Azaphenalene phthalocyanines: Phthalocyanine analogues with sixMembered-ring units instead of five-membered-ring units

Article abstract of DOI:10.1002/chem.201000642

Mixed-condensation reaction of 1,8-naphthalenedicarbonitrile and a 4,5-disubstituted phthalonitrile provided a series of phthalocyanine (Pc) analogues with azaphenalene (AP) moieties in place of the isoindole moieties. Monosubstituted species, APPc, and the two structural isomers of disubstituted species, adj-AP₂Pc and oppAP₂Pc, were successfully isolated by gel-permeation chromatography on HPLC apparatus. Their structures were elucidated by ¹H NMR spectroscopy and X-ray crystallographic analysis. Replacement of the isoindole moieties with azaphenalene moieties created six-membered-ring units in the core and caused distortion of the molecular structures. The Q-band absorption shifted to the red upon an increase in the number of azaphenalene units; the shape of the absorption spectra depended on the molecular symmetries. APPc and opp-AP₂Pc showed a large splitting of the Q band, whereas adjAP₂Pc exhibited a single broad Q band. These changes in the absorption spectra, as well as the unique electronic structures, are discussed in detail, based on magnetic circular dichroism spectra, electrochemical measurements, and density functional theory calculations.

Full text of DOI:10.1002/chem.201000642

FULL PAPER
DOI: 10.1002/chem.201000642
Azaphenalene Phthalocyanines: Phthalocyanine Analogues with Six-
Membered-Ring Units Instead of Five-Membered-Ring Units
Soji Shimizu, Hua Zhu, and Nagao Kobayashi*[a]
Abstract: Mixed-condensation reaction
of 1,8-naphthalenedicarbonitrile and a
4,5-disubstituted phthalonitrile provid-
ed a series of phthalocyanine (Pc) ana-
logues with azaphenalene (AP) moiet-
ies in place of the isoindole moieties.
Monosubstituted species, APPc, and
the two structural isomers of disubsti-
tuted species, adj-AP2Pc and opp-
AP2Pc, were successfully isolated by
gel-permeation chromatography on
HPLC apparatus. Their structures were
elucidated by 1H NMR spectroscopy
and X-ray crystallographic analysis.
Replacement of the isoindole moieties
with azaphenalene moieties created
six-membered-ring units in the core
and caused distortion of the molecular
structures. The Q-band absorption
shifted to the red upon an increase in
the number of azaphenalene units; the
shape of the absorption spectra de-
pended on the molecular symmetries.
APPc and opp-AP2Pc showed a large
splitting of the Q band, whereas adj-
AP2Pc exhibited
a single broad Q
band. These changes in the absorption
spectra, as well as the unique electronic
structures, are discussed in detail,
based on magnetic circular dichroism
spectra, electrochemical measurements,
and density functional theory calcula-
tions.
Keywords: aromaticity · azaphena-
lene
· conjugation · phthalocya-
nines · UV/Vis spectroscopy
Introduction
modified species, core-modified analogues, in which one or
two five-membered isoindole rings are replaced with other
aromatic rings, have been rather scarce, except for hemipor-
phyrazine and its derivatives.[2] Comparatively, a variety of
exterior-modified Pc analogues are known, in which the
benzo moieties of the isoindole units are replaced with
other aromatic-ring units, such as naphthalene (naphthalo-
cyanine) and anthracene (anthracocyanine) (Scheme 1).[3]
Phthalocyanines (Pcs) are well-known functional molecules
in view of their unique optical and electrochemical proper-
ties and ability to coordinate a wide range of metal ions.
They are utilized in a variety of research fields, such as
solar-energy conversion, photosensitizers, molecular elec-
tronics, and photoelectronic materials.[1] Their electronic
structure is delineated as an annulenic 18-p-electron, aro-
matic conjugation system comprising four isoindole units
and four bridging nitrogen atoms at meso positions. Due to
the presence of the meso-nitrogen atoms and the exterior
benzo moieties, Pcs generally exhibit intense Q-band ab-
sorption in the visible region.[1a] Modification of their elec-
tronic structure by substitution of the isoindole moieties
with other aromatic units has been actively pursued from
the early stages of phthalocyanine chemistry to tune their
properties to the respective applications.[1b] Among such
Scheme 1. Phthalocyanine (left), naphthalocyanine (middle), and hemi-
porphyrazine (right).
[a] Dr. S. Shimizu, H. Zhu, Prof. Dr. N. Kobayashi
Department of Chemistry, Graduate School of Science
Tohoku University, Sendai, 980-8578 (Japan)
Fax : (+81)227957719
Hemiporphyrazine and its derivatives, first synthesized by
Linstead et al., possess an alternative arrangement of two
isoindole units and two aromatic-ring units, such as benzene,
pyridine, or naphthalene.[4] Their unique coordination prop-
erties have been recently investigated by Ziegler and co-
workers,[5] but in most cases the absorption spectra are more
E-mail: nagaok@mail.tains.tohoku.ac.jp
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201000642.
Chem. Eur. J. 2010, 16, 11151 – 11159
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Scheme 2. Synthesis of azaphenalene phthalocyanines. Conditions: a) Ni
3308C, 15 min. c) Zn(OAc)2, hydroquinone, 2608C, 20 min.
