Probing molecular wires: Synthesis, structural, and electronic study of donor-acceptor assemblies exhibiting long-range electron transfer

Article abstract of DOI:10.1002/chem.200500073

A series of donor-acceptor arrays (C₆₀-oligo-PPV-exTTF; 16-20) incorporating π-conjugated oligo(phenylenevinylene) wires (oligo-PPV) of different length between π-extended tetrathiafulvalene (exTTF) as electron donor and C₆₀ as elect

Full text of DOI:10.1002/chem.200500073

FULL PAPER
Probing Molecular Wires: Synthesis, Structural, and Electronic Study of
Donor–Acceptor Assemblies Exhibiting Long-Range Electron Transfer
Francesco Giacalone,[a] JosØ L. Segura,[a] Nazario Martín,*[a] Jeff Ramey,[b] and
Dirk M. Guldi*[b]
Abstract: A series of donor–acceptor
arrays (C60–oligo-PPV–exTTF; 16–20)
incorporating p-conjugated oligo(phe-
nylenevinylene) wires (oligo-PPV) of
different length between p-extended
tetrathiafulvalene (exTTF) as electron
donor and C60 as electron acceptor has
been prepared by multistep convergent
synthetic approaches. The electronic in-
teractions between the three electroac-
tive species present in 16–20 were in-
vestigated by UV-visible spectroscopy
and cyclic voltammetry (CV). Our
studies clearly show that, although the
C60 units are connected to the exTTF
donors through a p-conjugated oligo-
PPV framework, no significant elec-
tronic interactions are observed in the
ground state. Interestingly, photoin-
duced electron-transfer processes over
distances of up to 50 Š afford highly
stabilized radical ion pairs. The mea-
sured lifetimes for the photogenerated
charge-separated states are in the
range of hundreds of nanoseconds
(~500 ns) in benzonitrile, regardless of
the oligomer length (i.e., from the
monomer to the pentamer). A different
lifetime (4.35 ms) is observed for the
heptamer-containing array. This differ-
ence in lifetime has been accounted for
by the loss of planarity of the oPPV
moiety that increases with the wire
length, as established by semi-empirical
(PM3) theoretical calculations carried
out with 19 and 20. The charge recom-
bination dynamics reveal a very low at-
tenuation factor (b=0.01ꢀ0.005 Šꢁ1).
This b value, as well as the strong elec-
tron coupling (V~5.5 cmꢁ1) between
the donor and the acceptor units, clear-
ly reveals a nanowire behavior for the
p-conjugated oligomer, which paves
the way for applications in nanotech-
nology.
Keywords: donor–acceptor
sys-
tems · electron transfer · fullerenes ·
nanostructures
vinylene)
· oligo(phenylene-
Introduction
and tune the magnitude of the electron-transfer parameters.
In this context, molecular chains or bridges provide endless
opportunities, since they determine not only the structural
features but also the size of the electronic coupling matrix
element, V, between the donor and acceptor fragments.[2]
An important characteristic of a spacer is the possibility of
introducing a systematic alteration of separation, orienta-
tion, and overlap without affecting the electronic nature of
the donor–acceptor pair, for which the coupling is propor-
tional to the overlap of their electronic clouds.[3] Important
The composition, the interchromophore separation/angular
relationship, the overall dynamical and stimulus-induced re-
organization, and the electronic coupling are crucial factors
in the development of charge-transfer reaction centers.[1] Of
particular interest are artificial model systems in which the
introduction of simple molecular changes is used to control
[a] Dr. F. Giacalone, Dr. J. L. Segura, Prof. Dr. N. Martín
Departamento de Química Orgµnica
Facultad de Ciencias Químicas, Universidad Complutense
28040 Madrid (Spain)
incentives for this work stem from nature, in which for pho-
[5]
tosynthetic reaction centers,[4] redoxproteins,
mem-
branes,[6] and nucleic acids,[7] this relationship has been rec-
ognized to control key biological steps/processes. In addi-
tion, emerging technologies, such as molecular electronics/
preparation of molecular devices, are, in part, based on simi-
lar paradigms.[8]
Fax: ( +34)91-394-4103
E-mail: nazmar@quim.ucm.es
[b] J. Ramey, Prof. Dr. D. M. Guldi
Institute for Physical and Theoretical Chemistry
University of Erlangen, 91058 Erlangen (Germany)
Fax: ( +49)913-185-28307
The electron-transfer processes in single molecules have
been investigated in some detail, and different mechanisms
have been considered which mainly depend on molecular
size and structure, as well as the temperature and the free-
E-mail: dirk.guldi@chemie.uni-erlangen.de
Supporting information for this article is available on the WWW
under http://www.chemeurj.org/ or from the author.
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DOI: 10.1002/chem.200500073
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energy difference between the donor and acceptor in
donor–bridge–acceptor systems. Several different mecha-
nisms, ranging from coherent tunneling or superexchange to
thermally activated electron transfer by hopping mecha-
nisms, are particularly relevant to molecular wires, and com-
plete discussions are available in several reviews to which
the reader is referred.[9]
Currently, monodisperse and soluble p-conjugated
oligomers with a well-defined length and composition are
receiving growing interest for the design/integration of mo-
lecular wires[10] and rods,[11] since they can be used as tuna-
ble building blocks[12] for nanoscale chemical entities in mo-
lecular and supramolecular electronic and photonic devi-
ces.[13] In this context, electronic conduction along “nano-
wires” is a key feature of nanochemistry and nanotechnolo-
gy.[14]
conjugated chains of PPV oligomers has been investigated
in only a few cases—pentameric oligo-PPV with terminal
pentamethylated ferrocene units,[16] or hexameric oligo-PPV
bearing two porphyrin groups in the terminal positions.[17]
More recently, a systematic study in which a tetracene
donor unit and pyromellitimide acceptor are connected
through an oligo-PPV of increasing length (TET–oPPV–
PYR) (TET=tetracene, PYR=pyromellitimide) has been
reported,[18] thus demonstrating the importance of energy
matching between the donor and bridge components for
achieving molecular-wire behavior. Quantum-chemical cal-
culations showed a competition between a direct superex-
change process and a two-step “bridge-mediated” process
whose efficiency depends primarily on the length and nature
of the conjugated bridge.[19]
We have recently reported different C60–exTTF[20]
(exTTF=p-extended tetrathiafulvalene) and C60–exTTF–
exTTF donor–acceptor arrays,[21] which, upon visible light ir-
radiation, undergo cascades of short-range electron-transfer
reactions transforming the adjacent radical ion pairs in C60–
exTTF–exTTF to distant radical ion pairs. A common char-
Among the different p-conjugated oligomers, oligo(p-phe-
nylenevinylene)s (oligo-PPVs) have been probed as versatile
model systems for poly(p-phenylenevinylene) derivatives
and as novel materials with chemically tailored properties.[15]
Much to our surprise, intramolecular electron transfer along
Abstract in Spanish: Mediante una aproximación sintØtica
convergente en varios pasos, se ha preparado una serie de sis-
temas dador–aceptor (C60–oligo-PPV–exTTF) (16–20) incor-
porando cables moleculares p-conjugados de oligo(fenilenvi-
nileno) (oligo-PPV) de diferente longitud entre la unidad de
tetratiafulvaleno p-extendido (exTTF) como dador de elec-
trones y C60 como unidad aceptora. Las interacciones electró-
nicas entre las tres especies electroactivas presentes en 16–20
fueron investigadas por espectroscopia UV-Vis y experimen-
tos de voltamperometría cíclica (CV). Nuestros estudios
muestran que, aunque las unidades de C60 estµn conectadas a
los dadores exTTF a travØs de un esqueleto p-conjugado de
oligo-PPV, no se observan interacciones electrónicas signifi-
cativas en el estado fundamental. Interesantemente, los proce-
sos de transferencia electrónica fotoinducida a distancias de
hasta 50Š forman pares ion radical altamente estabilizados.
Los tiempos de vida medidos para los estados fotogenerados
de separación de carga estµn en el rango de cientos de nano-
segundos (~500 ns) en benzonitrilo, independientemente de
la longitud del oligómero (desde el monómero al pentµmero).
Un tiempo de vida diferente (4.35 ms) se ha observado para el
sistema que contiene el heptµmero. Esta diferencia en el
tiempo de vida se ha justificado mediante la pØrdida de pla-
naridad del fragmento de oPPV, la cual aumenta con el au-
mento de la longitud del oligómero, segffln los cµlculos teóri-
cos semiempíricos (PM3) llevados a cabo para 19 y 20. La
dinµmica de recombinación de carga revela un factor de ate-
nuación muy bajo (b=0.01ꢀ0.005 Šꢁ1). Este valor de b así
como el fuerte acoplamiento electrónico (V~5.5 cmꢁ1) entre
las unidades dadora y aceptora muestran claramente un com-
portamiento de nanocable molecular para el oligómero p-
conjugado, abriendo así el camino a su aplicación en nano-
tecnología.
acteristic of these donor (i.e., exTTF) acceptor (i.e, C60)
arrays is that remarkable effects concerning the lifetime of
the charge-separated radical ion pair states evolve. For ex-
ample, values are observed that reach into the time domain
of milliseconds, which has never previously been accom-
plished in molecular triads. The unique delocalization of
electrons provided by the three-dimensional structure of the
fullerene core, in combination with the small reorganization
energy of C60 in electron-transfer reactions, prevents a fast
charge-recombination process in these donor–acceptor
arrays. This benefit is further augmented by probing a donor
system (i.e., exTTF), which, upon charge separation, leads
to a gain of aromaticity and planarity of the oxidized frag-
ment. In complementary work we focused on the electron-
transfer chemistry of different C60-p-conjugated oligomers[22]
and dendrimers.[23]
We describe here a new series of structurally well-defined
donor–acceptor arrays that incorporate a p-extended tetra-
thiafulvalene (exTTF) as electron donor and fullerene (C60)
as electron acceptor, linked by a number of p-phenylenevi-
nylene oligomers (oligo-PPV) to yield C60–oligo-PPV–
exTTF. Previous work has documented the myriad benefits
of testing exTTF/C60 donor–acceptor couples. In the current
work we take this example one step further and concentrate
on the following new aspects. Firstly, a systematic variation
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Probing Molecular Wires
FULL PAPER
Results and Discussion
Oligo-p-phenylenevinylenes (oligo-PPV) of higher molecu-
lar weight are intractable.[25] To overcome this general draw-
back, we prepared a homologous series of oligo-PPVs (3, 6,
and 8) with defined structure and chain length that carry
alkoxy chains at the phenylene units to enhance solubility
and formyl groups at the termini to allow further chemical
transformations.
