The role of isomeric effects on the luminescence lifetimes and electrochemistry of oligothienyl-bridged dinuclear tris(2,2′-bipyridine) ruthenium(II) complexes

Article abstract of DOI:10.1002/ejic.200701118

The luminescence lifetimes (in CH₃CN at room temperature) and electrochemical potentials (in CH₃CN) of a range of mono- and bis(bidentate) 2,2′-bipyridine-capped oligothiophene-bridged Ru ^II complexes based on the 6-(2-thienyl)-2,2′-bipyridine and 4-(2-thienyl)-2,2′-bipyridine motifs have been measured. The redox potentials occurred in a very narrow range and showed only small shifts from that of [Ru(bpy)₃]²⁺, which indicates that the inductive effects of the substituents on the 2,2′-bipyridine ligands are very similar across this series. In the complexes that incorporated a bithiophene moiety the oxidation of the bithienyl group occurred at higher potentials than the metal-centered Ru^III/II oxidation. No or very weak interaction between the metal cores in the dinuclear complexes was observed. It was found that the luminescence lifetimes of the complexes where the attachment point of the oligothiophene bridge is in the 4-position of a 2,2′-bipyridine ligand were extended compared to [Ru(bpy)₃]²⁺, whereas the luminescence was very short-lived (<30 ns) or completely quenched in the complexes where the oligothiophene bridge was attached in the 6-position. The difference in lifetimes is probably due to steric interactions between the thienyl bridge and the auxiliary bipyridyl ligands, resulting in disturbances in coordination symmetry of the metal core. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200701118

FULL PAPER
DOI: 10.1002/ejic.200701118
The Role of Isomeric Effects on the Luminescence Lifetimes and
Electrochemistry of Oligothienyl-Bridged Dinuclear
Tris(2,2Ј-bipyridine)ruthenium(II) Complexes
Robert O. Steen,[a] Lasse J. Nurkkala,[a] Sarah J. Angus-Dunne,[a] Chantal X. Schmitt,[b]
Edwin C. Constable,[b] Mark J. Riley,[c] Paul V. Bernhardt,[c] and Simon J. Dunne*[a]
Keywords: Luminescence / N ligands / Ruthenium / Cyclic voltammetry / Ligand design
The luminescence lifetimes (in CH3CN at room temperature)
and electrochemical potentials (in CH3CN) of a range of
mono- and bis(bidentate) 2,2Ј-bipyridine-capped oligo-
thiophene-bridged RuII complexes based on the 6-(2-thi-
enyl)-2,2Ј-bipyridine and 4-(2-thienyl)-2,2Ј-bipyridine motifs
have been measured. The redox potentials occurred in a very
narrow range and showed only small shifts from that of
[Ru(bpy)3]2+, which indicates that the inductive effects of the
substituents on the 2,2Ј-bipyridine ligands are very similar
across this series. In the complexes that incorporated a bi-
thiophene moiety the oxidation of the bithienyl group oc-
curred at higher potentials than the metal-centered RuIII/II
oxidation. No or very weak interaction between the metal
cores in the dinuclear complexes was observed. It was found
that the luminescence lifetimes of the complexes where the
attachment point of the oligothiophene bridge is in the 4-
position of a 2,2Ј-bipyridine ligand were extended compared
to [Ru(bpy)3]2+, whereas the luminescence was very short-
lived (Ͻ30 ns) or completely quenched in the complexes
where the oligothiophene bridge was attached in the 6-posi-
tion. The difference in lifetimes is probably due to steric in-
teractions between the thienyl bridge and the auxiliary bi-
pyridyl ligands, resulting in disturbances in coordination
symmetry of the metal core.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
1 µs at room temperature.[1] In solution this is long enough
to encounter another molecule and partake in a bimolecu-
lar energy-/electron-transfer process. If the possibility exists
for intramolecular energy/electron transfer, this process can
be made even more selective and effective.
The energy available to *[Ru(bpy)3]2+ for energy-transfer
processes is 2.12 eV, and its reduction and oxidation poten-
tials are +0.83 and –0.79 V (in CH3CN),[1a] making
*[Ru(bpy)3]2+ at the same time a good energy donor, a good
electron acceptor and a good electron donor.[1] Thus, (poly-
pyridine)ruthenium(II) complexes serve as excellent candi-
dates for use as an electron source/sink in molecular elec-
tronic applications. In order to unequivocally direct this en-
ergy/electron transfer to a specific target, a linker or a
bridge is required. A wide variety of bridges have been re-
ported with the most common being oligophenylenes,[2] oli-
go(phenylethylene)s[3] and oligothiophenes.[4] Due to their
Introduction
(Polypyridine)ruthenium(II) complexes have played and
are still playing a key role in the development of photo-
chemistry, photophysics, photocatalysis, electrochemistry
and electron and energy transfer. Their unique combination
of chemical stability, redox properties, excited-state reactiv-
ity, luminescence emission and long excited-state lifetimes
has attracted the attention of many researchers. (Poly-
pyridine)ruthenium(II) complexes can also act as light-ab-
sorption sensitizers, thus finding use in solar-energy conver-
sion and storage applications. A critical limitation on the
photoresponsiveness of these complexes is the concentra-
tion of the sensitizer excited state, and this notably depends
on the excited-state lifetime. Depending upon the solvent,
[Ru(bpy)3]2+ has a luminescence lifetime of approximately
[a] Department of Biology and Chemical Engineering, Mälardalen stability, coplanarity and ease of derivitisation, oligothio-
University,
phenes have gained prominence within the field of molecu-
Box 325, 63105 Eskilstuna, Sweden
lar electronics and have found applications in organic light-
emitting diodes and organic field-effect transistors. How-
ever, the attachment of a linker of any kind to one of the
2,2Ј-bipyridine ligands will affect the properties of the re-
sulting [Ru(bpy)2(L)]2+ complex. Steric effects between the
bridge and the auxiliary bipyridine ligands may alter the
coordination symmetry of the metal core,[5] leading to dras-
Fax: +46-16-153710
E-mail: simon.dunne@mdh.se
[b] Department of Chemistry, University of Basel,
Spitalstrasse 51, 4056 Basel, Switzerland
[c] Department of Chemistry, School of Molecular & Microbial
Sciences, University of Queensland,
Brisbane 4072, Qld, Australia
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
1784
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Photophysics and Electrochemistry of Ruthenium(II) Complexes
tic shortenings of luminescence lifetimes by opening up fast raphy, 1 was obtained as yellow crystals. The Stille reagent
non-radiative pathways, and minimizing the systems ca- 6-(5-tri-n-butylstannyl-2-thienyl)-2,2Ј-bipyridine (2) was ob-
pacity for directed energy/electron transfer.
tained by lithiation of 1 followed by quenching with
Pappenfus and Mann[6] have reported synthetic and elec- SnBu3Cl. Subsequent treatment of 2 with 2-bromothio-
trochemical studies on a series of 2,2Ј-bipyridine-capped phene in refluxing dry toluene with [Pd(PPh3)4] as catalyst
oligothiophene ligands and their RuII complexes with yielded 6-[5-(2,2Ј-bithienyl)]-2,2Ј-bipyridine[9] (3). 6-(5-
bridge lengths of 1, 3 and 6 thienyl units, in which the Bromo-2-thienyl)-2,2Ј-bipyridine[10] (4) was straightfor-
bridge was attached at the 4-position of the bipyridine unit. wardly synthesized by refluxing 1 in CH2Cl2 with 1 equiv.
However, no lifetime measurements were reported in their of Br2. 5,5Ј-Bis(2,2Ј-bipyridin-6-yl)-2,2Ј-bithiophene (5) was
study. In addition, Pappenfus and Mann reported that in then synthesized by a Stille cross-coupling between 2 and 4
bridges of 3 or more thienyl units, oxidation of the thio- in refluxing dry toluene. The bis(bidentate) ligand 5 was
phene bridge occurred before metal-centered oxidation. In obtained as a yellow microcrystalline powder that was in-
this work, we present a study of the role of the attachment soluble in most organic solvents.
4-(2-Thienyl)-2,2Ј-bipyridine[10,11] (6) was also obtained
position within a series of mono- and bis(bidentate) bipyr-
using the Kröhnke methodology,[8] by refluxing 3-(2-thi-
enyl)propenal with PPI and ammonium acetate in acetic
acid. After Soxhlet extraction and recrystallization, 6 was
obtained as yellow needles (see Scheme 2). The combina-
tion of 4-(5-bromo-2-thienyl)-2,2Ј-bipyridine[10] (7) and tri-
butyl(thiophen-2-yl)stannane yielded 4-[5-(2,2Ј-bithienyl)]-
2,2Ј-bipyridine[12] (8) in the presence of [Pd(PPh3)4]. The
Stille reagent 4-[5-(tri-n-butylstannyl)-2-thienyl]-2,2Ј-bipyr-
idine (9) was synthesized by lithiation of 7 at –78 °C in dry
THF and quenching with SnBu3Cl. The coupling of 7 and
9 yielded 5,5Ј-bis(2,2Ј-bipyridin-4-yl)-2,2Ј-bithiophene (10).
