Reversible molecular switching of ruthenium bis(bipyridyl) groups bonded to oligothiophenes: Effect on electrochemical and spectroscopic properties

Article abstract of DOI:10.1021/ja043573a

We report the preparation of complexes in which ruthenium(II) bis(bipyridyl) groups are coordinated to oligothiophenes via a diphenylphosphine linker and a thienyl sulfur (P,S bonding) to give [Ru(bpy)₂PT ₃-P,S](PF₆)₂

Full text of DOI:10.1021/ja043573a

Published on Web 04/12/2005
Reversible Molecular Switching of Ruthenium Bis(bipyridyl)
Groups Bonded to Oligothiophenes: Effect on
Electrochemical and Spectroscopic Properties
Carolyn Moorlag,† Michael O. Wolf,*,† Cornelia Bohne,‡ and Brian O. Patrick†
Contribution from the Department of Chemistry, The UniVersity of British Columbia,
VancouVer, British Columbia, V6T 1Z1, Canada, and Department of Chemistry,
The UniVersity of Victoria, P.O. Box 3065, Victoria, British Columbia, V8W 3V6, Canada
Received October 22, 2004; E-mail: mwolf@chem.ubc.ca
Abstract: We report the preparation of complexes in which ruthenium(II) bis(bipyridyl) groups are coordinated
to oligothiophenes via a diphenylphosphine linker and a thienyl sulfur (P,S bonding) to give [Ru(bpy)2PT3-
P,S](PF6)2 (bpy ) 2,2′-bipyridyl, PT3 ) 3′-(diphenylphosphino)-2,2′:5′,2′′-terthiophene), [Ru(bpy)2PMeT3-
P,S](PF6)2 (PMeT3 ) 3′-(diphenylphosphino)-5-methyl-2,2′:5′,2′′-terthiophene), [Ru(bpy)2PMe2T3-P,S](PF6)2
(PMe2T3 ) 5,5′′-dimethyl-3′-(diphenylphosphino)-2,2′:5′,2′′-terthiophene), and [Ru(bpy)2PDo2T5-P,S](PF6)2
(PDo2T5 ) 3,3′′′′-didodecyl-3′′-diphenylphosphino-2,2′:5′,2′′:5′′,2′′′:5′′′,2′′′′-pentathiophene). These com-
plexes react with base, resulting in the complexes [Ru(bpy)2PT3-P,C]PF6, [Ru(bpy)2PMeT3-P,C]PF6,
[Ru(bpy)2PMe2T3-P,C]PF6, and [Ru(bpy)2PDo2T5-P,C]PF6, where the thienyl carbon is bonded to ruthenium
(P,C bonding). The P,C complexes revert back to the P,S bonding mode by reaction with acid; therefore,
metal-thienyl bonding is reversibly switchable. The effect of interaction of the metal groups in the different
bonding modes with the thienyl backbone is reflected by changes in alignment of the thienyl rings in the
solid-state structures of the complexes, the redox potentials, and the π f π* transitions in solution. Methyl
substituents attached to the terthiophene groups allow observation of the effect of these substituents on
the conformational and electronic properties and aid in assignments of the electrochemical data. The PTn
ligands bound in P,S and P,C bonding modes also alter the electrochemical and spectroscopic properties
of the ruthenium bis(bipyridyl) group. Both bonding modes result in quenching of the oligothiophene
luminescence. Weak, short-lived Ru f bipyridyl MLCT-based luminescence is observed for [Ru(bpy)2-
PDo2T5-P,S](PF6)2, [Ru(bpy)2PT3-P,C]PF6, [Ru(bpy)2PMeT3-P,C]PF6, and [Ru(bpy)2PMe2T3-P,C]PF6, and
no emission is observed for the alternate bonding mode of each complex.
Introduction
tionalization, and alter the polymer properties. There has also
been interest in modifying the backbone with metal groups to
Polythiophenes are a class of π-conjugated organic polymers
that have stimulated interest for application in new generations
of electronic devices due to their many interesting physical
properties such as electronic conductivity, electrochromism, and
electroluminescence.1-7 Functionalized polythiophenes, such as
alkyl-8-10 and halo-11 substituted derivatives, have been syn-
thesized to increase solubility, create centers for further func-
alter the physical, chemical, and electronic properties of poly-
thiophene.12-14 Electronic interactions between metals and
polythiophenes may be modeled with shorter-chain oligoth-
iophene complexes due to their ease of characterization and
ability to be synthesized in pure form. Three methods of incor-
porating metals into oligo- or polythiophenes are as pendant
groups attached via a ligand;15,16 direct bonding to the backbone
via thiophene,17 bipyridyl18-21 or bithiazole groups;22 and metals
inserted directly into the chain.23-25 We are exploring the
† The University of British Columbia.
‡ The University of Victoria.
(1) MacDiarmid, A. G. Angew. Chem., Int. Ed. 2001, 40, 2581-2590.
(2) Heeger, A. J. Angew. Chem., Int. Ed. 2001, 40, 2591-2611.
(3) Kraft, A.; Grimsdale, A. C.; Holmes, A. B. Angew. Chem., Int. Ed. 1998,
37, 402-428.
(11) Li, Y.; Vamvounis, G.; Yu, J.; Holdcroft, S. Macromolecules 2001, 34,
3130-3132.
(4) Garnier, F.; Tourillon, G.; Gazard, M.; Dubios, J. C. J. Electroanal. Chem.
1983, 148, 299-303.
(12) Peng, Z.; Gharavi, A. R.; Yu, L. J. Am. Chem. Soc. 1997, 119, 4622-
4632.
(5) Tourillon, G.; Garnier, F. J. Phys. Chem. 1983, 87, 2289-2292.
(6) Andersson, M. R.; Berggren, M.; Inganas, O.; Gustafsson, G.; Gustafsson-
Carlberg, J. C.; Selse, D.; Hjertberg, T.; Wennerstrom, O. Macromolecules
1995, 28, 7525-7529.
(13) Walters, K. A.; Ley, K. D.; Cavalaheiro, C. S. P.; Miller, S. C.; Gosztola,
D.; Wasielewski, M. R.; Bussandri, A. P.; van Willigen, H.; Schanze, K.
S. J. Am. Chem. Soc. 2001, 123, 8329-8342.
(14) Wong, C. T.; Chen, W. K. AdV. Mater. 1999, 11, 455-459.
(15) Crayston, J. A.; Iraqi, A.; Morrison, J. J.; Walton, J. C. Synth. Met. 1997,
84, 441-442.
(7) Berggren, M.; Inganas, O.; Gustafsson, G.; Rasmusson, J.; Andersson, M.
R.; Hjertberg, T.; Wennerstrom, O. Nature 1994, 372, 444-446.
(8) Elsenbaumer, R. L.; Jen, K. Y.; Oboodi, R. Synth. Met. 1986, 15, 169-
174.
(16) Higgins, T. B.; Mirkin, C. A. Chem. Mater. 1998, 10, 1589-1595.
(17) Weinberger, D. A.; Higgins, T. B.; Mirkin, C. A.; Stern, C. L.; Liable-
Sands, L. M.; Rheingold, A. L. J. Am. Chem. Soc. 2001, 123, 2503-2516.
(18) Zhu, S. S.; Swager, T. M. AdV. Mater. 1996, 8, 497-500.
(19) Zhu, S. S.; Kingsborough, R. P.; Swager, T. M. J. Mater. Chem. 1999, 9,
2123-2131.
(9) Loewe, R. S.; Ewbank, P. C.; Liu, J.; Zhai, L.; McCullough, R. D.
Macromolecules 2001, 34, 4324-4333.
(10) Murray, K. A.; Moratti, S. C.; Baigent, D. R.; Greenham, N. C.; Pichler,
K.; Holmes, A. B.; Friend, R. H. Synth. Met. 1995, 69, 395-396.
9
6382
J. AM. CHEM. SOC. 2005, 127, 6382-6393
10.1021/ja043573a CCC: $30.25 © 2005 American Chemical Society

Molecular Switching of Ru Bis(bipyridyl) Groups
A R T I C L E S
attachment of pendant metal groups that are also designed to
bond to a thienyl group in the backbone.26-28
methyl-2,2′:5′,2′′-terthiophene) (2), and [Ru(bpy)2PMe2T3-P,S]-
(PF6)2 (PMe2T3 ) 5,5′′-dimethyl-3′-(diphenylphosphino)-2,2′:
5′,2′′-terthiophene) and compare the electronic properties of
these complexes with those of the carbon-bound complexes [Ru-
(bpy)2PT3-P,C]PF6 (4), [Ru(bpy)2PMeT3-P,C]PF6 (5), and [Ru-
(bpy)2PMe2T3-P,C]PF6 (6).
Thiophenes can bond to transition metals via various bonding
modes, including η1(S), η2-, η4-, or η5-coordination29 and
metal-carbon bonding, most frequently at the thienyl R-posi-
tion. Metals bonded to the thienyl group via a M-C bond may
be formed by the reaction of a thienyl ring with metal fragments
(cyclometalation)30-32 or by conversion from η1(S)-coordinated
complexes, as has been demonstrated for rhenium- and
ruthenium-thienyl complexes.33,34 The effects of different
bonding modes of a metal center to an oligothienyl chain on
the properties of the conjugated oligomer are interesting.
Ruthenium bis(bipyridyl) and ruthenium terpyridyl groups have
been reported to coordinate to thienyltetrazine35 and thienylbi-
pyridine,36,37 respectively, with the thiophene coordinated at the
sulfur. Acid-base mediated reversible switching between sulfur
coordination and a carbon bonding mode has been reported for
a ruthenium thienylbipyridine complex.38 In our approach, a
pendant metal is covalently anchored through a phosphine group
to an oligothiophene chain. The ruthenium bis(bipyridyl) (Ru-
(bpy)2) group is selected due to the relative chemical inertness
of the bpy spectator ligands, as well as the ability of some Ru-
(bpy)2-containing complexes to undergo electron and energy
transfer processes.39 Two open coordination sites are available,
allowing the possibility of bonding to a phosphino-oligoth-
iophene via sulfur (P,S) or carbon (P,C) bidentate bonding
modes. In a preliminary communication, we have reported the
complexation of Ru(bpy)2 to terthienyl units containing pendant
diphenylphosphino groups26 and demonstrated that coordination
could be reversibly switched between P,S and P,C bonding
modes.
