Corrole-porphyrin conjugates with interchangeable metal centers

Article abstract of DOI:10.1002/ejoc.201200836

Oligoporphyrinoid materials composed of two or three tetrapyrrolic macrocycles have been synthesized by either mono-or disubstitution (S _NAr) of a phenolic Zn-AB₃-porphyrin on a meso-dichloropyrimidinyl-substituted Cu-AB₂-corrole. Selective metallation/demetallation sequences were carried out on these mixed corrole-porphyrin conjugates to afford multichromophoric systems with variable metal centers. The absorption spectra of the free-base corrole-porphyrin systems were essentially additive, which demonstrates that only weak intercomponent interactions take place in these assemblies and therefore they can be regarded as supramolecular systems. Photophysical studies of the free-base conjugates showed that these species are highly fluorescent, with fluorescence occurring from the lowest-energy singlet state of the porphyrin subunit(s), which is (are) the lowest-energy state(s) of the assemblies. Pump-probe transient absorption spectroscopy experiments demonstrated that very efficient (>95 %) corrole-to-porphyrin singlet-singlet energy transfer takes place in these pyrimidinyl-bridged multichromophoric systems by a coulombic mechanism with rate constants on the picosecond timescale.

Full text of DOI:10.1002/ejoc.201200836

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FULL PAPER
DOI: 10.1002/ejoc.201200836
Corrole–Porphyrin Conjugates with Interchangeable Metal Centers
Thien H. Ngo,[a,b] Francesco Nastasi,[c] Fausto Puntoriero,[c] Sebastiano Campagna,*[c]
Wim Dehaen,[a] and Wouter Maes*[a,d]
Keywords: Porphyrinoids / Macromolecules / Energy transfer / Chromophores / UV/Vis spectroscopy
Oligoporphyrinoid materials composed of two or three tetra-
pyrrolic macrocycles have been synthesized by either mono-
or disubstitution (SNAr) of a phenolic Zn-AB3-porphyrin on a
meso-dichloropyrimidinyl-substituted Cu-AB2-corrole. Se-
lective metallation/demetallation sequences were carried out
on these mixed corrole–porphyrin conjugates to afford multi-
chromophoric systems with variable metal centers. The ab-
sorption spectra of the free-base corrole–porphyrin systems
were essentially additive, which demonstrates that only
weak intercomponent interactions take place in these as-
semblies and therefore they can be regarded as supramolec-
ular systems. Photophysical studies of the free-base conju-
gates showed that these species are highly fluorescent, with
fluorescence occurring from the lowest-energy singlet state
of the porphyrin subunit(s), which is (are) the lowest-energy
state(s) of the assemblies. Pump-probe transient absorption
spectroscopy experiments demonstrated that very efficient
(Ͼ95%) corrole-to-porphyrin singlet–singlet energy transfer
takes place in these pyrimidinyl-bridged multichromophoric
systems by a coulombic mechanism with rate constants on
the picosecond timescale.
roles and their applications in sensors, catalysis, medicine,
and molecular electronics.[4]
Introduction
The investigation of corroles, contracted porphyrin ana-
logues lacking one meso-carbon atom, dates back to the
early 1960s when the first corrole synthesis was reported by
Johnson and Kay.[1] For decades thereafter, however, cor-
role research has been overshadowed by porphyrin science,
partly due to the challenging corrole synthesis. Recent in-
creased interest in corrole-based materials and their appli-
cations is in great part due to the impressive synthetic pro-
gress that has been made in the field over the last
15 years,[2,3] and many studies now focus on the coordina-
tion chemistry or electrochemistry of diverse (metallo)cor-
The integration of multiple corroles (and their combina-
tion with porphyrins) into larger macromolecular structures
has scarcely been explored so far, although the potential of
such conjugates in a number of applications can easily be
seen. These systems may, for instance, be used as multisite
catalysts, mimics of biochemically important species (e.g.,
cytochrome c oxidase), or optical sensors. Moreover, they
are also appealing tools for gaining an understanding of the
basic photophysical phenomena that occur in corroles and
multiporphyrinoid structures en route towards their pos-
sible exploitation in molecular electronics and/or solar-en-
ergy conversion. To date, only a few corrole–porphyrin and
[a] Molecular Design and Synthesis, Department of Chemistry, corrole-corrole dyads have been prepared.[5–9] The tradi-
KU Leuven,
Celestijnenlaan 200F, 3001 Leuven, Belgium
tional syntheses of mixed porphyrin–corrole derivatives
have often involved either corrole synthesis starting from
porphyrin-containing precursors or porphyrin synthesis
starting from corrole-containing building blocks. The de-
scribed procedures are often not very straightforward, re-
quiring laborious multistep sequences and modifications at
the porphyrinoid level, and the modest yields imply the loss
of valuable (tetrapyrrolic) material. Bis-corrole systems
linked through the 10-position with phenyl spacers have
been prepared by Paolesse and co-workers through
multistep sequences.[5] Guilard and co-workers synthesized
a series of face-to-face bis-corroles and porphyrin–corrole
dyads with different (rigid or flexible) linkers starting from
dialdehyde linker precursors.[6] An atypical mixed macro-
cycle system from the same group involved a Rh-tetraphen-
ylporphyrin–Sn-corrole dyad with a metal–metal bond.[6d]
[b] Institut für Chemie und Biochemie – Organische Chemie, Freie
Universität Berlin,
Takustrasse 3, 14195 Berlin, Germany
[c] Dipartimento di Chimica Inorganica, Chimica Analitica e
Chimica Fisica, Università di Messina and Centro
Interuniversitario per la Conversione Chimica dell’Energia Sol-
are (SOLAR-CHEM),
98166 Vill. S. Agata, Messina, Italy
Fax: +39-090-393756
E-mail: campagna@unime.it
[d] Design & Synthesis of Organic Semiconductors (DSOS),
Institute for Materials Research (IMO-IMOMEC), Hasselt
University,
Agoralaan 1, Building D, 3590 Diepenbeek, Belgium
Fax: +32-11-268299
E-mail: wouter.maes@uhasselt.be
Homepage: http://www.uhasselt.be/UH/IMO/Visit-the-groups/
Design-and-synthesis-of-organic-semiconductors.html
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201200836.
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Osuka and Cavaleiro and their co-workers reported the syn- also be extended to porphyrin and/or corrole substituents
thesis of β,βЈ-linked corrole dimers by Suzuki–Miyaura and, depending on the type of pyrimidinylcorrole (AB2,
cross-coupling (after regioselective Ir-catalyzed direct bor- A2B, or A3),[10] multiple porphyrinoid chromophores can
ylation) or simple heating of tris(pentafluorophenyl)cor- be introduced on to the corrole framework. Combining this
role in 1,2,4-trichlorobenzene, respectively.[7a–7c] Gryko and with a recently developed method that allows the smooth
co-workers prepared a stable corrole–porphyrin dyad by copper metallation and demetallation of the corrolato li-
linking two preformed macrocycles through an amide gand,[12] multiple multichromophoric systems can be envis-
bridge.[7d] The same group also reported meso,mesoЈ-linked aged in which the porphyrin and corrole entities are
bis-corroles synthesized by cascade reactions of sterically equipped with different metal centers.