ACHTUGTNRENNUG(OAc)2, hydroquinone, 3008C, 15 min. b) NiAHCUTGNTRNE(NGUN OAc)2, (NH4)2MoO4, quinoline,
ACHTUNGTRENNUNG
similar to those of nonconjugated linear oligo-isoindole spe-
cies than those of Pcs. This indicates that the annulenic 18-
p-electron conjugation system (as seen in Pcs and its deriva-
tives) no longer exists in hemiporphyrazine and its deriva-
tives, mainly due to the predominant local conjugation of
the embedded aromatic ring units. Core modification with-
out any loss of aromaticity and macrocyclic conjugation has
remained a challenge in phthalocyanine chemistry. In 1997,
a novel Pc analogue with an azaphenalene unit in place of
an isoindole unit was synthesized by Kobayashi et al. from a
mixed-condensation reaction of 1,8-naphthalenedicarboni-
trile and 4,5-dibutoxyphthalonitrile, by using a zinc-ion tem-
plate.[6] Based on the absorption spectrum, in which the tail
of the Q band extended over 800 nm, it could be concluded
that the electronic structure of this novel derivative was
more similar to Pc than to hemiporphyrazine and, thus, the
embedded azaphenalene moiety had some contribution to
the Pc-like annulenic conjugation system. However, this
could not be investigated in detail at that time. Moreover, a
general accompanying issue in a mixed-condensation reac-
tion is the simultaneous formation of Pc, and it is difficult to
separate Pc from the target compounds if they possess simi-
lar polarity and molecular sizes. Although the reported aza-
phenalene analogue was thoroughly purified by basic-alumi-
na and gel-permeation (Bio-Beads S-x8, Bio-Rad) chroma-
tography, an intense absorption at 671 nm suggested possible
contamination by Pc and the total exclusion of Pc could not
be proven at that time, as mentioned in the paper. Further-
more, disubstituted species were not obtained in that study
but such species could be formed under suitable reaction
conditions. Recent progress in facilities, especially HPLC
apparatus, motivated us to reinvestigate these series of aza-
phenalene phthalocyanines (APPcs) to elucidate their opti-
cal and electrochemical properties.
phthalocyanine synthesis, especially nickel, copper, and zinc
ions. From these, diamagnetic nickel(II) and zinc(II) ions
were chosen for this study to enable characterization of the
molecular structures by NMR spectroscopic measurements.
To prevent aggregation at the concentrations required for
NMR spectroscopic measurements, phthalonitrile, which has
sterically bulky p-tert-butylphenyloxy substituents at the 4-
and 5-positions,[8] was used for the reaction.
From a mixed-condensation reaction of 1,8-naphthalene-
dicarbonitrile and 4,5-di-tert-butylphenyloxyphthalonitrile in
the presence of hydroquinone and nickel acetate at 3008C
for 15 min, nickel complexes of Pc (1) and mono- (APPc, 2)
and diazaphenalene phthalocyanines (AP2Pc) were obtained
in 9, 26, and 13% yield, respectively (Scheme 2, condi-
AHCTUNGTREGtNNNU ionsa). As depicted in Scheme 2, two structural isomers can
be expected for the disubstituted species AP2Pc. In adj-
AP2Pc (3) two azaphenalene moieties are arranged adja-
cently, whereas opp-AP2Pc (4) has two azaphenalene moiet-
ies arranged at opposite sites. Based on analysis of the
1H NMR and absorption spectra, the obtained AP2Pc spe-
cies was characterized as the adj-isomer 3. The absence of 4
under these solvent-free reaction conditions was mainly due
to preferable formation of a “half-Pc” intermediate,[9] com-
prising two isoindole units and a similar subunit composed
of two azaphenalene units. After several attempts to obtain
4, we found that a condensation reaction in quinoline with
ammonium molybdate as a catalyst provided all four com-
pounds (Scheme 2, conditionsb) in 11, 30, 15, and 1.4%
yield for 1–4, respectively. The complexes were purified by
chromatography on a short alumina column with CHCl3 as
eluent. Fractions containing both Pc and APPc complexes
were further separated by gel-permeation chromatography
performed on HPLC apparatus (GPC–HPLC). During the
purification process we observed decomposition of 4 on a
silica-gel column and slight decomposition on alumina-gel
and gel-permeation (BioBeads S-x1 and S-x8, Bio-Rad) col-
umns. Ultimately, complex 4 was isolated by GPC–HPLC
(JAIGEL-2H, 2.5H, and 3H columns, CHCl3 as eluent) and
subsequent preparative silica-gel TLC. TLC analysis of iso-
lated 4 still showed a very faint brown spot together with 4,
which was presumably due to decomposition of 4 during
TLC development. Purified 4 also decomposed on standing
in solution for a few hours. The instability of 4 can explain
Results and Discussion
Synthesis of azaphenalene phthalocyanines: 1,8-Naphtha-
ACHTUNGTRENNUNGlenedicarbonitrile, a key precursory nitrile for APPc synthe-
sis, was prepared in two steps from acenaphthenequinone in
approximately 60% total yield, by a reported procedure.[7]
In general, transition-metal ions are used as templates for
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Azaphenalene Phthalocyanines
FULL PAPER
the absence of 4 under the solvent-free reaction conditions
(Scheme 2, conditionsa) and the observed low yield in the
presence of solvent (Scheme 2, conditionsb). One plausible
explanation is that 4 was formed in both reactions, but grad-
ually decomposed due to the harsh reaction conditions.
