Novel zinc phthalocyanine-benzoquinone rigid dyad and its photoinduced electron transfer properties

Article abstract of DOI:10.1021/jo801293s

(Chemical Equation Presented) While preparing the first structurally rigid zinc phthalocyanine-benzoquinone (ZnPc-BQ) dyad as a model for photoinduced charge separation mimicking natural photosynthesis, a convenient method is developed for in situ generation of a benzoquinone chromophore in the dyad using an iso-butyryl mask. The dyad has no rotamers and possesses a fixed distance between ZnPc and BQ moieties (center-to-center and edge-to-edge distances are 9.40 and 2.14 A, respectively). The dyad displays unusual electronic perturbation in the ground state, resulting from the interactions between Pc and BQ, and exhibits photoinduced electron transfer with a lifetime of 40 ps of the charged separated states. The steady-state fluorescence and electrochemical behavior of the dyad are evaluated. This study opens a route to subsequent dyads, triads, and complex architectures of electron donor-acceptor arrays with rigid structures and long charge separation states.

Full text of DOI:10.1021/jo801293s

Novel Zinc Phthalocyanine-Benzoquinone Rigid Dyad and Its
Photoinduced Electron Transfer Properties
Chi-Hang Lee,† Jiangchang Guo,‡ Lin X. Chen,*,‡,§ and Braja. K. Mandal*,†
Department of Biological, Chemical and Physical Sciences, Illinois Institute of Technology,
3101 S. Dearborn St., Chicago, Illinois 60616, Chemical Sciences and Engineering DiVision, Argonne
National Laboratory, Argonne, Illinois 60439, and Department of Chemistry, Northwestern UniVersity,
EVanston, Illinois 60208
mandal@iit.edu; lchen@anl.goV
ReceiVed June 16, 2008
While preparing the first structurally rigid zinc phthalocyanine-benzoquinone (ZnPc-BQ) dyad as a model
for photoinduced charge separation mimicking natural photosynthesis, a convenient method is developed
for in situ generation of a benzoquinone chromophore in the dyad using an iso-butyryl mask. The dyad
has no rotamers and possesses a fixed distance between ZnPc and BQ moieties (center-to-center and
edge-to-edge distances are 9.40 and 2.14 Å, respectively). The dyad displays unusual electronic perturbation
in the ground state, resulting from the interactions between Pc and BQ, and exhibits photoinduced electron
transfer with a lifetime of 40 ps of the charged separated states. The steady-state fluorescence and
electrochemical behavior of the dyad are evaluated. This study opens a route to subsequent dyads, triads,
and complex architectures of electron donor-acceptor arrays with rigid structures and long charge
separation states.
Introduction
QA and QB.3 These chromophores are not covalently linked but
are “vitrified” in suitably close proximity by protein scaffolds.
A key strategy for mimicking natural photosynthesis or the
construction of synthetic solar energy conversion systems is by
In natural photosynthesis, the primary energy conversion
reactions involve efficient sequential photoinduced electron
transfer (PET) steps that result in charge separation across a
biological membrane. Thus, light is converted into an electro-
chemical potential that provides ammunition for the biosynthesis
of high-energy biological fuels, such as adenosine triphosphate
(ATP).1,2 In natural bacterial photosynthetic systems, the initial
PET occurs from a bacterial chlorophyll (BChl) dimer to a
bacterial pheophytin (Bph) and then to two quinone derivatives,
(1) (a) Photosynthetic Reaction Centers; Deisenhofer, J., Norris, J. R., Eds.;
Academic Press: New York, 1993; Vols. I, II. (b) Molecular Mechanisms of
Photosynthesis; Blakenship, R. E.; Blackwell Science: Malden, MA, 2002.
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P. D.; Zhang, Y.; Morris, A. L.; Snyder, S. W.; Ainsworth, C.; Greenfield, S. R.;
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Thurnauer, M. C. Photosynthesis Res. 1997, 52, 93–103. (c) O’Malley, P. J. J.
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† Illinois Institute of Technology.
‡ Argonne National Laboratory.
§ Northwestern University.
10.1021/jo801293s CCC: $40.75
Published on Web 10/10/2008
2008 American Chemical Society
J. Org. Chem. 2008, 73, 8219–8227 8219

Lee et al.
employing multistep PET among suitable chromophores with
optimal redox potentials, optimized electron donor (D) and
acceptor (A) orientation, distance, and environment. The most
attractive laboratory approach in synthesizing artificial photo-
synthetic systems has been by linking appropriate D and A
moieties with covalent bonds, instead of using proteins.
Phthalocyanines (Pc) and porphyrins (Por) have been used
as electron donor building blocks in artificial photosynthetic
systems due to their strong absorption in the solar spectrum for
light harvesting, their redox potentials enabling PET, and their
structural tunability by chemical synthesis. Also, benzoquinone
(BQ), perylenediimide (PDI), and C60 are a few of the most
commonly used electron acceptors. While a variety of electron
D-A dyads (e.g., Por-BQ,4-7 Pc-BQ,8 Por-C60,9 Pc-C60,10-13
Por-PDI,14 Pc-PDI15) and a few triads11a,16 (such as ꢀ-caro-
tenoid-Por-C60 and C60-Pc-C60) have been synthesized and
studied for generating and sustaining long-lived charge-separated
states, the correlation between the PET efficiencies and structural
factors may not be clearly established as a result of the
coexistence of conformers as a result of structural flexibility in
these synthetic systems. Most dyads and triads prepared
involving Pc, Por, and Chl (chlorophylls) blocks thus far lack
molecular structural rigidity (i.e., variation in center-to-center
distance (rDA) or the relative orientation between D and A).
Hence, dynamic structural factors need to be considered in order
to accurately establish the structural factor dependency of PET,
which often is not straightforward. Therefore, it is necessary to
construct structurally rigid D–A systems (only one conformer),
which will offer the opportunity to deconvolute the multiple
structural influence in PET and allows optimization of intended
structural variables for PET processes. In light of this awareness,
we initiated a research program in developing rigid metalloph-
thalocyanine-benzoquinone (MPc-BQ)-based dyads with varied
D–A distances and orientations. The goal of this research is to
obtain a reaction coordinate where these chromophores provide
the highest PET efficiency.
We have chosen ZnPc as an effective donor owing to its
optical absorption characteristics that are very similar to those
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8220 J. Org. Chem. Vol. 73, No. 21, 2008

NoVel Zinc Phthalocyanine-Benzoquinone Rigid Dyad
conducting a series of approaches (Schemes 1-4). An ideal
strategy to synthesize 1 would be by direct cyclotetramerization
of 3 with 5 (an oxidized form of 4a) in the presence of 1,8-
diazabicyclo[5.4.0]undec-7ene (DBU) and zinc acetate in 1-pen-
tanol. Unfortunately, our initial attempts to obtain 5 by one-pot
demethylation and oxidation of 4a with ceric ammonium nitrate
(CAN) were unsuccessful (vide infra). Attempts to demethylate
4a with BBr3 to form 6 were also fruitless, which derailed our
plan for subsequent oxidation with dichlorodicyanoquinone
(DDQ) to obtain 5. It appears that the nitrile group is very
sensitive toward these reagents. We then devised an alternate
strategy involving the preparation of a p-dimethoxybenzene-
fused phthalocyanine precursor (2a), a masked quinone of 1.