hindered dipyrromethanes and formaldehyde (in low
Lewis acid catalyzed (0.068 equiv. BF3·OEt2) condensa-
yields).[7e] Upon nitration of nonaromatic Ni-corroles with tion of mesityldipyrromethane[13] with 4,6-dichloro-2-
peripherally fused ring systems, obtained by ring contrac- (methylsulfanyl)pyrimidine-5-carbaldehyde (1:1 ratio) af-
tion of nickel meso-tetraarylporphyrins, a series of β,βЈ- forded Fb-AB2-pyrimidinylcorrole 1a (27%), which was
linked corrole dimers were synthesized by Callot and co- treated with copper acetate (in THF at room temp.) to yield
workers by electron-transfer-initiated coupling.[8,9]
the desired Cu-corrole scaffold 1b (Scheme 1).[10a] As a nu-
Metallation of tetrapyrrolic dyads is generally not selec- cleophilic porphyrinoid, phenolic AB3-porphyrin 2a was
tive (with a few notable exceptions).[5–9] Upon desired me- chosen due to its favorable solubilizing properties enabling
tallation of the corrolato ligand, the same metal will often easy synthetic routine handling and characterization of the
simultaneously insert into the porphinato ligand (albeit final corrole–porphyrin conjugates. The peripheral por-
normally in a lower oxidation state). To achieve selective phyrin unit was prepared by a mixed Rothemund condensa-
metallation of the individual tetrapyrrolic units within one tion of 3,5-di-tert-butylbenzaldehyde and 4-hydroxybenzal-
dyad, of particular interest to create energy funneling path- dehyde (2:1 ratio) with pyrrole.[11d,14] Subsequent metalla-
ways, the metals usually have to be inserted into the por- tion with zinc acetate (in CHCl3 at room temp.) or platinum
phyrinoid building blocks prior to combining them, which chloride (in benzonitrile at reflux) afforded Zn-porphyrin
considerably increases the effort required to obtain a variety derivative 2b and Pt-porphyrin 2c, respectively
of differently metallated systems for screening purposes.
From this literature survey, it is clear that novel synthetic
pathways with enlarged versatility and scope (e.g., regard-
ing the substitution pattern and metallation state) are
highly desirable to achieve further progress in the field and
to pursue realistic applications of such materials. The syn-
thetic route presented herein enables straightforward access
to either bis- or tris-porphyrinoid systems with different
metal centers in each macrocyclic ligand starting from a
single oligoporphyrinoid platform, readily available by com-
bination of a phenolic AB3-porphyrin and a meso-di-
chloropyrimidinyl-substituted AB2-corrole. Absorption
spectra and photophysical properties (both in fluid solution
at room temperature and in a rigid matrix at 77 K) of se-
lected compounds, that is, two free-base (Fb) corrole–por-
phyrin conjugates and their individual components, have
also been investigated. The corrole-to-porphyrin energy-
transfer processes occurring in such compounds have been
analyzed by pump-probe transient absorption spectroscopy.
(Scheme 1).[11d]
Results and Discussion
Synthesis of Corrole–porphyrin Conjugates
As described in previous work, the introduction of meso-
pyrimidinyl groups at the periphery of triarylcorroles[10]
(and analogous porphyrinoids[11]) allows a straightforward
introduction of different (functional) moieties on to the
tetrapyrrolic macrocycle by (post-macrocyclization) nucleo-
philic aromatic substitution (SNAr) or Pd-catalyzed cross-
coupling reactions. As such, pyrimidinylcorroles are versa-
tile synthons towards more complex functional corrole ma-
Scheme 1. Synthesis of the disubstituted conjugate 3 and the mono-
terials. This functionalization approach can, in principle, substituted dyad 4.
2
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Corrole–porphyrin Conjugates with Interchangeable Metal Centers
When Fb-pyrimidinylcorrole 1a and an excess (6 equiv.)
A more general (ultimately orthogonal) strategy for ob-
of Fb-porphyrin 2a were treated under SNAr conditions as taining variously metallated multiporphyrinoid systems can
optimized for AB2-pyrimidinylcorroles (K2CO3, 18-crown- be established based on our earlier reported corrole Cu-
6, DMF, microwave, 175 °C, 1 h),[10a] a complex product metallation/demetallation cycle.[12c] Both procedures are
mixture was obtained. Despite several purification attempts mild and only require purification by flash column
(column chromatography and preparative TLC on silica), chromatography, minimizing decomposition. As described
none of the envisaged products could be obtained in pure previously,[12c] Cu-pyrimidinylcorroles cannot be demetall-
form. To overcome this problem, which may be attributed ated in acidic medium without a suitable reducing agent
to the relative (photo-oxidative) instability of the Fb-AB2- (e.g., SnCl2). When Zn-porphyrin–Cu-corrole dyad 4 was
pyrimidinylcorrole, the same reaction was carried out with treated with HCl in CHCl3, the porphyrin entity was de-
Cu-corrole 1b and Zn-porphyrin 2b. After purification by metallated, whereas the Cu-corrole moiety remained un-
column chromatography (silica), the disubstituted product touched (Scheme 2). After purification by flash column
3 and monosubstituted analogue 4 were obtained in yields chromatography, 78% of pure dyad 5 was obtained. Further
of 55 and 27%, respectively (Scheme 1). The excess copper demetallation of bis-porphyrinoid 5 was carried out
(4 equiv.) of Zn-porphyrin 2b could easily be recovered.
under the optimized demetallation conditions and 63% of
An additional advantage of meso-pyrimidinyl moieties is pure Fb-corrole-Fb-porphyrin dyad
6
was obtained
that the extent of substitution (mono/di) can be regulated (Scheme 2). Addition of zinc(II) acetate to a solution of
to some extent by adjusting the reaction temperature.[10,11] conjugate 6 in CHCl3 readily led to 87% of Zn-porphyrin–
When the same reaction was carried out at 90 °C (conven- Fb-corrole 7. Dyad 6 could also be prepared directly from
tional heating) with only 1.5 equiv. of Zn-porphyrin 2b, fully metallated dyad 4 upon application of the optimized
monosubstituted dyad 4 was obtained more selectively in demetallation procedure for Cu-corroles. After purification,
72% yield. Some of the starting Cu-corrole 1b (10%) and Fb conjugate 6 was isolated in an essentially quantitative
the small excess of Zn-porphyrin 2b could be recovered dur- yield (Scheme 2).
ing the purification process.
This concept was then extended to tris-porphyrinoid sys-
tem 3 and other metal centers (Scheme 3). In this initial
study, emphasis is on the proof-of-concept and metals were
chosen for their easy insertion and/or resulting diamagne-
Metallation/Demetallation Sequences
Corrole–porphyrin conjugates (and ultimately more tism (towards NMR characterization) rather than for spe-
elaborate corrole-based dendritic structures[11d,15,16]) are cific photophysical (absorption/luminescence) purposes.
interesting photophysical probes in which the peripheral The same conditions as outlined above were applied to re-
corrole and/or porphyrin moieties can act as light-absorb- move zinc from the porphyrin units. After purification, 63%
ing antennae that transfer energy to a central porphyrinoid of pure Fb-porphyrin–Cu-corrole conjugate 8 was ob-
core. Suitable metal sites in the corrolato and porphinato tained. Upon further application of the Cu-corrole demetal-
ligands can have a major impact on the photophysical fea- lation procedure, full conversion to the Fb conjugate 9 was
tures of such systems. As mentioned above, the metals are achieved in a nearly quantitative yield. Zinc was introduced
usually introduced into each separate macrocycle before into the two porphyrin moieties without simultaneous me-
combining them into a multiporphyrinoid structure. Guil- tallation of the corrole chromophore. After flash column
ard and co-workers have reported the synthesis of cofacial chromatography, tris-porphyrinoid 10, containing two Zn-
heterodimetallic corrole–porphyrin dyads.[6] Cobalt metal- porphyrins and a Fb-corrole, was isolated in nearly quanti-
lation of the corrole moiety was performed on a Zn-por- tative yield. Upon further metallation of the corrole moiety
phyrin–Fb-corrole material.[6g] Alternatively, zinc and man- with gallium(III) trichloride (in pyridine at reflux),[19] Zn-
ganese were inserted into the porphyrin subunit of a Fb- porphyrin–Ga-corrole conjugate 11 was obtained in 76%
porphyrin–Co-corrole dyad. The same group also reported yield. Complete direct demetallation starting from Zn-por-
the selective metallation of a fully Fb-corrole–porphyrin dy- phyrin–Cu-corrole 3 afforded the Fb derivative 9 in 75%
ad.[6c] Cobalt could be inserted into the corrolato ligand yield.
