Highly efficient light-harvesting organofullerenes

Article abstract of DOI:10.1021/ol047451z

(Chemical Equation Presented) Diphenylmethanofullerene-perylenebisimide dyads and triads have been prepared as light harvesters and electron acceptors for the preparation of efficient organic solar cells. The presence of swallowtail chains on the perylene

Full text of DOI:10.1021/ol047451z

ORGANIC
LETTERS
2005
Vol. 7, No. 4
717-720
Highly Efficient Light-Harvesting
Organofullerenes
Rafael Go´mez, Jose´ L. Segura,* and Nazario Mart´ın*
Departamento de Qu´ımica Orga´nica, Facultad de Ciencias Qu´ımicas,
UniVersidad Complutense de Madrid, E-28040 Madrid, Spain
nazmar@quim.ucm.es
Received December 13, 2004
ABSTRACT
Diphenylmethanofullerene-perylenebisimide dyads and triads have been prepared as light harvesters and electron acceptors for the preparation
of efficient organic solar cells. The presence of swallowtail chains on the perylene unit provides enhanced solubility and allows its complete
characterization.
The possibility to use new organic semiconductor materials
in place of silicon wafers in the fabrication of photovoltaic
devices as substrates offers the prospect of lower manufac-
turing costs, particularly for large-area applications. Thus,
one of the most promising tasks in fullerene research involves
its potential application, mixed with π-conjugated polymers,
in mimicking photosynthesis and in related solar energy
conversion.1 Although the first solar cells based on [60]-
fullerene showed only poor performances, optimization of
devices has allowed efficiencies above 3%.2 However,
optimization of cells has been carried out with only a few
materials, and recent findings show that new developments
can be very successful if a broader scope of materials in the
composite layer becomes accessible. One of the limitations
of the [60]fullerene derivatives used so far is their low
absorption in the red and near-infrared region of the solar
spectrum, which strongly reduces the number of photons that
can be converted into electricity. To overcome this problem,
different [60]fullerene-based dyads3 and triads4 have been
synthesized as photoactive materials for solar cells.5 Pery-
lenebisimide dyes6 are of increasing interest for application
in molecular electronic devices,7 and they have been suc-
cessfully used in the fabrication of photovoltaic cells.8 Only
(3) (a) Segura, J. L.; Go´mez, R.; Mart´ın, N.; Luo, C.; Guldi, D. M. Chem.
Commun. 2000, 701. (b) Guldi, D. M.; Luo, C.; Swartz, A.; Go´mez, R.;
Segura, J. L.; Mart´ın, N.; Brabec, C.; Sariciftci, N. S. J. Org. Chem. 2002,
67, 1141. For reviews, see: (c) Mart´ın, N.; Sa´nchez, L.; Illescas, B.; Pe´rez,
I. Chem. ReV. 1998, 98, 2527. (d) Imahori, H.; Sakata, Y. AdV. Mater. 1997,
9, 537. (e) Imahori, H.; Sakata, Y. Eur. J. Org. Chem. 1999, 64, 2445.
(4) (a) Segura, J. L.; Mart´ın, N. Tetrahedron Lett. 1999, 40, 3239. (b)
van Hal, P. A.; Knol, J.; Langeveld-Voss, B. M. W.; Meskers, S. C. J.;
Hummelen, J. C.; Janssen, R. A. J. J. Phys. Chem. A 2000, 104, 5974. (c)
Martineau, C.; Blanchard, P.; Rondeau, D.; Delanauy, J.; Roncali, J. AdV.
Mater. 2002, 14, 283. (d) Guldi, D. M.; Luo, C.; Swartz, A.; Go´mez, R.;
Segura, J. L.; Mart´ın, N. J. Phys. Chem. A 2004, 108, 455.
(5) (a) Segura, J. L.; Mart´ın, N.; Guldi, D. M. Chem. Soc. ReV. In press.
(b) Nierengarten, J. F. Sol. Energy Mater. Sol. Cells 2004, 83, 187.
(6) (a) Wu¨rthner, F. Chem. Commun. 2004, 14, 1564. (b) Zollinger, H.
Color Chemistry, 3rd ed.; VCH: Weinheim, 2003. (c) Herbst, W.; Hunger,
K. Industrial Organic Pigments: Production, Properties, Aplications, 2nd
ed.; Wiley-VCH: Weinheim, 1997.
(1) (a) Yu, L.; Gao, J.; Hummelen, J. C.; Wudl, F.; Heeger, A. J. Science
1995, 270, 1789. (b) Organic PhotoVoltaics. Concepts and Realizations;
Brabec, C., Dyakonov, V., Parisi, J., Sariciftci, N. S., Eds.; Springer: Berlin,
2003. (c) Fullerenes: From Synthesis to Optoelectronic Properties; Guldi,
D. M., Mart´ın, N., Eds.; Kluwer Academic Publishers: Norwell, MA, 2002;
Chapter 12.
(2) Padinger, F.; Rittberger, R. S.; Sariciftci, N. S. AdV. Funct. Mater.
2003, 13, 85.
10.1021/ol047451z CCC: $30.25
© 2005 American Chemical Society
Published on Web 01/25/2005

