Air-stable, narrow-band-gap ambipolar C60 fullerene-hydrazone hybrid materials

Article abstract of DOI:10.1002/asia.201100781

Fullerene-hydrazone dyads have been synthesized using the Confalone reaction followed by condensation with phenylhydrazines. Room-temperature xerographic time-of-flight, ionization potential, and cyclic voltammetry measurements indicate that these narrow-

Full text of DOI:10.1002/asia.201100781

FULL PAPERS
DOI: 10.1002/asia.201100781
Air-Stable, Narrow-Band-Gap Ambipolar C60 Fullerene–Hydrazone Hybrid
Materials
Simona Urnikaite,[a] Tadas Malinauskas,[a] Valentas Gaidelis,[b]
Vygintas Jankauskas,[b] and Vytautas Getautis*[a]
Abstract: Fullerene–hydrazone dyads have been synthesized using the Confalone
reaction followed by condensation with phenylhydrazines. Room-temperature xe-
Keywords: donor–acceptor
rographic time-of-flight, ionization potential, and cyclic voltammetry measure-
systems · dyads · fullerenes · hydra-
ments indicate that these narrow-band-gap (Eg <1.5 eV), ambipolar charge-trans-
zones · ionization potentials
porting dyads with balanced hole- and electron mobilities, which operate in air,
are attractive materials for various optoelectronic applications.
Introduction
band-gaps of between 2 and 3 eV. Thus, injection from a
metal electrode with a given work function (high or low)
will always result in high injection barriers (>1 eV) for
either electrons or holes. Meijer et al. first pointed out that
this dilemma could be solved by using semiconductors with
a very narrow band-gap (less than 1.8 eV).[3] As a result, the
injection barrier for both charge carriers would become low-
ered and efficient ambipolar transport could take place. Just
like the efficient injection of both charge carriers, balanced
charge transport is equally important for obtaining optimal
performance. Unbalanced charge transport results in an
excess of one carrier type, thereby resulting in diminished
device performance. A number of methods can be used to
eliminate, or at least mitigate, this problem (for example,
hole- or electron-blocking layers in OLEDs), at a cost of
price and added complexity of the device.
Electronic devices and optoelectronic devices that use or-
ganic materials as their active elements, such as organic
light-emitting diodes (OLED), organic photovoltaic devices
(OPV), organic field-effect transistors (OFET), organic pho-
torefractive devices, have received a great deal of attention
owing to their potential technological applications as well as
from a fundamental scientific standpoint.[1] These devices
that use organic materials are attractive because they can
take advantage of the best traits of organic materials, such
as their light weight, their potentially low cost, and their ca-
pacity to form thin-film-, large-surface-area-, flexible devi-
ces. All of the devices described above utilize charge trans-
port as an essential operation process and hence, require
charge-transporting materials (TMs).
In comparison to the extensive literature on the hole- or
electron-transporting molecules, compounds capable of
transporting both electrons and holes have received much
less interest.[2] A series of paths have been reported to ach-
ieve ambipolar behavior in organic materials, and these
paths can be divided into three major groups: bilayers,
blends, and single components. Out of those three methods,
the single-component route could potentially offer the great-
est benefits in terms of ease of processing and device com-
plexity. The biggest challenges with this method lie in the ef-
ficient injection of both charge carriers.[2a] Most common or-
ganic semiconductors (small molecules and polymers) show
Fullerenes and their derivatives have been known to
behave as n-type semiconductors for some time,[4] and have
been successfully applied in bilayer and blend ambipolar
compositions. A lot of effort to both enable device fabrica-
tion from solution and to tune the electronic properties of
the fullerene through a variety of functionalization ap-
proaches have been developed and explored;[5] however, not
so many examples of ambipolar single-component charge-
transporting materials bearing fullerene fragment have been
reported to date. By attaching a hole-transporting oligothio-
phene unit, ambipolar transport was observed by Aso and
co-workers.[6a] Several other fullerene derivatives bearing,
for example, dendritic oligothiophene side chains,[6b] thioax-
anthenes,[6c] oligophenyleneethynylenes,[6d] hexa-peri-hexa-
benzocoronene,[6e] or oligophenylenevinylenes[6f] have also
been shown to exhibit ambipolar behavior, albeit with mod-
erate charge-carrier mobilities. These compounds are also
quite complex structures, and require expensive starting ma-
terials and/or elaborate multistep syntheses.
[a] S. Urnikaite, Dr. T. Malinauskas, Prof. V. Getautis
Department of Organic Chemistry
Kaunas University of Technology
Radvilenu pl. 19, LT-50254 Kaunas (Lithuania)
Fax : (+370)37-300152
E-mail: vytautas.getautis@ktu.lt
[b] Dr. V. Gaidelis, Dr. V. Jankauskas
Department of Solid State Electronics
Vilnius University
Herein, we report hydrazone moieties as efficient, easily
obtainable p-electron donor systems[7] to afford the covalent
hydrazone-C60 dyads FH1–FH3. These compounds function
Sauletekio 9, LT-10222 Vilnius (Lithuania)
614
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Chem. Asian J. 2012, 7, 614 – 620

as ambipolar, narrow-band-gap semiconductors under ambi-
ent conditions, in contrast to known examples in which the
drift mobilities of electrons were measured under high
vacuum or under an inert gas atmosphere. The balanced
charge transport was achieved in two ways: by varying the
acceptor part of the molecule or by changing the composi-
tion of the charge-transport layer.
were used in a subsequent condensation reaction with N-
methyl-N-phenylhydrazine or N,N-diphenylhydrazine to
yield the target fullerene–hydrazone dyads FH1–FH3. In ad-
dition, three reference compounds (hydrazones 3–5) and
host material 2,2-bis{4-[2-hydroxy-6-(carbazol-9-yl)-5-(carba-
zol-9-methyl)-4oxahexyloxy]-phenyl}propane (CBH) were
used in the study (Scheme 2); these materials were synthe-
sized according literature procedures.[10]
Absorption spectra of compounds FH1–FH3, recorded in
chloroform, are shown in Figure 1, together with the spectra
of reference compounds 4-methyl-4’-(N-methyl-N-phenylhy-
drazonomethyl)triphenylamine (3) and fullerene (C60).
