Efficient electron transfer in β-substituted porphyrin-C60 dyads connected through a p-phenylenevinylene dimer

Article abstract of DOI:10.1016/j.tet.2008.09.088

Two new porphyrin-C₆₀ dyads have been synthesized in which the electroactive moieties have been connected through a p-phenylenevinylene dimer. The electrochemical study confirms the amphoteric redox behavior of these dyads. Irradiation of these compounds gives rise to the corresponding radical pair confirming that substitution on the β-position of the porphyrin facilitates the electronic communication between the porphyrin and C₆₀.

Full text of DOI:10.1016/j.tet.2008.09.088

Tetrahedron 64 (2008) 11404–11408
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Efficient electron transfer in
b-substituted porphyrin-C60 dyads connected
through a p-phenylenevinylene dimer
a
a
b
c
c,
*
´
´
Jose Santos , Beatriz M. Illescas , Mateusz Wielopolski , Ana M.G. Silva , Augusto C. Tome
,
Dirk M. Guldi b , Nazario Martın
,
a,
*
*
´
a
´
´
´
Departamento de Quımica Organica, Facultad de Quımica, Universidad Complutense, E-28040 Madrid, Spain
b Department of Chemistry and Pharmacy and Interdisciplinary Center for Molecular Materials, University of Erlangen, 91058 Erlangen, Germany
c Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal
a r t i c l e i n f o
a b s t r a c t
Article history:
Two new porphyrin-C60 dyads have been synthesized in which the electroactive moieties have been
connected through a p-phenylenevinylene dimer. The electrochemical study confirms the amphoteric
redox behavior of these dyads. Irradiation of these compounds gives rise to the corresponding radical
Received 16 July 2008
Received in revised form
15 September 2008
Accepted 26 September 2008
Available online 8 October 2008
pair confirming that substitution on the
nication between the porphyrin and C60
b
-position of the porphyrin facilitates the electronic commu-
.
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
(w0.01 Åꢀ1) determined for exTTF-oPPV-C60 (1) systems can be
best understood in terms of the effective -conjugation between
the donor, the oligo-PPV bridge and the C60 moiety.5
This value is increased when either the donor moiety or the
bridge are changed, probably due to a lower effective conjugation.
factors of 0.2 Åꢀ1 or 0.09 Åꢀ1 have been obtained for exTTF-oPPE-
p
One of the central issues of molecular electronics is the study of
molecular charge transport.1 Donor-Bridge-Acceptor (DBA) systems
constitute excellent model compounds to assess electron transfer
over long distances.2 In these systems, photo-induced electron
transfer and irradiation can cause the transport of an electron from
the donor to the acceptor. The rate of electron transport is governed
by parameters related to the donor and acceptor properties, as the
b
b
C60 (2)6 and exTTF-oligofluorene-C60 (3)7 systems, respectively.
Also, in TPP-oPPV-C60 (4) systems, values of
b
¼0.03 Åꢀ1 were de-
termined, which are larger than those found when exTTF acts as the
donor moiety, thus evidencing the lower para conjugation between
driving force (D l), and also by
G0) and the reorganization energy (
the electronic coupling (V), which is affected both by the structure
of the bridge and the donor-bridge energy gap. The efficiency of
electron transfer (eT) decreases exponentially with increasing
molecular wire length according to the electron transfer rate
the TPP donor unit and the p
-conjugated oligomer.8 This loss of
conjugation has been accounted for the dihedral angles between
the TPP phenyl ring and the first ring of the oligomer unit (w30ꢁ)
and the deviation from planarity along the oligomer unit.
constant, kET
,
Schuster et al.9 have studied the energy and electron transfer
processes in alkynyl-linked porphyrin-C60 dyads and compared
b
RDA
kET ¼ k0eꢀ
the photophysical behaviors of b-alkynylZnP-C60 (5a–c) and
para-phenylalkynylZnP-C60 (6) dyads. They found that while the
electronic distribution favors through-bond communication in
the b-alkynylZnP-C60 dyad (5a–c), the para-phenylalkynylZnP-C60
(6) shows a much slower charge recombination process due, at
least in part, to unfavorable orbital interactions between the ZnP
and the C60 moieties (Fig. 1).
