Charge-transfer state and large first hyperpolarizability constant in a highly electronically coupled zinc and gold porphyrin dyad

Article abstract of DOI:10.1002/chem.200900262

We report the synthesis and the characterizations of a novel dyad composed of a zinc porphyrin (ZnP) linked to a gold porphyrin (AuP) through an ethynyl spacer. The UV/Vis absorption spectrum and the electrochemical properties clearly reveal that this dya

Full text of DOI:10.1002/chem.200900262

DOI: 10.1002/chem.200900262
Charge-Transfer State and Large First Hyperpolarizability Constant in a
Highly Electronically Coupled Zinc and Gold Porphyrin Dyad
Jꢀrꢁme Fortage,[a] Annabelle Scarpaci,[a] Lydie Viau,[a] Yann Pellegrin,[a] Errol Blart,[a]
Magnus Falkenstrçm,[b] Leif Hammarstrçm,*[b] Inge Asselberghs,[c] Ruben Kellens,[c]
Wim Libaers,[c] Koen Clays,*[c] Mattias P. Eng,*[d] and Fabrice Odobel*[a]
Abstract: We report the synthesis and
the characterizations of a novel dyad
composed of a zinc porphyrin (ZnP)
taken to determine the spectra of the
reduced and oxidized porphyrin units.
DFT quantum-chemical calculations.
This theoretical study confirms that the
observed intense band at l=739 nm
corresponds to an interporphyrin
charge-transfer transition from the
HOMO orbital localized on the zinc
porphyrin to LUMO orbitals localized
Femtosecond
transient
absorption
linked to
a
gold porphyrin (AuP)
spectroscopic analysis showed that the
photoexcitation of the heterometallic
through an ethynyl spacer. The UV/Vis
absorption spectrum and the electro-
chemical properties clearly reveal that
this dyad exhibits a strong electronic
coupling in the ground state as evi-
denced by shifted redox potentials and
the appearance of an intense charge-
transfer band localized at l=739 nm in
dyad leads to an ultrafast formation of
+
C
a charge-separated state ( ZnP–AuP )
that displays a particularly long lifetime
(t=4 ns in toluene) for such a short
separation distance. The molecular or-
bitals of the dyad were determined by
on the gold porphyrin. Finally, a
Hyper–Rayleigh scattering study shows
that the dyad possesses a large first
molecular hyperpolarizability coeffi-
cient (b=2100ꢀ10ꢀ30 esu at l=
1064 nm), thus highlighting the valua-
ble nonlinear optical properties of this
new type of push–pull porphyrin
system.
dichloromethane.
A
spectroelectro-
Keywords: charge
transfer
·
chemical study of the dyad along with
the parent homometallic system (i.e.,
ZnP–ZnP and AuP–AuP) was under-
fluorescence · nonlinear optics ·
photochemistry · porphyrinoids
Introduction
archetypal molecules used as chromophores for quadratic
hyperpolarizability and they have been found to exhibit
two- or three-photon absorption cross-sections, which is also
another useful property for optical limiting and fluorescence
imaging.[12–20] Additionally, the intramolecular charge-trans-
fer interactions generally found in such molecules render
them promising candidates to harvest photons of the solar
spectrum and to convert them into useful potentials (elec-
The development of highly conjugated donor/p-conjugated
acceptor molecular systems (D/p–A) is of particular interest
due to their unusual photophysical properties that can make
them particularly valuable for applications in molecular
electronics,[1–3] nonlinear optics,[4–7] and solar-energy transfor-
mations.[8–11] Electronically coupled D/p–A systems are the
[a] Dr. J. Fortage, Dr. A. Scarpaci, Dr. L. Viau, Dr. Y. Pellegrin,
Dr. E. Blart, Dr. F. Odobel
[c] I. Asselberghs, Dr. R. Kellens, Dr. W. Libaers, Prof. K. Clays
Department of Chemistry
University of Nantes, CEISAM
University of Leuven, Celestijnenlaan 200D
3001 Leuven (Belgium)
E-mail: koen.clays@fys.kuleuven.be
Chimie et Interdisciplinaritꢁ, Synthꢂse, Analyse, Modꢁlisation
Facultꢁ des Sciences et des Techniques
2, rue de la Houssiniꢂre
BP 92208, 44322 Nantes Cedex 3 (France)
E-mail: fabrice.odobel@univ-nantes.fr
[d] Dr. M. P. Eng
Department of Chemistry
Imperial College London
[b] Dr. M. Falkenstrçm, Prof. L. Hammarstrçm
Department of Photochemistry and Molecular Science
The ꢃngstrçm Laboratories, Uppsala University
Regementsvꢄgen 1, 752 37 Uppsala (Sweden)
E-mail: leif.hammarstrom@fotomol.uu.se
Exhibition Road, London, SW7 2AZ (UK)
E-mail: m.eng@imperial.ac.uk
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FULL PAPER
tricity or chemical fuels). For
examples, push–pull organic
sensitizers have been proved to
be particularly efficient com-
pounds in dye-sensitized solar
cells.[21–26] Alkynyl porphyrin
units have been the focus of in-
tensive
investigations
by
Arnold,[27–31] Anderson,[12,13,32–45]
Therien,[6,7,11,46–54] Osuka,[35,36,55,56]
and others.[57–65,68] Their peculiar
electronic properties generally
arise from the large electronic
interactions due to the extensive
p-electronic conjugation be-
tween triply bonded pigments.
Porphyrin heterodyads that ex-
hibit optical intramolecular elec-
tron transfer are, however,
scarce in spite of the abundance
of investigations for many types
of applications.[66] Herein, we de-
scribe the synthesis of a new het-
erometallic bisporphyrin that
presents a large first molecular
hyperpolarizability coefficient b
and
a
strong intramolecular
charge-transfer transition in the
visible spectrum that leads to a
charge-separated state that lives
for 4 ns in toluene at room tem-
perature. Zinc and gold porphy-
rin units were chosen because
they display electron-donating
and -accepting properties, re-
spectively, thus making this
couple of photoactive species an
interesting system for the con-
struction of a strongly polarized
chromophore that exhibits po-
Scheme 1. Preparation of the electronically coupled dyads 1–3. a) Trimethylsilylacetylene, CuI, [Pd
Et3N, THF, 308C (47%); b) K2CO3, CH2Cl2, MeOH (92%); c) 6 (1.5 equiv), 7 (1 equiv), CuI, [Pd
Et3N, DMF, 458C (73%); d) CuI, [Pd2A(dba)3]·CHCl3, Et3N, THF, 408C (41%); e) [Pd(PPh3)4], CuI, DMF,
1108C (52%). dba=dibenzylideneacetone, dppf=bis(diphenylphosphino)ferrocene, TMS=trimethylsilyl.
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
N
ACHTUNGTRENNUNG
tentially valuable photochemical properties. The new hetero-
metallic dyad 1 was thus prepared and its comprehensive pho-
tophysical properties are presented.
