Synthesis and properties of star-shaped multiporphyrin-phthalocyanine light-harvesting arrays

Article abstract of DOI:10.1021/jo991001g

Light-harvesting arrays containing four porphyrins covalently linked to a phthalocyanine in a star-shaped architecture have been synthesized. Cyclotetramerization of an ethyne-linked porphyrinphthalonitrile in 1- pentanol in the presence of MgCl₂

Full text of DOI:10.1021/jo991001g

9090
J . Org. Chem. 1999, 64, 9090-9100
Syn th esis a n d P r op er ties of Sta r -Sh a p ed
Mu ltip or p h yr in -P h th a locya n in e Ligh t-Ha r vestin g Ar r a ys
J unzhong Li,† J ames R. Diers,‡ J yoti Seth,‡ Sung Ik Yang,§ David F. Bocian,*,‡
Dewey Holten,*,§ and J onathan S. Lindsey*,†
Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204,
Department of Chemistry, University of California, Riverside, California 92521-0403, and
Department of Chemistry, Washington University, St. Louis, Missouri 63130-4889
Received J une 22, 1999
Light-harvesting arrays containing four porphyrins covalently linked to a phthalocyanine in a star-
shaped architecture have been synthesized. Cyclotetramerization of an ethyne-linked porphyrin-
phthalonitrile in 1-pentanol in the presence of MgCl2 and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)
afforded the all-magnesium porphyrin-phthalocyanine pentad in 45% yield. Similar reaction using
Zn(OAc)2‚2H2O afforded the all-zinc porphyrin-phthalocyanine pentad in 15% yield. Arrays with
different metals (free base, Mg, Zn) in the porphyrin and phthalocyanine macrocycles have been
prepared by selective demetalation and metalation steps. This approach provides rapid and
convergent access to multiporphyrin-phthalocyanine arrays in diverse metalation states. The arrays
are reasonably soluble in organic solvents such as toluene, THF, and CH2Cl2. The arrays exhibit
strong absorption in the blue and red regions. Time-resolved and static optical measurements
indicate that intramolecular singlet-excited-state energy transfer from the porphyrin to the
phthalocyanine moiety is extremely rapid (picoseconds) and efficient. Ground-state electronic
communication among the porphyrins is indicated by rapid hole/electron hopping among the
metalloporphyrins in the arrays as detected by EPR measurements on the singly oxidized pentads.
These physical measurements indicate that the porphyrin-phthalocyanine pentads possess
favorable characteristics for light harvesting and other photonics applications.
In tr od u ction
meso linkages formed via oxidative coupling,5 (3) sheetlike
arrays with Pd-coordinated pyridyl linkages prepared via
self-assembly,6 (4) star-shaped arrays with diphenyl-
ethyne linkers formed via Pd-coupling reactions,7,8 oli-
gophenylethyne linkers prepared via Pd-coupling reac-
tions,9 phenylene linkers constructed via condensations
of a porphyrin aldehyde,10,11 phenylenevinylene linkers
formed via Wittig reactions,12 or benzoxyphenyl linkers
joined via alkylation,13 (5) linear arrays with phenylene
linkers formed via porphyrin aldehyde + dipyrromethane
condensations14 or 1,3,5-triazine-aniline units con-
structed via condensation of amino porphyrins and
cyanuric acid,15 (6) cyclic arrays with diphenylbutadiyne
linkers formed via Cu-coupling reactions16 or diphenyl-
ethyne linkers prepared via Pd-coupling reactions,17 and
Natural photosynthetic systems employ elaborate light-
harvesting complexes to capture dilute sunlight and
funnel the captured energy to the reaction center through
rapid and efficient transfer processes.1 The light-harvest-
ing complexes in the natural system are generally
composed of chlorophylls (or bacteriochlorophylls) as-
sembled in protein matrices that absorb over a wide
spectral range. The challenge of creating artificial mimics
of the light-harvesting complexes has prompted the
development of routes to a diverse collection of multi-
porphyrin arrays. Examples of covalently linked archi-
tectures comprised of five or more porphyrins and their
method of preparation include the following: (1) dendritic
arrays with stilbene linkers formed via successive Wittig
reactions,2 diphenylethyne linkers constructed via Pd-
coupling reactions,3 or a combination of diphenylethyne
and ester linkers prepared via Pd-coupling and Mit-
sunobu reactions,4 (2) windmill arrays with direct meso-
(5) Nakano, A.; Osuka, A.; Yamazaki, I.; Yamazaki, T.; Nishimura,
Y. Angew. Chem., Int. Ed. 1998, 37, 3023-3027.
(6) Drain, C. M.; Nifiatis, F.; Vasenko, A.; Batteas, J . D. Angew.
Chem., Int. Ed. 1998, 37, 2344-2347.
(7) Prathapan, S.; J ohnson, T. E.; Lindsey, J . S. J . Am. Chem. Soc.
1993, 115, 7519-7520.
(8) Li, F.; Gentemann, S.; Kalsbeck, W. A.; Seth, J .; Lindsey, J . S.;
Holten, D.; Bocian, D. F. J . Mater. Chem. 1997, 7, 1245-1262.
(9) Mongin, O.; Papamicael, C.; Hoyler, N.; Gossauer, A. J . Org.
Chem. 1998, 63, 5568-5580.
† North Carolina State University.
‡ University of California.
§ Washington University.
(1) (a) Larkum, A. W. D.; Barrett, J . Adv. Bot. Res. 1983, 10, 1. (b)
Deisenhofer, J .; Epp, O.; Miki, K.; Huber, R.; Michel, H. J . Mol. Biol.
1984, 180, 385-398. (c) Hunter, C. N.; van Grondelle, R.; Olsen, J . D.
Trends Biochem. Sci. 1989, 14, 72-76. (d) Ku¨hlbrandt, W.; Wang, D.
N.; Fujiyoshi, Y. Nature 1994, 367, 614-621. (e) McDermott, G.;
Princes, S. M.; Freer, A. A.; Hawethornthwaite-Lawless, A. M.; Papiz,
M. Z.; Cogdell, R. J .; Isaacs, N. W. Nature 1995, 374, 517-521.
(2) Burrell, A. K.; Officer, D. L. Synlett 1998, 1297-1307.
(3) Kuciauskas, D.; Liddell, P. A.; J ohnson, T. E.; Weghorn, S. J .;
Lindsey, J . S.; Moore, A. L.; Moore, T. A.; Gust, D. J . Am. Chem. Soc.
1999, 121, 8604-8614.
(10) Wennerstrom, O.; Ericsson, H.; Raston, I.; Svensson, S.; Pimlott,
W. Tetrahedron Lett. 1989, 30, 1129-1132.
(11) Osuka, A.; Liu, B.-L.; Maruyama, K. Chem. Lett. 1993, 949-
952.
(12) Officer, D. L.; Burrell, A. K.; Reid, D. C. W. Chem. Commun.
1996, 1657-1658.
(13) Norsten, T.; Branda, N. Chem. Commun. 1998, 1257-1258.
Ibid. 2165.
(14) Osuka, A.; Tanabe, N.; Nakajima, S.; Maruyama, K. J . Chem.
Soc., Perkin Trans. 2 1996, 199-203.
(15) Ichihara, K.; Naruta, Y. Chem. Lett. 1995, 631-632.
(16) Anderson, S.; Anderson, H. L.; Sanders, J . K. M. Acc. Chem.
Res. 1993, 26, 469-475.
(4) Mak, C. C.; Bampos, N.; Sanders, J . K. M. Angew. Chem., Int.
Ed. 1998, 37, 3020-3023.
10.1021/jo991001g CCC: $18.00 © 1999 American Chemical Society
Published on Web 11/20/1999

Synthesis of Pentameric Light-Harvesting Arrays
J . Org. Chem., Vol. 64, No. 25, 1999 9091
Ch a r t 1
(7) backbone polymeric arrays with oligophenylenevi-
nylene linkers formed via Wittig reactions18 or condensa-
tion of porphyrin aldehydes and active methylene units19
or phenylethyne linkers synthesized via Pd-coupling
reactions.20
chlorophylls and bacteriochlorophylls absorb strongly
both in the blue and in the red. In contrast, phthalocya-
nines absorb strongly in the red region (600-700 nm)
but weakly in the blue.22 A mixed system of porphyrins
and phthalocyanines that retains the essential electronic
features of the respective pigments should absorb strongly
both in the blue and in the red, thereby covering a large
part of the solar spectrum. While many multiporphyrin
arrays have been prepared,2-20 relatively few arrays
comprised of multiple phthalocyanines23 and even fewer
porphyrin-phthalocyanine dyads24,25 and tetraporphy-
rin-phthalocyanine pentads26 have been prepared. Ex-
amination of the spectroscopic properties of several such
dyads revealed efficient energy transfer from porphyrin
to phthalocyanine.24,25,27 A further attraction of a por-
phyrin-phthalocyanine combination is that the lowest
singlet electronic state of a phthalocyanine lies lower in
energy than that of a porphyrin regardless of metalation
state.28 Thus, an inherent energy funnel exists even with
identical metals in the two types of chromophores, unlike
the all-porphyrin arrays where differential metalation
states are necessary to achieve directed energy flow.