The target oligo-PPVs were obtained from 2,5-bis(di-
methylphosphonatomethyl)-1,4-dihexyloxybenzene (1) by
Wittig–Horner olefination of suitable functionalized alde-
hydes. Scheme 1 sketches the general approach to the target
oligo-PPVs. For example, formyl-functionalized 3 was ob-
tained by reacting bis-phosphonate 1 with two equivalents
of 2, followed by hydrolysis under acidic conditions. The p-
phenylenevinylene pentamer 5, bearing cyano groups at the
terminal positions, was prepared from 3 by twofold reaction
with phosphonate 4[26] in 96% yield. Final treatment with
DIBAL-H afforded the diformyl-substituted pentamer 6,
which was isolated after flash chromatography in 54% yield.
On the other hand, treatment of the diethylketal of tereph-
thaldehyde (2) with an excess of bis-phosphonate 1 led,
under basic conditions, to 7, in 41% yield, as a yellow oil.
Suitably functionalized heptamer 8 was prepared from pre-
viously synthesized building blocks (i.e., 3 and 4): Wittig–
Horner olefination of stoichiometric amounts (2:1) and acid
hydrolysis resulted in a stable, orange solid in 77% yield.
The presence of up to sixsolubilizing alkoxy chains provides
of the oligo-PPV conjugation length.[24] Secondly, conjugat-
ing the exTTF moiety with the oligomeric bridge, thus favor-
ing the electronic coupling between them. Thirdly, determin-
ing and evaluating the structural and electronic effects of
distance and the rates with which the electron/hole transfer
through oligo-PPV fragments. Finally, testing the molecular-
wire behavior in oligo-PPV-based donor–acceptor systems.
Scheme 1.
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N. Martín, D. M. Guldi et al.
good solubility of all target
oligo-PPVs, which allows their
full spectroscopic characteriza-
tion (Scheme 1).
Compound 7 emerged as an
important building block for
controlling the length of the
oligo-PPV system in two or
four units as well as the integra-
tion of versatile formyl groups
at the terminal positions. An-
other benefit of our approach is
that the purification of 7 allows
the recovery of unreacted start-
ing material (1) and the diethyl-
ketal of trimer 3.
A number of spectroscopic
techniques were used to deter-
mine the structures of the syn-
thesized oligo-PPVs. The FTIR
spectra show the cyano and car-
bonyl groups at around 2225
and 1690–1700 cmꢁ1, respective-
ly, as well as the trans substitut-
ed double bonds in the region
of 960 cmꢁ1. The E configura-
1
tion was confirmed by H NMR
spectroscopy: the olefinic pro-
tons give rise to two doublets at
d~7.6 and 7.2 ppm with J cou-
3
Scheme 2.
pling constants of about
16.5 Hz. In addition, the
1H NMR spectra also contain signals for the protons of the
formyl groups (singlets at about d=10 ppm). In the
13C NMR spectra, the signals of the formyl groups are ob-
served at d~191 ppm. Additional analytical and mass spec-
troscopic data confirmed the proposed structures.[27]
In the next phase of our synthetic work-up, Wittig olefina-
tion was carried out to link p-extended tetrathiafulvalenes
(exTTF) to the respective oligo-PPVs (2, 3, 6, and 8). A
careful stoichiometric control of triphenylphosphonium bro-
mide 9 and the respective formyl derivatives is particularly
important (see Scheme 2).
small amounts of the corresponding cis-trans analogues. Pure
all-trans 10–13 were separated by chromatographic means.[30]
Compound 15, on the other hand, was prepared by the
Wittig–Horner reaction of formyl-exTTF (14)[31] and phos-
phonate 7. Subsequent acid hydrolysis gave 15 as the all-
trans conformer (Scheme 3).
Phosphonium salts, especially those that are based on
exTTF, are very valuable building blocks for this task. They
were prepared by refluxing 9,10-bis(1,3-dithiol-2-ylidene)-2-
hydroxymethyl-9,10-dihydroanthracene[28] and triphenyl-
phosphane hydrobromide.[21] Then, with toluene as solvent
and potassium tert-butoxide as base, Wittig reaction of phos-
phonium salt 9 and the aldehydes 2, 3, 6, and 8 gave 10–13,
respectively. An alternative route was pursued for com-
pound 10; that is, treating 9 with ketal 2 followed by acid
hydrolysis to generate the aldehyde groups.
Scheme 3.
Compounds 10–13 and 15 were fully characterized on the
basis of analytical and spectroscopic data. Importantly, they
show, in addition to the oligo-PPV features (vide supra), the
presence of exTTF. For example, the H NMR spectra con-
tain singlets at around d=6.3 ppm that correspond to the
Since Wittig reactions of triphenylphosphonium benzyl-
ides with aldehydes afford mixtures of (Z)- and (E)-alkenes
nonstereospecifically,[29] 10–13 were obtained as crude prod-
ucts containing the all-trans isomers contaminated with
1
protons of the 1,3-dithiole rings.
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Probing Molecular Wires
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Treatment of monoaldehydes 10–13 and 15 with C60 and
sarcosine (N-methylglycine), N-(3,6,9-trioxadecyl)glycine, or
N-octylglycine in refluxing toluene or chlorobenzene for
24 h afforded the respective final products in moderate
yields. This reaction, as outlined in Scheme 4, takes place by
1,3-dipolar cycloaddition of azomethyne ylides, generated in
situ, to C60, according to Pratoꢁs protocol,[32] to give 16–20 as
highly soluble brown solids in 17–47% yields.
The coupling constants of ~16.5 Hz derived from the
1H NMR spectra of 16–20 in CDCl3 attest that the cycload-
dition reactions have no appreciable impact on the stereo-
chemistry of the vinyl double bonds. In 18 and 19, however,
overlapping multiplets prevent the accurate determination
of the coupling constants. All the 13C NMR spectra show the
characteristic signals that correspond to the sp3 carbon
atoms of the pyrrolidine ring (between d=70 and 80 ppm)
and the tetragonal carbons of the solubilizing alkoxy chains.
For electrochemical and photophysical studies, reference
compounds 23, 25, and 26 were synthesized, as outlined in
Scheme 5. Trimer 23[33] was prepared similarly to 3, namely
by a Wittig–Horner reaction between bis-phosphonate 1 and
benzaldehyde (21), whereas pentamer 25 and heptamer 26
were prepared from 3 by olefination reactions with phos-
phonium salt 24 and phosphonate 22, respectively. The stil-
benic phosphonate 22 was prepared by following a synthetic
strategy analogous to that employed for the synthesis of 7—
treatment of 1 with benzaldehyde (21) in a 2:1 stoichiome-
try. Although pentamer 25 was obtained as an isomeric Z/E
mixture, thermal treatment in the presence of iodine yielded
the all-E stereoisomer quantitatively.
The electronic absorption spectra of the novel systems
reveal the characteristics of all components—C60, exTTF,
and oligo-PPV. Figure 1 (top) compares, as a representative
example, the UV-visible spectrum of 19 with those of the
different building blocks, namely exTTF, 25, and unsubsti-
tuted N-methylfulleropyrrolidine (27).
Bathochromic shifts ranging from 8 to 23 nm were ob-
served when comparing 16–20 with the respective oligo-PPV
Scheme 4.
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N. Martín, D. M. Guldi et al.
Scheme 5.
references. A better conjugation, stemming from orbital
overlaps between the exTTF and the oligo-PPVs, is thought
to be responsible for this effect. In parallel, the lmax values
of the diformyl-substituted oligo-PPVs increase from 3
(426 nm) to 6 (438 nm) and 8 (461 nm). exTTF–oligo-PPV
systems (10, 11–13, and 15 in Figure 1, bottom) show a simi-
lar trend.
sive phenylenevinylene subunits the number of accessible
[35]
redoxstates is enlarged.
In line with these considerations,
the only observable oligo-PPV reduction was noted in 19
and 20, with values that are similar to those observed for
references 25 and 26 (Table 1).
On the oxidation side, a two-electron quasi-reversible oxi-
dation forming the exTTF dication directly is observed at
around 0.45 V. This feature was confirmed by Coulometric
analysis[36] and other relevant studies.[37] Recent attempts to
generate and characterize the exTTF radical cation caused
the disproportionation of the dication species, which governs
the instability of the radical cation.[38] In addition, a second
oxidation wave appears at more positive values that corre-
sponds to oligo-PPV-centered processes. With increasing
conjugation length the oligo-PPV-centered processes shift
cathodically, thus revealing the stronger electron-donor abil-
ities of the larger oligomers.
Electrochemistry: All electrochemically determined redox
potentials are collected in Table 1, including those of the un-
substituted trimer 23, pentamer 25, heptamer 26, and N-
methylpyrrolidino[3’,4’:1,2][60]fullerene (27) as reference
systems.
Overall, the voltammograms of 16–20 indicate amphoteric
redox behavior. Figure 2 shows, for example, one oxidation
and four quasi-reversible reduction waves that correspond
to the first oxidation of exTTF and to the first four reduc-
tion steps of C60, respectively. The C60-centered processes
are similar to those found for the related unsubstituted C60
reference. However, the values are cathodically shifted rela-
tive to pristine C60 due to the saturation of a C60 double
bond; this raises the LUMO energy of the resulting C60 de-
rivative.[34] Previous electrochemical studies on oligo-PPVs
Similar redoxpotentials, as found for the donor (exTTF)
and acceptor (C60), reveal, in agreement with the data stem-
ming from the electronic spectra, only weak interactions be-
tween the redoxchromophores in their ground state.
