A nematic [60]fullerene supermolecule: When polyaddition leads to supramolecular self-organization at room temperature

Article abstract of DOI:10.1039/b700460e

The synthesis, liquid-crystalline properties and supramolecular organization of a [60]fullerene-based supermolecule are described, and the great potential of the spherical carbonated polyhedron to produce new materials through its multiple and addressable

Full text of DOI:10.1039/b700460e

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www.rsc.org/materials | Journal of Materials Chemistry
A nematic [60]fullerene supermolecule: when polyaddition leads to
supramolecular self-organization at room temperature{
Hind Mamlouk, Benoit Heinrich, Cyril Bourgogne, Bertrand Donnio, Daniel Guillon and
Delphine Felder-Flesch*
Received 11th January 2007, Accepted 12th February 2007
First published as an Advance Article on the web 1st March 2007
DOI: 10.1039/b700460e
The synthesis, liquid-crystalline properties and supramolecular organization of a [60]fullerene-
based supermolecule are described, and the great potential of the spherical carbonated
polyhedron to produce new materials through its multiple and addressable regioselective
functionalization is emphasized. Indeed, hexaaddition on the carbon sphere has allowed the
preparation, in 50% yield, of the first room-temperature enantiotropic nematic C60-based
material, even though the promoter was not mesomorphic. Despite the high molecular weight of
such a supermolecule, the resulting material was revealed to be easily oriented in its mesophase by
a magnetic field; this has allowed, by small angle X-ray diffraction investigations, a fine
description of the molecular organization and of the corresponding relevant interactions involved.
These results open the way to multifuntional materials that can take advantage of such an easy
orientation of the grafted active chromophores (donor and acceptor) to be particularly efficient
(for example in the design of photovoltaic materials).
as interactions are too weak to generate mesomorphism.7
Introduction
Examples of C60 derivatives possessing
character (bearing more than two anisotropic moieties
per C60 via
polyaddition8 or dendritic approach9)
a
high LC
Over the last decade, [60]fullerene has attracted considerable
attention in materials science.1 Notably, several efforts have
been aimed at producing liquid-crystalline C60-based materials
of added value in the form of increased processability, film
formation, and control over self-assembly. This requires
that some shape anisotropy should be imparted to C60,
which is perfectly isotropic. Indeed, for such systems, the
tendency of the anisotropic moieties to enforce an ordered
self-assembly must be sufficiently strong and properly
designed to accommodate spheres. There are two main
approaches to design fullerene-containing liquid crystals:
covalent and noncovalent modifications. Two examples of
the non-covalent approach are based on the formation of
inclusion complexes in which C60 either resides within cavities
of host molecules, such as dendritic porphyrins,2 cyclo-
triveratrylene,3 or is linked to hexaphenyltriphenylene
forming a 1 : 1 mixture with hexakis(4-nonylphenyl)dipyr-
a
showed either a transient nematic,8b a chiral nematic,10 or a
smectic A phase.8a,8c,10 In these cases, the properties of
the materials were mostly dominated by the anisotropic
moieties, due to dilution of the C60 unit. In another approach,
C60 is placed at the apex of cone-shaped molecules,
forming a new type of mesomorphic compound, which self-
assembles into thermo- and lyotropic columnar liquid-crystal-
line mesostructures.11
The design and selection of molecular building blocks to
reach such orientational orderings and particularly the nematic
phase close to or just above room temperature is therefore
challenging, as shown in reports on systems containing
multivalent cores ranging from soft and flexible such as
carbosilazane,12 siloxane,13 and silsesquioxane,14 to hard such
as gold nanoparticles.15 Such systems are technologically
relevant too, as the nematic phase often allows the control of
the macroscopic alignment in thin films, important for
potential technological applications.
azino[2,3-f:29,39-h]quinoxalene.4
Within
the
covalent
approach, a number of different mesogenic units have been
introduced to obtain a variety of fullerene-containing thermo-
tropic liquid-crystalline materials.5,6 For such systems, the
main criterion for LC phase induction is the adequacy of
the fullerene and mesogenic side-groups cross-sections.
