Efficient excitation energy transfer in long meso-meso linked Zn(II) porphyrin arrays bearing a 5,15-bisphenylethynylated Zn(II) porphyrin acceptor

Article abstract of DOI:10.1021/ja030002u

Electronically coupled porphyrin arrays are suitable for artificial light harvesting antenna in light of a large absorption cross-section and fast excitation energy transfer (EET). Along this line, an artificial energy transfer model system has been synth

Full text of DOI:10.1021/ja030002u

Published on Web 07/17/2003
Efficient Excitation Energy Transfer in Long Meso-Meso
Linked Zn(II) Porphyrin Arrays Bearing a
5,15-Bisphenylethynylated Zn(II) Porphyrin Acceptor
Naoki Aratani,† Hyun Sun Cho,‡ Tae Kyu Ahn,‡ Sung Cho,‡ Dongho Kim,*,‡
Hitoshi Sumi,*,§ and Atsuhiro Osuka*,†
Contribution from the Department of Chemistry, Graduate School of Science, Kyoto UniVersity,
and Core Research for EVolutional Science and Technology (CREST), Japan Science and
Technology Corporation, Sakyo-ku, Kyoto 606-8502, Japan, Center for Ultrafast Optical
Characteristics Control and Department of Chemistry, Yonsei UniVersity, Seoul 120-749, Korea,
and Institute of Materials Science, UniVersity of Tsukuba, Tsukuba 305-8573, Japan
Received January 3, 2003; E-mail: osuka@kuchem.kyoto-u.ac.jp
Abstract: Electronically coupled porphyrin arrays are suitable for artificial light harvesting antenna in light
of a large absorption cross-section and fast excitation energy transfer (EET). Along this line, an artificial
energy transfer model system has been synthesized, comprising of an energy donating meso-meso linked
Zn(II) porphyrin array and an energy accepting 5,15-bisphenylethynylated Zn(II) porphyrin linked via a 1,4-
phenylene spacer. This includes an increasing number of porphyrins in the meso-meso linked Zn(II)
porphyrin array, 1, 2, 3, 6, 12, and 24 (Z1A, Z2A, Z3A, Z6A, Z12A, and Z24A). The intramolecular singlet-
singlet EET processes have been examined by means of the steady-state and time-resolved spectroscopic
techniques. The steady-state fluorescence comes only from the acceptor moiety in Z1A-Z12A, indicating
nearly the quantitative EET. In Z24A that has a molecular length of ca. 217 Å, the fluorescence comes
largely from the acceptor moiety but partly from the long donor array, indicating that the intramolecular
EET is not quantitative. The transient absorption spectroscopy has provided the EET rates in real time
scale: (2.5 ps)-1 for Z1A, (3.3 ps)-1 for Z2A, (5.5 ps)-1 for Z3A, (21 ps)-1 for Z6A, (63 ps)-1 for Z12A, and
(108 ps)-1 for Z24A. These results have been well explained by a revised Fo¨rster equation (Sumi formula),
which takes into account an exciton extending coherently over several porphyrin pigments in the donor
array, whose length is not much shorter than the average donor-acceptor distance. Advantages of such
strongly coupled porphyrin arrays in light harvesting and transmission are emphasized in terms of fast
EET and a large absorption cross-section for incident light.
teria and red algae.4 In these cases, photosynthetic pigments
form aggregates whose excitation leads to the formation of
Introduction
Photosynthesis starts by the absorption of a photon by light-
harvesting (antenna) complexes that usually comprise of a large
number of pigments embedded in protein matrixes.1 This process
is followed by a rapid and an efficient energy migration over
many pigments within the antenna system until a reaction center
is encountered, where photoinduced charge separation takes
place for fixation of the solar energies harvested. Photosynthetic
organisms often utilize electronically coupled chromophores to
capture dilute sunlight as well as enhance the energy transfer
efficiency as seen in chlorosomes2 and LH13a and LH23b,c in
bacterial antenna systems and in phycobilisomes in cyanobac-
excitons with quantum-mechanical coherence extending over
many chromophores.
Numerous artificial molecular architectures based on por-
phyrins have been explored with the aim of achieving efficient
and directed energy transfer.5,6 Although some of these studies
help understand light-harvesting and energy-transfer phenomena
at the molecular level, there is only a limited number of reports
on the energy transfer system involving a strongly coupled array
of donor or acceptor.7 Strong electronic coupling (exciton
coupling) leads to the alteration of the absorption and emission
properties, hence affecting the EET efficiency. More impor-
† Kyoto University.
(3) (a) Karrasch, S.; Bullough, P. A.; Ghosh, R. EMBO J. 1995, 14, 631. (b)
McDermott, G.; Prince, S. M.; Freer, A. A.; Hawthornthwaite-Lawless, A.
M.; Papiz, M. Z.; Cogdell, R. J.; Isaacs, N. W. Nature 1995, 374, 517. (c)
Koepke, J.; Hu, X.; Muenke, C.; Schulten, K.; Michel, H. Structure 1996,
4, 581.
(4) (a) Gantt, E. Int. ReV. Cytol. 1980, 66, 45. (b) Yamazaki, I.: Mimuro, M.;
Tamai, N.; Yamazaki, T.; Fujita, Y. Photochem. Photobiol. 1984, 39, 233.
(c) Holzwarth, A. R.; Wendler, J.; Suter, G. W. Biophys. J. 1987, 51, 1.
(5) (a) Wasielewski, M. R. Chem. ReV. 1992, 92, 435. (b) Gust, D.; Moore, T.
A.; Moore, A. L. Acc. Chem. Res. 1993, 26, 198. (c) Gust, D.; Moore, T.
A.; Moore, A. L. Acc. Chem. Res. 2001, 34, 40. (d) Holten, D.; Bocian, D.
F.; Lindsey, J. S. Acc. Chem. Res. 2002, 35, 57.
‡ Yonsei University.
§ University of Tsukuba.
(1) (a) van Grondelle, R.; Dekker, J. P.; Gillbro, T.; Sundstro¨m, V. Biochim.
Biophys. Acta 1994, 1187, 1. (b) Pullerits, T.; Sundstro¨m, V. Acc. Chem.
Res. 1996, 29, 381.
(2) (a) Blankenship, R. E.; Olson, J. M.; Miller, M. In Anoxygenic Photosyn-
thetic Bacteria; Blankenship, R. E., Madigan, M. T., Bauer, C. E., Eds.;
Kluwer Academic Publishers: The Netherlands, 1995; p 399. (b) Holzwarth,
A. R.; Griebenow, K.; Shaffner, K. J. Photochem. Photobiol. A 1992, 65,
61. (c) Hildebrandt, P.; Tamiaki, H.; Holzwarth, A. R.; Shaffner, K. J.
Phys. Chem. 1994, 98, 2192.
9
9668
J. AM. CHEM. SOC. 2003, 125, 9668-9681
10.1021/ja030002u CCC: $25.00 © 2003 American Chemical Society

