Synthesis and electronic properties of regioisomerically pure oxochlorins

Article abstract of DOI:10.1021/jo025843i

We describe a two-step conversion of C-alkylated zinc chlorins to zinc oxochlorins wherein the keto group is located in the reduced ring (17-position) of the macrocycle. The transformation proceeds by hydroxylation upon exposure to alumina followed by dehydrogenation with DDQ. The reactions are compatible with ethyne, iodo, ester, trimethylsilyl, and pentafluorophenyl groups. A route to a spirohexyl-substituted chlorin/oxochlorin has also been developed. Representative chlorins and oxochlorins were characterized by static and time-resolved absorption spectroscopy and fluorescence spectroscopy, resonance Raman spectroscopy, and electrochemistry. The fluorescence quantum yields of the zinc oxochlorins (φ_f = 0.030-0.047) or free base (Fb) oxochlorins (φ_f = 0.13-0.16) are comparable to those of zinc tetraphenylporphyrin (ZnTPP) or free base tetraphenylporphyrin (FbTPP), respectively. The excited-state lifetimes of the zinc oxochlorins (τ = 0.5-0.7 ns) are on average 4-fold lower than that of ZnTPP, and the lifetimes of the Fb oxochlorins (τ = 7.4-8.9 ns) are ～40% shorter than that of FbTPP. Time-resolved absorption spectroscopy of a zinc oxochlorin indicates the yield of intersystem crossing is >70%. Resonance Raman spectroscopy of copper oxochlorins show strong resonance enhancement of the keto group upon Soret excitation but not with Q_y-band excitation, which is attributed to the location of the keto group in the reduced ring (rather than in the isocyclic ring as occurs in chlorophylls). The one-electron oxidation potential of the zinc oxochlorins is shifted to more positive potentials by approximately 240 mV compared with that of the zinc chlorin. Collectively, the fluorescence yields, excited-state lifetimes, oxidation potentials, and various spectral characteristics of the chlorin and oxochlorin building blocks provide the foundation for studies of photochemical processes in larger architectures based on these chromophores.

Full text of DOI:10.1021/jo025843i

Syn th esis a n d Electr on ic P r op er ties of Regioisom er ica lly P u r e
Oxoch lor in s
Masahiko Taniguchi,† Han-J e Kim,† Doyoung Ra,† J ennifer K. Schwartz,‡
Christine Kirmaier,‡ Eve Hindin,‡ J ames R. Diers,§ Sreedharan Prathapan,*,†,|
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, Washington University, St. Louis, Missouri 63130-4899, and
Department of Chemistry, University of California, Riverside, California 92521-0403
jlindsey@ncsu.edu
Received April 19, 2002
We describe a two-step conversion of C-alkylated zinc chlorins to zinc oxochlorins wherein the keto
group is located in the reduced ring (17-position) of the macrocycle. The transformation proceeds
by hydroxylation upon exposure to alumina followed by dehydrogenation with DDQ. The reactions
are compatible with ethyne, iodo, ester, trimethylsilyl, and pentafluorophenyl groups. A route to a
spirohexyl-substituted chlorin/oxochlorin has also been developed. Representative chlorins and
oxochlorins were characterized by static and time-resolved absorption spectroscopy and fluorescence
spectroscopy, resonance Raman spectroscopy, and electrochemistry. The fluorescence quantum yields
of the zinc oxochlorins (Φf ) 0.030-0.047) or free base (Fb) oxochlorins (Φf ) 0.13-0.16) are
comparable to those of zinc tetraphenylporphyrin (ZnTPP) or free base tetraphenylporphyrin
(FbTPP), respectively. The excited-state lifetimes of the zinc oxochlorins (τ ) 0.5-0.7 ns) are on
average 4-fold lower than that of ZnTPP, and the lifetimes of the Fb oxochlorins (τ ) 7.4-8.9 ns)
are ∼40% shorter than that of FbTPP. Time-resolved absorption spectroscopy of a zinc oxochlorin
indicates the yield of intersystem crossing is >70%. Resonance Raman spectroscopy of copper
oxochlorins show strong resonance enhancement of the keto group upon Soret excitation but not
with Qy-band excitation, which is attributed to the location of the keto group in the reduced ring
(rather than in the isocyclic ring as occurs in chlorophylls). The one-electron oxidation potential of
the zinc oxochlorins is shifted to more positive potentials by approximately 240 mV compared with
that of the zinc chlorin. Collectively, the fluorescence yields, excited-state lifetimes, oxidation
potentials, and various spectral characteristics of the chlorin and oxochlorin building blocks provide
the foundation for studies of photochemical processes in larger architectures based on these
chromophores.
In tr od u ction
thetic methods that can be employed to construct the
basic ring system and on the physical, electronic, and
spectral properties of the macrocycle. As a consequence,
the use of porphyrin surrogates typically involves trade
offs in either synthetic or physicochemical properties.
Synthetic building blocks that exhibit the spectral and
photochemical properties of chlorophyll would have wide
application in bioorganic and materials chemistry, par-
ticularly in areas such as photodynamic therapy, light-
harvesting model systems, and molecular photonics. In
many instances where chlorophyll-like molecules are
desired, porphyrins have been employed as surrogates.
Porphyrins and chlorophyll differ in two key structural
elements (Chart 1): (1) Chlorophyll is a dihydroporphyrin
in which one of the â-pyrrole bonds is saturated (com-
monly designated a chlorin). (2) Chlorophyll contains an
exocyclic ring bearing a keto group that is conjugated
with the π-electron system of the macrocycle. These
structural differences between porphyrins and chlorins
(chlorophylls) have significant effects both on the syn-
Porphyrins are generally superior to chlorins from the
standpoint of synthetic malleability and chemical stabil-
ity. In particular, the absence of a saturated â-pyrrole
bond makes porphyrins much less susceptible to oxidative
damage. These features of porphyrins have permitted the
preparation of a large variety of chemically robust
building blocks bearing peripheral substituents that
provide synthetic handles, impart desired solubility, and
tune redox potentials. On the other hand, chlorins are
superior to porphyrins for use in photosynthetic systems
and related photochemical systems wherein broad spec-
tral coverage and/or efficient through-space contributions
to energy transfer are desired. This superiority arises
because (1) the extinction coefficient of the long-wave-
length absorption band of chlorins is greater than that
of porphyrins,1 affording strong absorption in the near-
† North Carolina State University.
‡ Washington University.
§ University of California.
| Permanent address: Department of Applied Chemistry, Cochin
University of Science and Technology, Cochin, India 682022.
10.1021/jo025843i CCC: $22.00 © 2002 American Chemical Society
Published on Web 09/24/2002
J . Org. Chem. 2002, 67, 7329-7342
7329

Taniguchi et al.
CHART 1
recently developed a rational synthesis of C-methylated
chlorin building blocks.3,8,9 Each chlorin bears one gemi-
nal dimethyl group at the â-position in the reduced ring.
For building block applications, we have introduced
synthetic handles at several â-positions (2, 8, 12) and two
meso-positions (5, 10). One of our objectives is to create
arrays containing a large number of chlorin chro-
mophores, thereby obtaining synthetic materials with
features that more closely resemble the natural light-
harvesting systems. The utilization of chlorin building
blocks in multipigment arrays requires the ability to
manipulate the fundamental photophysical and electronic
properties of the chlorin chromophore, as is now routinely
done with porphyrins.
One type of modified chlorin that is frequently encoun-
tered is an oxochlorin, wherein a keto group is present
at one of the â-carbons in the reduced ring (Chart 1). The
motivation for forming an oxochlorin has typically
stemmed from synthetic considerations: treatment of a
â,â′-disubstituted porphyrin with an oxidizing agent such
18-21
as hydrogen peroxide14-17 or OsO4
followed by acid-
catalyzed pinacol rearrangement of the resulting diol14-21
yields the oxochlorin. In this manner, readily available
synthetic porphyrins serve as starting materials for
preparing chlorin derivatives.22 Though widely applied
with â-alkylated porphyrins, this approach has two
critical limitations: (1) Application to a â-unsubstituted
porphyrin would result in keto-enol tautomerism, thereby
causing reversion of the oxochlorin to the hydroxypor-
phyrin.20 (2) Multiple oxochlorin isomers typically result
with porphyrins wherein the four pyrrole rings bear
nonidentical substituents,17-19,23,24 different substituents
(e.g., methyl/ethyl) are present at the two â-positions of
the pyrrole ring that is attacked by OsO4,17-19 or the
presence of meso-substituents causes the symmetry of
the porphyrin to be less than 4-fold.24-27
IR region; and (2) chlorins are linear oscillators whereas
metalloporphyrins are planar oscillators,2 enabling greater
directionality in intermolecular energy transfer in the
former versus the latter.
The important photochemical properties of chlorins
have motivated the development of a number of new
syntheses of these green pigments in the past few
years.3-12 Earlier syntheses have been reviewed.13 We
In this paper, we report an efficient method for
converting C-alkylated chlorins to the corresponding
(12) Mironov, A. F.; Efremov, A. V.; Efremova, O. A.; Bonnett, R.;
Martinez, G. J . Chem. Soc., Perkin Trans. 1 1998, 3601-3608.
(13) (a) Montforts, F.-P.; Gerlach, B.; Ho¨per, F. Chem. Rev. 1994,
94, 327-347. (b) Flitsch, W. Adv. Heterocycl. Chem. 1988, 43, 73-126.
(c) Montforts, F.-P.; Glasenapp-Breiling, M. Prog. Heterocycl. Chem.
1998, 10, 1-24.
(14) Bonnett, R.; Dolphin, D.; J ohnson, A. W.; Oldfield, D.; Stephen-
son, G. F. Proc. Chem. Soc. London 1964, 371-372.
(15) Bonnett, R.; Dimsdale, M. J .; Stephenson, G. F. J . Chem. Soc.
C 1969, 564-570.
(16) Chang, C. K. Biochemistry 1980, 19, 1971-1976.
(17) Chang, C. K.; Wu, W. J . Org. Chem. 1986, 51, 2134-2137.
(18) Chang, C. K.; Sotiriou, C. J . Org. Chem. 1985, 50, 4989-4991.
(19) Chang, C. K.; Sotiriou, C. J . Heterocycl. Chem. 1985, 22, 1739-
1741.
(1) Smith, J . H. C.; Benitez, A. In Modern Methods of Plant Analysis;
Paech, K., Tracey, M. V., Eds.; Springer-Verlag: Berlin, 1955; Vol. IV,
pp 142-196.
(2) (a) Gurinovich, G. P.; Sevchenko, A. N.; Solov’ev, K. N. Opt.
Spectrosc. 1961, 10, 396-401. (b) Gouterman, M.; Stryer, L. J . Chem.
Phys. 1962, 37, 2260-2266.
(3) Taniguchi, M.; Ra, D.; Mo, G.; Balasubramanian, T.; Lindsey, J .
S. J . Org. Chem. 2001, 66, 7342-7354.
(20) Bru¨ckner, C.; Dolphin, D. Tetrahedron Lett. 1995, 36, 3295-
3298.
(21) Inhoffen, H. H.; Nolte, W. Liebigs Ann. Chem. 1969, 725, 167-
176.
(4) J acobi, P. A.; Lanz, S.; Ghosh, I.; Leung, S. H.; Lo¨wer, F.; Pippin,
D. Org. Lett. 2001, 3, 831-834.
(5) Montforts, F.-P.; Kutzki, O. Angew. Chem., Int. Ed. 2000, 39,
599-601.
(22) For a method for converting heme into an oxochlorin, see: Bats,
J . W.; Haake, G.; Meier, A.; Montforts, F.-P.; Scheurich, G. Liebigs
Ann. 1995, 1617-1631.
(6) Shea, K. M.; J aquinod, L.; Khoury, R. G.; Smith, K. M. Tetra-
hedron 2000, 56, 3139-3144.
(7) Burns, D. H.; Shi, D. C.; Lash, T. D. Chem. Commun. 2000, 299-
(23) Sotiriou, C.; Chang, C. K. J . Am. Chem. Soc. 1988, 110, 2264-
300.
2270.
(8) (a) Strachan, J .-P.; O’Shea, D. F.; Balasubramanian, T.; Lindsey,
J . S. J . Org. Chem. 2000, 65, 3160-3172. (b) Strachan, J .-P.; O’Shea,
D. F.; Balasubramanian, T.; Lindsey, J . S. J . Org. Chem. 2001, 66,
642.
(24) Chen, Y.; Medforth, C. J .; Smith, K. M.; Alderfer, J .; Dougherty,
T. J .; Pandey, R. K. J . Org. Chem. 2001, 66, 3930-3939.
(25) Osuka, A.; Marumo, S.; Maruyama, K. Bull. Chem. Soc. J pn.
1993, 66, 3837-3839.
(9) Balasubramanian, T.; Strachan, J . P.; Boyle, P. D.; Lindsey, J .
S. J . Org. Chem. 2000, 65, 7919-7929.
(26) Osuka, A.; Marumo, S.; Maruyama, K.; Mataga, N.; Tanaka,
Y.; Taniguchi, S.; Okada, T.; Yamazaki, I.; Nishimura, Y. Bull. Chem.
Soc. J pn. 1995, 68, 262-276.
(10) Krattinger, B.; Callot, H. J . Eur. J . Org. Chem. 1999, 1857-
1867.
(27) Osuka, A.; Marumo, S.; Mataga, N.; Taniguchi, S.; Okada, T.;
Yamazaki, I.; Nishimura, Y.; Ohno, T.; Nozaki, K. J . Am. Chem. Soc.
1996, 118, 155-168.
(11) J ohnson, C. K.; Dolphin, D. Tetrahedron Lett. 1998, 39, 4619-
4622.
7330 J . Org. Chem., Vol. 67, No. 21, 2002

