Photo-induced energy transfer and its switching in dyad and triad chromophore systems composed of coumarin, Ru(II) and Os(II) terpyridine-type complexes

Article abstract of DOI:10.1039/b212274j

A new dyad and two triad chromophore compounds containing coumarin, Ru(II) and Os(II) terpyridine-type complexes were synthesized. The dyad is composed of coumarin and Os(II) units, while the triads are composed of coumarin, Ru(II) and Os(II) units. One o

Full text of DOI:10.1039/b212274j

View Article Online / Journal Homepage / Table of Contents for this issue
Photo-induced energy transfer and its switching in dyad and triad
chromophore systems composed of coumarin, Ru(II) and Os(II)
terpyridine-type complexes†
Tetsuo Akasaka,a Toshiki Mutai,a Joe Otsuki*b and Koji Araki*a
a Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo,
153-8505, Japan. E-mail: araki@iis.u-tokyo.ac.jp
b College of Science and Technology, Nihon University, 1-8-14 Kanda Surugadai, Chiyoda-ku,
Tokyo, 101-8308, Japan. E-mail: otsuki@chem.cst.nihon-u.ac.jp
Received 13th December 2002, Accepted 21st February 2003
First published as an Advance Article on the web 10th March 2003
A new dyad and two triad chromophore compounds containing coumarin, Ru() and Os() terpyridine-type
complexes were synthesized. The dyad is composed of coumarin and Os() units, while the triads are composed of
coumarin, Ru() and Os() units. One of the triads has a phenylene spacer to connect the Ru() unit and the Os()
unit, while the other has an azo moiety. Energy transfer in these multichromophoric systems has been probed by
electronic absorption and luminescence spectroscopy. The switching behavior of photo-induced energy transfer by
redox stimuli in the latter triad has been examined. Photophysical and electrochemical analysis indicates that the
contribution of the energy transfer from the coumarin chromophores and the Ru() center to the Os()-centered
emission in the ‘switch-on state’ is estimated to be about 70%. This contribution is larger than that in the previously
reported Ru()/Os() dyad system, which was evaluated to be 40%. Thus, it is concluded that an improved switching
of directional energy transfer has been achieved from the coumarin moiety to the Os() center in this new triad
chromophore system.
coumarin (coumarin 151, C151) as the light harvesting unit,
because C151 (1) absorbs light around 390 nm where absorp-
tion by Ru() and Os() polypyridine complexes is relatively
weak, (2) emits fluorescence in the wavelength range at which
Introduction
The development of molecule-based electronic/photonic
devices performing processes including electron and energy
transfer processes has attracted considerable interest over the
the MLCT band of Ru() complexes lies, and (3) has an amino
past ten years.1 Switching of these processes in response to
group as a convenient derivatizing point for the synthesis of
external stimuli is required for processing information at the
triad systems. The triad system composed of chromophores
molecular level. Several molecular switches for intramolecular
with relatively long excited state lifetimes2c,d,4 will allow long
photo/electronic processes have been reported.2
We have previously shown that the Ru()/Os() tpy-type
(tpy = 2,2Ј:6Ј,2Љ-terpyridine) heterodinuclear complex bridged
by bis[2,6-bis(2-pyridyl)-4-pyridyl]diazene (azotpy), [(tpy)2-
range energy transfer through these chromophores, and various
functional groups can be introduced in between these chromo-
phores in order to tune or switch the energy transfer process.
Two triad chromophore compounds containing coumarin,
Ru(azotpy)Os(tpy)2]4ϩ (Ru-azo-Os), serves as a switch for
Ru() and Os() terpyridine-type complexes were synthesized.
intramolecular energy transfer.3 When the bridging ligand is
neutral, the metal-to-ligand charge-transfer (MLCT) excited
state is rapidly deactivated thermally. On the other hand, when
One of the compounds has a phenylene spacer to connect the
Ru() unit and the Os() unit, while the other has an azo
moiety. The switching behavior of photo-induced energy
the bridging ligand is electrochemically reduced, the photo-
transfer by redox stimuli in the latter triad has been examined.
excited state behaves more or less like the parent complexes,
A coumarin-Os() dyad was also prepared for comparative
purposes.
[M(tpy)2]2ϩ, leading to intramolecular energy transfer.
In the reduced form of this dyad complex, Ru-azo-Os, how-
ever, the contribution of the light absorption at the Ru() center
through the energy transfer to the Os()-centered emission is
estimated to be 40%, and the remaining 60% of luminescence
arises from the direct excitation of the Os() center. This is due
to the fact that the Ru() center and the Os() center are excited
simultaneously because of the spectral overlap of their MLCT
bands. The absorption by Os() polypyridine complexes covers
the whole range of wavelengths at which Ru() complexes can
absorb. Hence, it is not possible to selectively excite the ‘input
site’ (i.e. Ru() center) without exciting the ‘output site’ (i.e.
Os() center) directly. To circumvent this problem and improve
the contribution of the energy transfer, we have extended the
dyad chromophore system to the triad system by introducing a
light harvesting unit. We chose 7-amino-3-trifluoromethyl-
Results
Synthesis
The reaction scheme is illustrated in Fig. 1. The terpyridine
ligand having two coumarin chromophores ((C151)2-tpy) was
obtained in three steps starting with 3,5-bis(bromomethyl)-
anisole and C151 according to the literature procedure by
Fréchet et al.5 The Os() complex which has directly attached
coumarin moieties, (C151)2-Os, was prepared from the reaction
of (C151)2-tpy with Os(ttpy)Cl3 (ttpy = 4Ј-tolyl-2,2Ј:6Ј,2Љ-terpyr-
idine). The triad complexes were synthesized by the “com-
plexes as metals / complexes as ligands” strategy.6 The mono-
nuclear Os() building blocks, [Os(ttpy)(tpy-ph-tpy)][PF6]2
(tpy-ph-tpy = 4,4ЉЉ-(1,4-phenylene)bis(2,2Ј:6Ј,2Љ-terpyridine))
and [Os(ttpy)(azotpy)][PF6]2, containing a non-coordinated tpy
metal-binding domain were prepared from the reaction of
Os(ttpy)Cl3 with tpy-ph-tpy and azotpy, respectively. The di-
nuclear Os() complex, [(ttpy)Os(tpy-ph-tpy)Os(ttpy)][PF6]4
(Os-ph-Os) was obtained as a by-product in the former
† Electronic supplementary information (ESI) available: 1H NMR and
ES mass spectra of the new dyad and triad coumarin-containing
complexes, (C151)2-Os, (C151)2-Ru-ph-Os and (C151)2-Ru-azo-Os and
the emission spectra of (C151)2-tpy and (C151)2-Os. See http://
www.rsc.org/suppdata/dt/b2/b212274j/
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
D a l t o n T r a n s . , 2 0 0 3 , 1 5 3 7 – 1 5 4 4
1537

View Article Online
Fig. 1 Synthetic scheme for the preparation of the dyad and triad complexes. (i) RuCl3 hydrate–EtOH, reflux for 3 h; (ii) Os(ttpy)Cl3–ethylene
glycol, reflux for 1 h, then NH4PF6; (iii) Ru(ttpy)Cl3, N-ethylmorpholine–MeOH, reflux for 2 h, then NH4PF6; (iv) AgBF4–acetone, reflux for 2 h;
(v) [(tpy-ph-tpy)Os(ttpy)][PF6]2–N,N-dimethylacetamide, 120 ЊC for 3 h, then NH4PF6; (vi) Os(ttpy)Cl3–ethylene glycol, 160 ЊC, 30 min, then
NH4PF6; (vii) [(azotpy)Os(ttpy)][PF6]2–N,N-dimethylacetamide, 120 ЊC for 2 h, then NH4PF6.