Energy Donation of Meso−Meso Linked Zn(II) Porphyrin Array
A R T I C L E S
Scheme 1. Synthesis of Z2Aa
tantly, unless forming a stacked nonfluorescent energy sink, an
electronically coupled array of chromophores may be favorable
for the light harvesting antenna function owing to faster inter-
porphyrin energy hopping and a larger absorption cross-section.
Such effects have been only scarcely tested in structurally well-
defined synthetic models.
The peripheral antenna LH2 of the photosynthetic purple
bacteria forms two wheel-like structures with 9 bacteriochlo-
rophyll (Bchl) a molecules (B800) and 18 Bchl a molecules
(B850).4a While Bchl a molecules in B800 are electronically
weakly interacting with each other, those in B850 are electroni-
cally strongly coupled, causing the exciton states, due to a close
face-to-face arrangement with an Mg-Mg distance of 8.7 Å.
EET takes place very rapidly from B800 to B850 within a time
of 0.7-0.9 ps at room temperature.1 When a strict 9-fold
symmetry is assumed for B850, optically allowed is only the
second lowest exciton state with the lowest exciton state
becoming dipole-forbidden.8 In this situation, it would be
difficult to explain the very rapid energy transfer from B800 to
B850 within a framework of Fo¨rster mechanism, which allows
EET only between optically allowed states. The energy-
accepting optically allowed state in B850 is located too low
from the energy donating B800 state. This optically forbidden
lowest exciton state in B850 may be involved in the subsequent
EET to LH1 as an energy donor. Recently, Sumi proposed a
revised Fo¨rster formula for EET8 that occurs between a donor
and an acceptor in a situation where at least one of them is an
exciton holding aggregate of chromophores. When the physical
size of aggregate is not much smaller than the average donor-
acceptor distance, as found quite commonly in natural photo-
synthetic systems, individual chromophores retain their transition
dipoles against the EET partner, even if their overall sum is
nearly zero due to the dipole-forbidden nature of an exciton
state.8 This revised formula has explained the rapid EET from
B800 to B850 in a satisfactory manner.9
a Ar ) 3,5-dioctyloxyphenyl. Conditions: (a) (i) TFA, (ii) DDQ, 13%;
(b) (i) NBS, pyridine, CH2Cl2, (ii) Zn(OAc)2, 92%; (c) phenylacetylene,
CuI, PdCl2(PPh2)2, triethylamine, toluene, 64%; (d) Pd(Ph3)4, Cs2CO3, DMF,
toluene, 76%.
24, as shown in Schemes 1-3, in which a 5,15-bisphenylethyn-
ylated porphyrin acceptor is linked via a 1,4-phenylene spacer
at the end meso-carbon of a meso-meso linked Zn(II) porphyrin
array. Recently, we reported the synthesis of extremely long,
yet discrete meso-meso linked porphyrin arrays by Ag(I)-
promoted oxidative coupling.10,11 A key feature of these
porphyrin arrays is the good solubility in many organic solvents
including THF and CHCl3. Therefore, despite the large molec-
ular size, these molecules can be separated, purified, and
subjected to many chemical reactions in a manner similar to
those of normal organic molecules. Meso-meso linked por-
phyrin arrays thus prepared have two free meso-positions, which
Here, we report the synthesis and EET processes of covalently
linked donor-acceptor systems, ZnA; n ) 1, 2, 3, 6, 12, and
(6) (a) Dubowchik, G. M.; Hamilton, A. D. J. Chem. Soc., Chem. Commun.
1987, 293. (b) Osuka, A.; Maruyama, K.; Yamazaki, I.; Tamai, N. Chem.
Phys. Lett. 1990, 165, 392. (c) Sessler, J. L.; Capuano, V. L.; Harriman,
A. J. Am. Chem. Soc. 1993, 115, 4618. (d) Wagner, R. W.; Lindsey, J. S.
J. Am. Chem. Soc. 1994, 116, 9759. (e) Osuka, A.; Tanabe, N.; Kawabata,
S.; Yamazaki, I.; Nishimura, Y. J. Org. Chem. 1995, 60, 7177. (f) Officer,
D. L.; Burrell, A. K.; Reid, D. C. W. Chem. Commun. 1996, 1657. (g)
Osuka, A.; Tanabe, N.; Nakajima, S.; Maruyama, K. J. Chem. Soc., Perkin
Trans. 2 1996, 199. (h) Jensen, K. K.; van Berlekom, S. B.; Kajanus, J.;
Martensson, J.; Albinsson, B. J. Phys. Chem. A. 1997, 101, 2218. (i) Taylor,
P. L.; Wylie, A. P.; Huuskonen, J.; Anderson, H. L. Angew. Chem., Int.
Ed. 1998, 37, 986. (j) Mongin, O.; Papamicae¨l, C.; Hoyler, N.; Gossauer,
A. J. Org. Chem. 1998, 63, 5568. (k) Nakano, A.; Osuka, A.; Yamazaki,
I.; Yamazaki, T.; Nishimura, Y. Angew. Chem., Int. Ed. 1998, 37, 3023.
(l) Biemans, H. A. M.; Rowan, A. E.; Verhoeven, A.; Vanoppen, P.;
Latterini, L.; Foekema, J.; Schenning, A. P. H. J.; Meijer, E. W.; De
Schryver, F. C.; Nolte, R. J. M. J. Am. Chem. Soc. 1998, 120, 11054. (m)
Sugiura, K.; Tanaka, H.; Matsumoto, T.; Kawai, T.; Sakata, Y. Chem. Lett.
1999, 1193-1194. (n) Yeow, E. K. L.; Ghiggino, K. P.; Reek, J. N. H.;
Crossley, M. J.; Bosman, A. W.; Schenning, A. P. H. J.; Meijer, E. W. J.
Phys. Chem. B 2000, 104, 2596. (o) Benites, M. R.; Johnson, T. E.;
Weghorn, S.; Yu, L.; Rao, P. D.; Diers, J. R.; Yang, S. I.; Kirmaier, C.;
Bocian, D. F.; Holten, D.; Lindsey, J. S. J. Mater. Chem. 2001, 12, 65. (p)
Nakano, A.; Osuka, A.; Yamazaki, T.; Nishimura, Y.; Akimoto, S.;
Yamazaki, I.; Itaya, A.; Murakami, M.; Miyasaka, H. Chem.sEur. J. 2001,
7, 3134. (q) Choi, M.-S.; Aida, T.; Yamazaki, T.: Yamazaki, I. Chem.s
Eur. J. 2002, 8, 668.
(10) (a) Osuka, A.; Shimidzu, H. Angew. Chem., Int. Ed. Engl. 1997, 36, 135.
(b) Aratani, N.; Osuka, A.; Kim, Y. H.; Jeong, D. H.; Kim, D. Angew.
Chem., Int. Ed. 2000, 39, 1458. (c) Kim, Y. H.; Jeong, D. H.; Kim, D.;
Jeoung, S. C.; Cho, H. S.; Kim, S. K.; Aratani, N.; Osuka, A. J. Am. Chem.
Soc. 2001, 123, 76. (d) Nakano, A.; Yamazaki, T.; Nishimura, Y.;
Yamazaki, I.; Osuka, A. Chem.sEur. J. 2000, 6, 3254. (e) Yoshida, N.;
Aratani, N.; Osuka, A. Chem. Commun. 2000, 197. (f) Piet, J. J.; Taylor,
P. N.; Anderson, H. L.; Osuka, A.; Warman, J. M. J. Am. Chem. Soc. 2000,
122, 1749. (g) Yoshida, N.; Osuka, A. Org. Lett. 2000, 2, 2963.
(11) (a) Susumu, K.; Shimidzu, T.; Tanaka, K.; Segawa, H. Tetrahedron Lett.
1996, 37, 8399. (b) Khoury, R. G.; Jaquinod, L.; Smith, K. M. Chem.
Commun. 1997, 1057. (c) Senge, M. O.; Feng, X. Tetrahedron Lett. 1999,
40, 4165. (d) Wojaczynski, J.; Latos-Grazynski, L.; Chmielewski, P. J.;
Van Calcar, P.; Balch, A. L. Inorg. Chem. 1999, 38, 3040. (e) Shi, X.;
Liebeskind, L. S. J. Org. Chem. 2000, 65, 1655. (e) Miller, M. A.; Lammi,
R. K.; Prathapan, S.; Holten, D.; Lindsey, J. S. J. Org. Chem. 2000, 65,
6634. (f) Ogawa, K.; Kobuke, Y. Angew. Chem., Int. Ed. 2000, 39, 4070.
(g) Imahori, H.; Tamaki, K.; Araki, Y.; Sekiguchi, Y.; Ito, O.; Sakata, Y.;
Fukuzumi, S. J. Am. Chem. Soc. 2002, 124, 5165. (h) Bonifazi, D.;
Diederich, F. Chem. Commun. 2002, 2178.
(7) Tamiaki, H.; Miyatake, T.; Tanikaga, R.; Holzwarth, A. R.; Shaffner, K.
Angew. Chem., Int. Ed. Engl. 1996, 35, 772.
(8) (a) Sumi, H. J. Phys. Chem. B 1999, 103, 252. (b) Sumi, H. J. Luminesc.
2000, 87-89, 71. (c) Sumi, H. Chem. Record 2001, 1, 480.
(9) (a) Mukai, K.; Abe, S.; Sumi, H. J. Phys. Chem. B 1999, 103, 6096. (b)
Mukai, K.; Abe, S.; Sumi, H. J. Luminesc. 2000, 87-89, 818. (c) Scholes,
G. D.; Fleming, G. R. J. Phys. Chem. B 2000, 104, 1854. (d) Scholes, G.
D.; Jordanides, X. J.; Fleming, G. R. J. Phys. Chem. B 2001, 105, 1640.
9
J. AM. CHEM. SOC. VOL. 125, NO. 32, 2003 9669

A R T I C L E S
Aratani et al.
Scheme 2. Molecular Structures of Z1A-Z12Aa
a Ar ) 3,5-dioctyloxyphenyl.
Scheme 3. Molecular Structure of Z24Aa
a Ar ) 3,5-dioctyloxyphenyl.
are used for the attachment of the energy acceptor. Another
interesting feature is the direct meso-meso linkage, which gives
rise to substantially large electronic coupling, but the resultant
orthogonal conformation of the neighboring porphyrins disrupts
the electronic π-conjugation.10c,f These properties may be
favorable for achieving efficient energy transfer along the array.
In addition, the restricted linear geometry of meso-meso linked
porphyrin arrays avoids the formation of a stacked dimeric
energy sink that might disrupt the energy-transfer flow along
the array. The linear geometry is also interesting with regard to
the topological effect on antenna function.12 With this back-
ground, we have examined the excitation energy transfer in
ZnA.
Molecular Design and Synthesis. Scheme 1 shows the
synthetic route. Meso-meso linked Zn(II) porphyrin arrays Z2,
Z3, Z6, Z12, and Z24 were synthesized by the usual AgI-
(12) Van Patten, P. G.; Shreve, A. P.; Lindsey, J. S.; Donohoe, R. J. Phys.
Chem. B 1998, 102, 4209.
9
9670 J. AM. CHEM. SOC. VOL. 125, NO. 32, 2003