The spectra of dyads FH1–FH3 are very similar to the
sum of the spectra of the separate components; this similari-
ty indicates that there is no interaction at the ground state
between the fulleropyrollidine and hydrazone moieties. This
result was clearly observed by analyzing the UV/Vis spec-
trum of dyad FH1. At around 250, 325, and 450–700 nm
characteristic absorption maxima were observed that could
be attributed to fullerene, whilst an absorption at around
375 nm originated from the hydrazone moiety. The spectrum
of dyad FH2, which possesses two hydrazone moieties, was
shifted bathochromically and hyperchromically compared
with dyads FH1 or FH3 and this could be attributed to its
larger conjugated p-electron system.
Results and Discussion
C60 itself has a very limited use in modern technologies,
owing to its exceedingly low solubility in common organic
solvents. One of the methods commonly used for C60 func-
tionalization is the 1,3-cycloaddition of azomethine ylides
with the C60ACHTUNGTRENNUNG
[6,6] bond,[8] which leads to the selective forma-
tion of usually solution-processable fulleropyrrolidine deriv-
atives. This strategy was used in the synthesis of the fuller-
ene–hydrazone dyads FH1–FH3 from commercially avail-
4-(4-formyl-4’-methyldiphenylamino)-benzaldehyde
(1a), tris(4-formylphenyl)amine (1b), and N-(2-ethylhexyl)-
3,6-diformylcarbazole (1c; Scheme 1).
able
In a typical Confalone reaction,[9] according to a slightly
modified procedure,[9c] a solution of C60 in toluene was
heated to reflux with aldehydes 1a–1c in the presence of N-
methylglycine. The isolated intermediate derivatives (2a–
2c), which possessed either one or two aldehyde groups,
To determine the energetic conditions for energy- and
electron-transfer in dilute solutions, the HOMO/LUMO
Scheme 1. Synthesis of the fullerene-hydrazone dyads FH1–FH3.
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Table 1. EHOMO and ELUMO values, band-gap energies, ionization poten-
tials, and electrochemical properties of dyads FH1–FH3, and compounds
3–5.[a]
CV
opt
Entry E1/2red. vs. E1/2ox. vs.
Eg
Eg
Ip
EHOMO
ELUMO
[eV]
Fc [V]
Fc [V]
[eV] [eV][b] [eV][c] [eV][d]
3
4
5
FH1
FH2
FH3
–
–
–
0.20
0.24
0.34
0.22
0.25
0.36
–
–
–
1.34
1.36
1.48
2.93 5.40
2.76 5.28
2.93 5.40
À5.00
À5.04
À5.14
À5.02
À5.05
À5.16
À2.07[e]
À2.28[e]
À2.21[e]
À3.68
À1.12
À1.11
À1.12
–
–
–
5.21
5.26
5.41
À3.69
À3.68
[a] The measurements were carried out on a glassy carbon electrode in o-
dichlorobenzene/CH3CN (4:1 v/v) containing 0.1m tetrabutylammonium
hexafluorophosphate as the electrolyte and Ag/AgNO3 as the reference
electrode. [b] The optical band-gaps (Egopt) were estimated from the
edges of the electronic absorption spectra. [c] Ionization potentials were
measured by the ’’photoemission-in-air’’ method from films. [d] EHOMO,
opt
E
LUMO =4.8+E1/2 vs. Fc. [e] ELUMO =EHOMOÀEg
.
Scheme 2. Structures of the reference hydrazones (3–5) and host material
(CBH) used in the study.
Figure 2. Cyclic voltammogram of dyad FH2 (scan rate=50 mVsÀ1) in
argon-purged ortho-dichlorobenzene/acetonitrile solution (4:1 v/v).
caused a decrease in the EHOMO value of approximately
0.1 eV.
The energies of the LUMOs of all three fullerene–hydra-
zone dyads are very similar. When contrasted FH1–FH3
with pristine C60 fullerene, the LUMO energies were ap-
proximately 0.1 eV larger, quite similar to that of PCBM
(À3.73 eV).[11] This increase clearly reflects the saturation of
a double bond in the C60 core as a consequence of the func-
tionalization in dyads FH1–FH3.
The presence of both electron-accepting and -donating
moieties in the same molecule, separated by a aliphatic link-
ing group, results in the formation of materials with a
narrow band-gap (Eg); the gap was approximately half of
those measured for model hydrazones 3–5.
Figure 1. Absorption spectra of the investigated and reference com-
pounds in CHCI3 solutions.
values were also determined using cyclic voltammetry (CV;
Table 1). These values do not represent any absolute solid-
state- or gas-phase ionization energies, but can be used to
compare different compounds relative to one another. The
cyclic voltammograms of all three synthesized compounds
showed reversible oxidation and reduction couples; as an
example, a cyclic voltammogram of dyad FH2 is shown in
Figure 2.
