Hexaphyrin fused to two anthracenes

Article abstract of DOI:10.1002/anie.201204446

Gold standard: A bis(Au^III) complex containing the title compound was prepared and characterized (see scheme; DDQ=2,3-dichloro-5,6- dicyano-1,4-benzoquinone, Tf=trifluoromethanesulfonyl). Owing to the effective conjugative network over the flat and elongated rectangular molecular frame, this complex displays a remarkably red-shifted and sharp Q-band-like band at 1467 nm, multiple reversible redox potentials, and a large TPA cross-section value. Copyright

Full text of DOI:10.1002/anie.201204446

Angewandte
Chemie
DOI: 10.1002/anie.201204446
Porphyrinoids
Hexaphyrin Fused to Two Anthracenes**
Koji Naoda, Hirotaka Mori, Naoki Aratani, Byung Sun Lee, Dongho Kim,* and
Atsuhiro Osuka*
One of the current topics in porphyrin chemistry is the
synthesis of highly conjugated porphyrins that exhibit
absorption bands reaching into the near infrared (NIR)
region and a large range of nonlinear optical properties; such
molecules are promising in the fields of organic semiconduc-
tors and photovoltaics, two-photon excited photodynamic
therapy, and all-optical processing.[1–3] Effective synthetic
strategies are to bridge porphyrins with a conjugative link-
er,[2b,4] to directly fuse porphyrins,[5] and to fuse aromatic
segments to the porphyrin periphery.[6–8] Conjugated porphy-
rins prepared by these strategies exhibit strongly perturbed
optical and electronic properties, thus reflecting the flexible
electronic nature of porphyrins. Anderson and co-workers
have demonstrated that the fusion of anthracene is effective
in the expansion of the conjugated network of porphyrins by
exploring porphyrins fused to one, two, and four anthracenes,
all of which display highly red-shifted Q bands (lmax = 855,
973, and 1417 nm, respectively).[7]
In recent years, expanded porphyrins have emerged as
new functional chromophores, which encompass larger con-
jugated networks and are electronically more flexible than
porphyrins.[9] In this sense, these expanded porphyrins may be
Scheme 1. Substrates and hexaphyrin derivatives. Ar=3,5-di-tert-butyl-
phenyl, Mes=mesityl.
more promising as a component of highly conjugated
chromophores, when fused with appropriate aromatic seg-
ments. Despite this potential, except for porphyrin-fused
hexaphyrins 1 (Scheme 1), the peripheral fusion reactions of
expanded porphyrins have been rarely studied,[10] largely
because of synthetic difficulties. We envisioned that the fusion
of anthracenes to rectangular hexaphyrins, such as 2,[11] would
be feasible, because their short sides are similar in length to
the long side of anthracene, and the resultant anthracene-
fused [26]hexaphyrins would show highly perturbed optical
and electrochemical properties. Herein, we report the syn-
thesis of 10, a [26]hexaphyrin fused to two anthracenes, which
exhibits an extensively red-shifted and sharp absorption band
reaching into NIR region, and multiple reversible redox
potentials. 5,20-Dianthryl-substituted [26]hexaphyrin 5 was
prepared by the condensation of tripyrrane 3 and 9-formyl-
anthracene (4) in the presence of methanesulfonic acid
(MSA) at 08C for 2 hours followed by oxidation with
2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ).[12] For
easier separation, 5 was reduced with NaBH4 to its [28]hex-
aphyrin congener, which after purification on a silica gel
column was oxidized back to 5 with MnO2. After recrystal-
lization, hexaphyrin 5 was obtained in 26% yield as a brown
solid. The spectroscopic data of 5 are fully consistent with the
proposed structure, which was confirmed by X-ray diffraction
analysis (see the Supporting Information).[13] One anthryl
group was attached to each of the two short sides of the
hexaphyrin;[14] this structure is favorable for our purpose.
Oxidative fusion reactions of 5 were attempted with DDQ/
[*] K. Naoda, H. Mori, Dr. N. Aratani, Prof. Dr. A. Osuka
Department of Chemistry, Graduate School of Science
Kyoto University, Sakyo-ku, Kyoto 606-8502 (Japan)
E-mail: osuka@kuchem.kyoto-u.ac.jp
Dr. N. Aratani
PRESTO (Japan) Science and Technology Agency (Japan)
B. S. Lee, Prof. Dr. D. Kim
Spectroscopy Laboratory for Functional p-Electronic Systems and
Department of Chemistry, Yonsei University
Seoul 120-749 (Korea)
E-mail: dongho@yonsei.ac.kr
[**] The work at Kyoto was supported by Grants-in-Aid (Nos. 22245006
(A) and 20108001 “pi-Space”) for Scientific Research from MEXT of
Japan. The work at Seoul was supported by the Midcareer
Researcher Program (2010-0029668) and World Class University
(R32-2010-000-10217-0) Programs of MEST of Korea.