In addition, small anisotropic units are often insufficient
As C60 can be considered as a versatile hard building block
for dendritic systems due to its tunable core valency (1 to 6)
and regioselective polyaddition, we were interested in further
investigating its use as a template to build multicomponent
supermolecules. Applying the ‘‘orthogonal transposition’’
described by Krautler and Maynollo16 and Diederich’s method
of ‘‘tether-directed remote functionalization’’17 for specific
multifunctionalized [60]fullerene, it may be possible to
regioselectively prepare new three-dimensionally structured
molecules and thus new structural motives that can not be
obtained by starting from other cores such as silsesquioxanes14
or gold nanoparticles.15
IPCMS/GMO, UMR CNRS/ULP 7504, 23 rue du Loess BP 43, 67034,
Strasbourg Cedex, France. E-mail: Delphine.Felder@ipcms.u-strasbg.fr;
Fax: +33 (0)3 88 10 72 46; Tel: +33 (0)3 88 10 71 63
{ Electronic supplementary information (ESI) available: NMR [1H
(300 MHz) and 13C (75 MHz), CDCl3] and UV-visible spectra of 2 and
1, DSC curves of 5, 2 and 1, X-Ray diffraction pattern obtained for 2
at 80 uC, evolution of the X-ray pattern of 2 and 1 with temperature,
variation of the lamellar periodicity d with temperature for 2 and 1. See
DOI: 10.1039/b700460e
This journal is ß The Royal Society of Chemistry 2007
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Here, we report on the synthesis, liquid-crystalline pro-
perties and supramolecular organization of the first room-
temperature nematic [60]fullerene hexaadduct 1 (Scheme 1),
obtained in 50% yield, the highest yield so far reported for
hexaaddition on C60.8,10,22b Hexaadduct 1 can be easily
oriented under a magnetic field. As it will be shown, the
selected design, i.e. polyaddition of side-on connected
malonates on the carbon hard core, is a suitable method for
obtaining stable anisotropic materials, even starting from
non-mesomorphic promoters. Therefore, assembling 12
amorphous units around the 3-D focal template allows
mesomorphism through induced collective structural aniso-
tropy and hierarchical intermolecular interactions.
AM 300 (300 MHz) with solvent signal as reference (d in ppm).
MALDI-TOF mass spectra were measured on a Brucker
BIFLEXTM matrix-assisted laser desorption time-of-flight mass
spectrometer (MALDI-TOF).
POM, DSC and XRD measurements of the mesomorphic
materials
The optical textures of the mesophases were studied with a
Leitz polarizing microscope equipped with a Mettler FP80
hot-stage and a FP80 central processor. The transition
temperatures and enthalpies were measured by differential
scanning calorimetry with a Perkin-Elmer DSC-7 instrument
operated at a scanning rate of 10 uC min21 on heating. The
apparatus was calibrated with indium (156.6 uC, 28.4 J g21
)
Experimental
and gallium (29.8 uC) as the standards. The TGA measure-
ments were carried out on a SDTQ 600 apparatus at scanning
rate of 10 uC min21. The oriented XRD patterns were recorded
using a sealed-tube generator (900 W) equipped with a pinhole
General
All reagents were used as purchased from commercial sources
without further purification. Solvents were dried using
standard techniques prior to use. All reactions were performed
in standard glassware under an inert argon atmosphere.
