Bridging nanogap electrodes by in situ electropolymerization of a bis(terthiophenylphenanthroline)ruthenium complex

Article abstract of DOI:10.1002/chem.200400063

A novel complex containing a 3,8-bis[terthiophenyl-(1,10-phenanthroline)] ligand coordinated to [Ru(bpy)₂] was synthesized and characterized by electrochemical and spectroscopic techniques. The complex was shown to be a suitable starting material for the electrode position of functionalized molecular wires between nanogap electrodes to generate stable molecular nanodevices. Temperature-dependent nonlinear I-V curves were obtained at 80-300 K. The material can also be deposited on indium tin oxide (ITO) to form compact electrochromic films at surface concentrations lower than ≈ 1 × 10 ^-8 mol cm²; however, a more loosely bond fibrous form is preferentially deposited at higher surface concentrations.

Full text of DOI:10.1002/chem.200400063

FULL PAPER
Bridging Nanogap Electrodes by In Situ Electropolymerization of a
Bis(terthiophenylphenanthroline)ruthenium Complex
Koiti Araki,*[a, b, d] Hiroaki Endo,[a, b] Gou Masuda,[c] and Takuji Ogawa*[a, b]
Abstract: A novel complex containing
3,8-bis[terthiophenyl-(1,10-phenan-
electrodes to generate stable molecular
nanodevices. Temperature-dependent
nonlinear I V curves were obtained at
80 300 K. The material can also be de-
posited on indium tin oxide (ITO) to
form compact electrochromic films at
surface concentrations lower than
a
throline)] ligand coordinated to
[Ru(bpy)2] was synthesized and charac-
terized by electrochemical and spectro-
scopic techniques. The complex was
shown to be a suitable starting material
for the electrodeposition of functional-
ized molecular wires between nanogap
ꢀ1î10À8 molcm2; however,
a more
loosely bond fibrous form is preferen-
tially deposited at higher surface con-
centrations.
Keywords: conducting materials
electrochemistry ligands
nanogap devices ¥ ruthenium
¥
¥
¥
N
Introduction
fragile for practical applications. To overcome these difficul-
ties, we started to pursue the possibility of using arrays of
molecules and nanoparticles for that purpose. In previous
work, we showed that stable arrays of gold nanoparticles
can be easily obtained with 1,10-decanedithiol bridging
units.[6] This material exhibits semiconductor-like properties
with characteristic sigmoidal-shaped I V curves and a linear
logI versus 1/T relationship when attached to gold micro-
electrodes, in contrast with the bulk material that showed
ohmic behavior. The difference was attributed to mesoscop-
ic effects, and was explained by means of the Coulomb
blockade theory. Herein, we describe the synthesis and char-
acterization of new bis(thienyl)-1,10-phenanthrolines coordi-
nated to a [Ru(bpy)2] group (Scheme 1 and Scheme 2). The
bis(terthienyl) derivative is electropolymerizable and was
used to connect nanogap electrodes to generate stable mo-
lecular devices that exhibit temperature-dependent nonlin-
ear I V curves.
The development of molecular devices requires the prepara-
tion of functional materials with suitable properties.[1] Mo-
lecular wires based on, for example, phenylacetylene, thio-
phenylacetylene, and phenylenevinylene frameworks have
been proposed and realized;[2] however, the preparation of
long unidimensional conducting molecules is still hampered
by synthetic difficulties. Also, little has been reported on the
measurement of molecular conduction properties,[3 and
the majority of the devices were prepared by means of
break junction or electrical migration techniques. Such devi-
ces are very difficult to fabricate, and they seem to be too
5]
[a] Dr. K. Araki, H. Endo, Prof. Dr. T. Ogawa
Research Center for Molecular Nanoscience
Institute for Molecular Science
Okazaki National Research Institutes
Nishigo-Naka 38, Myodaiji-cho, Okazaki, Aichi, 444-8585 (Japan)
E-mail: koiaraki@iq.usp.br
ogawat@ims.ac.jp
Results and Discussion
[b] Dr. K. Araki, H. Endo, Prof. Dr. T. Ogawa
Japan and Core Research for Evolutional Science and Technology
(CREST) of Japan Science and Technology Agency (JST)
Hon-machi 4-1-8, Kawaguchi, Saitama, 332-0012 (Japan)
Fax : (+81)564-59-5635
p-Conjugated conducting polymers and oligomers contain-
ing electrochemically and photochemically active transition-
metal complexes, such as [Ru(bpy)3], are of great interest as
materials for molecular devices.[7,8] In particular, linear wires
with extended p systems interacting with metal complexes
are potential candidates for the preparation of functional
single-molecule devices. The molecular conduction is be-
lieved to occur by tunneling and should be proportional to
the negative exponential of the square root of the energy
gap and the chain length.[5] Both parameters can be varied;
[c] G. Masuda
Department of Chemistry, Faculty of Science
Ehime University
Bunkyo-cho 2 5, Matsuyama, Ehime, 790-8577 (Japan)
[d] Dr. K. Araki
Instituto de QuÌmica - Universidade de Sào Paulo
Av. Prof. Lineu Prestes, 748 - Butantà
05508 900 Sào Paulo (Brazil)
Chem. Eur. J. 2004, 10, 3331 3340
DOI: 10.1002/chem.200400063
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3331

FULL PAPER
however, the energy gap is particularly sensitive to the
A similar strategy was used to prepare the terthienyl-sub-
stituted phenanthroline derivatives. Initially, the synthesis of
the unsubstituted bis(terthienyl)phenanthroline was at-
tempted by the Ni-catalyzed reaction of the Grignard re-
agent of 5’’-bromo-2,2’:5’,2’’-terthiophene with 1; however,
the reaction was hindered by the low solubility of this re-
agent. To overcome this drawback, two n-butyl radicals
were introduced into the 3,4-positions of the middle thio-
phene ring (Scheme 2). This strategy was successful, and the
desired phenanthroline derivative 10 was obtained in 40%
yield. This was subsequently converted to the corresponding
ruthenium polypyridine complex 11 by reaction with [Ru-
(bpy)2(OH2)2](NO3)2 in DMF. Compound 10 was also al-
lowed to react with Br2 and KSCN to give the thiocyano de-
rivative 12, and subsequently converted to the ruthenium
complex 13, as described above. All steps gave reasonable-
to-high yields making the strategy convenient for the prepa-
ration of these functionalized thiophene derivatives. The
NMR and mass spectra and the elemental analysis of the
compounds were consistent with the structures shown in
Scheme 1 and Scheme 2.
11]
degree of p delocalization in the molecular wire.[9
The
metal complexes were assumed to impart some functionality,
for example, by acting as charge-trapping sites in single-elec-
tron transistors[3] or electron hopping and photoactive sites.
Finally, a simple method for deposition of a molecular mate-
rial directly in place to afford stable junctions was pursued.
Electropolymerization seemed to satisfy these requirements,
and compound 11 (Scheme 2) was chosen as prototype mon-
omer. Complexes 3 and 13 were utilized in the characteriza-
tion process.
Synthesis: The phenanthroline derivatives were obtained
after a multistep synthesis involving Pd- or Ni-catalyzed
cross-coupling to 3,8-dibromo-1,10-phenanthroline,[12] which
was obtained by bromination of commercially available
1,10-phenanthroline monohydrate in the presence of S2Cl2.
Compound 2 was obtained by Ni-catalyzed cross-coupling of
dibromophenanthroline with the appropriate Grignard re-
agent (Scheme 1).
UV/Vis spectra: The spectra of
oligothiophenes are known to
exhibit
a
band at around
245 nm, and a second band,
whose energy is dependent on
the chain length, at higher
Scheme 1. Procedure for the preparation of complex 3 from phenanthroline. a) Br2, S2Cl2, n-BuCl, py, 62%; b)
[Ni(Cl2(dppp)], THF, 94%; c) 1. [Ru(bpy)2(OH)2]/DMF, 2. NH4PF6, 80%.