Like 5, compound 10 was only sparingly soluble in organic
solvents. It was found to be insoluble in DMSO, CHCl3,
acetone and benzene. The only solvent capable of dissolving
idyl-capped oligothiophene ruthenium(II) complexes. In
particular, we focus upon systems with a short bithiophenyl
bridge in order to avoid the situation where the bridging
ligand oxidizes before the metal centres. We have chosen to
focus upon the two attachment positions which potentially
allow optimal mesomeric interaction between the bridging
and chelating atoms of the ligand – the 4- and 6-positions –
and have synthesized a series of ligands and their corre-
sponding RuII complexes to compare the influence of the
position and nature of the thienyl bridge on luminescence
lifetimes and redox properties of [Ru(bpy)2(L)]2+
.
Results and Discussion
1
5 and 10 enough to allow analysis by H NMR was [D4]-
Synthesis
acetic acid.
6-(2-Thienyl)-2,2Ј-bipyridine[7] (1) was synthesized ac-
cording to the Kröhnke methodology,[8] through the Man-
nich base salt N,N-dimethyl-N-[3-(2-thienyl)-3-oxopropyl]-
ammonium chloride which was refluxed with 2-[2-(1-pyrid-
inio)-1-oxoethyl]pyridine iodide (PPI) and ammonium ace-
A Stille coupling between 7 and 2 resulted in the unsym-
metrical bis(bidentate) ligand 5-(2,2Ј-bipyridin-4-yl)-5Ј-
(2,2Ј-bipyridin-6-yl)-2,2Ј-bithiophene[10] (11) (see Scheme
3).
The ruthenium complexes 12–19 and 22 (Scheme 4) were
tate in acetic acid (see Scheme 1). After column chromatog- synthesized by combining the appropriate ligand with
Scheme 1. Synthesis of ligands based on the 6-(2-thienyl)-2,2Ј-bipyridine motif.
Eur. J. Inorg. Chem. 2008, 1784–1794
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S. J. Dunne et al.
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Scheme 4. The majority of the complexes were synthesized by heat-
ing the corresponding ligands with cis-[Ru(bpy)2Cl2] in ethylene
glycol.
Scheme 2. Synthesis of ligands based on the 4-(2-thienyl)-2,2Ј-bi-
pyridine motif.
Keene et al.[13a] have reported differences in the photo-
physical and electrochemical properties of the dia-
stereomers of several strongly coupled dimetallic complexes
incorporating rigid bis(bidentate) ligands. It is well known
that [Ru(bpy)3]2+ exists as two diastereomers;[1b] however,
for the complexes presented in this study the presence of
diastereomeric forms of the complexes could not be evi-
denced by either 1H NMR spectroscopy or chromatog-
raphy, and as a result no separation according to the meth-
ods developed by Keene et al.[13b] was attempted.
The monometallic bis(bidentate) complexes 20 and 21
were obtained by Stille cross-coupling between a bromi-
nated (thienyl-2,2Ј-bipyridine)ruthenium complex and Stille
reagents 2 or 9.[10] The reagents were refluxed in dry aceto-
Scheme 3. Synthesis of the asymmetric ligand 11.
1 equiv. of cis-[Ru(bpy)2Cl2] (2 equiv. in the case of 18, 19 nitrile with [Pd(PPh3)4] as catalyst until TLC showed that
and 22) in ethylene glycol and heating under nitrogen to the reaction was complete. Precipitation and purification by
120 °C for 2–6 h. The complexes were precipitated as hexa- column chromatography yielded 20 (Scheme 5) and 21
fluorophosphate salts and purified by repeated precipitation (Scheme 6). No evidence of ligand scrambling or dimetallic
from CH3CN/Et2O.
complex formation was noted in either case.
Scheme 5. Stille cross-coupling on the complex, synthesis of bis(bidentate) monometallic complex 20.
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Photophysics and Electrochemistry of Ruthenium(II) Complexes
Scheme 6. Stille cross-coupling on the complex, synthesis of bis(bidentate) monometallic complex 21.
Electrochemistry
The redox potentials of the Ru complexes determined by
cyclic voltammetry in CH3CN (mV vs. Fc+/0 with 0.1 
Et4NClO4 as supporting electrolyte) are listed in Table 1.
The voltammograms are collected in Figure S1 (Supporting
Information), all measured at a sweep rate of 200 mVs–1.
Three examples are shown in Figure 1. It is well known that
(polypyridine)ruthenium(II) complexes exhibit rich and
complex electrochemistry in non-aqueous solutions com-
prising both metal-centred oxidation (RuIII/II) and bpy-
centred reduction reactions.[1,14,15] The RuIII/II couples are
all totally reversible and appear in a very narrow range
(Table 1), which shows that the inductive effects from the
various substituents on the unique bpy ligand are very sim-
ilar across this series and that the position at which substi-
tution on the bpy ligand occurs (4- or 6-position) does not
affect the metal’s redox potential. Indeed, the RuIII/II poten-
tials are not markedly different from that of [Ru(bpy)3]2+
Figure 1. Cyclic voltammograms (ν = 200 mVs–1) of compounds
measured here under the same conditions (Table 1, but not
shown in Figure S1).
As the anodic sweep is continued to higher potentials, a
second oxidation process is seen in most (but not all) vol-
tammograms. It is immediately apparent that the complexes
12, 13 and 14. Concentration of each compound was 1 m in
CH3CN, and the working electrode was glassy carbon (3 mm). The
arrow indicates the sweep direction. Peaks due to an impurity in
the solvent are marked with an asterisk.
giving rise to these additional high-potential responses enyl-based responses indicate that a single electron oxi-
(which vary considerably in their reversibility) all possess a dation of the bithienyl group is taking place (see voltammo-
bithienyl moiety attached to one bpy ligand, whereas those gram of 14 in Figure 1). Such oxidations have been pre-
that do not show this wave bear a single (uncoupled) thio- viously noted in related ter-, tetra- and sexithiophene-
phene ring. The relative wave heights of the Ru- and bithi- bridged bis(bipyridine) systems.[6,12] The only exception to
Table 1. Redox potentials [mV vs. Fc+/0]. Experimental conditions: 1 m complex in CH3CN with 0.1  Et4NClO4 as supporting electro-
lyte, T = 298 K, glassy carbon (3 mm) working electrode, Pt auxiliary electrode and Ag/Ag+ (CH3CN) reference electrode, ν = 200 mVs–1.
Complex[a]
No.
Bithienyl+/0
[Ru(bpy)2(L)]3+/2+
[Ru(bpy)2(L)]2+/+
[Ru(bpy)2(L)]+/0
[Ru(bpy)2(L)]0/–
[Ru(bpy)3]2+[b]
[Ru(bpy)2(1)]2+
[Ru(bpy)2(4)]2+
[Ru(bpy)2(3)]2+
+874
+869
+894
+900
+878
+867
+850
+865
+891
+854
+874
+839
–1728
–1706
–1700
–1687
–1684
–1670
–1694
–1687
–1788
–1679
–1636
–1608
–1912
–1915
–1815
–1903
–2162
–2227
–2224
–2211
12
13
14
+1120
+1290
[{Ru(bpy)2}2(5)]4+[c] 18
[{Ru(bpy)2}2(11)]4+[c] 19
[Ru(bpy)2(6)]2+
[Ru(bpy)2(7)]2+
[Ru(bpy)2(8)]2+
[Ru(bpy)2(11)]2+
[Ru(bpy)2(10)]2+
15
16
17
20
21
–1896
–1892
–2016
–1884
–1847
–1854 (irr.)
–2139
–2135
–2234
–2128
–2000
+1086 (irr.)
+1094
+1193
[{Ru(bpy)2}2(10)]4+[c] 22
+1260
–
[a] As PF6 salt. [b] [Ru(bpy)3]2+ data collected during this study. [c] The concentration of the dinuclear complexes were half those used
for the mononuclear complexes. The overall concentrations of Ru are the same (1 m) across the series.
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this is compound 18. Seemingly, the redox potential of the Table 2. Luminescence maxima and lifetimes for the RuII com-
plexes 12–22.
bithiophenyl group in this dinuclear complex is higher than
Complex[a]
[Ru(bpy)3]2+[b]
No. Luminescence peak [nm] τ [ns][c]
the positive limit governed by the electrolyte solution. In
the absence of any differences in substituents, the reason for
this may be an enforced nonplanarity of the bithiophenyl
610
1745
unit itself in 18 which makes oxidation more difficult in the [Ru(bpy)2(1)]2+
12
628, 731[d]
–
–
–
–
[Ru(bpy)2(4)]2+
13
378[d]
–
absence of extended conjugation (such as the monothio-
[Ru(bpy)2(3)]2+
phene analogues 12–17). The other two isomeric dinuclear
[{Ru(bpy)2}2(5)]4+
14
18
–
–
complexes (19 and 22) show the high-potential bithienyl
oxidation wave clearly (Figure S1).