The triphenylamine-based derivatives FH1 and FH2 ex-
hibited first oxidation wave half-wave potentials correspond-
ing to 0.22 V and 0.25 V vs Fc (ferrocene), respectively,
which resulted in EHOMO values of À5.02 eV and À5.05 eV
(on the basis of the EHOMO energy level of ferrocene being
4.8 eV). These results were quite similar to those demon-
strated by monohydrazone 3 and 4,4’-bis(diphenylhydrazo-
nomethyl)triphenylamine (4); only a very slight decrease in
the EHOMO value was observed. Substitution of the triphenyl-
amine fragment with a cazbazole moiety in dyad FH3
When considering the use of an organic material for hole-
transport applications it is important to have an understand-
ing of its solid-state ionization potential (Ip). This under-
standing can help to identify suitable partners for organic
transport and inorganic electrode materials. The ionization
potentials were measured using the ’’electron photoemission
in air’’ method (Figure 3) and the results are presented in
Table 1 (the measurement error was evaluated as (Æ
0.03) eV).[12] The measured Ip values were about 0.2–0.3 eV
higher than the HOMO levels found during the CV experi-
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Chem. Asian J. 2012, 7, 614 – 620

Ambipolar C60 Fullerene–Hydrazone Hybrid Materials
Figure 4. Layer composed of dyad FH3 and PC-Z (1:1 ratio by mass)
viewed under an optical microscope.
Figure 3. Photoemission spectra in air of the investigated dyads FH1–
FH3.
However, fullerene–hydrazone dyads doped with carba-
zolyl-based molecular glass, CBH (1:1), produced layers of
suitable quality. CBH was chosen because it has some struc-
tural similarities with the polycarbonate molecule as well as
four carbazole fragments for better compatibility with the
investigated materials. In addition, in our previous investiga-
tions, this type of carbazole-containing compound had
formed high-quality layers.[13] The host material, CBH, has a
relatively high ionization potential (5.90 eV) and was not in-
volved in the charge-transport process.
Charge-transport properties of the synthesized fullerene–
hydrazone dyads FH1–FH3 were studied by the xerographic
time-of-flight (XTOF) analysis. The charge-mobility-defin-
ing parameters: zero field mobility (m0), the Poole–Frenkel
parameter (a), and the mobility in an electric field of 6.4ꢁ
105 VcmÀ1, are given in Table 2.
All three of the investigated compounds were measured
without the use of a high vacuum or an inert atmosphere,
under ambient conditions, and were found to exhibit bipolar
charge transport in the range 1ꢁ10À6–1ꢁ10À5 cm2 VÀ1 sÀ1. A
negative Poole–Frenkel parameter (a) could indicate that
electron mobility was more-strongly influenced by positional
disorder. Figure 5 shows the room-temperature dependen-
cies of hole- and electron drift mobility on the electric field
in charge-transport layers of FH1–FH3 doped with CBH
(1:1 by mass).
It is interesting to note that structure of the investigated
TMs does influence the charge-transport balance quite no-
ticeably. The dihydrazone fragment in dyad FH2, which con-
tains a large p-conjugated system, ensures good hole-trans-
port properties, but it is also bulkier, thus increasing the dis-
tance between fullerene fragments and effectively reducing
ments. This difference may be caused by the different state
of the materials investigated (solution in the CV analysis
and a solid film in the photoemission method) or by the dif-
ferent methods of measurement.
The obtained Ip values for dyads FH2 and FH3 are very
similar to those of the reference hole-transporting hydra-
zones 4 and 5, the fragments of which are incorporated into
the structure of the synthesized dyads. The only noticeable
exception is compound FH1, its Ip value was about 0.2 eV
lower than that of its corresponding hydrazone (3). Howev-
er, if we look at the CV data, which is measured in dilute so-
lution, the difference is almost negligible (only 0.02 eV).
Most probably, molecules of compound 3 arrange them-
selves in such a manner that there is an interaction between
them in the solid state, whilst bulky fullerene groups in the
structure of dyad FH1 prevent this type of interaction and
so its Ip value is similar to those observed for compounds 4
and FH2.
Dyads FH1–FH3 are soluble in common organic solvents
such as chloroform, tetrahydrofuran, toluene, etc. We were
unable to measure the charge drift-mobility of neat FH1–
FH3 because the charge carrier transport was too dispersive
and because the traditional polymeric matrixes used for
layer preparation for mobility measurements, such as poly-
carbonate-Z (PC-Z) or polyvinylbutyral (PVB), were incom-
patible with the investigated materials. The fullerene–hydra-
zone dyads did not form homogeneous layers with the poly-
meric matrixes tested; instead, separation of the materials
was clearly observed (Figure 4).
Table 2. Hole-mobility data for FH1–FH3.