(2) Enhanced electronic communication. A Zn porphy-
rin and Fb porphyrin (each having a2u HOMOs) joined
at the meso-positions by a diphenylethyne linker exhib-
A star-shaped light-harvesting array that we previ-
ously synthesized and studied is shown in Chart 1. This
architecture functions as an energy funnel when the
peripheral porphyrins are metalated (Zn or Mg) and the
core porphyrin is in the free base (Fb) form.7,8 The
peripheral metalloporphyrins provide a large cross sec-
tion for light harvesting. The absorption of light is
followed by energy transfer to the energetically lower-
lying Fb porphyrin. The energy-transfer rate in toluene
at room temperature is ∼(20 ps)-1 in both Mg4FbU and
Zn4FbU, and in both cases the yields of energy transfer
are >99%. The photoinduced energy-transfer process
occurs predominantly by a through-bond mechanism
mediated by the diphenylethyne linker. To probe the
electronic interactions between the porphyrins in their
ground electronic states, the arrays were oxidized and
hole/electron hopping was examined.21 In the singly
oxidized all-Zn or all-Mg pentameric arrays, the hole is
delocalized over the five metalloporphyrins on the EPR
time scale. In the singly oxidized M4Fb arrays, the hole
is delocalized over the four metalloporphyrins. The rapid
hole/electron hopping in the oxidized arrays is indicative
of ground-state electronic communication between the
porphyrins mediated by the diphenylethyne linker.
The results obtained with the star-shaped pentamer
and related multiporphyrin arrays prompted the synthe-
sis and investigation of a new generation of light-
harvesting arrays. Our objectives included the following:
(1) Increased spectral coverage. Porphyrins absorb
strongly in the blue but weakly in the red, whereas
(22) Stillman, M. J .; Nyokong, T. In Phthalocyanines, Properties and
Applications; Leznoff, C. C., Lever, A. B. P., Eds.; VCH: New York,
1989; p 133.
(23) (a) Lam, H.; Marcuccio, S. M.; Svirskaya, P. I.; Greenberg, S.;
Lever, A. B. P.; Leznoff, C. C.; Cerny, R. L. Can. J . Chem. 1989, 67,
1087-1097. (b) Leznoff, C. C.; Svirskaya, P. I.; Khouw, B.; Cerny, R.
L.; Seymour, P.; Lever, A. B. P. J . Org. Chem. 1991, 56, 82-90. (c)
Vigh, S.; Lam, H.; J anda, P.; Lever, A. B. P.; Leznoff, C. C.; Cerny, R.
L. Can. J . Chem. 1991, 69, 1457-1461. (d) Bryant, G. C.; Cook, M. J .;
Ryan, T. G.; Thorne, A. J . Tetrahedron 1996, 52, 809-824. (e) Maya,
E. M.; Va´zquez, P.; Torres, T. Chem. Commun. 1997, 1175-1176. (f)
Gonza´lez, A.; Va´zquez, P.; Torres, T. Tetrahedron Lett. 1999, 40, 3263-
3266. (g) Maya, E. M.; Va´zquez, P.; Torres, T. Chem. Eur. J . 1999, 5,
2004-2013.
(24) Gaspard, S.; Giannotti, C.; Maillard, P.; Schaeffer, C.; Tran-
Thi, T.-H. J . Chem. Soc., Chem. Commun. 1986, 1239-1241.
(25) (a) Li, L.; Shen, S.; Yu, Q.; Zhou, Q.; Xu, H. J . Chem. Soc., Chem.
Commun. 1991, 619-620. (b) Li, X.; Zhou, Q.; Tian, H.; Xu, H. Chin.
J . Chem. 1998, 16, 97-108.
(17) Li, J .; Arounaguiry, A.; Seth, J .; Yang, S.-Y.; Kim, D.; Bocian,
D. F.; Holten, D.; Lindsey, J . S. J . Am. Chem. Soc. 1999, 121, 8927-
8940.
(18) J iang, B.; Yang, S.-W.; J ones, W. E., J r. Chem. Mater. 1997, 9,
2031-2034.
(19) J iang, B.; Yang, S.-W.; Niver, R.; J ones, W. E., J r. Synth. Met.
1998, 94, 205-210.
(26) (a) Kobayashi, N.; Nishiyama, Y.; Ohya, T.; Sato, M. J . Chem.
Soc., Chem. Commun. 1987, 390-392. (b) Kobayashi, N.; Ohya, T.;
Sato, M.; Nakajima, S. Inorg. Chem. 1993, 32, 1803-1808.
(27) Tran-Thi, T.-H.; Desforge, C.; Thiec, C.; Gaspard, S. J . Phys.
Chem. 1989, 93, 1226-1233.
(20) J iang, B.; Yang, S.-W.; Barbini, D. C.; J ones, W. E., J r. Chem.
Commun. 1998, 213-214.
(21) Seth, J .; Palaniappan, V.; J ohnson, T. E.; Prathapan, S.;
Lindsey, J . S.; Bocian, D. F. J . Am. Chem. Soc. 1994, 116, 10578-
10592.
(28) Tran-Thi, T.-H. Coord. Chem. Rev. 1997, 160, 53-91.

9092 J . Org. Chem., Vol. 64, No. 25, 1999
Li et al.
ited a photoinduced energy-transfer rate with a rate of
(24 ps)-1 (ref 29) whereas the analogue with a p-
phenylene linker underwent energy transfer with a rate
phthalonitriles for cyclization to the corresponding sub-
stituted phthalocyanine.35 Indeed, porphyrin-phthalo-
cyanine dyads (but not pentads) have been prepared by
mixed reaction of a porphyrin-phthalonitrile and a
second phthalonitrile in excess.24,25 Formation of the
phthalocyanine in the last step imposes some restrictions
on the range of available porphyrin and phthalocyanine
metalation states, as metal templating is used to facili-
tate phthalocyanine formation. An attractive feature of
this route is that the Pd-mediated coupling reactions are
used only in preparing small-molecule precursors, where
purification is more manageable. These considerations
prompted us to pursue the synthesis of the porphyrin-
phthalocyanine pentads via the phthalonitrile cyclotet-
ramerization strategy.
P or p h yr in -p h th a locya n in e P en ta d s. Treatment of
4-iodophthalonitrile and 4-ethynylbenzaldehyde under
Pd-mediated coupling conditions (triethylamine/THF (3:
1) at 35 °C in the presence of Pd2(dba)3 and AsPh3) gave
phthalonitrile-benzaldehyde (1) in 86% yield (Scheme
1). These general conditions have been used extensively
in the synthesis of multiporphyrin arrays, where the
yields in preparing porphyrin dimers are approximately
60-70%.36 A mixed condensation of 1, mesitaldehyde,
and pyrrole via the two-step one-flask method in CHCl3
with BF3‚O(Et)2 (BF3-ethanol cocatalysis)37 at room
temperature followed by oxidation with DDQ afforded a
mixture of porphyrins. Because the porphyrins bear
different numbers of polar groups (mesityl, 3,4-dicy-
anophenyl), the desired ethyne-linked porphyrin-phtha-
lonitrile (2) was easily isolated in 20% yield after one
flash silica column (Scheme 1).
of (3.5 ps)-1 30
. We sought to examine the energy-transfer
rate with a phenylethyne linker, where the ethyne moiety
is directly attached to a phthalocyanine.
(3) Convergent synthesis without Pd-mediated coupling
reactions.31 The star-shaped porphyrin arrays were pre-
pared by the Pd-mediated coupling of a monoethynyl Zn
porphyrin and a tetraiodo Fb porphyrin. The Pd-mediated
coupling reactions are well-suited for preparing small
arrays, but purification becomes increasingly difficult as
the size of the array increases.32 We sought to investigate
the use of phthalocyanine formation for the direct as-
sembly of a star-shaped energy-funnel architecture.
In this paper, we report the convergent synthesis of
star-shaped light-harvesting arrays comprised of four
porphyrins and a core phthalocyanine. This synthetic
route complements the Pd-mediated coupling employed
in the synthesis of a related set of porphyrin-phthalo-
cyanine dyads.33 Excited-state energy transfer in the
pentads has been examined by static and time-resolved
absorption and fluorescence spectroscopies. Ground-state
electronic communication has been investigated by EPR
studies of hole/electron hopping in the oxidized com-
plexes.
Resu lts a n d Discu ssion
1. Syn th esis. Str a tegy. The synthesis of ethyne-
linked porphyrin-phthalocyanine pentads could proceed
via two distinct strategies. In one approach, porphyrin
and phthalocyanine building blocks (a tetraiodophthalo-
cyanine and an ethynylporphyrin, or a tetraethynylphth-
alocyanine and an iodoporphyrin) are subjected to a Pd-
mediated coupling process,31,32 which is compatible with
different metals in the porphyrin and phthalocyanine
building blocks. This strategy mirrors that used in the
synthesis of a star-shaped porphyrin-phthalocyanine
complex involving condensation of an aminoporphyrin
with a phthalocyanine tetraanhydride.26 Limitations of
the Pd-mediated coupling approach include (1) incom-
plete reaction, which would afford a mixture composed
of phthalocyanines with various numbers of appended
porphyrins, and (2) side reactions, which result in
increasingly difficult separation as the size of the array
increases.32 Moreover, the core tetraiodo- and tetraethy-
nylphthalocyanine, which have been prepared for polym-
erization studies, are practically insoluble in organic
solvents, making purification and handling difficult.34
A complementary approach elaborates the phthalocya-
nine from a porphyrin-phthalonitrile in a final cyclotet-
ramerization step. Precedent for this route is seen in the
variety of large groups that have been attached to
The methods for preparing phthalocyanines from ph-
thalonitrile usually involve high-temperature condi-
tions.38 One of the milder methods to obtain phthalocy-
anines involves heating phthalonitrile in 1-pentanol in
the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)
and a metal salt.39 We employed this method with the
free base porphyrin-phthalonitrile. Porphyrin-phtha-
lonitrile (2) is soluble in 1-pentanol at room temperature.
