All-Fullerene Electron Donor–Acceptor Conjugates

Article abstract of DOI:10.1002/anie.201901863

The synthesis and characterization of a covalent all-fullerene C₆₀-Lu₃N@I_h-C₈₀ electron donor–acceptor conjugate has been realized by sequential 1,3-dipolar cycloaddition reactions of azomethine ylides on Lu₃N@I_h-C₈₀ and C₆₀. To the best of our knowledge, this is the first time that two fullerenes behaving as both electron donor (Lu₃N@I_h-C₈₀) and acceptor (C₆₀) are forming an electroactive dumbbell. DFT calculations reveal up to 16 diastereomeric pairs, that is, 8 with syn and 8 with anti orientation, with the anti-RSSS isomer being the most stable. Spectroelectrochemical absorption and femtosecond transient absorption experiments support the notion that a C₆₀^??-Lu₃N@I_h-C₈₀^?+ charge-separated state is formed. Spin conversion from the charge-separated singlet state C₆₀^??-Lu₃N@I_h-C₈₀^?+ into the corresponding triplet state is facilitated by the heavy-atom effect stemming from the Lu₃N-cluster, which, in turn, slows down the charge recombination by one order of magnitude.

Full text of DOI:10.1002/anie.201901863

A Journal of the Gesellschaft Deutscher Chemiker
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Accepted Article
Title: All-fullerene Electron Donor-Acceptor Conjugates
Authors: Marta Izquierdo, Benedikt Platzer, Antony J Stasyuk, Olga
Stasyuk, Alexander Voityuk, Sergio Cuesta, Miquel Solá, Dirk
M Guldi, and Nazario Martin
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201901863
Angew. Chem. 10.1002/ange.201901863
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10.1002/anie.201901863
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All-fullerene Electron Donor-Acceptor Conjugates
Marta Izquierdo,[a]+ Benedikt Platzer,[b]+ Antony J. Stasyuk,[c] Olga A. Stasyuk,[c,d]
Alexander A. Voityuk,[c,e] Sergio Cuesta,[a] Miquel Solà,[c]* Dirk M. Guldi,[b]* and
Nazario Martín[a]*
Dedicated to Prof. Jean-Marie Lehn on the occasion of his 80th birthday
Abstract: The synthesis and characterization of a covalent all-
fullerene C60-Lu3N@Ih-C80 electron donor-acceptor conjugate has
been realized by sequential 1,3-dipolar cycloaddition reactions of
azomethine ylides on Lu3N@Ih-C80 and C60. To the best of our
knowledge, this is the first time that two fullerenes behaving as both
electron donor (Lu3N@Ih-C80) and acceptor (C60) are forming an
mimicking those steps seen in natural photosynthesis.[3] To this
end, C60 stands out as a redox active component.[4] To a much
lower extend, endohedral fullerenes – which encapsulate atoms,
molecules, ions, or clusters – have been integrated into electron
donor–acceptor systems. Interesting is the fact that they stabilize
charge-separated states when compared to C60.[5]
electroactive dumbbell.
DFT calculations reveal up to 16
Notably, empty fullerenes, in general, and C60 in particular, turned
into electron acceptors of choice. In contrast, some endohedral
fullerenes exhibit remarkable electron donating features: In the
presence of strong electron acceptors such as tetracyano-p-
quinodimethanes (TCNQ)[6] or perylene bisdiimides (PDI),[7]
charge-separated states are formed, in which the endohedral
fullerene are one-electron oxidized.
