Electronic properties of oligophenylenevinylene and oligophenyleneethynylene arrays constructed on the upper rim of a calix[4]arene core

Article abstract of DOI:10.1039/b415063p

Heck and Sonogashira cross-coupling reactions have been used for the functionalization of the upper rim of a tetraiodinated calix[4]arene. In this way, oligophenylenevinylene (OPV) and oligophenyleneethynylene (OPE) arrays have been constructed on the cal

Full text of DOI:10.1039/b415063p

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P A P E R
Electronic properties of oligophenylenevinylene and
oligophenyleneethynylene arrays constructed on the upper rim of
a calix[4]arene core
Nicola Armaroli,*a Gianluca Accorsi,a Yannick Rio,a Paola Ceroni,*b Veronica Vicinelli,b
Richard Welter,c Tao Gu,d Mohamed Saddik,d Michel Hollerd and
Jean-Franc¸
ois Nierengarten*d
a
`
Laboratorio di Fotochimica, Istituto per la Sintesi Organica e la Fotoreattivita, Consiglio
Nazionale della Ricerche, via Gobetti 101, 40129 Bologna, Italy. E-mail: armaroli@isof.cnr.it;
Fax: +39-051-6399844
b
c
d
`
Dipartimento di Chimica ‘‘G. Ciamician’’, Universita di Bologna, via Selmi 2, 40126 Bologna,
Italy. E-mail: paola.ceroni@unibo.it
´
Laboratoire DECMET, Universite Louis Pasteur, 4, rue Blaise Pascal, 67000 Strasbourg,
France. E-mail: welter@chimie.u-strasbg.fr
`
`
´
´
Groupe de Chimie des Fullerenes et des Systemes Conjugues, Ecole Europeenne de Chimie,
Polymeres et Materiaux, Universite Louis Pasteur (CNRS UMR 7504), 25 rue Becquerel,
`
´
´
67087 Strasbourg cedex 2, France. E-mail: jfnierengarten@chimie.u-strasbg.fr
Received (in Toulouse, France) 20th April 2004, Accepted 28th September 2004
First published as an Advance Article on the web 17th November 2004
Heck and Sonogashira cross-coupling reactions have been used for the functionalization of the upper rim of
a tetraiodinated calix[4]arene. In this way, oligophenylenevinylene (OPV) and oligophenyleneethynylene
(OPE) arrays have been constructed on the calix[4]arene core to produce covalent assemblies of four
p-conjugated chromophores. Electrochemical properties have been investigated by cyclic voltammetry in
different solvent/electrolyte systems. Both OPV and OPE calixarenes show the simultaneous reduction of
three out of four units, followed, at more negative potential, by the reduction of the fourth unit. This
behaviour can be rationalized in view of a partial deconjugation in one OPV or OPE unit. On the other
hand, these calixarenes show only oxidation processes corresponding to the exchange of one electron, thus
demonstrating the lack of electrochemical equivalency of the OPV or OPE units, in contrast to the reduction
behaviour. Electronic absorption and emission spectra have been recorded in solvents of different polarity
(toluene, dichloromethane, and benzonitrile). The absorption spectra of the OPV calixarene do not match to
the sum of the component units as a consequence of the partial deconjugation of the OPV arms in the
calixarene structure. On the contrary, fluorescence spectra, quantum yields and excited state lifetimes of the
OPV calixarene are nearly identical to those of the corresponding model compound. The trend of the
absorption and emission spectra for the OPE calixarene is reversed relative to that of the OPV counterpart.
Absorption spectra are well-matched with those of four trimeric OPE fragments but emission spectra exhibit,
besides the typical OPE monomeric fluorescence, a broader and longer-lived emission feature on the
low-energy spectral side, attributable to excimer-type interactions. Therefore the arrangement of OPV or
OPE units within the same calix-4-arene skeleton brings about different effects on the electronic and
luminescence properties of the multicomponent system.
attractive molecular scaffold for the design of new molecules
Introduction
combining several chromophores in a controlled spatial arran-
gement to study chromophore-chromophore interactions.5–12
Conjugated organic polymers and monomers exhibit rela-
tively low HOMO-LUMO gaps and are potent fluorophores.
This make them attractive candidates for a variety of materials
science applications when semiconducting and luminescence
properties are required. A leading role in this area is played by
oligo- and polyphenylenevinylene (OPV and PPV) and oligo-
and polyphenyleneethynylene (OPE and PPE), which have
been investigated to a great extent.13 In such systems some of
the electronic/optical properties that are studied in solution are
profoundly modified in the solid state. For instance, trimeric
OPV molecules (3PV) are strongly luminescent in solution but
exhibit weak luminescence in the solid state, due to the forma-
tion of aggregates. Chemical modification of the 3PV structure
During the past decade, calix[4]arene derivatives have become
increasingly important tools in host–guest chemistry.1,2 The
unique molecular architecture of these macrocyclic compounds
enables the catching of ions and/or neutral guest molecules in a
well-defined manner. Furthermore, several conformational
isomers are possible for calix[4]arenes (cone, partial-cone,
1,2-alternate and 1,3-alternate), thus allowing the preparation
of cavities with different sizes or shapes. The structural features
of calix[4]arenes have also been beautifully exploited by
Hosseini and co-workers for the preparation of building blocks
allowing the construction of infinite networks based on co-
ordination to metal ions.3,4 In this case, the calix[4]arene core is
used as a support to control the spatial orientation of the
coordinating subunits. The calix[4]arene macrocycle is also an
T h i s j o u r n a l i s & T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 4
N e w J . C h e m . , 2 0 0 4 , 2 8 , 1 6 2 7 – 1 6 3 7
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to limit this drawback has been successfully proposed.14 In
general, although it would be convenient to transfer the knowl-
edge acquired at the molecular level to the aggregated (solid)
phase, this often turns out to be hardly feasible. Several
approaches have been proposed to model the properties of
solid state materials made of conjugated organic oligomers and
polymers. Dendrimers decorated with OPV terminal units (up
to 16) exhibit dependence of the optical properties on the
dendrimer generation, suggesting intramolecular interac-
tions.15 A larger number of OPV units (over 2000) has been
anchored to a silver nanoparticle.16 Monolayer LB films of
PPE reveal interesting structure-property relationships, indi-
cating the crucial role played by polymer conjugation and
intermolecular interactions in solid state films.17 Another
interesting approach is based on the modulation of solvent
polarity in order to control aggregation phenomena of OPE
and PPE in solution.18,19
We have recently proposed the covalent assembly of four
3PV units arising from a calix[4]arene core as a tool to
investigate stacking interactions of conjugated organic mole-
cules in dilute solution and possibly extrapolate information on
electronic properties in the solid state.12 UV-Vis absorption
and electrochemical properties of our calix[4]OPV, when com-
pared to those of a single OPV unit as reference compound,
seem to indicate intramolecular electronic interactions in the
calix[4]OPV array. We have also shown that the calix[4]OPV
unit can act as a rigid core for the preparation of liquid
crystalline derivatives.11 In this paper, we describe the synth-
esis, photophysics, and electrochemistry of calix[4]OPE 2
(Scheme 1). Comparison of the electrochemical and photo-
physical properties of 2 with those of the corresponding
calix[4]OPV analogue 1a11 in solution allows us to get a better
picture of the electronic properties of these intriguing archi-
tectures. Notably, the absorption and luminescence properties
of 1a and 2 are remarkably different with respect to each other
and also relative to the corresponding model OPV and OPE
compounds. These results, along with electrochemical data,
suggest that electronic properties of the calixarene architec-
tures 1a and 2 are affected by specific structural and conforma-
tional effects.