Theoretical calculations: The molecular structures of 19 and
20, bearing pentameric and heptameric oligo-PPVs, respec-
tively, were optimized by semi-empirical calculations at the
documented their poor electron-accepting ability (Er1ed
ꢁ2.0 V vs Ag/AgCl) and confirmed that upon adding succes-
ꢂ
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Probing Molecular Wires
FULL PAPER
Figure 2. Voltammogram of 16 (see Table 1 for experimental conditions).
even better than ab initio HF/6–31G* calculations—of the
molecular structure of exTTFs.[39] Furthermore, the PM3
method has also proved its reliability for describing fuller-
ene derivatives.[28,40]
As expected, our calculations show the butterfly-shaped
nonplanar geometry of exTTF. The planar conformation of
the exTTF moiety is strongly hindered by the short distance
between the peri-hydrogen atoms and the sulfur atoms
(1.78 Š). To avoid these interactions, the molecule adopts a
distorted geometry forcing the central ring into a boat con-
formation (distance S···H=2.48 Š).
The distortion from planarity is best described in terms of
a and g angles. While a corresponds to the angle formed by
the benzene rings, g defines the tilting of the dithiole units
and is the supplement of the C7-C2-C5-C5 dihedral angle
(Figure 3, left). In the most stable conformations, the calcu-
lated angles (19: a=138.78 and g=32.38; 20: a=138.48 and
g=32.88) are in good agreement with crystal packing in
pristine exTTF[41] (a=143.88 and g=33.38) and those deter-
mined from theoretical calculations (PM3: a=139.08 and
g=34.88; HF/6–31G*: a=136.38 and g=39.48; B3-P86/6–
31G*: a=142.18 and g=34.08).
Figure 1. Top: UV-visible spectrum of triad 19 together with that of its
building blocks (exTTF, pentamer 25, and unsubstituted N-methylfullero-
pyrrolidine (27)) as a reference; bottom: UV-visible spectra of exTTF–
oligoPPV dyads 10–13 and 15.
PM3 level. The alkoxy and oligoether chains were replaced
by methyl groups to facilitate the theoretical calculations.
Previous work has unequivocally shown that theoretical cal-
culations carried out for exTTFs show a good agreement be-
tween theory and experiment, thereby demonstrating that
the PM3 method provides a reasonably good description—
Figure 3 (right) shows the planarity of the oligo-PPV
moiety, which spans a dihedral angle between the exTTF
benzene ring and the benzene ring closest to the C60 unit of
98 for 19 and 388 for 20. These
findings are important, since
Table 1. Redoxpotentials of 16–20, oligo-PPVs 23, 25, and 26, fulleropyrrolidine (27) and C60 (V vs SCE).[a]
they unambiguously confirm
that the benzene ring of the
exTTF unit is conjugated with
the oligo-PPV moiety. Never-
theless, when comparing the
heptamer-containing 20 with
the pentamer-containing 19, a
strong deviation from planarity
is found. To confirm these data,
calculations were carried out on
the nonsynthesized hexamer
system 28 and, interestingly, an
intermediate value of 258 was
obtained.
Compound
Oxidation
E2pa E3pa
Reduction
olig
pc
E1pa
E4pa
E1pc
E2pc
E3pc
E4pc
E
16
17
18
19
20
0.44
0.46
0.45
0.44
0.47
1.72
1.09
1.02
0.87
0.80
–
–
1.34
1.06
1.59
–
–
–
1.73
–
ꢁ0.70
ꢁ0.68
ꢁ0.70
ꢁ0.70
ꢁ0.68
ꢁ1.10
ꢁ1.02
ꢁ1.14
ꢁ1.10
ꢁ1.07
ꢁ1.64
ꢁ1.66
ꢁ1.70
ꢁ1.65
ꢁ1.63
ꢁ2.10
ꢁ2.11
ꢁ2.04
ꢁ2.08
ꢁ2.06
–
–
–
ꢁ1.88
ꢁ1.80
ꢁ1.98
–
ꢁ1.94
ꢁ1.93
–
23
25
26
C60
27
1.11
0.99
0.88
–
1.27
1.28
1.35
–
1.53
1.41
1.65
–
2.03
1.74
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
ꢁ0.60
ꢁ1.07
ꢁ1.64
ꢁ1.93
–
–
–
ꢁ0.69
ꢁ1.10
ꢁ1.65
ꢁ2.12
–
[a] GCE (glassy carbon) as working electrode, SCE as reference electrode, Bu4NClO4 (0.1m) as supporting
electrolyte, and o-dichlorobenzene/acetonitrile mixture (4/1 v/v) as solvent. Scan rate 200 mVsꢁ1
.
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N. Martín, D. M. Guldi et al.
of the oligo-PPV moiety. To un-
ravel the mechanism producing
this emission, an excitation
spectrum was recorded. The ex-
citation spectra of the C60–
oligo-PPVs were found to be
exact matches of the ground-
state absorption of the oligo-
PPV moieties. This implies a
rapid transfer of singlet excited
state energy from the photoex-
cited oligo-PPV to the covalent-
ly linked fullerene.[42]
As regards the picosecond
transient absorption measure-
ments, immediately after the
18 ps laser excitation of C60–
oligo-PPV broadly absorbing
transients with maxima be-
Figure 3. Left: Atom numbering used in the text. Right: Molecular modeling for triads 19, 20, and the nonsyn-
thesized triad containing a hexamer oligo-PPV moiety (28).
Photophysics
tween 400 and 500 nm (i.e., singlet–singlet absorptions of
the oligo-PPV) were found. The spectral features recorded
right after the laser pulse clearly confirm, despite the pres-
ence of C60, the successful formation of the oligo-PPV sin-
glet excited state. While for the oligo-PPV references no sig-
nificant decay of the excited state absorption was observed
on the picosecond timescale (up to 6000 ps), C60–oligo-PPV
displays a drastically different kinetic behavior. In particu-
lar, the excited state absorption is short-lived with lifetimes
(<25 ps) that corroborate the efficient emission quenching.
Once the rapid disappearance of the excited oligo-PPV
absorption is complete (approx. 200 ps after the laser pulse),
only characteristics of the fullerene singlet excited state ab-
sorption remain. The noted maximum at 880 nm is reminis-
cent of that found for the reference C60. The singlet–singlet
absorption reveals a two-step grow-in dynamics, in line with
an energy-transfer mechanism. The faster process stems
from the direct excitation of the C60 core, while the slower
component is ascribed to the actual transfer of excited-state
energy. The latter assignment is based on the nearly identi-
cal dynamics (<25 ps) observed for the second component
relative to those of the decays at 500 nm.
References: In steady-state experiments, all reference com-
pounds (i.e., oligo-PPVs 23, 25, and 26 and C60) emit singlet
excited state energy, although in different regions of the
spectrum. While the fluorescence of oligo-PPV is typically
observed in the 400–500 nm range, C60 emits with a maxi-
mum at 715 nm. The quantum yields range between 0.8 and
6”10ꢁ4 for the trimer and C60 reference, respectively.
Characteristic features were also noted in our ultrafast
and fast transient absorption experiments (i.e., pico-, nano-,
and microsecond time regime). We saw, for example, singlet
excited states that are formed instantaneously: in the case of
the oligo-PPV references (23, 25, and 26) singlet–singlet ab-
sorptions develop with maxima in the 500–600 nm range.
For the C60 reference (27), on the other hand, the maximum
is in the red at 880 nm. A fast intersystem crossing process
(kisc ~108 sꢁ1) governs the fate of the metastable singlet excit-
ed states in all references. The correspondingly formed trip-
let–triplet absorptions of the oligo-PPV and C60 references
are all located in the range between 500 and 800 nm.
C60–oligo-PPV: Relative to the strong and long-lived
emission of the oligo-PPV references, the oligo-PPV emis-
sion in the C60–oligo-PPV systems[40c] is quenched nearly
quantitatively (see Table 2).
A familiar fullerene fluorescence spectrum was found
with a 0!0 emission at 715 nm, despite exclusive excitation
Another process, whose outcome on the timescale of a
few thousand picoseconds is the formation of a distinct, new
maximum at 700 nm, follows the conclusion of the energy-
transfer reaction in C60–oligo-PPV. This absorption is in ex-
cellent agreement with the trip-
let excited state absorption of
Table 2. Photophysical data of references and C60–oligo-PPV.
the C60 reference, which infers
that the underlying reaction in-
volves intersystem crossing
from the C60 singlet to the ener-
getically lower-lying triplet
27
Trimer (23)
Pentamer (24)
C60 trimer
C60 pentamer
fluorescence maxima [nm]
fluorescence maxima [nm]
FFLUOR. oligomer (toluene)
FFLUOR. fullerene (toluene)
ISC (toluene) [ns]
–
715
445
–
0.75
–
1.1
–
485
–
0.5
–
0.8
–
472
715
503
715
–
5.0”10ꢁ4
6.0”10ꢁ4
1.22
5.8”10ꢁ4
6.0”10ꢁ4
1.24
6.0”10ꢁ4
1.5
–
1.5
700
manifold.[43]
given in Scheme 6.
A
summary is
kenergy transfer [sꢁ1
]
>4.0”1010
1.48[a,b]
700
>4.0”1010
1.5[c,d]
700
tFLUOR fullerene (toluene) [ns]
triplet maxima [nm]
C60–oligo-PPV-exTTF: The
aforementioned energy transfer
(see Scheme 6) is nearly quanti-
520
650
[a] Fluorescence lifetime in THF: 1.45 ns; [b] Fluorescence lifetime in benzonitrile: 1.05 ns; [c] Fluorescence
lifetime in THF: 1.40 ns; [d] Fluorescence lifetime in benzonitrile: 0.95 ns.
4826
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Chem. Eur. J. 2005, 11, 4819 – 4834

Probing Molecular Wires
FULL PAPER
Scheme 6.
tative in all C60–oligo-PPVs and helps to concentrate the sin-
glet excited state energy at the fullerene end. Notably, the
contribution from an exothermic electron transfer is inap-
preciably small. This general pattern is not affected when
linking exTTF to the other end of the wire to give C60–
oligo-PPV–exTTF, thus signifying that the singlet excited
state energy trap is located at C60 (1.76 eV); we estimate the
singlet excited state energy of exTTF to be around 2.6 eV.