[through the addition of Co(OAc)2 in pyridine at 60 °C],
When conjugate 8 was subjected to the metallation con-
but no insertion into the porphyrin moiety was observed. ditions generally applied to introduce platinum into a por-
By raising the temperature to reflux, metallation of the por- phinato ligand (PtCl2 in benzonitrile at reflux[18]), the de-
phyrin unit also occurred. However, when this procedure sired Pt-porphyrin–Cu-corrole product 12 could not be ob-
was repeated for a mixture of our precursors 1a and 2a, tained (Scheme 3). This was attributed to the decomposi-
partial porphyrin metallation was observed by mass spec- tion of the Fb-porphyrin–Cu-corrole conjugate caused by
trometry (ESI-MS), even at room temperature. The same the rather harsh metallation conditions or to the instability
test experiment (metallation of a mixture of 1a and 2a) was of the product 12. After purification by column chromatog-
carried out for aluminium (AlMe3 in toluene at room raphy, only a very small amount (5%) of the starting mate-
temp.[17]) and platinum (PtCl2 in benzonitrile at re- rial was recovered. Pt-porphyrin–Cu-corrole conjugates 12
flux[11d,18]). Partial Al insertion into Fb-porphyrin 2a was and 13 were, however, obtained by carrying out the SNAr
observed, whereas decomposition of pyrimidinylcorrole 1a reaction with Cu-corrole precursor 1b and phenolic Pt-por-
occurred during the Pt insertion reaction.
phyrin 2c. Disubstituted conjugate 12 was obtained in 73%
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Scheme 3. Metallation/demetallation sequence starting from tris-
porphyrinoid conjugate 3.
yield by SNAr reaction under microwave irradiation condi-
tions. Selective monosubstitution was achieved by tuning
the reaction conditions (90 °C) and monosubstituted conju-
gate 13 was obtained in 19% yield (Scheme 3). The low
yield was again attributed to the decomposition of the
product formed as a result of exposure to high temperature
for a prolonged time (overnight).
Multichromophoric macromolecules 7 and 10 allow the
introduction of different metals into the corrole core with-
out exchanging the metals in the Zn-porphyrin moieties.
When Zn is selectively removed from the peripheral por-
phyrin chromophores (in slightly acidic medium) and new
Scheme 2. Metallation/demetallation sequence for corrole–por-
phyrin dyad 4.
4
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Corrole–porphyrin Conjugates with Interchangeable Metal Centers
metals are inserted instead, novel combinations of metall- the basis of the luminescence properties of their individual
oporphyrinoids can be envisaged. The opposite story can components, in particular, the difference between their
be told for Fb-porphyrin–Cu-corrole conjugates 5 and 8, emission spectra.
although the metalloporphyrin should be able to withstand
The absorption spectra of the investigated compounds
the harsher conditions used to remove the Cu from the cor- exhibit features typical of porphyrin and corrole com-
rolato ligand in this case.
pounds: Very intense Soret bands in the UV region and
intense, structured Q-bands in the visible region. Figure 2
shows the absorption spectra of 2a, 14, 15, 6, and 9, and
relevant data are presented in Table 1. Note that the absorp-
tion spectra of the dyad and triad species are essentially the
summation of the spectra of their model compounds (for
example, compare the spectrum of 6 and the summation of
the spectra of 2a and 14, Figure 2). This demonstrates that
the electronic interaction between the corrole and por-
phyrin subunits in the multichromophoric species studied
here is negligible and therefore these species can be re-
garded merely as supramolecular compounds. In particular,
the bands in the 530–580 nm region in the absorption spec-
tra of 6 and 9 receive significant independent contributions
from the Q-bands of both the corrole and porphyrin sub-
units and the absorption in the 380–440 nm region receives
independent contributions from the corrole and porphyrin
Soret bands (Figure 2). The negligible electronic interaction
between the corrole and porphyrin subunits in 6 and 9, as
inferred by the absorption spectra, contrasts with the non-
negligible interaction between the chromophores in the so-
called pacman-type corrole–porphyrin assemblies reported
by Gros et al.,[6j] inferred also on the basis of the absorption
spectra of the dyads and individual components. In the lat-
ter case, the face-to-face arrangement of the corrole and
porphyrin subunits leads to a more intense interaction,
whereas the less compact molecular structures of 6 and 9
apparently limit interchromophoric interactions, at least in
the ground state.
Absorption Spectra and Photophysical Properties
Because of the ortho,orthoЈ-di(hetero)aryl ether linkage(s)
in the conjugates, the corrole and porphyrin moieties are
positioned rather close in space. This could allow efficient
interchromophoric interactions, in particular, photoinduced
electronic energy transfer. As the excited-state energies of
Fb-corroles are usually slightly higher than the excited-state
energies of the corresponding Fb-porphyrins,[20] corrole-to-
porphyrin energy transfer should occur. To investigate this
topic, luminescence experiments were performed, both in
fluid solution at room temperature and in a rigid matrix at
77 K, on the dyad 6 and the triad 9 (containing a Fb-cor-
role and one or two Fb-porphyrins, respectively). The prop-
erties of the porphyrin model compound 2a have also been
studied, whereas some data on the corrole model species 14
and 15 (Figure 1) are available from a former study[10b] and
have been used here whenever necessary. All the important
photophysical data are presented in Table 1. At this point
the photophysical investigation was limited to the multi-
chromophoric Fb species because our main interest was to
study the eventual occurrence of intercomponent energy
transfer in the pyrimidinyl-linked tetrapyrrolic conjugates.
In fact, multichromophoric free bases 6 and 9 are the sys-
tems that allow clear-cut results instrumental to our aim on
The luminescence properties of model compound 2a
(Table 1) are in line with the general properties of standard
tetraphenylporphyrins.[21] The emission has been assigned
to fluorescence from the lowest-energy singlet state. Com-
parison with the luminescence properties of the corrole
model species 14 and 15 (Figure 1, Table 1) indicates that
energy transfer from the Fb-corrole unit to the Fb-por-
phyrin unit(s) in the multichromophoric systems 6 and 9 is
thermodynamically allowed. The excited-state energy levels
of the individual subunits are approximate to the higher-
Figure 1. Pyrimidinylcorroles 14 and 15 used as model compounds
in the photophysical studies.
Table 1. Absorption and luminescence properties of Fb conjugates 6 and 9 and their model species.[a]
Absorption
Luminescence
λmax [nm] (ε [m–1 cm–1])
λmax [nm]
τ [ns]
Φ
λmax [nm] τ [ns]
298K
298 K
298 K
77 K
77 K
2a
6
420 (420000), 515 (17000), 550 (9500), 590 (5000), 650 (4500)
420 (496000), 516 (28000), 555 (26300), 568 sh (23700), 600
(15700), 635 sh (5300), 650 (6400)
655
10
0.11
0.10
655
650
13
12
605,[b] 650
0.20,[c]
9
9
422 (691000), 517 (35000), 555 (25500), 593 (14300), 600sh (13700), 605,[b] 650
650 (8600)
0.12,[c] 10
0.10
650
12
14
15
410 (103000), 428 (90000), 570 (21300), 603 (10500), 634 (3100)
410 (102100), 428 (91700), 571 (19300), 605 (10700), 637 (3100)
605sh, 645
605sh, 645
4.2
5.9
0.098
0.152
600
602
7
12
[a] Data were recorded in air-equilibrated toluene, unless stated otherwise. [b] Very weak contribution, see onset of the emission spectra
in Figure 3. [c] This component was only obtained by recording the lifetime in the 600–620 nm range.
