Arylamine-substituted oligo(ladder-type pentaphenylene)s: Electronic communication between bridged redox centers

Article abstract of DOI:10.1021/ja073148s

Novel bis(arylamine-substituted) oligo(ladder-type pentaphenylene)s 1-3, with bridge lengths estimated to be 2.2, 4.2, and 6.3 nm, respectively, have been developed, and the model compound 4 with a mono-arylamine substituent was also synthesized. Their ab

Full text of DOI:10.1021/ja073148s

Published on Web 09/19/2007
Arylamine-Substituted Oligo(ladder-type pentaphenylene)s:
Electronic Communication between Bridged Redox Centers
Gang Zhou, Martin Baumgarten, and Klaus Mu¨llen*
Contribution from the Max-Planck-Institute for Polymer Research, Ackermannweg 10,
D-55128 Mainz, Germany
Received May 4, 2007; E-mail: muellen@mpip-mainz.mpg.de
Abstract: Novel bis(arylamine-substituted) oligo(ladder-type pentaphenylene)s 1-3, with bridge lengths
estimated to be 2.2, 4.2, and 6.3 nm, respectively, have been developed, and the model compound 4 with
a mono-arylamine substituent was also synthesized. Their absorption spectra in different solvents are almost
identical, while distinct bathochromic shifts of the photoluminescence (PL) spectra were observed with
increasing solvent polarity due to the polarized excited states. The cyclic voltammetry (CV) and differential
pulse voltammetry (DPV) spectra display a two-step oxidation of the bridged diamines in compound 1,
which suggests that the electron and charge delocalize in mixed-valence (MV) cation 1+• and that both
redox centers can communicate through the pentaphenylene bridge. Only unresolved curves in CV and
DPV spectra were observed in the first two oxidation processes of diamines 2 and 3, indicating that the
bridges are too long for efficient delocalization over the entire molecules and the radical cations localize at
each arylamine center. This finding was further supported by chemical oxidation with SbCl5 and studies of
the corresponding UV-vis-NIR absorption spectra of compounds 1-4. A significant intervalence charge-
transfer (IVCT) band around 5283 cm-1 (1893 nm) was observed in 1+•. This is the first report of such a
highly intense IVCT band in the NIR region with intensity similar to that of the visible band of the radicals,
enabling further analysis of the CT process and the coupling matrix element V, classifying 1+• as a class
II derivative (V ) 1.6 kcal/mol). This study may offer an effective way to improve the understanding of
charge transfer and charge-carrier transport in various conjugated oligomers or polymers and facilitate
their ongoing exploration in optoelectronic applications.
Introduction
introduced because of their ability to transport positive charge
via their radical cations.12
Conjugated organic oligomers and polymers are widely
investigated in view of their optoelectronic and biological
applications, such as light-emitting diodes (LEDs),1 photovoltaic
devices,2 field-effect transistors (FETs),3 nonlinear optics,4 and
chemical and biological sensors.5 Of those, phenylene-based
π-conjugated systems are the most important class of conjugated
materials for electronic applications due to their efficient blue
emission.6 In particular, p-phenylene-,7 fluorene-,8 indenofluo-
rene-,9 phenanthrylene-,10 and ladder-type11 phenylene-based
oligomers and polymers have been developed as efficient LED
materials. To achieve better hole-transport, triarylamines are
Purely organic mixed-valence (MV) cations have received
increasing attention since they provide the simplest models for
the investigation of basic electron-transfer (ET) and charge-
transfer (CT) processes.13 Usually, the most essential organic
MV systems are complexes in which two organic redox centers
with different oxidation states are connected by saturated or
unsaturated bridges, where the two corresponding valence
structures are R+•-bridge-R and R-bridge-R+• (R is the
redox center).14 Among the numerous redox groups, bis-
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J. AM. CHEM. SOC. 2007, 129, 12211-12221
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A R T I C L E S
Chart 1
Zhou et al.
triarylamines are of great interest in studying hole-transfer
processes from one redox center to the other15 because triary-
lamines are widely used as hole-conducting materials in LEDs,16
photovoltaic cells,17 photorefractive materials for optical data
storage,18 electrochromic polymers,19 and xerographic pro-
cesses.20 In general, there are a number of advantages in utilizing
triarylamines in MV compounds.21 First, triarylamines guarantee
reversible redox behavior as long as the para-positions of the
phenyl rings are protected. This stability is due to the delocal-
ization of the positive charge and the spin within the triarylamine
moiety.22 Second, the spacer between the two triarylamine redox
centers can be varied over a broad range very easily. Third, the
intervalence charge-transfer (IVCT) band associated with opti-
cally induced hole transfer from one triarylamine center to the
other is usually quite intense and well separated from other
bands so as to allow accurate band fits. Fourth, the redox
potentials of the triarylamine centers can be tuned by substituents
in the para-position.23
In early research, Stickley et al.24 investigated the simplest
MV compounds with phenylene as spacer and triarylamine as
redox center, such as compound C1 (Chart 1), and discovered
the solution-stable monocationic, dicationic, and tricationic states
of N,N,N′,N′,N′′,N′′-hexaphenyl/hexaanisyl-1,3,5-triaminoben-
zene. Lambert et al.25 extended the bridge of organic MV
compounds to p-phenylene and p-phenylene ethynylene systems
(C2-C4), with spacer distances varying from 0.5 to 2 nm, and
found that the electronic coupling integral decreased with
increasing spacer distance. Heckmann et al.26 then built up a
2.87 nm spacer (C5) with electron-deficient cyano groups to
raise the energy of the bridge state and observed the IVCT along
with a rather weak electronic interaction. However, although a
lot of conjugated bridges with long distance have been designed
and their IVCT properties investigated, most of the spacer
backbones were not planar due to the torsion about formal single
bonds, which may weaken the π-conjugation in the molecules.
Herein, a planar and better conjugated spacer, ladder-type
pentaphenylene, was used to bridge the two redox centers. In
order to combine the good hole-transport of triarylamines with
efficient blue luminescence of oligopentaphenylenes, a set of
three novel bis(arylamine-substituted) oligo(ladder-type pen-
(15) (a) Bonvoisin, J.; Launay, J.-P. J. Phys. Chem. 1994, 98, 5052. (b) Lambert,
C.; No¨ll, G.; Schelter, J. Nat. Mater. 2002, 1, 69. (c) Szeghalmi, A.;
Erdmann, M.; Engel, V.; Schmitt, M.; Amthor, S.; Kriegisch, V.; No¨ll, G.;
Rainer, S.; Lambert, C.; Leusser, D.; Stalke, D.; Zabel, M.; Popp, J. J.
Am. Chem. Soc. 2004, 126, 7834. (d) Wu, J.; Baumgarten, M.; Debije, M.
G.; Warman, J. M.; Mu¨llen, K. Angew. Chem., Int. Ed. 2004, 43, 5331. (e)
Nishiumi, T.; Nomura, Y.; Chimoto, Y.; Higuchi, M.; Yamamoto, K. J.
Phys. Chem. B 2004, 108, 7992. (f) Coropceanu, V.; Malagoli, M.; Andre´,
J. M.; Bre´das, J. L. J. Am. Chem. Soc. 2002, 124, 10519. (g) Bonvoisin, J.;
Launay, J.-P.; Verbouwe, W.; Van der Auweraer, M.; de Schryver, F. C.
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C.; Veciana, J. Angew. Chem. 1994, 106, 2190; Angew. Chem., Int. Ed.
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Trifonov, A. J. Am. Chem. Soc. 2005, 127, 10600.
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2006, 18, 5832.
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2001, 46, 2035.
(20) Bender, T. P.; Graham, J. F.; Duff, J. M. Chem. Mater. 2001, 13, 4105.