reaction. [Os(ttpy)(tpy-ph-tpy)][PF6]2 was reacted with
[((C151)2-tpy)Ru(acetone)3]2ϩ, prepared by the complexation of
(C151)2-tpy with RuCl3 followed by substitution reaction of
Cl atoms,7 to yield the triad complex, (C151)2-Ru-ph-Os. The
reference dyad complex without coumarin chromophore,
Ru-ph-Os,8 was synthesized from the reaction of [Os(ttpy)-
(tpy-ph-tpy)][PF6]2 with Ru(ttpy)Cl3. Finally, the triad complex
containing azotpy, (C151)2-Ru-azo-Os, was prepared by the
reaction of [Os(ttpy)(azotpy)][PF6]2 with [((C151)2-tpy)Ru-
(acetone)3]2ϩ. Each complex was purified by column chromato-
graphy or preparative TLC on silica with CH3CN/0.4 M
aqueous KNO3 as eluent. Purity of the complexes was carefully
confirmed by TLC, and all new compounds were characterized
by 1H NMR spectroscopy and FAB or ES mass spectrometry.†
Absorption and emission spectra
The absorption spectra of the dyad and triad complexes,
together with those of the reference compounds (1.00 × 10Ϫ5
M) were measured in CH3CN at 25 ЊC, and are shown in
Fig. 2a–c, and the data are collected in Table 1. The high-
intensity absorption band at about 300 nm can be ascribed to
D a l t o n T r a n s . , 2 0 0 3 , 1 5 3 7 – 1 5 4 4
1538

View Article Online
Table 1 Absorption and emission (λex = 390 nm) properties at 25 ЊC in CH3CN
Emission
Absorption
λmax/nm (rel. int.)
Compound
λmax/nm (10Ϫ4ε/cmϪ1 MϪ1
)
Coumarin
Os based
(C151)2-tpya
(C151)2-Os
Os
(C151)2-Ru-ph-Os
Ru-ph-Os
266 (4.29)
285 (6.59)
286 (5.93)
287 (12.25)
287 (11.14)
288 (10.56)
287 (12.48)
278 (4.29)
315 (7.27)
315 (7.30)
311 (15.08)
312 (14.41)
314 (14.02)
469 (2.19)
390 (3.04)
378 (3.60)
491 (2.62)
360 (5.73)
500 (6.95)
500 (6.38)
625 (4.19)
485 (≡1)
491 (2.62)
667 (0.68)
500 (7.30)
672 (1.01)
673 (1.79)
773 (1.16)
669 (0.68)
670 (0.95)
460 (0.0054)
738 (2.92)
738 (≡1)
752 (2.06)
757 (0.96)
757 (1.23)
461 (0.0070)
Os-ph-Os
(C151)2-Ru-azo-Os
a In DMF.
the emission from the coumarin and the Os() centers are
reported in parentheses as relative values to those of (C151)2-
tpy and Os, respectively, under the same conditions. In (C151)2-
Os and (C151)2-Ru-ph-Os, more than 99% of the emission from
the coumarin moiety was quenched, suggesting that intra-
molecular energy transfer takes place very efficiently from the
coumarin units to the Os() and Ru() centers, respectively. The
azotpy-containing complex, (C151)2-Ru-azo-Os, exhibited no
luminescence, suggesting that the coumarin-to-Ru() energy
transfer efficiency is very high in this compound as well.
Electrochemistry
Cyclic voltammetry of the compounds in N,N-dimethyl-
formamide (DMF) was carried out in the range between ϩ1.4
V and Ϫ2.1 V vs. Fc/Fcϩ, and the redox potentials are summar-
ized in Table 2. In the positive region, the complexes exhibited
reversible one-electron redox peaks due to the Ru2ϩ/Ru3ϩ
couple in the range ϩ0.77 to ϩ0.80 V vs. Fc/Fcϩ and/or revers-
ible one-electron redox peaks due to the Os2ϩ/Os3ϩ couple in the
range ϩ0.44 to ϩ0.49 V vs. Fc/Fcϩ.
In the negative region, (C151)2-Ru-azo-Os exhibited revers-
ible one-electron reduction couples successively at Ϫ0.82 V and
Ϫ1.19 V vs. Fc/Fcϩ due to the reduction of the azo group,3
which were less negative than those of the two-electron reduc-
tion due to the ttpy ligands. This provides evidence that the
π* level of azotpy is lower in energy than that of ttpy. Thus, it
is possible to carry out redox reaction of the azotpy ligand
without affecting the ttpy ligands and metal centers.
Spectroelectrochemistry
Fig. 2 Absorption spectra of (a) (C151)2-tpy (---), Os (ؒ ؒ ؒ) and
(C151)2-Os (—), (b) Ru-ph-Os (—), Os-ph-Os (ؒ ؒ ؒ) and (c) (C151)2-Ru-
ph-Os (—) and (C151)2-Ru-azo-Os (ؒ ؒ ؒ) in CH3CN except for (C151)2-
tpy (in DMF) at 25 ЊC.
We carried out spectroelectrochemical measurements in order
to study the switching behavior of (C151)2-Ru-azo-Os. A solu-
tion of the complex (1.00 × 10Ϫ5 M) in DMF containing 0.1 M
tetrabutylammonium hexafluorophosphate (Bu4NPF6) was
electrolyzed at a constant potential (Ϫ0.95 V vs, Fc/Fcϩ) in a
modified 1 × 1 cm2 quartz cell until the completion of changes
in the electronic spectra was attained. The absorption and emis-
sion spectra before and after this one-electron reduction of
(C151)2-Ru-azo-Os are shown in Fig. 3.
the ligand-centered π–π* transition. A broad band between 420
and 550 nm consists of the spin-allowed MLCT (1MLCT)
band. For the Os() containing complexes, the spin-forbidden
MLCT (3MLCT) band appeared between 550 and 750 nm. In
the case of (C151)2-Ru-azo-Os, Ru and Os
ttpy 1MLCT (469
azotpy MLCT and Os ttpy
3
1
nm) band, a mixture of Ru
3MLCT (625 nm), and Os
azotpy MLCT (773 nm) bands
were observed.3,9 The spectra of the multichromophore com-
pounds match nearly exactly the summation of those of the
component chromophore units. This allows us to estimate
accurately the amount of light absorbed by each chromophore
at a given wavelength.
Discussion
Energy transfer in the dyad system, (C151)2-Os
In (C151)2-tpy, the absorption band due to the coumarin
moiety appears at 390 nm (ε = 30400 MϪ1 cmϪ1), where Ru()/
Os() complexes have only a small absorption. Therefore, good
coumarin-selective excitation in this wavelength region can be
achieved. The molar extinction coefficients at 390 nm increase
from 7800 MϪ1 cmϪ1, 15400 MϪ1 cmϪ1 and 12600 MϪ1 cmϪ1 for
the complexes having no coumarin moieties, Os, Ru-ph-Os and
Ru-azo-Os,3 respectively, to 34100 MϪ1 cmϪ1, 45600 MϪ1 cmϪ1
and 41800 MϪ1 cmϪ1 for the complexes containing coumarin
The emission spectra of the compounds (1.00 × 10Ϫ5 M) were
measured at 25 ЊC by excitation at 390 nm, and the data are
collected in Table 1.† Emission from the coumarin center
appeared at 460–485 nm, while those from the Os() center
appeared at 738–752 nm in (C151)2-Os and (C151)2-Ru-ph-Os.
However, no emission from the Ru() center was observed for
these compounds. To enhance the comparison, intensities of
D a l t o n T r a n s . , 2 0 0 3 , 1 5 3 7 – 1 5 4 4
1539

View Article Online
Table 2 Redox potentials (V vs. Fc/Fcϩ)
Compound
Other reductions
azotpy1Ϫ/2Ϫ
azotpy0/1Ϫ
Os3+/2+
Ru3+/2+
(C151)2-tpy
Ϫ2.00a
Ϫ1.89
(C151)2-Os
Ϫ1.61
0.45
0.44
0.49
(C151)2-Ru-ph-Os
(C151)2-Ru-azo-Os
Ϫ1.88b
Ϫ1.91b
Ϫ1.60b
0.77
0.80
Ϫ1.19
Ϫ0.82
a Peak potential of the reduction wave. b Two electron reduction.