Drying in vacuo was done at 1022 Torr. Products were isolated
by column chromatography (silica gel 60, particle size 40–
63 mm, 230–400 mesh, Merck). TLC was performed using
precoated glass sheets with silica gel 60 F254, Merck. UV/Vis
spectra (lmax in nm (e)) were measured on a Hitachi U-3000
spectrophotometer. NMR spectra were recorded on a Bruker
˚
CuKa (l = 1.542 A) parallel beamline based on a home-
mounted Kirkpatrick-Baez optics coupled with a HiStar
detector (Bruker AXS). The crude sample was placed in
Lindemann capillary of 1 mm diameter and 10 mm wall
thickness and aligned in a home-made permanent magnetic
field oven (1.0 T). The sample temperature was controlled to
within ¡0.03 uC. Two different detector–sample distances
were used: 111.5 and 328.0 mm. The patterns were analyzed
using home-made ImageJ plug-ins (Q and 2h profiles).
Scheme 1 Synthesis of mesomorphic hexaadduct 1: (a) 10-bromodecanol,19 K2CO3, KI, DMF, 80 uC, 96%; (b) NaOH–H2O, MeOH, reflux, 97%;
(c) 4-octyloxyphenol,20 DCC, 4-(N-pyrrolidino)pyridine, CH2Cl2, Ar, rt, 78%; (d) 10% Pd/C, H2, 1,4-dioxane, 93%; (e) 4-octyloxybenzoic acid,21
DCC, 4-(N-pyrrolidino)pyridine, THF, Ar, rt, 71%; (f) malonyl dichloride, Et3N, CH2Cl2, Ar, rt, 80%; (g) i) C60, DMA, toluene, Ar, rt, 2 h, ii) 8,
CBr4, DBU, 3 weeks, 50%.
2200 | J. Mater. Chem., 2007, 17, 2199–2205
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Computational modeling
23.04 mmol) and 4-(N-pyrrolidino)pyridine (7.1 g, 47.95 mmol)
in dry CH2Cl2 (375 mL) was stirred overnight at room
temperature under argon. The solvent was removed and the
residue purified by column chromatography (SiO2, CH2Cl2)
and then washed with hexane to yield 8.86 g (78%) of 5 as a
white solid, Mp 53.8 uC. Elemental analysis: calc. (found) for
The molecular mechanics studies have been performed on SGI
Origin 2800 and Octane2 calculators using Insight II and
Discover 3 software from Accelrys (www.accelrys.com) with
the cvff forcefield.
1
C38H52O6, C 75.46 (75.15), H 8.67 (8.78). H NMR (CDCl3,
Synthetic procedures and analytical data
300 MHz): d 0.89 (t, J = 7 Hz, 3H), 1.23 (m, 24H), 1.80
(m, 4H), 3.63 (t, J = 6 Hz, 2H), 3.95 (t, J = 6 Hz, 2H), 4.01 (t,
J = 6 Hz, 2H), 5.13 (s, 2H), 6.60 (m, 2H), 6.89 (d, J = 9 Hz,
2H), 7.08 (d, J = 9 Hz, 2H), 7.39 (m, 5H), 8.02 (d, J = 9 Hz,
1H). 13C NMR (CDCl3, 75 MHz): d 14.08, 22.65, 25.68, 25.94,
26.04, 29.10, 29.23, 29.28, 29.36, 29.40, 29.46, 31.80, 32.78,
63.06, 68.44, 68.94, 70.23, 100.71, 105.49, 112.05, 115.02,
115.95, 122.57, 127.54, 128.27, 128.71, 134.32, 144.50, 156.61,
161.42, 163.73, 164.50.
4-Octyloxyphenol,20 methyl 4-octyloxybenzoate and 4-octyl-
oxybenzoic acid,21 methyl 2-hydroxy-4-benzyloxybenzoate 218
and 10-bromodecanol19 were synthesized according to litera-
ture procedures.