(21) Lambert, C.; No¨ll, G. J. Chem. Soc., Perkin Trans. 2 2002, 2039.
(22) Neugebauer, F. A.; Bamberger, S.; Groh, W. R. Chem. Ber. 1975, 108,
2406.
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12212 J. AM. CHEM. SOC. VOL. 129, NO. 40, 2007

Electronic Communication between Bridged Redox Centers
A R T I C L E S
Chart 2
taphenylene)s, 1-3 (Chart 2), was designed and synthesized,
with spacer lengths estimated to be 2.2, 4.3, and 6.3 nm,
respectively. Model compounds 4, with a monoarylamine
substituent, and 5, with no arylamine substituent, were also
prepared for comparison. Their IVCT behaviors among the
spacer and the two redox centers were investigated by means
of cyclic voltammetry, differential pulse voltammetry, and
chemical oxidation monitored by UV-vis-NIR absorption
spectra. It is believed that the in-depth characterization of the
oxidative formation of radical cations and higher charged states
provides further insight into the intramolecular charge transfer
and charge-carrier transport in this kind of conjugated oligomers
and polymers.
arylamine-substituted ladder-type pentaphenylene materials by
direct Buchwald coupling of brominated pentaphenylene with
diphenylamine is not applicable because the attachment of
diphenylamine to the bulky pentaphenylene does not bring a
remarkable change to the polarity of pentaphenylene and it is
not straightforward to separate the mixture of non-, mono- and
bis(arylamine-substituted) pentaphenylenes. An alternative two-
step approach begins with a Buchwald coupling of primary
anilines with aryl bromides, followed by an Ullmann-type
reaction carried out by arylation of the secondary amine with
aryl iodide. In this work, a modified Buchwald coupling28 of
bromide 6 and 3 equiv of p-toluidine with palladium acetate as
catalyst in toluene generated the symmetrical secondary amine
7 (85%), which was purified by chromatography on silica gel
with dichloromethane/hexane ) 1/15 as eluent. An Ullmann-
type reaction29 was then carried out by refluxing amine 7 with
p-iodotoluene in toluene. This gave the corresponding tertiary
amine, diamine 1 (70%), which was chromatographed on silica
gel with cyclohexane as eluent. The p-methyl substituents were
chosen to ensure reversible oxidation of the arylamine groups
Results and Discussion
Synthesis and Structure Characterization. The synthetic
approach to compounds 1-4 is depicted in Scheme 1. It started
from alkyl- and aryl-substituted ladder-type pentaphenylene 5,
which was previously developed in our laboratory.27 Compound
5 was easily converted into the corresponding dibromopen-
taphenylene 6 (91%) by bromination with copper bromide on
alumina in carbon tetrachloride. Our further synthesis of
1
and clear assignments of the aryl hydrogen in the H NMR
spectrum.
(27) Jacob, J.; Sax, S.; Piok, T.; List, E. J. W.; Grimsdale, A. C.; Mu¨llen, K. J.
Am. Chem. Soc. 2004, 126, 6987.
(28) Sadighi, J. P.; Harris, M. C.; Buchwald, S. L. Tetrahedron Lett. 1998, 39,
5327.
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A R T I C L E S
Zhou et al.
Scheme 1. Synthetic Route of Compounds 1-3a
a Reagents and conditions: (i) CuBr2/alumina, CCl4, 90 °C, 16 h; (ii) p-toluidine, Pd(OAc)2, bis[2-(diphenylphosphino)phenyl] ether, t-C4H9Na, toluene,
80 °C, 8 h; (iii) p-iodotoluene, 1,10-phenanthroline, CuCl, KOH, toluene, 140 °C, 24 h; (iv) n-BuLi, -78 °C, H2O, room temperature, 4 h; (v) n-BuLi,
-78 °C, 2-isoproxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane, room temperature, 24 h; (vi) Ni(COD), bipyridine, COD, DMF, toluene, 80 °C, 48 h; (vii)
Pd(PPh3)4, K2CO3, toluene, H2O, 80 °C, 48 h.
When bromide 6 was treated with 1.2 equiv of p-toluidine
as shown above, the asymmetrically substituted secondary
arylamine 8 was obtained with a yield of 35% and then
transformed via an Ullmann-type reaction to the corresponding
tertiary arylamine 9 (83%). A nickel(0)-mediated Yamamoto
coupling30 of compound 9 produced the crude diamine 2, and
after chromatography on silica gel with cyclohexane as eluent,
the pure product was obtained with a yield of 74%.
Addition of n-butyllithium to the solution of compound 9 in
tetrahydrofuran and quenching with water afforded model
compound 4 (93%). Lithiation of compound 9 with n-butyl-
lithium, followed by addition of 2-isopropoxy-4,4,5,5-tetram-
ethyl-1,3,2-dioxaborolane, produced the corresponding boronate
ester 10 (29%). The diamine 3 was then synthesized by Suzuki
coupling31 of 6 and 10 with Pd(PPh3)4 as catalyst and purified
by chromatography on silica gel with cyclohexane as eluent in
Figure 1. MALDI-TOF MS spectra of diamines 1-3.
49% yield.
The structures of diamines 1-3 are validated by comparing
and the R-protons of the p-octylphenylene close to the bridging
the integration of the singlet peaks at δ ) 2.2 ppm and triplet
methylene (9-position of fluorene) units, respectively. In addition
1
peaks at δ ) 2.5 ppm in the H NMR spectra, which are
to 1H NMR and 13C NMR spectroscopic and elemental analysis
attributed to the p-methyl protons of the bis(p-tolyl)amine units
evidence, MALDI-TOF mass spectra exhibited single intense
signals corresponding to the calculated masses of compounds
1-3, as illustrated in Figure 1, together with an expanded view
of the molecular-ion region.
(29) Zhang, Q.; Chen, J.; Cheng, Y.; Wang, L.; Ma, D.; Jing, X.; Wang, F. J.
Mater. Chem. 2004, 14, 895.
(30) Yamamoto, T. Macromol. Rapid. Commun. 2002, 23, 583.
(31) Miyaura, N.; Suzuki, A. Chem. ReV. 1995, 95, 2457.
9
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Electronic Communication between Bridged Redox Centers
A R T I C L E S
Table 1. Optical Data of Compounds 1-5
toluene solutiona
dichloromethane solutiona
film
λAmbasx(nm)
λPmLax(nm)b
φPL
λAmbasx(nm)
λPmLax(nm)b
φPL
λAmbasx(nm)
λPmLax(nm)b
c
c
compd
1
2
3
4
5
409, 434
411, 435
411, 435
401, 423
376, 397
441, 468
444,469
445, 466
437, 460
399, 420
0.81
0.82
0.81
0.82
0.79
409, 432
411, 435
411, 435
401, 418
374, 395
465
465
465
460
0.84
0.76
0.76
0.71
0.62
413, 439
413, 439
413, 439
403, 426
378,400
446, 471
447, 469
452,469
438, 462
402, 423
401, 420
a Measured in solution with a concentration of 5 × 10-6 M. b Excited at 355 nm. c Fluorescence quantum yield measured relative to 9,10-diphenylanthracene.36
units from one to three leads only to negligible shifts of the
absorption spectra upon going from 1 to 2 and from 2 to 3.