When exciting the oligo-PPV part in C60–oligo-PPV–exTTF
(in the 300–500 nm range), a rapid intramolecular transduc-
tion of energy, as evidenced by fluorescence quantum yields
of about 5.0”10ꢁ4, funnels the excited state energy to the
C60 core and generates 1*C60 with nearly 100% quantum
yields.[44,45] Examples are illustrated in Figure 4 and summar-
ized in Table 3.
Note that, in contrast to C60–oligo-PPV, the C60-centered
fluorescence in Figure 4 is barely visible. The lack of quanti-
tative C60 fluorescence suggests that exTTF enhances the
fluorescence deactivation (vide infra). Excitation of C60
leads to a similar picture, namely notably reduced quantum
yields.
To shed light on the nature of the product formed by this
intramolecular deactivation, complementary time-resolved
fluorescence and transient absorption measurements were
necessary (i.e., with picosecond through millisecond time
resolution) after 337 and/or 355 nm laser pulses.
Figure 4. Fluorescence spectra (shown as quantum yields) of 16 (mono-
mer, dotted line), 18 (trimer, full line), and 19 (pentamer, dashed line) in
THF at room temperature, with matching absorption at the 450 nm exci-
tation wavelength (OD450 =0.2).
Letꢁs first direct our attention to the fluorescence lifetime
measurements. In C60–oligo-PPV–exTTF, a notable shorten-
ing of the C60 fluorescence lifetime is seen (see Table 3),
which in THF reaches a factor of sixrelative to that seem
for the C60 reference and C60–oligo-PPV. Illustrations are
given in Figure 5 for 16 and 19.[46] Upon modifying the sol-
vent polarity from THF (e=7.6) and benzonitrile (e=24.8)
to DMF (e=36) a gradual intensification of the quenching
is discernible. We postulate that the underlying solvent de-
pendence is due to an intramolecular electron transfer be-
tween the exTTF donor and the photoexcited C60 to yield
C60Cꢁ–oligo-PPV–exTTFC+.
On the other hand, in transient absorption measurements,
detection of the two-step grow-in (at 18 ps) of the 880 nm
absorption affirms the successful C60 singlet excited state
formation in C60–oligo-PPV–exTTF (not shown). However,
instead of seeing the slow intersystem crossing dynamics, as
for the C60 reference and the C60–oligo-PPV, the singlet–sin-
glet absorption decays faster in the presence of exTTF
donors. The singlet excited state lifetimes, as determined
Table 3. Photophysical features of C60–oligo-PPV–exTTF systems
THF
Benzonitrile
DMF
Fluorescence Singlet
Radical-pair Electronic Fluorescence Singlet
Radical-pair Electronic Fluorescence Singlet
Radical-pair
[ns]
lifetime[a]
[ns]
lifetime[b] lifetime[c]
coupling[d] lifetime[a]
lifetime[b] lifetime[c]
coupling[d] lifetime[a]
lifetime[b] lifetime[c]
[ns]
[ns]
[cmꢁ1
]
[ns]
[ns]
[ns]
[cmꢁ1
]
[ns]
[ns]
16 0.26
0.32
0.28
0.33
0.35
0.42
295ꢀ15
5.3
6.1
6.9
5.8
0.16
0.16
0.17
0.18
0.28
0.18
0.2
0.2
0.21
0.25
430ꢀ20
6.2
6.1
5.9
5.5
!0.1
!0.1
0.09
0.11
0.16
17 0.27
18 0.27
19 0.3
20 0.4
321ꢀ15
365ꢀ15
465ꢀ20
499ꢀ25
0.1
650ꢀ30
411ꢀ20
557ꢀ25
0.13
0.13
3190ꢀ150
4350ꢀ200
6100ꢀ300
[a] Determined by monitoring the fullerene fluorescence decay at 720 nm in time-resolved fluorescence lifetime measurements; [b] Determined by moni-
toring the fullerene singlet–singlet absorption at 900 nm in time-resolved transient absorption measurements; [c] Determined by monitoring both fea-
tures of the radical ion pair state, that is, the 660 nm absorption maximum of the one-electron oxidized donor (exTTF) and the 1000 nm absorption maxi-
mum of the one-electron reduced acceptor (C60) in time-resolved transient absorption measurements; [d] Determined from the following relation for a
ꢀ
ꢁ
ꢂ
ꢃ
4p3
h2lkBT
ꢁDGꢀ
nonadiabatic electron transfer: ket =
1/2V2exp
, where h =Planck constant, kB =Boltzmann constant (0.025 eV at 298 K), T =absolute
kBT
2
ðDGCS þ lÞ
4l
temperature (298 K), l=reorganization energy (1 eV), and DGꢀ =Gibbs activation energy, determined as: DGCꢀS
=
.
Chem. Eur. J. 2005, 11, 4819 – 4834
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ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4827

N. Martín, D. M. Guldi et al.
Figure 6. Differential absorption spectrum (visible and near-infrared) ob-
tained upon nanosecond flash photolysis (355 nm) of approximately 1.0”
10ꢁ5 m solutions of C60–oligo-PPV–exTTF (17) in nitrogen-saturated THF
with a time delay of 200 ns at room temperature (upper part) and of ap-
proximately 1.0”10ꢁ5 m solutions of C60–oligo-PPV–exTTF (20) in nitro-
gen-saturated THF with a time delay of 200 ns at room temperature
(lower part).
Figure 5. Fluorescence lifetime decays of 16 (monomer; top) and of 19
(pentamer; bottom) in THF (full lines), recorded at 720 nm, together
with laser scatterer (dashed lines).
from an average of first-order fits of the time-absorption
profiles at various wavelengths (850–950 nm), are listed in
Table 3. An important aspect is that the singlet excited state
lifetimes match quantitatively the values derived from the
fluorescence experiments. Spectroscopically, the transient
absorption changes, taken after the completion of the decay,
bear no resemblance to the C60 triplet excited state (vide
infra). Again, varying the solvent polarity from THF to
DMF leads to an acceleration of the singlet deactivation.
This supports our earlier hypothesis that an intramolecular
served that would suggest involvement of a transient oxi-
dized C60Cꢁ–oligo-PPVC+–exTTF oligomer.
The spectral fingerprints of the C60 p-radical anion
(1000 nm; e~10000 mꢁ1 cmꢁ1) and that of the exTTF p-radi-
cal cation (665 nm; e~25000 mꢁ1 cmꢁ1) are useful probes to
examine the charge-recombination dynamics. Both spectral
attributes are persistent on the picosecond timescale and
only start to decay slowly in the nanosecond regime. Time-
absorption profiles, as depicted in Figure 7, illustrate that
the C60Cꢁ–oligo-PPV–exTTFC+ species decay in a single step.
The charge recombination dynamics within these systems
were determined accurately by fitting the decays of both fin-
gerprints to a mono-exponential rate law.[47] To ensure a reli-
able interpretation of the data, the only fits admitted were
those whose quality factor (reduced chi-square statistics, c2)
was 0.98 or better.
+
electron transfer, yielding C60Cꢁ–oligo-PPV–exTTFC , gov-
erns the C60 singlet excited state deactivation.
Spectroscopic evidence for the radical-pair formation was
found from the features developing in parallel with the dis-
appearance of the C60 singlet–singlet absorption (see
Figure 6). In the visible region, the observed maximum at
660 nm corresponds to the one-electron-oxidized p-radical
+
cation of exTTF (exTTFC ), while in the near-infrared
+
region the 1000 nm maximum resembles the signature of the
one-electron-reduced form of C60 (C60Cꢁ). Particularly strik-
ing is the fact that in the trimer-, pentamer-, and heptamer-
based systems charge-separation occurs within a single step
over remarkably long distances—no intermediate was ob-
The C60Cꢁ–oligo-PPV–exTTFC radical pair in the mono-
mer-based assembly is subject to a notable stabilization rela-
tive to the donor–acceptor system in which the anthracenoid
part of the exTTF moiety is attached directly to the pyrroli-
dine functionality (C60-exTTF). In benzonitrile, for instance,
4828
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Chem. Eur. J. 2005, 11, 4819 – 4834

Probing Molecular Wires
FULL PAPER
Figure 8. Dependence of electron-transfer rate constants (ln kCR) for C60–
oligo-PPV–exTTF in nitrogen-saturated THF (solid line) and benzonitrile
(dashed line) at room temperature on the center-to-center distances
(Rcc). The lines represent the best fits (b=0.01ꢀ0.005 Šꢁ1, V=2.3 cmꢁ1
in THF).
(2.3 cmꢁ1 in THF; cf. the values listed in Table 3). Most im-
+
portantly, the coupling in C60Cꢁ–oligo-PPV–exTTFC (19),
with values of 5.8 and 5.5 cmꢁ1 in benzonitrile and THF, re-
spectively, is unusually strong considering that a distance of
40 Š separates the electron donor from the electron accep-
tor. For comparison, the V-value for a molecular tetrad that
spans over a similar distance is 1.6”10ꢁ4 cmꢁ1. The wirelike
behavior in our C60–oligo-PPV–exTTF can be best under-
stood in terms of the p-conjugation effective between the
anthracenoid part of the donor, the oligo-PPV bridge, and
the pyrrolidine ring of the C60 derivative.[48]
To analyze the charge-recombination mechanism we
probed the radical-pair lifetimes between 272 and 350 K,
which are summarized in Figure 9. The Arrhenius plots for
the monomer, dimer (not shown), and trimer can be sepa-
rated into two distinct sections: the low-temperature regime
(<320 K) and the high-temperature regime (>320 K). The
weak temperature-dependence in the 272 to 320 K range
suggests that a stepwise charge-recombination via a transi-
Figure 7. Time-absorption profiles at 1000 nm monitoring the C60Cꢁ decay
dynamics in 16 (top) and 20 (bottom) obtained upon nanosecond flash
photolysis (355 nm) of approximately 1.0”10ꢁ5 m deoxygenated benzoni-
trile solutions.
a lifetime of 204 ns has been found for this closely spaced
system (RCC =9.7 Š), whereas the monomer-based assembly
(C60–oligo-PPV–exTTF, 16), with RCC =16.2 Š, has a life-
time of 430 ns under the same experimental conditions. This
reflects the larger separation and diminished electronic cou-
pling. The use of a dimer-, trimer-, or pentamer-based oligo-
PPV to integrate C60 and exTTF led to only marginal effects
on the stability of the radical pair. To illustrate this phenom-
enon, lifetimes that range between 465 and 557 ns should be
considered. However, radical-pair lifetimes about ten times
+
longer were found for C60Cꢁ–oligo-PPV–exTTFC (20), both
in THF and benzonitrile.