The trimetallic nitride template (TNT) family with the general
formula M3N@C2n is more stable than any other endohedral
metallofullerenes (EMF). In particular, Lu3N@C80 is one of the
best-studied endohedral metallofullerenes. Considering a much
lower oxidation when compared to C60, renders TNTs a much
better choice as electron-donor in electron donor-acceptor
conjugates.[8]
As far as electron transfer reactions are concerned, TNTs have
been shown to provide the ways and means to spin convert
charge separated states. To this end, the stabilization of a triplet
charge separated state relative to a singlet charge separated
state is quite significant. But, it is not solely the difference in spin,
which is decisive, the energy difference, which is due to the
exchange interaction, is another important factor for slowing down
diastereomeric pairs, that is, 8 syn and 8 with anti orientation, being
the anti-RSSS isomer the most stable. Spectroelectrochemical
absorption and femtosecond transient absorption experiments
support the notion that a C60•--Lu3N@Ih-C80 charge-separated state
•+
is formed. Spin conversion of the singlet C60•--Lu3N@Ih-C80•+ charge-
separated state into the triplet C60•--Lu3N@Ih-C80•+ charge-separated
state is facilitated by the heavy atom affect stemming from the Lu3N-
cluster and, in turn, slows down the charge recombination by one
order of magnitude.
Converting light into chemical energy by means of photoinduced
electron transfer (ET) is key to natural photosynthesis of plants
and bacteria. In the reaction centers, a cascade of charge
separation and charge shift reactions yields long-lived charge-
separated states in nearly quantitative quantum yields.[1][2]
broad variety of artificial photosynthetic systems based on multi-
component electron donor-acceptor conjugates have enabled
A
[a]
[b]
Dr. M. Izquierdo, Mr. S. Cuesta, Prof. Dr. N. Martín
Departamento de Química Orgánica, Facultad de Ciencias
Químicas, Universidad Complutense, 28040 Madrid, Spain.
E-mail: nazmar@ucm.es
Mr. Benedikt Platzer, Prof. Dr. Dirk M. Guldi
Department of Chemistry and Pharmacy
Friederich-Alexander Univesität Erlangen-Nürnberg
Nikolaus-Fiebiger-Str. 10
E-mail: dirk.guldi@fau.de
Dr. A. J. Stasyuk, Dr. O. A. Stasyuk, Prof. Dr. A. A. Voityuk, Prof. Dr.
M. Solà, miquel.sola@udg.edu
Institute of Computational Chemistry and Catalysis and Department
of Chemistry
University of Girona
the charge recombination.
Formation of a triplet charge
separated state was recently shown for the case of TNT, when
linked covalently to a PDI. Remarkable was the stabilization when
contrasted with the singlet charge separated state: an impressive
factor of nearly 1000 evolved. Notable is, however, that electron
accepting PDIs reveal rather large reorganization energies in
electron transfer reactions. Quite different is the scenario for
C60:[9],[10] What stands out among the many unique features of C60
is it small reorganization energy in electron transfer reactions.
The consequences of the small reorganization energy are far
reaching: For example, charge recombination, as the most critical
parameter to impact photocatalysis and photovoltaics, is pushed
into the Marcus inverted region and, in turn, slowed down.
[c]
[d]
C/ M. Aurèlia Capmany, 69, 17003 Girona, Spain.
Dr. O. A. Stasyuk
Institute of Organic Chemistry and Biochemistry
Academy of Sciences of Czech Republic
Flemingo nám. 2, 166 10 Prague, Czech Republic.
Instituciꢀ Catalana de Recerca i Estudis Avancats (ICREA), 08010
Barcelona, Spain.
In light of the aforementioned, integrating, for example, Lu3N@Ih-
C80 as electron donor together with C60 as electron acceptor into
an electron donor-acceptor conjugate is the way to go en-route
towards long-lived charge separation. This is, where the current
work makes a significant contribution; we have designed,
synthesized, and probed a C60-Lu3N@Ih-C80 dumbbell and have
demonstrated that the triplet charge separated state is longer-
[e]
+
These authors contributed equally to the work.
Supporting information for this article is given via a link at the end of
the document.
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10.1002/anie.201901863
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lived by nearly two orders of magnitude when compared to the
corresponding singlet charge separated state. Our work has been
rounded off by DFT calculations at the BLYP-D3(BJ)/def2-SVP
level of theory to shed light onto relative thermodynamic stability
of the 16 possible stereoisomers!
