Supramolecular zinc phthalocyanine-imidazolyl perylenediimide dyad and triad: Synthesis, complexation, and photophysical studies

Article abstract of DOI:10.1002/asia.201100273

Two new supramolecular architectures based on zinc phthalocyanine (Pc) and imidazolyl-substituted perylenediimide (PDI), ZnPc/DImPDI/ZnPc 1 and ZnPc/ImPDI 2, have been prepared. A strong electron-donor, ZnPc-8, which contained eight tert-octylphenoxy groups was synthesized to ensure high solubility, thereby reducing aggregation in solution and providing δ-donor features while avoiding regioisomeric mixtures. Also, PDI units were functionalized with tert-octylphenoxy groups at the bay positions, which provide solubility to avoid aggregation in solution, together with one and two imidazole moieties in the amide position, PDI-6 and PDI-4, respectively, to be able to strongly coordinate with the ZnPc complex. Supramolecular complexation studies by ¹H NMR spectroscopy and ESI-MS demonstrate a high coordinative binding constant between imidazole-substituted PDI-4 or PDI-6 and ZnPc-8. The same results were confirmed by UV/Vis and fluorescence titration studies. UV/Vis titration studies revealed the formation of a 1:1 complex ZnPc/ImPDI 2 for the systems ZnPc-8 and PDI-6 and a 2:1 complex ZnPc/DImPDI/ZnPc 1 for the interaction of ZnPc-8 and PDI-4. The binding constant in both cases was determined to be on the order of 10⁵ M^-1. Femtosecond laser flash photolysis measurements provided a direct proof of the charge-separated state within both supramolecular assemblies by observing the transient absorption band at 820 nm due to the zinc phthalocyanine radical cation. The lifetimes of charge-separated states are (9.8±3) ns for triad 1 and (3±1) ns for dyad 2. As far as we know, this is the first time that a radical ion pair has been detected in a supramolecular assembled ZnPc-PDI system and has obtained the longest lifetime of a charge-separated state published for ZnPc-PDI assemblies.

Full text of DOI:10.1002/asia.201100273

FULL PAPERS
DOI: 10.1002/asia.201100273
Supramolecular Zinc Phthalocyanine–Imidazolyl Perylenediimide Dyad and
Triad: Synthesis, Complexation, and Photophysical Studies
F. Javier Cꢀspedes-Guirao,[a] Kei Ohkubo,[b] Shunichi Fukuzumi,*[b, c]
Fernando Fernꢁndez-Lꢁzaro,*[a] and ꢂngela Sastre-Santos*[a]
Dedicated to Prof. Dr. Dr. h.c. Tomꢀs Torres on the occasion of his 60th birthday
Abstract: Two new supramolecular ar-
chitectures based on zinc phthalocya-
nine (Pc) and imidazolyl-substituted
perylenediimide (PDI), ZnPc/DImPDI/
ZnPc 1 and ZnPc/ImPDI 2, have been
ZnPc complex. Supramolecular com-
plexation studies by H NMR spectros-
binding constant in both cases was de-
termined to be on the order of 105 mꢀ1.
Femtosecond laser flash photolysis
measurements provided a direct proof
of the charge-separated state within
both supramolecular assemblies by ob-
serving the transient absorption band
at 820 nm due to the zinc phthalocya-
nine radical cation. The lifetimes of
charge-separated states are (9.8ꢁ3) ns
for triad 1 and (3ꢁ1) ns for dyad 2. As
far as we know, this is the first time
that a radical ion pair has been detect-
1
copy and ESI-MS demonstrate a high
coordinative binding constant between
imidazole-substituted PDI-4 or PDI-6
and ZnPc-8. The same results were
confirmed by UV/Vis and fluorescence
titration studies. UV/Vis titration stud-
ies revealed the formation of a 1:1
complex ZnPc/ImPDI 2 for the sys-
tems ZnPc-8 and PDI-6 and a 2:1 com-
plex ZnPc/DImPDI/ZnPc 1 for the in-
teraction of ZnPc-8 and PDI-4. The
prepared.
A strong electron-donor,
ZnPc-8, which contained eight tert-oc-
tylphenoxy groups was synthesized to
ensure high solubility, thereby reducing
aggregation in solution and providing
s-donor features while avoiding regioi-
someric mixtures. Also, PDI units were
functionalized with tert-octylphenoxy
groups at the bay positions, which pro-
vide solubility to avoid aggregation in
solution, together with one and two
imidazole moieties in the amide posi-
tion, PDI-6 and PDI-4, respectively, to
be able to strongly coordinate with the
ed in
a supramolecular assembled
ZnPc–PDI system and has obtained
the longest lifetime of a charge-sepa-
rated state published for ZnPc–PDI as-
semblies.
Keywords: electron transfer · pery-
lenediimide · photophysics · supra-
molecular chemistry · zinc pthalo-
cyanine
Introduction
[a] F. J. Cꢀspedes-Guirao, Prof. Dr. F. Fernꢁndez-Lꢁzaro,
Prof. Dr. ꢂ. Sastre-Santos
Divisiꢃn de Quꢄmica Orgꢁnica Instituto de Bioingenierꢄa
Universidad Miguel Hernꢁndez
Elche 03202 (Spain)
Photoinduced electron transfer in donor–acceptor molecules
has been extensively studied in solution as model systems of
natural photosynthesis to efficiently harvest solar energy.[1–7]
The controlled organization of functional molecules into
highly ordered self-assembled arrays is expected to yield
supramolecular architectures with unique properties, and
offers an interesting way to design new donor–acceptor sys-
tems.[8] Supramolecular systems of multifunctional donor–ac-
ceptor hybrids in which the complementary electroactive
constituents are phthalocyanines (Pcs) and perylenediimides
(PDIs) can be interesting targets due to the outstanding
properties displayed by each moiety.
E-mail: asastre@umh.es
fdofdez@umh.es
[b] Dr. K. Ohkubo, Prof. Dr. S. Fukuzumi
Department of Material and Life Science
Graduate School of Engineering
Osaka University, ALCA
Japan Science and Technology Agency (JST)
2-1 Yamada-oka, Suita, Osaka 565-0871 (Japan)
Fax : (+81)6-6879-7370
E-mail: fukuzumi@chem.eng.osaka-u.ac.jp
[c] Prof. Dr. S. Fukuzumi
Department of Bioinspired Science
Ewha Womans University
Seoul, 120-750 (Korea)
Pcs have emerged as promising molecular components for
artificial photosynthetic systems because they contain large
conjugated p systems suitable for efficient electron-transfer
processes, they possess reducing or oxidizing characteristics
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201100273.
3110
ꢅ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2011, 6, 3110 – 3121