where k0 is a kinetic prefactor, RDA represents the donor–acceptor
distance, and is the attenuation factor, which depends on the
intrinsic electronic properties of the bridge. Typical values for
range between 1.0 and 1.4 Åꢀ1 for proteins, and between 0.01 and
0.06 Åꢀ1 for highly efficient -conjugated bridges.3
b
b
p
A key aspect for achieving efficient molecular wire behavior in
DBA systems is the effective matching of orbital energies between
the donor and bridge components, and between the acceptor
As the
very low (w0.03 Åꢀ1), the objective of this paper is to study eT
processes in -P-oPPV-C60 triads and to assess the para conjugation
along the p-phenylenevinylene dimer as a -conjugated system of
b values obtained in TPP-oPPV-C60 systems (4) are still
b
and bridge components.4 Thus, the extraordinarily low
b value
p
precise length, and using the free-base and Zn-porphyrins as
electron donors. The efficiency in the formation of the radical pairs
will determine a further study with other related p-conjugated
oligomers of different lengths.
* Corresponding authors. Tel.: þ34 91 394 4227; fax: þ34 91 394 4103.
´
E-mail address: nazmar@quim.ucm.es (N. Martın).
0040-4020/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.09.088

J. Santos et al. / Tetrahedron 64 (2008) 11404–11408
11405
Oct
H3C
S
C6H13
O
S
HexO
N
N
S
S
3
OC6H13
OHex
S
S
1
2
S
S
H3C
S
H3C
S
C6H13
O
N
Ar
Zn
Ar
N
n
n
N
N
N
N
n
C6H13
C6H13
OC6H13
Ar
S
S
3
4: n = 1,2
Ph
N
CH3
N
N
N
N
N
Ph
CH3
Zn
M
n
N
Ph
N
Ph
6: n = 2,3,4
5a: M = Zn
5b: M = H2
5c: M = Ni
Figure 1. Some fullerene-containing representative DBA examples for the assessment of the molecular wire behavior of the
p-conjugated oligomers.
2. Results and discussion
2.1. Synthesis
triads H2P-oPPV-C60 (9a) and ZnP-oPPV-C60 (9b) were synthesized
in 18% and 41% yields, respectively. This is, to the best of our
knowledge, the first time that the Wadsworth–Emmons reaction
has been carried out using a fullerene derivative.
The synthesis of the new derivatives was carried out as depicted
in Scheme 1.
The structures of the new compounds were confirmed by
a number of spectroscopic techniques (NMR, FTIR, MS). The 1H
NMR spectrum of 8 shows the characteristic signals for the pyrro-
H2P-oPPV-C60 (9a) and ZnP-oPPV-C60 (9b) triads were synthe-
sized by olefination of porphyrin aldehydes with C60-oPPV-phos-
phonate (8). This new oPPV-C60 phosphonate (8) was prepared by
1,3-dipolar cycloaddition of the formyl-oPPV-phosphonate (7),
previously reported in our group,5b to C60 following Prato’s pro-
cedure.10 Phosphonate derivative 8 was thus obtained in 55% yield.
By Wadsworth–Emmons olefination reaction of porphyrin alde-
hydes H2P-CHO or ZnP-CHO11 with C60-oPPV-phosphonate (8),
lidine ring as two doublets at
constants of 9.3 Hz, and one singlet at
of the phosphonate are observed as a doublet at
of 10.8 Hz, and the CH2 in of the phosphonate unit appears as
d
w5.01 and 4.28 with coupling
w4.96. The methyl groups
w3.69 with 3JH,P
d
d
a
a doublet at
d
w2.10 with a 2JH,P of 22.1 Hz. For H2P-oPPV-C60 (9a)
and ZnP-oPPV-C60 (9b) triads, the 1H NMR spectra show signals
around 9 ppm for the pyrrolic protons of the porphyrin core. A trans
H3C
H3C
C6H13
O
N
C6H13
O
N
Ph
N
OC6H13
PO(OMe)2
N
i)
ii) Ph
(MeO)2OP
OC6H13
OC6H13
M
N
OC6H13
Ph
N
OHC
7
8
9a: M = H2
9b: M = Zn
Ph
D
; (ii) H2P-CHO or ZnP-CHO/tBuOK/THF.