As depicted in Scheme 1, cyclotetramerization of 3 with a
p-dimethoxybenzene-fused triptycene derivative (4a) provided
the desired low-symmetric phthalocyanine, 2a, which was easily
separated from other undesired statistical analogs using a silica
gel column with 2:1 hexane-ethyl acetate as the starting eluent,
with gradual increase in ethyl acetate proportion. In order to
increase the yield of 2a, an excess molar ratio of 3 was essential,
which also produced octa-substituted alkoxy phthalocyanine (7)
as the major product but was easily separable from 2a by column
chromatography. Although CAN in aqueous acetonitrile has
been widely used as a reagent for converting the p-dimethoxy-
benzene moiety to p-benzoquinone,20 this method was ineffec-
tive for this phthalocyanine system. Treatment of 2a with CAN
led to an ill-defined mixture of products with degradation of
the phthalocyanine ring, as revealed by the loss of the Q-band
in UV-vis spectrometry. Treatment of 2a with BBr3 also led
to a mixture of uncharacterizable products due to cleavage of
the sec-butyloxy groups. Consequently, another quinone-masked
phthalonitrile derivative, 4b, was prepared to address the issue
of deprotection and oxidation.
FIGURE 1. Structure of 1 (below is the space-filled model).
of chlorophylls and outstanding thermal and chemical stability,
including much simpler synthetic protocols compared with
chlorophyll. Similar to the natural systems, BQ remained our
choice as the preferred acceptor. It is important to note that
although a few rigid dyads18 (some of them synthesized for
different studies) have been described, the preparation of MPc-
BQ-based “rigid dyads” has not yet been reported.
The synthesis of quinone-masked phthalonitrile analogs 4a
and 4b was accomplished by starting with previously reported
compounds 1,4-dimethoxyanthracene (8)21 and 1,4-dibenzy-
loxyanthracene (9),21b respectively (Scheme 2). Diels-Alder
reaction of these compounds with 1,2,4,5-tetrabromobenzene
(via in situ benzyne formation) afforded the corresponding
dibromotriptycenes (10 and 11), which were conveniently
cyanated via the Rosenmund-von Braun reaction to give the
phthalonitrile analogs (4a and 4b) in good yields. As mentioned
earlier, we have not yet been successful in preparing the desired
quinone (5), which could be used to synthesize 1 by direct
cyclotetramerization with 3. Moreover, it should be noted that
there is no literature precedence pertaining to the cyclotetramer-
ization of phthalonitriles in the presence of a quinone moiety,
and we are uncertain whether 1 can be prepared by reaction of
3 with 5, since there is concern about possible side reactions of
quinone under cyclotetramerization conditions. To address this
issue, alternative deprotection strategies using pyridinum hy-
drochloride for 4a and benzyl deprotection by hydrogenolysis
In this paper, we elucidate the synthesis and photophysical
properties of the first member of a new class of a highly rigid
D-A dyad, 1, by annulating ZnPc and BQ into an “iptycene”
scaffold (Figure 1). This system 1 consists of multiple rigid
covalent bonds to “lock” the distance and orientation of
benzoquinone relative to the metal center of the phthalocyanine.
The center-to-center and edge-to-edge distances between ZnPc
and BQ have been determined by an energy minimized structure
(calculated by Hyperchem7.0 from Hypercube) at 9.40 and 2.14
Å, respectively. The angle between the planes of ZnPc and BQ
is estimated near 120°.
Results and Discussion
Dyad Synthesis. The preparation of triptycene-fused phtha-
locyanines by Luk′yanets et al.19 dates back to 1972. However,
the construction of rigid artificial photosynthetic systems by
forging phthalocyanine and benzoquinone around a triptycene
framework has, until now, not been explored. The synthesis of
the substituted ZnPc-BQ dyad (1) was accomplished after
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Antolovich, M.; Keyte, P. J.; Oliver, A. M.; Paddon-Row, M. N.; Kroon, J.;
Verhoeven, J. W.; Jonker, S. A.; Warman, J. M. J. Phys. Chem. 1991, 95 (5),
1933–1941.
J. Org. Chem. Vol. 73, No. 21, 2008 8221

Lee et al.
SCHEME 1. Synthesis of PcZn-BQ Dyad Precursors
SCHEME 2. Synthesis of Quinone-Masked Phthalonitrile
Analogs
SCHEME 4. Synthesis of ZnPc-BQ Dyad 1
SCHEME 3. Synthesis of Phthalonitrile Derivative 3
property of phthalocyanines bearing linear alkyl chains.22 An
aggregation-free phthalocyanine system is desirable to obtain
accurate photophysical properties of the dyad. Our studies
concluded that the sec-butyloxy group provides a higher yield
(45%) compared to yields using longer branched or bulky
alkanes (e.g., 10% for the iso-pentyloxy group with monosub-
stitution as the major product, caused by more steric crowding).
While searching for a suitable masking system, we discovered
that the iso-butyryl group provides a solution to prepare the
coveted rigid dyad 1, without the need for deprotection or an
oxidation step. The iso-butyryl masked dinitrile compound 4d
was prepared according to the protocol outlined in Scheme 4.
The iso-butyryl group was found very resistive to the cyanation
reaction conditions as we obtained 4d in 82% yield. However,
deprotection occurs very slowly via trans-esterification under
of 4b, including a follow-up DDQ oxidation step, are in
progress. While there is uncertainty about cyclotetramerization
of 5 with 3, we have successfully prepared the benzyl-masked
dyad precursor, 2b. Benzyl masking, which involves very mild
deprotection conditions (palladium-catalyzed hydrogenolysis),
was chosen to preserve the alkoxyl groups on the peripheral
sites of the phthalocyanine ring. However, poor solubility of
2b in ethanol (common solvent for catalytic hydrogenation)
deprived us of complete removal of benzyl groups from 2b.
The use of other solvent systems, which dissolve 2b, such as
THF and dioxane, also did not provide completely deprotected
hydroquinone product.
(22) (a) Piechochi, C.; Simon, J.; Skoulios, A.; Guillon, D.; Weber, P. J. Am.
Chem. Soc. 1982, 104 (19), 5245. (b) Snow, A. W.; Barger, W. R. Phthalocya-
nines Properties and Applications; Leznoff, C. C., Lever, A. B. P., Eds.; VCH:
New York, 1989; Vol. 1, p 343. (c) van Nosteum, C. F.; Bosman, A. W.; Gelinck,
G. H.; Schouten, P. G.; Warman, J. M.; Kentgens, A. P. M.; Devillers, M. A. C.;
Meijerink, A.; Picken, S. J.; Sohling, U.; Schouten, A.-J.; Nolte, R. J. M. Chem.
