Synthesis and characterization of tetraanthroporphyrins

Article abstract of DOI:10.1021/ol8008842

(Chemical Equation Presented) Linearly π-expanded novel tetraanthroporphyrins with and without aromatic rings at the meso-positions were prepared quantitatively for the first time from the corresponding precursors by a retro-Diels-Alder reaction.

Full text of DOI:10.1021/ol8008842

ORGANIC
LETTERS
2008
Vol. 10, No. 14
2947-2950
Synthesis and Characterization of
Tetraanthroporphyrins
Hiroko Yamada,*,†,‡ Daiki Kuzuhara,† Tetsuro Takahashi,† Yusuke Shimizu,†
Keisuke Uota,† Tetsuo Okujima,† Hidemitsu Uno,§ and Noboru Ono†
Department of Chemistry, Faculty of Science, Ehime UniVersity, Matsuyama 790-8577,
Japan, PRESTO, JST, Kawaguchi 332-0012, Japan, and INCS, Ehime UniVersity,
Matsuyama 790-8577, Japan
yamada@chem.sci.ehime-u.ac.jp
Received April 17, 2008
ABSTRACT
Linearly π-expanded novel tetraanthroporphyrins with and without aromatic rings at the meso-positions were prepared quantitatively for the
first time from the corresponding precursors by a retro-Diels-Alder reaction.
Tetrabenzoporphyrins (TBPs) and linearly π-expanded de-
rivatives, tetranaphthoporphyrins (TNPs) and tetraanthro-
porphyrins (TAnPs), have attracted great attention for
applications such as dye stuffs, optical materials, nonlinear
optics, conducting materials, photosensitizers for photody-
namic therapy (PDT), and solar systems.1 Although TBPs,
TNPs, and nonlinearly expanded TAnP analogues have been
reported to date, linearly expanded TAnPs have been rarely
reported to our knowledge.2 As Kobayashi et al. have
theoretically predicted, π-ring expansion results in the
destabilization of the third LUMOs and the first HOMOs of
the porphyrins, and therefore, they become unstable against
oxidation and reduction.3 The π-expansion also induces
strong π-π stacking between molecules, which results in
low solubility of the porphyrins and difficulties in purification
and derivatization. To overcome these obstacles, a few
methods have been reported in the synthesis of TBPs and
TNPs,1,2,4,5 e.g., an introduction of bulky substituents at the
meso positions or peripheral aromatic rings, and an annealing
of peripheral cyclohexyl structures to the aromatic rings in
the presence of oxidants such as DDQ.6 However, these
(4) Kopranenkov, V. N.; Vorotnikov, A. M.; Dashkevich, S. N.;
Luk’yanets, E. A. Zh. Obsch. Khim. (Russ.) 1985, 900
.
† Department of Chemistry, Ehime University.
‡ PRESTO.
(5) Rein, M.; Hanack, M. Chem. Ber. 1988, 121, 1601
.
(6) (a) Finikova, O. S.; Cheprakov, A. V.; Carroll, P. J.; Vinogradov,
S. A. J. Org. Chem. 2003, 68, 7517. (b) Rozhkov, V. V.; Khajehpour, M.;
Vinogradov, S. A. Inorg. Chem. 2003, 42, 4253. (c) Finikova, O. S.;
Cheprakov, A. V.; Beletskaya, I. P.; Carroll, P. J.; Vinogradov, S. A. J.
Org. Chem. 2004, 69, 522. (d) Finikova, O. S.; Aleshchenkov, S. E.; Brinˇas,
R. P.; Cheprakov, A. V.; Carroll, P. J.; Vinogradov, S. A. J. Org. Chem.
2005, 70, 4617–4628. (e) Finikova, O. S.; Cheprakov, A. V.; Vinogradov,
§ INCS, Ehime University.
(1) Lash, T. D. The Porphyrin Handbook; Academic Press: New York,
2000; Vol. 2.