Scheme 2. Scheme for the preparation of complexes 11, 13, and poly-11. a) Br2, CHCl3, 90%; b) Zn, AcOH, H2O, 86%; c) [NiCl2(dppp)], Et2O, 85%,
CH3(CH2)3MgBr; d) Br2, AcOH, CHCl3, 87%; e) [NiCl2(dppp)], Et2O, 84%; f) AcOH/CHCl3, NBS, 61%; g) 1. Mg/THF, 2. [NiCl2(dppp)]/THF, 40%; h)
1. [Ru(bpy)2(OH2)2]/DMF, 2. NH4PF6, 71%; i) electropolymerization in MeCN/TBAClO4 0.1m; j) Br2, KSCN, MeOH, CHCl3, 94%; k) 1. [Ru-
(bpy)2(OH2)2]/DMF, 2. NH4PF6, 84%. dppp=1,3-bis(diphenylphosphanyl)propane; NBS= N-bromosuccinimide.
3332
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2004, 10, 3331 3340

In Situ Electropolymerization
3331 3340
wavelengths. The first one is assigned to an intraring p p*
transition, and the second to a p p* transition of the conju-
gated p system. This band is strongly influenced by the pres-
ence of electron-accepting groups, such as pyridine deriva-
tives, directly bonded to the thiophene chain. Accordingly,
the red shift was attributed to contributions from donor ac-
ceptor charge-transfer interactions by Yamamoto et al.[13,14]
Nevertheless, relatively modest shifts were observed in oli-
gothiophene-bridged 2,2’-bpy derivatives by Pappenfus
et al., who found a linear correlation between the energy of
that transition and the number of conjugated rings when the
pyridine rings were considered.[15] Accordingly, the red shift
was assigned to the participation of the bpy rings in the ex-
tended p system of the oligothiophene chain, because the
p p* transition is known to be shifted to lower energies as
the number of thiophene rings is increased.[16,17] The 3,8-bis-
(thiophene)-1,10-phenanthroline derivatives 2, 10, and 12
also belong to such a class of compounds and should exhibit
a similar behavior. The lowest energy band appeared at
340 nm in the spectrum of compound 2 in DMF. It is shifted
to 419 and 422 nm (Figure 1) in compounds 12 and 10, re-
spectively. These wavelengths are comparable to those of
other analogous oligothiophene derivatives.[7,9,15]
the conjugated p system. A weak band, assigned to a d d
transition, is also expected at about 350 nm; however, it
should be hidden under the more intense p p* bands
nearby. Only one intense and broad band is visible at about
442 nm in the case of the complexes 11 and 13. This enve-
lope contains the terthiophene p p* and ruthenium complex
charge-transfer transitions, as can be inferred by its higher
molar absorptivity (7.8î104 mÀ1 cmÀ1) compared to a conven-
tional MLCT band in similar compounds (ꢀ1.5î
104 mÀ1 cmÀ1).[18] This means that the electronic absorption
spectra can be satisfactorily explained if the energy levels
are considered to be essentially localized in the thiophene
backbone and the ruthenium polypyridine complex.
Electrochemistry: The electrochemical behavior of the
ruthenium complexes 3, 11, and 13 was examined by cyclic
voltammetry and is summarized in Table 1. The voltammo-
grams in DMF were generally more reversible than in aceto-
nitrile where adsorption occurred more promptly, particular-
ly because of their much lower solubilities in the last sol-
vent. Compound 3 exhibited five reversible monoelectronic
processes at 1.31, À1.18, À1.45, À1.68 and À1.94 V versus
SCE, in DMF and acetonitrile solution (Figure 2). The re-
versible redox couple at 1.31 V is readily assigned to the
RuIII/RuII process. No other oxidation reaction could be
found up to 2 V, in analogy with the results obtained by
Pappenfus et al. for the binuclear [Ru(bipy)3] complex
bridged by a thienyl ring.[15]
The assignment of the reduction processes is more com-
plicated. A comparison of the potentials in Table 1 indicated
that the first ligand-centered reduction of complex 3 is shift-
ed to more positive potentials by about 200 mV than those
of the [Ru(bpy)3] and [Ru(phen)3] complexes. However,
even more pronounced shifts have been reported for analo-
gous ruthenium complexes with a bipyridine ligand bonded
to thienyl and bisthienyl radicals at the 5,5’-positions.[11,19,20]
Consequently, the reduction process at À1.18 V was attribut-
ed to the monoelectronic reduction of the phenanthroline
ligand. The following processes at À1.45 and À1.68 V were
then assigned to the successive monoelectronic reductions of
Figure 1. UV/Vis spectra of complexes 3, 11, and 13 in DMF.
The
coordination
of
[Ru(bpy)2] should strongly in-
fluence the electronic proper-
ties of the phenanthroline ring,
which may affect the degree of
p conjugation in the thiophene
backbone. Complex 3 exhibits
the ruthenium complex bands
at 290 and 454 nm, respectively,
assigned to the characteristic
bpy p p* transition and
Table 1. Redox potentials (V versus SCE) of the ruthenium complexes in DMF and acetonitrile solutions. The
E1/2 values were estimated as the average of the cathodic and anodic peak potentials. The potentials were cor-
rected considering the potential of the Fc/Fc+ process as being 0.40 V versus SCE.
0/À
0/À[b]
Complex[a]
E1/2(ox)[b]
L/LÀ[b]
bpy1
bpy2
LÀ/L2À
0/À
[Ru(bpy)3][15,19,26]
[Ru(bpy)2(phen)][26]
[Ru(bpy)2(tpbpy)][c][19]
[Ru(bpy)2(btbpy)][c][11]
[Ru(bpy)2(2)][c]
1.26 (RuIII/RuII)
1.26
1.54
À1.34 (bpy1
À1.36
)
À1.52
À1.54
À1.34
À1.44
À1.44
À1.45
À1.44
À1.44
À1.30
À1.33
À1.50cp
À1.78
À1.79
À1.02
À1.10
À1.63
À1.67
À1.68
À1.64
À1.66
1.32
À1.17
À1.97
À2.03
À1.82
À1.88
[Ru(bpy)2(2)][d]
1.22
À1.18
[Ru(bpy)2(10)][d]
[Ru(bpy)2(12)][d]
P4 Ru[c][19]
1.06ap, 1.24ap
À1.13
1.22ap
À1.15
RuII(dp)-to-bpy(pp*) and
-
0.94, 1.10, 1.37(RuIII/RuII)
0.79, 0.95, 1.31(RuIII/RuII)
0.85, 1.02, 1.36(RuIII/RuII)
À1.02
phen(pp*) charge-transfer tran-
sitions. The band at 372 nm can
be attributed to the thiophene
p p* transition. The red shift
reflects the effect of the ruthe-
P6 Ru[c][19]
À1.02
Poly-[Ru(bpy)2(10)][c]
À1.13cp
À1.84cp
not observed
[a] tpbpy
= 4,4’-bis(3-dioctylthienyl)-2,2’-bipyridine, btbpy = 4,4’-bithienyl-2,2’-bipyridine, P4-Ru = poly-
{(bpy)2Ru(1,10-phen-5,5’-bis(3,3’,3’’,3’’’-tetraoctyl-2,2’:5’,2’’:5’’,2’’’:5’’’,2’’’’-quaterthiophene), P6 Ru = analogous
to P4 Ru, but with hexathienyl radicals. [b] ap = anodic peak potential, cp = cathodic peak potential. [c] In
nium complex coordination on acetonitrile. [d] In DMF.
Chem. Eur. J. 2004, 10, 3331 3340
www.chemeurj.org
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3333

K. Araki, T. Ogawa, et al.
FULL PAPER
Figure 2. Cyclic voltammograms of complex 3 in A) 2.5 mm DMF and B) 3.5 mm acetonitrile, containing 0.1m of TBAClO4. The voltammograms in the
0.3 1.6 V range were shifted by 115 mA to facilitate visualization. The scan rates are indicated in the figure.
each of the bpy ligands. As expected, these redox potentials
remained more or less constant for all three complexes.