To predict the structure of 6a/6b we considered the following:
First, cycloaddition to Lu3N@Ih-C80 takes place on a [5,6]-bond
affording the thermodynamic product.[13] Second, 6a/6b possess
four chiral centers, that is, two at the nitrogen atoms and two at
the C2 of the pyrrolidine rings, and, in turn, a total of 16
stereoisomers are possible. Third, depending on the relative
orientation of C60 and Lu3N@Ih-C80 with respect to the plane of the
phenyl linker, 6a/6b might be a syn- or an anti-isomer. As such,
32 is the maximum theoretical number of isomers. However,
since enantiomeric pairs are physically and chemically
indistinguishable, only 16 stereoisomers, namely 8 of them
corresponding to syn and 8 corresponding to anti orientation,
were considered in the present theoretical study (see Figure 1 for
syn and anti RSSS).
Synthesis of all-fullerene 6a/6b. It is well known that the
reactivity of TNTs is different from that of empty fullerenes;
therefore, it requires a specific strategy. The retrosynthetic
analysis of the all-fullerene dumbbell, in which C60 and Lu3N@Ih-
C80 are linked via a phenyl linker indicates two possible synthetic
routes – Scheme 1.
Figure 1. Structures of the anti RSSS and syn RSSS stereoisomers of 6a/6b.
CAM-B3LYP-D3(BJ)/def2-SVP//BLYP-D3(BJ)/def2-SVP relative energies for
all 16 isomers. The three most stable isomers (within 5 kcal/mol) are marked
with red.
Scheme 1. Synthesis of 6a/6b from 1,3-dipolar cycloaddition reaction (see
theoretical calculations).
Stability of all-fullerene 6a/6b stereoisomers. DFT and TDA-
DFT calculations at the CAM-B3LYP-D3(BJ)/def2-SVP//BLYP-
D3(BJ)/def2-SVP level of theory (see SI for complete
computational details) revealed that all isomers are in the
energetic range of 14 kcal/mol – Figure 1. The most stable isomer
is anti-RSSS. Two syn-isomers, that is, syn-RRSS and syn-
RSSS, lie in the range of 5 kcal/mol. In order to understand the
relative stability QTAIM calculations for the most stable structures
have been performed.[14]
To characterize the excited states, each isomer was divided into
6 fragments – Figure S16: (1) Lu3N; (2) Ih-C80 + pyrrolidine; (3) C60
+ pyrrolidine; (4) C8 chains attached to Ih-C80 (5) and C8 chains
attached to C60; (6) phenyl linker. Next, exciton delocalization and
charge transfer contributions in each fragment were analyzed for
the lowest 80 excited states of each isomer. Locally excited
states (LE), where the exciton is mostly localized on a single
fragment (charge separation value < 0.1e), charge separated
In route A, the reaction of terephthalaldehyde 1 and N-octylglycine
2 with C60 afforded exclusively aldehyde 3. The 1,3-dipolar
cycloaddition reaction with Lu3N@Ih-C80 was, however,
unsatisfactory. The lack of dumbbell formation is rationalized by
the lower reactivity of Lu3N@Ih-C80 relative to C60. Route B
yielded the desired 6a/6b from aldehyde 4. Formation of
aldehyde 4 also afforded side-product 5, which lacked the p-
formylphenyl group.[11] 5 was formed by the addition of the N-
octylglycine to the fullerene in competition to the 1,3-dipolar
cycloaddition, presumably through an electron transfer/radical
mechanism. Similar reactions have been reported for C60 and
Gd@C82.[12] When monoadduct 4 was refluxed in toluene in the
presence of C60 and N-octylglycine, 6a/6b were obtained as main
products. The structure of 6a/6b was confirmed by mass
spectrometry showing molecular peaks at m/z= 2605.039 uma.