Energy Donation of Meso−Meso Linked Zn(II) Porphyrin Array
A R T I C L E S
promoted coupling of 5,15-diaryl Zn(II) porphyrin Z1.10a-e
Controlled NBS bromination of Z1, Z2, Z3, Z6, Z12, and Z24
gave a mixture of meso-bromo- and meso,meso′-dibromo Zn-
(II) porphyrins. The meso-monobrominated porphyrins, Z1B,
Z2B, Z3B, Z6B, Z12B, and Z24B, were coupled with boronate
Zn(II) porphyrin 3 under Suzuki coupling conditions to furnish
Z1A, Z2A, Z3A, Z6A, Z12A, and Z24A, respectively. These
model compounds have meso-meso linked Zn(II) porphyrin
arrays as the energy donor and a 5,15-bisphenylethynylated Zn-
(II) porphyrin13 as the energy acceptor. The latter has been
shown to act as an energy acceptor owing to its red-shifted
Q-band and hence favorable spectral overlap for the energy
transfer from the meso-meso linked porphyrin array.14
(calcd for C1600H2028N100O98Zn25, 25 865.1) in the MALDI-TOF
mass spectra (Figure 1).
Steady-State Spectra. Figure 2 shows the absorption spectra
of Z1A, Z2A, Z3A, Z6A, Z12A, and Z24A in THF, along with
those of 1:1 mixtures of acceptor-free meso-meso linked
porphyrin arrays (Z1, Z2, Z3, Z6, Z12, and Z24) and the
porphyrin 4. In line with the previous studies,10 the exciton-
split Soret bands of the meso-meso linked porphyrin arrays
are observed at 417-423 nm and at >466 nm. The Soret bands
of the bisphenylethynylated Zn(II) porphyrin are observed
constantly at 448 nm. The Q-bands of the meso-meso linked
porphyrin arrays are observed at 550-588 nm with progressive
intensification and red shift upon the increase of the number of
porphyrins, while the Q-bands of the bisphenylethynylated
Zn(II) porphyrin are observed at 649 nm. Comparisons of the
respective absorption spectra revealed that the absorption spectra
of ZnA in the Q-band region are essentially given by the sum
of the spectra of meso-meso linked porphyrin arrays Zn and
4, indicating that electronic interactions in the ground state are
weak. On the other hand, there are some differences in the Soret-
bands region, which are caused by the exciton coupling between
the Zn and the 5,15-bisphenylethylated Zn(II) porphyrin part
owing to the large transition moments of the Soret bands
(S0 f S2).14b It is interesting to note that a selective photoex-
citation of the meso-meso linked porphyrin arrays is possible
at 550-560 nm.
The steady-state fluorescence spectra of Z1A-Z24A are
shown in the insets of Figure 2, along with those of 1:1 mixtures
of acceptor-free meso-meso linked porphyrin arrays (Z1, Z2,
Z3, Z6, Z12, and Z24) and the porphyrin 4. Upon photoexci-
tation at 550-560 nm corresponding to a selective excitation
at the meso-meso linked porphyrin array, 1:1 mixtures of
meso-meso linked Zn(II) porphyrin arrays and 4 exhibit the
fluorescence predominantly from the meso-meso linked Zn-
(II) porphyrin arrays. The models Z1A-Z12A exhibit the
fluorescence predominantly coming from the bisphenylethyny-
lated Zn(II) porphyrin moiety, indicating the efficient, nearly
quantitative EET processes. The fluorescence of Z24A comes
largely from the acceptor moiety but also partly from the long
donor porphyrin array (Supporting Information II). Here, it is
noted that the donor emissions are completely overlapping the
Q-band of the energy-accepting unit, being favorable for the
rapid EET.
Results
Synthesis. p-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)-
benzaldehyde was prepared in 92% yield by pinacol protection
of 4-formylphenylboronic acid. The porphyrin boronate 1 was
prepared in 13% yield from the acid-catalyzed condensation of
3,5-dioctyloxybenzaldehyde10b and the protected boronate with
2.0 equiv of 2,2′-dipyrromethane followed by oxidation with 3
equiv of DDQ.15,16 Subsequent bromination of 1 with 2.2 equiv
of NBS followed by zinc metalation yielded Zn(II) dibromopor-
phyrin 2 in 92% yield. Sonogashira coupling of the porphyrin
2 with an excess of phenylacetylene (bis(triphenylphosphine)
palladium(II) chloride and CuI, triethylamine/toluene, at 50 °C,
for 3 h) gave 5,15-bisphenylethynylated boronate Zn(II) por-
phyrin 3 in 64% yield.14,17 Finally, Suzuki cross-coupling
reaction of the porphyrin 3 with Z1B, Z2B, Z3B, Z6B, Z12B,
and Z24B (10 mol % Pd(PPh3)4, 3 equiv Cs2CO3, DMF/toluene,
at 80 °C, for 4 h) gave models Z1A, Z2A, Z3A, Z6A, Z12A,
and Z24A in 10-77% yields.18 Models ZnA were difficult to
separate over the usual silica gel column but were obtained in
a pure form by using the recycling preparative GPC-HPLC.
In the case of Z24A, as many as 16 recycling separations over
our GPC-HPLC setup enabled the isolation of pure Z24A in
28% (Supporting Information I). 5,15-Bisphenylethynyl-10,20-
bis(3,5-dioctyloxyphenyl) Zn(II) porphyrin 4 was prepared as
a reference molecule.14b All new compounds were fully
characterized by 1H NMR spectra, FAB or MALDI-TOF mass
spectroscopy, UV-vis absorption spectroscopy, and GPC
analysis. Among these, the long porphyrin arrays Z12A and
Z24A contain 13 and 25 porphyrin units in a linear fashion
with a molecular length of 113 and 217 Å, respectively. The
corresponding parent ions were clearly detected at m/e ) 13 423
(calcd for C832H1044N52O50Zn13, 13 423.9) and m/e ) 25 862
Figure 3a shows the comparison of the absorption spectra of
Z1A-Z24A at the same concentration (9 × 10-8 M). At this
dilute concentration, there is no serious aggregation, since the
absorbance reflects the number of the porphyrins in the
molecule. It is evident that the extensive exciton coupling within
the meso-meso linked porphyrin array gives rise to a larger
cross-section between 350 and 650 nm. This spectral feature is
favorable for the light harvesting antenna function. Figure 3b
compares the steady-state fluorescence taken for the excitation
at 508 nm, where the Z1A model has practically no absorbance
and Z12A and Z24A have the large absorbance due to the
exciton coupling. In Z2A-Z12A, the incident light at this
wavelength (508 nm) is efficiently delivered to the end energy
acceptor, since the resultant fluorescence intensification is
parallel to the increase in the absorbance at 508 nm. But the
fluorescence intensity of Z24A is somewhat less than a value
(13) (a) Lin, V. S.-Y.; DiMagno, S. G.; Therien, M. J. Science, 1994, 264, 1105.
(b) Arnold, D. P.; Nitschinsk, L. Tetrahedron Lett. 1993, 34, 693. (c)
Anderson, H. L. Inorg. Chem. 1994, 33, 972.
(14) (a) Nakano, A.; Shimidzu, H.; Osuka, A. Tetrahedron Lett. 1998, 39, 9489.
(b) Nakano, A.; Yasuda, Y.; Yamazaki, T.; Akimoto, S.; Yamazaki, I.;
Miyasaka, H.; Itaya, A.; Murakami, M.; Osuka, A. J. Phys. Chem. A 2001,
105, 4822.
(15) Lindsey, J. S.; Schreiman, I. C.; Hsu, H. C.; Kearney, P. C.; Marguerettaz,
A. M. J. Org. Chem. 1987, 52, 827.
(16) DiMagno, S. G.; Lin, V. S.-Y.; Therien, M. J. J. Org. Chem. 1993, 58,
5983.
(17) (a) Sonogashira, K.; Tohda, Y.; Hagihara, N. Tetrahedron Lett. 1975, 4467.
(b) Lindey, J. S.; Prathapan, S.; Johnson, T. E.; Wagner, R. W. Tetrahedron
1994, 50, 8941.
(18) (a) Zhou, X.; Chan, K. S. J. Org. Chem. 1998, 63, 99. (b) Shultz, D. A.;
Lee, H.; Kumar, R. K.; Gwaltney, K. P. J. Org. Chem. 1999, 64, 9124. (c)
Mizutani, T.; Wada, K.; Kitagawa, S. J. Am. Chem. Soc. 2001, 123, 6459.
(d) Deng, Y.; Chang, C. K.; Nocera, D. G. Angew. Chem., Int. Ed. 2000,
39, 1066. (e) Aratani, N.; Osuka, A. Org. Lett. 2001, 3, 4213. (f) Yu, L.;
Lindsey, J. S. Tetrahedron 2001, 57, 9285. (g) Hyslop, A. G.; Kellett, M.
A.; Iovine, P. M.; Therien, M. J. J. Am. Chem. Soc. 1998, 120, 12676.
9
J. AM. CHEM. SOC. VOL. 125, NO. 32, 2003 9671

A R T I C L E S
Aratani et al.
Figure 1. MALDI-TOF mass spectra of Z12A (upper) and Z24A (lower) recorded in positive ion mode with 9-nitroanthracence as matrix.
expected from its absorbance, indicating that the intramolecular
EET is also efficient but not quantitative.
Transient Absorption Anisotoropy Decay Analysis. We
have also carried out the femtosecond transient absorption
anisotropy decay measurements for Z1A, Z2A, Z3A, and Z6A
(Figure 6). The transition dipole of the S1-state of the meso-
meso linked porphyrin-array donor has been shown to align
along the long molecular axis,10c and that of the lowest S1-state
of the 5,15-bisphenylethynyl Zn (II) porphyrin acceptor has been
considered to align along the 5,15-direction.13a Therefore, in
Z2A, Z3A, and Z6A, the key transition dipole moments of the
donor and acceptor are placed in an orthogonal arrangement in
their lowest excited states. Accordingly, a large anisotropy
change is expected during the energy transfer processes.10c The
anisotropy dynamics of Z1A probed at 480 nm exhibit only a
rapid decay with τ ) 0.2 ps. In the case of Z2A, at 470 nm
probe wavelength, we observed an initial rapid anisotropy decay
with τ ) 0.2 ps, followed by an anisotropy rise with τ ) 3.3 ps
(Figure 6b). The time constant of the anisotropy rise matches
nicely with the EET rate constant. We observed similar
behaviors for both Z3A and Z6A, a rapid anisotropy decay with
τ ) 0.2 ps followed by an anisotropy rise with τ ) 5.5 ps in
Z3A and a rapid anisotropy decay with τ ) 0.2 ps followed by
Transient Absorption Spectra.The transient absorption
spectra of Z1A, Z2A, Z3A, Z6A, Z12A, and Z24A were taken
by the selective S1-excitation of the meso-meso linked por-
phyrin arrays at the Q-bands (Figure 4). The transient absorption
spectrum of Z1A at a 2-ps delay time indicated a bleaching
around 420 nm due to the depletion of the meso-meso linked
porphyrin array (energy donor), which decayed quickly with τ
) 1.6 ps (Figure 5a). Along this spectral change, a new
bleaching at 650 nm due to the depletion of the bisphenylethyn-
ylated Zn(II) porphyrin (energy acceptor) was observed to be
growing with τ ) 2.5 ps (Figures 4a and 5a). Therefore, these
two spectral changes indicate the efficient intramolecular EET
from the meso-meso linked porphyrin array to the bisphenyl-
ethynylated Zn(II) porphyrin. Essentially the similar transient
absorption spectra and temporal profiles were observed for Z2A,
Z3A, Z6A, Z12A, and Z24A (Figures 4 and 5). On the basis
of these data, the EET rate constants have been determined for
Z2A, (3.3 ps)-1; Z3A, (5.5 ps)-1; Z6A, (21 ps)-1; Z12A,
(63 ps)-1; and Z24A, (108 ps)-1
.
9
9672 J. AM. CHEM. SOC. VOL. 125, NO. 32, 2003

