Supramolecular fullerene materials: Dendritic liquid-crystalline fulleropyrrolidines

Article abstract of DOI:10.1021/ma051359g

[60]Fullerene-containing liquid-crystalline dendrimers were synthesized from the first to the fourth generation by applying the 1,3-dipolar cycloaddition reaction from a mesomorphic dendritic-type aldehyde derivative, sarcosine (N-methylglycine) or glycin

Full text of DOI:10.1021/ma051359g

Macromolecules 2005, 38, 7915-7925
7915
Supramolecular Fullerene Materials: Dendritic Liquid-Crystalline
Fulleropyrrolidines
Ste´phane Campidelli,† Julie Lenoble,† Joaquı´n Barbera´,*,‡ Francesco Paolucci,*,§
Massimo Marcaccio,§ Demis Paolucci,§ and Robert Deschenaux*,†
Institut de Chimie, Universite´ de Neuchaˆtel, Avenue de Bellevaux 51, Case Postale 2, 2007 Neuchaˆtel,
Switzerland, Quı´mica Orga´nica, Facultad de Ciencias-Instituto de Ciencia de Materiales de Arago´n,
Universidad de Zaragoza-CSIC, 50009 Zaragoza, Spain, and Dipartimento di Chimica
“G. Ciamician”, Universita` di Bologna, via Selmi 2, 40126 Bologna, Italy
Received June 25, 2005; Revised Manuscript Received July 20, 2005
ABSTRACT: [60]Fullerene-containing liquid-crystalline dendrimers were synthesized from the first to
the fourth generation by applying the 1,3-dipolar cycloaddition reaction from a mesomorphic dendritic-
type aldehyde derivative, sarcosine (N-methylglycine) or glycine and C60. The cyanobiphenyl unit was
used as a liquid-crystalline promoter. With the exception of the first-generation fullerene dendrimer,
which was found to be nonmesomorphic, all fullerene-based dendrimers gave rise to a smectic A phase.
The liquid-crystalline fullerenes led to two different supramolecular organizations within the smectic
layers: for the second-generation dendrimers, the molecules are oriented in a head-to-tail fashion within
the layers; for each molecule the cyanobiphenyl units point in the same direction. For the dendrimers of
third and fourth generations, the dendritic core extends laterally, parallel to the layer planes; the
mesogenic units are oriented above and below the dendritic core. For the aldehyde precursors, only one
organization inside the layers was obtained, similar to the one observed for the third and fourth fullerene-
based dendrimers. Cyclic voltametry investigations displayed several one-electron and multielectron
reduction processes; no significant interaction in the ground state between the fullerene and the dendrimer
was noticed. The title compounds showed the typical electrochemical stability of fulleropyrrolidines.
Introduction
crystals was obtained, such as fullerene-ferrocene
dyads (smectic A phases),12a,b,d,14b fullerene-OPV conju-
gates (smectic A phases),14a fullerene-TTF dyads (smec-
tic A and B phases),12g a hexa-adduct of C60 (smectic A
phase),12c a chiral C60 derivative (cholesteric phase),12f
and dendritic liquid-crystalline methanofullerenes (smec-
tic A phases; an additional short-range nematic phase
was observed for the second-generation dendrimer).12e
A bis(methano)fullerene was also reported (mesophase
not identified).15 Two other approaches were described:
in the first one, C60 was complexed by mesomorphic
cyclotriveratrylene (CTV) derivatives (nematic and cubic
phases),16 and in the second one, five aromatic groups
were attached around one pentagon of C60, yielding
conical molecules (columnar phases).17
Whereas methanofullerenes undergo retro-Bingel re-
action upon chemical18 and electrochemical19 reduction,
fulleropyrrolidines lead to stable reduced species.13
Dendritic liquid-crystalline fulleropyrrolidines would
represent an interesting family of electroactive macro-
molecules, as they would combine the electrochemical
behavior2 of C60 with the rich mesomorphism of den-
drimers.20
We describe, herein, the synthesis, characterization,
liquid-crystalline properties, and supramolecular or-
ganization of the dendritic liquid-crystalline fullero-
pyrrolidines 1-7 (Charts 1 and 2). By means of cyclic
voltammetry experiments carried out on the second-
generation dendrimer 2, it is demonstrated that such
materials are electrochemically stable. The cyanobi-
phenyl derivatives, acting as mesomorphic groups, are
located at the periphery of the dendritic core. The
dendrimers were prepared by applying a convergent
synthetic methodology.21 The mesomorphic properties
of 2 were already reported.10b
Fullerodendrimers,1 which combine the outstanding
electrochemical2 and photophysical3 properties of C60
with the unique structural features of dendrimers,4
generated fascinating studies in supramolecular chem-
istry and materials science.5 Dendrimers play two major
roles depending upon their architecture and function-
alities: they increase the solubility of C60 in organic
solvents6 or in water7 (solubilizing effect), and they
isolate C60 from the external environment such as
oxygen and solvent molecules (protection effect).8 Both
effects can be adjusted to specific experimental condi-
tions by synthetic chemistry at the dendrimer level.
Dendrimers prevent also the formation of aggregates
resulting from strong interactions between C60 units;
highly ordered Langmuir and Langmuir-Blodgett films
were so obtained.9
With the view to construct supramolecular fullerene
materials, whose properties could be of interest in
nanotechnology (e.g., molecular switches, solar cells), we
became interested in fullerene-containing thermotropic
liquid crystals. We developed two concepts to design
liquid-crystalline fullerenes:10 in the first concept, C60
was functionalized with liquid-crystalline malonates by
applying the Bingel reaction11 (leading to mesomorphic
methanofullerenes12), and in the second one, C60 was
functionalized with liquid-crystalline aldehydes and
N-methylglycine or an amino acid derivative by applying
the 1,3-dipolar addition reaction13 (leading to meso-
morphic fulleropyrrolidines14). A great variety of liquid
* Corresponding author. E-mail: robert.deschenaux@unine.ch.
† Universite´ de Neuchaˆtel.
‡ Universidad de Zaragoza-CSIC.
§ Universita` di Bologna.
10.1021/ma051359g CCC: $30.25 © 2005 American Chemical Society
Published on Web 08/20/2005