The longer pentathiophene PDo2T5 (3,3′′′′-didodecyl-3′′-
diphenylphosphino-2,2′:5′,2′′:5′′,2′′′:5′′′,2′′′′-pentathiophene) (7)
has been synthesized via selective coupling of dodecylthiophene
groups to the terminal positions of tribromoterthiophene. The
phosphine PDo2T5 was used to prepare [Ru(bpy)2PDo2T5-P,S]-
(PF6)2 (8), which can be reversibly switched to the carbon-bound
complex [Ru(bpy)2PDo2T5-P,C]PF6 (9). The effect of the
ruthenium bonding mode on the longer oligothiophene is
compared with the results from the terthiophene complexes. The
pentathiophene Do2T5 (3,3′′′′-didodecyl-2,2′:5′,2′′:5′′,2′′′:5′′′,2′′′′-
pentathiophene) (10) was also synthesized for comparison to
the ligand and complexes.
In this article, we fully report the characterization of the model
complexes [Ru(bpy)2PT3-P,S](PF6)2 (bpy ) 2,2′-bipyridyl, PT3
) 3′-(diphenylphosphino)-2,2′:5′,2′′-terthiophene) (1), [Ru-
(bpy)2PMeT3-P,S](PF6)2 (PMeT3 ) 3′-(diphenylphosphino)-5-
(20) Trouillet, L.; De Nicola, A.; Guillerez, S. Chem. Mater. 2000, 12, 1611-
1621.
(21) Walters, K. A.; Touillet, L.; Guillerez, S.; Schanze, K. S. Inorg. Chem.
2000, 39, 5496-5509.
(22) Wolf, M. O.; Wrighton, M. S. Chem. Mater. 1994, 6, 1526-1533.
(23) Zhu, Y.; Millet, D. B.; Wolf, M. O.; Rettig, S. J. Organometallics 1999,
18, 1930-1938.
(24) Fraysse, S.; Coudret, C.; Launay, J.-P. J. Am. Chem. Soc. 2003, 125, 5880-
5888.
(25) Hjelm, J.; Constable, E. C.; Figgemeier, E.; Hagfeldt, A.; Handel, R.;
Housecroft, C. E.; Mukhtar, E.; Schofield, E. Chem. Commun. 2002, 284-
285.
(26) Moorlag, C.; Clot, O.; Wolf, M. O.; Patrick, B. O. Chem. Commun. 2002,
3028-3029.
(27) Clot, O.; Wolf, M. O.; Yap, G. P. A.; Patrick, B. O. J. Chem. Soc., Dalton
Trans. 2000, 2729-2737.
(28) Clot, O.; Wolf, M. O.; Patrick, B. O. J. Am. Chem. Soc. 2001, 123, 9963-
9973.
(29) Angelici, R. J. NATO ASI Ser., Ser. 3 1998, 89-127.
(30) Wang, R.; Groux, L. F.; Zargarian, D. J. Organomet. Chem. 2002, 660,
98-107.
(31) Morikita, T.; Hirano, M.; Sasaki, A.; Komiya, S. Inorg. Chim. Acta 1999,
291, 341-354.
(32) Bianchini, C.; Jimenez, M. V.; Meli, A.; Moneti, S.; Vizza, F. J. Organomet.
Chem. 1995, 504, 27-31.
(33) Benson, J. W.; Angelici, R. J. Inorg. Chem. 1993, 32, 1871-1874.
(34) Robertson, M. J.; White, C. J.; Angelici, R. J. J. Am. Chem. Soc. 1994,
116, 5190-5195.
(35) Sarkar, B.; Kaim, W.; Klein, A.; Schwederski, B.; Fiedler, J.; Duboc-Toia,
C.; Lahiri, G. K. Inorg. Chem. 2003, 42, 6172-6174.
(36) Constable, E. C.; Henney, R. P. G.; Tocher, D. A. Chem. Commun. 1989,
913-914.
(37) Constable, E. C.; Henney, R. P. G.; Tocher, D. A. J. Chem. Soc., Dalton
Trans. 1991, 2335-2347.
Results
(38) Constable, E. C.; Dunne, S. J.; Rees, D. G. F.; Schmitt, C. X. Chem.
Commun. 1996, 1169-1170.
Synthesis and Structures of Complexes and Related
Compounds. The preparation of the ligands PT3, PMeT3, and
(39) Kalyanasundaram, K. Photochemistry of Polypyridine and Porphyrin
Complexes, 1st ed.; Academic Press: London, 1992.
9
J. AM. CHEM. SOC. VOL. 127, NO. 17, 2005 6383

A R T I C L E S
Scheme 1
Moorlag et al.
intermolecular S1 and S3′ thienyl rings are weakly π-stacked
with a plane-to-plane distance between centroids of 3.947 Å.
Sulfur atoms of stacked rings are aligned anti to one another.
P,C complexes 4-6 are prepared by reaction of the corre-
sponding P,S complexes 1-3 with NaOH dissolved in methanol
and heating to reflux (Scheme 1). Yields (50-85%) are higher
than those that have been previously reported for reactions with
NaOH in CH3CN/H2O (10-50%).26 Switching of the bonding
mode, essentially a deprotonation and cyclometalation reaction,
does not proceed without heating. A color change from yellow
to dark brown indicates the onset of the cyclometalation reaction.
Analysis of crude samples of the P,C complexes indicates the
presence of some oxidized ligand, which is removed by
crystallization. The solid-state structures of 426 and 6 (Figure
1, Table 1) were established by X-ray crystallography from
crystals grown by slow diffusion of hexanes into a solution of
the complex in acetone. The cyclometalated thienyl ring is tilted
very little from the Ru-C bond, with tilt angles of 7.3° for 4
and 8.6° for 6. The Ru1-C35 bond lengths (2.076 and 2.095 Å)
PMe2T3 has been previously reported.27,28 Complexes 1-3 are
prepared by reaction of Ru(bpy)2Cl2‚2H2O with AgBF4 and
complexation with the appropriate ligand. The products are
metathesized to the PF6 salts and recrystallized in eth-
anol-acetone to give air-stable complexes 1-3 in good yield
(Scheme 1).
The solid-state structures of 126 and 3 were established by
X-ray crystallography of crystals grown from slow diffusion
of hexanes into a solution of the complex in acetone. The
structure of 3 is shown in Figure 1, and selected bond lengths
and torsion angles are collected in Table 1. The ligands bind to
Ru in a P,S bonding mode, with the metal coordinated to the
S1 thienyl ring in a η1(S) fashion, resulting in the formation of
a six-membered ring. We have observed this mode previously
in other ruthenium and palladium complexes.27,28 The Ru1-S1
bond lengths of 1 and 3 are 2.3640 and 2.3621 Å, which is
within the observed range for other S-bound ruthenium-
thiophene complexes. The plane of the bound thiophene is tilted
from the Ru-S bond at angles of 58.3° (1) and 53.6° (3), which
minimizes π-antibonding interactions between the thiophene and
the metal.40 Some π-antibonding overlap is indicated by
S1-C33 and S1-C36 bonds for 1 and 3 (1.74-1.76 Å) that
approach C-S single bond lengths41 and are elongated compared
with calculated bond lengths for terthiophene (1.7206 and 1.7351
Å, respectively).42 The S1-C36-C37-S2 and S2-C40-C41-S3
torsion angles of 1 (147.02°, 146.0°) are close to the calculated
torsion angles of terthiophene (147.6°),42 while the correspond-
ing torsion angles of 3 (150.71°, 165.48°) indicate increased
coplanarity and therefore greater π-orbital overlap of adjacent
thienyl rings. Plane-to-plane distances of 3.3-3.8 Å between
aromatic rings in solid-state molecular structures are indicative
of π-stacking.43,44 There is evidence for weak π-stacking
between the tilted S1 thienyl and N2 pyridyl rings of 1 (plane-
to-plane distance between centroids ) 3.708 Å) and 3 (3.675
Å) and the N4 pyridyl and C21 phenyl rings of both 1 (3.777 Å)
and 3 (3.580 Å). These intramolecular π-stackings could
promote the preferential crystallization of the diastereomers
observed in the crystal structures of 1 and 3, in which the S1
thienyl ring is tilted toward the N2 pyridyl ring rather than
toward the edge of the N4 pyridyl ring. Single peaks are
observed in the 31P NMR spectra, also providing no evidence
for different diastereomers in solution. Intermolecular π-stacking
between rings is not observed for 1. Figure 2 depicts the
alignment in the crystal structure of 3, where the offset
+
are longer than the calculated double bond length in RudCH2
(1.88 Å),45 but shorter than Ru-C single bonds reported for
ruthenium bound to alkyl ligands (2.22 Å),46,47 indicating that
there is some double bond character. π-Antibonding overlap
greater than that for the P,S complexes would be expected due
to the end-on bonding mode and is indicated by elongated
thienyl C-C double bonds, notably for the C35-C36 bond, which
is elongated by 0.044 Å for 4 and by 0.040 Å for 6 compared
to 1 and 3. The S1-C36-C37-S2 torsion angles of 4 (10.7°)
and 6 (19.7°) correspond to syn S1 and S2 thienyl rings, while
the P,S complexes show an anti arrangement of these rings,
and the P,C complexes show greater coplanarity between all
three thienyl rings compared to the P,S complexes. Intramo-
lecular π-stacking is observed between the adjacent N4 pyridyl
and C21 phenyl rings of 4 based on a plane-to-plane distance of
3.510 Å, while in 6 the corresponding distance is 3.901 Å.
Intermolecular thienyl rings of 4 and 6 are separated by >4 Å.
Complete reversion of P,C complexes 4-6 to the P,S
complexes occurs rapidly with the addition of HPF6 or HCl at
room temperature, concomitant with a color change from deep
brown to bright yellow. Analysis by 31P NMR spectroscopy
indicates that this conversion occurs quantitatively with no side
products.
The ligand PDo2T5 (7) is synthesized in three steps from
5,3′,5′′-tribromo-2,2′:5′,2′′-terthiophene (Scheme 2). Selective
coupling at the terminal bromo substituents is carried out via
palladium-catalyzed Kumada coupling48 with the Grignard
reagant 2-bromo-3-dodecylthienyl-magnesium bromide to give
3′′-bromo-3,3′′′′-didodecyl-2,2′:5′,2′′:5′′,2′′′:5′′′,2′′′′-penta-
thiophene in good yield. The use of Pd(dppf)Cl2 as a catalyst
rather than Ni(dppp)Cl2 results in preferential reaction at the
R-positions. Exceeding 2 equiv of the Grignard reagant results
in the formation of the T-shaped 3′′-(2-(3-dodecyl)thiophene)-
3,3′′′′-didodecyl-2,2′:5′,2′′:5′′,2′′′:5′′′,2′′′′-pentathiophene as a
side product. The phosphine PDo2T5 could not be prepared by
(40) Harris, S. Polyhedron 1997, 16, 3219-3233.
