Ruthenium (II) polypyridyl complexes based on bipyridine and two novel diimine ligands with carrier-transporting unit: Synthesis, photoluminescence and redox properties

Article abstract of DOI:10.1016/j.jorganchem.2010.04.037

A series of ruthenium (II) complexes, [Ru(bpy)₂L]X₂ (L = L1, L2; X = Cl^-, PF₆^-, SCN^-), were synthesized based on bipyridine and two novel diimine ligands L1 and L2 (L1 = 1-(4-5′-phenyl-1,3,4-oxadiazolylphenyl)-2-pyridinyl-benzoimidazole, L2 = 1-(4-carbazolylphenyl)-2-pyridinylbenzimidazole); and the crystal structure of [Ru(bpy)₂L1]Cl₂ was also described. [Ru(bpy) ₂(Pybm)]X₂ (Pybm = 2-(2-pyridine)benzimidazole) complexes were also prepared as reference samples. In the UV-vis absorption spectra there are one strong π → π (*) transition and two dπ (Ru) → π (*) transitions. By comparisons of photoluminescence properties between [Ru(bpy)₂L]X (L = L1, L2) and the reference complexes we find that the complexes with carrier-transporting groups of carbazole and oxadizole have the higher emission intensity and quantum efficiency. One reversible oxidation process in the range 0.80-1.00 V exists in each of the complexes which is assigned to the metal oxidation, [Ru(III)(bpy)₂L]²⁺ + e^-[Ru(II)(bpy)₂L]⁺. The comparisons of PL and quantum efficiency between the [Ru(bpy)₂L]X₂ (L = L1 (1-(4-5′-phenyl-1,3,4-oxadiazolylphenyl)-2-pyridinyl-benzoimidazole), L2 (1-(4-carbazolylphenyl)-2-pyridinylbenzimidazole), X = Cl^-, PF ₆^-, SCN^-) and [Ru(bpy)₂(Pybm)]X ₂ (X = Cl^-, PF₆^-, SCN^-) suggest these ligands containing carrier-transporting groups are more benefit to the luminescence of the ruthenium (II) complexes than the based starting ligand (Pybm) due to the more rigid structure and more efficient shielding of the Ru (II) core towards external quenching.