1/2
Composition
d [mm]
Type
m0 [cm2/Vs][a]
m [cm2/Vs][b]
a [(cmVÀ1
) ]
FH1+CBH (1:1)
3.3
hole
electron
hole
electron
hole
electron
hole
2.2ꢁ10À7
ꢀ7ꢁ10À6
5.7ꢁ10À6
2ꢁ10À6
1.5ꢁ10À6
7ꢁ10À6
0.0034
ꢀ0.0001
0.0009
FH2+CBH (1:1)
5.5
2.0
3.8
1.15ꢁ10À5
1.6ꢁ10À6
1.5ꢁ10À6
2.7ꢁ10À6
3.4ꢁ10À6
2.2ꢁ10À6
À0.0003
FH3+CBH (1:1)
1.5ꢁ10À7
1.1ꢁ10À6
2ꢁ10À6
0.0029
0.00011
0.0006
À0.0009
FH1+FH2+CBH (1:1:2)
electron
4.6ꢁ10À6
[a] Mobility at zero field strength. [b] Mobility at field strength=6.4ꢁ105 VcmÀ1
.
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Figure 7. Electron- and hole drift-mobilities in a charge-transport layer of
FH1, FH2, and CBH (1:1:2 ratio by mass).
Figure 5. Electron- and hole drift-mobilities in charge-transport layers of
FH1–FH3 with CBH (1:1 ratio by mass).
the electron mobility. A similar but opposite effect was ob-
served in case of dyad FH1 (Figure 6).
The more-compact monohydrazone segment in dyad FH1
allowed better packing of the C60 moieties, thereby resulting
ed that there was no interaction at the ground state between
the acceptor and donor moieties. We found that these deriv-
atives have a narrow band-gap (<1.5 eV) and act as ambi-
polar charge-transport materials even under ambient condi-
tions without any protection from oxygen or moisture. The
hole- and electron mobilities could be successfully balanced
by modifying the structure of the dyads. Very similar
HOMO and LUMO energy levels also allowed us to achieve
balanced charge-transport by blending these dyads together
in different proportions. Uncomplicated and short syntheses,
narrow band-gaps, and balanced bipolar charge-transport
under ambient conditions without any encapsulation makes
these fullerene–hydrazone dyads attractive materials for var-
ious optoelectronic applications.
Experimental Section
Figure 6. Dependence of hole- and electron-transport balance on the
structure of TM and on the composition of the layer (mobility at an elec-
tric field of 6.4ꢁ105 VcmÀ1).
Materials and Methods
All reagents were purchased from Aldrich Chemical Co. and used with-
out purification. All solvents were purified using standard procedures.
The reference compounds 4-methyl-4’-(N-methyl-N-phenylhydrazonome-
thyl)triphenylamine (3), 4,4’-bis(diphenylhydrazonomethyl)triphenyla-
mine (4), and 2,2-bis{4-[2-hydroxy-6-(carbazol-9-yl)-5-(carbazol-9-
methyl)-4oxahexyloxy]phenyl}propane (CBH) were synthesized accord-
ing to procedures described previously.[10] The reactions were monitored
by thin-layer chromatography (TLC) on ALUGRAM SIL/UV254 plates
that were developed with iodine or UV light. Column chromatography
was performed on silica gel (grade 62, 60–200 mesh, 150 ꢂ, Aldrich).
in an increase in electron mobility. However, owing to small-
er p-conjugated system of the monohydrazone the hole
transport was reduced. The most-balanced charge transport
was observed in dyad FH3 which contained the carbazole
monohydrazone moiety, as its size lies somewhere in be-
tween the compact monohydrazone in dyad FH1 and the
large dihydrazone in dyad FH2.
Very similar ionization potentials of dyads FH1 and FH2
allowed us to investigate the possibility of balancing their
mobilities by mixing these two TMs. A blend of dyads FH1
and FH2 (1:1 by mass) doped in CBH demonstrated well-
balanced hole- and electron mobilities (Figure 7).
The NMR spectra were taken on a Varian Unity Inova (300 MHz) spec-
trometer. The UV spectra were recorded on a Perkin–Elmer Lambda 35
spectrometer in CHCl3. A solution of the investigated charge-transport-
ing material (TM; 10À4 m) and a microcell with an internal width of 1 mm
was used. Cyclic voltammetry (CV) measurements were carried out using
a three-electrode assembly cell from Bio-Logic SAS and a micro-AUTO-
LAB Type III potentiostat galvanostat. The measurements were carried
out on a glassy carbon electrode in ortho-dichlorobenzene/acetonitrile
(4:1 v/v) solutions containing 0.1m tetrabutylammonium hexafluorophos-
phate as the electrolyte, Ag/AgNO3 as the reference electrode, and a
platinum-wire counter electrode.
Conclusions
The samples for charge-carrier mobility measurements were prepared
from different mass-proportion compositions of FH1–FH3 with poly-
carbonate-Z (PC-Z) (Iupilon Z-200 from Mitsubishi Gas Chemical Co.)
or CBH in CHCl3 and coated on the polyester film with an aluminum
New fullerene–hydrazone dyads FH1–FH3 were synthesized
and investigated. Absorption spectra of these dyads indicat-
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Chem. Asian J. 2012, 7, 614 – 620

Ambipolar C60 Fullerene–Hydrazone Hybrid Materials
layer. After coating, the samples were heated at 808C for 1 h. The hole
drift-mobility was measured by the xerographic time of flight (XTOF)
technique.[14] Positive corona charging created an electric field inside the
TM layer. The charge carriers were generated at the layer surface by illu-
mination with pulses of nitrogen laser (pulse duration=2 ns, wave-
length=337 nm). The decrease in layer surface-potential as a result of
pulse illumination was up to 1–5% of the initial potential before illumi-
nation. The capacitance probe that was connected to the wide frequency-
band electrometer measured the rate of the decrease in surface potential
(dU/dt). The transit time, tt, was determined by the kink in the curve of
the dU/dt transient on a linear- or double-logarithmic scale. The drift mo-
bility was calculated by the formula m=d2/U0tt, where d is the layer thick-
ness and U0 is the surface potential at the moment of illumination.
analysis: calcd (%) for C83H20N2O2: C 92.56, H 1.87, N 2.60; found:
C 92.62, H 1.80, N 2.50.