7916 Campidelli et al.
Macromolecules, Vol. 38, No. 19, 2005
Chart 1

Macromolecules, Vol. 38, No. 19, 2005
Supramolecular Fullerene Materials 7917
Chart 2
Results and Discussion
i.e., 11 f 2 (Scheme 2), 14 f 3 (Scheme 3), and 17 f 4
(Scheme 4). The syntheses of 5 and 6 are described in
Scheme 5. Second-generation phenol derivative 11 was
esterified either with 4-carboxybenzaldehyde or with
4-(6-hydroxyhexyloxy)benzoic acid to give 20 and 21,
respectively. Aldehyde 20 was reacted with sarcosine
and C60 to furnish 5. Alcohol 21 was condensed with
4-carboxybenzaldehyde to give 22, the addition of which
with sarcosine and C60 led to 6. Fulleropyrrolidine 7 was
obtained by addition of 13 with glycine to C60 (Scheme
2).
The structure and purity of all compounds were
confirmed by NMR spectroscopy, GPC (all compounds
were found to be monodisperse) and elemental analysis.
The vis spectra of 1-7 were in agreement with the
fulleropyrrolidine structure; an illustrative example is
shown in Figure 1. The syntheses of phenol precursors
(8, 11, 14, and 17) and 4-(10-hydroxydecyloxy)benzoic
were already described;12e they were used for the
preparation of dendritic liquid-crystalline methano-
fullerenes.12e 4-(6-Hydroxyhexyloxy)benzoic acid was
prepared according to a literature procedure.22
Design. This study is based on three different struc-
tural modifications. First, we modified the dendrimer
generation (first generation, 1; second generation, 2;
third generation, 3; fourth generation, 4) (Chart 1).
Second, we modified the length of the flexible bridge
between the second-generation dendrimer and the pyr-
rolidine ring (5, none; 6, six carbon atoms; 2, 10 carbon
atoms) (Charts 1 and 2). Third, we modified the sub-
stituent located on the nitrogen atom of the pyrrolidine
ring for the second-generation dendrimers (2, methyl
group; 7, hydrogen atom) (Charts 1 and 2). These
compounds were designed to emphasize the role played
by the dendrimer, the spacer and the pyrrolidine ring
on the liquid-crystalline properties and supramolecular
organization. Owing to the N-H group, 7 could be used
as synthetic platform for the preparation of multifunc-
tional liquid-crystalline fulleropyrrolidines.
Syntheses. The preparation of 1 is depicted in
Scheme 1. Condensation of first-generation dendron 8
with 4-(10-hydroxydecyloxy)benzoic acid gave alcohol
derivative 9. Treatment of 9 with 4-carboxybenzalde-
hyde furnished aldehyde 10. Addition of 10 and N-
methylglycine (sarcosine) to C60 led to 1. Fulleropyrroli-
dines 2-4 were prepared analogously to the synthesis
of 1 from the corresponding phenol-based dendrimer,
Liquid-Crystalline Properties. The mesomorphic
and thermal properties of alcohol (9, 12, 15, 18, and 21),
aldehyde (10, 13, 16, 19, 20, and 22) and fulleropyrroli-
dine (1-7) derivatives were investigated by polarized

7918 Campidelli et al.
Macromolecules, Vol. 38, No. 19, 2005
Scheme 1a
a Key: (a) 4-(10-hydroxydecyloxy)benzoic acid, N,N′-dicyclohexylcarbodiimide (DCC), 4-(dimethylamino)pyridinium toluene-p-
sulfonate (DPTS), 4-pyrrolidinopyridine (4-PPy), CH2Cl2, room temperature, 15 h, 78%; (b) 4-carboxybenzaldehyde, DCC, DPTS,
4-PPy, CH2Cl2, room temperature, 17 h, 80%; (c) C60, sarcosine, toluene, reflux, 17 h, 28%.
optical microscopy (POM) and differential scanning