determined by the nature of the peripheral groups, they are
very robust, and they exhibit very high extinction coeffi-
cients around 700 nm (at which point the maximum solar
photon flux occurs) for efficient photon harvesting.[9–12] In
particular, we want to emphasize the importance of ZnPcs
in electron-transfer processes[13,14] and in the development of
dye-sensitized solar cells.[15] The UV/Vis properties of Pcs
have a limitation owing to the lack of absorption between
400 and 600 nm. Therefore, it might be interesting to use
Pcs in combination with an appropriate dye to achieve pan-
chromatic sensitization.
On the other hand, PDIs are highly thermostable n-type
semiconductors, with both relatively high electron affinity
and facile electrochemical reduction. They also possess an
extremely efficient fluorescent emission.[16] Because of this,
PDI dyes have been used extensively as light absorbers,
energy-transfer agents, and charge carriers.[17–20] Moreover,
PDIs exhibit high extinction coefficients in the 400–600 nm
region, thus matching the UV/Vis optical window of Pcs.
Therefore, the coupling of Pcs and PDIs could be a promis-
ing strategy to build light-harvesting antennae. Previous re-
ports on the linked Pc–PDI motif are scarce, and include co-
valent hybrids of the two chromophores connected through
either the PDI imido or the bay positions,[13,14,21–25] or supra-
molecular hybrids through axial coordination of the pery-
lene moiety.[26,27]
To achieve this supramolecular system, the chromophores
need to have the capability of self-organizing into higher-or-
dered and stable structures. Metal–ligand interactions have
been used as an appropriate strategy to construct supra-
molecular entities. Several investigation groups have been
particularly interested in the implementation of an assem-
bling strategy exploiting the coordination ability of peripher-
al pyridyl groups of different photoactive dyes (porphyrins,
perylenes, fullerenes, and so on) to the metal center of por-
phyrins[28–36] or Pcs.[27,37,38] The key to the stability of axially
ligated dyes is the strength of the coordinative bond be-
tween the ligand and metal ion. For example, ligation of a
pyridyl ring to zinc porphyrin and ZnPc is intrinsically weak
(binding constant of K=1ꢆ103 mꢀ1).[27,29] Thus, in solution,
coordination oligomers are generally in equilibrium with the
monomers.[28]
A well-established method in the field of porphyrin
chemistry, developed by Kobuke et al., is the preparation of
imidazolyl-substituted porphyrins that can coordinate
through the imidazolyl moiety to the central zinc(II) ion of
a different porphyrin[39–41] or phthalocyanine[42,43] unit, with
large association constants. D’Souza et al. also used the
better coordinating ability of imidazole moieties to form
dyes by means of axial coordination of zinc porphyrins and
phthalocyanines with fullerenes and carbon nano-
tubes.[35,44–47]
The objective of the current work was to prepare two
electron donor–acceptor hybrids that bear PDI chromo-
phores as the acceptor unit and two (ZnPc/DImPDI/ZnPc,
1) or one (ZnPc/ImPDI, 2) units of ZnPc as the donor coun-
terparts by means of strong imidazolyl-mediated metal coor-
dination. The complexation studies and the photophysics of
these constructs are examined in detail. We observed for the
first time the presence of a radical ion pair in a supramolec-
ular ZnPc–PDI system.
Abstract in Spanish: Se han preparado dos nuevos sistemas
supramoleculares basados en ftalocianina de zinc y en peri-
lenobisimida sustituida con grupos imidazolilo, ZnPc/
DImPDI/ZnPc 1 y ZnPc/ImPDI 2. Se ha sintetizado la ftalo-
cianina ZnPc-8 con ocho grupos terc-octilfenoxilo con
objeto de aumentar la solubilidad, reducir la agregaciꢃn en
disoluciꢃn, introducir grupos dadores de electrones y, por
fflltimo, evitar mezclas de regioisꢃmeros. Ademꢁs, las PDI-6
y PDI-4 tambiꢀn se han funcionalizado con grupos terc-oc-
tilfenoxilo en las posiciones bahꢄa, los cuales les confieren
solubilidad e impiden la agregaciꢃn en disoluciꢃn, y con una
o dos unidades de imidazol en la posiciꢃn imida, respectiva-
mente, con objeto de coordinar fuertemente la ZnPc. Los
estudios de complejaciꢃn supramolecular llevados a cabo
1
por H-RMN y MS-ESI han demostrado una constante de
complejaciꢃn muy alta entre las PDI-4 o PDI-6 sustituidas
con imidazol y la ZnPc-8. Los mismos resultados han sido
confirmados mediante estudios de valoraciꢃn realizados por
UV-vis y fluorescencia. Los estudios de valoraciꢃn realiza-
dos mediante UV-vis indican la formaciꢃn de un complejo
1:1 ZnPc/ImPDI 2 para los sistemas ZnPc-8 y PDI-6, y un
complejo 2:1 ZnPc/DImPDI/ZnPc 1 para los sistemas ZnPc-
8 y PDI-4. Las constantes de complejaciꢃn en los dos son
del orden de 105 mꢀ1. En ambos sistemas supramoleculares
tambiꢀn ha sido posible determinar el estado de separaciꢃn
de cargas mediante medidas de fotꢃlisis por destello lꢁser,
observando la banda de absorciꢃn transiente a 820 nm
debida al catiꢃn radical de la ftalocianina de zinc. Los tiem-
pos de vida de los estados de separaciꢃn de carga son (9.8ꢁ
3) ns para la trꢄada 1 y (3ꢁ1) ns para la dꢄada 2. Segffln
nuestros datos, esta es la primera vez que ha sido detectada
la existencia de un par iꢃn radical en un sistema de ZnPc–
PDI ensamblado de manera supramolecular, obteniendo el
tiempo de vida mꢁs largo, conocido hasta la fecha, de un
estado de separaciꢃn de cargas en un sistema ZnPc–PDI.
Results and Discussion
Synthesis
Unsubstituted Pc and PDI are very insoluble in organic sol-
vents. Therefore, functionalization of both molecular precur-
sors is necessary. Hereby the choice of the substituent is de-
cisive for processing and characterization. In the context of
the ZnPc unit, tert-octylphenoxy groups were selected, as
eight units of this bulky substituent are expected to ensure
high solubility, reduce aggregation in solution, and provide
s-donor features, while avoiding regioisomer mixtures typi-
cal of the commonly used tetra(tert-butyl)ZnPc. As a conse-
Chem. Asian J. 2011, 6, 3110 – 3121
ꢅ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
3111

S. Fukuzumi, F. Fernꢁndez-Lꢁzaro, ꢂ. Sastre-Santo et al.
FULL PAPERS
commercially available 4-(1H-
imidazol-1-yl)aniline
in
N-
methyl-2-pyrrolidone (NMP) to
give the corresponding PDI-3
with two imidazole groups at
the peri positions. This com-
pound is not very soluble in
chloroform or dichloromethane,
but this problem was overcome
when PDI-3 was treated with
tert-octylphenol and K2CO3 in
NMP
to
yield
PDI-4
(Scheme 1).
Synthesis of PDI-6 started
from N-(2’-ethylhexyl)-1,6,7,12-
tetrakis-[4’(1’’,1’’,3’’,3’’-tetrame-
thylbutyl)phenoxy]perylene-
9,10-dicarboximide-3,4-dicar-
boxyanhydride (5),[20] which
was treated with 4-(1H-imida-
zol-1-yl)aniline in molten imi-
dazole (Scheme 2).
As depicted in Scheme 3,
phthalonitrile 7 was prepared
by ipso substitution on 4,5-di-
chlorophthalonitrile with tert-
octylphenol in dry dimethyl
sulfoxide by using K2CO3.
ZnPc-8 was obtained by cyclo-
tetramerization of 7 with ZnCl2
(0.5m in THF) in the presence
of
dimethylaminoethanol
(DMAE).
All new compounds were
characterized by UV/Vis, FTIR,
1H NMR, and 13C NMR spec-
troscopy, and mass spectrome-
try, whereas purity was checked
quence, the corresponding ZnPc would bear a strong elec-
tron-donor character.[13,14,26] Equally, functionalization at the
bay positions of the PDI with
the same tert-octylphenoxy sub-
stituents would provide solubili-
ty (despite the existence of two
imidazole polar groups at the
imide positions of the PDI) and
would avoid aggregation.[48]
by elemental analysis. The UV/Vis spectrum of ZnPc-8
(Figure 1) shows the Q-band and B-band absorptions char-
The synthetic routes for the
preparation of the imidazolyl–
PDI derivatives 4 and 6 are in-
dicated in Schemes 1 and 2, re-
spectively.
Our synthesis of PDI-4 start-
ed from commercial 1,6,7,12-
tetrachloroperylene-3,4:9,10-
tetracarboxylic acid bisanhy-
dride, which was treated with Scheme 1. Synthetic route to PDI-4.
3112
www.chemasianj.org
ꢅ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2011, 6, 3110 – 3121

Supramolecular Zinc
spectrum of ZnPc-8 shows only
one singlet for the nonperipher-
al protons of the phthalocya-
nine core (for a total of eight
protons) at d=8.96 ppm. The
signals are so well-resolved, as
shown in Figure 2, because the
eight t-octylphenoxy groups
preclude aggregation, thus in-
creasing the solubility of the
compound and the resolution of
the spectrum.
Scheme 2. Synthetic route to PDI-6.
Figure 2. 1H NMR spectrum (300 MHz, [D8]THF, 258C) of ZnPc-8 (en-
largement of the aromatic region).
!
*
Figure 1. UV/Vis spectra of ZnPc-8 ( ), PDI-4 ( ), and PDI-6 (c) in
CH2Cl2
Supramolecular Complexation
1
Figure 3 (top) represents a comparison of the H NMR spec-
acteristic of nonaggregated compounds, which may arise
from the steric hindrance of the bulky tert-octylphenoxy
groups. On the other hand, there are few, if any, differences
tra of PDI-4 and complex 1 when all PDI are assembled
with two ZnPcs ([ZnPc-8]/ACTHNURGTNE[UNG PDI-4]=2). In this complex,
PDI-4 is located between two ZnPc-8 rings; thus it experi-
ences the influence of the diamagnetic ring currents of two
1
between UV/Vis spectra of PDI-4 and PDI-6. The H NMR
Scheme 3. Synthetic route to ZnPc-8
Chem. Asian J. 2011, 6, 3110 – 3121
ꢅ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
3113

