Liquid-crystalline hybrid materials based on [60]fullerene and bent-core structures

Article abstract of DOI:10.1002/anie.201104866

What a core-ker! By the appropriate combination of promesogenic bent-core structures and the C₆₀ unit, lamellar polar liquid-crystal phases were induced (see scheme). The supramolecular organization of the functional fullerene-based assemblies,

Full text of DOI:10.1002/anie.201104866

DOI: 10.1002/anie.201104866
Supramolecular Chemistry
Liquid-Crystalline Hybrid Materials Based on [60]Fullerene and Bent-
Core Structures**
Jorge Vergara, Joaquꢀn Barberꢁ, Josꢂ Luis Serrano, M. Blanca Ros,* Nerea Sebastiꢁn,
Rosario de la Fuente, David O. Lꢃpez, Gustavo Fernꢁndez, Luis Sꢁnchez, and Nazario Martꢀn
The incorporation of the [60]fullerene moiety into molecular
materials is currently a common strategy for the design of
functional materials, particularly in the field of molecular
electronics.[1] The appeal of this strategy is due to the unique
properties of the [60]fullerene structure,[2] which can be
chemically manipulated for incorporation into suitable
molecular structures.[2h,i,3] Moreover, the design and develop-
ment of new functional C60 derivatives in combination with
other organic structures in a cost-effective way is a challeng-
ing target for fullerene and supramolecular chemists.[4]
With regard to this aim, liquid crystals are excellent
candidates for organizing fullerenes within supramolecular
ordered structures, and various morphologies of C60-contain-
ing liquid crystals, such as nematic, cholesteric, smectic, or
columnar phases, have been reported in the last decade.[4d,5–7]
Outstanding results have been achieved with liquid-crystal-
line fullerodendrimers with a low C60 content.[4d,7] In contrast,
studies on C60-based liquid-crystal materials with a high
fullerene content and with simpler molecular structures are
scarce,[5,8] possibly because the appropriate combination of
C60 units with other organic functional structures to attain
mesomorphism is not an easy task.
Herein, we report the synthesis and characterization of a
new class of nondendritic hybrid C60-containing bent-shaped
molecules. The aim of this work was to take advantage of the
unique properties derived from the compact packing of bent-
core structures. In 1996 this class of kinked structure was
found to form bent-core liquid crystals, which is a less
common and intriguing type of mesomorphism.[9] In contrast
to calamitic mesophases, bent-shaped molecules, through
dense arrangements that hinder the molecular rotation, lead
to strong polar order within either layers or columns, in many
cases producing supramolecular chirality with achiral mole-
cules. The molecules can often be switched in these meso-
phases by external stimuli, and they have afforded excep-
tionally good macroscopic polarization values and piezo-
electric, flexoelectric, and nonlinear optical responses.[10] We
report herein four C60-based bent-core compounds
(Scheme 1). Compounds 1a and 1b are fulleropyrrolidine
monoadducts with a 1:1 C60/promesogenic-core ratio. In
contrast, a 1:2 ratio is present in the case of the methano-
fullerene derivatives 2a and 2b. In both types of molecules,
two rigid cores of different lengths have been used to promote
the liquid-crystal order.
[*] Dr. J. Vergara, Dr. J. Barberꢀ, Prof. M. B. Ros
Dpto. Quꢁmica Orgꢀnica
Fullerene derivatives 1a, 1b, 2a, and 2b were synthesized
by the synthetic routes depicted in Schemes S1, S2, and S3
(see the Supporting Information). Fulleropyrrolidines 1a and
1b were prepared from a C60-containing acid. This inter-
mediate was synthesized by the [3+2] dipolar cycloaddition of
Instituto de Ciencia de Materiales de Aragꢂn (I.C.M.A.)