(2) Lash, T. D. J. Porphyrins Phthalocyanines 2001, 5, 267.
(3) (a) Kobayashi, N.; Konami, H. J. Porphyrins Phthalocyanines 2001,
5, 233. (b) Mack, J.; Asano, Y.; Kobayashi, N.; Stillman, M. J. J. Am.
Chem. Soc. 2005, 127, 17697.
S. A. J. Org. Chem. 2005, 70, 9562–9572
.
10.1021/ol8008842 CCC: $40.75
Published on Web 06/17/2008
2008 American Chemical Society

methodologies are not suitable for preparing TAnPs because
TAnPs are less stable against oxidants compared to TNPs
and TBPs, and only 5,10,15-tribiphenyl-ZnTAnP has been
reported so far.7,8
Scheme 1. Preparation of TAnPs 2
Recently, we have developed an efficient synthetic method
for various benzoporphyrin-type compounds including TBPs
and TNPs using a retro-Diels-Alder reaction.9,10 With this
method, soluble porphyrins fused with bicyclo[2.2.2]octadiene
were converted quantitatively into insoluble benzoporphyrins
by simply heating at around 200-290 °C; which temperature
to use was decided by thermogravimetric analysis (Tg) and
differential thermal analysis (DTA) measurements. As the
thermal process does not require any reagents, solvents, or
purification steps, it is the ideal method for the preparation
of low-soluble and highly planar π-conjugated porphyrins.
Aramaki et al. and Kanicki et al. have observed comparable
performance with pentacene in carrier mobility using TBP
films prepared by spin coating of bicyclo[2.2.2]octadiene-
fused porphyrins on a silicon substrate followed by heat-
ing.11,12 Yamada et al. have reported the photoenergy
conversion system of BPs and PCBM prepared by spin-
coating.13 Using this procedure, we have succeeded in
preparing meso-free and meso-substituted TAnPs 2a-c from
the corresponding bicyclo[2.2.2]octadiene-fused precursors
(1a-c), as shown in Scheme 1.
The preparation of the TAnPs is shown in Scheme 1. The
addition of phenylsulfenyl chloride to 1,4-dihydro-1,4-
ethanonanthracene 314 at -78 °C gave compound 4 in 86%
yield, and the oxidation of 4 with m-CPBA gave 5 in 89%
yield. When a dry THF solution of 5 was treated with
isocyanoacetate ethyl ester in the presence of 2.7 equiv of
t-BuOK at -20 °C, followed by stirring at room temperature
for 18 h, pyrrole 6 was obtained in 89% yield. Treatment of
pyrrole 6 with potassium hydroxide gave pyrrole 7.
(7) (a) Sapunov, V. V.; Solov’ev, K. N.; Kopranekov, V. N.; Vorotnikov,
A. M. Opt. Spectrosc. (USSR) 1988, 64, 464. (b) Vorotnikov, A. M.;
Kopranekov, V. N.; Luk’yanets, E. A. Zh. Obsch. Khim. (Russ.) 1991, 61,
1241
(8) Kobayashi, N.; Nevin, W. A.; Mizunuma, S.; Awaji, H.; Yamaguchi,
M. Chem. Phys. Lett. 1993, 205, 51
.
.
(9) (a) Ito, S.; Murashima, T.; Ono, N.; Uno, H. Chem. Commun. 1998,
1661. (b) Ito, S.; Murashima, T.; Ono, N.; Uno, H. Chem. Commun. 1999,
2275. (c) Ito, S.; Ochi, N.; Murashima, T.; Ono, N.; Uno, H. Chem.
Commun. 2000, 893. (d) Ito, S.; Uno, H.; Murashima, T.; Ono, N.