S. Fukuzumi, F. Fernꢁndez-Lꢁzaro, ꢂ. Sastre-Santo et al.
FULL PAPERS
dination of PDI-4 to ZnPc-8.
The addition of increasing
amounts of ZnPc-8 to a solu-
tion of PDI-4 produced a signif-
icant upfield shift of the pro-
tons of PDI-4 (discussed
above). This shift can only be
observed when [PDI-4]/ACHTUNGTRENNUNG[ZnPc-
8]<0.5 (Figure 3, lower part).
As the mole fraction of the co-
ordinated partner increases, the
signals for PDI-4 were broad-
ened (in the case of H-1 pro-
tons of PDI-4) or missing (in
the case of H-4, H-5, H-6, H-7,
and H-8). Concomitantly, a new
set of signals appears that can
be attributed to the 2:1 hetero-
triad 1 (ZnPc/DImPDI/ZnPc).
This behavior indicates that the
host–guest complexation equi-
librium has a similar exchange
rate compared to the NMR
spectroscopic timescale, so by
using this technique it is impos-
sible to study the complexa-
tion,[50] which may be attributed
to the generally strong binding
between imidazole ligands and
ZnPcs.[42] Because of this, it was
not possible to assess the stoi-
chiometry of the supramolec-
ular complex and to determine
its binding constant with
1H NMR spectroscopy experi-
ments. We obtained the same
results by using PDI-6 and
ZnPc-8 in a 1H NMR spectro-
scopic titration experiment.
Figure 3. a) Comparison of 1H NMR spectra in CDCl3 for PDI-4 and 1 (ZnPc/DImPDI/ZnPc). b) Partial
1H NMR spectra (CDCl3, 300 MHz, 258C) showing the shift of the protons in PDI-4 upon the addition of in-
creasing quantities of ZnPc-8 (number of equiv indicated to the right) to a solution of PDI-4 (concentration of
PDI was fixed at 0.44 mm).
Moreover, the strong interac-
tion in this type of complex was
confirmed by electrospray ioni-
zation (ESI) mass spectrometry
(see the Supporting Informa-
tion; m/z 3670 [M]+ of complex
ZnPc-8. As a result, all PDI-4 signals are shifted upfield;
the magnitude of this effect depends on the distance be-
tween a given proton and the Pc core. The effect is particu-
larly pronounced for the imidazole moiety, which displays a
strong upfield shift: H-6, H-7, and H-8 protons of imidazole
substituents go from d=7.89, 7.32, and 7.23 ppm to d=5.72,
3.99, and 3.06 ppm, respectively. Analogous changes in the
chemical shifts of protons in zinc porphyrin–perylene[28,29,49]
and ZnPc–perylene[27] supramolecular systems had been re-
ported, but using pyridyl moieties.
2). The expected peak of complex 1 was not observed with
this method, probably due to poor transmission around the
expected high mass (m/z 5909 [M]+).
The complexation of the imidazolyl perylenes and ZnPc-8
was also studied by UV/Vis spectroscopy. PDI-6 was first
studied to know the changes in the UV/Vis when only one
ZnPc interacts with one PDI (1:1 stoichiometry) and to ex-
trapolate the data to 2:1 stoichiometry with PDI-4. The ab-
sorption spectrum of ZnPc-8 displays a Soret band at
348 nm and an intense Q band at 681 nm (Figure 1). The ad-
dition of increasing amounts of PDI-6 to a constant concen-
tration of ZnPc-8 induced spectral changes (Figure 4).
1
A H NMR spectroscopic titration experiment was carried
out in deuterated chloroform at 258C to evaluate the coor-
3114
www.chemasianj.org
ꢅ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2011, 6, 3110 – 3121

Supramolecular Zinc
Figure 5. UV/Vis titration curve (CH2Cl2) showing the changes in the ab-
sorbance at 365 nm (due to formation of 2 (ZnPc/ImPDI) complex)
when increasing amounts of PDI-6 were added to ZnPc-8 solution
([ZnPc-8]=0.0056 mm); the regression coefficient for the nonlinear least-
squares curve-fitting analysis is r2 =0.99497. Inset: UV/Vis Job plot of
Figure 4. Absorption spectral changes of ZnPc-8 on addition of increas-
ing concentrations of PDI-6 in CH2Cl2. The concentration for ZnPc-8
was kept constant at 0.11ꢆ10ꢀ3 mm. The inset shows the enlarged UV/
Vis spectrum between 325 and 400 nm (region in which complex 2 ab-
sorbs).
ZnPc-8 versus PDI-6. [PDI-6]+[ZnPc-8]ꢄ0.023 mm.
G
ometry of the binding between PDI-6 and ZnPc-8. The Job
plot[52,53] obtained in this way (Figure 5, inset) exhibited a
maximum at a mole ratio of 0.48, consistent with a 1:1 inter-
action. Titration experiments were carried out in dichloro-
methane at 258C to determine the binding constant for the
coordination of PDI-6 to ZnPc-8. The concentration of
ZnPc-8 was kept constant, and the changes in the absorb-
ance at 365 nm of the Soret band [see the previous “back-
ground absorbance” method using Eq. (2)] were plotted as a
function of the increasing concentration of PDI-6, these
data being subjected to a nonlinear least-squares curve-fit-
ting analysis[52] (Figure 5). The binding constant for the 1:1
complex 2 (ZnPc/ImPDI) was determined to be K=3.42ꢆ
The Q band of ZnPc-8 was gradually increased, as the
Soret band also does but with a major change in the maxi-
mum (from 348 to 365 nm; Figure 4, inset). Previous UV/Vis
titration experiments[27] with ZnPc and a pyridyl-bearing
PDI found no change in the Soret band, and this may be
due to the strong interaction between ZnPc and the imida-
zole moiety of PDI. This new maximum can be attributed to
the formation of the complex, so the absorbance at 365 nm
was used to evaluate a titration experiment. The “back-
ground absorbance” method[51,52] was used to calculate the
absorbance that corresponds to complex 2 (ZnPc/ImPDI),
because both PDI and ZnPc absorb at this wavelength
[Eq. (1)]:
105
ACHTUNGTRENNUNG
as others described in the literature,[42,43] for imidazolyl–
ZnPc complexes.
Aobsð365nmÞ ¼ APDIð365nmÞ þ AZnPcð365nmÞ þ Acomplexð365nmÞ
The complexation study to evaluate complex 1 (ZnPc/
DImPDI/ZnPc) was carried out using the same approach. A
continuous variation UV/Vis spectroscopic experiment was
carried out in dichloromethane to determine the stoichiome-
try of the binding between PDI-4 and ZnPc-8. The Job
plot[52,53] obtained in this way (Figure 6, inset) exhibited a
maximum at a mole ratio of 0.34, consistent with a 2:1 inter-
action. Titration experiments were carried out in dichloro-
methane at room temperature to determine the binding con-
stants for the coordination of PDI-4 to ZnPc-8. In this case,
the mathematical treatment to evaluate the binding con-
stants K1 and K2 using a 2:1 stoichiometry, is very complicat-
ed. Normally, in this type of study an analysis with a 1:2
model (host/guest) is used, which is simpler.[54,55] But we
needed to evaluate the changes in the absorbance at
365 nm, so we could not use PDI-4 as a host. Because of
this, we were forced to make an approach in which K1 of 1
(ZnPc/DImPDI/ZnPc)=K of 2 (ZnPc/ImPDI)=3.42ꢆ105
(ꢁ0.1)mꢀ1. We believe this approach is correct because both
in which Aobs(365nm) is the total absorption of mixture at
365 nm, APDI(365nm) is the absorption that corresponds to
PDI-6 at 365 nm, AZnPc(365nm) is the absorption that corre-
sponds to ZnPc-8 at 365 nm, and Acomplex(365nm) is the absorp-
tion that corresponds to complex 2 (ZnPc/ImPDI) at
365 nm. Then, substituting the Beer–Lambert law in Equa-
tion (1) affords Equation (2):
Acomplexð365nmÞ ¼ Aobsdð365nmÞ ꢀ ½PDIꢂ0 ꢃ ePDIð365nmÞ
ꢀ½ZnPcꢂ0 ꢃ eZnPcð365nmÞ
in which [PDI]0 is the gradually increased concentration of
PDI-6, ePDI(365nm) is the molar extinction coefficient of PDI-6
at 365 nm, [ZnPc]0 is the constant concentration of ZnPc-8,
and eZnPc(365nm) is the molar extinction coefficient of ZnPc-8
at 365 nm.
A continuous variation UV/Vis spectroscopic experiment
was carried out in dichloromethane to determine the stoichi-
Chem. Asian J. 2011, 6, 3110 – 3121
ꢅ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
3115