Synthesis and Properties of Oxochlorins
SCHEME 1
oxochlorins. Our motivation for preparing oxochlorins
stems not as a means of converting porphyrins to chlorins
but from the greater redox stability of oxochlorins
compared with chlorins.25,28-30 The keto group is intro-
duced at the site (17-position) adjacent to the geminal
dialkyl group (18-position), forming only one oxochlorin
isomer regardless of the substitution pattern at the
perimeter of the macrocycle. The method has been
applied to chlorins bearing a variety of substituents,
including chlorins with a spiroalkyl unit in place of the
geminal dimethyl unit in the reduced ring. Oxochlorins
in various metalation states (Zn, Mg, Cu, free base (Fb))
also have been prepared. The metallo and Fb oxochlorins
have been characterized by electrochemistry, static and
time-resolved absorption and fluorescence spectroscopy,
and resonance Raman spectroscopy.
Resu lts a n d Discu ssion
A. Syn th esis. 1. Meth od for F or m in g Oxoch lor in s.
Reagents for the oxidation of a benzylic methylene unit
to the corresponding carbonyl or hydroxy group are well-
known, including MnO2, Cu(OAc)2, SeO2, and CrO3.
However, treatment of Zn 18 with MnO2, Cu(OAc)2, or
SeO2 proved ineffective, while CrO3 led to extensive
decomposition. Given the facile hydroxylation of certain
chlorins during chromatography on neutral alumina,31
and in some cases the direct formation of oxochlorins
(albeit in low yield),32 we decided to explore this “side-
reaction” as the first step in a procedure for converting
chlorins to oxochlorins. Thus, treatment of a mixture of
Zn 1 and basic alumina (activity I) in toluene at 60 °C
exposed to air for 22 h resulted in three components
identified by TLC and laser desorption mass spectrom-
etry (LD-MS) analysis as unchanged starting material
(Zn 1, 2%), oxochlorin (Oxo-Zn 1, 23%), and hydroxychlo-
rin (HO-Zn 1, 52%) (Scheme 1). The three components
were easily separated by column chromatography on
silica.
During the development of this method, a number of
factors that affect the course of hydroxylation were
identified. (1) The reaction proceeded well in toluene but
not in dichloromethane. (2) The reaction was more
efficient with basic alumina (activity I) than with neutral
alumina or basic alumina (activity V). (3) The reaction
at 50-60 °C required 4-20 h whereas up to 60 h was
required at room temperature. (4) Attempts to use the
Fb chlorin or the Cu chlorin led to recovery of starting
material.
The success of these two reactions prompted the
development of a two-step process without purification
of the intermediate hydroxychlorin. Thus, treatment of
Zn 1 with alumina (activity I) in toluene at 50 °C for 6.5
h, filtration to remove the alumina, and treatment of the
crude product from the filtrate with DDQ in toluene for
5 min gave Oxo-Zn 1 in 53% yield. This procedure
provides a simple means of transforming the chlorin to
the corresponding oxochlorin.
The scope of the method was evaluated by the applica-
tion to chlorins bearing a variety of peripheral functional
groups. The functional groups include strong electron-
withdrawing groups (Zn 2), groups for surface attachment
following deprotection (Zn 3), and groups for the Pd-
mediated synthesis of multi-chlorin arrays (Zn 4, Zn 5).3
Zn chlorins Zn 2-Zn 5 were readily converted into Zn
oxochlorins Oxo-Zn 2-Oxo-Zn 5 via the two-step alumina/
DDQ procedure described above (Scheme 2). This method
is complementary to the CrO3-dimethylpyrazole oxida-
tion employed in the synthesis of the dioxobacteriochlorin
compound tolyporphin.33
The conversion of the hydroxychlorin HO-Zn 1 to the
corresponding oxochlorin was examined. After surveying
several reagents (SeO2, p-chloranil, MnO2), we turned to
the use of DDQ. The oxidation of HO-Zn 1 with ∼2 equiv
of DDQ in toluene proceeded rapidly and gave Oxo-Zn 1
in 47% yield.
2. Sp ir o-Ch lor in s/Oxoch lor in s. A typical design of
porphyrin building blocks employs several peripheral
sites for attachment of synthetic handles and others for
positioning of groups that impart high solubility in
organic solvents. Methodology has been developed for
introducing four different groups of wide variety at the
four meso-positions of porphyrins.34 In the case of chlo-
rins, methodology exists for introducing two meso-sub-
(28) Chang, C. K.; Barkigia, K. M.; Hanson, L. K.; Fajer, J . J . Am.
Chem. Soc. 1986, 108, 1352-1354.
(29) Stolzenberg, A. M.; Glazer, P. A.; Foxman, B. M. Inorg. Chem.
1986, 25, 983-991.
(30) Zaleski, J . M.; Chang, C. K.; Nocera, D. G. J . Phys. Chem. 1993,
97, 13206-13215.
(31) Burns, D. H.; Li, Y. H.; Shi, D. C.; Delaney, M. O. Chem.
Commun. 1998, 1677-1678.
(33) (a) Minehan, T. G.; Kishi, Y. Tetrahedron Lett. 1997, 38, 6811-
6814. (b) Wang, W.; Kishi, Y. Org. Lett. 1999, 1, 1129-1132.
(34) Rao, P. D.; Dhanalekshmi, S.; Littler, B. J .; Lindsey, J . S. J .
Org. Chem. 2000, 65, 7323-7344.
(32) Battersby, A. R.; Fookes, C. J . R.; Snow, R. J . J . Chem. Soc.,
Perkin Trans. 1 1984, 2725-2732.
J . Org. Chem, Vol. 67, No. 21, 2002 7331

Taniguchi et al.
of pyrrole 68 required two steps and a tedious workup
procedure. A simplified two-step, one-flask synthesis was
developed that avoids isolation of the intermediate nitro-
vinyl pyrrole. In this manner, 6 was obtained in 66% yield
compared with 45% in the prior procedure.
SCHEME 2
A key step in the synthesis of the desired spirohexyl
Western half is the Michael addition of nitroethyl pyrrole
6 to an R,â-unsaturated ketone bearing a spirohexyl
group at the â-positions. Cyclohexanone reacted smoothly
with dimethyl (2-oxopropyl)phosphonate via a Wittig-
Horner reaction37 to yield the R,â-unsaturated ketone 7.38
Reaction of 7 with nitroethyl pyrrole 6 in the presence
of CsF gave the Michael addition product 8, from which
tetrahydrodipyrrin N-oxide 9 was obtained following a
straightforward procedure.3 The latter was deoxygenated
to form the tetrahydrodipyrrin Western half 10.
The reaction of Western half 6 and Eastern half 11-
OH8 under the standard two-step chlorin-forming condi-
tions3 gave the chlorin Zn 12 in 19% yield. Oxidation of
Zn 12 under the conditions described above (alumina/
DDQ) led to the corresponding oxochlorin Oxo-Zn 12,
albeit in only 20% yield (Scheme 3).
3. F r ee Ba se, Cop p er , a n d Ma gn esiu m Oxoch lo-
r in s. The Fb chlorins 1-5 and oxochlorins Oxo-1-Oxo-5
were obtained by demetalation of the corresponding Zn
chelates with TFA in CH2Cl2 (Scheme 4). For resonance
Raman studies, the Cu chelates of several chlorins and
oxochlorins were prepared by treating the Fb species with
Cu(OAc)2 in CH2Cl2/methanol (1:1) at room temperature.
Treatment of Fb oxochlorin Oxo-1 or Oxo-2 to the
heterogeneous magnesium insertion procedure (MgI2,
DIEA, CH2Cl2)39 at room temperature afforded the cor-
responding Mg chelate Oxo-Mg1 or Oxo-Mg2. However,
attempts to metalate 1 to give the Mg chlorin Mg1 were
unsuccessful as demetalation occurred upon workup.
4. Ch em ica l Ch a r a cter iza tion . The chlorins and
oxochlorins generally were characterized by absorption
spectroscopy, fluorescence emission spectroscopy, LD-MS
stituents, two â-substituents and one meso-substituent,
or two meso-substituents and one â-substituent, but not
for introducing more than three different groups.3,8 The
chief limitation is that the two meso-sites flanking the
reduced ring are not yet accessible toward modification.
To broaden the range of synthetic control over substit-
uents at the perimeter of the chlorin macrocycle, we
sought to investigate whether the site of the geminal
dialkyl group (18-position) could serve as a position for
introducing substituents. We investigated the synthesis
of a chlorin bearing a spirohexyl group in lieu of a
geminal dimethyl group (Scheme 3). Spirochlorins have
been made previously as a means of converting a por-
phyrin to a chlorin35 or as a side product from the
intramolecular cyclization of a linker joining two chlorins
in a photosynthetic model system.36
1
and/or high-resolution mass spectrometry, and H NMR
spectroscopy. The 1H NMR spectra of the oxochlorins
were generally unremarkable. As with the corresponding
chlorins, each of the six â-protons and two meso-protons
is unique and gives a distinctive resonance(s). In the
metallo or free base oxochlorins, the resonances due to
the protons at the 15 and 20 positions are shifted
downfield by ∼0.9 and 0.4 ppm, respectively, compared
with those of the corresponding chlorins. Downfield shifts
albeit of lesser magnitude also were observed for the
peaks stemming from the meso-protons. One hallmark
distinguishing the free base oxochlorins and chlorins
stems from the resonances of the central NH protons. In
both the free base chlorins and oxochlorins, the NH
protons are not equivalent. However, the free base
chlorins tend to give a single broad peak while the free
base oxochlorins studied herein give two distinct peaks
(∆δ ∼0.15 ppm) at ∼0.4 ppm higher field.
The synthesis of C-alkylated chlorins entails the join-
ing of an Eastern half and a Western half.3,8,9 The
synthesis of a spirohexyl-substituted Western half begins
in the same manner as for the gem-dimethyl-substituted
Western half, with the conversion of pyrrole-2-carboxal-
dehyde to the nitroethyl pyrrole 6. The prior synthesis
B. P h ysica l P r op er t ies. 1. Ab sor p t ion Sp ect r a .
Representative UV/vis absorption spectra of the chlorins
(35) (a) Collier, G. L.; J ackson, A. H.; Kenner, G. W. J . Chem. Soc.
C 1967, 66-72. (b) Smith, K. M.; Baptista de Almeida, J . A. P.; Lewis,
W. M. J . Heterocycl. Chem. 1980, 17, 481-487. (c) Kai, S.; Suzuki, M.
Tetrahedron Lett. 1996, 37, 5931-5934.
(36) (a) Zheng, G.; Alderfer, J . L.; Senge, M. O.; Shibata, M.;
Dougherty, T. J .; Pandey, R. K. J . Org. Chem. 1998, 63, 6434-6435.
(b) Zheng, G.; Shibata, M.; Dougherty, T. J .; Pandey, R. K. J . Org.
Chem. 2000, 65, 543-557.
(37) Corey, E. J .; Smith, J . G. J . Am. Chem. Soc. 1979, 101, 1038-
1039.
(38) Fukuda, Y.; Utimoto, K. Bull. Chem. Soc. J pn. 1991, 64, 2013-
2015.
(39) Lindsey, J . S.; Woodford, J . N. Inorg. Chem. 1995, 34, 1063-
1069.
7332 J . Org. Chem., Vol. 67, No. 21, 2002