(41) Rozsondai, B.; Schultz, G.; Hargittai, I. J. Mol. Struct. 1981, 70, 309-
310.
(45) Carter, E. A.; Goddard, W. A., III. J. Am. Chem. Soc. 1986, 108, 2180-
(42) DiCesare, N.; Belletete, M.; Marrano, C.; Leclerc, M.; Durocher, G. J.
Phys. Chem. A 1998, 102, 5142-5149.
2191.
(46) Watanabe, M.; Murata, K.; Ikariya, T. J. Am. Chem. Soc. 2003, 125, 7508-
(43) Curtis, M. D.; Cao, J.; Kampf, J. W. J. Am. Chem. Soc. 2004, 126, 4318-
7509.
4328.
(47) Bibal, C.; Pink, M.; Smurnyy, Y. D.; Tomaszewski, J.; Caulton, K. G. J.
Am. Chem. Soc. 2004, 126, 2312-2313.
(48) Nakanishi, H.; Sumi, N.; Aso, Y.; Otsubo, T. J. Org. Chem. 1998, 63,
8632-8633.
(44) Yamamoto, T.; Komarudin, D.; Maruyama, T.; Arai, M.; Lee, B.-L.;
Suganuma, H.; Asakawa, N.; Inoue, Y.; Kubota, K.; Sasaki, S.; Fukuda,
T.; Matsuda, H. J. Am. Chem. Soc. 1998, 120, 2047-2058.
9
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Molecular Switching of Ru Bis(bipyridyl) Groups
A R T I C L E S
Figure 1. X-ray crystal structures of [Ru(bpy)2PMe2T3-P,S](PF6)2 (3, left) and [Ru(bpy)2PMe2T3-P,C]PF6 (6, right). Hydrogen atoms are omitted for clarity,
and thermal ellipsoids are drawn at 50% probability.
structure of pentathiophene53 but may also be due to the long
dodecyl chains. Intramolecular π-stacking is observed between
Table 1. Selected Bond Lengths and Angles for
[Ru(bpy)2PMe2T3-P,S](PF6)2 (3) and [Ru(bpy)2PMe2T3-P,C]PF6 (6)
3
6
the N4 pyridyl and C45 phenyl rings and between the S2 thienyl
and N1 pyridyl rings, with interplanar distances of 3.520 and
3.671 Å, respectively. Similar to 1 and 3, there is a preference
for the diastereomeric arrangement of the S2 thienyl ring as
depicted that may be due to π-stacking within the molecule.
Intermolecular π-stacking is not seen in the crystal structure,
possibly due to the observed alignment of the dodecyl chains
between the molecules.
bond length, Å
bond length, Å
Ru1-S1
Ru1-P1
S1-C33
S1-C36
C33-C34
C34-C35
C35-C36
C36-C37
2.3621(6)
Ru1-C35
2.095(2)
2.2954(7)
1.734(3)
1.758(2)
1.370(4)
1.450(3)
1.398(3)
1.448(4)
2.3397(6)
1.764(2)
1.750(2)
1.347(3)
1.433(3)
1.356(3)
1.449(3)
Ru1-P1
S1-C33
S1-C36
C33-C34
C34-C35
C35-C36
C36-C37
[Ru(bpy)2PDo2T5-P,C]PF6 (9) is a very dark red solid of
which crystals could not be obtained for X-ray analysis, likely
due to disorder of the pentathienyl group or the dodecyl chains
combined with a reduction in the number of counterions
compared to 8. Reversion to the P,S complex 8 proceeded as
for 4-6, with addition of acid to a dissolved sample resulting
in a color change from deep red to bright orange. The reaction
is quantitative, and the lack of side products is clear from the
data shown in Figure 4.
3,3′′′′-Didodecyl-2,2′:5′,2′′:5′′,2′′′:5′′′,2′′′′-pentathiophene (10)
is prepared in quantitative yield by exchange of 3,3′′′′-didodecyl-
3′′-iodo-2,2′:5′,2′′:5′′,2′′′:5′′′,2′′′′-pentathiophene with butyl-
lithium followed by quenching with H2O (Scheme 4). Because
of the stability of the charged pentathiophene, the reaction of
the anion with water is slow. The resulting dark yellow powder
is susceptible to oxidation in air.
Cyclic Voltammetry. The cyclic voltammograms of 1-3 are
displayed in Figure 5a. Addition of electron-donating methyl
substituents lowers the oxidation potentials, and progressively
lower irreversible ruthenium oxidation waves at 1.48, 1.44, and
1.41 V are observed (Table 3). The only prominent thienyl
oxidation wave is a shoulder at 1.69 V for 3. New return waves
observed on the first and subsequent scans of 1 and 2 at 1.14
and 1.12 V could be due to oxidative electropolymerization or
dimerization at the terthienyl R-positions. A new return wave
is not observed for methyl-capped complex 3. The first
bipyridine reduction is irreversible for 1, which could indicate
interaction of the reduced bipyridyl group with the relatively
electron-poor terthienyl group. Two reversible bipyridine reduc-
torsion angle, deg
torsion angle, deg
S1-C36-C37-S2
S2-C40-C41-S3
150.71(12)
-165.48(12)
S1-C36-C37-S2
S2-C40-C41-S3
-19.7(3)
16.0(3)
bromo-lithium exchange followed by addition of PPh2Cl due
to low reactivity of the lithio anion. An alternative high-
temperature copper-catalyzed halogen exchange reaction49 is
used to form 3,3′′′′-didodecyl-3′′-iodo-2,2′:5′,2′′:5′′,2′′′:5′′′,2′′′′-
pentathiophene in high yield, and subsequent palladium-
catalyzed cross-coupling with diphenylphosphine50 yields PDo2T5
(7). The overall yield of 87% for the two-step process is an
improvement over reported yields for phosphino-oligothiophenes
prepared via lithiation and addition of PPh2Cl.27,28
Ruthenium bipyridyl complexes [Ru(bpy)2PDo2T5-P,S](PF6)2
(8) and [Ru(bpy)2PDo2T5-P,C]PF6 (9) are synthesized by the
same procedures as for the P,S and P,C terthiophene complexes
(Scheme 3). Repeated crystallizations of 8 in ethanol containing
minimal acetone produced brightly colored orange needle-
shaped crystals for X-ray analysis. In the crystal structure of 8
(Figure 3), one [PF6]- counterion is replaced with [BF4]-.
Compared to 1 and 3, the Ru-S bond is shorter (2.3578 Å,
Table 2), and the tilt angle between the thiophene ring and the
Ru-S bond (58.4°) is comparable. The S2-C5 (1.762 Å) and
S2-C8 (1.745 Å) bonds are elongated 0.011-0.028 Å compared
to the inner ring of terthiophene (1.7342 Å).42 The torsion angle
between the two bound thiophene rings (147.9°) is very close
to the corresponding torsion angle for 1 and the expected torsion
angles for pentathiophene.51,52 The disorder of the S4 and S5
rings of 8 is similar to the disorder observed in the crystal
(51) Becker, R. S.; de Melo, J. S.; Macanita, A. L.; Elisei, F. J. Phys. Chem.
1996, 100, 18683-18695.
(52) DiCesare, N.; Belletete, M.; Donat-Bouillud, A.; Leclerc, M.; Durocher,
G. J. Lumin. 1999, 81, 111-125.
(49) Klapars, A.; Buchwald, S. L. J. Am. Chem. Soc. 2002, 124, 14844-14845.
(50) Herd, O.; Hessler, A.; Hingst, M.; Tepper, M.; Stelzer, O. J. Organomet.
Chem. 1996, 522, 69-76.
(53) Azumi, R.; Goto, M.; Honda, K.; Matsumoto, M. J. Chem. Soc. Jpn. 2003,
76, 1561-1567.
9
J. AM. CHEM. SOC. VOL. 127, NO. 17, 2005 6385

A R T I C L E S
Moorlag et al.
Figure 2. A portion of the unit cell of [Ru(bpy)2PMe2T3-P,S](PF6)2 (3) viewed normal to the 010 plane. Lines are drawn between thienyl groups that are
stacked relative to one other. Hydrogen atoms, [PF6]-, and occluded solvent have all been removed for clarity, and thermal ellipsoids are drawn at 50%
probability.
Scheme 2
Scheme 3
Table 2. Selected Bond Lengths and Angles for
[Ru(bpy)2PDo2T5-P,S](PF6)2 (8)
bond length, Å
Ru1-S2
Ru1-P1
S2-C8
2.3578(14)
2.3404(17)
1.745(6)
C6-C7
C7-C8
C8-C9
S2-C5
1.433(8)
1.353(8)
1.469(8)
1.762(6)
C5-C6
1.358(8)
tions are observed at -1.24 and -1.46 V for 2 and 3; the
reversibility is possibly due to donation of electron density from
the methyl substituents. Terthienyl reduction waves are observed
torsion angle, deg
S1-C4-C5-S2
S2-C8-C9-S3
S3-C12-C13-S4a
32.0(6)
S3-C12-C13-S4b
S4a-C16a-C17a-S5a
S4b-C16b-C17b-S5b
177.1(4)
154.8(9)
50.2(19)
-147.9(4)
127.9(5)
at -1.79 and -1.81 V for 2 and 3, respectively, with a negative
shift in potential with addition of a methyl substituent.
The cyclic voltammograms of the P,C complexes 4, 5, and 6
(Figure 5b) display RuII/III oxidations (0.49-0.57 V), ter-
thienyl oxidations (0.96-1.11 V), and two bipyridyl reductions
(1.53-1.55, 1.78 V). Ruthenium oxidations decrease ∼0.9 V
and terthienyl oxidations decrease >0.6 V compared to the
P,S complexes, while the bipyridyl reductions are less af-
fected by conversion to the P,C bonding mode. Assignments
of the oxidation and reduction potentials of the P,C com-
plexes are substantiated by addition of two methyl substituents
having an effect on the thienyl oxidation potential (0.15 V
decrease) greater than that on the ruthenium oxidation potential
(0.08 V decrease), and almost no effect on bipyridyl reduction
potentials.
Figure 3. X-ray crystal structure of [Ru(bpy)2PDo2T5-P,S](PF6)2 (8)
(conformation B). Only the first carbon atoms of the dodecyl chains are
included, and the remaining carbon atoms of the chains and all hydrogen
atoms are omitted for clarity. Thermal ellipsoids are shown at 50%
probability.