very recently have they been used in combination with
fullerene to form thermally stable dyes.9 Thus, in this
communication we present a new approach toward the
synthesis of [60]fullerene derivatives covalently linked to
perylenebisimide dyes specifically designed to be used in
the fabrication of photovoltaic devices.
Scheme 1
The synthesis of the fullerene-perylene dyad 10 and triad
11 was carried out by condensation of the soluble N-(10-
nonadecyl)-3,4,9,10-perylenetetracarboxylic acid 3,4-anhydride-
9,10-imide (9)10 with the corresponding amino or diamino-
diphenylmethano fullerenes (3, 8) (Scheme 2).
The synthesis of 3 and 8 was carried out by 1,3-dipolar
cycloaddition reaction of diazo compounds generated in situ
by Bamford-Stevens reaction between tosylhydrazones and
sodium methoxide (Scheme 1). Thus, the synthesis of the
target tosylhydrazones bearing one or two amino groups was
designed starting with the commercially available 4-ami-
nobenzophenone (1) or 4,4pm′-diaminobenzophenone (4).
Condensation of 1 with p-tosylhydrazide in ethanol affords
tosylhydrazone 2, which after sequential treatment with
sodium methoxide in pyridine and [60]fullerene in refluxing
o-dichlorobenzene (o-DCB) affords 3 in 26% yield. Although
both [6,6]-closed and [5,6]-open isomers could be expected
from the cycloaddition reaction, the high temperature at
which the reaction proceeds allows the obtention of the
thermodynamically more stable [6,6]-closed isomer solely.
Thus, only the corresponding [6,6]-closed isomer of 3 is
detected by 13C NMR.
However, when 4,4′-diaminobenzophenone (4) was reacted
with p-tosylhydrazide under the same reaction conditions,
the expected condensation product could not be obtained.
Not even under a wide range of conditions and catalysts did
the condensation reaction afford the desired product. This
fact can be accounted for by the presence of the second
electron-donor amino group in 4, which increases the elec-
tron density of the carbonyl group. Thus, a protecting-
deprotecting strategy was developed to prepare 7. Reaction
of 4,4′-diaminobenzophenone with trifluoracetic anhydride
affords the corresponding N-protected diamido compound
(5), which readily yields the corresponding p-tosylhydrazone
(6) under mild conditions. Hydrolysis of the trifluoroaceta-
mido groups with sodium carbonate affords the correspond-
ing diamino p-tosylhydrazone (7). Treatment of this deriva-
tive with sodium methoxide in the presence of [60]fullerene
under the previously stated conditions yields the correspond-
ing diamino-substituted [6,6]-closed diphenylmethano-
fullerene (8).
Further condensation between the fullerene derivatives
bearing one (3) or two (8) functionalizable amino groups
and the perylene monoanhydride derivative 9 (Scheme
2) was accomplished by refluxing them in a mixture of
o-DCB and pyridine in the presence of a Lewis acid catalyst
(Zn(OAc)2). Thus, the target compounds 10 and 11 were
obtained as deep red solids in 65 and 60% yields, respec-
tively.
The presence of the swallowtail solubilizing chains on the
perylene unit provides to these systems enough solubility to
allow their full electrochemical and spectroscopical11 char-
acterization. Thus, the FTIR spectra of 10 and 11 show,
together with the typical band corresponding to the [60]-
fullerene moiety at 526 cm-1, the characteristic absorption
pattern of the perylene skeleton with bands at 1580 and 1593
cm-1.12 Besides, the absorption bands at 1655 and 1697 cm-1
indicate the presence of the imide group. No significant bands
around 1733 and 1772 cm-1 are observed, proving the
disappearance of the anhydride functionality. The 1H NMR
spectra in chloroform show the expected signals for the
(7) (a) Katz, H. E.; Bao, Z.; Gilat, S. L. Acc. Chem. Res. 2001, 34, 359.
(b) Wu¨rthner, F. Angew. Chem., Int. Ed. 2001, 40, 1037. (c) Angadi, M.
A.; Gostzola, D.; Wasielewski, M. R. Mater. Sci. Eng. B 1999, 63, 191.
(d) Kraft, A.; Grimsdale, A. C.; Holmes, A. B. Angew. Chem., Int. Ed.
1998, 37, 402.
(8) (a) Breeze, A. J.; Salomon, A.; Ginley, D. S.; Gregg, B. A.; Tillman,
H.; Ho¨rhold, H.-H. Appl. Phys. Lett. 2002, 81, 3085. (b) Yakimov, A.;
Forrest, S. R. Appl. Phys. Lett. 2002, 80, 1667. (c) Schmidt-Mende, L.;
Fechtenko¨tter, A.; Mu¨llen, K.; Moons, E.; Friend, R. H.; MacKenzie, J. D.
Science 2001, 293, 1119.
(9) (a) Hua, J. L.; Meng, F. S.; Ding, F.; Li, F. Y.; Tian, H. J. Mater.
Chem. 2004, 1849. (b) Hua, J.; Meng, F.; Ding, F.; Tian, H. Chem. Lett.
2004, 33, 432.
(10) (a) Kaiser, H.; Lindner, J.; Langhals, H. Chem. Ber. 1991, 124, 529.
(b) Langhals, H.; Sprenger, S.; Brandherm, M. T. Liebigs Ann. 1995, 481.
718
Org. Lett., Vol. 7, No. 4, 2005