This indicates that the conjugation of the pentaphenylene
backbone no longer extends over two pentaphenylene units,27
unlike typical oligofluorene systems, where the effective
conjugation length reaches the maximum in the 16-mer.32 One
plausible explanation is that the pentaphenylene-substituted
arylamine groups are stronger electron donors than the pen-
taphenylene groups themselves and have a higher impact on
the bathochromic shift of optical absorption than the extension
of the number of pentaphenylene units themselves. Thereby the
effect of conjugation length extension is minimized. The
corresponding PL spectra of compounds 1-5 in toluene
solutions demonstrate two resolved emission bands which are
symmetrical to the absorption spectra and assigned to the 0-0
and 0-1 singlet transitions (Figure 3a).33 The absorption and
PL spectra of compounds 1-5 in dichloromethane solutions
were also investigated. As shown in Figure 2b, the absorption
maxima of compounds 1-5 in dichloromethane solutions are
not significantly distinct from those in toluene solutions. In
contrast, the differences in the PL spectra between dichlo-
romethane solutions and toluene solutions are more remarkable,
except for model compound 5 without an arylamine unit. The
PL spectra of compounds 1-4 in dichloromethane solutions
display a 20-24 nm bathochromic shift of the maximum
intensity compared with those in toluene solutions. In addition,
the resolution of vibrational modes in the PL spectra completely
disappeared, and only one intense broad signal was left. Since
no aggregation absorption or excimer emission was observed,
we attribute this bathochromic shift to a polarized excited state.34
Due to the electron transition from the highest occupied
molecular orbital (HOMO), localized primarily on the arylamine
moieties, to the lowest unoccupied molecular orbital (LUMO),
localized on the pentaphenylene moieties, upon excitation, a
dipole is created in the excited S1 state, much larger than that
of the ground state. Dichloromethane is a more polar solvent
than toluene and therefore is able to stabilize this polarized
excited state by the reorientation of the solvent molecules to
accommodate the increased dipole, lowering the energy of the
system, which induced the even further bathochromic shift of
the PL spectrum of compound 1 in N,N-dimethylformamide
(DMF) solution (λmax ) 467 nm). The absence of aggregation
is also evidenced by the relatively high fluorescence quantum
yield (Φ) of diamines 1-3 in dichloromethane solutions (g76%,
shown in Table 1). This phenomenon of solvent relaxation and
the accompanying increase in Stokes shift with increasing
solvent polarity were also investigated in other donor-substituted
π-bridged systems, where the π-system acts as a acceptor.35
Figure 2. Absorption spectra of compounds 1-5 in toluene and dichlo-
romethane solutions and in solid states.
Figure 3. Photoluminescence spectra of compounds 1-5 in toluene and
dichloromethane solutions and in solid states.
Optical Properties. Compounds 1-5 are soluble in common
organic solvents, such as toluene, dichloromethane, and chlo-
roform. The optical absorption (Figure 2) and photolumines-
cence (PL) (Figure 3) spectra in different solutions were
measured at a concentration of ca. 5 × 10-6 M, and the results
are summarized in Table 1. As shown in Figure 2a, stepwise
incorporation of pentaphenylene with bis(p-tolyl)amine from
compounds 5 to 4 and from 4 to 1 induces 26 and 11 nm
bathochromic shifts, respectively, due to the extended conjuga-
tion. However, the increase in the number of pentaphenylene
(32) Geng, Y.; Trajkovska, A.; Katsis, D.; Ou, J. J.; Culligan, S. W.; Chen, S.
H. J. Am. Chem. Soc. 2002, 124, 8337.
(33) Valeur, B. Molecular Fluorescence; Wiley-VCH: Weinheim, 2002.
(34) Clarke, T. M.; Gordon, K. C.; Kwok, W. M.; Phillips, D. L.; Officer, D.
L. J. Phys. Chem. A 2006, 110, 7696.
(35) Amthor, S.; Lambert, C.; Du¨mmler, S.; Fischer, I.; Schelter, J. J. Phys.
Chem. A 2006, 110, 5204.
(36) Demas, J. N.; Crosby, G. A. J. Phys. Chem. 1971, 75, 991-1024.
9
J. AM. CHEM. SOC. VOL. 129, NO. 40, 2007 12215

A R T I C L E S
Zhou et al.
Figure 4. Cyclic voltammograms of compounds 1 (a), 2 (b), 3 (c), 4 (d),
and 5 (e) in dichloromethane solutions.
Figure 5. Differential pulse voltammograms of compounds 1 (a), 2 (b), 3
(c), 4 (d), and 5 (e) in dichloromethane solutions.
Table 2. Cyclic Voltammetry and Differential Pulse Voltammetry
Data of Compounds 1-5 in Dichloromethanea
Thin films of compounds 1-5 were fabricated by spin-casting
their toluene solutions with the concentration of 20 mg/mL onto
quartz substrates. Compared with the absorption and PL spectra
of compounds 1-5 in toluene solutions, the absorption (Figure
2c) and PL spectra (Figure 3c) of the thin films of compounds
1-5 are almost identical, except that a 1-5 nm bathochromic
shift was observed in their film spectra, probably due to the
slight aggregation of the extended benzenoid system in their
solid states.
compd
E11 2(V)
E21 2(V)
E31 2(V)
E41 2(V)
E51 2(V)
/
/
/
/
/
1
2
3
4
5
0.62 (1e) 0.72 (1e) 1.24 (1e) 1.56 (1e)
0.67 (2e) 1.08 (1e) 1.18 (1e) 1.54 (1e) 1.68 (1e)
0.67 (2e) 1.04 (1e) 1.16 (2e) 1.40 (1e) 1.65 (1e or 2e)
0.67 (1e) 1.14 (1e)
1.11 (1e) 1.52 (1e)
a 1e ) one-electron transfer; 2e ) two-electron transfer. Calculated from
the integral of the DPV.
Electrochemical Properties. The electrochemical behavior
of the diamines 1-3 was investigated by cyclic voltammetry
(CV) (Figure 4) and differential pulse voltammetry (DPV)
(Figure 5), and all data are summarized in Table 2. The CV
and DPV measurements were performed in a solution of Bu4-
NPF6 (0.1 M) in water-free dichloromethane with a scan rate
of 50 mV/s at room temperature under argon. A platinum
electrode was used as the working electrode and an Ag/Ag+
electrode as the reference electrode. For comparison, the CV
and DPV of non- and monoarylamine-substituted pentaphe-
nylenes 4 and 5 were also obtained under the same conditions,
which facilitates the assignment of the individual redox waves.
From the potential of the oxidation onset, the HOMOs of
diamines 1-3 can be estimated to be around -4.9 eV according
to eq 1,37 and then the LUMOs of diamines 1-3 can be
calculated to be around -2.2 eV by subtraction of the optical
sequential removal of electrons from triarylamine and pentaphe-
nylene moieties to form the stable radical cation, dication,
trication, and tetracation. Compared with the CV of monoary-
lamine-substituted pentaphenylene 4 (Figure 4d), the first low-
potential redox wave fits well with that of 4 (E11/2 ) 0.67 V),
indicating that the first electron is removed from one of the
triarylamine units. However, unlike one reversible redox couple
found for compound 4, diamine 1 shows two reversible redox
processes in the low potential region at E11/2 ) 0.62 V and E12/2
) 0.72 V, respectively, which means that the two electrons are
removed successively from the two triarylamine moieties and
a higher potential is needed to transform 1+• into 12+•. This
corresponds to a comproportionation constant of 49, according
to eq 2,38 and suggests diamine 1 to be a class II39 derivative.
Although electrochemical splittings have been often claimed
band gap (2.7 eV) from the -EHOMO
.
Kco ) 10(∆E/0.059)
(2)
EHOMO ) -(E ox + 4.34)
(1)
as probes of delocalization in MV systems, the contribution of
As shown in Figure 4a, diamine 1 displays four reversible
one-electron anodic redox steps, which correspond to the
(38) Richardson, D. E.; Taube, H. Inorg. Chem. 1981, 20, 1278.
(39) Robin, M.; Day, P. AdV. Inorg. Radiochem. 1967, 10, 247. Robin and Day
distinguish among totally independent redox centers (class I), weakly or
medium coupling (valence-trapped) redox centers (class II), and strongly
coupling/completely delocalized centers (class III).