Fig. 3 Absorption spectral change of (C151)2-Ru-azo-Os in DMF
containing 0.1 M Bu4NPF6 before (ؒ ؒ ؒ) and after (—) reduction at
25 ЊC. The inset shows the corresponding emission spectral change.
λex = 390 nm.
units, (C151)2-Os, (C151)2-Ru-ph-Os and (C151)2-Ru-azo-Os,
respectively. Thus, the coumarin chromophores are estimated to
account for 77, 66 and 70% of the light absorbed at 390 nm in
(C151)2-Os, (C151)2-Ru-ph-Os and (C151)2-Ru-azo-Os, respect-
ively, confirming that the coumarin-based absorptions are
largely responsible at 390 nm in all the complexes having the
coumarin moieties. Another advantage of using C151 as the
light input site is manifested in the fact that (C151)2-tpy shows a
strong coumarin-based emission band peaked at 485 nm,† which
overlaps effectively with the absorption band of the Ru()/
Os() polypyridine complexes, enabling efficient energy transfer
to these metal complexes.
The emission intensity from the coumarin moiety in (C151)2-
Os upon excitation at 390 nm is greatly decreased by the pres-
ence of the Os() unit, which is only 0.5% of (C151)2-tpy.
Assuming that the fluorescence quenching is due to the intra-
molecular energy transfer from the coumarin units to the Os()
center (the distance between two units was estimated to be 2.15
nm by molecular mechanics calculation10), the energy transfer
efficiency is estimated to be 99.5%. Though the lifetimes of
related coumarin-based emissions are known to be of the order
of ns,11 those in this coumarin-containing complexes were too
fast11b,c to be measured with our instruments.2l,12 Therefore,
photophysical processes within these complexes have been ana-
lyzed by comparison with the reference complexes. To estimate
the contribution of light absorption at the coumarin units to
the Os()-centered emission, excitation spectra of (C151)2-Os
and Os were compared (Fig. 4a). The emission was monitored at
740 nm, which is the maximum wavelength of the Os()-based
emission, and the spectra are normalized at the 660 nm peak, at
which only the Os()-based component is excited. Except for
the range between 350 and 450 nm where the absorption band
of C151 lies, the excitation spectra of the two compounds
agreed well with each other. The intensity of (C151)2-Os was
3.45 times higher than that of Os at 390 nm, indicating that the
light absorbed by the coumarin units is 2.45 times higher than
that of the Os() unit, and accounts for 71% of the Os()-
centered emission in (C151)2-Os. As the absorbance at 390 nm
of the coumarin units is 3.37 times larger than that of the Os()
unit in (C151)2-Os, the efficiency of excitation transfer from the
coumarin center to the Os() center is determined as 73%. The
Fig. 4 Excitation spectra for (a) (C151)2-Os (—) and Os (ؒ ؒ ؒ),
monitored at 740 nm in CH3CN at 25 ЊC, the intensity is normalized at
660 nm where only the Os()-based unit is excited, (b) (C151)2-Ru-ph-
Os monitored at 750 nm (—), Ru-ph-Os monitored at 756 nm (ؒ ؒ ؒ) and
Os-ph-Os monitored at 756 nm (---) in CH3CN at 25 ЊC, the intensity is
normalized at 660 nm where only the Os()-based unit is excited and
(c) the reduced (C151)2-Ru-azo-Os (—) and Ru-azo-Os (ؒ ؒ ؒ) containing
0.1
M Bu4NPF6 ((C151)2-Ru-azo-Os) or Bu4NClO4 (Ru-azo-Os),
monitored at 790 ((C151)2-Ru-azo-Os) or 775 (Ru-azo-Os) nm in DMF
at 25 ЊC, the intensity is normalized at the respective peaks around 600
nm where only the Os()-based unit is excited.
efficiency obtained by this method is smaller than that sug-
gested from the quenching of the donor emission (>99%, vide
supra). This apparent discrepancy can be explained by consider-
ing that the factors causing the quenching of the donor emis-
sion should include non-radiative excited-energy dissipation
through the Os() complex moiety, in addition to the excitation
transfer to the Os() center.13
Energy transfer in the triad system, (C151)2-Ru-ph-Os
Photophysical properties of (C151)2-Ru-ph-Os were analyzed
similarly by comparing with those of (C151)2-tpy, Ru-ph-Os
and Os-ph-Os. In (C151)2-Ru-ph-Os, more than 99% of the
emission from the coumarin moiety was quenched, suggesting
D a l t o n T r a n s . , 2 0 0 3 , 1 5 3 7 – 1 5 4 4
1540

View Article Online
that the energy transfer efficiency from the coumarin center is
very high. The excitation spectra of (C151)2-Ru-ph-Os, Ru-ph-
Os and Os-ph-Os normalized at the 660 nm peak are shown in
Fig. 4b. From the height of these spectra at 390 nm, the relative
contributions of the coumarin units, the Ru() center and the
Os() center to the Os()-centered emission are similarly esti-
mated to be 51 (1.62), 18 (0.56) and 31% (≡1), respectively
(relative values are shown in parentheses). Therefore, approxi-
mately 70% of the Os()-centered emission originates from the
excitation of the coumarin and/or the Ru() center and
subsequent energy transfer. From the absorbance at 390 nm of
Ru-ph-Os (ε = 15400 MϪ1 cmϪ1) and Os-ph-Os (ε = 19700 MϪ1
cmϪ1, or 9850 MϪ1 cmϪ1 per Os() unit), the absorbance of
(C151)2-Ru-ph-Os is the sum of the contributions of the
coumarin units, the Ru() center and the Os() center in pro-
portions of 66 (3.03), 12 (0.56) and 22% (≡1), respectively. Thus,
the energy transfer efficiencies from the coumarin moiety and
the Ru() center to the Os() center in (C151)2-Ru-ph-Os are
estimated to be 54 and 100%, respectively. The distance from
the coumarin moiety to the Os() center in this triad system was
estimated to be 3.7 nm by molecular mechanics calculation.10
The estimated energy transfer efficiency from the coumarin
units to the Os() center is comparable to that of the Ru()/
Os() dyad system having the same distance connected by the
all-conjugated oligophenylene spacer.14
intramolecular energy transfer, which comprises 56% of the
Os()-centered emission. In Ru-azo-Os, 40% of the Os()-
centered emission was shown to originate from the excitation of
the Ru() center and subsequent energy transfer.3 Therefore,
absorption at the Ru() center is responsible for approximately
18% of the Os()-centered emission in (C151)2-Ru-azo-Os.
Thus, it is estimated that the energy transfer from the coumarin
units and the Ru() center through the reduced azo group
accounts for 74%, or roughly 70% of the Os()-centered emis-
sion. This contribution of energy transfer is nearly matched in
the case of phenylene-bridged triad system, (C151)2-Ru-ph-Os.
This directional energy transfer process is switched on and off
by the redox reaction of the azo group, as schematically shown
in Fig. 5.
Conclusion
In conclusion, we have examined energy transfer processes in
the new dyad, (C151)2-Os, and the triads, (C151)2-Ru-ph-Os
and (C151)2-Ru-azo-Os, focusing mainly on the contribution of
the input chromophores to achieve truly directional processes.
The latter triad compound, (C151)2-Ru-azo-Os, is an improve-
ment from the previously reported molecular energy transfer
switch, Ru-azo-Os, in terms of this directionality. The contribu-
tion of the coumarin moieties and the Ru() center to the
Os()-centered emission is increased, by introducing the
chromophores, which absorb light in a wavelength range in
which Ru()/Os() complexes show only a small absorption,
into the Ru-azo-Os dyad, and extending to the triad chromo-
phore system, (C151)2-Ru-azo-Os. In this study, the energy
transfer among three chromophores separated by a distance of
3.5 nm has been switched, demonstrating a way toward the
realization of more elaborate multichromophore systems in
which various functional groups, which are responsive to
external stimuli, are introduced between chromophores.