Scheme 2
perylene moiety at around 8.6 ppm together with the aromatic
The cyclic voltammograms of 10 and 11 show four
protons corresponding to the diphenylmethane fragment and
those corresponding to the alkyl chains. In the 13C NMR
spectra, a signal at 79 ppm corresponding to the bridgehead
atom and a signal at around 58 ppm corresponding to those
of the sp3 carbon atoms of the [60]fullerene unit are observed,
analogously to other diphenylmethanofullerenes.13
reduction waves (Figure 1). By comparison (Table 1) with
The solution electrochemistry of the fullerene-perylene
derivatives 10 and 11 was carried out in a mixture of o-DCB/
CH3CN (4:1), due to the poor solubility of 3 (used as a
reference) in other solvents. The experiments were carried
out using tetrabutylammonium perchlorate as the supporting
electrolyte, glassy carbon as the working electrode, a
platinum wire as the counter electrode, and Ag/Ag+ as the
reference electrode.
(11) Selected data for 10. 1H NMR (CDCl3, 500 MHz) δ: 8.72 (d, J )
8.02 Hz, 2H), 8.70-8.60 (m, 6H), 8.36 (d, J ) 8.36 Hz, 2H), 8.18 (d, J )
8.36 Hz, 2H), 7.55-7.44 (m, 3H), 7.23-7.19 (m, 2H), 5.21 (m, 1H), 2.27
(m, 4H), 1.89 (m, 4H), 1.58-1.23 (m, 24H), 0.86 (m, 6H). 13C NMR
(CDCl3, 125 MHz) δ: 163.87, 148.52, 148.48, 145.73, 145.71, 145.58,
145.57, 145.49, 145.15, 145.13, 145.12, 145.11, 145.05, 145.04, 144.68,
144.67, 144.65, 144.64, 144.26, 144.25, 144.24, 144.22, 143.39, 143.38,
143.36, 143.36, 143.35, 143.33, 142.88, 142.64, 142.57, 142.56, 142.52,
141.31, 141.26, 139.85, 138.96, 138.77, 138.59, 138.59, 135.63, 135.62,
135.06, 134.56, 134.56, 134.55, 134.54, 132.99, 132.24, 132.21, 132.20,
131.62, 130.95, 130.21, 130.01, 129.92, 129.49, 129.29, 128.78, 128.11,
127.04, 126.88, 126.78, 123.76, 123.74, 123.56, 123.52, 123.50, 123.43,
115.00, 79.29, 58.11, 55.27, 55.18, 53.81, 43.23, 32.76, 32.34, 30.10, 29.91,
29.90, 29.89, 29.84, 29.82, 29.68, 27.37, 27.36, 23.06, 23.03, 23.02, 14.42,
14.40. FT-IR (KBr) ν: 526, 746, 810, 1251, 1340, 1580, 1593, 1655, 1697,
2850, 2920 cm-1. MS (ESI): 1541 (M+ + H+).
Figure 1. Cyclic voltammograms of dyad 10 and triad 11 along
with references 3 and 12.
the cyclic voltammograms of references 3 and the sym-
metrical bis(N,N′-nonadecyl)perylene bisimide (12, Scheme
2),10 the second reduction wave can be attributed to the
second reduction potential of the perylenebisimide moiety,
whereas the third and the fourth reduction waves arise from
the second and third reduction processes of the fullerene
moiety. Although no coulombimetric experiments have been
carried out yet, the higher intensity of the first reduction wave
observed for 10 and 11 in comparison with references 3 and
12 suggests that the first reduction processes of fullerene
(12) Langhals, H. Heterocycles 1995, 1, 477.
(13) (a) Gonza´lez, S.; Mart´ın, N.; Guldi, D. M. J. Org. Chem. 2003, 68,
779. (b) Herranz, M. A.; Beulen, M. W. J.; Rivera, J. A.; Echegoyen, L.;
D´ıaz, M. C.; Illescas, B.; Mart´ın, N. J. Mater. Chem. 2002, 12, 2048.
Org. Lett., Vol. 7, No. 4, 2005
719