When zinc acetate was used instead of nickel acetate
under solvent-free reaction conditions at the lower reaction
temperature of 2608C (Scheme 2, conditionsc), only Zn–Pc
and Zn–APPc complexes 5 and 6 were obtained, in 6.0 and
1.7% yield, respectively. The low yield of 6 relative to 2 and
the absence of zinc complexes of adj-AP2Pc and opp-AP2Pc
can be explained in terms of the inherent instability of zinc
complexes of Pc analogues relative to nickel–Pc com-
plexes.[1]
which arises from a Pc-like 18-p-electron aromatic conjuga-
tion system. The H NMR spectrum of 6 in [D8]toluene with
1
a drop of [D5]pyridine exhibited three a-benzo proton sig-
nals at d=9.04, 9.01, and 8.67 ppm and the tert-butyl proton
signals were observed at d=1.29, 1.24, and 1.23 ppm (see
the Supporting Information). This pattern of signals is in
agreement with a C2-symmetric molecular structure of 6,
similar to that of 2.
1
The H NMR spectrum of 3 in [D8]toluene exhibited two
signals due to the a protons of the benzo moieties at d=
8.36 and 8.20 ppm and tert-butyl proton signals were ob-
served at d=1.24 and 1.23 ppm (Figure 2). Based on COSY
1
ESI–FT-ICR–MS and H NMR spectroscopy: The high-reso-
lution electrospray ionization Fourier transform ion cyclo-
tron resonance (ESI–FT-ICR) mass spectra of the APPc
species 2–4, and
6 exhibited molecular-ion peaks at
1531.6229 ([M++Na]), 1262.4712 ([M+]), 1262.4712 ([M+]),
and 1514.6269 ([M+]), respectively (see the Experimental
Section for calculated values). The isotopic-distribution pat-
terns of all of these compounds matched well with the theo-
retical patterns (see the Supporting Information). Although
mass spectrometry does not indicate the purity of the
sample, contamination of 4 by Pc or other APPcs can be
ruled out after thorough purification by GPC–HPLC and
preparative TLC.
Figure 2. 1H NMR spectrum of adj-AP2Pc complex 3 in [D8]toluene. *=
solvent peaks.
measurements, signals at d=8.34, 8.01, 7.28, 7.25, and
7.08 ppm were assigned to the protons of the naphthalene
moieties, although one of them was overlapped by a residual
solvent signal (see the Supporting Information). This
1H NMR spectrum clearly reflects the C2-symmetric molecu-
lar structure of adj-AP2Pc, which was further supported by
in-depth analysis on the absorption and magnetic circular di-
chroism (MCD) spectra (see below). Downfield shifts of the
signals from the a protons of the benzo moieties were ob-
served, but the extent of the shifts was modest compared
with the case of 2. This result can be illustrated in terms of a
much-enhanced distortion of the structure of 3, predicted by
theoretical calculations (see below). In contrast to 3, a clear
1H NMR spectrum of 4 has not been obtained, even in
[D8]toluene, probably due to severe aggregation of 4 at the
concentrations used for NMR spectroscopy (see the Sup-
porting Information).
1
The H NMR spectrum of 2 in CDCl3 showed broad and
indistinguishable signals, probably due to aggregation de-
spite the presence of bulky tert-butylphenyloxy substituents.
This aggregation behavior was improved by using
[D8]toluene as a solvent (Figure 1). Based on COSY experi-
Figure 1. 1H NMR spectrum of APPc complex 2 in [D8]toluene. *=sol-
vent peaks.
X-ray crystallographic analysis: Suitable crystals of 6 for
single-crystal X-ray diffraction analysis were obtained by
slow diffusion of methanol into a solution of 6 and pyridine
in dichloromethane. The structure of 6 was unambiguously
elucidated and is shown in Figure 3.[10] Complex 6 adopts an
almost planar conformation with a zinc ion coordinated in a
square-pyramidal fashion by an axial pyridine ligand, one
azaphenalene ring, and three isoindole rings. The azaphena-
lene unit is slightly tilted by 3.38 from the mean plane de-
fined by four metal-coordinating nitrogen atoms (4N mean
plane). The central zinc ion is deviated by 0.33 ꢁ from the
4N mean plane due to the axial coordination (Figure 4). In
the molecular-packing diagram (see Figure S10 in the Sup-
porting Information) it can be seen that two molecules form
a p-stacking arrangement in a head-to-tail manner, with an
ments, all of the signals were assigned (see the Supporting
Information). Three a-benzo proton signals appeared at d=
8.65, 8.58, and 8.30 ppm because of the C2 symmetry of the
complex. The tert-butyl proton signals were observed at d=
1.29 and 1.24 ppm with an integral ratio of 1:2, respectively.
One of the naphthalene proton signals was observed at d=
8.46 ppm as a broad singlet; the other two signals at d=7.31
and 7.12 ppm were overlapped by signals due to the tert-bu-
tylphenyloxy substituents and residual solvent. Signals due
to the a positions of the benzo moieties exhibited significant
downfield shifts relative to 4,5-di-tert-butylphenyloxyphtha-
lonitrile (d=7.82 ppm in CDCl3). These downfield shifts
suggest the presence of a diamagnetic ring-current effect,
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N. Kobayashi et al.
intermolecular separation of approximately 3 ꢁ. No signifi-
ꢀ
cant bond-length alternation is observed for the C N and
ꢀ
C C bonds of the core structure of 6, which is indicative of
the nature of a conjugated molecule and a general feature
of crystal structures of Pc molecules (Table 1).