Generally, no other wave can be found next to this set of
waves, but a fourth reversible process was observed for all
ruthenium complexes at about À1.94 V. Similar results were
reported for analogous heteroleptic ruthenium complexes
with diimine ligands carrying electron-withdrawing groups
or having larger aromatic structures.[21] Accordingly, it was
tentatively assigned to the second monoelectronic reduction
of the substituted phenanthroline ligand. The anodic coun-
terpeak of this last process decreased as the scan rate dimin-
ished, exhibiting a typical EC mechanism profile, probably
attributable to the reaction of that reduced species with
some trace impurities present in the solvent. All processes
were diffusion-controlled, as attested by the linear relation-
ship between the current and the square root of the scan
rate (not shown). The electrochemical behavior of complex
3 in MeCN is similar to that in DMF, except that sharp ad-
sorption peaks are superimposed on the diffusion-controlled
waves, as can be seen in Figure 2B. This effect is more pro-
nounced for the cathodic peak at À1.7 V, whose relative in-
tensity increases dramatically at low scan rates. But when
the measurements were limited to the 0.3 1.6 V range, a
typical diffusion-controlled reversible behavior was ob-
served for the RuIII/RuII process at 1.32 V (Figure 2B).
The electrochemical behavior of the ruthenium complexes
11 and 13 was slightly different from that described above
for compound 3. The difference is associated with the elec-
trochemical activity of the terthiophene moiety as well as
the tendency of the oxidized species, with free terminal a-
positions, to polymerize.[17] The comparative electrochemical
study was carried out only in DMF because of the low solu-
bility of compound 13 in acetonitrile.
the first cathodic peak was slightly enhanced, probably at-
tributable to an EC mechanism involving the reduction of
the thiocyano radical. This assumption is confirmed by the
appearance of an irreversible oxidation wave at À80 mV,
which is absent in the voltammograms of compound 11
(Figure 3). This chemical process did not change the voltam-
metric behavior of the three subsequent processes (monoe-
lectronic and reversible), nor the profile of the anodic wave
at À1.15 V, corresponding to its counterpeak. The oxidation
profile was irreversible for both complexes, showing a
couple of intense peaks at 1.0 and 1.2 V for compound 11, a
peak at 1.2 V for 13, and a reduction peak at about À0.6 V
(not shown). This is consistent with the irreversible oxida-
tion of polythiophenepyridines[13] and oligothiophenes
bonded to ferrocene.[9] However, no associated reduction
process was observed for the RuIII/RuII reaction regardless
of its reversible character. This strongly suggests that the
RuIII species was being rapidly reduced to RuII by the ter-
thienyl radicals. Interestingly, the Pt electrode remained
clean in the case of compound 11, but a white solid was de-
posited in the case of compound 13. Clearly, this is a reac-
tion by-product and no attempt was made to characterize it
further.
Preparation and properties of the polymer film: The electro-
chemical behavior of compound 11 in acetonitrile contrasts
with that in DMF solution. In this case, a pattern typically
found for the deposition of an electrochemically active ma-
terial on the electrode surface was observed (Figure 4A).
This electropolymerization process leads to the formation of
linear hexathiophene chains bridged by phenanthroline[Ru-
(bipy)2] units through the 3,8-positions. The details of the
electropolymerization process and its electrochemical and
optical properties are described below.
The reduction of compound 11 in the 0 to À2.2 V range
led to four reversible processes at À1.13, À1.44, À1.64, and
À1.82 V versus SCE (Figure 3A), which were assigned in
the same way as for compound 3. The CVs of compound 13
were similar to that described above (Figure 3B); however,
Two reversible processes were found at À1.12 and
À1.34 V when the potentials were scanned from 0 to À1.6 V.
Nevertheless, the anodic wave of the second process is more
intense and bell-shaped, as can be seen in the first scan
3334
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2004, 10, 3331 3340

In Situ Electropolymerization
3331 3340
Figure 3. Cyclic voltammograms of A) 2.1 mm 11 and B) 2.0 mm 13 in a DMF solution containing 0.1m TBAClO4 with a Pt electrode. The scan rates are
indicated in the figure.
Figure 4. A) 10 successive cyclic voltammograms of a saturated solution of compound 11 from À1.6 to 1.5 V, 0.1m TBAClO4, Pt electrode. B) Cyclic vol-
tammograms of an electrode modified with poly-11 (G = 1î10À8 molcmÀ2) at different scan rates. C) Two successive scans from À1.3 to 1.5 V with the
modified electrode obtained in (A) after scanning from 0.3 1.5 V. D) Cyclic voltammogram of poly-11 in the 0.3 2.3 V range (c) followed by a scan in
the 0.3 1.8 V range (a). All experiments were carried out in a 0.1m TBAClO4 solution prepared with anhydrous acetonitrile.
Chem. Eur. J. 2004, 10, 3331 3340
www.chemeurj.org
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3335

K. Araki, T. Ogawa, et al.
FULL PAPER
trace. Accordingly, the doubly reduced species was adsorb-
ing, and a relatively intense cathodic wave was found at
about À1.8 V, when the potentials were scanned up to
À2.0 V. The two most negative redox processes were irrever-
sible, and a broadened anodic wave was found at À1.7 V
(not shown). On the positive side, an irreversible and a re-
versible wave were found at Eap = 1.08 and 1.38 V and as-
signed to the monoelectronic oxidation of ligand 10 and to
the RuIII/RuII process, respectively. In the reverse scan, the
wave attributed to the reoxidation of the RuIII sites was fol-
lowed by a couple of waves at Ecp = 0.96 and 0.77 V, attrib-
uted to the reduction of the electrochemically generated
oxidized poly-11 (Figure 4A). This contrasts with the elec-
trochemical behavior in DMF solution described above.
In the subsequent scans, the waves related to the reduc-
tion of the phenanthroline and bipyridine ligands were built
up, as well as an irreversible cathodic peak at about
À0.86 V, which shifted to more negative potentials as a func-
tion of the number of scans. It should be noted, however,
that the reoxidation waves at À1.37 and À1.02 V were small-
er than the corresponding reduction waves, and they stop-
ped growing after about seven cycles, while the other peaks
continue to rise. This indicates that the reoxidation reactions
were incomplete at those potentials, and is in fact occurring
at 0.6 V. This irreversible peak is absent when the eletropo-
lymerization process is carried out in the 0.0 1.5 V range
and, after few cycles, the successive voltammograms became
similar to that shown in Figure 4B. The low reversibility of
these reoxidation processes in the polymer film becomes
evident in the CV of a modified Pt electrode (À1.3 to 1.5 V
range) in neat electrolyte solution (Figure 4C). In this case,
a sharp anodic wave appeared superimposed on the reversi-
ble polymer waves at 0.8 V, but only after the reduction of
the polymer at about À1.2 V. The following successive vol-
tammograms (up to 10 scans) remained almost unchanged,
except for a shift and decrease of that peak. However, the
film is rapidly destroyed if the potentials are scanned up to
À2.0 V. Also, the hexathiophene chain becomes electro-
chemically inactive when oxidized at 1.65 V, as shown in Fig-
ure 4D. Only the hexathienyl segments were affected by the
process, as confirmed by the presence of the RuIII/RuII wave
in the subsequent voltamograms. Consequently, only the
processes in the 0.3 1.5 V range are electrochemically rever-
sible, and their respective currents are directly proportional
to the scan rate (Figure 4B).
Figure 5. Spectroelectrochemistry of poly-11 on ITO-glass in acetonitrile
containing 0.1m TBAClO4. The spectra of the starting polymer RuIIHT0
(0.52 V), the hexathienyl radical cation RuIIHT+ (0.92 V), the dication
RuIIHT2+ (1.22 V), and the RuIIIHT2+ (1.52 V) species are shown. The
spectrum of complex 11 in DMF solution was included for comparison.
HT = hexathienyl radical.
for the broadening of the respective voltammetric waves in
our complex; however, the contribution of some nonhomo-
geneity in the local microenvironment cannot be ruled out.