Scheme 1. (i) C60/sarcosine, ClPh/

11406
J. Santos et al. / Tetrahedron 64 (2008) 11404–11408
configuration of the vinyl protons of the new formed double bond,
with Jw16 Hz, was observed, as expected from the stereoselectivity
of the Wadsworth–Emmons reaction.
H2P
The absorption spectra of 9a and 9b in CH2Cl2 reveal a linear
combination of the spectra of H2P or ZnP and C60 components.
Remarkably, compound 8 is an interesting building block, which
opens up the possibility of employing the Wadsworth–Emmons
reaction in fullerene chemistry.
8
9b
9a
2.2. Electrochemistry
The electrochemical features of new compounds were studied
by cyclic voltammetry at room temperature, in ODCB/CH3CN 4:1 as
the solvent. The obtained redox potentials for 9a and 9b are col-
lected in Table 1, together with the phosphonate derivative 8 and
tetraphenyl porphyrin as reference compounds.
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
-2.5
For compound 8, three reduction waves corresponding to the
first three reductions of the fullerene unit were observed. These
Potential / V
waves are shifted to more negative potentials than the parent C60
,
Figure 2. Cyclic voltammograms of H2P, 8, and 9a,b.
as a consequence of the saturation of a double bond in the C60
cage.12
Compounds 9a,b show an amphoteric redox behavior with
waves under both oxidation and reduction. Compound 9b exhibits
two oxidation waves at potentials similar to those observed for the
reference TPP.13 In the reduction part, four quasi-reversible waves
are observed.12 The first and second reduction waves correspond to
the first two reductions of the C60 moiety. The third wave may be
assigned to the first reduction of the porphyrin while the fourth
should correspond to the third reduction of the fullerene together
with the second reduction of the porphyrin subunit, as suggested
by the higher intensity of the peak. For compound 9a the oxidation
waves could not be detected owing to their low intensity. On the
reduction side, however, five quasi-reversible reduction waves
were observed, corresponding to the three reductions of C60 and
the two reduction peaks of the porphyrin moiety (Fig. 2).
in the red at 880 nm. A fast intersystem crossing process (i.e., in
the range of 108 sꢀ1) governs the fate of the metastable singlet
excited states in all references (i.e., C60, oligo-PPV, ZnP/H2P). The
correspondingly formed triplet–triplet absorptions are all located
in the range between 500 and 900 nm.
2.3.2. H2P-oPPV-C60/ZnP-oPPV-C60
In contrast to previously studied C60-oligo-PPE-donor systems,5
ZnP and H2P not only absorb notably in the current C60-oligo-
PPV-donor systems, but their strong fluorescence dominates large
parts of the spectrum (Fig. 3). Interestingly, the ZnP/H2P centered
fluorescence is appreciably quenched in all ZnP-oPPV-C60
(5.4ꢂ10ꢀ3–2.6ꢂ10ꢀ3)/H2P-oPPV-C60 (0.06–0.03)dregardless of the
excitation wavelength (i.e., Soret- or Q-band region)dprompting to
the fact that C60 must enhance the fluorescence deactivation (vide
infra). Interestingly, increasing the solvent polarity intensifies the
quenching.