Thus, condensation of 2 in 1-pentanol with MgCl2 in the
presence of DBU at 140 °C under argon for 24 h afforded
(35) (a) Snow, A. W.; J arvis, N. L. J . Am. Chem. Soc. 1984, 106,
4706-4711. (b) Okur, A. I.; Gu¨l, A.; Cihan, A.; Tan, N.; Bekaroglu, O¨ .
Synth. React. Inorg. Met.-Org. Chem. 1990, 20, 1399-1412. (c) Rihter,
B. D.; Bohorquez, M. D.; Rodgers, M. A. J .; Kenney, M. E. Photochem.
Photobiol. 1992, 55, 677-680. (d) Kobayashi, N.; Ashida, T.; Osa, T.
Chem. Lett. 1992, 2031-2034. (e) van Nostrum, C. F.; Picken, S. J .;
Nolte, R. J . M. Angew. Chem., Int. Ed. Engl. 1994, 33, 2173-2175. (f)
Linssen, T. G.; Du¨rr, K.; Hanack, M.; Hirsch, A. J . Chem. Soc., Chem.
Commun. 1995, 103-104. (g) Duro, J . A.; De la Torre, G.; Torres, T.
Tetrahedron Lett. 1995, 36, 8079-8082. (h) van Nostrum, C. F.; Picken,
S. J .; Schouten, A.-J .; Nolte, R. J . M. J . Am. Chem. Soc. 1995, 117,
9957-9965. (i) Yilmaz, I.; Bekaroglu, O¨ . Chem. Ber. 1996, 129, 967-
971. (j) Kimura, M.; Nakada, K.; Yamaguchi, Y.; Hanabusa, K.; Shirai,
H.; Kobayashi, N. Chem. Commun. 1997, 1215-1216. (k) Brewis, M.;
Clarkson, G. J .; Humberstone, P.; Makhseed, S.; McKeown, N. B.
Chem. Eur. J . 1998, 4, 1633-1640. (l) Kimura, M.; Hamakawa, T.;
Muto, T.; Hanabusa, K.; Shirai, H.; Kobayashi, N. Tetrahedron Lett.
1998, 39, 8471-8474.
(36) Wagner, R. W.; J ohnson, T. E.; Lindsey, J . S. J . Am. Chem.
Soc. 1996, 118, 11166-11180.
(37) (a) Lindsey, J . S.; Wagner, R. W. J . Org. Chem. 1989, 54, 828-
836. (b) Wagner, R. W.; Li, F.; Du, H.; Lindsey, J . S. Org. Proc. Res.
Dev. 1999, 3, 28-37.
(38) (a) Hanack, M.; Lang, M. Adv. Mater. 1994, 6, 819-833. (b)
Hanack, M.; Lang, M. Chemtracts 1995, 8, 131-165. (c) Hanack, M.;
Subramanian, L. R. In Handbook of Organic Conductive Molecules and
Polymers; Nalwa, H. S., Ed.; Wiley: New York, 1997; p 687.
(39) (a) Tomoda, H.; Saito, S.; Ogawa, S.; Shiraishi, S. Chem. Lett.
1980, 1277-1280. (b) Tomoda, H.; Saito, S.; Shiraishi, S. Chem. Lett.
1983, 313-316.
(29) Hsiao, J .-S.; Krueger, B. P.; Wagner, R. W.; Delaney, J . K.;
Mauzerall, D. C.; Fleming, G. R.; Lindsey, J . S.; Bocian, D. F.; Donohoe,
R. J . J . Am. Chem. Soc. 1996, 118, 11181-11193.
(30) Yang, S. I.; Lammi, R. K.; Seth, J .; Riggs, J . A.; Arai, T.; Kim,
D.; Bocian, D. F.; Holten, D.; Lindsey, J . S. J . Phys. Chem. B 1998,
102, 9426-9436.
(31) Wagner, R. W.; J ohnson, T. E.; Li, F.; Lindsey, J . S. J . Org.
Chem. 1995, 60, 5266-5273.
(32) Wagner, R. W.; Ciringh, Y.; Clausen, C.; Lindsey, J . S. Chem.
Mater. 1999, 11, 2974-2983.
(33) Yang, S.-Y.; Li, J .; Kim, D.; Holten, D.; Lindsey, J . S. J . Mater.
Chem., in press.
(34) Maya, E. M.; Haisch, P.; Va´zquez, P.; Torres, T. Tetrahedron
1998, 54, 4397-4404.

Synthesis of Pentameric Light-Harvesting Arrays
J . Org. Chem., Vol. 64, No. 25, 1999 9093
Sch em e 1
aromatic protons, consistent with the presence of regio-
isomers (see the Experimental Section). The presence of
four regioisomers from such phthalocyanine-forming
reactions is well-known and expected.42 The IR spectrum
of each array was devoid of nitrile peaks as well as peaks
in the region 1650-1800 cm-1, indicating the absence of
impurities typically observed in crude samples from
phthalocyanine-forming reactions. The pentads obtained
display good solubility in organic solvents such as
toluene, methylene chloride, or THF. The solubility of the
porphyrin-phthalocyanine pentads can be attributed
both to the bulky nature of the peripheral porphyrin
groups and to the existence of regioisomers. Given that
unsubstituted phthalocyanines are practically insoluble
in organic solvents, it appears that the four trimesi-
tylporphyrin macrocycles serve as solubilizing groups.
Selective Meta la tion a n d Dem eta la tion of P or -
p h yr in -P h th a locya n in e P en ta d s. The photochemical
properties of metalloporphyrins and metallophthalocya-
nines depend significantly on the nature of the metal.
In designing light-harvesting arrays, it is desirable for
the energy-transfer donor unit to have a long-lived
excited singlet state. For porphyrins, this requirement
is met by Mg (τ ≈ 9 ns) or the free base (τ ≈ 13 ns) more
so than Zn (τ ≈ 2 ns).8 On the other hand, for applications
such as light harvesting or directed energy flow, it is
desirable to avoid non-energy-transfer quenching reac-
tions such as electron transfer. To examine various
combinations of metals for efficacy in energy-transfer
(and avoidance of excited-state quenching) processes, we
examined the preparation of mixed-metal complexes of
the porphyrin-phthalocyanine arrays. Three distinct
demetalation/metalation manipulations were performed
(Scheme 3).
a very dark green mixture. Chromatography on one
alumina column removed nearly all of the non-phthalo-
cyanine species, and one subsequent size exclusion chro-
matography (SEC) column gave the all-magnesium por-
phyrin-phthalocyanine pentad (MgP)4MgPc in 45% yield
(Scheme 2). The similar treatment of 2 using zinc acetate
instead of magnesium chloride gave the all-zinc porphy-
rin-phthalocyanine pentad (ZnP)4ZnPc in 15% yield. The
difference in yields of the Mg versus Zn pentad mirrors
the phthalocyanine yields observed with the two metals
with simple phthalonitriles. Indeed, of a variety of metals
examined with simple phthalonitriles, magnesium was
one of the most effective in forming phthalocyanines.40
The facile metal insertion that occurs under the phtha-
locyanine-forming conditions is not surprising; zinc inser-
tion in porphyrins and phthalocyanines occurs under
mild conditions, and the conditions for phthalocyanine
formation resemble those used in classical methods for
magnesium insertion.41 In neither reaction was any free
base porphyrinic component isolated from the reaction
mixture. In the phthalocyanine-forming reaction, there
are four expected regioisomers due to the two possible
positions of substitution of each ethyne at the periphery
of the phthalocyanine; such species were not resolved by
column chromatography in either reaction.
(1) Selective demetalation. Magnesium porphyrins are
labile toward acids, and even chromatography on silica
gel will cause demetalation of magnesium porphyrins and
chlorins.41,43 However, magnesium phthalocyanines are
less labile toward demetalation, with no demetalation
occurring for magnesium phthalocyanines even after they
are stirred for several hours in the presence of silica gel.
Thus, stirring (MgP)4MgPc for 12 h in CH2Cl2 containing
silica gel gave (H2P)4MgPc in 74% yield. No demetalation
of the phthalocyanine moiety was observed at the end of
the reaction as verified by laser-desorption mass spec-
trometry and absorption spectroscopy.
(2) Selective metalation. Treatment of a solution of
(H2P)4MgPc in CHCl3 with zinc acetate at room temper-
ature afforded (ZnP)4MgPc in nearly quantitative yield.
Though the reaction was carried out overnight with a
large excess of zinc acetate, no transmetalation of mag-
nesium by zinc in the phthalocyanine moiety was ob-
served.
(3) Comprehensive demetalation. Treatment of (MgP)4-
MgPc with TFA gave the all-free base pentad (H2P)4H2-
Pc in 68% yield. Alternatively, treatment of (ZnP)4MgPc
with TFA in a manner similar to that of (MgP)4MgPc also
afforded (H2P)4H2Pc in 70% yield. In principle, (H2P)4H2-
Pc could also be prepared by cyclotetramerization of 2 in
the absence of metal salts; however, condensation under
Shiraishi conditions without a metal template generally
affords a much lower yield of the phthalocyanine.39,40
The 1H NMR spectrum of each pentad recorded in
THF-d8 showed multiple peaks from the phthalocyanine
(40) (a) Moser, F. H.; Thomas, A. L. The Phthalocyanines; CRC:
Boca Raton, FL, 1983; p 201. (b) Lever, A. B. P. Chemtech 1987, 17,
506. (c) Schultz, H.; Lehmann, H.; Rein, M.; Hanack, M. Struct.