ACHTUNGTRNE(NGNU dppf)Cl2] and copper iodide because good yields for the
formation of other compounds containing the gold porphy-
rin was obtained as observed before.[68] Homometallic dimer
2 was prepared by coupling 4 with 6 under conditions re-
ported before for similar compounds.[62] The preparation of
dyad 3 gave us more difficulties than expected. We started
with the demetallation of 2 to obtain the free-base porphy-
rin, but we failed to achieve the bis-metallation of the latter
with gold. The classical conditions (i.e., KAuCl4 in AcOH in
presence of AcONa)[69] or milder conditions developed by
Chambron et al.[70] did not afford the expected bis-gold por-
phyrin 3, but only the monometallated species along with
some degraded compounds. Gratifyingly, dyad 3 could be
prepared by using a Stille cross-coupling reaction between
the commercially available bis(trimethylstannyl)acetylene
and gold porphyrin 7 under the classical conditions (i.e.,
Results and Discussion
Synthesis: The preparation of heterometallic dyad 1 and ho-
mometallic bis-zinc 2 and bis-gold 3 reference compounds is
shown in Scheme 1. The iodo trisaryl porphyrin 4 was first
subjected to a Sonogashira cross-coupling reaction with tri-
methylsilylacetylene under the Lindsey conditions[67] to give
5. The trimethylsilyl group was subsequently cleaved with
potassium carbonate. The next step was a Sonogashira
cross-coupling reaction between porphyrin 7,[68] which is an
equimolar mixture of bromo- and chloroporphyrin units,
and porphyrin 6. This coupling was catalyzed by [Pd-
[PdACHTNUTGRNEUNG
(PPh3)4] and CuI in DMF).[32]
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F. Odobel, L. Hammarstrçm, K. Clays, M. P. Eng et al.
UV/Vis absorption spectra: The UV/Vis electronic spectra
of dyad 1 and the parent homometallic dimers 2 and 3 are
represented in Figure 1 and the spectroscopic data gathered
in Table 1. The spectra of the reference homometallic dyads
units has been reported but leads to an intermolecular tran-
sition at much higher energy (around l=600 nm).[72] Anoth-
er piece of evidence of the charge-transfer nature of the ab-
sorption band at around l=740 nm for dyad 1 comes from
the marked solvatochromism observed for this transition.
The maximum absorbance of this transition is progressively
red shifted when we pass from toluene (l=699 nm; n˜ =
14306 cmꢀ1)
to
dichloromethane
(l=739 nm;
n˜ =
13532 cmꢀ1) and to DMF (l=758 nm; n˜ =13193 cmꢀ1), a
net total red shift of dl=59 nm or dn˜ =1113 cmꢀ1. This
bathochromic shift, when the polarity of the solvent increas-
es (“positive solvatochromism”), indicates that the excited
state is stabilized by a polar solvent due to its larger dipole
moment relative to the ground state. The positive solvato-
chromism may be surprising in view of the formally charge-
shift nature of the transition, for which the band maximum
would instead increase in energy with increasing solvent re-
organization energy.[73,74] We propose that this apparent con-
tradiction may be explained by the fact that the ground
state of AuP+ may be partially ion paired with its counter-
anion, at least in the less polar solvents, which would give a
more charge-transfer character and thus a positive solvato-
chromism.
Figure 1. UV/Vis absorption spectra of dyad 1 (solid line) and the refer-
ence bis(zinc–porphyrin)
2 (dotted line) and bis(gold–porphyrin) 3
(dashed line) recorded in dichloromethane.
Table 1. Spectroscopic and electrochemical data of the dyads recorded in
dichloromethane.[a]
As has been carried out before for other donor/acceptor
compounds that exhibit a charge-transfer transition, we esti-
Dyad lmax [nm] (e [mꢀ1 cmꢀ1])
E1/2 (red) E1/2 (Ox)
[52,75,76]
mated the magnitude of the electronic coupling VAB
[V]
[V]
based on the Mulliken–Hush theory [Eq. (1)]:[77]
1
425 (2.4ꢀ105), 454 (1.4ꢀ105),
ꢀ0.57,
ꢀ1.07
0.81,
1.16
515
565
ACHTUNGTRENNUNG
(2.9ꢀ104),
1=2
VAB ¼ 2:06 ꢁ 10ꢀ2 ðemaxnmaxDn=
1
Þ
ðRccÞꢀ1
ACHTUNGTRENNUNG
(1.4ꢀ104), 739 (3.5ꢀ104)
ð1Þ
2
2
3
413 (1.2ꢀ105), 431 (1.1ꢀ105), 443 (8.8ꢀ104),
480 (2.2ꢀ105), 550 (1.5ꢀ104), 695 (4.6ꢀ104)
0.57,
0.77
where emax is the molar extinction coefficient (mꢀ1 cmꢀ1), nmax
417 (2.2ꢀ105), 461 (1.9ꢀ105), 533 (3.2ꢀ104), ꢀ0.38,
ꢀ1
1
the energy (cm ) of the charge-transfer absorption, Dn = the
624 (4.3ꢀ104)
ꢀ0.54
2
bandwidth at half-maximum (cmꢀ1), and Rcc the center-to-
[a] All the potentials are referenced versus SCE.
center separation distance between the donor and acceptor
(ꢃ). From the charge-transfer transition measured in di-
chloromethane, the following values can be deduced: emax
=
ꢀ1
34700mꢀ1 cmꢀ1, nmax =13530 cmꢀ1, Dn = =2270 cm , and
1
2 and 3 exhibit the usual red-shifted Q-bands located at l=
695 and 624 nm for the zinc and gold porphyrin units, re-
spectively, and a broad split Soret band. These features are
in agreement with previously described homometallic zinc
porphyrin arrays linked by an ethynyl linker.[39,49,62] The
clear Soret band split in the reference dyads 2 and 3 can be
attributed to excitonic coupling between the two parallel
strong dipolar transitions of each porphyrin along the acety-
lene axis with close energy levels.[46,55,71]
The spectrum of the heterometallic dyad 1 differs signifi-
cantly from those of homometallic dyads 2 and 3 because its
spectrum is clearly not a linear combination of the spectra
of 2 and 3. The Soret band split is not observed in 1 because
of the energy mismatch between the porphyrin units. More-
over, it exhibits a new absorption band at l=739 nm, which
is characteristic of neither the zinc dimer 2 nor the gold
dimer 3. We assigned this transition to an intramolecular
charge-transfer band, which is the consequence of the strong
through-bond electronic interactions between ZnP and
AuP+ through the ethynyl linkage (see below). The forma-
tion of heteroaggregates between zinc and gold porphyrin
2
Rcc =11.3 ꢃ[44]; thus, the electronic coupling can be calculat-
ed to be VAB =1880 cmꢀ1. In comparison with other cova-
lently linked ZnP/AuP+ dyads,[68,78–80] this value is signifi-
cantly larger and indicates that the ethynyl group promotes
a very strong electronic communication between the two
porphyrin units due to effective mixing of the frontier mo-
lecular orbitals of each unit.
The strong coupling suggests that the system could be
close to the limit between a “localized” and “delocalized”
description (classes II and III, respectively, in the mixed-va-
lence terminology[81]), with the limit given by the condition
lꢂ2VAB (l is, herein, the reorganization energy). We note,
however, that the inherent asymmetry in the redox proper-
ties of ZnP and AuP+ would, even at the strong coupling
limit, give a ground-state energy minimum with a character
of mainly ZnP/AuP+ (1), as opposed to a strong admixture
of the biradical state. A detailed analysis of the charge-
transfer parameters from the absorption band is beyond the
scope of this report. We also note that the straightforward
evaluation of the driving force and reorganization energy is
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Photophysical Investigation of a Zinc–Porphyrin/Gold–Porphyrin Dyad
FULL PAPER
only possible for a weakly coupled system in which l>
2VAB
.
Electrochemistry and spectroelectrochemistry: The redox
properties of the zinc and gold porphyrin units in dyads 1–3
were examined by cyclic voltammetry and differential pulse
voltammetry in dichloromethane (Table 1). Interestingly, the
oxidation of the two zinc porphyrin units in 2 and the reduc-
tion of the two gold porphyrin units in 3 do not coalesce in
a single bielectronic wave but they appear as two stepwise
processes that occur at different potentials due to the strong
electronic coupling (Table 1). The two first oxidation poten-
tials of ZnP in dyad 2 and the two first reduction potentials
of AuP+ in dyad 3 are separated by 200 and 160 mV, respec-
tively. From these values, the comproportionation constant
Kc can be calculated by using the classical equation[76,81]
[Eq. (2)]:
Figure 2. Transient spectra recorded upon one-electron oxidation of dyad
2 in dichloromethane. The arrows indicate the changes upon oxidation.