Synthesis of 1’-methyl-2’-{[9-(2-ethylhexyl)-6-formyl]carbazol-3-
yl}pyrrolydino-[3’,4’:1,2][60]fullerene (2c)
A
mixture of C60 (400 mg, 0.555 mmol), N-methylglycine (494 mg,
5.55 mmol), and N-(2-ethylhexyl)-3,6-diformylcarbazole (186 mg,
0.555 mmol) in toluene (200 mL) was heated to reflux for 3 h (TLC: tolu-
ene/EtOAc, 24:1 v/v). After cooling to RT, the mixture was subjected to
column chromatography on silica gel, eluted first with toluene to collect
any unreacted C60 and traces of the bis-adduct, followed by toluene/
EtOAc (1:49 v/v) to collect compound 2c as a dark-brown solid (82 mg,
14%). Rf =0.43 (toluene/EtOAc, 49:1); 1H NMR (300 MHz, CDCl3,
258C, TMS): d=10.02 (s, 1H), 8.56 (s, 2H), 7.95 (d, J=8.6 Hz, 2H),
7.53–7.36 (m, 2H), 5.13 (s, 1H), 5.02 (d, J=9.4 Hz, 1H), 4.32 (d, J=
9.4 Hz, 1H), 4.17 (d, J=7.4 Hz, 2H), 2.85 (s, 3H), 2.12–1.94 (m, 1H),
1.48–1.11 (m, 8H), 0.92 (t, J=7.4 Hz, 3H), 0.82 ppm (t, J=7.0 Hz, 3H);
13C NMR (75 MHz, CS2/CDCl3 1:1, 258C, TMS): d=192.82, 156.60,
154.34, 153.83, 153.73, 147.56, 147.00, 146.79, 146.59, 146.52, 146.46,
146.38, 146.21, 146.04, 145.90, 145.82, 145.76, 145.69, 145.59, 145.55,
145.49, 145.44, 145.42, 145.01, 144.98, 144.83, 144.70, 144.65, 143.44,
143.32, 142.98, 142.87, 142.86, 142.81, 142.59, 142.47, 142.45, 142.44,
142.35, 142.24, 142.19, 142.00, 141.96, 141.82, 140.52, 140.48, 140.29,
139.77, 137.17, 136.92, 136.22, 136.11, 129.34, 129.06, 127.27, 124.71,
123.30, 109.70, 84.18, 70.40, 69.28, 48.13, 40.51, 39.84, 31.42, 29.17, 24.98,
23.58, 14.52, 11.39 ppm; elemental analysis: calcd (%) for C84H30N2O:
C 93.14, H 2.79, N 2.59; found: C 93.20, H 2.81, N 2.62.
Samples for the measurement of the ionization potential were prepared
by dissolving the TM in CHCl3 and coating aluminum plates that were
precoated with methylmethacrylate (ca. 0.5 mm thick) and a methacrylic
acid copolymer sub-layer. The thickness of the TM layers was 0.5–1 mm.
The ionization potential was measured by the ’’electron photoemission in
air’’ method, similar to the one used[12] and described previously.[13b] Ip
values for the films of the synthesized and reference compounds were es-
tablished by an electron photoemission technique from the dependencies
of photocurrent (I) on the incident light quanta energy, which are named
as electron photoemission spectra and plotted as I0.5 =f(hn). Usually, the
photoemission experiments are carried out under high vacuum, which is
one of the main requirements for these measurements; if the vacuum is
not high enough, surface oxidation of the sample and gas adsorption are
possible, and this would influence the measurements. However, in our
case the organic materials investigated were stable enough to oxygen and
the measurements were carried out in air.
Synthesis of 1’-methyl-2’-{4-[4-(1-methyl-1-penylhydrazono-2-methyl)-4’-
methyl]di-phenylamino}phenylpyrrolydino-[3’,4’:1,2][60]fullerene (FH1)
Synthesis of 1’-methyl-2’-(4-formyl-4’-
methyldiphenylamino)phenylpyrrolydino-[3’,4’:1,2][60]fullerene (2a)
A mixture of compound 2a (142 mg, 0.133 mmol) and N-methyl-N-phe-
nylhydrazine (0.047 mL, 0.4 mmol) in toluene (5 mL) was stirred at 708C
for 6 h. The mixture was subjected to column chromatography on silica
gel (toluene) to collect compound FH1 as a dark-brown solid (100 mg,
64%). Rf =0.38 (toluene/n-hexane, 3:2); 1H NMR (300 MHz, CDCl3,
258C, TMS): d=7.53–6.82 (m, 18H), 4.94 (d, J=9.3 Hz, 1H), 4.88 (s,
1H), 4.23 (d, J=9.3 Hz, 1H), 2.84 (s, 3H), 2.29 ppm (s, 3H); 13C NMR
(75 MHz, CS2/CDCl3 1:1, 258C, TMS): d=192.44, 156.19, 153.88, 153.55,
153.34, 147.70, 147.18, 147.14, 146.75, 146.39, 146.29, 146.18, 146.04,
145.98, 145.83, 145.68, 145.42, 145.35, 145.23, 145.17, 145.09, 145.03,
144.55, 144.27, 143.05, 142.86, 142.56, 142.47, 142.14, 142.03, 141.93,
141.71, 141.54, 140.05, 139.96, 139.82, 139.17, 137.64, 136.55, 136.47,
135.78, 135.69, 133.02, 131.49, 130.81, 130.73, 129.95, 128.89, 128.15,
126.82, 125.44, 125.22, 124.97, 123.50, 123.19, 120.17, 114.91, 82.96, 69.88,
68.82, 40.00, 32.87, 30.24, 29.73 ppm; UV/Vis (THF): lmax (e)=374
(43900), 308 (55500), 255 nm (111440 molÀ1 dm3 cmÀ1); elemental analy-
sis: calcd (%) for C90H30N4: C 92.61, H 2.59, N 4.80; found: C 92.52,
H 2.61, N 4.87.