(37) Bard A. J.; Faulkner, L. A. Electrochemical MethodssFundamentals and
Applications; Wiley: New York, 1984.
9
12216 J. AM. CHEM. SOC. VOL. 129, NO. 40, 2007

Electronic Communication between Bridged Redox Centers
A R T I C L E S
electronic coupling to the comproportionation constant was
shown to be small.40 Thus, the electron coupling would
contribute only ca. 5 mV to the comproportionation constant,
while it is likely that the remaining 95 mV of the experimental
splitting is largely due to Coulomb effects. Nevertheless, it is
still not clear how the separations (largely determined by
electrostatics) can be interpreted as evidence of delocalization.
Correspondingly, the DPV of diamine 1 (Figure 5a) also displays
two one-electron oxidations at 0.63 and 0.70 V. The splitting
of the oxidations of two triarylamine units into two steps
suggests effective charge delocalization through the conjugated
ladder-type pentaphenylene in its MV radical monocation 1+•
and long-distance electron communication between the two
triarylamine branches. Compared with the CV and DPV spectra
of pentaphenylene 5 without an arylamine unit, the third (E13/2
) 1.24 V) and the fourth (E41/2 ) 1.56 V) reversible redox
waves of diamine 1 correspond to the oxidation of the
pentaphenylene unit into the radical cation and dication.
However, small positive shifts for the third (∆E3 ) 0.13 V)
and the fourth (∆E4 ) 0.05 V) redox waves suggest that the
triarylamine units are positively charged and withdraw the
electron density from the conjugated pentaphenylene systems.41
More interestingly, the first redox half-wave potential (E1/2
) 0.67 V) of diamine 2 (Figure 4b) is close to that of diamine
1. However, in the case of the diamine 2, the first redox couples
cover two unresolved oxidation processes, indicating that the
two electrons are almost simultaneously removed from the two
triarylamines to form a dication. The corresponding DPV also
shows only one two-electron oxidation process at 0.66 V.
Neither electrostatic effects nor electron coupling could be
observed due to the absence of electrochemical splitting, and
the absence of electron coupling was further proved by chemical
oxidation monitored by UV-vis-NIR absorption spectra. This
is not surprising because the distance between the two redox
centers is so large that they are definitely separated and behave
independently. Another plausible explanation for the lack of
electronic communication could invoke the pentaphenylene-
pentaphenylene torsional junction. In contrast to the third redox
wave of diamine 1, the second oxidation processes of diamine
2 splits into two reversible redox processes at different potentials
(E21/2 ) 1.08 V and E13/2 ) 1.18 V), and the redox waves are
slightly shifted negatively (∆E ) -0.11 V). With the increasing
chain length of the oligopentaphenylenes, the first oxidation
potential of the pentaphenylene shifts gradually to negative
values and the number of possible redox processes successively
increases because of the extension of the conjugated π system.
This is a well-known behavior in homologous series of
conjugated oligomers.42 Similarly, the DPV measurement
(Figure 5b) also gave two oxidation peaks at E ) 1.08 and 1.16
V (∆E ) 0.08 V), which demonstrates that the electrons
delocalize between the two pentaphenylene units and a weak
electron coupling exists in the MV radical trication. In com-
of diamine 2 into its pentacation 25+• and hexacation 26+•
demonstrates an effective intervalence charge transfer between
the pentaphenylene units.
The CV and DPV characterizations of the electrochemical
properties of diamine 3 are shown in Figures 4c and 5c,
respectively. Similar to diamine 2, the first two-electron couples
(E11/2 ) 0.67 V) can be assigned to the simultaneous oxidation
of the two triarylamine branches, as explained above for diamine
2, and there is no evidence for electronic communication
between the two triarylamine centers because of the even longer
distance. Due to the increased number of pentaphenylene units,
the oxidation processes of pentaphenylene units became more
complicated. As illustrated in Figure 5c, the first set of oxidation
processes of the pentaphenylene system splits into a one-electron
process (E21/2 ) 1.04 V) and a two-electron process (E31/2
)
1.16 V), and the oxidation potentials of the oligopentaphenylene
moieties shift slightly negatively (∆E ) -0.03 V) with the same
trend as found for diamine 2. The two-step oxidation processes
are also found in higher potential regions (E41/2 ) 1.40 V, E15/2
) 1.65 V), with ∆E ) 0.25 V, and indicate a stronger electron
coupling among the pentaphenylene units.
UV-Vis-NIR Absorption Spectra of Radical Cations. In
order to further investigate the electronic communication
behavior of the diamines 1-3, chemical oxidation processes of
diamines 1-3 in dichloromethane solutions (ca. 5 × 10-6 M)
were performed, monitoring changes in their UV-vis-NIR
absorption spectra with a stepwise addition of a SbCl5-CH2-
Cl2 solution (ca. 10-4 M). The corresponding spectral properties
of the mono- and dications are shown in Figure 6a-d. For
comparison, the chemical oxidation of monotriarylamine-
substituted pentaphenylene 4 into its monocation 4+• was also
performed, and the result is shown in Figure 6e.
As expected, the oxidation procedure of diamine 1 was
divided into two subprocesses, as shown in Figure 6a,b. With
the stepwise addition of 1 equiv of SbCl5, besides a normal
band at 17 700 cm-1, another very broad band appears in the
NIR region at 5283 cm-1 (1893 nm), which is characteristic
for an extended bridged triarylamine radical monocation and
assigned to the intervalence charge transfer between the two
redox triarylamine centers. The assignment of this long-
wavelength absorption band in the NIR region is consistent with
a previous report on the IVCT band.43 However, unlike other
IVCT systems with similar bridge length, the IVCT band of
1+• is very clear and intense. Furthermore, the molar extinction
coefficients at 17 700 and 5283 cm-1 are almost the same (ꢀ5283
) 15 239 M-1 cm-1). Upon further oxidation with 2 equiv of
SbCl5, the NIR band at 5283 cm-1 completely disappears and
the intensity of the band at 17 700 cm-1 decreases a little, while
an intense band at 7770 cm-1, with a clear isosbestic point at
6270 cm-1, increases continuously, obviously due to the
triarylamine radical dication formation. For a more precise
assignment of the triarylamine radical cation and dication bands,
chemical oxidation with 1 equiv of SbCl5 in dichloromethane
was performed on monoamine 4, a model compound in which
there is only one triarylamine center and a triarylamine-to-
triarylamine IVCT transition is impossible. A rather intense band
was observed in the NIR region (7184 cm-1), which corresponds
to the electron transition from the highest bridge-based orbital
parison to diamine 1, the higher oxidation potential (E14/2
)
1.54 V) of the pentaphenylene units also shifts to negative
potentials (∆E ) -0.02 V) due to the extended conjugation.
However, with increasing number of pentaphenylene units, a
resolved new redox wave appears in the higher potential region
(E51/2 ) 1.68 V). The splitting of the oxidation (∆E ) 0.14 V)
(40) Creutz, C. Prog. Inorg. Chem. 1983, 30, 1.
(41) Cremer, J.; Mena-Osteritz, E.; Pschierer, N. G.; Mu¨llen, K.; Ba¨uerle, P.
Org. Biomol. Chem. 2005, 3, 985.
(42) Heinze, J.; Tschunky, P. Electronic Materials: The Oligomer Approach;
Wiley-VCH: Weinheim, 1998.
(43) Lambert, C.; No¨ll, G. Chem. Eur. J. 2002, 8, 3467.
9
J. AM. CHEM. SOC. VOL. 129, NO. 40, 2007 12217

A R T I C L E S
Zhou et al.
