A supramolecular oligophenylenevinylene-C60 conjugate

Article abstract of DOI:10.1016/S0040-4039(03)00561-6

A new methanofullerene derivative with an ammonium subunit has been prepared and its ability to form a supramolecular complex with an oligophenylenevinylene (OPV)-crown ether conjugate evidenced by NMR, electrospray mass spectrometry and luminescence expe

Full text of DOI:10.1016/S0040-4039(03)00561-6

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 44 (2003) 3043–3046
A supramolecular oligophenylenevinylene–C conjugate
6
0
a
b
a
b,
Manuel Guti e´ rrez-Nava, H e´ l e` ne Nierengarten, Patrick Masson, Alain Van Dorsselaer * and
a,
Jean-Fran c¸ ois Nierengarten *
a
Groupe des Mat e´ riaux Organiques, Institut de Physique et Chimie des Mat e´ riaux de Strasbourg, Universit e´ Louis Pasteur et
CNRS, 23 rue du Loess, BP 43, 67034 Strasbourg Cedex 2, France
b
Laboratoire de Spectrom e´ trie de Masse Bio-Organique, Universit e´ Louis Pasteur et CNRS, 25 rue Becquerel,
67087 Strasbourg Cedex 2, France
Received 30 January 2003; revised 24 February 2003; accepted 27 February 2003
Abstract—A new methanofullerene derivative with an ammonium subunit has been prepared and its ability to form a
supramolecular complex with an oligophenylenevinylene (OPV)–crown ether conjugate evidenced by NMR, electrospray mass
spectrometry and luminescence experiments. © 2003 Elsevier Science Ltd. All rights reserved.
2
,3
In light of their unique electronic properties, fullerene
derivatives are suitable building blocks for the prepara-
tion of molecular devices displaying photoinduced
described so far. As part of our research on com-
4
pounds combining C60 with p-conjugated oligomers,
we have decided to develop a non-covalent approach
for their preparation. The assembly of the two molecu-
lar components by using supramolecular interactions
rather than covalent chemistry appears particularly
attractive since the range of systems that can be investi-
gated is not severely limited by the synthetic route. In
1
energy and electron transfer processes. Whereas
research focused on the use of C60 as the acceptor in
covalently bound donor–acceptor pairs has received
1
considerable attention, only a few related examples of
fullerene-containing non-covalent assemblies have been
Figure 1. The supramolecular C –OPV assembly obtained from ammonium 1 and crown ether 2.
60
*
0
Corresponding authors. Fax: 33 388 10 72 46; e-mail: niereng@ipcms.u-strasbg.fr
040-4039/03/$ - see front matter © 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0040-4039(03)00561-6

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044
M. Guti e´ rrez-Na6a et al. / Tetrahedron Letters 44 (2003) 3043–3046
Scheme 1. Reagents and conditions: (i) Boc O, KOH, THF, H O, rt (91%); (ii) LiAlH , THF, 0°C (93%); (iii) 5, DCC, DMAP,
2
2
4
CH Cl , 0°C to rt (63%); (iv) C , I , DBU, toluene, rt (61%); (v) CF CO H, CH Cl , rt (99%).
2
2
60
2
3
2
2
2
this paper, we show that methanofullerene derivative 1
of 1, 2 and a 1:1 mixture of both compounds (Fig. 2)
revealed complexation-induced changes in chemical
shifts for some protons, in particular for those of the
4-(aminomethyl)benzyl moiety in 1 and of the benzo-
crown ether unit in 2. The latter observations are in
good agreement with the proposed structure of the
supramolecular complex obtained from 1 and 2. The
bearing an ammonium unit is able to form a supra-
molecular complex with the oligophenylenevinylene
5
(
OPV)–crown ether conjugate 2 by using the well6-
known ammonium–crown ether interaction (Fig. 1).
Preliminary luminescence studies also reveal the occur-
rence of an intramolecular photoinduced process in this
new supramolecular C –OPV assembly.
association constant (K ) and the Gibbs free energy of
6
0
a
0
complexation (DG ) for the binding of 1 to 2 were
The strategy employed for the preparation of the func-
deduced from the complexation-induced changes in
tionalized methanofullerene derivative 1 is based upon
7
Bingel type chemistry. To this end, malonate 7 was
prepared in three steps from methyl 4-(aminomethyl)-
benzoate hydrochloride (3) (Scheme 1). The commer-
cially available compound 3 was converted to its t-
8
butylcarbonyl (Boc) derivative as previously described.
LAH reduction of the resulting protected derivative 4
afforded 5 in 93% yield. N,N%-Dicyclohexylcarbodi-
imide (DCC)-mediated esterification of benzylic alcohol
9
5
with carboxylic acid 6 yielded malonate 7. The
reaction of C60 with compound 7, iodine and 1,8-diaz-
abicyclo[5.4.0]undec-7-ene (DBU) under Bingel condi-
tions then gave methanofullerene 8 in 61% yield.
Finally, removal of the Boc group with CF CO H
3
2
afforded the targeted derivative 1 as its trifluoroacetate
salt in a quantitative yield. The structure and purity of
1
13
all new compounds were confirmed by H and
C
NMR spectroscopy, mass spectrometry and elemental
analysis.
The ability of the fullerene derivative 1 to form a
supramolecular complex with the OPV–crown ether
1
1
conjugate 2 was first evidenced by H NMR studies in
Figure 2. H NMR spectra (200 MHz, CDCl ) of 1 (A), 2 (C)
3
1
CDCl . The comparison between the H NMR spectra
and a 1:1 mixture of both compounds (B).
3