Eur. J. 1995, 1, 171. (d) McKeown, N. B.; Helliwell, M.; Hassan, B. M.;
Hayhurst, D.; Li, H; Thompson, N.; Teat, S. J. Chem. Eur. J. 2007, 13 (1),
228–234. (e) de la Escosura, A.; Martinez-Diaz, M. V.; Thordarson, P.; Rowan,
A. E.; Nolte, R. J. M.; Torres, T. J. Am. Chem. Soc. 2003, 125 (40), 12300–
12308.
The phthalonitrile derivative, 3, a new compound, was
prepared according to the strategy outlined in Scheme 3. There
are several reasons for the selection of the sec-butyloxy group.
In addition to improved solubility of the resulting phthalocya-
nine, sec-butyloxy groups prevent aggregation, a common
8222 J. Org. Chem. Vol. 73, No. 21, 2008

NoVel Zinc Phthalocyanine-Benzoquinone Rigid Dyad
FIGURE 2. UV-vis spectra of 1, 2a, 2c, and 7 in toluene (left, overall; right, focus on the Q-bands).
the conditions of cyclotetramerization (DBU in refluxing
1-pentanol) but does not interfere with the mechanism of the
formation of phthalocyanine. The presence of excess 1-pentanol
shifts the equilibrium toward the formation of n-pentyl iso-
butyrate and unmasked hydroquinone intermediate,23 which we
believe slowly undergoes air oxidation to 1 over a period of
time. Thus, this one-pot reaction involving cyclotetramerization
of dinitrile derivatives, cleavage of iso-butyryl groups, and self-
oxidation of the hydroquinone moiety to quinone is the highlight
of the present work, which provides easy access to a new class of
D-A molecules. The structure of 1 was confirmed by FTIR
Aggregation Properties. Most Pc derivatives have strong
tendencies to form aggregates via π-π stacking, forming
H-aggregate-like assemblies.22 Hence, the spectra in the Q-band
region will have blue shifts and an overall broadening of the
absorption peak. We have confirmed that 1 does not aggregate
since a plot of the Q-band intensity against the sample
concentration at selected absorption wavelengths displays linear
correlation between the two, following Beer-Lambert’s Law.29
Steady-State Fluorescence Properties. Comparison of the
steady-state fluorescence spectra of 1 with the reference
compound 2c indicates significant fluorescence quenching due
to the presence of the BQ moiety that could prompt the PET
process. As seen in Figure 3, the fluorescence of ZnPc in 2c
has been reduced by a factor of 8.7 in THF and of 5.8 in toluene,
respectively, due to the presence of the acceptor BQ, corre-
sponding to 88% and 82% quenching of the fluorescence. Hence,
only 12% and 18% excited-state population decays through
channels other than PET, such as internal conversion to the
ground state and the intersystem crossing to the triplet state
whose lower energy compared to that of the singlet excited state
may not provide sufficient driving force for the PET reaction.
In addition, the fluorescence quenching ratio of the D–A differs
in THF and toluene, with the latter showing less quenching as
expected for the PET reaction being promoted by the polar
1
(sharp quinone carbonyl peak at 1655 cm-1), H NMR, 13C
NMR (carbonyl carbon at 183.7 ppm), and mass spectrometry
(M+ ) 1216.7).
Ground-State Absorption Properties. Figure 2 shows the
UV-vis absorption spectra of 1 as well as three relevant
reference compounds, 2a, 2c (low symmetric triptycenophtha-
locyanine), and 7 (symmetric Pc generated from 3). Interestingly,
1 showed splitting of the Q-band into a doublet (peaks at 675
and 688 nm) compared to the singlet for 2a (682 nm), 2c (682
nm), and 7 (675 nm). Such a phenomenon has been observed
previously in other asymmetric substituted Pc derivatives24 and
has been attributed to the perturbation from the substituted group
(i.e., the linked benzoquinone)25 or simply the change in the
Pc symmetry from D4h (7) or C2V (2c) to Cs (2a, 1), breaking
the molecular orbital degeneracy with respect to x and y axes
that aligned with two orthogonal N-Zn-N directions in the Pc
plane. When we compare the spectra of 2a, 2c with 1, it is clear
that the symmetry change alone is insufficient to cause the
Q-band splitting.10g,26 Although all compounds are asymmetric,
the splitting of the Q-band only occurs in the latter when the
BQ moiety is present. Consequently, the doublet in 1 is mostly
likely due to the perturbation of the BQ to the electronic
structure of the ground-state Pc core. Such interference is
common in the triptycene system with aromatic substituents
involving π-conjugated systems with double/triplet bond link-
ages27 or NO2 groups.28 This perturbation also causes progres-
sive red shifts of both Soret and Q-bands from 7 to 2c and then
to 1.
(26) (a) Reddy, P. Y.; Giribabu, L.; Lyness, C.; Snaith, H. J.; Vijaykumar,
C.; Chandrasekharam, M.; Lakshmikantam, M.; Yum, J.-H.; Kalyanasundaram,
K.; Gra¨tzel, M.; Nazeeruddin, M. K. Angew. Chem., Int. Ed. 2007, 46, 373–
376. (b) Mathews, S. J.; Kumar, S. C.; Giribabu, L.; Rao, S. V. Opt. Commun.
2007, 280, 206–212. (c) Chen, W.; Duan, W.-B.; He, C.-Y.; Zuo, X.; Wu, Y.-
Q. Spectrosc. Spectral Anal. (Guangpuxue Yu Guangpu Fenxi) 2007, 27 (3),
543–546. (d) Berera, R.; Herrero, C.; van Stokkum, I. H. M.; Vengris, M.; Kodis,
G.; Palacios, R. E.; van Amerongen, H.; van Grondelle, R.; Gust, D.; Moore,
T. A.; Moore, A. L. Proc. Natl. Acad. Sci. U.S.A. 2006, 103 (14), 5343–5348.
(e) Kalkan, A.; Koca, A.; Bayir, Z. A. Polyhedron 2004, 23, 3155–3162. (f)
Gonza´lez-Cabello, A.; Va´zquez, P.; Torres, T.; Guldi, D. M. J. Org. Chem. 2003,
68 (22), 8635–8642. (g) Tian, M.; Wada, T.; Sasabe, H. Dyes Pigments 2002,
52, 1–8. (h) Maya, E. M.; Garcia, C.; Garcia-Frutos, E. M.; Va´zquez, P.; Torres,
T. J. Org. Chem. 2000, 65 (9), 2733–2739. (i) Muto, T.; Kimura, M.; Hanabusa,
K.; Shirai, H. Tetrahedron Lett. 1999, 40 (16), 3199–3202. (j) Gonza´lez, A.;
Va´zquez, P.; Torres, T. Tetrahedron Lett. 1999, 40 (16), 3263–3266. (k) Rojo,
G.; de la Torre, G.; Graca´-Ruiz, J.; Ledous, I.; Torres, T.; Zyss, J.; Agullo´-
Lo´pez, F. Chem. Phys. 1999, 245, 27–34. (l) Maya, E. M.; Va´zquez, P.; Torres,
T. Chem. Eur. J. 1999, 5 (7), 2004–2013. (m) Ali, H.; Sim, S. K.; van Lier,
J. E. J. Chem. Res. 1999, 8, 496–497. (n) Polley, R.; Line´n, T. G.; Stihler, P.;
Hanack, M. J. Porphyrins Phthalocyanines 1997, 1 (2), 169–179.