Energy Donation of Meso−Meso Linked Zn(II) Porphyrin Array
A R T I C L E S
Figure 2. Absorption and fluorescence spectra of (a) Z1A, (b) Z2A, (c) Z3A, (d) Z6A, (e) Z12A, and (f) Z24A. Fluorescence spectra (shown in insets)
were taken for excitation at their Q-bands. Solid lines are for ZnA, and broken lines are for 1:1 mixtures of Zn and 4.
Figure 3. (a) Absorption and (b) fluorescence spectra of Z1A-Z24A at 9 × 10-8 M in THF. Fluorescence spectra were taken for excitation at 508 nm.
an anisotropy rise with τ ) 21 ps in Z6A, respectively (Figure
6c and d). The fast anisotropy decay with τ ) 0.2 ps indicates
a coherent coupling time, while the observed anisotropy rise
with slower time constants can be ascribed to the intramolecular
energy transfer.
Z2A, Z3A, Z6A, and Z12A but is not quantitative in Z24A as
judged from Figure 3. The large electronic interaction between
the directly meso-meso linked neighboring porphyrins must
be responsible for the EET.
The anisotropy decay measurements have indicated that the
present EET processes are accompanied by a large change in
the direction of the transition dipole moment. In the case of
Z1A, the anisotropy decay dynamics become complicated
mainly due to the fact that a broad absorption band around 450
nm is not solely due to the acceptor Soret band but a mixture
with the exciton split Soret band arising from excitonic
interactions between donor and acceptor. Thus, even in the
magic angle detection at 460 nm upon photoexcitation of Z1A
at 400 nm, we observed rise and decay components due to the
simultaneous participation of donor and acceptor bleaching
Discussion
The intramolecular EET events in Z1A-Z24A have been
confirmed by the steady-state fluorescence and transient absorp-
tion measurements. The exciton coupling within the meso-meso
linked Zn(II) porphyrin arrays causes the alteration and extension
of the absorption spectral shapes, which are quite favorable for
the light harvesting antenna function. Captured light energy is
then delivered efficiently to the energy-accepting site in all the
models Z1A-Z24A. The EET is almost quantitative in Z1A,
9
J. AM. CHEM. SOC. VOL. 125, NO. 32, 2003 9673

A R T I C L E S
Aratani et al.
Figure 4. Transient absorption and fluorescence spectra of (a) Z1A, (b) Z2A, (c) Z3A, (d) Z6A, (e) Z12A, and (f) Z24A.
recoveries in the energy transfer process (Supporting Information
III). In the case of Z2A, we observed similar phenomena
especially at 470 nm probe wavelength, which contains a
contribution from the exciton split Soret band between donor
and acceptor. This process should be sensitive to the probe
wavelength because the exciton split Soret band and the Soret
band of the acceptor are overlapped at around 450 nm in the
case of Z1A. At 480 nm probe, the contribution from the exciton
split Soret band becomes reduced. The anisotropy dynamics of
Z1A, probed at 480 nm, contains the initial rise due to the fast
equilibrium between Bx and By polarizations of the donor part
followed by a relatively slow energy transfer process with τ )
∼2 ps. The initial anisotropy decay of Z6A has also been
assigned to the fast equilibrium between Bx and By polarizations,
which reflects the coherent coupling time in preparing a large
dipole (coherently coupled one) along the long axis of the array,
while a slow anisotropy rise with τ ) ∼21 ps can be assigned
to the EET, because the time constant agrees with the EET rate
constant (21 ps)-1 and the donor and acceptor dipole moments
are arranged orthogonal to each other. We observed similar
behaviors in Z2A and Z3A.
let us consider that excited states on the porphyrin array are
excitons, and their quantum-mechanical wave functions extend
coherently over the entire array. Such exciton states are formed
due to ample inter-porphyrin interactions which, as the first
approximation, can be regarded as brought about by the
electrostatic interaction between transition dipoles at neighboring
porphyrins in the array. Participating in the interaction at each
porphyrin is a component with a transition dipole parallel to
the array axis in the doubly degenerate S1 transitions. When
the array is composed of N porphyrins, the lowest exciton state
on the array can be represented by
N
2
π
|d )
sin
n |n
(1)
∑
(
)
x
N + 1n)1
N + 1
where |n represents a state of the array that the nth porphyrin
therein is excited with a transition dipole parallel to the array
while all the other porphyrins are unexcited. The energy
eigenvalue of |d is given by
Ed ) E0 + 2∆ cos[π/(N + 1)]
(2)
In the next step, we consider the dependence of the EET rate
constant upon the number of the porphyrins in the array. First,
where E0 represents the excitation energy of the S1 transition
9
9674 J. AM. CHEM. SOC. VOL. 125, NO. 32, 2003

Energy Donation of Meso−Meso Linked Zn(II) Porphyrin Array
A R T I C L E S
Figure 5. Temporal time profiles of the transient absorption spectra of (a) Z1A, (b) Z2A, (c) Z3A, (d) Z6A, (e) Z12A, and (f) Z24A.
of a single porphyrin, and ∆ represents the excitonic interaction
between neighboring porphyrins in the array. The total transition
dipole of this donor state |d is parallel to the array axis with a
magnitude
porphyrin-array donor covers completely the absorption spec-
trum of the acceptor porphyrin in the energy region of its S1
transitions, as mentioned earlier. In this situation, it seems
reasonable to consider that the acceptor state for the EET is a
mixture of the S1 component with the 5,15-transition dipole and
the other component with the perpendicular 10,20-transition
dipole. The 5,15-transition dipole is perpendicular to the long
molecular axis of the porphyrin-array donor, while the 10,20-
transition dipole is parallel to it. Since all the porphyrins in the
array have a transition dipole parallel to the array axis in the
donor state for the EET, they do not interact with the former at
the acceptor porphyrin at least in the transition-dipole ap-
proximation. Therefore, we consider that the observed rapid EET
from the donor to the acceptor takes place via the S1 component
with the 10,20-transition dipole at the acceptor porphyrin.
The traditional theory on the EET rate constant is Fo¨rster’s
one,19 which considers that EET arises by the electrostatic
interaction between transition dipoles at the donor and the
N
2
π
2
π
sin
n µ )
cot
µ
(3)
∑
(
)
(
)
x
x
N + 1n)1
N + 1
N + 1
2N + 2
where µ represents the magnitude of the S1 transition dipole of
a single porphyrin.
Next, we consider the acceptor state of the EET at the 5,-
15-bisphenylethynyl porphyrin. The attachment of phenyl-
acethylene moieties at the 5 and 15 positions breaks the 2-fold
degeneracy of the S1 transitions at the acceptor porphyrin in
such a way that the component with a transition dipole parallel
to the 5,15 direction becomes the lowest excited state.13a EET
from the donor takes place with energies of its fluorescence
spectrum as long as it overlaps the absorption spectrum of the
acceptor. In the present case, the fluorescence spectrum of the
(19) (a) Fo¨rster, T. Ann. Phys. 1948, 2, 55. (b) Fo¨rster, T. Discuss. Faraday
Soc. 1959, 27, 7.
9
J. AM. CHEM. SOC. VOL. 125, NO. 32, 2003 9675

A R T I C L E S
Aratani et al.
Figure 6. Femtosecond transient absorption anisotropy decays of (a) Z1A, (b) Z2A, (c) Z3A, and (d) Z6A.
acceptor. In the present problem, the donor is regarded as the
tightly bound entire porphyrin array with a single total transition
dipole of eq 3 parallel to the array axis and located at the center
of the array. Its EET interaction with the 10,20-transition dipole
on the acceptor porphyrin is given by [2/(N + 1)]1/2 cot[π/(2N
+ 2)](R1/R)3J, where R represents the distance from the acceptor
porphyrin to the center of the porphyrin array and R1 and J
represent, respectively, the distance and the EET coupling in
Z1A for N ) 1. Fo¨rster’s formula is given by the lowest (i.e.,
second-order) perturbation in the EET interaction, that is, by
Fermi’s Golden Rule.8c The rate constant for the EET obtained
is given by
The value of J is concerned with the actual degree of mixture
of the S1 component with the 10,20-transition dipole in the
acceptor state. Instead of actually calculating the degree of the
mixture, let us be content with estimating J as an effective EET
coupling from the observed value of k1, since J is practically
more useful. For N ) 1, eq 4 reduces to
2π
p
k1 ) J2 I (E)L (E) dE
(6)
∫
a
1
We observed k1 ) (∼2.5 ps)-1, and also ∫Ia(E)L1(E) dE, called
Fo¨rster’s overlap integral, to be (∼2500 cm-1 -1
) . These values
enable us to derive J ≈ 29 cm-1 from eq 6.
6
4πJ2
p(N + 1)
π
R1
cot2
I (E)L (E) dE (4)
a N
Dependence of the EET rate constant on the number (N) of
porphyrins in the donor-array manifests itself most purified in
the ratio of kN/k1, which is given by
kN )
∫
)
( )
(
R
2N + 2
where Ia(E) and LN(E) represent respectively the absorption
spectrum of the acceptor porphyrin and the fluorescence
spectrum of the array of N porphyrins as the donor, both being
normalized as
6
I (E)L (E) dE
∫
kN
R1
a
N
2
π
)
cot2
(7)
( )
(
)
k1 N + 1 R
2N + 2
I (E)L (E) dE
∫
a
1
I (E) dE ) L (E) dE ) 1
(5)
∫
∫
a
N
In kN of eq 4, both the effective EET coupling J in Z1A and
Fo¨rster’s overlap integral have some ambiguities arising from
the approximation for Ia(E) mentioned below eq 5. The ratio of
kN/k1 does not include J, and also the ratio of Fo¨rster’s overlap
integrals at the right-hand end of eq 7 is nearly independent of
N with a magnitude of about 1.0 except for N ) 3 where it is
about 0.87. Therefore, the N dependence of kN/k1 can be used
as a check of theories for EET.
In eq 4, it has been assumed that the absorption spectrum of
the S1 component with the 5,15-transition dipole and that of
the other component with the perpendicular 10,20-transition
dipole on the acceptor porphyrin can be regarded as similar to
each other in the energy range covered by the fluorescence
spectrum of the porphyrin-array donor, both being approximated
as proportional to Ia(E).
9
9676 J. AM. CHEM. SOC. VOL. 125, NO. 32, 2003