S. Fukuzumi, F. Fernꢁndez-Lꢁzaro, ꢂ. Sastre-Santo et al.
FULL PAPERS
584 nm, at which ZnPc-8 is rel-
atively transparent) upon titra-
tion with ZnPc-8. The fluores-
cence emission due to PDI-6 at
611 nm diminishes gradually,
whereas a very weak emission
band at 687 nm emerges, which
is due to the added ZnPc-8.
From the functional point of
view, it is noteworthy that the
fluorescence of PDI-6 is
quenched upon complexation
of ZnPc-8, which is probably a
result of a photoinduced elec-
tron-transfer process.[29,56,57] The
binding constant K for complex
2
[ZnPc-ImPDI] was deter-
Figure 6. UV/Vis titration curve (CH2Cl2) showing the changes in the absorbance at 365 nm (due to the forma-
tion of 1 (ZnPc/DImPDI/ZnPc) complex) when increasing amounts of PDI-4 were added to ZnPc-8 solution
([ZnPc-8]=0.01 mm); the regression coefficient for the nonlinear least-squares curve-fitting analysis is r2 =
mined by the Benesi–
Hildebrand equation I0/(I0ꢀI)=
1/A+1/AK [ZnPc-8], for which
I0 and I represent the fluores-
cence intensities of PDI-6 with
0.99774. Inset: UV/Vis Job plot of ZnPc-8 versus PDI-4. [PDI-4]+[ZnPc-8]ꢄ0.012 mm.
G
molecules are very similar; they differ only in an imidazole
group at the peri position of PDI-4.
and without the addition of ZnPc-8, respectively, and A is a
constant related to the difference in the emission quantum
yield of the complexed and uncomplexed PDI-6.[58] When
The data obtained were plotted as a function of increasing
concentration of PDI-4, these data being subjected to a non-
linear least-squares curve-fitting analysis[54] (Figure 6). The
second binding constant for the 2:1 complex 1 (ZnPc/
DImPDI/ZnPc) was determined to be K2 =1.5ꢆ105-
I /
straight line was obtained from which the value of k was de-
termined to be 1ꢆ106
0 A
ACHTUNGTRENUN[NG ZnPc-8] (inset of Figure 7) was plotted, a
AHCTUNGTRENNUNG
ment with that obtained from the absorption-based studies
discussed above. UV/Vis and fluorescence techniques have
demonstrated the high binding constants of these imidazolyl
PDI–ZnPc complexes.
ACHTUNGTRENNUNG
by fluorescence spectroscopy to evaluate the relationship
between UV/Vis and fluorescence binding constants.
Figure 7 shows the change in the fluorescence spectrum of
PDI-6 (0.25 mm) in dichloromethane (after excitation at
Electrochemical Studies and Theoretical Calculations
Cyclic voltammograms of 1 and 2 are shown in Figure 8.
The comparison with the uncomplexed compounds shows
that the cyclic voltammograms consist of two-electron re-
Figure 7. Change in the fluorescence spectrum of PDI-6 (0.25 mm) upon
titration with ZnPc-8 in CH2Cl2 (excited at 584 nm). The inset shows the
corresponding Benesi–Hildebrand plot for the determination of the bind-
ing constant; the regression coefficient for the nonlinear least-squares
curve-fitting analysis is r2 =0.99843.
Figure 8. Cyclic voltammograms of a) 2 (1.0 mm) and b) 1 (1.0 mm) in
deaerated CH2Cl2 containing TBAPF6 (0.1m); sweep rate: 0.1 Vsꢀ1
.
3116
www.chemasianj.org
ꢅ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2011, 6, 3110 – 3121

Supramolecular Zinc
Figure 9. HOMO and LUMO orbitals of ZnPc-PDI dyad 2. The structur-
al optimization was carried out by DFT B3LYP/3-21G(d) basis set.
duction processes of imidazolyl–PDI and the one-electron
oxidation process of ZnPc. The HOMO and LUMO orbitals
of dyad 2 (Figure 9) are localized separately on each moiety.
The energy of the charge-separated states determined from
the one-electron reduction and oxidation potentials are
1.38 eV for 2 and 1.36 eV for 1, respectively. These values
are smaller than those of the energies of singlet excited
states of ZnPc (1.80 eV) and PDI (2.31 eV), so the free-
energy changes of photoinduced electron transfer are nega-
tive. Thus, photoinduced electron transfer from the singlet
excited state of ZnPc to PDI as well as from ZnPc to the
singlet excited state of PDI is possible in the supramolecular
complexes to form the charge-separated states.
Figure 10. a) Femtosecond transient absorption spectra of ZnPc-8 in dea-
erated PhCN taken at 2 and 3000 ps after laser excitation at 410 nm.
b) Time profile of absorbance at 480 nm. The gray line was drawn by
single-exponential fitting.
Femtosecond Transient Absorption Spectral Investigations
The confirmation of the charge-separated state and evalua-
tion of the charge-recombination rate were performed by
the femtosecond transient absorption spectral technique
using dearated dichloromethane as a solvent to avoid de-
complexation due to the solvent competition effect. A dea-
erated solution of ZnPc-8 in dichloromethane gave rise
upon a 410 nm femtosecond laser pulse to a transient ab-
sorption band at 480 nm due to the singlet–singlet transition
band of ZnPc with strong bleaching at 680 nm, as shown in
Figure 10. The strong bleaching at 680 nm is ascribed to the
fluorescence and absorption of the ZnPc moiety. The decay
obeyed first-order kinetics, and the rate constant could be
determined as 9.0ꢆ108 sꢀ1(Figure 10).
excited state in dichloromethane was determined to be 5.5
and 4.3 ps for the ZnPc/DImPDI/ZnPc triad 1 (Figure 12b)
and for the ZnPc/ImPDI dyad 2 (Figure 11b), respectively.
The transient absorption band observed at 3000 ps is the
charge-separated state. The slower decay process shown in
Figures 11c and 12c can be assigned to the charge recombi-
nation. The lifetimes of charge-separated states are (9.8ꢁ
3) ns for triad 1 and (3ꢁ1) ns for dyad 2. To our knowledge,
this is the first time that a radical ion pair has been detected
in a supramolecularly assembled ZnPc–PDI system. More-
over, the supramolecular approach clearly avoids the fast re-
combination process observed in covalently bonded electro-
chemically decoupled[13,14a] and electrochemically coupled[24]
ZnPc–PDI structures, thus obtaining the longest lifetime of
a charge-separated state published for ZnPc–PDI assem-
blies.
The transient absorption spectra of supramolecular triad
ZnPc/DImPDI/ZnPc 1 and dyad ZnPc/ImPDI 2 upon irradi-
ation at 410 nm revealed the characteristic bands at 955 and
1030 nm of the perylenediimide singlet excited state[59] fol-
lowed by the apparition of the band at 820 nm that corre-
sponded to the zinc phthalocyanine radical cation; this
served as a direct proof of the charge-separated state (CS)
within both supramolecular assemblies (Figures 11 and 12).
The bands of the perylene radical anion, expected at ap-
proximately 970 and 1080 nm, are masked under the bands
of the PDI singlet excited state. From the decay of the ab-
Conclusions
We have applied the very strong coordination between zinc
complexes with imidazole ligands to synthesize a supra-
molecular ZnPc–PDI dyad and ZnP–PDI–ZnPc triad. We
1
sorbance of the band at 955 nm, the lifetime of the PDI*
Chem. Asian J. 2011, 6, 3110 – 3121
ꢅ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
3117