Switching of energy transfer in triad system, (C151)2-Ru-azo-Os
The one-electron reduction of the azotpy bridging ligand in
(C151)2-Ru-azo-Os caused a decrease in absorption of the
longer wavelength band and an increase in the shorter wave-
length one as shown in Fig. 3. The change in the absorption
spectrum can be explained by assuming that the reduction of
azotpy in (C151)2-Ru-azo-Os makes the π* level of azotpy
higher in energy, at least up to that of ttpy.3 It is noted that the
absorbance of 390 nm in the reduced form (ε = 38700 MϪ1
cmϪ1) is almost the same as that in the neutral form, and the
coumarin chromophores account for 79% of the light absorbed
at this wavelength, taking into consideration that the molar
extinction coefficient of (C151)2-tpy at 390 nm is 30400 MϪ1
cmϪ1. Thus, this system is an improvement from the previously
reported Ru-azo-Os3 in terms of input selectivity for the
attainment of directional photophysical processes in molecular
systems. The reduced form exhibited the Os()-based emission
at 790 nm by the excitation at 390 nm, whereas the neutral form
showed no emission (Fig. 3, inset). Upon reoxidation, the
absorption and emission spectra of the reduced form of this
complex nearly returned to the original shapes, although the
repetition of this redox cycle resulted in some deterioration of
response (the absorbance at 600 nm recovered to 64% of the
original value after three cycles).
In order to evaluate the contribution of the energy transfer
from the coumarin moieties and the Ru() center to the Os()-
centered emission in the reduced form, we compared the excit-
ation spectra for the reduced forms of Ru-azo-Os and (C151)2-
Ru-azo-Os (Fig. 4c). The emission was monitored at the
maximum wavelength of the Os()-based emission, 775 nm for
Ru-azo-Os and 790 nm for (C151)2-Ru-azo-Os. The spectra are
also normalized at their respective peaks around 600 nm. It is
noted that these spectra differ at wavelengths longer than 450
nm. This is due to the fact that Ru-azo-Os has tpy ligands while
(C151)2-Ru-azo-Os has a ttpy ligand with an additional phenyl
substituent at the 4Ј-position of tpy. Another difference
observed in the excitation spectra of the reduced forms of
(C151)2-Ru-azo-Os and Ru-azo-Os in the range 350 nm to 450
nm is, on the other hand, due to the presence of the coumarin
units in the former complex. As indicated by the arrow in the
figure, the increased intensity of the Os()-based emission in the
reduced form of (C151)2-Ru-azo-Os, when excited at 390 nm
comes from the excitation of the coumarin moiety through
Experimental
General methods
DMF used on photopysical and electorochemical studies was
distilled over P2O5. CH3CN used for spectral measurements was
of spectrophotometric grade from DOJIN Chem. Co. and used
1
as received. The H NMR spectra were recorded on a JEOL
JNM-LA400 spectrometer in CDCl3, CD3COCD3 or CD3CN.
Mass spectra were recorded on a JEOL JMS-600H spectro-
meter equipped with MS-ESIP09 for ES-MS. Elemental analy-
ses were carried out on FISONS Instruments EA1108
Elemental Analyzer. Absorption and emission spectra were
measured with a Shimadzu UV-2500PC spectrophotometer and
Shimadzu RF-5300PC spectrofluorophotometer, respectively.
Emission spectra were measured in N2-purged solutions. Cyclic
voltammetry was conducted in N2-purged DMF containing
0.1 M Bu4NPF6 as supporting electrolyte with a BAS Electro-
chemical Analyser Model 720 A. A platinum disk was used as
the working electrode, a Ag/Agϩ electrode as the reference and
a Pt wire as the counter electrode. All redox waves were refer-
enced to internal ferrocene added at the end of each experi-
ment. Redox potentials are quoted vs. the ferrocene/ferro-
cenium couple (Fc/Fcϩ = 0.0 V). Spectroelectrochemical
experiments were performed on 1.00 × 10Ϫ5 M samples in N2-
purged DMF containing 0.1 M Bu4NPF6 in a spectrofluori-
metric cell (optical path 1 cm), with a Pt mesh, a Ag/Agϩ and a
Pt wire separated with absorbent cotton, as the working,
reference and counter electrodes, respectively.
Synthesis
All reactions were performed under an N2 atmosphere. Solvents
and reagents were of reagent grade quality and used as received
D a l t o n T r a n s . , 2 0 0 3 , 1 5 3 7 – 1 5 4 4
1541

View Article Online
Fig. 5 Schematic illustration of the energy transfer switching in (C151)2-Ru-azo-Os. The percentage numbers indicate the proportion of light
absorbed by each chromophore that contributes to the emission from the Os() unit in the reduced species.
unless otherwise specified. CH2Cl2 and CH3CN were distilled
over P2O5, and tetrahydrofuran (THF) over Na wire, immedi-
ately before use. Potassium carbonate was ground and dried
in vacuo at 70 ЊC overnight before use. 3,5-Bis(bromomethyl)-
anisole,5 4Ј-(para-bromomethylphenyl)-2,2Ј:6Ј,2Љ-terpyridine,15
dense. After stirring for 3 h at room temperature, H2O (100 mL)
was added to this solution. The pale yellow organic phase was
extracted, and washed with saturated NaHCO3 aq. (100 mL)
and H2O (100 mL), and evaporated to dryness to yield a yellow
viscous solid (134 mg) which was recrystallized from ethyl acet-
ate (ca. 2 mL) to give a yellowish-orange microcrystalline solid
(82 mg, 76%). Mp 259.6–260.7 ЊC; 1H NMR (400 MHz,
CD3COCD3, 20 ЊC): δ = 8.51 (s, 1H, OH), 7.42 (dd, J = 9.0, 2.0
Hz, 2H, H-5Ј), 6.97 (s, 1H, H-4), 6.88 (t, J = 5.4 Hz, 2H, NH),
6.78–6.81 (overlapping dd, 2H, H-6Ј ϩ s, 2H, H-2, J = 9.0,
2.4 Hz), 6.51 (d, J = 2.4 Hz, 2H, H-8Ј), 6.38 (s, 2H, H-3Ј),
4.44 (d, J = 5.4 Hz, 4H, CH2); FAB-MS m/z = 577 [M ϩ H]ϩ;
Elemental analysis calcd. (%) for C28H18F6N2O5: C, 58.34; H,
3.15; N, 4.86; found: C, 58.09; H, 3.34; N, 4.97.
[Os(ttpy)2][PF6]2 (Os),15 Ru(ttpy)Cl3,15 Os(ttpy)Cl3 and azo-
16
tpy3 were prepared according to the literature procedures.
3,5-Bis(N-(3-trifluoromethyl-7-aminocoumarin)methyl)-
anisole. A solution of 3,5-bis(bromomethyl)anisole (270 mg,
0.92 mmol) in dry CH3CN (7 mL) was added to a mixture of
7-amino-3-trifluoromethylcoumarin (coumarin 151) (630 mg,
2.75 mmol, 3 equiv.) and potassium carbonate (760 mg,
5.5 mmol, 6 equiv.) in dry CH3CN (50 mL) dropwise over 2 h at
50 ЊC, and this mixture was refluxed for 4 days. The reaction
mixture was cooled to room temperature and filtered. The fil-
trate was evaporated and the residue was dried in vacuo to give a
yellowish-brown powder (752 mg). The crude product was
purified by column chromatography on silica with CH2Cl2–
CHCl3 (1 : 1) as eluent. The first major fraction was unreacted
coumarin 151 (335 mg), and the second major fraction was
collected to give the desired compound as a pale yellow powder
(123 mg, 23%). Mp 249.0–249.6 ЊC; 1H NMR (400 MHz,
CDCl3, 20 ЊC): δ = 7.47 (dd, J = 9.0, 2.0 Hz, 2H, H-5Ј), 6.89
(s, 1H, H-4), 6.81 (s, 2H, H-2), 6.59 (dd, J = 9.0, 2.4 Hz, 2H,
H-6Ј), 6.46 (d, J = 2.4 Hz, 2H, H-8Ј), 6.44 (s, 2H, H-3Ј), 4.86 (t,
J = 5.4 Hz, 2H, NH), 4.40 (d, J = 5.4 Hz, 4H, CH2), 3.80 (s, 3H,
OCH3); FAB-MS m/z = 591 [M ϩ H]ϩ; Elemental analysis
calcd. (%) for C29H20F6N2O5: C, 58.99; H, 3.41; N, 4.74; found:
C, 58.66; H, 3.47; N, 4.46.