Both of them were isolated by HPLC and characterized by a
variety of spectroscopic techniques (SI).
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(CS) states, where the electron density is redistributed between
fragments (charge separation > 0.9e), as well as mixed states (CT
states) with partial charge transfer (charge separation between
0.1e and 0.9e), where significant LE and CS contributions are
present, were identified.
As expected, the dipole moments of the CS/CT states differ
significantly from those of the LE and GS states – Table S3. For
the lowest CS/CT states in syn-RRSS, syn-RSSS, and anti-
RSSS, the dipole moments are calculated to be 23, 25, and 63 D,
respectively. The differences in dipole moment of the syn- and
anti-stereoisomers are rationalized by a larger electron donor-
acceptor distance in anti-RSSS of 14 Å, as compared to syn-
RRSS and syn-RSSS of 10 Å. Also, charge transfer for syn-
RRSS and syn-RSSS involve about 0.5 – 0.6 e-, whereas for anti-
RSSS it is equivalent to 1 e-. Figure 2 displays the GS, LE, and
CS/CT energies for the singlet excited states in the gas phase and
in DCM. As seen, the population generation of CS1 and CS2
through charge separation of LE1 state is possible only for the
anti RSSS isomer in DCM (CS states have lower energies than
LE1 state).
Excited state calculations were performed for the three isomers of
lowest energy: syn-RRSS and syn-RSSS as well as anti-RSSS.
In the gas phase, the energies of the predicted singlet excited
states range from 2.0 to 3.8 eV –Table S2. For each isomer, the
LE states on Lu3N@Ih-C80 have the lowest energy. They are best
described as HOMO-to-LUMO+2 transitions. LE states on C60 are
0.22-0.32 eV higher and correspond to HOMO-4-to-LUMO
transitions. The first CS/CT states (CS1/CT1) are found at around
3.0 eV for all three isomers – Table S2. In the case of syn-RRSS
and syn-RSSS, the charge transferred from Lu3N@Ih-C80 to C60 is
about 0.5 – 0.6 e- (CT states), while almost 1 e- is transferred in
anti-RSSS (CS states). In the gas-phase, Lu3N@Ih-C80-to-C60
CS/CT states have relatively small probabilities with oscillator
strengths that are in the range from 0.001 to 0.02. Notably,
similarly low oscillator strengths were associated with the lowest
LE states. Molecular orbitals representing both LE, CS, and CT
states shown in Figure S17.
Electron transfer rates in all-fullerene 6a/6b. The non-adiabatic
ET rates, kET, were estimated using the classical Marcus
equation[15] (for details see SI). To this end, three key ET
parameters were computed: free energy G, electronic coupling
V and, reorganization energy including both the internal and
solvent terms (for fragment definition see Figure S18). Using the
computed data, which is listed in Table 1, we estimated the rates
for charge separation and charge recombination
Solvent effects for all-fullerene 6a/6b. A COSMO-like model
was applied with dichloromethane (DCM) as solvent. Solvation
energies for the syn- and anti-isomers are around 0.24 eV for their
ground states (GS) and they exert no notable effects on the
relative energies of the LE states relative to the ground states. By
virtue of similar dipole moments for the GS and LE states, the
energies of the LE excitations remain almost unchanged.
Table 1. Electron transfer parameters and rates for charge separation reactions
in DCM calculated for anti-RSSS.
Reorganizatio
n energy 
Rate constant, s-
Type
G0, eV
|V|
1
eV
LE1CS1
LE1CS2
-0.313
-0.133
0.0041
0.0183
0.828
0.813
1.3611010
2.4641010
Charge separation, LE1  CS1 and LE1  CS2, is fast with kCS
 13 and 24 ns-1, respectively. Note that the corresponding
charge recombination reactions are in the inverted Marcus region
and cannot accurately be estimated. Figure 3 highlights the
electron transfer processes following photoexcitation of the anti-
RSSS and the syn-RRSS isomers. Analysis of excited states
revealed that the singlet and triplet CS states have similar
energies, which facilitate intersystem crossing between them.
