Porphyrin arrays responsive to additives. Fluorescence tuning

Article abstract of DOI:10.1021/ja809851d

The application of low-flux sunlight begins with the synthesis of effective antenna systems. This requires the development of dye integrates with optimized dye orientation for effective energy transfer. We here report a series of peptide-linked porphyrin arrays, denoted by Boc-(Por^Zn,S) _n-OBu^t (n = 2, 4, and 8), that change their dye orientation to increase fluorescence responsively to additive reagents. The B-band absorption (AB) regions of the arrays show blue shifts (dimer, 407.6 nm; tetramer, 408.2 nm; octamer, 407.8 nm) in organic solvents as compared to that of Boc-Por^Zn,S-OBu^t (monomer, 422.6 nm) and the fluorescence yield Φ? of the arrays decreases with increasing n, obeying the relationship Φ? = 0.03/n^1.5.; however, the arrays are tuned up in fluorescence emission by the addition of 1,2-diaminoethane (en). The addition of a sufficient amount of en increases the fluorescence of the porphyrins in monomer, dimer, tetramer, and octamer by ～5, ～12, ～12, and >730 times, respectively, when compared with that observed in the absence of en. This also causes asymptotic red shifts in absorption (AB) bands (B-band λ_max: 410 to 429-430 nm), as well as changes in circular dichroism (CD) spectra, and makes porphyrins approach new mutual asymmetric orientations. Our results show the potentiality of the tunable dye polymers that are a posteriori optimized in dye orientation and fluorescence emission by additive reagents for the development of effective light-harvesting materials.

Full text of DOI:10.1021/ja809851d

Published on Web 08/03/2009
Porphyrin Arrays Responsive to Additives. Fluorescence
Tuning
,
†
†
†
‡
Takeshi Yamamura,* Shingo Suzuki, Tomotaka Taguchi, Akira Onoda,
§
⊥
Toshiaki Kamachi, and Ichiro Okura
Department of Chemistry, Faculty of Science, Science UniVersity of Tokyo, Kagurazaka,
Shinjuku-ku, Tokyo 162-0825, Japan, Department of Applied Chemistry, Graduate School of
Engineering, Osaka UniVersity, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan, Department of
Molecular Design and Engineering, Graduate School of Engineering, Nagoya UniVersity,
Chikusa, Nagoya 464-8603, Japan, and Department of Bioscience and Biotechnology,
Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama-shi,
Kanagawa Pref. 226-8501, Japan
Received December 20, 2008; E-mail: tyamamur@rs.kagu.tus.ac.jp
Abstract: The application of low-flux sunlight begins with the synthesis of effective antenna systems. This
requires the development of dye integrates with optimized dye orientation for effective energy transfer. We
here report a series of peptide-linked porphyrin arrays, denoted by Boc-(PorZn,S
)
-OBu (n ) 2, 4, and 8),
t
n
that change their dye orientation to increase fluorescence responsively to additive reagents. The B-band
absorption (AB) regions of the arrays show blue shifts (dimer, 407.6 nm; tetramer, 408.2 nm; octamer,
Zn,S
t
4
07.8 nm) in organic solvents as compared to that of Boc-Por -OBu (monomer, 422.6 nm) and the
1.5
fluorescence yield Φ′ of the arrays decreases with increasing n, obeying the relationship Φ′ ) 0.03/n
;
however, the arrays are tuned up in fluorescence emission by the addition of 1,2-diaminoethane (en). The
addition of a sufficient amount of en increases the fluorescence of the porphyrins in monomer, dimer,
tetramer, and octamer by ∼5, ∼12, ∼12, and >730 times, respectively, when compared with that observed
in the absence of en. This also causes asymptotic red shifts in absorption (AB) bands (B-band λmax: 410
to 429-430 nm), as well as changes in circular dichroism (CD) spectra, and makes porphyrins approach
new mutual asymmetric orientations. Our results show the potentiality of the tunable dye polymers that are
a posteriori optimized in dye orientation and fluorescence emission by additive reagents for the development
of effective light-harvesting materials.
1
. Introduction
The application of low-flux sunlight begins with the synthesis
systems mimicked by chemists for the synthesis of artificial
light-harvesting systems. The beautiful arrangement of Chls
observed in these systems led to the introduction of π-π stacked
of effective antenna systems. This requires the development of
dye integrates equipped with optimized dye orientation for
effective energy transfer. However, photon energies absorbed
in integrated dye systems are easily lost through thermal
quenching when the mutual orientations of the dyes are
unsuitable for energy transfer. Therefore, it is required to
develop dye integrates that achieve optimal orientations for
effective energy transfer. Antenna chlorophylls (Chls) observed
in LH1, LH2, chlorosomes, green plants, and cyanobac-
teria, as well as that of Fenna-Matthews-Olson (FMO)
proteins, are good solutions to this orientation control problem.
Among these natural systems, LH1 and LH2 were the first
8
-10
and flat-ring arrays of porphyrins.
On the other hand, the antenna Chls of cyanobacteria, green
plants, and FMO are not π-π-stacked. The nearest-neighbor
Chls of these light-harvesting systems are asymmetrically
1
2
3,4
5
(4) Amakawa, M.; Tamiaki, H. Bioorg. Med. Chem. 1999, 7, 1141–1144.
(
5) (a) Liu, Z.-f.; Yan, H.-c.; Wang, K.; Kuang, T.-g.; Zhang, J.-p.; Gui,
L.-l.; An, X.-m.; Chang, W.-r. Nature 2004, 428, 287–292. (b) Hino,
T.; Kanamori, E.; Shen, J.-R.; Kouyama, T. Acta Crystallogr. 2004,
D60, 803–809.
6
7
(
6) (a) Krauss, N.; Schubert, W. D.; Klukas, O.; Fromme, P.; Witt, H. T.;
Saenger, W. Nat. Struct. Biol. 1996, 3, 965–973. (b) Ferreira, K. N.;
Iverson, T. M.; Maghlaoul, K.; Barber, J.; Iwata, S. Science 2004,
303, 1831–1838. (c) Loll, B.; Kern, J.; Saenger, W.; Zouni, A.;
Biesiadka, J. Nature 2005, 438, 1040–1044.
†
Science University of Tokyo.
Osaka University.
Nagoya University.
Tokyo Institute of Technology.
‡
§
⊥
(7) (a) Fenna, R. E.; Matthews, B. W. Nature 1975, 258, 573–577. (b)
Tronrud, D. E.; Schmidt, M. F.; Matthews, B. W. J. Mol. Biol. 1986,
261, 443–454.
(
(
1) Roszak, W.; Howard, T. D.; Southall, J.; Gardinar, A. T.; Law, C. J.;
Isaaks, N. W.; Cogdell, R. J. Science 2003, 302, 1969–1972.
2) (a) McDermott, G.; Prince, S. M.; Freer, A. A.; Hawthornthwaite-
Lawless, A. M.; Papiz, M. Z.; Cogdell, R. J.; Isaacs, N. W. Nature
(8) Takahashi, R.; Kobuke, Y. J. Am. Chem. Soc. 2003, 125, 2372–2373.
(9) Peng, X.; Aratani, N.; Takagi, A.; Matsumoto, T.; Kawai, T.; Hwang,
I.-W.; Ahn, T. K.; Kim, D.; Osuka, A. J. Am. Chem. Soc. 2004, 126,
4468–4469.