4Ј-(4-(3,5-Bis(N-(3-trifluoromethyl-7-aminocoumarin)-
methyl)phenoxymethyl)phenyl)-2,2Ј:6Ј,2Љ-terpyridine ((C151)2-
tpy). A mixture of 4Ј-(para-bromomethylphenyl)-2,2Ј:6Ј,2Љ-
terpyridine (33 mg, 0.082 mmol), 3,5-bis(N-(3-trifluoromethyl-
7-aminocoumarin)methyl)phenol (56 mg, 0.097 mmol, 1.2
equiv.), potassium carbonate (70 mg, 0.51 mmol, 6 equiv.) and
18-crown-6 (9 mg, 0.034 mmol, 0.4 equiv.) in dry THF (10 mL)
was refluxed for 2 days. The reaction mixture was cooled to
room temperature and filtered. The filtrate was evaporated and
dried in vacuo to give a yellowish-brown viscous solid (124 mg).
This solid was dissolved in CHCl3 (30 mL) and the solution was
washed with brine (3 × 20 mL) and dried over Na2SO4. The
solvent was evaporated to give a yellowish-orange viscous solid,
which solidified after standing for several hours and dried in
vacuo overnight at 70 ЊC (70 mg, 95%). Mp 262.1–263.3 ЊC; 1H
NMR (400 MHz, CDCl3, 20 ЊC): δ = 8.74 (d, J = 7.6 Hz, 2H,
H-t6), 8.72 (s, 2H, H-t3Ј), 8.68 (d, J = 7.6 Hz, 2H, H-t3), 7.88–
7.92 (overlapping d, 2H, H-o ϩ t, 2H, H-t4, J = 8.0, 7.6 Hz),
7.52 (d, J = 8.0 Hz, 2H, H-m), 7.46 (dd, J = 9.0, 2.0 Hz, 2H,
H-c5Ј), 7.37 (t, J = 7.6 Hz, 2H, H-t5), 6.90–6.92 (overlapping s,
1H, H-4 ϩ s, 2H, H-2), 6.60 (dd, J = 9.0, 2.4 Hz, 2H, H-c6Ј),
6.47 (d, J = 2.4 Hz, 2H, H-8Ј), 6.42 (s, 2H, H-3Ј), 5.13 (s, 2H,
O–CH2), 4.91 (t, J = 5.4 Hz, 2H, NH), 4.40 (d, J = 5.4 Hz, 4H,
3,5-Bis(N-(3-trifluoromethyl-7-aminocoumarin)methyl)-
phenol. To a solution of 3,5-bis(N-(3-trifluoromethyl-7-amino-
coumarin)methyl)anisole (110 mg, 0.19 mmol) in dry CH2Cl2
(300 mL) was added a solution of BBr3 in CH2Cl2 (1.0 M, 2 mL,
2 mmol, 11 equiv.) dropwise for 10 min at room temperature.
The solution initially turned to pale orange, and then a dense
orange precipitate appeared as the color of the solution turned
D a l t o n T r a n s . , 2 0 0 3 , 1 5 3 7 – 1 5 4 4
1542

View Article Online
N–CH2); FAB-MS m/z = 898 [M ϩ H]ϩ; Elemental analysis
calcd. (%) for C50H33F6N5O5: C, 66.89; H, 3.70; N, 7.80; found:
C, 66.63; H, 3.92; N, 7.60.
[(ttpy)Ru(tpy-ph-tpy)Os(ttpy)][PF6]4 (Ru-ph-Os). A solution
of [(tpy-ph-tpy)Os(ttpy)][PF6]2 (50 mg, 0.037 mmol) and
Ru(ttpy)Cl3 (20 mg, 0.038 mmol) in MeOH (20 mL) with 6
drops of N-ethylmorpholine was stirred at reflux for 2 h. The
reaction mixture was cooled to room temperature, and filtered
through Celite to remove unreacted Ru(ttpy)Cl3. To the filtrate,
excess aqueous NH4PF6 (200 mg) was added. The precipitate
was collected by filtration on Celite, washed with water and
diethyl ether, and re-dissolved in CH3CN. The filtrate was evap-
orated and the residue was dried in vacuo to give a reddish-
purple powder (66 mg). The crude product was purified by pre-
parative TLC on silica with CH3CN–0.4 M aqueous KNO3
(5 : 1) to give a reddish-purple powder (6.5 mg, 8.5%). Rf (Silica)
= 0.50: CH3CN–0.4 M aqueous KNO3 (5 : 1); Mp > 375 ЊC; 1H
NMR (400 MHz, CD3CN, 20 ЊC): δ = 9.19 (s, 2H), 9.17 (s, 2H),
9.06 (s, 2H), 9.03 (s, 2H), 8.75 (d, J = 8.1 Hz, 2H), 8.73 (d,
J = 8.1 Hz, 2H), 8.68 (d, J = 8.8 Hz, 2H), 8.65 (d, J = 8.8 Hz,
2H), 8.59 (d, J = 3.4 Hz, 2H), 8.57 (d, J = 3.7 Hz, 2H), 8.14(d,
J = 8.1 Hz, 2H), 8.10 (d, J = 8.1 Hz, 2H), 8.01 (dt, J = 8.1, 7.8,
1.5, 1.2 Hz, 2H), 7.98 (dt, J = 8.1, 7.8, 1.5, 1.2 Hz, 2H), 7.87 (dt,
J = 8.1, 7.8, 1.5, 1.2 Hz, 2H), 7.84 (dt, J = 8.1, 7.8, 1.5, 1.2 Hz,
2H), 7.60 (d, J = 8.1 Hz, 4H), 7.49 (d, J = 4.6 Hz, 2H), 7.48 (d,
J = 4.2 Hz, 2H), 7.37 (d, J = 5.9 Hz, 2H), 7.35 (d, J = 6.6 Hz,
2H), 7.24 (dt, J = 5.9, 5.6, 1.2 Hz, 2H), 7.22 (dt, J = 5.9, 1.2 Hz,
2H), 7.17 (dt, J = 7.6, 1.2 Hz, 2H), 7.15 (dt, J = 7.6, 1.2 Hz, 2H),
2.59 (s, 3H), 2.56 (s, 3H); ES-MS m/z = 1913 [M Ϫ PF6]ϩ, 884
(Ru((C151)2-tpy))Cl3. A mixture of (C151)2-tpy (40 mg, 0.045
mmol) and ruthenium trichloride hydrate (12 mg, 0.046 mmol)
in EtOH (10 mL) was refluxed for 3 h. The reaction mixture was
cooled to room temperature to give a brown precipitate which
was filtered from the yellowish-brown solution. The residue was
washed with EtOH and diethyl ether, and dried in vacuo to give
a brown powder (42 mg, 85%). FAB-MS m/z = 1070 [M Ϫ Cl]ϩ,
1034 [M Ϫ 2Cl]ϩ, 899 [M Ϫ (RuCl3) ϩ H]ϩ.
[((C151)2-tpy)Os(ttpy)][PF6]2 ((C151)2-Os). A solution of
(C151)2-tpy (30 mg, 0.033 mmol) and Os(ttpy)Cl3 (21 mg, 0.034
mmol) in ethylene glycol (10 mL) was stirred at reflux for 1 h.
