A New Dyad Based on C60 and a Conjugated Dimethylaniline-Substituted Dithienylethylene Donor

Article abstract of DOI:10.1021/jo990287m

A facile synthesis of the title compound is described, and its optical and electrochemical properties are discussed.

Full text of DOI:10.1021/jo990287m

4
884
J . Org. Chem. 1999, 64, 4884-4886
A New Dya d Ba sed on C60 a n d a Con ju ga ted
Dim eth yla n ilin e-Su bstitu ted Dith ien yleth ylen e Don or
†
†
‡
†
§
Sheng-Gao Liu, Lianhe Shu, J os e´ Rivera, Haiying Liu, J ean-Manuel Raimundo,
§
§
,†
J ean Roncali, Alain Gorgues, and Luis Echegoyen*
Department of Chemistry, University of Miami, Coral Gables, Florida 33124, Department of Chemistry,
Pontifical Catholic University, Ponce, Puerto Rico 00732, and Laboratoire d’Ing e´ nierie Mol e´ culaire et
Mat e´ riaux Organiques, associ e´ au CNRS, Universit e´ d’Angers, 2, Bd Lavoisier, F-49045 Angers, France
Received February 17, 1999
A facile synthesis of the title compound is described, and its optical and electrochemical properties
are discussed.
In recent years, a number of electron donors have been
Ch a r t 1
covalently linked to the C60 cage by different synthetic
procedures in an effort to obtain efficient intramolecular
energy and electron or charge transfer and to generate
long-lived charge-separated states in these donor-ac-
ceptor (D-A) molecular assemblies.1
-10
Diekers et al.
recently pointed out that three types of dyads and triads
involving a C60 moiety with various donor molecules have
1
1
been developed. Although spontaneous intramolecular
charge-transfer interactions have been claimed in some
cases, unequivocal evidences are still lacking.7
In an attempt to enhance intramolecular electron or
charge transfer, we report here a novel donorsC60
involving dimethylaniline-substituted dithienylethylene
reported to show intramolecular photoinduced charge
separation in polar solvents,12 and (ii) push-pull chro-
mophores based on the DADTE system, such as 2 (Chart
(DADTE) as the donor part. This approach is based on
1
), are known to exhibit high second-order nonlinear
the following rationale: (i) compound 1 (Chart 1 ), which
contains a donating aniline group linked to the C60 cage
by a saturated heterocyclic bridge, has been recently
optical (NLO) susceptibilities due to, among other factors,
an easily attainable charge-asymmetry thanks to the low
1
3,14
aromatic stabilization energy of the thiophene ring.
*
To whom correspondence should be addressed. E-mail:
On this basis, we report here the synthesis of a new
donor-C60 compound (4c) in which a DADTE donor
group is linked to C60 through a pyrrolidine ring and
we discuss some of its optical and electrochemical proper-
ties using the related compounds 4a and 4b as reference
compounds.
The synthetic approach to prepare compounds 4a -c
relies upon the [3 + 2] 1,3-dipolar cycloaddition of
azomethine ylides to C60 (Scheme 1).15
lechegoyen@umiami.ir.miami.edu. Fax: 305-284-4571.
†
University of Miami.
Pontifical Catholic University.
Universit e´ d’Angers.
‡
§
(
1) Recent reviews related to C60-based donor-acceptor molecular
assemblies: (a) Martin, N.; S a´ nchez, L.; Illescas, B.; P e´ rez, I. Chem.
Rev. 1998, 98, 2527-2547. (b) Prato, M.; Maggini, M. Acc. Chem. Res.
1
998, 31, 519-530.
(2) (a) Drovetskaya, T.; Reed, C. A.; Boyd, P. Tetrahedron Lett. 1995,
3
6, 7971-7974. (b) Linssen, T. G.; D u¨ rr, K.; Hanack, M.; Hirsch, A. J .
Chem. Soc., Chem. Commun. 1995, 103-104. (c) Qiu, W. F.; Liu, Y.
Q.; Zhu, D. B. Chin. Chem. Lett. 1997, 8, 363-366.
This methodology has proven to be one of the most
powerful procedures for the functionalization of [60]-
fullerene due to its versatility and the ready availability
(3) Maggini, M.; Karlsson, A.; Scorrano, G.; Sandon a` , G.; Farnia,
G.; Prato, M. J . Chem. Soc., Chem. Commun. 1994, 589-590.
4) Mart ´ı n, N.; S a´ nchez, L.; Seoane, C.; Andreu, R.; Gar ´ı n, J .;
Ordu n˜ a, J . Tetrahedron Lett. 1996, 37, 5979-5982.