9
6386 J. AM. CHEM. SOC. VOL. 127, NO. 17, 2005

Molecular Switching of Ru Bis(bipyridyl) Groups
A R T I C L E S
Figure 4. 31P NMR spectra of [Ru(bpy)2PDo2T5-P,S](PF6)2 (8, top) and [Ru(bpy)2PDo2T5-P,C]PF6 (9, middle). Addition of HPF6 (concd) to a solution of
9 results in reversion to [Ru(bpy)2PDo2T5-P,S](PF6)2 (bottom) as is observed by the reappearance of the peak at δ 27.7 and a dramatic color change from
deep red to bright orange.
Scheme 4
Table 3. Cyclic Voltammetry Dataa
compound
E1
/
±
0.01 V
E1
/
± 0.01 V
2,red
2,ox
[Ru(bpy)2PT3-P,S]2+ (1)
+1.48b (RuII/III
+1.44b (RuII/III
)
)
-1.28b (bpy0/-
-1.24 (bpy0/-
-1.46 (bpy-/2-
)
[Ru(bpy)2PMeT3-P,S]2+ (2)
)
)
0/-
-1.79 (PMeT3
)
Cyclic voltammetry was performed on PDo2T5 (7), complexes
[Ru(bpy)2PMe2T3-P,S]2+ (3) +1.41(sh)b,d (RuII/III
+1.69(sh)b,d (PMe2T3
)
-1.24 (bpy0/-
-1.46 (bpy-/2-
-1.81 (PMe2T3
)
[Ru(bpy)2PDo2T5-P,S](PF6)2 (8) and [Ru(bpy)2PDo2T5-P,C]PF6
(9), and Do2T5 (10). Two irreversible oxidation waves are
observed for 7 that are more positive than the first and second
0/+
)
)
0/-
)
[Ru(bpy)2PT3-P,C]+ (4)
+0.57 (RuII/III
)
-1.53 (bpy0/-
)
+1.11 (PT3
)
)
-1.78 (bpy-/2-
-1.54 (bpy0/-
-1.78 (bpy-/2-
-1.55 (bpy0/-
-1.78 (bpy-/2-
)
0/+
[Ru(bpy)2PMeT3-P,C]+ (5)
+0.51 (RuII/III
)
0/+
+1.04 (PMeT3
)
)
)
[Ru(bpy)2PMe2T3-P,C]+ (6) +0.49 (RuII/III
)
)
0/+
+0.96 (PMe2T3
)
0/+
PDo2T5 (7)
+0.99 (PDo2T5
+1.37b (PDo2T5
)
+/2+
)
[Ru(bpy)2PDo2T5-P,S]2+ (8) +1.21b (RuII/III
)
-1.22 (bpy0/-
-1.36 (bpy-/2-
-1.52 (bpy0/-
-1.83 (bpy-/2-
)
+1.71(sh)b,d (PDo2T5
)
)
)
0/+
[Ru(bpy)2PDo2T5-P,C]+ (9) +0.49 (RuII/III
)
+0.80 (PDo2T5
+1.46 (PDo2T5
)
0/+
)
+/2+
)
Do2T5 (10)c
+0.82 (Do2T5
+1.07 (Do2T5
)
0/+
+/2+
)
a Measurements carried out in CH3CN/0.1 M [(n-Bu)4N]PF6 solution with
a Pt working electrode, Pt counter electrode, and a Ag wire quasi reference
at 20 °C. Potentials are referenced to a decamethylferrocene standard and
reported in volts vs SCE. b Irreversible wave, Ep. c CH2Cl2/0.1 M [(n-
Bu)4N]PF6 solution. d sh ) shoulder.
reversible oxidations of 10 (Table 3). The oxidation waves of
7 are likely pentathiophene-based processes, since phosphine
oxidation is expected at ∼2 V when compared with triph-
enylphosphine and are in similar positions compared to 10.
Interaction of the oxidized terthienyl group with the phosphino
group may contribute to the observed irreversibility. The cyclic
voltammogram of 8 (Figure 5c) shows lower ruthenium and
thienyl oxidation potentials compared with 1-3. Reduction of
8 shows a wave at -1.22 V that is slightly higher than for 2
and 3 and is most likely a bipyridyl reduction. The second quasi-
reversible reduction (-1.36 V) is at a potential higher than
would be expected for the second bipyridyl reduction compared
to 2 and 3 and may be thienyl-based. The pentathienyl group
has a greater ability to accept an electron due to the increased
Figure 5. Cyclic voltammetry of (a) 1-3 (b) 4-6, and (c) 8-9 in
CH3CN containing 0.1 M [(n-Bu)4N]PF6, scan rate ) 100 mV/s. All
complexes are PF6 salts at 4.0 × 10-3 M concentrations.
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J. AM. CHEM. SOC. VOL. 127, NO. 17, 2005 6387

A R T I C L E S
Moorlag et al.
increased π-orbital overlap related to stacking interactions
observed in the crystal structures. Overall, smaller red-shifts
are observed for 8; the presence of the long dodecyl groups
may result in a disordered solid state upon drop casting.
Conversion from the P,S complexes to P,C complexes 4-6
and 9 alters the UV-vis spectra with an accompanying color
change from bright yellow or orange to deep brown or red
(Figure 6b). For 4-6, there is an approximately 30-nm red-
shift for the terthienyl π f π* transitions compared to 1-3.
Additionally, the MLCT transitions red-shift 56-63 nm, and
weak “spin-forbidden” MLCT transitions54-58 are observed as
shoulders at 617-633 nm. Switching from P,S to P,C bonding
does not affect the transitions as strongly in the UV-vis spectra
of the pentathienyl complexes as for the terthienyl complexes.
The primary MLCT peak red-shifts only 20 nm from 8 to 9,
and the pentathienyl π f π* transition shifts from 371 nm for
8 to a broad peak at 360 nm with a shoulder at 380 nm for 9.
This fine structure could correspond to conformations of the
pentathienyl group that are unable to interconvert rapidly in
solution due to the constrained nature of the bonding to
ruthenium. This is supported by the observation that the polarity
of the solvent affects the relative intensities of these peaks; the
peak at 360 nm is more intense in CH2Cl2, while the peak at
380 nm is prominent in CH3CN. Calculations have been reported
that predict the ground state of the pentathienyl group is twisted
while the excited state is planar (quinoidal); therefore, multiple
ground state conformations would result in different π f π*
transition energies.51 There is also a weak spin-forbidden MLCT
transition observed as a shoulder at 615 nm, as was observed
for 4-6. The bpy π f π* transitions of 4-6 and 9 at 295 nm
are red-shifted from the corresponding P,S complexes.
Figure 6. UV-vis spectra of (a) P,S complexes 1, 2, 3, and 8 and (b) P,C
complexes 4, 5, 6, and 9. All complexes are PF6 salts.
conjugation length compared to 2 and 3. The sharp return peak
for 8 indicates a fast process which is characteristic of desorption
from the electrode surface. Switching from P,S to P,C bonding
(9) decreases the ruthenium oxidation potential from 1.21 to
0.49 V and significantly lowers the pentathienyl oxidation
potentials to 0.80 and 1.46 V. The first thienyl oxidation is at
a potential similar to that for 10 (0.82 V), while the second
thienyl oxidation is at a potential higher than that for 7 or 10,
but corresponds with the removal of a third electron from the
complex. The new wave observed with repeat scans of 9 (0.94
V), similar to that for 4 and 5, is likely oxidative coupling of
the pentathienyl group. Quasireversible (-1.52 V) and irrevers-
ible (-1.83 V) reductions are observed that are similar in
potential to the bipyridyl reductions observed for 4-6.
UV-Visible Spectroscopy. The UV-vis spectra of the P,S
bound complexes 1-3 and 8 are shown in Figure 6a. Bipyridyl
π f π* transitions occur between 280 and 282 nm (Table 4).
Terthienyl π f π* transitions are observed as shoulders at ∼320
nm for 1-3. In comparison, the pentathienyl transition is
significantly shifted to 371 nm for 8, though blue-shifted
compared with 7 (406 nm) and 10 (407 nm). Phenyl π f π*
transitions are also expected at around 320 nm and are likely
obscured for 1-3. The 323-nm shoulder observed for 8 is in a
position similar to the 340-nm phenyl transition observed for
PDo2T5 (7). The Ru d f bpy π* MLCT transition shifts
dramatically with extension of the oligothiophene, from ∼400
nm for 1-3 to 465 nm for 8. These data can be linearly
correlated to the electrochemistry data by plotting the MLCT
energy converted to electronvolts (Eop) versus the difference in
potential between the one-electron first oxidation wave of
ruthenium and the one-electron reduction potential of the
bipyridyl group (∆E), further substantiating the assignments of
the ruthenium oxidation potentials, the bipyridyl first reduction
potentials, and the MLCT transitions (Figure S1a).
There is a linear correlation between the MLCT energies and
the ruthenium oxidation and bipyridyl reduction potentials ob-
tained from cyclic voltammetry for 4-6 (Figure S1b). Complex
9 displays a large red-shift in the MLCT compared with 4-6
but does not show a significant decrease in the oxidation
potential of the ruthenium center. This results in a nonlinear
correlation between Eop and ∆E for 9 compared to 4-6.
Correlations of this type are generally valid when charge transfer
occurs by a very similar process for complexes in a series, which
is evidently not the case for 9, and could differ due to lower
vibrational (øi) or solvation (øo) reorganizational energies.59
Compared to the solution spectra, the solid-state UV-vis
spectra of P,C complexes 4-6 and 9 display red-shifts for the
bipyridyl (9-20 nm), MLCT (13-26 nm), and thienyl (13-28
nm) transitions that could be due to intramolecular stacking
interactions observed in the crystal structures of 4 and 6 (Figure
S2). Broader bands are observed that may be due to different
equilibrium geometries of the excited states compared to the
ground states.59
Luminescence Spectroscopy. Excitation of the thienyl π f
π* transition of PDo2T5 (7) and Do2T5 (10) produces emission
(Table 4) that is slightly red-shifted from that reported for T5
(54) Lytle, F. E.; Hercules, D. M. J. Am. Chem. Soc. 1969, 91, 253-257.
(55) Felix, F.; Ferguson, J.; Guedel, H. U.; Ludi, A. Chem. Phys. Lett. 1979,
62, 153-157.
Solid-state UV-vis spectra of 1-3 and 8 were also obtained
(Figure S2). MLCT transitions red-shift 19-26 nm for 1-3 and
12 nm for 8 compared with solution spectra. Thienyl π f π*
transitions red-shift 6-10 nm, while the bipyridine π f π*
transition remains in the same position for 8, but red-shifts ∼20
nm for 1-3. Red-shifts in the UV-vis spectra may be due to
(56) Felix, F.; Ferguson, J.; Guedel, H. U.; Ludi, A. J. Am. Chem. Soc. 1980,
102, 4096-102.
