Calix[4]oligophenylenevinylene: A new rigid core for the design of π-conjugated liquid crystalline derivatives

Article abstract of DOI:10.1016/S0040-4039(01)00169-1

The synthesis and the liquid crystalline properties of a new class of conjugated derivatives that assembled four oligophenylenevinylene (OPV) moieties arising from a calix[4]arene core are described. Photophysical investigations also revealed strong elect

Full text of DOI:10.1016/S0040-4039(01)00169-1

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 2309–2312
Calix[4]oligophenylenevinylene: a new rigid core for the design of
p-conjugated liquid crystalline derivatives
Tao Gu,a Gianluca Accorsi,b Nicola Armaroli,b,* Daniel Guillona and Jean-Franc¸ois Nierengartena,*
aGroupe des Mate´riaux Organiques, Institut de Physique et Chimie des Mate´riaux de Strasbourg,
Universite´ Louis Pasteur et CNRS, 23 rue du Loess, 67037 Strasbourg, France
bIstituto di Fotochimica e Radiazioni d’Alta Energia del CNR, via Gobetti 101, 40129 Bologna, Italy
Received 27 January 2001; accepted 30 January 2001
Abstract—The synthesis and the liquid crystalline properties of a new class of conjugated derivatives that assembled four
oligophenylenevinylene (OPV) moieties arising from a calix[4]arene core are described. Photophysical investigations also revealed
strong electronic coupling between the four OPV fragments of the calix[4]OPV derivative. © 2001 Elsevier Science Ltd. All rights
reserved.
Organic semiconducting materials have been extensively
investigated in the past few years for their electronic
properties,1 and structural studies of these kind of
compounds appear today as an important issue in their
applications. Actually, in light-emitting diodes (LEDs)2
or photovoltaic devices,3 the functional characteristics
are affected by the morphology of the organic films.4
For the purpose of gaining insight into the relationship
between the morphology of the thin films and the
electroluminescence or the charge-transport properties,
p-conjugated derivatives exhibiting liquid crystalline
properties are of particular interest5 because they spon-
taneously form ordered assemblies that can be easily
oriented. As part of this research, we now report the
synthesis and the liquid crystalline properties of a new
strongly luminescent conjugated derivative that assem-
bles four oligophenylenevinylene (OPV) moieties arising
from a calix[4]arene core. We also show that the elec-
tronic properties of the calix[4]oligophenylenevinylene
derivative 1 are not directly related to the correspond-
ing OPV model compound 2, suggesting strong elec-
tronic coupling between the four OPV fragments of the
calix[4]OPV derivative.
The synthesis of the calix[4]OPV derivative 1 is depicted
in Scheme 1. Reaction of 4-hydroxybenzyl alcohol (3)
with 1-bromododecane in DMF at 70°C in the presence
of K2CO3, followed by oxidation of the resulting 4-
* Corresponding authors. Fax: 33 388 10 72 46 (J.-F.N.); e-mail: niereng@michelangelo.u-strasbg.fr
0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)00169-1