Tetrahedron Lett. 2001, 42, 45. (e) Okujima, T.; Komobuchi, N.; Shimizu,
Y.; Uno, H.; Ono, N. Tetrahedron Lett. 2004, 45, 5461. (f) Okujima, T.;
Jin, G.; Hashimoto, Y.; Yamada, H.; Uno, H.; Ono, N. Heterocycles 2006,
70, 619. (g) Okujima, T.; Komobuchi, N.; Uno, H.; Ono, N. Heterocycles
2006, 67, 255. (h) Yamada, H.; Kushibe, K.; Okujima, T.; Uno, H.; Ono,
N. Chem. Commun. 2006, 383. (i) Uno, H.; Nakamoto, K.-I.; Kuroki, K.;
Porphyrin 1a-2H was prepared from pyrrole 6 in two steps:
(1) reduction of pyrrole 6 by LAH and (2) acid-catalyzed
condensation in CHCl3 in the presence of p-toluenesulfonic
acid, followed by oxidation with DDQ. Metalation of
porphyrin 1a-2H with Zn(OAc)2 gave porphyrin zinc com-
plex 1a. Porphyrin 1a was converted into pure TAnP 2a
quantitatively by heating at around 300 °C under vacuum
for 2 h. The temperature of the retro-Diels-Alder reaction
was determined by thermogravimetric analyses of porphyrin
1a as shown in Figure 1. The weight loss seen in the retro-
Diels-Alder reaction was 11.1%, which is similar to the
calculated value of 10.3%. Porphyrin 1a was characterized
Fujimoto, A.; Ono, N. Chem. Eur. J. 2007, 13, 5773
.
(10) (a) Giraud-Roux, M.; Proni, G.; Nakanishi, K.; Berova, N.
Heterocycles 2003, 61, 417. (b) Senge, M. O.; Bischoff, I. Tetrahedron
Lett. 2004, 45, 1647
.
(11) Aramaki, S.; Sakai, Y.; Ono, N. Appl. Phys. Lett. 2004, 84, 2085
.
(12) (a) Shea, P. B.; Kanicki, J.; Cao, Y.; Ono, N. Appl. Phys. Lett.
2005, 87, 173506. (b) Shea, P. B.; Johnson, A. R.; Ono, N.; Kanicki, J.
IEEE 2005, 52, 1497. (c) Shea, P. B.; Kanicki, J.; Ono, N. J. Appl. Phys.
2005, 98, 014503. (d) Shea, P. B.; Kanicki, J.; Pattison, L. R.; Petroff, P.;
Kawano, M.; Yamada, H.; Ono, N. J. Appl. Phys. 2006, 100, 034502. (e)
Shea, P. B.; Pattison, L. R.; Kawano, M.; Chen, C.; Chen, J.; Petroff, P.;
Martin, D. C.; Yamada, H.; Ono, N.; Kanicki, J. Synth. Met. 2007, 157,
190. (f) Shea, P. B.; Chen, C.; Kanicki, J.; Pattison, L. R.; Petroff, P.;
1
by FAB and MALDI-TOF mass spectrometry, H NMR
spectroscopy, and elemental analysis. Although it is a mixture
of isomers, the NMR spectrum of 1a was relatively simple
as shown in Figure S7 (Supporting Information). Because
of its planarity, the solubility of tetraanthroporphyrin 2a was
Yamada, H.; Ono, N. Appl. Phys. Lett. 2007, 90, 233107
.
(13) Yamada, H.; Kamio, N.; Ohishi, A.; Mawano, M.; Okujima, T.;
Ono, N. J. Porphyrins Phthalocyanines 2007, 11, 383.
(14) Amrein, W.; Schaffner, K. HelV. Chim. Acta 1975, 58, 380.
2948
Org. Lett., Vol. 10, No. 14, 2008

Figure 3.
1H NMR spectra of porphyrins (a) 1c and (b) 2c in
CD2Cl2.
Figure 1. Thermogravimetric analysis of porphyrin 1a, heating at
10 °C/min.