Figure 6. UV-vis-NIR absorption spectra of compounds 1 (a,b), 2 (c), 3 (d), and 4 (e) in dichloromethane solutions upon addition of SbCl5.
to the terminal redox center (bridge f R+•).44 The absorption
spectrum of dication 12+• is similar to that of monocation 4+•
in the low-energy region with approximately twice the absorp-
tivity, suggesting that the intense band at 7770 cm-1 of dication
shape using eq 3,48 where V˜max is the band energy in cm-1, V˜1/2
0.0206
V )
V˜max V˜1/2 ꢀ
x
(3)
d
1
2+• also originates from the charge transfer from the electron-
is the bandwidth at half-height in cm-1, ꢀ is the molar extinction
coefficient, and d in Å is taken as the distance between the two
N atoms. V˜max is found to be 5283 cm-1. Since the spectra could
not be measured in a lower energy region, for crude estimation
of the V˜1/2 value, we assumed that the IVCT band was
symmetrical and took the double dispersion from the IVCT band
maximum to its half-height of the high-energy wavelength with
the value of 4250 cm-1. The electronic coupling energy V is
then calculated to be 548 cm-1 (1.6 kcal/mol). This result is
close to that for another reported IVCT compound, C425 (500
cm-1), with a shorter bridge length (1.93 nm) but stronger donor
(anisylamine), and demonstrates that diamine 1 can really be
classified into class II,39 as suggested already from eq 2. A
problem in applying Hush’s eq 3 is in determining the
appropriate value of the diabatic electron-transfer distance, d.44
In traditional inorganic MV systems, the metal-metal geometric
separation is often used as an approximation, but in organic
systems, there is more difficulty in defining the appropriate
center of the charge-bearing unit. Especially when the conju-
gated bridge is electron-rich, the oxidation may not be centered
rich and easily oxidized bridge to the donor radical cations.
Moreover, higher energy transitions were observed at 17 510
cm-1, with a shoulder at 18 940 cm-1 and the decreasing band
at 23 920 cm-1. The new absorption band is close to that of
[(p-MeC6H4)3N]+• (15 000 cm-1 in acetonitrile),45 and the
hypsochromic shift was also reported elsewhere,44 which
indicates that the higher energy absorption bands are assigned
to the localized electron transitions from the HOMO to the
LUMO.46 The absorption shoulder at around 18 940 cm-1 is
probably due to the 0-1 singlet transition, and the slight
hypsochromic shift in the higher energy region observed upon
going from 1+• to 12+• could be ascribed to the changes of the
electron energy levels between 1+• and 12+•
.
The IVCT band found for 1+• should be analyzed as is often
done for CT compounds. According to Hush,47 the electronic
coupling can be calculated from the IVCT band maximum and
(44) (a) Barlow, S.; Risko, C.; Chung, S.-J.; Tucker, N. M.; Coropceanu, V.;
Jones, S. C.; Levi, Z.; Bre´das, J.-L.; Marder, S. R. J. Am. Chem. Soc. 2005,
127, 16900. (b) Rosokha, S. V.; Sun, D.-L.; Kochi, J. K. J. Phys. Chem. A
2002, 106, 2283.
(45) Walter, R. I. J. Am. Chem. Soc. 1966, 88, 1923.
(46) Zimmer, K.; Go¨dicke, B.; Hoppmeier, M.; Mayer, H.; Schweig, A. Chem.
Phys. 1999, 248, 263.
(48) Creutz, C.; Newton, M. D.; Sutin, N. J. Photochem. Photobiol. A 1994,
82, 47.
(47) Hush, N. S. Electrochim. Acta 1968, 13, 1005.
9
12218 J. AM. CHEM. SOC. VOL. 129, NO. 40, 2007

Electronic Communication between Bridged Redox Centers
A R T I C L E S
exactly at the nitrogen atom but displaced somewhat into the
bridge. Moreover, in both organic and inorganic cases, any
delocalization of the charge away from the formal charge-
bearing center toward the bridging group (for the diabatic states)
will lead to reduced d. Thus, the value of V is likely to be a
lower limit; i.e., the appropriate value of the diabatic electron-
transfer distance is likely shorter than the N-N distance.
Figure 6c,d shows the evolution of absorption spectra of
diamines 2 and 3 in dichloromethane solutions with the titration
of SbCl5. However, quite different from the spectrum of diamine
1, no IVCT band is observed when diamines 2 and 3 are
chemically oxidized into monocations 2+• and 3+• with 1 equiv
of SbCl5. Only “bridge f R+•” transitions at around 7000 cm-1
were observed in the low-energy region, along with localized
nylene ethynylene, which results in a better electron delocal-
ization. Moreover, the electron coupling and hopping may be
different if anisylamine instead of tolylamine groups are used
due to the better charge localization at the triarylamine, and
this will be discussed in our future work. Furthermore, we also
have a stable bridge which can be reversibly charged up to the
tetracation for diamine 1, hexacation for 2, and octacation for
3. These findings provide evidence for long π-bridging, still
allowing effective charge transfer between the redox centers
with bridge lengths of 5-10 phenylene rings. Ongoing work is
focused on their other optoelectronic applications, such as LED
and two-photon absorption studies.
Experimental Section
transitions of the arylamine monocation around 17 180 cm-1
.
All chemicals and reagents were used as received from commercial
sources without further purification. Solvents for chemical synthesis
were purified or freshly distilled prior to use according to standard
procedures. All chemical reactions were carried out under an inert
atmosphere. Intermediate ladder-type pentaphenylene 5 and dibromo-
functionalized pentaphenylene 6 were synthesized according to previous
work in our group.27 1H and 13C NMR spectra were recorded on a
Bruker AMX 300 NMR instrument (300 and 75 MHz, respectively)
with dichloromethane-d as solvent and tetramethylsilane as internal
standard. The UV-vis-NIR absorption measurements were performed
on a Perkin-Elmer Lambda 15 spectrophotometer, and the PL measure-
ments on a SPEX Fluorolog 2 type F212 steady-state fluorometer.
Cyclic voltammetry and differential pulse voltammetry were performed
on an EG&G Princeton Applied Research potentiostat, model 273, in
a solution of Bu4NPF6 (0.1 M) in dry dichloromethane with a scan
rate of 50 mV/s at room temperature under argon. A platinum electrode
was used as the working electrode, an Ag/AgCl electrode as the
reference electrode, and a platinum wire as the counter electrode.
Synthesis of Compound 7. Under nitrogen atmosphere, a mixture
of 6 (895 mg, 0.5 mmol), p-toluidine (161 mg, 1.5 mmol), Pd(OAc)2
(11 mg, 0.05 mmol), bis[2-(diphenylphosphino)phenyl] ether (DPEphos)
(54 mg, 0.1 mmol), and sodium tert-butoxide (144 mg, 1.5 mmol) in
toluene (50 mL) was stirred and heated at 80 °C for 8 h. After the
reaction solution cooled to room temperature, a saturated ammonium
chloride solution was added. The solution was extracted with ethyl
acetate, and the extract was washed with brine and dried over
magnesium sulfate. The crude product obtained was purified by flash
column chromatography (silica gel, dichloromethane/hexane ) 0 to
1/15 v/v). A yellowish solid was obtained with a yield of 85% (780
With further charging toward dications 22+• and 32+•, the radical
bands show almost double the absorbance of the mono-oxidized
2+• and 3+•. This proves that the bridge distance is so long that
the two triarylamines are absolutely isolated and the charge is
localized at different redox centers. The absorption intensity of
the neutral pentaphenylene at 22 990 cm-1 in dication 32+• is
much higher than those for dications 12+• and 22+• due to a
neutral central pentaphenylene unit.