1
995, 374, 517–521. (b) Koepke, J.; Hu, X.; Muenke, C.; Schulten,
K.; Michel, H. Structure 1996, 4, 581–597.
(
3) Boer, I.; Matysik, J.; Amakawa, M.; Yagai, S.; Tamiaki, H.; Holzwarth,
(10) Hwang, I.-W.; Ko, D. M.; Ahn, T. K.; Yoon, Z. S.; Kim, D.; Peng,
X.; Aratani, N.; Osuka, A. J. Phys. Chem. B. 2005, 109, 8643–8651.
A. R.; de Groot, H. J. M. J. Am. Chem. Soc. 2003, 125, 13374–13375.
10.1021/ja809851d CCC: $40.75  2009 American Chemical Society
J. AM. CHEM. SOC. 2009, 131, 11719–11726 9 11719

A R T I C L E S
Yamamura et al.
1
1
aligned within the distance of 21 Å. They probably obey the
orientation rules that are different from those followed by LH1,
LH2, and chlorosomes. Recent pump-probe experiments on
alignments of porphyrins via covalent bonds, such as those
represented by dendritic porphyrins, peptide-linked porphy-
2
4
2
5
26
rins, polymerized porphyrins, metal-linked coordination
1
2
13
27
CP43 and two-dimensional spectroscopy on FMO, as well
as theoretical studies on PS1 based on F o¨ rster’s mechanism
bonds, and (3) the aggregation of porphyrins through nonco-
valent interactions in solutions, on the surface of solutions,
14
15
28
29
1
6
30
and exciton theory, showed that chlorophylls are ingeniously
aligned in these light-harvesting systems, forming small clusters
to collect and transfer the photon energy to the photosynthetic
reaction center (RC).
How can we approach the antenna Chls of PS1, PS2, green
plants, and FMO by porphyrin synthesis? Stimulated by the
integration forms of Chls in LH1, LH2, and RC sthey are
analogous to J-aggregates in stack structuresextensive studies
on porphyrin arrays and aggregates have been conducted over
the past decades aiming at the development of model systems
for LH1, LH2, and RC, as well as new electrooptical
and in protein and proteinoid cavities. Among the porphyrin
arrays synthesized using these methods, those reported by
Takahashi and Peng effectively mimic the ring-stacked and
flat-ring morphologies, respectively, of the antenna Chls of LH1
and LH2.
8
9
1
,2
17
(23) (a) Kelley, R. F.; Lee, S. J.; Wilson, T. M.; Nakamura, Y.; Tiede,
D. M.; Osuka, A.; Hupp, J. T.; Wasielewski, M. R. J. Am. Chem.
Soc. 2008, 130, 4277–4284. (b) Kelley, R. F.; Tauber, M. J.; Wilson,
T. M.; Wasielewski, M. R. Chem. Commun. 2007, 4407–4409. (c)
Kelley, R. F.; Shin, W.-S.; Rybtchinski, B.; Wasielewski, M. R. J. Am.
Chem. Soc. 2007, 129, 3173–3181. (d) Kelley, R. F.; Tauber, M. J.;
Wasielewski, M. R. Angew. Chem., Int. Ed. 2006, 45, 7979–7982. (e)
Song, H.-E.; Kirmaier, C.; Yu, L.; Bocian, D. F.; Lindsey, J. S.; Holten,
D. J. Phys. Chem. B 2006, 110, 19121–19130. (f) Song, H.-E.;
Kirmaier, C.; Yu, L.; Bocian, D. F.; Lindsey, J. S.; Holten, D. J. Phys.
Chem. B 2006, 110, 19131–19139. (g) Hindin, E.; Forties, R. A.;
Loewe, R. S.; Ambroise, A.; Kirmaier, C.; Bocian, D. F.; Lindsey,
J. S.; Holten, D.; Knox, R. S. J. Phys. Chem. B 2004, 108, 12821–
18
19
8
,9,20,21
devices.
To synthesize porphyrin arrays and aggregates,
three methods have thus far been proposed: (1) the direct binding
of porphyrin skeletons via meso-meso linkage, coordination
8
,9,22
23
bonds,
and acetylene and olefin linkage, (2) indirect
1
2832. (h) Rucareunu, S.; Mongin, O.; Schuwey, A.; Hoyler, N.;
(
11) The 90 antenna Chls (Chl a) of cyanobacterial PS1 are distributed in
three parallel ellipsoid rings so as to surround the reaction center (RC)
maintaining the nearest-neighbor Mg-Mg distance within 7.6-21.0
Å (pdb 1jbo), whereas the 33 antenna Chls of PS2 are kept within
Gossauer, A. J. Org. Chem. 2001, 66, 4973–4988. (i) Vicente,
M. G. H.; Jaquinod, L.; Smith, K. M. Chem. Commun. 1999, 1771–
1782. (j) Wytko, J.; Berl, V.; McLaughlin, M.; Tykwinski, R. R.;
Schreiber, M.; Diederich, F.; Boudon, C.; Gisselbrecht, J.-P.; Gross,
M. HelV. Chim. Acta 1998, 81, 1964–1977. (k) Yashnski, D. V.;
Ponomarev, G. V. Tetrahedron Lett. 1995, 36, 8485–8488.
8
.3-13.4 Å (pdb 1s5l) also surrounding the RC. The light-harvesting
complexes, LHC-II, in the thylakoid membrane of chloroplasts exist
as trimers, each of which comprises five Chl a and three Chl b on the
stromal side, whereas there are three Chl a and three Chl b on the
lumenal side. The antenna Chls on the stromal side form an ellipsoid
ring (Mg-Mg; 9.8-12.8 Å); on the other hand those of the lumenal
side form dimer (Mg-Mg; 9.3 Å) and tetramer (Mg-Mg; 8.2-12.5
Å) clusters (pdb 1rwt). The bacteriochlorophylls of FMO are
distributed in a shallow funnel maintaining the Mg-Mg distance within
(24) (a) Choi, M.-S.; Aida, T.; Yamazaki, T.; Yamazaki, I. Angew. Chem.,
Int. Ed. 2001, 40, 3194–3198. (b) Yeow, E. K. L.; Ghiggino, K. P.;
Reek, J. N.; Crossley, M. J.; Bosman, A. W.; Schenning, A. P. H. J.;
Meujer, E. W. J. Phy. Chem. B. 2000, 104, 2596–2606.
(25) (a) Mihara, H.; Hareta, Y.; Sakamoto, S.; Nishino, N.; Aoyagi, H.
Chem. Lett. 1997, 54, 731–737. (b) Tamiaki, H.; Onishi, M. Tetra-
hedron: Asymmetry 1999, 10, 1029–1032. (c) Solladi e´ , H.; Hamel,
A.; Gross, M. Tetrahedron Lett. 2000, 41, 6075–6078. (d) Fujitsuka,
M.; Hara, M.; Tojo, S.; Okada, A.; Troiani, V.; Solladi e´ , N.; Majima,
T. J. Phys. Chem. B, 2005, 109, 33–35.
1
1.4-13.8 Å (pdb 4bcl).
(
(
12) Di Donato, M.; van Grondelle, R.; van Stokkum, I. H. M.; Groot,
M. L. J. Phys. Chem. B 2007, 111, 7345–7352.
13) (a) Brixner, T.; Stenger, J.; Vaswani, H. M.; Cho, M.-H.; Blankenship,
R. E.; Fleming, G. R. Nature 2005, 434, 625–628. (b) Engel, G. S.;
Calhoun, T. R.; Read, E. L.; Ahn, T.-K.; Man cˇ al1, T.; Cheng, Y.-C.;
Blankenship, R. E.; Fleming, G. R. Nature 2007, 446, 782–786.