Facultad de Ciencias, Universidad de Zaragoza
C.S.I.C., 50009-Zaragoza (Spain)
E-mail: bros@unizar.es
Prof. J. L. Serrano
Dpto. Quꢁmica Orgꢀnica, Instituto de Nanociencia de Aragꢂn
Universidad de Zaragoza, 50009-Zaragoza (Spain)
C
60 with a suitably functionalized azomethine ylide, which was
generated in situ from a substituted benzaldehyde and
N-methylglycine, followed by hydrogenolysis.[11] The ester-
ification of the C60-containing acid with a 3,4’-biphenyl-based
biphenol,[12] with 4-(N,N-dimethylamino)pyridinium-4-tolu-
enesulfonate (DPTS)/dicyclohexylcarbodiimide (DCC),
gave the bent-core fulleropyrrolidines 1a and 1b. Two
alternative synthetic routes were assessed to prepare the
methano[60]fullerene monoadducts 2a and 2b. Both syn-
thetic approaches were based on the Bingel reaction to join
the [60]fullerene to the malonate structures.[13] Route 1
involved esterification of the C60 diacid with the correspond-
ing 3,4’-biphenyl derivatives, also using DPTS/DCC, to give
compounds 2a and 2b. A second synthetic pathway (Route 2)
was also used for compound 2b, but this gave lower yields
than Route 1 and the preparation of a bent-core malonate
(compound M; see Scheme 1 and Scheme S3 in the Support-
ing Information) was required prior to the addition to C60 in
the final synthetic step.
N. Sebastiꢀn, Prof. R. de la Fuente
Dpto. Fꢁsica Aplicada II, Facultad de Ciencia y Tecnologꢁa
Universidad del Pais Vasco, Apdo 644, 48080-Bilbao (Spain)
Dr. D. O. Lꢂpez
Grup de les Propietats Fꢁsiques dels Materials (GRPFM)
Departament de Fꢁsica i Enginyeria Nuclear
E.T.S.E.I.B. Universitat Politꢃcnica de Catalunya
Diagonal, 647, 08028 Barcelona (Spain)
Dr. G. Fernꢀndez, Dr. L. Sꢀnchez, Prof. N. Martꢁn
Departamento de Quꢁmica Orgꢀnica
Facultad de Ciencias Quꢁmicas
Ciudad Universitaria s/n, 28040 Madrid (Spain)
[**] This research is supported by the MICINN-FEDER of Spain-UE
MAT2009-14636-CO3, CT2008-00795, CSD2007-00010, the Aragꢂn
(E04), Basque (GI/IT-449-10), and Madrid (S2009/PPQ-1533)
governments. We are also grateful to BSCH-UZ and the Aragon
government (J.V.) and Basque Country (N.S.) for fellowship grants
and Dr. B. Villacampa from ICMA for the SHG measurements.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201104866.
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Communications
py (POM), X-ray diffraction (XRD) at variable
temperature, and differential scanning calorimetry
(DSC and MDSC).[15] Thus, the phase-transition
enthalpy and specific-heat (Cp) changes were ana-
lyzed. The phase-transition temperatures and enthal-
pies are reported in Table 1.
In spite of their dark brown color, optical textures
of the annealed samples could be observed and these
showed very small defects that exhibit birefringence
and confirmed the fluid nature of 1b, 2a, and 2b at a
range of temperatures (Figure 1).
Differential scanning calorimetery revealed the
unique thermal behavior of these [60]fullerene com-
pounds as well as slow kinetic transitions. Upon
heating, endothermic peaks corresponding to the
crystalline-to-mesomorphic and mesomorphic-to-iso-
tropic phase transitions were detected for 1b, 2a, and
2b. However, on cooling of the isotropic liquid,
different evolutions were observed. Concerning tran-
sitions from the liquid phase, significant thermal
hysteresis was shown by 1b and 2a on cooling and
this prevented the formation of a stable mesophase.
However, this was not the case for 2b, which exhibited
an enantiotropic mesophase (Figure 2). Interestingly,
successive heating and cooling processes revealed
repetitive thermal behavior for these hybrid com-
pounds. Moreover, Cp studies by MDSC at a rate of
18CminÀ1 revealed further changes below 608C for all
the [60]fullerene compounds and this is consistent with
a glass transition (see the Supporting Information).
To analyze the supramolecular organization of
these mesomorphic molecules, powder XRD studies
Scheme 1. Chemical structures of the C60-based bent-core compounds prepared
and the intermediate malonate M.
Table 1: Phase-transition behavior of the [60]fullerene bent-core com-
pounds and malonate M.