Scheme 1 Calix[4]OPV derivatives 1a,b and calix[4]OPE 2.
Results and discussion
Synthesis
calixarene core and free rotation of the four substituents on the
upper rim of the calix[4]arene core is necessary to produce a
NMR spectrum with sharp signals corresponding to a C4v
symmetrical structure. Restricted rotation in 1a can easily be
explained by steric hindering resulting from the size of the
upper-rim substituents and, in good agreement with molecular
modelling studies, the four OPV units may not easily accom-
modate simultaneously an extended planar conjugated con-
formation. The latter observations are quite important since
they have a dramatic effect on the photophysical properties (see
below). Interestingly, mesomorphic properties have been
The preparation of compound 1a was achieved by following
the procedure we have recently developed for the synthesis of
related calix[4]OPV derivatives.12 This synthesis is based on the
functionalization of the upper rim of tetraiodinated calix[4]
arene 3 (Scheme 2) with styrene derivatives under Heck
conditions.
To this end, styrene 9 was prepared first (Scheme 3). Con-
densation of benzaldehyde 4 with aniline in refluxing benzene
afforded benzaldimine 5 in 80% yield. Treatment of 5 with
compound 6 under Siegrist conditions20–22 gave stilbene 7 in
50% yield. The E stereochemistry of the double bond in 7 was
confirmed by a coupling constant of ca. 17 Hz for the AB
system,corresponding to the resonance of the vinylic protons in
the 1H NMR spectrum. Deprotection with CF3CO2H in
CH2Cl2–H2O, followed by reaction of the resulting 8 with
methyl triphenylphosphonium bromide under Wittig condi-
tions afforded 9 in an 80% overall yield. Calix[4]OPV 1a was
then obtained in 68% yield from 3 and 9 under Heck-type
cross-coupling conditions. Compound 1a was characterized by
1H and 13C NMR spectroscopy, elemental analysis and mass
spectrometry. As previously observed for calix[4]OPV deriva-
tives, 1a gave a complicated 1H NMR spectrum.12 Actually, all
the anticipated signals are present but some of them are large.
This broadening suggests the existence of several conformers.
Indeed, the OPV moieties in 1a are not perpendicular to the
Scheme 2
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N e w J . C h e m . , 2 0 0 4 , 2 8 , 1 6 2 7 – 1 6 3 7

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Fig. 1 ORTEP drawing of 11 showing the two conformers (left:
conformer II; right: conformer V) seen in the crystal lattice.
good agreement with a cone conformation as previously shown
in the literature.25,26 For compound 11, crystals suitable for
X-ray crystal-structure analysis were obtained by slow diffu-
sion of Et2O into a CH3CN–MeOH (1 : 1) solution of 11. In the
structure, two different conformers, II and V, are observed in a
2 : 1 ratio. As shown in Fig. 1, the main difference among them
is the orientation of the four butyl chains as well as the
orientation of the four terminal phenyl subunits. Both II and
V adopt a ‘‘pinched’’ cone conformation in which two opposite
aromatic units of the calixarene macrocycle are parallel in a
face-to-face arrangement while the other two are flipped out-
ward. Close inspection of the packing revealed a tangled array
of molecules with a complicated network of intermolecular
p-stacking interactions between the aromatic rings of neigh-
bouring molecules. At the same time, the empty space resulting
from the pinched cone conformation are filled with the butyl
chains. The best way to describe the packing is to consider first
the threesome formed by two conformers II and one conformer
V (Fig. 2). Interestingly, the empty space resulting from the
pinched conformation of the central V molecule is filled by one
of the alkyl chains of both neighboruing II conformers. At the
same time, there is a butyl unit of V located within one of the
cavities of each neighbouring II molecules.
Scheme 3 Reagents and conditions: (a) aniline, C6H6, D, Dean–Stark
trap, 24 h (80%); (b) t-BuOK, DMF, 80 1C, 2 h (50%); (c) CF3CO2H,
CH2Cl2, H2O, rt, 5 h (99%); (d) methyltriphenylphosphonium bro-
mide, t-BuOK, THF, rt, 1 h (80%); (e) 3, tri-o-tolylphosphine (TOP),
Pd(OAc)2, Et3N, xylene, 120 1C, 48 h (68%).
observed for compound 1a. These have been described in detail
in a preliminary communication11 and will not be discussed
herein.
The synthetic approach to prepare the calix[4]OPE deriva-
tive 2 relies upon a Sonogashira cross-coupling23,24 reaction of
a terminal alkyne derivative on the upper rim of tetraiodinated
calix[4]arene 3. The conditions for the cross-coupling reaction
involving 3 were first adjusted with commercially available
terminal alkynes, namely trimethylsilylacetylene and phenyla-
cetylene (Scheme 4). The best results were obtained with
PdCl2(PPh3)2/CuI in Et3N at room temperature. Under these
conditions, reaction of 3 with an excess of trimethylsilylacety-
lene (10 equiv.) afforded compound 10 in 89% yield. Similarly,
compound 11 was obtained in 81% yield from 3 and pheny-
lacetylene.
Observation of the crystal lattice down the crystallographic
axis b reveals that the threesomes are arranged alternatively up
and down in linear infinite chains (Fig. 3). Except for the
interpenetration of the alkyl units into the cavity of neighbour-
ing molecules to fill the voids, there are no remarkable inter-
molecular interactions within these linear arrays. In contrast,
The cone conformation of both 10 and 11 was deduced from
1
their H and 13C NMR spectra. In particular, the 13C NMR
chemical shift of the methylene groups connecting the aromatic
rings (d 30.7 and 30.8 ppm for 10 and 11, respectively) was in
Fig. 2 Stacking within the crystal lattice of 11: two views of the
threesome formed by two conformers: II (in orange) and one con-
former V (in blue). The corresponding schematic representations have
been added to help the visualization; ‘‘+’’ indicates that the upper rim
of the calixarene molecule is seen and ‘‘–’’ that the lower rim is seen.
Molecular graphics images were produced using the UCSF Chimera
package from the Computer Graphics Laboratory, University of
California, San Francisco.36
Scheme
4 Reagents and conditions: (a) trimethylsilylacetylene,
PdCl2(PPh3)2, CuI, Et3N, rt, 72 h (10: 89%) or phenylacetylene,
PdCl2(PPh3)2, CuI, Et3N, rt, 48 h (11: 81%).
N e w J . C h e m . , 2 0 0 4 , 2 8 , 1 6 2 7 – 1 6 3 7
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Fig. 3 Stacking within the crystal lattice of 11: view down the
crystallographic axis b showing the infinite parallel chains formed by
the successive threesomes II–V–II arranged alternatively up and down.
The corresponding schematic representations have been added to help
the visualization. Molecular graphics images were produced using the
UCSF Chimera package (see caption to Fig. 2).
Scheme
5
Reagents and conditions: (a) p-bromobenzaldehyde,
PdCl2(PPh3)2, CuI, Et3N, rt, 72 h (70%); (b) CBr4, PPh3, Zn, CH2Cl2,
0 1C to rt, 12 h (95%); (c) LDA, THF, ꢀ70 to 0 1C, 3 h (86%); (d) 3,
PdCl2(PPh3)2, CuI, Et3N, rt, 72 h (71%).
there are several intermolecular p-p interactions between mo-
lecules belonging to neighbouring parallel chains. Interestingly,
the peculiar orientation of the two central phenyl units in V can
be explained by the packing forces resulting from their inter-
molecular p-p interactions with the phenyl moieties of two II
molecules belonging each to a different neighbouring linear
chain. Due to the presence of butyl groups of the other
neighbouring molecules, the two central phenyl units in V
cannot accommodate the face-to-face conformation observed
for II but are forced to turn around to interact in an edge-to-
edge manner. As a result, the bond angles at sp C atoms deviate
significantly from 1801. The observed angles are effectively
169.91 and 175.51. Additional p-p interactions can also be
observed between the layers formed by the parallel linear
arrays of infinite chains. The example highlighted in Fig. 4
shows how two II molecules are coupled by p-stacking inter-
actions among successive layers. Similar pairing is also ob-
served for the V conformers.
subjected to a Pd-catalyzed cross-coupling reaction with
p-bromobenzaldehyde to give 13 in 70% yield. Subsequent
treatment with CBr4/PPh3/Zn under the conditions described
by Corey–Fuchs27 afforded dibromoolefin 14 in 95% yield.