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phyrin singlet state takes place in the multichromophoric
systems, both at room temperature in fluid solution and at
77 K in a rigid matrix. As additional confirmation of the
energy-transfer process, note that the excitation spectra of
6 and 9, recorded at 730 nm, closely resemble the respective
absorption spectra, which clearly demonstrates that the
light absorbed by the corrole subunit contributes to the
(porphyrin-based) emission. The absorption and excitation
spectra of dyad 6 are compared in Figure 4.
Figure 2. Absorption spectra (in toluene solution) of dyad 6, triad
9, and their model species. In the panel containing the spectrum of
6, the spectrum 2a+14 is obtained by the sum of the individual
spectra.
energy feature of the model emission band, which is located
at about 605 nm for the corrole chromophores 14 and 15,
and at 655 nm for the porphyrin model species 2a. With
such an assumption, a driving force of around 0.15 eV was
calculated for the corrole-to-porphyrin energy-transfer pro-
cess. Indeed, both in fluid solution at room temperature and
in a rigid matrix at 77 K (spectra not shown), the lumines-
Figure 3. Luminescence spectra (in toluene solution at room temp.)
of dyad 6, triad 9, and their model species.
A very small contribution to the emission spectra is pres-
cence spectra of 6 and 9 are similar to those of 2a (Figure 3; ent at about 605 nm in the emission spectra of 6 and 9 re-
the comparison in intensity between the emission bands at corded at room temperature. On recording the emission life-
650 and 715 nm, due to vibrational progression, is particu- time at 610 nm, minor decay components appear with life-
larly diagnostic). The luminescence lifetimes and quantum times of about 0.20 and 0.12 ns for 6 and 9, respectively. In
yields are also nearly identical to those of 2a (Table 1) when both cases, such a component can be assigned to the
experimental uncertainties are taken into account. These re- quenched corrole fluorescence in the dyad and triad species.
sults indicate that quite efficient energy transfer from the By using such lifetimes and considering the fluorescence
higher-energy corrole singlet state to the lower-energy por- lifetimes of the model compounds 14 and 15 (4.2 and 5.9 ns,
6
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Corrole–porphyrin Conjugates with Interchangeable Metal Centers
the corrole. It is indeed known that the triplet state of cor-
roles appears as a constant bleach (on the ns timescale) in
the 540–600 nm region.[20e] The transient absorption spec-
trum of 2a (Figure 5, middle panel) is typical for porphyrin
singlet states.[7d] An intense transient is clearly present in
the visible region, which largely compensates for the bleach-
ing of the Q-bands. Similarly to what happens for 14, and
in agreement with the luminescence data (Table 1), the tran-
sient spectrum of 2a decays to the ground state on a longer
timescale than the time limit of the equipment (see inset of
Figure 5, middle).
Figure 4. Comparison between the absorption (solid line) and exci-
tation (dashed-dotted, emission wavelength 730 nm) spectra of the
corrole–porphyrin dyad 6 in toluene at room temp. For complete-
ness, the absorption spectra of the individual components 2a
(dashed) and 14 (dotted) are also shown. The absorption spectra
are represented on the same molar absorption scale.
respectively; Table 1), energy-transfer rate constants of
about 5ϫ109 and 8ϫ109 s–1 can be calculated for 6 and 9,
respectively [from the usual relationship kq = (1/τ) – (1/τ0),
in which kq is the energy-transfer rate constant and τ and
τ0 are the fluorescence lifetimes of the corrole-based fluo-
rescence in the quenched (i.e., 6 and 9) species and the
model systems]. These rates should, however, be considered
with care as the measured lifetimes are close to the lower
limit of our time-resolved luminescence equipment (ca.
100 ps, essentially due to the electronic delay of the instru-
ment). Therefore the calculated energy-transfer rate con-
stants are associated with some uncertainty. Nevertheless,
from the luminescence experiments it can be concluded that
for both conjugates 6 and 9 a highly efficient (Ͼ95%) cor-
role-to-porphyrin singlet–singlet energy transfer takes place.
To investigate the corrole-to-porphyrin energy-transfer
processes occurring in the Fb conjugates in more detail,
pump-probe transient absorption spectroscopy using fem-
tosecond time resolution was performed. Figure 5 shows
the transient absorption spectra (in toluene) of the parent
chromophores 2a and 14 and corrole–porphyrin conjugate
6 at room temperature (excitation wavelength 400 nm at
2 mJ). In the transient spectrum of monosubstituted corrole
14, bleaching of the corrole absorption in the visible region
is clearly apparent in the range 540–620 nm, although it is
partially compensated by the presence of a transient ab-
sorption between 450 and 540 nm (Figure 5, top panel).
Following a fast (few ps rate constant) initial process,
mainly assigned to internal conversion and vibrational cool-
ing, the transient absorption decays towards the ground
state without showing any other spectral evolution. On the
timescale used for pump-probe spectroscopy (3.2 ns), the
ground state is not fully recovered (see inset of Figure 5,
top panel; 517 nm decay). This finding is in agreement with
the luminescence data, which indicate a lifetime of about
10 ns for the emissive lowest-energy singlet state of 14. Note
that, upon recording the kinetics of the bleaching recovery
at 567 nm (Figure 5, top), besides the processes observed
for the transient decay at 517 nm, a very long-living contri-
Figure 5. Transient absorption spectra (in toluene solution at room
temp., excitation wavelength 400 nm at 2 mJ) of the corrole model
compound 14 (top panel), the porphyrin model compound 2a
(middle panel) and dyad 6 (bottom panel). The kinetics are shown
in the insets. Time delays and wavelengths at which the kinetics
bution is also present, most likely due to the triplet state of were studied are given in the figures.
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S. Campagna, W. Maes et al.
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Corrole–porphyrin dyad 6 (Figure 5, bottom panel) sembles the transient spectrum of 2a (Figure 5, middle
shows a more complicated transient spectrum. Intense tran- panel), the corresponding Fb-porphyrin building block of
sient absorption features in the visible region are present. dyad 6.
The bleaching of the Q-bands of both the corrole and por-
The situation is more complicated for tris-porphyrinoid
phyrin subunits appear as “negative” contributions to the derivative 9 as a consequence of the presence of two por-
main transient absorption in the 540–650 nm region. In phyrin subunits, the transient spectra of which tend to ob-
fact, laser excitation (400 nm) produces both corrole and scure the transient absorption of the single corrole chromo-
porphyrin excited chromophores as selective excitation is phore. However, even for this multichomophoric species,
not possible. However, in this case, the transient spectrum the initial transient spectrum evolves, showing a biphasic
formed after a few picoseconds undergoes a spectral evol- decay when monitored at 567 nm (Figure 7), with a risetime
ution during which an increased transient absorption takes of 139(Ϯ15) ps, followed by a transient decay on the ns
place in the typical porphyrin transient absorption region timescale. The fast process has been assigned to corrole-to-
(540–620 nm). The increased transient absorption is par- porphyrin energy transfer, and
a rate constant of
ticularly evident at about 560 nm, at which there is the 7.2ϫ109 s–1 can be calculated for such an energy-transfer
largest difference between the transient absorption spectra process, with the slower processes assigned to the decay of
of 2a and 14. The risetime of such a transient is the porphyrin singlet state. The kinetics of the energy-trans-
225(Ϯ40 ps), assigned to the energy transfer from the sing- fer process are also in good agreement with the lumines-
let state of the corrole subunits to the singlet porphyrin cence decay results (Table 1). The faster rate for the corrole-
state. Successively, the transient absorption decays with a to-porphyrin singlet–singlet energy transfer in triad 9 com-
lifetime that is close to that of 2a (see inset of Figure 5, pared with in dyad 6 is reasonable when it is considered
bottom) and is therefore assigned to the decay of the singlet that there are two acceptor units present in 9, whereas only
state involving the porphyrin subunit of 6. The 225 ps rise- one in 6. As a result, the probability of the process is ex-
time for corrole-to-porphyrin energy transfer obtained from pected to be roughly doubled in 9 compared with in 6.
pump-probe spectroscopy, which corresponds to a rate con-
stant of 4.4ϫ109 s–1 for the energy-transfer process, is in
very good agreement with the rate constant of 5ϫ109 s–1
estimated for the same process from luminescence lifetime
data (see above). To confirm this interpretation, we per-
formed a global fitting analysis for dyad 6. Figure 6 illus-
trates the result of such a fitting, which allows the main
transient spectra and kinetics of the various species present
in the excited state to be determined. Note, the solid curve
of Figure 6 has been assigned to the transient absorption
spectrum of a species that decays with a lifetime of 219 ps,
and is similar to the transient spectrum of 14, the corrole
subunit of 6 (see Figure 5, top), whereas the longer-living
transient spectrum (dotted curve in Figure 6) largely re-
Figure 7. Transient absorption spectra (in toluene solution at room
temp., excitation wavelength 400 nm at 2 mJ) of 9. The kinetics are
shown in the inset. Time delays and the wavelength at which the
kinetics were studied are given in the figure.