[{Ru(bpy)2}2(11)]4+ 19
–
[Ru(bpy)2(6)]2+
[Ru(bpy)2(7)]2+
[Ru(bpy)2(8)]2+
[Ru(bpy)2(11)]2+
[Ru(bpy)2(10)]2+
15
16
17
20
21
627
634
642
633
620
624
3000
3800
4300
1920
2260
2910
The ability to reversibly oxidize a bridging ligand may
offer unique properties to a molecular switching device;
however, the irreversible nature of the oxidation in un-
capped oligothiophenes (most likely due to electrochemical
dimerization) sets a limitation to the incorporation of such
motifs within a molecular electronic device.
Upon sweeping to low potential, most complexes un-
dergo two or three consecutive ligand-centered reductions
in a manner similar to that of [Ru(bpy)3]2+ itself.[14,15] In
some cases the reductions were complicated by coupled
chemical reactions which obscured all of the bpy-centred
[{Ru(bpy)2}2(10)]4+ 22
[a] As PF6– salt. [b] [Ru(bpy)3]2+ data collected during this study. [c]
Luminescence lifetimes at 610 nm, under continuous argon purge,
17.5 °C. [d] The blue luminescence at 378 nm and the near-IR lumi-
nescence at 731 nm were too weak to be quantified (lifetimes
Ͻ30 ns).
The luminescence measurements fell into two groups de-
reductions. Reductive debromination is a particular feature pending upon the attachment point of the oligothiophene
apparent from the enhanced size of the first low-potential to the chelating bipyridine unit. If the ligand coordinated
cathodic peaks in the voltammograms of compounds 13 to the luminescent RuII center possessed a thiophene sub-
and 16 (but no other ones). The dinuclear complexes 18, 19 stituent in the 6-position of the 2,2Ј-bipyridine, lumines-
and 22 all show a pronounced spike on the return anodic cence was weak and the lifetimes too short to be measured
sweep which is characteristic of desorption of the reduced accurately (Ͻ30 ns). This may be due to a disruption in
complexes upon reoxidation. None of the mononuclear the symmetry within the coordination sphere around the
complexes show this feature and evidently are less inclined ruthenium centre, arising from steric interactions between
to adsorb on the electrode due to their smaller size and this pendant thiophenyl substituent and an adjacent bipyr-
greater solubility.
idine auxiliary ligand.[5] This lowering of symmetry can be
Both Ru-based oxidations in the dinuclear complexes clearly seen in a comparison of the COSY spectra of
(18, 19, 22) occurred at the same potential, or at least could [{Ru(bpy)2}2(5)]4+ (18) and [{Ru(bpy)2}2(10)]4+ (22) (see
not be resolved into separate couples here. This suggests Figures 2 and 3) where the lack of interligand interaction
that the metal atoms undergo redox reactions independent
of one another within the complex, which are in accord
with results from Pappenfus and Mann,[6] and no strong
metal–metal coupling exists. Keene et al.[13a] reported a
high degree of metal–metal interaction in RuII complexes
of dipyrido[2,3-a;2Ј,3Ј-h]phenazine, which indicates that
metal–metal coupling requires bridging ligands with a strict
coplanarity and orbital overlap between the d-π orbitals of
the ruthenium atom with the completely delocalized orbit-
als of the bis(bidentate) ligands.
Luminescence Properties
Of the eleven compounds examined the red [Ru-
(bpy)3]2+-type MLCT luminescence was quenched in four
cases; [Ru(bpy)2(3)]2+ (14), [Ru(bpy)2(4)]2+ (13), [{Ru-
(bpy)2}2(5)]4+ (18) and [{Ru(bpy)2}2(11)]4+ (19) and present
(in various intensities) in the remaining seven [Ru(bpy)2-
(1)]2+(12), [Ru(bpy)2(6)]2+ (15), [Ru(bpy)2(7)]2+ (16),
[Ru(bpy)2(8)]2+ (17), [Ru(bpy)2(10)]2+ (21), [Ru(bpy)2(11)]2+
(20) and [{Ru(bpy)2}2(10)]4+ (22). One compound, 12, also
displayed a weak near-IR luminescence at 731 nm, whilst
Figure 2. COSY spectrum of [{Ru(bpy)2}25]4+ (18) recorded in
CD3CN at 298 K.
its brominated derivative 13 displayed a weak blue lumines-
cence at 378 nm (see Table 2).
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Photophysics and Electrochemistry of Ruthenium(II) Complexes
in 22 is reflected in the near-degeneracy of all equivalent
The extension of conjugation within the 4-(2-thienyl)-
bipyridine shifts. When substituted in the 4-position with 2,2Ј-bipyridine system leads to longer luminescence life-
an oligothiophene substituent, however, red luminescence times, as seen in the series 15 to 16 to 17. The emission of
was observed with lifetimes longer than that of [Ru- [Ru(bpy)2(8)]2+ (17) was broader than that of the others (see
(bpy)3]2+ (see Table 2).[16] All of the excitation spectra were Figure 4) with a shoulder appearing at ca. 670 nm. The lu-
very similar, showing only small shifts from the spectra ob- minescence lifetimes were all characterized by a single ex-
served for [Ru(bpy)3]2+ (see Table 2), thereby indicating that ponential decay and had similar values (see Table 2), al-
3
the emissions arise from similar MLCT transitions. There though the value for 17 was somewhat larger. The emission
is no significant change in the emission band maxima with intensity decreases along the series 15, 16, 17 (Figure 4) to-
increasing nuclearity, which has been observed by Con- gether with smaller shifts to longer wavelengths and longer
stable et al. in a series of related 4-thiophen-2-yl-2,2Ј:6Ј,2ЈЈ- lifetimes (Table 2). The bis(bidentate) systems (20–22) bear-
terpyridine complexes with RuII and OsII.[17]
ing this motif do not extend this trend and demonstrate
lifetimes more typical of that of the monometallic proto-
type 15. It is interesting to note that the presence of the
second metal centre in 22 does not result in quenching as it
did in 18 and 19.
Conclusions
There are clear indications that the points of attachment
and the resulting steric interactions have significant effects
upon the photophysics and small effect on the electrochem-
istry of the (bipyridine)ruthenium(II) complexes assembled
using these 6-(2-thienyl)-2,2Ј-bipyridine and 4-(2-thienyl)-
2,2Ј-bipyridine motifs. In the former, a weak blue and a
near-IR luminescence are observed in some cases and with
the parent system even a short-lived red luminescence.
Those systems incorporating the 4-(2-thienyl)-2,2Ј-bipyr-
idine motif all displayed red luminescence with lifetimes
somewhat longer than that of the reference compound
[Ru(bpy)3]2+, except in the case of [{Ru(bpy)2}2(11)]4+ (19)
where all luminescence was quenched. The luminescence in-
tensities in these cases are comparable to that shown by
Figure 3. COSY spectrum of [{Ru(bpy)2}210]4+ (22) recorded in [Ru(bpy)3]2+ and also has the same extreme sensitivity to
CD3CN at 298 K.
dissolved O2, indicating that it shares similar triplet-state
characteristics of the excited state. These results strongly
suggest that the position of attachment has important con-
sequences as to the establishment of a long-lived excited
state, which can facilitate directed electron or energy trans-
fer through the bridging ligand. The non-existent or very
weak metal–metal interaction in the dinuclear complexes
has led us to investigate a range of pyridylthienopyridine
ligands in which the first member of the oligothiophene
chain is fused to either the b- or c-face of one of the pyr-
idine rings of the bipyridine unit,[18] thereby ensuring a
completely planar interface between the chelating and the
conducting elements.
Experimental Section
General: All moisture- and air-sensitive reactions were performed
in oven-dried (120 °C, 12 h) glassware under nitrogen. Analytical
TLC was performed on commercially prepared plates coated with
0.20 mm of Macherey–Nagel silica gel 60. The compounds were
visualized by illumination with UV light (254 nm). Column
chromatography was performed using Matrex Normal Phase Sil-
ica 60 (particle size 35–70 µm). All melting points were determined
with an Electrothermal 9200 melting point apparatus and are un-
Figure 4. Luminescence (εex = 450 nm) and excitation (λfl
=
610 nm) spectra of 15, 16, 17 and 20 in 1ϫ10–5  CH3CN solu-
tions.
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corrected. Infrared spectra (IR) were measured with a Perkin–El-
mer Spectrum One spectrophotometer. Mass spectra (MS) were ob-
tained with a Fisions Instrument Trio 1000 spectrometer equipped
with a Hewlett Packard 5MS GC column. NMR spectra were re-
corded with a Bruker DPX Avance 300 MHz spectrometer, and
the chemical shifts are expressed in ppm from tetramethylsilane as
internal standard. Abbreviations for signal coupling are as follows:
s, singlet; d, doublet; t, triplet; q, quartet; dd, doublet of doublets;
ddd, doublet of doublets of doublets; dt, doublet of triplets; m,
multiplet; dm, doublet of multiplets; br., broad; br. m, broad mul-
tiplet. All commercially available chemicals were used as received
unless otherwise noted. THF was distilled from sodium/benzophe-
trated to yield a yellow oil. Column chromatography (silica; hex-
ane/EtOAc, 4:1) yielded 2 as a pale yellow oil Yield: 0.96 g (87%).