Elimination of HBr and halogen-metal exchange was best
achieved with an excess of LDA23,28,29 in THF at ꢀ78 1C
and the resulting anion was quenched with NH4Cl to give
terminal alkyne 15 in 86% yield. Subsequent Sonogashira
coupling with 3 gave calix[4]OPE 2 in 71% yield.
1
In contrast with calix[4]OPV 1a, the H NMR spectrum of
2 recorded at room temperature is well-resolved. In addition to
the signals corresponding to the alkyloxy chains, the spectrum
is characterized by a singlet for the aromatic calix[4]arene
protons, two sets of AA’XX’ signals for the protons of the two
p-substituted aromatic rings and an AB quartet for the calix[4]-
arene methylene groups. Clearly, the four OPE units in 2
appear equivalent in the 1H NMR spectrum recorded at room
temperature. However, computational studies revealed that
calix[4]OPE does not adopt a regular C4v symmetry, but rather
a C2v symmetry with a ‘‘pinched’’ cone conformation in which
two distal OPE units are upright while the other two distal
OPE units are flattened. These observations are also consistent
with the X-ray crystal structure of 11 showing a ‘‘pinched’’
cone conformation in the solid state while its 1H NMR
spectrum reveals an apparent C4v symmetry. Hence, as pre-
viously observed for other O-alkylated cone calix[4]arenes,2 the
C2v–C2v interconversion is faster than the NMR time scale.
Therefore, the four OPE units of 2 appear equivalent. The cone
conformation of 2 was further deduced from the chemical shift
of the methylene groups connecting the aromatic rings (d 30.8
ppm) in the 13C NMR spectrum. Finally, the structure of 2 was
also confirmed by FAB mass spectrometry showing the ex-
pected molecular ion peak at m/z 2187.0 (M+, calculated for
The preparation of the terminal alkyne 15 precursor of
calix[4]OPE 2 is depicted in Scheme 5. Compound 12 was
C
156H184O8: 2187.2). It is also worth noting that whereas liquid
Fig. 4 Stacking within the crystal lattice of 11: view highlighting
intermolecular p-p stacking interactions. Molecular graphics images
were produced using MERCURY 1.2.1 from the Cambridge Crystal-
lographic Data Centre.37
crystalline properties have been evidenced for calix[4]OPV
1a,11 the corresponding calix[4]OPE derivative 2 does not show
any mesomorphic behaviour.
1630
N e w J . C h e m . , 2 0 0 4 , 2 8 , 1 6 2 7 – 1 6 3 7

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Fig. 5 Cyclic voltammogram of 1a at room temperature in (a) THF
and (b) DCM solution with TBAPF6 as supporting electrolyte. c = 0.7
mM, v = 0.2 V sꢀ1.
Scheme 6 Reagents and conditions: (a) 9, TOP, Pd(OAc)2, Et3N,
xylene, 120 1C, 48 h (89%); (b) 15, PdCl2(PPh3)2, CuI, Et3N, rt, 24 h
(80%).
irreversibility and the corresponding E1/2 value was estimated
by cyclic voltammograms recorded with scan rates higher than
5 V sꢀ1. The model OPV compound 17 shows two one-electron
transfer processes with some degree of chemical irreversibility
at potential values very close to that observed for 1a.
The preparation of the model compounds 17 and 18 is
depicted in Scheme 6. The OPV derivative 17 was obtained
in 89% yield from 9 and 16 under Heck conditions. Coupling
constants of ca. 17 Hz for the two AB systems corresponding
to the two sets of vinylic protons in the 1H NMR spectrum
confirmed the E stereochemistry of both double bonds in 17.
The OPE model compound 18 was prepared in 80% yield by
Pd-catalyzed cross-coupling between 15 and 16.
Therefore, the redox processes observed for 1a can undoubt-
edly be assigned to the OPV moieties, but a careful investiga-
tion was necessary to determine whether the OPV units are
equivalent from an electrochemical point of view and if the
dianionic form of each OPV unit can be obtained also in the
calix[4]arene structure, as for the model compound 17. The
number of exchanged electrons in each redox process was
estimated through chronoamperometric measurements with a
Pt ultramicroelectrode (r = 25 mm).31 In the case of 1a the first
reduction process corresponds to the exchange of three elec-
trons with a slight negative shift (50 mV) compared to the
model compound, while the second process involves only one
electron. Therefore, the first peak is due to the simultaneous
reduction of three OPV units of the calixarene, while the
second one can be likely assigned to the reduction of the fourth
OPV unit. Indeed, although its E1/2 value (ꢀ2.35 V vs. SCE) is
almost coincident with that observed for the second reduction
of the OPV model compound (ꢀ2.34 V vs. SCE), the simulta-
neous presence in the calixarene of dianionic and neutral OPV
units is quite unlikely.
Electrochemistry
The electrochemical properties of calix[4]arenes 1a and 2 and
of their model compounds, 17 and 18, respectively, were
investigated by cyclic voltammetry in different solvent/electro-
lyte systems. In particular, dichloromethane (DCM) was espe-
cially used to investigate the anodic potential region, while
dimethylformamide (DMF) and tetrahydrofuran (THF) the
cathodic one; the supporting electrolyte was tetrabutylamo-
nium hexafluorophosphate (TBAPF6) in all cases. The values
of half-wave potentials (E1/2) of the investigated compounds
under different experimental conditions are gathered in
Table 1.
In THF solution calix[4]arene 1a shows two reduction
processes [Fig. 5(a)]: the first one (peak I) is reversible,30 while
the second one (peak II) shows some degree of chemical
In DCM solution both 1a [Fig. 5(b)] and 17 show two one-
electron oxidation processes, the second one (peak B) with a
certain degree of chemical irreversibility. The first OPV unit is
easier to oxidize (DE1/2 = 120 mV) inside the calix[4]arene than
Table 1 Half-wave potentials (E1/2 in V vs. SCE) of compound 1a, 2,
17 and 18a
Compound
Solvent
Peak B
Peak A
Peak I
Peak II
1a
THF
—
—
—
ꢀ2.03b
ꢀ2.08d
—
ꢀ2.35
—
—
DMF
DCM
DMF
DCM
+1.06c
+0.95
+1.34c
+1.37c
(+1.30)d
—
+1.09
—
—
2
ꢀ2.11b
ꢀ2.32
—
—
17
18
a
THF
—
—
ꢀ1.98
ꢀ2.05
—
ꢀ2.34
—
—
DMF
DCM
DMF
DCM
+1.00c
+1.07
+1.41c
+1.46c
(+1.42)
+1.30
—
—
ꢀ2.06
—
—
—
Cyclic voltammetry experiments at 298 K and, in parentheses, at
223 K in degassed DCM, DMF, or THF; TBAPF6 as supporting
b
electrolyte. Three-electron transfer. Chemically irreversible process,
Ep value at 0.2 V sꢀ1
electrons is prevented by solubility problems.
c
Fig. 6 Cyclic voltammogram of 2 at room temperature in (a) DMF
and (b) DCM solution with TBAPF6 as supporting electrolyte. c = 0.5
mM, v = 0.5 V sꢀ1. The small cathodic peak at ꢀ1 V is due to dioxygen
impurities.
d
.