calorimetry (DSC). The phase transition temperatures
and enthalpy changes are reported in Table 1.
agreement with results obtained for other fullerene-
containing liquid crystals and is attributed to the
presence of the bulky C60 unit.12a,b,d-f Comparison of the
clearing points of second-generation dendrimers 2 (10
carbon atoms in the flexible spacer), 6 (6 carbon atoms
in the flexible spacer) and 5 (no flexible spacer) showed
that the stability of the mesophase increased when the
length of the spacer decreased. This result should be
the consequence of reduced molecular motion when the
spacer is shorter. Finally, the substituent on the nitro-
gen had limited influence on the stability of the meso-
phase (clearing point of 2, 168 °C; clearing point of 7,
162 °C). This is due to the fact that the difference in
size between the H atom and the methyl group is small
in comparison with the size of the molecule.
Supramolecular Organization. To gain informa-
tion regarding the supramolecular organization of the
liquid-crystalline fulleropyrrolidines 2-7 and of their
aldehyde precursors 13, 16, 19, 20, and 22 within the
liquid-crystalline state, the smectic phases were
analyzed by variable-temperature X-ray diffraction
(XRD).
The XRD patterns of fulleropyrrolidines 2-7 showed
either one or two intense reflection peaks in the low-
angle region and a diffuse signal in the wide-angle
region. When two peaks were detected in the low-angle
region, their spacings were in a 1:2 ratio, and they
corresponded to the first- and second-order reflections,
respectively. Such patterns are characteristic of disor-
dered smectic phases. The d-layer spacings determined
by XRD were found to be nearly independent of tem-
perature, which is in agreement with the nature of the
smectic A phase.
With the exception of 1, which was found to be
nonmesomorphic, all compounds displayed liquid-
crystalline properties. First generation alcohol 9 and
aldehyde 10 gave rise to a nematic phase. From the
second generation, all materials displayed a smectic A
phase. The liquid-crystalline phases were identified by
POM from their textures (smectic A phase: focal-conic
and homeotropic textures; nematic phase: schlieren and
homeotropic textures). The texture of the smectic A
phase developed by 2 is shown in Figure 2 as an
illustrative example.
The fact that 1 did not show mesomorphism was
unexpected taking into account that a methano-
fullerene12e carrying also two mesogenic units (the same
as those used in 1) exhibited a smectic A phase. Two
structural factors could have prevented 1 to be meso-
morphic: (1) the bent structure induced by the fullero-
pyrrolidine moiety and (2) the benzene nucleus located
next to the nitrogen atom of the pyrrolidine ring, the
presence of which increases the bulkiness around the
fullerene. As a consequence, the mesomorphic part in 1
is not large enough to thwart the steric effects generated
by the fulleropyrrolidine framework.
The clearing temperature increased with the den-
drimer generation. This trend was observed for other
liquid-crystalline dendrimers12e and confirmed that the
stability of the mesophases increases with the number
of mesogenic units. The isotropization temperatures of
the fulleropyrrolidines were lower than those of the
corresponding aldehyde promoters. This behavior is in