The bold traces indicate the initial and final spectra.
DE1=2 ¼ 0:059 log Kc
ð2Þ
tion dipole perpendicular to the linkage. The new absorp-
tion at l=890 nm is probably an intramolecular charge-
transfer transition (mixed-valence compound) with the
nearby zinc porphyrin unit.
The spectrum of the monoradical of the gold porphyrin
unit in the homometallic dyad 3 is shown in Figure 3. The
reduction of AuP+ induces a collapse of the second Soret
The value of Kc is 2500 and 520mꢀ1 for dyads 2 and 3, re-
spectively, and gives an estimation of the stability of the
monoradical over the corresponding diradical (2ZnP–ZnP+
QZnP+–ZnP+ +ZnP–ZnP or 2AuP –AuP QAuP –AuP +
AuP+–AuP+) and it strongly depends on the electronic cou-
pling between the two linked units. Such large compropor-
tionation constants mean that the electronic interaction be-
tween the two porphyrin units is relatively high and that the
radical is relatively stable with respect to the dismutation re-
action.
+
C
C
C
If we compare the redox potentials of the heterometallic
dyad 1 with the homometallic dyads 2 and 3, we notice that
the oxidation potential of ZnP is anodically shifted by
240 mV and the reduction potential of AuP+ is cathodically
shifted by 190 mV. This outcome is certainly a consequence
of the adjacent porphyrin unit in the homometallic dyad un-
dergoing a stabilizing effect on the nearby radical (ZnP+ or
C
AuP ) with respect to the heterometallic dyad 1 and further
confirms the strong electronic interactions of the two por-
phyrin units.
Spectroelectrochemical experiments were undertaken to
elucidate the spectra of the radical cation of zinc porphyrin
and the radical of gold porphyrin in dyads 1–3. Note that all
these electrochemical processes were reversible because re-
versing the potential led us to retrieve almost entirely the
original spectrum. Besides, the observation of clean isosbes-
tic points supports the transformation of one species into an-
other without the occurrence of coupled chemical transfor-
mations (Figures 2–5). The spectrum of the radical cation of
ZnP in dyad 2 upon electrolysis in situ is shown in Figure 2.
The oxidation of ZnP is accompanied by a decrease in the
intensity of the lower-energy Soret transition and the Q-
band located at l=696 nm. This result confirms that the
former absorption (second Soret transition at l=480 nm)
corresponds to the excitonic coupling of the parallel transi-
tions aligned along the ethynyl linker axis, whereas the high-
energy Soret band (at l=413 nm) is assigned to the transi-
Figure 3. Transient spectra recorded upon one-electron reduction of dyad
3 in dichloromethane. The arrows indicate the changes upon oxidation.
The bold traces indicate the initial and final spectra.
band (at around l=460 nm) and a diminution of intensity
of the Q band, whereas a new absorption band grows at
around l=830 nm. The bleaching of the Soret and Q bands
is not as strong as with the oxidation of ZnP in dyad 2. Ac-
cordingly, we suggest that the site of reduction is probably
mostly metal centered with a contribution from the p-aro-
matic system of the porphyrin unit, as indicated by the dis-
tribution of the LUMO orbitals of this dyad (Table 2).[82]
The new absorption band at l=830 nm is also tentatively at-
tributed to an intramolecular charge-transfer transition as
proposed above for the monooxidized bis-zinc dimer (ZnP–
ZnP+).
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F. Odobel, L. Hammarstrçm, K. Clays, M. P. Eng et al.
during the reduction of AuP+,
Table 2. Calculated Kohn–Sham (KS) orbitals of the optimized structures of dyads 1–3.
but the changes are different
from those observed with the
oxidation of ZnP. This behavior
KS orbitals ZnP–AuP (1)
ZnP–ZnP (2)
AuP–AuP (3)
confirms the formation of
gold(II) species rather than a p-
a
LUMO+2
radical anion of the porphyrin.
Transient absorption spectros-
copy: The photophysical prop-
erties of dyad 1 were also inves-
tigated by transient absorption
spectroscopy. First, the fluores-
cence of the zinc porphyrin unit
in dyad 1 is completely extinct.
Excitation of 1 with an approxi-
mate 120-fs laser pulse in the
Soret or charge-transfer band
gave rise to an instant transient
absorption, which we attribute
LUMO+1
LUMO
to the charge-transfer state
HOMO
+
C
C
ZnP –AuP (Figure 6). In addi-
tion to bleaching of the Soret
band, there are positive absorp-
tion peaks around l=500 and
The oxidation of the zinc porphyrin in the heterometallic
dyad 1 is accompanied with a bleaching of the absorption
band at l=739 nm (Figure 4). This observation is in agree-
Figure 5. Transient spectra recorded upon one-electron reduction of dyad
1 in dichloromethane. The arrows indicate the changes upon reduction.
The bold traces indicate the initial and final spectra.
580 nm, which correspond to changes observed upon the re-
duction and oxidation of 1, respectively (Figures 4 and 5).
These transient spectra recorded in DMF and dichlorome-
thane are evolved within the instrumental time resolution
(<200 fs). Some further evolution is observed in toluene on
the 100-ps timescale (Figure 6).
No significant differences were observed between experi-
ments with the Soret and charge-transfer excitation, thus in-
dicating that the same charge-transfer state is formed within
200 fs by either photoinduced electron transfer or direct op-
tical electron transfer. The charge-transfer state recombined
completely to the ground state with single-exponential ki-
netics (<4% remaining signal), as illustrated by the Soret-
Figure 4. Transient spectra recorded upon one-electron oxidation of dyad
1 in dichloromethane. The arrows indicate the changes upon oxidation.
The bold traces indicate the initial and final spectra.
ment with the attribution of the charge-transfer nature of
this transition, which naturally disappears when the donor
part (upon oxidation of ZnP) or acceptor part (upon reduc-
tion of AuP+, see below) of dyad 1 is removed. The spec-
trum of the reduced gold porphyrin unit in dyad 1 is shown
in Figure 5. As expected, the intensity of the charge-transfer
band at l=739 nm is strongly affected by the reduction of
AuP+. Again, the Soret band is decreased in intensity
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Photophysical Investigation of a Zinc–Porphyrin/Gold–Porphyrin Dyad
FULL PAPER
Figure 7. Schematic representation of the free-energy surfaces for the
charge transfer and ground states. Left: no coupling; right: strong cou-
pling.
account for relativistic effects. To decrease the computation-
al cost, the tert-butyl groups were replaced by methyl
groups. Each dyad was first geometry optimized with C2
(dyad 1) or D2 (dyads 2 and 3) symmetry constraints by
using the B3LYP functional.[87–89] Full optimizations were
verified by frequency calculations that showed no virtual
frequencies. The optimizations resulted in slightly saddle-
shaped structures due to the steric interactions between the
porphyrin units.
Figure 6. a) Transient absorption spectra of ZnP–AuP (1) recorded after
350 fs (solid lines) and 200 ps (dashed lines); excitation at l=435 and
705 nm (upper and lower spectra, respectively). b) Transient absorption
traces at l=420 nm after excitation at l=435 nm of ZnP–AuP (1) in
DMF (circles), CH2Cl2 (squares), and toluene (triangles). The solid lines
show the corresponding traces after excitation at l=705 nm.