Figure 2. Relative energies in eV of the ground states (GS), the first LE state,
(LE1), and the CS/CT states (CS1/CT1, CS2/CT2), in the anti-RSSS, syn-
RRSS, and syn-RSSS computed in vacuum (VAC) and dichloromethane
(DCM). CS1/CT1 and CS2/CT2 are due C80  C60
.
Figure 3. Summary of the computational results for the first LE and CS of singlet
and triplet states for the anti-RSSS and the syn-RRSS computed in DCM.
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Ground-state characterization of all-fullerene 6a/6b[16] The
absorption spectrum of 6a/6b (Figure S19) reveals, on one hand,
the same features as those seen for C60, namely a maximum at
432 nm, which evolves as a well-known marker for the successful
functionalization of C60, followed by a weaker maximum at around
700 nm.[17] On the other hand, a rather broad maximum is
observed for 6a/6b at about 860 nm, similar to that of 850 nm for
4. Changing the polarity of the solvent lacks any notable impact
on the overall absorption spectra (Figure S20).
a newly formed 500 nm maximum matches the fingerprint
absorption of the one-electron oxidized form of Lu3N@Ih-C80 next
to the 750 nm absorption. In the near-infrared, a 1010 nm
maximum resembles the marker of the one-electron reduced form
of C60. Once formed, the C60•--Lu3N@Ih-C80•+ CS state decays
biphasic with rate constants of 8.48 ± 0.12 x 108 and 1.18 ± 0.01
x 108 s-1.
In complementary nanosecond pump-probe experiments, the
•+
presence of two C60•--Lu3N@Ih-C80
CS states were
Acquiring the absorption spectra of the one-electron oxidized form
of 4 and of the one-electron reduced form of C60 deemed
necessary to identify possible charge separation products in the
femto- and nanosecond pump-probe experiments – vide infra. All
measurements were conducted in deaerated anisole with 0.1 M
TBAPF6 as supporting electrolyte. Differential absorption spectra
of 4 upon one-electron oxidation include maxima at 500 and 750
nm as well as a minimum around 855 nm. One electron reduction
of C60 results in a weak maximum at 760 nm as well as a strong
maximum at 1000 nm along with a shoulder at 1075 nm (Figure
S21).
independently corroborated. In addition, the triplet excited state
of Lu3N@Ih-C80 was verified to be the product of charge
recombination. To this end, the broad 690 nm fingerprint
absorption as seen in reference experiments with Lu3N@Ih-C80
evolves after the charge recombination. It is then the latter, which
reinstates slowly the ground state with 1.88 ± 0.01 x 106 s-1 – a
rate constant that fits the decay seen in reference experiments.[19]
Next, deconvolution of the transient spectra into species-
associated spectra was performed by means of target analysis.
In particular, a kinetic model was employed, which was based on
five species. We imply the simultaneous excitation of two different
species. On one hand, it is the singlet excited state of Lu3N@Ih-
C80 with its characteristic 495 and 580 nm maxima as the first
species. On the other hand, the CT state is excited and evolves
as the second species. Our notion of an excited CT state is
confirmed by transient maxima at 500 and 597 nm as opposed to
490 and 577 nm for the singlet excited state of Lu3N@Ih-C80. The
CT state decays, however, directly to the ground state with 3.79
± 0.01 x 1010 s-1 but without giving rise to any notable charge
separation. It is only the singlet excited state, which undergoes
charge separation to afford the C60•--Lu3N@Ih-C80•+ CS state as
the third species. The transient, which evolves throughout the
decay of the CS state, still features all the spectroscopic markers
of the C60•--Lu3N@Ih-C80•+ CS state. As such, we infer that the
initially formed CS state is of singlet nature and undergoes a spin
flip to yield a triplet CS state as fourth species. Helpful is in this
respect the heavy atom affect stemming from the Lu3N-cluster.