14) Byrdin, M.; Jordan, P.; Kraus, N.; Fromme, P.; Stehlik, D.; Schlodder,
E. Biophys. J. 2002, 83, 433–457.
(26) (a) Takei, F.; Nakamura, S.; Onitsuka, K.; Ishida, A.; Tojo, S.; Majima,
T.; Takahashi, S. Chem. Lett. 2003, 32, 506–507. (b) Takei, F.;
Kodama, D.; Nakamura, S.; Onitsuka, K.; Takahashi, S. J. Polym.
Sci., Part A: Polym. Chem. 2006, 44, 585–595. (c) Guildy, D. M.;
Taieb, H.; Rahman, G. M. A.; Tagmatarchis, N.; Prato, M. AdV. Mater.
2005, 17, 871–875.
(
(
(
15) F o¨ rster, Th. Discuss. Faraday Soc. 1959, 27, 7–17.
(27) (a) Kelley, R. F.; Goldsmith, R. H.; Wasielewski, M. R. J. Am. Chem.
Soc. 2007, 129, 6384–6385. (b) Drain, C. M.; Hupp, J. T.; Suslick,
K. S.; Wasielewski, M. R.; Chen, X. J. Porphyrins Phthalocyanines
2002, 6, 243–258. (c) Ikeda, A.; Ayabe, M.; Shinkai, S. Chem. Lett.
2001, 1138–1139. (d) Richeter, S.; Jeandon, C.; Gisselbrecht, J.-P.;
Ruppert, R.; Callot, H. J. J. Am. Chem. Soc. 2002, 124, 6168–6179.
(e) Wilson, G. S.; Anderson, H. L. Chem. Commun. 1999, 1539–1540.
(f) Fan, J.; Whiteford, J. A.; Olenyuk, B.; Levin, M. D.; Stang, P. J.;
Fleischer, E. B. J. Am. Chem. Soc. 1999, 121, 2741–2752.
16) Rosenfeld, V. L. Z. Phys 1928, 52, 161. Bohm, D. Quantum Theory;
Prentice-Hall: New York, 1961; p 427. Davydov, A. S. Theory of
Molecular Excitons; McGraw-Hill: New York, 1962; pp 141-155.
Davydov, A. S. Theory of Molecular Excitons; Plenum Press: New
York, London, 1971; pp 23-112. Kasha, M.; Rawls, H. R.; El-
Bayoumi, A. Pure Appl. Chem. 1965, 11, 371–392. Kasha, M. Radiat.
Res. 1963, 20, 55–71.
(17) Deisenhofer, J.; Epp, O.; Miki, K.; Huber, R.; Michel, H. Nature 1985,
3
18, 618–624.
(28) (a) Okamura, M. Y.; Feher, G.; Nelson, N. Photosynthesis; Govindjee,
Ed.; Academic Press: New York, 1982; pp 195-272. (b) Pasternack,
R. F.; Huber, P. R.; Boyd, P.; Engasser, G.; Francesconi, L.; Gibbs,
E.; Fasella, P.; Venturo, G. C.; Hinds, L. D. J. Am. Chem. Soc. 1972,
94, 4511–4517. (c) Yamamura, T. Chem. Lett. 1977, 773. (d)
Yamamura, T. Chem. Lett. 1978, 193. (e) Barber, D. C.; Freitag-
Beeston, R. A.; Whitten, D. G. J. Phys. Chem. 1991, 95, 4074–4086.
(f) Ribo, J. M.; Crusats, J.; Farrera, J.-A.; Valero, M. L. J. Chem.Soc.,
Chem. Commun. 1994, 681–682. (g) Pasternack, R. F.; Schaefer, K. F.;
Hambright, P. Inorg. Chem. 1994, 33, 2062–2065. (h) Akins, D. L.;
Zhu, H.-R.; Guo, C. J. Phys. Chem. 1994, 98, 3612–3618. (i) Maiti,
N.; Ravikanth, M.; Mazumdar, S.; Periasamy, N. J. Phys. Chem. 1995,
99, 17192–17197. (j) Akins, D. L.; Zhu, H.-R.; Guo, C. J. Phys. Chem.
1996, 100, 5420–5425. (k) Jin, R.-H.; Aoki, S.; Shima, K. J. Chem.
Soc., Faraday Trans. 1997, 93, 3945–3953. (l) Bhyrappa, P.; Wilson,
S. R.; Suslick, K. S. J. Am. Chem. Soc. 1997, 119, 8492–8502. (m)
Maiti, N. C.; Mazumdar, S.; Periasamy, N. J. Phys. Chem. B 1998,
102, 1528–38. (n) Choi, M. Y.; Pollard, J. A.; Webb, M. A.; McHale,
J. L. J. Am. Chem. Soc. 2003, 125, 810–820.
(
18) (a) Jelley, E. E. Nature (London) 1936, 138, 1009. (b) Scheibe, G.
Angew. Chem. 1936, 49, 563. (c) Fleisher, E. B.; Palmer, J. M.;
Srivastava, T. S.; Chatterjee, A. J. Am. Chem. Soc. 1971, 93, 3162–
3
167. (d) Pasternack, R. F.; Huber, P. R.; Boyd, P.; Engasser, G.;
Francesconi, L.; Gibbs, E.; Fasella, P.; Venturo, G. C.; Hinds, L. de
C. J. Am. Chem. Soc. 1972, 94, 4511–4517. (e) Ohno, O.; Kaizu, Y.;
Kobayashi, H. J. Chem. Phys. 1993, 99, 4128–4139.
(
(
19) (a) Wasielewski, M. R. J. Org. Chem. 2006, 71, 5051–5066. (b)
Wasielewski, M. R. Chem. ReV. 1992, 92, 435–461.
20) (a) Aratani, N.; Osuka, A.; Kim, Y. H.; Jeong, D. H.; Kim, D. Angew.
Chem., Int. Ed. 2000, 39, 1458–1462. (b) Nakano, A.; Yamazaki, T.;
Nishimura, Y.; Akimoto, S.; Yamazaki, I.; Osuka, A. Chem.sEur. J.
2
000, 6, 3254–3271. (c) Tsuda, A.; Osuka, A. Science 2001, 293, 79–
8
2.
(
21) (a) Dalton, L. R.; Harper, A. W.; Ghosn, R.; Steier, W. H.; Ziari, M.;
Fetterman, H.; Shi, Y.; Mustacich, R. V.; Jen, A. K.-Y.; Shea, K.
J. Chem. Mater 1995, 7, 1060–1081. (b) Ogawa, K.; Ohashi, A.;
Kobuke, Y. J. Am. Chem. Soc. 2003, 125, 13356–13357. (c) Collini,
E.; Ferrante, C.; Bozio, R.; Lodib, A.; Ponterini, G. J. Mater. Chem.
(29) (a) Xu, W.; Guo, H.; Akins, D. L. J. Phys. Chem. B 2001, 105, 1543–
1546. (b) Okada, S.; Segawa, H. J. Am. Chem. Soc. 2003, 125, 2792–
2796. (c) Sadasivan, S.; K o¨ hler, K.; Sukhorukov, G. B. AdV. Funct.