Energy Donation of Meso−Meso Linked Zn(II) Porphyrin Array
A R T I C L E S
Table 1. Observed and Calculated EET Rate Constants
of the EET rate constant. In reality, individual porphyrins
coupled coherently with each other in the donor state of eq 1
carry well-defined transition dipoles whose vectorial sum gives
the total transition dipole of eq 3 appearing in Fo¨rster’s formula
of eq 4. These individual transition dipoles [2/(N + 1)]1/2 sin-
[πn/(N + 1)]µ for n ) 1, 2, ‚ ‚ ‚, N at each porphyrin in the
donor array interact with the transition dipole at the acceptor
porphyrin with different strengths because of differences in the
interaction distance. Interaction of the nth porphyrin in the array
is given by [2/(N + 1)]1/2 sin[πn/(N + 1)](R1/Rn)3J, where Rn
represents the center-to-center distance between the nth pro-
phyrin in the array and the acceptor porphyrin and J represents
the effective EET coupling between the n ) 1 porphyrin in the
array and the acceptor porphyrin in eq 6. Taking into account
the interaction of these transition dipoles with the acceptor
transition dipole, we get the correct total interaction strength
for EET between the porphyrin-array donor and the acceptor
porphyrin, as
a
model
R (Å)
kobs-1 b (ps)
kN-1 c (ps)
kN-1 d (ps)
kN-1 e (ps)
Z1A
Z2A
Z3A
Z6A
Z12A
Z24A
12.7
16.9
21.0
33.6
58.6
109
2.5 ( 0.1
3.3 ( 0.2
5.5 ( 0.5
21 ( 2
6.9
20
160
2300
49 000
5.0
7.5
15
30
60
3.4
5.9
23
70
163
63 ( 5
108 ( 7
a Center-to-center distances between the donor and the acceptor. b EET
rate constants measured by the transient absorption spectra. c EET rate
constants calculated by eq 7. d EET rate constants calculated by eq 8. e EET
rate constants calculated by eqs 13 and 14 for L ) 4.
The center-to-center distance R between the donor and the
acceptor was estimated by the CPK models, being listed in Table
1. For k1 ) (∼2.5 ps)-1, this eq 7 gives k2 ) (∼6.9 ps)-1, k3 )
(∼20 ps)-1, k6 ) (∼160 ps)-1, k12 ) (∼2.3 ns)-1, and k24
)
(∼49 ns)-1. These values are too small in comparison with the
observed ones, as shown also in Table 1. We see thus that the
observed data cannot be described by Fo¨rster’s theory. The rate
constant with the R-6 dependence therein decreases too rapidly
with R to reproduce the observed data.
3
N
R1
2
π
VN ) J
sin
n
(9)
∑
(
)( )
x
N + 1n)1
N + 1 Rn
Origins of inapplicability of Fo¨rster’s theory mentioned above
can be found in its two assumptions that excited states on the
porphyrin array are excitons which extend coherently over the
entire array and that the entire array can be regarded as a single
suprachromophore with a single transition dipole in the calcula-
tion of the EET rate constant. Concerning the first assumption,
it is very difficult to consider that the coherence length of an
exciton extends over the entire array for long models Z12A
and Z24A. As a limit for breaking the first assumption, let us
consider that excited states on the porphyrin array have no
coherence among porphyrins. In this limit, an excitation is
localized at a single porphyrin in the array, and it carries
correctly a single transition dipole. Considering further the weak-
coupling limit in the EET, excitations on the porphyrin array
are regarded as maintained in thermal equilibrium in the course
of EET from the donor to the acceptor. Since each porphyrin
in the array has the same excitation energy, an excitation can
be found at each porphyrin with the same probability given by
1/N in thermal equilibrium. An excitation found at the n ) 1
porphyrin can be transferred to the acceptor porphyrin with a
probability k1 given by eq 6, and that found at the n ) 2
porphyrin can be transferred with a probability of k1(R1/R2)6
where R2 represents the center-to-center distance between the
n ) 2 porphyrin in the array and the acceptor porphyrin. Since
(R1/R2)6 ) ∼0.049, we can neglect EET from an excitation
found at the n ) 2 porphyrin and also from that found at remoter
porphyrins for n g 3. Therefore, the rate constant for EET to
the acceptor porphyrin from the donor array composed of N
porphyrins is given by
Since (R1/R2)3 ) ∼0.22 and (R1/R3)3 ) ∼0.081, terms at least
for n ) 2 and 3 in the summation on the right-hand side cannot
be neglected in comparison with the term for n ) 1. On the
basis of Fermi’s Golden Rule,8c the rate constant for the EET
caused by VN of eq 9 is given by
2π
p
2
kN ) VN I (E)L (E) dE
(10)
∫
a
N
It must be taken into account also here that the coherence
length of an exciton in the donor array is not so long as the
entire array at least for Z12A and Z24A, because of decoherence
disturbances increasing in number with the array length.
Therefore, let us consider that the lowest exciton state on the
array can cover coherently at most L porphyrins. Accordingly,
it is only when N e L that we can use eq 10 with eq 9 for
describing the rate constant of the EET. When N > L, an exciton
with the coherence length L can be found at N - L + 1 locations
on the array composed of N porphyrins, with the same energy
given by eq 2 for N ) L therein. Considering the weak-coupling
limit in the EET, excitations on the porphyrin array are regarded
as maintained in thermal equilibrium in the course of EET from
the donor to the acceptor. In thermal equilibrium, each exciton
state can be realized with the same probability given by 1/(N
- L + 1). An exciton found at the location nearest to the
acceptor porphyrin transfers its excitation energy to the acceptor
with a probability of kL given by eq 10 for N ) L therein. An
exciton found at the location next nearest to the acceptor
porphyrin transfers its excitation energy with a probability of
kL′ given by eq 10 with VN therein changed into
kN ) k1/N
(8)
3
L
R1
2
π
For k1 ) (∼2.5 ps)-1, this eq 8 gives k2 ) (∼5.0 ps)-1, k3 )
VL′ ) J
sin
n
(11)
∑
(∼7.5 ps)-1, k6 ) (∼15 ps)-1, k12 ) (∼30 ps)-1, and k24
)
(
)(
)
x
N + 1n ) 1
N + 1 Rn+1
(∼60 ps)-1. These values are not very bad but differ consider-
ably from the observed EET rate constants (Table 1).
instead of VL for kL. Since kL′ has only a magnitude on the order
of (R1/R2)6 ()∼0.049) times as small as kL, we can neglect EET
from an exciton found at the next-nearest location and also
excitons found at remoter locations even if they exist. Therefore,
Let us check the second assumption in Fo¨rster’s formula that
the entire porphyrin array can be regarded as a single supra-
chromophore with a single transition dipole in the calculation
9
J. AM. CHEM. SOC. VOL. 125, NO. 32, 2003 9677