Bonding 1991, 74, 41. (d) Mikhalenko, S. A.; Barkanova, S. V.; Lebedev,
O. L.; Luk’yanets, E. A. J . Gen. Chem. USSR 1971, 41, 2770-2773.
(41) Lindsey, J . S.; Woodford, J . N. Inorg. Chem. 1995, 34, 1063-
1069.
(42) Sommerauer, M.; Rager, C.; Hanack, M. J . Am. Chem. Soc.
1996, 118, 10085-10093.
(43) O’Shea, D. F.; Miller, M. A.; Matsueda, H.; Lindsey, J . S. Inorg.
Chem. 1996, 35, 7325-7338.

9094 J . Org. Chem., Vol. 64, No. 25, 1999
Sch em e 2. Con ver gen t Syn th esis of P or p h yr in -P h th a locya n in e P en ta d s
Li et al.
a
Each pentad is composed of a mixture of regioisomers.
Sch em e 3. Selective Meta la tion a n d Dem eta la tion of P or p h yr in -P h th a locya n in e P en ta d s
2. P h ysica l P r op er ties of th e Neu tr a l Com p lexes.
Absor p tion Sp ectr a . The absorption spectrum in tolu-
ene of each pentad resembles, but does not equal, the
sum of the spectra of the corresponding monomeric
components. A representative example is shown for
(H2P)4H2Pc in toluene at room temperature (Figure 1).
The absorption spectrum of each pentad is dominated by
the intense Soret band of the multiple porphyrin con-
stituents near 420 nm. The net molar absorption coef-
ficient of the porphyrin Soret band in each pentad is
approximately 1.4 × 106 M-1 cm-1 with only slight
broadening (fwhm ) ∼14 nm) compared with monomeric
porphyrins. The weaker Q-bands of the porphyrins lie
between 500 and 650 nm, with the exact wavelengths
depending on the metalation state; for example, the
absorption near 515 nm in Figure 1 is the QY(1,0) band

Synthesis of Pentameric Light-Harvesting Arrays
J . Org. Chem., Vol. 64, No. 25, 1999 9095
both series are (0.77, 5.5 ns), (0.62, 5.4 ns), and (0.38,
2.8 ns) for the free base, Mg, and Zn complexes, respec-
tively.
Two differences from the static emission properties of
the other pentads are observed in the case of (MgP)4MgPc.
(1) Some emission is observed from the Mg components,
and can be ascribed largely if not completely to the
greater photolability of this array, liberating monomeric
MgP. (2) The emission yield of the phthalocyanine core
obtained upon excitation of the porphyrin is reduced by
40-50% from the reference monomers. We ascribe this
finding to a contribution of charge transfer involving the
excited porphyrin and the ground-state phthalocyanine
core. This conclusion is based on the greater ease of
oxidation of Mg porphyrins relative to the Zn and free
base analogues, and results of extensive studies on a
series of porphyrin-phthalocyanine dyads.33
Fluorescence lifetimes of the phthalocyanine core unit
in selected porphyrin-phthalocyanine pentads were
determined by fluorescence modulation spectroscopy in
which both the phase shift and modulation amplitude
were monitored. The results are included in Table 1. The
free base and magnesium phthalocyanines have lifetimes
of about 4.5 ns, whereas the zinc analogue has a value
of about 2.5 ns. These lifetimes are similar to those found
for benchmark phthalocyanine monomeric reference com-
pounds. As is the case for phthalocyanine monomers, the
error limits on the emission lifetimes for the phthalo-
cyanine in each pentad are larger than normal because
of potential complexities such as effects of aggregation.
In particular, aggregation tends to lengthen the phtha-
locyanine lifetimes as concentrations are increased (even
in the several micromolar range), and the effect is more
pronounced along the series pentads < dyads < mono-
mers.33 This difference can account for any potential
slight shortening of the phthalocyanine lifetimes in the
pentads compared to the monomers, although a minor
contribution of charge transfer cannot be ruled out.
Nonetheless, the comparable fluorescence lifetime of the
central phthalocyanine in each array and the reference
monomer indicates that appending multiple porphyrins
via phenylethyne units does not significantly perturb the
excited-state properties of the phthalocyanine component.
Due to rapid energy transfer to the phthalocyanine, the
photoexcited porphyrins in the porphyrin-phthalocya-
nine arrays were far too weakly emissive (vide supra)
and short-lived (vide infra) to monitor via fluorescence
spectroscopy. Therefore, the decay properties of the
excited porphyrins were monitored using time-resolved
absorption spectroscopy.
Tr a n sien t Absor p tion Sp ectr a . The energy-transfer
rate from the photoexcited porphyrin constituents to the
ground-state phthalocyanine of selected pentads was
assessed using transient absorption spectroscopy. Rep-
resentative data for (H2P)4H2Pc are shown in Figure 2.
Excitation of the porphyrin with a 130 fs pulse at 420
nm causes the absorption difference spectra (∆A )
Aexcited state - Aground state) at early times to be dominated
by bleaching of the porphyrin Soret band near 420 nm
(solid spectrum in Figure 2). However, even at 0.2 ps after
excitation, bleaching is observed to some degree in the
ground-state absorption bands of the phthalocyanine,
notably in the Q-bands near 685 and 720 nm. The
bleaching in the phthalocyanine bands even at this early
time after excitation may arise from several factors, the
predominant of which appears to be an extremely fast
F igu r e 1. Absorption (solid line) and fluorescence emission
(dashed line, λexc ) 515 nm) spectra of (H2P)4H2Pc in toluene
at room temperature. The porphyrin Soret band (ꢀ421
) 1.5
nm
× 106 M-1 cm-1), phthalocyanine Q(0,0) band (ꢀ723
) 2.3 ×
nm
105 M-1 cm-1), and weaker bands from 500 to 700 nm provide
effective absorption across a broad range. Excitation of the
porphyrin (515 nm) is followed by efficient energy transfer to
the phthalocyanine. The latter fluoresces with high intensity
(Φf ) 0.76).
of the free base porphyrin units of (H2P)4H2Pc. The Soret
band of the phthalocyanine core component lies near 350
nm, and the Q-bands of this unit give rise to the relatively
strong absorption near 720 nm (ꢀ ≈ 2.5 × 105 M-1 cm-1
)
and 690 nm. The phthalocyanine Q(0,0) bands in all the
pentads are red shifted ∼20 nm relative to those in tetra-
tert-butylphthalocyanine ((t-Bu)4H2Pc)44 and its Mg and
Zn chelates (t-Bu)4MgPc44 and (t-Bu)4ZnPc;27 the red shift
is ∼10 nm relative to those in phthalocyanine monomers
bearing a total of either eight heptyl groups or six heptyl
groups and one ethyne group at the peripheral carbons
of the fused benzene rings.33 This red shift is attributed
to extension of the conjugated π-system involving the four
phenylethynyl linkers from the attached porphyrins.
Flu or escen ce P r oper ties. Upon excitation of (H2P)4H2-
Pc at 515 nm, where the porphyrin is the dominant
absorber, fluorescence was observed exclusively from the
phthalocyanine moiety (Figure 1). These results indicate
very efficient photoinduced intramolecular energy trans-
fer from the porphyrin to the phthalocyanine. Similar
results were observed for (ZnP)4ZnPc, (ZnP)4MgPc, and
(H2P)4MgPc. The fluorescence yields of the phthalocya-
nine components in these four pentads, obtained upon
excitation of either the porphyrin or the phthalocyanine,
are similar to those of phthalocyanine reference mono-
mers (Table 1). For example, the fluorescence properties
of tetra-tert-butylphthalocyanine ((t-Bu)4H2Pc) and its
metal chelates are as follows: (t-Bu)4H2Pc, Φf ) 0.77, τ
) 5.3 ns;44 (t-Bu)4MgPc, Φf ) 0.84, τ ) 4.9 ns;44,45
(t-Bu)4ZnPc, Φf ) 0.23, τ ) 3.3 ns.27 We have obtained
similar results for phthalocyanine monomers bearing a
total of either eight heptyl groups or six heptyl groups
and one ethyne group at the peripheral carbons of the
fused benzene rings.33 The approximate (Φf, τ) values for
(44) Teuchner, K.; Pfarrherr, A.; Stiel, H.; Freyer, W.; Leupold, D.
Photochem. Photobiol. 1993, 57, 465-471.
(45) (a) Freyer, W.; Da¨hne, S.; Minh, L. Q.; Teuchner, K. Z. Chem.
1986, 26, 334-336. (b) Stiel, H.; Teuchner, K.; Paul, A.; Freyer, W.;
Leupold, D. J . Photochem. Photobiol., A. 1994, 80, 289-298.

9096 J . Org. Chem., Vol. 64, No. 25, 1999
Ta ble 1. Excited -Sta te P r op er ties of P or p h yr in -P h th a locya n in e Ar r a ysa
Li et al.
-1
array
porphyrin lifetime (ps)b
phthalocyanine lifetime (ns)
phthalocyanine Φfc
(ktrans
)
avg
d (ps)
Φ
trans (%)
(H2P)4H2Pc
1.2 ( 0.2 (62%)
13 ( 3 (38%)
0.8 ( 0.3 (68%)
15 ( 3 (32%)
0.9 ( 0.3 (55%)
7 ( 2 (45%)
4.6 ( 0.7
0.76
5.6
5.3
3.6
>99
(MgP)4MgPc
(ZnP)4ZnPc
4.3 ( 0.7
2.4 ( 0.4
∼0.4e
∼60e
>99
0.38
a
b
All data acquired in toluene at room temperature. The energy-transfer rates and efficiencies are obtained using eqs 1 and 2. Average
of values from decay of the porphyrin bleaching and growth of the phthalocyanine bleaching in transient absorption measurements.
c Phthalocyanine fluorescence yield ((15%) obtained upon excitation of the porphyrin near 420 nm. These yields were determined using
meso-tetraphenylporphyrin as a reference (Φf ) 0.11), a method that also reproduced literature values for the corresponding phthalocyanine
d
monomers. Derived assuming a lifetime for the photoexcited porphyrin that is the amplitude-weighted average value given in the second
column (obtained using porphyrin-Soret excitation). e The yields of phthalocyanine fluorescence and porphyrin-to-phthalocyanine energy
transfer are reduced for (MgP)4MgPc relative to the other pentads due to competing electron transfer from the photoexcited porphyrin
(see the text).