1H NMR (CDCl3, 300 MHz): δ = 8.68 (dm, 1 H), 8.61 (d, J =
7.8 Hz, 1 H), 8.26 (d, J = 7.8 Hz, 1 H), 7.86 (td, J = 2.0, 7.8 Hz, 1
H), 7.80 (t, J = 7.8 Hz, 1 H), 7.66 (d, J = 7.8 Hz, 1 H), 7.77 (d, J
= 3.4 Hz, 1 H), 7.29–7.34 (m, 1 H), 7.20 (d, J = 3.4 Hz, 1 H), 1.55–
1.68 (m, 6 H), 1.30–1.44 (m, 6 H), 1.16 (dd, J = 7.8, 8.3 Hz, 6 H),
0.92 (t, J = 7.3 Hz, 9 H) ppm. FT-IR (KBr): ν = 3053 (w), 2955
˜
(s), 2926 (s), 2870 (s), 2852 (s), 1579 (s), 1564 (s), 1525 (m), 1455
(s), 1429 (s), 1376 (w), 1340 (w), 1321 (w), 1285 (w), 1262 (w), 1207
(w), 1155 (w), 1092 (w), 1081 (w), 1045 (w), 998 (w), 936 (m), 875
(w), 801 (m), 778 (s), 745 (m), 691 (m), 434 (s, br) cm–1. UV
none immediately prior to use. Steady-state luminescence spectra (CH3CN): λmax (logε) = 240.6 (4.23), 283.0 (4.26), 308.5 (4.33),
were acquired with an ISS PC1 fluorimeter in photon-counting
mode. Lifetimes were measured using the 337 nm excitation of an
N2 laser at 2 Hz. After a long-pass filter and Jobin Yvon H-20
monochromator centred at 610 nm, the luminescence was detected
by an S-20 photomultiplier tube. The signal was amplified by two
stages of a Stanford 445 preampliflier and collected with a Tek-
tronix TDS4010 digital storage oscilloscope. The solutions were
purged with argon for 20 min before and during the lifetime mea-
surements. The red-emitting compounds show a strong sensitivity
to dissolved oxygen. All luminescence measurements were per-
formed in 10–5 mol–1 L–1 acetonitrile solutions at 17.5 °C. Cyclic
voltammetry was performed with a BAS100B/W electrochemical
workstation employing a glassy-carbon (3 mm) working electrode,
an Ag/Ag+ (CH3CN) non-aqueous reference electrode and a Pt-
wire counter electrode. All solutions contained ca. 1 m complex
in CH3CN, and the supporting electrolyte was Et4NClO4. The elec-
trochemical cell was purged with nitrogen before measurement and
maintained anaerobic during measurement with a blanket of nitro-
gen. All potentials are cited relative to the ferrocene/ferrocenium
redox couple [measured here as +87 mV vs. Ag/Ag+(CH3CN)].
318.8 (4.31 dm3 mL–1 cm–1) nm.
6-[5-(2,2Ј-Bithienyl)]-2,2Ј-bipyridine (3): Compound
2 (0.211 g,
0.40 mmol), 2-bromothiophene (0.065 g, 0.40 mmol) and [Pd(PPh3)4]
(0.023 g, 0.020 mmol) were dissolved in dry toluene (15 mL) and
heated to reflux under argon for 16 h. The mixture was cooled,
filtered and the filtrand washed with CH2Cl2 (3ϫ20 mL). The
combined filtrate and washings were concentrated under a reduced
pressure to yield a yellow solid. Column chromatography (silica;
hexane/EtOAc, 1:1) gave the product as a pale yellow microcrystal-
line solid. Yield: 0.117 g (91%). M.p. 123–125 °C. 1H NMR
(CDCl3, 300 MHz): δ = 8.68 (dm, 1 H), 8.58 (dd, J = 1.0, 7.8 Hz,
1 H), 8.28 (d, J = 7.8 Hz, 1 H), 7.86 (td, J = 2.0, 7.8 Hz, 1 H), 7.81
(t, J = 7.8 Hz, 1 H), 7.64 (d, J = 7.8 Hz, 1 H), 7.53 (d, J = 3.9 Hz,
1 H), 7.29–7.34 (m, 1 H), 7.29 (dd, J = 1.0, 3.9 Hz, 1 H), 7.25 (dd,
J = 1.0, 4.9 Hz, 1 H), 7.20 (d, J = 3.9 Hz, 1 H), 7.13–7.17 (m, 1
H) ppm. FT-IR (KBr): ν = 3060 (w), 3048 (w), 3007 (w), 1579 (m),
˜
1562 (s), 1516 (w), 1468 (m), 1448 (w), 1425 (s), 1327 (w), 1289 (w),
1272 (w), 1261 (w), 1226 (w), 1203 (w), 1152 (m), 1093 (m), 1080
(m), 1045 (m), 993 (m), 840 (m), 805 (m), 777 (s), 744 (w), 682 (m),
633 (w), 486 (w) cm–1. UV (CH3CN): λmax (logε) = 236.5 (4.31),
250.7 sh (4.19), 264.9 sh (4.09), 282.5 sh (4.00), 291.6 sh (3.96),
357.3 (4.49), 373.9 sh (4.36 dm3 mL–1 cm–1) nm. C18H12N2S2
(320.43): calcd. C 67.47, H 3.77, N 8.74; found C 67.52, H 3.83, N
8.68.
Ligands 1–11
6-(2-Thienyl)-2,2Ј-bipyridine (1): This compound was prepared ac-
cording to the method of Constable, Henney and Leese.[7] Yield:
1
65%. M.p. 78 °C (ref.[7] 78 °C). H NMR (CDCl3, 300 MHz): δ =
8.68 (dm, 1 H), 8.58 (d, J = 7.8 Hz, 1 H), 8.29 (dd, J = 1.0, 7.8 Hz,
1 H), 7.85 (td, J = 2.0, 7.8 Hz, 1 H), 7.81 (t, J = 7.8 Hz, 1 H), 7.66
(dd, J = 1.0, 7.8 Hz, 1 H), 7.65 (dd, J = 1.0, 3.4 Hz, 1 H), 7.42 (dd,
J = 1.0, 4.9 Hz, 1 H), 7.29–7.34 (m, 1 H), 7.13 (dd, J = 3.4, 4.9 Hz,
6-(5-Bromo-2-thienyl)-2,2Ј-bipyridine (4): Compound
1 (1.70 g,
7.1 mmol) and sodium hydrogen carbonate (1.00 g, 25.6 mmol)
were dissolved in chloroform (20 mL). A solution of bromine
(0.4 , 20 mL) in chloroform was added dropwise over 1 h, re-
sulting in the formation of a pale yellow precipitate. The mixture
was refluxed for 16 h, then cooled before pouring into water
(100 mL). The aqueous layer was extracted with CH2Cl2
(2ϫ50 mL), the organic extracts were combined and subsequently
washed with a saturated NaHCO3 solution (2ϫ50 mL) and water
(50 mL). After drying with MgSO4, the solvent was removed in
vacuo to yield a yellow-green oil from which crystallised colourless
prisms. Recrystallization from hexane and activated carbon gave
the product as pale yellow crystals. Yield: 1.41 g (63%). Mp. 116.5–
1 H) ppm. FT-IR (KBr): ν = 3051 (w), 1578 (m), 1561 (s), 1530
˜
(m), 1475 (m), 1454 (s), 1425 (s), 1349 (w), 1311 (w), 1290 (w), 1268
(w), 1227 (w), 1152 (m), 1091 (w), 1079 (m), 1045 (w), 996 (m), 967
(w), 905 (w), 852 (m), 825 (w), 778 (s), 746 (w), 737 (w), 717 (s),
689 (m), 652 (w), 625 (m), 569 (w), 508 (w) cm–1. UV (CH3CN):
λmax (logε) = 239.8 (4.28), 279.6 (4.28), 298.4 sh (4.21), 316.0
(4.17 dm3 mL–1 cm–1) nm.
6-[5-(Tri-n-butylstannyl)-2-thienyl]-2,2Ј-bipyridine (2):[10] Com-
pound 1 (0.500 g, 2.1 mmol) was dissolved in dry THF (40 mL)
under nitrogen, then cooled to –78 °C with a dry ice/acetone bath.
n-Butyllithium (1.6  solution in hexanes, 1.60 mL, 2.52 mmol) was
added dropwise, resulting in the formation of a deep purple-brown
colouration. The mixture was stirred at this temperature for 30 min
before SnBu3Cl (96%, 0.85 mL, 3.15 mmol) was added over a
2 min period. After several minutes, the solution turned distinctly
blue, and stirring was continued at this temperature for 30 min be-
fore warming to –10 °C at which point water (5 mL) was added to
quench the reaction. After stirring in air for 5 min, the solution
turned from blue to clear yellow. The THF was removed under
reduced pressure and the product extracted into CH2Cl2
(3ϫ50 mL). The extracts were dried with Na2SO4 and concen-
1
117.0 °C. H NMR (CDCl3, 300 MHz): δ = 8.67 (dm, 1 H), 8.51
(d, J = 7.8 Hz, 1 H), 8.29 (d, J = 7.8 Hz, 1 H), 7.83 (td, J = 2.0,
7.8 Hz, 1 H), 7.79 (t, J = 7.8 Hz, 1 H), 7.55 (dd, J = 1.0, 7.8 Hz, 1
H), 7.33 (d, J = 3.9 Hz, 1 H), 7.26–7.32 (m, 1 H), 7.06 (d, J =
3.9 Hz, 1 H) ppm. FT-IR (KBr): ν = 3055 (w), 1577 (m), 1558 (s),
˜
1473 (m), 1457 (m), 1427 (s), 1325 (w), 1287 (w), 1267 (w), 1212
(w), 1156 (w), 1139 (w), 1088 (w), 1077 (m), 1045 (w), 1000 (m),
958 (w), 880 (w), 796 (m), 772 (s), 741 (w), 690 (w), 643 (w), 629
(w), 617 (w), 496 (w) cm–1. UV (CH3CN): λmax (logε) = 240.4
(4.25), 282.1 (4.30), 305.2 (4.31), 320.5 (4.32 dm3 mL–1 cm–1) nm.