Optimized structures: Structural optimization, based on
DFT calculations with a B3LYP/6-31G(d) combination of
hybrid functional and basis sets as implemented in the
Gaussian 03 package, was performed on model compounds
of 1–4 to obtain further insight into structural variation
upon the introduction of the azaphenalene moieties
(Figure 5). tert-Butylphenyloxy substituents were replaced
with hydrogen atoms for simplicity in the model compounds.
The free-base forms were also optimized (see the Support-
ing Information). Compared with the planar structure of 1
and the crystal structure of 6, the optimized structures of
the APPcs are severely distorted. The displacement of all of
Figure 3. X-ray crystal structure of 6; top view (top) and side view
(bottom). The thermal ellipsoids are scaled to the 50% probability level.
In the side view, p-tert-butylphenyloxy substituents and hydrogen atoms
are omitted for clarity.
Figure 5. Optimized structures for model compounds of a) 1, b) 2, c) 3,
and d) 4; top view (top) and side view (bottom). Hydrogen atoms are
omitted for clarity.
Figure 4. The deviation of selected atoms (in 0.001 ꢁ) from the 4N mean
plane.
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Azaphenalene Phthalocyanines
FULL PAPER
Table 1. Selected bond lengths and coordination bond lengths [ꢁ] in the crystal structure of 6.
in its crystal structure is ach-
ieved by the longer Zn–N coor-
dination distance of 1.98–2.20 ꢁ
(Table 1). Introduction of more
ꢀ
ꢀ
ꢀ
ꢀ
Zn N(1)
1.984(3)
1.992(3)
1.366(5)
1.319(5)
1.358(5)
1.357(5)
1.364(5)
1.302(5)
1.348(5)
1.314(5)
1.460(5)
Zn N(3)
2.101(3)
2.202(3)
1.388(5)
1.334(5)
1.345(5)
1.313(5)
1.369(5)
1.342(5)
1.378(5)
1.349(5)
1.387(6)
C(7) C(8)
1.467(5)
1.406(6)
1.458(5)
1.478(5)
1.385(6)
1.377(8)
1.383(7)
1.422(7)
1.388(6)
1.434(6)
C(9) C(10)
1.460(6)
1.445(6)
1.373(6)
1.475(6)
1.404(6)
1.369(8)
1.410(6)
1.355(7)
1.388(6)
1.439(6)
ꢀ
ꢀ
ꢀ
ꢀ
Zn N(5)
Zn N(7)
C(10) C(15)
C(15) C(16)
ꢀ
ꢀ
ꢀ
ꢀ
N(1) C(1)
N(1) C(8)
C(17) C(18)
C(18) C(23)
ꢀ
ꢀ
ꢀ
ꢀ
N(2) C(8)
N(3) C(9)
N(4) C(16)
N(5) C(17)
N(6) C(24)
N(7) C(25)
N(8) C(1)
N(2) C(9)
C(23) C(24)
C(25) C(26)
azaphenalene
units
causes
ꢀ
ꢀ
ꢀ
ꢀ
N(3) C(16)
C(26) C(27)
C(26) C(35)
greatly enhanced saddle-like
distortion, as in the case of
AP2Pcs 3 and 4 (Figures 5 and
6), which is also mainly due to
the smaller size of the low-spin
NiII ion compared to the cavity
size of 3 and 4. The degree of
distortion can be clearly esti-
ꢀ
ꢀ
ꢀ
ꢀ
N(4) C(17)
C(27) C(28)
C(28) C(29)
ꢀ
ꢀ
ꢀ
ꢀ
N(5) C(24)
C(29) C(30)
C(30) C(35)
ꢀ
ꢀ
ꢀ
ꢀ
N(6) C(25)
C(30) C(31)
C(31) C(32)
ꢀ
ꢀ
ꢀ
ꢀ
N(7) C(36)
C(32) C(33)
C(33) C(34)
ꢀ
ꢀ
ꢀ
ꢀ
N(8) C(36)
C(34) C(35)
C(34) C(36)
ꢀ
ꢀ
C(1) C(2)
C(2) C(7)
the atoms from the 4N mean plane clearly reveals ruffle-like
distortion for 2 and saddle-like molecular distortion for 3
and 4, as depicted in Figure 6. The three isoindole moieties
mated by the root-mean-square deviation of each atom
from the 4N mean plane (0.51, 1.32, and 1.47 for 2, 3, and 4,
respectively).
Electronic absorption and MCD spectroscopy: The absorp-
tion and MCD spectra of APPc complexes 2–4 and 6 were
measured in CHCl3 and no aggregation behavior was ob-
served at the measurement concentration (see the Support-
ing Information).[12] In the absorption spectra the APPcs ex-
hibit a fairly broad absorption in the Q-band region. Rela-
tive to the Q-band absorption of Ni–Pc complex 1 at
675 nm, the APPc complexes exhibit a significant redshift.