Plotting the electron-transfer behavior as a function of
donor–acceptor separation, except for the heptameric as-
sembly, led to linear dependencies with THF and benzoni-
trile as solvents. From these plots, as shown in Figure 8, we
determined the attenuation factors (b) for our assemblies as
0.01ꢀ0.005 Šꢁ1, which are exceptionally small. Interestingly,
fitting the charge separation the same way led to slightly
lower b values (THF: 0.008ꢀ0.005 Šꢁ1). We also used this
method and the Marcus formalism for nonadiabatic electron
transfer to assess the electronic coupling matrixelement
(V). Both approaches afforded nearly identical values
Figure 9. Arrhenius analyses of the temperature-dependent electron-
transfer rate constants (kCR) for 16, 18, and 19 in deoxygenated benzoni-
trile.
Chem. Eur. J. 2005, 11, 4819 – 4834
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4829

N. Martín, D. M. Guldi et al.
ent C60Cꢁ–oligo-PPVC+–exTTF species can be ruled out, leav-
ing electron tunneling via superexchange as the operative
mode. This picture is in sound agreement with the thermo-
dynamic barrier that must be overcome to form C60Cꢁ–oligo-
which have nearly isoenergetic levels, diminishes the energy
penalty for initial electron injection from the wire to *C60.
1
Paraconjugation, which extends into the exTTF donor, and
the exothermic nature of the charge-shift reaction are then
responsible for extremely fast charge-shift dynamics to form
+
PPVC –exTTF. At higher temperatures (>320 K) this pic-
+
ture changes and the charge recombination is accelerated.
The strong temperature-dependence observed suggests a
thermally activated charge recombination. The activation
barriers (Ea), derived from the slopes (16: 0.8 eV; 18:
0.6 eV; 19: 0.5 eV), confirm the HOMO(C60)–HOMO(wire)
energy gap. Interestingly, C60Cꢁ–oligo-PPV–exTTFC+ (19) re-
veals the opposite trend: the charge recombination slows
down substantially in the high-temperature region. A tem-
perature-induced decoupling, for example, by effecting an
orbital alignment in the oligo-PPV bridge, is thought to be
responsible for the slow-down of the charge recombination.
Finally, comparing solvents of different polarity, namely
THF, benzonitrile, and DMF, stabilizing effects for all C60Cꢁ–
exTTFC+ radical pairs were seen for the more-polar sol-
vents.[20–22] Since better solvation of the radicals, which is
particularly important in polar media, lowers the energy of
the charge-separated state, this trend suggests charge-recom-
bination dynamics that are in the normal region of the
Marcus parabola. We believe that two aspects are responsi-
ble for the overall observation. Firstly, due to the low oxida-
tion potential of the donor the driving forces are kept quite
low, relative, for example, to those assumed for metallopor-
phyrin-based analogues. Secondly, the structural changes of
the donor, which accompany the oxidation, attenuate the re-
organization energy of the donor–acceptor system.
C60Cꢁ–oligo-PPV–exTTFC .
In principle, two different transfer processes may contrib-
ute to the charge recombination. Figure 10 shows that large
LUMO(C60)–LUMO(wire) gaps of at least 1.1 eV result ex-
clusively in an electron tunneling mechanism. Charge trans-
fer from the HOMO at C60 (i.e., C60Cꢁ) to the HOMO at
+
exTTF (i.e., exTTFC ), on the other hand, may proceed by
superexchange or hopping. In fact, the temperature depen-
dence helps to recognize the interplay between both proc-
esses. Once the hopping mechanism dominates, especially in
18 and 19, and the hole migrates first to the wire, good
HOMO(C60)–HOMO(wire) energy matching and strong
electronic coupling lead to a kinetically fast and spectro-
scopically unresolvable recovery of the ground state.
Conclusion
In summary, we have carried out the rational design of
linear donor–acceptor arrays by integrating fully conjugated
oligomers with a well-defined length and constitution. The
novel compounds were prepared by a convergent synthetic
strategy involving iterative olefination Wittig–Horner reac-
tions and a final Prato reaction to introduce the C60 unit
into the final molecular arrays (16–20).
A superexchange mechanism leading directly to C60Cꢁ–
oligo-PPV–exTTFC+ (see Figure 10) is imposed in 16 by the
large HOMO(C60)–HOMO(wire) gap of 0.7 eV. In 17–20,
however, good electronic mixing of these two HOMOs,
The electrochemical study reveals an amphoteric redox
behavior and a lack of significant electronic communication
between the donor (exTTF) and the acceptor (C60) moieties
through the p-conjugated oligomer in the ground state; this
was also confirmed by the electronic spectra. However, we
have succeeded in demonstrating photoinduced electron
transfer over distances of up to 50 Š with formation of the
respective radical pairs (C60Cꢁ–oligo-PPV–exTTFC+). The
charge-recombination dynamics show the presence of highly
stabilized charge-separated states with lifetimes in the range
between 465 ns and 557 ns in benzonitrile, which indicates a
very low influence of the oligomer length on the electron
rate. These findings, as well as the very low value deter-
mined for the attenuation factor (b=0.01ꢀ0.005 Šꢁ1), clear-
ly indicate a nanowire behavior. A longer radical-pair life-
time (10 times) was observed for the heptamer-containing
array C60Cꢁ–oligo-PPV–exTTFC+, which has been accounted
for by the loss of planarity of the oligomer moiety, with cal-
culated (PM3) dihedral angles between the two terminal
benzenes of 388. The strong electron coupling between the
donor and acceptor moieties through the p-conjugated
oligomer, with coupling constants of about 5.5 cmꢁ1, is par-
ticularly important for the observed wire-like behavior.
These results open the way to use the current examples as
integrated components in the construction of optoelectronic
devices and nanotechnology.
Figure 10. HOMO (solid line) and LUMO (traced line) levels of C60,
oligomers, and exTTF (determination was carried out as reported in ref-
erence [5]).
4830
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Chem. Eur. J. 2005, 11, 4819 – 4834

Probing Molecular Wires
FULL PAPER
13C NMR (CDCl3, 75 MHz, 258C): d=150.92, 150.77, 144.28, 144.15,
135.09, 134.32, 130.21, 129.49, 128.41, 127.27, 125.12, 115.93, 110.91, 65.40,
69.13, 68.18, 31.58, 29.68, 29.43, 25.88, 22.61, 14.00 ppm; FTIR (KBr): n˜ =
2848, 1604, 1512, 1450, 1225, 1036, 870, 812 cmꢁ1; UV/Vis (CH2Cl2): lmax
(e)=297 (19000), 350 nm (18200 molꢁ1 cm3 dmꢁ1); MS (EI): m/z (%): 604
(100) [M+], 559 (35), 445 (15), 362 (13), 251 (18).
Experimental Section
Picosecond laser flash photolysis experiments were carried out with
355 nm laser pulses from a mode-locked, Q-switched Quantel YG-501
DP Nd:YAG laser system (pulse width 18 ps, 2–3 mJ per pulse). Nanosec-
ond laser studies were performed with laser pulses from a Molectron
UV-400 nitrogen laser system (337.1 nm, 8 ns pulse width, 1 mJ per
pulse) or from a Qunta-Ray CDR Nd: YAG system (355 nm, 20 ns pulse
width). The photomultiplier output was digitized with a Tektronix7912
AD programmable digitizer. The quantum yields of the triplet excited
states (FTRIPLET) were determined by the triplet–triplet energy transfer
method using b-carotene as an energy acceptor. For all photophysical ex-
periments an error of 10% must be considered.
Compound 8: 2,5-Bis[(1E)-2’-(4-formylphenyl)vinyl]-1,4-dihexyloxyben-
zene (3; 100 mg, 0.19 mmol) was treated with 7 (230 mg, 0.38 mmol), ac-
cording to the general procedure, to afford 191 mg (76%) of 8 as an
orange solid (silica gel; hexane/dichloromethane, 7:3). 1H NMR (CDCl3,
200 MHz, 258C): d=10.00 (s, 2H; -CHO), 7.88 (d, 3JH,H =8.3 Hz, 4H),
3
7.67 (d, 3JH,H =8.3 Hz, 4H), 7.61 (s, 2H), 7.54 (s, 8H), 7.52 (d, JH,H
=
16.3 Hz, 4H), 7.18 (d, 3JH,H =16.3 Hz, 4H), 7.17 (d, 3JH,H =16.3 Hz, 2H),
7.15 (d, 3JH,H =16.3 Hz, 2H), 7.14 (s, 4H), 4.08 (m, 12H), 1.90 (q, J=
6.6 Hz 12H), 1.57–1.26 (m, 36H), 0.95 ppm (m, 18H); 13C NMR (CDCl3,
75 MHz, 258C): d=191.59, 151.53, 151.19, 151.08, 144.21, 137.38, 137.01,
135.09, 130.23, 129.03, 128.07, 127.28, 12.14, 127.00, 126.90, 126.82, 125.89,
123.37, 123.04, 110.90, 110.58, 110.43, 69.63, 69.52, 31.64, 29.47, 25.98,
22.66, 14.05 ppm; FTIR (KBr): n˜ =2930, 2906, 2858, 1697 (CHO), 1624,
1595, 1491, 1423, 1384, 1207,1035, 961 cmꢁ1; UV/Vis (CH2Cl2): lmax (e)=
246 (67600), 340 (69200), 461 nm (269000 molꢁ1 cm3 dmꢁ1); MS(ESI): m/
z (%): 1370 (100) [M++Na].