A R T I C L E S
Aratani et al.
we obtain the rate constant for EET to the acceptor porphyrin
from the array composed of N porphyrins as
physical size of the aggregate is not much smaller than the
average donor-acceptor distance. In this situation, Fo¨rster’s
formula is not correct in a sense that it deviates from the rate
constant of EET derived correctly from the lowest (i.e., second-
order) perturbational expansion in the EET coupling between
the donor and the acceptor, although Fo¨rster’s formula itself is
also second order in the coupling. Such a formula that is correct
in the weak-coupling limit has been presented by one of the
present authors, Sumi.8 It may be called a revised Fo¨rster
formula. It has successfully been applied to EET in the antenna
system of photosynthesis where the situation mentioned above
can widely be found.9 In fact, the rate constant of eq 10 with
eq 9 for the present problem corresponds to a special case in
the general formula for the rate constant of EET given in ref 8.
In the present models, the acceptor porphyrin is connected
with the adjacent porphyrin (P1) through a 1,4-phenylene spacer
with the center-to-center distance R1 ) ∼12.7 Å. P1 is naturally
the edge porphyrin in the donor array. Additional attachment
of the second porphyrin (P2) to Z1A leads to Z2A that has a
center-to-center donor-acceptor distance of R2 ) ∼21.0 Å. In
such situations, the EET interaction between two molecules
might have to be calculated more appropriately than by the
transition-dipole approximation. For example, it might be
calculated by the so-called monopole approximation22 with a
correct account of the spatial extension of the wave functions
in the excited states of the molecules or by taking into account
also electron-exchange effects. In these cases, the (R1/Rn)3
dependence of the terms for n g 2 in the summation on the
right-hand side of eq 9 might be a little revised. After such a
revision, these terms for n g 2 should still retain magnitudes
not negligible in comparison with the first term therein. This
situation is essential in reproducing the N dependence of the
observed EET rate constant by kN of the revised Fo¨rster’s
formula eq 10 with eq 9. On the contrary, eq 8 obtained by
completely neglecting the spatial coherence of the exciton state
gives kN considerably smaller than the observed ones, mainly
because it has been approximated in eq 8 to be only the n ) 1
porphyrin in the donor array that takes part in EET to the
acceptor porphyrin.
kN ) kL/(N - L + 1), for N > L
(12)
As mentioned earlier, the N dependence of the ratio kN/k1
can be used as a check of theories for EET. It is given by
kN
)
k1
3
2
I (E)L (E) dE
N
∫
∫
R1
a
N
2
π
sin
n
, for N e L
∑
(
)
( )
[
]
N + 1
N + 1 Rn
n)1
I (E)L (E) dE
a
1
(13)
and
kN/k1 ) (kL/k1)/(N - L + 1), for N > L.
(14)
We note here that eq 8 is a special case of eq 14 for L ) 1.
The coherent length L has been estimated to be about 4 on
the present porphyrin array.20,21 When L ) 4 and k1 ) (∼2.5
ps)-1, eqs 13 and 14 give k2 ) (∼3.4 ps)-1, k3 ) (∼5.9 ps)-1
k6 ) (∼23 ps)-1, k12 ) (∼70 ps)-1, and k24 ) (∼163 ps)-1
,
.
These values are in good agreement with the observed ones
except the longest model Z24A (Table 1). Therefore, this
approach seems most suitable in reproducing the observed rate
constants of EET from the porphyrin array to the acceptor
porphyrin.
The deviation of k24 from the observed value may be due to
a breakdown of the assumption that an exciton with a coherence
length L (∼4) can be found with the same probability at any
site in the entire porphyrin-array donor in thermal equilibrium
even when it has a number of porphyrins as many as 24. In
such a long donor array, a little slanting in the porphyrin-site
energy causes a substantial deviation from the assumed equal
distribution of exciton location. In the present case, donor
porphyrins near to the acceptor porphyrin could have site
energies lower than remoter porphyrins due to influence from
the acceptor porphyrins, and an exciton could be found more
on the former than on the latter in thermal equilibrium in a long
array. Such an unequal distribution in exciton location will give
a k24 larger than that given in Table 1. Increased conformational
heterogeneity in such a long array might be another cause for
this deviation. Such an effect may be also responsible for the
incomplete EET in Z24A.
If the center-to-center distance R1 between the n ) 1
porphyrin in the donor array and the acceptor porphyrin was
much larger than the total length ∆R of the donor array
composed of N porphyrins, differences among Rn’s could be
neglected on the right-hand side of eq 9. Accordingly, all the
Rn’s could be approximated by the distance R between the
acceptor porphyrin and the center of the porphyrin-array donor.
Thereby, eq 10 would reduce to eq 4 that can be obtained by
Fo¨rster’s formula. In reality, however, R1 () ∼12.7 Å) is not
much larger than ∆R () ∼8.3 Å) even for N ) 2, and eq 10
gives the kN value much different from eq 4, the difference
becoming enormous when N becomes larger. Such a difference
can be regarded as a size effect of the donor and/or the acceptor
for EET, where at least one of them is a molecular aggregate
whose excited states are excitons and simultaneously the
Conclusion
A series of meso-meso linked Zn(II) porphyrin arrays bearing
a 5,15-bisphenylethynylated Zn(II) porphyrin were prepared for
(20) Previously, the coherent length (L) in the S1-state of a meso-meso linked
Zn(II) porphyrin array has been estimated to be ∼5 on the basis of the
equation developed by Knoester (Bakalis, L. D.; Knoester, J. J. Phys. Chem.
B 1999, 103, 6620); L )
3π2|∆E |/γ - 1 by letting the coupling
x
strength |∆E0| ) 270 cm-1 and γ ) 2306 cm-1. The coupling strength was
estimated from the ratio of the absorption coefficients of Soret and Q-bands
1
in monomer (∼ /16). In this estimation, we only considered the dipole-
dipole interaction between porphyrin moieties and may neglect the coupling
originated from the through-bond effect. In the present work, we obtained
a coupling strength V of ∼ 570 cm-1 by plotting the peak positions of
Q-bands and fitting to the equation of Ek ) E0 + 2V cos(π/(N + 1)). Now,
L has been estimated to be ∼4 on the basis of the following equation
(Kakitani, T.; Kimura, A. J. Phys. Chem. A 2002, 106, 2173); L ) 1.38 +
1.33V/γ. This empirical formula seems to be more applicable in our
porphyrin array system because this model is based on the one-dimensional
linear array system.
(21) A detailed study on the energy relaxation dynamics of a meso,meso′-
dibrominated Zn(II) porphyrin array also predicts Nc ) ∼4; Ha, J. H.; Cho,
H. S.; Kim, D.; Aratani, N.; Osuka, A. Submitted for publication.
(22) (a) Chang, J. C. J. Chem. Phys. 1977, 67, 3901. (b) Warshel, A.; Parson,
W. W. J. Am. Chem. Soc. 1987, 109, 6143. (c) Parson, W. W.; Warshel,
A. J. Am. Chem. Soc. 1987, 109, 6152. (d) Nagae, H.; Kakitani, T.; Katoh,
T.; Mimuro, M. J. Chem. Phys. 1993, 98, 8012. (e) Alden, R. G.; Johnson,
E.; Nagarajan, V.; Parson, W. W.; Law, C. J.; Cogdell, R. G. J. Phys.
Chem. B, 1997, 101, 4667. (f) Krueger, B. P.; Scholes, G. D.; Fleming, G.
R. J. Phys. Chem. B, 1998, 102, 5378.
9
9678 J. AM. CHEM. SOC. VOL. 125, NO. 32, 2003

Energy Donation of Meso−Meso Linked Zn(II) Porphyrin Array
A R T I C L E S
which was again split into two parts. One part of the white light
continuum was overlapped with the pump beam at the sample to probe
the transient, while the other part of the beam was passed through the
sample without overlapping the pump beam. The time delay between
pump and probe beams was controlled by making the pump beam travel
along a variable optical delay line. The white light continuum beams
after the sample were sent to a 15 cm focal length spectrograph (Acton
Research) through each optical fiber and then detected by a dual-channel
512 channel photodiode array (Princeton Instruments). The intensity
of the white light continuum of each 512 channel photodiode array
was processed to calculate the absorption difference spectrum at the
desired time delay between pump and probe pulses. For the transient
absorption anisotropy decay (r(t)) measurements, the probe white light
continuum pulse was set to have vertical polarization by using a sheet
polarizer. Then, the excitation pulse was changed to have parallel or
perpendicular polarization by rotating a half wave plate centered at
400 nm with respect to the polarization of the probe pulse. Finally, the
transient absorption anisotropy decay can be obtained by the following
equation.
the examination of EET systems involving a strongly coupled
array of donor or acceptor. In all the model compounds including
Z24A, the efficient intramolecular EET processes have been
proven by the steady-state fluorescence measurement as well
as the time-resolved transient absorption spectroscopy and
ultrafast anisotropy decay measurements. The EET is almost
quantitative in Z1A to Z12A but is competitive in Z24A. Long-
distance yet efficient EET processes are realized through the
exciton states whose coherence is extended over several
porphyrin pigments in the meso-meso linked Zn(II) porphyrin
arrays, as such in the natural photosynthetic light harvesting
systems such as chlorosomes, LH1, and LH2. This strategy is
very useful for the design of efficient artificial EET systems in
the future. For these EET systems involving an aggregate,
Sumi’s revised Fo¨rster formula has been demonstrated to be
useful for the analysis. These results may encourage further
application of meso-meso linked porphyrin arrays for even
longer EET and directed EET from a well-defined donor to an
acceptor over an extremely long distance, since such a long
array is now available in a discrete form. Finally, advantages
of strongly coupled arrays of chromophores in antenna function
should be emphasized in terms of fast EET and large absorption
cross-section unless forming an energy-wasting sink.
∆A| - ∆A
r(t) )
(15)
∆A| + 2∆A
5-[4-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl]-15-(3,5-
dioctyloxyphenyl)porphyrin 1. 4-(4,4,5,5-Tetramethyl-1,3,2-diox-
aborolan-2-yl)benzaldehyde was prepared from 4-formylphenylboronic
acid and 2,3-dimethyl-2,3-butandiol (pinacol, 1.2 equiv) by using a
Dean-Stark trap apparatus in 92% yield. A solution of 2,2′-dipyrryl-
methane23 (1.40 g, 9.50 mmol), 3,5-dioctyloxybenzaldehyde (1.74 g,
4.75 mmol), and the boronate-appended benzaldehyde (1.10 g, 4.75
mmol) in dry CH2Cl2 (1.5 L) was stirred under N2 and shielded from
light. Trifluoroacetic acid (TFA) (0.460 mL, 5.60 mmol) was added
via syringe, and the solution was stirred for 3 h at room temperature.
DDQ (3.78 g, 16.6 mmol) was added to the solution, and the resulting
solution was stirred for an additional 3 h. After the reaction mixture
was neutralized by triethylamine and passed over a short silica gel
column to remove polymeric materials, the solvent was removed by a
rotary evaporator and the residue was separated by silica gel column
chromatography with CH2Cl2/n-hexane. The first fraction was 5,15-
bis(3,5-dioctyloxyphenyl)porphyrin, and the second fraction was the
desired porphyrin 2. The product was recrystallized from CH2Cl2-
MeOH. Yield; 541 mg, 13%. 1H NMR (CDCl3) δ 10.30 (s, 2 H, meso),
9.38 (d, J ) 5 Hz, 4 H, â), 9.19 (d, J ) 4 Hz, 2 H, â), 9.07 (d, J ) 5
Hz, 2 H, â), 8.30 (d, J ) 8 Hz, 2 H, Ar), 8.26 (d, J ) 8 Hz, 2 H, Ar),
7.43 (d, J ) 3 Hz, 1 H, Ar), 6.93 (t, J ) 3 Hz, 2 H, Ar), 4.16 (t, J )
7 Hz, 4 H, octyloxy), 1.90 (t-t, J ) 7 Hz, 4 H, octyloxy), 1.38-1.27
(m, 20 H, octyloxy), 0.88 (t, J ) 7 Hz, 6 H, octyloxy), and -3.11 (s,
2 H, N-H); FAB MS m/z 844.1, calcd for C54H65B1N4O4 m/z 844.5.
5,15-Dibromo-10-[4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
phenyl]-20-(3,5-dioctyloxyphenyl)porphyrin Zinc(II) 2. The por-
phyrin 1 (200 mg, 0.237 mmol) was dissolved in a mixture of CHCl3
(100 mL) and pyridine (0.5 mL). NBS (0.480 mmol) was added to
this solution, and the resulting solution was stirred for 2 h at 0 °C. The
mixture was poured into water and extracted with CHCl3. The combined
organic extracts were dried over anhydrous Na2SO4. A saturated solution
of Zn(OAc)2 in MeOH was added to the solution, and the resulting
mixture was stirred for 2 h. The mixture was poured into water and
extracted with CHCl3. After the combined organic extracts were dried
over Na2SO4, the solvent was removed by a rotary evaporator and the
residue was purified by silica gel column chromatography with CH2-
Cl2. The product was recrystallized from CHCl3-MeOH. Yield; 232
Experimental Section
General Procedure. All reagents and solvents were of the com-
mercial reagent grade and were used without further purification except
when noted. Dry toluene and DMF were obtained by distillation. H
1
NMR spectra were recorded on a JEOL ALPHA-500 spectrometer, and
chemical shifts were reported as the delta scale in ppm relative to CHCl3
(δ ) 7.260). The spectroscopic grade THF was used as solvent for the
spectroscopic measurements. UV-visible absorption spectra were
recorded on a Shimadzu UV-2400PC spectrometer. Steady-state
fluorescence emission spectra were recorded on a Shimadzu RF-5300PC
spectrometer. Mass spectra were recorded on a JEOL HX-110
spectrometer, using a positive-FAB ionization method with accelerating
voltage 10 kV and a 3-nitrobenzyl alcohol matrix, and/or on a
Shimadzu/KRATOS KOMPACT MALDI4 spectrometer, using a
positive-MALDI-TOF method. Preparative separations were performed
by silica gel flash column chromatography (Merck Kieselgel 60 H Art.
7736) and silica gel gravity column chromatography (Wakogel C-200).
Recycling preparative GPC-HPLC was carried out on a JAI LC-908
model using a combination of preparative JAI-GEL-3H and 2.5H
columns for Z1A-Z6A, JAI-GEL 4H, 3H, and 2.5H for Z12A, and
JAI-GEL 4H, 3H, and 3H for Z24A (chloroform eluant; flow rate 3.8
mL min-1).
The dual-beam femtosecond time-resolved transient absorption
spectrometer consisted of a self-mode-locked femtosecond Ti:sapphire
oscillator (Coherent, MIRA), a Ti:sapphire regenerative amplifier (Clark
MXR, CPA-1000) pumped by a Q-switched Nd:YAG laser (Clark
MXR, ORC-1000), a pulse stretcher/compressor, OPA (Light Conver-
sion, TOPAS) system, and an optical detection system. A femtosecond
Ti:sapphire oscillator pumped by a CW Nd:YVO4 laser (Coherent,
Verdi) produces a train of ∼80 fs mode-locked pulses with an averaged
power of 650 mW at 800 nm. The amplified output beam regenerated
by chirped pulse amplification (CPA) had ca. 150 fs pulse width and
an average power of ca. 1 W at 1 kHz repetition rate, which was divided
into two parts by a 1:1 beam splitter. One was color-tuned for the pump
beam by an optical parametric generation and amplification (OPG-
OPA) technique. The resulting laser pulse had a temporal width of
∼150 fs in the UV/Vis/IR range. The pump beam was focused to a 1
mm diameter spot, and the laser fluence was adjusted to avoid damage
to the sample by using a variable neutral-density filter. The other was
focused onto a flowing water cell to generate a white light continuum,
1
mg, 92%. H NMR (CDCl3) δ 9.70 (m, J ) 5 Hz, 4 H, â), 9.05 (d, J
) 5 Hz, 2 H, â), 8.91 (d, J ) 5 Hz, 2 H, â), 8.21 (d, J ) 8 Hz, 2 H,
Ar), 8.17 (d, J ) 8 Hz, 2 H, Ar), 7.32 (d, J ) 3 Hz, 2 H, Ar), 6.90 (t,
(23) Ka, J.-W.; Lee, C.-H. Tetrahedron Lett. 2000, 41, 4609.
9
J. AM. CHEM. SOC. VOL. 125, NO. 32, 2003 9679