Mater. 2006, 16, 2083–2088.
2
006, 16, 1573–1578.
(
22) Morikawa, S.; Ikeda, C.; Kazuya Ogawa, K.; Kobuke, Y. Lett. Org.
Chem. 2004, 1, 6–11.
1
1720 J. AM. CHEM. SOC. 9 VOL. 131, NO. 33, 2009

Porphyrin Arrays Responsive to Additives
A R T I C L E S
Figure 1. Schematic drawing of the a posteriori fluorescence optimization
in porphyrin arrays.
H2,S
t
In comparison with the antenna Chls in LH1, LH2, and
chlorosomes, the asymmetric orientation of antenna Chls in
cyanobacterial PS1, PS2, green plants, and FMO seems to be
too complex to be mimicked by porphyrin synthesis. It is clear
Figure 2. Protected metal-free monomer Boc-(Por )-OBu , 4, and its
Zn,S
t
zinc oligomers Boc-(Por
) -OBu (n ) 2, 4, t and 8): dimer
n
Zn,S
Zn,S
t
Zn,S
Boc-(Por
Boc-(Por
)
)
2
-OBu , 6′; tetramer Boc-(Por
4
) -OBu , 7′; and octamer
t
8
-OBu , 8′. The lowest-energy structures of 6′, 7′, and 8′
calculated by AMBER6.0. are shown here.
8
,9
that the deterministic approach such as those adopted for the
π-π stacked Chl systems of LH1 and LH2 is not applicable.
The asymmetry may be achieved through cross-linkage such
Scheme 1. 1 Synthetic Route for Boc-(PorM,S)
t
n
2
-OBu (M ) H and
a
Zn; n ) 1, 2, 4, and 8)
31
32
as adopted by Crossley and Pandy for the synthesis of dimer
porphyrins; however, the synthesis will require a tremendous
amount of work for the arrays or clusters larger than dimer and
for the arrays optimized in fluorescence emission.
A simple means involves (1) the reduction in dimensionality
from 2 or 3 to 1, that is, to use oligomeric or polymeric
porphyrins conserving the distance among neighboring porphy-
rins within 6-20 Å (like that in naturally occurring antenna
Chls) and (2) the construction of a tunable system that is
responsive to additives in fluorescence emission. Such systems
allow the a posteriori optimization of fluorescence emission and
dye orientation. For this purpose, peptide-linked porphyrin arrays
in which compact porphyrins are bound to the peptide chains
via a “short linker” are suitable. Porphyrins in such an array
are proximally constrained and maintain their mutual orientation
through the balance of the van der Waals interaction (π-π
interaction), ligand coordination, and peptide folding. The
addition of a ligand that coordinates to the central atoms of
porphyrins or interacts with the amide moiety of the peptide
chain by hydrogen bonds would break this balance to force
porphyrins to form a new conformation (Figure 1). By searching
for such ligands, we expect to find an optimal additive for
efficient fluorescence emission, which is an index of the
suppression of the thermal quenching of absorbed photon
energies.
a
3
Reagents and conditions: (a) DMF, POCl , 1,2-dichloroethane, reflux,
2.5 h, followed by NaOAc, 60%; (b) conc. H SO , silica gel column
2
4
(CHCl
CH Cl
CH Cl
DIEA, rt, 2 h, 92%; (h) PyBOP, DIEA, DMF, 0°C f rt, 2 h, 88%.
3
), 30%; (c) NaBH
, -78°C, 95%; (e) THF, Ar, rt, 1 h, 78%; (f) TFA, thioanisole,
Cl , rt, 15 h; (Boc) O,
4
, THF, 45°C, 15 min, 85%; (d) SOCl
2
, pyridine,
2
2
2
2
, 0°C f rt, 1 h, 90%; (g) TFA, thioanisole, CH
2
2
2
The porphyrin arrays used in this study are Boc-
M,S
t
(
Por
n
) -OBu (M ) H2 and Zn; n ) 2, 4, and 8; Figure 2;
details of the synthesis, see Supporting Information1) elon-
H2,S
R
with the C of cysteine via a C-S-C linker. This short linker
gated from the protected unnatural amino acid Boc-Por
-
ꢀ
t
33
helps in maintaining the nearest-neighbor porphyrins in the
arrays within 6-20 Å in Zn-Zn distancesclose to the Mg-Mg
distance of Chls in PS1 and others. In comparison with the
known peptide-type arrays that have bulky porphyrins attached
OBu (4; Scheme 1) that were synthesized by connecting the
-pyrrole position of 5,10,15,20-tetra-n-butyl porphyrin (H TBP)
ꢀ
2
(
30) (a) Rabanal, F.; DeGrado, W. F.; Dutton, P. L. J. Am. Chem. Soc.
996, 118, 473–474. (b) Nango, M.; Kashiwada, A.; Watanabe, H.;
Yamada, S.; Yamada, T.; Ogawa, M.; Tanaka, T.; Iida, K. Chem. Lett.
2
5
1
to them via long side chains of Lys, Orn, and Glu, our arrays
are characteristic of the compactness of the used porphyrin, as
well as the shortness of the linker part (C-S-C ). However,
ꢀ
the linker is not too short to hinder the rotations of porphyrins,
but it is moderately short to allow the arrays to flexibly respond
to additives.
2
002, 312–313. (c) Endo, M.; Fujitsuka, M.; Majima, T. Chem.sEur.
J. 2007, 13, 8660–8666.
(
31) Crossley, M. J.; Hambley, T. W.; Mackay, L. G.; Try, A. C.; Walton,
R. J. Chem. Soc., Chem. Commun. 1995, 1077–1072. Crossley, M. J.;
Mackay, L. G.; Try, A. C. J. Chem. Soc., Chem. Commun. 1995, 1925–
1
927.
(
(
32) Zheng, G.; Shibata, M.; Dougherty, T. J.; Pandey, R. K. J. Org. Chem.
A search for additives that optimize the fluorescence of
oligomers revealed the superiority of 1,2- diaminoethane (en).
Sufficient amounts of en increased the fluorescence integrated
intensities of the dimer, tetramer, and octamer by ∼12, ∼12,
2
000, 65, 543–557.
33) Abbreviations: Boc, tert-butoxycarbonyl; DIEA, diispropylethylamine;
t
OBu , tert-butyl ester; PyBOP, benzotriazole-1-yl-oxy-tris-pyrroridino-
phosphonium hexafluorophosphate; TFA, trifluoroacetic acid.
J. AM. CHEM. SOC. 9 VOL. 131, NO. 33, 2009 11721

A R T I C L E S
Yamamura et al.
a
and >730 timessexcited at 564 nms, respectively, when
compared with those observed in the absence of en.
Our results demonstrate the potentiality of the tunable dye
polymers that are a posteriori optimized in fluorescence
emission by additive reagents for the development of effective
light-harvesting materials.