Fluorescence lifetimes were measured with a laser strobe fluorescence
lifetime spectrometer (Photon Technology International) with 337 nm
laser pulses from a nitrogen laser fiber-coupled to a lens-based T-formal
sample compartment equipped with a stroboscopic detector. Details of
the laser strobe systems are described on the manufacturerꢁs web site
(http://www.pti-nj.com).
Emission spectra were recorded with an SLM 8100 Spectrofluorometer.
The experiments were performed at room temperature. When measuring
the fullerene emission in the 700 nm region, a 570 nm long-pass filter in
the emission path was used in order to eliminate the interference from
the solvent and stray light for recording the fullerene fluorescence. Each
spectrum is an average of at least five individual scans and the appropri-
ate corrections were applied. The fluorescence quantum yields were de-
termined with respect to a 9,10-diphenylanthracene reference (Aldrich,
99+ %) (F=1) and are an average value of three fluorophore concen-
trations with ODs at an excitation wavelength ranging from 0.1 to 0.5.
General procedure for the preparation of exTTF-OPPV dyads 10–13 and
15: Triphenylphosphonium salt 9 (0.22 mmol) and potassium tert-butox-
ide (54 mg, 0.48 mmol) were dissolved in toluene and heated to reflux.
After 1 h a solution of the corresponding aldehyde (2, 3, 6, or 8; 0.33–
0.44 mmol) in toluene was added with a syringe in one portion and the
reaction was kept under refluxfor 12 h. After the reaction reached room
temperature, methanol was added (5 mL), the solvent was removed
under vacuum, and the resulting mixture was treated with 2.0n HCl,
washed with water, and extracted with dichloromethane. The organic
layer was dried with magnesium sulfate and the solvent was removed
under vacuum. The resulting solid was purified by silica gel chromatogra-
phy using hexane/dichloromethane as eluent to afford a dark-red solid.
All solvents were dried and distilled according to standard procedures.
Reagents were used as purchased. All air-sensitive reactions were carried
out under an argon atmosphere. Flash chromatography was performed
on silica gel 60 Š (Merck, 40–60 mm). TLC was performed on silica gel
60 F254 coated aluminum sheets (Merck) with detection by UV at 254 nm.
Melting points were determined on a Gallenkamp apparatus. NMR spec-
tra were recorded on Bruker AC-200 (1H: 200 MHz; 13C: 50 MHz),
Bruker AC-300 or Varian XL-300 (1H: 300 MHz; 13C: 75 MHz), or
Bruker DRX-500 or AMX-500 (1H: 500 MHz; 13C: 125 MHz) spectrome-
ters at 298 K using partially deuterated solvents as internal standards.
Coupling constants (J) are denoted in hertz and chemical shifts (d) in
ppm. FT-IR spectra were recorded on a Nicolet-Magna-IR 5550 spec-
trometer. Electrospray ionization (ESI) mass spectra were recorded on a
HP1100mSD spectrometer.
1
Compound 10: 61% yield; m.p.: 192–1948C; H NMR (CDCl3, 200 MHz,
258C): d=9.93 (s, 1H), 7.87 (d, 3JH,H =7 Hz, 3H), 7.70 (t, 3JH,H =7 Hz,
4H), 7.47 (m, 1H), 7.33 (t, 3JH,H =7 Hz, 1H), 7.19 (t, 3JH,H =7 Hz, 4H),
6.33 ppm (s, 4H); 13C NMR (CDCl3, 50 MHz, 258C): d=191.5, 144.7,
135.9, 135.6, 135.3, 132.9, 131.9, 130.2, 130.1, 1129.9, 129.8, 127.2, 126.9,
126.0, 125.4, 124.9, 123.2, 117.3, 116.9 ppm; FTIR (KBr): n˜ =3421, 2924,
2852, 1695, 1541, 1508, 1195, 1165, 964 cmꢁ1; UV/Vis (CH2Cl2): lmax (e)=
246
(676000),
337
(645600),
387
(417000),
454 nm
(251200 molꢁ1 cm3 dmꢁ1); MS(EI): m/z (%): 510 (100) [M+], 306 (4), 94
(18), 69 (32).
General procedure for Wittig–Horner olefination: Potassium tert-butox-
ide was added portionwise to a solution of the corresponding phospho-
nate and aldehyde in dry THF under argon. The mixture was stirred at
08C for 90 min and then methanol (10 mL) was added. The mixture was
extracted twice with dichloromethane, the combined organic layers were
dried over magnesium sulfate, and the solvent was removed under
vacuum to yield a residue which was purified by chromatography as de-
scribed in each case.
Compound 11: 32% yield (37% based on recovered starting material);
m.p: 182–1848C; 1H NMR (CDCl3, 200 MHz, 258C): d=9.92 (s, 1H;
-CHO), 7.80 (t, 3JH,H =4 Hz, 4H), 7.60 (m, 5H), 7.55 (d, 3JH,H =7 Hz,
2H), 7.47 (s, 4H), 7.38 (t, 3JH,H =7 Hz, 2H), 7.23 (m, 2H), 7.07 (m, 4H),
6.24 (s, 4H), 4.06 (m, 4H), 1.88 (m, 4H; -CH2-), 1.59 (s, 2H;) 1.40 (m,
4H), 1.25 (s, 4H), 0.88 ppm (m, 6H; -CH3); 13C NMR (CDCl3, 50 MHz,
258C): d=191.6, 151.5, 151.1, 144.2, 137.2, 136.7, 136.3, 135.8, 135.3,
135.1, 134.8, 130.2, 128.3, 128.0, 126.9, 126.8, 126.0, 125.9, 125.0, 117.3,
117.2, 114.0, 110.5, 110.4, 69.5, 53.4, 31.6, 29.7, 26.0, 22.6, 14.0 ppm; FTIR
(KBr): n˜ =3448, 2924, 2852, 1691, 1595, 1508, 1211, 1029, 956 cmꢁ1; UV/
Where deprotection of an aldehyde functionality was required, the crude
was dissolved in chloroform, a 1n solution of HCl was added, and the
mixture stirred overnight.
Vis
(CH2Cl2):
lmax
(e)=242
(9100),
354
(6300),
434 nm
(13800 molꢁ1 cm3 dmꢁ1); MS (ESI): m/z (%): 914 (100) [M+], 856 (17),
744 (80), 685 (80), 643 (40). elemental analysis calcd (%) for C57H54O3S4:
C 74.83, H 5.95; found: C 75.21, H 6.29.
Compound 7: Potassium tert-butoxide was added portionwise (180 mg,
1.6 mmol) to a stirred solution of compound 1 (2.0 g, 3.8 mmol) in dry
THF (120 mL). After 20 min
a solution of compound 2 (265 mg,
1.3 mmol) in dry THF (50 mL) was added dropwise. After 2 h, workup
was carried out according to the general procedure. The residue was puri-
fied by chromatography on silica gel (hexane/dichloromethane 2:3; di-
chloromethane; dichloromethane/methanol 100:1) to yield compound 7
Compound 12: 27% yield (61% based on recovered starting material);
m.p.: 276–2778C (decomp); 1H NMR (CDCl3, 200 MHz, 258C): d=10.00
3
(s, 1H; -CHO), 7.87 (t, 3JH,H =8 Hz, 2H), 7.84 (s, 1H), 7.67 (t, JH,H
=
3
7 Hz, 5H), 7.53 (m, 8H), 7.49 (m, 4H), 7.41 (d, JH,H =8 Hz, 2H), 7.31 (d,
3JH,H =8 Hz, 2H), 7.25 (m, 3H), 7.13 (m, 8H), 6.33 (s, 4H), 4.07 (m, 4H),
1.90 (m, 4H; -CH2-), 1.59–1.25 (m, 12H), 0.89 ppm (m, 6H; -CH3);
13C NMR (CDCl3, 50 MHz, 258C): d=190.2, 150.1, 142.5, 137.4, 136.4,
134.9, 134.6, 134.5, 130.9, 129.3, 128.9, 127.4, 127.2, 126.4, 125.9, 125.8,
125.0, 124.7, 124.0, 123.1, 122.4, 121.2, 116.3, 109.4, 68.5, 31.1, 30.8, 28.9,
28.7, 28.6, 25.2, 21.9, 13.3 ppm; FTIR (KBr): n˜ =2923, 2852, 2164, 1685,
(313 mg, 41%) as a yellow oil. 1H NMR (CDCl3, 200 MHz, 258C): d=
3
7.86 (d, 3JH,H =8.1 Hz, 2H), 7.64 (d, 3JH,H =8.1 Hz, 2H), 7.60 (d, JH,H
=
3
16.1 Hz, 1H), 7.14 (d, JH,H =16.1 Hz, 1H), 7.08 (s, 1H), 6.94 (s, 1H), 5.30
(s, 1H; -CH(OEt)2), 4.01 (t, 3JH,H =6.3 Hz, 4H), 3.74 (q, 3JH,H =6.8 Hz,
4H), 3.69 (d, 3JH,P =11.0 Hz, 6H), 3.27 (d, 3JH,P =22.0 Hz, 2H), 1.82 (m,
4H), 1.54–1.28 (m, 12H), 1.24 (t, 3JH,H =6.8 Hz, 6H), 0.91 ppm (m, 6H);
Chem. Eur. J. 2005, 11, 4819 – 4834
www.chemeurj.org
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4831

N. Martín, D. M. Guldi et al.
1570, 1205, 758 cmꢁ1
;
UV/Vis (CH2Cl2): lmax (e)=244 (44700), 367
Compound 17: Eluent: hexane/toluene (1:1); 47% yield; 1H NMR
(42600), 440 nm (89100 molꢁ1 cm3 dmꢁ1); MS (ESI): m/z (%): 1118 (100)
[M+], 1033 (18); elemental analysis calcd (%) for C73H66O3S4: C 78.31, H
5.94; found: C 77.89, H 6.37.