2.3. Photophysics
2.3.1. Reference compounds
To shed light on the nature of the product, evolving from this
intramolecular deactivation, complementary time-resolved tran-
sient absorption measurements were necessary. In transient ab-
sorption measurements, we focused exclusively on the generation
of the singlet excited states of ZnP/H2P. The overlapping absorptions
of all components renders any other analysis ambiguous, though we
In steady-state experiments, all reference compounds (i.e., C60
,
oligo-PPV, ZnP/H2P) emit singlet excited state energy in, however,
different spectral regions of the solar spectrum. While the fluo-
rescence of oligo-PPV is typically observed in the 400–500 nm
range, ZnP/H2P emit in the 600–700 nm range, and C60 emits with
a maximum at 715 nm. The quantum yields vary substantially with
values that range between 0.2 and 6ꢂ10ꢀ4 for the H2P and C60
reference, respectively.
Also characteristic features were recorded in our ultrafast and
fast transient absorption experiments. We see, for example,
singlet excited states that are formed instantaneously: in case of
the oligo-PPV singlet-singlet absorptions develop with maxima in
the 500–700 nm region (range). Characteristics for ZnP/H2P are
480 nm. For the C60 reference, on the other hand, the maximum is
1.5 105
1 105
5 104
0
0.025
0.02
0.015
0.01
0.005
0
Φ
Table 1
a
Redox potentials at room temperature (in V vs Ag/Agþ
)
Compd
E1,ox
E2,ox
E1,red
E2,red
E3,red
E4,red
E5,red
C60
8
H2P
9a
9b
ꢀ0.72
ꢀ0.86
ꢀ1.43
ꢀ0.86
ꢀ0.84
ꢀ1.12
ꢀ1.24
ꢀ1.75
ꢀ1.23
ꢀ1.22
ꢀ1.60
ꢀ1.78
d
d
d
d
d
0.89
1.18
d
d
ꢀ1.36
ꢀ1.52
ꢀ1.60
ꢀ1.78
ꢀ1.77
400
500 600
Wavelength / nm
700
800
0.65
0.88
a
GCE (glassy carbon) as working electrode, Ag/AgNO3 as reference electrode,
Bu4NClO4 (0.1 M) as supporting electrolyte, and ODCB/CH3CN 4:1 (v/v) as solvent.
Figure 3. Normalized Absorption and emission spectra of H2P-oPPV-C60 (red color)
and ZnP-oPPV-C60 (black color) in benzonitrile at room temperature.
Scan rate 100 mV sꢀ1
.

J. Santos et al. / Tetrahedron 64 (2008) 11404–11408
11407
must assume in accordance with previous work that starting
4. Experimental
with the C60 singlet excited state a similar reaction pattern will
evolve.5
4.1. Photophysical experiments
Instead of seeing, however, the slow intersystem crossing dy-
namics, as the ZnP (i.e., 2.1 ns)/H2P (i.e., 10.1 ns) references, the
singlet–singlet absorption decays in the presence of C60 with
accelerated dynamics. The singlet excited state lifetimes, as they
were determined from an average of first-order fits of the time-
absorption profiles at various wavelengths (850–950 nm) are in
the range of 0.49 ns (i.e, H2P-oPPV-C60) to 0.19 ns (i.e., ZnP-oPPV-
C60). Spectroscopically, the transient absorption changes, taken
after the completion of the decay, bear no resemblance with any
triplet excited statedsee Figure 4. Again, varying the solvent
polarity from ortho-dichlorobenzene to benzonitrile leads to an
acceleration of the singlet deactivation: ZnP-oPPV-C60 (0.09 and
0.07 ns), H2P-oPPV-C60 (0.31 and 0.26 ns). This supports our
earlier hypothesis that an intramolecular electron transfer,
yielding ZnPꢃþ-oPPV-C6ꢃ0ꢀ/H2Pꢃþ-oPPV-C6ꢃ0ꢀ, governs the ZnP/H2P
singlet excited state deactivation.