(23) (a) Vasquez-Martinez, Y.; V. Ohri, R.; Kenyon, V.; Holman, T. R.;
Sepu´lveda-Boza, S. Bioorg. Med. Chem. 2007, 15, 7408–7425. (b) Ng, A. C. H.;
Li, X-Y.; Ng, D. K. P. Marcromolecules 1999, 32, 5292–5289. (c) Drechsler,
U.; Pfaff, M.; Hanack, M. Eur. J. Org. Chem. 1999, 3441–3453.
(27) (a) de la Escosura, A.; Claessens, C. G.; Ledoux-Rak, I.; Zyss, J.;
Mart´ınez-D´ıaz, M. V.; Torres, T. J. Porphyrins Phthalocyanines 2005, 9, 788–
793. (b) Maya, E. M.; Garcia-Frutos, E. M.; Va´zquez, P.; Torres, T.; Mart´ın,
G.; Rojo, G.; Agullo´-Lo´pez, F.; Gonzalez-Jonte, R. H.; Ferro, V. R.; de la Vega,
J. M. G.; Ledoux, I.; Zyss, J. J. Phys. Chem. A. 2003, 107 (12), 2110–2117. (c)
Gonza´lez-Cabello, A.; Va´zquez, P.; Torres, T. J. Organomet. Chem. 2001, 637-
639, 751–756. (d) Torres, T.; de la Torre, G.; Grac´ıa-Ruiz, J. Eur. J. Org. Chem.
1999, 2323–2326. (e) Lenzoff, C. C.; McArthur, C. R.; Qin, Y. Can. J. Chem.
1993, 71 (9), 1319–1326.
(24) (a) Chen, B.; Wang, M.; Wu, Y.; Tian, H. Chem. Commun. 2002, 1060–
1061. (b) Kobayashi, N.; Togashi, M.; Osa, T.; Ishii, K.; Yamauchi, S.; Hino,
H. J. Am. Chem. Soc. 1996, 118 (5), 1073–1085. (c) Baumann, T. F.; Nasir,
M. S.; Sibert, J. W.; White, A. J. P.; Olmstead, M. M.; Williams, D. J.; Barrett,
A. G. M.; Hoffman, B. M. J. Am. Chem. Soc. 1996, 118 (43), 10479–10486. (d)
Odobel, F.; Zabri, H. Inorg. Chem. 2005, 44 (16), 5600–5611.
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(28) Arslanolu, Y.; Koca, A.; Hamuryudan, E. Polyhedron 2007, 26891, 896.
(25) Kitaguchi, N. Bull. Chem. Soc. Jpn. 1989, 62 (3), 800–807.
(29) See Supporting Information for additional data.
J. Org. Chem. Vol. 73, No. 21, 2008 8223

Lee et al.
FIGURE 4. Cyclic voltammogram of 1.
FIGURE 3. Steady-state fluorescence spectra of 1 and 2c (normalized
with the same optical density at the excitation wavelength 365 nm). In
order to have the same (0, 0) band intensity, the fluorescence of 1 must
be multiplied by a factor of 8.7 in THF and 8.2 in toluene, corresponding
to the fluorescence quenching in the two solvents as 88% and 82%,
respectively.
this observation also supports the long-range electronic interac-
tions between the Pc macrocycle and BQ as inferred from
UV-vis spectrometry.
The redox potentials, in particular the 0-0 transition energy
for the Pc donor, and the oxidation and reduction potentials of
the ground-state donor and acceptor, respectively, will allow
us to estimate the driving force for the PET reaction. For the
TABLE 1. Comparison of Electrochemical Properties of 1 with
Reference Compounds
reduction
oxidation
charge separation (CS) process, ∆GCS ) Eox - Ered - E0-0
+
second
first
first
second
∆Gd and the charge recombination process, ∆GCR ) -Eox
+
Zn(obxPc)
7
2c
1
ferrocene
quinone
-1.47
-1.43
-1.49
-1.86
-1.05
-1.08
-1.16
(-0.49)
0.54
0.43
0.41
0.46
0.45
Ered - ∆Gd where the Eox, Ered, and E0-0 are potentials for the
oxidation potential of the donor, the reduction potential of the
acceptor, and the energy of the lowest excited state from which
the PET takes place. ∆Gd is the free energy by which the ion
pairs are destabilized. Ignoring the Coulombic interactions, the
CS state energy of the dyad can be determined from the
difference between potentials (Table 1), and the energy differ-
1.09
1.07
1.05
-1.36
-1.08
-0.33
solvent to gain the driving force from reorganization energy of
the solvent molecules.
1
ence between the reactant ZnPc*-Q and the product ZnPc+-
Electrochemical Properties. The electrochemical properties
of 1, 2c, and 7 were examined, and the results are summarized
in Table 1. The cyclic voltammogram (CV) of 7 shows two
irreversible one-electron oxidations (0.43 and 1.09 V) and two
quasi-reversible reductions (-1.08 and -1.43 V). These values
match those of the reported isomeric compound, 2,3,9,10,16,17,
23,24-octa(n-butyloxy)phthalocyaninato zinc(II)[Zn(obxPc)],30
which have all n-butyloxy substituents.
The redox potential of 2c is also in the same range as for 7.
The first ring oxidation is separated from the first ring reduction
by ∼1.5 V, suggesting that the energy difference between the
HOMO and LUMO of the macrocyclic ring is not affected by
the triptyceno linkage.31In other words, the interaction between
the iptyceno phenyl ring and the phthalocyanine macrocycle is
insignificant.
In general, Pc derivatives show two irreversible one-electron
oxidations and up to four quasi-reversible reductions and do
not have redox peaks in the 0 to -0.5 V range. Comparing
CVs of 7 and 2c with that of 1 shows similarities in the oxidation
reactions with two irreversible oxidation potentials (at 0.46 and
1.05 V) for the latter. However, the reduction potentials are
shifted toward more negative values, from -1.1 to -1.4 V for
the first reduction and from -1.5 to -1.9 V for the second
reduction. A closer look at the CV curve of 1 revealed a redox
couple near 0.49 V (Figure 4). This is attributed to the presence
of BQ (with its first reduction ∼0.34 V) and its influence on
the redox potential of Pc through the iptyceno phenyl ring. Thus,
Q- is ∼0.8 eV, which warrants a sufficient driving force ∆GCS
for the PET to take place.