Evaluation of the number of exchanged
N e w J . C h e m . , 2 0 0 4 , 2 8 , 1 6 2 7 – 1 6 3 7
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Fig. 7 Top: Absorption spectra of 1a (TT) and 17 (multiplied by a
factor of 4, --). The grey profile is obtained by summing three units of
17 and one unit of an OPV dimer. Solvents: toluene (TOL), dichloro-
methane (DCM), and benzonitrile (BN). Bottom: Absorption spectra
of 2 (TT) and 18 (multiplied by a factor of 4,--).
Fig. 8 Top: Fluorescence spectra of 1a (TT) and 17 (--); lexc = 365
nm, A = 0.15. Bottom: Fluorescence spectra of 2 (TT) and 18 (--);
lexc = 300 nm, A = 0.15. Solvents: toluene (TOL), dichloromethane
(DCM), and benzonitrile (BN), 298 K. A = Absorbance.
Fig. 6(b) the cathodic peak A0 is likely due to the product of the
chemical reaction coupled to the first oxidation. This process
attains chemical reversibility only at 223 K and scan rates
higher than 1 V sꢀ1: the corresponding E1/2 value of 2 is
significantly positively shifted (120 mV) compared to the
OPE model compound, demonstrating a higher electron-do-
nating capability of the OPE units inside the calixarene. The
number of electrons involved in the oxidation process of 2
cannot be estimated since at room temperature the peak height
can be affected by the coupled chemical reaction, while at
223 K solubility problems arise.
in the model compound. Furthermore, in the calix[4]arene 1a,
we observed the oxidation of only two out of four OPV units
and these processes occur at different potentials [peaks A and B
in Fig. 5(b)], thus demonstrating the lack of electrochemical
equivalency of the OPV units, in contrast to the cathodic
region behaviour.
The electrochemical properties of 1a and 17 were investi-
gated also in DMF solution: the results are similar to the
previously described ones, but a quantitative discussion of the
number of electrons exchanged is prevented by solubility
problems.
The comparison between 1a and 2 shows that upon reduc-
tion three out of four substituents are equivalent in both cases.
This result is not in contrast with the pinched cone conforma-
tion inferred before for the neutral state, since the injection of
three electrons can significantly alter the stability of the
different conformations because of electrostatic repulsions.
Furthermore, the OPE units of 2 are oxidized at more positive
potentials than the OPV groups of 1a and for 2 a chemical
reaction is coupled to the electron transfer.
The reduction behaviour of calix 1a is quite different from
that of the previously investigated calix 1b.12 The comparison
of the E1/2 values of the two calix[4]arenes shows that 1a is
significantly easier to oxidize and to reduce than the previously
investigated compound, evidencing a different relative stability
of the reduced and oxidized species in the two calix[4]arenes
because of the presence of a different number of electron
withdrawing –OC12H25 substituents. Furthermore, upon re-
duction, the previously investigated compound showed the
electrochemical equivalency of only two OPV units: this de-
monstrates the influence of the long alkyl chains in determining
the conformation of the calixarene structure. On the other
hand, in both cases the OPV units are not equivalent from the
oxidation point of view.
The same electrochemical investigations were performed for
calix[4]arene 2 and its model compound 18. The results are very
similar to that of 1a: three OPE units are reduced at the same
potential [E1/2 = ꢀ2.11 V vs. SCE, Fig. 6(a)] and the fourth
one is reduced at a more negative value (E1/2 = ꢀ2.32 V vs.
SCE, not shown in Fig. 6) in DMF solution. The cyclic
voltammetric experiments in THF solutions are not reported
because of adsorption problems on the working electrode. In
DCM solution the anodic scan of both 2 [Fig. 6(b)] and 18
shows one chemically irreversible electron transfer. Indeed, in
Table 2 Fluorescence band maxima and emission quantum yields
at 298 Ka
TOL
max/nm
DCM
max/nm
BN
l
Fem
l
Fem
lmax/nm
Fem
1a
17
2
434
426
432
378
0.84
0.93
0.22b
0.79
436
428
430
380
0.61
0.81
0.38b
1.00
440
432
396
386
0.85
1.00
0.57b
1.00
18
a
b
Excitation on the absorption maximum in each case. This value is
rather low if compared to the other compounds and corresponds to the
overall observed Fem, including excimer contribution (see Fig. 8,
bottom).
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Table 3 Luminescence decay times at the specified emission wave-
lengtha
spectra of 1a in any solvent are superimposable on the corre-
sponding absorption profiles. These results are consistent with
the above picture where the calixarene structure is made of
three 3PV and one 2PV units and light excitation of 2PV is
followed by singlet energy transfer to the 3PV units.
TOL
em/nm t/ns
DCM
em/nm t/ns
BN
l
l
lem/nm t/ns
The absorption and luminescence spectra of the OPE calix-
arene 2, relative to the reference compound 18, show an
opposite trend relative to the OPV systems 1a and 17. Absorp-
tion spectra of 2 and 18 are very similar (Fig. 7, bottom), but
luminescence spectra are remarkably different (Fig. 8, bottom).
This trend is observed in all of the investigated solvents.
The structure of the fluorescence profile of 18 is solvent
dependent and the most resolved profile is obtained in TOL.
This might reflect a less pronounced distribution of OPE
conformers, displaying different conjugation lengths,17 in an
apolar aromatic medium. The quantum yield of fluorescence is
unitary in DCM and BN, and lower in TOL (Table 2). The
excited state lifetime is very short (o1 ns) and monoexponen-
tial in any solvent, confirming that OPE-type molecules do not
exhibit any anomalous luminescence behaviour, as recently
pointed out by Beeby et al.32 When compared to OPE 18, the
luminescence band of the calix-OPE is broadened on the low-
energy side and the overall spectral shape appears to be the
sum of two overlapping bands (Fig. 8, bottom). One is the
regular OPE fluorescence, the other is a broader profile located
at longer wavelength. The shape of the excitation spectra is
independent of the emission frequency and matches the ab-
sorption profile of 18. Thus the low-energy emission band is
unambiguously assigned to intramolecular excimer-type inter-
actions between OPE arms. Excimer emission bands have been
already recorded for OPE19 and PPE33 aggregated systems.
The lifetime decays of 2 at 298 K in the three solvents are
biexponential with the shorter component (o1 ns) assigned to
regular OPE fluorescence (see 18 above) and the longer com-
ponent attributable to the excimer-type emission (Table 3,
Fig. 9).12
1a 450
17 450
0.9
0.8
436
428
1.0
1.0
450
450
0.9
0.9
2
366
400
480
0.8 (90%) 366
3.5 (10%)
0.8 (80%) 366
5.5 (20%)
0.7 (75%)
5.0 (25%)
0.8 (62%)
4.7 (38%)
4.6
0.5 (50%) 400
3.0 (50%)
1.0 (63%) 400
5.5 (37%)
2.9
0.7
0.8
480
366
400
5.2
0.7
0.9
480
366
400
18 366
400
0.7
0.7
a
lexc = 337 nm (D2 lamp).
Photophysical properties
The photophysical properties of calix[4]arenes 1a and 2, and of
their reference compounds 17 and 18, were investigated in three
solvents of different polarity, namely toluene (TOL, static
dielectric constant e = 2.4) dichloromethane (DCM, e =
8.9), and benzonitrile (BN, e = 25.2).