All new compounds were characterized by MALDI-TOF
mass spectrometry and 1H NMR, 13C NMR, and FTIR
spectroscopy. The presence of C60 monoadducts was also
confirmed by UV/Vis spectroscopy from the observation of
the characteristic absorption peaks at around 430 nm. Ther-
mogravimetric analysis (TGA) studies showed that these
compounds exhibit weight loss above 3208C (see the Sup-
porting Information).
The redox features of the C60 derivatives reported here
were investigated by cyclic voltammetry (CV) in ODCB/
CH3CN 4:1 (ODCB = o-dichlorobenzene) at room temper-
ature using a glassy carbon working electrode, standard Ag/
AgCl as the reference electrode, and tetrabutylammonium
perchlorate (0.1m) as the supporting electrolyte. The voltam-
mograms of all the fullerene derivatives exhibit three quasi-
reversible one-electron reduction waves at potentials of
À0.86, À1.29, and À1.79 V in the case of 1a and 1b, and
À0.78, À1.18, and À1.66 V for methanofullerene monoad-
ducts 2a and 2b (see the Supporting Information). These
values are slightly anodically shifted in comparison to pure
[60]fullerene because of saturation of one of the double bonds
of the C60 cage with the subsequent raising of the correspond-
ing LUMO level (see Ref. [14]).
Compound
Phase transitions[a–c]
1a
Cr 62 (11) I
I 49 g
1b
2a
2b
M
Cr-SmCP 183 (25)[d]
I 110 (20) Cr
I
Cr 102 (20) SmCP 134 (14) I
I 100 (28) Cr
g 57 SmCP 160 (28) I
I 141 (27) SmCP 54 g
Cr-Col 137 (62)[e]
I 134 Col 81 Cr
I
[a] Transition temperature (8C) at the slope of the peak and [b] enthalpies
(kJmolÀ1, in parenthesis), determined on the second scans by DSC
(108CminÀ1). [c] Cr=crystalline, g=glass, I=isotropic liquid,
SmCP=smectic C polar mesophase, Col=columnar mesophase.
[d] From a broad peak and combined enthalpies. [e] Associated with a
very slow kinetic of transition. A similar enthalpy value has been obtained
from specific-heat data in MDSC measurements at 1 KminÀ1. On
cooling, the observed peak does not correspond to the full trans-
formation to the stable mesophase.
were performed (Table 2). The XRD patterns recorded at
high temperatures for compounds 1b, 2a, and 2b show a
broad halo in the high-angle region centered at 4.5–4.6 ꢀ.
The thermal and liquid-crystalline properties of the
compounds were investigated by polarized optical microsco-
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the (001), (003), and (004) reflections of a lamellar structure.
For 2a a room temperature pattern could also be recorded by
freezing the mesophase (by rapid cooling from 1268C to avoid
crystallization). For 2b a room temperature pattern was
recorded for the glassy mesophase. The layer thicknesses,
measured from the small-angle reflections, are shown in
Table 2. This kind of pattern is unambiguously consistent with
a lamellar bent-core mesophase-like order.
Figure 1. Microphotographs of the textures corresponding to the
mesophases of the compounds: a) 1b (1788C, SmCP), b) 2b (1348C,
SmCP), and c) compound M (1328C, Col).[19]
Furthermore, the diffraction patterns of the two methane
adducts, 2a and 2b, also contain a middle-angle diffuse signal
at about 9 ꢀ, which has been reported for other C60-
containing liquid crystals[5d,f,6d,16] and has been attributed to
interactions between the fullerene units. This finding points to
a more-organized packing of the molecules for the mesophase
of these two compounds, with close contact between the
C
60 units compared to the mesophase of 1b. These features,
the measured layer spacing, as well as the POM observations,
and mesomorphic-to-isotropic phase-transition enthalpies are
consistent with a bilayer assembly of tilted bent-shaped
molecules (tentatively assigned as a smectic C polar (SmCP)
mesophase).[17] In the mesophase each molecule is folded with
the two bent-core units oriented in the same direction
(Figure 3), a situation consistent with the reported simulation
studies on C60-calamitic and C60-discotic dimesogens.[8c] The
Figure 2. Specific-heat data for compound 2b on heating (black
symbols) and on cooling (gray symbols). The inset shows typical DSC
scans on heating (black curve) and on cooling (gray curve) at
18CminÀ1. gl=glassy, ls=isotropic liquid phase.