Kinetics of Photoinduced Electron Transfer Processes.32 As
mentioned above, the 0.8 eV energy difference between the
1
reactant ZnPc*-BQ and the product ZnPc+-BQ-, as well as
the solvent polarity dependence of the fluorescence quenching,
suggest that the PET process takes place in 1. This is further
confirmed by the absorption of ZnPc+ identified as featured
absorption in the 520-550 nm region.33 The absorption feature
appears in the transient absorption (TA) spectra of 1 but not in
2c (Figure 5a and b).
The ground-state bleaching and recovery kinetics of 1 in THF
and toluene differ significantly from those of 2c (Figure 5c),
distinguished by a drastic change in the rates for the rise and
recovery of the ground-state bleaching signal. When the acceptor
BQ is absent, hence the PET, the rise of the ground-state
bleaching of 2c in toluene can be described by a biexponential
function with time constants of 0.3 ps (88%) and 19 ps (12%),
while the recovery of the ground-state bleaching signal can be
described by another biexponential function with time constants
of >6 ns (82%) and 117 ps (18%).
When the acceptor BQ is present in 1, the ground-state
recovery in toluene is much faster than in 2c and can be
described by a biexponential function with time constants of
40 ps (75%) and more than several nanoseconds (25%), which
is beyond the time delay limit of the experimental setup. In
THF, the biexponential ground-state recovery kinetics has time
(30) Takahashi, K.; Kawashima, M.; Tomita, Y.; Itoh, M. Inorg. Chim. Acta
1995, 232, 69–73.
(32) Chen, L. X.; Xiao, S.; Yu, L. J. Phys. Chem. B 2006, 110, 11730–
11738.
(33) Kahnt, A.; Guldi, D. M.; de la Escosura, A.; Mart´ınez-D´ıaz, M. V.;
Torres, T. J. Mater. Chem. 2008, 18, 77–82.
(31) Phthalocyanines-Properties and Applications; Leznoff, C. C.; Lever,
A. B. P., Eds.; VCH: New York, 1993; Vol. 3, Chapter 1.
8224 J. Org. Chem. Vol. 73, No. 21, 2008

NoVel Zinc Phthalocyanine-Benzoquinone Rigid Dyad
FIGURE 5. Transient absorption spectra of 1 and 2c in (a) THF and (b) toluene at 1 ps delay, showing the differences in absorption features in
the 500-600 nm region; (c) kinetics curves of 1 and 2c monitored by the ground-state bleaching signal in toluene and THF; (d) kinetics of ZnPc+
in 1 monitored at 550 in THF. All measurements were made at room temperature.
constants of 3.5 ps (80%) and more than several nanoseconds
(20%), which is also beyond the time delay range of the
experiment. The ground-state recovery time for 1 gives an upper
limit of the D+-A- lifetime, which is as short as 2-3 ps in
THF (Figure 5d) and 40 ps in toluene. The long time constant
for the remaining 20-25% of the ground-state recovery signals
reflects that in 2c when the PET is absent. This result combined
with the steady fluorescence quenching where there is still
15-20% unquenched fluorescence in 1, suggests that the energy
level of the triplet state (3ZnPc*) is nearly equal to or slightly
lower than that of the charge separation species, ZnPc+-BQ-.
Hence, the intersystem crossing competes with the PET process,
which survives the 20-25% excited-state population to path-
ways other than PET.
spatial distance between the D and A species has any effect on
efficiency (e.g., charge transfer state lifetimes) of this class of
molecules.
Experimental Section
General Synthesis of Phthalocyanine (1, 2a-c, 7). To a stirred
solution of 3 and 4a-d in a stoichiometric ratio of about 2:3 were
added zinc acetate and 1-pentanol. The solution was refluxed for
24-48 h. The product was column chromatographed with a gradient
of hexane/EA from 2:1 to 1:3 and yielded different portions.
1
Data for 1: H NMR (CDCl3 δ ) 7.26) 8.5-9.0 (br, 8H), 7.9
(br, 2H), 7.4 (br, 2H), 6.6 (br, 2H), 6.2 (br, 2H), 5.0 (br, 6H),
1.9-2.2 (br, 12H), 1.6-1.8 (m, 18H), 1.2-1.3(m, 18H); 13C NMR
(CDCl3 δ ) 77.0) 183.7, 154.6, 154.3, 152.8, 152.0, 151.9, 151.5,
151.4, 151.2, 143.7, 143.5, 135.9, 135.7, 135.5, 132.7, 132.1, 128.2,
126.0, 125.5, 125.2, 118.1, 110.1, 109.9, 108.7, 65.8, 48.1, 34.2,
30.3, 29.6, 29.4, 23.8, 21.2, 19.8, 19.7, 19.6, 19.4, 10.1, 10.0; IR
(cm-1) ν ) 2967, 2933, 2877, 1655, 1606, 1488, 1459, 1401, 1381,
1346, 1275, 1217, 1188, 1091, 1040, 990, 923, 747, 730, 568, 511;
[M+] ) 1216.7; UV-vis (toluene) [λmax nm (log ε)] 291 (4.71),
356 (4.87), 612 (4.51), 675 (5.20), 688 (5.20). Anal. Calcd for
C70H70N8O8Zn: C (69.10) H (5.80) N (9.21). Found: C (69.05) H
(5.83) N (9.27).
Conclusion
In conclusion, we have discovered a novel method for in situ
generation of the quinone moiety by using a iso-butyryl mask.
This methodology provides access to a new generation of
phthalocyanine-benzoquinone dyads. Most importantly, 1 rep-
resents one of the very few artificial photosynthetic systems,
first with the Pc-BQ family, which have no rotamers and a fixed
distance between D and A moieties. The preparation of a second
member of this family (one more annulated benzene ring
between Pc and BQ, which are separated by 11.5 Å) is in
progress and is expected to provide an answer to whether the
Data for 2a: 1H NMR (CDCl3 δ ) 7.26) 8.3-9.2 (br, 8H), 7.9
(br, 2H), 7.4 (br, 2H), 6.6 (br, 2H), 6.4 (br, 2H), 4.8 (br, 6H), 3.9
(br, 6H), 1.9-2.2 (br, 12H), 1.6-1.8 (m, 18H), 1.2-1.3(m, 18H);
13C NMR (CDCl3 δ ) 77.0) 153.5, 152.9, 152.5, 151.7, 151.5,
151.4, 149.1, 146.8, 145.7, 135.8, 135.2, 132.5, 132.2, 131.9, 125.4,
124.5, 117.6, 109.8, 109.6, 108.9, 65.5, 56.4, 48.9, 48.2, 29.6, 19.6,
J. Org. Chem. Vol. 73, No. 21, 2008 8225

Lee et al.