Conclusions
In summary, a series of oligo(ladder-type pentaphenylene)s
1-5, with or without ending bis(p-tolyl)amine substituents, has
been designed and synthesized. The key intermediate is a
monobromide-functionalized pentaphenylene 9, obtained in
moderate yields by an alternative two-step approach which
involves an asymmetrical Buchwald coupling and an Ullmann-
type arylation. Compared with the PL spectra of compounds
1-4 in toluene solutions, the PL spectra in dichloromethane
solutions exhibit a 20-24 nm bathochromic shift due to the
solvent-induced polarized excited states. The CV spectrum of
diamine 1 shows a resolved splitting of oxidation with ∆E )
0.10 V, corresponding to the stepwise oxidation of the two
arylamines into 1+• and 12+•. Chemical oxidation of diamine 1
by SbCl5 in dichloromethane solution reveals a broad IVCT
band around 5283 cm-1 (1893 nm) which disappears upon
further oxidation of 1+• into 12+•. Thus, a charge-transfer band
indicating the hopping between the two arylamine centers was
found only for compound 1. No electronic communication
between the two arylamine moieties was observed in diamines
2 and 3. Here, the distances between the two arylamine centers
in diamine 1 is comparable to that of the long phenylene
ethynylene bridges used by Lambert et al. for studying intramo-
lecular charge transfer. However, in their two cases, the bridge
lengths of compounds C425 and C526 were 1.93 and 2.87 nm,
respectively, and the IVCT bands were so weak that they could
only be observed as small shoulders on the outer rings of the
cation absorption spectra. Only for a much shorter dipheny-
lacetylene bridge between the two arylamines, such as com-
pound C349 with a bridge length of 1.25 nm, were similar intense
IVCT bands reported. There, as here, the intensity of the NIR
bands reaches an intensity comparable with those of the cation
bands in the visible region. The relatively higher electronic
coupling energy in MV cation 1+• can probably be ascribed to
the more planar ladder-type pentaphenylene spacer than phe-
1
mg). H NMR (300 MHz, CD2Cl2): δ (ppm) 7.68 (s, 2H), 7.54 (s,
2H), 7.45 (s, 2H), 7.39 (s, 1H), 7.35 (s, 1H), 7.16 (d, 8H, J ) 7.8 Hz),
7.02 (d, 8H, J ) 8.4 Hz), 6.98-6.84 (m, 10H), 6.81 (d, 2H, J ) 8.4
Hz), 5.72 (s, 2H), 2.51 (t, 8H, J ) 7.5 Hz), 2.20 (s, 6H), 1.88 (m, 8H),
1.50 (m, 8H), 1.21-1.11 (m, 40H), 1.05-0.99 (m, 40H), 0.79-0.68
(m, 24H), 0.62 (m, 8H). 13C NMR (75 MHz, CD2Cl2): δ (ppm) 153.21,
152.30, 151.73, 150.62, 144.14, 143.49, 141.86, 141.71, 141.12, 140.44,
138.66, 134.46, 130.94, 130.24, 128.74, 128.65, 120.84, 118.59, 117.53,
116.38, 114.79, 112.08, 64.78, 41.17, 35.95, 32.32, 32.25, 31.96, 30.52,
29.96, 29.89, 29.77, 29.67, 24.41, 23.10, 23.03, 20.80, 14.32. MALDI-
TOF: m/z 1841.7. Elemental Analysis for C136H180N2, calculated: C,
88.64; H, 9.84; N, 1.52. Found: C, 88.68; H, 9.62; N, 1.38.
Synthesis of Diamine 1. To a 100 mL Schlenk flask containing 7
(450 mg, 0.24 mmol), p-iodotoluene (262 mg, 1.2 mmol), 1,10-
phenanthroline (6 mg, 0.03 mmol), cuprous chloride (3 mg, 0.03 mmol),
and potassium hydroxide (560 mg, 10 mmol), using argon as the purge
gas and a Dean-Stark trap under a reflux condenser, was added 60
mL of toluene. The reaction mixture was reluxed at 140 °C for 24 h
and quenched with acetic acid. After cooling to room temperature, the
solution was extracted with ethyl acetate, washed with ammonia and
water, and then dried by magnesium sulfate. After evaporation of the
solvent under vacuum, the residue was purified by flash column
(49) Lambert, C.; No¨ll, G. Angew. Chem., Int. Ed. 1998, 37, 2107.
9
J. AM. CHEM. SOC. VOL. 129, NO. 40, 2007 12219

A R T I C L E S
Zhou et al.
chromatography (silica gel) using cyclohexane as eluent. A yellow solid
was obtained with a yield of 70% (346 mg). 1H NMR (300 MHz, CD2-
Cl2): δ (ppm) 7.68 (s, 2H), 7.53 (s, 2H), 7.45 (s, 2H), 7.35 (s, 1H),
7.32 (s, 1H), 7.15 (d, 8H, J ) 8.4 Hz), 7.02 (d, 10H, J ) 8.1 Hz), 6.97
(d, 10H, J ) 7.8 Hz), 6.88 (d, 8H, J ) 6.9 Hz), 2.47 (t, 8H, J ) 7.5
Hz), 2.21 (s, 12H), 1.82 (m, 8H), 1.50 (m, 8H), 1.22-1.17 (m, 40H),
1.12-0.98 (m, 40H), 0.80-0.71 (m, 24H), 0.60 (m, 8H). 13C NMR
(75 MHz, CD2Cl2): δ (ppm) 152.76, 152.30, 151.72, 144.01, 141.83,
140.40, 132.52, 130.24, 130.10, 129.91, 128.68, 128.58, 124.77, 124.44,
124.37, 124.25, 124.18, 124.14, 118.66, 117.55, 116.70, 114.77, 64.72,
40.89, 35.88, 32.26, 32.21, 31.89, 30.40, 30.07, 29.89, 29.82, 29.70,
29.61, 24.36, 23.04, 23.00, 20.84, 14.25. MALDI-TOF: m/z 2023.7.
Elemental analysis for C150H192N2, calculated: C, 89.05; H, 9.57; N,
1.38. Found: C, 89.25; H, 9.61; N, 1.34.
Synthesis of Compound 4. Under nitrogen atmosphere and at
-78 °C, n-BuLi (0.1 mL, 1.6 M in hexane) was added dropwise to a
dry tetrahydrofuran (20 mL) solution containing 9 (240 mg, 0.13 mmol).
After the reactin solution was stirred for 10 min at -78 °C, 0.1 mL of
saturated brine was added slowly. The solution was brought back to
room temperature, and after being stirred for another 4 h, the reaction
was quenched by brine. The solution was extracted with ethyl acetate,
and the extract was washed with brine and dried over magnesium
sulfate. The crude product was subjected to flash column chromatog-
raphy (silica gel, petroleum ether). Compound 4 was obtained as a
1
yellow powder with a yield of 93% (215 mg). H NMR (300 MHz,
CD2Cl2): δ (ppm) 7.71 (s, 1H), 7.69 (s, 1H), 7.59 (s, 1H), 7.56 (s,
1H), 7.54 (s, 1H), 7.51 (m, 1H), 7.46 (s, 1H), 7.34 (d, 1H, J ) 8.1
Hz), 7.24 (s, 1H), 7.16 (d, 10H, J ) 7.5 Hz), 7.02 (d, 8H, J ) 8.1 Hz),
6.96 (d, 5H, J ) 8.4 Hz), 6.87 (d, 4H, J ) 8.4 Hz), 6.78 (d, 1H, J )
8.1 Hz), 2.47 (t, 8H, J ) 7.8 Hz), 2.20 (s, 6H), 1.92 (m, 4H), 1.79 (m,
4H), 1.50 (m, 8H), 1.21-1.16 (m, 40H), 1.11-0.96 (m, 40H), 0.79-
0.67 (m, 24H), 0.60 (m, 8H). 13C NMR (75 MHz, CD2Cl2): δ (ppm)
152.78, 152.43, 152.33, 151.77, 151.65, 151.49, 151.17, 151.05, 147.94,
146.02, 144.02, 141.87, 141.48, 141.40, 140.68, 140.26, 139.94, 138.91,
135.83, 132.53, 130.12, 128.72, 128.60, 127.23, 126.99, 125.81, 124.39,
124.34, 123.26, 122.70, 120.50, 119.95, 118.66, 117.77, 117.61, 117.43,
116.73, 114.93, 114.84, 64.76, 41.02, 40.93, 35.91, 32.29, 32.25, 32.18,
31.93, 30.50, 30.44, 29.92, 29.85, 29.74, 29.64, 24.38, 24.30, 23.07,
23.03, 22.98, 20.89, 14.29, 14.24. MALDI-TOF: m/z 1827.4. Elemental
analysis for C136H179N, calculated: C, 89.36; H, 9.87; N, 0.77. Found:
C, 89.47; H, 9.65; N, 0.57.