This halo is assigned to the melting of the terminal chains and
it confirms the liquid-crystalline nature of the phases. In
addition, up to three sharp peaks in a 1:3:4 ratio were
observed at small angles, which can be respectively indexed as
Table 2: X-ray diffraction data for the [60]fullerene bent-core compounds.
Cmpd.
T [8C]
Measured
spacing [ꢄ]
Miller
index
Layer
thickness (d) [ꢄ]
Figure 3. Proposed molecular packing in the lamellar mesophase and
the glassy mesophase of compound 2b and X-ray diffraction patterns
at room temperature. The 001 reflection is partially hidden under the
beam stop, but is clearly detected in the small-angle XRD experiments.
1b
175[a]
97.0
32.9
24.5
4.5[d]
31.3
9.0[d]
4.5[d]
87.5
29.4
9.0[d]
4.6[d]
88.6
29.6
22.5
9.0[d]
4.6[d]
87.3
29.2
9.0[d]
4.6[d]
001
003
004
98.0
126[a]
RT[b]
003
94
fullerenes occupy the central area of the bilayer in a head-to-
head arrangement and the hydrocarbon chains form an
aliphatic region between neighboring layers.
2a
001
003
87.8
This kind of organization allows for a reasonable fit
between the cross-sectional areas of the C60 and the meso-
genic units,[5b,7b] and ensures efficient space filling because the
fullerene cross-section accommodates two mesogenic units.[18]
Therefore, practically no interdigitation is expected
between the C60 heads, a situation which is in reasonable
agreement with the XRD results reported for alkylated
fullerenes.[8b] The differences observed in the measured layer
spacing can be accounted for by changes in the tilt angle of the
molecule. The mesophase of 1b also probably has a bilayer
structure, based on the measured layer spacing. However, in
this case a dramatic mismatch must take place between the
140[c]
001
003
004
89.1
87.5
2b
RT[c]
001
003
[a] Heating process. [b] After rapid cooling to prevent crystallization.
[c] Cooling process. [d] Diffuse maximum.
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Communications
cross-sections of fullerene and the single mesogenic unit, and
this may explain the difficulty for the molecules of this
compound to organize themselves in the cooling process from
the isotropic liquid. In turn, the poor space-filling efficiency of
this strucure produces a less-organized mesophase. The C60
units are not as closely packed as in 2a and 2b, and they adopt
a more random arrangement, as suggested by the absence of
the middle-angle diffuse maximum in the X-ray patterns of
1b. The (002) reflection is absent in all the X-ray patterns,
whereas the (003) reflection is unusually strong. This suggests
that the projection of the electron density profile on the
direction normal to the layers contains three well-defined
maxima with a period of about d/3 (d = measured spacing).
These electron density maxima correspond to three regions
respectively containing the fullerene sublayer and the two
sublayers of bent-shaped units. Therefore the distribution of
the X-ray intensities, dominated by the contribution of the
third-order harmonic, agrees well with the features of the
proposed structure.
Figure 4. Bottom: Typical schematic representations of bent-core mol-
ecules. Top: Polarization switching current in the lamellar polar phase
of compound 2b at 1358C, under a triangular-wave electric field:
10 Hz, 42 VppmmÀ1. The molecular switching under an electric field in
the mesophase is also proposed.
From the data discussed above it can be stated that, with
the exception of compound 1a, in a subtle balance of
intermolecular interactions, increases in temperature help
disturb the solid arrangements of these simple nondendritic
fullerene monoadducts, but the bent-core structures retain the
molecular contacts to form compact lamellar mesophases
through the microsegregation of the structural motifs.