685 nm. The most significant contribution to this effect
stems from the presence of stimulated emission in the
longer-wavelength feature (fluorescence stimulated by
the white light probe pulse). Over the next tens of
picoseconds, the spectrum shows only a minor evolution
from the spectrum at 16 ps, mainly in the amplitude of
the feature at 720 nm.
The time evolution of the decay of porphyrin Soret
bleaching near 420 nm and of the growth of the phtha-
locyanine bleaching near 720 nm for (H2P)4H2Pc is dual
exponential in nature. Representative kinetic data and
dual-exponential fits are given in the lower panel of
Figure 2. It can be seen that the time constant pairs in
the two regions are in good agreement, with average
values of ∼1 and ∼10 ps having ∼60/40 relative ampli-
tudes. Very similar transient absorption characteristics
and time profiles were observed for the (MgP)4MgPc and
(ZnP)4ZnPc pentads (Table 1). Essentially the same
behavior was also observed for (H2P)4H2Pc using Q-region
excitation at 550 nm. The latter finding indicates that
the dual-exponential behavior is not associated with
energy or electron transfer associated with the S2 (Soret)
versus S1 (Q) states of the porphyrin components. The
biphasic kinetic behavior cannot be ascribed to a sub-
population of a particular porphyrin-phthalocyanine
regioisomer, because the same dual-exponential kinetics
were observed in the related porphyrin-phthalocyanine
dyads where no regioisomers are present.33 Possible
origins of the dual-exponential behavior and other com-
plexities are discussed in the context of the studies on
the dyads where comparisons among a large body of data
can be made.46 One candidate for the ∼10 ps component
F igu r e 2. Time-resolved absorption data for (H2P)4H2Pc in
toluene at 298 K, acquired using excitation of the porphyrin
components with a 130 fs flash at 420 nm. The top panel shows
absorption difference spectra corresponding to the porphyrin
excited state (solid) and the phthalocyanine excited state
(dashed). The bottom panel gives kinetic data for decay of
bleaching in the porphyrin Soret band (open squares) and
growth of bleaching in the phthalocyanine Q-band (closed
circles). Date before t ) 0 and along the instrument rise are
not shown for clarity.
is intermolecular energy transfer involving two closely
associated arrays.
En er gy-Tr an sfer Rates an d Mech an ism s. The tran-
sient absorption data, as well as the static and time-
resolved fluorescence data, lead to the assessment that
energy transfer from the photoexcited porphyrin units
to the central phthalocyanine core in the arrays is a rapid
(46) For (H2P)4H2Pc, the growth of bleaching in the 685 nm band
occurs essentially completely with the ∼1 ps component, with perhaps
a very minor subsequent decay over the time scale of about 10 ps. For
the other metal-containing pentads, the splitting in the ground-state
spectrum is not observed, and so the presence or extent of this
phenomenon cannot be cleanly delineated in those arrays. This
difference in the contribution of the slow component to the rise of the
bleaching in the two Q-bands of (H2P)4H2Pc is not directly connected
with the origin of the dual-exponential decay of the porphyrin excited
state and the behavior for the growth of the phthalocyanine lowest
excited singlet state, but rather may reflect dynamics within the
phthalocyanine manifold after energy transfer. These dynamics in free
base phthalocyanines may involve symmetry effects associated with
the proton axis with respect to the site(s) of linker attachment.
(∼1 ps) component of energy transfer from the photoex-
cited porphyrin to the ground-state phthalocyanine. At
increasing times after excitation, the bleaching in the
porphyrin Soret band diminishes dramatically, reflecting
decay of the porphyrin component to the ground elec-
tronic state. Concomitantly, the bleaching in the phtha-
locyanine bands in the Q-region increases (see the dashed
spectrum taken at 16 ps in Figure 2). In this longer-time
spectrum, there appears to be a proportionately larger
increase in the apparent bleaching near 720 nm than at

Synthesis of Pentameric Light-Harvesting Arrays
J . Org. Chem., Vol. 64, No. 25, 1999 9097
and highly efficient process. The efficiency is only reduced
when ultrafast electron transfer from the photoexcited
porphyrin to the phthalocyanine can occur in arrays such
as (MgP)4MgPc where the thermodynamics of the process
are favorable. The major fraction of the energy-transfer
process appears to occur with a time constant of about 1
ps, with a somewhat lesser amount occurring with a time
constant of about 10 ps. To assess the overall rate and
efficiency of excited-state energy transfer, an amplitude-
weighted average of the two components will be used for
the lifetime of the photoexcited porphyrin in the arrays.
Note that these lifetimes are at least 400-fold shorter
(and up to about 2000-fold shorter) than the lifetimes of
the relevant photoexcited monomeric porphyrin reference
compounds (Table 1). This difference, as with the reduced
emission yields of the porphyrins in the arrays, reflects
the high efficiency of energy transfer to the central
phthalocyanine unit.
which revealed that hole/electron hopping rates between
the ZnP constituents are 107 s-1 (or faster).21 The rapid
hole/electron hopping in Zn4FbU indicates that the
central Fb constituent serves as an effective superex-
change mediator. This role for the Fb constituent in the
all-porphyrin arrays is dictated by the fact that the hole
cannot physically reside on this porphyrin due to its
substantially higher oxidation potential compared with
the Zn porphyrin.47 The oxidation potential of the Pc unit
is anticipated to be much higher still than that of the
corresponding porphyrin due to the electron-withdrawing
influence of the four additional nitrogen atoms;48 accord-
ingly, the hole cannot reside on this constituent of the
(MP)4MPc complexes. The issue in question is whether
the MPc constituent of the pentads functions as an
efficient superexchange mediator for hole/electron hop-
ping.
The pentad (ZnP)4ZnPc exhibits two E1/2 values at 0.61
and 0.89 V (vs Ag/Ag+; E1/2 (FeCp2/FeCp2+) ) 0.22 V).
These potentials are essentially identical to those of the
first and second oxidations of monomeric Zn porphyrins
with the same aryl substituents.49 Quantitative coulom-
etry of (ZnP)4ZnPc indicates that the lowest potential
peak is due to four overlapped one-electron oxidations of
the Zn porphyrins. Square wave voltammetry shows that
this peak is slightly asymmetric, owing to small differ-
ences in the E1/2 values of the overlapping one-electron
oxidations of the Zn porphyrins. This behavior directly
parallels that previously observed for the Zn constituents
of the Zn4FbU array.21 The redox behavior of (MgP)4MgPc
is different from that of (ZnP)4ZnPc. In particular, the
Mg complex exhibits a single broad wave at ∼0.39 V and
no other resolved features. Cycling the potential resulted
in degradation of the complex, as evidenced by the
appearance of new features that were irreproducible with
successive scans. Due to the instability of the oxidation
products of (MgP)4MgPc, spectroscopic studies of these
π-cations were not pursued. It is noteworthy that phtha-
locyanines bearing other types of redox-active units, such
as four ferrocene groups50 or eight tetrathiafulvalene
groups,51 also exhibited complex electrochemical behav-
ior.
The rate and yield of excited-state energy transfer in
each array can be derived using the following expres-
sions:
1/τD ) krad + kisc + kic
1/τDA ) krad + kisc + kic + ktrans
ktrans ) 1/τDA - 1/τD
(1)
(2)
(3)
(4)
Φtrans ) ktransτDA ) 1 - τDA/τD
Here, τDA is the excited-state lifetime of the excited
porphyrin donor in the presence of the phthalocyanine
acceptor, τD is the excited-state lifetime of the benchmark
porphyrin monomer, ktrans is the energy-transfer rate, and
Φtrans is the energy-transfer efficiency. These equations
assume that, besides energy transfer, there are no
pathways for depopulating the excited porphyrin (P*) in
the arrays other than the intrinsic processes (radiative
decay (rad), intersystem crossing (isc), internal conver-
sion (ic)) also present in the monomer. The transient
absorption and static emission data support this assump-
tion. However, within experimental uncertainty we can-
not exclude the possibility of a small amount of electron
transfer from the photoexcited porphyrin.
Table 1 gives the energy-transfer rate constants and
yields obtained by application of eqs 1-4 to the excited-
state lifetimes. The rate of excited-state energy transfer
in each case is effectively given by the amplitude-
weighted average excited-state lifetime of ∼(5 ps)-1. The
energy-transfer yield is >99% except for (MgP)4MgPc,
where electron transfer provides an alternative decay
channel for the porphyrin excited state. For (H2P)4H2Pc
and (ZnP)4ZnPc, the efficiency would not fall below 99%
even if one based the calculation solely using the slower
component of the energy transfer (∼10 ps), and would
be even closer to 99.9% if the major component of the
porphyrin excited-state decay time (∼1 ps) were used.
Hence, although there is a complexity associated with
the dual-exponential kinetics in these porphyrin-phtha-
locyanine arrays, the data are unequivocal in indicating
an extremely rapid energy-transfer process.