The absorption spectrum of 1a exhibits remarkable differ-
ences (shape and intensity) from that of the reference com-
pound 17, whatever the solvent (Fig. 7, top). This can be
attributed to ground state electronic intramolecular inter-
actions among OPV branches or, alternatively, to partial
electronic deconjugation of the p system in (some) OPV arms
when assembled on the calixarene scaffold, which would result
in absorption intensity decrease.12 Interestingly, the spectrum
obtained by summing three units of 17 and one unit of an OPV
dimer previously reported (2PV, which corresponds to a trans-
stilbene unit), is fairly comparable to the experimental spec-
trum of 1a (Fig. 7, DCM, top). This result is somewhat in
agreement with electrochemical data. The E1/2 value for the
second reduction of 1a [ꢀ2.35 V, peak II in Fig. 5(a)] is very
close to that observed for the above mentioned OPV dimer
(E1/2 = ꢀ2.34 V) in THF/TBAPF6 solution. Therefore, partial
deconjugation of one 3PV arm is the most likely explanation
for the odd profile of the absorption spectrum.
The relative amplitude of the two decays is dependent on the
emission wavelength: the longer the monitored wavelength the
stronger the contribution of the longer-lived component
(Table 3). Excimer-type emission tends to be favoured by
increasing solvent polarity as revealed by the ratio of the
lifetime relative amplitudes at 366 and 400 nm where both
emission bands contribute to the observed luminescence signal.
At 480 nm only the long-lived decay is monitored in all solvents
(Table 3, Fig. 9). The relative intensity between monomer and
excimer emission bands in 2 is concentration independent
in the typical range for spectroscopic measurements, i.e.
Contrary to the trend observed for absorption spectra, the
shape of the fluorescence bands of 1a is unaffected relative to
17 (Fig. 8, top). Little emission quantum yield decrease is
observed (Table 2) and the fluorescence lifetime, strictly mono-
exponential, is substantially unchanged (Table 3). Excitation
Fig. 9 Luminescence decays in TOL, DCM, and BN of 18 (black full circles) and 2 (grey full circles) at 400 nm and of 2 at 480 nm (black empty
circles); lexc = 337 nm. The intermediate traces (grey full circles) evidence biexponential decays.
N e w J . C h e m . , 2 0 0 4 , 2 8 , 1 6 2 7 – 1 6 3 7
1633

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the calixarenes 1a and 1b, respectively, while the second
reduction process corresponds to one and two equivalent
2PV units on 1a and 1b, respectively. The close vicinity of
the OPV or OPE moieties in the calix[4]arene structures and
the different trends of absorption, luminescence, and electro-
chemical properties in the two cases might provide clues on the
solid state electronic properties of simple OPV and OPE
chromophores.
Experimental
General methods
Reagents and solvents were purchased as reagent grade and
used without further purification. THF was distilled over
12
sodium benzophenone ketyl. Compounds 312 and 16
were
Fig. 10 Absorption spectra in DCM of 1b (TT) and its reference
trimeric unit 19 (ꢁ 4, --), see ref. 12. The grey profile is obtained by
summing two units of reference molecule 19 plus two units of reference
molecule 20.
prepared according to previously reported procedures. All
reactions were performed in standard glassware under an inert
Ar atmosphere. Evaporation and concentration were done at
water aspirator pressure and drying in vacuo at 10ꢀ2 Torr.
Column chromatography silica gel 60 (230–400 mesh, 0.040–
0.063 mm) was purchased from E. Merck. Thin layer chroma-
tography (TLC) was performed on glass sheets coated with
silica gel 60 F254 purchased from E. Merck, visualization by
UV light. NMR spectra were recorded on a Bruker AC 200
(200 MHz) or a Bruker AM 400 (400 MHz) with solvent peaks
as reference. FAB-mass spectra (MS) were obtained on a ZA
HF instrument with 4-nitrobenzyl alcohol as matrix. Elemental
analyses were performed by the analytical service of the Institut
Charles Sadron, Strasbourg. The molecular modelling studies
have been performed on a SGI Octane2 workstation using
Spartan’02 software.
10ꢀ7–10ꢀ5 M. Therefore excimer emission is only attributable
to intramolecular interactions occurring between the two frag-
ments facing each other in the pinched cone conformation (see
above). The fact that substantial residual monomer fluores-
cence is detected in all solvents indicates that a fraction of
calixarene molecules cannot adopt an excited state interchro-
mophoric distance leading to effective excimer interaction.
The opposite trends in absorption and luminescence proper-
ties of 1a and 2 vs. the corresponding model compounds 17 and
18 are in line with the NMR data and the molecular modelling
studies revealing differences in the average conformation be-
tween the two calixarenes (see above). Excited state interac-
tions are observed for 2 (Fig. 8, bottom) but not for 1a (Fig. 7,
bottom). This suggests that more effective intramolecular
excited state facing between calixarene branches occurs when
the more rigid and linear OPE fragments are involved. There
do not seem to be steric or electronic reasons as to why face-to-
face interactions should be more effective for 1a than for 2 in
the ground state. Thus, partial deconjugation of some calixar-
ene OPV branches and not ground state electronic interactions
are likely to be responsible for the depressed absorption
intensity of 1a (see above).
Syntheses
Compound 5. A solution of 4 (39.62 g, 139 mmol) and aniline
(14.3 ml, 153 mmol) in C6H6 (600 ml) was refluxed for 24 h
using a Dean–Stark trap. After cooling, the solution was
evaporated to dryness and recrystallization (EtOH) yielded 5
1
(40 g, 80%) as a colourless solid (mp 61 1C). H NMR (200
MHz, C6D6): 8.30 (s, 1H), 7.97 (d, J = 8 Hz, 2H), 7.34–7.10
(m, 5H), 6.94 (d, J = 8 Hz, 2H), 3.69 (t, J = 6.5 Hz, 2H), 1.75
(m, 2H), 1.50–1.30 (m, 18H), 1.04 (t, J = 6 Hz, 3H). Anal.
calcd. for C25H35NO: C 82.14, H 9.65, N 3.83. Found: C 82.09,
H 9.66, N 3.78.
The absorption spectrum of 1a in DCM (lmax = 350 nm,
e = 146 000 Mꢀ1 cmꢀ1; Fig. 7) is rather different in shape and
intensity relative to that of 1b (lmax = 350 nm, e = 111 000
M
ꢀ1 cmꢀ1; Fig. 10).12 Thus, steric effects induced by the long –
Compound 7. t-BuOK (8.94 g, 75 mmol) was added to a
solution of 5 (10.63 g, 29 mmol) and 6 (6.00 g, 29 mmol) in dry
DMF (50 ml) under argon at 80 1C. The mixture was stirred for
2 h at 80 1C and, after cooling, poured into an aqueous 0.5 M
HCl solution (500 ml). The mixture was extracted with
CH2Cl2. The organic layer was washed with water, dried
(MgSO4) and evaporated to dryness. Column chromatography
(SiO2, hexane–CH2Cl2 1 : 1) gave 7 (7.02 g, 50%) as a colour-
less solid (mp 135 1C). 1H NMR (200 MHz, CDCl3): 7.49
(s, 4H), 7.44 (d, J = 8 Hz, 2H), 7.01 (AB, J = 17 Hz, 2H), 6.88
(d, J = 8 Hz, 2H), 5.40 (s, 1H), 3.97 (t, J = 6.5 Hz, 2H), 3.70
(AB, J = 11 Hz, 4H), 1.80 (m, 2H), 1.55–1.30 (m, 18H), 1.28 (s,
3H), 0.89 (t, J = 6 Hz, 3H), 0.81 (s, 3H). 13C NMR (50 MHz,
CDCl3): 158.9, 138.2, 137.3, 129.8, 128.6, 127.7, 126.5, 126.1,
126.0, 114.7, 101.6, 77.6, 68.0, 31.9, 30.2, 29.6, 29.5, 29.4, 29.3,
26.1, 23.1, 22.7, 21.9, 14.2. Anal. calcd. for C32H46O3: C 80.29,
H 9.69. Found: C 80.21H 9.70.