Synthesis of Compound 8. Under nitrogen atmosphere, a mixture
of 6 (1.79 g, 1.0 mmol), p-toluidine (128 mg, 1.2 mmol), Pd(OAc)2
(23 mg, 0.1 mmol), DPEphos (107 mg, 0.2 mmol), and sodium tert-
butoxide (144 mg, 1.5 mmol) in toluene (50 mL) was stirred and heated
at 80 °C for 8 h. After the reaction solution cooled to room temperature,
saturated ammonium chloride solution was added. The solution was
extracted with ethyl acetate, and the extract was washed with brine
and dried over magnesium sulfate. The crude product was subjected
to flash column chromatography (silica gel, dichloromethane/hexane
) 0 to 1/15 v/v). A yellowish solid was obtained with a yield of 35%
1
(635 mg). H NMR (300 MHz, CD2Cl2): δ (ppm) 7.71 (s, 1H), 7.69
(s, 1H), 7.57 (s, 1H), 7.54 (s, 2H), 7.45 (s, 1H), 7.41-7.30 (m, 4H),
7.17 (d, 8H, J ) 8.4 Hz), 7.03 (d, 9H, J ) 8.1 Hz), 6.95-6.91 (m,
3H), 6.84 (d, 1H, J ) 8.1 Hz), 5.74 (s, 1H), 2.48 (t, 8H, J ) 7.8 Hz),
2.21 (s, 3H), 1.88 (m, 8H), 1.50 (m, 8H), 1.27-1.17 (m, 40H), 1.11-
0.99 (m, 40H), 0.79-0.68 (m, 24H), 0.59 (b, 8H). 13C NMR (75 MHz,
CD2Cl2): δ (ppm) 153.79, 153.19, 152.43, 152.31, 151.85, 151.73,
150.81, 150.61, 144.01, 143.85, 143.52, 141.93, 141.86, 141.04, 140.98,
140.64, 140.48, 140.16, 139.87, 138.42, 135.97, 134.32, 133.29, 130.95,
130.19, 130.11, 128.70, 128.59, 126.52, 121.37, 121.03, 118.66, 118.58,
118.51, 117.82, 117.53, 116.31, 114.85, 64.73, 41.10, 40.92, 35.88,
32.26, 32.18, 32.14, 31.90, 30.46, 30.34, 29.90, 29.83, 29.70, 29.61,
24.36, 24.22, 23.04, 22.97, 20.74, 14.25, 14.22. MALDI-TOF: m/z
1816.9. Elemental analysis for C129H172BrN, calculated: C, 85.29; H,
9.54; Br, 4.40; N, 0.77. Found: C, 85.28; H, 9.48; N, 0.74.
Synthesis of Compound 10. Under nitrogen atmosphere and at
-78 °C, n-BuLi (0.43 mL, 1.6 M in hexane) was added dropwise to a
dry tetrahydrofuran (20 mL) solution containing 9 (1.20 g, 0.63 mmol).
After the reaction solution was stirred for 30 min at -78 °C, 0.25 mL
(1.2 mmol) of 2-isoproxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane was
added slowly. The solution was brought back to room temperature,
and after being stirred for another 24 h, the reaction was quenched
with brine. The solution was extracted with ethyl acetate, and the extract
was washed with brine and dried over magnesium sulfate. The crude
product was separated by flash column chromatography (silica gel,
dichloromethane/hexane ) 0 to 1/5 v/v). Compound 10 was obtained
as a yellow powder with a yield of 29% (230 mg). 1H NMR (300 MHz,
CD2Cl2): δ (ppm) 7.73 (s, 1H), 7.70 (s, 1H), 7.60 (d, 2H, J ) 6.9 Hz),
7.53 (d, 2H, J ) 6 Hz), 7.46 (s, 2H), 7.36 (s, 1H), 7.33 (s, 1H), 7.16
(d, 8H, J ) 8.1 Hz), 7.02 (d, 8H, J ) 7.8 Hz), 6.97 (d, 5H, J ) 8.4
Hz), 6.87 (d, 4H, J ) 8.7 Hz), 6.78 (d, 1H, J ) 8.1 Hz), 2.48 (t, 8H,
J ) 7.8 Hz), 2.22 (s, 6H), 1.94 (m, 4H), 1.82 (m, 4H), 1.50 (m, 8H),
1.27 (s, 12H), 1.20-1.17 (m, 40H), 1.08-0.98 (m, 40H), 0.80-0.67
(m, 24H), 0.60-0.57 (m, 8H). 13C NMR (75 MHz, CD2Cl2): δ (ppm)
161.97, 159.06, 151.61, 151.15, 150.61, 150.52, 149.47, 147.84, 144.84,
142.82, 142.77, 140.74, 140.71, 140.22, 131.95, 131.37, 128.94, 127.53,
127.42, 125.14, 123.21, 122.42, 121.52, 116.71, 116.42, 112.67, 103.56,
100.37, 99.25, 93.84, 93.38, 92.92, 82.90, 63.58, 34.73, 31.11, 31.06,
30.99, 30.74, 29.25, 28.74, 28.67, 28.55, 28.46, 28.41, 23.98, 21.89,
21.85, 21.80, 19.70, 13.10. FD-MASS: m/z 1953.2.
Synthesis of Compound 9. To a 100 mL Schlenk flask containing
8 (600 mg, 0.33 mmol), p-iodotoluene (218 mg, 1 mmol), 1,10-
phenanthroline (6 mg, 0.03 mmol), cuprous chloride (3 mg, 0.03 mmol),
and potassium hydroxide (560 mg, 10 mmol), using argon as the purge
gas and a Dean-Stark trap under a reflux condenser, was added 60
mL of toluene. The reaction mixture was reluxed at 140 °C for 24 h
and quenched with acetic acid. After cooling to room temperature, the
solution was extracted with ethyl acetate, washed with ammonia and
water, and then dried by magnesium sulfate. After evaporation of the
solvent under vacuum, the residue was purified by flash column
chromatography (silica gel) with petroleum ether as eluent. A yellow
solid was obtained with a yield of 83% (520 mg). 1H NMR (300 MHz,
CD2Cl2): δ (ppm) 7.71 (s, 1H), 7.69 (s, 1H), 7.57 (s, 1H), 7.54 (s,
2H), 7.46 (s, 1H), 7.40-7.29 (m, 4H), 7.15 (d, 8H, J ) 7.5 Hz), 7.02
(d, 8H, J ) 8.1 Hz), 6.96 (d, 5H, J ) 8.4 Hz), 6.87 (d, 4H, J ) 8.4
Hz), 6.78 (d, 1H, J ) 8.1 Hz), 2.47 (t, 8H, J ) 7.5 Hz), 2.20 (s, 6H),
1.91 (m, 4H), 1.79 (m, 4H), 1.49 (m, 8H), 1.21-1.16 (m, 40H), 1.11-
0.97 (m, 40H), 0.79-0.68 (m, 24H), 0.60 (b, 8H). 13C NMR (75 MHz,
CD2Cl2): δ (ppm) 153.80, 152.78, 152.48, 152.37, 151.88, 151.79,
151.07, 150.83, 147.96, 146.00, 143.98, 143.85, 141.95, 141.89, 141.57,
140.91, 140.65, 140.47, 140.22, 139.99, 138.81, 137.58, 135.78, 132.54,
131.61, 130.12, 128.75, 128.72, 128.58, 126.52, 124.40, 121.39, 121.08,
120.50, 118.63, 117.86, 117.58, 116.73, 64.75, 40.91, 35.90, 32.28,
32.24, 32.16, 31.92, 30.42, 30.37, 29.91, 29.85, 29.73, 29.63, 24.37,
24.23, 23.06, 23.03, 22.98, 20.88, 14.28, 14.24. MALDI-TOF: m/z
1905.8. Elemental analysis for C136H178BrN, calculated: C, 85.67; H,
9.41; Br, 4.19; N, 0.73. Found: C, 85.85; H, 9.16; N, 0.77.