UV–vis spectra were recorded on a Varian Cary 50 Scan spec-
trophotometer in toluene solution. Steady-state fluorescence
studies were carried out on a Fluoromax-3 (Horiba) instrument and
all spectra were corrected for the instrument response. The fem-
tosecond transient absorption studies were performed with
387 nm laser pulses (1 Khz 150 fs pulse width, 200 mJ) from an
amplified Ti:sapphire laser system (Model CPA 2101, Clark-MXR
Inc.). Fluorescence quantum yields FF were determined according
to the comparative method of Williams et al.16 We have used the
corresponding tetraphenyl porphyrins (free-base and zinc) with
their known quantum yields as standard samples. The quantum
yields FF have been calculated according to
I ODR n2
FF
¼
FFR
nR2
IR OD
Spectroscopic evidence for the radical pair formation was pro-
vided by the features developing in parallel with the disappearance
of the ZnP/H2P singlet–singlet absorptiondsee Figure 4. In the
visible region, the observed maxima between 500 and 700 nm as
where FF is the quantum yield, I is the integrated intensity, n is the
refractive index, and OD is the optical density. The subscript R refers
to the tetraphenyl porphyrin reference fluorophore of known
quantum yield.
well as 480 nm correspond to the one-electron oxidized
p-radical
cations of ZnP (ZnPꢃþ) and H2P (H2Pꢃþ), respectively,14 while in the
near-infrared region, the 1000 nm maximum resembles the
signature of the one-electron reduced form of C60 (C6ꢃ0ꢀ).15
4.1.1. Synthesis of compound 8
A solution of C60 (348 mg, 0.483 mmol), {4-[2-(4-diethoxy-
methylphenyl)vinyl]-2,5-bishexyloxybenzyl} dimethyl phospho-
nate 7 (64 mg, 0.12 mmol), and sarcosine (53 mg, 0.60 mmol) was
refluxed in chlorobenzene (100 mL) for 5 h. The solvent was re-
moved under reduced pressure and the crude material was care-
fully chromatographed over silica using carbon disulfide, toluene,
and toluene/acetonitrile 19:1 as eluents. Further purification was
accomplished by repetitive precipitation and centrifugation by
using cyclohexane as solvent (85 mg, 55%). 1H NMR (300 MHz,
3. Conclusions
In summary, we have synthesized two new dyads connected
through a p-phenylenevinylene dimer as p-conjugated system and
determined their amphoteric redox character. Photophysical
studies reveal that these molecules undergo an efficient electron
transfer process upon light irradiation affording the respective
CDCl3):
d
¼7.79 (br s, 2H), 7.59 (d, J¼7.9 Hz, 2H), 7.47 (d, J¼16.4 Hz,
1H), 7.09 (d, J¼16.4 Hz, 1H), 7.06 (s, 1H), 6.91 (d, J¼2.5 Hz, 1H), 5.01
(d, J¼9.3 Hz, 1H), 4.96 (s, 1H), 4.28 (d, J¼9.3 Hz, 1H), 3.98 (t,
J¼6.4 Hz, 4H), 3.69 (d, J¼10.8 Hz, 6H), 2.10 (d, J¼22.1 Hz, 2H), 2.84
(s, 3H), 1.85–1.79 (m, 4H), 1.51–1.48 (m, 4H), 1.36–1.34 (m, 8H),
charge separated states. These results confirm that b-substitution
on a porphyrin moiety results in good electronic coupling and
facilitates electronic communication between the donor and
acceptor units. Work is currently in progress to prepare related
systems with a different length of the p-phenylenevinylene oligo-
0.92–0.90 (m, 6H). 13C NMR (75 MHz, CDCl3):
d
¼156.68, 154.47,
153.88, 153.80, 151.24, 151.14, 151.00, 150.95, 147.71, 147.19, 146.89,
146.72, 146.63, 146.55, 146.51, 146.34, 146.18, 145.95, 145.88, 145.72,
145.66, 145.56, 145.11, 145.01, 144.80, 143.55, 143.39, 143.09, 142.98,
142.68, 142.66, 142.54, 142.47, 142.44, 142.41, 142.34, 142.26, 142.09,
141.94, 140.58, 140.55, 140.29, 139.98, 138.45, 137.22, 136.94, 136.49,
136.25, 136.15, 130.02, 128.63, 127.14, 126.32, 126.26, 124.37, 120.82,
120.69, 116.29, 116.22, 110.10, 83.86, 70.46, 69.83, 69.49, 53.20,
53.11, 40.47, 32.03, 32.00, 29.85, 29.76, 26.29, 26.20, 23.05, 14.48,
14.45. HR-MALDI-TOF: calcd for C92H49NO5P: 1278.3343, found:
mer to determine the
b
value for these b-substituted systems.