10.0, 9.9; IR (cm-1) ν ) 3070, 2968, 2934, 2877, 2833, 1606, 1492,
{5,10-[1,2]Benzeno}-7,8-dicyano-5,10-dihydro-1,4-dimethoxy-
anthracene (4a). To a stirred solution of 2,5-dimethoxy-8,9-
dibromotriptycene (2.6 g, 5.4 mmol) in DMF (25 mL) was added
CuCN (3.9 g, 43.5 mmol) was added in one portion. The solution
was refluxed, and the reaction was followed by TLC. Then, the
solution was cooled after 6 h when the reaction was done. The
reaction mixture was poured into 300 mL of aqueous ammonia
and stirred overnight with air bubbling into the solution. The
precipitate was filtered and column chromatographed with CHCl3
1459, 1403, 1380, 1346, 1274, 1188, 1092, 1040, 987, 922, 865,
747, 730, 569; [M+] ) 1154.8; UV-vis (toluene) [λ
nm (log
max
ε)] 290 (4.72), 356 (4.86), 613 (4.56), 681 (5.32). Anal. Calcd for
C72H76N8O8Zn: C (69.36) H (6.14) N (8.99). Found: C (69.48) H
(6.27) N (8.79).
1
Data for 2b: H NMR (CDCl3 δ ) 7.26) 9.4 (br, 2H), 8.9 (br,
4H), 8.7 (br, 2H), 7.7-8.1 (t, 8H), 7.39-7.61 (dt, 10H), 5.5-5.8
(br, 4H), 5.0 (br, 6H), 1.9-2.2 (br, 12H), 1.6-1.8 (m, 18H),
1.2-1.3(m, 18H); IR (cm-1) ν ) 2967, 2930, 2874, 1608, 1485,
1459, 1404, 1379, 1334, 1275, 1180, 1104, 1040, 990, 923, 746,
573, 565; [M+] ) 1339.8; UV-vis (toluene) [λmax nm (log ε)] 290
(4.73), 356 (4.90), 613 (4.62), 682 (5.39). Anal. Calcd for
C84H84N8O8Zn: C (72.11) H (6.05) N (8.01). Found: C (72.35) H
(6.34) N (8.17).
1
to yield a pale green solid (1.48 g, 74%). H NMR (CDCl3 δ )
7.26) 7.77 (s, 2 H), 7.43-7.46 (dd, J ) 5.7, 3.4 Hz, 2H), 7.04-7.07
(dd, J) 5.7, 3.4 Hz, 2 H), 6.56 (s, 2H), 5.99 (s, 2H), 3.82 (s, 6H);
13C NMR (CDCl3 δ ) 77.0) 151.9, 149.0, 143.1, 132.5, 128.0,
1360, 124.5, 115.7, 112.7, 109.2, 56.0, 46.9; IR (cm-1) ν ) 3064,
2942, 2836, 2232, 1607, 1497, 1463, 1260, 1237, 1074, 795, 760,
714; [M+] ) 364; UV-vis (CH2Cl2) [λmax nm (log ε)] 217 (4.49),
264 (3.76). Anal. Calcd for C24H16N2O2: C (79.11) H (4.43) N
(7.69). Found: C (79.37) H (4.51) N (7.81). Mp 170-172 °C.
1
Data for 2c: H NMR (CDCl3 δ ) 7.26) 8.74-8.78 (d, 4H),
8.00-8.40 (br, 2H), 7.60-8.00 (br, 4H), 7.20-7.40 (br, 6H),
6.70-6.90 (s, 2H), 4.80-4.90 (s, 4H), 4.30-4.60 (s, 2H), 1.80-2.20
(m, 12H), 1.30-1.80 (m, 18H), 1.10-1.30 (m, 18H); 13C NMR
(CDCl3 δ ) 77.0) 154.0, 153.7, 152.6, 152.0, 151.8, 151.7, 151.4,
146.0, 145.3, 135.4, 132.6, 132.2, 125.5, 124.3, 116.9, 110.2, 109.9,
109.0, 54.8, 29.7, 29.6, 29.4, 19.8, 19.7, 19.3, 15.2, 10.1, 10.0, 9.9;
IR (cm-1) ν ) 2969, 2933, 2877, 1606, 1489, 1459, 1401, 1380,
1347, 1275, 1124, 1188, 1092, 1040, 986, 922, 746, 573, 481; [M+]
) 1186.8; UV-vis (toluene) [λmax nm (log ε)] 291 (4.76), 356
(4.93), 613 (4.64), 682 (5.40). Anal. Calcd for C70H72N8O6Zn: C
(70.84) H (6.12) N (9.44). Found: C (70.92) H (6.17) N (9.49).
{5,10-[1,2]Benzeno}-1,4-dibenzyloxy-7,8-dicyano-5,10-dihy-
droanthracene (4b). To a stirred solution of {5,10-[1,2]benzeno}-
1,4-dibenzyloxy-7,8-dibromo-5,10-dihydroanthracene (1.1 g, 1.8
mmol) in DMF (22 mL) was added CuCN (0.95 g, 10.6 mmol) in
one portion. The solution was refluxed, and the reaction was
followed by TLC. Then, the solution was cooled down after 6 h
when the reaction was done. The reaction mixture was poured into
300 mL of aqueous ammonia and stirred overnight with air bubbling
into the solution. The precipitate was filtered and column chro-
matographed with CHCl3 to yield a pale green solid (0.53 g, 58%).
1H NMR (CDCl3 δ ) 7.26) 7.92-7.94 (m, 4 H), 7.77-7.80 (dd,
J ) 6.2, 3.3 Hz, 2H), 7.63-7.66 (d, 4 H), 7.41-7.55 (m, 8 H),
7.21 (s, 2H), 5.27-5.41 (m, 4H); 13C NMR (CDCl3 δ ) 77.0)
150.1, 138.5, 138.0, 136.0, 131.2, 129.0, 128.1, 128.0, 126.9, 126.5,
124.6, 119.8, 115.7, 113.2, 85.3, 69.3. Anal. Calcd for C36H24N2O2:
C (83.70) H (4.68) N (5.42). Found: C (83.92) H (4.76) N (5.61).
{5,10-[1,2]Benzeno}-7,8-dicyano-5,10-dihydroanthracene (4c).
To a stirred solution of 8,9-dibromotriptycene (1.5 g, 3.6 mmol) in
DMF (30 mL) was added CuCN (1.3 g, 14.6 mmol) in one portion.
The solution was refluxed, and the reaction was followed by TLC.
Then, the solution was cooled after 10 h when the reaction was
done. The reaction mixture was poured into 200 mL of aqueous
ammonia and stirred overnight with air bubbling into the solution.
The precipitate was filtered and column chromatographed with
CHCl3 to yield a pale green solid (0.55 g, 50%). 1H NMR (CDCl3
δ )7.26) 7.76 (s, 2 H), 7.42-7.45 (dd, J ) 5.4, 3.2 Hz, 4H),
7.06-7.09 (dd, J) 5.4, 3.2 Hz, 4 H), 5.55 (s, 2H); 13C NMR (CDCl3
δ ) 77.0) 151.3, 142.6, 128.0, 126.3, 124.3, 115.6, 113.0, 53.6;
IR (cm-1) ν ) 3063, 3022, 2962, 2925, 2854, 2229, 1611, 1597,
1456, 1385, 1190, 1154, 1124, 1018, 970, 896, 801, 754, 628, 571,
513, 479; [M+] ) 304; UV-vis (CH2Cl2) [λmax nm (log ε)] 275
(3.09), 266 (2.82), 232 (4.03). Anal. Calcd for C22H12N2: C (86.82)
H (3.97) N (9.20). Found: C (86.90) H (4.02) N (9.33). Mp
235-238 °C.