M. Guti e´ rrez-Na6a et al. / Tetrahedron Letters 44 (2003) 3043–3046
3045
−
4
Figure 3. ES mass spectrum (Vc=40 V) recorded from an equimolar mixture (10 M) of 1 and 2 in CH Cl .
2
2
chemical shifts of the 4-(aminomethyl)benzyl protons in
1
10
H NMR binding titrations (CDCl , 298 K). The Ka
3
value for the 1:1 complex was determined to be 3500±
−
1
0
2
00 M corresponding to a DG of −4.8 kcal/mol.
The formation of the 1:1 complex [(1)·(2)] was also
evidenced in the gas phase by electrospray mass spec-
3
a
trometry (ES-MS). Unlike other mass spectrometric
methods, ES-MS allows pre-existing ions in solution to
be transferred to the gas phase without fragmentation.
The soft ionization technique, mainly developed by
11
Fenn and co-workers, is now commonly applied to
12
the study of large non-covalent assemblies
and
appears as ideally suited to characterize the non-cova-
lent complex formed from 1 and 2. The positive ES
mass spectrum (Fig. 3) recorded from a 1:1 mixture of
1
and 2 displayed only one singly charged ion peak at
Figure 4. Emission spectra (uexc=372 nm corresponding to
the maximum of absorption of 2) of an equimolar mixture of
1 and 2 in CH Cl before and after addition of DABCO (1.5
m/z=2471.4 which can be assigned to the 1:1 complex
after loss of the trifluoroacetate counteranion (calcu-
lated m/z=2471.3).
2
2
equiv.).
The complexation between 1 and 2 was also investi-
found to be similar to that of the reference solution
containing 8 and 2. In other words, the treatment with
a base deprotonates the ammonium moiety of 1 and,
thereby, disrupts the non-covalent bonding interactions
that brought the components together. Addition of
trifluoroacetic acid (2 equiv.) to the CH Cl solution
regenerates the ammonium center, thus allowing the
formation of the supramolecular complex, and the
luminescence intensity of final solution is the same as
that of the starting 1:1 mixture of 1 and 2. The
observed decrease in luminescence intensity originates
from either energy or electron transfer from the pho-
toexcited OPV to the C60 acceptor in the supramolecu-
lar complex [(1)·(2)]. Steady state measurements are not
sufficient to determine the nature of the quenching
because the residual OPV emission overlaps the much
weaker fullerene emission, thus prohibiting clean excita-
tion spectroscopy. Detailed photophysical studies are
currently under investigation and will be reported in
due time.
gated in CH Cl by luminescence studies. A large
2
2
decrease in intensity of the characteristic OPV emission
was observed when the fullerene ammonium salt 1 was
1
3
added to a CH Cl solution of 2. This decrease can be
2
2
attributed, at least in part, to the reabsorption of the
OPV luminescence by the fullerene derivative 1. How-
ever, experiments carried out in parallel with mixtures
of 2 and 8 which are not able to form a supramolecular
complex show that the decrease in luminescence inten-
sity mainly originates from an intramolecular photoin-
duced process in the supramolecular C –OPV
2
2
60
3
a
conjugate [(1)·(2)]. Further evidence for an intra-
molecular quenching of the OPV excited state by the
fullerene moiety in [(1)·(2)] was obtained from the
experiment depicted in Figure 4.
Addition of 1,4-diazabicyclo[2.2.2]octane (DABCO)
(
1.5 equiv.) to the 1:1 mixture of 1 and 2 in CH Cl
2
2
causes an increase of the OPV emission. Actually, the
fluorescence intensity of the resulting solution was

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M. Guti e´ rrez-Na6a et al. / Tetrahedron Letters 44 (2003) 3043–3046
ioannou, G. J. Am. Chem. Soc. 2000, 122, 7467–7479; (c)
Acknowledgements
Gu, T.; Tsamouras, D.; Melzer, C.; Krasnikov, V.; Gis-
selbrecht, J.-P.; Gross, M.; Hadziioannou, G.; Nieren-
garten, J.-F. ChemPhysChem. 2002, 124–127; (d)
Armaroli, N.; Accorsi, G.; Gisselbrecht, J.-P.; Gross, M.;
Krasnikov, V.; Tsamouras, D.; Hadziioannou, G.;
Gomez-Escalonilla, M. J.; Langa, F.; Eckert, J.-F.;
Nierengarten, J.-F. J. Mater. Chem. 2002, 12, 2077–2087.
. Guti e´ rrez-Nava, M.; Jaeggy, M.; Nierengarten, H.; Mas-
son, P.; Guillon, D.; Van Dorsselaer, A.; Nierengarten,
J.-F. Tetrahedron Lett. 2003, 44, 3039–3042.
This research was supported by the French Ministry of
Research (ACI Jeunes Chercheurs) and a fellowship
from the CONACyT to M.G.N. We further thank L.
Oswald for technical help and Dr. N. Armaroli for
helpful discussions.
5
6
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2
2
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