Synthesis of methyl 2-[(10-hydroxy)decyloxy]-4-
benzyloxybenzoate 3
10-Bromodecanol19 (5.95 g, 25.09 mmol) was added to a
mixture of methyl 2-hydroxy-4-benzyloxybenzoate 218 (5.40 g,
20.91 mmol), anhydrous potassium carbonate (14.45 g,
104.55 mmol) and potassium iodide (7 mg, 0.04 mmol) in
DMF (100 mL) and the reaction mixture was heated at 80 uC
for 20 h. The resulting mixture was cooled to room tem-
perature, filtered through celite and the filter pad was washed
with CH2Cl2. The solvent was evaporated and the residue
taken up in diethyl ether. The organic layer was washed with
aqueous NaCl (2 6 200 mL) and water, then dried (MgSO4),
filtered and evaporated to dryness. Column chromatography
(SiO2, CH2Cl2) yielded 8.31 g (96%) of 3 as white crystals, Mp
57.5 uC. Elemental analysis: calc. (found) for C25H34O5, C
Synthesis of 49-octyloxyphenyl 2-[(10-hydroxy)decyloxy]-4-
hydroxybenzoate 6
A solution of 5 (8 g, 13.23 mmol) and 10% palladium-
on-carbon catalyst (533 mg) in 1,4-dioxane (200 mL) was
stirred under a hydrogen atmosphere for 3 days. The crude
mixture was then filtered through celite and the filter pad
washed with CH2Cl2. The solvent was removed and the
crude product re-crystallized in toluene to yield 6.33 g (93%)
of 6 as a white solid, Mp 110.4 uC. Elemental analysis:
calc. (found) for C31H46O6, C 72.34 (72.10), H 9.01 (9.10).
1H NMR (CDCl3, 300 MHz): d 0.89 (t, J = 7 Hz, 3H),
1.27 (m, 24H), 1.80 (m, 4H), 3.65 (t, J = 4 Hz, 2H), 3.95 (t,
J = 6 Hz, 2H), 4.00 (t, J = 6 Hz, 2H), 5.95 (s, 1H), 6.46
(m, 2H), 6.90 (d, J = 9 Hz, 2H), 7.08 (d, J = 9 Hz, 2H),
7.96 (d, J = 9 Hz, 1H). 13C NMR (CDCl3, 75 MHz): d 14.08,
22.64, 25.57, 25.78, 26.02, 28.94, 29.08, 29.18, 29.20, 29.23,
29.26, 29.34, 31.80, 32.59, 63.12, 68.46, 68.88, 100.51, 107.35,
111.09, 115.03, 122.56, 134.50, 144.43, 156.62, 161.66, 161.86,
164.79.
1
72.44 (72.85), H 8.27 (8.38). H NMR (CDCl3, 300 MHz): d
1.32 (m, 14H), 1.83 (m, 2H), 3.64 (t, J = 5 Hz, 2H), 3.85 (s,
3H), 3.98 (t, J = 7 Hz, 2H), 5.09 (s, 2H), 6.55 (m, 2H), 7.40 (m,
5H), 7.84 (d, J = 9 Hz, 1H). 13C NMR (CDCl3, 75 MHz): d
25.68, 25.87, 29.01, 29.23, 29.34, 29.43, 29.46, 32.75, 51.56,
63.00, 68.87, 70.14, 100.73, 105.33, 112.81, 127.51, 128.19,
128.64, 133.73, 136.23, 160.74, 163.18, 166.34.
Synthesis of 2-[(10-hydroxy)decyloxy]-4-benzyloxybenzoic acid 4
Synthesis of 49-octyloxyphenyl 2-[(10-hydroxy)decyloxy]-4-
NaOH (9.61 g, 240 mmol) was added to a solution of 3 (8.3 g,
20.02 mmol) in methanol–water (400 : 42 mL) and heated at
reflux for 2 h. The mixture was cooled to room temperature,
diluted in water (200 mL) and concentrated. Hydrochloric acid
was added (to reach pH 2) leading to a white precipitate, which
was filtered off and washed with water (until pH 7 was reached).