S. Fukuzumi, F. Fernꢁndez-Lꢁzaro, ꢂ. Sastre-Santo et al.
FULL PAPERS
have demonstrated the associa-
tion between ZnPc and PDI
moieties by 1H NMR spectros-
copy, ESI, UV/Vis, and fluores-
cence measurements. Moreover,
for the first time the existence
of a charge-separated state in a
supramolecular complex be-
tween a ZnPc and a perylene-
diimide has been confirmed by
femtosecond laser flash photol-
ysis. This supramolecular ap-
proach delays the back-electron
transfer to obtain a charge-sep-
arated state with a longer life-
time than those of the covalent-
bond approximation between a
ZnPc and a PDI system. The
application of these types of
supramolecular phthalocyanine-
acceptor systems in photovolta-
ic applications has been recent-
ly reviewed, thus making them
promising candidates for highly
efficient solar cells.[60]
Figure 11. a) Femtosecond transient absorption spectra of ZnPc/ImPDI 2 in deaerated CH2Cl2 taken at 1, 10,
500, and 3000 ps after laser excitation at 410 nm. b) and c) Time profiles of absorbance at 955 nm in the time
range of 50 and 3000 ps. The gray lines were drawn by double-exponential fitting.
Experimental Section
Synthetic Procedures
All chemicals were reagent-grade, pur-
chased from commercial sources, and
used as received unless otherwise
specified. Column chromatography:
silica (40–63 mm) TLC plates coated
with silica 60F254 were visualized by
UV light. NMR spectra were mea-
sured with a Bruker AC 300 instru-
ment. UV/Vis spectra were recorded
with a Helios Gamma spectrophotom-
eter. Fluorescence spectra were re-
corded with a Perkin–Elmer LS 55 lu-
minescence spectrometer and IR spec-
tra with a Nicolet Impact 400D spec-
trophotometer. Mass spectra were ob-
tained with
a Bruker Reflex III
matrix-assisted laser desorption/ioniza-
tion time-of-flight (MALDI-TOF) in-
strument and from a VG AutoSpec in-
strument (FAB). Mass spectra of the
complex
2
was obtained with
a
QSTAR-Applied Biosystems (ESI)
QTOF hybrid analyzer. Elemental
analyses were performed with
a
LECO CHNS-932 elemental analyzer.
Compound 3
1,6,7,12-Tetrachloroperylene-3,4:9,10-
tetracarboxylic
acid
bisanhydride
Figure 12. a) Femtosecond transient absorption spectra of ZnPc/DImPDI/ZnPc 1 in deaerated CH2Cl2 taken at
1, 10, 500, and 3000 ps after laser excitation at 410 nm. b) and c) Time profiles of absorbance at 955 nm in the
time ranges of 50 and 3000 ps. The gray lines were drawn by double-exponential fitting.
(0.5 g, 0.94 mmol), acetic acid (0.37 g,
6.25 mmol), 4-(1H-imidazol-1-yl)ani-
line (0.41 g, 2.6 mmol), and dry NMP
3118
www.chemasianj.org
ꢅ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2011, 6, 3110 – 3121