The reaction mixture was cooled to room temperature, to which
excess aqueous NH4PF6 (150 mg) was added. The precipitate
was collected by filtration on Celite, washed with water and
diethyl ether, and re-dissolved in CH3CN. The filtrate was evap-
orated and the residue was dried in vacuo to give a dark brown
powder (51 mg). The crude product was purified by column
chromatography on silica with CH3CN–0.4 M aqueous KNO3
(100 : 1) to give a dark brown powder (11 mg, 19%). Rf (Silica) =
0.31: CH3CN–0.4 M aqueous KNO3 (19:1); 0.92: NH4PF6
1
(4 mg)–CH3CN (1 mL); Mp > 375 ЊC; H NMR (400 MHz,
CD3CN, 20 ЊC): δ = 9.03 (s, 2H), 9.00 (s, 2H), 8.63 (d, J = 8.3 Hz,
4H), 8.10 (d, J = 8.1 Hz, 2H), 8.08 (d, J = 8.1 Hz, 2H), 7.80 (dt,
J = 8.1, 1.5 Hz, 4H), 7.72 (d, J = 8.1 Hz, 2H), 7.59 (d, J = 8.1 Hz,
2H), 7.43 (dd, J = 9.0, 2.0 Hz, 2H), 7.33 (d, J = 4.9 Hz, 2H), 7.32
(d, J = 4.9 Hz, 2H), 7.12 (d, J = 6.1 Hz, 2H), 7.09 (d, J = 5.9 Hz,
2H), 7.01 (s, 1H), 6.98 (s, 2H), 6.70 (dd, J = 9.0, 2.4 Hz, 2H),
6.41 (d, J = 2.4 Hz, 2H), 6.33 (s, 2H), 6.13 (t, J = 6.1 Hz,
2H), 5.31 (s, 2H), 4.42 (d, J = 6.1 Hz, 4H), 2.57 (s, 3H); ES-MS
[M Ϫ 2PF6]2ϩ
.
[((C151)2-tpy)Ru(tpy-ph-tpy)Os(ttpy)][PF6]4 ((C151)2-Ru-ph-
Os). A solution of (Ru((C151)2-tpy))Cl3 (22 mg, 0.020 mmol)
and AgBF4 (12 mg, 0.062 mmol, 3 equiv.) in acetone (5 mL) was
heated at reflux in air for 2 h. The reddish-brown reaction mix-
ture was cooled to room temperature and filtered to remove
AgCl. The filtrate was evaporated and N,N-dimethylacetamide
(3 mL) was added to the resulting residue. This solution was
added to a solution of [(tpy-ph-tpy)Os(ttpy)][PF6]2 (27 mg,
0.020 mmol) in N,N-dimethylacetamide (3 mL) and this mixed
solution was heated at 120 ЊC under N2 for 3 h. The reaction
mixture was cooled to room temperature and filtered through
Celite, and the filtrate was evaporated and the residue dried.
The resulting solid was dissolved in a minimum amount of
CH3CN and excess aqueous NH4PF6 (150 mg) was added. The
precipitate was collected by filtration, washed with water and
diethyl ether, and the reddish-brown powder (50 mg) was puri-
fied by chromatography on silica with CH3CN–0.4 M aqueous
KNO3 (initially 20 : 1) as eluent to give a reddish-brown powder
(10 mg, 19%), which was characterized as (C151)2-Ru-ph-Os. Rf
(Silica) = 0.63: CH3CN–0.4 M aqueous KNO3 (5 : 1); 0.35:
NH4PF6 (4 mg)–CH3CN (1 mL); Mp > 375 ЊC; 1H NMR (400
MHz, CD3CN, 20 ЊC): δ = 9.21 (s, 2H), 9.19 (s, 2H), 9.06 (s, 2H),
9.02 (s, 2H), 8.77 (d, J = 8.5 Hz, 2H), 8.75 (d, J = 8.5 Hz,
2H), 8.68 (d, J = 8.1 Hz, 2H), 8.66 (d, J = 8.8 Hz, 2H), 8.61 (d,
J = 8.4 Hz, 2H), 8.57 (d, J = 8.4 Hz, 2H), 8.16 (d, J = 8.1 Hz,
2H), 8.10 (d, J = 8.1 Hz, 2H), 8.02 (t, J = 7.8 Hz, 2H), 7.98
(t, J = 8.1 Hz, 2H), 7.88 (t, J = 8.4 Hz, 2H), 7.84 (t, J = 7.8 Hz,
2H), 7.74 (d, J = 8.1 Hz, 2H), 7.60 (d, J = 8.1 Hz, 2H), 7.52
(d, J = 5.4 Hz, 2H), 7.51 (d, J = 5.6 Hz, 2H), 7.44 (dd, J = 9.0,
2.0 Hz, 2H), 7.37 (d, J = 5.9 Hz, 2H), 7.36 (d, J = 5.6 Hz, 2H),
7.24 (t, J = 6.1, 5.9 Hz, 4H), 7.17 (t, J = 6.5 Hz, 2H), 7.15 (t,
J = 6.1 Hz, 2H), 7.02 (s, 1H), 6.99 (s, 2H), 6.71 (dd, J = 9.0,
2.4 Hz, 2H), 6.42 (d, J = 2.4 Hz, 2H), 6.35 (s, 2H), 6.15 (t, J = 6.1
Hz, 2H), 5.31 (s, 2H), 4.43 (d, J = 6.1 Hz, 4H), 2.59 (s, 3H);
ES-MS m/z = 2487 [M Ϫ PF6]ϩ, 1172 [M Ϫ 2PF6]2ϩ, 732
m/z = 1556 [M Ϫ PF6]ϩ, 706 [M Ϫ 2PF6]2ϩ
.
[(tpy-ph-tpy)Os(ttpy)][PF6]2. A solution of tpy-ph-tpy (436
mg, 0.81 mmol, 2 equiv.) and Os(ttpy)Cl3 (250 mg, 0.403 mmol)
in ethylene glycol (40 mL) was stirred at reflux for 1 h. The
reaction mixture was cooled to room temperature, to which
excess aqueous NH4PF6 (1000 mg) was added. The precipitate
was collected by filtration on Celite, washed with water and
diethyl ether, and re-dissolved with CH3CN. The filtrate was
evaporated and the residue was dried in vacuo to give a dense
purple powder (469 mg). A portion of this crude product (200
mg) was purified by column chromatography on silica with
CH3CN–0.4 M aqueous KNO3 (initially 10 : 1) to give a brown-
purple powder (70 mg, 30%), which was characterized as
[(tpy-ph-tpy)Os(ttpy)][PF6]2. Mp > 375 ЊC; 1H NMR (400
MHz, CD3CN, 20 ЊC): δ = 9.11 (s, 2H), 9.03 (s, 2H), 8.93 (s, 2H),
8.79 (dd, J = 4.7, 1.9 Hz, 2H), 8.76 (d, J = 8.1 Hz, 2H), 8.67 (d,
J = 8.1 Hz, 2H), 8.63 (d, J = 8.3 Hz, 2H), 8.39 (d, J = 8.3 Hz,
2H), 8.30 (d, J = 8.3 Hz, 2H), 8.08 (d, J = 8.1 Hz, 2H), 8.03 (dt,
J = 7.8, 2.0, 1.7 Hz, 2H), 7.83 (dt, J = 7.6, 1.2 Hz, 2H), 7.81 (dt,
J = 7.8, 1.5 Hz, 2H), 7.59 (d, J = 7.8 Hz, 2H), 7.52 (dt, J = 5.9,
1.2 Hz, 2H), 7.33 (d, J = 5,6 Hz, 4H), 7.14 (dt, J = 5.9, 1.5, 1.2
Hz, 2H), 7.12 (dt, J = 5.9, 1.5, 1.2 Hz, 2H), 2.58 (s, 3H); ES-MS
m/z = 1200 [M Ϫ PF6]ϩ.