0.03
0.02
0.01
0
1278.3331. FTIR (KBr) n
(cmꢀ1) 3452, 2924, 2853, 2779, 1628, 1498,
1463, 1420, 1209, 1057, 1033, 868, 527. UV–vis (CHCl3) lmax (nm)
430, 373, 307, 255, 231.
4.1.2. Synthesis of compound 9a
To a stirred solution of 8 (50 mg, 0.039 mmol) and H2P-CHO
(25 mg, 0.039 mmol) in anhydrous THF (20 mL), potassium tert-
butoxide (6.5 mg, 0.058 mmol) was added under argon atmo-
sphere. The resulting solution was refluxed overnight. Methanol
(5 mL) and water (25 mL) were added. The mixture was extracted
with chloroform and the organic layer dried over sodium sulfate.
The solvent was removed under reduced pressure and the resulting
residue was chromatographed on a silica gel column, using carbon
disulfide/dichloromethane 4:1 as eluent. Compound 9a (12.7 mg,
18%) was thus obtained as a black solid. 1H NMR (500 MHz, CDCl3):
-0.01
-0.02
400
600
800
Wavelength / nm
1000
1200
Figure 4. Differential absorption spectra (visible and near-infrared) obtained upon
femtosecond flash photolysis (387 nm) of ZnP-oPPV-C60 in nitrogen saturated benzo-
nitrile with several time delays (i.e., 1 ps, black spectrum; 10 ps, gray spectrum; 300 ps,
brown spectrum) at room temperature.
d¼9.05 (s, 1H), 8.85–8.80 (m, 4H), 8.76 (d, J¼4.8 Hz, 1H), 8.66 (d,

11408
J. Santos et al. / Tetrahedron 64 (2008) 11404–11408
J¼4.8 Hz, 1H), 8.27–8.20 (m, 8H), 7.85–7.76 (m, 14H), 7.65 (d,
J¼7.8 Hz, 2H), 7.45 (d, J¼16.4 Hz, 1H), 7.16 (d, J¼16.4 Hz, 1H), 7.11 (s,
1H), 6.91 (d, J¼16.2 Hz, 1H), 6.68 (s, 1H), 4.89 (d, J¼9.3 Hz, 1H), 4.84
(s, 1H), 4.15 (d, J¼9.3 Hz, 1H), 4.11 (t, J¼6.5 Hz, 2H), 4.04 (t, J¼6.5 Hz,
2H), 2.81 (s, 3H), 2.05–2.00 (m, 2H),1.90–1.85 (m, 2H),1.74–1.70 (m,
2H), 1.41–1.39 (m, 8H), 1.02–0.96 (m, 6H), ꢀ2.56 (br s, 2H). 13C NMR
110.99, 110.00, 83.89, 70.47, 70.25, 69.94, 69.39, 40.48, 32.36, 32.15,
30.29, 29.95, 26.75, 26.37, 23.39, 23.32, 14.69. HR-MALDI-TOF: calcd
for C135H69N5O2Zn: 1855.4737, found 1855.4758. FTIR (KBr)
n
(cmꢀ1) 3452, 2922, 2851, 1636, 1464, 1003, 795, 700, 526. UV–vis
(CHCl3) lmax (nm) 599, 558, 425, 328, 255.