To investigate the mechanism of the energy-transfer pro-
cess, we calculated the theoretical coulombic energy-trans-
fer rate constants by using a simplified Förster equation
[Equations (1) and (2)].[22]
(1)
Figure 6. Transient absorption spectra of species contributing to
the transient spectrum of 6 (shown in Figure 5), obtained by global
kinetic analysis. The solid line is a species exhibiting a lifetime of
219 ps, the dotted line is a species with a lifetime on the ns times-
cale.
(2)
8
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Corrole–porphyrin Conjugates with Interchangeable Metal Centers
In Equation (1), keFnis the rate constant of the energy- construction of (dendritic) macromolecules containing mul-
transfer process, K is an orientation factor that accounts for tiple porphyrinoid chromophores in an effective manner.
the directional nature of the dipole–dipole interaction (K2 is For the first time a triad composed of an AB2-pyrimidinyl-
2/3 for a random orientation), Φ and τ are the luminescence corrole and two porphyrin units has been prepared by a
quantum yield and lifetime of the donor, respectively, n is straightforward nucleophilic aromatic substitution protocol
the solvent refractive index (1.497 for toluene at room and a selective metallation/demetallation procedure has
temp.), rAB is the distance (in Å) between donor and ac- been shown to afford various pyrimidinyl-bridged (hetero-
ceptor, and JF [see Equation (2)] is the Förster overlap inte- bimetallic) corrole–porphyrin systems with readily ex-
gral between the luminescence spectrum of the donor, F(ν), changeable metal centers. Absorption spectra and photo-
˜
and the absorption spectrum of the acceptor, ε(ν), on an physical features have indicated that the multichromophoric
˜
energy scale (cm–1). By using the spectral and kinetic val- Fb-corrole–porphyrin conjugates experience only weak in-
ues,[23] and assuming an rAB through-space center-to-center terchromophoric electronic interactions, which allow for
distance of 13.7 Å, calculated from energy-minimized com- fast (rate constants of about 109–1010 s–1) and efficient
puter-generated structures, rate constants of 1.5ϫ1010 and (Ͼ95%) corrole-to-porphyrin singlet–singlet energy transfer
3.2ϫ1010 s–1 have been obtained for the corrole-to-por- operating by a coulombic mechanism. These systems can
phyrin energy transfer in 6 and 9, respectively. These values hence be regarded as molecular assemblies of porphyrins
are larger than the experimental values by a factor of 3–4. and corroles with supramolecular (photophysical) features
However, by taking into account the experimental uncer- and therefore represent quite realistic model systems for
tainties and the approximations assumed in the Förster natural photosynthetic complexes. Future work will focus
equation used,[24] they are in fair agreement with the experi- on more elaborate dendritic multiporphyrinoid systems
mental values and so it can be concluded that Förster en- with variable metallation states (mainly those of interest for
ergy transfer is the mechanism operating in the process ob- potential photophysical applications, e.g., Ga, Ir, Al)[4c,20,25]
served in the corrole–porphyrin conjugates.
that are capable of exhibiting tailor-made photophysical
Note, the residual emission at 600 nm is not visible in the properties (e.g., a logical gradient for energy or electron
emission spectra of the multichromophoric species recorded transfer[26]), building on both the synthetic and photophysi-
at 77 K (Table 1), which can be attributed to experimental cal knowledge gained in this study.
reasons. In fact, the longer excited-state lifetime of the do-
nor(s) at 77 K coupled with the relatively high energy-trans-
fer rate constants would result in a residual corrole-based
emission Ͻ2% of the unquenched emission, probably lower
Experimental Section
General: NMR spectra were acquired with commercial instruments
than the detectable limit.
(Bruker Avance 300 MHz, AMX 400 MHz, or Avance II+
Finally, it should be noted that our results differ from
600 MHz) and chemical shifts (δ) are reported in parts per million
the recent report of Flamigni et al. on energy transfer be-
(ppm) referenced to tetramethylsilane (1H) or residual NMR sol-
tween Fb-corrole and -porphyrin subunits in a corrole–por-
phyrin dyad[7d] in which unidirectional energy transfer does
not take place but rather excited-state equilibration between
the two chromophoric subunits. However, in this case, the
vent signals (13C). Mass spectra were recorded with an ESI
(Thermo Finnigan LCQ Advantage) or MALDI-TOF (Bruker
Daltonics UltraFlex II TOF/TOF) mass spectrometer (with
smartbeam™ laser and 2,5-dihydroxybenzoic acid matrix). High-
corrole unit contains two pentafluorophenyl meso substitu- resolution mass spectra were obtained with a Bruker Daltonics
Apex2 FT-ICR mass spectrometer equipped with a combined
MALDI/ESI ion source. All microwave irradiation experiments
were carried out in a dedicated CEM-Discover mono-mode micro-
wave apparatus operating at a frequency of 2.45 GHz using sealed
(aluminium-Teflon® crimp-top), large (10 mL) microwave process
vials. For column chromatography 70–230 mesh silica 60 (Merck)
was used as the stationary phase. Chemicals received from commer-
cial sources were used without further purification. DMF was dried
with molecular sieves (4 Å). UV/Vis absorption spectra were re-
corded with a Jasco V-560 spectrophotometer. For steady-state lu-
ents. Such substituents apparently have the effect of lower-
ing the excited-state energy of the corrole unit so that the
energy gap between the lower-lying singlet states of the cor-
role and porphyrin subunits is close to zero (the energy of
the singlet state of the corrole unit was calculated to be less
than 100 cm–1 higher than that of the singlet state of the
porphyrin unit[7d]), so allowing for equilibration at room
temperature. For the multichromophoric species investi-
gated in this work, the energy separation between the cor-
role- and porphyrin-based singlet states is larger (the energy minescence measurements, a Jobin Yvon-Spex Fluoromax 2 spec-
trofluorimeter was used equipped with a Hamamatsu R3896 pho-
tomultiplier. The spectra were corrected for photomultiplier re-
sponse by using a program purchased with the fluorimeter. For the
luminescence lifetimes, an Edinburgh OB 900 time-correlated sin-
gle-photon-counting spectrometer was used. A Hamamatsu PLP 2
laser diode (59 ps pulse width at 408 nm) and/or nitrogen discharge
(pulse width 2 ns at 337 nm) were employed as excitation sources.
Emission quantum yields for deaerated solutions were determined
by the optically diluted method[27] with [Ru(bpy)3]2+ (bpy = 2,2Ј-
bipyridine) in air-equilibrated aqueous solution as quantum yield
levels of the singlet states are calculated from the higher-
energy feature of the corresponding emission spectra), and
taking into account the relatively fast intrinsic decay of the
porphyrin-based singlet (ca. 1ϫ108 s–1), room-temperature
equilibration cannot take place.