Then eluent was changed to CH3CN–0.4 M aqueous KNO3
(8 : 1 to 5 : 1) to give a dense purple powder (51 mg, 22%),
which was characterized as [(ttpy)Os(tpy-ph-tpy)Os(ttpy)]-
[PF6]4 (Os-ph-Os). Rf (Silica) = 0.45: CH3CN–0.4 M aqueous
1
KNO3 (5 : 1); Mp > 375 ЊC; H NMR (400 MHz, CD3CN,
20 ЊC): δ = 9.19 (s, 4H), 9.06 (s, 4H), 8.74 (d, J = 8.3 Hz,
4H), 8.66 (d, J = 8.3 Hz, 4H), 8.57 (d, J = 8.1 Hz, 4H), 8.10
(d, J = 8.1 Hz, 4H), 7.87 (dt, J = 8.1, 7.8, 1.5 Hz, 4H), 7.84
(dt, J = 8.1, 7.8, 1.2 Hz, 4H), 7.60 (d, J = 8.1 Hz, 4H), 7.37 (d,
J = 5.9 Hz, 4H), 7.35 (d, J = 5.9 Hz, 4H), 7.17 (dt, J = 6.5, 1.2
Hz, 4H), 7.15 (dt, J = 7.3, 1.2 Hz, 4H), 2.59 (s, 6H); ES-MS
[M Ϫ 3PF6]3ϩ
.
Then eluent was changed to CH3CN–0.4 M aqueous KNO3
(10 : 1) to give a brown-purple powder (1.3 mg, 2.5%), which
was characterized as [(ttpy)Os(tpy-ph-tpy)Ru(tpy-ph-tpy)-
Os(ttpy)]6ϩ. Rf (Silica) = 0.51: CH3CN–0.4 M aqueous KNO3
(5 : 1); Mp > 375 ЊC; 1H NMR (400 MHz, CD3CN, 20 ЊC): δ =
9.22 (s, 4H), 9.21 (s, 4H), 9.06 (s, 4H), 8.80 (d, J = 8.1 Hz, 4H),
m/z = 2001 [M Ϫ PF6]ϩ, 929 [M Ϫ 2PF6]2ϩ
.
D a l t o n T r a n s . , 2 0 0 3 , 1 5 3 7 – 1 5 4 4
1543

View Article Online
8.75 (d, J = 8.1 Hz, 4H), 8.66 (d, J = 8.1 Hz, 4H), 8.63 (d, J = 8.8
Hz, 4H), 8.61 (d, J = 8.5 Hz, 4H), 8.10 (d, J = 8.1 Hz, 4H), 8.05
(dt, J = 8.1, 7.8, 1.5, 1.2 Hz, 4H), 7.88 (dt, J = 8.3, 7.8, 1.5,
1.2 Hz, 4H), 7.84 (dt, J = 8.3, 8.1, 1.5, 1.2 Hz, 4H), 7.61 (d,
J = 7.8 Hz, 4H), 7.55 (d, J = 8.1 Hz, 4H), 7.37 (d, J = 6.4 Hz,
4H), 7.36 (d, J = 6.6 Hz, 4H), 7.28 (dt, J = 7.6, 1.2 Hz, 4H), 7.17
(dt, J = 7.6, 1.2 Hz, 4H), 7.16 (dt, J = 7.6, 1.2 Hz, 4H), 2.59 (s,
6H); ES–MS m/z = 2932 [M(PF6)5]ϩ, 1394 [M(PF6)4]2ϩ, 881
Acknowledgements
This study was partly supported by a Grant-in-Aid for
Scientific Research (No. 10450339) from the Ministry of
Education, Science, Sports and Culture, Japan.
References and notes
[M(PF6)3]3ϩ, 1354 [M(PF6)3(NO3)]2ϩ, 854 [M(PF6)2(NO3)]3ϩ
.
1 For reviews, see: (a) J. Otsuki, Recent Res. Dev. Pure Appl. Chem.,
1998, 2, 427–439; (b) J.-M. Lehn, Supramolecular Chemistry; VCH,
Weinheim, 1995; (c) F. Barigelleti and L. Flamigni, Chem. Soc. Rev.,
2000, 29, 1–12; (d ) L. De Cola and P. Belser, Coord. Chem. Rev.,
1998, 177, 301–346; (e) M. D. Ward and F. Barigelletti, Coord.
Chem. Rev., 2001, 216–217, 127–154; ( f ) C. Joachim, J. K.
Gimzewski and A. Aviram, Nature (London), 2000, 408, 541–548;
(g) V. Balzani, A. Credi, F. M. Raymo and J. F. Stoddart,
Angew. Chem., Int. Ed., 2000, 39, 3348–3391.
2 (a) N. Aubert, V. Troiani, M. Gross and N. Solladié, Tetrahedron
Lett., 2002, 43, 8405–8408; (b) I. B. Ramsteiner, A. Hartschuh and
H. Port, Chem. Phys. Lett., 2001, 343, 83–90; (c) R. K. Lammi,
R. W. Wagner, A. Ambroise, J. R. Diers, D. F. Bocian, D. Holten and
J. S. Lindsey, J. Phys. Chem. B, 2001, 105, 5341–5352; (d ) R. W.
Wagner, J. S. Lindsey, J. Seth, V. Palaniappan and D. F. Bocian,
J. Am. Chem. Soc., 1996, 118, 3996–3997; (e) M. T. Albelda, P. Daíz,
E. García-España, J. C. Lima, C. Lodeiro, J. S. de Melo, A. J. Parola,
F. Pina and C. Soriano, Chem. Phys. Lett., 2002, 353, 63–68;
( f ) L. Flamigni, G. Marconi, I. M. Dixon, J.-P. Collin and J.-P.
Sauvage, J. Phys. Chem. B, 2002, 106, 6663–6671; (g) E. Zahavy and
M. A. Fox, Chem. Eur. J., 1998, 4, 1647–1652; (h) S. Fraysse,
C. Coudret and J.-P. Launay, Eur. J. Inorg. Chem., 2000, 1581–1590;
(i) A. J. Myles and N. R. Branda, J. Am. Chem. Soc., 2001, 123,
177–178; (j) J. Otsuki, K. Sato, M. Tsujino, N. Okuda, K. Araki
and M. Seno, Chem. Lett., 1996, 847–848; (k) J. Otsuki, M. Tsujino,
T. Iizaki, K. Araki, M. Seno, K. Takatera and T. Watanabe, J. Am.
Chem. Soc., 1997, 119, 7895–7896; (l ) T. Akasaka, H. Inoue,
M. Kuwabara, T. Mutai, J. Otsuki and K. Araki, Dalton Trans.,
2003, 815–821.
3 T. Akasaka, J. Otsuki and K. Araki, Chem. Eur. J., 2002, 8, 130–136.
4 (a) N. D. McClenaghan, F. Loiseau, F. Puntoriero, S. Serroni and
S. Campagna, Chem. Commun., 2001, 2634–2635; (b) M.
Sommovigo, G. Denti, S. Serroni, S. Campagna, C. Mingazzini,
C. Mariotti and A. Juris, Inorg. Chem., 2001, 40, 3318–3323;
(c) S. Kawahara, T. Uchimaru and S. Murata, Chem. Commun.,
1999, 563–564; (d ) Y. Ohya, K. Yabuki, M. Komatsu and T. Ouchi,
Polym. Adv. Technol., 2000, 11, 845–855.
5 S. L. Gilat, A. Adronov and J. M. J. Fréchet, J. Org. Chem., 1999, 64,
7474–7478.
6 G. Denti, S. Serroni, S. Campagna, A. Juris, M. Ciano and
V. Balzani, in Perspectives in Coordination Chemistry, ed. A. F.
Williams, C. Floriani and A. E. Merbach, VHCA and VCH,
Weinheim and Basel, 1992, p. 153.