The optimized structures were used for time-dependent
DFT (TD-DFT) calculations of the vertical excited states by
using the same functional and basis sets as for the geometry
optimizations.[90–92] The solvent effects of dichlorobenzene
were approximated by using the nonequilibrium version[93]
of the polarizable conductor calculation model CPCM.[94,95]
All the calculations were performed using the Gaussian03
software suite.[95] For simulation of the absorption spectra,
each transition was approximated by a Gaussian peak with a
bandwidth of 1500 cmꢀ1 and the area of each peak was set
to that of the calculated oscillator strength f.
Table 2 shows the KS orbitals of 1–3. It can be seen that
in the symmetric compounds (i.e., 2 and 3) all the orbitals
are equally distributed over the two porphyrin units. In
these compounds, no transitions with a net charge transfer
are possible from the ground state. On the other hand, there
is a clear separation in 1 into orbitals localized mainly on
either the zinc or gold porphyrin moieties. If the electronic
coupling between the two moieties is sufficient, this arrange-
ment should give rise to a set of transitions with a net
charge transfer. The calculated properties of the lowest tran-
sition with a considerable contribution to the absorptions
spectra for each compound and the experimental wave-
lengths for these transitions are compiled in Table 3.
Figure 8 shows the simulated absorption spectra of 1–3. On
comparison of Figures 8 and 1, it can be seen that the calcu-
lations give a fairly good description of the experimental ab-
sorption spectra. It can, thus, be concluded from Tables 2
and 3 that the calculations support that the lowest transition
observed in the absorption spectrum of dyad 1 is a charge-
transfer transition. The energy of this transition is a bit un-
derestimated, as is often the case for charge-transfer bands
calculated with DFT.[96]
band bleach recovery in Figure 6 (right panel). No evidence
of long-lived local porphyrin triplet states formed in the re-
combination process was seen. The lifetime of the charge-
transfer state increased with decreasing solvent polarity
from 200 ps in DMF to 1 ns in dichloromethane and 4 ns in
toluene. This behavior is expected for recombination in the
Marcus inverted region, in which the driving force is larger
than the reorganization energy [ꢀDG0 >l; Eq. (3)]. From
the electrochemical data, the charge-transfer state should lie
approximately 1.4 eV above the ground state in dichlorome-
thane, and the value of l in this type of system should be
smaller than that. The energy of the charge-transfer state in-
creases and the l value decreases in low-polarity solvents,
which increases the barrier to recombination and thus the
charge-transfer lifetime, in agreement with our observations.
2
kET ¼ A exp½ꢀðDG0 þ lÞ =4 lRTꢃ
ð3Þ
It may be surprising that this strongly coupled system
leads to a similar or even longer lifetime of the charge-sepa-
rated state relative to more weakly coupled hetero zinc–
gold porphyrin dyads reported previously, in which the two
porphyrin units were separated by a longer distance.[27,39]
However, a strong coupling induces an avoided crossing be-
tween the charge-transfer and ground-state surfaces
(Figure 7), and the Frank–Condon factors for the recombi-
nation becomes small. The situation is then similar to the
case of nonradiative decay of a rigid fluorophore.[38]
Quantum-chemical calculations: To gain deeper insight into
the nature of the excited states of 1–3, a set of DFT calcula-
tions were performed. For all atoms except gold, the 6-
31G(d) basis set was used.[83] For the gold centers, the
LanL2DZ basis set was used,[84–86] in which the core elec-
trons are replaced with an effective core potential (ECP) to
A recent, combined experimental and computational
study of gold
that the LUMO of gold
The study concluded that this orbital introduces a number
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
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F. Odobel, L. Hammarstrçm, K. Clays, M. P. Eng et al.
Table 3. The calculated and experimental wavelengths l and calculated
oscillator strengths f of the lowest transitions that significantly contribute
to the absorption spectra for compounds 1–3.
performed HRS at l=800 and 1064 nm. Although the latter
wavelength is provided by nanosecond pulsed lasers,[100] the
former wavelength is the output of a femtosecond pulsed
laser that additionally allows for discrimination between po-
tential multiphoton fluorescence and nonlinear scatter-
ing.[101,102] We analyzed the HRS signal toward a single
major dipolar hyperpolarizability tensor component bzzz, in
which the z axis is the molecular charge-transfer axis.
Table 4 gives the results of this analysis and the largest hy-
perpolarizability value from a porphyrin derivative calculat-
ed by Therien and co-workers.[50] Please note that the latter
are elaborate push–pull chromophores with moieties that by
themselves already exhibit nonlinear optical properties.
The first hyperpolarizability of dyad 1 is very large. The
large second-order nonlinearity is a direct consequence of
the strong charge-transfer interaction through this linkage.
The dispersion of the first hyperpolarizability for porphyrin-
based charge-transfer molecules is quite unusual.[50,53] There-
fore, it is difficult to relate structure to property in a fully
quantitative way at all the measurement wavelengths. The
dispersion has been related to the two contributions (from
the Soret and Q bands) to the nonlinear response. A much
stronger effect can be expected from the one-photon reso-
nance enhancement at l=800 nm caused by the charge-
transfer band at l=740 nm in dyad 1. This effect explains
the large hyperpolarizability value at l=800 nm. A full
quantitative analysis of the combined effect of conjugation
and dispersion on the value of the first hyperpolarizability
for porphyrin derivatives or dyads is beyond the present
level of understanding.[50,53]
Dyad
lcalcd [nm] lexp [nm]
f
Dominant configurations
ZnP–AuP (1) 791
739
1.2 HOMO!LUMO (15%)
HOMO!LUMO+1 (73%)
1.3 HOMO!LUMO (86%)
1.1 HOMO!LUMO (48%)
HOMO!LUMO+2 (39%)
ZnP–ZnP (2) 682
AuP–AuP (3) 652
695
625
Figure 8. The simulated absorption spectra of dyads 1 (solid line), 2
(dotted line), and 3 (dashed line).
of states that does not show in the absorption spectrum but
strongly dictates the excited-state dynamics. In the present
case, this orbital indeed takes part in the ground-state pho-
tophysics (Tables 2 and 3). This behavior is due to symmetry
breaking induced by the saddle-shaped structures and por-
phyrin–porphyrin interactions.
Conclusion
We have reported the preparation of a new heterometallic
bisporphyrin system that displays a strong electronic cou-
pling with an intense charge-transfer transition that yields to
a relatively long-lived charge-separated state. Furthermore,
this ZnP–AuP dyad exhibits interesting nonlinear optical
properties that manifest by a particularly large first hyperpo-
larizability coefficient. The dispersion of the first hyperpo-
larizability value could be explained in terms of resonance
enhancement caused by the spectral position of the charge-
transfer band. The femtosecond
Quadratic hyperpolarizability: In addition, we studied the
second-order nonlinear optical properties of dyad 1. Be-
cause of the charged nature of this compound, Hyper–Ray-
leigh Scattering (HRS)[98,99] was used to assess the first hy-
perpolarizability (second-order nonlinear polarizability) in
solution. Because the dispersion (wavelength dependence)
of this molecular parameter for porphyrin-based chromo-
phores has been previously described as unusual,[50,53] we
transient absorption spectrosco-
py study revealed that light ex-
citation of the dyad either in
Table 4. Nonlinear optical data measured in dichloromethane.[a]
Compound
bzzz (l=800 nm)
[10ꢀ30 esu]
bzzz (l=1064 nm)
the Soret or charge-transfer
transition leads to the immedi-
ate formation of the charge-
separated state, the lifetime of
which is particularly long if one
refers to other zinc–gold por-
phyrin dyads separated by a
long spacer.[68] This new elec-
tronically coupled heterometal-
lic bisporphyrin species repre-
[10ꢀ30 esu]
1
3800ꢄ300
2100ꢄ300
5000[a]
[a] Data is taken from ref. [6].