Based on the fact that nonconjugated hemiporphyrazines
show absorption at much shorter wavelengths, it can be con-
cluded that the electronic structures of APPcs are quite sim-
ilar to that of Pc and that a macrocyclic 18-p-electron conju-
gation system is predominant in APPcs. Complex 3 shows a
broad single Q band at 871 nm with a shoulder at 773 nm,
whereas the Q-band absorptions of 2 and 4 are split into
two at 816 and 740 nm, and 992 and 763 nm, respectively
(Figure 7). The absorption spectrum of 6 exhibits similar
splitting of the Q bands at 813 and 758 nm. The energy sepa-
ration of the Q bands of 4 is greater than in 2 and 6. MCD
measurements on Pc and its derivatives generally provide
information about the degeneracy of the ground and excited
states and the difference in energy separation of these fron-
tier-molecular orbitals.[13] APPcs 2 and 4 exhibit negative
and positive signs in ascending energy, which correspond to
the split Q-band absorption (Figure 7). These signal patterns
are assigned as Faraday B terms based on the MCD theory,
which indicates that the excited states of these molecules
are nondegenerate.[13,14] The negative sign of the lower-
energy Q band suggests that the energy difference between
the HOMO and HOMOꢀ1 (DHOMO) is larger than that of
the LUMO and LUMO+1 (DLUMO). On the other hand,
compound 3 shows a dispersion-type signal with negative
and positive signs in ascending energy. This signal pattern in
the Q-band region is typical of Faraday A terms, which sug-
gests a degeneracy of the excited states, and the sign of the
Q band indicates that DHOMO>DLUMO. Faraday A
terms are generally observed for Pc and its derivatives with
higher symmetry than C3. Therefore, the pattern observed
for 3 is more likely assigned as pseudo Faraday A terms,
which can be observed when a molecule exhibits low sym-
Figure 6. Views of the skeletal deviation of the atoms from the 4N mean
*
*
plane for a) 2, b) 3, and c) 4. and indicate carbon atoms of azaphena-
&
lene units and isoindole units, respectively. & and
indicate nitrogen
atoms at meso-positions and coordinating nitrogen atoms, respectively.
of 2 were arranged in a fairly planar manner, whereas the
azaphenalene moiety was tilted by approximately 308 from
the 4N mean plane. On the other hand, an optimized struc-
ture of the free base of 2 and the crystal structure of 6 both
exhibit planar conformations, indicative of the flexibility of
the APPc structure. Compared with Pcs, the cavity size of 2
becomes larger due to the broader C-N-C bond angle of the
azaphenalene moiety relative to isoindole moieties. Consid-
ering that the coordination bond length of low-spin NiII–N is
approximately 1.96 ꢁ in the case of Pc and porphyrin com-
plexes,[11] the molecular distortion of 2 is caused mainly to
fit a nickel ion into the cavity of 2. The planar structure of 6
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11155

N. Kobayashi et al.
HOMO
to
LUMO
and
LUMO+1 (Table 2) and reveal
that the absorption spectra of
2–4 can be described using
Goutermanꢂs four-orbital model
as a theoretical framework.[16]
In the cases of 2 and 4, the two
transitions appear at separate
positions (729 and 647 nm for 2
and 886 and 734 nm for 4),
whereas they are close in
energy in the case of 3 (780 and
768 nm). These results correlate
well with the observed differen-
ces in shape of the Q bands in
the absorption spectra and with
the Faraday B terms for 2 and 4
and pseudo Faraday A terms
for 3 in the MCD spectra.
Electrochemistry: Cyclic vol-
tammograms in o-dichloroben-
zene (o-DCB)/0.1m tetrabu-
A
perchlorate
(TBAP) exhibit two quasi-re-
versible oxidations and two re-
versible reductions for all of the
compounds (see Figure 8 and
the Supporting Information).
The nickel and zinc ions show
no redox behavior in this mea-
surement window, hence, all of
the observed redox couples can
be characterized as ligand-
based oxidation and reduction
processes. It is well established
for Pc and its analogues that
the potential difference (DE)
between the first oxidation and
reduction potentials has a good
Figure 7. Electronic absorption (bottom) and MCD (top) spectra of a) 1, b) 2, c) 3, d) 4, and e) 6 in CHCl3.
metry but the excited states are
Table 2. Selected transition energies and wave functions calculated by the TD-DFT (B3LYP/6-31G(d))
method.
nearly degenerate, that is, when
two Faraday B terms lie close
in energy.[15]
Complex
Energy [nm]
f[a]
Wave function[b]
!
2
729
647
780
768
886
734
0.24
0.49
0.33
0.37
0.18
0.61
0.608jL H>+…
!
!
!
0.585jL+1 H>ꢀ0.121jL Hꢀ5>+0.112jL+2 H>+…
!
!
Calculated absorption spectra:
Transition energies and oscilla-
tor strengths were calculated
for the optimized structures of
2, 3, and 4 by the time-depen-
dent DFT (TD-DFT) method
by using the B3LYP/6-31G(d)
3
4
0.535jL H>ꢀ0.251jL+1 H>+…
!
!
0.249jL H>+0.543jL+1 H>+…
!
0.596jL H>+…
!
0.580jL+1 H>+…
[a] Oscillator strength. [b] The wave functions based on the eigenvectors predicted by TD-DFT. Eigenvectors
greater than 0.10 are included. L=LUMO, H=HOMO.
combination of hybrid functional and basis sets. The TD-
DFT calculations predict two transitions with oscillator
strengths greater than 0.1 in the Q-band region for all of the
compounds, which mainly comprise transitions from the
correlation with the lowest transition energies.[17] Plots of
the potentials (Table 3) clearly indicate a sizable negative
shift of the first oxidation potential upon an increase in the
number of azaphenalene units (0.42, 0.085, ꢀ0.13, and
11156
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Azaphenalene Phthalocyanines
FULL PAPER
Figure 8. Cyclic voltammograms of 2 (top), 3 (middle), and 4 (bottom) in
o-DCB/0.1m TBAP.