Sc(OTf)3 and FeCl3,[15] but neither attempt was successful.
[7d]
We thought that the bis(AuIII) complex 6, which is a more-
conformationally rigid substrate, and might be more suitable
for the oxidative fusion reaction. Our previous metalation
procedure using Na[AuCl4]·2H2O[16] did not work well for 5,
but we found that stirring a solution of 5 in CH2Cl2/MeOH
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201204446.
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(4:1) in the presence of Na[AuCl4]·2H2O, NaOAc, and
Ag2CO3 resulted in a significant improvement in metalation,
to give 6 in 47% yield. Disappointingly, however, the
oxidative fusion reaction of 6 failed, merely giving a small
amount of chlorinated products.
FeCl3. Thus, AuIII metalation of 7 was conducted under the
same conditions to give bis(AuIII) complex 9 in 36% yield.
The single-crystal X-ray analysis displays a considerably bent
structure[13] of 9, as a consequence of AuIII metalation
(Figure 1b).[16] Gratifyingly, heating of a toluene solution of
9 to reflux in the presence of 10 equivalents of DDQ and
10 equivalents of Sc(OTf)3 for 5 hours caused a drastic color
change with formation of a discrete product that eluted slower
than 9 on TLC. After the standard work up, compound 10,
a [26]hexaphyrin fused to two anthracenes was obtained in
24% yield as a dark blue solid, which showed a characteristic
greenish blue color in CH2Cl2. High resolution electrospray
ionization time-of-flight mass spectroscopy detected the
parent ion peak of 10 at m/z = 2398.3689, which was smaller
We thus tried a different substrate, [26]hexaphyrin 7,
bearing two 1,8-di(mesityloxy)anthracen-10-yl substituents,
which are more electron-donating than the anthryl substitu-
ents and hence this substrate should be more appropriate for
the oxidative fusion reaction.[7,8c] 1,8-Dimesityloxy-10-formyl-
anthracene 8 was prepared by reported synthetic routes[7] to
which we had added our own improvements (see the
Supporting Information). Then, the MSA-catalyzed conden-
sation of 3 and 8 produced [26]hexaphyrin 7 in 29% yield. The
spectroscopic data of 7 are fully consistent with the proposed
structure, which was confirmed by an X-ray crystallographic
analysis performed on a single crystal of 7 (Figure 1a). This
analysis revealed that the two anthryl groups are attached to
the short sides of the hexaphyrin similarly to the case of 5, and
the hexaphyrin moiety is more planar than that of 5.[13]
Next, we examined the oxidative fusion reaction of 7; this
reaction did not work well either with DDQ/Sc(OTf)3 or
1
by 8 mass units than that of 9. The H NMR spectrum is
simple, featuring a singlet at 9.94 ppm that corresponds to the
outer b-protons of the hexaphyrin and a pair of doublets at
9.50 and 7.22 ppm (J = 8.4 Hz) that correspond to the 2,3- and
6,7-anthryl protons, thus indicating the formation of the
doubly fused structure. The unambiguous structural determi-
nation of 10 was obtained by X-ray analysis.[13] Crystals of 10
were grown by allowing hexane vapor to diffuse into its
CH2Cl2 solution. Compound 10 displays a remarkably elon-
gated, rectangular (7.28 ꢀ 19.94 ꢁ), almost planar structure;
the dihedral angle of the two anthracene segments is 141.38
(Figure 2). In the crystal-packing structure of 10, an infinite
molecular network is observed, and features an alternate
packing arrangement wherein two molecules are positioned
in an offset manner with their concave sides facing each other
so that half the molecule overlaps (see the Supporting
Information, FigureS8-8). This arrangement is held by
ꢀ
favorable C H/p interactions between the mesityloxy sub-
stituents and hexaphyrin.
Figure 3 shows the absorption spectra of solutions of 9 and
10 in CH2Cl2. The bis(AuIII) hexaphyrin complex 9 exhibits
a slightly split Soret-like band at 672 nm, which is red-shifted
from that of 7 by 96 nm, and Q-band-like bands at 831 and
Figure 1. X-Ray crystal structures of a) 7 and b) 9. Top: top view.