Synthesis and Properties of Oxochlorins
F IGURE 1. Absorption spectra of chlorin Zn 1 and oxochlorin
Oxo-Zn 1 in toluene at room temperature.
and oxochlorins in toluene at room temperature are
shown in Figures 1 and 2. For each compound, the
position of the long-wavelength absorption band is listed
in Table 1. The wavelength maxima of all the prominent
features along with extinction coefficients are given in
the Experimental Section.
The major absorption features of the chlorins and
oxochlorins, and general differences between the two
types of chromophore, are illustrated for Oxo-Zn 1 and
Zn 1 in Figure 1. The strong near-UV Soret (B) band of
the oxochlorin is red shifted by ∼10 nm from its chlorin
counterpart, while the Qy(0,0) band is relatively un-
changed (609 versus 608 nm). Both bands are slightly
sharper for the oxochlorin. Between these two major
features for both compounds are the weaker Qy vibronic
transitions such as Qy(1,0) at ∼575 nm and the corre-
sponding Qx bands in the green spectral region. The same
spectral features are observed for the other Zn chlorin/
oxochlorins, including Zn 4 and Oxo-Zn 4 (Figure 2B,D
and Table 1).
F IGURE 2. Absorption spectra (solid) and fluorescence
spectra (dashed) of chlorins 4 (A) and Zn 4 (B) and oxochlorins
Oxo-4 (C) and Oxo-Zn 4 (D) in toluene at room temperature.
The emission was elicited by excitation in the Soret region.
The spectra of Fb chlorins and oxochlorins are gener-
ally similar to those for the Zn-containing species, with
several differences. (1) The long-wavelength absorption
feature, the Qy(0,0) band, of each Fb compound is at ∼640
nm, which is ∼30 nm to the red of the corresponding Zn
chelate (Table 1). This difference can be seen for 4 versus
Zn 4 (Figure 2A,B) and for Oxo-4 versus Oxo-Zn 4
(Figure 2C,D). (2) The near-UV Soret absorption of each
Fb chromophore is much broader and is split into at least
two features. The breadth and splitting in the Soret
SCHEME 3
J . Org. Chem, Vol. 67, No. 21, 2002 7333

Taniguchi et al.
SCHEME 4
These characteristics ultimately derive from the presence
of the reduced ring in the chlorins/oxochlorins, and to a
much lesser degree to the asymmetric peripheral sub-
stituent patterns examined herein. These structural/
electronic factors lower the symmetry compared to por-
phyrins, eliminate degeneracies associated with excited
states and transitions, and influence the nature, energies
and electron-density distributions of the frontier molec-
ular orbitals. These issues have been discussed previously
in comparing the electronic spectra of chlorins and
porphyrins.40
2. F lu or escen ce P r op er ties. Fluorescence spectra of
the chlorins 4 and Zn 4 and the oxochlorin analogues
Oxo-4 and Oxo-Zn 4 are shown in Figure 2 (dashed). The
wavelength of the Qy(0,0) emission maximum for each of
these compounds and the other chlorins and oxochlorins
are given in Table 1 along with the emission yields and
fluorescence lifetimes. The emission wavelengths includ-
ing the Q(0,1) position are given in the Experimental
section.
The fluorescence spectra of all the chlorins and oxochlo-
rins are dominated by a Qy(0,0) band and a weaker Qy-
(0,1) feature to longer wavelengths. One of the most
notable characteristics of these emission spectra is the
minimal “Stokes” shift between the Qy(0,0) absorption
and emission maxima. This shift is well within 3 nm (<75
cm-1) for all the chlorins and is typically within 1 nm
(<25 cm-1) for the oxochlorins. These absorption-
fluorescence spacings are typically smaller than those of
porphyrin analogues such as Zn(II)-meso-tetraphenylpor-
phyrin (Zn TP P ), meso-tetraphenylporphyrin (F bTP P ),
and â-octaethylporphyrins Zn OEP and F bOEP .40,41 The
especially small shifts for the oxochlorins must reflect
particularly close similarity of the equilibrium structure
in the ground and lowest excited singlet electronic states
and, likely, only modest differences in the overall distri-
bution of electron density.
The fluorescence quantum yield (Φf) of each Zn oxo-
chlorin Oxo-Zn 1 - Oxo-Zn 4 is in the range of 0.030-
0.047, which is similar to the value of 0.03340 for Zn TP P .
Each Fb oxochlorin Oxo-1-Oxo-4 has a Φf value in the
range of 0.13-0.16, which is comparable to the yield of
0.1142 for F bTP P . The Φf for Mg oxochlorin Oxo-Mg1
of 0.10 is slightly lower than the value of 0.1640,43,44 for
MgTP P and related compounds. In general, each oxo-
chlorin examined has a Φf value that is approximately
one-half to one-third that of the corresponding chlorin
(Table 1). The values are generally in good agreement
with the results of the measurements on the emission
properties of chlorins and oxochlorins reported pre-
viously.40,45-47
region is particularly noteworthy for the Fb chlorins such
as 4 (Figure 2A), but is also present for the oxochlorin
analogues such as Oxo-4 (Figure 2C). (3) The general
contour and amplitude ratios of the Qx features in the
500-600 nm region are different for the Fb versus Zn
complexes, including increased extinction coefficients for
the Qx features in the vicinity of 515 and 550 nm.
Some of the above characteristics are similar to those
of the porphyrin analogues, including the red shift of the
long-wavelength absorption band in Fb versus Zn com-
plexes. However, for the chlorins and oxochlorins, this
long-wavelength feature is the Qy(0,0) band, whereas it
is the Qx(0,0) band in Fb porphyrins and the combined
(degenerate) Qx(0,0) and Qy(0,0) band for the Zn porphy-
rins. Additionally, the extinction coefficient of the long-
wavelength feature is on the average about 5-fold larger
for the chlorin/oxochlorin. The splitting of the Soret band
of the Fb versions of the latter macrocycles is also a
prominent difference from the porphyrin counterparts.
(40) Gouterman, M. In The Porphyrins; Dolphin, D., Ed.; Academic
Press: New York, 1978; Vol. III, pp 1-165.
(41) Retsek, J . L.; Medforth, C. J .; Nurco, D. J .; Gentemann, S.,
Chirvony, V. S.; Smith, K. M.; Holten, D. J . Phys. Chem. B 2001, 105,
6396-6411.
(42) Seybold, P. G.; Gouterman, M. J . Mol. Spectrosc. 1969, 31,
1-13.
(43) 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.
(44) (a) Gradyushko, A. T.; Tsvirko, M. P. Opt. Spectrosc. 1971, 31,
291-295. (b) Harriman, A. J . Chem. Soc., Faraday Trans. 2 1981, 77,
1281-1291. (c) Politis, T. G.; Drickamer, H. G. J . Chem. Phys. 1982,
76, 285-291. (d) Ohno, O.; Kaizu, Y.; Kobayashi, H. J . Chem. Phys.
1985, 82, 1779-1787.
7334 J . Org. Chem., Vol. 67, No. 21, 2002

Synthesis and Properties of Oxochlorins
TABLE 1. P h ysica l P r op er ties of Ch lor in s a n d Oxoch lor in sa
b
compd
Ar1 (10-position)
Ar2 (5-position)
λab (nm)
λemc (nm)
Φfd
τe (ns)
(krad
)
-1 f (ns)
E1/2g (V)
1
2
3
4
Zn 1
Zn 2
Zn 3
Zn 4
Zn 12
Oxo-1
Oxo-2
Oxo-3
Oxo-4
Oxo-Zn 1
Oxo-Zn 2
Oxo-Zn 3
Oxo-Zn 4
Oxo-Zn 12
Oxo-Mg1
Oxo-Mg2
mesityl
C6F5
p-tolyl
C6F5
p-tolyl
3,5-di-t-Bu-phenyl
p-tolyl
C6F5
p-tolyl
3,5-di-t-Bu-phenyl
p-tolyl
p-tolyl
C6F5
p-tolyl
3,5-di-t-Bu-phenyl
p-tolyl
C6F5
p-tolyl
3,5-di-t-Bu-phenyl
p-tolyl
p-tolyl
C6F5
641
645
640
641
608
616
609
609
610
643
645
643
643
609
614
610
610
611
617
620
641
646
641
642
609
619
611
612
611
643
645
643
643
609
615
611
612
612
617
621
0.26h
0.25h
0.28
9.2
7.3
9.6
9.6
1.4
1.0
1.5
1.4
1.3
8.9
7.4
8.8
8.8
0.9
0.6
0.6
0.7j
0.7
3.0
2.6
35
29
33
31
17
11
16
12
4
68
49
55
63
22
20
12
16
18
30
20
Ari
4-ethynylphenyl
mesityl
C6F5
0.30
0.083h
0.087h
0.095
0.085
0.15
0.35
0.55
Ari
4-ethynylphenyl
mesityl
mesityl
C6F5
0.13
0.15
0.16
0.14
0.040
0.030
0.047
0.044
0.04
Ari
4-ethynylphenyl
mesityl
C6F5
0.59
0.78
Ari
4-ethynylphenyl
mesityl
mesityl
C6F5
0.10
0.13
0.41
0.65
a
b
Spectral measurements were performed in toluene at room temperature unless noted otherwise. Position of the long-wavelength,
Qy(0,0) absorption band rounded to the nearest nanometer. c Position of the Qy(0,0) emission band rounded to the nearest nanometer.
Fluorescence yield ((10%). e Excited-state lifetime determined for deoxygenated samples by fluorescence-modulation spectroscopy unless
d
noted otherwise; the error is (10% except for OxoZn 1-OxoZn 4 where the error is (0.1 ns. f Inverse of the radiative rate constant calculated
-1
g
from the fluorescence yield and excited-state lifetime data in the previous two columns using the relationship (krad
)
) τ/Φf. E1/2 vs
+
h
Ag/Ag+ in CH2Cl2 containing 0.1 M Bu4NPF6; E1/2 of FeCp2/FeCp2 is 0.19 V. Revised from the following values in ref 8: 1 (0.29), 2
i
j
(0.26), Zn 1 (0.065), Zn 2 (0.072). Ar is 4-[2-(trimethylsilyl)ethoxycarbonyl]phenyl. The same value was obtained from fluorescence and
transient absorption measurements in toluene; the lifetime is 0.6 ns in benzonitrile (average from fluorescence and transient absorption
measurements).
The lifetimes of the lowest excited singlet states were
measured using fluorescence techniques and, in some
cases, by time-resolved absorption spectroscopy as well.
The results are listed in Table 1. The excited-state
lifetime (τ) of each Zn oxochlorin Oxo-Zn 1-Oxo-Zn 4 is
in the range of 0.5-0.7 ns, which is on average 4-fold
shorter than the value of 2.0-2.4 ns for Zn TP P and
related Zn porphyrins.43,48,49 The lifetime of 3 ns for Oxo-
Mg1 is about 3-fold shorter than that of ∼10 ns for
MgTP P 44 and other Mg porphyrins.43 On the other hand,
each of the corresponding Fb oxochlorins Oxo-F b1-Oxo-
F b4 has a lifetime in the range 7.4-8.9 ns, which is only
modestly reduced from the lifetime of ∼13 ns for F bTP P
and related Fb porphyrins.43,48,49 In general, the excited-
state lifetime of each Zn oxochlorin is approximately
2-fold shorter than that of the corresponding chlorin,
while the Fb oxochlorins have lifetimes more comparable
to their chlorin counterparts (Table 1). The excited-state
lifetimes measured here are generally in good agreement
with the limited number of values determined previously
for related chlorins and oxochlorins.26,27,45-47
Knowledge of the excited-singlet-state lifetime (τ) and
fluorescence quantum yield (Φf) for each chlorin and
oxochlorin allows calculation of the natural radiative rate
constant (krad) via eqs 1-3.
-1
τ ) (krad + kic + kisc
)
(1)
-1
Φf ) krad(krad + kic + kisc
krad ) Φf /τ
)
(2)
(3)
Here, kic and kisc are the rate constants by which the
excited singlet state decays by internal conversion to the
ground state and intersystem crossing to the excited
triplet state, the two processes competing with fluores-
cence emission in the chromophores. The radiative rate
constant is proportional to the fluorescence intensity and
to the total oscillator strength of the absorption bands
associated with transitions from the ground to lowest
energy (Qy) excited state (via the relationship of the
respective Einstein coefficients). Indeed, for each com-
pound, a second measure of krad was obtained by integra-
tion through the Qy(1,0) and Qy(0,0) absorption bands
using the measured extinction coefficients (Experimental
Section) and the Strickler-Berg relationship as imple-
mented in the program PhotochemCad.50 The krad values
determined from the absorption spectrum are generally
in reasonable agreement with those obtained using the
fluorescence yield and excited-state lifetime data (eq 3)
considering the errors associated with each method.
From Table 1, it is seen that the Zn chlorins and the
Zn oxochlorins have an average radiative rate constant
(krad) of ∼(15 ns)-1. This value is 4-fold greater than the
(45) Gradyushko, A. T.; Sevchenko, A. N.; Solovyov, K. N.; Tsvirko,
M. P. Photochem. Photobiol. 1970, 11, 387-400.
(46) (a) Grewer, Ch.; Schermann, G.; Schmidt, R.; Vo¨lcker, A.;
Brauer, H.-D.; Meier, A.; Montforts, F.-P. J . Photochem. Photobiol. B:
Biol. 1991, 11, 285-293. (b) Pandey, R. K.; Sumlin, A. B.; Constantine,
S.; Aoudia, M.; Potter, W. R.; Bellnier, D. A.; Henderson, B. W.;
Rodgers, M. A.; Smith, K. M.; Dougherty, T. J . Photochem. Photobiol.
1996, 64, 194-204. (c) Zenkevich, E.; Sagun, E.; Knuykshto, V.; Shulga,
A.; Mironov, A.; Efremova, O.; Bonnett, R.; Songca, S. P.; Kassem, M.
J . Photochem. Photobiol. B: Biol. 1996, 33, 171-180. (d) Bonnett, R.;
Charlesworth, P.; Djelal, B. D.; Foley, S.; McGarvey, D. J .; Truscott,
T. G. J . Chem. Soc., Perkin Trans. 2 1999, 325-328.
(47) Papkovsky, D. B.; Ponomarev, G. V.; Wolfbeis, O. S. Spectro-
chim. Acta A 1996, 52, 1629-1638.
(48) Hsiao, J .-S.; Krueger, B. P.; Wagner, R. W.; J ohnson, T. E.;
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.
(49) Li, F.; Gentemann, S.; Kalsbeck, W. A.; Seth, J .; Lindsey, J . S.;
Holten, D.; Bocian, D. F. J . Mater. Chem. 1997, 7, 1245-1262.
(50) Du, H.; Fuh, R.-C. A.; Li, J .; Corkan, L. A.; Lindsey, J . S.
Photochem. Photobiol. 1998, 68, 141-142.
J . Org. Chem, Vol. 67, No. 21, 2002 7335