Table 1. Results of Fluorescent Search
Q-band shift
(nm)
fluorescence shift
(nm)
b
ligand
Φ′
en
pn
im
bn
dabco
hmta
13, 17
15, 17
15, 18
-
25
13
13
3
0
9
0.078
0.041
0.034
0.021
0.014
0.013
-
2
. Results and Discussion
.1. Porphyrin Interactions in the Arrays. The results of the
-
2
a
2 2
Porphyrins were excited at 564 nm in CH Cl . Data were collected
1
-6
H NMR experiments suggest that porphyrins in Boc-
Por
at sufficiently diluted concentration (∼2 × 10 M) using a cell with a
Zn,S
t
b
(
)
2
-OBu (6′) are in a face-to-face-like interaction. The
optical path length of 5 mm to avoid self-absorption. Corrected for the
Zn,S
fluorescence yield of ZnTPP or the monomer Boc-Por -OMe.
signals of 6′ in the ring-proton region showed a large high-
field shift from 9.2-9.4 ppm of the monomer and spread over
zero-cross point at 413 nm. The peak at 390 nm is concentration
dependent in the concentration range from 10 to 10 M and
particularly increases in the concentration range from 10 to
M with a decrease in the intensities of the 399 and 429
nm peaks. Consequently, all porphyrins in these arrays are
asymmetrically arranged to each other.
2.2. Fluorescence Behavior of Boc-(Por ) -OBu . The
porphyrin interaction predominated by a face-to-face-like
-
8
-4
7
.82-9.08 ppm accompanying a strong line broadening (Sup-
-
5
porting Information 2). This result indicates that the ꢀ-pyrrole
protons of 6′ are under the influence of mutual ring currents.
Because of this broadening, NOESY experiments were impos-
-
4
1
0
3
7
3
4
sible in the temperature range from -50 to +50 °C.
Zn,S
t
On the other hand, the B-band regions of the AB spectra of
n
Zn,S
t
Zn,S
t
6
′, Boc-(Por
)
4
-OBu (7′), and Boc-(Por
)
8
-OBu (8′)
show blue shifts (about 14 nm from 424 nm of ZnTBP) and
band splittings (Supporting Information 3). This result indicates
that the porphyrins of these oligomers assume weakly skidded
face-to-face orientations in the arrays, corresponding to the result
of the NMR measurement mentioned above. The B-bands obey
orientation is not advantageous for efficient fluorescence emis-
sion because of photon energy quenching through the thermal
processes. In practice, the apparent fluorescence yield of
Zn,S
t
Boc-(Por ) -OBu decreases with increasing n, obeying Φ′
n
1.5
) 0.03/n (Supporting Information 5). Therefore, we searched
for the additives that enhance fluorescence emission.
Beer’s law in organic solvents such as CH
2
Cl
2
and benzene
-4
(<10 M) in appearance, suggesting that the blue shift originates
2.3. Fluorescence Control of 6′. Considering the results of the
AB experiments on 7′ and 8′, which suggest the mixing of pairwise
face-to-face-like interactions of porphyrins similar to that of 6′,
we subjected 6′ to the fluorescence condition search. In this search,
we compared the effect of monodentate, bidentate, and multidentate
ligands to control the porphyrin orientation: 1,3-diazacyclopenta-
2,4-diene (im; imidazole), en, 1,3-diaminopropane (pn), 1,4-
diaminobutame (bn), 1,4-diazabicyclo[2.2.2]octane (dabco), and
from an intramolecular porphyrin interaction. The deconvolution
of the B band regions of 6′, 7′, and 8′ indicate that their spectra
are composed of four common peaks: peak 1 (410 nm,
predominant), peak 2 (422-427 nm, shoulder), peak 3 (389 nm),
and peak 4 (434 nm) (Supporting Information 4). The last two
peaks appear at the lower- and higher-energy tails of the
predominant peaks of the tetramer and octamer. The relative
ratio of peak 2 decreases with increasing n; however, those of
3,7
1,3,5,7-tetraazatricyclo[3.3.1.1 ]decane (hmta; hexamethylenetet-
ramine). The results of this search are listed in Table 1. Evidently,
en is superior to the other ligands in terms of fluorescence recovery.
The table seems to indicate that (1) the bulkier the ligand, the
smaller the fluorescence recovery and (2) the lower the coordination
ability of the ligand, the weaker the fluorescence recovery. Figure
3 demonstrates that en induces marked fluorescence intensity and
line shape, as well as absorption, changes in 6′. Although ligands
other than en cause line shape changes in the fluorescence spectra,
they are not as efficient as en in fluorescence recovery (Supporting
Information 6). Molecular modeling showed that en is sufficiently
small to penetrate into the interstitial spaces of the arrays and to
interact with hidden Zn2 ions, amide moieties, and sulfur atoms.
As shown in Figure 3, the Q-band absorption peaks at 564
and 602 nm of 6′ asymptotically approach 577 and 620 nm,
respectively, with the addition of en. The titration curves
observed at 564 and 620 nm indicate that it requires more than
3
5
peaks 3 and 4 increase with the line width broadening.
′ shows a weak positive exciton chirality (Supporting
Information 3), whereas 7′ shows a negative exciton chirality
6
2
-1
larger than that of 6′, giving peaks at 412 (48.1 cm ·mmol )
2
-1
and 427 nm (-67.6 cm ·mmol ), which correspond to the first
and second peaks, respectively, of the AB spectrum of this
compound. The CD spectrum of 8′ has two types of CD peaks
that differ in line width and concentration dependence: a sharp
and negative one at 390 nm and a broad one showing positive
and negative peaks at 399 and 429 nm, respectively, with the
36
+
t
(
34) Boc-(PorH2,S)
2
-OBu showed more than 18 lines of a complicated
mixture of singlets, doublets, quartets, and multiplets spread over 0.7
ppm in the ꢀ-pyrrole region. The signals showed high-field shifts as
H2,S
t
compared to those of the monomer Boc-Por -OBu . Unfortunately,
we could not assign the off-diagonal peaks arising from the porphyrin-
porphyrin interaction in 6′ in the NOESY spectrum. However, note
H2,S
t
that the NMR chart of Boc-(Por
2
) -OBu showed the existence
∼
5 equiv of en to complete the spectral change. The addition
of a water molecule that interacts with the pyrrole NH. Further addition
of water had no effect on the visible AB, CD, or NMR spectra.
H2,S
t
(
35) The metal-free base monomer Boc-Por -OBu exhibits a B-band
peak at 412 nm. This peak splits into two showing a new shoulder on
the higher-energy side (405-406 nm) in organic solvents such as
(37) The intensity of the peak at 390 nm, as well as the peaks at 399 and
429 nm, is proportional to the logarithm of the concentration, probably
indicative of the consecutive aggregation of the octamer. Considering
the small occupancy of the peak at 390 nm in the AB spectrum, the
3 2 2 6 6
CHCl , CH Cl , and C H , indicating that the number of face-to-face
2
-1
stacks of porphyrins increases in the arrays with n. The porphyrin
interactions in the free-base oligomers 6, 7, and 8 are weak when
compared with those in the Zn compounds 6′, 7′, and 8′. The
deconvolution of the B bands of 6, 7, and 8 showed that the bands
are also composed of four common bands similar to those of the Zn
compounds.
estimated molar ellipticity [θ] reached up to ∼108 mdeg ·cm ·mol . The
molar ellipticity, strong blue shift, and sharp linewidth of the species
giving the peak at 390 nm suggest that the species originates from
H-like aggregation. MD calculations suggest that the main chain of
8′ assumes a pleated helix structure. The strong CD of the peak at
390 nm may originate from the formation of an intermolecular double-
stranded ꢀ-sheet, where the porphyrins are aligned with a face-to-
face (and π-π-stacked) conformation.
(
36) The molar ellipticities of metal-free bases (6, 7, and 8) were much
different from those of the zinc compounds 6′, 7′, and 8′.