(57) Caspar, J. V.; Meyer, T. J. Inorg. Chem. 1983, 22, 2444-2453.
(58) Mamo, A.; Stefio, I.; Poggi, A.; Tringali, C.; Di Pietro, C.; Campagna, S.
New J. Chem. 1997, 21, 1173-1185.
(59) Dodsworth, E. S.; Lever, A. B. P. Chem. Phys. Lett. 1986, 124, 152-158.
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Molecular Switching of Ru Bis(bipyridyl) Groups
A R T I C L E S
Table 4. UV-Vis and Luminescence Data
UV
−
visa
104) M-1 cm-
luminescenceb
max, nm
1
compound
λ
max, nm [(ꢀ ± 0.01
×
]
λ
[Ru(bpy)2PT3-P,S]2+ (1)
280 (3.79 × 104), 320 (sh)e (1.83 × 104),
-
-
-
393 (1.80 × 104)
[Ru(bpy)2PMeT3-P,S]2+ (2)
[Ru(bpy)2PMe2T3-P,S]2+ (3)
[Ru(bpy)2PT3-P,C]+ (4)
[Ru(bpy)2PMeT3-P,C]+ (5)
[Ru(bpy)2PMe2T3-P,C]+ (6)
PDo2T5 (7)
282 (3.91 × 104), 320 (sh)e (1.97 × 104),
396 (1.89 × 104)
282 (4.01 × 104), 320 (sh)e (2.11 × 104),
404 (1.95 × 104)
295 (4.63 × 104), 347 (2.00 × 104),
456 (1.84 × 104), 617 (sh)e (2.25 × 103)
295 (4.72 × 104), 350 (1.91 × 104),
459 (2.03 × 104), 628 (sh)e (2.20 × 103)
295 (4.64 × 104), 351 (1.97 × 104),
460 (2.07 × 104), 633 (sh)e (2.10 × 103)
251 (2.13 × 104), 340 (sh)e (1.47 × 104),
406 (3.36 × 104)
754 (τ ) 22 ( 2 ns)c
763
772
499, 528
[Ru(bpy)2PDo2T5-P,S]2+ (8)
[Ru(bpy)2PDo2T5-P,C]+ (9)
280 (4.27 × 104), 323 (sh)e (2.24 × 104),
371 (2.07 × 104), 465 (2.68 ×104)
295 (5.24 × 104), 360 (2.63 × 104),
380 (sh)e (2.59 × 104), 485 (3.15 × 104),
615 (sh)e (2.62 × 103)
602 (τ < 10 ns)d
-
Do2T5 (10)
252 (1.27 × 104), 407 (3.27 × 104)
487, 516
a Measurements carried out in CH2Cl2 solution. b Degassed CH3CN solution. c Lifetime determined from emission at 750 nm. d Lifetime determined from
emission at 600 nm. e sh ) shoulder.
Figure 7. Emission and excitation spectra of (a) 8 and (b) P,C complexes 4 (λex ) 456 nm, λem ) 748 nm), 5 (λex ) 459 nm, λem ) 751 nm), and 6 (λex
) 460 nm, λem ) 761 nm) in deaerated CH3CN. The inset shows emission where λex ) 616 nm for 4 and 5, and λex ) 620 nm for 6. All solutions abs )
0.1 at the excitation wavelength and the solvent spectra have been subtracted for clarity.
(482, 514 nm, φ ) 0.54).60 The approximate quantum yields of
the emission from 7 and 10 are 0.093 and 0.16, respectively,
measured by comparison to T3 in CH3CN (φ ) 0.056).51
Complexation of the oligothienyl groups to Ru(bpy)2 quenches
the thienyl-based fluorescence. Luminescence, which is gener-
ally observed from the MLCT excited state for complexes
containing the Ru(bpy)2 fragment, is quenched for 1-3, possibly
due to thermal population of a low-lying nonemissive energy
level (vide infra). The very weak luminescence from the MLCT
state of 8 at 602 nm (approximate quantum yield of 0.01%) is
shown in Figure 7a. The luminescence lifetime of 8 was
measured at 600 nm; however, the lifetime was shorter than
the lower limit measurable with the instrumentation used. Thus,
the lifetime of 8 is less than 10 ns. The short emission lifetime
compared with [Ru(bpy)3]2+ (τ ) 870 ns) and other [Ru(bpy)2-
(LL)]2+ complexes39 and the low quantum yield support the
conclusion that either significant thermal population of a low-
lying, nonemissive d-d state is occurring or vibrational
relaxation pathways are competitive with emission from the
MLCT state. When the bonding mode is switched from P,S to
P,C, there are changes in the luminescence that are related to
shifting of the MLCT levels. Complexes 4-6 have a low-lying
MLCT level available and display low-energy emission at 754-
772 nm. Approximate quantum yields are ∼0.001% and
decrease in intensity with the addition of methyl substituents
(Figure 7b). The emission lifetime of 4 was measured at 750
nm and was determined to be 22 ( 2 ns (Figure S4a). A short-
lived (<10 ns, Figure S4a) species was observed for 4 that emits
below 620 nm (Figure S4b). This emission decays within the
laser pulse and is much shorter lived than the emission at 750
nm; it is likely due to the formation of a decomposition product
(vide infra). [Ru(bpy)2PDo2T5-P,C]PF6 (9) does not display any
observable emission, which, combined with the decrease in
intensity with the addition of methyl substituents, indicates that
there is increased deactivation of the excited state with an
increase in vibrational modes.
Earlier, emission at ∼450 nm for 1, 3, 4, and 6 was reported.26
We have now determined that higher energy emission is
(60) Fichou, D. Handbook of Oligo- and Polythiophenes; Wiley-VCH: Wein-
heim, Germany, 1999.
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A R T I C L E S
Moorlag et al.
observed as a result of small amounts of side product that form
in solution and exhibit more intense ligand-like emission. These
side products form more rapidly in chlorinated solvents such
as CHCl3 or CH2Cl2 than in CH3CN or acetone. Since the
MLCT states are expected to be the lowest energy states,21 the
appearance of higher-energy emission suggests that the ligand
detaches from the metal. Complex 8 displays a new lumines-
cence band at 514 nm shortly after dissolution in CH3CN (Figure
S5), and the excitation and emission spectra and higher intensity
of this new luminescence match those of PDo2T5 (7). The side
products appear to form in very small concentrations and are
not easily observed by techniques other than emission measure-
ments or at higher concentrations in solution. The side product
is not observed for 8 at higher concentrations (∼25 mM) by
31P NMR spectroscopy; after 11 days in CO(CD3)2, there are
no new peaks in the spectrum. Complex 9 shows greater
instability in solution compared to 8, and the 31P NMR in CO-
(CD3)2 shows a minor peak at δ 41.2 after 1 h in CO(CD3)2
and multiple minor peaks are formed after 24 h. Similar re-
sults were observed for the terthienyl complexes, though side
products form less rapidly. 31P NMR experiments show that
the side products formed by the P,S or P,C complexes in solu-
tion disappear with the addition of concentrated acid, to re-
form only the P,S complex. These experiments suggest that
there is an equilibrium between the complexes and the side
products.
also removes sufficient electron density to increase the terthienyl
reduction potentials of 2 and 3, shown by the reversible third
reduction waves observed at -1.79 and -1.81 V. The Ru-S
bond length of the P,S complexes can be correlated to the
availability of electron density in the oligothienyl rings; 3 and
8 show 0.0019 and 0.0043 Å reductions, respectively, in the
Ru-S bond lengths compared to 1.
When the complexes are switched to the P,C bonding mode,
a forced π-antibonding orbital overlap between ruthenium and
the bound thienyl rings is indicated in the solid-state structures
of 4 and 6. The hybridization at the bound carbon does not
allow significant deviation from a trigonal arrangement; there-
fore, there is only a 9-10° tilting of the bound ring and 0.033-
0.042 Å elongation of the C35-C36 bonds of 4 and 6 compared
to 1 and 3. While there is clearly a disruption of conjugation
around the bound thienyl rings, there are marked increases in
coplanarity of the three thienyl rings when 1 and 3 are converted
to 4 and 6. The P,C complexes are also electron-rich as a result
of the loss of a proton during the cyclometalation reaction, and
the overall charge of the complexes is +1 rather than +2. This
is reflected by the 0.7-0.9 V decrease in the thienyl oxidation
potentials compared to the P,S complexes to yield oxidations
at 1.11, 1.04, 0.96, and 0.80 V for 4-6 and 9, respectively.
Overall, the thienyl ligands of 4-6 are more electron-rich and
more coplanar than those in 1-3, resulting in ∼30-nm red-
shifts of the thienyl π f π* transitions.
The two thienyl π f π* transitions at 360 and 380 nm that
are observed for 9 are not significantly removed from the
transition for 8 (371 nm), and both transitions are still blue-
shifted from 7 (406 nm). Pentathiophenes do not normally show
conformational structure in solution, but it is observed at low
temperature,51 and the P,C bonding mode may result in a barrier
to interconversion between two conformers. The presence of a
conformer of 9 that is blue-shifted from 8 indicates poor
π-overlap of the orbitals and a less planar structure, though the
orientation of the rings is unknown since a solid-state structure
for 9 could not be obtained. Interconversion between two
conformers that could be present would still be relatively fast
since only single peaks are observed by 31P NMR spectroscopy
and cyclic voltammetry at room temperature. It has been
established that for both bonding modes, complexation of the
metal affects the conjugation of the thienyl rings and related
properties but does not remove the ring from π-conjugation with
the unbound rings, as has been observed for other metal-bound
thienyl systems.61
It is evident that the C-H bond cleavage that occurs during
the cyclometalation reaction involves the ruthenium center.