(125 MHz, CDCl3):
d
¼156.53, 154.27, 153.73, 153.68, 151.59, 151.39,
Acknowledgements
147.48, 147.08, 146.68, 146.51, 146.42, 146.16, 146.01, 145.77, 145.68,
145.56, 145.37, 144.90, 144.62, 143.37, 143.21, 143.04, 142.93, 142.80,
142.73, 142.48, 142.37, 142.25, 142.15, 141.85, 140.40, 140.20, 139.91,
139.35, 139.19, 138.62, 137.16, 136.81, 136.52, 136.12, 135.99, 135.05,
135.02, 134.94, 134.88, 134.54, 130.49, 130.27, 130.12, 129.04, 128.70,
128.52, 128.11, 127.91, 127.33, 127.21, 127.10, 127.01, 126.83, 125.32,
124.87, 124.46, 123.97, 120.91, 120.34, 120.25, 120.13, 111.05, 110.53,
109.92, 83.86, 70.45, 70.24, 69.96, 69.38, 40.46, 32.32, 32.08, 30.23,
29.89, 26.69, 26.33, 23.32, 23.19, 14.68, 14.65. HR-MALDI-TOF: calcd
This work has been supported by the MEC of Spain (CTQ2005-
02609/BTQ and Consolider-Ingenio 2010 CSD2007-0010, Nano-
ciencia Molecular), Comunidad de Madrid (P-PPQ-000225-0505),
and the Deutsche Forschungsgemeinschaft (SFB and Clusters of
Excellence Engineering of Advanced Materials), FCI, the Office of
Basic Energy Sciences of the U.S. J.S. is indebted to MEC for a
research grant.
for C135H72N5O2: 1794.5681, found 1794.5653. FTIR (KBr)
3443, 2923, 2852, 1599, 1463, 798, 527. UV–vis (CHCl3) lmax (nm)
n )
(cmꢀ1
References and notes
655, 602, 570, 519, 422, 327, 255.
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2. James, D. K.; Tour, J. M. Chem. Mater. 2004, 16, 4423.
3. Weiss, E. A.; Wasielewski, M. R.; Ratner, M. A. Top. Curr. Chem. 2005, 257, 103.
4. Davis, W. B.; Svec, W. A.; Ratner, M. A.; Wasielewski, M. R. Nature 1998, 396, 60.
4.1.3. Synthesis of compound 9b
To a stirred solution of 8 (45 mg, 0.035 mmol) and ZnP-CHO
(25 mg, 0.035 mmol) in anhydrous THF (20 mL), potassium tert-
butoxide (5 mg, 0.043 mmol) was added under argon. After
refluxing overnight, methanol (5 mL) and water (25 mL) were
added. The mixture was extracted with chloroform and the organic
layer dried over sodium sulfate. The solvent was removed under
reduced pressure and the resulting residue was chromatographed
on a silica gel column, using carbon disulfide/dichloromethane 4:1
as eluent. Compound 9b (27.1 mg, 41%) was thus obtained as a black
´
5. (a) Giacalone, F.; Segura, J. L.; Martın, N.; Guldi, D. M. J. Am. Chem. Soc. 2004, 126,
5340; (b) Giacalone, F.; Segura, J. L.; Martı´n, N.; Ramey, J.; Guldi, D. M. Chem.dEur. J.
2005, 11, 4819.
´
6. (a) Atienza, C.; Martın, N.; Wielopolski, M.; Haworth, N.; Clark, T.; Guldi, D. M.
Chem. Commun. 2006, 3202; (b) Wielopolski, M.; Atienza, C.; Clark, T.; Guldi, D.
´
M.; Martın, N. Chem.dEur. J. 2008, 14, 6379.
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R.; Filippone, S.; Martı´n, N. Chem. Commun. 2007, 5164.
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2005, 11, 1267.
´
9. (a) Vail, S. A.; Krawczuk, P. J.; Guldi, D. M.; Palkar, A.; Echegoyen, L.; Tome, J. P.