No further purification was necessary to yield 7.77 g (97%) of 4
as white crystals, Mp 82 uC. Elemental analysis: calc. (found) for
[(octyloxyphenyl)- 4 benzoyloxy]benzoate 7
A solution of 6 (6.3 g, 12.24 mmol), 4-octyloxybenzoic acid21
(3.06 g, 12.24 mmol), N,N9-dicyclohexylcarbodiimide (3.03 g,
14.68 mmol) and 4-(N-pyrrolidino)pyridine (453 mg,
3.06 mmol) in dry THF (150 mL) was stirred overnight at
room temperature under argon. The reaction mixture was
evaporated to dryness and the crude product purified by
column chromatography (SiO2, CH2Cl2). Re-crystallization in
petroleum ether–toluene yields 6.53 g (71%) of 7 as white
crystals, Mp 89.6 uC. Elemental analysis: calc. (found) for
1
C24H32O5, C 71.97 (71.73), H 8.05 (8.16). H NMR (CDCl3,
300 MHz): d 1.32 (m, 14H), 1.89 (m, 2H), 3.65 (t, J = 8 Hz, 2H),
4.18 (t, J = 6 Hz, 2H), 5.12 (s, 2H), 6.60 (d, J = 2 Hz, 1H), 6.72
(dd, J = 9 Hz and 2 Hz, 1H), 7.74 (m, 5H), 8.14 (d, J = 9 Hz, 1H).
13C NMR (CDCl3, 75 MHz): d 25.65, 25.77, 28.75, 29.05, 29.23,
29.26, 29.33, 32.70, 62.98, 70.17, 70.46, 100.25, 107.34, 110.71,
127.54, 128.42, 128.74, 135.48, 135.75, 158.91, 164.06, 165.22.
1
C46H66O8, C 73.96 (73.58), H 8.91 (9.01). H NMR (CDCl3,
300 MHz): d 0.90 (t, J = 6 Hz, 6H), 1.25 (m, 34H), 1.79 (m,
6H), 3.62 (t, J = 6 Hz, 2H), 3.96 (t, J = 6 Hz, 2H), 4.00 (t,
J = 6 Hz, 4H), 6.90 (m, 6H), 7.12 (d, J = 9 Hz, 2H), 8.06 (d, J =
9 Hz, 2H), 8.14 (d, J = 9 Hz, 1H). 13C NMR (CDCl3, 75 MHz):
d 14.09, 22.64, 25.67, 25.90, 25.97, 26.03, 29.04, 29.07, 29.20,
29.23, 29.28, 29.31, 29.34, 29.39, 29.44, 31.79, 31.81, 32.78,
63.06, 68.38, 68.45, 69.18, 107.11, 113.40, 114.39, 115.06,
116.73, 121.01, 122.48, 132.38, 133.36, 144.36, 155.67, 156.75,
160.55, 163.79, 164.32, 164.47.
Synthesis of 49-octyloxyphenyl 2-[(10-hydroxy)decyloxy]-4-
benzyloxybenzoate 5
A solution of 4 (7.5 g, 18.73 mmol), 4-octyloxyphenol20
(4.16 g, 18.73 mmol), N,N9-dicyclohexylcarbodiimide (4.75 g,
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Synthesis of malonate 8
based on DMA-templating. Hexaadduct 1 was obtained in
50% yield (0.35 g) as a pale orange glassy solid.
Et3N (1.22 mL, 8.66 mmol) was added to a mixture of 7 (6.5 g,
8.7 mmol) and malonyl dichloride (0.42 mL, 4.33 mmol) in dry
CH2Cl2 (230 mL). The mixture was stirred overnight at room
temperature and evaporated to dryness. The residue purified
by column chromatography (SiO2, CH2Cl2) to yield 5.41 g
(80%) of 8 as white crystals, Mp 75 uC. Elemental analysis:
calc. (found) for C95H132O18, C 73.05 (72.98), H 8.52 (8.53). 1H
NMR (CDCl3, 300 MHz): d 0.90 (t, J = 7 Hz, 12H), 1.30 (m,
68H), 1.80 (m, 12H), 3.36 (s, 2H), 3.95 (t, J = 6 Hz, 4H), 4.05
(t, J = 6 Hz, 8H), 4.12 (t, J = 6 Hz, 4H), 6.87 (m, 12H), 7.11 (d,
J = 9 Hz, 4H), 8.06 (d, J = 9 Hz, 4H), 8.14 (d, J = 9 Hz, 2H).