Conclusions
meso-Pyrimidinylcorroles allow easy post-macrocycliza-
tion functionalization of the corrole scaffold, enabling the standard (Φem = 0.028[28]). Time-resolved transient absorption ex-
Eur. J. Org. Chem. 0000, 0–0
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S. Campagna, W. Maes et al.
FULL PAPER
periments were performed by using a pump-probe setup based on
the Spectra-Physics MAI-TAI Ti:sapphire system as the laser
source and the Ultrafast Systems Helios spectrometer as the detec-
tor. The pump pulse was generated with a Spectra-Physics 800 FP
OPA instrument. The probe pulse was obtained by continuum gen-
eration on a sapphire plate (spectral range 450–800 nm). The effec-
tive time resolution was around 200 fs, and the temporal chirp over
the white-light 450–750 nm range around 150 fs; the temporal win-
dow of the optical delay stage was 0–3200 ps. The time-resolved
data were analyzed with the Ultrafast Systems Surface Explorer
Pro software.[29] Experimental uncertainties on the absorption and
photophysical data are as follows: absorption maxima, 2 nm; molar
absorption, 15%; luminescence maxima, 4 nm; luminescence life-
times, 10%; luminescence quantum yields, 20%; transient absorp-
tion decay and rise rates, 10%.
5.3 μmol) in CHCl3 (10 mL). The mixture was stirred for 10 min
under Ar and diethyl ether was added. The mixture was washed
with 1 m HCl followed by water until neutral. After drying of the
organic fraction with MgSO4 and subsequent filtration, the solvent
was evaporated under reduced pressure. After flash column
chromatography (silica, eluent CH2Cl2/heptane, 1:1), pure dyad 5
was obtained as a red-brown solid (7.1 mg, 78%). 1H NMR
(300 MHz, CDCl3, 25 °C, TMS): δ = 8.89 (s, 4 H, Hβ porph), 8.86
[d, J(H,H) = 4.9 Hz, 2 H, Hβ porph], 8.75 [d, J(H,H) = 4.9 Hz, 2
H, Hβ porph], 8.17 [d, J(H,H) = 8.3 Hz, 2 H], 8.07–8.04 (m, 6 H),
8.01 (br. s, 2 H, Hβ corr), 7.79 (br. s, 3 H), 7.40–7.28 (m, 8 H, HPh
,
Hβ corr), 7.05/7.02 (2 s, 4 H, Hmesit), 2.63 (s, 3 H, SMe), 2.39 (s, 6
H), 2.13/2.11 (2 s, 12 H), 1.51 (s, 54 H, HtBu), –2.73 (br. s, 2 H,
NH) ppm. HRMS (ESI+): calcd. for C110H111ClCuN10OS
1717.7648 [M + H]+; found 1717.7629.
Procedures for the synthesis of pyrimidinylcorrole 1a,[10a] its Cu-
metallated counterpart 1b,[10b] and porphyrins 2a–c[11d,14] have been
reported before.
Fb-Porphyrin–Fb-Corrole Dyad 6: The general Cu-corrole demetal-
lation procedure was applied to dyad 4.[12c] SnCl2·2H2O (45.2 mg,
0.2 mmol) was added to a solution of dyad 4 (33.8 mg, 19 μmol) in
CH3CN/CH2Cl2 (2:1; 15 mL) and the resulting mixture was stirred
for 30 min at room temp. under Ar. Subsequently, concentrated
aqueous HCl (1 mL) was added and stirring was continued for
30 min at room temp. under Ar. The completion of the demetalla-
tion process was monitored by ESI-MS and TLC. The mixture was
diluted with diethyl ether, washed with water until neutral, dried
with Na2SO4, and the drying agent was filtered off. The solvent
was evaporated under reduced pressure and the pure Fb dyad was
obtained as a purple solid in a nearly quantitative yield (31 mg,
98%) after flash column chromatography (silica, eluent CH2Cl2/
heptane, 1:1). 1H NMR (300 MHz, CDCl3, 25 °C, TMS): δ = 8.88–
8.81 (m, 6 H, Hβ porph), 8.77 [d, J(H,H) = 4.7 Hz, 2 H, Hβ porph],
8.64–8.57 (m, 6 H, Hβ corr), 8.30 [d, J(H,H) = 4.1 Hz, 2 H, Hβ
corr], 8.10–8.00 (m, 8 H), 7.78–7.75 (m, 3 H), 7.34 [d, J(H,H) =
8.3 Hz, 2 H], 7.28/7.26 (2 s, 4 H, Hmesit), 2.78 (s, 3 H, SMe), 2.59
(s, 6 H), 1.98/1.96 (2 s, 12 H), 1.50/1.48 (2 s, 54 H, HtBu), –2.78
(br. s, 2 H, NH) ppm. HRMS (ESI+): calcd. for C110H114ClN10OS
1657.8586 [M + H]+; found 1657.8624.
Bis(Zn-Porphyrin)–Cu-Corrole Conjugate 3: A mixture of Cu-pyr-
imidinylcorrole 1b (81 mg, 103 μmol), Zn-porphyrin 2b (649 mg,
630 μmol, 6.1 equiv.), 18-crown-6 (10 mg, 38 μmol), and (finely
ground) K2CO3 (105 mg, 760 μmol) in dry DMF (10 mL) was
heated by microwave irradiation at 175 °C (100 W) for 1 h. After
cooling to room temp. diethyl ether was added and the mixture was
washed with distilled water. The organic fraction was dried with
MgSO4 and filtered. The solvent was evaporated and, after purifi-
cation by column chromatography (silica, eluent CH2Cl2/heptane,
3:7), pure conjugate 3 (157.5 mg, 55%) was obtained as a red-
brown solid together with a smaller quantity of dyad 4 (50 mg,
27%). 1H NMR (300 MHz, CDCl3, 25 °C, TMS): δ = 9.05–8.97
(m, 16 H, Hβ porph), 8.23 [d, J(H,H) = 7.9 Hz, 4 H], 8.12 (br. s,
12 H), 8.03 (br. s, 2 H, Hβ corr), 7.83–7.80 (m, 6 H), 7.72 (br. s, 2
H, Hβ corr), 7.52 [d, J(H,H) = 7.9 Hz, 4 H], 7.48 (br. s, 2 H, Hβ
corr), 7.40 (br. s, 2 H, Hβ corr), 7.05 (s, 4 H, Hmesit), 2.71 (s, 3 H,
SMe), 2.39 (s, 6 H), 2.18 (s, 12 H), 1.55 (s, 108 H, HtBu) ppm. 13C
NMR (100 MHz, CDCl3, 25 °C, TMS): δ = 150.7, 150.6, 150.3,
148.8, 142.0, 137.8, 135.0 (CH), 132.5/132.4 (CH), 132.3, 131.7
(CH), 129.8 (CH), 128.4 (CH), 122.8, 122.7, 121.0 (CH), 120.1/
119.9 (CH), 35.2, 31.9 (CH3), 21.3 (CH3), 20.1 (CH3), 14.6
(SCH3) ppm. HRMS (ESI+): calcd. for C178H185CuN14O2SZn2
1388.1204 [M + 2H]2+; found 1388.1233.