1
Data for 7: H NMR (CDCl3 δ ) 7.26) 8.50-8.90 (br, 8H),
4.87-4.88 (br, 8H), 1.90-2.12 (m, 16H), 1.61-1.66 (m, 24H),
1.19-1.25 (m, 24H); 13C NMR (CDCl3 δ) 77.0) 153.0, 151.3,
132.1, 109.5, 77.6, 29.4, 27.9, 19.5, 9.9, 9.5; IR (cm-1) ν ) 3075,
2968, 2934, 2878, 1606, 1485, 1456, 1404, 1379, 1347, 1275, 1191,
1095, 1041, 987, 923, 889, 862, 743; [M+] ) 1154.8; UV-vis
(toluene) [λmax nm (log ε)] 289 (4.81), 249 (4.94), 608 (4.71), 646
(4.67), 675 (5.53). Anal. Calcd for C64H80N8O8Zn: C (66.57) H
(6.98) N (9.70). Found: C (66.41) H (7.02) N (9.81).
1,2-Dibromo-4,5-di-sec-butoxybenzene. To a stirred solution
of 4,5-dibromobenzene-1,2-diol (48.1 g, 180 mmol) in DMSO were
added KOH (94.8 g, 1.44 mol) and 2-bromobutane (93.5 g, 682
mmol). The solution was stirred at 60 °C for 3 days. The mixture
was partitioned between water and CHCl3. The organic layer was
dried under vacuum and column chromatographed with hexane to
yield a colorless solution (56%). 1H NMR (CDCl3 δ ) 7.26)
7.10-7.11 (d, J ) 1.1 Hz, 2H), 4.17-4.23 (m, 2 H), 1.57-1.79
(m, 4 H), 1.25-1.28 (m, 6 H), 0.95-1.00 (m, 6 H); 13C NMR
(CDCl3 δ ) 77.0) 149.2, 121.8, 121.6, 115.2, 115.1, 77.7, 77.6,
29.1, 19.1, 9.7; IR (cm-1) ν ) 2972, 2934, 2878, 1578, 1479, 1378,
1340, 1289, 1252, 1189, 1116, 1028, 987, 916, 880, 653; [M+] )
380 UV-vis (CH2Cl2) [λmax nm (log ε)] 296 (2.93), 237 (3.54).
Anal. Calcd for C14H20Br2O2: C (44.24) H (5.30). Found: C (44.51)
H (5.44).
4,5-Di-sec-butoxyphthalonitrile (3). To a stirred solution of 1,2-
dibromo-4,5-di-sec-butoxybenzene (16.0 g, 42 mmol) in DMF (320
mL) was added CuCN (22.5 g, 252 mmol) in one portion. The
solution was refluxed, and the reaction was followed by TLC until
the end of the reaction. Then, the solution was cooled down after
6 h when the reaction was done. The reaction mixture was poured
into 600 mL of aqueous ammonia and stirred overnight with air
bubbling into the solution. The precipitate was filtered and column
chromatographed with chloroform to yield a pale green solid (1.48
{5,10-[1,2]Benzeno}-7,8-dibromo-5,10-dihydro-1,4-dihydroxy-
anthracene. To a stirred solution of {5,10-[1,2]benzeno}-7,8-
dibromo-5,10-dihydro-1,4-dimethoxyanthracene (1.5 g, 3.2 mmol)
in anhydrous CH2Cl2 (25 mL) at -78 °C was added boron
tribromide (1.8 mL, 1.9 mmol) dropwise. The reaction was warmed
to room temperature and stirred overnight. The reaction mixture
was poured into icy water (200 mL), and ethyl acetate (50 mL)
was added. The creamy yellow conglomerate formed was filtered
and dissolved in an ethyl acetate/brine mixture. The organic layer
was separated, dried, and column chromatographed with ethyl
1
g, 74%). H NMR (CDCl3 δ ) 7.26) 7.12-7.13 (d, J ) 1.1 Hz,
2H), 4.32-4.38 (m, 2 H), 1.66-1.84 (m, 4 H), 1.32-1.36 (m, 6
H), 0.96-1.01 (m, 6 H); 13C NMR (CDCl3 δ ) 77.0) 152.6, 152.5,
118.6, 118.3, 116.0, 108.2, 108.1, 77.8, 77.7, 29.0, 28.9, 19.0, 9.5;
IR (cm-1) ν ) 3119, 3053, 2976, 299, 2882, 2227, 1764, 1585,
1518, 1466, 1402, 1384, 1359, 1290, 1228, 1213, 1125, 1087, 970,
893, 537; [M+] ) 272; UV-vis (CH2Cl2) [λmax nm (log ε)] 285
(4.05), 239 (4.61). Anal. Calcd for C16H20N2O2: C (70.56) H (7.40)
N (10.29). Found: C (70.43) H (7.42) N (10.34). Mp 72-73 °C.
1
acetate to yield a pale brown solid (1.4 g, 100%). H NMR (d-
acetone δ ) 2.05) 7.65 (s, 2 H), 7.42-7.45 (dd, J ) 5.3, 3.2 Hz,
2H), 6.99-7.02 (dd, J) 5.3, 3.2 Hz, 2 H), 6.44 (s, 2H), 5.96 (s,
2H); 13C NMR (d-acetone δ ) 205.1) 147.1, 144.5, 144.2, 130.5,
127.8, 124.4, 123.1, 128.7, 122.7, 45.6; IR (cm-1) ν ) 3218, 1488,
1446, 1195, 992, 917, 884, 800, 744, 727, 643 547; [M+] ) 444.
8226 J. Org. Chem. Vol. 73, No. 21, 2008

NoVel Zinc Phthalocyanine-Benzoquinone Rigid Dyad
Anal. Calcd for C20H12Br2O2: C (54.09) H (2.72). Found: C (54.15)
H (2.91). Mp > 330 °C.
in toluene (545 mL) at 0 °C was added n-butyllithium (1.6 M in
hexane, 27 mL diluted with 200 mL hexane) dropwise. The solution
was warmed to room temperature and stirred overnight. The organic
layer was dried under vacuum and partitioned between CH2Cl2 and
water. The organic layer was washed with brine and then dried
over anhydrous Na2SO4. The resulting solution was dried under
vacuum and column chromatographed with gradient change from
hexane/CH2Cl2 (5:1 to 1:1) to yield a white solid (8.3 g, 41%). 1H
NMR (CDCl3 δ)7.26) 7.64 (s, 2 H), 7.38-7.41 (dd, J ) 5.3, 3.2
Hz, 2H), 6.99-7.02 (dd, J) 5.3, 3.2 Hz, 2 H), 6.53 (s, 2H), 5.81
(s, 2H), 3.81 (s, 6H); 13C NMR (CDCl3 δ)77.0) 148.9, 146.8,
144.6, 134.0, 128.7, 125.4, 124.0, 120.3, 109.0, 56.2, 46.4; IR
(cm-1) ν ) 3069, 2994, 2968, 2939, 2904, 2835, 1606, 1494, 1447,
1362, 1327, 1259, 1073, 796, 787, 767, 734, 711; [M+] ) 472;
UV-vis (CH2Cl2) [λmax nm (log ε)] 206 (4.11), 243 (3.02), 267
(3.50). Anal. Calcd for C22H16Br2O2: C (55.96) H (3.42). Found:
C (56.10) H (3.39). Mp 284-286 °C.