C14H9BrN2S (317.20): calcd. C 53.01, H 2.86, N 8.83; found C
52.70, H 2.88, N 8.79.
1790
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 1784–1794

Photophysics and Electrochemistry of Ruthenium(II) Complexes
5,5Ј-Bis(2,2Ј-bipyridin-6-yl)-2,2Ј-bithiophene (5): Compound
2
3048 (w), 2999 (w), 1598 (s), 1580 (s), 1563 (s), 1547 (s), 1522 (m),
1457 (s), 1424 (m), 1395 (s), 1357 (w), 1345 (w), 1286 (w), 1270 (w),
1256 (w), 1233 (w), 1196 (w), 1151 (w), 1094 (w), 1054 (w), 1054
(w), 990 (m), 910 (w), 891 (w), 855 (w), 823 (w), 795 (s), 741 (w),
700 (s), 659 (w), 637 (w), 617 (w) cm–1. UV (CH3CN): λmax (logε)
= 243.3 sh (4.20), 256.9 (4.32), 283.9 (4.43), 304.6 sh (4.25), 320.0
sh (3.85 dm3 mL–1 cm–1) nm. C14H10N2S (238.31): calcd. C 70.56,
H 4.23, N 11.75; found C 70.62, H 4.10, N 11.66.
(0.320 g, 0.61 mmol), 4 (0.159 g, 0.50 mmol) and [Pd(PPh3)4]
(0.014 g, 0.012 mmol) were dissolved in dry toluene (10 mL) and
heated to reflux under argon for 24 h. After the mixture was co-
oled, the resultant yellow crystalline precipitate was filtered and
the solid washed with toluene (3ϫ20 mL), hexane (3ϫ20 mL) and
diethyl ether (3ϫ20 mL). After drying in vacuo, the product was
obtained as a yellow microcrystalline solid. Yield: 0.164 g (69%).
1
Mp. Ͼ 270 °C. H NMR ([D4]acetic acid, 300 MHz): δ = 9.0 (br.
4-(5-Bromo-2-thienyl)-2,2Ј-bipyridine (7):[10] Compound 6 (1.50 g,
6.3 mmol) was dissolved in CH2Cl2 (30 mL), after which Br2 (2.0 g,
12.6 mmol, 0.64 mL) was added in one portion. The resulting mix-
ture was stirred at room temp. for 10 min. Then Na2CO3 (aq., satd.
50 mL) was added, and the mixture was stirred for a further
30 min. The solution was then transferred to a separating funnel,
and the organic phase was removed. The water phase was then
washed with CH2Cl2 (30 mL). The organic phases were combined
and washed with H2O (2ϫ50 mL) and brine (50 mL) and dried
with MgSO4. The solvent was evaporated under reduced pressure
yielding 7 as a pale brown powder which was Ͻ95% pure according
to NMR spectroscopy. The product was stored in a desiccator over
P2O5 and used in the next step without further purification. Yield:
m, 2 H), 8.68 (d, J = 8.2 Hz, 2 H), 8.31 (dm, 2 H), 8.23 (d, J =
7.4 Hz, 2 H), 7.9–8.8 (m, 4 H), 7.84 (br. m, 2 H), 7.8 (d, J = 3.4 Hz,
2 H), 7.45 (d, J = 3.7 Hz, 2 H) ppm. FT-IR (KBr): ν = 2922 (w),
˜
1578 (m), 1561 (s), 1457 (m), 1441 (w), 1427 (s), 1266 (w), 1161
(w), 1094 (w), 1083 (w), 998 (w), 803 (m), 774 (s), 743 (w), 689 (w),
635 (w), 507 (w) cm–1. MS (EI): m/z (calcd. value; intensity) = 474
(474.60; base peak) [M+], 237 (237.30; 16.54%) [C14H10N2S+].
C28H18N4S2 (474.60): calcd. C 68.43, H 3.76, N 11.30; found C
68.75, H 3.98, N 11.29.
3-(2-Thienyl)propenal: NaOH (4.48 g, 106 mmol) was dissolved in a
mixture of ethanol (24 mL) and water (46 mL) in a 500 mL round-
bottomed flask. The mixture was cooled to 0 °C in a well-isolated
ice bath. Thiophene-2-carbaldehyde (17.9 g, 160 mmol) was then
added dropwise through an addition funnel over 1 h. Ethanal
(25.4 g, 728 mmol, dissolved in 250 mL of water) was then added
dropwise during ca. 4.5 h through an addition funnel. The ice was
continuously replenished to keep the temperature at 0 °C. The reac-
tion was then quenched by addition of acetic acid (10%, 100 mL),
and the pH was adjusted to 4.5. The yellow solution was extracted
with benzene (2ϫ100 mL). The organic phases were combined and
washed with NaHCO3 (aq., satd. 2ϫ100 mL), H2O (2ϫ100 mL)
and brine (100 mL) and then dried with MgSO4. The solvent was
carefully evaporated under reduced pressure yielding a yellow oil
which was purified by column chromatography (silica; toluene/
EtOAc, 95:5). The oil was stored in a freezer until use. Yield: 13.5 g
(61%). 1H NMR (CDCl3, 300 MHz): δ = 9.65 (d, J = 7.7 Hz, 1 H),
7.60 (d, J = 15.6 Hz, 1 H), 7.51 (d, J = 5.1 Hz, 1 H), 7.38 (d, J =
3.1 Hz, 1 H), 7.12 (dd, J = 5.1, 3.7 Hz, 1 H), 6.51 (dd, J = 15.6,
7.7 Hz, 1 H) ppm. 13C NMR (CDCl3, 75 MHz): δ = 193.0, 144.6,
1
1.82 g (91%). M.p. 140–143 °C. H NMR (CDCl3, 300 MHz): δ =
8.73 (dm, 1 H), 8.67 (d, J = 5.2 Hz, 1 H), 8.6 (d, J = 1.5 Hz, 1 H),
8.48 (d, J = 8.0 Hz, 1 H), 7.88 (dt, J = 7.7, 1.7 Hz, 1 H), 7.48–7.33
(m, 3 H), 7.11 (d, J = 3.9 Hz) ppm. UV (CH3CN): λmax (logε) =
241.0 (4.19), 258.0 sh (4.22), 286.4 sh (4.41), 291.5 (4.41), 304.6 sh
(4.38), 322.8 sh (4.14 dm3 mL–1 cm–1) nm.
4-[5-(2,2Ј-Bithienyl)]-2,2Ј-bipyridine (8):[12] Compound 7 (0.95 g,
3.0 mmol) and 2-(tributylstannyl)thiophene (97%, 1.05 mL,
3.3 mmol) was then added to dry toluene (25 mL). Then [Pd-
(PPh3)4] (5 mol-%, 0.17 g) was added. The resulting mixture was
heated to 110 °C with stirring under nitrogen. After 8 h, TLC
(EtOAc/hexane, 1:1) showed that 7 had been consumed. The solu-
tion was cooled to room temperature, and most of the solvent was
evaporated. The residue was taken up in diethyl ether (100 mL) and
transferred to a separatory funnel. The organic phase was washed
with water (2ϫ50 mL) and brine (50 mL). The organic phase was
dried with MgSO4 and concentrated under reduced pressure, yield-
ing a yellow/brown powder. The product was recrystallized from
EtOH/H2O yielding 8 as small pale yellow needles. Yield: 0.7 g
(73%). M.p. 111–112 °C (ref.[12] 112–113 °C). 1H NMR (CDCl3,
300 MHz): δ = 8.72 (dm, 1 H), 8.65 (d, J = 5.2 Hz, 1 H), 8.61 (d,
J = 1.3 Hz, 1 H), 8.42 (d, J = 8.0 Hz, 1 H), 7.4 (dt, J = 7.8, 1.8 Hz,
1 H), 7.56 (d, J = 3.8 Hz, 1 H), 7.47 (dd, J = 5.2, 1.8 Hz, 1 H),
7.34 (ddd, J = 7.5, 4.8, 1.1 Hz, 1 H), 7.3–7.23 (m, 2 H), 7.2 (d, J
= 3.8 Hz, 1 H), 7.05 (dm, J = 5.0, 3.7 Hz, 1 H) ppm. 13C NMR
(CDCl3, 75 MHz): δ = 157.0, 156.0, 149.9, 149.4, 142.2, 140.0,
139.4, 137.2, 137.1, 128.2, 126.6, 125.4, 125.0, 124.6, 124.1, 121.5,
119.6, 117.0 ppm. C18H12N2S2 (320.43): calcd. C 67.47, H 3.77, N
8.74; found C 67.31, H 3.69, N 8.65.