The electropolymerization reaction should lead to linear
chains containing many ruthenium complexes bridged by
hexathienyl segments. Despite the strong p delocalization in
the conjugated backbone, bridging oligothiophenes[9,15] were
shown to weakly couple transition-metal sites, even when
two ruthenium bis(bipyridine) or terpyridine[22] complexes
are connected by a single ring. Similar behavior has also
been observed for large highly conjugated macrocycles, such
as porphyrins,[23] but a strong coupling was reported for
small heterocyclic ligands, such as pyrazines and benzotria-
zole.[24] In this case, the electronic states of the binuclear
complexes are highly mixed, and the redox processes involv-
ing the metal sites are no longer degenerate. In our case,
only one sharp and bell-shaped pair of peaks, displaced by
ꢀ30 mV, were found for the RuIII/RuII process. This means
that the full-width at half-maximum (FWHM = 115 mV at
100 mVsÀ1) is close to the theoretical value of 90 mV, and
that there is almost no interaction between the electrochem-
ically active sites. Also, the chemical environment around
the ruthenium sites should be very similar. The pattern de-
scribed above is valid for thin films, such that much broader
peaks separated further apart were found at higher surface
concentrations. This effect is probably caused by impedances
associated with the formation of a less firmly bound fibrous
material, as confirmed by SEM microscopy (Figure 6).
The hexathiophene/ruthenium ion ratio in the polymer is
1:1, and the charge consumed for the oxidation of the hexa-
thienyl segments is about twice as large. Consequently, the
two broad waves that precede the RuIII/RuII wave can be as-
signed to two successive monoelectronic oxidation processes.
Accordingly, the hexathiophene moiety is oxidized to the
radical cation at 0.85 V and to the dication at 1.02 V, as con-
firmed by spectroelectrochemistry (Figure 5). Zhu et al.
have shown that the electronic properties of the bpy ligand
are dependent on the substitution position by the thienyl
radicals.[9,15] The 4,4’-substituted bpy (equivalent to 3,8-sub-
stituted phen) was found to favor the delocalization along
the chain to the detriment of the electronic coupling to the
metal center. The same kind of effect may be responsible
Poly-11 films can be deposited on different substrates,
such as glassy carbon, gold, and ITO; however, they are rel-
atively fragile. The films deposited on ITO exhibited absorp-
tion bands spanning the visible region up to 650 nm, at 440
and 540 nm (Figure 5, c). These bands can be assigned to
the RuII-to-polypyridine and -hexathiophene p p* transi-
tions, which were red-shifted after electropolymerization
and formation of longer oligothiophene segments. When the
polymer film was oxidized at 0.92 V, a characteristic band
3336
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2004, 10, 3331 3340

In Situ Electropolymerization
3331 3340
oxidation states were estimated from the electrochemistry
and UV/Vis spectroscopy data, and compared with the Au
Fermi level (Scheme 3).[7] It is easy to see that the HOMO
of the neutral species is very close to the Au Fermi level, as
Figure 6. SEM microscopy images of ITO modified with poly-11, Gꢀ1î
10À8 molcmÀ2, showing A) the fibrous structures (î3300), and B) the ITO
grains covered by a film of poly-11 in an apparently clean region (î
45000).
appeared at 805 nm, and the absorbance at 540 nm de-
creased to approximately half its initial intensity. The
second oxidation process at 1.22 V led to the appearance of
a very broad band at 1100 nm and to the complete disap-
pearance of the bands at 805 and 540 nm. These changes
contrast with what is generally observed during the oxida-
tion of analogous RuII complexes and are consistent with
the formation of the hexathiophene radical cation and dica-
tion,[15,17] respectively. When the polymer was further oxi-
dized at 1.52 V, the band characteristic of the dication at
1100 nm was significantly enhanced, and the absorbance in
the 400 to 600 nm range diminished. This is attributed to the
disappearance of the RuII(dp)-to-bpy(pp*) and -phen(pp*)
charge-transfer transitions. The hexathiophene-to-ruthenium
complex charge-transfer transition is absent in poly-11, in
contrast with oligothiophenes bond to ferrocene,[7,9] because
the RuIII ion is an electron acceptor rather than a donor.
The morphology of poly-11 deposited on ITO was ana-
lyzed by optical and scanning electron microscopy (SEM).
The red-brown color of the polymer and the area covered
by a fibrous material increased as a function of the surface
concentration in the Gꢀ10À8 molcmÀ2 range. An inspection
of the modified surface by SEM with a similar magnification
showed analogous structures (Figure 6A). However, the
amount of poly-11 on the surface seemed to be too low
compared to the surface concentration. Accordingly, a
closer inspection of the modified surface was carried out in
comparison with the clean substrate. The result shown in
Figure 6B revealed that the indium tin oxide (ITO) grains
in apparently clean regions are in fact covered by a thin
layer of poly-11, explaining the apparent inconsistency. This
suggests that, at the beginning of the electropolymerization
process, the polymer is obtained preferentially as a tight
film on the surface of the grains. Nevertheless, a more loose-
ly attached fibrous form seems to be favored as the surface
concentration increases.
Scheme 3. Energy level[eV] diagram of poly-11 in different oxidation
states with reference to the vacuum level estimated from the electronic
spectra and electrochemistry data; EF(Au) = 5.31 eV.[27]
expected for a p-type material. The hole injection barrier is
zero and the HOMO LUMO gap, estimated from the ab-
sorption onset, is 1.77 eV. Temperature-dependent nonlinear
I V curves with similar profiles were obtained, as shown in
Figure 7. The devices were stable enough to allow the col-
Figure 7. Typical temperature-dependent I V(T) curves for poly-11 on a
gold nanoelectrode with a 15 nm gap at 80 300 K.
lection of more than a hundred I V curves as a function of
the temperature without significant changes. They were gen-
erally symmetric, and the conductivity of the device de-
creased as the temperature was decreased from 300 to 80 K.
Concomitantly, the ™blockaded∫ region was widened and
reached about 2.7 eV at 80 K, which is about 1 eV higher
than the HOMO LUMO gap. The strong temperature-de-
pendence was successfully explained based on the thermion-
ic and tunneling models, and is being published elsewhere.[25]
Smaller energy gaps (1.25 and ~0.8 eV) are anticipated for
poly-11+ and poly-112+, respectively (Scheme 3).
Current voltage characteristics of poly-11: Electropolymeri-
zation was shown to be a suitable strategy for the prepara-
tion of poly-11 directly between nanogap electrodes. This
avoids complicated techniques to manipulate the molecular
species for proper positioning and contact. Furthermore, the
polymer chains may grow preferentially oriented along the
electric field, forming a bunch of wires connecting the two
electrodes. The HOMO and LUMO energies in different
Conclusion
A new bis(terthienyl)-1,10-phenanthroline coordinated to
[Ru(bpy)2] was synthesized and characterized by UV/Vis
Chem. Eur. J. 2004, 10, 3331 3340
www.chemeurj.org
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3337

K. Araki, T. Ogawa, et al.
FULL PAPER
(15 mL) was prepared in a two-necked round-bottom flask connected to
a fritted glass filter, and was then cooled to 08C in an ice/water bath. The
previously prepared Grignard reagent was carefully added by means of a
cannula, through the filter. The mixture was left to stand for 2 h at room
temperature, and was then refluxed for 12 h. The reaction mixture was
quenched with saturated NH4Cl aqueous solution, extracted with CHCl3,
washed with a NaCl solution, and purified by column chromatography
(silica gel, CHCl3/n-hexane 1:1). A yellow crystalline product (1.45 g,
94%) was obtained after removal of the solvent and drying in vacuo. 1H
NMR (270 MHz, CDCl3): d = 9.45 (d, J = 2.3 Hz, 2H, phen), 8.34 (d, J
= 2.3 Hz, 2H, phen), 7.82 (s, 2H, phen), 7.59 (dd, J = 3.7, 0.6 Hz, 2H,
thiophenyl), 7.45 (dd, J = 5.3, 0.6 Hz, 2H, thiophenyl), 7.20 ppm (dd, J
spectroscopy and cyclic voltammetry. The electrochemistry
of the three derivatives was consistent with that of analo-
gous compounds: four reversible reduction processes were
exhibited in the 0 to À2.2 V range. The voltammetric behav-
ior was irreversible in the 0 1.5 V range for the terthienyl
derivatives on account of its fast oxidation by the electro-
chemically generated RuIII complexes. This reaction leads to
electropolymerization and the build up of an electrochemi-
cally and electrochromically active material on the electrode
surface from an acetonitrile solution. A tight film is generat-
ed on ITO at low surface concentrations, and a lose fibrous
form is preferentially formed at higher concentrations. The
monomer was shown to be a suitable starting material for
the electrodeposition of functionalized molecular wires di-
rectly between gold electrodes separated by a nanometer-
sized gap. Stable molecular devices exhibiting temperature-
dependent nonlinear I V curves were obtained in this way.