1
1722 J. AM. CHEM. SOC. 9 VOL. 131, NO. 33, 2009

Porphyrin Arrays Responsive to Additives
A R T I C L E S
Figure 3. Results of titration for Boc-(PorZn,S)
-OMe, 6′, in CH
Cl
(2.24
2
2
2
Zn,S
-
6
Figure 4. Results of titration for Boc-(Por
Boc-(PorZn,S)
-OMe (right) in CH Cl
)
4
-OMe (left) and
×
10 M) with 1,2-diaminoethane (en, 0-20 equiv). All the spectra were
-6
8
2
2
(2.00 × 10 M) with en followed
observed in an Ar atmosphere. Cells with optical path lengths of 1.0 mm,
mm, and 10 mm were used for the absorption experiments; on the other
by fluorescence spectroscopy. A cell with a 5-mm optical path length was
used. The spectra corrected for self-absorption are shown in a thinned-out
form for clarity. All the spectra were observed in an Ar atmosphere. The
spectra shown in red are those observed in the absence of en. The spectra
shown in blue are those observed in the presence of 70 and 200 equiv of
en for 7′ and 8′, respectively.
5
hand a cell with an optical path length of 5 mm was used for fluorescence
experiments. The absorption change in the Q-band region (left: per molecule)
and the fluorescence change (right: per porphyrin, corrected for self-
absorption, excited at 564 nm) are presented. The spectra are shown in a
thinned-out form for clarity. Spectra shown by the thick solid red lines are
those observed in the absence of en. Spectra shown by the thick solid blue
lines are those observed in the presence of an excess amount (22 equiv) of
en. The insets show the titration curves observed by the absorption and
fluorescence methods.
39
monotonic and indicate that more than 200 equiv of en is
necessary to relax the porphyrin-porphyrin interaction. The line
shapes of 7′ and 8′ in the absence or presence of en indicate
that these oligomers differ in exciton interactions and electronic
relaxation. In any event, the addition of a sufficient amount of
en increases the fluorescence of the tetramer and octamer by
of an excess amount of en to 6′ enhances the fluorescence
intensity to a level about 12 times larger than that observed in
the absence of en in integrated (580-800 nm) intensity.
Considering the fact that en also increases more than 4-5
∼
12 and >760 times, respectively, when compared with that
observed in the absence of en. The recovery ratio per porphyrin
reaches up to the 20 and 67% of 4′/en for 7′ and 8′, respectively,
in integrated intensities. In comparison with the fluorescence
of 4′ itself, the values reach up to 87 and 287% of the monomer.
3
8
times the fluorescence intensity of the monomer (Boc-
Zn,S
t
Por -OBu , 4′) (Supporting Information 7), the recovery ratio
per porphyrin reaches up to 63% of the monomer level. When
it is compared with that of 4′ itself, the value reaches 370% of
the monomer. Further, en causes marked changes in fluorescence
line shape. The fluorescence peaks of 6′ at 617 and 672 nm
asymptotically approach 646 and 692 nm, respectively, during
en titration. The titration curves at 646 and 692 nm also indicate
that more than 5 equiv of en is necessary to complete change
of the spectrum of 6′. Note that any of these fluorescence
maxima differ from those of 4′ (609 and 660 nm in the absence
of en and 640 and 686 nm in the presence of an excess amount
of en).
2
.5. Fluorescence Lifetime. The fluorescence lifetimes of the
arrays are short in the absence of en (Figure 5) concurrent with
the decrease in the fluorescence yield (Φ′) (Supporting Informa-
tion 5). The fluorescence of ZnTBP obeys single-lifetime (1.58
ns) decay, whereas those of 6′, 7′, and 8′ obey two- lifetime
) 0.49, 0.54, and 0.55 ns, respectively)
and long (τ ) 1.58. 1.48, and 1.46 ns, respectively). The
contribution of long-lifetime decay decreases with the array
size (Figure 5, upper four plots). This result is consistent with
the estimation that Zn porphyrins in 7′ and 8′ are face-to-face-
like paired similarly to those in 6′ (see the section of Porphyrin
Interactions in the Arrays). The short lifetime may correspond
to the paired porphyrins, whereas the long lifetime may arise
from the unpaired porphyrins that are generated at the termini
of peptide chains during array fluctuations. On the other hand,
in the presence of sufficient amounts of en (22.0 equiv for 6′,
0 equiv for 7′, and 200 equiv for 8′), the lifetimes of the arrays
τ ) 2.24, 2.04, and 1.98 ns for 6′, 7′, and 8′, respectively) are
close to that of ZnTBP (τ ) 2.10 ns). This means that en
decreases the face-to-face-like pairwise interactions among
porphyrins in the arrays (Figure 5, lower four plots). Note that
en also elongates the lifetime of ZnTBP itself from 1.58 to 2.10
ns through coordination.
decay, namely, short (τ
s
l
2
.4. Fluorescence Recovery in Tetramer and Octamer. En-
couraged by the success in investigating 6′, we studied the
effects of en on 7′ and 8′. Here, en also caused marked changes
in fluorescence line shape and intensity. The results corrected
for self-absorption at excitation and emission wavelengths are
shown in Figure 4. The fluorescence peaks of 7′, observed at
7
(
6
6
23 and 678 nm in the absence of en, asymptotically approach
47 and 687 nm, respectively, and the fluorescence titration
curve observed at 623 nm indicates that more than ∼12 equiv
of en are necessary for sufficient increase of the fluorescence.
The fluorescence peaks of 8′ at 636 and 667 nm, observed in
the absence of en, asymptotically approach 643 and 685 nm,
respectively. However, the titration feature is apparently different
from those of 6′ and 7′. The fluorescence titration curves
observed at 623 and 685 nm are neither asymptotic nor
2
.6. Asymptotic Changes of the AB and CD Spectra of 6′,
7
′, and 8′. To study the conformation changes of 6′, 7′, and 8′
through exciton chirality before and after en addition, we
monitored the AB and CD spectra of the B-band region. The
Zn,S
t
(
38) The absorption change of Boc-Por -OBu (4′) in CH
2
Cl
M) upon addition of 1,2-diaminoethane (en) was simulated by
assuming the simple association equilibrium A + B / AB, where A
2
(2.08 ×
(39) The spectra are corrected for the absorption at excitation and emission
wavelengths. The absorption of 8′ at the excitation wavelength (564
nm) increases with increasing the amounts of en, whereas those of 6′
and 7′ decrease at 564 nm; therefore, the feature of fluorescence
increase of 8′ is expected to be larger than those of 6′ and 7′ because
of this correction. The reason for the abnormal increase of 8′,
particularly the increase in the region of en >100 equiv, is not clear.
The addition of excess amounts of en might cause a local change of
the media around the molecule considering the results together with
those of the fluorescence changes of 4′.
-
6
1
0
)
4′, B ) en, and AB ) 4′·en. This afforded an association constant
-1
K ) 28100 mol (see Figure S-8b in Supporting Information).
However, the gradual increase of the fluorescence of 4′ observed at
6
41 nmsit increases up to ∼5 timessupon addition of en (see the
inset of Figure S-7a in Supporting Information) and that observed at
09 nm are not accounted for by the simple association equilibrium
adopted for the simulation of the absorption change.
6
J. AM. CHEM. SOC. 9 VOL. 131, NO. 33, 2009 11723

A R T I C L E S
Yamamura et al.