This segregated organization arises from a combination of
efficient space filling and strong interactions within each
microdomain. Regions of C60 units are intercalated between
regions of well-organized bent-shaped units, which are
responsible for the supramolecular layer organization. Never-
theless, the role of the fullerene moiety also seems to be
significant in these compounds. Thus, on cooling of the
isotropic liquid, 1b and 2a slowly self organize, thus
discouraging the formation of the liquid-crystal state, while
a longer bent-core structure (as in 2b) appears to lead to a
faster soft-matter rearrangement, thus recovering the lamel-
lar liquid-crystalline order. In addition, a comparison of the
liquid-crystalline properties of compound 2b and the malo-
nate M (see Ref. [19]) also points to the supramolecular
stabilizing role of the fullerene units in this system. The
presence of the C60 units seems to promote changes in the
supramolecular arrangement of the bent-core structures with
effects on both the type of molecular packing and the
stabilization of the liquid-crystal order. On the other hand,
the bulky C60 structure also appears to be responsible for the
vitrification processes detected in some of these compounds.
Interestingly, the hybrid material 2b forms a glass that retains
the order of the previous mesophase at room temperature
(glassy mesophase) for very long periods of time through
reversible thermal processes, as demonstrated by XRD and
MDSC.
knowledge has not been reported previously for a mesomor-
phic C60-containing compound, confirms the polar character
of the mesophase. The increase of the dielectric permittivity
at the isotropic-to-mesophase transition is another sign of the
polar order in the materials (see the Supporting Information,
Figures S8 and S9). This increase is due to the appearance of a
low-frequency mode that should be related to a collective
motion of the molecules in the smectic layers possessing polar
order.
Based on electrooptic and dielectric results, the response
can be attributed to the bent-core switching around the
molecular long axis rather than an azimuthal rotation from an
antiferroelectric ground state. Spontaneous polarization
values of around 60 nCcmÀ2 were measured for 2b and,
interestingly, preliminary studies on this switched sample
showed second harmonic generation (SHG) activity at room
temperature and in the absence of an electric field.[20]
Unfortunately this kind of study could not be carried out on
compounds 1b and 2a because the high temperature tran-
sitions prevented the preparation of suitable cells for 1b, and
owing to the dielectric breakdown of the cells in the case of
2a. A study of the dielectric behavior of 2a and 2b confirmed
the presence of a mesophase in both compounds (see the
Supporting Information).
In summary, we have prepared innovative nondendritic
hybrid C60-containing bent-core molecules that form lamellar
organizations. The potential of [60]fullerene units in an
ordered and easily processed soft phase could be combined
with organic functional moieties and the unique bent-core
liquid-crystal properties, such as supramolecular chirality,
optoelectronic features, and polar order. The temperature
range of the mesophase, the nanosegregation of the C60 units,
the stabilization of the soft supramolecular order even at
room temperature, and the molecular responses to external
stimuli, such as electric fields, for these C60-containing bent-
core molecules, all depend on the molecular structure and can
be modified by changing the molecular design. Furthermore,
the dielectric response of these materials, as well as their
An attractive feature of some bent-core liquid-crystalline
phases is their switching response under electric fields. This
behavior was investigated for these compounds in 5 mm
indium tin oxide (ITO) coated cells (see the Supporting
Information). The application of a triangular-wave field led to
a switching current response without a clear texture change
for 2b (Figure 4). This polarization current, which to our
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[7] a) T. Chuard, R. Deschenaux, J. Mater. Chem. 2002, 12, 1944 –
1951; b) B. Dardel, D. Guillon, B. Heinrich, R. Deschenaux, J.
Mater. Chem. 2001, 11, 2814 – 28311.
[8] a) T. Nakanishi, Y. Shen, J. Wang, S. Yagai, M. Funahashi, T.
Kato, P. Fernꢂndez, H. Mçhwald, D. G. Kurth, J. Am. Chem. Soc.
2008, 130, 9236 – 9237; b) P. A. L. Fernandes, S. Yagai, H.
Mçhwald, T. Nakanishi, Langmuir 2010, 26, 4339 – 4335; c) S.
Orlandi, L. Muccioli, M. Ricci, C. Zannoni, Soft Mater. 2009, 5,
4484 – 4491.
[9] a) G. Pelzl, S. Diele, W. Weissflog, Adv. Mater. 1999, 11, 707;
b) C. Tschierske, G. Dantlgraber, Pramana. J. Phys. 2003, 61,
455 – 481; c) D. M. Walba, Top. Stereochem. 2003, 24, 457 – 476;
d) M. B. Ros, J. L. Serrano, M. R. De La Fuente, C. L. Folcia, J.