9064
www.chemeurj.org
ꢅ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 9058 – 9067

Photophysical Investigation of a Zinc–Porphyrin/Gold–Porphyrin Dyad
FULL PAPER
Hphenyl), 8.93 (dd, 3J=4.5, 3J=14.1 Hz, 4H; Hb), 9.06 (d, 3J=4.8 Hz, 2H;
Hb), 9.69 ppm (d, 3J=4.8 Hz, 2H; Hb); MALDI-TOF: m/z: calcd for
C56H56N4Zn: 848.38 [M+]; found: 848.58.
sents a valuable system to be used for molecular electronics,
solar-energy conversion, or nonlinear optical applications.
Dyad 1: Zinc(II) 5,15-bis-(3,5-di-tert-butylphenyl)-10-phenyl-20-ethynyl-
porphyrin (78 mg, 0.92 mmol), an equimolar mixture of gold
bis-(3,5-di-tert-butylphenyl)-10-phenyl-20-bromoporphyrin and gold
5,15-bis-(3,5-di-tert-butylphenyl)-10-phenyl-20-chloroporphyrin (81 mg,
0.61 mmol), copper iodide (2.3 mg, 0.12 mmol), [Pd(dppf)Cl2] (9.2 mg,
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
Experimental Section
AHCTUNGTRENNUNG
General methods: The 1H and 13C NMR spectra were recorded on a
0.12 mmol), distilled DMF (4 mL), and distilled Et3N (0.6 mL) were
placed in a sealed tube. The mixture was degassed, protected from light,
and heated at 458C overnight. Dichloromethane was added to the crude
mixture. The organic phase was washed three times, dried over MgSO4,
and concentrated to dryness. The solid was purified by column chroma-
tography on silica gel (CH2Cl2), thus affording a dark-green solid (95 mg,
73%). 1H NMR (400 MHz, C6D6, 658C): d=1.57 (s, 72H; HtBu), 7.49–
7.54 (m, 6H; Hphenyl), 8.05 (m, 2H; Hpara), 8.08 (m, 2H; Hphenyl), 8.10 (m,
2H; Hpara), 8.20–8.21 (m, 2H; Hphenyl), 8.35 (m, 4H; Hortho), 8.42 (m, 4H;
Hortho), 8.94 (m, 2H; Hb), 8.98 (m, 2H; Hb), 9.12 (m, 2H; Hb), 9.15 (m,
4H; Hb), 9.23 (m, 2H; Hb), 9.42 (m, 2H; Hb), 9.49 ppm (m, 2H; Hb); ele-
mental analysis calcd (%) for C110H110AuN8ZnPF6·8.5MeOH: C 64.0, H
6.5, N 5.0; found: C 64.5, H 6.2, N 4.5; UV/Vis (CH2Cl2): lmax (e)=425
(240000), 454 (140000), 515 (29000), 565 (14000), 739 nm
Bruker 300 MHz or AMX 400 MHz Bruker spectrometer. Chemical
shifts for the H NMR spectra are referenced relative to residual protium
1
in the deuterated solvent (d=7.26 and 7.16 ppm in CDCl3 and C6D6, re-
spectively). The mass spectra were recorded on a EI-MS HP 5989 A
spectrometer or a JMS-700 double-focusing mass spectrometer of re-
versed geometry equipped with an electrospray ionization (ESI) source
(JEOL LTD, Akishima, Tokyo, Japan). Fast-atom bombardment mass
spectrometry (FAB-MS) analyses were performed in a meta-nitrobenzyl-
ACHTUNGTRENNUNGalcohol matrix (MBA) on a ZAB-HF-FAB spectrometer. MALDI-TOF
analyses were performed on an Applied Biosystems Voyager DE-STR
spectrometer positive linear mode with an acceleration voltage 20 kV and
a-cyano-4-hydroxycinnamic acid (CHCA) as the matrix. Electrochemical
measurements were realized with an Autolab PGSTAT 302N potentio-
stat. A heart-shaped electrochemical cell equipped with a platinum-disk
working electrode, a steel-gauze auxiliary electrode, a SCE reference
electrode, and an argon inlet was used for cyclic and square-wave voltam-
metry. Spectroelectrochemical measurements were carried out with an
optically transparent thin-layer electrochemical (OTTLE) cell fitted in
the cavity of a Shimadzu UV2501-PC spectrophotometer with a platinum
grid as the working electrode.
(35000 molꢀ1 dm3 cmꢀ1);
HR-MALDI-TOF:
m/z:
calcd
for
C110H110AuN8Zn: 1803.7796 [MꢀPF6]+; found: 1803.7805.
Dyad 2: Zinc(II) 5,15-bis-(3,5-di-tert-butylphenyl)-10-phenyl-20-ethynyl-
porphyrin (27 mg, 0.030 mmol), zinc(II) 5,15-bis-(3,5-di-tert-butylphenyl)-
10-phenyl-20-bromoporphyrin (31 mg, 0.034 mmol), triphenylarsine
(12 mg, 0.039 mmol), [Pd2ACTHNUGTRNEUNG(dba)3]·CHCl3 (5 mg, 0.005 mmol), distilled
THF (3.3 mL), and distilled Et3N (0.7 mL) were placed in a sealed tube.
The reaction mixture was degassed, protected from light, and heated at
408C for 4 h. The solvents were evaporated and the crude solid was puri-
fied by column chromatography on silica gel (petroleum ether/THF
Preparative TLC analysis was performed with on Merk Kieselgel 60PF254
plates. Column chromatography was carried out with Merk 5735 Kiesel-
gel 60F (0.040–0.063-mm mesh). Air-sensitive reactions were carried out
under argon in dry solvents and glassware. Chemicals were purchased
from Aldrich and used as received. Compounds zinc(II)-5,15-bis-(3,5-di-
99:1), thus affording
a
dark-green solid (21 mg, 41%). 1H NMR
(400 MHz, CDCl3): d=1.57 (s, 72H; HtBu), 7.76 (m, 2H; Hphenyl), 7.77 (m,
4H; Hphenyl), 7.84 (m, 4H; Hpara), 8.16 (m, 8H; Hortho), 8.22 (m, 4H;
Hphenyl), 8.90 (m, 4H; Hb), 8.96 (m, 4H; Hb), 9.24 (m, 4H; Hb), 10.50 ppm
tert-butylphenyl)-10-phenyl-20-iodoporphyrin (4) and goldACTHNUTRGNE(UNG III)-5,15-bis-
(3,5-di-tert-butylphenyl)-10-phenyl-20-bromoporphyrin (7) were prepared
according to previously reported methods.[68]
(m,
4H;
Hb);
elemental
analysis
calcd
(%)
for
Hyper–Rayleigh light scattering (HRS) measurements: The experimental
setup for the HRS experiments has been described in detail else-
where.[100–102]
C110H110N8Zn2·1.5CHCl3·2.5THF: C 71.7, H 6.5, N 5.5; found: C 72.1, H
6.1, N 5.2; UV/Vis (CH2Cl2): lmax (e)=413 (120000), 431 (1150000), 443
(88000), 480 (220000), 550 (15000), 695 nm (46000 molꢀ1 dm3 cmꢀ1); HR-
MALDI-TOF: m/z: calcd for C110H110N8Zn2: 1670.7431 [M+]; found:
1670.7439.