(CDCl3/CS2, 500 MHz, 258C): d=8.33–8.22 (m, 4H), 7.87–7.63 (m, 6H),
3
7.53 (d, J=8.3 Hz, 2H), 7.43 (d, 3JH,H =16.4 Hz, 1H), 7.22 (d, JH,H
=
3
16.4 Hz, 1H), 7.08 (d, JH,H =16.6 Hz, 2H), 7.04 (s, 1H), 6.76 (s, 4H), 5.10
(d, 3JH,H =9.2 Hz, 1H), 5.05 (s, 1H), 4.12 (d, 3JH,H =9.2 Hz, 1H), 4.04 (m,
4H), 3.25 (m, 1H), 2.56 (m, 1H), 1.88 (m, 6H), 1.55–1.24 (m, 22H),
0.92 ppm (m, 9H); 13C NMR (CDCl3/CS2, 125 MHz, 258C): d=156.26,
153.97, 153.30, 151.30, 150.74, 147.08, 146.60, 146.26, 146.03, 145.72,
145.57, 145.30, 145.03, 144.48, 144.18, 143.78, 142.96, 142.80, 142.38,
142.09, 141.93, 141.81, 141.49, 141.35, 140.00, 139.74, 139.37, 137.74,
136.67, 136.51, 136.39, 135.64, 135.53, 133.80, 133.67, 133.57, 133.39,
131.61, 130.83, 129.56, 128.69, 127.74, 126.99, 126.62, 125.43, 124.86,
123.48, 118.21, 110.53, 109.95, 82.28, 69.06, 68.69, 66.72, 32.04, 31.70,
29.81, 29.49, 28.50, 27.66, 26.02, 22.91, 22.84, 14.28, 14.16 ppm; FTIR
(KBr): n˜ =2921, 2853, 1632, 1505, 1460, 1107, 527 cmꢁ1. UV/Vis (CH2Cl2)
lmax (e)=56 (309000), 328 (131800), 397 (shoulder, 69200), 431 (53700),
451 nm (49000 molꢁ1 cm3 dmꢁ1); MS (ESI): m/z (%): 1659 (100) [M+
+H], 1573 (52), 1432 (17).
Compound 13: 25% yield (34% based on recovered starting material);
1H NMR (CDCl3, 300 MHz, 258C): d=10.00 (s, 1H), 7.89–7.85 (m, 3H),
7.73–7.61 (m, 3H), 7.54–7.45 (m, 21H), 7.34–7.29 (m, 2H), 7.22–7.11 (m,
3
14H), 6.33 (s, 4H), 4.08 (t, JH,H =6.3 Hz, 12H), 1.90 (q, J=6.6 Hz, 12H),
1.57–1.25 (m, 36H), 0.95 ppm (m, 18H); 13C NMR (CDCl3, 75 MHz,
258C): d=191.66, 151.49, 151.14, 151.04, 144.20, 137.37, 137.17, 136.96,
136.52, 135.81, 135.78, 135.67, 135.35, 135.29, 135.25, 135.20, 135.16,
135.04, 134.72, 130.91, 130.25, 129.01, 128.83, 128.39, 128.35, 128.14,
128.02, 127.24, 127.11, 127.00, 126.96, 126.83, 125.99, 125.82, 125.30,
125.01, 124.95, 124.28, 123.34, 123.18, 122.97, 122.81, 117.31, 117.25,
117.11, 110.81, 110.49, 110.33, 69.57, 69.46, 31.92, 31.65, 29.70, 29.48,
29.36, 25.98, 22.67, 14.13, 14.07 ppm; FTIR (KBr): n˜ =2954, 2923, 2853,
1782, 1596, 1464, 1377, 1262, 1207, 1073, 961, 721 cmꢁ1; UV/Vis (CH2Cl2):
lmax (e)=48 (29500), 351 (23400), 459 nm (64500 molꢁ1 cm3 dmꢁ1); MS
(ESI): m/z (%): 1723 (100) [M++H].
Compound 18: Eluent: cyclohexane/toluene (3:7); 19% yield; m.p.:
>3008C; 1H NMR (CDCl3/CS2, 500 MHz, 258C): d=8.29 (m, 2H), 7.89
(m, 2H), 7.80 (t, 3JH,H =5 Hz, 3H), 7.62 (m, 1H), 7.53 (m, 3H), 7.47 (m,
2H), 7.44 (t, 3JH,H =5 Hz, 2H), 7.41 (s, 1H), 7.35 (s, 1H), 7.23 (m, 2H),
7.05 (d, 3JH,H =16.7 Hz, 2H), 7.03 (s, 1H), 7.01 (d, 3JH,H =16.7 Hz, 1H),
6.31 (s, 4H), 5.01 (d, 3JH,H =9.5 Hz, 1H; CH2-N-), 4.97 (s, 1H; -CH-N-),
4.30 (d, 3JH,H =9.5 Hz, 1H; CH2-N-),4.04 (t, 3JH,H =6 Hz, 4H), 2.87 (s,
3H; N-CH3), 1.89 (m, 4H), 1.58 (m, 4H), 1.57–1.27 (m, 8H), 0.97 ppm
(m, 6H); 13C NMR (CDCl3/CS2, 125 MHz, 258C): d=156.04, 153.85,
153.34, 153.10, 151.06, 147.31, 146.73, 146.36, 146.25, 146.18, 145.97,
145.66, 145.59, 145.41, 145.28, 144.74, 144.70, 144.42, 143.20, 143.05,
142.73, 142.63, 142.28, 142.20, 142.09, 141.97, 141.73, 141.61, 140.27,
140.03, 139.68, 138.63, 138.37, 136.98, 136.70, 135.87, 135.79, 135.43,
133.93, 133.80, 133.73, 132.74, 132.07, 131.57, 131.35, 129.63, 129.37,
128.05, 127.60, 127.26, 127.08, 127.02, 126.76, 126.63, 126.54, 126.39,
126.02, 124.85, 124.26, 124.18, 124.13, 118.43, 118.27, 110.23, 83.10, 76.85,
69.66, 68.89, 68.58, 39.75, 32.10, 29.93, 26.42, 23.28, 14.57 ppm; FTIR
Compound 15: Potassium tert-butoxide (240 mg, 2.10 mmol) was added
portionwise to a solution of 14 (133 mg, 0.25 mmol) and phosphonate 7
(88 mg, 0.25 mmol) in dry THF (35 mL) under argon. The mixture was
stirred at room temperature for 16 h and then methanol (10 mL) was
added. The solvent was removed under reduced pressure, the resulting
mixture was dissolved in dichloromethane (50 mL), and 1m HCl (50 mL)
was added. The mixture was stirred at room temperature for 16 h and
then, after separation, the organic layers were dried over magnesium sul-
fate and the solvent was removed under vacuum to yield a solid residue,
which was purified by chromatography (silica gel, hexane/dichlorome-
thane 1/1) to yield 115 mg (66%) of 15 as a red solid. 1H NMR (CDCl3,
300 MHz, 258C): d=10.00 (s, 1H), 7.87 (d, 3JH,H =8 Hz, 3H), 7.73–7.61
(m, 6H), 7.55 (d, 3JH,H =16.6 Hz, 1H), 7.50 (d, 3JH,H =16.6 Hz, 1H), 7.30
(m, 2H), 7.27 (d, JH,H =16.1 Hz, 2H), 7.15 (d, JH,H =4.6 Hz, 2H), 6.32 (s,
4H), 4.08 (q, J=6.1 Hz, 4H), 1.90 (q, J=6.3 Hz, 4H), 1.56–1.26 (m,
12H), 0.95 ppm (m, 6H); 13C NMR (CDCl3, 75 MHz): d=191.59, 151.55,
151.12, 144.23, 135.80, 135.64, 135.59, 135.31, 135.28, 135.08, 134.69,
130.23, 129.05, 128.09, 127.24, 127.18, 126.82, 125.97, 125.89, 125.28,
124.97, 124.35, 123.40, 122.92, 122.26, 117.30, 117.24, 117.04, 110.92,
110.48, 69.63, 69.55, 31.71, 31.62, 29.54, 29.44, 26.02, 25.97, 22.69, 22.65,
14.11, 14.03 ppm; FTIR (KBr): n˜ =2954, 2924, 2853, 1630, 1593, 1493,
1421, 1208, 1163, 964, 801, 649 cmꢁ1; UV/Vis (CH2Cl2) lmax =229, 339,
429 nm; MS (ESI): m/z (%): 812 (100) [M+], 704 (15).
3
3
(KBr): n˜ =2923, 2852, 1633, 1556, 1421, 1033, 876, 796, 526, 468 cmꢁ1
;
UV/Vis (CH2Cl2): lmax (e)=56 (107100), 327 (46800), 413 nm
(38900 molꢁ1 cm3 dmꢁ1); MS (ESI): m/z (%): 1661 (95) [M+], 1619 (100),
1577 (62), 1332 (37), 806 (31).
Compound 19: Eluent: toluene/ethyl acetate (9:1); 27% yield; m.p.: 216–
1
2198C; H NMR (CDCl3/CS2, 500 MHz, 258C): d=8.42 (m, 1H), 8.26 (m,
2H), 7.91 (m, 2H), 7.80 (m, 1H), 7.66 (t, 3JH,H =7 Hz, 2H), 7.55 (d,
3JH,H =7 Hz, 4H), 7.49 (m, 9H), 7.38 (m, 3H), 7.27 (m, 4H), 7.10 (m,
7H), 6.32 (s, 4H), 5.35 (s, 1H; CH2-N-), 5.30 (s, 1H; CH-N-), 4.41 (s, 1H;
CH-N-), 4.04 (t, 3JH,H =6 Hz, 4H), 3.83 (d, 3JH,H =5 Hz, 2H), 3.79 (d,
General procedure for the preparation of exTTF–oPPV–C60 triads 16–
20: The corresponding aldehyde (6, 8, 10, 12, and 16; 0.05 mmol),
[60]fullerene (38 mg, 0.05 mmol), and the respective amino acid [sarco-
sine, N-(3,6,9-trioxadecyl)glycine, or N-octylglycine; 0.15–0.25 mmol]
were dissolved in toluene or chlorobenzene (30 mL) and the mixture was
refluxed for 24 h. After this time, the reaction was allowed to reach room
temperature, and then the solvent was partially vacuum evaporated and
then poured onto a silica-gel column. The black solid obtained after chro-
matography was further purified by repeated centrifugation in methanol
and diethyl ether to yield the corresponding triads as black solids.