[(azotpy)Os(ttpy)][PF6]4. A solution of azptpy (79 mg, 0.16
mmol, 1.2 equiv.) and Os(ttpy)Cl3 (83 mg, 0.13 mmol) in ethyl-
ene glycol (80 mL) was stirred at 160 ЊC for 30 min. The reac-
tion mixture was cooled to room temperature, to which excess
aqueous NH4PF6 (500 mg) was added. The precipitate was
collected by filtration on Celite, washed with water and diethyl
ether, and re-dissolved in CH3CN. The filtrate was evaporated
and the residue was dried in vacuo to give a dense purple
powder (166 mg). The crude product was purified by column
chromatography on silica with CH3CN–0.4 M aqueous KNO3
(20 : 1) to give, after [Os(ttpy)2]2ϩ (19 mg, 13%) as a brown
powder, a reddish-purple powder which was characterized as
1
[(azotpy)Os(ttpy)][PF6]2 (16 mg, 9%). Mp > 375 ЊC; H NMR
(400 MHz, CD3CN, 20 ЊC): δ = 9.34 (s, 2H), 9.13 (s, 2H), 9.07 (s,
2H), 8.82 (d, J = 5.9 Hz, 2H), 8.80 (d, J = 9.5 Hz, 2H), 8.73 (d,
J = 8.1 Hz, 2H), 8.64 (d, J = 8.1 Hz, 2H), 8.09 (d, J = 8.1 Hz,
2H), 8.08 (dt, J = 6.1, 1.5 Hz, 2H), 7.87 (dt, J = 8.1, 7.8, 1.5,
1.2 Hz, 2H), 7.83 (dt, J = 8.1, 7.8, 1.5, 1.2 Hz, 2H), 7.60 (d,
J = 8.3 Hz, 2H), 7.57 (dd, J = 7.6, 1.0 Hz, 2H), 7.40 (d, J = 5.6
Hz, 2H), 7.30 (d, J = 5,6 Hz, 2H), 7.22 (dt, J = 6.7, 6.5, 1.5, 1.2
Hz, 2H), 7.11 (t, J = 7.1, 6.1 Hz, 2H), 2.59 (s, 3H); FAB-MS
m/z = 1008 [M Ϫ 2PF6]ϩ.
[((C151)2-tpy)Ru(azotpy)Os(ttpy)][PF6]4
((C151)2-Ru-azo-
Os). A solution of (Ru((C151)2-tpy))Cl3 (16 mg, 0.015 mmol)
and AgBF4 (9 mg, 0.046 mmol, 3 equiv.) in acetone (4 mL) was
heated at reflux in air for 2 h. The reddish-brown reaction mix-
ture was cooled to room temperature and filtered to remove
AgCl. The filtrate was evaporated and N,N-dimethylacetamide
(3 mL) was added to the resulting residue. This solution was
added to a solution of [(azotpy)Os(ttpy)][PF6]2 (18 mg, 0.014
mmol) in N,N-dimethylacetamide (2 mL) and this mixed solu-
tion was heated at 120 ЊC under N2 for 2 h. The reaction mix-
ture was cooled to room temperature and filtered through
Celite. The filtrate was evaporated and the residue dried. The
resulting solid was dissolved in a minimum amount of CH3CN
and excess aqueous NH4PF6 (150 mg) was added. The resulting
precipitate was collected by filtration, washed with water and
diethyl ether. The thus obtained purple powder (39 mg) was
purified by chromatography on silica with CH3CN–0.4 M
aqueous KNO3 (20 : 1) as eluent to give, after the unreacted
[(azotpy)Os(ttpy)][PF6]2 as a reddish-purple powder (7 mg,
19%), a blue-purple powder which was characterized as
(C151)2-Ru-azo-Os (4 mg, 11%). Rf (Silica) = 0.55: CH3CN–0.4
M aqueous KNO3 (5 : 1); 0.32: NH4PF6 (4 mg)–CH3CN
7 (a) D. Armspach, E. C. Constable, F. Diederich, C. E. Housecroft
and J.-F. Nierengarten, Chem. Eur. J., 1998, 4, 723–733; (b) M. Beley,
S. Chodorowski, J.-P. Collin, J.-P. Sauvage, L. Flamigni and
F. Barigelletti, Inorg. Chem., 1994, 33, 2543–2547.
8 The same complex was synthesized by coordination of the Ru() site
at the first step; F. Barigelletti, L. Flamigni, V. Balzani, J.-P. Collin,
J.-P. Sauvage, A. Sour, E. C. Constable and A. M. W. C. Thompson,
J. Am. Chem. Soc., 1994, 116, 7692–7699.
9 R.-A. Fallahpour and M. Neuburger, Helv. Chim. Acta, 2001, 84,
715–721.
10 MM2 force field in the CambridgeSoft Chem3D 6.0 package,
U. Burkert and N. L. Allinger, Molecular Mechanics, ACS Mono-
graph 177, American Chemical Society, Washington, DC, 1982.
11 (a) K. Na and K. Ol, Usp. Khim., 1992, 61, 1243–1267; (b) X. Zhou,
D. S. Tyson and F. N. Castellano, Angew. Chem., Int. Ed., 2000, 39,
4301–4305; (c) D. S. Tyson and F. N. Castellano, Inorg. Chem., 1999,
38, 4382–4383.
12 C.-S. Choi, L. Mishra, T. Mutai and K. Araki, Bull. Chem. Soc. Jpn.,
2000, 73, 2051–2058.
13 (a) A. Adronov, S. L. Gilat, J. M. J. Fréchet, K. Ohta, F. V. R.
Neuwahl and G. R. Fleming, J. Am. Chem. Soc., 2000, 122, 1175–
1185; (b) M. Sirish, R. Kache and B. G. Maiya, J. Photochem.
Photobiol. A: Chem., 1996, 93, 129–136.
14 B. Schlicke, P. Belser, L. De Cola, E. Sabbioni and V. Balzani, J. Am.
Chem. Soc., 1999, 121, 4207–4214.
15 J.-P. Collin, S. Guillerez, J.-P. Sauvage, F. Barigelletti, L. De Cola,
L. Flamigni and V. Balzani, Inorg. Chem., 1991, 30, 4230–4238.
16 J.-P. Collin, S. Guillerez, J.-P. Sauvage, F. Barigelletti, L. De Cola,
L. Flamigni and V. Balzani, Inorg. Chem., 1992, 31, 4112–4117.
1
(1 mL); Mp > 375 ЊC; H NMR (400 MHz, CD3CN, 20 ЊC):
δ = 9.50 (s, 2H), 9.45 (s, 2H), 9.11 (s, 2H), 9.05 (s, 2H), 8.84 (dd,
J = 8.1, 1.2 Hz, 4H), 8.70 (d, J = 7.6 Hz, 2H), 8.68 (d, J = 8.1 Hz,
2H), 8.18 (d, J = 8.3 Hz, 2H), 8.11 (d, J = 8.3 Hz, 2H), 8.06 (dt,
J = 8.1, 1.2 Hz, 2H), 8.00 (dt, J = 8.1, 1.2 Hz, 2H), 7.92 (dt,
J = 8.1, 1.2 Hz, 2H), 7.85 (dt, J = 8.1, 1.2 Hz, 2H), 7.75 (d,
J = 8.3 Hz, 2H), 7.62 (d, J = 7.8 Hz, 2H), 7.57 (dd, J = 4.9, 1.2
Hz, 2H), 7.52 (dd, J = 5.6, 1.2 Hz, 2H), 7.44 (dd, J = 5.6, 0.7 Hz,
4H), 7.36 (d, J = 5.1 Hz, 2H), 7.30 (dt, J = 6.5, 6.1, 1.5, 1.2 Hz,
2H), 7.27 (dt, J = 6.5, 6.1, 1.5, 1.2 Hz, 2H), 7.23 (dt, J = 7.3, 6.1,
5.9, 1.5, 1.2 Hz, 2H), 7.15 (dt, J = 7.3, 6.1, 5.9, 1.5 Hz, 2H), 7.02
(s, 1H), 6.99 (s, 2H), 6.71 (dd, J = 9.0, 2.4 Hz, 2H), 6.42 (d,
J = 2.4 Hz, 2H), 6.35 (s, 2H), 6.14 (t, J = 6.1 Hz, 2H), 5.32 (s,
2H), 4.43 (d, J = 6.1 Hz, 4H), 2.60 (s, 3H); ES-MS m/z = 2439
[M Ϫ PF6]ϩ, 1147 [M Ϫ 2PF6]2ϩ, 716 [M Ϫ 3PF6]3ϩ
.
D a l t o n T r a n s . , 2 0 0 3 , 1 5 3 7 – 1 5 4 4
1544