Formally, the cyclometalation reaction is a deprotonation, and
reversion to a P,S complex is protonation; however, oligoth-
iophenes are not normally deprotonated by NaOH. Mo/Co
catalysts are known to promote dehydrosulfurization of thienyl
rings, and activation of C-H bonds on thienyl rings has been
reported for Ru, Re, and Rh complexes.33,34,62,63 In these studies,
migration of a metal from sulfur to carbon on the ring is
observed, and the suggested mechanism of C-H activation via
the formation of a η2-coordinated intermediate is supported. In
the presence of base, the metal may migrate to the inner C-C
Discussion
The elongated lengths (0.011-0.043 Å) of the S-C bonds
of the bound thienyl ring in the solid-state structures of P,S
complexes 1, 3, and 8 relative to calculated bond lengths of
terthiophene42 indicate that the sulfur atom is partially or fully
removed from conjugation, as expected due to sp3 hybridization
of a thienyl sulfur bound to a metal. Bond length changes of
the C-C bonds in the bound ring are <0.01 Å; therefore,
complexation of the thienyl sulfur would not be expected to
interrupt conjugation across all of the rings. Despite the large
tilt angles (53.7-58.4°) observed for the P,S complexes and
the preferred orientation of the bound thienyl rings coinciding
with intramolecular π-stacking between the phenyl and thienyl
rings, both torsion angles between the adjacent rings of 1 are
close in value to that of terthiophene (147.6°).42 Complex 3
has a more coplanar conformation, which would be expected
as a result of electron donation by the methyl substituents. The
torsion angle between the bound rings of 8 is equivalent to that
of terthiophene, while the exterior rings align cis and trans and
with multiple conformations, similar to T5.51 These results
suggest that the alterations of properties of the oligothienyl
groups upon P,S complexation with Ru(bpy)2 are mainly
electronic in nature rather than steric.
A decrease in electron density across the rings is indicated
by a ∼35 nm blue-shift of the thienyl π f π* transitions of
1-3 and 8 compared to the terthienyl ligands28 and 7, and is
likely due to a combination of decreased electron density at
the ring coordinated to a RuII center and possibly near the
complexed phosphino group. Removal of electron density from
the thienyl rings is consistent with thienyl oxidation waves
(>1.69 V) that are substantially higher in potential compared
with the terthienyl ligands (1.05-1.30 V)28 or 7 (0.99 V), and
which would contribute to larger thienyl π f π* energy gaps,
as observed in the UV-vis spectra. Complexation to Ru(bpy)2
(61) Graf, D. D.; Mann, K. R. Inorg. Chem. 1997, 36, 150-157.
(62) Dong, L.; Duckett, S. B.; Ohman, K. F.; Jones, W. D. J. Am. Chem. Soc.
1992, 114, 151-160.
(63) Angelici, R. J. Organometallics 2001, 20, 1259-1275.
9
6390 J. AM. CHEM. SOC. VOL. 127, NO. 17, 2005

Molecular Switching of Ru Bis(bipyridyl) Groups
A R T I C L E S
double bond in the P,S complexes, and the removal of electron
density from the ring is expected to promote deprotonation,
providing a site on the thienyl ring for carbon-metal bonding.
The thienyl groups bound in different modes also affect the
properties of the attached Ru(bpy)2 group. Compared to the
oxidation potential of [Ru(bpy)3]2+ (1.01 V versus SCE),39
oxidation potentials are >0.40 V higher for the P,S complexes,
which suggests poor electron donation from a thienyl sulfur and
phosphine compared to a pyridine ring. The MLCT absorptions
are also blue-shifted 50 nm compared to [Ru(bpy)3]2+ (452
nm),39 which is consistent with phosphine coordination desta-
bilizing the MLCT state to a greater extent than for pyridine
coordination, as has been reported,57 while the effect of
coordination of the thienyl sulfur on the MLCT state is
unknown. The 0.72-0.92 V decrease in the ruthenium oxidation
potentials when the bonding is switched from P,S to P,C reflects
the substantial increase in electron donation from the thienyl
carbon. Lower oxidation potentials have been observed for other
cyclometalated Ru complexes.38,64 The effect of switching on
the bipyridyl reduction potentials is only a 0.20-0.32 V decrease
and a 13-nm red-shift of the π f π* transition. Since the
bonding mode more strongly affects the ruthenium oxidation
potential, there is a contraction of the energy differences between
the ruthenium oxidation and the first bipyridyl reduction, which
are known to correlate to the MLCT transitions of [Ru(bpy)3]2+
complexes.59,65 The lowering of the RuII oxidation potentials
results in 56-63-nm red-shifts in the MLCT for 4-6, and a
20-nm red-shift for 9. The low energy band that is observed
for the P,C complexes is a transition to a low-lying state that is
mostly triplet in character. Transition to a low-lying “forbidden”
level is observed as a relatively strong transition in osmium
polypyridine complexes57,58,66 due to spin-orbit coupling,54,67,68
and as a much weaker transition in [Ru(bpy)3]2+ 54-56 and some
[Ru(bpy)2(LL)]2+ complexes.57,58 This transition, due to its very
weak intensity, is often covered by superimposed, allowed
MLCT transitions that are much stronger in intensity. The weak,
low-lying state is likely underneath the symmetry-allowed
MLCT transitions for the P,S complexes; therefore, at wave-
lengths <550 nm. In the P,C bonding mode, this transition is
dramatically shifted to longer wavelengths to form a broad
shoulder observed for all P,C complexes, extending to 700 nm
and covering the visible range, similar to Ru(bpy)2L2 complexes
that have been synthesized as black absorbers for possible
applications in photovoltaic cells.69,70 The anionic character of
the cyclometalated oligothienyl ligands stabilizes the excited
states by electron donation to RuIII to shift the bands, which
has also been observed in Ru/Os polypyridine complexes.58,66
The overall effect of stabilizing the RuIII excited state, a
reduction in the MLCT absorption energy, is the same as
incorporating a bpy-type acceptor ligand.71
with spin-orbit coupling mixing the singlet and triplet
states.21,57,66,72 It was found that P,S complexes 1-3 do not emit;
therefore, the MLCT-based luminescence is quenched. This
quenching of the MLCT emission is observed in systems
containing phosphines due to destabilization of the MLCT state
without destabilization of a low-lying, metal-centered dd
state.57,65 This results in a low barrier for energy transfer to the
nonemissive dd state and a major deactivation route at room
temperature. Weak emission is observed at 602 nm for the P,S
pentathienyl complex 8 that is expected to have a stabilized
MLCT* state according to the red-shifted transition energy;
therefore, there may be a higher barrier to the dd state compared
with 1-3. A low-lying, ligand-based triplet state has been
observed in other thienyl/Ru(bpy)2 systems,21 resulting in a
weakly emitting MLCT state with a characteristically longer
lifetime; however, the observation of a substantially shorter
lifetime (<10 ns) for 8 than is normally observed for Ru(bpy)2
complexes is in accordance with the presence of an accessible
nonemissive dd state. For the P,C complexes, very weak
luminescence that approaches the near-infrared region (754-
772 nm) is observed for 4-6 but not for 9. The emission is
from a “forbidden” MLCT state that should be low enough in
energy to create a barrier to a low-lying dd level. Lowering of
the MLCT state when switching to the P,C bonding mode is
due to the formation of a more electron-rich complex, which
has been observed to promote luminescence in another Ru-
(bpy)2L2 switchable system.73 The reduction in intensity of
emission from 4 to 6 and the absence of emission for 9 are
likely due to competing nonradiative relaxation that increases
with increasing vibrational modes introduced by the addition
of alkyl substituents to the ligands and is in accordance with
the energy gap law.74,75 The short 22 ( 2 ns lifetime observed
for the emission of 4 is also in agreement with the presence of
competing deactivation pathways. The complexes display P,S
-ON, P,C -OFF emission behavior for the pentathienyl
complexes 8 and 9, respectively, and P,S -OFF, P,C- ON
emission behavior for the terthienyl complexes 1-3 and 4-6,
respectively.
Crystalline and drop-cast solid-state samples of P,S and P,C
complexes display stability in air and under UV and visible light.
There may be contributions from the intra- and intermolecular
π-stacking of the bpy, phenyl, and thienyl rings toward the
stability of the complexes. Bound Ru(bpy)2 groups could be
used to dope the thienyl chains via the Ru f bpy MLCT,
provided there was effective overlap of the ruthenium and
thienyl oxidation potentials, and we are currently investigating
this approach. Additionally, π-stacking of the terthienyl com-
plexes between thienyl rings potentially would increase con-
ductivity of an oxidatively doped oligomeric solid. Complexes
containing longer oligothiophene chains or polythiophene would
improve the processibility and flexibility of these materials, and
disordered systems would also create materials with new
properties.
It is generally accepted that, in Ru(bpy)2L2, Os(bpy)2L2 and
related complexes, absorption is primarily to a singlet-based
MLCT state and emission is from a triplet-based MLCT state,
(64) Beley, M.; Collin, J. P.; Louis, R.; Metz, B.; Sauvage, J. P. J. Am. Chem.
Soc. 1991, 113, 8521-8522.
(70) Anderson, P. A.; Keene, F. R.; Meyer, T. J.; Moss, J. A.; Strouse, G. F.;
Treadway, J. A. J. Chem. Soc., Dalton Trans. 2002, 3820-3831.
(71) Rillema, D. P.; Mack, K. B. Inorg. Chem. 1982, 21, 3849-3854.
(72) Kober, E. M.; Sullivan, B. P.; Meyer, T. J. Inorg. Chem. 1984, 23, 2098-
2104.
(73) Wang, K.-Z.; Gao, L.-H.; Bai, G.-Y.; Jin, L.-P. Inorg. Chem. Commun.
2002, 5, 841-843.
(74) Caspar, J. V.; Meyer, T. J. J. Am. Chem. Soc. 1983, 105, 5583-5590.
(75) Caspar, J. V.; Meyer, T. J. J. Phys. Chem. 1983, 87, 952-957.
(65) Sullivan, B. P.; Salmon, D. J.; Meyer, T. J. Inorg. Chem. 1978, 17, 3334-
3341.
(66) Mamo, A.; Juris, A.; Calogero, G.; Campagna, S. Chem. Commun. 1996,
1225-1226.
(67) Kober, E. M.; Meyer, T. J. Inorg. Chem. 1984, 23, 3877-3886.
(68) Kober, E. M.; Meyer, T. J. Inorg. Chem. 1983, 22, 1614-1616.
(69) Anderson, P. A.; Strouse, G. F.; Treadway, J. A.; Keene, F. R.; Meyer, T.
J. Inorg. Chem. 1994, 33, 3863-3864.
9
J. AM. CHEM. SOC. VOL. 127, NO. 17, 2005 6391

A R T I C L E S
Moorlag et al.
electrode. Either decamethylferrocene or ferrocene was used as an
internal reference to correct the measured potentials with respect to
saturated calomel electrode (SCE). The supporting electrolyte was 0.1
M [(n-Bu)4N]PF6 that was purified by recrystallizing three times from
ethanol and drying for 3 days at 90 °C under vacuum. Lifetime
measurements were obtained by exciting samples at 480 nm in 7 × 7
mm Suprasil cells at 20 ( 2 °C with a Coherent Infinity OPO tunable
laser, using the laser flash photolysis system previously described.76
Deoxygenated samples were dissolved in acetonitrile to achieve
absorbances between 0.3 and 0.5 (l ) 7 mm) at 480 nm. Emission
decays were measured at fixed wavelengths, averaging at least 5 kinetic
traces, and emission spectra were obtained by collecting data at fixed
wavelengths and averaging the values between set time windows after
the laser pulse. The voltage on the photomultiplier used to detect the
emission signal was kept constant throughout the collection of a
spectrum.