The UV-vis absorption characteristics of oxidation
products of (ZnP)4ZnPc (not shown) are typical of those
of other porphyrin π-cation radicals, namely, blue-shifted
B-bands (relative to the neutral complexes) and very
weak, broad bands in the visible and near-infrared
regions.47 The absorption spectra of the oxidized com-
plexes appear to be a superposition of neutral and
cationic species. This observation and the results of the
electrochemical studies are consistent with weak interac-
tions between the constituent porphyrins.52-54
(47) Felton, R. H. In The Porphyrins; Dolphin, D., Ed.; Academic
Press: New York, 1978; Vol. V, pp 53-126.
(48) The reported electrochemical potentials of simple phthalocya-
nine monomers often reflect aggregation, making direct comparison
with porphyrins difficult. See: Lever, A. B. P.; Milaeva, E. R.; Speier,
G. In Phthalocyanines, Properties and Applications; Leznoff, C. C.,
Lever, A. B. P., Eds.; VCH Publishers: New York, 1993; Vol. 1, pp
1-69.
3. P h ysica l P r op er ties of th e Oxid ized Com -
p lexes. The oxidation products of (ZnP)4ZnPc and
(MgP)4MgPc were examined explicitly to assess the
mobility of the hole/electron(s) among the MP arms of
each star-shaped array. These studies were motivated
by our earlier work on the pentaporphyrin array Zn4FbU,
(49) Seth, J .; Palaniappan, V.; Wagner, R. W.; J ohnson, T. E.;
Lindsey, J . S.; Bocian, D. F. J . Am. Chem. Soc. 1996, 118, 11194-
11207.
(50) J in, Z.; Nolan, K.; McArthur, C. R.; Lever, A. B. P.; Leznoff, C.
C. J . Organomet. Chem. 1994, 468, 205-212.
(51) Wang, C.; Bryce, M. R.; Batsanov, A. S.; Stanley, C. F.; Beeby,
A.; Howard, J . A. K. J . Chem. Soc., Perkin Trans. 2 1997, 1671-1678.

9098 J . Org. Chem., Vol. 64, No. 25, 1999
Li et al.
spectrum can be achieved. This behavior indicates that
the hole/electron of [(ZnP)4ZnPc]+ is completely delocal-
ized on the EPR time scale.47,49 This time scale is
determined by the 14N hyperfine coupling, which is ∼4
MHz. Thus, the hole/electron hopping rate in [(ZnP)4ZnPc]+
must be considerably faster (i.e., g107 s-1). The hole/
electron hopping characteristics of [(ZnP)4ZnPc]+ exactly
parallel those previously observed for [Zn4FbU]+.21 Ac-
cordingly, the central ZnPc unit in (ZnP)4ZnPc is an
effective superexchange mediator for hole/electron hop-
ping.
Con clu sion
Porphyrin-phthalocyanine light-harvesting arrays have
been prepared by cyclotetramerization of substituted
phthalonitriles. This straightforward method permits the
easy isolation of the desired arrays by column chroma-
tography. The complementary absorption properties of
porphyrin and phthalocyanine chromophores make them
ideal components of light-harvesting systems. Excited-
state energy transfer from the porphyrin constituents to
the phthalocyanine core in the arrays is rapid and
generally extremely efficient, despite some complexities
associated with dual-exponential behavior and charge
transfer in limited cases where the thermodynamics are
appropriate. Similarly, ground-state hole/electron hop-
ping is rapid on the EPR time scale for the singly oxidized
all-metal pentads. These results indicate that electronic
communication is very effective among the constituents
of these arrays. The efficient convergent synthesis and
efficient light-harvesting properties augurs well for the
construction of larger multiporphyrin-phthalocyanine
light-harvesting arrays by this approach.
F igu r e 3. EPR spectra of [(ZnP)4ZnPc]+ and [ZnTMP]+ in
CH2Cl2/CHCl3 (1:1) at 298 K. The dashed lines shown are
simulated spectra.
Exp er im en ta l Section
Gen er a l P r oced u r es. 1H NMR spectra were collected at
300 MHz. Mass spectra of porphyrins and multiporphyrin-
phthalocyanine arrays were obtained via laser desorption mass
spectrometry (LD-MS) in the absence of an added matrix.56
High-resolution fast atom bombardment (FAB) mass spec-
trometry of the arrays was carried out at greater than unit
resolution. Signal-to-noise levels were not sufficient to allow
measurement of the nominal exact mass ion, but the base peak
in the isotope cluster was observed. Triphenylarsine, tris-
(dibenzylideneacetone)dipalladium(0) (Pd2(dba)3), and 1,8-
diazabicyclo[5.4.0]undec-7-ene (DBU) were used as received
from Aldrich. 4-Iodobenzaldehyde was obtained from Karl
Industries, Ltd.
Solven ts. All solvents were dried by standard methods.
CH2Cl2 (Fisher, reagent grade) and CHCl3 (Fisher, certified
ACS grade, stabilized with 0.75% ethanol) were distilled from
K2CO3. Simple distillation does not significantly alter the
ethanol content. Toluene (Fisher, certified ACS) and triethy-
lamine (Fluka, puriss) were distilled from CaH2. Pyrrole
(Acros) was distilled at atmospheric pressure from CaH2. All
other solvents were used as received.
The EPR spectrum of the one-electron oxidation prod-
uct of (ZnP)4ZnPc at 298 K is shown in Figure 3. For
comparison, the spectrum of the one-electron oxidation
product of zinc tetramesitylporphyrin (ZnTMP) is also
shown in the figure. In liquid solution, [ZnTMP]+ exhibits
a partially resolved nine-line hyperfine pattern due to
interaction of the unpaired electron with the four pyrrole
14N nuclei (a(14N) ≈ 1.5 G). This hyperfine pattern is
liquid solution EPR spectrum of [(ZnP)4ZnPc]+ exhibits
a much narrower line than [ZnTMP]+, with no resolved
hyperfine structure. Simulations of the EPR spectrum
of [(ZnP)4ZnPc]+ indicate that the line shape can be
reasonably well accounted for by reducing the hyperfine
coupling by a factor of 4 and quadrupling the number of
interacting nuclei, while holding the line width constant
(dashed line in the figure). If the constraint on the line
width is relaxed, an essentially perfect fit to the EPR
2
characteristic of a A2u porphyrin π-cation radical.55 The
Ch r om a togr a p h y. Adsorption column chromatography
was performed using alumina (Fisher A-540, 80-200 mesh),
grade V alumina,8 or flash silica gel (Baker, 60-200 mesh).
Preparative-scale size exclusion chromatography (SEC) was
performed using BioRad Bio-beads SX-1. A preparative scale
glass column was packed using Bio-Beads SX-1 in tetrahy-
drofuran and eluted with gravity flow. Following purification,
the SEC column was washed with two volume equivalents of
solvents used.
(52) Elliot, C. M.; Hershenhart, E. J . Am. Chem. Soc. 1982, 104,
7519-7526.
(53) Edwards, W. D.; Zerner, M. C. Can. J . Chem. 1985, 63, 1763-
1772.
(54) (a) Angel, S. M.; DeArmond, M. K.; Donohoe, R. J .; Wertz, D.
W. J . Phys. Chem. 1985, 89, 282-285. (b) Donohoe, R. J .; Tait, C. D.;
DeArmond, M. K.; Wertz, D. W. Spectrochim. Acta 1986, 42A, 233-
240. (c) Tait, C. D.; MacQueen, D. B.; Donohoe, R. J .; DeArmond, M.
K.; Hanck, K. W.; Wertz, D. W. J . Phys. Chem. 1986, 90, 1766-1771.
(d) Donohoe, R. R.; Tait, C. D.; DeArmond, M. K.; Wertz, D. W. J . Phys.
Chem. 1986, 90, 3923-3926. (e) Donohoe, R. J .; Tait, C. D.; DeArmond,
M. K.; Wertz, D. W. J . Phys. Chem. 1986, 90, 3927-3930.
(55) Fajer, J .; Davis, M. S. In The Porphyrins; Dolphin, D., Ed.;
Academic Press: New York, 1979; Vol. IV, pp 197-256.
(56) Srinivasan, N.; Haney, C. A.; Lindsey, J . S.; Zhang, W.; Chait,
B. T. J . Porphyrins Phthalocyanines 1999, 3, 283-291.

Synthesis of Pentameric Light-Harvesting Arrays
J . Org. Chem., Vol. 64, No. 25, 1999 9099
Analytical scale SEC was performed to assess the purity of
the arrays. Analytical SEC columns (styrene-divinylbenzene
copolymer) were purchased from Hewlett-Packard and Phe-
nomonex. Analytical SEC was performed with a Hewlett-
Packard 1090 HPLC using 100 Å (7.5 × 300 mm) columns
eluting with THF (flow rate 0.8 mL/min). Sample detection
was achieved by absorption spectroscopy using a diode array
detector with quantitation at 420 and 354 nm ((10 nm
bandwidth).