Synthesis of Diamine 2. A solution of bis(1,5-cyclooctadiene)nickel
(100 mg, 0.36 mmol), 2,2′-bipyridine (60 mg, 0.38 mmol), and 1,5-
cyclooctadiene (0.05 mL, 0.4 mmol) was dissolved in dry toluene (4
mL) and dry N,N-dimethylformamide (4 mL) in a Schlenk flask within
a glovebox. The mixture was heated to 60 °C with stirring under argon
for 30 min. A solution of bromide 9 (570 mg, 0.30 mmol) in 8 mL of
dry toluene was then added, and the reaction mixture was stirred at
80 °C for 2 days. After cooling to room temperature, the reaction
mixture was poured into chloroform and washed with water and brine.
The separated organic layer was dried over magnesium sulfate, and
the solvent was evaporated. Chromatography of the crude product on
silica gel with cyclohexane as eluent gave diamine 2 as a yellow powder
1
(405 mg, 74%). H NMR (300 MHz, CD2Cl2): δ (ppm) 7.73 (s, 2H),
7.70 (s, 2H), 7.61 (d, 4H, J ) 4.8 Hz), 7.58 (s, 2H), 7.55 (s, 5H), 7.51
9
12220 J. AM. CHEM. SOC. VOL. 129, NO. 40, 2007

Electronic Communication between Bridged Redox Centers
A R T I C L E S
(s, 1H), 7.47 (s, 2H), 7.36 (s, 1H), 7.33 (s, 1H), 7.18 (d, 8H, J ) 8.4
Hz), 7.16 (d, 8H, J ) 5.4 Hz), 7.04 (d, 8H, J ) 8.4 Hz), 7.03 (d, 8H,
J ) 8.4 Hz), 6.96 (d, 10H, J ) 8.4 Hz), 6.88 (d, 8H, J ) 8.4 Hz), 6.78
(d, 2H, J ) 7.5 Hz), 2.49 (t, 16H, J ) 7.8 Hz), 2.21 (s, 12H), 2.00 (m,
8H), 1.80 (m, 8H), 1.53-1.46 (m, 16H), 1.22-1.17 (m, 80H), 1.09-
0.99 (m, 80 H), 0.79-0.62 (m, 64H). 13C NMR (75 MHz, CD2Cl2): δ
(ppm) 152.77, 152.45, 152.34, 152.26, 151.76, 151.52, 151.05, 147.95,
146.10, 146.07, 146.02, 145.99, 144.01, 143.98, 141.91, 141.87, 141.48,
141.10, 140.72, 140.56, 140.24, 139.97, 138.89, 135.85, 135.80, 132.53,
130.12, 128.72, 128.61, 126.21, 124.39, 122.74, 122.70, 121.63, 120.24,
118.65, 117.77, 117.60, 117.47, 116.73, 114.99, 114.85, 64.77, 41.05,
40.91, 35.90, 32.28, 32.23, 32.15, 31.92, 30.42, 29.91, 29.85, 29.72,
29.63, 24.37, 24.29, 23.06, 23.02, 22.96, 20.87, 14.27, 14.22. MALDI-
TOF: m/z 3655.3. Elemental analysis for C272H356N2, calculated: C,
89.41; H, 9.82; N, 0.77. Found: C, 89.29; H, 9.73; N, 0.70.
7.73 (s, 2H), 7.70 (s, 2H), 7.63-7.51 (m, 21H), 7.46 (s, 2H), 7.36 (s,
1H), 7.33 (s, 1H), 7.21-7.15 (m, 25H), 7.06-7.01 (m, 25H), 6.97 (d,
11H, J ) 8.4 Hz), 6.87 (d, 9H, J ) 8.4 Hz), 6.79 (d, 2H, J ) 8.1 Hz),
2.49 (t, 24H, J ) 7.2 Hz), 2.21 (s, 12H), 2.00 (b, 8H), 1.82 (b, 4H),
1.80, 1.51 (m, 24H), 1.22-1.17 (m, 120H), 1.12-0.99 (m, 120H),
0.79-0.63 (m, 96H). 13C NMR (75 MHz, CD2Cl2): δ (ppm) 152.76,
152.47, 152.44, 152.32, 152.25, 151.78, 151.75, 151.51, 151.04, 147.91,
145.99, 144.00, 143.96, 141.93, 141.90, 141.86, 141.46, 141.17, 141.08,
140.69, 140.52, 140.23, 139.96, 139.89, 138.88, 135.81, 132.52, 131.79,
130.10, 128.74, 128.60, 126.21, 124.37, 122.68, 121.62, 120.49, 120.25,
120.21, 117.78, 117.47, 116.71, 64.76, 41.05, 40.92, 35.89, 32.26, 32.22,
32.14, 32.03, 31.91, 30.41, 30.08, 29.90, 29.83, 29.71, 29.61, 24.35,
24.27, 23.04, 23.00, 22.95, 20.85, 14.25, 14.20. MALDI-TOF: m/z
5283.0. Elemental analysis for C394H520N2, calculated: C, 89.55; H,
9.92; N, 0.53. Found: C, 89.30; H, 9.82; N, 0.49.
Synthesis of Diamine 3. The dibromopentaphenylene 6 (90 mg, 1
mmol) and boronate ester 10 (220 mg, 3 mmol) in toluene (25 mL)
and 2 M aqueous Na2CO3 solution (25 mL) were mixed together in a
100 mL Schlenk flask. The solution was purged with argon for 20 min,
6 mg (10% mol) of tetrakis(triphenylphosphine)palladium was added.
and the reaction was heated at 85 °C for 48 h. The cooled mixture was
extracted with ethyl acetate, and the extract was washed with saturated
brine and then dried over magnesium sulfate. After removal of the
solvent, the residue was purified by column chromatography using
cyclohexane as eluent. The diamine 3 was isolated as a yellow powder
Acknowledgment. This work was financially supported by
the Bundesministerium fu¨r Bildung and Forschung (Projects
13N8165 OLAS and 13N8215 OLED) and by Dupont Displays.
G.Z. gratefully acknowledges the Alexander von Humboldt
Stiftung for the grant of a research fellowship.
Supporting Information Available: 1H NMR spectra of
compounds 1-10. This material is available free of charge via
the Internet at http://pubs.acs.org.
1
(130 mg, 49%). H NMR (300 MHz, CD2Cl2): δ (ppm) 7.75 (s, 2H),
JA073148S
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J. AM. CHEM. SOC. VOL. 129, NO. 40, 2007 12221