Mater. Chem. 2005, 15, 5093 – 5098; e) R. Amaranatha Reddy, C.
Tschierske, J. Mater. Chem. 2006, 16, 907 – 961; f) H. Takezoe, Y.
Takanishi, Jpn. J. Appl. Phys. 2006, 45, 597 – 625; g) W. Weiss-
flog, H. N. Sheenivasa Murthy, S. Diele, G. Pelzl, Philos. Trans.
R. Soc. London Ser. A 2006, 364, 2657 – 2679; h) G. Pelzl, W.
Weissflog in Thermotropic liquid crystals, Recent advances (Ed.:
A. Ramamoorthy), Springer, Dordrecht, 2007, chap. 1.
[10] a) A. Jꢂkli, C. Bailey, J. Harden in Thermotropic liquid crystals,
Recent advances (Ed.: A. Ramamoorthy), Springer, Dordrecht,
2007, chap. 2; b) J. Etxebarria, M. B. Ros, J. Mater. Chem. 2008,
18, 2919 – 2926; c) A. Jꢂkli, I. Pintre, J. L. Serrano, M. B. Ros,
M. R. De La Fuente, Adv. Mater. 2009, 21, 3784 – 3788; d) I. C.
Pintre, J. L. Serrano, M. B. Ros, J. Martꢁnez-Perdiguero, I.
Alonso, J. Ortega, C. L. Folcia, J. Etxebarria, R. Alicante, B.
Villacampa, J. Mater. Chem. 2010, 20, 2965 – 2971.
redox properties, confirm that this new type of C60-based
liquid crystal represents an advantageous strategy for the
design of new functional systems.
Received: July 12, 2011
Published online: November 4, 2011
Keywords: fullerenes · liquid crystals · molecular electronics ·
.
organic functional materials · supramolecular chemistry
[1] Special features on molecular electronics: C. Joachim, M. A.
Ratner, Proc. Natl. Acad. Sci. USA 2005, 102, 8800 and related
papers in this issue; Chem. Rev. 2010, 110, 1 – 574.
[2] a) N. Martꢁn, L. Sanchez, B. Illescas, I. Perez, Chem. Rev. 1998,
98, 2527 – 2548; b) L. Echegoyen, L. E. Echegoyen in The
Electrochemistry of C60 and Related Compounds (Eds.: L.
Henning, O. Hammerich), Marcel Dekker, New York, 2001;
c) D. Gust, T. A. Moore, A. L. Moore, Acc. Chem. Res. 2001, 34,
40 – 48; d) D. M. Guldi, Chem. Soc. Rev. 2002, 31, 22 – 36; e) H.
Imahori, J. Phys. Chem. B 2004, 108, 6130 – 6143; f) H. Imahori,
Org. Biomol. Chem. 2004, 2, 1425; g) J. L. Segura, N. Martꢁn,
D. M. Guldi, Chem. Soc. Rev. 2005, 34, 31 – 47; h) F. Langa, J. F.
Nierengarten, Fullerene Principles and Applications, RSC Pub-
lishing, London, 2007; i) “Carbon Nanotubes and Related
Structures: Synthesis Characterization, Functionalization, and
Applications” (Eds.: D. M. Guldi, N. Martꢁn), Wiley-VCH,
Weinheim, 2010.
[3] a) S. R. Wilson, D. L. Schuster, B. Nuber, M. S. Meier, M.
Maggini, M. Prato, R. Taylor in Organic Chemistry of Fullerenes
(Eds.: K. M. Kadish, R. S. Ruoff), Wiley Interscience, New York,
2000; b) A. Hirch, M. Brettreich in Fullerenes: Chemistry and
Reactions, Wiley-VCH, Weinheim, 2004; c) N. Martꢁn, Chem.
Commun. 2006, 2093 – 2104.
[4] a) L. Sꢂnchez, N. Martꢁn, D. M. Guldi, Angew. Chem. 2005, 117,
5508 – 5516; Angew. Chem. Int. Ed. 2005, 44, 5374 – 5382;
b) E. M. Pꢃrez, N. Martꢁn, Chem. Soc. Rev. 2008, 37, 1512 –
1519; c) T. Nakanishi, Chem. Commun. 2010, 46, 3425 – 3436;
d) S. S. Babu, H. Mçhwald, T. Nakanishi, Chem. Soc. Rev. 2010,
39, 4021 – 4035; e) D. Canevet, E. Pꢃrez, N. Martꢁn, Angew.