Macromolecules, Vol. 38, No. 19, 2005
Supramolecular Fullerene Materials 7919
Scheme 2a
a Key: (a) 4-(10-hydroxydecyloxy)benzoic acid, DCC, DPTS, 4-PPy, CH2Cl2, room temperature, 24 h, 83%; (b) 4-carboxy-
benzaldehyde, DCC, DPTS, 4-PPy, CH2Cl2, room temperature, 15 h, 91%; (c) C60, sarcosine, toluene, reflux, 20 h, 53%; (d) C60,
glycine, toluene, reflux, 40 h, 47%. For abbreviations, see footnote a of Scheme 1.
The d-layer spacings were compared to the molecular
lengths in the extended molecular conformation (Table
2). The dendrimers of second generation (2 and 5-7)
gave d/L ratios of 1.3, whereas the dendrimers of third
(3) and fourth (4) generations gave d/L values of 0.7.
These data indicated that two different supramolecular
organizations are obtained depending upon the den-
drimer generation, i.e., generation 2, on one hand, and
generations 3 and 4, on the other hand. Furthermore,
for the second-generation dendrimers (2 and 5-7), the
supramolecular organization is independent of the
length of the spacer and of the substituent located on
the nitrogen atom of the fulleropyrrolidine.
For the dendrimers of second generation (2 and 5-7),
for which the d-layer spacings are larger than their
molecular lengths, the organization within the smectic
layers requires the adequacy between the cross-sectional
area of C60 (90-100 Å2) and that of four mesogens (22-
25 Å2 per mesogenic unit). For efficient space filling, the
molecules are oriented in a head-to-tail fashion within
the layers, and for each molecule the cyanobiphenyl
units point in the same direction interdigitating with