13C NMR (CDCl3, 75 MHz): d 14.08, 22.64, 25.74, 25.89,
25.97, 26.03, 28.43, 29.07, 29.16, 29.20, 29.23, 29.27, 29.31,
29.34, 29.40, 31.78, 31.80, 41.63, 65.63, 68.37, 68.41, 69.17,
107.11, 113.39, 114.38, 115.03, 116.71, 121.01, 122.47, 132.36,
133.35, 144.34, 155.67, 156.75, 160.56, 163.78, 164.29, 164.39,
166.68.
All of the spectroscopic measurements were consistent with
the proposed molecular structure. The 13C-NMR spectrum
of 1 shows the diagnostic three signals of Th-symmetrical
[60]fullerene hexaadduct at 66.94 ppm (Csp3), 141.06 ppm
(Csp2) and 145.74 ppm (Csp2). The structure and purity of
1
compound 1 was also confirmed by H-NMR and MALDI-
TOF spectra. The GPC analysis showed a monomodal
molecular weight distribution, with a polydispersity of 1.03.
The thermal behaviour of the hexaadduct 1 was studied by
differential scanning calorimetry (DSC), polarized optical
microscopy with a heating stage (POM) and temperature
dependent wide- and small-angle X-ray diffraction (WAXS,
SAXS). POM observations on the first heating showed that
the compound is birefringent and very fluid above 38 uC,
suggesting the occurrence of a mesophase. On slow cooling
from the isotropic liquid (Fig. 1), point singularities with
2- and 4-Schlieren brushes slowly developed in the natural
texture, indicative of a nematic phase.
Synthesis of [60]fullerene hexaadduct 1
Two phase transitions were detected by DSC during the first
heating run (Fig. 2); a broad exothermic transition at 38 uC
followed by a sharp transition at 60 uC could be measured,
corresponding to the crystal/solid-to-mesophase and to the
mesophase-to-isotropic liquid transformations, respectively.
On cooling, the same sharp peak at 60 uC was detected, but
the mesophase was strongly supercooled down to room
temperature and froze into a glassy solid (Tg = 13 uC). On
subsequent heating–cooling cycles, a stable and reproducible
behaviour took place with the reversible sequence Glass (G) 13
Nematic (N) 60 Isotropic (I).
A solution of 9,10-dimethylanthracene (DMA) (173 mg,
0.84 mmol) and C60 (50 mg, 0.07 mmol) in dry toluene
(50 mL) was stirred for 2 h under argon at room temperature.