The fifth and final species is the triplet excited state of Lu3N@Ih-
C80. The aforementioned model and analyses are summarized in
Figures 5 and S26-S28.
Excited-state characterization of all-fullerene 6a/6b
2
5
10
20
0.006
0.005
0.004
0.003
0.002
0.001
0.000
50
100
200
500
1000
2000
5500
500
600
700
800
1000
1200
1400
Wavelength /nm
Figure 4. Differential absorption spectra obtained upon femtosecond flash
photolysis (387 nm) of C60-Lu3N@Ih-C80 in deaerated anisole with several time
delays between 2 and 5500 ps at room temperature.
1*(C60)-(Lu3N@C80
)
0.006
0.004
0.002
0.000
-0.002
d+
.+
(C60
)
d--(Lu3N@C80
)
x 0.2
1[(C60).--(Lu3N@C80
3[(C60).--(Lu3N@C80
)
]
]
The nature of the singlet excited-state deactivation in 6a/6b, that
is, charge separation and charge recombination, was
corroborated by means of time-resolved transient absorption
spectroscopy. 387 nm was chosen to photoexcite 6a/6b. In
reference experiments with 4 (Figures S22-25), its singlet excited
state with its characteristic 495 and 580 nm maxima decay within
less than 100 ps to afford the triplet excited state in good
agreement with earlier findings on TNTs.[7,18] The latter is
characterized by a broad absorption, which maximizes at around
690 nm and a slow reinstatement of the ground state with 1.02 ±
0.01 x 106 s-1.
.+
)
500
600
700
800 1000 1200 1400
Wavelength /nm
Figure 4 documents the same singlet excited state features upon
photoexcitation of 6a/6b. A fast decay of the singlet excited state
starts, however, in 6a/6b and with 1.83 ± 0.03 x 1011 s-1 changes
in the differential absorption spectra are associated with the
transformation into a C60•--Lu3N@Ih-C80•+ CS state. In the visible,
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10.1002/anie.201901863
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COMMUNICATION
Acknowledgements
0.0016
0.0014
0.0012
0.0010
0.0008
0.0006
0.0004
0.0002
0.0000
.+
1[(C60).--(Lu3N@C80
3[(C60).--(Lu3N@C80
)
)
]
]
.+
Financial support from the European Research Council (ERC-
320441-Chirallcarbol) and the MINECO of Spain (Projects
CTQ2017-83531-R, CTQ2017-85341-P, and CTQ2017-84327-P,
network CTQ2016-81911-REDT, and Juan de la Cierva
formación contracts FJCI-2016-29448 to A.J.S. and FJCI-2017-
32757 to O.A.S.) is acknowledged. This work was also funded by
the Deutsche Forschungsgemeinschaft (DFG) via SFB 953
“Synthetic Carbon Allotropes”, the Catalan DIUE (2017SGR39,
XRQTC, and ICREA Academia 2014 Award to M.S.), and the
FEDER fund (UNGI10-4E-801).
(C60)-3*(Lu3N@C80
)
500
600
700
800 1000 1200 1400
Wavelength /nm
1.0
0.8
0.6
0.4
0.2
0.0
Keywords: fullerenes · electroactive dyads · photoinduced
electron transfer · stereoisomers · excited states
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Figure 5. (Top) Species associated spectra of first singlet excited state, CT
state, singlet CS state, and triplet CS state obtained upon target analysis of
femtosecond transient absorption data of 6a/6b in anisole. (Center) Evolution
associated spectra of singlet CS state, triplet CS state, and triplet excited state
of Lu3N@C80 obtained upon global analysis of nanosecond transient absorption
data of 6a/6b in anisole. (Bottom) Corresponding relative concentration profiles
of the observed transient species.
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A. Palkar, A. J. Athans, N. Martín, A. Rodríguez-Fortea, J. M. Poblet, G.