11.0 and 5.8%, respectively, which showed good accordance
with the calculated values of 8.1 and 6.1%, respectively. The
solubility of the TAnPs was improved, and the measurement
of 1H NMR spectra of porphyrins 2b and 2c was possible in
THF-d8 and CD2Cl2, respectively. Porphyrins 2b and 2c were
not stable in the solution in the light; NMR spectra as well
as absorption and emission spectra were measured in the
dark. Portions of the NMR spectra of porphyrins 1c and 2c
are shown in Figure 3 (see also Figures S9 and S12 in the
Supporting Information). The aromatic region of 1c is very
complicated because of the existence of isomers of the
bicyclo[2.2.2]octadiene moieties. After the retro-Diels-Alder
reaction, the NMR spectrum became simple and proton peaks
at the bridgehead (3.8-4.0 ppm) disappeared.
The absorption spectra of TAnPs 2b and 2c and their
precursor porphyrins 1b and 1c in CHCl3 are shown in Figure
4, and the data are summarized in Table 1. The Soret peaks
of 1b and 1c are shown at 430 and 426 nm, respectively,
and their Q bands are at 553 and 547 nm, respectively. Soret
peaks of 1b and 1c are 24 and 20 nm red-shifted, respec-
tively, compared to meso-free porphyrin 1a, probably
because of the distortion from planarity. The Soret band of
1b with a meso-phenyl group is broadened and 4 nm red-
shifted compared to 1c with its bulky 3,5-di(tert-butyl)phenyl
substituents at the meso position. The absorption spectra of
TAnPs 2b and 2c show Soret bands at 498 and 493 nm,
respectively, with strong Q bands at 802 and 799 nm,
respectively. Because of their low solubility, absorption
coefficients could not be determined for 2b and 2c. Since
π-conjugation was linearly enlarged, broadening and 60 nm
red shifts of the Soret and Q bands were observed for 2b
and 2c compared to precursors 1b and 1c. The relative
intensities of Q bands to Soret bands of 2b and 2c are quite
large: 0.98 and 0.94, respectively. The trend of the change
and the shift of the absorption spectra are consistent with
the results of MO calculations.3 When the TAnPs were stored
in pyridine (2a) or CHCl3 (2b and 2c) in UV cells under air
under room light, the shape of the absorption spectra changed
over several hours. Mass spectroscopy of TAnPs showed an
M+ + 32 peak, indicating that a reaction with oxygen had
occurred (Figures S11-S13 in the Supporting Information).
The fluorescence spectra of 1b and 1c are shown in Figure
4a, and the data are summarized in Table 1 with absolute
quite poor. Therefore, the characterization of porphyrin 2a
was confirmed only by mass spectroscopy and UV-vis
absorption spectroscopy. The absorption and emission spectra
of 2a were measured in the dark because it was unstable in
solution under air in the light. The normalized UV-vis and
fluorescence spectra of 1a in CHCl3 and 2a in pyridine are
shown in Figure 2. Compared to the absorption spectrum of
1a, that of anthroporphyrin 2a is broad and the Q-band of
2a was shifted to 800 nm. The relative intensity of the
Q-band to the Soret band is high. These changes are due to
the effect of the linear expansion of π-conjugation as
theoretically predicted.3 The luminescence of 2a was shown
to occur at around 900 nm, which is in the near-IR region.
In order to improve the solubility, the meso-positions of
1a were substituted with aromatic rings, such as phenyl and
3,5-di(tert-butyl)phenyl groups. Porphyrins 1b and 1c were
prepared by the acid condensation of pyrrole 7 with the
corresponding aldehydes in the presence of BF3·Et2O fol-
lowed by oxidation with DDQ and metalation. The porphy-
rins 1b and 1c were converted to TAnPs 2b and 2c
quantitatively by heating at around 300 °C under vacuum
for 2 h. TG analyses of porphyrins 1b and 1c are shown in
Figure S1 (Supporting Information). The retro-Diels-Alder
reaction was performed at 300 °C, and the weight losses were
Figure 2. Normalized UV-vis spectra (black lines) and fluores-
cence spectra (red lines) of porphyrin 1a in CHCl3 (solid line) and
2a in pyridine (dotted line). Absorbance and fluorescence are
normalized to 1.