Figure 6. B-band regions of the visible AB (left) and CD (right) spectra
Zn,S
-6
Zn,S
of Boc-(Por
)
2
-OMe (2.00 × 10 M, upper), Boc-(Por
4
) -OMe
-
6
Zn,S
-6
(
2.00 × 10 M, middle), and Boc-(Por
)
8
-OMe (1.97 × 10 M, lower)
2 2
in CH Cl upon the addition of en. Cells with an optical path length of 10
mm were used for AB and CD experiments. All of the spectra were observed
in an Ar atmosphere. Insets show the titration curves. Spectra shown in red
are those observed in the absence of en. Spectra shown in blue are those
observed in the presence of excess amounts of en (22.0 equiv for 6′, 70
equiv for 7′, and 200 equiv for 8′). All of the spectra are corrected for
those per porphyrin.
Figure 5. Results of fluorescence lifetime measurements for monomer (4′),
dimer (6′), tetramer (7′), and octamer (8′). The upper four plots are those
measured at 640 nm in the absence of en; the lower four plots are those
measured at 660 nm in the presence of sufficient amounts of en (22.0 equiv
for 6′, 70 equiv for 7′, and 200 equiv for 8′).
These results indicate the following: (1) at least two en
molecules interact with 6′; (2) each porphyrin is under the
influence of the ring current of the partner porphyrin in the
absence or presence of en, but the effect of ring current is slight
in the latter; and (3) the mutual positions of the two porphyrins
in the new structure is fixed. Consequently, in conjunction with
the results of the visible AB experiments, it is probable that
two en molecules coordinate with Zn2 at the first stage, which
makes each porphyrin almost independent of the influence of
the ring current of its partner; then, the third en may interact
with the amide moiety of the main chain. However, the
porphyrins are still sufficiently within the range of exciton
interactions. Unfortunately, it is impossible to obtain the NOESY
or ROESY spectrum that is useful for the structural analysis of
results are shown in Figure 6. The figure clearly shows that the
porphyrins in the arrays do not lose exciton chirality even in
the presence of sufficient amounts of en and that the porphyrin
of the oligomers asymptotically approach new orientations. The
AB spectrum observed in the presence of a sufficient amount
of en is similar to the B-band spectrum of the monomeric
pentacoordinate ZnTBP (λmax ) 427 nm). The absorption
intensity of 6′ at 408 nm decreases with the addition of en,
whereas that at 427 nm increases. The titration curve of the
latter indicates that 6′ binds two or three en molecules at first,
which markedly changes the absorption, then binds additional
two or three en. Several isosbestic points were observed in the
expanded spectra (Supporting Information 8). The spectra shifted
stepwise with the addition of en showing three or four cross
points, which indicates that consecutive multistep interactions
occur between porphyrins and en in the mixture. This result is
+
6
′/en.
Irrespective of the absence or presence of en, it was
impossible to deconvolute the CD spectra of 6′ using ideal
positive and negative pairs of Cotton-effect that exhibit zero-
4
0
cross points at the absorption maxima. This suggests that
several energy bands that differ in wavelength, intensity, and
line width contribute to the AB and CD spectra. The CD
spectrum of 6′ in the presence of a sufficient amount of en shows
the contribution of two components: a small one observed in
the short-wavelength region and a large one observed in the
1
in agreement with that of the H NMR experiments observed
3
in CDCl (Supporting Information 2), where the broad and high-
field-shifted spectrum of 6′ without en returns, in the presence
of en, to the original low field of the monomeric porphyrin
showing signal narrowing. However, it approaches a new
spectrum composed of approximately nine signals, which differs
from the monomer spectrum composed of only three signals
(
40) Yamamura, T.; Mori, T.; Tsuda, Y.; Taguchi, T.; Josha, N. J. Phy.
Chem., A 2007, 111, 2128–2138.
(
1H at 9.534 ppm, 4H at 9.446 ppm, and 2H at 9.409 ppm).
1
1724 J. AM. CHEM. SOC. 9 VOL. 131, NO. 33, 2009

Porphyrin Arrays Responsive to Additives
A R T I C L E S
4
3
long-wavelength region. Both components show the negative
first and positive second Cotton effects that are characteristic
of negative chirality. The zero-cross point (432 nm) of the large
component is close to the absorption maximum (427 nm).
method of Lindsey et al.
H
2
TBP was converted to 5,10,15,20-
tetra(n-butyl)porphyrin-2-carbaldehyde, H
ing through [5,10,15,20-tetra(n-butyl) porphyrinato(2-)]nickel(II)-
-carbaldehyde, NiTBP-CHO, which was prepared from [5,10,15,20-
2
TBP-CHO (2), by pass-
2
tetra(n-butyl)porphyrinato(2-)]nickel(II) employing the Vilsmeier
Tetramer 7′ and octamer 8′ also show asymptotic changes in
the AB and CD spectra of the B-band region (Figure 6). The
addition of en to 7′ decreases the absorption intensity at 408
nm and increases that of the new peak at 429 nm. The titration
curves of 7′ observed at 408 and 429 nm (shown in the inset)
indicate that more than 10 equiv of en is necessary for 7′ to
relax its π-π interaction. The addition of en to 8′ also decreases
the intensity of the absorption peak at 408 nm, simultaneously
increasing the intensity of the new peak at 429 nm. The titration
curves at 408 and 429 nm (shown in the inset) indicate that
more than 100 equiv of en is necessary for 8′ to relax its π-π
interaction.
44
reaction. The demetalation of NiTBP-CHO to 2 was carried
4
5
out using conc. H
2
SO
4
.
4
2 was reduced by NaBH in THF to
2-hydroxymethyl-5,10,15,20-tetra(n-butyl)porphyrin, H TBP-CH -
OH, from which 2-chloromethyl-5,10,15,20-tetra(n-butyl)porphyrin,
TBP-CH Cl (3), was derived by treatment with SOCl /CH Cl
in the presence of pyridine. The chloromethyl group of 3 was so
labile that 3 was not purified on silica gel columns. It should only
be washed quickly with water and dried in vacuo and then used
2
2
H
2
2
2
2
2
t
for coupling with Boc-Cys(SNa)-OBu , which was prepared from
t
t
Boc-Cys(SH)-OBu and NaH in THF. Boc-Cys(SH)-OBu was
t
prepared by reducing Boc-cystine-OBu with dithiothreitol in
t
CHCl . Boc-cystine-OBu was derived from commercial cys-
3
t
tine-OBu by the reaction with Boc
2
O in dioxane/water. The
t
coupling of Boc-Cys(SNa)-OBu with 3 afforded 2-tert-butoxy-
As mentioned above, our tunable porphyrin arrays asymptoti-
cally approach new CD-active structures. The morphological
analogy of the asymmetric orientation of an antenna model can
be discussed by the R, Θ, Φ, φ, θ, and Ψ of the nearest-neighbor
dyes, where R, Θ, and Φ denote the polar coordinates between
the central atoms of adjacent dyes; on the other hand, φ, θ, Ψ
denote the Euler angles between the planes of the adjacent dyes
carbonylamino-3-[5,10,15,20-tetra(n-butyl)porphyrin]-2-yl-methyl-
H2,S
t
sulfanyl-propionic acid tert-butyl ester, Boc-Por -OBu (4). The
H2,S
t
elongation of this monomer to the dimer Boc-(Por
)
2
-OBu (6)
H2,S
t
H2,S
was carried out by coupling Por -OBu (5) with Boc-Por
(
5′) in DMF using PyBOP and DIEA as coupling reagents. The
H2,S t H2,S t
oligomers Boc-(Por ) -OBu (7), and Boc-(Por ) -OBu (8)
4
8
were similarly prepared from the corresponding precursors. Final-
Zn,S
t
(
Supporting Information 9), because an orientation analysis of
ly, their Zn correspondents Boc-(Por
)
2
-OBu (6′), Boc-
Zn,S
Zn,S
t
(
Por
)
4
-OBut (7′), and Boc-(Por
)
8
-OBu (8′) were respec-
the nearest-neighbor Chls in cyanobacterial PS1, PS2, green
plants, and FMO shows that they distribute in specific areas of
tively derived from 6, 7, and 8 by reacting them with
Zn(CH COO) ·2H O in CHCl . Details of the synthesis are given
in Supporting Information 1.