Taniguchi et al.
average radiative rate constant of ∼(60 ns)-1 for metal-
loporphyrins.40,42 In analogy, the average value of krad
∼
(30 ns)-1 for the Fb chlorins 1-4 or ∼(60 ns)-1 for the Fb
oxochlorins Oxo-1-Oxo-4 are approximately 4-fold or
2-fold greater, respectively, than the average value of krad
∼(120 ns)-1 for Fb porphyrins.40,42 These differences are
obviously reflected in the strength of the long-wavelength
(Qy) absorption band of the chlorins and oxochlorins
compared to the visible-region transitions of the porphy-
rins.
The strong red-region absorption of the chlorins and
oxochlorins represents an advantage compared to the
porphyrins in multi-chromophore arrays for light-har-
vesting applications due to (1) increased utilization of the
solar spectrum and (2) increased through-space contribu-
tion to inter-pigment energy transfer (depending on the
subunits and architecture) due to enhanced transition-
dipole transition-dipole coupling. On the other hand, the
chlorins and oxochlorins have shortened excited-state
lifetimes (and diminished fluorescence yields) compared
with porphyrins, with the extent depending on the
chromophore. Although longer excited-state lifetimes
than ∼0.7 ns for the zinc oxochlorin monomers is desir-
able, efficient energy transfer in arrays comprising these
chromophores can be supported depending on the linker
and attachment motif and thus the energy-transfer rate.
The lifetimes for the free base oxochlorins (∼8 ns) provide
little if any impediment compared to porphyrins toward
energy transfer in arrays. The choice of components in a
synthetic light-harvesting array51 is often a compromise
among a number of factors.52 In terms of absorption,
fluorescence, and excited-state decay characteristics, the
oxochlorins represent a step forward in extending the
properties of porphyrins while attempting to maintain a
good balance of properties.
F IGURE 3. Transient absorption spectra at two time delays
after excitation of Oxo-Zn 4 in toluene with a 130-fs 585-nm
excitation flash. The inset shows a kinetic trace at 610 nm
and a single-exponential fit giving with time constant of 720
( 50 ps; data before and during the instrument response have
been deleted for clarity.
near-infrared regions. The bleaching and stimulated
emission features are coincident with the bands in the
static absorption and fluorescence spectra for this com-
pound (Figure 2D).
As time progresses, the stimulated emission contribu-
tions decay, but the Qy(0,0) ground-state bleaching
remains (3.5 ns spectrum in Figure 3, dashed line). These
changes are expected for the (nonfluorescent) lowest
excited triplet state of Oxo-Zn 4 formed by intersystem
crossing from the lowest excited singlet state (the Qy
excited state). The larger transient absorption near 450
nm (i.e., just to longer wavelengths than the Soret
bleaching) for the excited triplet versus excited singlet
state is analogous to the situation for zinc porphyrins
such as ZnTPP.53 The spectral evolution for Oxo-Zn 4
occurs with a time constant of 720 ( 50 ps in toluene
(Figure 3 inset) and 750 ( 70 ps in benzonitrile (not
shown), in agreement with the values determined by
fluorescence detection (Table 1). Comparison of the
magnitude of the bleaching at ∼610 nm at long times
(relative to the broad transient absorption) and the
combined (50/50) bleaching and stimulated emission at
early times indicates that very little of the excited singlet
state decays to the ground state (by fluorescence and
internal conversion). Accordingly, the yield of intersystem
crossing to give the excited triplet state is high (likely
>70%). This situation is analogous to that for porphyrins,
where triplet yields are typically 80-90% for Fb and
closed-shell metal chelates.40,45,54
3. Tim e-Resolved Absor p tion Sp ectr a . Figure 3
shows representative transient absorption spectra for
Oxo-Zn 4 in toluene acquired using 130-fs 585-nm excita-
tion flashes. Similar results were obtained using excita-
tion at other wavelengths and for this compound in
benzonitrile. The spectrum at the early time delay (solid
line) can be assigned to the excited singlet state of the
oxochlorin. The spectrum is dominated by a feature at
∼610 nm that is expected to have equal contributions of
bleaching of the Qy(0,0) ground-state band and Qy(0,0)
stimulated emission, the latter stemming from fluores-
cence from the excited singlet state stimulated by the
white-light probe pulse. The spectra obtained immedi-
ately after the flash show a slightly smaller feature at
∼610 nm than found in the 30-ps spectrum of Figure 3,
likely due to a smaller stimulated emission contribution.
The initial spectrum evolves into the one at 30 ps with a
time constant of ∼10 ps, indicating a possible vibrational/
conformational relaxation process within the excited
singlet state of the chromophore. The 30-ps spectrum also
shows Qy(0,1) stimulated emission at ∼660 nm along with
broad transient absorption throughout the visible and
4. Reson a n ce Ra m a n Sp ectr a . The high-frequency
regions of the Soret-excitation (λex ) 413 nm) and Qy-
excitation (λex ) 610 nm) resonance Raman spectra of
Cu 1 and Oxo-Cu 1 are shown in Figure 4. The spectra
(53) Rodriguez, J .; Kirmaier, C.; Holten, D. J . Am. Chem. Soc. 1989,
111, 6500-6506.
(51) Burrell, A. K.; Officer, D. L.; Plieger, P. G.; Reid, D. C. W. Chem.
Rev. 2001, 101, 2751-2796.
(52) (a) Tomizaki, K.-Y.; Loewe, R. S.; Kirmaier, C.; Schwartz, J .
K.; Retsek, J . L.; Bocian, D. F.; Holten, D.; Lindsey, J . S. J . Org. Chem.
2002, 67, in press. (b) Wagner, R. W.; Lindsey, J . S. Pure Appl. Chem.
1996, 68, 1373-1380. (c) Wagner, R. W.; Lindsey, J . S. Pure Appl.
Chem. 1998, 70 (8), p. i.
(54) (a) Hurley, J . K.; Sinai, N.; Linschitz, H. Photochem. Photobiol.
1983, 38, 9-14. (b) Kajii, Y.; Obi, K.; Tanaka, I.; Tobita, S. Chem. Phys.
Lett. 1984, 111, 347-349. (c) Kikuchi, K.; Kurabayashi, Y.; Kokubun,
H.; Kaizu, Y.; Kobayashi, H. J . Photochem. Photobiol. A: Chem. 1988,
45, 261-263. (d) Bonnett, R.; McGarvey, D. J .; Harriman, A.; Land,
E. J .; Truscott, T. G.; Winfield, U.-J . Photochem. Photobiol. 1988, 48,
271-276.
7336 J . Org. Chem., Vol. 67, No. 21, 2002

Synthesis and Properties of Oxochlorins
F IGURE 4. High-frequency regions of the Soret-excitation (λex ) 413 nm) and Qy-excitation (λex ) 610 nm) resonance Raman
spectra of Cu 1 and Oxo-Cu 1. The bands marked by asterisks are due to the solvent (CH2Cl2).
observed for Cu 2/Cu 4 and Oxo-Cu 2/Oxo-Cu 4 (not
shown) are similar to those of Cu 1 and Oxo-Cu 1,
respectively. Note that the resonance Raman spectra
were acquired for the Cu complexes because this metal
causes quenching of the fluorescence from the Qy state.
This fluorescence compromises the acquisition of Qy-
excitation resonance Raman spectra of Zn, Mg, or Fb
complexes in solution. The scattering characteristics for
the chlorins and oxochlorins are generally similar to those
that have been previously reported for these types of
macrocycles.55,56 In general, the resonance Raman spectra
of the chlorins and oxochlorins are much richer than
those of porphyrins. This spectral richness arises because
of the lower symmetry of the chlorins (and oxochlorins),
which results primarily from saturation of one of the
â-pyrrole bonds.
A key spectral feature that distinguishes the oxochlo-
rins from the chlorins is the band due to the stretching
vibration of the keto group (νCdO).56 The νCdO mode is
observed at ∼1722 cm-1 and is strongly resonance
enhanced with Soret excitation (Figure 4, right panel,
bottom trace). The νCdO mode is much less strongly
enhanced with Qy excitation. The relatively weak Qy
enhancement is due to the fact that the keto group of
the oxochlorin is at the 17-position, thus lying primarily
along the x-axis of the macrocycle (Chart 1).55,56 In
contrast, the νCdO vibration of the keto group of chloro-
phyll is strongly enhanced with Qy excitation.55,56 In the
case of chlorophyll, the keto group is not appended to the
saturated pyrrole ring of the macrocycle, but rather is
attached to the 13-position as part of an exocyclic five-
membered ring; the keto group thus lies along the y-axis
of the chlorophyll chromophore. Finally, an additional
vibrational feature that is observed for Cu 4 and Oxo-
Cu 4 is the stretching vibration of the ethyne group (νCtC).
The νCtC mode is observed at ∼2215 cm-1 and is most
strongly enhanced with Soret excitation (not shown). This
mode is also resonance enhanced in metalloporphyrins
bearing an ethyne group on a phenyl substituent.57
5. Electr och em istr y. The oxidation potentials of
selected chlorins and oxochlorins were determined as
described previously.43 The E1/2 value for Zn 1 is 0.35 V
whereas that for Oxo-Zn 1 is 0.59 V (vs Ag/Ag+; E1/2(Fc/
Fc+) ) 0.19 V). Turning to the analogues in which the
p-tolyl and mesityl groups are replaced by penta-
fluorophenyl rings, the E1/2 value of Zn 2 is 0.55 V
whereas that for Oxo-Zn 2 is 0.78 V (Table 1). These
results indicate that a single oxo group imparts es-
sentially the same electron-withdrawing effect on the
chlorin as achieved with two meso-pentafluorophenyl
groups. This result is explainable on the basis of the
(57) (a) Seth, J .; Palaniappan, V.; J ohnson, T. E.; Prathapan, S.;
Lindsey, J . S.; Bocian, D. F. J . Am. Chem. Soc. 1994, 116, 10578-
10592. (b) 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. (c) 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. (d) Strachan, J .-P.; Gentemann, S.; Seth, J .; Kalsbeck,
W. A.; Lindsey, J . S.; Holten, D.; Bocian, D. F. Inorg. Chem. 1998, 37,
1191-1201.
(55) (a) Schick, G. A.; Bocian, D. F. Biochim. Biophys. Acta 1987,
895, 127-154. (b) Boldt, N. J .; Donohoe, R. J .; Birge, R. R.; Bocian, D.
F. J . Am. Chem. Soc. 1987, 109, 2284-2298.
(56) (a) Andersson, L. A.; Loehr, T. M.; Wu, W.; Chang, C. K.;
Timkovich, R. FEBS Lett. 1990, 267, 285-288. (b) Mylrajan, M.;
Andersson, L. A.; Loehr, T. M.; Wu, W.; Chang, C. K. J . Am. Chem.
Soc. 1991, 113, 5000-5005.
J . Org. Chem, Vol. 67, No. 21, 2002 7337