7920 Campidelli et al.
Scheme 3a
Macromolecules, Vol. 38, No. 19, 2005
cyano-substituted mesogens to interdigitate in an anti-
parallel way promoted by dipole-dipole interactions.
For dendrimers 2 and 5-7 the supramolecular organi-
zation is thus governed by steric constraints.
For the dendrimers of third (3) and fourth (4) genera-
tions, for which the d-layer spacings are significantly
smaller than their molecular lengths, the dendritic core
extends laterally, parallel to the layer planes. With such
an orientation, the d-layer spacing does not increase
(practically) when the size of the dendrimer increases;
this result is in agreement with literature data.20a The
mesogenic units are oriented above and below the
dendritic core and, as for 2 and 5-7, interdigitation
occurs from one layer to the adjacent one. In this case,
C60 is hidden in the dendritic core and has no influence
on the supramolecular organization. Therefore, from the
third generation, the supramolecular organization is
governed by the nature and structure of the mesogenic
units (parts b and c of Figure 3). This result opens
avenues for the design of fullerene-containing liquid-
crystalline dendrimers with tailored mesomorphic prop-
erties: fine tuning of the liquid-crystalline properties
could be achieved when the adequate mesomorphic
promoter (polar, apolar, chiral) is associated with the
appropriate dendrimer (stiff, flexible).
The d-layer spacings (d), molecular lengths (L) and
d/L ratios of the aldehyde precursors are reported in
Table 3. The aldehydes of third (16: d/L ) 0.8) and
fourth (19: d/L ) 0.7) generations give a similar
supramolecular organization than their corresponding
fullerene counterparts (i.e., 3 and 4, repectively); this
result strenghtens the model proposed for 3 and 4 (parts
b and c of Figure 3). The aldehydes of second generation
yielded d-layer spacings similar to those of third and
fourth generations. This result suggests that the pack-
ing model is the same for all aldehydes (the higher d/L
value observed for 20 reflects a slightly different ori-
entation of the dendritic core for this chemical, most
likely, because of lack of flexible bridge between the
dendrimer and the aromatic ring carrying the aldehyde
group). This is not unexpected taking into account that,
in the absence of C60, there are no steric constraints
leading to the model proposed in Figure 3a and,
therefore, the organization is similar to the ones shown
in parts b and c of Figure 3. It is interesting to note
that the intensity of the Bragg signals for the aldehydes
is low. This is, most likely, related to the interdigitation
which makes the interface between the layers diffuse.
Although in the fullerene-containing dendrimers inter-
digitation is also present, the layered structure is better
defined due to the sublayer of C60 moieties.
The above-mentioned results are in agreement with
the data we have obtained for dendritic liquid-crystal-
line methanofullerenes, for which we have also found
that steric contraints are responsible for the supra-
molecular organization when C60 is functionalized with
small addends, whereas the mesogenic groups govern
the supramolecular organization when C60 is function-
alized with dendrimers.12e The harmony of the structure-
supramolecular organization relationship between both
series of materials is due to the fact that in both cases
the same type of dendritic core and mesomorphic units
were used.
a Key: (a) 4-(10-hydroxydecyloxy)benzoic acid, DCC, DPTS,
4-PPy, CH2Cl2, room temperature, 20 h, 68%; (b) 4-carboxy-
benzaldehyde, DCC, DPTS, 4-PPy, CH2Cl2, room temperature,
48 h, 66%; (c) C60, sarcosine, toluene, reflux, 15 h, 48%. For R,
see Chart 1. For abbreviations, see footnote a of Scheme 1.
Electrochemistry. The cyclic voltammetric (CV)
behavior of 2 and of reference compound 13 (Figure 4)
was investigated in THF solution under strictly aprotic
conditions.23,24 The CV curve (Figure 4a) relative to a
the cyanobiphenyl groups of the adjacent layer (Figure
3a). This model is consistent with the tendency of the