{5,10-[1,2]Benzeno}-1,4-dibenzyloxy-7,8-dibromo-5,10-dihy-
droanthracene (11). To a stirred solution of 1,4-bis-benzyloxy-
anthracene (9.5 g, 24 mmol) and 1,2,4,5-tetrabromobenzene (15 g,
39 mmol) in toluene (760 mL) at 0 °C was added n-butyllithium
(1.6 M in hexane, 27 mL diluted with 100 mL hexane) dropwise.
The solution was warmed to room temperature and stirred overnight.
The organic layer was dried under vacuum and was partitioned
between CH2Cl2 and water. The organic layer was washed with
brine and then dried over anhydrous Na2SO4. The resulting solution
was dried under vacuum and column chromatographed with hexane/
CH2Cl2 with gradient change from 5:1 to 1:1 to yield a white solid.
(6.3 g, 54%). 1H NMR (CDCl3 δ ) 7.26) 7.91 (s, 2 H), 7.83 (s, 2
H), 7.77-7.80 (dd, J ) 6.3, 3.3 Hz, 2H), 7.67-7.69 (m, 4 H),
7.40-7.55 (m, 8 H), 7.17 (s, 2H), 5.28-5.38 (m, 4H); 13C NMR
(CDCl3 δ ) 77.0) 145.1, 140.3, 138.6, 136.3, 131.2, 128.8, 127.9,
127.8, 126.5, 126.3, 125.3, 121.3, 118.8, 85.2, 69.0; IR (cm-1) ν
) 3059, 3033, 2919, 1868, 1607, 1497, 1454,1421, 1386, 1353,
1236, 1193, 1106, 1049, 889, 748, 734, 694, 618, 569, 480. Anal.
Calcd for C34H24Br2O2: C (65.41) H (3.87). Found: C (65.54) H
(3.99).
{5,10-[1,2]Benzeno}-7,8-dibromo-5,10-dihydroanthracene-1,4-
diyl-(2-methylpropanoate). To a stirred solution of {5,10-[1,2]ben-
zeno}-7,8-dibromo-5,10-dihydro-1,4-dihydroxyanthracene (1.4 g,
3.2 mmol) in CH2Cl2 (10 mL) and pyridine (1 mL) was added iso-
butyryl chloride (1.4 mL, 13 mmol) in one portion. The reaction
was stirred overnight. The reaction mixture was concentrated under
vacuum and then poured into water (50 mL) and hexane (50 mL).
The organic layer was separated while the aqueous layer was
extracted with hexane (2 x50 mL). The combined organic layer
was dried and recrystalized in MeOH/CHCl3 to yield a pale orange
1
product (1.3 g, 73%). H NMR (CDCl3 δ ) 7.26) 7.59 (s, 2 H),
7.32-7.35 (dd, J ) 5.3, 3.2 Hz, 2H), 7.02-7.08 (dd, J ) 5.4, 3.2
Hz, 2 H), 6.80 (s, 2H), 5.36 (s, 2H), 2.94-3.04 (m, 2H), 1.41-1.49
(m, 12H); 13C NMR (CDCl3 δ ) 77.0) 183.8, 175.0, 145.2, 143.1,
143.0, 137.6, 128.9, 125.9, 124.2, 121.0, 119.9, 47.7, 34.2, 19.2;
IR (cm-1) ν ) 3054, 2980, 2930, 1756, 1469, 1446, 1421, 1265,
1216, 1179, 1127, 1097, 896, 38, 705. [M+] ) 584. Anal. Calcd
for C28H24Br2O4: C (57.56) H (4.14). Found: C (57.62) H (4.23).
Mp 149-150 °C.
{5,10-[1,2]Benzeno}-7,8-dicyano-5,10-dihydroanthracene-1,4-
diyl-(2-methylpropanoate) (4d). To a stirred solution of {5,10-
[1,2]benzeno}-7,8-dibromo-5,10-dihydroanthracene-1,4-diyl-(2-
methylpropanoate) (1.3 g, 2.3 mmol) in DMF (20 mL) was added
CuCN (0.82 g, 10 mmol) was added in one portion. The solution
was refluxed, and the reaction was followed by TLC. Then, the
solution was cooled down after 6 h when the reaction was done.
The reaction mixture was poured into 200 mL of aqueous ammonia
and stirred overnight with air bubbling into the solution. The
precipitate was filtered and column chromatographed with CHCl3
1
to yield a pale green solid (0.89 g, 82%). H NMR (CDCl3 δ )
7.26) 7.73 (s, 2 H), 7.39-7.41 (dd, J ) 5.4, 3.2 Hz, 2H), 7.09-7.12
(dd, J) 5.4, 3.2 Hz, 2 H), 6.83 (s, 2H), 5.50 (s, 2H), 2.97-3.04
(m, 2H), 1.47-1.51 (m, 12H); 13C NMR (CDCl3 δ ) 77.0) 175.1,
150.2, 143.4, 141.6, 136.4, 126.5, 128.4, 126.5, 124.6, 120.4, 115.5,
113.2, 48.3, 34.1, 19.2, 19.1; IR (cm-1) ν ) 3069, 2977, 2937,
2877, 2234, 1756, 1483, 1467, 1387, 1347, 1322, 1240, 1215, 118,
1123, 1049, 912, 868, 768, 738, 641, 535, 497, 444; [M+] ) 476;
UV-vis (CH2Cl2) [λmax nm (log ε)] 212 (4.52). Anal. Calcd for
C30H24N2O4: C (75.61) H (5.08) N (5.88). Found: C (75.77) H (5.31)
N (5.67). Mp 205-206 °C.
Acknowledgment. This research was supported in part by a
grant from the National Science Foundation (CHE-0203245.)
Supporting Information Available: Complete experimental
details and spectral data of all new compounds. This material
is available free of charge via the Internet at http://pubs.acs.org.
{5,10-[1,2]Benzeno}-7,8-dibromo-5,10-dihydro-1,4-dimethoxy-
anthracene (10). To a stirred solution of 1,4-dimethoxyanthracene
(6.82 g, 29 mmol) and 1,2,4,5-tetrabromobenzene (16.9 g, 43 mmol)
JO801293S
J. Org. Chem. Vol. 73, No. 21, 2008 8227