Zn-Porphyrin–Fb-Corrole Dyad 7: A mixture of Fb conjugate 6
(30 mg, 18 μmol) and Zn(OAc)2 (10 mg, 54 μmol) in CHCl3 (5 mL)
was stirred at room temp. for 2 h under Ar. The solvent was evapo-
rated under reduced pressure and, after purification by flash col-
umn chromatography (silica, eluent CH2Cl2/heptane, 1:1), pure Zn-
porphyrin–Fb-corrole dyad 7 was obtained as a pink-purple solid
(27 mg, 87%). 1H NMR (300 MHz, CDCl3, 25 °C, TMS): δ = 9.00–
8.92 (m, 4 H, Hβ), 8.88 [d, J(H,H) = 4.7 Hz, 2 H, Hβ], 8.84 [d,
J(H,H) = 4.1 Hz, 2 H, Hβ], 8.70 [d, J(H,H) = 4.7 Hz, 2 H, Hβ],
8.66–8.58 (m, 4 H, Hβ), 8.30 [d, J(H,H) = 4.1 Hz, 2 H, Hβ], 8.10–
8.01 (m, 8 H), 7.76 (br. s, 3 H), 7.33 [d, J(H,H) = 8.3 Hz, 2 H],
7.28/7.26 (2 s, 4 H, Hmesit), 2.79 (s, 3 H, SMe), 2.59 (s, 6 H), 1.99/
1.97 (2 s, 12 H), 1.50/1.49 (2 s, 54 H, HtBu) ppm. HRMS (ESI+):
Zn-Porphyrin–Cu-Corrole Dyad 4: A mixture of Cu-pyrimidinyl-
corrole 1b (21.7 mg, 28 μmol), Zn-porphyrin 2b (42.6 mg, 41 μmol,
1.5 equiv.), 18-crown-6 (2 mg, 7.6 μmol), and (finely ground)
K2CO3 (8.3 mg, 60 μmol) in dry DMF (3 mL) was heated overnight
at 90 °C under Ar. After cooling to room temp. diethyl ether was
added and the mixture was washed with distilled water. The organic
fraction was dried with MgSO4 and filtered. The solvent was evap-
orated and, after purification by column chromatography (silica,
eluent CH2Cl2/heptane, 1:1), pure dyad 4 (35.3 mg, 72%) was ob-
tained as a red-brown solid. 1H NMR (300 MHz, CDCl3, 25 °C,
TMS): δ = 9.03–8.95 (m, 6 H, Hβ porph), 8.87 [d, J(H,H) = 4.7 Hz,
2 H, Hβ porph], 8.18 [d, J(H,H) = 8.3 Hz, 2 H], 8.09–8.07 (m, 6
H), 8.01 (br. s, 2 H, Hβ corr), 7.80–7.77 (m, 3 H), 7.41–7.30 (m, 8
H, Hβ corr, HPh), 7.05/7.03 (2 s, 4 H, Hmesit), 2.63 (s, 3 H, SMe),
2.39 (s, 6 H), 2.14/2.12 (2 s, 12 H), 1.52 (s, 54 H, HtBu) ppm. 13C
NMR (100 MHz, CDCl3, 25 °C, TMS): δ = 150.7, 150.6, 150.1,
148.8, 137.9, 135.0 (CH), 132.5 (CH), 129.7 (CH), 128.4 (CH),
122.7, 121.0 (CH), 119.5 (CH), 35.2, 31.9 (CH3), 21.3 (CH3), 20.0
(CH3), 14.6 (SCH3) ppm. HRMS (ESI+): calcd. for C110H109ClCu-
N10OSZn 1779.6783 [M + H]+; found 1779.6757.
calcd. for C110H112ClN10OSZn 1719.7721 [M
1719.7777.
+
H]+; found
Bis(Fb-Porphyrin)–Cu-Corrole Conjugate 8: HCl (37%, 5 drops)
was added to a solution of bis(Zn-porphyrin)–Cu-corrole conjugate
3 (16.7 mg, 6 μmol) in CHCl3 (10 mL). The mixture was stirred for
10 min under Ar and diethyl ether was added. The solution was
washed with 1 m HCl followed by water until neutral. After drying
the organic fraction with MgSO4 and subsequent filtration, the sol-
vent was evaporated under reduced pressure. After flash column
chromatography (silica, eluent CH2Cl2/heptane, 1:1), pure conju-
gate 8 was obtained as a red-brown solid (10.1 mg, 63%). 1H NMR
(300 MHz, CDCl3, 25 °C, TMS): δ = 8.91–8.80 (m, 16 H, Hβ
Fb-Porphyrin–Cu-Corrole Dyad 5: HCl (37%, 5 drops) was added
to
a
solution of Zn-porphyrin–Cu-corrole dyad
4
(9.4 mg,
porph), 8.19 [d, J(H,H) = 8.3 Hz, 4 H], 8.09–8.02 (m, 14 H, HPh,
10
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Corrole–porphyrin Conjugates with Interchangeable Metal Centers
2Hβ corr), 7.81–7.77 (m, 6 H), 7.67 (br. s, 2 H, Hβ corr), 7.49–7.45
(m, 6 H, HPh, 2Hβ corr), 7.37 (br. s, 2 H, Hβ corr), 7.04 (s, 4 H,
Hmesit), 2.66 (s, 3 H, SMe), 2.38 (s, 6 H), 2.15 (s, 12 H), 1.53/1.52
(2 s, 108 H, HtBu), –2.70 (br. s, 4 H, NH) ppm. MS (ESI+): m/z =
Bis(Pt-Porphyrin)–Cu-Corrole Conjugate 12: A mixture of Cu-pyr-
imidinylcorrole 1b (5.1 mg, 6.5 μmol), Pt-porphyrin 2c (45 mg,
39 μmol, 6 equiv.), 18-crown-6 (1 mg, 4 μmol), and (finely ground)
K2CO3 (6 mg, 43 μmol) in dry DMF (3 mL) was heated by micro-
2647.8 [M + H]+, 1325.7 [M + 2H]2+. HRMS (ESI+): calcd. for wave irradiation at 165 °C (100 W) for 1 h. After cooling to room
C178H189CuN14O2S 1325.2084 [M + 2H]2+; found 1325.2087.
temp. diethyl ether was added and the mixture was washed with
distilled water. The organic fraction was dried with MgSO4 and
filtered. The solvent was evaporated and, after purification by col-
umn chromatography (silica, eluent CH2Cl2/heptane, 3:7), pure
Bis(Fb-Porphyrin)–Fb-Corrole Conjugate 9: The general Cu-corrole
demetallation procedure was applied to conjugate 8.[12c]
SnCl2·2H2O (45.2 mg, 0.2 mmol) was added to a solution of 8
(30 mg, 11 μmol) in CH3CN/CH2Cl2 (2:1, 15 mL) and the resulting
mixture was stirred for 30 min at room temp. under Ar. Sub-
sequently, concentrated aqueous HCl (1 mL) was added and stir-
ring was continued for 30 min at room temp. under Ar. The com-
pletion of the demetallation process was monitored by ESI-MS and
TLC. The mixture was diluted with diethyl ether, washed with
water until neutral, dried with Na2SO4, and the drying agent was
filtered off. The solvent was evaporated under reduced pressure and
the pure Fb conjugate was obtained as a purple solid in a nearly
quantitative yield (28.5 mg, 97%) after flash column chromatog-
raphy (silica, eluent CH2Cl2/heptane, 1:1). 1H NMR (300 MHz,
CDCl3, 25 °C, TMS): δ = 9.01 [d, J(H,H) = 4.7 Hz, 2 H, Hβ], 8.89
(s, 8 H, Hβ), 8.85 [d, J(H,H) = 4.1 Hz, 2 H, Hβ], 8.79 [d, J(H,H)
= 4.7 Hz, 4 H, Hβ], 8.73 [d, J(H,H) = 4.7 Hz, 2 H, Hβ], 8.65 [d,
J(H,H) = 4.9 Hz, 4 H, Hβ], 8.31 [d, J(H,H) = 4.1 Hz, 2 H, Hβ],
8.13–8.04 (m, 16 H), 7.79 (br. s, 6 H), 7.48 [d, J(H,H) = 8.5 Hz, 4
H], 7.27 (s, 4 H, Hmesit), 2.83 (s, 3 H, SMe), 2.58 (s, 6 H), 2.01 (s,
12 H), 1.52 (s, 108 H, HtBu), –2.75 (br. s, 4 H, NH) ppm. HRMS
(ESI+): calcd. for C178H192N14O2S 1295.2553 [M + 2H]2+; found
1295.2518.