=
5.3, 3.7 Hz, 2H, thiophenyl); 13C NMR (67.8 MHz, CDCl3): d
=
148.12, 140.3, 131.6, 129.5, 128.6, 128.5, 127.2, 126.6, 125.0, 99.1 ppm; MS
(DI-EI): m/z: 344 [C20H12N2S2]+.
[Ru(bpy)2(OH2)2](NO3)2: This complex was synthesized as a reactive in-
termediate in order to obtain the desired [Ru(bpy)2(L)] complexes (L =
3,8-bis(thiophene)-1,10-phenanthroline ligands) under mild conditions.
The required amount was prepared immediately before use. Typically,
[Ru(bipy)2Cl2]¥H2O (Aldrich, 0.1 g, 0.71 mmol) was suspended in a 1:1
methanol/water mixture (15 mL), heated to 708C, and the dissociated ClÀ
ion precipitated by the addition of two equivalents of Ag(NO)3 (Cica Re-
agents) in a N2 atmosphere. The reaction mixture was stirred for 30 min,
and the suspension was filtered through a thick Celite (Aldrich) bed. The
clean solution was dried in the rotary evaporator to obtain the aqua com-
plex as a dark solid, which was dissolved in DMF and reacted with the li-
gands 2, 10, and 12, as described below.
Experimental Section
All reagents and solvents were of analytical grade and used without fur-
ther purification. The anhydrous solvents were drawn up into a syringe
under a flow of dry N2 gas and were directly transferred into the reaction
flask to avoid contamination. The intermediates and products were char-
acterized by elemental analysis and spectroscopic methods.
Bis(2,2’-bipyridine)(3,8-(thiophen-2’,2’’-yl)-1,10-phenanthroline)ruthenium-
(ii) ([Ru(bpy)2(DTphen)](PF6)2, 3): Compound 2 (0.24 g, 0.71 mmol) in
CHCl3 (10 mL) was reacted with an equivalent amount of [Ru-
(bpy)2(OH2)2](NO3)2 in DMF (20 mL) for 10 min (608C). This intermedi-
ate was prepared from [Ru(bpy)2Cl2]¥H2O (0.34 g), as described above.
The solvent was removed in the rotary evaporator. The solid was redis-
solved in DMF (15 mL), and the solution was added into an aqueous
NH4PF6 solution (30 mL). The resultant brown solid was filtered, thor-
oughly washed with water, and dried in vacuo. Yield: 0.46 g (61%); 1H
NMR (500 MHz, DMSO): d = 9.05 (d, J = 1.8 Hz, 2H, phen), 8.92 (d,
J = 8.2 Hz, 2H, bpy), 8.83 (d, J = 8.2 Hz, 2H, bpy), 8.35 (s, 2H, phen),
8.29 (t, J = 7.9 Hz, 2H, bpy), 8.12 (t, J = 7.9 Hz, 2H, bpy), 8.03 (d, J =
1.8 Hz, 2H, phen), 7.96 (d, J = 5.5 Hz, 2H, bpy), 7.84 (d, J = 5.8 Hz,
2H, bpy), 7.78 (d, J = 5.0 Hz, 2H, thienyl), 7.66 (t, J = 6.7 Hz, 2H,
bpy), 7.55 (d, J = 3.6 Hz, 2H, thienyl), 7.39 (t, J = 6.7 Hz, 2H, bpy),
7.24 ppm (dd, J = 5.2 and 3.6 Hz, 2H, thienyl); elemental analysis calcd
(%) for C40H28N6S2P2F12Ru: C 45.85, H 2.69, N 8.02; found: C 45.07, H
2.90, N 7.90.
The UV/Vis spectra, in solution or as a polymeric film on ITO glass,
were recorded with a Shimadzu UV-3150 double-beam spectrophotome-
ter. The IR spectra were recorded in a Horiba FT-700 spectrophotome-
ter. Cyclic voltammograms were registered with a BAS CV-50W voltam-
metric analyzer in a conventional three-electrode cell arrangement com-
prising a Pt coil counterelectrode, a Ag/Ag+ (0.01m, TBAClO4 0.1m in
CH3CN) reference electrode, and a Pt working electrode (0.16 mm diam-
eter). The spectra of oxidized poly-11 were obtained in a electrochemical
minicell mounted inside a quartzcuvette with an ITO glass modified
with the polymer as the working electrode. 1H NMR spectra were collect-
ed on a Varian Unit 500 MHzspectrometer and a JEOL GSX 270 MHz
spectrometer with TMS (d = 0.0) as the reference. 13C NMR data were
recorded at 67.8 MHzwith
a JEOLGSX spectrometer. The DI-EI
(70 eV) mass spectra were recorded with a Hitachi M80-B spectrometer.
The SEM images were collected with a Jeol JSM-6700F microscope.
2,3,4,5-Tetrabromothiophene (4): Thiophene (0.3 mol) and CHCl3
The I V curves were collected with an Advantest R6245 2Channels Volt-
age Current Source Monitor interfaced to a microcomputer through a
GPIB-SCSI board and NI-488.2 protocol. The data were acquired with a
homemade procedure and IgorPro 4.0 (Wavemetrics) software. Triaxial
cables were used to connect the molecular devices and the I V monitor
in order to minimize external noise. All measurements were carried out
inside a vacuum chamber (P<2î10À4 Pascal) equipped with a thermo-
stat (Æ0.0018C) and with liquid nitrogen as the coolant. The polymer
was successfully prepared in situ between the gold nanogap electrodes
(250 nm wide, gap width ~15 nm) by electropolymerization from a satu-
rated solution of 11 in acetonitrile (0.1m TBAClO4). The nanogap elec-
trodes were used as working and counterelectrodes, and a silver wire was
employed as a pseudoreference electrode. The potentials were scanned
10 times in the 0 800 mV range. The procedure was repeated after the
polarization had been reversed. The samples were then washed thorough-
ly with methanol and acetone and dried in vacuo. The details of the
nanogap electrode fabrication were published elsewhere.[25]
(12 mL) were transferred to
a round-bottom flask and Br2 (69 mL,
1.35 mol) was added dropwise into the vigorously stirred solution. The re-
action mixture was kept at room temperature for 17 h and then refluxed
for 2 h. After cooling to room temperature, a KOH solution (33 g) in eth-
anol (180 mL) was added. The mixture was refluxed for 4 h, poured into
an ice/water mixture (400 mL), and extracted with CHCl3. Colorless crys-
tals of the desired product were obtained in 90% yield after recrystalliza-
tion from a CHCl3/EtOH mixture. 13C NMR (CDCl3): d
110.28 ppm; MS (EI): m/z: 400 (C4Br4S+), 321, 240, 161.
= 116.94,
3,4-Dibromothiophene (5): An acetic acid/water mixture (1:2, 180 mL)
was transferred to a round-bottom flask, followed by the alternate addi-
tion of powdered zinc (60 g, 918 mmol) and 4 (113 g, 283 mmol) in small
portions. The resultant mixture was kept at room temperature for 1 h
and then refluxed for 3 h. The mixture was filtered through a celite bed
and the product extracted with diethyl ether from the filtrate. The solu-
tion was dried with Na2SO4, the solvent was removed, and the residue
then distilled under vacuum. A colorless liquid was obtained in 86%
yield. 1H NMR (270 MHz, CDCl3): d = 7.29 ppm (s, 2H); 13C NMR
(CDCl3): d = 123.73, 113.88 ppm.