Bottom: side view. The thermal ellipsoids are scaled to 50% proba-
bility. Solvent molecules and pentafluorophenyl groups are omitted for
clarity.
Figure 2. X-Ray crystal structure of 10. Top: top view. Bottom: side
view. The thermal ellipsoids are scaled to 30% probability. Solvent
molecules and pentafluorophenyl groups are omitted for clarity.
2
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Figure 3. UV/Vis/NIR absorption spectra of 9 and 10 in CH2Cl2.
1193 nm. These spectral features are common for bis(AuIII)
hexaphyrins, as reported previously.[16] The absorption spec-
trum of 10 exhibits a red-shifted and intensified Soret-like
band at 743 nm and Q-band-like bands at 873, 943, and
1467 nm. Of these bands, the most red-shifted band is
remarkably sharp and intensified (optical HOMO–LUMO
gap; 0.84 eV, fwhm = 223 cmꢀ1). These absorption character-
istics originate from the elongated conjugation along the long
molecular axis of 10.
Third-order nonlinear optical (NLO) responses of 9 and
10 are also of interest in view of their extended p-conjugation
pathways through fused anthracene units. Two-photon
absorption (TPA) measurements were conducted for 9 and
10 by using a wavelength-scanning open-aperture Z-scan
method in the wavelength region ranging from 1400 to
2400 nm and from 1700 to 2400 nm, respectively, where one-
photon absorption contribution is negligible (see the Sup-
porting Information, Figure S11).[17] It was difficult to mea-
sure accurate TPA values by photoexcitations shorter than
1400 for 9, and 1700 nm for 10. Bis(AuIII) hexaphyrin complex
9 showed the maximum TPA cross section s(2) value of
2500 GM by photoexcitation at 1700 nm, whereas anthra-
cene-fused [26]hexaphyrin 10 exhibited the maximum s(2)
value of 7600 GM by photoexcitation at the same wavelength.
The much higher s(2) value for 10 compared to that for 9 can
be explained by the extended p-conjugation in 10. Further-
more, both 9 and 10 compounds showed larger TPA values
than hexakis(pentafluorophenyl) substituted [26]hexaphyrin
2 (ca. 1000 GM). This result can be explained by the effect
structural changes can have on donor(D)/acceptor(A)-type
multichromophoric systems: the introduction of electron-rich
anthryl substituents and electron-deficient pentafluorophenyl
substituents perturbs the charge redistribution, and elongates
the effective p-conjugation length. We can conclude that
a combination of elongation of the p-conjugation, as well as
D/A perturbation to hexaphyrin improves the overall TPA
properties.
Figure 4. Cyclic Voltammograms of 5, 6, 7, 9, and 10 in anhydrous
CH2Cl2 with 0.1m Bu4NPF6 as supporting electrolyte, and Ag/AgClO4
as reference electrode. Fc/Fc+ was used as external reference.
ation of the hexaphyrins 5 and 7 led to positive shifts of the
waves as a result of the electron-withdrawing property of AuIII
ion. Also, the replacement of the unsubstituted anthryl groups
by electron-rich ones (5!7 and 6!9) caused negative shifts
of the waves. The cyclic voltammogram of 10 in CH2Cl2 is
remarkable, displaying seven redox potentials at 1.02, 0.48,
0.16, ꢀ0.63, ꢀ0.97, ꢀ1.42, and ꢀ1.76 V all as fully reversible
waves, thus implying multicharge storage ability of 10. The
fused structure causes low oxidation potentials. The electro-
chemical HOMO–LUMO gap is thus 0.79 eV. DFT calcula-
tions at the B3LYP/6-31G(d) level using the Gaussian pack-
age revealed that 10 has a more delocalized HOMO and
LUMO than 7 and 9 (see the Supporting Information). In
accord with the electrochemical studies, the HOMO of 10 is
higher in energy than those of 7 and 9 and HOMO–LUMO
gap of 10 has been calculated to be 1.12 eV.
In summary, bis(AuIII) complex 10, containing a hexa-
phyrin fused to two anthracenes, was prepared and charac-
terized. Owing to the flat and elongated rectangular con-
jugated network, 10 displays a remarkably red-shifted and
sharp Q-band-like band at 1467 nm, higher reversible oxida-
tion potentials, multicharge storage ability, and a large TPA
cross-section value. Hence, this work demonstrates the utility
of [26]hexaphyrin as an electronically more-flexible unit to
create extensively p-conjugated networks.