Sta tic Absor p tion a n d Em ission . Static absorption and
fluorescence measurements were performed as described
previously.8,57 Nondeaerated samples with an absorbance
e0.15 at λexc were used for the emission measurements; the
detection band-pass was 4-5 nm, and the spectra were
corrected for the detection-system spectral response. Emission
quantum yields were measured relative to meso-tetraphe-
nylporphyrin (Φf ) 0.11).58
Tim e-Resolved Flu or escen ce. Fluorescence lifetimes were
determined by modulation (phase shift) techniques using a
Spex Tau2 spectrometer. Samples (1-50 µM) in toluene were
deaerated by bubbling with N2. Samples were excited at
several wavelengths in the Soret- and Q-band regions, and the
emission at wavelengths >680 nm was detected using a long-
pass filter. Modulation frequencies from 20 to 300 MHz were
utilized, and both the fluorescence phase shift and modulation
amplitude were analyzed in modeling the data. Lifetimes of a
number of control samples obtained by this technique were
found to be the same as obtained by us or others using time-
resolved techniques.59
Tim e-Resolved Absor p tion . Transient absorption data
were acquired as described elsewhere.30,60 In short, samples
(∼0.2 mM in toluene) in 2 mm path length cuvettes at room
temperature were excited at 10 Hz with a ∼130 fs, 4-7 µJ
pulse at 420 or 550 nm from an optical parametric amplifier
(OPA) pumped by an amplified Ti:sapphire laser system
(Spectra Physics). Transient absorption difference spectra were
obtained using broad-band detection methods utilizing a ∼130
fs white light probe pulse. The time evolution of the spectra
was obtained by varying the pump-probe delay with an optical
delay pump pulse. The kinetic data shown in Figure 2 were
generated by averaging the ∆A values in 10 nm intervals about
the specified center wavelength, namely, 420 nm for the
porphyrin bleaching and 685 or 718 nm for the phthalocyanine
bleaching. The kinetic traces were then fit to a function
consisting of either a single or dual exponential plus a constant
using a nonlinear least squares algorithm (taking into account
the instrument rise and pre-zero-time data, which are not
shown in Figure 2 for clarity).
not be generated quantitatively due to instability of the
complex (vide supra). For all of the oxidized complexes,
spectroscopic studies were performed immediately after oxida-
tion and transfer of the samples to an optical cuvette or quartz
capillary.
EP R Sp ectr oscop y. The EPR spectra were recorded as
previously described.21 The sample concentrations for all of the
experiments were typically 0.05 mM. The microwave power
and magnetic field modulation amplitude were typically 5.7
mW and 0.32 G, respectively.
Syn th eses. The synthesis of each complex was performed
as follows.
4-[2-(3,4-Dicya n op h en yl)et h yn yl]b en za ld eh yd e (1).
Samples of 4-iodophthalonitrile61 (0.98 g, 3.85 mmol), 4-ethy-
nylbenzaldehyde62 (0.50 g, 3.85 mmol), Pd2(dba)3 (35.6 mg, 0.04
mmol), and AsPh3 (95.0 mg, 0.31 mmol) were added to a 25
mL three-neck round-bottom flask equipped with a condenser.
The reaction vessel headspace including the condenser was
deaerated with a high flow rate of argon for 30 min. Then
deaerated triethylamine (15 mL) and THF (5 mL) were added
via a syringe, and argon was purged through the vessel for
another 5 min. At this point the argon flow was decreased,
the reaction vessel was immersed in an oil bath at 35 °C, and
the mixture was stirred overnight. Upon completion of the
reaction as judged by TLC, CH2Cl2 (100 mL) was added to the
reaction mixture to dissolve the product, and the resulting
solution was washed with 5% NaHCO3, H2O, and dried (Na2-
SO4). After removal of the solvent under reduced pressure, the
resulting brown solid was redissolved in CH2Cl2/hexanes (3:
2), and loaded onto a silica gel column (3.5 × 25 cm) packed
with the same solvent. Elution with CH2Cl2/hexanes (3:2)
afforded AsPh3 as the first colorless fraction, followed by a
brown band and then a yellow band which contained traces of
uncharacterized species. The desired compound then eluted
as a colorless band, which after removal of the solvent afforded
0.85 g (86%) of a white solid: mp 155-156 °C; IR (neat film)
1
ν 2212 (CN), 1696 (CO), 1599, 1205, 1157, 833, 768 cm-1; H
NMR (CDCl3) δ 7.70-7.73 (m, 2 H), 7.84-7.86 (m, 2 H), 7.91-
7.96 (m, 3 H), 10.06 (s, 1 H); 13C NMR (CDCl3) δ 88.99, 95.23,
114.78, 115.13, 115.20, 116.65, 127.41, 128.67, 129.87, 132.71,
133.78, 135.91, 136.33, 136.65, 191.33; HRMS (EI) calcd for
C
17H18N2O 256.0637, found 256.0628. Anal. Calcd: C, 79.68;
H, 3.15; N, 10.93. Found: C, 79.80; H, 3.10; N, 10.92.
5,10,15-Tr im esityl-20-{4-[2-(3,4-dicyan oph en yl)eth yn yl]-
p h en yl}p or p h yr in (2). Samples of mesitaldehyde (0.79 mL,
5.3 mmol), 1 (453 mg, 1.77 mmol), and pyrrole (0.49 mL, 7.1
mmol) were condensed in CHCl3 (700 mL) with BF3‚O(Et)2
(0.86 mL of 2.5 M stock solution in CHCl3) at room tempera-
ture for 1 h. Then DDQ (1.22 g, 5.38 mmol) was added, and
after the mixture was stirred for 1 h at room temperature,
the solvent was removed under reduced pressure. The residue
was then dissolved in CH2Cl2/hexanes (1:1, 50 mL) and passed
through a short silica gel column to remove the non-porphy-
rinic components from the crude reaction mixture. The result-
ing mixture of porphyrins was redissolved in CH2Cl2/hexanes
(2:3) and loaded onto a flash silica gel column (6 × 10 cm).
Elution with the same solvent afforded tetramesitylporphyrin,
and then elution with CH2Cl2/hexanes (1:1) gave the desired
compound as the second band, affording 320 mg (20%) of a
purple solid: IR (neat film) ν 3309 (NH), 2917 (CH), 2209 (CN),
1592, 1467, 1347, 1211, 1189, 965, 851, 802, 737 cm-1; 1H NMR
(CDCl3) δ -2.57 (s, 2 H), 1.85 (s, 18 H), 2.63 (s, 9 H), 7.28 (s,
6 H), 7.85-8.07 (m, 5 H), 8.24 (d, J ) 8.1 Hz, 2 H), 8.64 (m, 4
H), 8.69 (d, J ) 5.3 Hz, 2 H), 8.74 (d, J ) 5.3 Hz, 2 H); LD-MS
calcd av mass 891.1, obsd 889.5; HRMS (FAB) calcd for
C63H50N6 890.4097, found 890.4144; λabs (toluene) 421, 516, 549,
593, 650 nm.
Electr och em istr y. The oxidized complexes were prepared
and manipulated in a glovebox as previously described.21 The
solvent used for the studies consisted of a 1:1 mixture of CH2-
Cl2/CHCl3. This mixture was used because the solubility in
pure CH2Cl2 was poor. Tetrabutylammonium hexafluorophos-
phate (0.1 M) (Aldrich, recrystallized three times from metha-
nol and dried under vacuum at 110 °C) was used as the
supporting electrolyte. The potentials reported are vs Ag/Ag+;
E
1/2(FeCp2/FeCp2+) ) 0.22 V. The integrity of the samples was
checked by cyclic voltammetry after oxidation. For (ZnP)4ZnPc,
the cyclic voltammograms were reproducible upon repeated
scans and exhibited no scan-rate dependence in the 20-100
mV/s range. For (MgP)4MgPc, the π-cation radical species could
(57) (a) Strachan, J . P.; Gentemann, S.; Seth, J .; Kalsbeck, W. A.;
Lindsey, J . S.; Holten, D.; Bocian, D. F. J . Am. Chem. Soc. 1997, 119,
11191-11201. (b) Strachan, J . P.; Gentemann, S.; Seth, J .; Kalsbeck,
W. A.; Lindsey, J . S.; Holten, D.; Bocian, D. F. Inorg. Chem. 1998, 37,
1191-1201.
(58) Yang, S. I.; Seth, J .; Strachan, J . P.; Gentemann, S.; Kim, D.;
Holten, D.; Lindsey, J . S.; Bocian, D. F. J . Porphyrins Phthalocyanines
1999, 3, 117-147.
(59) (a) Yang, S. I.; Seth, J .; Balasubramanian, T.; Kim, D.; Lindsey,
J . S.; Holten, D.; Bocian, D. F. J . Am. Chem. Soc. 1999, 121, 4008-
4018. (b) Balasubramanian, T.; Lindsey, J . S. Tetrahedron 1999, 55,
6771-6784.
(60) (a) Kirmaier, C.; Holten, D. Biochemistry 1991, 30, 609-613.
(b) Drain, C. M.; Kirmaier, C.; Medforth, C. J .; Nurco, D. J .; Smith, K.
M.; Holten, D. J . Phys. Chem. 1996, 100, 11984-11993.
2(3),9(10),16(17),23(24)-Tet r a k is{2-[4-(m a gn esiu m -5,-
10,15-t r im esit yl-20-p or p h in yl)p h en yl]et h yn yl}p h t h a l-
ocya n in a tom a gn esiu m [(MgP )4MgP c]. A mixture of 2 (100
(61) Marcuccio, S. M.; Svirskaya, P. I.; Greenberg, S.; Lever, A. B.
P.; Leznoff, C. C. Can. J . Chem. 1985, 63, 3057-3069.
(62) Ravikanth, M.; Strachan, J .-P.; Li, F.; Lindsey, J . S. Tetrahe-
dron 1998, 54, 7721-7734.

9100 J . Org. Chem., Vol. 64, No. 25, 1999
Li et al.
mg, 0.11 mmol), MgCl2 (100 mg, 1.1 mmol), and two drops of
DBU in dry 1-pentanol (4 mL) was heated at reflux with
stirring under an argon atmosphere. The reaction mixture
started to change from red to green after 1 h, and the reaction
mixture was refluxed for 24 h. After being cooled to room
temperature, the green mixture was poured into a solution of
CH3OH/H2O (5:1, 20 mL). The resulting precipitate was
collected by centrifugation and washed with CH3OH. Column
chromatography on alumina (grade V, 4 × 20 cm) with toluene/
ethyl acetate (10:1) gave two bands (red first and then green),
the second band of which (green) was the desired compound.