A R T I C L E S
Aratani et al.
J ) 3 Hz, 1 H, Ar), 4.13 (t, J ) 7 Hz, 4 H, octyloxy), 1.88 (t-t, J )
7 Hz, 4 H, octyloxy), 1.38-1.26 (m, 20 H, octyloxy), and 0.87 (t, J )
7 Hz, 6 H, octyloxy); FAB MS m/z 1064.25, calcd for C54H61B1Br2N4O4-
Zn m/z 1064.24.
H, octyloxy), 0.88 (t, J ) 7 Hz, 6 H, octyloxy), and 0.80 (t, J ) 7 Hz,
24 H, octyloxy); MALDI-TOF MS m/z 3056.7, calcd for C192H224N12O10-
Zn3 m/z 3055.5; UV-vis (THF) λmax 423, 448, 465, 564, 604, and 649
nm; Fluorescence (THF, λex ) 564 nm) λem 655 and 716 nm.
5-[4-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl]-10,20-
bis(phenylethynyl)-15-(3,5-dioctyloxyphenyl)porphyrin Zinc(II) 3.
The bromoporphyrin 2 (200 mg, 0.19 mmol) and phenylacetylene (153
mg, 1.50 mmol) were dissolved in a mixture of dry toluene (20 mL)
and triethylamine (4 mL), and this solution was purged with Ar for 30
min. Pd(PPh3)2Cl2 (30 mg) and CuI (12 mg) were added, and the
resulting solution was heated at 50 °C for 3 h under Ar. After the
reaction mixture was filtered, the filtrate was separated by chromatog-
raphy on a silica gel column (eluant CH2Cl2/n-hexane) to give 3. The
product was recrystallized from CH2Cl2-MeOH. Yield; 132 mg, 64%.
1H NMR (CDCl3) δ 9.70 (d, J ) 5 Hz, 2 H, â), 9.69 (d, J ) 5 Hz, 2
H, â), 9.04 (d, J ) 5 Hz, 2 H, â), 8.89 (d, J ) 5 Hz, 2 H, â), 8.22 (m,
4 H, Ar), 7.95 (d, J ) 8 Hz, 4 H, Ph), 7.52 (t, J ) 7 Hz, 4 H, Ph), 7.44
(t, J ) 8 Hz, 2 H, Ph), 7.36 (d, J ) 3 Hz, 2 H, Ar), 6.89 (t, J ) 3 Hz,
1 H, Ar), 4.14 (t, J ) 7 Hz, 4 H, octyloxy), 1.89 (t-t, J ) 7 Hz, 4 H,
octyloxy), 1.51-1.28 (m, 20 H, octyloxy), and 0.86 (t, J ) 7 Hz, 6 H,
octyloxy); FAB MS m/z 1106.6, calcd for C70H71B1N4O4Zn m/z 1106.5;
UV-vis (THF) λmax 448 and 648 nm.
General Procedure for Preparation of ZnA via Palladium-
Catalyzed Cross-Coupling. Brominated meso-meso linked Zn(II) 5,-
15-bis(3,5-dioctyloxyphenyl)porphyrin arrays, porphyrin boronate 3,
Cs2CO3 (1.5 equiv for 3), and Pd(PPh3)4 (10 mol % for the bromopor-
phyrin) were dissolved in a mixture of dry DMF and toluene. The
solution was deoxygenated three times via freeze-pump-thaw degas
cycles, and the resulting mixture was heated at 80-90 °C for 3 h under
Ar. At the endpoint, the reaction was quenched with water and extracted
with ether. The organic layer was dried over anhydrous Na2SO4, passed
through a short silica gel column, and evaporated. The product
separation was performed on a preparative size exclusion column.
Larger oligomers elute first, and then smaller oligomers were separated.
Selected physical properties and detailed isolation procedures are
presented below.
Z3A. (37%) 1H NMR (CDCl3) δ 10.40 (s, 1H, meso), 10.00 (d, J )
5 Hz, 2 H, â), 9.87 (d, J ) 5 Hz, 2 H, â), 9.54 (d, J ) 5 Hz, 2 H, â),
9.51 (d, J ) 5 Hz, 2 H, â), 9.48 (d, J ) 5 Hz, 2 H, â), 9.38 (d, J ) 5
Hz, 2 H, â), 9.30 (d, J ) 5 Hz, 2 H, â), 9.14 (d, J ) 5 Hz, 2 H, â),
8.93 (d, J ) 5 Hz, 2 H, â), 8.91 (d, J ) 5 Hz, 2 H, â), 8.86 (d, J ) 5
Hz, 2 H, â), 8.82 (d, J ) 5 Hz, 2 H, â), 8.77 (d, J ) 8 Hz, 2 H, Ar),
8.69 (d, J ) 8 Hz, 2 H, Ar), 8.28 (d, J ) 5 Hz, 2 H, â), 8.26 (d, J )
5 Hz, 2 H, â), 8.23 (d, J ) 5 Hz, 2 H, â), 8.15-8.12 (m, 6 H, â + Ph),
7.64 (t, J ) 7 Hz, 4 H, Ph), 7.55 (t, J ) 8 Hz, 2 H, Ph), 7.54 (d, J )
3 Hz, 4 H, Ar), 7.46 (d, J ) 3 Hz, 4 H, Ar), 7.43 (d, J ) 3 Hz, 2 H,
Ar), 7.41 (d, J ) 3 Hz, 4 H, Ar), 6.96 (t, J ) 3 Hz, 1 H, Ar), 6.90 (t,
J ) 3 Hz, 2 H, Ar), 6.85 (t, J ) 3 Hz, 2 H, Ar), 6.69 (t, J ) 3 Hz, 2
H, Ar), 4.20 (t, J ) 7 Hz, 4 H, octyloxy), 4.15-4.09 (m, 16 H,
octyloxy), 3.98 (t, J ) 7 Hz, 8 H, octyloxy), 1.93 (t-t, J ) 7 Hz, 4 H,
octyloxy), 1.84 (t-t, J ) 7 Hz, 16 H, octyloxy), 1.71 (t-t, J ) 7 Hz,
8 H, octyloxy), 1.55-1.15 (m, 140 H, octyloxy), and 0.92-0.72 (m,
42 H, octyloxy); MALDI-TOF MS m/z 4094.9, calcd for C256H306N16O14-
Zn4 m/z 4092.9; UV-vis (THF) λmax 418, 448, 480, 573, and 649 nm;
Fluorescence (THF, λex ) 560 nm) λem 655 and 715 nm.
1
Z6A. (10%) H NMR (CDCl3) δ 10.41 (s, 1 H, meso), 10.03 (d, J
) 5 Hz, 2 H, â), 9.87 (d, J ) 5 Hz, 2 H, â), 9.56 (d, J ) 5 Hz, 2 H,
â), 9.52 (d, J ) 5 Hz, 2 H, â), 9.48 (d, J ) 5 Hz, 2 H, â), 9.40 (d, J
) 5 Hz, 2 H, â), 9.30 (d, J ) 5 Hz, 2 H, â), 9.14 (d, J ) 5 Hz, 2 H,
â), 8.96-8.90 (m, 18 H, â), 8.84 (d, J ) 5 Hz, 2 H, â), 8.78 (d, J )
8 Hz, 2 H, Ar), 8.69 (d, J ) 8 Hz, 2 H, Ar), 8.35-8.31 (m, 14 H, â),
8.28 (d, J ) 5 Hz, 2 H, â), 8.26 (d, J ) 5 Hz, 2 H, â), 8.16 (d, J ) 5
Hz, 2 H, â), 8.13 (d, J ) 8 Hz, 4 H, Ph), 7.64 (t, J ) 7 Hz, 4 H, Ph),
7.56 (d, J ) 3 Hz, 4 H, Ar), 7.55 (t, J ) 8 Hz, 2 H, Ph), 7.49-7.48
(m, 16 H, Ar), 7.45 (d, J ) 3 Hz, 4 H, Ar), 7.43 (d, J ) 3 Hz, 2 H,
Ar), 6.96 (t, J ) 3 Hz, 1 H, Ar), 6.90 (t, J ) 3 Hz, 2 H, Ar), 6.85 (t,
J ) 3 Hz, 2 H, Ar), 6.77-6.72 (m, 8 H, Ar), 4.20-4.04 (m, 52 H,
octyloxy), 1.89-1.19 (m, 312 H, octyloxy), and 0.91-0.74 (m, 78 H,
octyloxy); MALDI-TOF MS m/z 7203.8, calcd for C448H552N28O26Zn7
m/z 7203.2; UV-vis (THF) λmax 417, 448, 499, 582, and 649 nm;