Taniguchi et al.
in turn for characterizing the properties of these multi-
chromophore architectures.
Exp er im en ta l Section
A. Syn th etic P r oced u r es. 1. Gen er a l P r oced u r es. All
1H NMR spectra (300 or 400 MHz) were obtained in CDCl3
unless noted otherwise. IR spectra were obtained from films
evaporated from CH2Cl2 on a NaCl window. Basic alumina
(60-325 mesh, activity grade I) and neutral alumina (80-200
mesh) were obtained from Fisher Scientific. Activity grade V
alumina was prepared from grade I alumina.49 Chlorins and
oxochlorins were analyzed by laser desorption mass spectrom-
etry without a matrix (LD-MS) or with the matrix POPOP
(MALDI-MS).61 Fast atom bombardment mass spectrometry
(FAB-MS) data are reported for the molecule ion or protonated
molecule ion. Column chromatography was performed with
flash silica (Baker).
F IGURE 5. Highest occupied molecular orbital of a chlorin
(a2 orbital). Note the very large electron density at the site
adjacent to the methylene unit in the reduced ring.
electron density distribution in the HOMO of the chlorin,
which is characterized by small orbital coefficients at the
meso-positions (Figure 5).58-60 The ability to substantially
alter the electrochemical potential of the chlorins by
introduction of a single oxo group in the reduced ring
enables the meso and â-positions to be employed for
synthetic handles and solubilizing groups. Further tuning
of potentials can be achieved by formation of the Mg
chelate, which shifts the potentials to less positive values
compared with those of the Zn chelates (compare Oxo-
Mg1 or Oxo-Mg2 versus the corresponding Zn chelates).
Thus, our strategy to tune the redox properties of the
chlorin macrocycle by the incorporation of an oxo group
in the reduced ring is superior to the incorporation of
electronegative substituents at the meso positions.
2. Solven ts. THF was distilled from sodium benzophenone
ketyl as required. Toluene was distilled from CaH2. CH3CN
(A.C.S. grade) for use in the condensation process was distilled
from CaH2 and stored over powdered molecular sieves. Nitro-
methane was stored over CaCl2. Anhydrous methanol was
prepared by drying over CaH2 for 12 h followed by distillation.
All other solvents were used as received.
3. Non com m er cia l Com p ou n d s. The chlorins Zn 1-Zn 5,3
1 and 2,8 and Eastern half 11-OH8 were prepared as described
in the literature.
Ch lor in H yd r oxyla t ion Usin g Ba sic Alu m in a , E x-
em p lified for Zn (II)-17,18-d ih yd r o-18,18-d im et h yl-5-(4-
m eth ylp h en yl)-10-m esityl-17-oxop or p h yr in (Oxo-Zn 1). A
mixture of Zn 1 (100 mg, 0.163 mmol) and basic alumina
(activity I, 7.0 g) in 8 mL of toluene was stirred at 60 °C for
22 h exposed to air. TLC (silica, CH2Cl2/ethyl acetate, 19:1)
showed three components: a blue component (Rf ) 0.82; Zn 1),
a green component (Rf ) 0.38; Oxo-Zn 1), and a blue compo-
nent (Rf ) 0.15; HO-Zn 1). The alumina was removed by
filtration and washed (CH2Cl2/CH3OH, 19:1) until the wash-
ings were colorless. The filtrate was concentrated and the
residue was chromatographed (silica, CH2Cl2), affording Zn 1
(2.0 mg, 2%) as the first fraction and Oxo-Zn 1 (23.4 mg, 23%)
as the second fraction. Further elution (CH2Cl2/ethyl acetate,
49:1) gave hydroxychlorin HO-Zn 1 (52.9 mg, 52%). Data for
Con clu sion s
Oxochlorins have absorption spectral features nearly
identical to those of chlorins, but are more resistant to
oxidation. Indeed, an oxochlorin exhibits an oxidation
potential similar to that of the corresponding porphyrin.
On the other hand, the fluorescence yield of an oxochlorin
is diminished relative to that of a chlorin, again resem-
bling that of a porphyrin. In general, oxochlorins have
spectral features resembling chlorins but the oxidation
and fluorescence yield properties resembling a porphyrin.
The lifetime of the lowest excited singlet state of Zn
oxochlorins (∼0.7 ns) is roughly 2- or 4-fold shorter than
that of Zn chlorins or porphyrins, respectively, whereas
the lifetimes for Fb chlorins and oxochlorins (∼8 ns) are
only modestly (∼40%) shorter than for a porphyrin. These
excited-state lifetimes are sufficiently long to support
efficient excited-state energy transfer in arrays utilizing
chlorins or oxochlorins. The ability to prepare C-alkylated
oxochlorin building blocks in a rational manner, by way
of the corresponding chlorins, sets the stage for the
preparation of diverse multipigment arrays containing
oxochlorin components. The spectral and electronic stud-
ies reported herein of chlorin and oxochlorin monomers
provide the foundation for designing monomers with
desired properties for incorporation into such arrays and
1
Oxo-Zn 1: IR 1717 cm-1 (br); H NMR δ 1.82 (s, 6H), 2.03 (s,
6H), 2.59 (s, 3H), 2.67 (s, 3H), 7.22 (s, 2H), 7.50 (d, J ) 8.1
Hz, 2H), 7.98 (d, J ) 8.1 Hz, 2H) 8.46 (d, J ) 4.2 Hz, 1H),
8.54 (d, J ) 4.2 Hz, 1H) 8.64 (d, J ) 4.2 Hz, 1H), 8.83 (d, J )
4.2 Hz, 1H), 8.80-8.95 (m, 2H), 8.94 (s, 1H), 9.55 (s, 1H); LD-
MS obsd 622.16; FAB-MS obsd 624.1869, calcd 624.1868
(C38H32N4OZn); λabs 423 (log ꢀ ) 5.32), 563 (3.82), 609 (4.60)
nm; λem 609, 650, 669 nm. Data for Zn(II)-17,18-dihydro-18,18-
dimethyl-17-hydroxy-5-(4-methylphenyl)-10-mesitylporphy-
rin (HO-Zn 1): LD-MS obsd 625.01, calcd 626.01 (C38H34N4-
OZn).
Con ver sion of Hyd r oxych lor in (HO-Zn 1) to Oxoch lo-
r in (Oxo-Zn 1) u sin g DDQ. To a solution of HO-Zn 1 (96.6
mg, 0.154 mmol) in 80 mL of toluene was added DDQ (52.4
mg, 0.231 µmol). The mixture was stirred for 5 min, 2 mL of
triethylamine was added, and the solvent was removed under
reduced pressure. The residue was immediately chromato-
graphed (silica, CH2Cl2), affording a purple solid (45.6 mg,
47%).
Tw o-Step P r oced u r e for th e Syn th esis of Oxoch lor in s
(Oxo-Zn 1). A mixture of Zn 1 (50.0 mg, 81.7 µmol) and basic
alumina (activity I, 3.0 g) in 4 mL of toluene was stirred at 50
°C for 6.5 h exposed to air. The alumina was removed by
filtration and washed (CH2Cl2/CH3OH, 19:1) until the wash-
(58) Fajer, J .; Davis, M. S. In The Porphyrins; Dolphin, D., Ed.;
Academic Press: New York, 1979; Vol. IV, pp 197-256.
(59) Ozawa, S.; Watanabe, Y.; Morishima, I. J . Am. Chem. Soc. 1994,
116, 5832-5838.
(60) (a) Parusel, A. B. J .; Ghosh, A. J . Phys. Chem. A 2000, 104,
2504-2507. (b) Ghosh, A. J . Phys. Chem. B 1997, 101, 3290-3297.
(61) (a) Fenyo, D.; Chait, B. T.; J ohnson, T. E.; Lindsey, J . S. J .
Porphyrins Phthalocyanines 1997, 1, 93-99. (b) Srinivasan, N.; Haney,
C. A.; Lindsey, J . S.; Zhang, W.; Chait, B. T. J . Porphyrins Phthalo-
cyanines 1999, 3, 283-291.
7338 J . Org. Chem., Vol. 67, No. 21, 2002