3
3
3JH,H =5 Hz, 2H), 3.73 (t, JH,H =5 Hz, 4H), 3.57 (t, JH,H =5 Hz, 4H), 3.37
(s, 3H; N-CH3), 1.89 (m, 4H), 1.57 (m, 4H), 1.41–1.26 (m, 8H), 0.89 ppm
(m, 6H); 13C NMR (CDCl3/CS2, 125 MHz, 258C): d=150.16, 146.37,
145.56, 145.37, 145.21, 144.99, 144.88, 144.63, 144.37, 144.31, 143.79,
143.67, 143.41, 142.21, 142.05, 141.67, 141.25, 141.14, 141.00, 140.70,
140.57, 139.18, 138.98, 138.65, 137.12, 137.02, 136.65, 136.47, 136.13,
135.52, 135.28, 135.12, 134.75, 134.62, 133.42, 132.94, 130.87, 130.71,
130.47, 129.83, 129.64, 129.83, 129.10, 128.76, 128.50, 128.24, 128.06,
127.84, 127.30, 127.08, 127.03, 126.86, 126.58, 126.39, 126.29, 125.97,
125.56, 125.05, 124.01, 123.47, 123.17, 122.60, 117.24, 116.76, 116.36,
109.43, 82.28, 71.98, 70.62, 69.34, 58.94, 52.45, 30.87, 28.93, 28.70, 25.19,
21.94, 13.27 ppm; FTIR (KBr): n˜ =3434, 2921, 2852, 1631, 1461, 1419,
1178, 1106, 957, 525 cmꢁ1; UV/Vis (CH2Cl2): lmax (e)=55 (19500), 311
(shoulder, 91200), 333 (95500), 435 nm (155000 molꢁ1 cm3 dmꢁ1); MS
(ESI): m/z (%): 1998 (36) [M+], 1913 (100), 1827 (85), 1738 (35), 1597
(27).
Compound 16: Eluent: toluene/ethyl acetate (9:1); 17% yield; m.p.: >
3008C; 1H NMR (CDCl3, 500 MHz, 258C): d=7.83 (s, 2H), 7.70 (m,
3H), 7.59 (d, 3JH,H =5 Hz, 2H), 7.38 (d, 3JH,H =5 Hz, 1H), 7.28 (m, 2H),
7.17 (s, 1H), 7.16 (d, 3JH,H =16.3 Hz, 1H), 7.14 (d, 3JH,H =16.3 Hz, 1H),
6.29 (s, 4H), 5.35 (s, 1H; CH2-N-), 5.30 (s, 1H), 3.99 (s, 1H), 3.82 (d,
3JH,H =4 Hz, 2H), 3.79 (d, 3JH,H =4 Hz, 2H), 3.72 (t, 3JH,H =5 Hz, 4H),
3.57 (t, 3JH,H =5 Hz, 4H), 3.36 ppm (s, 3H); 13C NMR (CDCl3, 125 MHz,
258C): d=147.29, 146.26, 146.13, 145.89, 145.53, 145.29, 144.70, 144.56,
144.31, 143.09, 142.95, 142.55, 142.14, 142.04, 141.60, 141.46, 140.09,
139.87, 139.55, 137.84, 135.80, 135.65, 135.52, 135.22, 134.88, 134.77,
130.00, 129.71, 129.19, 128.99, 128.19, 128.00, 126.95, 125.98, 125.27,
124.91, 124.38, 122.86, 121.99, 117.23, 117.08, 82.30, 71.99, 70.68, 70.64,
70.60, 68.82, 65.75, 59.08, 52.39, 48.67 ppm; FTIR (KBr): n˜ =3434, 2921,
2851, 1632, 1508, 1455, 1107, 527 cmꢁ1; UV/Vis (CH2Cl2): lmax (log e)=57
(6.85), 326 (6.58), 378 (6.29), 432 (shoulder, 6.14), 441 nm (6.13); MS
(ESI): m/z (%): 1389 (100) [M+], 1219 (65), 551 (62).
Compound 20: Eluent: hexane/toluene (1:1); 30% yield; m.p.: >3008C;
H NMR (CDCl3/CS2, 500 MHz, 258C): d=7.79 (m, 3H), 7.65 (m, 3H),
7.56–7.42 (m, 17H), 7.41 (d, 3JH,H =16.3 Hz, 4H), 7.30 (m, 2H), 7.13 (s,
2H), 7.10 (s, 4H), 7.09 (d, 3JH,H =15.3 Hz, 4H), 7.08 (d, 3JH,H =16.3 Hz,
4H), 6.32 (s, 4H), 5.13 (d, 3JH,H =9.2 Hz, 1H), 5.07 (s, 1H), 4.14 (d,
3JH,H =9.2 Hz, 1H), 4.05 (q, J=6.3 Hz, 12H), 3.28 (m, 1H), 2.59 (m, 1H),
1.90 (m, 14H), 1.60–1.26 (m, 46H), 0.98 ppm (m, 21H); 13C NMR
4832
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2005, 11, 4819 – 4834

Probing Molecular Wires
FULL PAPER
(CDCl3/CS2, 125 MHz, 258C): d=156.31, 154.01, 153.36, 153.28, 150.87,
147.09, 146.63, 146.29, 145.96, 145.74, 145.59, 145.05, 144.50, 144.21,
142.97, 142.82, 142.39, 142.11, 141.94, 141.83, 141.49, 141.36, 140.00,
139.77, 139.40, 137.95, 136.98, 136.65, 136.42, 136.34, 136.25, 135.92,
135.63, 135.08, 134.53, 129.55, 128.10, 126.70, 126.45, 126.33, 125.88,
125.17, 124.79, 124.15, 123.70, 123.03, 122.74, 121.95, 117.16, 117.07,
110.15, 110.00, 82.32, 69.16, 68.7, 66.73, 53.39, 53.13, 32.04, 31.74, 30.13,
29.81, 29.57, 28.50, 27.66, 26.75, 26.06, 22.85, 14.28, 14.16 ppm; FTIR
(KBr): n˜ =2923, 2853, 1632, 1461, 1422, 1178, 1107, 957, 527 cmꢁ1; UV/
Vis (CH2Cl2): lmax (e)=54 (141200), 330 (30200), 458 nm
(155000 molꢁ1 cm3 dmꢁ1).
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Compound 25: Dialdehyde 3 (60 mg, 0.11 mmol) and lithium ethoxide
(1m, 0.22 mL, 0.22 mmol) were added to a stirred solution of triphenyl-
phosphonium salt 24 (65 mg, 0.22 mmol) in dry ethanol (20 mL) at 508C
under argon. After 3 h the solvent was vacuum evaporated, and the resi-
due was suspended in xylene (10 mL) and heated to reflux for 24 h after
addition of a catalytic amount of iodine. After the reaction mixture had
cooled, methanol was added to form a precipitate, which was purified by
chromatography (silica gel, hexane/dichloromethane 4:1) to yield 42 mg
1
(54%) of 25 (all-E isomer) as a yellow solid. H NMR (CDCl3, 200 MHz,
258C); d=7.53 (s, 8H), 7.52 (d, 3JH,H =16.5 Hz, 4H), 7.39 (m, 4H), 7.30
3
3
3
(d, JH,H =16.5 Hz, 2H), 7.29 (d, JH,H =1.3 Hz, 2H), 7.23 (t, JH,H =1.3 Hz,
1H), 7.14 (d, 3JH,H =16.5 Hz, 2H), 7.13 (s, 6H), 4.07 (t,3JH,H =6.4 Hz,
4H), 1,90 (q, 3JH,H =6.4 Hz, 4H), 1.60–1.25 (m, 8H), 0.93 ppm (t, J=
6.8 Hz, 6H); 13C NMR (CDCl3, 50 MHz, 258C): d=151.16, 137.41,
137.38, 136.47, 128.69, 128.41, 128.36, 127.60, 126.95, 126.83, 126.49,
123.41, 110.57, 69.59, 31.65, 29.48, 25.98, 22.66, 14.07 ppm; FTIR (KBr):
n˜ =2925, 2854, 1591, 1512, 1491, 1423, 1387, 1261, 1202, 1047, 980, 810,
750, 688 cmꢁ1
;
MS (EI): m/z (%): 686 (100) [M+], 510 (7) [M+ꢁ
2(C6H13)], 286 (28), 207 (51), 149 (29); UV/Vis (CH2Cl2): lmax (e)=36
(30900), 296 (13200), 354 (20400), 424 nm (40700 molꢁ1 cm3 dmꢁ1).
Compound 26: Following the general procedure for Wittig–Horner olefi-
nation, compound 3 (100 mg, 0.19 mmol) was treated with compound 22
(230 mg, 0.38 mmol) to afford 65 mg (50%) of 26 as an orange solid
(silica gel, hexane/dichloromethane 7/3). 1H NMR (CDCl3, 200 MHz,
258C): d=7.53 (s, 12H), 7.52 (d, 3JH,H =16.4 Hz, 6H), 7.48–7.28 (m, 6H),
7.15 (s, 6H), 7.14 (d, 3JH,H =16.4 Hz, 6H), 4.07 (t, 3JH,H =6.3 Hz, 12H),
1,89 (q, 3JH,H =6.3 Hz, 12H), 1.55–1.26 (m, 36H), 0.95 ppm (t, J=6.8 Hz,
18H); 13C NMR (CDCl3, 50 MHz, 258C): d=151.21, 138.02, 137.21,
128.79, 128.64, 128.46, 127.04, 126.99, 126.84, 126.53, 123.57, 123.29,
110.76, 110.67, 69.67, 31.66, 29.59, 25.98, 22.67, 14.04 ppm; FTIR (KBr):
n=2928, 2857, 1586, 1492, 1464, 1422, 1341, 1258, 1207, 961, 691 cmꢁ1
;
UV/Vis (CH2Cl2): lmax (e)=44 (31600), 328 (38900), 450 nm
(151300 molꢁ1 cm3 dmꢁ1); MS (ESI): m/z (%): 1291 (100) [M++H].
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Financial support for this project came from the MCYT of Spain (Project
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Received: January 21, 2005
Published online: June 1, 2005
4834
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www.chemeurj.org
Chem. Eur. J. 2005, 11, 4819 – 4834