Further purification was achieved by dissolving the desired
compound in THF and chromatography on a preparative SEC
column packed with THF (3 × 45 cm). Gravity elution afforded
the desired compound as the first band, affording 46.5 mg
(45%) of a purple solid: IR (neat film) ν 2917, 1609, 1477, 1200,
mass for C252H200N24Mg 3588.8, obsd 3592.6; HRMS (FAB)
obsd 3588.5; λabs (log ꢀ) (toluene) 421 (6.21, fwhm ) 16 nm),
516 (4.96), 551 (4.63), 702 (5.37) nm.
2(3),9(10),16(17),23(24)-Tetr a k is{2-[4-(zin c-5,10,15-tr i-
m e sit yl-20-p or p h in yl)p h e n yl]e t h yn yl}p h t h a lo c y a n -
in a tom a gn esiu m [(Zn P )4MgP c]. To a solution of (H2P)4-
MgPc (6.0 mg, 1.7 µmol) in CHCl3 (15 mL) was added
Zn(OAc)2‚2H2O (20 mg, 0.091 mmol) in CH3OH (2 mL), and
the reaction mixture was stirred magnetically at room tem-
perature overnight under an argon atmosphere. The metala-
tion was complete as judged by TLC and LD-MS. The green-
brown mixture was then diluted with CHCl3 (25 mL), washed
with 5% NaCHCO3, dried (Na2SO4), and filtered and the
solvent removed under reduced pressure. Column chromatog-
raphy on flash silica gel (3.5 × 10 cm) eluting with toluene/
ethyl acetate (20:1) gave the product as a black solid. The solid
was suspended in methanol, centrifuged, and dried under
vacuum, affording 6.18 mg (96.2%): IR (neat film) ν 2914,
1
1060, 997, 799, 721 cm-1; H NMR (THF-d8) δ 1.80-1.90 (m,
72 H), 2.44-2.62 (m, 36 H), 7.21-7.31 (m, 24 H), 8.16-8.40
(m, 16 H), 8.48-8.85 (m, 32 H), 9.63-9.71 (m, 4 H), 9.87, 9.92
(m, 4 H), 10.84 (br s, 4 H); LD-MS calcd av mass for
1
1611, 1483, 1449, 1332, 1198, 1087, 998, 798 cm-1; H NMR
(THF-d8) δ 1.79-1.93 (m, 72 H), 2.42-2.62 (m, 36 H), 7.21-
7.31 (m, 24 H), 8.22-8.40 (m, 16 H), 8.58-8.74 (m, 24 H),
8.84-8.93 (m, 8 H), 9.62-9.70 (m, 4 H), 9.87-9.92(m, 4 H),
C
252H192N24Mg5 3677.8, obsd 3675.0; HRMS (FAB) obsd 3677.3;
λabs (toluene) 310, 365, 427, 566, 608, 710 nm.
2(3),9(10),16(17),23(24)-Tet r a k is{2-[4-(5,10,15-t r im esi-
tyl-20-porphinyl)phenyl]ethynyl}phthalocyanine[(H2P)4H2Pc].
A sample of (MgP)4MgPc (10 mg, 2.7 µmol) was dissolved in
CHCl3 (10 mL), then TFA (1 mL) was added, and the solution
was stirred under argon for 1 h. Dichloromethane (20 mL) was
then added, and the solution was washed carefully with 5%
NaHCO3, then triethylamine (1 mL) was added, and the
resulting solution was washed again with 5% NaHCO3 and
then dried (Na2SO4). After removal of the solvent, the solid
was dissolved in a minimum volume of toluene and loaded onto
a flash silica gel column (3.5 × 12 cm). Elution with toluene
afforded the desired compound as the first (green-brown) band.
Removal of the solvent and washing the resulting solid with
methanol afforded 6.6 mg (68%) of a black solid: IR (neat film)
ν 3316 (NH), 2921, 1605, 1467, 1215, 1093, 1013, 970, 799,
10.83, 10.84 (m, 4 H); LD-MS calcd av mass for C252H192N24-
MgZn4 3842.3, obsd 3844.5; HRMS (FAB) obsd 3842.4; λabs (log
ꢀ) toluene 424 (6.10, fwhm ) 14 nm), 551 (4.83), 634 (4.59),
702 (5.29) nm.
2(3),9(10),16(7),23(24)-Tet r a k is{2-[4-(zin c-5,10,15-t r i-
m e sit yl-20-p o r p h in y l)p h e n yl]e t h y n y l}p h t h a lo c y a n -
in a tozin c [(Zn P )4Zn P c]. A mixture of 2 (50 mg, 0.055 mmol),
zinc acetate (50 mg, 0.30 mmol), and two drops of DBU in dry
1-pentanol (2 mL) was heated at reflux for 36 h with stirring
under an argon atmosphere. After being cooled to room
temperature, the green mixture was poured into a solution of
CH3OH/H2O (5:1, 15 mL). The resulting precipitate was
collected by centrifugation and washed with CH3OH. Column
chromatography on silica gel (3.5 × 20 cm) eluting with
toluene/ethyl acetate (20:1) afforded the desired compound as
the first band. The compound obtained was further purified
by dissolving it in THF with chromatography on a preparative
SEC column (3 × 45 cm) packed with THF. Gravity elution
afforded the desired compound as the first band. Removal of
solvent and washing the solid with methanol afforded 8.0 mg
(15%) of a purple solid: IR (neat film) ν 2918, 1613, 1494, 1336,
1
740 cm-1; H NMR (THF-d8) δ -2.56 (br s, 10 H), 1.30-1.62
(m, 72 H), 2.44-2.53 (m, 36 H), 6.65-7.21 (m, 24 H), 8.18-
9.03 (m, 48 H), 9.08-9.37 (m, 8 H), 10.84 (m, 4 H); LD-MS
calcd av mass for C252H202N24 3566.5, obsd 3565.3; HRMS
(FAB) obsd 3565.8; λabs (log ꢀ) (toluene) 421 (6.17, fwhm ) 15
nm), 515 (4.90), 688 (5.29), 723 (5.37) nm. Alternatively, a
solution of (ZnP)4MgPc (6.0 mg, 1.6 µmol) in CHCl3 (10 mL)
was treated with TFA (1 mL), and the reaction mixture was
worked up and the product purified in identical fashion,
affording 3.9 mg (70%) of a black solid.
1204, 1090, 998, 798, 723 cm-1 1H NMR (THF-d8) δ 1.79-
;
1.85 (m, 72 H), 2.43-2.55 (m, 36 H), 7.13-7.29 (m, 24 H),
8.34-8.45 (m, 16 H), 8.57-8.98 (m, 32 H), 9.40-9.64 (m, 8
H), 10.84, (br s, 4 H); LD-MS calcd av mass for C252H192N24
-
2(3),9(10),16(17),23(24)-Tet r a k is{2-[4-(5,10,15-t r im esi-
t yl-20-p or p h in yl)p h e n yl]e t h yn yl}p h t h a locya n in a t o-
m a gn esiu m [(H 2P )4MgP c]. To a solution of (MgP)4MgPc (10
mg, 2.7 µmmol) in CH2Cl2 (10 mL) was added silica gel (1.0
g). The mixture was stirred overnight at room temperature
under an argon atmosphere with shielding from ambient light.
Upon completion of the demetalation as judged by LD-MS, the
reaction mixture was filtered under vacuum through a fritted
glass funnel, and the filtrate was washed with CH2Cl2/ethyl
acetate (1:1) until it was colorless. The filtrate was then
evaporated to dryness under reduced pressure, and purified
by column chromatography (silica gel, 3.5 × 10 cm, toluene/
ethyl acetate; 20:1), affording the desired product as a green-
brown band. Removal of the solvent and washing the solid with
methanol afforded 7.2 mg (74%) of a black solid: IR (neat film)
ν 3313 (NH), 2914, 1610, 1464, 1345, 1210, 1081, 968, 800,
Zn5 3883.4, obsd 3888.9; HRMS (FAB) obsd 3883.1; λabs (log ꢀ)
(toluene) 421 (6.21, fwhm ) 14 nm), 550 (4.93), 631 (4.74), 701
(5.49) nm.
Ack n ow led gm en t. This research was supported by
the Division of Chemical Sciences, Office of Basic
Energy Sciences, Office of Energy Research, U.S. De-
partment of Energy. Mass spectra were obtained at the
Mass Spectrometry Laboratory for Biotechnology at
North Carolina State University. Partial funding for the
Facility was obtained from the North Carolina Biotech-
nology Center and the NSF.
Su p p or tin g In for m a tion Ava ila ble: 1H NMR and LD-
MS spectra for all porphyrins and porphyrin-phthalocyanine
arrays, and absorption and fluorescence spectra for all por-
phyrin-phthalocyanine arrays. This material is available free
of charge via the Internet at http://pubs.acs.org.
1
736 cm-1; H NMR (THF-d8) δ -2.44, -2.37 (m, 8 H), 1.78-
1.94 (m, 72 H), 2.43-2.62 (m, 36 H), 7.21-7.33 (m, 24 H),
8.25-8.43 (m, 16 H), 8.59-8.95 (m, 32 H), 9.62-9.68 (m, 4
H), 9.86, 9.92 (m, 4 H), 10.83, 10.85 (m, 4 H); LD-MS calcd av
J O991001G