139.3, 132.3, 130.5, 128.6, 127.3 ppm. IR (neat): ν = 2424.8 (w),
˜
1665.1 (s), 1608.5 (s), 1421.0 (m), 1225.8 (w), 1113.3 (m), 1044.2
(w), 958.5 (m), 856.4 (m), 702.6 (s ) cm–1. MS (EI): m/z = 138 [M+].
4-(2-Thienyl)-2,2Ј-bipyridine (6):[10] 3-(2-Thienyl)propenal (5.86 g,
42 mmol), 2-[2-(1-pyridinio)-1-oxoethyl]pyridine iodide (16.6 g,
50.4 mmol) and NH4OAc (16.2 g, 210 mmol) were added to acetic
acid (250 mL) The mixture was heated to 80 °C which caused the
colour to change from pale red to dark red, almost black. The
reaction was continued with stirring at 80 °C for 48 h. The reaction
mixture was then made alkaline by addition of NaOH (aq. 10 ,
ca. 450 mL), resulting in the formation of a black precipitate. The
precipitate was recovered by suction filtration. The red/black fil-
trate was extracted with CH2Cl2 (3ϫ250 mL). The organic phases
were combined and concentrated under reduced pressure, yielding
a brown powder. The black precipitate and the brown powder were
combined in a thimble and subjected to Soxhlet extraction with
petroleum ether (boiling range 40–60 °C) for 72 h. The organic
phase was filtered to remove dark insolubles and then concentrated
under reduced pressure, yielding 6 as a yellow powder. Recrystalli-
zation from methanol yielded large pale yellow prisms. Yield: 1.05 g
(44%). M.p. 106–107.5 °C. 1H NMR (CDCl3, 300 MHz): δ = 8.70–
8.73 (dm, 1 H), 8.63 (m, 2 H), 8.40 (dm, 1 H), 7.82 (td, J = 2.0,
7.8 Hz, 1 H), 7.63 (dd, J = 1.0, 3.9 Hz, 1 H), 7.49 (dd, J = 2.0,
4-[5-(Tri-n-butylstannyl)-2-thienyl]-2,2Ј-bipyridine (9): Compound 7
(1.0 g, 3.2 mmol) was dissolved in dry THF, and the resulting solu-
tion was cooled to –78 °C in a dry ice/acetone bath. Then nBuLi
(1.6  in hexanes, 2.2 mL, 3.5 mmol) was added dropwise during
15 min, taking care that the temperature did not exceed –70 °C.
When the addition was completed, the mixture was stirred at
–78 °C for 30 min after which SnBu3Cl (96%, 0.9 mL, 3.3 mmol)
was added in one portion. The reaction mixture was then allowed
to reach room temp. overnight. The reaction was quenched by ad-
dition of H2O (25 mL). Most of the solvents were removed under
5.4 Hz, 1 H), 7.42 (dd, J = 1.0, 4.9 Hz, 1 H), 7.30–7.35 (m, 1 H), reduced pressure, the residue was taken up in diethyl ether
7.14 (dd, J = 3.9, 4.9 Hz, 1 H) ppm. FT-IR (KBr): ν = 3074 (w), (100 mL) and washed with KF (aq., 2 , 100 mL), H2O
˜
Eur. J. Inorg. Chem. 2008, 1784–1794
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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1791

S. J. Dunne et al.
FULL PAPER
(2ϫ50 mL) and brine (50 mL). The organic phase was dried with
MgSO4 and concentrated under reduced pressure, yielding 9 as a
dark green oil which was subsequently purified by column
chromatography (silica; EtOAc/hexane, 1:1). After evaporation, 9
(ca. 90% pure according to NMR spectroscopy) was recovered as
a yellow oil. It was used in the next step without further purifica-
was cooled to –20 °C overnight and the product collected by fil-
tration. Yield: 0.201 g (75%). 1H NMR (CD3CN, 300 MHz): δ =
8.59 (m, 2 H), 8.48 (d, 1 H), 8.42 (d, 1 H), 8.40 (d, 1 H), 8.31 (dm,
1 H), 8.11 (td, 1 H), 8.10 (d, 1 H), 8.09 (m, 2 H), 8.08 (td, 1 H),
7.94 (td, 1 H), 7.70 (dm, 1 H), 7.65 (td, 1 H), 7.56 (dm, 1 H), 7.52
(m, 1 H), 7.48 (d, 1 H), 7.39 (dm, 1 H), 7.38 (m, 1 H), 7.33 (m, 1
H), 7.21 (m, 1 H), 7.11 (dm, 1 H), 7.04 (d, 1 H), 6.89 (m, 1 H),
6.40 (m, 1 H) ppm. The signal of the proton in the 3-position of
the pendant thiophene was not observed at 298 K. FT-IR (KBr):
1
tion. Yield: 0.85 g (50%). H NMR (CDCl3, 300 MHz): δ = 8.73
(dm, 1 H), 8.64 (d, J = 3.2 Hz, 1 H), 8.63 (s, 1 H), 8.42 (d, J =
8.0 Hz, 1 H), 7.84 (dt, J = 7.8, 1.7 Hz, 1 H), 7.76 (d, J = 3.4 Hz, 1
H), 7.53 (dd, J = 5.0, 2.0 Hz, 1 H), 7.33 (ddd, J = 7.5, 4.8, 1.1 Hz,
ν = 1604 (m), 1561 (w), 1465 (m), 1447 (m), 1426 (m), 1385 (w),
˜
1 H), 7.22 (d, J = 3.4 Hz, 1 H), 1.66–1.55 (m, 6 H), 1.42–1.29 (m, 838 (s), 764 (m), 730 (w), 558 (m) cm–1. UV (CH3CN): λmax (logε)
6 H), 1.2–1.12 (m, 6 H), 0.92 (m, 9 H) ppm. 13C NMR (CDCl3, = 245.0 (4.44), 288.3 (4.77), 447.7 (4.04 dm3 mL–1 cm–1) nm. MS
75 MHz): δ = 156.9, 156.3, 149.9, 149.4, 147.1, 142.6, 140.6, 137.1,
136.8, 126.8, 124.0, 121.4, 120.1, 117.4, 29.1, 27.5, 13.9, 11.1 ppm.
MS (EI): m/z = 527 [M+].
(MALDI-TOF): m/z (calcd. value) = 653 (651.7) [M + H – PF6]+.
C34H26F12N6P2RuS (941.68) + 1/3 CH2Cl2: calcd. C 42.51, H 2.77,
N 8.66; found C 42.74, H 2.92, N 8.57.
5,5Ј-Bis(2,2Ј-bipyridin-4-yl)-2,2Ј-bithiophene (10): The stannylated [Ru(bpy)2(4)](PF6)2 (13): Yield: 72%. 1H NMR ([D6]DMSO,
compound 9 (0.20 g, 0.38 mmol) and brominated compound 7
(0.10 g, 0.32 mmol) were added to dry toluene (10 mL). [Pd(PPh3)4]
(5 mol-%, 0.02 g) was then added. The resulting mixture was heated
to 105 °C with stirring under nitrogen. After approximately 1 h, a
pale precipitate started to form. After 10 h, TLC (EtOAc/hexane,
1:1) showed that all 7 had been consumed. The solution was cooled
to room temperature, and the precipitate was recovered by suction
300 MHz): δ = 8.95 (d, J = 6.6 Hz, 2 H), 8.82 (d, J = 8.1 Hz, 2 H),
8.75 (d, J = 8.1 Hz, 2 H), 8.45 (d, J = 8.0 Hz, 1 H), 8.35 (d, J =
5.4 Hz, 1 H), 8.15–8.35 (m, 4 H), 8.05 (dd, J = 7.5, 1.4 Hz, 1 H),
7.59 (dd, 1 H), 7.7 (d, J = 5.4 Hz, 1 H), 7.3–7.64 (m, 7 H), 7.05–
7.2 (m, 2 H), 6.5 (br. s, 1 H) ppm. UV (CH3CN): λmax (logε) =
247 (4.57), 288 (4.83), 443 (4.16 dm3 mL–1 cm–1) nm.
C34H25BrF12N6P2RuS (1020.57): calcd. C 40.01, H 2.47, N 8.18;
filtration. The yellow precipitate was triturated with water found C 39.84, H 2.66, N 7.91.
(3ϫ10 mL), CHCl3 (3ϫ10 mL) and diethyl ether (3ϫ10 mL) and
[Ru(bpy)2(3)](PF6)2 (14): Yield: 95%. 1H NMR (CD3CN,
subsequently dried in a desiccator over P2O5. The product was
found to be insoluble in most organic solvents. Yield: 0.13 g (87%).