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T. Gu et al. / Tetrahedron Letters 42 (2001) 2309–2312
Scheme 1. Reagents and conditions: (i) 1-bromododecane, K2CO3, DMF, 70°C, 24 h (80%); (ii) MnO2, CH2Cl2, rt, 3 h (83%); (iii)
aniline, C6H6, D, 24 h (80%); (iv) 2,2-dimethylpropane-1,3-diol, p-TsOH, C6H6, D, 24 h (96%); (v) t-BuOK, DMF, 80°C, 2 h
(50%); (vi) CF3CO2H, H2O, CH2Cl2, rt, 5 h (99%); (vii) methyl triphenylphosphonium bromide, t-BuOK, THF, rt (80%); (viii)
CF3CO2Ag, I2, CHCl3, D, 3 h (91%); (iv) Pd(OAc)2, tri-o-tolylphosphine, Et3N, xylene, D, 48 h (68%).
dodecyloxybenzyl alcohol with MnO2 in CH2Cl2,
yielded 4 in an overall 66% yield. Subsequent condensa-
tion of benzaldehyde 4 with aniline in refluxing benzene
afforded benzaldimine 5 in 80% yield. Reaction of
p-tolualdehyde (6) with 2,2-dimethylpropane-1,3-diol in
refluxing benzene in the presence of a catalytic amount
of p-toluenesulfonic acid (p-TsOH) gave the protected
aldehyde 7 in 96% yield. Benzaldimine 5 was subjected
to the Siegrist reaction with compound 7 to give pro-
tected stilbene 8 in 50% yield. Subsequent treatment
with CF3CO2H in CH2Cl2/H2O and reaction of the
resulting aldehyde with methyl triphenylphosphonium
bromide under Wittig conditions afforded 9 in an over-
all 80% yield. Treatment of the tetra-O-alkylated cone
calix[4]arene 106 with iodine in the presence of
CF3CO2Ag in refluxing CHCl3 yielded 11 in 91% yield.
For both 10 and 11, the cone conformation was
deduced from the 1H and 13C NMR spectra. In particu-
lar, the 13C NMR chemical shifts (around l 31 ppm) of
the methylene groups connecting the aromatic rings
were in good agreement with a cone conformation, as
previously shown in the literature.7 Calix[4]OPV 1 was
then obtained in 68% yield from 9 and 11 under Heck
tion of the four substituents on the upper rim of the
calix[4]arene core is necessary to produce an NMR
spectrum with sharp symmetric signals. A study of the
temperature-dependent NMR spectrum shows a nar-
rowing of some signals at 120°C, but a sharp symmetric
spectrum could not be obtained below the maximum
measurement temperature.
The absorption spectrum of 1 in CH2Cl2 solution is
significantly different (both in shape and intensity) from
that obtained by summing four model units 2 (Fig. 1).
Compounds 1 and 2 display the typical intense fluores-
1
type cross-coupling conditions. In the H NMR spec-
trum of 1, all the anticipated signals were present but
some of them were large. The broadening observed in
the spectrum of 1 suggests the existence of several
conformers. Indeed, due to conjugation, the OPV moi-
eties of 1 are not perpendicular to the calixarene core
and restricted rotation can easily be explained by the
tendency of the OPV moieties to stay in an extended
planar conjugated conformation.8 Therefore, two dia-
metrically opposite OPV units can either be in an
eclipsed or a staggered relative orientation. Free rota-
Figure 1. Absorption spectra of 2 (dashed line, multiplied by
a factor of four) and 1 (full line). Inset: fluorescence spectra of
optically matched solutions of 2 (dashed line) and 1 (full line);
uexc=365 nm, O.D.=0.17. The dotted lines represent the
excitation spectra. All the experiments were carried out in
CH2Cl2 solutions at 298 K.

T. Gu et al. / Tetrahedron Letters 42 (2001) 2309–2312
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a
Table 1. Luminescence data in CH2Cl2
298 K
(ns)
77 K
b
b
umax (nm)
~
bem
umax (nm)
~
(ns)
1
2
436
428
1.0
1.0
0.61
0.81
425
412
1.0 (90%), 4.2 (10%)
1.2 (85%), 5.6 (15%)
a The fluorescence spectra and quantum yields were obtained upon excitation on the absorption maxima.
b uexc=337 nm, single photon counting apparatus.3b
layers. From these data, we can deduce a thickness of
,
66 A corresponding to approximately twice the length
of compound 1, and therefore to
a
bilayered
arrangement.
A conjugated derivative that assembles four OPV moi-
eties arising from a calix[4]arene core has been prepared
and we have shown that it can act as a rigid core for
the design of new p-conjugated liquid crystalline deriva-
tives. As well as the potential use of such a compound
in optoelectronic devices, the calix[4]OPV presented
here is a strongly luminescent receptor and, therefore, is
also potentially useful in the field of host–guest
chemistry.9,10
Figure 2. X-ray diffraction pattern of 1 recorded at 160°C.
Acknowledgements
cence of OPV’s in CH2Cl2 both at 298 K and in a rigid
77 K matrix (Table 1). The luminescence lifetimes at
room temperature are monoexponential (1.0 ns),
whereas at 77 K biexponential decays are recorded
(Table 1), probably as a consequence of the presence of
different ‘frozen’ rotameric forms in the solid matrix.3b
The luminescence spectra of 1 and 2 are qualitatively
similar; however, it is worth pointing out that the
fluorescence maxima of the calix[4]OPV is slightly red-
shifted and the emission quantum yield lower (Table 1).
The differences in the absorption and luminescence
properties of 1 and 2 seem to suggest that interchromo-
phoric interactions in the calix[4]OPVs take place.9
The authors would like to thank Dr. B. Heinrich for his
help with the X-ray measurements and L. Oswald for
technical assistance in the synthesis. T.G. thanks the
Direction de la Recherche of the French Ministry of
Research for a post-doctoral fellowship.
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