Macromolecules, Vol. 38, No. 19, 2005
Supramolecular Fullerene Materials 7921
Scheme 4a
a Key: (a) 4-(10-hydroxydecyloxy)benzoic acid, DCC, DPTS, 4-PPy, CH2Cl2, room temperature, 24 h, 95%; (b) 4-carboxybenz-
aldehyde, DCC, DPTS, 4-PPy, CH2Cl2, room temperature, 20 h, 77%; (c) C60, sarcosine, toluene, reflux, 20 h, 41%. For R, see
Chart 1. For abbreviations, see footnote a of Scheme 1.
0.5 mM 2 THF solution, at 25 °C and at a scan rate of
1.0 V/s, displays a series of subsequent reduction peaks
which were, in part, attributable to the fulleropyrroli-
dine moiety and, for the remaining ones, to the den-
drimer. In particular, peaks I, II, and III (E1/2 ) -0.47,
-1.04, and -1.65 V) are located at potentials that are
typical of fulleropyrrolidines studied under similar
conditions,25,26 and they were therefore attributed to the
reversible subsequent reductions of the fullerene unit
in 2. At variance with fulleropyrrolidines, peak III
comprises two electrons, thus suggesting the occurrence
of two one electron reduction processes, accidentally
located at very close potentials, one centered in the
fullerene moiety, the other one in the dendritic part.
This was confirmed by comparison with the CV curve
of 13 (Figure 4b), in which a one electron peak (I) is
located at the same potential as peak III in the CV curve
of 2. At more negative potentials, the CV curves of both
species were characterized by intense (and only partly
irreversible) reduction peaks (II-IV in 13 and IV and
V in 2) that were attributed to the dendrimer. In fact,
this moiety contains various functional groups that are

7922 Campidelli et al.
Macromolecules, Vol. 38, No. 19, 2005
Scheme 5a
a Key: (a) 4-carboxybenzaldehyde, DCC, DPTS, 4-PPy, CH2Cl2, room temperature, 6 h, 57%; (b) C60, sarcosine, toluene, reflux,
20 h, 52%; (c) 4-(6-hydroxyhexyloxy)benzoic acid, DCC, DPTS, 4-PPy, CH2Cl2, rt, 20 h, 90%; (d) 4-carboxybenzaldehyde, DCC,
DPTS, 4-PPy, CH2Cl2, room temperature, 48 h, 72%; (e) C60, sarcosine, toluene, reflux, 20 h, 53%. For abbreviations, see footnote
a of Scheme 1.
Table 1. Phase Transition Temperaturesa and Enthalpies
of Alcohol, Aldehyde, and Fulleropyrrolidine Derivatives
compound Tg (°C) transition temp (°C) ∆H (kJ‚mol-1
)
9
Cr f N
N f I
Cr f N
N f I
Cr f I
123b
190
102b
179
178
185c
185
168
231d
223
196
256d
250e
231e
219
189
203
195
171
162
67.2
3.0
43.5
3.7
10
1
23.0
10.9
12.8
13.5
42.7
43.8
22.8
97.1
97.6
81.5
16.6
16.3
14.7
13.8
13.7
10.7
12
13
2
38
35
44
41
47
51
45
36
36
45
f
SA f I
SA f I
SA f I
SA f I
SA f I
SA f I
SA f I
SA f I
SA f I
SA f I
SA f I
SA f I
SA f I
SA f I
SA f I
15
16
3
18
19
4
20
5
21
22
6
44
37
f
7
f
a Cr ) semicrystalline solid, Tg ) glass transition temperature,
SA ) smectic A phase, N ) nematic phase, I ) isotropic liquid.
Temperatures are given as the onset of the peak obtained during
the second heating run except where stated otherwise. Tg’s are
determined during the first cooling run. b Observed only during
the first heating run. c Large transition. d Large transition with
some decomposition; determined as the maximum of the peak
obtained during the first heating run. e Determined as the onset
of the peak obtained during the first heating run. f Too small to
be determined.
Figure 1. Visible spectrum of fulleropyrrolidine 2.
capable to undergo reduction processes at such negative
potentials, e.g., the four equivalent cyanobiphenyl groups
and the three equivalent isophthaloyl ester groups.
An attribution of the various multielectron reduction
peaks to the corresponding electroactive groups in the
dendrimer was attempted on the basis of the cor-