Synthesis and Properties of Oxochlorins
ings were colorless. The filtrate was concentrated, and the
residue was dissolved in toluene (40 mL). DDQ (37.0 mg, 163
µmol) was added, the mixture was stirred for 5 min, 1 mL of
triethylamine was added, and the solvent was removed under
reduced pressure. The residue was immediately chromato-
graphed (silica, CH2Cl2), affording a purple solid as the only
isolable product (27.2 mg, 53%).
δ 1.51 (s, 18H), 2.06 (s, 6H), 7.77 (t, J ) 1.6 Hz, 1H), 7.84 (d,
J ) 8.4 Hz, 2H), 7.94 (d, J ) 1.6 Hz, 2H), 8.05 (d, J ) 8.4 Hz,
2H), 8.60 (d, J ) 4.4 Hz, 1H), 8.63 (d, J ) 4.4 Hz, 1H), 8.78 (d,
J ) 4.4 Hz, 1H), 8.88 (d, J ) 4.4 Hz, 1H), 8.94 (d, J ) 4.4 Hz,
1H), 8.98 (s, 1H), 9.00 (d, J ) 4.4 Hz, 1H), 9.61 (s, 1H); LD-
MS obsd 804.57; FAB-MS obsd 806.1472, calcd 806.1460
(C42H39IN4OZn); λabs 425 (log ꢀ ) 5.25), 563 (3.84), 609 (4.49)
nm; λem 610, 649, 668 nm.
2-(2-Nitr oeth yl)pyr r ole (6). Pyrrole-2-carboxaldehyde (2.85
g, 30.0 mmol) was dissolved in 90 mL of dry methanol and
treated with nitromethane (4.85 mL, 90.0 mmol), sodium
acetate (2.71 g, 33.0 mmol), and methylamine hydrochloride
(2.23 g, 33.0 mmol). Stirring at room temperature for 12 h
afforded a yellow/brown mixture. DMF (60 mL) and methanol
(50 mL) were added to the reaction mixture. Sodium borohy-
dride (3.97 g, 105 mmol) was added portionwise. The reaction
mixture was stirred at room temperature for 1 h, neutralized
with acetic acid (∼5 mL), and evaporated. The mixture was
dissolved in dichloromethane (150 mL) and washed with water.
The organic layer was dried (Na2SO4), concentrated, and
chromatographed (silica, CH2Cl2) to give an orange oil (2.79
g, 66%). The 1H NMR spectrum and the 13C NMR spectrum
were identical with the literature data:8 IR 3406, 1552, 1380
cm-1; Anal. Calcd for C6H8N2O2: C, 51.42; H, 5.75; N, 19.99.
Found: C, 51.38; H, 5.71; N, 19.92.
Zn (II)-17,18-d ih yd r o-18,18-d im et h yl-17-oxo-5,10-b is-
(p en ta flu or op h en yl)p or p h yr in (Oxo-Zn 2). Following the
procedure for preparing Oxo-Zn 1, a mixture of chlorin Zn 2
(21.0 mg, 28.5 µmol) and basic alumina (activity I, 1.4 g) in
0.75 mL of toluene was stirred for 120 h. Solvent was removed
under reduced pressure, and the residue was washed (CH2-
Cl2/CH3OH, 19:1) until the washings were colorless. The
filtrate was removed, and the residue was chromatographed
(silica). Elution with hexanes/CH2Cl2 (1:4) gave Zn 2 (8.0 mg,
38%); elution with CH2Cl2 gave Oxo-Zn 2 (3.0 mg, 14%);
elution with CH2Cl2/ethyl acetate (49:1) gave hydroxychlorin
HO-Zn 2 (7.0 mg, 33%). LD-MS data for HO-Zn 2: obsd 752.72
calcd 750.05 (C34H16F10N4OZn). DDQ (4.2 mg, 18 µmol) was
added to a solution of HO-Zn 2 (7.0 mg, 9.3 µmol) in toluene
(200 µL). The mixture was stirred for 45 min. Triethylamine
(100 µL) was added, and the solvent was removed under
reduced pressure. The residue was chromatographed (silica,
CH2Cl2), affording a green solid (5.2 mg, 74%): IR 1719 cm-1
;
1H NMR δ 1.94 (s, 6H), 8.56 (d, J ) 4.8 Hz, 1H), 8.61 (d, J )
4.8 Hz, 1H), 8.72-8.76 (m, 2H) 9.03 (d, J ) 4.8 Hz, 1H), 9.07
(d, J ) 4.8 Hz, 1H), 9.08 (s, 1H), 9.60 (s, 1H); LD-MS obsd
746.43; FAB-MS obsd 748.0339, calcd 748.0299 (C34H14F10N4-
OZn); λabs 423 (log ꢀ ) 5.23), 567 (3.80), 613 (4.54) nm; λem
614, 653, 671 nm.
1-Cycloh exylid en e-2-p r op a n on e (7). Following a stan-
dard procedure,37 a solution of KOH (840 mg, 15.0 mmol) in
ethanol/H2O (30.0 mL, 4:1) was treated with cyclohexanone
(1.04 mL, 10.0 mmol). Stirring at room temperature for 28 h
afforded a light brown mixture. The mixture was extracted
with petroleum ether. The organic layer was washed with
water, dried (Na2SO4), and evaporated. The residue was
purified by column chromatography (silica, dichloromethane)
to give a colorless oil (1.45 g, 95%). Analytical data were
consistent with the literature for the title compound prepared
via a different route.38
Zn (II)-17,18-dih ydr o-18,18-dim eth yl-5-(4-m eth ylph en yl)-
10-[4-[2-(tr im eth ylsilyl)eth oxyca r bon yl]p h en yl]-17-oxo-
p or p h yr in (Oxo-Zn 3). A mixture of Zn 3 (25.0 mg, 35.0 µmol)
and basic alumina (activity I, 1.5 g) in 2 mL of toluene was
stirred for 4 h at 50 °C exposed to air. After standard workup,
the residue was dissolved in 1.5 mL of toluene, and DDQ (19.9
mg, 87.5 µmol) was added. Standard workup and chromatog-
raphy [silica, ethyl acetate/CH2Cl2 (1:5)] gave a bluish-purple
solid (8.2 mg, 31%): 1H NMR δ 0.17 (s, 9H), 1.22-1.27 (m,
2H), 2.04 (s, 6H), 2.68 (s, 3H), 4.47-4.54 (m, 2H), 7.52 (d, J )
8.0 Hz, 2H), 7.97 (d, J ) 8.0 Hz, 2H), 8.15 (d, J ) 8.0 Hz, 2H),
8.30 (d, J ) 8.0 Hz, 2H), 8.54 (d, J ) 4.4 Hz, 1H), 8.61 (d, J )
4.4 Hz, 1H), 8.72 (d, J ) 4.4 Hz, 1H), 8.86 (d, J ) 4.4 Hz, 1H),
8.93 (d, J ) 4.4 Hz, 1H), 8.97 (d, J ) 4.4 Hz, 1H), 8.98 (s, 1H),
9.56 (s, 1H); LD-MS obsd 727.45; FAB-MS obsd 726.2002, calcd
726.2005 (C41H38N4O3SiZn); λabs 425 (log ꢀ ) 5.39), 564 (3.96),
610 (4.62) nm; λem 610, 651, 669 nm.
Zn (II)-5-(3,5-d i-ter t-bu tylp h en yl)-10-(4-eth yn ylp h en yl)-
17,18-dih ydr o-18,18-dim eth yl-17-oxopor ph yr in (Oxo-Zn 4).
A mixture of Zn 4 (50.0 mg, 72.2 µmol) and basic alumina
(activity I, 3.0 g) in 4 mL of toluene was stirred for 8 h at 50
°C. After standard workup, the residue was dissolved in 40
mL of toluene, and DDQ (32.7 mg, 144 µmol) was added.
Standard workup and chromatography (silica, CH2Cl2) gave
a bluish-purple solid (30.4 mg, 60%): 1H NMR δ 1.51 (s, 18H),
2.01 (s, 6H), 3.30 (s, 1H), 7.77 (t, J ) 1.6 Hz, 1H), 7.84 (d, J )
8.4 Hz, 2H), 7.95 (d, J ) 1.6 Hz, 2H), 8.07 (d, J ) 8.4 Hz, 2H),
8.59 (d, J ) 4.4 Hz, 1H), 8.64 (d, J ) 4.4 Hz, 1H), 8.76 (d, J )
4.4 Hz, 1H), 8.88 (d, J ) 4.4 Hz, 1H), 8.94 (d, J ) 4.4 Hz, 1H),
8.97 (s, 1H), 8.98 (d, J ) 4.4 Hz, 1H), 9.51 (s, 1H); LD-MS
obsd 704.88; FAB-MS obsd 704.2507, calcd 704.2494 (C44H40N4-
OZn); λabs 426 (log ꢀ ) 5.40), 564 (4.01), 610 (4.73) nm; λem
610, 650, 668 nm.
1-[1-[1-Nitr o-2-(1H-pyr r ol-2-yl)eth yl]cycloh exyl]pr opan -
2-on e (8). Following a general procedure,8,32 cesium fluoride
(3.58 g, 23.6 mmol, 3.00 molar equiv, freshly dried by heating
to 100 °C under vacuum for 1 h and then cooling to room
temperature under argon) was placed in a flask under argon.
A mixture of 6 (1.10 g, 7.85 mmol) and 7 (7.17 g, 47.1 mmol)
in 50 mL of dry acetonitrile was transferred to the flask by
cannula. The mixture was heated at 70 °C for 7 h, whereupon
the reaction was deemed to be complete by TLC analysis. The
reaction mixture was filtered. The filtrate was evaporated and
chromatographed [alumina, ethyl acetate/hexanes (1:3)], af-
fording a light yellow oil that solidified upon storing in the
freezer (1.11 g, 51%): mp 82 °C; IR 3395, 1712, 1547, 1366
1
cm-1; H NMR δ_1.20-1.98 (m, 10H), 2.18 (s, 3H), 2.63, 2.70
2
3
2
(AB, J ) 17.7 Hz, 2H), 3.10 (ABX, J ) 2.7 Hz, J ) 15.3 Hz,
3
2
1H), 3.30 (ABX, J ) 11.7 Hz, J ) 15.3 Hz, 1H), 5.18 (ABX,
3J ) 2.7 Hz, J ) 11.7 Hz, 1H), 5.94-5.98 (m, 1H), 6.07-6.12
3
(m, 1H), 6.64-6.67 (m, 1H), 8.10-8.22 (br, 1H); 13C NMR δ
21.3, 25.3, 26.2, 30.9, 31.0, 32.2, 40.0, 43.8, 94.6, 107.1, 108.6,
117.7, 126.1, 207.7. Anal. Calcd for C15H22N2O3: C, 64.73; H,
7.97; N, 10.06. Found: C, 64.46; H, 7.88; N, 10.12.
3-Meth yl-1-(1H-p yr r ol-2-ylm eth yl)-2-a za sp ir o[4.5]d ec-
2-en e 2-Oxid e (9). Following a general procedure,3 a vigor-
ously stirred solution of 8 (700 mg, 2.51 mmol) in 12 mL of
acetic acid and 12 mL of ethanol at 0 °C was treated with Zn
dust (4.11 g, 62.8 mmol) in small portions over 5 min. The
reaction mixture was stirred at 0 °C for 15 min and then was
filtered through Celite. The filtrate was concentrated under
high vacuum. The resulting brown solid was purified by
column chromatography [silica; packed and eluted with ethyl
acetate/CH2Cl2 (1:1), then eluted with CH2Cl2/methanol (9:1)],
affording a brown oil that solidified to brownish crystals on
standing at room temperature (498 mg, 81%): mp 109-110
Zn (II)-5-(3,5-d i-ter t-bu tylp h en yl)-17,18-d ih yd r o-10-(4-
iod op h en yl)-18,18-d im eth yl-17-oxop or p h yr in (Oxo-Zn 5).
A mixture of Zn 5 (75.0 mg, 94.4 µmol) and basic alumina
(activity I, 4.5 g) in 6 mL of toluene was stirred for 5 h at 50
°C. After standard workup, the residue was dissolved in 60
mL of toluene, and DDQ (42.9 mg, 189 µmol) was added.
Standard workup and chromatography [silica, hexanes/CH2-
Cl2 (1:3)] gave a bluish purple solid (49.8 mg, 65%): 1H NMR
1
°C; IR 3200, 1216 cm-1; H NMR δ 1.25-1.89 (m, 10 H), 2.01
3
2
(s, 3H), 2.28-2.44 (m, 2H), 3.00 (ABX, J ) 3.7 Hz, J ) 16.1
Hz, 1H), 3.17 (ABX, 3J ) 6.6 Hz, 2J ) 16.1 Hz, 1H), 3.83-3.91
J . Org. Chem, Vol. 67, No. 21, 2002 7339