Malonate 8 (1.31 g, 0.84 mmol), CBr4 (278 mg, 0.84 mmol) and
1,8-diazabicyclo[5.4.0]undec-7-ene (0.21 mL, 1.4 mmol) were
then added and the resulting solution was stirred at room
temperature for 3 weeks before solvent evaporation. The crude
mixture was separated by flash chromatography (SiO2, hexane
to remove DMA then toluene–AcOEt 96 : 4 to elute 1) and the
fraction corresponding to expected hexaadduct was later
purified by gel permeation chromatography (SX-1 biobeads,
CH2Cl2) to yield 350 mg (50%) of 1 as a pale orange
In order to identify the mesophase and elucidate the
supramolecular organization, wide- and small-angle XRD on
aligned samples with a magnetic field was used (1.0 T). The
diffractogram registered at 50 uC revealing three reflections
(Fig. 3): i) a rather diffuse reflection in the small angle part,
glassy solid. MALDI-TOF MS: (C630H780O108
) 9858.95
1
[M2C14H21O2]. H NMR (CDCl3, 300 MHz): d 0.88 (t, J =
7 Hz, 72H), 1.30 (m, 408H), 1.79 (m, 72H), 3.92 (br s (t), 24H),
4.02 (br s (t), 48H), 4.20 (br s (t), 24H), 6.87 (m, 72H), 7.07 (d,
J = 7 Hz, 24H), 8.03 (d, J = 9 Hz, 24H), 8.10 (d, J = 9 Hz,
12H). 13C NMR (CDCl3, 75 MHz): d 14.08, 22.63, 25.81,
25.96, 26.03, 28.41, 29.07, 29.19, 29.21, 29.26, 29.31, 29.34,
centred on the field direction (Q = 0u), with a spacing dA
=
˚
33.35 A (A, Fig. 3). The correlation length of this reflection
˚
(radial extension) was estimated to be ca. L y 190 A (from
D2h using the Scherrer formula), with an azimuthal distribu-
tion DQ = 40u (FWHM); ii) a diffuse reflection in the medium-
angle part, tilted with respect to the field direction with a
3
29.53, 31.78, 45.35, 66.94 (Csp of C60), 68.35, 69.07, 69.16,
107.09, 113.35, 114.35, 114.99, 116.63, 120.99, 122.44, 132.32,
133.29, 141.06 (Csp2 of C60), 144.33, 145.74 (Csp2 of C60),
155.67, 156.72, 160.56, 163.73, 163.79, 164.23.
˚
maximum intensity at Q = 45u, with a spacing of dB = 18.1 A
˚
and a much shorter correlation length, L9 (B, Fig. 3, L9 y 22 A,
DQ = 50u); iii) a diffuse wide-angle reflection, perpendicular to
Results and discussion
The synthesis of the hexaadduct 1 is depicted in Scheme 1.
Reaction of methyl 2-hydroxy-4-benzyloxybenzoate 218 with
10-bromodecanol19 under etherification conditions (K2CO3,
KI, DMF, 80 uC) followed by hydrolysis of the corresponding
methyl ester 3 afforded benzoic acid 4, which was then
esterified with 4-octyloxyphenol20 using standard DCC/4-PP
coupling conditions. Hydrogenation of benzyl-protected com-
pound 5 followed by esterification with 4-octyloxybenzoic
acid21 led to the primary alcohol 7. Treatment of 7 with
malonyl dichloride in the presence of triethylamine afforded
compound 8, which was subjected to the Hirsch methodo-
logy22 for the preparation of ‘‘all-e’’ [60]fullerene hexaadduct
Fig. 1 POM image obtained for hexaadduct 1 at 55 uC on slow
cooling from the isotropic liquid.
2202 | J. Mater. Chem., 2007, 17, 2199–2205
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Fig. 2 DSC curves obtained for hexaadduct 1: top, first heating;
bottom, second heating–cooling cycle. G = glass, N = nematic phase
and I = isotropic phase.
˚
the field direction (Q = 90u), with a spacing of dC = 4.4 A (C,
Fig. 3). The correlation length is of the same magnitude as that
˚
of the medium reflection B (L0 y 21 A, DQ = 50u).
Both the reflections A and C reflect the nematic ordering of
the system; C is assigned to the molten chains, and to the
mesogenic side-groups, which are aligned in the same direction
Fig. 3 X-Ray pattern recorded at 50 uC for the hexaadduct 1: (a)
oriented pattern in the magnetic field (right) and sketch representing
the three reflections (right); (b) top, 2h profile of oriented pattern by
integration over full azimuthal Q range; bottom, 2h profile obtained
from pattern with larger film–sample distance (328.0 mm) and peak
deconvolution.
as the magnetic field, whilst A corresponds to a short range
2
˚
lamellar ordering with a mean molecular area of about 500 A
(cybotactic groups, vide infra).23 Since the maximum intensities
of A and C are located along the meridian and the equator,
respectively, the mesogenic subunits are not tilted within the
layers embryos.