A
mixture of C60 (800 mg, 1.11 mmol), N-methylglycine (988 mg,
11.09 mmol), and 4-(4-formyl-4’-methyldiphenylamino)benzaldehyde
(350 mg, 1.11 mmol) in toluene (400 mL) was heated to reflux for 2.5 h.
After cooling to RT, the mixture was subjected to column chromatogra-
phy on silica gel (toluene) to collect compound 2a as a dark-brown solid
(179 mg, 15%). Rf =0.4 (toluene/EtOAc, 49:1); 1H NMR (300 MHz,
CDCl3, 258C, TMS): d=9.74 (s, 1H), 7.25–6.85 (m, 12H), 4.96 (d, J=
9.3 Hz, 1H), 4.93 (s, 1H), 4.27 (d, J=9.3 Hz, 1H), 2.86 (s, 3H), 2.32 ppm
(s, 3H); 13C NMR (75 MHz, CS2/CDCl3 1:1, 258C, TMS): d=192.37,
155.97, 153.66, 153.50, 153.10, 152.95, 152.84, 147.16, 146.51, 146.26,
146.16, 146.06, 146.03, 145.96, 145.81, 145.57, 145.43, 145.34, 145.23,
145.16, 145.10, 145.00, 144.57, 144.48, 144.24, 144.19, 143.13, 143.04,
142.88, 142.56, 142.50, 142.45, 142.09, 142.02, 141.92, 141.84, 141.72,
141.61, 141.53, 141.48, 140.07, 140.03, 139.79, 139.00, 136.63, 136.33,
135.81, 135.57, 135.39, 134.98, 133.34, 131.09, 130.34, 129.00, 128.88,
128.10, 126.23, 125.68, 125.19, 119.17, 82.74, 69.86, 68.74, 39.92,
29.77 ppm; elemental analysis: calcd (%) for C83H22N2O: C 93.77, H 2.09,
N 2.64; found: C 93.88, H 2.20, N 2.52.
Synthesis of 1’-methyl-2’-{4-[4,4’-bis(1,1-diphenylhydrazono-2-
methyl)phenyl]amino}-phenyl-[3’,4’:1,2][60]fullerene (FH2)
Synthesis of 1’-methyl-2’-(4,4’-diformyldiphenylamino)phenylpyrrolydino-
[3’,4’:1,2][60]fullerene (2b)
N,N-Diphenylhydrazine (120 mg, 0.543 mmol) was treated with a mixture
of aqueous potassium carbonate (50%, 75 mg, 0.543 mmol) and toluene
(5 mL). Compound 2b (150 mg, 0.139 mmol) and a catalytic amount of
acetic acid were added to the separated organic layer and the mixture
was stirred at 708C for 2.5 h. After cooling to RT, the solution was treat-
ed with toluene and washed with distilled H2O. The organic layer was
dried over anhydrous Na2SO4 and filtered. The solvent was evaporated
and the mixture was subjected to column chromatography on silica gel
(toluene) to collect compound FH2 as a dark-brown solid (80 mg, 42%).
Rf =0.56 (toluene/n-hexane 3:2); 1H NMR (300 MHz, CDCl3, 258C,
TMS): d=7.79–6.81 (m, 32H), 4.93 (d, J=9.4 Hz, 1H), 4.88 (s, 1H), 4.22
(d, J=9.4 Hz, 1H), 2.84 ppm (s, 3H); 13C NMR (75 MHz, CS2/CDCl3 1:1,
258C, TMS): d=156.23, 153.91, 153.55, 153.29, 147.26, 147.06, 146.75,
146.45, 146.25, 146.16, 146.12, 146.06, 145.90, 145.74, 145.49, 145.42,
145.29, 145.25, 145.21, 145.14, 145.11, 144.66, 144.62, 144.34, 143.64,
146.12, 142.94, 142.63, 142.56, 142.54, 142.22, 142.20, 142.11, 142.00,
141.76, 141.60, 140.12, 140.07, 139.88, 139.16, 136.63, 136.50, 135.90,
A
mixture of C60 (400 mg, 0.555 mmol), N-methylglycine (494 mg,
5.55 mmol), and tris(4-formylphenyl)amine (183 mg, 0.555 mmol) in tolu-
ene (200 mL) was heated to reflux for 2.5 h. After cooling to RT, the
mixture was subjected to column chromatography on silica gel, eluted
first with toluene to collect any unreacted C60 and traces of the bis-
adduct, followed by toluene/EtOAc (49:1 v/v) to obtain compound 2b as
a
dark-brown solid (90 mg, 15%). Rf =0.23 (toluene/EtOAc, 49:1);
1H NMR (300 MHz, CDCl3, 258C, TMS): d=9.84 (s, 2H), 8.16–6.84 (m,
12H), 4.33 (s, 1H), 4.29 (d, J=9.4 Hz, 1H), 3.84 (d, J=9.4 Hz, 1H),
2.89 ppm (s, 3H); 13C NMR (75 MHz, CS2/CDCl3 1:1, 258C, TMS): d=
192.42, 151.53, 145.49, 144.36, 141.59, 132.24, 131.92, 131.33, 131.18,
130.74, 130.09, 129.89, 128.92, 128.74, 128.45, 128.38, 128.12, 127.18,
126.93, 126.62, 125.21, 122.65, 113.96, 82.64, 82.20, 81.38, 81.31, 80.11,
69.91, 69.57, 68.94, 68.81, 67.81, 43.62, 39.96, 39.56, 30.24 ppm; elemental
Chem. Asian J. 2012, 7, 614 – 620
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
619