Taniguchi et al.
(m, 1H), 5.92-5.96 (m, 1H), 6.04-6.09 (m, 1H), 6.66-6.71 (m,
1H), 10.35-10.60 (br, 1H); 13C NMR δ 13.2, 22.4, 25.6, 25.7,
30.8, 30.9, 37.0, 40.1, 42.8, 81.3, 106.4, 107.2, 117.3, 128.3,
146.1; FAB-MS obsd 247.1813, calcd 247.1810 (C15H22N2O).
(s, 2H), 7.51 (d, J ) 7.6 Hz, 2H), 8.00 (d, J ) 7.6 Hz, 2H), 8.20
(d, J ) 8.0 Hz, 2H), 8.38 (d, J ) 8.0 Hz, 2H), 8.40 (d, J ) 4.4
Hz, 1H), 8.51 (d, J ) 4.4 Hz, 1H), 8.70 (d, J ) 4.8 Hz, 1H),
8.78-8.82 (m, 2H), 8.84 (d, J ) 4.8 Hz, 1H), 8.88 (s, 1H), 8.97
(s, 1H); LD-MS obsd 649.96; FAB-MS obsd 651.3171, calcd
651.3155 (C41H42N4O2Si) [M + H]+; λabs 415 (log ꢀ ) 5.58), 509
(4.54), 589 (3.09), 640 (4.97) nm; λem 641, 683, 707 nm.
5-(3,5-Di-ter t-bu tylp h en yl)-10-(4-eth yn ylp h en yl)-17,18-
d ih yd r o-18,18-d im eth ylp or p h yr in (4). Treatment of a solu-
tion of Zn 4 (22.0 mg, 31.8 µmol) in 10 mL of CH2Cl2 with a
50-fold excess of TFA for 1 h followed by standard workup and
chromatography [silica, hexanes/CH2Cl2 (2:1)] gave a reddish
purple solid (12.5 mg, 62%): 1H NMR δ -1.88 to -1.84 (br,
2H), 1.50 (s, 18H), 2.06 (s, 6H), 3.29 (s, 1H), 4.62 (s, 2H), 7.75
(t, J ) 1.6 Hz, 1H), 7.84 (d, J ) 7.6 Hz, 2H), 7.97 (d, J ) 1.6
Hz, 2H), 8.09 (d, J ) 7.6 Hz, 2H), 8.44 (d, J ) 4.4 Hz, 1H),
8.53 (d, J ) 4.4 Hz, 1H), 8.72 (d, J ) 4.8 Hz, 1H), 8.80 (d, J )
4.8 Hz, 1H), 8.81-8.85 (m, 2H), 8.87 (s, 1H), 8.96 (s, 1H); LD-
MS obsd 627.09; FAB-MS obsd 628.3550, calcd 628.3566
(C44H44N4); λabs 416 (log ꢀ ) 5.16), 510 (4.13), 590 (3.67), 641
(4.54) nm; λem 641, 683, 707 nm.
5-(3,5-Di-ter t-b u t ylp h en yl)-17,18-d ih yd r o-10-(4-iod o-
p h en yl)-18,18-d im eth ylp or p h yr in (5). Treatment of a solu-
tion of Zn 5 (67.6 mg, 85.1 µmol) in 25 mL of CH2Cl2 with a
50-fold excess of TFA for 1.5 h followed by standard workup
and chromatography [silica, hexanes/CH2Cl2 (3:1)] gave a
reddish purple solid (43.7 mg, 70%): 1H NMR δ -1.92 to -1.84
(br, 2H), 1.50 (s, 18H), 2.06 (s, 6H), 4.61 (s, 2H), 7.75 (t, J )
1.5 Hz, 1H), 7.86 (d, J ) 8.1 Hz, 2H), 7.97 (d, J ) 1.5 Hz, 2H),
8.04 (d, J ) 8.1 Hz, 2H), 8.44 (d, J ) 4.4 Hz, 1H), 8.53 (d, J )
4.4 Hz, 1H), 8.72 (d, J ) 5.1 Hz, 1H), 8.79 (d, J ) 5.1 Hz, 1H),
8.80-8.86 (m, 2H), 8.87 (s, 1H), 8.96 (s, 1H); LD-MS obsd
729.33; FAB-MS obsd 730.2539, calcd 730.2532 (C42H43IN4);
λabs 416 (log ꢀ ) 5.19), 510 (4.16), 592 (3.71), 641 (4.59) nm;
λem 641, 683, 708 nm.
17,18-Dih yd r o-18,18-d im et h yl-5-(4-m et h ylp h en yl)-10-
m esityl-17-oxop or p h yr in (Oxo-1). Treatment of a solution
of Oxo-Zn 1 (6.2 mg, 9.6 µmol) in 0.4 mL of CH2Cl2 with 40
µL of TFA for 2 h followed by standard workup and chroma-
tography [silica, hexanes/CH2Cl2 (3:1)] gave a reddish purple
solid (5.2 mg, 93%): IR 1723 cm-1; 1H NMR δ -2.32 to -2.23
(br, 1H), -2.23 to -2.17 (br, 1H), 1.85 (s, 6H), 2.11 (s, 6H),
2.63 (s, 3H), 2.70 (s, 3H), 7.55 (d, J ) 7.2 Hz, 2H), 8.04 (d, J
) 7.2 Hz, 2H), 8.50 (d, J ) 4.5 Hz, 2H), 8.58 (d, J ) 4.5 Hz,
2H), 8.74 (d, J ) 4.5 Hz, 1H), 8.94 (d, J ) 4.5 Hz, 1H) 9.08 (d,
J ) 4.5 Hz, 1H), 9.11 (d, J ) 4.5 Hz, 1H) 9.21 (s, 1H), 9.82 (s,
1H); LD-MS obsd 560.08; FAB-MS obsd 562.2753, calcd
562.2733 (C38H34N4O); λabs 414 (log ꢀ ) 5.24), 512 (4.10), 545
(3.86), 586 (3.74), 643 (4.31) nm; λem 643, 685, 713 nm.
3-Meth yl-1-(1H-p yr r ol-2-ylm eth yl)-2-a za sp ir o[4.5]d ec-
2-en e (10). Following a procedure for the deoxygenation of
tetrahydrodipyrrin N-oxides,3 TiCl4 (1.51 mL, 13.7 mmol) was
slowly added with stirring to dry THF (30 mL) under argon
at 0 °C. To the resulting yellow solution was slowly added
LiAlH4 (370 mg, 9.75 mmol). The resulting black mixture was
stirred at room temperature for 15 min, and then triethyl-
amine (12.2 mL, 87.8 mmol) was added. The black mixture
was then poured into a solution of 9 (480 mg, 1.95 mmol) in
dry THF (20 mL). The mixture was stirred for 30 min at room
temperature, and then water (25 mL) was added. The mixture
was filtered. The filtrate was extracted with CH2Cl2. The
organic layer was dried (Na2SO4) and evaporated under
reduced pressure. The resulting yellow oil was purified by
chromatography (silica, ethyl acetate) to give a pale yellow oil,
which solidified to a pale yellow solid on cooling (228 mg,
51%): mp 54-55 °C; IR 3358, 1648 cm-1 1H NMR δ 1.16-
;
2
1.71 (m, 10H), 2.04 (s, 3H), 2.31, 2.46 (AB, J ) 17.6 Hz, 2H),
3
2
3
2.53 (ABX, J ) 11.0 Hz, J ) 14.7 Hz, 1H), 2.85 (ABX, J )
2
2.9 Hz, J ) 14.7 Hz, 1H), 3.63-3.73 (m, 1H), 5.92-5.96 (m,
1H), 6.08-6.13 (m, 1H), 6.68-6.73 (m, 1H), 9.70-9.95 (br, 1
H); 13C NMR δ 20.8, 23.6, 24.1, 26.4, 28.4, 31.3, 37.2, 45.9,
49.7, 81.1, 105.5, 107.5, 116.6, 131.9, 174.2; FAB-MS obsd
379.1349, calcd 379.1328 (C18H22N2O5S).
Sp ir oh exylch lor in Zn 12. Following a general procedure,3
a solution of 11 (140 mg, 0.304 mmol) in 10 mL of anhydrous
THF/methanol (4:1) was treated with NaBH4 (115 mg, 3.04
mmol). The resulting Eastern half (11-OH) was dissolved in
3 mL of anhydrous CH3CN, and then the Western half (10,
70.0 mg, 0.304 mmol) and TFA (23.4 µL, 0.304 mmol) were
added. The solution was stirred at room temperature for 30
min. The reaction was quenched with 10% aqueous NaHCO3
(50 mL). The resulting mixture was extracted with distilled
CH2Cl2. The combined organic layers were washed with water,
dried (Na2SO4), and concentrated in vacuo without heating.
The residue, which contains the crude tetrahydrobilene-a, was
dissolved in 30 mL of toluene, to which AgOTf (137 mg, 0.534
mmol), Zn(OAc)2 (490 mg, 2.67 mmol), and 2,2,6,6-tetrameth-
ylpiperidine (447 µL, 2.67 mmol) were added. The reaction
mixture was refluxed for 24 h. The reaction mixture was
concentrated and chromatographed [silica, hexanes/CH2Cl2 (2:
1)], affording a blue solid (37 mg, 19%): 1H NMR δ 0.80-2.70
(m, 22H), 4.55 (s, 2H), 7.20 (s, 2H), 7.47 (d, J ) 8.1 Hz, 2H),
7.95 (d, J ) 8.1 Hz, 2H), 8.22 (d, J ) 4.5 Hz, 1H), 8.36 (d, J )
4.5 Hz, 1H), 8.48 (d, J ) 4.5 Hz, 1H), 8.54-8.67 (m, 5H); LD-
MS obsd 649.89; FAB-MS obsd 650.2399, calcd 650.2388
(C41H38N4Zn); λabs 412, 610 nm; λem 610, 654, 666 nm.
Sp ir oh exyloxoch lor in Oxo-Zn 12. A mixture of Zn 12 (25
mg, 38 µmol) and basic alumina (activity I, 1.7 g) in 3 mL of
toluene was stirred at 85 °C for 15 h. After standard workup,
the residue was dissolved in 3 mL of toluene, and DDQ (16.9
mg, 76.1 µmol) was added. Standard workup and chromatog-
raphy (silica, CH2Cl2) gave a bluish-purple solid (5.0 mg,
20%): 1H NMR δ 0.85-2.70 (m, 22H), 7.23 (s, 2H), 7.51 (d, J
) 8.1 Hz, 2H), 7.98 (d, J ) 8.1 Hz, 2H), 8.22 (d, J ) 4.5 Hz,
1H), 8.45 (d, J ) 4.5 Hz, 1H), 8.53 (d, J ) 4.5 Hz, 1H), 8.80-
8.93 (m, 3H), 8.98 (s, 1H), 9.45 (s, 1H); LD-MS obsd 664.70;
FAB-MS obsd 664.2198, calcd 664.2181 (C41H36N4OZn); λabs
424, 611 nm; λem 611, 651, 669 nm.
17,18-Dih yd r o-18,18-d im et h yl-17-oxo-5,10-b is(p en t a -
flu or op h en yl)p or p h yr in (Oxo-2). Treatment of a solution
of Oxo-Zn 2 (7.5 mg, 10 µmol) in 0.4 mL of CH2Cl2 with 40 µL
of TFA for 2 h followed by standard workup and chromatog-
raphy [silica, hexanes/CH2Cl2 (3:2)] gave a reddish purple solid
1
(5.6 mg, 82%): IR 1725 cm-1; H NMR δ -2.76 to -2.70 (br,
1H), -2.63 to -2.57 (br, 1H), 2.13 (s, 6H), 8.63 (d, J ) 4.5 Hz,
1H), 8.68 (d, J ) 4.5 Hz, 1H), 8.88-8.94 (m, 2H), 9.26-9.30
(m, 1H), 9.30-9.35 (m, 1H), 9.45 (s, 1H), 10.04 (s, 1H); LD-
MS obsd 688.26; FAB-MS obsd 686.1151, calcd 686.1164
(C34H16F10N4O); λabs 413 (log ꢀ ) 5.08), 508 (3.99), 541 (3.71),
592 (3.60), 645 (4.30) nm; λem 645, 686, 715 nm.
17,18-Dih yd r o-18,18-d im e t h yl-5-(4-m e t h ylp h e n yl)-
10-[4-[2-(tr im eth ylsilyl)eth oxyca r bon yl]p h en yl]-17-oxo-
p or p h yr in (Oxo-3). Treatment of a solution of Oxo-Zn 3
(6.5 mg, 8.9 µmol) in 5 mL of CH2Cl2 with a 50-fold excess of
TFA for 30 min followed by standard workup and chroma-
tography [silica, hexanes/CH2Cl2 (1:3)] gave a purple solid
(5.4 mg, 91%): 1H NMR δ -2.46 to -2.42 (br, 1H), -2.31 to
-2.27 (br, 1H), 0.17 (s, 9H), 1.26-1.32 (m, 2H), 2.11 (s, 6H),
2.70 (s, 3H), 4.59-4.63 (m, 2H), 7.55 (d, J ) 8.0 Hz, 2H), 8.02
(d, J ) 8.0 Hz, 2H), 8.23 (d, J ) 8.0 Hz, 2H), 8.44 (d, J ) 8.0
Hz, 2H), 8.56 (d, J ) 4.8 Hz, 1H), 8.62 (d, J ) 4.8 Hz, 1H),
17,18-Dih yd r o-18,18-d im e t h yl-5-(4-m e t h ylp h e n yl)-
10-[4-[2-(t r im e t h ylsilyl)e t h oxyca r b on yl]p h e n yl]p or -
p h yr in (3). A solution of Zn 3 (16.0 mg, 22.4 µmol) in 5 mL of
CH2Cl2 was treated with a 50-fold excess of TFA. The de-
metalation was complete in 1 h as confirmed by UV/vis and
TLC analyses. Standard workup and chromatography [silica,
hexanes/CH2Cl2 (1:1)] gave a reddish purple solid (10.8 mg,
74%): 1H NMR δ -1.94 to -1.87 (br, 2H), 0.17 (s, 9H), 1.25-
1.32 (m, 2H), 2.06 (s, 6H), 2.67 (s, 3H), 4.53-4.64 (m, 2H), 4.62
7340 J . Org. Chem., Vol. 67, No. 21, 2002