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In conclusion, we have successfully synthesized and
characterized a covalent all-fullerene C60-Lu3N@Ih-C80 electron
donor-acceptor conjugate.
This is, to the best of our
[6]
[7]
[8]
Y. Takano, S. Obuchi, N. Mizorogi, R. García, M. Á. Herranz, M. Rudolf,
D. M. Guldi, N. Martín, S. Nagase, T. Akasaka, J. Am. Chem. Soc. 2012,
134, 19401-19408.
knowledge, the first time that fullerenes have been chosen as
both electron donors and acceptors in an integrated conjugate.
Of great importance is the presence of the Lu3N cluster, which
accelerates spin conversion. Accordingly, combined results
from spectroelectrochemical absorption and femtosecond
transient experiments support the notion that a C60•--Lu3N@Ih-
C80•+ charge-separated state is formed. Spin conversion of the
L. Feng, M. Rudolf, S. Wolfrum, A. Troeger, Z. Slanina, T. Akasaka, S.
Nagase, N. Martín, T. Ameri, C. J. Brabec, D. M. Guldi, J. Am. Chem.
Soc. 2012, 134, 12190-12197.
a) K. Sato, M. Kako, M. Suzuki, N. Mizorogi, T. Tsuchiya, M. M.
Olmstead, A. L. Balch, T. Akasaka, S. Nagase, J. Am. Chem. Soc. 2012,
134, 16033-16039; b) N. Chen, J. R. Pinzón, L. Echegoyen,
ChemPhysChem 2011, 12, 1422-1425; c) M. Rudolf, L. Feng, Z. Slanina,
W. Wang, S. Nagase, T. Akasaka, D. M. Guldi, Nanoscale, 2016, 8,
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Tsuchiya, T. Akasaka, L. Echegoyen, Chem. Eur. J., 2012, 18, 5136-
5148.
•+
singlet C60•--Lu3N@Ih-C80 charge-separated state into the
triplet C60•--Lu3N@Ih-C80•+ charge-separated state slows down
the charge recombination by one order of magnitude.
[9]
D. M. Guldi, Chem. Commun. 2000, 321-327.
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Chem. Commun. 2006, 3202-3204.
Experimental Section
[11] M. R. Cerón, V. Maffeis, S. Stevenson, L. Echegoyen, Inorg. Chim. Acta,
2017, 468, 16–27 and references cited therein. Compound 5: MALDI-
TOF: MS(+) (m/z): [M]+ calcd. for C90H21N2Lu3, 1655.043, found,
1655.022.
Experimental Details are exhibited in the supporting information.
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[12] a) D. Zhou, H. Tan, C. Luo, L. Gan, C. Huang, J. Pan, M. Lü, Y. Wu,
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[19] No evidence for the involvement of any C60 triplet excited state in the
overall deactivation cascade was noted (see: D. M. Guldi, M. Prato, Acc.
Chem. Res., 2000, 33, 695-703).
[13] M. N. Chaur, F. Melin, A. L. Ortiz, L. Echegoyen, Angew. Chem. Int. Ed.
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[14] By means of this approach we have identify that Lu3N@Ih-C80 / C60
interactions in syn-RRSS and syn-RSSS, phenyl / C60 interactions, and
C60 / aliphatic C8 chain interactions in anti-RSSS impact the relative
stabilities. These as well as the characteristics for selected BCPs are
shown in Figure S15 and Table S1.
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[16] All experiments were performed with both isomers, 6a and 6b, without
observing any notable differences. Thus, in the following we focus our
discussions on 6a.
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Spin conversion of the singlet
charge-separated state into
the triplet charge-separated
state slows down the charge
recombination by one order of
magnitude.
Marta Izquierdo, Benedikt Platzer, Antony, J.
Stasyuk, Olga A. Stasyuk, Alexander A.
Voityuk, Sergio Cuesta, Miquel Solà,* Dirk M.
Guldi,* and Nazario Martín*
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All-fullerene Electron Donor-Acceptor
Conjugates
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