Supramolecular Zinc
(15 mL) were stirred under argon for 6 h at 858C. After being cooled to
room temperature, the resulting orange precipitate was filtered and
washed with MeOH (100 mL). At this point, CH2Cl2 was added to the
precipitate and filtered (unreacted perylene bisanhydride remained in
the filter). The solvent was evaporated under reduced pressure, and the
orange solid was washed and centrifuged twice with MeOH to give pery-
lene 3 as a red-orange solid (651 mg, 85%). 1H NMR (300 MHz, CDCl3/
MeOD 5:1): d=7.63 (d, J=8.8 Hz, 4H; phenyl), 7.65 (br, 2H; imida-
zole), 7.75 (br, 2H; imidazole), 7.84 (d, J=8.8 Hz, 4H; phenyl), 8.78 (s,
4H; perylene), 9.20 ppm (br, 2H; imidazole); 13C NMR (75 MHz,
CDCl3/MeOD 4:1): d=118.26, 122.21, 122.92, 128.80, 129.54, 130.11,
131.33, 133.06, 133.51, 135.23, 135.41, 162.21 ppm; UV/Vis (CDCl3/
MeOD 5:1): l (loge)=429 (4.04), 489 (4.49), 522 nm (4.65); FTIR (KBr):
n˜ =1710 (C=O imide), 1674 (C=O imide), 1558, 1521, 1384, 1299, 1244,
1196, 1057 cmꢀ1; MS (MALDI-TOF, dithranol): m/z: 811 [M++1]; ele-
mental analysis calcd (%) for C42H18Cl4N6O4·H2O: C 60.74, H 2.43, N
10.12; found: C 60.99, H 2.50, N 10.13.
1589, 1503, 1409, 1341, 1286, 1214, 1174 cmꢀ1; MS (MALDI-TOF, dithra-
nol): m/z: 1461 [M+], 1462 [M++1]; MS (MALDI-TOF, dithranol): m/z:
1461 [M+], 1462 [M++1]; elemental analysis calcd (%) for
C97H112N4O8·0.5H2O: C 79.20, H 7.74, N 3.81; found: C 79.09, H 7.74, N
3.85.
Compound 7
4,5-Dichlorophthalonitrile (2 g, 10.14 mmol), 4-(2,4,4-trimethylpentan-2-
yl)phenol (t-octylphenol; 6.3 g, 30.42 mmol) and dry DMSO (30 mL)
were heated while stirring at 908C under argon. Powdered K2CO3
(22.1 g, 0.16 mol; 8ꢆ20 mmol every 5 min) was added. The mixture was
stirred for 3 h, cooled to room temperature, and treated with water. The
white precipitate obtained was filtered, washed several times with water,
and dried. Purification by chromatography (silica, CH2Cl2) afforded 7
1
(3.2 g, 60%) as a white powder. H NMR (300 MHz, CDCl3): d=0.73 (s,
ꢀ
ꢀ
ꢀ
18H; tert-butyl), 1.40 (s, 12H; CH3), 1.75 (s, 4H; CH2 ), 6.99 (d, J=
ꢀ
8.8 Hz, 4H; phenol), 7.11 (s, 2H; Ar H), 7.45 ppm (d, J=8.8 Hz, 4H;
phenol); 13C NMR (75 MHz, CDCl3): d=31.51, 31.71, 32.38, 38.46, 57.09,
109.83, 115.16, 119.33, 121.25, 128.25, 148.13, 151.39, 152.16 ppm; UV/Vis
(CH2Cl2): l (loge)=231 (4.49), 286 nm (4.18); FTIR (KBr): n˜ =3046,
2952, 2898, 2238 (CꢅN), 1588, 1559, 1496, 1390, 1365, 1311, 1219, 1170,
911, 883 cmꢀ1; MS (MALDI-TOF, dithranol): m/z : 537 [M++1]; elemen-
tal analysis calcd (%) for C36H44N2O2: C 80.56, H 8.26, N 5.22; found: C
80.60, H 8.28, N 5.25.
Compound 4
Perylene 3 (0.4 g, 0.49 mmol), tert-octylphenol (1 g, 4.92 mmol), K2CO3
(0.34 g, (2.46 mmol), and dry NMP (15 mL) were stirred under argon for
16 h at 908C. During the course of the reaction, the color changed from
the red of the initial mixture to dark purple. After being cooled to room
temperature, the reaction mixture was treated with HCl (2n) and stirred
for 2 h. The purple precipitate was collected by vacuum filtration and
washed several times with water. The crude product was dissolved in
CH2Cl2 and this organic phase was washed with a saturated dissolution of
NaHCO3, water, and then dried with anhydrous MgSO4. Purification by
chromatography (silica, EtOAc) afforded 4 (367 mg, 50%) as a red-
Compound 8
Anhydrous ZnCl2 (1.86 mL, 0.93 mmol; in THF, 0.5m) was added to di-
methylaminoethanol (DMAE; 4 mL) and heated to 908C under a contin-
uous argon flow. After all the THF was evaporated, the mixture was
cooled to 608C. At this point, phthalonitrile 7 (0.5 g, 0.93 mmol) was
added and the reaction mixture was stirred under argon for 24 h at
1408C. During the course of the reaction, the color changed from white
of the initial mixture to dark green of the phthalocyanine. After being
cooled to room temperature, the resulting dark green mass was poured
into MeOH (50 mL), and the precipitate was filtered and washed twice
with MeOH. Purification by chromatography (silica, toluene/acetone
1
purple powder. H NMR (300 MHz, CDCl3): d=0.74 (s, 36H; tert-butyl),
ꢀ
ꢀ
ꢀ
1.33 (s, 24H; CH3), 1.71 (s, 8H, CH2 ), 6.88 (d, J=8.2 Hz, 8H;
phenol), 7.23 (br, 2H; imidazole), 7.27 (d, J=8.2 Hz, 8H; phenol), 7.32
(br, 2H; imidazole), 7.38 (d, J=8.4 Hz, 4H; phenyl), 7.53 (d, J=8.4 Hz,
4H; phenyl), 7.89 (br, 2H; imidazole), 8.20 ppm (s, 4H; perylene);
13C NMR (75 MHz, CDCl3): d=31.52, 31.82, 32.39, 38.33, 56.97, 118.28,
119.51, 119.54, 119.73, 120.52, 122.30, 122.34, 127.72, 130.35, 130.60,
133.02, 134.35, 135.63, 137.44, 146.98, 152.37, 156.39, 163.43 ppm; UV/Vis
(CH2Cl2): l (loge)=454 (4.23), 547 (4.47), 586 nm (4.69); FTIR (KBr):
n˜ =2953, 2902, 1708 (C=O imide), 1675 (C=O imide), 1586, 1520, 1503,
1407, 1364, 1340, 1319, 1286, 1210, 1174, 837 cmꢀ1; MS (MALDI-TOF, di-
thranol): m/z: 1492 [M++1]; elemental analysis calcd (%) for
C98H102N6O8: C 78.90, H 6.89, N 5.63; found: C 78.48, H 6.96, N 5.63.
1
100:1) afforded 8 (335 mg, 65%) as a green powder. H NMR (300 MHz,
ꢀ
CDCl3): d=0.72 (s, 72H; tert-butyl), 1.36 (s, 48H; CH3), 1.72 (s, 16H;
ꢀ
ꢀ
CH2 ), 6.98 (d, J=9 Hz, 16H; phenol), 7.29 (d, J=9 Hz, 16H; phenol),
8.46 ppm (s, 8H; Pc); 13C NMR (75 MHz, CDCl3): d=31.55, 31.81, 32.36,
38.18, 57.13, 117.38, 119.12, 127.28, 127.93, 144.90, 147.19, 150.17,
154.99 ppm; UV/Vis (CH2Cl2): l (loge)=286 (4.89), 348 (4.95), 614
(4.60), 681 nm (5.39); FTIR (KBr): n˜ =2954, 2903, 1506, 1486, 1451, 1400,
1365, 1271, 1218, 1180, 1087, 1029, 892 cmꢀ1; MS (MALDI-TOF, dithra-
nol): m/z: 2209 [M+]; elemental analysis calcd (%) for
C144H176N8O8Zn·2H2O: C 76.92, H 8.07, N 4.98; found: C 76.65, H 8.15,
N 4.78.
Compound 6
N-(2’-Ethylhexyl)-1,6,7,12-tetrakis-[4’(1’’,1’’,3’’,3’’-tetramethylbutyl)phe-
noxy]perylene-9,10-dicarboximide-3,4-dicarboxyanhydride (5; 95 mg,
0.072 mmol), 4-(1H-imidazol-1-yl)aniline (114 mg, 0.72 mmol), and imida-
zole (1 g) were stirred under argon for 24 h at 1608C. After being cooled
to room temperature, the reaction mixture was treated with ethanol and
this suspension was added into HCl (2n) and stirred for 24 h. The prod-
uct was extracted twice with CH2Cl2, and the organic phase was washed
with a saturated dissolution of NaHCO3, water, and then dried with an-
hydrous MgSO4. Purification by chromatography (silica, CH2Cl2/acetone
1H NMR Spectroscopic Experiments
NMR spectroscopic titrations of ZnPc-8 with PDI-4 were performed as
follows. An initial volume of 600 mL of a 0.44 mm solution of PDI-4 in
CDCl3 was placed in an NMR tube. Aliquots of a solution of ZnPc-8
(8 mm) and PDI-4 (0.44 mm) in CDCl3 were subsequently added, and a
spectrum was recorded after each addition (300 MHz, 298 K). PDI-4 was
added to avoid dilution effects. The same procedure was used to perform
the NMR spectroscopic titrations of ZnPc-8 with PDI-6.
20:3) afforded
(300 MHz, CDCl3): d=0.75 (s, 18H; tert-butyl), 0.79 (s, 18H; tert-butyl),
6 (52.5 mg, 50%) as a
red-purple powder. 1H NMR
ꢀ
ꢀ
0.86 (t, J=7.2 Hz, 3H; CH3), 0.88 (t, J=7.2 Hz, 3H; CH3), 1.33–1.19
ꢀ
ꢀ
ꢀ
ꢀ
(m, 8H; CH2 ), 1.33 (s, 12H; CH3), 1.37 (s, 12H; CH3), 1.71 (s, 4H,
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
CH2 ), 1.73 (s, 4H; CH2 ), 1.87 (m, 1H; CH ), 4.04 (m, 2H; CH2
N) 6.86 (d, J=8.7 Hz, 4H; phenol), 6.87 (d, J=8.7 Hz, 4H; phenol), 7.22
(br, 1H; imidazole), 7.26 (d, J=8.7 Hz, 4H; phenol), 7.28 (d, J=8.7 Hz,
4H; phenol), 7.30 (br, 1H; imidazole), 7.37 (d, J=8.7 Hz, 2H; phenyl),
7.52 (d, J=8.7 Hz, 2H; phenyl), 7.89 (br, 1H; imidazole), 8.17 (s, 2H;
perylene), 8.18 ppm (s, 2H; perylene); 13C NMR (75 MHz, CDCl3): d=
10.63, 14.09, 23.04, 24.13, 28.71, 29.29, 30.74, 31.52, 31.82, 31.88, 32.40,
32.44, 37.99, 38.32, 38.37, 44.24, 57.00, 57.07, 119.23, 119.43, 119.59,
119.78, 120.80, 122.00, 122.34, 122.82, 127.69, 127.72, 130.36, 132.81,
132.92, 134.43, 146.83, 146.85, 152.47, 156.14, 156.47, 163.49, 163.71 ppm;
UV/Vis (CH2Cl2): l (loge)=288 (4.68), 452 (4.27), 544 (4.49), 585 nm
(4.71); FTIR (KBr): n˜ =2955, 1703 (C=O imide), 1666 (C=O imide),
UV/Vis Titration Experiments
Job plots to determine the stoichiometry of the binding between PDI-6
and ZnPc-8 were carried out using a continuous variation of the UV/Vis
absorption that corresponded to complex 2 (ZnPc/ImPDI) at 365 nm [see
the previous “background absorbance” method using Eq. (2)]. An initial
volume of 1.6 mL of a 10 mm solution of ZnPc-8 in CH2Cl2 was placed in
a sealed quartz cuvette. Aliquots (100 mL) of a solution of PDI-6 in
CH2Cl2 (10 mm) were subsequently added, and a UV/Vis spectrum was re-
corded after each addition.
Job plots to determine the stoichiometry of the binding between PDI-4
and ZnPc-8 were carried out using a continuous variation of the UV/Vis
Chem. Asian J. 2011, 6, 3110 – 3121
ꢅ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
3119