Table 3. Redox potentials (V vs. Fc+/Fc) in o-DCB/0.1m TBAP.
Complex 2nd reduction 1st reduction 1st oxidation 2nd oxidation
1
2
3
4
6
–
ꢀ1.39
ꢀ1.35
ꢀ1.41
ꢀ1.28
ꢀ1.60
0.42
0.085
ꢀ0.13
ꢀ0.23
ꢀ0.18
–
ꢀ1.69
ꢀ1.85
ꢀ1.70
ꢀ1.98
0.50
0.14
0.04
0.43
Figure 9. Partial MO energy diagram and frontier orbitals of a) 1, b) 2,
c) 3, and d) 4 derived from the DFT calculations.
ꢀ0.23 V vs. Fc+/Fc for 1–4, respectively), whereas the first
reduction potential shows very little variation (ꢀ1.39, ꢀ1.35,
ꢀ1.41, and ꢀ1.28 V vs. Fc+/Fc for 1–4, respectively). The
DE values thus decrease in the same order (1.81, 1.44, 1.28,
and 1.05 V vs. Fc+/Fc for 1–4, respectively). These results
are in good agreement with the observed redshift of the
lower-energy Q band in this order. Compared with nickel–
APPc complex 2, zinc–APPc complex 6 exhibits negative
shifts of all of the redox potentials due to the alteration of
the central-metal ion (Table 3)[18] but the DE value (1.42 V
vs. Fc+/Fc) is comparable to that of 2.
bilized in energy, which causes orbital nondegeneracy with
an energy separation (DLUMO) of 0.12 eV. In the case of 3
both the LUMO and LUMO+1 are equally destabilized and
degenerate, with a DLUMO value of 0.05 eV, due to the
presence of two azaphenalene moieties on both the x- and
y-molecular axes. In the case of 4 only the LUMO+1 is de-
stabilized (DLUMO=0.13 eV), due to the presence of aza-
phenalene moieties on the same molecular axis. Changes in
the energy of the frontier orbitals observed for the series of
APPcs are essentially similar to those of benzene-fused low-
symmetry Pcs.[17,19] This indicates that, despite the greatly
distorted structures, the variation of the frontier MOs of
APPcs from those of Pcs with D4h symmetries can be under-
stood in terms of their molecular symmetries. The contribu-
tion of the exterior naphthalene moieties of the azaphena-
lene units to the macrocyclic-conjugation system is similar
to that of the exterior benzene and naphthalene rings of
naphthalocyanine and anthracocyanine.[3]
Electronic structures: Molecular orbital (MO) calculations
based on DFT methods at the B3LYP/6-31G(d) level led to
further understanding of the electronic structures of APPcs.
Partial MOs related to the Q-band absorptions are depicted
in Figure 9. The amplitude of the frontier MO coefficients
of the APPcs exhibit similarities to that of 1, which is indica-
tive of successful incorporation of the azaphenalene units
into the macrocyclic-conjugation system. For each com-
pound, the HOMO is delocalized over the molecule, where-
as the LUMO and LUMO+1 are localized along the x- and
y-molecular axes, respectively. Upon increasing the number
of azaphenalene units, the HOMOs are energetically desta-
bilized to a certain extent (ꢀ4.95, ꢀ4.65, ꢀ4.35, and
ꢀ4.26 eV for 1–4, respectively), whereas the LUMO ener-
gies appear to be less dependent on the number of azaphe-
nalene units, consistent with the electrochemical results. Be-
cause of the delocalization of the LUMO and LUMO+1
along the x- and y-molecular axes, alteration in these MOs
of APPcs largely depends on the positions of the azaphena-
lene moieties. In the case of 2, only the LUMO+1 is desta-
Conclusion
Novel phthalocyanine analogues with azaphenalene moieties
instead of isoindole moieties were synthesized and their
structures were unambiguously elucidated by mass spec-
1
trometry, H NMR spectroscopy, and X-ray crystallographic
analysis. Despite the significant distortion of the molecules,
caused mainly by coordination of the central nickel ion, the
electronic structures of these novel analogues are more simi-
lar to those of Pcs than hemiporphyrazines. The azaphena-
Chem. Eur. J. 2010, 16, 11151 – 11159
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11157

N. Kobayashi et al.
phy (GPC) on HPLC apparatus (detection at 810 nm). Three fractions,
colored blue, green, and brown, were collected, and recrystallized
(CHCl3/MeOH) to give nickel complexes of 1 (4.0 mg, 9.1%), 2 (13.3 mg,
26.4%), and 3 (8.3 mg, 13.1%), respectively.
lene units were successfully incorporated into Pc-like macro-
cyclic-conjugation systems. The electronic structures and,
hence, their optical and electrochemical properties largely
depend on the number and positions of the azaphenalene
units. Based on MO calculations, a series of changes in the
frontier MOs is similar to that seen for benzene-fused low-
symmetry Pcs but the extent of the destabilization of the
HOMO and redshift of the Q bands are much more signifi-
cant. Replacement of the inner five-membered-ring units
with larger-ring units can be a good protocol for the creation
of molecules with unique optical and electrochemical prop-
erties. Incorporation of larger-ring units into the core is of
interest with respect to the variation of macrocyclic-conjuga-
tion systems and research along this direction is under inves-
tigation in our laboratory.