Zinc(II) 5,15-bis-(3,5-di-tert-butylphenyl)-10-phenyl-20-(trimethylsilyle-
thynyl)porphyrin
(5):
Zinc(II)-5,15-bis-(3,5-di-tert-butylphenyl)-10-
phenyl-20-iodoporphyrin (4; 146 mg, 0.15 mmol), distilled Et3N (1.5 mL),
distilled THF (5 mL), copper iodide (1.5 mg, 7.67 mmol), and [Pd-
ACHTUNGTRENNUNG(PPh3)2Cl2] (5.4 mg, 7.67 mmol) were placed in a sealed tube, and the mix-
Dyad 3: Gold
porphyrin (60 mg, 0.051 mmol), copper iodide (3 mg, 0.017 mmol), [Pd-
AHCTUNTGREGUN(NN PPh3)4] (10 mg, 0.0085 mmol), and distilled DMF (3 mL) were placed in
ACHTUNGERTN(NUNG III) 5,15-bis-(3,5-di-tert-butylphenyl)-10-phenyl-20-bromo-
ture was degassed through several freeze/thaw cycles. Trimethylsilylacety-
lene (65 mL, 0.46 mmol, d=0.69) was added to the reaction mixture,
which was stirred for 15 h at 358C under argon. The solvents were re-
moved under vacuum and dichloromethane was added. The organic
phase was washed with water and the aqueous phase was extracted with
dichloromethane. The organic phases were collected, dried over MgSO4,
and concentrated to dryness. The crude mixture was purified by column
chromatography on silica gel (petroleum ether/CH2Cl2 8:2), thus afford-
ing a purple solid (66 mg, 47%). 1H NMR (300 MHz, CDCl3, 258C): d=
0.65 (s, 9H; HTMS), 1.58 (s, 36H; HtBu), 7.75 (m, 3H; Hphenyl), 7.85 (s, 2H;
Hpara), 8.11 (s, 4H; Hortho), 8.20 (m, 2H; Hphenyl), 8.94 (dd, 3J=4.5, 3J=
16.8 Hz, 4H; Hb), 9.08 (d, 3J=4.8 Hz, 2H; Hb), 9.81 ppm (d, 3J=4.8 Hz,
2H; Hb); MALDI-TOF: m/z: calcd for C59H64N4SiZn: 920.4 [M+];
found: 920.4.
a sealed tube. The reaction mixture was degassed and bis(trimethylstan-
nyl)acetylene (9 mg, 0.025 mmol) was added. The sealed tube was pro-
tected from light and heated at 1108C for 12 h. Diethyl ether and KPF6
(100 mg) were added to the crude mixture. The organic phase was
washed three times with water, dried over MgSO4, and concentrated to
dryness. The solid was purified by column chromatography on silica gel
(dichloromethane/methanol 96:4), thus affording
a dark-green solid
(27 mg, 52%). 1H NMR (300 MHz, CDCl3): d=1.57 (s, 72H; HtBu), 7.8–
7.9 (m, 8H; Hphenyl), 8.16 (d, J=1.5 Hz, 8H; Hortho), 8.25 (m, 4H; Hphenyl),
9.25 (m, J=5.1 Hz, 4H; Hb), 9.31 (d, J=5.1 Hz, 4H; Hb), 9.60 (d, J=
4.8 Hz, 4H; Hb,), 10.70 ppm (d, J=4.8 Hz, 4H; Hb,); UV/Vis (CH2Cl2):
lmax (e)=417 (220000), 461 (190000), 533 (32000), 624 nm
(43000 molꢀ1 dm3 cmꢀ1);
HR-MALDI-TOF:
m/z:
calcd
for
C110H110Au2N8: 1936.8160 [M+]; found: 1936.8179.
Zinc(II) 5,15-bis-(3,5-di-tert-butylphenyl)-10-phenyl-20-ethynylporphyrin
(6): Zinc(II)-5,15-bis-(3,5-di-tert-butylphenyl)-10-phenyl-20-(trimethylsily-
lethynyl)porphyrin (5; 92 mg, 99.9 mmol) and K2CO3 (138 mg, 1.0 mmol)
were dissolved in a mixture of dichloromethane (1.5 mL) and methanol
(3 mL). The reaction mixture was protected from light and stirred for
3.5 h at 258C. Dichloromethane was added and the organic phase was
washed twice with water. The organic phase was dried over MgSO4 and
concentrated to dryness to yield a green solid (78 mg, 92%). 1H NMR
(300 MHz, CDCl3, 258C): d=1.57 (s, 36H; HtBu), 3.99 (s, 1H; Hethynyl),
7.74 (m, 3H; Hphenyl), 7.85 (s, 2H; Hpara), 8.11 (s, 4H; Hortho), 8.20 (m, 2H;
Acknowledgements
I.A. is a postdoctoral research fellow of the Fund for Scientific Research
Flanders (FWO). The authors acknowledge financial support from the
French Ministry of Research with the ACI “jeunes chercheurs” 4057 (fel-
lowship of J.F.) for ANR “PhotoCumElec” from the Fund for Scientific
Research Flanders (G.0312.08) and the Research Council of the Universi-
Chem. Eur. J. 2009, 15, 9058 – 9067
ꢅ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
9065

F. Odobel, L. Hammarstrçm, K. Clays, M. P. Eng et al.
ty of Leuven (GOA/2006/03). L.H. acknowledges support from the Swed-
ish Foundation for Strategic Research, the K&A Wallenberg Foundation,
and the Swedish Energy Agency. M.P.E. acknowledges the Knut and
Alice Wallenberg Foundation for funding.
[26] S. Kim, J. K. Lee, S. O. Kang, J. Ko, J. H. Yum, S. Fantacci, F.
De Angelis, D. Di Censo, M. K. Nazeeruddin, M. Graetzel, J. Am.
Chem. Soc. 2006, 128, 16701–16707.
[27] R. Stranger, J. E. McGrady, D. P. Arnold, I. Lane, G. A. Heath,
Inorg. Chem. 1996, 35, 7791–7797.
[28] D. P. Arnold, G. A. Heath, D. A. James, J. Porphyrins Phthalocya-
nines 1999, 3, 5–31.
[29] D. P. Arnold, G. A. Heath, J. Am. Chem. Soc. 1993, 115, 12197–
12198.
[1] K. Mꢆllen, G. Wegner, Electronic Materials: The oligomer Ap-
proach, Wiley-VCH, Weinheim, 1998.
[2] J. Park, N. Pasupathy Abhay, I. Goldsmith Jonas, C. Chang, Y.
Yaish, R. Petta Jason, M. Rinkoski, P. Sethna James, D. Abruna
Hector, L. McEuen Paul, C. Ralph Daniel, Nature 2002, 417, 722–
725.
[3] C. Joachim, J. K. Gimzewski, A. Aviram, Nature 2000, 408, 541–
548.
[4] L. R. Dalton, W. H. Steier, B. H. Robinson, C. Zhang, A. Ren, S.
Garner, A. Chen, T. Londergan, L. Irwin, B. Carlson, L. Fifield, G.
Phelan, C. Kincaid, J. Amend, A. Jen, J. Mater. Chem. 1999, 9,
1905–1920.
[5] Nonlinear Optical Properties of Organic Molecules and Crystals,
Vol. 2, (Eds.: D. S. Chemla, J. Zyss), Academic Press, Orlando,
1987.
[6] S. M. LeCours, H.-W. Guan, S. G. DiMagno, C. H. Wang, M. J.
Therien, J. Am. Chem. Soc. 1996, 118, 1504–1510.
[7] S. Priyadarshy, M. J. Therien, D. N. Beratan, J. Am. Chem. Soc.
1996, 118, 1497–1503.
[8] J. Jortner, M. Bixon, Electron Transfer-From Isolated Molecules to
Biomolecules, Wiley, New York, 1999.