300 MHz): δ = 8.61 (d, 1 H), 8.59 (d, 1 H), 8.48 (d, 1 H), 8.41 (d,
1 H, d), 8.38 (d, 1 H), 8.21 (d, 1 H), 8.14 (m, 1 H), 8.09 (m, 3 H),
8.04 (d, 1 H), 7.94 (m, 1 H), 7.72 (d, 1 H), 7.57 (d, 1 H), 7.55 (m,
2 H), 7.53 (m, 1 H), 7.41 (m, 1 H), 7.39 (d, 1 H), 7.33 (m, 2 H),
7.22 (m, 1 H), 7.18 (d, 1 H), 7.07 (m, 1 H), 7.03 (d, 1 H), 6.76 (m,
1 H), 6.46 (m, 1 H) ppm. Analogously to complex 12, the signal of
the thiophene proton adjacent to the bipyridine was not observed
1
M.p. 314 °C (decomp.) H NMR ([D4]acetic acid, 300 MHz): δ =
8.89 (dm, 2 H), 8.84 (d, J = 5.7 Hz, 2 H), 8.57 (d, J = 1.4 Hz, 2
H), 8.41 (d, J = 8.0 Hz, 2 H), 8.16 (dt, J = 7.7, 1.7 Hz, 2 H), 7.92
(d, J = 4.0 Hz, 2 H), 7.87 (dd, J = 5.6, 1.8 Hz, 2 H), 7.68 (dd, J =
5.1, 1.0 Hz, 2 H), 7.53 (d, J = 4.0 Hz, 2 H) ppm. C28H18N4S2
(474.60) + 2 H2O: calcd. C 65.86, H 4.34, N 10.97; found C 66.19,
H 4.04, N 10.67.
at 298 K. FT-IR (KBr): ν = 1638 (m), 1603 (w), 1465 (m), 1467
˜
(m), 1444 (m), 1423 (w), 1401 (w), 1243 (w), 840 (vs), 763 (m), 557
5-(2,2Ј-Bipyridin-4-yl)-5Ј-(2,2Ј-bipyridin-6-yl)-2,2Ј-bithiophene (11): (ms) cm–1. UV (CH3CN): λmax (logε) = 247.0 (4.45), 288.7 (4.79),
This compound was prepared according to the method of Dunne
448.2 (4.04 dm3 mL–1 cm–1) nm. MS (MALDI-TOF): m/z (calcd.
value) = 879 (878.84) [M – PF6]+, 733 (733.88) [M – 2 PF6]+.
and Constable.[10] Yield: 74%. M.p. 263–265 °C. 1H NMR (CDCl3,
300 MHz): δ = 8.75 (dm, 1 H), 8.72–8.63 (m, 3 H), 8.62 (d, J = C38H28F12N6P2RuS2 (1023.8): calcd. C 44.58, H 2.76, N 8.21;
8.0 Hz), 8.4 (d, J = 8.0 Hz, 1 H), 8.32 (d, J = 7.5 Hz, 1 H), 7.9 (dt,
J = 1.7, 7.5 Hz, 1 H), 7.88–7.8 (m, 2 H), 7.69 (d, J = 7.5 Hz, 1 H),
7.62 (d, J = 3.8 Hz, 1 H), 7.58 (d, J = 3.8 Hz, 1 H), 7.51 (dd, J =
1.9, 5.1 Hz, 1 H), 7.4–7.32 (m, 2 H), 7.34 (d, J = 3.7 Hz, 1 H), 7.3
found C 44.70, H 3.00, N 7.93.
[Ru(bpy)2(6)](PF6)2 (15): Yield: 81%. 1H NMR (CD3CN,
300 MHz): δ = 8.68 (d, 1 H), 8.65 (s, 1 H), 8.47–8.53 (d, 4 H), 8.08
(td, 1 H), 8.03–8.10 (td, 4 H), 7.90 (dd, 1 H), 7.76 (dm, 1 H), 7.84
(dm, 4 H), 7.71 (dd, 1 H), 7.64 (d, 1 H), 7.56 (d, 1 H), 7.42 (m, 1
(d, J = 3.7 Hz, 1 H) ppm. FT-IR (KBr): ν = 3060 (w), 3045 (w),
˜
2923 (w), 1594 (m), 1581 (s), 1562 (s), 1543 (m), 1459 (s), 1439 (m),
1427 (s), 1390 (w), 1324 (w), 1262 (w), 1150 (w), 1092 (w), 990 (w),
801 (s), 776 (s), 742 (w), 692 (w), 618 (w) cm–1. C28H18N4S2
(474.60): calcd. C 70.86, H 3.82, N 11.81; found C 70.68, H 4.00,
N 11.63.
H), 7.37–7.45 (m, 4 H), 7.27 (m, 1 H) ppm. FT-IR (KBr): ν = 1636
˜
(w), 1612 (m), 1466 (m), 1445 (m), 1430 (w), 840 (s), 761 (m), 730
(w), 558 (m) cm–1. UV (CH3CN): λmax (logε) = 244.8 (4.40), 252.2
sh (4.38), 287.2 (4.81), 287.2 (4.81), 326.8 (4.33), 432.8 sh (4.11),
457.3 (4.37 dm3 mL–1 cm–1) nm. MS (MALDI-TOF): m/z (calcd.
value) = 796 (796.7) [M – PF6]+, 652 (651.7) [M – 2 PF6]+.
C34H26F12N6P2RuS (941.68) + 1/3 CH2Cl2: calcd. C 42.51, H 2.77,
N 8.66; found C 42.59, H 2.83, N 8.45.
RuII Complexes 12–22
The synthesis of 12 is representative for the synthesis of all the
monometallic RuII complexes.
[Ru(bpy)2(7)](PF6)2 (16): Yield: 75%. Red powder. 1H NMR
(CD3CN, 300 MHz): δ = 8.68 (dm, 1 H), 8.58 (d, J = 1.8 Hz, 1 H),
8.52 (d, J = 8.2 Hz, 4 H), 8.14–8.03 (m, 5 H), 7.83 (d, J = 5.0 Hz,
1 H), 7.8–7.72 (m, 4H), 7.69 (d, J = 4.0 Hz, 1 H), 7.67 (d, J =
6.1 Hz, 1 H), 7.48 (dd, J = 6.1, 2.0 Hz, 1 H), 7.43–7.38 (m, 5 H),
7.33 (d, J = 4.0 Hz, 1 H) ppm. MS (MALDI-TOF): m/z (calcd.
value) = 875 (874.1) [M – PF6]+, 730 (730.1) [M – 2 PF6]+.
C34H25BrF12N6P2RuS (1020.57) + 1 H2O: calcd. C 39.32, H 2.62,
N 8.09; found C 39.58, H 2.51, N 7.89.
[Ru(bpy)2(1)](PF6)2 (12): cis-[Ru(bpy)2Cl2] (0.138 g, 0.286 mmol)
and ligand 1 (0.238 g, 0.290 mmol) were dissolved in 1,2-ethanediol
(8 mL), and the solution was stirred at 120 °C for 2 h. After cooling
to room temperature, NH4PF6 (0.178 g, 1.0 mmol) was added. An
orange-red product was precipitated by the addition of water
(20 mL) and isolated by filtration after cooling at 3 °C overnight.
The precipitate was washed with diethyl ether (3ϫ5 mL) and air-
dried. The crude product was purified by column chromatography
(silica; CH2Cl2/MeOH, 19:1). The orange fraction was collected,
concentrated to dryness, redissolved in the minimum amount of
CH2Cl2 and added dropwise to diethyl ether (50 mL). The slurry
[Ru(bpy)2(8)](PF6)2 (17): Yield: 74%. Orange/red powder. 1H NMR
(CD3CN, 300 MHz): δ = 8.68 (d, J = 8.1 Hz, 1 H), 8.63 (d, J =
1792
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Eur. J. Inorg. Chem. 2008, 1784–1794

Photophysics and Electrochemistry of Ruthenium(II) Complexes
1.75 Hz, 1 H), 8.57–8.48 (m, 4 H), 8.15–8.03 (m, 5 H), 7.86 (d, J
= 4.0 Hz, 2 H), 7.8–7.72 (m, 4 H), 7.65 (d, J = 6.1 Hz, 1 H), 7.54
(dd, J = 6.1, 2.0 Hz, 1 H), 7.49 (dd, J = 5.1, 1.1 Hz, 1 H), 7.47–
7.38 (m, 7 H), 7.15 (dd, J = 5.1, 3.7 Hz, 1 H) ppm. MS (MALDI-
TOF): m/z (calcd. value) = 879 (878.9) [M – PF6]+, 734 (733.1) [M –
2 PF6]+. C38H28F12N6P2RuS2 (1023.8) + 4 H2O: calcd. C 41.65, H
3.31, N 7.67, S 5.85; found C 41.62, H 2.96, N 7.52, S 5.84.
[Ru(bpy)2(11)](PF6)2 (20):[10] Compound 2 (0.075 g, 0.14 mmol), the
brominated complex 16 (0.102 g, 0.10 mmol) and [Pd(PPh3)4]
(0.006 g, 0.005 mmol) were dissolved in dry acetonitrile (15 mL)
and heated to 50 °C under argon for 5 h. The mixture was cooled
and the solvent removed under reduced pressure to yield a red oil.