OR terminal units may influence the calixarene conformation
and OPV p conjugation. Finally, it is interesting to note that
the absorption spectrum of 1b is well-recovered by the profile
obtained with two 3PV plus two 2PV residues, while a spectral
comparison of 1b with four 3PV fragments is extremely
unsatisfactory, even more so than for 1a (Fig. 10).
Conclusions
Heck and Sonogashira cross-coupling reactions were used for
the successful functionalization of tetraiodinated calix[4]arene
3. In this way, OPV and OPE arrays were constructed on the
upper rim of a calix[4]arene core to produce covalent assem-
blies of four p-conjugated chromophores. Despite the fact that
conformational flexibility might make it difficult to predict any
regular trends, we emphasize the correlation between electro-
chemical and UV-Vis absorption for the OPV calixarenes 1a
and 1b, which, taken in concert, seem to indicate conforma-
tional peculiarities. The absorption spectra in DCM are rela-
tively well-matched with three 3PV plus one 2PV residues in the
case of 1a, whereas two 3PV plus two 2PV residues are found to
give the best match with 1b. In parallel the electrochemical
experiments reveal that the first reduction process corresponds
to three (peak I in Table 1) and two12 equivalent 3PV units on
Compound 8. A mixture of 7 (2.50 g, 5.22 mmol) and
CF3CO2H (50 ml) in CH2Cl2–H2O 2 : 1 (150 ml) was stirred
at rt for 5 h. The organic layer was then washed with water
(3ꢁ), dried (MgSO4) and evaporated to give 8 (2.03 g, 99%) as
a pale yellow solid (mp 133 1C). 1H NMR (200 MHz, CDCl3):
8.61 (s, 1H), 7.86 (d, J = 8 Hz, 2H), 7.63 (d, J = 8 Hz, 2H),
1634
N e w J . C h e m . , 2 0 0 4 , 2 8 , 1 6 2 7 – 1 6 3 7

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7.48 (d, J = 8 Hz, 2H), 7.15 (AB, J = 17 Hz, 2H), 6.91 (d, J =
8 Hz, 2H), 3.99 (t, J = 7 Hz, 2H), 1.78 (m, 2H), 1.55–1.30 (m,
18H), 0.89 (t, J = 6.5 Hz, 3H). 13C NMR (50 MHz, CDCl3):
191.5, 159.6, 143.9, 134.9, 131.8, 130.2, 129.0, 128.2, 126.5,
124.9, 114.8, 68.1, 31.9, 29.5, 29.4, 29.3, 29.2, 26.0, 22.6, 14.1.
Anal. calcd. for C27H36O2: C 82.61, H 9.24. Found: C 82.79,
H 9.36.
134.7, 131.8, 131.5, 128.0, 127.5, 123.6, 117.1, 89.8, 88.1, 75.1,
32.2, 30.8, 19.3, 14.0. Anal. calcd. for C76H72O4: C 86.99, H
6.92. Found: C 86.86, H 6.99.
Compound 13. PdCl2(PPh3)2 (3 mol %) and CuI (5 mol %)
were added to a stirred degassed solution of 12 (4.30 g, 15
mmol) and 4-bromobenzaldehyde (4.16 g, 22.5 mmol) in dry
triethylamine (40 ml) at rt. The resulting mixture was stirred at
rt for 48 h, then concentrated. The residue was taken up in
CH2Cl2. The organic layer was washed with water, dried
(MgSO4), filtered and evaporated. Column chromatography
(SiO2, hexane–CH2Cl2 7 : 3) gave 13 (4.10 g, 70%) as a colour-
less solid glassy product. 1H NMR (200 MHz, CDCl3): 8.58 (s,
1H), 7.86 (d, J = 8 Hz, 2H), 7.65 (d, J = 8 Hz, 2H), 7.49 d,
J = 8 Hz, 2H), 6.89 (d, J = 8 Hz, 2H), 3.98 (t, J = 6.5 Hz,
2H), 1.77 (m, 2H), 1.60–1.30 (m, 18H), 0.89 (t, J = 6.5 Hz,
3H). 13C NMR (50 MHz, CDCl3): 191.3, 159.7, 135.0, 133.3,
131.8, 130.0, 129.5, 114.6, 114.2, 93.9, 87.4, 68.1, 31.9, 29.6,
29.5, 29.3, 29.1, 25.9, 22.6, 14.1. Anal. calcd. for C27H34O2: C
83.03, H 8.77. Found: C 83.29, H 8.99.
Compound 9. A mixture of 8 (1.90 g, 4.84 mmol), t-BuOK
(0.56 g, 5.32 mmol) and methyltriphenylphosphonium bromide
(1.90 g, 5.32 mmol) in dry THF (30 ml) was stirred at rt for 1 h.
A saturated aqueous NH4Cl solution was then added and the
resulting mixture concentrated. The aqueous layer was ex-
tracted twice with CH2Cl2. The combined organic layers were
washed with water, dried (MgSO4), and evaporated to dryness.
Column chromatography (SiO2, hexane–CH2Cl2 7 : 3) gave 9
1
(1.51 g, 80 %) as a pale yellow solid (mp 160 1C). H NMR
(200 MHz, CDCl3) 7.48 (d, J 8 Hz, 2H), 7.41 (AB, J = 8 Hz,
4H), 7.01 (AB, J = 17 Hz, 2H), 6.89 (d, J = 8 Hz, 2H), 6.70
(dd, J = 17 and 11 Hz, 1H), 5.75 (dd, J = 17 and 2 Hz, 1H),
5.23 (d, J = 11 and 2 Hz, 1H), 3.98 (t, J = 6.5 Hz, 2H), 1.76
(m, 2H), 1.56–1.28 (m, 18H), 0.83 (t, J = 6 Hz, 3H). Anal.
calcd. for C28H38O2: C 82.71, H 9.42. Found: C 82.50, H 9.55.
Compound 14. A mixture of CBr4 (17.18 g, 51.8 mmol), PPh3
(13.64 g, 51.8 mmol) and Zn dust (3.39 g, 51.8 mmol) in dry
CH2Cl2 (200 ml) was stirred at rt for 24 h. The suspension was
then cooled to 0 1C and a solution of 13 (4.05 g, 10.37 mmol) in
CH2Cl2 (30 ml) was added at once. The resulting mixture was
slowly warmed up to rt (1 h) and stirred at this temperature
overnight. The resulting thick suspension was filtered over SiO2
(CH2Cl2) to remove the zinc salts and some of the P-containing
by-products. The solution was concentrated and column chro-
matography (SiO2, CH2Cl2–hexane 1 : 1) gave 14 (5.4 g, 95%)
as colourless glassy product. 1H NMR (200 MHz, CDCl3):
7.50 (AB, J = 8 Hz, 4H), 7.47 (s, 1H), 7.45 (d, J = 8 Hz, 2H),
6.85 (d, J = 8 Hz, 2H), 3.97 (t, J = 6.5 Hz, 2H), 1.77 (m, 2H),
1.60–1.30 (m, 18H), 0.89 (t, J = 6.5 Hz, 3H). 13C NMR (50
MHz, CDCl3): 159.4, 136.2, 134.5, 133.0, 131.3, 128.3, 123.9,
114.5, 92.3, 91.0, 90.0, 87.7, 68.1, 31.9, 29.6, 29.5, 29.4, 29.2,
26.0, 22.7, 14.1. Anal. calcd. for C28H34OBr2: C 61.55, H 6.27.