[9] R. F. Kelley, M. J. Tauber, M. R. Wasielewski, Angew. Chem. 2006,
118, 8147–8150; Angew. Chem. Int. Ed. 2006, 45, 7979–7982.
[10] R. F. Kelley, M. J. Tauber, T. M. Wilson, M. R. Wasielewski, Chem.
Commun. 2007, 4407–4409.
[30] D. P. Arnold, L. J. Nitschinsk, Tetrahedron Lett. 1993, 34, 693–696.
[31] D. P. Arnold, R. D. Hartnell, Tetrahedron 2001, 57, 1335–1345.
[32] M. J. Frampton, H. Akdas, A. R. Cowley, J. E. Rogers, J. E. Slagle,
P. A. Fleitz, M. Drobizhev, A. Rebane, H. L. Anderson, Org. Lett.
2005, 7, 5365–5368.
[33] I. M. Blake, A. Krivokapic, M. Katterle, H. L. Anderson, Chem.
Commun. 2002, 1662–1663.
[34] T. E. O. Screen, I. M. Blake, L. H. Rees, W. Clegg, S. J. Borwick,
H. L. Anderson, J. Chem. Soc. Perkin Trans. 1 2002, 320–329.
[35] J. J. Piet, P. N. Taylor, B. R. Wegewijs, H. L. Anderson, A. Osuka,
J. M. Warman, J. Phys. Chem. B 2001, 105, 97–104.
[36] J. J. Piet, P. N. Taylor, H. L. Anderson, A. Osuka, J. M. Warman, J.
Am. Chem. Soc. 2000, 122, 1749–1757.
[37] S. M. Kuebler, R. G. Denning, H. L. Anderson, J. Am. Chem. Soc.
2000, 122, 339–347.
[38] H. L. Anderson, Angew. Chem. 2000, 112, 2552–2554; Angew.
Chem. Int. Ed. 2000, 39, 2451–2453.
[39] I. M. Blake, L. H. Rees, T. D. W. Claridge, H. L. Anderson, Angew.
Chem. 2000, 112, 1888–1891; Angew. Chem. Int. Ed. 2000, 39,
1818–1821.
[40] J. R. G. Thorne, S. M. Kuebler, R. G. Denning, I. M. Blake, P. N.
Taylor, H. L. Anderson, Chem. Phys. 1999, 248, 181–193.
[41] H. L. Anderson, Chem. Commun. 1999, 2323–2330.
[42] H. L. Anderson, A. P. Wylie, K. Prout, J. Chem. Soc. Perkin Trans.
1 1998, 1607–1611.
[11] N. P. Redmore, I. V. Rubtsov, M. J. Therien, J. Am. Chem. Soc.
2003, 125, 8769–8778.
[12] M. Drobizhev, Y. Stepanenko, Y. Dzenis, A. Karotki, A. Rebane,
P. N. Taylor, H. L. Anderson, J. Phys. Chem. B 2005, 109, 7223–
7236.
[13] M. Drobizhev, Y. Stepanenko, Y. Dzenis, A. Karotki, A. Rebane,
P. N. Taylor, H. L. Anderson, J. Am. Chem. Soc. 2004, 126, 15352–
15353.
[14] R. Kannan, G. S. He, T.-C. Lin, P. N. Prasad, R. A. Vaia and L.-S.
Tan, Chem. Mater. 2004, 16, 185–194.
[43] I. M. Blake, H. L. Anderson, D. Beljonne, J.-L. Bredas, W. Clegg, J.
Am. Chem. Soc. 1998, 120, 10764–10765.
[44] P. N. Taylor, J. Huuskonen, R. T. Aplin, H. L. Anderson, J. Huusko-
nen, G. Rumbles, E. Williams, Chem. Commun. 1998, 909–910.
[45] H. L. Anderson, Tetrahedron Lett. 1992, 33, 1101–1104.
[46] V. S. Lin, S. G. DiMagno, M. J. Therien, Science 1994, 264, 1105–
1111.
[47] V. S. Y. Lin, M. J. Therien, Chem. Eur. J. 1996, 1, 645–651.
[48] S. M. LeCours, S. G. DiMagno, M. J. Therien, J. Am. Chem. Soc.
1996, 118, 11854–11864.
[15] G. S. He, P. P. Markowicz, T.-C. Lin, P. N. Prasad, Nature 2002, 415,
767–770.
[49] R. Shediac, M. H. B. Gray, H. T. Uyeda, R. C. Johnson, J. T. Hupp,
P. J. Angiolillo, M. J. Therien, J. Am. Chem. Soc. 2000, 122, 7017–
7033.
[50] H. T. Uyeda, Y. Zhao, K. Wostyn, I. Asselberghs, K. Clays, A. Per-
soons, M. J. Therien, J. Am. Chem. Soc. 2002, 124, 13806–13813.
[51] K. Susumu, M. J. Therien, J. Am. Chem. Soc. 2002, 124, 8550–8552.
[52] I. V. Rubtsov, Y. K. Kang, N. P. Redmore, R. M. Allen, J. Zheng,
D. N. Beratan, M. J. Therien, J. Am. Chem. Soc. 2004, 126, 5022–
5023.
[53] T.-G. Zhang, Y. Zhao, I. Asselberghs, A. Persoons, K. Clays, M. J.
Therien, J. Am. Chem. Soc. 2005, 127, 9710–9720.
[54] T. V. Duncan, K. Susumu, L. E. Sinks, M. J. Therien, J. Am. Chem.
Soc. 2006, 128, 9000–9001.
[16] M. Albota, D. Beljonne, J.-L. Brꢁdas, J. E. Ehrlich, J.-Y. Fu, A. A.
Heikal, S. E. Hess, T. Kogej, M. D. Levin, S. R. Marder, D.
McCord-Maughon, J. W. Perry, H. Rçckel, M. Rumi, G. Subrama-
niam, W. W. Webb, X.-L. Wu, C. Xu, Science 1998, 281.
[17] T. Ishi-i, Y. Taguri, S.-i. Kato, M. Shigeiwa, H. Gorohmaru, S.
Maeda, S. Mataka, J. Mater. Chem. 2007, 17, 3341–3346.
[18] M.-C. Yoon, S. B. Noh, A. Tsuda, Y. Nakamura, A. Osuka, D. Kim,
J. Am. Chem. Soc. 2007, 129, 10080–10081.
[19] O. Rubio-Pons, Y. Luo, H. Agren, J. Chem. Phys. 2006, 124,
094310/094311–094310/094315.
[20] M. Drobizhev, Y. Stepanenko, Y. Dzenis, A. Karotki, A. Rebane,
P. N. Taylor, H. L. Anderson, J. Am. Chem. Soc. 2004, 126, 15352–
15353.
[55] Y. H. Kim, D. H. Jeong, D. Kim, S. C. Jeoung, H. S. Cho, S. K. Kim,
N. Aratani, A. Osuka, J. Am. Chem. Soc. 2001, 123, 76–86.
[56] A. Osuka, H. Shimidzu, Angew. Chem. 1997, 109, 93–95; Angew.
Chem. Int. Ed. Engl. 1997, 36, 135–137.
[57] D. A. Shultz, K. P. Gwaltney, H. Lee, J. Org. Chem. 1998, 63, 769–
774.
[21] H. Choi, C. Baik, S. O. Kang, J. Ko, M.-S. Kang, M. K. Nazeerud-
din, M. Graetzel, Angew. Chem. 2008, 120, 333–336; Angew.
Chem. Int. Ed. 2008, 47, 327–330.
[22] S. Hwang, J. H. Lee, C. Park, H. Lee, C. Kim, C. Park, M.-H. Lee,
W. Lee, J. Park, K. Kim, N.-G. Park, C. Kim, Chem. Commun.
2007, 4887–4889.
