)
127(1)
136(2)
states of the
observed between 1m-red and 1m-ox or 1p-red and 1p-ox (Sup-
plementary data Fig. S1). In the present -conjugated systems,
p-conjugated moiety. The redox switching was also
p
2o-red
emission wavelength is largely dependent on the substituent posi-
tion of the ethoxycarbonyl group on the terminal benzene rings.
Phenylenediamine 1p-red showed a red-shift of the maximum
emission wavelength as compared with 1o-red (Table 2 and
Fig. 4b). Further red-shift of the maximum emission wavelength
was observed in the case of 1m-red. This result might be contrib-
a
The molecule sits on an inversion center.
the terminal and central benzene rings as shown in Figure 3b. This
structure is considered to be caused by the steric repulsion be-
tween the ortho-hydrogen atoms at each benzene ring due to the
short imine bond length. Phenylaminophenol 2o-red was found
to form intramolecular hydrogen bonds between not only OH
and CO but also NH and CO in a crystal structure (Fig. 3c).
uted to the difference of the
p-conjugated electronic states. Phe-
nylaminophenol 2o-red showed the maximum wavelength at
511 nm, wherein the luminescent intensity was lower as compared
with that of 1o-red (Table 2).
The phenylenediamine 1o-red exhibits an intense yellow emis-
sion at 543 nm even in a solid state (Fig. 4c). The quantum yield of
Figure 3. Crystal structures of (a) 1o-red, (b) 1o-ox, and (c) 2o-red.
Figure 4. (a) Emission spectra of 1o-red (kex = 430 nm) and 1o-ox (kex = 449 nm) and (b) 1o-red (kex = 430 nm), 1m-red (kex = 458 nm), 1p-red (kex = 446 nm), and 2o-red
(kex = 415 nm) in CH2Cl2 (1.0 ꢀ 10ꢁ5 M). (c) Photographs (under 365 nm) of (i) 1o-red, (ii) 1m-red, (iii) 1p-red, and (iv) 2o-red.

3192
S. D. Ohmura et al. / Tetrahedron Letters 51 (2010) 3190–3192
Yersin, H., Ed.; Wiley-VCH: Weinheim, 2008; (c) Grimsdale, A. C.; Chan, K. L.;
Table 2
Martin, R. E.; Jokisz, P. G.; Holms, A. B. Chem. Rev. 2009, 109, 897–1091.
2. (a) Hirao, T.; Iida, K. Chem. Commun. 2001, 5, 431–432; (b) Shen, X.; Moriuchi, T.;
Hirao, T. Tetrahedron Lett. 2003, 44, 7711–7714; (c) Moriuchi, T.; Shiori, J.; Hirao,
T. Tetrahedron Lett. 2007, 48, 5970–5972.
3. Zhang, Y.; Starynowicz, P.; Christoffers, J. Eur. J. Org. Chem. 2008, 20, 3488–3495.
4. Liebermann, H. Justus Liebigs Ann. Chem. 1914, 404, 272–321.
5. 1o-red and 2o-red: Ethyl 2-aminobenzoate (793 mg, 4.8 mmol) was added to a
solution of diethyl 2,5-dioxocyclohexane-1,4-dicarboxylate (505 mg, 2.0 mmol)
in AcOH (10 mL). The mixture was stirred at 100 °C for 25 h and then cooled to
ambient temperature. The orange solution was neutralized with saturated
NaHCO3 aqueous solution (20 mL ꢀ 2) and extracted with CH2Cl2. After
separating and discarding the water phase, the organic phase was dried on
Na2SO4 and filtered. After evaporation of the solvent, a mixture of 1o-red, 2o-
Emission data for 1 and 2o-red
a
CH2Cl2
(nm)
In a solid state
(nm) UF
b
c
kem,
UF
kem,
max
max
1o-red
1m-red
1p-red
2o-red
1o-ox
536
554
543
511
536
552
543
0.58
0.27
0.39
0.20
0.15
0.01
0.01
543
589
604
531
0.47
0.08
0.17
0.26
1m-ox
1p-ox
a
1.0 ꢀ 10ꢁ5 M.
red, and unreacted substrate was obtained as
a yellow–orange solid. The
mixture was purified by silica gel column chromatography (from hexane to 4/1,
hexane/EtOAc) to give 1o-red (289 mg, 0.53 mmol) as a pale-orange solid,
Rf = 0.59 (5/2, hexane/EtOAc) and 2o-red (50.1 mg, 0.12 mmol) as a yellow solid,
Rf = 0.65 (5/2, hexane/EtOAc).
1m-red: A mixture of ethyl 3-aminobenzoate (330 mg, 2.0 mmol) and diethyl
2,5-dioxocyclohexane-1,4-dicarboxylate (252 mg, 1.0 mmol) in AcOH (10 mL)
was stirred at 100 °C for 25 h. After cooling to ambient temperature, the
precipitate was isolated by filtration, washed with EtOH, and dried in vacuo. The
phenylenediamine 1m-red (236 mg, 0.43 mmol) was obtained as an orange-
needle crystal by recrystallization from EtOAc.
b
The relative fluorescence quantum yield was determined with Ru(bpy)3Cl2
(kex = 450 nm).
c
The quantum yield was measured in an integrating sphere for packed powder
samples at ambient temperature (kex = 450 nm).