V. Getautis et al.
FULL PAPERS
135.75, 135.11, 131.95, 130.78, 129.73, 127.20, 124.35, 123.76, 122.43, 82.91,
69.92, 68.90, 40.04 ppm; UV/Vis (THF): lmax (e)=394 (51200), 308
(50600), 254 nm (106800 molÀ1 dm3 cmÀ1); elemental analysis: calcd (%)
for C107H40N6: C 91.18, H 2.86, N 5.96; found: C 91.25, H 2.92, N 5.83.
[4] M. Bendikov, F. Wudl, D. F. Perepichka, Chem. Rev. 2004, 104, 4891.
[5] a) C. Yang, S. Cho, A. J. Heeger, F. Wudl, Angew. Chem. 2009, 121,
1620; Angew. Chem. Int. Ed. 2009, 48, 1592; b) M. Chikamatsu, A.
Itakura, Y. Yoshida, R. Azumi, K. Yase, Chem. Mater. 2008, 20,
7365; c) P. H. Wobkenberg, J. Ball, D. D. C. Bradley, T. D. Antho-
poulos, F. Kooistra, J. C. Hummelen, D. M. de Leeuw, Appl. Phys.
Lett. 2008, 92, 143310; d) P. H. Wçbkenberg, D. D. C. Bradley, D.
Kronholm, J. C. Hummelen, D. M. de Leeuw, M. Colle, T. D. Antho-
poulos, Synthetic Met. 2008, 158, 468; e) T. Morita, W. Takashima, K.
Kaneto, Jpn. J. Appl. Phys. Part 2 2007, 46, L256.
[6] a) Y. Kunugi, K. Takimiya, N. Negishi, T. Otsubo, Y. Aso, J. Mater.
Chem. 2004, 14, 2840; b) N. Negishi, Y. Ie, H. Tada, T. Kaneda, Y.
Aso, Chem. Lett. 2007, 36, 544; c) S. Amriou, A. Mehta, M. R.
Bryce, J. Mater. Chem. 2005, 15, 1232; d) J. F. Nierengarten, T. Gu,
T. Aernouts, W. Geens, J. Poortmans, G. Hadziioannou, D. Tsamou-
ras, Appl. Phys. A 2004, 79, 47; e) W. W. H. Wong, D. Vak, T. B.
Singh, S. Ren, C. Yan, D. J. Jones, I. I. Liaw, R. N. Lamb, A. B.
Holmes, Org. Lett. 2010, 12, 5000; f) J.-F. Nierengarten, J.-F. Eckert,
J.-F. Nicoud, L. Ouali, V. Krasnikov, G. Hadziioannou, Chem.
Commun. 1999, 617.
[7] R. Lygaitis, V. Getautis, J. V. Grazulevicius, Chem. Soc. Rev. 2008,
37, 770.
[8] a) M. Prato, M. Maggini, Acc. Chem. Res. 1998, 31, 519; b) N. Tag-
matarchis, M. Prato, Synlett 2003, 6, 768; c) A. Bianco, T. Da Ros,
M. Prato, C. Toniolo, J. Pept. Sci. 2001, 7, 208.
[9] a) M. Maggini, G. Scorrano, M. Prato, J. Am. Chem. Soc. 1993, 115,
9798; b) M. Prato, M. Maggini, C. Giacometti, G. Scorrano, G. San-
dona, G. Farnia, Tetrahedron 1996, 52, 5221; c) G. Rotas, N. Tagma-
tarchis, Tetrahedron Lett. 2009, 50, 398.
[10] a) S. Urnikaite, M. Daskeviciene, T. Malinauskas, V. Jankauskas, V.
Getautis, Monatsh. Chem. 2009, 140, 1453; b) T. Satoko, H. Tamotsu,
Jpn. Kokai Tokkyo Koho JP 10111578, 1998; c) J. Ostrauskaite, V.
Voska, J. Antulis, V. Gaidelis, V. Jankauskas, J. V. Grazulevicius, J.
Mater. Chem. 2002, 12, 3469; d) V. Getautis, V. Gaidelis, A. Stani-
sauskaite, M. Daskeviciene, J. Sidaravicius, R. Rinkunas, E. Montri-
mas, V. Jankauskas, R. Matuliauskas, S. Brazinskas, LT 5444, 2007.
[11] M. Al-Ibrahim, H.-K. Roth, M. Schroedner, A. Konkin, U. Zhokha-
vets, G. Gobsch, P. Scharff, S. Sensfuss, Org. Electron. 2005, 6, 65.