Org. Lett., Vol. 10, No. 14, 2008
2949

Table 1. Absorbance, Fluorescence, and Absolute Fluorescence Quantum Yields (Φ) of Porphyrins 1a-2H, 1a, 1b, 1c, 2b, and 2c in
CHCl3
porphyrins
λmax/nm (log ꢀ)
fluorescence/nm
Φ/% (λEX/nm)
1a-2H
1a
1b
1c
2b
396 (5.22), 496 (4.28), 529 (3.90),564 (3.90), 615 (3.41)
406 (5.42), 530 (4.20), 563 (4.08)
430 (5.56), 553 (4.34)
426 (5.75), 509 (4.05) 547 (4.46)
327, 365, 498, 728, 756, 802
620,685
570,623
652
645
819
4.5 (396)
3.7 (406)
0.7 (430)
1.7 (426)
3.7 (498)
4.3 (493)
2c
364, 403, 493, 726, 747, 799
811
but it might be because the porphyrin rings are distorted into
a saddle shape by the aromatic rings at the meso-position.
Fluorescence spectra of 2b and 2c are shown in Figure 4b.
The emission peaks are at 819 and 811 nm, respectively,
and are about 160 nm red-shifted compared to the precursors
(1b and 1c). Stokes shifts of 2b and 2c are only 17 and 12
nm, respectively. Vinogradov has reported that meso-
arylnaphthoporphyrins show larger Stokes shifts than meso-
free tetranaphthoporphyrins.6e In that study, the naphtho-
porphyrins had periphederal 1,4-substituents and might have
shown large distortions due to steric hindrance between the
meso-aryl rings and the substituents on the naphthalene rings.
In our case, the anthracene moiety does not have substituents,
so the distortion might be smaller. For the precursors 1b and
1c, steric hindrance is larger because of the bridgehead
protons, and therefore, the Stokes shift might be larger.
We have succeeded in preparing tetraanthroporphyrins for
the first time via the retro-Diels-Alder reaction of bicyclo-
[2.2.2]octadiene-fused precursors. The compounds have
strong absorption in the near-IR region and may have
interesting conducting properties.
Figure 4
.
UV-vis absorption and fluorescence spectra of (a)
Acknowledgment. We thank Venture Business Labora-
tory, Ehime University, for its help in using TOF-MS
spectroscopy. We are also grateful for a Grant-in-Aid for
Scientific Research from the Ministry of Education, Culture,
Sports, Science and Technology, Japan (H.Y. and N.O.) and
the Nissan Science Foundation for partial financial support
(H.Y.).
precursors 1b and 1c and (b) TAnPs 2b and 2c in CHCl3. Solid
lines: 1b and 2b; broken lines: 1c and 2c; black lines: absorption
spectra; red lines: fluorescence spectra. (a) Fluorescence spectra
were measured at 2.8 × 10-7 M. (b) Absorption spectra were
normalized at Soret peaks for TAnPs 2b and 2c.
fluorescence quantum yields (Φ). Interestingly, the Stokes
shifts for 1b and 1c (around 100 nm) are larger than that of
1a (7 nm). The fluorescence intensity of 1b is smaller than
that of 1c. These results are consistent with their absolute
fluorescence quantum yields (1b: 0.7%, 1c: 1.7%). The
reason for the difference in fluorescence intensity is not clear,
Supporting Information Available: Experimental details
and thermogravimetric analysis of 1b and 1c. This material
is available free of charge via the Internet at http://pubs.acs.org.
OL8008842
2950
Org. Lett., Vol. 10, No. 14, 2008