Found: C 61.52, H 6.36.
Compound 1a. A mixture of 3 (300 mg, 0.26 mmol), 9 (458
mg, 1.17 mmol), TOP (6 mg) and Pd(OAc)2 (3 mg) in NEt3–
xylene 1 : 4 (25 ml) was stirred at 120 1C under argon for 48 h.
After cooling to rt, the mixture was filtered through celite
(CH2Cl2) and evaporated. The residue was dissolved in
CH2Cl2. The solution was washed with water (3ꢁ), dried
(MgSO4) and evaporated. Column chromatography (SiO2,
hexane–CH2Cl2 1 : 1), followed by recrystallization (CH2Cl2–
MeOH) afforded 1a (390 mg, 68%) as a yellow solid (140 1C
smectic liquid crystalline phase; 180 1C isotropic liquid). 1H
NMR (200 MHz, CD2Cl2): 7.44–6.50 (m, 56H), 4.50 (br d, J =
13 Hz, 4H), 3.90 (m, 16H), 3.24 (br d, J = 13 Hz, 4H), 1.94 (m,
8H), 1.78 (m, 8H), 1.55–1.30 (m, 80H), 1.03 (t, J = 7 Hz, 12H),
0.88 (t, J = 6.5 Hz, 12H). FAB-MS: 2203.5 (M+ calcd. for
C156H200O8: 2203.3). Anal. calcd. for C156H200O8: C 85.04,
H 9.15. Found: C 85.39, H 8.99.
Compound 15. A 2.0 M solution of LDA in THF (30 ml, 60
mmol) was added dropwise to a solution of 14 (5.35 g, 9.79
mmol) in dry THF (120 ml) at ꢀ78 1C under argon. The
resulting was stirred for 2 h at ꢀ78 1C, then allowed to warm
up to 0 1C (1 h) and a saturated aqueous NH4Cl solution (60
ml) was added. The mixture was then diluted with hexane. The
organic layer was washed with H2O (2ꢁ), dried (MgSO4),
filtered and evaporated. Column chromatography (SiO2, hex-
ane–CH2Cl2 7 : 3) gave 15 (3.25 g, 86%) as pale yellow glassy
product. 1H NMR (200 MHz, CDCl3): 7.46 (d, J = 8 Hz, 2H),
7.45 (s, 4H), 6.87 d, J = 8 Hz, 2H), 3.97 (t, J = 6.5 Hz, 2H),
3.16 (s, 1H), 1.78 (m, 2H), 1.55–1.30 (m, 18H), 0.88 (t, J = 6.5
Hz, 3H). 13C NMR (50 MHz, CDCl3): 159.4, 136.2, 133.1,
132.0, 131.2, 128.3, 124.2, 121.4, 114.7, 114.5, 91.6, 87.5, 83.3,
78.7, 68.0, 31.9, 29.7, 29.6, 29.4, 29.2, 26.0, 22.7, 14.1. Anal.
calcd. for C28H34O: C 87.00, H 8.86. Found: C 86.88, H 9.01.
Compound 10. PdCl2(PPh3)2 (3 mol %) and CuI (5 mol %)
were added to a degassed solution of 3 (200 mg, 0.174 mmol)
and trimethylsilylacetylene (0.25 ml, 1.73 mmol) in dry triethyl-
amine (40 ml) at rt. The resulting mixture was stirred under
argon at rt for 72 h, then concentrated. The residue was taken
up in CH2Cl2. The organic layer was washed with water, dried
(MgSO4), filtered and evaporated. Column chromatography
(SiO2, hexane–CH2Cl2 9 : 1) gave 10 (160 mg, 89%) as a
colourless solid. 1H NMR (200 MHz, CDCl3): 6.94 (s, 8H),
4.35 (d, J = 13 Hz, 4H), 3.88 (t, J = 7 Hz), 3.10 (d, J = 13 Hz,
4H), 1.89 (m, 8H), 1.42 (m, 8H), 0.98 (t, J = 6.5 Hz, 12H), 0.25
(s, 36H). 13C NMR (50 MHz, CDCl3): 156.8, 134.3, 132.4,
116.9, 105.5, 92.7, 75.2, 32.1, 30.7, 19.3, 14.0, 0.15. Anal. calcd.
for C64H88O4Si4: C 74.36, H 8.58. Found: C 74.50, H 8.45.
Compound 11. PdCl2(PPh3)2 (3 mol %) and CuI (5 mol %)
were added to a degassed solution of 3 (200 mg, 0.174 mmol)
and phenylacetylene (0.2 ml, 1.74 mmol) in dry triethylamine
(40 ml) at rt. The resulting mixture was stirred under argon at
rt for 48 h, then concentrated. The residue was taken up in
CH2Cl2. The organic layer was washed with water, dried
(MgSO4), filtered and evaporated. Column chromatography
(SiO2, hexane–CH2Cl2 4 : 1) gave 11 (149 mg, 81%) as a
Compound 2. PdCl2(PPh3)2 (3 mol %) and CuI (5 mol %)
were added to a degassed solution of 3 (100 mg, 0.087 mmol)
and 15 (325 mg, 0.87 mmol) in dry triethylamine (40 ml) at rt.
The resulting mixture was stirred under argon at rt for 48 h,
then concentrated. The residue was taken up in CH2Cl2. The
organic layer was washed with water, dried (MgSO4), filtered
and evaporated. Column chromatography (SiO2, hexane–
CH2Cl2 4 : 1) gave 2 (135 mg, 71%) as a pale yellow solid
(mp 126 1C). 1H NMR (400 MHz, CD2Cl2): 7.41 (d, J = 8 Hz,
8H), 7.36 (AB, J = 8 Hz, 16H), 6.97 (s, 8H), 6.77 (d, J = 8 Hz,
8H), 4.52 (d, J = 13 Hz, 4H), 3.99 (t, J = 6.5 Hz, 8H), 3.97
1
colourless solid. H NMR (200 MHz, CDCl3): 7.43 (m, 8H),
7.17 (m, 12H), 6.97 (s, 8H), 4.44 (d, J = 13 Hz, 4H), 3.95 (t,
J = 7 Hz), 3.19 (d, J = 13 Hz, 4H), 1.92 (m, 8H), 1.45 (m, 8H),
1.02 (t, J = 6.5 Hz, 12H). 13C NMR (50 MHz, CDCl3): 156.8,
N e w J . C h e m . , 2 0 0 4 , 2 8 , 1 6 2 7 – 1 6 3 7
1635

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(t, J = 6.5 Hz, 8H), 3.21 (d, J = 13 Hz, 4H), 1.97 (m, 8H), 1.81
(m, 8H), 1.58–1.29 (m, 80H), 1.03 (t, J = 6.5 Hz, 12H), 0.90 (t,
J = 6.5 Hz, 12H). 13C NMR (50MHz, CDCl3): 159.1, 157.0,
134.7, 133.0, 131.8, 131.2, 131.1, 122.9, 122.8, 116.8, 115.0,
114.4, 91.5, 91.0, 88.1, 88.0, 75.1, 68.0, 32.2, 31.9, 30.8, 29.6,
29.4, 29.3, 29.2, 26.0, 22.7, 19.3, 14.1, 14.0. FAB-MS: 2187.0
(M+, calcd. for C156H184O8: 2187.2). Anal. calcd. for
Electrochemistry
The electrochemical experiments were carried out in argon-
purged DCM, DMF (Romil Hi-Dryt) or THF (Aldrich)
solutions at 298 or 223 K with an EcoChemie Autolab 30
multipurpose instrument interfaced to a personal computer. In
cyclic voltammetry (CV) the working electrode was a glassy
carbon electrode (0.08 cm2, Amel) or a Pt disk ultramicroelec-
trode (r = 25 mm). In all cases, the counter electrode was a Pt
spiral, separated from the bulk solution with a fine glass frit,
and a silver wire was employed as a quasi-reference electrode
(AgQRE). The potentials reported are referred to SCE by
measuring the AgQRE potential with respect to ferrocene.