5) (a) Llacay, J .; Mas, M.; Molins, E.; Veciana, J .; Powell, D.; Rovira,
(
1
6
of the starting materials. Thus, reaction of aldehydes
(
17
3
a -c (0.273 mmol), with N-methylglycine (64 mg, 0.718
C. J . Chem. Soc., Chem. Commun. 1997, 659-660. (b) Llacay, J .;
Veciana, J .; Vidal-Gancedo, J .; Bourdelande, J . L.; Gonzalez-Moreno,
R.; Rovira, C. J . Org. Chem. 1998, 63, 5220-5225. (c) Boulle, C.;
Rabreau, J . M.; Hudhomme, P.; Cariou, M.; J ubault, M.; Gorgues, A.;
Orduna, J .; Garin, J . Tetrahedron Lett. 1997, 38, 3909-3910.
(12) Williams, R. M.; Zwier, J . M.; Verhoeven, J . W. J . Am. Chem.
Soc. 1995, 117, 4093-4099.
(13) Rao, V. P.; J en, A. K. Y.; Wong, K. Y.; Drost, K. J . J . Chem.
Soc., Chem. Commun. 1993, 1118-1120.
(6) Lawson, J . M.; Oliver, A. M.; Rothenfluh, D. F.; An, Y. Z.; Ellis,
G. A.; Ranasinghe, M. G.; Khan, S. I.; Franz, A. G.; Ganaphthi, P. S.;
Stephard, M. J .; Paddon-Row, M. N.; Rubin, Y. J . Org. Chem. 1996,
(14) (a) J en, A. K. Y.; Rao, V. P.; Wong, K. Y.; Drost, K. J . J . Chem.
Soc., Chem. Commun. 1993, 90-93. (b) Rao, V. P.; J en, A. K. Y.; Wong,
K. Y.; Drost, K. J . Tetrahedron Lett. 1993, 34, 1747-1750. (c) Drost,
K. J .; Rao, V. P.; J en, A. K. Y. J . Chem. Soc., Chem. Commun. 1994,
369-371. (d) J en, A. K. Y.; Rao, V. P.; Drost, K. J .; Wong, K. Y.; Cava,
M. P. J . Chem. Soc., Chem. Commun. 1994, 2057-2058. (e) Shu, C.
F.; Tsai, W. J .; Chen, J . Y.; J en, A. K. Y.; Zhang, Y.; Chen, T. A. J .
Chem. Soc., Chem. Commun. 1996, 2279-2280.
6
1, 5032-5054.
7) Matsubara, Y.; Tada, H.; Nagase, S.; Yoshida, Z. J . Org. Chem.
995, 60, 5372-5373.
8) Nakamura, Y.; Minowa, T.; Tobita, S.; Shizuka, H.; Nishimura,
J . J . Chem. Soc., Perkin Trans. 2 1995, 2351-2357.
9) Williams, R. M.; Koeberg, M.; Lawson, J . M.; An, Y. Z.; Rubin,
Y.; Paddon-Row, M. N.; Verhoeven, J . W. J . Org. Chem. 1996, 61,
055-5062.
10) G u¨ ldi, D. M.; Maggini, M.; Scorrano, G.; Prato, M. J . Am. Chem.
Soc. 1997, 119, 974-980.
11) Diekers, M.; Hirsch, A.; Pyo, S.; Rivera, J .; Echegoyen, L. Eur.
J . Org. Chem. 1998, 1111-1121 and references therein.
(
1
(
(
(15) Xu, J . H.; Li, Y. L.; Zheng, D. G.; Yang, J . K.; Mao, Z.; Zhu, D.
B. Tetrahedron Lett. 1997, 38, 6613-6616.
5
(
(16) Maggini, M.; Scorrano, G.; Prato, M. J . Am. Chem. Soc. 1993,
115, 9798-9799.
(
(17) 3c was synthesized by the methodology developed by J en et al.
with a slight modification; see ref 14a.
1
0.1021/jo990287m CCC: $18.00 © 1999 American Chemical Society
Published on Web 06/06/1999

Dyad Based on C60 and a Dithienylethylene Donor
J . Org. Chem., Vol. 64, No. 13, 1999 4885
Sch em e 1
F igu r e 1. UV-vis spectra of 4a (dashed), 4b (dotted), 4c
(solid), and 3c (-‚-) in cyclohexane.