Chem. 2011, 123, 9416 – 9427; Angew. Chem. Int. Ed. 2011, 50,
9248 – 9259.
[5] a) S. Campidelli, C. Eng, M. I. Saez, J. W. Goodby, R. Desche-
naux, Chem. Commun. 2003, 1520 – 1521; b) S. Campidelli, J.
Lenoble, J. Barberꢂ, F. Paolucci, M. Marcaccio, D. Paolucci, R.
Deschenaux, Macromolecules 2005, 38, 7915 – 7925; c) H. Mam-
louk, B. Heinrich, C. Bourgogne, B. Donnio, D. Guillon, D.
Felder-Flesch, J. Mater. Chem. 2007, 17, 2199 – 2205; d) N.
Maringa, J. Lenoble, B. Donnio, D. Guillon, R. Deschenaux, J.
Mater. Chem. 2008, 18, 1524 – 1534; e) S. Campidelli, P. Bourgun,
B. Guintchin, J. Furrer, H. Stoeckli-Evans, I. M. Saez, J. W.
Goodby, R. Deschenaux, J. Am. Chem. Soc. 2010, 132, 3574 –
3581; f) S. Campidelli, L. Pꢃrez, J. Rodrꢁguez-Lꢄpez, J. Barberꢂ,
F. Langa, R. Deschenaux, Tetrahedron 2006, 62, 2115 – 2122;
g) L. Pꢃrez, J. Lenoble, J. Barberꢂ, P. De La Cruz, R. Desche-
naux, F. Langa, Chem. Commun. 2008, 4590 – 4592.
[11] a) M. Maggini, G. Scorrano, M. Prato, J. Am. Chem. Soc. 1993,
115, 9798 – 9799; b) N. Tagmatarchis, M. Prato, Synlett 2003,
768 – 779. c) N. Martꢁn, M. Altable, S. Filippone, A. Martꢁn-
Domenech, L. Echegoyen, C. M. Cardona, Angew. Chem. 2006,
118, 116 – 120; Angew. Chem. Int. Ed. 2006, 45, 110 – 114.
[12] a) D. Shen, A. Pegenau, S. Diele, I. Wirth, C. Tschierske, J. Am.
Chem. Soc. 2000, 122, 1593 – 1601; b) N. Gimeno, M. B. Ros, J. L.
Serrano, R. De La Fuente, Angew. Chem. 2004, 116, 5347 – 5350;
Angew. Chem. Int. Ed. 2004, 43, 5235 – 5238; c) J. Barberꢂ, N.
Gimeno, L. Monreal, R. Pinol, M. R. Ros, J. L. Serrano, J. Am.
Chem. Soc. 2004, 126, 7190 – 7191.
[13] a) C. Bingel, Chem. Ber. 1993, 126, 1957 – 1959; b) X. Camps, A.
Hirsch, J. Chem. Soc. Perkin Trans. 1 1997, 1595 – 1596.
[14] Although Bingel cycloadducts can undergo a retro-cyclopropa-
nation reaction (retro-Bingel reaction) under electrochemical
and chemical reduction conditions, those processes occur under
specific experimental conditions (controlled potential electrol-
ysis). In our case, and under the CVexperimental conditions, the
observed waves can be reasonably assigned to the reduction
processes occurring on the fullerene unit. For more details, see:
a) R. Kessinger, J. Crassous, A. Herrmann, M. Ruttimann, L.
Echegoyen, F. Diederich, Angew. Chem. 1998, 110, 2022 – 2025;
Angew. Chem. Int. Ed. 1998, 37, 1919 – 1922; b) R. Kessinger,
N. S. Fender, L. E. Echegoyen, C. Thilgen, L. Echegoyen, F.
Diederich, Chem. Eur. J. 2000, 6, 2184 – 2192; c) M. W. J. Beulen,
L. Echegoyen, J. A. Rivera, M. A. Herranz, A. Martꢁn-Dome-
nech, N. Martꢁn, Chem. Commun. 2000, 917 – 918; d) M. W. J.