The concentration of the compounds examined was of the
order of 5 ꢁ 10ꢀ4 M; 0.05 M tetrabuthylammonium hexa-
fluorophosphate (TBAPF6) was added as supporting electro-
lyte. Cyclic voltammograms were obtained with scan rates in
the range 0.05–20 V sꢀ1. The CV simulations were carried out
by the DIGISIM program. The diffusion coefficients and the
number of electrons exchanged in each electron transfer pro-
cess were determined by chronoaperometric experiments per-
formed with a Pt disk ultramicroelectrode (r = 25 mm) by the
method reported by Bard et al.31
C
156H184O8: C 85.67, H 8.48. Found: C 85.68, H 8.27.
Compound 17. A mixture of 16 (300 mg, 1.07 mmol), 9 (435
mg, 1.07 mmol), TOP (25 mg) and Pd(OAc)2 (10 mg) in NEt3–
xylene 1 : 4 (25 ml) was stirred at 120 1C under argon for 48 h.
After cooling to rt, the mixture was filtered through celite
(CH2Cl2) and evaporated. The residue was dissolved in
CH2Cl2. The solution was washed with water (3ꢁ), dried
(MgSO4) and evaporated. Column chromatography (SiO2,
hexane–CH2Cl2 2 : 1 to 1 : 1) afforded 17 (540 mg, 89%) as a
pale yellow solid (110 1C smectic C liquid crystalline phase;
149 1C smectic A liquid crystalline phase; 154 1C nematic liquid
crystalline phase; 181 1C isotropic liquid). 1H NMR (200 MHz,
CDCl3): 7.47 (s, 4H), 7.43 (d, J = 8 Hz, 2H), 7.19 (s, 2H), 7.03
(AB, J = 17 Hz, 2H), 7.01 (AB, J = 17 Hz, 2H), 6.90 (d, J = 8
Hz, 2H), 3.98 (t, J = 6.5 Hz, 2H), 3.78 (t, J = 6.5 Hz, 2H), 2.31
(s, 6H), 1.80 (m, 4H), 1.60–1.30 (m, 20H), 1.01 (t, J = 6.5 Hz,
3H), 0.89 (t, J = 6.5 Hz, 3H). 13C NMR (50MHz, CDCl3):
158.9, 155.9, 136.7, 136.5, 133.0, 132.6, 131.1, 129.9, 128.0,
127.6, 127.0, 126.9, 126.5, 126.5, 126.0, 114.7, 72.1, 68.0, 32.5,
31.8, 29.6, 29.5, 29.4, 29.3, 26.0, 22.6, 19.3, 16.3, 14.1, 13.9,
Anal. calcd. for C40H54O2: C 84.75, H 9.60. Found: C 84.62
H 9.39.
Photophysics
The photophysical investigations were carried out in CH2Cl2
and toluene (Carlo Erba, spectrofluorimetric grade), and in
benzonitrile (Aldrich, HPLC grade). The samples were placed
in fluorimetric 1 cm path cuvettes. Absorption spectra were
recorded with a Perkin–Elmer l40 spectrophotometer. Uncor-
rected emission spectra were obtained with a Spex Fluorolog II
spectrofluorimeter (continuous 150 W Xe lamp), equipped with
a Hamamatsu R-928 photomultiplier tube. The corrected
spectra were obtained via a calibration curve. Fluorescence
quantum yields obtained from spectra on an energy scale
(cmꢀ1) were measured with the method described by Demas
and Crosby34 using as standards air-equilibrated solutions of
quinine sulfate in 1 N H2SO4 (Fem = 0.546).35 To record the
77 K luminescence spectra, the samples were put in glass tubes
(2 mm diameter) and inserted in a special quartz dewar, filled
up with liquid nitrogen. Emission lifetimes on the nanosecond
time scale were determined with an IBH single-photon-count-
ing spectrometer equipped with a thyratron gated nitrogen
lamp working in the range 2–40 kHz (lexc = 337 nm, 0.5 ns
time resolution); the detector was a red-sensitive (185–850 nm)
Hamamatsu R-3237-01 photomultiplier tube. Experimental
uncertainties are estimated to be 8% for lifetime determina-
tions, 20% for emission quantum yields, and 1 nm and 5 nm
for absorption and emission peaks, respectively.
Compound 18. PdCl2(PPh3)2 (3 mol %) and CuI (5 mol %)
were added to a degassed solution of 16 (200 mg, 0.658 mmol)
and 15 (254 mg, 0.658 mmol) in dry triethylamine (15 ml) at rt.
The resulting mixture was stirred under argon at rt for 24 h,
then concentrated. The residue was taken up in CH2Cl2. The
organic layer was washed with water, dried (MgSO4), filtered
and evaporated. Column chromatography (SiO2, hexane–
CH2Cl2 4 : 1) gave 2 (300 mg, 80%) as a pale yellow solid
1
(mp 128 1C). H NMR (200 MHz, CDCl3): 7.46 (s, 4H), 7.44
(d, J = 8 Hz, 2H), 7.21 (s, 2H), 6.88 (d, J = 8 Hz, 2H), 3.98
(t, J = 6.5 Hz, 2H), 3.78 (t, J = 6.5 Hz, 2H), 2.28 (s, 6H), 1.78
(m, 4H), 1.60–1.28 (m, 20H), 1.00 (t, J = 6.5 Hz, 3H), 0.89 (t,
J = 6.5 Hz, 3H). 13C NMR (50 MHz, CDCl3): 159.4, 156.6,
133.0, 132.1, 131.3, 131.2, 123.2, 123.0, 118.0, 114.8, 114.5,
91.3, 91.2, 88.0, 87.8, 72.1, 68.0, 32.4, 31.9, 31.6, 29.6, 29.6,
29.3, 29.2, 29.0, 26.9, 26.0, 22.6, 19.3, 16.1, 14.1, 13.9. Anal.
calcd. for C40H50O2: C 85.36, H 8.95. Found: C 85.47, H 8.79.
Crystal structure determination of 11
Acknowledgements
The colourless crystal used for the diffraction study was
produced by slow diffusion of Et2O into a CH3CN–MeOH
(1 : 1) solution of 11. Diffraction data were collected on a
Kappa CCD diffractometer using graphite-monochromated
MoKa radiation (l = 0.710 73 A). Data were collected using
phi- scans and the structures were solved by direct methods
using SHELX97 software38 and the refinements were con-
ducted by full-matrix least squares on F2. No absorption
correction was used. All non-hydrogen atoms were refined
anisotropically. Hydrogen atoms were generated according to
This work was supported by the CNR, MIUR (Supramolecu-
lar Devices Project), FIRB (Manipolazione molecolare per
macchine nanometriche), the CNRS and the French Ministry
of Research (ACI Jeunes Chercheurs). G. A. thanks the project
‘‘Photomed’’ 184/02 of Spinner Agency (European Commu-
nity and Regione Emilia Romagna) for his research fellow-
ships. We further thank L. Oswald for technical help and
M. Schmitt for high-field NMR measurements.
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