Method b: Under a nitrogen atmosphere, a mixture of 1,8-naphthalenedi-
carbonitrile (890 mg, 5 mmol) and 4,5-di-4-tert-butylphenyloxyphthaloni-
trile (430 mg, 1 mmol) was reacted in freshly distilled quinoline (5 mL) in
the presence of anhydrous nickel acetate (120 mg, 0.6 mmol) and a cata-
lytic amount of ammonium molybdate at 3308C for 20 min. After remov-
al of the solvent under reduced pressure, the resultant mixture was chro-
matographed quickly on a short alumina column (CHCl3) to give a green
fraction. During purification, 4 was inclined to decompose on silica gel in
CHCl3 and although decomposition was also observed on alumina-gel,
the level was more acceptable. A recycling GPC–HPLC system (detec-
tion at 990 nm) was employed subsequently to perform further isolation,
and the first (blue), second (bottle green), and fourth (brown) fractions
were collected and recrystallized from CHCl3/MeOH, to afford nickel
complexes of
1 (47 mg, 10.9%), 2 (153 mg, 30.5%), and 3 (93 mg,
14.8%), respectively. The third fraction (green) was purified by prepara-
tive silica-gel TLC (6:1 CHCl3/MeOH) and was recrystallized from
CHCl3/CH3CN to afford the nickel complex 4 as a green solid (8.7 mg,
1.4%).
Nickel–APPc complex (2): 1H NMR ([D8]toluene, 600 MHz, 298 K): d=
8.65 (s, 2H; a-benzo), 8.58 (s, 2H; a-benzo), 8.46 (brs, 2H; naphthalene),
8.30 (s, 2H; a-benzo), 7.31 (brs, 2H; naphthalene), 7.30–7.15 (m, 24H;
phenyl), 7.12 (brs, 2H; naphthalene), 1.29 (s, 18H; tert-butyl), 1.24 ppm
(s, 36H; tert-butyl); UV/Vis (CHCl3): lmax (e)=310 (51000), 353 (47000),
740 (50000), 816 nm (42000 molꢀ1 dm3 cmꢀ1); MS (ESI–FT-ICR): m/z:
calcd for C96H90N8O6Ni: 1508.6337 [M+]; found: 1508.6331; calcd for
C96H90N8O6NaNi: 1531.6235 [M++Na]; found: 1531.6229.
Nickel–adj-AP2Pc complex (3): 1H NMR ([D8]toluene, 600 MHz, 298 K):
d=8.36 (s, 2H; a-benzo), 8.34 (d, J=7.4 Hz, 2H; naphthalene), 8.20 (s,
2H; a-benzo), 8.01 (d, J=7.6 Hz, 2H; naphthalene), 7.28 (d, J=8.0 Hz,
2H; naphthalene), 7.25 (d, J=8.0 Hz, 2H; naphthalene), 7.23–7.15 (m,
16H; phenyl), 7.08 (m, 4H; naphthalene), 1.24 (s, 18H; tert-butyl),
1.23 ppm (s, 18H; tert-butyl); UV/Vis (CHCl3): lmax (e)=370 (51000),
773 (sh, 41000), 871 nm (100000 molꢀ1 dm3 cmꢀ1); MS (ESI–FT-ICR):
m/z: calcd for C80H68N8O4Ni: 1262.4717 [M+]; found: 1262.4712.
Experimental Section
General: Electronic absorption spectra were recorded on a JASCO V-
570 spectrophotometer. Magnetic circular dichroism (MCD) spectra were
recorded on a JASCO J-725 spectrodichrometer equipped with a JASCO
electromagnet, which produces magnetic fields of up to 1.09 T with both
parallel and antiparallel fields. The magnitudes ([q]M) were expressed in
terms of molar ellipticity per tesla (deg dm3 molꢀ1 cmꢀ1 Tꢀ1). 1H NMR
spectra were recorded on a JEOL ECA-600 spectrometer (operating at
594.17 MHz), the residual solvent was used as the internal reference (d=
7.26 ppm for CDCl3 and d=2.09 ppm for [D8]toluene). HRMS were re-
corded on a Bruker Daltonics Apex-III spectrometer. Cyclic and differ-
ential-pulse voltammetry (CV and DPV) measurements were recorded
with a Hokuto Denko HZ5000 potentiostat under a nitrogen atmosphere
in o-dichlorobenzene (o-DCB) solutions with 0.1m of tetrabutylammoni-
um perchlorate (TBAP) as the supporting electrolyte. Measurements
were made with a glassy-carbon electrode (area=0.07 cm2), an Ag/AgCl
reference electrode, and a Pt-wire counter electrode. The concentration
of the solution was fixed at 0.5 mm and the sweep rates were 100 and
10 mVsꢀ1 for CV and DPV measurements, respectively. The ferroceni-
um/ferrocene (Fc+/Fc) couple was used as an internal standard. Prepara-
tive separations were performed by silica-gel column chromatography
(Merck Kieselegel 60H), alumina-gel column chromatography (Wako),
and recycling preparative GPC–HPLC (JAI LC-9201 with preparative
JAIGEL-2H, 2.5H, and 3H columns).