4
30 and 703 nm, typical of C60 monoadducts, can be
observed at higher magnification. Upon introduction of
the DADTE moiety in the structure, a broad and intense
absorption band develops in the 400-500 nm region with
a λmax around 440 nm in cyclohexane. This absorption
band shows a well-resolved vibronic fine structure with
three maxima equally spaced by ∼25 nm (ca. 0.15 eV),
which is consistent with the energy of a CdC stretching
mode in the DADTE-conjugated system. The similarity
of this spectrum with that of compound 3c or that of other
mmol) and C60 (197 mg, 0.273 mmol) in toluene (75 mL)
at reflux for 5-24 h, gave the corresponding fulleropyr-
rolidine 4a -c in 10-40% overall isolated yield after two
chromatographic separations (silica gel, CS
toluene/CS or CH Cl /cyclohexane).
2
followed by
push-pull chromophores based on the dithienylethylene
20
2
2
2
(
DTE) system clearly shows that this band is related
1
8
The structures of compounds 4b and 4c were fully
to the π-π* transition of a DADTE conjugated system.
The λmax of 4c (436 nm in cyclohexane) is substantially
blue-shifted compared to that of related push-pull NLO
chromophores containing acceptor groups such as formyl
supported by analytical and spectroscopic data. For
example, in the case of 4c, a parent ion at m/e 1114
+
(
100%) is observed in the FAB mass spectrum along
with the C60 + 1 (721, 30%) and a fragment at 394 (M+
60, 80%). High-resolution FABMS spectra completely
agree with the theoretically predicted pattern of isotopic
distribution (calcd for C83 1112.1381, found
112.1381). The H NMR spectrum of 4c in CDCl
+
14b
14a
3
c (467 nm), nitro (506 nm), dicyanovinyl (547 nm),
-
C
13
and tricyanovinyl (653 nm) but slightly red-shifted for
∼
12 nm relative to the unsubstituted analogue HR (424
24 2 2
H S N
nm, R was defined in Scheme 1 as that of 3c). These data
suggest that 4c behaves as a push-pull system in which
the C60-pyrrolidine group acts as a weak electron accep-
tor.
1
1
3
solution exhibits the expected features with the correct
integration ratios. The signals of the pyrrolidine protons
appear at δ 4.97 and 4.26 ppm as doublets (J ) 9.2 Hz;
geminal hydrogens) and at δ 5.22 (CH, s), in good4
agreement with the results for similar derivatives.
Furthermore, all the double-bond linkages were con-
Cyclic voltammetric (CV) analysis of 4c in THF shows
four quasireversible reduction waves with cathodic peak
potentials (Epc) at -1.052, -1.594, -2.208, and -2.428
V versus Fc/Fc and two irreversible reductions at -2.704
and -2.883 V (Figure 2a). In addition, two quasirevers-
ible oxidation processes occur with anodic peak potentials
+
1
4a
firmed to be all-trans by careful NMR analysis. The
1
3
C NMR spectrum shows two different NCH
3
groups at
δ 40.24 (2 C) and 40.33 (1 C) ppm, the sp carbons of the
,6-ring junction and the remaining pyrrolidine carbons
3
1
2
(Epa and Epa ) at 0.140 and 0.364 V. Comparison of these
6
values with those for 3c (0.219 and 0.475 V) suggests that
4
at δ 68.65, 77.04 and 69.99, 79.42 ppm, respectively, and
all the sp2 carbons in both C60 and the donor moiety
between 112.45 and 155.71 ppm.19
the two oxidation processes are related to the DADTE
1
2
system, the higher Epa and Epa values observed in the
latter case reflecting the larger electron-withdrawing
effect of the formyl group compared to the C60-pyrrolidine
one, in good agreement with the optical data.
Figure 1 shows the electronic absorption spectra of
compounds 4a , 4b, 3c, and 4c. The spectrum of com-
pounds 4a and 4b is essentially dominated by the three
characteristic absorption bands of C60 in the 200-350 nm
region. Very weak absorption bands (not shown) around
(19) Careful 13C NMR analysis (CS
6 sp carbons in both C60 and the donor moiety listed as follows (one
2
3
/CDCl 1/1) of 4c shows the total
2
7
carbon for each piece of data unless otherwise indicated in parenthe-
ses): 112.45 (2 C), 117.59, 120.67, 122.28, 125.23, 125.29, 125.58,
127.53, 127.64 (2 C), 128.26, 128.59, 129.00, 129.37, 135.56, 135.78,
136.66, 137.03, 139.43, 139.79, 139.87, 139.94, 140.15 (2 C), 141.59,
141.62, 141.90 (2 C), 141.95, 142.01, 142.05, 142.10 (2 C), 142.15,
142.24, 142.55 (2 C), 142.66, 142.94, 143.12, 143.61, 143.98, 144.30,
144.33, 144.65 (2 C), 145.12, 145.17, 145.21 (2 C), 145.26, 145.34,
145.38, 145.41, 145.53, 145.60, 145.72, 145.88 (2 C), 146.03, 146.08,
146.12, 146.16, 146.19, 146.23, 146.26, 146.30, 146.77, 147.23, 147.26,
149.80, 152.91, 153.00, 153.72, 155.71 ppm.