[12] a) M. Kirkus, M. H. Tsai, J. V. Grazulevicius, C. C. Wu, L. C. Chi,
K. T. Wong, Synthetic Met. 2009, 159, 729; b) E. Miyamoto, Y. Ya-
maguchi, M. Yokoyama, Electrophotography 1989, 28, 364; c) M.
Cordona, L. Ley, Top. Appl. Phys. 1978, 26, 1.
Synthesis of 1’-methyl-2’-{[9-(2-ethylhexyl)-6-(1,1-diphenylhydrazono-2-
methyl)]carbazol-3-yl}-[3’,4’:1,2][60]fullerene (FH3)
N,N-Diphenylhydrazine (105 mg, 0.475 mmol) was treated with a mixture
of aqueous potassium carbonate (50%, 66 mg, 0.475 mmol) and toluene
(5 mL). Compound 2c (206 mg, 0.190 mmol) and a catalytic amount of
acetic acid were added to the separated organic layer and the mixture
was stirred at 708C for 4 h. After cooling to RT, the solution was treated
with toluene and washed with distilled H2O. The organic layer was dried
over anhydrous Na2SO4 and filtered. The solvent was evaporated and the
mixture was subjected to column chromatography on silica gel (toluene/
n-hexane, 49:1 v/v) to collect compound FH3 as a dark-brown solid
(140 mg, 59%). Rf =0.4 (toluene/EtOAc, 49:1); 1H NMR (300 MHz,
CDCl3, 258C, TMS): d=8.22 (s, 1H), 7.90 (d, J=8.6 Hz, 1H), 7.55–6.87
(m, 15H), 5.09 (s, 1H), 5.03 (d, J=9.3 Hz, 1H), 4.30 (d, J=9.4 Hz, 1H),
4.14 (d, J=7.4 Hz, 2H), 2.85 (s, 3H), 2.15–1.90 (m, 1H), 1.51–1.09 (m,
8H), 0.89 (t, J=6.8 Hz, 3H), 0.80 ppm (t, J=6.9 Hz, 3H); 13C NMR
(75 MHz, CS2/CDCl3 1:1, 258C, TMS): d=156.57, 156.40, 154.35, 153.98,
147.75, 147.42, 147.28, 147.03, 146.70, 146.43, 146.34, 146.25, 146.23,
146.20, 146.03, 145.91, 145.74, 145.69, 145.67, 145.60, 145.47, 145.42,
145.38, 145.33, 145.30, 145.25, 145.13, 144.82, 144.68, 144.51, 144.15,
143.59, 143.24, 143.09, 142.79, 142.66, 142.64, 142.42, 142.28, 142.24,
142.20, 142.16, 142.08, 141.80, 141.62, 141.50, 141.28, 140.28, 140.23,
139.60, 137.39, 129.91, 129.47, 127.64, 125.67, 124.34, 122.72, 122.49,
121.12, 119.41, 117.92, 109.55, 77.93, 70.24, 69.16, 47.74, 40.39, 39.50,
30.46, 28.80, 24.60, 23.14, 14.20, 11.10 ppm; UV/Vis (THF): lmax (e)=351
(19600), 313 (31700), 255 nm (70600 molÀ1 dm3 cmÀ1); elemental analysis:
calcd (%) for C96H40N4: C 92.29, H 3.23, N 4.48; found: C 92.25, H 3.29,
N 4.46.
Acknowledgements
This research was funded by the European Social Fund under the Global
ˇ
Grant measure (VP1-3.1-SMM-07K-01-078).
[13] a) S. Kutkevicius, A. Stanisauskaite, V. Getautis, A. Railaite, J.
Prakt. Chem. 1995, 337, 315; b) M. Daskeviciene, V. Getautis, J. V.
Grazulevicius, A. Stanisauskaite, J. Antulis, V. Gaidelis, V. Jankaus-
kas, J. Sidaravicius, J. Imaging Sci. Technol. 2002, 46, 467; c) G. Bub-
niene, T. Malinauskas, V. Getautis, A. Stanisauskaite, V. Jankauskas,
J. Sidaravicius, Synthetic Met. 2008, 158, 670.
[1] a) S. R. Forrest, Nature 2004, 428, 911; b) U. Mitschke, P. Bꢃuerle, J.
Mater. Chem. 2000, 10, 1471; c) H. Spanggaard, F. C. Krebs, Sol.
Energy Mater. Sol. Cells 2004, 83, 125; d) C. D. Dimitrakopoulos,
P. R. L. Malenfant, Adv. Mater. 2002, 14, 99; e) J. E. Anthony, A.
Facchetti, M. Heeney, S. R. Marder, X. Zhan, Adv. Mater. 2010, 22,
3876–3892.
[14] E. Montrimas, V. Gaidelis, A. Pazera, Lithuanian J. Phys. 1966, 6,
659.
[2] a) J. Zaumseil, H. Sirringhaus, Chem. Rev. 2007, 107, 1296; b) Y.
Shirota, H. Kageyama, Chem. Rev. 2007, 107, 953.
Received: September 15, 2011
[3] E. J. Meijer, D. M. de Leeuw, S. Setayesh, E. van Veenendaal, B. H.
Huisman, P. W. M. Blom, J. C. Hummelen, U. Scherf, T. M. Klap-
wijk, Nat. Mater. 2003, 2, 678.
Published online: December 23, 2011
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Chem. Asian J. 2012, 7, 614 – 620