Conclusions
The effect of the two bonding modes, P,S and P,C, on the
electrochemical and spectroscopic properties of oligothiophenes
has been examined. The P,S coordinated complexes exhibit
properties different from those of the thienyl ligands, indicated
by a blue-shift in the thienyl absorption bands, as well as large
increases in oxidation potentials. Switching to the P,C bonding
mode lowers the thienyl oxidation potentials to less than those
in the corresponding ligands. Because of a combination of a
more electron-rich system and increased planarity of the thienyl
chains with P,C bonding, there are large red-shifts observed
for the terthienyl π f π* transitions compared to the P,S
complexes. There is a smaller red-shift for the pentathienyl π
f π* transition with switching from P,S to P,C bonding that
indicates a difference in the conformation of the P,C bound
pentathienyl group compared to the P,C bound terthienyl groups,
which could be due to steric interaction between the two external
rings or the dodecyl substituents. All of the P,C bound
complexes can be reverted to the P,S bound form by the addition
of acid; therefore, the two bonding modes are reversibly
switchable. The Ru f bpy MLCT emission observed from these
complexes is too weak for most applications; however, the
results demonstrate how switching the binding mode affects the
observation of luminescence from the MLCT level, and for the
P,C bound complexes, the luminescence emission wavelengths
can be pushed to the near-IR region. Compared to the oligoth-
ienyl ligands, the electrochemical and photophysical properties
of the P,S complexes are primarily influenced by electronic
interactions, while the properties observed for the P,C complexes
are due to both electronic interactions and steric effects. In
metal-thienyl systems, oxidation or ligand exchange at the
metal is used to affect the properties of the complexed oligo-
or polythiophene; however, we have found that switching of
the binding mode provides an effective handle to substantially
alter the electrochemical and the photophysical properties of
the thienyl chain. Solid-state films of these complexes would
have potential as conductors, with the advantageous ability to
affect the properties of the thienyl groups through interaction
with the metal. Results encourage further investigation of the
effect of direct coordination of metals to an oligothiophene or
polythiophene backbone on the electronic properties.
[Ru(bpy)2PMeT3-P,S](PF6)2 (2). AgBF4 (230 mg, 1.15 mmol) was
added to a deaerated solution of Ru(bpy)2Cl2‚2H2O (300 mg, 0.576
mmol) in acetone (30 mL), stirred for 6 h, and filtered under nitrogen.
To the red filtrate 3′-(diphenylphosphino)-5-methyl-2,2′:5′,2′′-ter-
thiophene (PMeT3) (272 mg, 0.610 mmol) was added, and the mixture
was heated to reflux for 18 h. The resulting solution was concentrated
to 10 mL and precipitated by addition to a solution of NH4PF6 (1.89 g,
11.6 mmol) in 100 mL of H2O. Recrystallization in 9:1 ethanol-acetone
gave 2 as bright, pale orange crystals. Yield: 0.340 g (51%). 1H NMR
(300.1 MHz, CO(CD3)2): δ 9.13 (d, J ) 5.7 Hz, 1H), 8.89 (d, J ) 5.2
Hz, 1H), 8.78 (d, J ) 8.2 Hz, 1H), 8.69 (d, J ) 7.5 Hz, 1H), 8.68 (d,
J ) 8.1 Hz, 1H), 8.60 (d, J ) 8.2 Hz, 1H), 8.28-8.22 (m, 3H), 8.09
(t, J ) 8.0 Hz, 1H), 7.96 (d, J ) 5.7 Hz, 1H), 7.83-7.81 (m, 1H),
7.69 (t, J ) 6.9 Hz, 1H), 7.63-7.55 (m, 3H), 7.50 (d, J ) 5.0 Hz,
2H), 7.45-7.32 (m, 6H), 7.22-7.16 (m, 3H), 708 (dd, J ) 4.8 Hz, J
) 3.9 Hz, 1H), 6.95-6.88 (m, 3H), 6.78-6.77 (m, 1H), 1.48 (s, 3H).
31P{1H} NMR (121.5 MHz, CO(CD3)2): δ 28.5 (s), -143.0 (septet,
JPF ) 708 Hz, PF6). Anal. C45H35F12N4S3P3Ru requires C, 47.00; H,
3.07. Found: C, 46.60; H, 3.05%.
[Ru(bpy)2PMeT3-P,C]PF6 (5). NaOH (0.72 g, 18 mmol) was
dissolved in deaerated methanol (18 mL) to give a 1.0 M solution. 2
(0.600 g, 0.521 mmol) was dissolved into the solution and stirred at
reflux for 18 h. A color change from yellow to dark brown was
observed. The solution was then cooled to room temperature, concen-
trated to 10 mL, and pipetted dropwise into a solution of NH4PF6 (1.70
g, 10.4 mmol) in H2O (90 mL) to form a brownish-black precipitate.
The precipitate was isolated by filtration, washed with water (10 mL)
and then ether (15 mL), and recrystallized in 9:1 ethanol-acetone to
give 5 as black, shiny crystals. Yield: 0.376 g (72%). 1H NMR (400.1
MHz, CO(CD3)2): δ 8.85 (m, 1H), 8.56-8.49 (m, 2H), 8.42-8.38 (m,
3H), 8.03 (m, 1H), 7.92 (m, 2H), 7.83 (m, 2H), 7.6-7.61 (m, 3H),
7.41 (m, 5H), 7.32 (m, 1H), 7.24 (m, 1H), 7.12 (m, 2H), 7.02 (m, 1H),
6.89 (m, 3H), 6.61 (m, 1H), 6.49 (m, 2H), 6.06 (m, 1H) 2.16 (s, 3H).
31P{1H} NMR (162.0 MHz, CO(CD3)2): δ 44.9 (s), -143.0 (septet,
JPF ) 708 Hz, PF6). Anal. C49H34F6N4S3P2Ru requires C, 53.83; H,
3.41. Found: C, 54.04; H, 3.49%.
Experimental Section
General. All reactions were performed using standard Schlenk
techniques with dry solvents under nitrogen. PT3, PMeT3, and PMe2T3
were prepared according to published procedures,28 as were [Ru-
(bpy)2PT3-P,S](PF6)2 (1) and [Ru(bpy)2PMe2T3-P,S](PF6)2 (3).26 Previ-
ously reported complexes [Ru(bpy)2PT3-P,C]PF6 (4) and [Ru(bpy)2-
PMe2T3-P,C]PF6 (6)26 have been prepared by the revised procedure
used to prepare [Ru(bpy)2PMeT3-P,C]PF6 (5) with improved yields
(50-85%). All other reagents were purchased from Aldrich or Strem
Chemicals. N,N′-Dimethylethylenediamine, bis-2-methoxyethyl ether,
and xylenes were distilled before use. All other reagents were used as
3′′-Bromo-3,3′′′′-didodecyl-2,2′:5′,2′′:5′′,2′′′:5′′′,2′′′′-pen-
tathiophene (BrDo2T5). Mg (1.36 g, 56 mmol) and I2 (5 mg, 0.02
mmol) were brought to reflux in 60 mL of THF, and 2-bromo-3-
dodecylthiophene (9.29 g, 28 mmol) dissolved in THF (10 mL) was
slowly added by syringe. The green-brown mixture was heated at reflux
for 2 h and allowed to cool. The Grignard solution was then slowly
added by cannula to a condenser-fitted flask containing 5,3′,5′′-tribromo-
2,2′:5′,2′′-terthiophene (6.79 g, 14 mmol), Pd(dppf)Cl2‚CH2Cl2 (300
mg, 0.367 mmol), diethyl ether (80 mL), and toluene (60 mL). The
yellow-brown solution was heated at reflux for 16 h and then quenched
with saturated aq. NH4Cl and stirred for 1 h. The crude product was
extracted with CH2Cl2 and washed with saturated NaHCO3 once and
1
received. H and 31P NMR experiments were performed on either a
Bruker AV-300 or a Bruker AV-400 Spectrometer, and spectra were
referenced to residual solvent (1H) or external 85% H3PO4 (31P). UV-
visible spectra were obtained on a Cary 5000 in HPLC grade CH2Cl2.
Emission spectra were obtained on a Cary Eclipse in HPLC grade CH2-
Cl2 or CH3CN, and emission slits were opened to 20 nm for
measurement of metal complexes. Cyclic voltammetry experiments were
carried out on a Pine AFCBP1 bipotentiostat using a Pt disk working
electrode, Pt coil wire counter electrode, and a silver wire reference
(76) Liao, Y.; Bohne, C. J. Phys. Chem. 1996, 100, 734-743.
9
6392 J. AM. CHEM. SOC. VOL. 127, NO. 17, 2005

Molecular Switching of Ru Bis(bipyridyl) Groups
A R T I C L E S
then three times with water to give a bright orange solution that was
condensed to give an orange-red oil. The crude product was run through
a short silica gel plug with hexanes to remove side product (3-
dodecylthiophene) and catalyst, and then it was purified by column
chromatography on silica gel with hexanes. The initial yellow band
was a mixture of tetrathiophene side products. The second orange band
was collected, and the solvent was removed to give BrDo2T5 as a soft,
waxy bright orange solid. Yield: 7.61 g (66%). 1H NMR (200.1 MHz,
CDCl3): δ 7.37 (d, J ) 5.4 Hz, 1H), 7.18 (d, J ) 7.7 Hz, 2H), 7.11 (d,
J ) 5.7 Hz, 1H), 7.07 (s, 1H), 7.06 (d, J ) 5.7 Hz, 1H), 7.01 (d, J )
5.4 Hz, 1H), 6.93 (d, J ) 7.8 Hz, 2H), 2.77 (m, 4H), 1.65 (m, 4H),
1.25 (m, 36H), 0.87 (t, J ) 6.8 Hz, 6H). Anal. C44H59S5Br requires C,
72.09; H, 8.67. Found: C, 72.10; H, 8.97%.