C.; Fazio, M. A.; Schuster, D. I. Chem.dEur. J. 2005, 11, 3375; (b) Vail, S. A.;
Schuster, D. I.; Guldi, D. M.; Isosomppi, M.; Tkachenko, N.; Lemmetyinen, H.;
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14155.
solid. 1H NMR (500 MHz, CDCl3):
d
¼9.13 (s, 1H), 8.96–8.91 (m, 4H),
8.88 (d, J¼4.6 Hz, 1H), 4.77 (d, J¼4.6 Hz, 1H), 8.27–8.26 (m, 2H),
8.23–8.20 (m, 6H), 7.80–7.72 (m, 14H), 7.61 (d, J¼7.3 Hz, 2H), 7.51 (d,
J¼16.4 Hz, 1H), 7.13 (d, J¼16.4 Hz, 1H), 7.07 (s, 1H), 6.92 (d,
J¼16.1 Hz, 1H), 6.66 (s, 1H), 4.98 (d, J¼9.3 Hz, 1H), 4.93 (s, 1H), 4.25
(d, J¼9.3 Hz,1H), 4.10 (t, J¼6.5 Hz, 2H), 4.04 (t, J¼6.5 Hz, 2H), 2.87 (s,
3H), 2.05–2.01 (m, 2H), 1.90–1.87 (m, 2H), 1.75–1.72 (m, 4H), 1.45–
1.42 (m, 8H), 1.02–0.96 (m, 6H). 13C NMR (125 MHz, CDCl3):
10. Prato, M.; Maggini, M. Acc. Chem. Res. 1998, 31, 519.
11. Annoni, E.; Pizzotti, M.; Ugo, R.; Quici, S.; Morotti, T.; Bruschi, M.; Mussini, P. Eur.
J. Inorg. Chem. 2005, 3857.
12. (a) Echegoyen, L.; Echegoyen, L. E. Acc. Chem. Res. 1998, 31, 593; (b) Martı´n, N.;
Sa´nchez, L.; Illescas, B.; Pe´rez, I. Chem. Rev. 1998, 98, 2527.
13. (a) D’Souza, F.; Deviprasad, G. R.; El-Khouly, M. E.; Fujitsuka, M.; Ito, O. J. Am.
Chem. Soc. 2001, 123, 5277; (b) D’Souza, F.; Deviprasad, G. R.; Zandler, M. E.;
Hoang, V. T.; Klykov, A.; VanStipdonk, M.; Perera, A.; El-Khouly, M. E.; Fujitsuka,
M.; Ito, O. J. Phys. Chem. A 2002, 106, 3243; (c) Fungo, F.; Otero, L.; Borsarelli, C.
D.; Durantini, E. N.; Silber, J. J.; Sereno, L. J. Phys. Chem. B 2002, 106, 4070; (d)
D’Souza, F.; Deviprasad, G. R.; Zandler, M. E.; El-Khouly, M. E.; Fujitsuka, M.; Ito,
O. J. Phys. Chem. B 2002, 106, 4952; (e) Guldi, D. M.; Giacalone, F.; de la Torre, G.;
d
¼151.56, 151.45, 151.32, 151.02, 150.85, 150.80, 150.69, 150.46,
149.46, 147.57, 147.41, 147.12, 146.73, 146.62, 146.50, 146.44, 146.22,
146.07, 145.80, 145.72, 145.61, 144.97, 144.68, 143.73, 143.41, 143.26,
143.18, 142.98, 142.86, 142.51, 142.42, 142.35, 142.29, 141.90, 140.49,
139.98, 134.93, 134.83, 134.71, 132.72, 132.66, 132.56, 132.37, 131.98,
130.69, 130.03, 128.76, 128.47, 128.34, 128.22, 127.93, 127.20, 127.04,
127.02, 126.95, 124.94, 124.68, 124.54, 122.02, 121.47, 121.36, 120.95,
´
Segura, J. L.; Martın, N. Chem.dEur. J. 2005, 11, 7199.
14. Guldi, D. M. Chem. Soc. Rev. 2002, 31, 22.
15. Guldi, D. M.; Prato, M. Acc. Chem. Res. 2000, 33, 695.
16. Williams, A. T. R.; Winfield, S. A.; Miller, J. N. Analyst 1983, 108, 1067.