(
18) Selected data for 4b: HRFABMS calcd for C67
H
9
SN 859.0456,
1/1, one carbon for each piece
of data unless otherwise indicated in parentheses) 40.27, 70.01, 79.14,
1
3
2 3
found 859.0455; C NMR (in CS /CDCl
6
1
1
1
1
1
1
8.60, 125.31, 126.55 (2 C), 126.60 (2 C), 127.85 (2 C), 128.21, 128.97,
35.58, 135.81, 136.61, 136.97, 139.59, 139.87, 140.14, 140.67, 141.55,
41.62, 141.86, 141.92, 142.00, 142.07, 142.11 (2 C), 142.14, 142.23,
42.55 (2 C), 142.65, 142.94, 143.11, 144.31, 144.60, 144.66, 145.10,
45.19 (2 C), 145.21, 145.28, 145.32, 145.42, 145.53, 145.57, 145.71,
45.88 (2 C), 146.03, 146.06, 146.10, 146.15, 146.19, 146.22 (2 C),
46.30, 146.78, 147.25 (2 C), 153.00, 153.07, 153.75, 155.77.
(20) Chou, S. S. P.; Sun, D. J .; Huang, J . Y.; Yang, P. K.; Lin, H. C.
Tetrahedron Lett. 1996, 37, 7279-7282.

4
886 J . Org. Chem., Vol. 64, No. 13, 1999
Liu et al.
F igu r e 2. Cyclic voltammograms in THF at room tempera-
ture of compounds (a) 4c, (b) 3c (working conditions: 100 mV/
s, 0.1 M TBAPF , L 3 mm glassy carbon as the working
6
electrode, L 1 mm Pt wire as the counter electrode, internal
ferrocene as the reference).
F igu r e 3. Cyclic voltammograms in THF at room tempera-
ture of compounds (a) 4a , (b) 4b, (c) 4c, and (d) 3c. All were
recorded under identical conditions with a scan rate of 100
mV/s. Internal ferrocene was added as an internal reference
in all cases but is not shown for b-d.
To assign the origin of the reduction processes, we
carefully compared the CVs of compounds 4a -c and 3c
recorded under essentially identical conditions. Figure
The electrochemical reduction of 3c exhibits two re-
versible processes at E1/2 -1.921 and -2.230 V vs Fc/Fc
+
with ∆E values of 75 and 61 mV, respectively. Obviously,
p
3
clearly shows that the first three successive and nearly
these reductions in 3c are more positive than those of
the corresponding reductions in 4c due to the stronger
acceptor ability of the carbonyl group and also to its direct
conjugation with the donor group, also in good agreement
with the optical data.
In summary, a novel C60-based thiophene-containing
donor-acceptor compound has been synthesized and
characterized. Work is now underway in order to analyze
the possible charge-transfer interactions between the
donor and acceptor parts of the molecule.
equally spaced reductions and the fifth reduction are C60
-
based. This is not only in good agreement with our
previous work on the electrochemistry of fullerene de-
rivatives21 but also in good agreement with our ESR
results measured for the corresponding mono-, di-, and
trianion of 4c.22 On the basis of the observed g values
for all of these species (g
1
) 2.00067, g
2
) 2.00119, g )
3
2
.00138), these reductions are all based on the fullerene
core. The fourth and sixth reductions are centered on the
conjugated donor part.
(
21) Arias, F.; Echegoyen, L.; Wilson, S. R.; Lu, Q.; Lu, Q. Y. J . Am.
Chem. Soc. 1995, 117, 1422-1427.
22) We performed the successive reductions from the neutral 4c
Ack n ow led gm en t. The authors thank the National
Science Foundation, grant CHE-9816503, for generous
support of this work.
(
to its mono-, di-, and trianion species in THF under high vacuum. The
ESR signals for these three different anions are C60-based and are in
accord with our previous work with C60 derivatives.
J O990287M