.2. Physicochemical Measurements. Reagents for physico-
3
2
2
3
(
R, Θ, Φ, φ, θ, Ψ) (Supporting Information 10). Search of the
synthetic modelssirrespective of polymer types, such as those
we provided here, or cross-linked typessthat show an analogy
in the distribution of (R, Θ, Φ, φ, θ, Ψ) among the nearest-
neighbor dyes, as well as efficient fluorescence yields, may lead
to the development of new antenna models for any of PS1, PS2,
green plants, and FMO.
3
chemical measurements were purchased from Sigma-Aldrich Corp.
UV-visible absorption (AB) spectra were recorded on a Shimadzu
UV2450 spectrophotometer using quartz cells with optical path
lengths of 0.01, 0.1, and 1 cm at room temperature in an Ar
atmosphere. The CD spectra were recorded on a JASCO J-725
spectropolarimeter using a quartz cell with an optical path length
of 0.1 cm in an Ar atmosphere. They were averaged for three or
five measurements and then smoothed. Fluorescence spectra were
recorded on a Shimadzu RF-5300PC fluorescence spectrometer
using a quartz cell with a optical path length of 0.5 cm at room
temperature in an Ar atmosphere and were corrected on 4-dim-
ethylamino-4-nitrostilben, 4-aminophtalimide, and quinine sulfate.
The fluorescence lifetime was measured at 645 and 660 nm in the
absence and presence of en, respectively, using a Hamamatsu
Photonics Picosecond Fluorescence Lifetime Measurement System
C4780 (composed of the dye laser LN203S2 with 2-(4-biphenyl)-
2
Por
.7. Concluding Remarks. (1) Peptide-linked porphyrins Boc-
Zn,S t
(
n
) -OBu (n ) 2, 4, and 8) were synthesized. The
oligomers showed a blue shift in the B-band regions of the
absorption spectra and a decrease in the fluorescence intensity
with increasing n, as well as circular dichroism. The fluorescence
was markedly recovered by the addition of 1,2-diaminoethane
(
en). (2) We succeeded in demonstrating the potentiality of the
dye oligomers responsive to additive reagents as light-harvesting
materials. Tunable dye polymers may be potential for the
modeling of the antenna chlorophylls observed in nature.
6
-phenylbenzoxazole (peak wavelength: 400 nm), the streak scope
C4334-02, and the triggering unit C4792) with a time range of 20
ns.
3
. Experimental Section
t
3
.1. Synthetic Route. The synthesis of Boc-(PorM,S)
-OBu
n
Acknowledgment. We thank Professor Masa-aki Haga of Chuo
University for assisting in the mass spectral measurement and
Professor Makoto Onaka of The University of Tokyo for the
discussions on meso-alkyl porphyrin synthesis. This work was
supported by a Grant-in-Aid for Scientific Research on Priority
Areas (417) from the Ministry of Education, Culture, Sports,
Science and Technology (MEXT) of the Japanese Government.
(
M ) H and Zn; n ) 1, 2, 4, and 8) was performed according the
2
route shown in Scheme 1. All the reactions were carried out in an
Ar atmosphere. The reactions involving porphyrinic amino acids
were conducted in the dark. The synthesis of porphyrinic amino
4
1
acids started from 5,10,15,20-tetra(n-butyl)porphyrin, H TBP (1),
2
42
which was prepared from pyrrole and diethoxypentane using the
(
41) (a) Jentzen, W.; Simpson, M. C.; Hobbs, J. D.; Song, X.; Ema, T.;
Nelson, N. N. Y.; Medforth, C. J.; Smith, K. M.; Veyrat, M.; Mazzanti,
M.; Ramasseul, R.; Marchon, J.-C.; Takeuchi, T.; Goddard, W. A.;
Shelnutt, J. A. J. Am. Chem. Soc. 1995, 117, 11085–11097. (b) Senge,
M. O.; Bischoff, I.; Nelson, N. Y.; Smith, K. M. J. Porphyrins
Phthalocyanines 1999, 3, 99–116.
(43) (a) Lindsey, J. S.; Schreiman, I. C.; Hsu, H. C.; Kearney, P. C.;
Marguerettaz, A. M. J. Org. Chem. 1987, 52, 827–836. (b) Li, F.;
Yang, K.; Tyhonas, J. S.; MacCrum, K. A.; Lindsey, J. S. Tetrahedron
1997, 53, 12339–12360. (c) Gonsalves, A. M. d’A. R.; Pereira, M. M.
J. Heterocycl. Chem. 1985, 22, 931–933.
(44) (a) Vilsmeier, A.; Haack, A. Chem. Ber. 1927, 60, 119–122. (b)
Ponomarev, G. V.; Maravin, G. B. Chem. Heterocycl. Compd. 1982,
18, 50–55. (c) Callot, H. J. Tetrahedron 1973, 29, 899–901.
(45) (a) Yeh, Chen-Y.; Miller, S. E.; Carpenter, S. D.; Nocera, D. G. Inorg.
Chem. 2001, 40, 3643–3646. (b) Lavallee, D. K. Coord. Chem. ReV.
1985, 61, 55–96.
(42) 1,1-Diethoxypentane was synthesized by treating n-valeraldehyde (100
-
1
g, 0.89 mol) with CaCl
The organic layer was washed with water three times, dried on K
and LiAlH , and finally distilled under reduced pressure. The yield
was 143.2 g (77%).
2
(20.6 g, 1.86 × 10 mol) in ethanol for 2 h.
2
CO
3
4
J. AM. CHEM. SOC. 9 VOL. 131, NO. 33, 2009 11725

A R T I C L E S
Yamamura et al.
Supporting Information Available: Synthesis of the porphyrin
of the monomer, stepwise change of the dimer spectrum upon
addition of en, definition of (R, Θ, Φ, φ, θ, Ψ), and specific
distribution of the nearest-neighbor Chls in natural organs. This
material is available free of charge via the Internet at http://
pubs.acs.org.
1
Zn,S
t
arrays, H NMR spectral change of Boc-(Por
2
) -OBu , Soret
band regions of absorption and circular dichroism spectra of
the dimer, deconvolution of visible absorption spectra of
Zn,S
t
Boc-(Por
number n of Boc-(Por
of ligands other than en, effect of en on the fluorescence intensity
n
) -OBu (n ) 1, 2, 4, and 8), effect of condensation
Zn,S
t
n
) -OBu on fluorescence yield, effect
JA809851D
1
1726 J. AM. CHEM. SOC. 9 VOL. 131, NO. 33, 2009