Nickel–opp-AP2Pc complex (4): UV/Vis (CHCl3): lmax (e)=368 (44000),
763 (45000), 992 nm (33000 molꢀ1 dm3 cmꢀ1); MS (ESI–FT-ICR): m/z:
calcd for C80H68N8O4Ni: 1262.4717 [M+]; found: 1262.4712.
Zinc–APPc complex (6): Under a nitrogen atmosphere, in a screw-
capped test tube, 1,8-naphthalenedicarbonitrile (350 mg, 1.96 mmol) was
reacted
with
4,5-di-4-tert-butylphenyloxyphthalonitrile
(430 mg,
1.01 mmol) in the presence of zinc acetate (70 mg, 0.40 mmol) and hydro-
quinone (400 mg, 3.6 mmol) at 2608C for 20 min. The resultant black
mixture was dissolved in CHCl3 then chromatographed on a short alumi-
na column (CHCl3) to give a green fraction. A recycling GPC–HPLC
system was employed to perform further purification, and the second
fraction was collected and recrystallized from CHCl3/MeOH to afford
Crystallographic data collection and structure refinement: Data collec-
tion for 6 was carried out at ꢀ1738C on a Bruker APEXII CCD diffrac-
tometer with MoKa radiation (l=0.71073 ꢁ). The structure was solved by
direct methods (Sir 2004)[20] and refined by using a full-matrix least-
squares technique (SHELXL-97).[21] Solvent molecules in the lattice of 6
were severely disordered and could not be resolved. The program
SQUEEZE in PLATON was used to remove the solvent electron densi-
ty.[22] CCDC-767425 contains the supplementary crystallographic data for
this paper. These data can be obtained free of charge from the Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
the zinc complex of
6 as a
black solid (8.8 mg, 1.7%). 1H NMR
([D8]toluene with a drop of [D5]pyridine, 600 MHz, 298 K): d=9.04 (s,
2H; a-benzo), 9.01 (s, 2H; a-benzo), 8.98 (brs, 2H; naphthalene), 8.67
(s, 2H; a-benzo), 7.31 (d, J=7.9 Hz, 2H; naphthalene), 7.28–7.15 (m,
24H; phenyl), 7.14–7.13 (m, 2H; naphthalene), 1.29 (s, 18H; tert-butyl),
1.24 (s, 18H; tert-butyl), 1.23 ppm (s, 18H; tert-butyl); UV/Vis (CHCl3):
lmax (e)=360 (61000), 690 (32000), 758 (87000), 813 nm
Molecular-orbital calculations: The Gaussian 03 software package[23] was
used to carry out DFT and TD-DFT calculations at the B3LYP level with
6-31G(d) basis sets.
(56000 molꢀ1 dm3 cmꢀ1);
MS
(ESI–FT-ICR):
m/z:
calcd
for
C96H90N8O6Zn: 1514.6275 [M+]; found: 1514.6269; calcd for
C96H90N8O6NaZn: 1537.6172 [M++Na]; found: 1537.6167.
Synthesis of nickel–APPc complexes
Method a: 1,8-Naphthalenedicarbonitrile (89.0 mg, 0.50 mmol), 4,5-di-4-
tert-butylphenyloxyphthalonitrile (42.4 mg, 0.10 mmol), anhydrous nickel
acetate (10.6 mg, 0.06 mmol), and hydroquinone (50.0 mg, 0.45 mmol)
were added to a screw-capped test tube. The mixture was stirred at
1708C under nitrogen until it melted, then heated at 3008C for 15 min.
The resultant mixture was purified, first, by silica-gel column chromatog-
raphy (CHCl3), then isolated by recycling gel-permeation chromatogra-
Acknowledgements
This work was partly supported by a Grant-in-Aid for Scientific Research
on Innovative Areas (No. 20108001, “pi-Space“) from the Ministry of
11158
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Chem. Eur. J. 2010, 16, 11151 – 11159

Azaphenalene Phthalocyanines
FULL PAPER
Education, Culture, Sports, Science, and Technology (MEXT) and a
Grant-in-Aid for Young Scientists (B) (No. 20750025) from Japan Society
for the Promotion of Science (JSPS). S.S. is grateful to Tokuyama Science
Foundation and the Exploratory Research Program for Young Scientists
from Tohoku University for financial support. H.Z. thanks the Global
Center of Excellence (G-COE) program of Tohoku University. The au-
thors thank Prof. Takeaki Iwamoto and Dr. Shintaro Ishida, Tohoku Uni-
versity for X-ray measurements and Prof. Masahiro Hirama and Dr.
Shuji Yamashita, Tohoku University for MALDI-TOF mass measure-
ments.
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[10] Crystallographic data for 6: C101H95N9O6Zn; Mr =1596.23; monoclin-
ic; space group P21/c (no. 14); a=19.070(12), b=19.572(12), c=
26.904(17) ꢁ, b=90.520(8)8, V=10042(11) ꢁ3; Z=4; 1calcd
=
1.056 gcmꢀ3
;
T=ꢀ1738C; 89566 measured reflections; 17665
unique reflections (Rint =0.0766); R=0.0884; Rw =0.2681 (all data);
GOF=1.023.
Received: March 12, 2010
Published online: August 2, 2010
Chem. Eur. J. 2010, 16, 11151 – 11159
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
11159