Beulen, J. A. Rivera, M. A. Herranz, A. Martꢁn-Domenech, N.
Martꢁn, L. Echegoyen, Chem. Commun. 2001, 407 – 408;
e) M. W. J. Beulen, J. A. Rivera, M. A. Herranz, B. Illescas, N.
Martꢁn, L. Echegoyen, J. Org. Chem. 2001, 66, 4393 – 4398;
f) M. A. Herranz, M. W. J. Beulen, J. A. Rivera, L. Echegoyen,
M. C. Dꢁaz, B. M. Illescas, N. Martıꢁn, J. Mater. Chem. 2002, 12,
2048 – 2053.
[6] a) M. Sawamura, K. Hawai, Y. Matsuo, K. Kanie, T. Kato, E.
Nakamura, Nature 2002, 419, 702 – 705; b) Y. Matsuo, A.
Muramatsu, Y. Kamikawa, T. Kato, E. Nakamura, J. Am.
Chem. Soc. 2006, 128, 9586 – 9587; c) S. Campidelli, T. Brand-
muller, A. Hirsch, I. M. Saez, J. W. Goodby, R. Deschenaux,
Chem. Commun. 2006, 4282 – 4284; d) J. Lenoble, N. Maringa, S.
Campidelli, B. Donnio, D. Guillon, R. Deschenaux, Org. Lett.
2006, 8, 1851 – 1854; e) Y. W. Zhong, Y. Matsuo, E. Nakamura, J.
Am. Chem. Soc. 2007, 129, 3052 – 3053.
[15] For details about the MDSC technique and its application to
liquid-crystal materials see: a) M. B. Sied, J. Salud, D. O. Lꢄpez,
M. Barrio, J. L. Tamarit, Phys. Chem. Chem. Phys. 2002, 4, 2587 –
2593; b) N. Sebastiꢂn, M. R. de La Fuente, D. O. Lꢄpez, M. A.
Angew. Chem. Int. Ed. 2011, 50, 12523 –12528
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www.angewandte.org 12527

Communications
Pꢃrez-Jubindo, J. Salud, S. Diez-Berart, M. B. Ros, J. Phys.
Chem. B 2011, 115, 9766 – 9775.
Figure 1 and see the Supporting Information). This mesophase is
consistent with a columnar order according to the optical
texture; unfortunately, crystallization prevented further charac-
terization by XRD.
[16] a) D. Felder-Flesch, L. Rupnicki, C. Bourgogne, B. Donnio, D.
Guillon, J. Mater. Chem. 2006, 16, 304 – 309; b) J. Wang, Y. Shen,
S. Kessel, P. Fernandes, Y. Kaname, Y. Shiki, D. G. Kurth, H.
Mçhwald, T. Takanishi, Angew. Chem. 2009, 121, 2200 – 2204;
Angew. Chem. Int. Ed. 2009, 48, 2166 – 2170.
[20] SHG activity of the sample cell (5 mm thick) was surveyed at
room temperature, as a fingerprint indication of polar order
(noncentrosymmetric arrangement). A very weak signal at
953 nm was detected when rotating the cell around a vertical
axis, perpendicular to the incidence plane of the 1907 nm
excitation light. However, it must be noted that proper
characterization of the dij coefficients of these materials requires
well-aligned samples (J. Ortega, J. A. Gallastegui, C. L. Folcia, J.
Etxebarria, N. Gimeno, M. B. Ros, Liq. Cryst. 2004, 31, 579 –
584) and more precise measurements will be performed as part
of a future project.
[17] Further studies on the aligned samples should enable the
determination of the tilted (SmCP) or nontilted (SmAP)
structure of these materials (L. Guo et al., Soft. Mater. 2011, 7,
2895 – 2899; R. A. Reddy, Science 2011, 332, 72 – 77).
[18] The cross-sectional area is 90–100 ꢀ2 for C60 and 22–25 ꢀ2 for
classical rod-like units. The cross-section of a bent-core molecule
is larger and tilting also increases this area.
[19] The dimer M exhibits a narrow liquid-crystal phase on heating,
as deduced from DSC, MDSC, and dielectric studies (Table 1,
12528 www.angewandte.org
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2011, 50, 12523 –12528