The electrochemical properties of 5, 6, 7, 9, and 10 were
studied by cyclic voltammetry (Figure 4). Bis(AuIII) metal-
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Pascu, G. Accorsi, N. Armaroli, H. L. Anderson, Chem. Sci.
2012, 3, 1541.
[7] a) N. K. Davis, M. Pawlicki, H. L. Anderson, Org. Lett. 2008, 10,
3945; b) N. K. S. Davis, A. L. Thompson, H. L. Anderson, Org.
Lett. 2010, 12, 2124; c) N. K. S. Davis, A. L. Thompson, H. L.
Anderson, J. Am. Chem. Soc. 2011, 133, 30.
[8] a) C. Jiao, L. Zhu, J. Wu, Chem. Eur. J. 2011, 17, 6610; b) C. Jiao,
K.-W. Huang, C. Chi, J. Wu, J. Org. Chem. 2011, 76, 661; c) C.
Jiao, N. Zu, K.-W. Huang, P. Wang, J. Wu, Org. Lett. 2011, 13,
3652.
[9] a) J. L. Sessler, D. Seidel, Angew. Chem. 2003, 115, 5292; Angew.
Chem. Int. Ed. 2003, 42, 5134; b) H. Furuta, H. Maeda, A.
Osuka, Chem. Commun. 2002, 1795; c) T. K. Chandrashekar, A.
Venkatraman, Acc. Chem. Res. 2003, 36, 676; d) Z. S. Yoon, A.
Received: June 8, 2012
Published online: && &&, &&&&
Keywords: anthracene · conjugation · hexaphyrin ·
.
porphyrinoids · two-photon absorption
[1] a) M. G. H. Vicente, L. Jaquinod, K. M. Smith, Chem. Commun.
1999, 1771; b) H. L. Anderson, Chem. Commun. 1999, 2323;
c) D. P. Arnold, Synlett 2000, 296; d) D. Holten, D. F. Bocian,
J. S. Lindsey, Acc. Chem. Res. 2002, 35, 57; e) M. O. Senge, M.
Fazekas, E. G. A. Notaras, W. J. Blau, M. Zawadzka, O. B. Locos,
E. M. N. Mhuircheartaigh, Adv. Mater. 2007, 19, 2737; f) M.
Pawlicki, H. A. Collins, R. G. Denning, H. L. Anderson, Angew.
Chem. 2009, 121, 3292; Angew. Chem. Int. Ed. 2009, 48, 3244.
[2] a) D. P. Arnold, G. A. Heath, J. Am. Chem. Soc. 1993, 115,
12197; b) V. S.-Y. Lin, S. G. DiMagno, M. J. Therien, Science
1994, 264, 1105; c) L. Jaquinod, O. Siri, R. G. Khoury, K. M.
Smith, Chem. Commun. 1998, 1261; d) M. Hoffmann, C. J.
Wilson, B. Odell, H. L. Anderson, Angew. Chem. 2007, 119,
3183; Angew. Chem. Int. Ed. 2007, 46, 3122.
´
Osuka, D. Kim, Nat. Chem. 2009, 1, 113; e) M. Ste˛pien, N.
´
Spritta, L. Latos-Graz˙ynski, Angew. Chem. 2011, 123, 4376;
Angew. Chem. Int. Ed. 2011, 50, 4288; f) S. Saito, A. Osuka,
Angew. Chem. 2011, 123, 4432; Angew. Chem. Int. Ed. 2011, 50,
4342.
[10] a) T. Tanaka, N. Aratani, J. M. Lim, K. S. Kim, D. Kim, A.
Osuka, Chem. Sci. 2011, 2, 1414; b) T. Tanaka, N. Aratani, A.
Osuka, Chem. Asian J. 2012, 7, 889.
[11] a) M. G. P. M. S. Neves, R. M. Martins, A. C. Tomꢂ, A. J. D.
Silvestre, A. M. S. Silva, V. Fꢂlix, M. G. B. Drew, J. A. S.
Cavaleiro, Chem. Commun. 1999, 385; b) J.-Y. Shin, H. Furuta,
K. Yoza, S. Igarashi, A. Osuka, J. Am. Chem. Soc. 2001, 123,
7190.
[3] a) D. Kim, A. Osuka, Acc. Chem. Res. 2004, 37, 735; b) N.