1o-red at ambient temperature, measured in an integrating sphere
for a packed powder samples, is 0.47 using kex = 450 nm (Table 2).
1p-red: A mixture of ethyl 4-aminobenzoate (330 mg, 2.0 mmol) and diethyl
2,5-dioxocyclohexane-1,4-dicarboxylate (252 mg, 1.0 mmol) in AcOH (10 mL)
was stirred at 100 °C for 25 h. After cooling to ambient temperature, the
precipitate was isolated by filtration, washed with EtOH, and dried in vacuo. The
phenylenediamine 1p-red (249 mg, 0.45 mmol) was obtained as an orange-
needle crystal by recrystallization from EtOAc.
Rigid
have been reported to provide attractive photophysical proper-
ties.9 In the case of 1o-red, a rigid
-conjugated structure is consid-
ered to be induced by the formation of intramolecular hydrogen
bonds between NH and CO at the central and terminal benzene
rings.
In conclusion, a series of luminescent phenylenediamines were
synthesized to control the luminescent properties. The lumines-
cent switching was demonstrated by changing the redox states of
p-conjugated frameworks without conformational disorder
p
6. 1-ox: A mixture of the phenylenediamine 1-red (54.9 mg, 0.10 mmol) and
Pb(IV) acetate (53.2 mg, 0.12 mmol) in dry CH2Cl2 (5.0 mL) was stirred under
argon atmosphere at ambient temperature for 3 h. The resulting mixture was
filtered and the filtrate was evaporated in vacuo. The quinonediimine 1-ox was
isolated quantitatively as a brown solid and by recrystallization from acetone
(1o-ox: 54.5 mg, quant.; 1m-ox: 54.8 mg, quant.; 1p-ox: 54.7 mg, quant.).
7. Mann, B. J.; Paul, I. C.; Curtin, D. Y. J. Chem. Soc., Perkin Trans. 2 1981, 12, 1583–
1590.
the
p-conjugated phenylenediamines. Further investigation
including tuning of the color is now in progress.
8. Crystal data for 1o-red: C30H32N2O8, M = 548.59, triclinic, space group P ꢁ 1 (No.
2), a = 8.1742(5) Å, b = 8.7541(6) Å, c = 10.8412(8) Å,
a = 100.156(2)°, b =
= 97.572(2)° V = 703.06(8) Å3, Z = 1, T = 4.0 °C, Dcalcd
(MoK radiation (k = 0.71075 Å), R1 = 0.079,
) = 0.94 cmꢁ1, MoK
=
Acknowledgment
109.775(2)°,
c
l
1.296 g cmꢁ3
,
a
a
wR2 = 0.240. Crystal data for 1o-ox: C30H30N2O8, M = 546.58, monoclinic, space
group P21/c (No. 14), a = 9.2400(2) Å, b = 15.0566(3) Å, c = 10.4578(2) Å, b =
We thank Dr. N. Tohnai and Prof. M. Miyata at Osaka University
for the measurement of the quantum yield. Thanks are due to the
Analytical Center, Graduate School of Engineering, Osaka Univer-
sity, for the use of the NMR and MS instruments.
102.5477(8)°, V = 1420.17(5) Å3, Z = 2, T = 4.0 °C, Dcalcd = 1.278 g cmꢁ3
,
l
(CuK
Crystal data for 2o-red: C21H23N1O5, M = 369.42, triclinic, space group P ꢁ 1 (No.
2), a = 8.3035(6) Å, b = 10.3553(8) Å, c = 12.899(1) Å, = 73.132(3)° b =
a a radiation (k = 1.54186 Å), R1 = 0.039, wR2 = 0.165.
) = 7.76 cmꢁ1, CuK
a
88.385(3)°,
c
= 75.938(2)°
V = 1028.6(2) Å3,
MoK radiation (k = 0.71075 Å), R1
Z = 2,
T = 4.0 °C,
Dcalcd
=
=
1.193 g cmꢁ3
,
l(MoK
a
) = 0.85 cmꢁ1
,
a
Supplementary data
0.071, wR2 = 0.271. Crystallographic data (excluding structure factors) for the
structures reported in this Letter have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication no. CCDC-755547
for 1o-red, CCDC-755548 for 1o-ox, and CCDC-755549 for 2o-red. Copies of the
data can be obtained free of charge on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK [Fax: (internat.) +44-1223/336-033; E-mail:
deposit@ccdc.cam.ac.uk].
Supplementary data (general information, synthesis, procedure,
and spectral data) associated with this article can be found, in the
online version, at doi:10.1016/j.tetlet.2010.04.028.
9. (a) Bohnen, A.; Koch, K.-H.; Lüttke, W.; Müllen, K. Angew. Chem. 1990, 102, 525–
527; (b) Delnoye, D. A. P.; Sijbesma, R. P.; Vekemans, J. A. J. M.; Meijer, E. W. J.
Am. Chem. Soc. 1996, 118, 8717–8718; (c) Fukazawa, A.; Yamaguchi, S. Chem.
Asian J. 2009, 4, 1386–1400.
References and notes
1. (a)Organic Light-Emitting Devices. Synthesis, Properties and Applications; Müllen,
K., Scherf, U., Eds.; Wiley-VCH: Weinheim, 2006; (b)Highly Efficient OLEDs with