3,8-Dibromo-1,10-phenanthroline (1): was prepared according to a previ-
ously reported method.[12]
3,8-Di(thiophen-2’,2’’-yl)-1,10-phenanthroline (Dtphen, 2): Activated
3,4-Dibutylthiophene (6): Magnesium (5.74 g, 236 mmol) was transferred
to a three necked round-bottom flask and heated to 1008C in a N2 atmos-
phere. Dry diethyl ether (90 mL) and some I2 were added, and the mix-
ture was left to react for 10 min. n-Butylbromide (18.0 mL, 167.6 mmol)
was carefully added to avoid excessive increase of temperature, and the
magnesium (0.672 g, 27.7 mmol) and dry THF (12 mL) were transferred
to
a round-bottom flask in a N2 atmosphere. 2-Bromothiophene
(1.22 mL, 12.6 mmol) was carefully added, and the mixture was left to
react for 2 h at room temperature with constant stirring. A solution of 1
(1.52 g, 4.5 mmol) and [NiCl2(dppp)] (0.069 g, 0.127 mmol) in dry THF
3338
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2004, 10, 3331 3340

In Situ Electropolymerization
3331 3340
mixture was refluxed for an hour to obtain the corresponding Grignard
reagent. Thiophene 5 (6.8 mL, 60.1 mmol) and [NiCl2(dppp)] (1.02 g,
1.88 mmol) were transferred to a separate three-necked round-bottom
flask connected to a sintered glass filter. After purging with N2, dry dieth-
yl ether (80 mL) was added and the Grignard reagent was carefully trans-
ferred through the filter. The reaction mixture was refluxed for 2 h, left
to stand at room temperature for 12 h, and then quenched with 1n HCl.
It was then filtered through a celite bed and extracted with diethyl ether.
The solvent was removed in a flash evaporator, and the residue was dis-
fluxed for 10 h. The reaction was quenched with 1m aqueous HCl, ex-
tracted with CHCl3, washed with water, and purified by silica-gel column
chromatography (60% CHCl3 in n-hexane) followed by recrystallization
from a CHCl3/n-hexane mixture. The product was obtained as yellow
crystals in 40% yield. 1H NMR (270 MHz, CDCl3): d = 9.43 (d, J =
2.1 Hz, 2H), 8.30 (d, J = 2.1 Hz, 2H), 7.82 (s, 2H), 7.54 (d, J = 3.7 Hz,
2H), 7.33 (dd, J = 5.0, 1.2 Hz, 2H), 7.20 (d, J = 3.7 Hz, 2H), 7.17 (dd, J
= 3.7, 1.2 Hz, 2H), 7.08 (dd, J = 5.0, 3.7 Hz, 2H), 2.79 (t, J = 9.3, 4H),
2.73 (t, J = 9.3 Hz, 4H), 1.59 1.47 (br, 16H), 1.01 (t, J = 7.2 Hz, 6H),
0.97 ppm (t, J = 7.2 Hz, 6H); 13C NMR (68 MHz, CDCl3): d = 147.82,
144.81, 140.61, 140.29, 139.51, 137.74, 136.00, 130.98, 130.45, 129.37,
129.24, 128.45, 127.40, 127.20, 126.84, 125.99, 125.48, 125.27, 32.90, 32.82,
27.99, 27.82, 23.05, 22.99, 13.88, 13.85 ppm; MS (FAB): m/z: 897.3
[C52H52N2S6]+ ; FT-IR (KBr): n˜ = 2954, 2931, 1558, 1521, 1473 cmÀ1; ele-
mental analysis calcd (%) for C52H54N2S6O: C 68.23, H 5.95, N 3.06;
found: C 68.54, H 5.81, N 2.83.
1
tilled. A colorless liquid was obtained in 85% yield. H NMR (270 MHz,
CDCl3): d = 6.88 (s, 2H), 2.51 (t, J = 7.3 Hz, 4H), 1.66 1.52 (m, 4H),
1.47 1.36 (m, 4H), 0.95 ppm (t, J = 7.3 Hz, 4H); 13C NMR (68 MHz,
CDCl3): d = 142.04, 119.86, 31.82, 28.48, 22.65, 13.99 ppm; MS (DI-EI):
m/z: 196 [C12H20S]+ ; elemental analysis calcd (%) for C12H20S: C 73.40,
H 10.27; found: C 73.15, H 10.07.
2,5-Dibromo-3,4-dibutylthiophene (7): Bromine (7.85 mL, 154.7 mmol)
diluted in CHCl3 (20 mL) was added to a solution obtained by mixing 6
(12.5 g, 63.7 mmol) and CHCl3/acetic acid (1:2, 100 mL) in a round-
bottom flask. The mixture was stirred overnight at room temperature
and washed with water. The organic phase was washed five more times
with water, the CHCl3 was removed in a flash evaporator, and the resi-
due was distilled in vacuo. A pale yellow liquid was obtained in 87%
yield. 1H NMR (270 MHz, CDCl3): d = 2.52 (t, J = 7.6 Hz, 4H), 1.42
(m, 8H), 0.94 ppm (t, J = 7.2 Hz, 6H); 13C NMR (68 MHz, CDCl3): d =
141.38, 107.81, 31.69, 28.65, 22.63, 13.87 ppm; MS (DI-EI): m/z: 354
[C12H18Br2S]+.
Bis(2,2’-bipyridyl)(3,8-bis(3’,4’-dibutyl-2,2’:5’,2’’-terthiophen-5-yl)-1,10-
phenanthroline)ruthenium(ii), [Ru(bipy)2(10)](PF6)2 (11): The ruthenium
complex was obtained by the reaction of compound 11 (50 mg,
0.056 mmol/5 mL CHCl3) and an equivalent amount of [Ru(b-
py)2(OH2)2](NO3)2 in DMF (10 mL), as described above. This mixture
was concentrated in a flash evaporator and added to an aqueous NH4PF6
solution. The precipitate was collected, washed with water, and dried in
vacuo. A dark-red solid was obtained in 71% yield (59 mg). 1H NMR
(500 MHz, [D6]DMSO): d = 9.04 (d, J = 1.7 Hz, 2H, phen), 8.90 (d,
J = 8.3 Hz, 2H, bpy), 8.84 (d, J = 8.3 Hz, 2H, bpy), 8.35 (s, 2H, phen),
8.28 (t, J = 7.9, 2H, bpy), 8.13 (t, J = 7.9 Hz, 2H, bpy), 8.07 (d, J =
1.9 Hz, 2H, phen), 7.94 (d, J = 5.1 Hz, 2H, bpy), 7.86 (d, J = 5.1 Hz,
2H, bpy), 7.68 (d, J = 5.1, 2H, thienyl), 7.65 (t, J = 6.7, 2H, bpy), 7.54
(d, J = 3.9 Hz, 2H, thienyl), 7.41 (t, J = 6.7, 2H, bpy), 7.34 (d, J =
3.9 Hz, 2H, thienyl), 7.25 (d, J = 3.5 Hz, 2H, thienyl), 7.18 (dd, J = 5.1
and 3.5 Hz, 2H, thienyl), 2.70 (br, 8H, butyl), 1.49 (br, 8H, butyl), 1.41
(br, 8H, butyl), 0.95 ppm (br, 12H, butyl); MS (FAB): m/z: 1600.3
3,4-Dibutyl-2,2’:5’,2’’-terthiophene (8): Magnesium (7.62 g) was transfer-
red to a round-bottom flask and heated to 1008C in a N2 atmosphere.
After the mixture was cooled down to room temperature, dry diethyl
ether (140 mL) and some iodine were added, and the mixture was left to
react for 10 minutes under magnetic stirring. 2-Bromothiophene
(21.7 mL, 224 mmol, Aldrich) was then carefully added, and the mixture
was refluxed for an hour to obtain the corresponding Grignard reagent.
This was slowly added to a solution obtained by dissolving 7 (28.33 g,
80.0 mmol) and [NiCl2(dppp)] (1.46 g, 2.70 mmol) in dry diethyl ether
(150 mL). The mixture was refluxed for 4 h in a N2 atmosphere. The reac-
tion mixture was stirred for 12 h at room temperature, quenched with 1n
HCl, extracted with CHCl3, and purified by silica column chromatogra-
phy (n-hexane). A yellow liquid was obtained in 84% yield. 1H NMR
(270 MHz, CDCl3): d = 7.27 (dd, J = 5.2, 1.1 Hz, 2H), 7.12 (dd, J = 3.7,
1.1 Hz, 2H), 7.04 (dd, J = 5.2, 3.7 Hz, 2H), 2.70 (t, J = 8.1 Hz, 4H),
1.51 1.41 (m, 8H), 0.94 ppm (t, J = 7.2 Hz, 6H); 13C NMR (68 MHz,
CDCl3): d = 139.99, 136.19, 129.80, 127.31, 125.81, 125.24, 32.90, 27.79,
22.98, 13.84 ppm; MS (DI-EI): m/z: 360 [C20H24S3]+ ; FT-IR (NaCl): n˜ =
2954, 2931, 2870, 2858, 1466, 845, 827, 692 cmÀ1; elemental analysis calcd
(%) for C20H24S3: C 66.62, H 6.71; found: C 66.43, H 6.71.