Fluorescence (THF, λex ) 560 nm) λem 654 and 717 nm.
Z1A. A round-bottomed flask was charged with 3 (11 mg, 0.0099
mmol), 5-bromo-10,20-bis(3,5-dioctyloxyphenyl)porphyrin (5.0 mg,
0.0041 mmol), Cs2CO3, Pd-catalyst, dry toluene(2 mL), and dry DMF
(1 mL). After the usual workup, the oligomers were separated by an
SEC. Fractions of 2-mer and 1-mer were separated, and the solvent
was removed by a rotary evaporator. The desired product was a dark
1
Z12A. (34%) H NMR (CDCl3) δ 10.41 (s, 1H, meso), 10.03 (d, J
) 5 Hz, 2 H, â), 9.87 (d, J ) 5 Hz, 2 H, â), 9.56 (d, J ) 5 Hz, 2 H,
â), 9.52 (d, J ) 5 Hz, 2 H, â), 9.48 (d, J ) 5 Hz, 2 H, â), 9.40 (d, J
) 5 Hz, 2 H, â), 9.30 (d, J ) 5 Hz, 2 H, â), 9.14 (d, J ) 5 Hz, 2 H,
â), 8.96-8.90 (m, 42 H, â), 8.84 (d, J ) 5 Hz, 2 H, â), 8.78 (d, J )
8 Hz, 2 H, Ar), 8.69 (d, J ) 8 Hz, 2 H, Ar), 8.35-8.31 (m, 38 H, â),
8.28 (d, J ) 5 Hz, 2 H, â), 8.26 (d, J ) 5 Hz, 2 H, â), 8.16 (d, J ) 5
Hz, 2 H, â), 8.13 (d, J ) 8 Hz, 4 H, Ph), 7.64 (t, J ) 7 Hz, 4 H, Ph),
7.56-7.48 (m, 52 H, Ar), 6.96 (t, J ) 3 Hz, 1 H, Ar), 6.90 (t, J ) 3
Hz, 2 H, Ar), 6.85 (t, J ) 3 Hz, 2 H, Ar), 6.77-6.72 (m, 20 H, Ar),
4.20-4.04 (m, 100 H, octyloxy), 1.89-1.19 (m, 600 H, octyloxy), and
0.91-0.74 (m, 150 H, octyloxy); MALDI-TOF MS m/z 13423, calcd
for C832H1044N52O50Zn13 m/z 13423.9; UV-vis (THF) λmax 415, 448,
506, 586, and 649 nm; Fluorescence (THF, λex ) 560 nm) λem 654 and
717 nm.
1
green solid in 77% yield. H NMR (CDCl3) δ 10.32 (s, 1 H, meso),
10.00 (d, J ) 5 Hz, 2 H, â), 9.84 (d, J ) 5 Hz, 2 H, â), 9.47-9.45 (m,
4 H, â), 9.42 (d, J ) 5 Hz, 2 H, â), 9.35 (d, J ) 5 Hz, 2 H, â), 9.30
(d, J ) 5 Hz, 2 H, â), 9.11 (d, J ) 5 Hz, 2 H, â), 8.66 (d, J ) 8 Hz,
2 H, Ar), 8.61 (d, J ) 8 Hz, 2 H, Ar), 8.11 (d, J ) 7 Hz, 4 H, Ph),
7.61 (t, J ) 7 Hz, 4 H, Ph), 7.54-7.51 (m, 6 H, Ar + Ph), 7.42 (d, J
) 3 Hz, 2 H, Ar), 6.97 (t, J ) 3 Hz, 2 H, Ar), 6.94 (t, J ) 3 Hz, 1 H,
Ar), 4.21-4.19 (m, 12 H, octyloxy), 1.93-1.90 (m, 12 H, octyloxy),
1.51-1.27 (m, 60 H, octyloxy), and 0.87 (t, J ) 7 Hz, 18 H, octyloxy);
MALDI-TOF MS m/z 2020.7, calcd for C128H142N8O6Zn2 m/z 2019.0;
UV-vis (THF) λmax 419, 448, 550, 590, and 650 nm; Fluorescence
(THF, λex ) 550 nm) λem 654 and 716 nm.
1
1
Z2A. (76%) H NMR (CDCl3) δ 10.40 (s, 1 H, meso), 10.01 (d, J
Z24A. (28%) H NMR (CDCl3) δ 10.42 (s, 1H, meso), 10.04 (d, J
) 5 Hz, 2 H, â), 9.86 (d, J ) 5 Hz, 2 H, â), 9.52 (d, J ) 5 Hz, 2 H,
â), 9.50 (d, J ) 5 Hz, 2 H, â), 9.45 (d, J ) 5 Hz, 2 H, â), 9.35 (d, J
) 5 Hz, 2 H, â), 9.28 (d, J ) 5 Hz, 2 H, â), 9.13 (d, J ) 5 Hz, 2 H,
â), 8.86 (d, J ) 5 Hz, 2 H, â), 8.84 (d, J ) 5 Hz, 2 H, â), 8.75 (d, J
) 8 Hz, 2 H, Ar), 8.66 (d, J ) 8 Hz, 2 H, Ar), 8.18 (d, J ) 5 Hz, 2
H, â), 8.12-8.10 (m, 6 H, â + Ph), 7.61 (t, J ) 7 Hz, 4 H, Ph), 7.54
(t, J ) 8 Hz, 2 H, Ph), 7.50 (d, J ) 3 Hz, 4 H, Ar), 7.44 (d, J ) 3 Hz,
4 H, Ar), 7.43 (d, J ) 3 Hz, 2 H, Ar), 6.95 (t, J ) 3 Hz, 1 H, Ar), 6.85
(t, J ) 3 Hz, 2 H, Ar), 6.82 (t, J ) 3 Hz, 2 H, Ar), 4.19 (t, J ) 7 Hz,
4 H, octyloxy), 4.10 (m, 16 H, octyloxy), 1.92 (t, J ) 7 Hz, 4 H,
octyloxy), 1.81 (t-t, J ) 7 Hz, 16 H, octyloxy), 1.51-1.22 (m, 100
) 5 Hz, 2 H, â), 9.87 (d, J ) 5 Hz, 2 H, â), 9.56 (d, J ) 5 Hz, 2H,
â), 9.52 (d, J ) 5 Hz, 2 H, â), 9.48 (d, J ) 5 Hz, 2 H, â), 9.40 (d, J
) 5 Hz, 2 H, â), 9.30 (d, J ) 5 Hz, 2 H, â), 9.14 (d, J ) 5 Hz, 2 H,
â), 8.96-8.90 (m, 90 H, â), 8.84 (d, J ) 5 Hz, 2 H, â), 8.78 (d, J )
8 Hz, 2 H, Ar), 8.69 (d, J ) 8 Hz, 2 H, Ar), 8.35-8.31 (m, 86 H, â),
8.28 (d, J ) 5 Hz, 2 H, â), 8.26 (d, J ) 5 Hz, 2 H, â), 8.16 (d, J ) 5
Hz, 2 H, â), 8.13 (d, J ) 8 Hz, 4H, Ph), 7.64 (t, J ) 7 Hz, 4 H, Ph),
7.56-7.48 (m, 100 H, Ar), 6.96 (t, J ) 3 Hz, 1 H, Ar), 6.90 (t, J ) 3
Hz, 2 H, Ar), 6.85 (t, J ) 3 Hz, 2 H, Ar), 6.77-6.72 (m, 44 H, Ar),
4.20-4.04 (m, 196 H, octyloxy), 1.89-1.19 (m, 1176 H, octyloxy),
and 0.91-0.74 (m, 294 H, octyloxy); MALDI-TOF MS m/z 25862,
9
9680 J. AM. CHEM. SOC. VOL. 125, NO. 32, 2003

Energy Donation of Meso−Meso Linked Zn(II) Porphyrin Array
A R T I C L E S
calcd for C1600H2028N100O98Zn25 m/z 25865.1; UV-vis (THF) λmax 415,
448, 509, 588, and 649 nm; Fluorescence (THF, λex ) 560 nm) λem
654 and 717 nm.
Supporting Information Available: The GPC chromatogram
for Z24A, the absorption spectra and the fluorescence spectra
of ZnA taken upon excitation with the absorbance adjusted,
the transient absorption spectra at magic angle of Z1A and Z2A,
and the steady-state fluorescence anisotropy spectra of Z1A-
Z6A. This material is available free of charge via the Internet
at http://pubs.acs.org.
Acknowledgment. This work was supported by Grant-in-
Aid for Scientific Research (No. 1123205 and No. 12440196).
The work at Yonsei University was financially supported by
the Creative Research Initiatives Program of the Ministry of
Science and Technology of Korea. N.A. thanks the JSPS
Research Fellowship for Young Scientists. We thank Ms.
Victoria Browne for helpful discussions.
JA030002U
9
J. AM. CHEM. SOC. VOL. 125, NO. 32, 2003 9681