In addition, the FWHM associated to the distribution
around both the maximum intensity centres extend up to
40–50u (DQ), which correspond to the nematic director
fluctuations. As for the radial distribution width (2h), the
FWHM associated to the A reflection is unusually small for a
nematic phase, corresponding to a large correlation length of
about 6–7 molecular layers. Finally, there is a diffuse reflection
(B), which is not present in any X-ray pattern of oriented
classical nematics. This additional reflection is in a direction
tilted with respect to the field direction and should correspond
to some additional periodicity within the cybotactic clusters.
The periodicity of B and the abnormal width of A are
specific to the structure of the hexaadduct molecule 1 with
respect to classical nematogens, in that the supermolecule has
a hierarchical structure, made of 12 lateral side-mesogenic
groups that are covalently connected to C60. Thus, this
periodicity of B is necessarily associated to the position of
the C60 moieties, which should be slightly correlated between
two adjacent neighbouring layers. This additional ordering
within the nematic phase is consistent with the abnormal large
correlation length of the reflection A. The absence of any
visible signal corresponding to some correlations between the
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C60 moieties within these layers embryos can be attributed
to the continuity of the electronic density between the C60
embedded by the polarizable parts of the mesogens, as
proposed by the model in Fig. 4 resulting from a Molecular
Dynamics simulation. Such a periodic molecular model for 1
was built by retracting the parameters of a cell containing
isotherm at 323 K, and confirmed the proposed molecular
self-organization (Fig. 4).
Conclusions
This work is the first step towards our attempt to reach and to
control ordered arrays containing [60]fullerenes. Hexaaddition
on the carbonated polyhedron has allowed the preparation,
in high yield, of an enantiotropic, room-temperature
nematic material, despite the absence of mesomorphism of
the malonate side-group promoter. Here, we showed that the
specific architecture of the hexaadduct induces a nematic phase
with unusual features. The highly symmetric [60]fullerene
accordingly represents a particularly versatile scaffold for the
regioselective covalent assembly of a variety of regular three-
dimensionally structured molecules, some of which may
enlarge the existing repertoire of programmed molecular
components for the construction of useful ordered materials.
Thus, combining the two classes of materials i.e. mesomorphic
[60]fullerene-based compounds (spontaneous organization)
and donor–acceptor dyads, will allow exploration of one of
the most promising ways towards efficient exciton dissocia-
tion, in order to reach high charge mobility and therefore high
conversion yields. As such, derivatization of compound 1 by
appropriate electron donors and acceptors using regioselective
hexaaddition on the carbon sphere (multicomponent sys-
8 molecules down to the estimated molecular volume, VM
y
3
˚
16500 A . Indeed, the cell parameters were set from the
experimental X-ray data, assuming a hexagonal 2-D close-
packing of the supermolecules and considering two molecular
layers (a = b = 21/2?321/4(VM/dA)1/2 = 25 A, c = 2dA = 66.7 A,
c = 120u, a = b = 90u, Vcell = abc = ca2!3, Z = 4); the resulting
density was close to 1. The simulation consisted of a 100 ps
˚
˚
tems8a), following the methods of Krautler16 and Diederich17
,
is currently in progress in our laboratory. These investigations
should permit the understanding of new relationships between
photo-induced inter- and/or intramolecular energy and/or
electron transfer versus molecular architecture and supra-
molecular order. We anticipate that this versatile strategy
for producing covalent donor–acceptor [60]fullerene-based
nematic hexaadducts will lead to a new class of potentially
interesting photovoltaic materials.
This work was supported by the CNRS and University
Louis Pasteur, Strasbourg. We would like to thank the Re´gion
Alsace for a fellowship to Mrs Hind Mamlouk. We also
warmly thank Ms Laurence Oswald and Emilie Couzigne´ for
technical assistance and Mr Nicolas Beyer for the design and
construction of the XRD punctual beam experiment.
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