Synthesis and Properties of Oxochlorins
8.84 (d, J ) 4.8 Hz, 1H), 8.96 (d, J ) 4.8 Hz, 1H), 9.10 (d, J )
4.8 Hz, 1H), 9.17 (d, J ) 4.8 Hz, 1H), 9.25 (s, 1H), 9.86 (s,
1H); LD-MS obsd 663.06; FAB-MS obsd 665.2961, calcd
665.2948 (C41H40N4O3Si) [M + H]+; λabs 416 (log ꢀ ) 5.28), 513
(4.10), 547 (3.92), 593 (3.79), 643 (4.25) nm; λem 643, 686, 713
nm.
85%): LD-MS obsd 790.57; FAB-MS obsd 791.1719, calcd
791.1672 (C42H41CuIN4); λabs 409 (log ꢀ ) 5.37), 510 (3.76), 604
(4.60) nm.
Cu (II)-17,18-d ih yd r o-10-m esit yl-18,18-d im et h yl-5-(4-
m eth ylp h en yl)-17-oxop or p h yr in (Oxo-Cu 1). A solution of
Oxo-1 (3.4 mg, 6.1 µmol) in 2.5 mL of CH2Cl2 was treated with
a solution of Cu(OAc)2‚H2O (120 mg, 600 µmol) in 0.5 mL of
methanol. The mixture was stirred at room temperature for
36 h followed by 35 °C for 6 h. Standard workup and
chromatography (silica, CH2Cl2) gave a blue solid (3.1 mg,
82%): IR 1719 cm-1; LD-MS obsd 623.00; FAB-MS obsd
623.1861, calcd 623.1872 (C38H32CuN4O); λabs 419 (log ꢀ ) 5.24),
605 (4.43) nm.
Cu (II)-17,18-d ih yd r o-18,18-d im et h yl-17-oxo-5,10-b is-
(p en ta flu or op h en yl)p or p h yr in (Oxo-Cu 2). A solution of
Oxo-2 (2.9 mg, 4.2 µmol) in 2.5 mL of CH2Cl2 was treated with
a solution of Cu(OAc)2‚H2O (100 mg, 500 µmol) in 0.5 mL of
methanol. The mixture was stirred at room temperature for
48 h followed by 35 °C for 6 h. Standard workup and
chromatography (silica, CH2Cl2) gave a blue solid (2.3 mg,
73%): LD-MS obsd 744.33; FAB-MS obsd 747.0341, calcd
747.0304 (C34H14CuN4O); λabs 418 (log ꢀ ) 5.27), 610 (4.51) nm.
Cu (II)-5-(3,5-di-ter t-bu tylph en yl)-10-(4-eth yn ylph en yl)-
17,18-dih ydr o-18,18-dim eth yl-17-oxopor ph yr in (Oxo-Cu 4).
A solution of Oxo-4 (14.8 mg, 23.0 µmol) in 5 mL of CH2Cl2/
methanol (1:1) was treated with Cu(OAc)2‚H2O (115 mg, 0.575
mmol) at room temperature for 2 h. Standard workup and
chromatography [silica, hexanes/CH2Cl2 (1:1)] gave a blue solid
(15.3 mg, 94%): LD-MS obsd 702.78; FAB-MS obsd 703.2512,
calcd 703.2498 (C44H40CuN4O); λabs 420 (log ꢀ ) 5.41), 560
(3.88), 605 (4.55) nm.
5-(3,5-Di-ter t-bu tylp h en yl)-10-(4-eth yn ylp h en yl)-17,18-
d ih yd r o-18,18-d im eth yl-17-oxop or p h yr in (Oxo-4). Treat-
ment of a solution of Oxo-Zn 4 (9.8 mg, 14 µmol) in 5 mL of
CH2Cl2 with a 50-fold excess of TFA for 1 h followed by
standard workup and chromatography [silica, hexanes/CH2-
Cl2 (1:1)] gave a reddish purple solid (7.5 mg, 86%): 1H NMR
δ -2.40 to -2.36 (br, 1H), -2.27 to -2.24 (br, 1H), 1.52 (s,
18H), 2.11 (s, 6H), 3.32 (s, 1H), 7.80 (t, J ) 1.6 Hz, 1H), 7.88
(d, J ) 8.0 Hz, 2H), 7.99 (d, J ) 1.6 Hz, 2H), 8.13 (d, J ) 8.0
Hz, 2H), 8.60 (d, J ) 4.4 Hz, 1H), 8.63 (d, J ) 4.4 Hz, 1H),
8.87 (d, J ) 4.4 Hz, 1H), 8.97 (d, J ) 4.4 Hz, 1H), 9.10 (d, J )
4.4 Hz, 1H), 9.17 (d, J ) 4.4 Hz, 1H), 9.23 (s, 1H), 9.85 (s,
1H); LD-MS obsd 641.80; FAB-MS obsd 643.3448, calcd
643.3437 (C44H42N4O) [M + H]+; λabs 417 (log ꢀ ) 5.30), 514
(4.10), 550 (3.92), 593 (3.77), 643 (4.25) nm; λem 643, 686, 713
nm.
5-(3,5-Di-ter t-b u t ylp h en yl)-17,18-d ih yd r o-10-(4-iod o-
p h en yl)-18,18-d im eth yl-17-oxop or p h yr in (Oxo-5). Treat-
ment of a solution of Oxo-Zn 5 (10.2 mg, 12.6 µmol) in 5 mL
of CH2Cl2 with a 50-fold excess of TFA for 1 h followed by
standard workup and chromatography [silica, hexanes/CH2-
Cl2 (2:1)] gave a reddish purple solid (8.4 mg, 90%): 1H NMR
δ -2.42 to -2.38 (br, 1H), -2.29 to -2.25 (br, 1H), 1.52 (s,
18H), 2.10 (s, 6H), 7.80 (s, 1H), 7.90 (d, J ) 7.6 Hz, 2H), 7.99
(s, 2H), 8.09 (d, J ) 7.6 Hz, 2H), 8.60 (d, J ) 4.4 Hz, 1H), 8.63
(d, J ) 4.4 Hz, 1H), 8.87 (d, J ) 4.4 Hz, 1H), 8.97 (d, J ) 4.4
Hz, 1H), 9.10 (d, J ) 4.4 Hz, 1H), 9.17 (d, J ) 4.4 Hz, 1H),
9.24 (s, 1H), 9.85 (s, 1H); LD-MS obsd 742.81; FAB-MS obsd
745.2429, calcd 745.2403 (C42H41IN4O) [M + H]+; λabs 416 (log
ꢀ ) 5.29), 513 (4.11), 547 (3.92), 589 (3.79), 643 (4.26) nm; λem
643, 687, 714 nm.
Cu (II)-5-(3,5-d i-ter t-bu tylp h en yl)-17,18-d ih yd r o-10-(4-
iod op h en yl)-18,18-d im eth yl-17-oxop or p h yr in (Oxo-Cu 5).
A solution of Oxo-5 (17.2 mg, 23.1 µmol) in 5 mL of CH2Cl2/
methanol (1:1) was treated with Cu(OAc)2‚H2O (115 mg, 0.575
mmol) at room temperature for 2 h. Standard workup and
chromatography [silica, hexanes/CH2Cl2 (1:1)] gave a blue solid
(16.8 mg, 90%): LD-MS obsd 805.45; FAB-MS obsd 805.1486,
calcd 805.1465 (C42H39CuIN4O); λabs 420 (log ꢀ ) 5.41), 560
(3.88), 605 (4.55) nm.
Cu (II)-17,18-d ih yd r o-10-m esit yl-18,18-d im et h yl-5-(4-
m eth ylp h en yl)p or p h yr in (Cu 1). A solution of 1 (20 mg, 36
µmol) in 18 mL of CH2Cl2 was treated with a solution of Cu-
(OAc)2‚H2O (160 mg, 800 µmol) in 2 mL of methanol at room
temperature. The mixture was stirred overnight. Standard
workup and chromatography [silica, CH2Cl2/hexanes (2:3)]
gave a blue solid (19 mg, 85%): LD-MS obsd 608.43; FAB-MS
obsd 609.2103, calcd 609.2079 (C38H34CuN4); λabs 408 (log ꢀ )
5.21), 501 (3.70), 569 (3.81), 605 (4.43) nm.
Mg(II)-17,18-d ih yd r o-10-m esit yl-18,18-d im et h yl-5-(4-
m eth ylp h en yl)p or p h yr in (Mg1). Following a standard pro-
cedure,39 a mixture of 1 (5.0 mg, 9.1 µmol), MgI2 (25 mg, 89
µmol), and N,N-diisopropylethylamine (31 µL, 180 µmol) in 0.5
mL of CH2Cl2 was stirred for 3 h at room temperature. The
fluorescence excitation spectrum of an aliquot taken at this
stage indicated total consumption of 1. The mixture was
treated with 10% aqueous NaHCO3. The organic layer was
separated, dried (Na2SO4), and concentrated. The title com-
pound underwent demetalation during workup. A peak cor-
responding to M+ was not visible in the LD-MS spectrum.
Mg(II)-17,18-d ih yd r o-10-m e sit yl-18,18-d im e t h yl-5-
(4-m eth ylp h en yl)-17-oxop or p h yr in (Oxo-Mg1). Following
a standard procedure,39 a mixture of Oxo-1 (5.0 mg, 8.9 µmol),
MgI2 (25 mg, 89 µmol), and N,N-diisopropylethylamine (31 µL,
180 µmol) in 0.5 mL of CH2Cl2 was stirred for 3 h. Standard
workup and chromatography [basic alumina, grade V, CH2-
Cl2/methanol (199:1)] gave a green solid (2.0 mg, 38%): IR 1717
Cu (II)-17,18-d ih yd r o-18,18-d im et h yl-5,10-b is(p en t a -
flu or op h en yl)p or p h yr in (Cu 2). A solution of 2 (4.1 mg, 6.1
µmol) in 2 mL of CH2Cl2 was treated with a solution of Cu-
(OAc)2‚H2O (100 mg, 500 µmol) in 0.5 mL of methanol at room
temperature for 36 h. Standard workup and chromatography
[silica, CH2Cl2/hexanes (2:3)] gave a blue solid (3.8 mg, 87%):
LD-MS obsd 733.07; FAB-MS obsd 733.0533, calcd 733.0511
(C34H16CuF10N4); λabs 410 (log ꢀ ) 5.23), 505 (3.60), 568 (3.78),
611 (4.54) nm.
Cu (II)-5-(3,5-di-ter t-bu tylph en yl)-10-(4-eth yn ylph en yl)-
17,18-d ih yd r o-18,18-d im eth ylp or p h yr in (Cu 4). A solution
of 4 (17.0 mg, 27.0 µmol) in 4 mL of CH2Cl2/methanol (1:1)
was treated with Cu(OAc)2‚H2O (135 mg, 0.675 mmol) at room
temperature for 1.5 h. Standard workup and chromatography
[silica, hexanes/CH2Cl2 (1:1)] gave a blue solid (16.0 mg,
86%): LD-MS obsd 688.68; FAB-MS obsd 689.2736, calcd
689.2705 (C44H42CuN4); λabs (log ꢀ ) 5.31), 500 (3.75), 604 (4.55)
nm.
1
(weak), 1675 (strong) cm-1; H NMR δ (THF-d8) 1.84 (s, 6H),
2.00 (s, 6H), 2.58 (s, 3H), 2.65 (s, 3H), 7.24 (s, 2H), 7.49 (d, J
) 8.4 Hz, 2H), 7.95 (d, J ) 8.4 Hz, 2H), 8.30 (d, J ) 4.4 Hz,
1H), 8.39 (d, J ) 4.4 Hz, 1H), 8.44 (d, J ) 4.4 Hz, 1H), 8.61 (d,
J ) 4.4 Hz, 1H), 8.78 (d, J ) 4.4 Hz, 1H), 8.81 (d, J ) 4.4 Hz,
1H), 8.87 (s, 1H), 9.38 (s, 1H); MALDI-MS obsd 583.77; FAB-
MS obsd 584.2445, calcd 584.2427 (C38H32N4OMg); λabs 425 (log
ꢀ ) 5.28), 568 (3.92), 617 (4.54) nm; λem 617, 659, 672 nm.
Mg(II)-17,18-d ih yd r o-18,18-d im et h yl-17-oxo-5,10-b is-
(p en ta flu or op h en yl)p or p h yr in (Oxo-Mg2). Following a
standard procedure,39 a mixture of Oxo-2 (7.80 mg, 11.4 µmol),
MgI2 (31.7 mg, 114 µmol), and N,N-diisopropylethylamine (40
µL, 230 µmol) in 1 mL of CH2Cl2 was stirred for 2 h. Additional
MgI2 (31.7 mg, 114 µmol) and N,N-diisopropylethylamine (40
Cu (II)-5-(3,5-d i-ter t-bu tylp h en yl)-17,18-d ih yd r o-10-(4-
iod op h en yl)-18,18-d im eth ylp or p h yr in (Cu 5). A solution of
5 (14.5 mg, 19.8 µmol) in 4 mL of CH2Cl2/methanol (1:1) was
treated with Cu(OAc)2‚H2O (98.8 mg, 0.495 mmol) at room
temperature for 2 h. Standard workup and chromatography
[silica, hexanes/CH2Cl2 (1:1)] gave a blue solid (13.4 mg,
J . Org. Chem, Vol. 67, No. 21, 2002 7341

Taniguchi et al.
µL, 230 µmol) were added, and then the mixture was stirred
for 2 h. Standard workup and chromatography [basic alumina,
grade V, CH2Cl2 then CH2Cl2/methanol (199:1)] gave a purple
solid (6.8 mg, 84%): 1H NMR δ (THF-d8) 2.07 (s, 6H), 8.64 (d,
J ) 4.4 Hz, 1H), 8.69 (d, J ) 4.4 Hz, 1H), 8.75-8.81 (m, 2H),
9.05 (d, J ) 4.4 Hz, 1H), 9.90 (d, J ) 4.4 Hz, 1H), 9.23 (s, 1H),
9.69 (s, 1H); MALDI-MS obsd 707.50; FAB-MS obsd 708.0887,
calcd 708.0858 (C34H14F10MgN4O); λabs 425, 537, 620 nm; λem
621, 663, 680 nm.
B. P h ysica l Meth od s. 1. Sta tic Absor p tion a n d Em is-
sion Sp ectr oscop y. Static absorption (HP-8453 or Cary 100)
and fluorescence (Spex Fluoromax or Tau2) measurements
were performed as described previously.62 For emission stud-
ies, nondeaerated samples with an absorbance e0.15 at λexc
(typically 0.3-0.8 µM) were employed, with λexc in either the
Soret or Q-band region; the detection band-pass was 2-5 nm,
and the spectra were corrected for the detection-system
spectral response. Emission quantum yields were measured
relative to the reference compounds F bTP P (Φf ) 0.11)42 or
Zn TP P (Φf ) 0.033).40
2. Tim e-Resolved F lu or escen ce Sp ectr oscop y. Fluo-
rescence lifetimes were obtained on samples that had concen-
trations of 0.5-10 µM and were deaerated by bubbling with
N2. Lifetimes were determined by fluorescence modulation
(phase shift) techniques using a Spex Tau2 spectrofluorimeter.
Samples were excited at various wavelengths and detected
through appropriate colored glass filters. Modulation frequen-
cies from 20 to 300 MHz were utilized, and both the fluores-
cence phase shift and modulation amplitude were analyzed.
3. Tim e-Resolved Absor p tion Sp ectr oscop y. Transient
absorption data were acquired as described previously.62
Samples (∼10 µM in toluene) in 2 mm path length cuvettes at
room temperature were excited at 10 Hz with ∼130 fs, 5-30
µJ pulses at the appropriate wavelength and probed with
white-light probe pulses of comparable duration.
4. Reson a n ce Ra m a n Sp ectr oscop y. The resonance
Raman spectra were recorded using the same instrumentation
(spectrometer, lasers, etc.) as previously described.63 The
samples typically had a concentration of 100 µM (in CH2Cl2)
and were contained in 1 mm i.d. capillary tubes. The laser
power at the sample was typically 10 mW, and the spectral
resolution was ∼3 cm-1 at a Raman shift of 1600 cm-1
.
5. Electr och em istr y. The electrochemical measurements
were performed using instrumentation and methods previously
described.43 The solvent was CH2Cl2 containing 0.1 M Bu4-
NPF6.
Ack n ow led gm en t. This research was supported by
grants from the NIH (GM36238) (to J .S.L.) and the NSF
(CHE-9988142). Mass spectra were obtained at the
Mass Spectrometry Laboratory for Biotechnology. Par-
tial funding for the Facility was obtained from the North
Carolina Biotechnology Center and the National Science
Foundation. S.P. thanks Cochin University of Science
and Technology for a sabbatical leave.
Su p p or tin g In for m a tion Ava ila ble: Complete spectral
1
data (absorption, fluorescence, H NMR, LD-MS) for all new
chlorins and oxochlorins. This material is available free of
charge via the Internet at http://pubs.acs.org.
J O025843I
(62) (a) Yang, S. I.; Li, J .; Cho, H. S.; Kim, D.; Bocian, D. F.; Holten,
D.; Lindsey, J . S. J . Mater. Chem. 2000, 10, 283-296. (b) 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.
(63) Zhou, C.; Diers, J . R.; Bocian, D. F. J . Phys. Chem. B 1997,
101, 9635-9644.
7342 J . Org. Chem., Vol. 67, No. 21, 2002