Column chromatography (silica; MeOH/CH2Cl2, 15:85), concen-
tration of the fractions containing the product and precipitation
from CH2Cl2/CH3CN gave the product as a red microcrystalline
solid Yield: 0.097 g (81%). 1H NMR (CD2Cl2, 300 MHz): δ = 8.65
(dm, 1 H), 8.57 (d, 1 H), 8.54 (d, 1 H), 8.50 (s, 1 H), 8.42–8.47 (d,
4 H), 8.28 (d, 1 H), 8.07 (td, 1 H), 8.03–8.10 (td, 4 H), 7.89 (td, 1
H), 7.87 (dm, 1 H), 7.86 (t, 1 H), 7.77 (d, 1 H), 7.71 (d, 1 H), 7.70–
7.74 (dm, 4 H), 7.60 (d, 1 H), 7.59 (d, 1 H), 7.54 (d, 1 H), 7.49 (m,
1 H), 7.45–7.52 (m, 4 H), 7.37 (d, 1 H), 7.36 (m, 1 H), 7.35 (d, 1
H) ppm. UV (CH3CN): λmax (logε) = 243.9 (4.55), 287.4 (4.85),
326.5 (4.31), 413.2 (4.39), 463.2 (4.40 dm3 mL–1 cm–1) nm. MS
(electrospray): m/z (calcd. value) = 1032.9 (1033.0) [M – PF6]+.
C48H34F12N8P2RuS2 (1177.97) + 4 H2O: calcd. C 46.12, H 3.39, N
8.96; found C 46.43, H 3.37, N 8.37.
[Ru(bpy)2(10)](PF6)2 (21): Yield: 23%. Dark red precipitate. 1H
NMR ([D6]DMSO, 300 MHz): δ = 9.2 (d, J = 8.2 Hz, 1 H), 9.08
(br. s, 1 H), 8.92–8.8 (m, 4 H), 8.79–8.69 (m, 2 H), 8.6 (br. s, 1 H),
8.43 (d, J = 8.0 Hz, 1 H), 8.29–8.12 (m, 6 H), 8.05–7.94 (m, 2 H),
7.91 (d, J = 5.2 Hz, 1 H), 7.81 (d, J = 5.0 Hz, 1 H), 7.78–7.68 (m, 6
H), 7.68–7.6 (m, 2 H), 7.6–7.48 (m, 6 H) ppm. C48H34F12N8P2RuS2
(1177.97) + 2 H2O: calcd. C 47.49, H 3.15, N 9.23, S 5.28; found
C 47.41, H 2.99, N 8.95, S 5.23.
The synthesis of 18 is representative for the synthesis of the dime-
tallic RuII complexes.
[Ru2(bpy)4(5)](PF6)4 (18): cis-[Ru(bpy)2Cl2] (0.102 g, 0.211 mmol)
and 5,5Ј-bis(2,2Ј-bipyridin-6-yl)-2,2Ј-bithiophene (5) (0.027 g,
0.057 mmol) were dissolved in 1,2-ethanediol (8 mL), and the solu-
tion was stirred at 105 °C for 2 h. NH4PF6 (0.072 g, 0.442 mmol)
was added to the solution and stirring was continued at 100 °C for
22 h. After cooling to room temperature, further NH4PF6 (0.265 g,
1.626 mmol) was added, and the solution was placed in the freezer
(–20 °C) overnight. An orange-brown powder was precipitated by
the addition of water (15 mL) and isolated by filtration. The pre-
cipitate was washed with diethyl ether (3ϫ5 mL) and air-dried.
The crude product was purified by column chromatography [silica;
CH3CN/KNO3(aq. satd.)/H2O, 14:2:1]. The orange fraction was
collected (Rf = 0.43), concentrated to a small volume (ca. 3 mL)
and reprecipitated with NH4PF6. KNO3 coprecipitated with the
product was removed by redissolving the product in H2O and preci-
pitating with NH4PF6, followed by dissolution in CH3CN and pre-
cipitation with diethyl ether. The resultant orange powder was col-
lected by filtration. Yield: 0.075 g (64%). 1H NMR (CD3CN,
300 MHz): δ = 8.63 (d, 2 H), 8.61 (d, 2 H), 8.46 (d, 2 H), 8.38 (d,
2 H), 8.37 (d, 2 H), 8.18 (d, 2 H), 8.17 (m, 2 H), 8.14 (d, 2 H), 8.10
(m, 6 H), 7.94 (m, 2 H), 7.71 (d, 2 H), 7.60 (m, 2 H), 7.55 (d, 2 H),
7.52 (m, 4 H), 7.41 (m, 2 H), 7.35 (d, 2 H), 7.34 (m, 2 H), 7.22 (m,
2 H), 7.09 (d, 2 H), 6.68 (m, 2 H), 6.26 (br. m, 2 H) ppm. Analo-
gously to complexes 12 and 14 the signal of the thiophene proton
adjacent to the bipyridine was not observed at 298 K. FT-IR
[{Ru(bpy)2}2(10)](PF6)4 (22): Yield: 66%. Red powder. 1H NMR
(CD3CN, 300 MHz): δ = 8.68 (d, J = 8.1 Hz, 1 H), 8.62 (d, J =
1.8 Hz, 1 H), 8.5 (d, J = 8.3 Hz, 4 H), 8.13–8.02 (m, 5 H), 7.89 (d,
J = 4.0 Hz, 1 H), 7.83 (dd, J = 5.6, 0.7 Hz, 1 H), 7.78–7.71 (m, 4
H), 7.66 (d, J = 6.1 Hz, 1 H), 7.53 (d, J = 8.0 Hz, 1 H), 7.52 (d, J
= 4.0 Hz, 1 H), 7.45–7.37 (m, 5 H) ppm. C68H50F24N12P4Ru2S2
(1881.3) + 7 H2O: calcd. C 40.69, H 3.21, N 8.37, S 3.19; found C
40.62, H 2.93, N 8.23, S 3.17.
(KBr): ν = 1604 (w), 1561 (w), 1447 (m), 1384 (w), 841 (s), 764
˜
(m), 731 (w), 558 (m) cm–1. UV (CH3CN): λmax (logε) = 287 (4.80),
448 (4.20 dm3 mL–1 cm–1) nm. MALDI-TOF MS: m/z (calcd.
value) = 1738 (1736.35) [M + H – PF6]+, 1592 (1591.35) [M – 2
PF6]+. C68H50F24N12P4Ru2S2 (1881.3) + KNO3 + 4 H2O: calcd. C
39.75, H 2.85, N 8.86; found C 39.42, H 3.04, N 8.98.
Supporting Information (see footnote on the first page of this arti-
cle): Cyclic voltammograms of complexes 12–22.
Acknowledgments
[Ru2(bpy)4(11)](PF6)4 (19): Ligand 11 was treated with 2 equiv. of
cis-[Ru(bpy)2Cl2] in 1,2-ethanediol to give the homodinuclear com-
plex 19 in 73% yield. H NMR (CD3CN, 300 MHz): δ = 8.69 (d,
The authors would like to thank the Faculty of Science and Engi-
neering, Mälardalen University, for their continued support of this
project. R. S. would like to thank the Dentist Gustav Dahl Memo-
rial Fund for its generous support. We also wish to thank the Uni-
versity of Basel and the Swiss National Science Foundation for
support. The authors also would like to thank Mr. George Blazak
at the University of Queensland, Australia, for performing micro-
analysis and Dr. Conor Brennan at the University of Basel, Swit-
zerland, for performing MALDI-TOF analysis.
1
1 H), 8.62 (d, 1 H), 8.61 (s, 1 H), 8.59 (d, 1 H), 8.52 (d, 1 H), 8.52
(d, 4 H), 8.46 (d, 1 H), 8.37 (d, 1 H), 8.20 (dm, 1 H), 8.15 (td, 1
H), 8.14 (t, 1 H), 8.13 (d, 1 H), 8.11 (td, 1 H), 8.09 (m, 1 H), 8.07
(td, 1 H), 8.06–8.12 (td, 4 H), 7.94 (td, 1 H), 7.83 (d, 1 H), 7.82
(dm, 1 H), 7.77 (dm, 1 H), 7.75 (dm, 4 H), 7.65 (d, 1 H), 7.61 (td,
1 H), 7.56 (m, 2 H), 7.55 (m, 1 H), 7.52 (d, 1 H), 7.46 (m, 1 H),
7.40 (m, 1 H), 7.39 (dm, 1 H), 7.38–7.46 (m, 4 H), 7.36 (dm, 1 H),
7.34 (m, 1 H), 7.22 (m, 1 H), 7.19 (dm, 1 H), 7.14 (d, 1 H), 6.77
(br. m, 1 H), 6.60 (br. m, 1 H) ppm. Analogously to complexes 12,
14 and 18 the signal of the thiophene proton adjacent to the bi-
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˜
1465 (m), 1446 (m), 1385 (w), 1240 (w), 1120 (m), 840 (s), 762 (m),
730 (w), 557 (m) cm–1. UV (CH3CN): λmax (logε) = 287 (5.13),
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The synthesis of 20 is representative for the synthesis of the mono-
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Eur. J. Inorg. Chem. 2008, 1784–1794
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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1793

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Received: October 16, 2007
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1794
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