[58] D. A. Shultz, K. P. Gwaltney, H. Lee, J. Org. Chem. 1998, 63, 4034–
4038.
[23] I. Jung, J. K. Lee, K. H. Song, K. Song, S. O. Kang, J. Ko, J. Org.
Chem. 2007, 72, 3652–3658.
[59] D. A. Shultz, H. Lee, K. P. Gwaltney, J. Org. Chem. 1998, 63, 7584–
7585.
[24] M. Liang, W. Xu, F. Cai, P. Chen, B. Peng, J. Chen, Z. Li, J. Phys.
Chem. C 2007, 111, 4465–4472.
[25] N. Koumura, Z.-S. Wang, S. Mori, M. Miyashita, E. Suzuki, K.
Hara, J. Am. Chem. Soc. 2006, 128, 14256–14257.
[60] J. J. Gosper, M. Ali, J. Chem. Soc. Chem. Commun. 1994, 1707–
1708.
9066
www.chemeurj.org
ꢅ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 9058 – 9067

Photophysical Investigation of a Zinc–Porphyrin/Gold–Porphyrin Dyad
FULL PAPER
[61] H. Higuchi, T. Maeda, K. Miyabayashi, M. Miyake, K. Yamamoto,
Tetrahedron Lett. 2002, 43, 3097–3100.
[84] P. J. Hay, R. W. Willard, J. Chem. Phys. 1985, 82, 270–283.
[85] R. W. Willard, P. J. Hay, J. Chem. Phys. 1985, 82, 284–298.
[86] P. J. Hay, R. W. Willard, J. Chem. Phys. 1985, 82, 299–310.
[87] A. D. Becke, J. Chem. Phys. 1993, 98, 5648–5652.
[88] C. Lee, W. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785.
[89] S. H. Vosko, L. Wilk, M. Nusair, Can. J. Phys. 1980, 58, 1200–1211.
[90] R. Bauernschmitt, R. Ahlrichs, Chem. Phys. Lett. 1996, 256, 454.
[91] E. C. Mark, J. Christine, C. C. Kim, R. S. Dennis, J. Chem. Phys.
1998, 108, 4439–4449.
[62] T.-H. Huang, Y.-J. Chen, S.-S. Lo, W.-N. Yen, C.-L. Mai, M.-C.
Kuo, C.-Y. Yeh, Dalton Trans. 2006, 2207–2213.
[63] M. Yeung, A. C. H. Ng, M. G. B. Drew, E. Vorpagel, E. M. Brei-
tung, R. J. McMahon, D. K. P. Ng, J. Org. Chem. 1998, 63, 7143–
7150.
[64] H. Yamada, K. Kushibe, T. Okujima, H. Uno, N. Ono, Chem.
Commun. 2006, 383–385.
[65] J. Wytko, V. Berl, M. McLaughlin, R. R. Tykwinski, M. Schreiber,
F. Diederich, C. Boudon, J.-P. Gisselbrecht, M. Gross, Helv. Chim.
Acta 1998, 81, 1964–1977.
[66] K. M. Kadish, K. M. Smith, R. Guilard, The Porphyrin Handbook,
1999, p. .
[67] R. W. Wagner, T. E. Johnson, F. Li, J. S. Lindsey, J. Org. Chem.
1995, 60, 5266–5273.
[68] a) J. Fortage, J. Boixel, E. Blart, L. Hammarstrçm, H.-C. Becker, F.
Odobel, Chem. Eur. J. 2008, 14, 3467–3480; b) J. Fortage, J. Boixel,
E. Blart, L. Hammarstrçm, H.-C. Becker, F. Odobel, Inorg. Chem.
2009 48, 518–526.
[69] A. Antipas, D. Dolphin, M. Gouterman, E. C. Johnson, J. Am.
Chem. Soc. 1978, 100, 7705–7709.
[70] J.-C. Chambron, V. Heitz, J.-P. Sauvage, New J. Chem. 1997, 21,
237–240.
[71] Y. Kobuke, Eur. J. Inorg. Chem. 2006, 2333–2351.
[72] H. Segawa, C. Takehara, K. Honda, T. Shimidzu, T. Asahi, N.
Mataga, J. Phys. Chem. 1992, 96, 503–506.
[73] P. Chen, T. J. Meyer, Chem. Rev. 1998, 98, 1439–1478.
[74] N. Sutin, Prog. Inorg. Chem. 1983, 30, 441–498.
[75] D. M. Guldi, A. Gouloumis, P. Vazquez, T. Torres, Chem.
Commun. 2002, 2056–2057.
[92] R. E. Stratmann, E. S. Gustavo, J. F. Michael, J. Chem. Phys. 1998,
109, 8218–8224.
[93] M. Cossi, V. Barone, J. Chem. Phys. 2001, 115, 4708–4717.
[94] V. Barone, M. Cossi, J. Phys. Chem. A 1998, 102, 1995–2001.
[95] Gaussian 03, Revision D.02, M. J. Frisch, G. W. Trucks, H. B. Schle-
gel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, J. A. Montgom-
ery, J. Vreven, T., K. N. Kudin, J. C. Burant, J. M. Millam, S. S.
Lyengar, 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. Gom-
perts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Po-
melli, 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. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko, P. Pis-
korz, I. Komaromi, 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., Wallingford CT, 2004.
[76] J. E. Sutton, P. M. Sutton, H. Taube, Inorg. Chem. 1979, 18, 1017–
1021.
[96] A. Dreuw, J. L. Weisman, M. Head-Gordon, J. Chem. Phys. 2003,
119, 2943.
[77] P. F. Barbara, T. J. Meyer, M. A. Ratner, J. Phys. Chem. 1996, 100,
13148–13168.
[97] M. P. Eng, T. Ljungdahl, J. Andrꢁasson, J. Mꢇrtensson, B. Albins-
son, J. Phys. Chem. A 2005, 109, 1776–1784.
[78] J. C. Chambron, A. Harriman, V. Heitz, J. P. Sauvage, J. Am.
Chem. Soc. 1993, 115, 7419–7425.
[79] M. Andersson, M. Linke, J.-C. Chambron, J. Davidsson, V. Heitz,
L. Hammarstrçm, J.-P. Sauvage, J. Am. Chem. Soc. 2002, 124,
4347–4362.
[80] K. Pettersson, J. Wiberg, T. Ljungdahl, J. Martensson, B. Albinsson,
J. Phys. Chem. A 2006, 110, 319–326.
[81] D. E. Richardson, H. Taube, Inorg. Chem. 1981, 20, 1278–1285.
[82] K. M. Kadish, E. Wenbo, Z. P. Ou, J. G. Shao, P. J. Sintic, K.
Ohkubo, S. Fukuzumi, M. J. Crossley, Chem. Commun. 2002, 356–
357.
[98] K. Clays, A. Persoons, Phys. Rev. Lett. 1991, 66, 2980–2983.
[99] K. Clays, A. Persoons, L. De Maeyer, Adv. Chem. Phys. 1993, 85,
455–498.
[100] K. Clays, A. Persoons, Rev. Sci. Instrum. 1992, 63, 3285–3289.
[101] G. Olbrechts, R. Strobbe, K. Clays, A. Persoons, Rev. Sci. Instrum.
1998, 69, 2233–2241.
[102] K. Clays, G. Olbrechts, T. Munters, A. Persoons, O.-K. Kim, L.-S.
Choi, Chem. Phys. Lett. 1998, 293, 337–342.
[83] R. Ditchfield, W. J. Hehre, J. A. Pople, J. Chem. Phys. 1971, 54,
724–728.
Received: January 30, 2009
Published online: July 31, 2009
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9067