S. Fukuzumi, F. Fernꢁndez-Lꢁzaro, ꢂ. Sastre-Santo et al.
FULL PAPERS
absorption that corresponded to complex 1 (ZnPc/ImPDI) at 365 nm [see
the previous “background absorbance” method using Eq. (2)]. An initial
volume of 1.5 mL of a 5.5 mm solution of ZnPc-8 in CH2Cl2 was placed in
a sealed quartz cuvette. Aliquots (100 mL) of a solution of PDI-4 in
CH2Cl2 (5.5 mm) were subsequently added, and a UV/Vis spectrum was
recorded after each addition.
Acknowledgements
Dr. Luis Martin is thanked for his valuable discussion. This work was par-
tially supported by Grants-in-Aid (nos. 23750014 and 20108010) from the
Ministry of Education, Culture, Sports, Science, and Technology, Japan,
KOSEF/MEST through WCU project (R31-2008-000-10010-0), and by
Grants Consolider-Ingenio 2010 project HOPE CSD2007-00007,
CTQ2008-05901/BQU, CTQ2010-20349, ACOMP/2009/039 and ACOMP/
2009/056 from MICINN, FEDER, and Generalitat Valenciana. F. J. C.-G.
thanks the Spanish Government MICINN for an FPU fellowship.
Analyses of the interactions between receptor ZnPc-8 and guests PDI-6
and PDI-4 were also carried out using UV/Vis spectroscopy. UV/Vis ti-
trations of PDI-6 with ZnPc-8 were performed as follows. An initial
volume of 1.6 mL of a 5.6 mm solution of ZnPc-8 in CH2Cl2 was placed in
a sealed quartz cuvette. Aliquots of a solution of PDI-6 (111.5 mm) and
ZnPc-8 (5.6 mm) in CH2Cl2 were subsequently added, and a UV/Vis spec-
trum was recorded after each addition (298 K). PDI-6 was added to
avoid dilution effects. The data were analyzed using standard curve-fit-
ting methods,[52] and the binding constants were evaluated by nonlinear
least-squares regression analysis from the changes in the absorbance at
365 nm of the Soret band [see the previous “background absorbance”
method using Eq. (2)].
[1] D. Gust, T. A. Moore, A. L. Moore, Acc. Chem. Res. 2001, 34, 40.
[2] M. R. Wasielewski, Chem. Rev. 1992, 92, 435.
[3] D. M. Guldi, Chem. Soc. Rev. 2002, 31, 22.
[4] M. N. Paddon-Row, Acc. Chem. Res. 1994, 27, 18.
[5] M. J. Blanco, M. C. Jimꢀnez, J.-C. Chambron, V. Heitz, M. Linke, J.-
P. Sauvage, Chem. Soc. Rev. 1999, 28, 293.
UV/Vis titrations of PDI-4 with ZnPc-8 were performed as follows. An
initial volume of 1.6 mL of a 7.5 mm solution of ZnPc-8 in CH2Cl2 was
placed in a sealed quartz cuvette. Aliquots of a solution of PDI-4 (74 mm)
and ZnPc-8 (7.5 mm) in CH2Cl2 were subsequently added, and a UV/Vis
spectrum was recorded after each addition (298 K). PDI-4 was added to
avoid dilution effects. The data were analyzed using standard curve-fit-
ting methods,[54] and the binding constants (K1 and K2) were evaluated by
nonlinear least-squares regression analysis (we made an approach in
[6] S. Fukuzumi, D. M. Guldi, Electron Transfer in Chemistry, Vol. 2
(Ed.: V. Balzani), Wiley-VCH, Weinheim, 2001, pp. 270–337.
[7] S. Fukuzumi, Org. Biomol. Chem. 2003, 1, 609.
[8] F. J. M. Hoeben, P. Jonkheijm, E. W. Meijer, A. P. H. J. Schenning,
Chem. Rev. 2005, 105, 1491.
[9] G. de la Torre, M. Nicolau, T. Torres, Phthalocyanines: Synthesis
Supramolecular Organization and Physical Properties (Supramolec-
ular Photosensitive and Electroactive Materials) 2001, Academic
Press, New York.
which K1 =K of complex 2=3.42ꢆ105
ACHTUNGTRENNUNG
absorbance at 365 nm of the Soret band [see the previous “background
absorbance” method using Eq. (2)].
[10] C. C. Leznoff, A. B. P. Lever, Phthalocyanines: Properties and Appli-
cations, Vols. 1–4, 1989, 1993, 1996, VCH, Weinheim, Germany.
[11] G. de la Torre, P. Vazquez, F. Agullꢃ-Lꢃpez, T. Torres, Chem. Rev.
2004, 104, 3723.
Fluorescence Titration Experiments
[12] G. de la Torre, C. G. Claessens, T. Torres, Chem. Commun. 2007,
2000.
[13] a) S. Fukuzumi, K. Ohkubo, J. Ortiz, A. M. Gutiꢀrrez, F. Fernꢁndez-
Lꢁzaro, ꢂ. Sastre-Santos, Chem. Commun. 2005, 3814; b) S. Fukuzu-
mi, K. Ohkubo, J. Ortiz, A. M. Gutiꢀrrez, F. Fernꢁndez-Lꢁzaro, ꢂ.
Sastre-Santos, J. Phys. Chem. A 2008, 112, 10744.
[14] a) F. J. Cꢀspedes-Guirao, K. Ohkubo, S. Fukuzumi, ꢂ. Sastre-Santos,
F. Fernꢁndez-Lꢁzaro, J. Org. Chem. 2009, 74, 5871; b) F. J. Cꢀs-
pedes-Guirao, L. Martꢄn-Gomis, K. Ohkubo, S. Fukuzumi, F.
Fernꢁndez-Lꢁzaro, ꢂ. Sastre-Santos, Chem. Eur. J. 2011, DOI:
10.1002/chem.201100320.
The fluorescence binding constant was obtained as follows. An initial
volume of 1.7 mL of a 0.25 mm solution of PDI-6 in CH2Cl2 (spectrosol
quality) was placed in a sealed quartz cuvette. Aliquots of a solution of
ZnPc-8 (5.1 mm) and PDI-6 (0.25 mm) in CH2Cl2 (spectrosol quality)
were subsequently added, and a fluorescence spectrum was recorded
after each addition (after excitation of PDI-6 at 584 nm, 298 K). PDI-6
was added to avoid dilution effects. The binding constant k was deter-
mined by the Benesi–Hildebrand equation [Eq. (3)] from the changes in
the fluorescence of PDI-6.
Laser Flash Photolysis
[15] J. J. Cid, J. H. Yum, S. R. Jang, M. K. Nazeeruddin, E. Martꢄnez-
Femtosecond transient absorption spectroscopy experiments were con-
ducted with an ultrafast source (Integra-C, Quantronix Corp.), an optical
parametric amplifier (TOPAS, Light Conversion Ltd.), and a commercial-
ly available optical detection system (Helios, provided by Ultrafast Sys-
tems LLC). The source for the pump and probe pulses was derived from
the fundamental output of Integra-C (780 nm, 2 mJ per pulse, and full
width at half-maximum=130 fs) at a repetition rate of 1 kHz. The funda-
mental output of the laser (75%) was introduced into TOPAS, which has
optical frequency mixers that result in a tunable range from 285 to
1660 nm, whereas the rest of the output was used for white-light genera-
tion. Typically, 2500 excitation pulses were averaged for 5 s to obtain the
transient spectrum at a set delay time. Kinetic traces at appropriate
wavelengths were assembled from the time-resolved spectral data. All
measurements were conducted at 298 K. The transient spectra were re-
corded by using fresh solutions in each laser excitation.
AHCTUNGTREGFNNUN errero, E. Palomares, J. Ko, M. Grätzel, T. Torres, Angew. Chem.
2007, 119, 8510; Angew. Chem. Int. Ed. 2007, 46, 8358.
[16] F. Würthner, Chem. Commun. 2004, 1564.
[17] T. van der Boom, R. T. Hayes, Y. Zhao, P. J. Bushard, E. A. Weiss,
M. R. Wasielewski, J. Am. Chem. Soc. 2002, 124, 9582.
[18] B. Rybtchinski, L. E. Sinks, M. R. Wasielewski, J. Am. Chem. Soc.
2004, 126, 12268.
[19] A. Herrmann, K. Müllen, Chem. Lett. 2006, 35, 978.
[20] a) M. Planells, F. J. Cꢀspedes-Guirao, A. Forneli, ꢂ. Sastre-Santos,
F. Fernꢁndez-Lꢁzaro, E. Palomares, J. Mater. Chem. 2008, 18, 5802;
b) M. Planells, F. J. Cꢀspedes-Guirao, L. GonÅalves, ꢂ. Sastre-
Santos, F. Fernꢁndez-Lꢁzaro, E. Palomares, J. Mater. Chem. 2009,
19, 5818.
[21] S.-G. Liu, Y.-Q. Liu, Y. Xu, X.-Z. Jiang, D.-B. Zhu, Tetrahedron
Lett. 1998, 39, 4271.
Theoretical Calculations
[22] X. Li, L. E. Sinks, B. Rybtchinski, M. R. Wasielewski, J. Am. Chem.
Soc. 2004, 126, 10810.
[23] Y. Chen, Y. Lin, M. E. El-Khouly, X. Zhuang, Y. Araki, O. Ito, W.
Zhang, J. Phys. Chem. C 2007, 111, 16096.
[24] A. J. Jimꢀnez, F. Spänig, M. S. Rodrꢄguez-Morgade, K. Ohkubo, S.
Fukuzumi, D. M. Guldi, T. Torres, Org. Lett. 2007, 9, 2481.
[25] M. O. Liu, C.-H. Tai, A. T. Hu, J. Photochem. Photobiol. A 2004,
165, 193.
[26] M. S. Rodrꢄguez-Morgade, T. Torres, C. Atienza-Castellanos, D. M.
Guldi, J. Am. Chem. Soc. 2006, 128, 15145.
Density functional theory (DFT) calculations were performed with a
COMPAQ DS20E computer. Geometry optimizations of supramolecular
systems were carried out with the Becke 3LYP functional and 3-21G*
basis set,[31–33] with the restricted Hartree–Fock (RHF) formalism and as
implemented in the Gaussian 03 program.[61] Graphical outputs of the
computational results were generated with the GaussView software pro-
gram.[62]
[27] B. Gao, Y. Li, J. Su, H. Tian, Supramol. Chem. 2007, 19, 207.
3120
www.chemasianj.org
ꢅ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2011, 6, 3110 – 3121