(d, J ) 5.6 Hz, 1H), 8.71 (d, J ) 7.6 Hz, 1H), 8.63 (d, J ) 7.6 Hz,
1H), 8.58 (d, J ) 8.0 Hz, 1H), 8.55 (d, J ) 8.4 Hz, 1H), 8.31 (t, J )
8.0 Hz, 1H), 8.25 (t, J ) 8.0 Hz, 1H), 8.05 (t, J ) 7.8 Hz, 1H), 7.80
(t, J ) 8.0 Hz, 1H), 7.81 (d, J ) 5.6 Hz, 1H), 7.75 (t, J ) 6.6 Hz, 1H),
7.64-7.60 (m, 2H), 7.55-7.48 (m, 2H), 7.46 (d, J ) 4.0 Hz, 1H),
7.42-7.38 (m, 5H, phenyl), 7.30 (t, J ) 6.8 Hz, 1H), 7.25-7.22 (m,
3H), 7.18 (d, J ) 5.2 Hz, 1H), 7.14 (d, J ) 4.0 Hz, 1H), 7.08 (d, J )
2.8 Hz, 1H), 7.04 (d, J ) 4.8 Hz, 1H), 6.98-6.95 (m, 4H), 6.74 (d,
JPH ) 4.4 Hz, 1H), 2.75 (t, J ) 7.8 Hz, 2H), 2.22-2.06 (m, 2H), 1.61
(q, J ) 7.4 Hz, 2H), 1.45 (m, 2H), 1.28-1.25 (m, 36 H), 0.89-0.83
(m, 6H). 31P{1H} NMR (162.0 MHz, CO(CD3)2): 27.7 (s), -143.0
(septet, JPF ) 708 Hz, PF6). Anal. C76H85F12N4S5P3Ru requires C, 55.77;
H, 5.23; N, 3.42. Found: C, 55.38; H, 5.40; N, 3.31%.
3,3′′′′-Didodecyl-3′′-iodo-2,2′:5′,2′′:5′′,2′′′:5′′′,2′′′′-pen-
tathiophene (IDo2T5). NaI (2.75 g, 18.36 mmol), CuI (87.5 mg, 0.459
mmol), and BrDo2T5 (7.61 g, 9.18 mmol) were dissolved in xylenes/
bis-2-methoxyethyl ether (160 mL/40 mL). The addition of N,N′-
dimethylethylenediamine (0.098 mL, 81 mg, 0.92 mmol) caused a white
precipitate to form, and the resulting mixture was heated to 165 °C for
16 h. After cooling, a dark yellow organic layer and a green aqueous
layer were formed with the addition of CH2Cl2 and water. The organic
layer was separated, washed three times with water, dried with MgSO4,
and filtered. The solvent was removed, and the xylenes and bis-2-
methoxyethyl ether were distilled away to leave an oily crude product.
Purification by column chromatography on silica gel with hexanes gave
IDo2T5 as a soft, waxy bright orange solid after removal of solvent.
[Ru(bpy)2PDo2T5-P,C]PF6 (9). To a deaerated solution of NaOH
(12 g, 0.30 mol) dissolved in methanol (300 mL), 8 (1.00 g, 0.611
mmol) was added and the solution was heated to reflux. After 1 h, the
solution turned from orange to a deep red. After being stirred at reflux
for 16 h, the burgundy-red solution was condensed to 150 mL and
pipetted dropwise into a solution of NH4PF6 (3.00 g, 17.3 mmol) in
H2O (200 mL) and stirred 1 h to give a red-black precipitate.
Recrystallization from ethanol gave 9 as a very dark, red powder.
1
Yield: 410 mg (45%). H NMR (400.1 MHz, CO(CD3)2): δ 8.89 (d,
J ) 5.2 Hz, 1H), 8.63 (d, J ) 8.0 Hz, 1H), 8.56 (d, J ) 7.6 Hz, 1H),
8.48-8.44 (m, 3H), 8.12-8.08 (m, 1H), 8.00-7.89 (m, 4H), 7.77-
7.72 (m, 2H), 7.66 (m, 1H), 7.50-7.43 (m, 5H), 7.37 (d, J ) 5.2 Hz,
1H), 7.31 (t, J ) 6.0 Hz, 1H), 7.19-7.13 (m, 3H), 7.06 (d, J ) 4.0
Hz, 1H), 7.03 (d, J ) 4.8 Hz, 1H), 6.98-6.92 (m, 3H), 6.86 (d, J )
5.2 Hz, 1H), 6.72 (d, J ) 2.4 Hz, 1H), 6.54 (t, J ) 8.0 Hz, 2H), 6.44
(s, 1H), 2.77 (m, 2H), 2.45 (m, 2H), 1.63 (m, 2H), 1.44 (m, 2H), 1.26
(m, 36 H), 0.84 (m, 6H). 31P{1H} NMR (162.0 MHz, CO(CD3)2): d
44.8 (s), -143.0 (septet, JPF ) 708 Hz, PF6). Anal. C76H84F6N4S5P2Ru
requires C, 60.98; H, 5.66; N, 3.74. Found: C, 61.29; H, 5.78; N, 4.00%.
3,3′′′′-Didodecyl-2,2′:5′,2′′:5′′,2′′′:5′′′,2′′′′-pentathiophene (Do2T5,
10). A solution of IDo2T5 (300 mg, 0.343 mmol) in diethyl ether (100
mL) was cooled to -20 °C, and n-BuLi (0.26 mL, 1.6 M in hexanes,
0.41 mmol) was added. The yellow-orange solution immediately
changed color to dark orange. H2O (0.10 mL, 5.55 mmol) was injected
into the solution, and with slow warming after 0.5 h, the solution turned
yellow. The ether solution was washed three times with H2O, dried
with MgSO4, and filtered, and the solvent was removed to leave a
yellow residue. Purification by column chromatography on silica gel
with hexanes gave 10 as a dark-yellow powder after removal of solvent.
1
Yield: 7.58 g (94%). H NMR (200.1 MHz, CDCl3): δ 7.38 (d, J )
4.0 Hz, 1H), 7.19-7.16 (m, 2H), 7.16 (s, 1H), 7.11 (d, J ) 3.6 Hz,
1H), 7.08 (d, J ) 4.0 Hz, 1H), 7.01 (d, J ) 3.8 Hz, 1H), 6.93 (d, J )
5.2 Hz, 2H), 2.77 (m, 4H), 1.65 (m, 4H), 1.25 (m, 36H), 0.87 (t, J )
6.6 Hz, 6H). Anal. C44H59S5I requires C, 60.38; H, 6.79. Found: C,
60.78; H, 6.88%.
3,3′′′′-Didodecyl-3′′-diphenylphosphino-2,2′:5′,2′′:5′′,2′′′:5′′′,2′′′′-
pentathiophene (PDo2T5, 7). [Pd(OCOCH3)2] (5 mg, 0.022 mmol) and
IDo2T5 (4.33 g, 4.95 mmol) were dissolved in acetonitrile (250 mL),
and distilled triethylamine (1.4 mL, 1.0 g, 9.9 mmol) was injected into
the flask. The orange suspension darkened to a greenish-brown with
heating at reflux for 16 h, and a black, gelatinous layer was formed on
the flask bottom. Solvent and volatiles were removed under reduced
pressure, and the crude product was extracted with CH2Cl2 and washed
with 1 M aq KOH, 2 M aq HCl, then three times with water. Removal
of solvent left a brown oil. Purification by column chromatography on
silica gel with acetone-hexanes (5/95) resulted in elution of starting
material IDo2T5, followed by 7 as an orange band, and an orange band
containing the phosphine oxide eluting much later. The isolated product
was a bright orange oil after removal of solvent. Yield: 4.29 g (93%).
1H NMR (200.1 MHz, CDCl3): δ 7.37 (m, 10H, phenyl), 7.15 (d, J )
5.2 Hz, 2H), 7.03 (d, J ) 3.6 Hz, 1H), 7.01 (d, J ) 4.0 Hz, 1H), 6.99
(d, J ) 4.4 Hz, 1H), 6.96, (d, J ) 3.8 Hz, 1H), 6.91 (d, J ) 5.0 Hz,
2H), 6.63 (s, 1H), 2.73 (m, 4H), 1.61 (m, 4H), 1.25 (m, 36H), 0.87 (m,
6H). 31P{1H} NMR (81.0 MHz, CDCl3): δ -23.5 (s). Anal. C56H69S5P
requires C, 72.05; H, 7.45. Found: C, 71.65; H, 7.49%.
[Ru(bpy)2PDo2T5-P,S](PF6)2 (8). AgBF4 (1.79 g, 9.18 mmol) was
added to a deaerated solution of Ru(bpy)2Cl2‚2H2O (2.39 g, 4.59 mmol)
in acetone (150 mL), stirred for 3 h, and filtered under nitrogen. The
resulting red filtrate was added to a suspension of 7 (4.29 g, 4.60 mmol)
in deaerated acetone (25 mL), and the mixture was heated at reflux for
20 h. The resulting solution was condensed to 30 mL and pipetted
dropwise into a solution of NH4PF6 (15 g, 92 mmol) in H2O (300 mL)
and stirred for 0.5 h to give dark orange precipitate. The precipitate
was recovered and dissolved in acetone, the remaining solids were
filtered off, and the solvent was removed. Recrystallization in 9:1
ethanol-acetone gave 8 as bright orange crystals. Yield: 3.44 g (46%).
1H NMR (400.1 MHz, CO(CD3)2): δ 9.25 (d, J ) 6.0 Hz, 1H), 9.09
1
Yield: 257 mg (100%). H NMR (400.1 MHz, CDCl3): δ 7.17 (d, J
) 5.2 Hz, 2H), 7.11 (d, J ) 3.6 Hz, 2H), 7.08 (s, 2H), 7.01 (d, J ) 3.6
Hz, 2H), 6.93 (d, J ) 5.2 Hz, 2H), 2.77 (t, J ) 7.8 Hz, 4H), 1.64 (m,
4H), 1.37-1.25 (m, 36 H), 0.87 (t, J ) 6.6 Hz, 6H). Anal. C44H60S5
requires C, 70.53; H, 8.07. Found: C, 70.93; H, 8.27%.
Acknowledgment. M.O.W. and C.B. thank the Natural
Sciences and Engineering Research Council of Canada (NSERC)
for support of this research. C.M. thanks NSERC and the
University of British Columbia for Fellowship support. We
thank Dr. Frank van Veggel, Peter Diamente, and Luis Netter
for assistance with lifetime measurements.
Supporting Information Available: Selected bond lengths
and angles for 1 and 4 and X-ray crystallographic files (CIF)
for 3, 6, and 8. Eop/∆E correlation plots, solid-state UV-vis
spectra and data, plots for lifetime measurements of 4 and 8,
and time-delayed luminescence spectra of 8. This material is
available free of charge via the Internet at http://pubs.acs.org.
JA043573A
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J. AM. CHEM. SOC. VOL. 127, NO. 17, 2005 6393