11, bearing two perylenebisimide moieties, was higher than
that of dyad 10 in the visible region (Figure 2).
Table 1. Redox Potentialsa (V) of Fullerene Derivatives 10
and 11 and Reference Compounds 3 and 12
Unlike the UV-vis spectra that are noninteractive, emis-
sion spectra show interactions in the dyad and triad. Although
11 also shows an emission spectra with characteristic features
of the perylenebisimide unit, its luminescence is largely
quenched (95%). Luminescence quenching above 99% was
observed for 10 indicating a more efficient quenching of the
perylenebisimide fluorescence in the system containing one
fullerene unit per perylenebisimide moiety.
Together with the quenching of the fluorescence of the
perylene moiety, the characteristic methanofullerene fluo-
rescence with a maximun at 709 nm3 can be observed despite
the selective excitation of the perylenebisimide moiety.
The excitation spectra of 10 and 11 taken at 710 nm
resemble the absorption spectrum of perylene, indicating that
the energy deposited into the perylene excited state migrates
to the fullerene excited-state orbitals. The perfect match
between the excitation and the absorption spectrum strongly
suggests a quantitative energy transfer. This behavior is in
agreement with the energy position of the lowest singlet
excited state of the perylenebisimide and fullerene units,
which can be estimated at 2.33 and 1.75 eV, respectively.15
Competition with electron-transfer process can be ruled out
considering that the fullerene singlet excited state (1.75 eV)
is stabilized in comparison with the charge separated state
(2.00 eV) as determined by the ∆G values (see Supporting
Information).16
compd
E1
E2
E3
E4
red
Eox
red
red
red
10
11
3
-0.61
-0.62
-0.61
-0.63
-0.85
-0.84
-1.00
-0.89
-0.99
-0.98
-1.53
-1.56
-1.54
+1.75
+1.79
12
+1.78
a Values recorded in a 4:1 o-DCB/CH3CN solution using Bu4NClO4 (0.3
mg L-1) as the supporting electrolyte and Ag/Ag+, platinun wire, and glassy
carbon as reference, counter, and working electrodes, respectively. Cathodic
peak values. Scan rate: 200 mV/s.
and perylenebisimide are overlapping, and only a broader
single wave can be observed. These redox potentials are
similar to those reported for other diphenylmethanofullerene
derivatives14 showing very high values of open circuit
voltages in photovoltaic devices. On the other hand, these
values suggest that no significant interaction takes place
between both electroactive moieties in the ground state.
The UV-vis spectra of 10, 11, and 12 (Figure 2) show
the three typical perylene absorptions at 459, 490, and 527
In conclusion, we have developed a synthetic route toward
the preparation of novel [60]fullerene derivatives bearing one
or two perylenebisimide moieties. These new materials show
analogous electrochemical behavior to that observed in other
diphenylmethanofullerene derivatives exhibiting high open-
circuit voltages when combined with conjugated polymers
in photovoltaic devices. This fact, together with the high light
absorption exhibited by these materials throughout the whole
visible spectrum, make them suitable candidates for the
fabrication of photovoltaic devices. Work is in progress in
order to investigate their potential use in organic solar cells.
Acknowledgment. This work has been supported by the
MCyT of Spain (Project BQU2002-00855). R. Go´mez is
indebted to the “Programa Ramo´n y Cajal” (MCyT) for
financial support. This work is dedicated to the memory of
our colleague Dr. Juan Carlos del Amo Aguado, killed during
the terrorist attacks in Madrid on March 11, 2004.
Figure 2. UV-vis absorption spectra of 3 and 10-12 in
dichloromethane solution (c ) 3.55 10-5 M).
nm, respectively, with high extinction coefficients. The
UV-vis spectra of 10 and 11 match the profile obtained by
superimposition of the spectra of their component units 3
and 12 within experimental error. This is in agreement with
the lack of interaction observed in the electrochemical
measurements between the electroactive moieties in the
ground state. As expected, the relative absorption of triad
Supporting Information Available: Experimental details
and photoluminescence. This material is available free of
charge via the Internet at http://pubs.acs.org.
OL047451Z
(15) Values corresponding to the peak of highest energy featured in the
fluorescence spectra.
(16) Weller, A. Z. Phys. Chem. Neue Folge 1982, 133, 93.
(14) Riedel, I.; Mart´ın, N.; Giacalone, F.; Segura, J. L.; Chirvase, D.;
Parisi, J.; Dyakonov, V. Thin Solid Films 2004, 451, 431.
720
Org. Lett., Vol. 7, No. 4, 2005