Supramolecular Zinc
[28] A. Prodi, C. Chiorboli, F. Scandola, E. Iengo, E. Alessio, R. Dobra-
wa, F. Würthner, J. Am. Chem. Soc. 2005, 127, 1454.
[51] S. Nygaard, C. N. Hansen, J. O. Jeppesen, J. Org. Chem. 2007, 72,
1617.
[29] C.-C. You, F. Würthner, Org. Lett. 2004, 6, 2401.
[52] K. Hirose, J. Inclusion Phenom. Macrocyclic Chem. 2001, 39, 193.
[53] P. Job, Annal. Chim. France 1928, 9, 113.
[54] K. A. Connors, The Measurement of Molecular Complex Stability,
Wiley, New Work, 1987.
[30] E. B. Fleischer, A. M. Shachter, Inorg. Chem. 1991, 30, 3763.
[31] C. A. Hunter, R. K. Hyde, Angew. Chem. 1996, 108, 2064; Angew.
Chem. Int. Ed. Engl. 1996, 35, 1936.
[32] F. Würthner, A. Sautter, C. Thalacker, Angew. Chem. 2000, 112,
1298; Angew. Chem. Int. Ed. 2000, 39, 1243.
[33] C. A. Hunter, R. Tregonning, Tetrahedron 2002, 58, 691.
[34] T. S. Balaban, R. Goddard, M. Linke-Schaetzel, J.-M. Lehn, J. Am.
Chem. Soc. 2003, 125, 4233.
[35] A. L. Schumacher, A. S. D. Sandanayaka, J. P. Hill, K. Ariga, P. A.
Karr, Y. Araki, O. Ito, F. D’Souza, Chem. Eur. J. 2007, 13, 4628.
[36] F. D’Souza, M. E. El-Khouly, S. Gadde, M. E. Zandler, A. L. McCar-
ty, Y. Araki, O. Ito, Tetrahedron 2006, 62, 1967.
[37] F. D’Souza, S. Gadde, M. E. El-Khouly, M. E. Zandler, Y. Araki, O.
Ito, J. Porphyrins Phthalocyanines 2005, 9, 698.
[38] a) D. M. Guldi, J. Ramey, M. V. Martꢄnez-Dꢄaz, A. de la Escosura,
T. Torres, T. D. Ros, M. Prato, Chem. Commun. 2002, 2774; b) F. J.
Cꢀspedes-Guirao, F. Fernꢁndez-Lꢁzaro, L. Martꢄn-Gomis, ꢂ. Sastre-
Santos, J. Porphyrins Phthalocyanines 2009, 13, 266.
[39] K. Ogawa, Y. Kobuke, Angew. Chem. 2000, 112, 4236; Angew.
Chem. Int. Ed. 2000, 39, 4070.
[40] R. Takahashi, Y. Kobuke, J. Am. Chem. Soc. 2003, 125, 2372.
[41] H. Ozeki, A. Nomoto, K. Ogawa, Y. Kobuke, M. Murakami, K.
Hosoda, M. Ohtani, S. Nakashima, H. Miyasaka, T. Okada, Chem.
Eur. J. 2004, 10, 6393.
[42] K. Kameyama, M. Morisue, A. Satake, Y. Kobuke, Angew. Chem.
2005, 117, 4841; Angew. Chem. Int. Ed. 2005, 44, 4763.
[55] K. A. Nielsen, G. H. Sarova, L. Martꢄn-Gomis, P. C. Stein, L. Sangui-
net, E. Levillain, J. L. Sessler, D. M. Guldi, F. Fernꢁndez-Lꢁzaro, ꢂ.
Sastre-Santos, J. O. Jeppesen, J. Am. Chem. Soc. 2008, 130, 460.
[56] A. Berg, Z. Shuali, M. Asano-Someda, H. Levanon, M. Fuhs, K.
Mobius, R. Wang, C. Brown, J. L. Sessler, J. Am. Chem. Soc. 1999,
121, 7433.
[57] A. J. Myles, N. R. Branda, J. Am. Chem. Soc. 2001, 123, 177.
[58] H. A. Benesi, J. H. Hildebrand, J. Am. Chem. Soc. 1949, 71, 2703.
[59] W. Seitz, A. J. Jimꢀnez, E. Carbonell, B. Grimm, M. S. Rodrꢄguez-
Morgade, D. M. Guldi, T. Torres, Chem. Commun. 2010, 46, 137.
[60] G. Bottari, G. de la Torre, D. M. Guldi, T. Torres, Chem. Rev. 2010,
110, 6768–6816.
[61] Gaussian 03 (Revision C.02), M. J. Frisch, G. W. Trucks, H. B. Schle-
gel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, J. A. Montgom-
ery, Jr., T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S.
Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani,
N. Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,
O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian,
J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E.
Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W.
Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J.
Dannenberg, V. G. Zakrzewski, S. Dapprich, A. D. Daniels, M. C.
Strain, O. Farkas, D. K. Malick, A. D. Rabuck, K. Raghavachari,
J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J. Cio-
slowski, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaro-
mi, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng,
A. Nanayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W.
Chen, M. W. Wong, C. Gonzalez, J. A. Pople, Gaussian, Inc., Wall-
ingford CT, 2004.
[43] M. Morisue, Y. Kobuke, Chem. Eur. J. 2008, 14, 4993.
[44] R. Chitta, A. S. D. Sandanayaka, A. L. Schumacher, L. D’Souza, Y.
Araki, O. Ito, F. D’Souza, J. Phys. Chem. C 2007, 111, 6947.
[45] F. D’Souza, P. M. Smith, M. E. Zandler, A. L. McCarty, M. Itou, Y.
Araki, O. Ito, J. Am. Chem. Soc. 2004, 126, 7898.
[46] F. D’Souza, O. Ito, Coord. Chem. Rev. 2005, 249, 1410.
[47] M. E. El-Khouly, L. M. Rogers, M. E. Zandler, G. Suresh, M. Fujit-
suka, O. Ito, F. D’Souza, ChemPhysChem 2003, 4, 474.
[62] GaussView, Version 3.09, Semichem, Inc., Shawnee Mission, KS,
2003.
[48] F. Würthner, C. Thalacker, A. Sautter, W. Schärtl, W. Ibach, O. Holl-
richer, Chem. Eur. J. 2000, 6, 3871.
[49] F. Würthner, A. Sautter, J. Schilling, J. Org. Chem. 2002, 67, 3037.
[50] H. Xu, D. K. P. Ng, Inorg. Chem. 2008, 47, 7921.
Received: March 16, 2011
Published online: August 29, 2011
Chem. Asian J. 2011, 6, 3110 – 3121
ꢅ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
3121