1
triad 12 (14 mg, 73%) was obtained as an orange-brown solid. H
NMR (400 MHz, CDCl3, 25 °C, TMS): δ = 8.82–8.71 (m, 16 H,
Hβ), 8.11 [d, J(H,H) = 8.0 Hz, 4 H], 8.01 (br. s, 14 H, HPh, 2Hβ),
7.78 (br. s, 6 H), 7.63 (br. s, 2 H, Hβ), 7.47–7.42 (m, 6 H, HPh, 2
Hβ), 7.36 (br. s, 2 H, Hβ corr), 7.04 (s, 4 H, Hmesit), 2.63 (s, 3 H,
SMe), 2.38 (s, 6 H), 2.14 (s, 12 H), 1.51/1.50 (s, 108 H, HtBu) ppm.
MS (MALDI-TOF): calcd. for C178H183CuN14O2Pt2S 3033.3
[M]+; found 3033.5.
Pt-Porphyrin–Cu-Corrole Dyad 13: A mixture of Cu-pyrimidinyl-
corrole 1b (15 mg, 19 μmol), Pt-porphyrin 2c (25 mg, 22 μmol,
1.2 equiv.), 18-crown-6 (1 mg, 4 μmol), and (finely ground) K2CO3
(4.5 mg, 33 μmol) in dry DMF (5 mL) was heated overnight at
90 °C under Ar. After cooling to room temp. diethyl ether was
added and the mixture was washed with distilled water. The organic
fraction was dried with MgSO4 and subsequently filtered. The sol-
vent was evaporated and, after purification by column chromatog-
raphy (silica, eluent CH2Cl2/heptane, 7:3), pure dyad 13 (6.3 mg,
19%) was obtained as an orange-brown solid. 1H NMR (300 MHz,
CDCl3, 25 °C, TMS): δ = 8.82–8.73 (m, 6 H, Hβ), 8.65 [d, J(H,H)
= 5.1 Hz, 2 H, Hβ], 8.10 [d, J(H,H) = 8.3 Hz, 2 H], 8.01–7.98 (m,
8 H, 2Hβ, HPh), 7.77 (br. s, 3 H), 7.38–7.25 (m, 8 H, 6 Hβ, HPh),
7.05/7.02 (2 s, 4 H, Hmesit), 2.61 (s, 3 H, SMe), 2.39 (s, 6 H), 2.13/
2.11 (2 s, 12 H), 1.50 (s, 54 H, HtBu) ppm. HRMS (ESI+): calcd.
for C110H109ClCuN10OPtS 1910.7139 [M + H]+; found 1910.7209.
Bis(Zn-Porphyrin)–Fb-Corrole Conjugate 10: A mixture of Fb con-
jugate 9 (56 mg, 21.6 μmol) and Zn(OAc)2 (20 mg, 109 μmol) in
CHCl3 (10 mL) was stirred at room temp. for 2 h under Ar. The
solvent was evaporated under reduced pressure and, after purifica-
tion by column chromatography (silica, eluent CH2Cl2), bis(Zn-
porphyrin)–Fb-corrole conjugate 10 was obtained as a pink-purple
solid in a nearly quantitative yield (57.2 mg, 97%). 1H NMR
(300 MHz, CDCl3, 25 °C, TMS): δ = 9.02–8.97 (m, 10 H, Hβ), 8.89
[d, J(H,H) = 4.7 Hz, 4 H, Hβ], 8.85 [d, J(H,H) = 4.0 Hz, 2 H, Hβ],
8.76 [d, J(H,H) = 4.5 Hz, 4 H, Hβ], 8.72 [d, J(H,H) = 4.4 Hz, 2 H,
Hβ], 8.31 [d, J(H,H) = 3.8 Hz, 2 H, Hβ], 8.12–8.03 (m, 16 H), 7.78
(br. s, 6 H), 7.47 [d, J(H,H) = 7.9 Hz, 4 H], 7.24 (s, 4 H, Hmesit),
2.83 (s, 3 H, SMe), 2.58 (s, 6 H), 2.00 (s, 12 H), 1.51 (s, 108 H,
Supporting Information (see footnote on the first page of this arti-
cle): NMR spectra (1H, 13C) of corrole–porphyrin conjugates 3–13
and selected (high-resolution) mass spectra.
Acknowledgments
The authors thank the Institute for the Promotion of Innovation
through Science and Technology in Flanders (IWT) and the Alex-
ander von Humboldt Foundation for a doctoral and postdoctoral
fellowship, respectively, to T. H. N., the Fund for Scientific Re-
search - Flanders (FWO) for financial support and a postdoctoral
fellowship to W. M., and the KU Leuven and the Ministerie voor
Wetenschapsbeleid for continuing financial support. The Univer-
sity of Messina (Progetti di Ricerca di Ateneo and Fondi per Giov-
ani Ricercatori) and Ministero dell’Università e della Ricerca
(MIUR) (PRIN contract number 20085ZXFEE and FIRB
RBAP11C58Y, “NanoSolar”) are also acknowledged for financial
support.
H
tBu) ppm. HRMS (ESI+): calcd. for C178H188N14O2SZn2
1358.1673 [M + 2H]2+; found 1358.1666.
Bis(Zn-Porphyrin)–Ga-Corrole Conjugate 11: A large excess of
GaCl3 (0.5 m in pentane, 2 mL) was added to a solution of bis(Zn-
porphyrin)–Fb-corrole conjugate 10 (7.5 mg, 2.8 μmol) in pyridine
(5 mL). The solution was stirred at reflux for 1 h under Ar and
then the pyridine was evaporated under reduced pressure. After
purification by column chromatography (silica, eluent CH2Cl2/hep-
tane/pyridine, 3:2:0.02), pure bis(Zn-porphyrin)–Ga-corrole conju-
gate 11 (6.0 mg, 76%) was obtained as a purple-green solid. 1H
NMR (600 MHz, CDCl3, 25 °C, TMS): δ = 9.06–9.02 (m, 4 H,
Hβ), 8.99–8.93 (m, 8 H, Hβ), 8.88 [d, J(H,H) = 4.5 Hz, 4 H, Hβ],
8.81 [d, J(H,H) = 4.5 Hz, 2 H, Hβ], 8.76 [d, J(H,H) = 4.5 Hz, 4 H,
Hβ], 8.57 [d, J(H,H) = 3.8 Hz, 2 H, Hβ], 8.08 [d, J(H,H) = 8.3 Hz,
4 H, HPh], 8.06–8.03 (m, 12 H), 7.77 (br. s, 6 H), 7.43 [d, J(H,H)
= 7.9 Hz, 4 H, HPh], 7.25 (s, 4 H, Hmesit), 6.72–6.67 (m, 1 H,
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H
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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S. Campagna, W. Maes et al.
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12
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Corrole–porphyrin Conjugates with Interchangeable Metal Centers
the acceptor is considered to be twice that of 6, taking into
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Received: June 22, 2012
Published Online: ᭿
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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S. Campagna, W. Maes et al.
FULL PAPER
Porphyrinoid Multichromophores
Corrole–porphyrin multichromophoric sys-
tems containing a variety of (readily ex-
changeable) metals in the tetrapyrrolic li-
gands have been successfully synthesized
starting from a versatile meso-pyrimidinyl-
corrole scaffold. Although the conjugates
show only weak interchromophoric elec-
tronic interactions, fast and efficient cor-
role-to-porphyrin singlet–singlet energy
transfer was observed.
T. H. Ngo, F. Nastasi, F. Puntoriero,
S. Campagna,* W. Dehaen,
W. Maes* ........................................ 1–14
Corrole–Porphyrin Conjugates with Inter-
changeable Metal Centers
Keywords: Porphyrinoids
/
Macromo-
lecules / Energy transfer / Chromophores /
UV/Vis spectroscopy
14
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