Macromolecules, Vol. 38, No. 19, 2005
Supramolecular Fullerene Materials 7923
Table 2. Layer Spacings d001, Molecular Lengths L, and
d/L Ratios of Liquid-Crystalline Fulleropyrrolidines
compound
d001a (Å)
Lb (Å)
d/L
2
3
4
5
6
7
88
50
54
67
84
88
68
73
76
50
64
68
1.3
0.7
0.7
1.3
1.3
1.3
a Determined by X-ray diffraction at 150 °C. b The molecular
length was estimated for the fully extended conformation obtained
by means of HyperChem software with the branching part and
the mesogenic units pointing in the same direction.
nIV ) 3. Peak III (at about -2.30 V in Figure 4b) is not
observed for 2 and likely involves the aldehyde group
in 13. On the basis of the above n values and of the
occurrence of the various electroactive groups within the
dendritic structure, peak II in Figure 4b was attributed
to the reduction of the four equivalent cyanobiphenyl
groups, while the processes comprised in peak IV are
likely to involve the three equivalent isophthaloyl ester
moieties in the dendrimer core. Finally, the one electron
reduction peak I might involve the (single) benzoic ester
moiety which is linked to the dendritic core. On the
other hand, the fulleropyrrolidine moiety in 2 is known
to undergo another two subsequent reduction processes
Figure 2. Thermal optical micrograph of the focal-conic fan
texture displayed by 2 in the smectic A phase upon cooling
the sample from the isotropic liquid to 167 °C.
respondence between the number of electrons (n) as-
sociated with each peak and the number of equivalent
electroactive groups in the structure. As far as 13 is
concerned, the convolutive analysis27 of the CV curve
gave the following results: nI ) 1, nII ) 4, nIII ) 1, and
Figure 3. Postulated supramolecular organization of fulleropyrrolidines 2 (a), 3 (b), and 4 (c) within the smectic A phases.
Figure 4. CV curves of (a) fulleropyrrolidine 2 (0.5 mM) and (b) aldehyde 13 (0.5 mM) in THF (0.05 M TBAH), at 25 °C and at
a scan rate of 1V/s.

7924 Campidelli et al.
Macromolecules, Vol. 38, No. 19, 2005
Table 3. Layer Spacings d001, Molecular Lengths L, and
d/L Ratios of Liquid-Crystalline Aldehydes
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Lb (Å)
d/L
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16
19
20
22
54.5
55
64
68
74
44
59
0.85
0.8
0.7
1.2
0.9
55
53
54
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in this potential region, at -2.15 and -2.96 V, respec-
tively.26 While the reduction process at -2.16 V was
expected to contribute to the multielectronic peak IV
in the CV curve of 2, the fifth reduction of the fullero-
pyrrolidine moiety is instead likely located outside the
potential window investigated in the CV experiment of
Figure 4a.
Conclusions
Liquid-crystalline fulleropyrrolidines were synthe-
sized from mesomorphic aldehyde-based dendimers of
first to fourth generation, sarcosine or glycine and C60
by applying the 1,3-dipolar cycloaddition reaction. They
gave rise to smectic A phases. The supramolecular
organization of the mesomorphic fullerenes within the
smectic layers could be established from X-ray diffrac-
tion data and molecular modeling. Two different orga-
nizations were found depending upon the dendrimer
generation. In the first model, which was observed for
the second-generation dendrimers, the molecules are
oriented in a head-to-tail fashion within the layers. In
the second model, observed for the third- and fourth-
generation dendrimers, the mesogenic units are oriented
above and below the dendritic core. In both types of
structural model, there is segregation into distinct
sublayers, giving rise to an alternating superstructure:
one sublayer which contains the mesogenic units and
the rest of the molecule (fullerene and branching part)
which is located between the mesogenic sublayers.
Finally, electrochemical investigations were in agree-
ment with the redox-active nature of the subunits found
in the compounds.
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Acknowledgment. R.D. would like to thank the
Swiss National Science Foundation (Grant No. 200020-
103424) for financial support. This work received sup-
port from the Italian MIUR and the University of
Bologna.
Supporting Information Available: Text giving tech-
niques, instruments, synthetic procedures, and analytical data
of all new compounds. This material is available free of charge
via the Internet at http://pubs.acs.org.
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