[C72H68N6RuS6P2F12]+, 1455.3 [C72H68N6RuS6PF6]+ ; FT-IR (KBr): n˜
630, 2343, elemental analysis calcd (%)
2329 cmÀ1
=
;
for
C72H68N6S6P2F12Ru: C 54.02, H 4.28, N 5.25; found: C 54.30, H 4.26, N
5.28.
3,8-Bis(3’,4’-dibutyl-5’’-thiocyanato-2,2’:5’,2’’-terthiophen-5-yl)-1,10-phe-
nanthroline (12): A solution of compound 10 (1.35 g) in CHCl3 (60 mL)
was added to
a mixture of KSCN (1.35 g, 1.5 mmol), Br2 (4.6 mL,
89.8 mmol), and CHCl3 (15 mL) at À708C. This mixture was stirred for
4 h at room temperature, quenched with water, extracted with CHCl3,
and purified by silica-gel column chromatography (CHCl3). A yellow
crystalline product was obtained (94% yield) after recrystallization from
CHCl3/n-hexane. 1H NMR (270 MHz, CDCl3): d = 9.44 (d, J = 2.1 Hz,
2H), 8.34 (d, J = 2.1 Hz, 2H), 7.86 (s, 2H), 7.57 (d, J = 3.7 Hz, 2H),
7.41 (d, J = 4.0 Hz, 2H), 7.24 (d, J = 3.7 Hz, 2H), 7.12 (d, J = 4.0 Hz,
5-Bromo-3’,4’-dibutyl-2,2’:5’,2’’-terthiophene (9):
A solution of NBS
(1.24 g, 6.96 mmol) in acetic acid/CHCl3 (1:1, 100 mL) was added drop-
wise to a solution of 8 (2.51 g, 6.96 mmol) in the same solvent (100 mL)
cooled by an ice/water bath. The mixture was stirred overnight at room
temperature, poured onto an aqueous NaCl solution (400 mL), and ex-
tracted with CHCl3. The organic phase was washed five more times with
distilled water. The solvent was removed in a flash evaporator, and the
residue was purified by silica-gel column chromatography. A yellow
2H), 2.77 (m, 8H), 1.56 1.25 (br, 16H), 1.01 (t, J
= 7.0 Hz, 6H),
0.99 ppm (t, J = 7.0 Hz, 6H); 13C NMR (68 MHz, CDCl3): d = 147.77,
144.49, 141.88, 140.89, 140.09, 138.10, 137.03, 131.15, 131.06, 128.59,
127.36, 127.27, 126.48, 125.39, 116.39, 110.23, 32.81, 27.94, 23.02, 22.98,
13.86, 13.83 ppm; MS (FAB): m/z: 1011.3 [C54H50N4S8]+ ; FT-IR (KBr):
n˜ = 2954, 2156, 1558, 1506, 1419, 796 cmÀ1; elemental analysis calcd (%)
for C54H50N4S8: C 64.12, H 4.98, N 5.54; found: C 64.19, H 5.02, N 5.52.
1
liquid was obtained in 61% yield. H NMR (270 MHz, CDCl3): d = 7.29
Bis(2,2’-bipyridyl)(3,8-bis(3’,4’-dibutyl-5’’-thiocyanato-2,2’:5’,2’’-terthio-
phen-5-yl)-1,10-phenanthroline)ruthenium(ii) ([Ru(bipy)2(12)](PF6)2, 13):
This ruthenium complex was obtained by the reaction of compound 12
(114 mg, 0.11 mmol) in CHCl3 (5 mL) with an equivalent amount of
[Ru(bpy)2(OH2)2](NO3)2 dissolved in DMF (10 mL). The product, pre-
(dd, J = 5.2, 1.2 Hz, 1H), 7.12 (dd, J = 3.7, 1.2 Hz, 1H), 7.05 (dd, J =
5.2, 3.7 Hz, 1H), 7.00 (d, J = 3.7 Hz, 1H), 6.86 (d, J = 3.7 Hz, 1H), 2.68
(t, J = 7.6 Hz, 2H), 2.65 (t, J = 7.9 Hz, 2H), 1.53 1.41 (br, 8H), 0.95 (t,
J = 7.0 Hz, 3H), 0.94 ppm (t, J = 7.0 Hz, 3H); 13C NMR (68 MHz,
CDCl3): d = 140.49, 140.00, 137.73, 135.89, 130.36, 130.14, 128.79, 127.34,
126.02, 126.98, 125.45, 32.96, 32.87 27.79, 27.75, 22.96, 13.83 ppm; MS
(DI-EI): m/z: 440 [C20H23BrS3]+ ; FT-IR (NaCl): n˜ = 2954, 2929, 2870,
2858, 1464, 970, 829, 790, 692 cmÀ1; elemental analysis calcd (%) for
C20H23BrS3: C 54.66, H 5.27; found: C 54.77, H 5.28.
À
cipitated as the PF6 salt, was recrystallized as a red-orange solid by
dropwise addition of methanol into a concentrated acetone solution.
Yield: 153 mg (84%); 1H NMR (500 MHz, [D6]DMSO): d = 9.06 (d,
J = 2.0 Hz, 2H, phen), 8.90 (d, J = 8.5 Hz, 2H, bpy), 8.83 (d, J = 8.0 Hz,
2H, bpy), 8.36 (s, 2H, phen), 8.28 (t, J = 7.5 Hz, 2H, bpy), 8.12 (t, J =
8.5 Hz, 2H, bpy), 8.08 (d, J = 2.0 Hz, 2H, phen), 7.93 (d, J = 5.5 Hz,
2H, bpy), 7.85 (d, J = 5.5 Hz, 2H, bpy), 7.69 (d, J = 4.5 Hz, 2H, thien-
yl), 7.65 (t, J = 7.0 Hz, 2H, bpy), 7.56 (d, J = 3.5 Hz, 2H, thienyl), 7.40
(t, J = 6.5 Hz, 2H, bpy), 7.39 (d, J = 4.5 Hz, 2H, thienyl), 7.31 (d, J =
4.0 Hz, 2H, thienyl), 2.72 (br, 8H, butyl), 1.49 (br, 8H, butyl), 1.40 (br,
8H, butyl), 0.93 (br, 12H, butyl); elemental analysis calcd (%) for
3,8-Bis(3’,4’-dibutyl-2,2’:5’,2’’-terthiophen-5-yl)-1,10-phenanthroline
(DBTT-phen, 10): A solution of terthiophene 9 (8.90 g, 20.25 mmol) in
dry THF (15 mL) was added dropwise into a suspension of magnesium
(0.77 g, 31.7 mmol, activated with I2) in the same solvent (40 mL). The
mixture was refluxed for 4 h in a N2 atmosphere. A solution of 1 (2.59 g,
7.7 mmol) and [NiCl2(dppp)] (0.43 g, 0.79 mmol) in dry THF (70 mL)
was prepared, the Grignard reagent was added, and the mixture was re-
Chem. Eur. J. 2004, 10, 3331 3340
www.chemeurj.org
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3339

K. Araki, T. Ogawa, et al.
FULL PAPER
C76H72F12N8P2RuS8 C 52.31, H 4.16, N 6.42; found: C 51.49, H 4.25, N
6.38.
Maruyama, Y. Nakamura, T. Fukuda, B. L. Lee, N. Ooba, S.
Tomaru, T. Kurihara, T. Kaino, K. Kubota, S. Sasaki, J. Am. Chem.
Soc. 1996, 118, 10389 10399.
[14] a) T. Yamamoto, Z. H. Zhou, T. Maruyama, T. Kanbara, Synth. Met.
1993, 55, 1209 1213; b) Z. H. Zhou, T. Maruyama, T. Kanbara, T.