Aratani, D. Kim, A. Osuka, Chem. Asian J. 2009, 4, 1172.
[4] a) H. L. Anderson, Inorg. Chem. 1994, 33, 972.
[5] a) A. Tsuda, A. Nakano, H. Furuta, H. Yamochi, A. Osuka,
Angew. Chem. 2000, 112, 572; Angew. Chem. Int. Ed. 2000, 39,
558; b) A. Tsuda, H. Furuta, A. Osuka, Angew. Chem. 2000, 112,
2649; Angew. Chem. Int. Ed. 2000, 39, 2549; c) A. Tsuda, H.
Furuta, A. Osuka, J. Am. Chem. Soc. 2001, 123, 10304; d) A.
Tsuda, A. Osuka, Science 2001, 293, 79; e) Y. Nakamura, S. Y.
Young, T. Tanaka, N. Aratani, J. M. Kim, K. S. Kim, D. Kim, A.
Osuka, Chem. Eur. J. 2008, 14, 8289.
[6] a) M. J. Crossley, P. L. Burn, J. Chem. Soc. Chem. Commun.
1991, 1569; b) H. J. Callot, E. Schaetfer, R. Cromer, F. Metz,
Tetrahedron 1990, 46, 5253; c) L. Barloy, D. Dolphin, D. Dupre,
T. Wijesekera, J. Org. Chem. 1994, 59, 7976; d) S. Richeter, C.
Jeandon, J.-P. Gisselbrecht, R. Ruppert, H. J. Callot, J. Am.
Chem. Soc. 2002, 124, 6168; e) H. S. Gill, M. Harmjanz, J.
Santamaria, I. Finger, M. J. Scott, Angew. Chem. 2004, 116, 491;
Angew. Chem. Int. Ed. 2004, 43, 485; f) O. Yamane, K. Sugiura,
H. Miyasaka, K. Nakamura, T. Fujimoto, K. Nakamura, T.
Kaneda, Y. Sakata, M. Yamashita, Chem. Lett. 2004, 33, 40; g) S.
Fox, R. W. Boyle, Chem. Commun. 2004, 1322; h) M. Pawlicki,
M. Morisue, N. K. S. Davis, D. G. McLean, J. E. Haley, E.
Beuerman, M. Drobizhev, A. Rebane, A. L. Thompson, S. I.
[12] R. Taniguchi, S. Shimizu, M. Suzuki, J.-Y. Shin, H. Furuta, A.
Osuka, Tetrahedron Lett. 2003, 44, 2505.
[13] CCDC 884114 (5), 884115 (7), 884116 (9), and 884113 (10)
contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
[14] Another conformer bearing two anthryl substituents on the
longer side of the hexaphyrin was detected in 1H NMR spectrum
in CDCl3 but upon heating this conformer was converted into 5.
[15] M. D. Watson, A. Fechtenkçtter, K. Mꢃllen, Chem. Rev. 2001,
101, 1267.
[16] a) S. Mori, A. Osuka, J. Am. Chem. Soc. 2005, 127, 8030; b) S.
Mori, K. S. Kim, Z. S. Yoon, S. B. Noh, D. Kim, A. Osuka, J. Am.
Chem. Soc. 2007, 129, 11344.
[17] M. Ishida, J.-Y. Shin, J. M. Lim, B. S. Lee, M.-C. Yoon, T. Koide,
J. L. Sessler, A. Osuka, D. Kim, J. Am. Chem. Soc. 2011, 133,
15533.
4
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Angew. Chem. Int. Ed. 2012, 51, 1 – 5
These are not the final page numbers!

Angewandte
Chemie
Communications
Porphyrinoids
Gold standard: A bis(AuIII) complex con-
taining the title compound was prepared
and characterized (see scheme; DDQ=
2,3-dichloro-5,6-dicyano-1,4-benzoqui-
none, Tf=trifluoromethanesulfonyl).
Owing to the effective conjugative net-
work over the flat and elongated rectan-
gular molecular frame, this complex
displays a remarkably red-shifted and
sharp Q-band-like band at 1467 nm,
multiple reversible redox potentials, and
a large TPA cross-section value.
K. Naoda, H. Mori, N. Aratani, B. S. Lee,
D. Kim,* A. Osuka*
&&&& — &&&&
Hexaphyrin Fused to Two Anthracenes
Angew. Chem. Int. Ed. 2012, 51, 1 – 5
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
5
These are not the final page numbers!