Ikeda, K. Ichimura, T. Yamamoto, K. Tokuda, J. Chem. Soc. Chem.
Commun. 1991, 1210 1212.
Acknowledgement
[15] T. M. Pappenfus, K. R. Mann, Inorg. Chem. 2001, 40, 6301 6307.
[16] Y. Yu, E. Gunic, B. Zinger, L. L. Miller, J. Am. Chem. Soc. 1996,
118, 1013 1018; L. L. Miller, Y. Yu, J. Org. Chem. 1995, 60, 6813
6819.
This work was supported by a Grant-in-Aid for Scientific Research
(No. 15201028 and No. 14654135) from the Ministry of Culture, Educa-
tion, Science Sports, and Technology of Japan.
[17] J. Roncali, Chem. Rev. 1992, 92, 711 738.
[18] A. Juris, V. Balzani, F. Barigelletti, S. Campagna, P. Belser, A. Von-
zelewsky, Coord. Chem. Rev. 1988, 84, 85 277.
[19] K. A. Walters, L. Trouillet, S. Guillerez, F. S. Schanze, Inorg. Chem.
2000, 39, 5496 5509.
[20] L. Trouillet, A. De Nicola, S. Guillerez, Chem. Mater. 2000, 12,
1611 1621.
[21] a) M. Maggini, D. M. Guldi, S. Mondini, G. Scorrano, F. Paolucci, P.
Ceroni, S. Roffia, Chem. Eur. J. 1998, 4, 1992 2000; b) S. Roffia, M.
Marcaccio, C. Paradisi, F. Paolucci, V. Balzani, G. Denti, S. Serroni,
S. Campagna, Inorg. Chem. 1993, 32, 3003 3009.
[1] a) C. Joachim, J. K. Gimzewski, A. Aviram, Nature 2000, 408, 541
548; b) Molecular Electronics (Eds.: M. A. Reed, T. Lee), American
Scientific Publishers, Stevenson Ranch, CA, 2003.
[2] a) P. Kovacic, M. B. Jones, Chem. Rev. 1987, 87, 357 379; b) J. Ron-
cali, Chem. Rev. 1997, 97, 173 205; c) T. Yamamoto, Y. Yoneda, K.
Kizu, 1995, 16, 549 556; d) N. Aratani, A. Tsuda, A. Osuka, Synlett
2001, 11, 1663 1674; e) A. Osuka, N. Tanabe, S. Nakajima, K. Mar-
uyama, J. Chem. Soc. Perkin Trans. 2 1996, 2, 199 203.
[3] a) J. Park, A. N. Pasupathy, J. I. Goldsmith, C. Chang, Y. Yaish, J. R.
Petta, M. Rinkoski, J. P. Sethna, H. D. Abrunà, P. L. McEuen, D. C.
Ralph, Nature 2002, 417, 722 725; b) W. Liang, M. P. Shores, M.
Bockrath, J. R. Long, H. Park, Nature 2002, 417, 725 729.
[4] a) S. Kubatkin, A. Danilov, M. Hjort, J. Cornil, J.-L. Bredas, N.
Stuhr-Hansen, P. Hedegard, T. Bj˘rnholm, Nature 2003, 425, 698
701; b) J. Chen, T. Lee, J. Su, W. Wang, M. A. Reed, M. A. Rawlett,
M. Kozaki, Y. Yao, R. C. Jagessar, S. M. Dirk, D. S. Grubisha, D. W.
Bennett in Molecular Nanoelectronics: Molecular Electronic Devices
(Eds.: M. A. Reed, T. Lee), American Scientific Publishers, Steven-
son Ranch, CA, 2003, pp. 39 114; c) M. L. Chabinyc, X. Chen,
R. E. Holmlin, H. Jacobs, H. Skulason, C. D. Frisbie, V. Mujica,
M. A. Ratner, M. A. Rampi, G. M. Whitesides, J. Am. Chem. Soc.
2002, 124, 11730 11736; d) C. P. Collier, J. O. Jeppesen, Y. Luo, J.
Perkins, E. W. Wong, J. R. Heath, J. F. Stoddart, J. Am. Chem. Soc.
2001, 123, 12632 12641.
[5] A. Nitzan, M. A. Ratner, Science 2003, 300, 1384 1389.
[6] T. Ogawa, K. Kobayashi, G. Masuda, T. Takase, S. Maeda, Thin
Solid Films 2001, 393, 374 378.
[7] L. Tan, M. D. Curtis, A. H. Francis, Macromolecules 2002, 35, 4628
4635.
[8] a) H. Sirringhaus, N. Tessler, R. H. Friend, Science 1998, 280, 1741
1744; b) T. Yamamoto, H. Suganuma, T. Maruyama, T. Inoue, Y.
Muramatsu, M. Arai, D. Komarudin, N. Ooba, S. Tomaru, S. Sasaki,
K. Kubota, Chem. Mater. 1997, 9, 1217 1225.
[9] Y. Zhu, M. O. Wolf, J. Am. Chem. Soc. 2000, 122, 10121 10125.
[10] B. J. MacLean, P. G. Pickup, J. Mater. Chem. 2001, 11, 1357 1363.
[11] S. S. Zhu, R. P. Kingsborough, T. M. Swager, J. Mater. Chem. 1999,
9, 2123 2131.
[22] S. Encinas, L. Flamigni, F. Barigelletti, E. C. Constable, C. E. House-
croft, E. R. Schofield, E. Figgemeier, D. Fenske, M. Neuburger, J. G.
Vos, M. Zehnder, Chem. Eur. J. 2002, 8, 137 150.
[23] a) M. C. Hodgson, A. K. Burrell, P. D. W. Boyd, P. J. Brothers,
C. E. F. Rickard, J. Porphyrins Phthalocyanines 2002, 6, 737 747;
b) H. E. Toma, K. Araki, Coord. Chem. Rev. 2000, 196, 307 329;
c) H. E. Toma, K. Araki, A. D. P. Alexiou, S. Nikolaou, S. Dovidaus-
kas, Coord. Chem. Rev. 2001, 219, 187 234; d) K. Araki, P. Losco,
F. M. Engelmann, H. Winnischofer, H. E. Toma, J. Photochem. Pho-
tobiol. A 2001, 142, 25 30; e) S. W. Rhee, Y. H. Na, Y. Do, J. Kim,
Inorg. Chim. Acta 2000, 309, 49 56; f) J. L. Sessler, V. L. Capuano,
A. K. Burrell, Inorg. Chim. Acta 1993, 204, 93 101.
[24] a) J. F. Endicott, H. B. Schlegel, M. J. Uddin, D. S. Seniveratne,
Coord. Chem. Rev. 2002, 229, 95 106; b) M. Marcaccio, F. Paolucci,
C. Paradisi, M. Carano, S. Roffia, C. Fontanesi, L. J. Yellowlees, S.
Serroni, S. Campagna, V. Balzani, J. Electroanal. Chem. 2002, 532,
99 112; c) M. Marcaccio, F. Paolucci, C. Paradisi, S. Roffia, C. Fon-
tanesi, L. J. Yellowlees, S. Serroni, S. Campagna, C. Denti, V. Balza-
ni, J. Am. Chem. Soc. 1999, 121, 10081 10091; d) R. C. Rocha, K.
Araki, H. E. Toma, Inorg. Chim. Acta 1999, 285, 197 202.
[25] K. Araki, H. Endo, H. Tanaka, T. Ogawa, Jap. J. Appl. Phys. 2004,
43 (5A), L634 L636.
[26] P. Belser, A. V. Zelewsky, Helv. Chim. Acta 1980, 63, 1675 1702.
[27] H. Chen, J. Q. Lu, J. Wu, R. Note, H. Mizuseki, Y. Kawazoe, Phys.
Rev. B 2003, 67, 4.
[12] Y. Saitoh, T. Yamamoto, Chem. Lett. 1995, 785 786.
[13] a) B. L. Lee, T. Yamamoto, Macromolecules 1999, 32, 1375 1382;
b) T. Yamamoto, Z. H. Zhou, T. Kanbara, M. Shimura, K. Kizu, T.
Received: January 20, 2004
Published online: April 29, 2004
3340
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2004, 10, 3331 3340