Full text of DOI:10.1016/j.jorganchem.2010.04.037

Journal of Organometallic Chemistry 695 (2010) 2048e2056
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Ruthenium (II) polypyridyl complexes based on bipyridine and two novel
diimine ligands with carrier-transporting unit: synthesis, photoluminescence
and redox properties
Jing Wu, Hong-Yan Li, Ling-Chen Kang, Dong-Ping Li, Qiu-Lei Xu, Yu-Cheng Zhu, Yun-Mei Tao,
*
You-Xuan Zheng , Jing-Lin Zuo, Xiao-Zeng You
State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing National Laboratory of Microstructures,
Nanjing 210093, P.R.China
a r t i c l e i n f o
a b s t r a c t
A series of ruthenium (II) complexes, [Ru(bpy)2L]X2 (L ¼ L1, L2; X ¼ Clꢀ, PF6ꢀ, SCNꢀ), were synthesized
based on bipyridine and two novel diimine ligands L1 and L2 (L1 ¼ 1-(4-50-phenyl-1,3,4-oxadiazolyl-
phenyl)-2-pyridinyl-benzoimidazole, L2 ¼ 1-(4-carbazolylphenyl)-2-pyridinylbenzimidazole); and the
crystal structure of [Ru(bpy)2L1]Cl2 was also described. [Ru(bpy)2(Pybm)]X2 (Pybm ¼ 2-(2-pyridine)
benzimidazole) complexes were also prepared as reference samples. In the UV-vis absorption spectra
Article history:
Received 8 March 2010
Received in revised form
27 April 2010
Accepted 30 April 2010
Available online 6 May 2010
there are one strong
p / p* transition and two dp (Ru) / p* transitions. By comparisons of photo-
luminescence properties between [Ru(bpy)2L]X (L ¼ L1, L2) and the reference complexes we find that the
complexes with carrier-transporting groups of carbazole and oxadizole have the higher emission
intensity and quantum efficiency. One reversible oxidation process in the range 0.80e1.00 V exists in
each of the complexes which is assigned to the metal oxidation, [Ru(III)(bpy)2L]2þ þ eꢀ#[Ru(II)
(bpy)2L]þ.
Keywords:
Ruthenium
Diimine ligands
Oxadiazole
Carbazole
Photoluminescence
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
judicious choice of the ligands bound to the metal center [23e29].
The basic strategies behind all of these activities are either to
In the last few decades a variety of luminescent polypyridyl
complexes employing a range of transition metal ions and ligand
architectures have been reported. The luminescent and redox
properties of Ru (II) complexes of 2,20-bipyridine (bpy) and related
bidentate ligands have been extensively studied due to their
significant MLCT absorption in the visible spectral region [1e3],
their ability to undergo MLCT excitations [4,5], the relative
longevity [6,7] and photoreactivity [8] of the MLCT excited states,
the relative inertness of the metal centers in a variety of oxidation
states, and the rapidity of redox reactions involving the excited
states. These complexes have been employed as building blocks
for the design of supramolecular assemblies [9e11], metal-
lodendrimers [12e15], molecular electronics [16,17], molecular
machines, molecular motors [18], the fabrication of dye-sensitized
solar cells [19,20], and as light harvesting antennas [21,22]. The
photophysics, photochemistry, and redox behavior of these
complexes are ligand-dependent and therefore can be tuned by
introduce different groups within the bipyridine moiety of Ru
(bpy)3 or to substitute one or two bipyridine molecule(s) from the
Ru(bpy)3 core by other types of donor sites to form mixed ligand
tris-chelates to modulate the photo-redox activities of this class of
complexes.
Herein, we designed two original diimine ligands, 1-(4-50-
phenyl-1,3,4-oxadiazolyl phenyl)-2-pyridinylbenzoimidazole (L1)
and 1-(4-carbazolylphenyl)-2-pyridinylbenzimidazole (L2) by
introducing carrier-transporting groups (oxadiazole and carbazole)
into 2-(2-pyridine)-benzimidazole (Pybm). Replace one molecule
of Ru(bpy)3 core with L1/L2 to produce [Ru(bpy)2L]2þ (L ¼ L1, L2)
according to the follow three reasons: (i) novel diimine ligands
with different ligand-field are applied in molecular design to adjust
the molecular orbital energy levels in the Ru (II) complexes which
are related to the photochemical, photophysical and electro-
chemical events and (ii) functional groups with electro-donating or
-accepting properties are added into diimine ligands to improve the
luminescent properties of Ru (II) complexes and avoiding the
tripletetriplet annihilation because of the steric hindrance effect;
(iii) the oxadiazole and carbazole moieties can enhance the carrier-
transporting properties of the molecular in the devices. The
* Corresponding author. Tel.: þ86 25 83596775; fax: þ86 25 83314502.
E-mail address: yxzheng@nju.edu.cn (Y. -X. Zheng).
0022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.04.037

J. Wu et al. / Journal of Organometallic Chemistry 695 (2010) 2048e2056
2049
different anions in these complexes are Clꢀ, PF6ꢀ and SCNꢀ, [Ru
(bpy)2(Pybm)]X2 (X ¼ Clꢀ, PF6ꢀ, SCNꢀ) complexes are also synthe-
sized to be used as reference samples.
Smart Apex CCD diffractometer equipped with graph-
itemonochromated Mo K -2
a
(l
¼ 0.71073 Å) radiation using a
u q
scan mode at 293 K. The highly redundant data sets were reduced
using SAINT and absorption corrections were applied using SADABS
supplied by Bruker. The structures were solved by direct methods
and refined by full-matrix least-squares methods on F2 using
SHELXTL-97.
The luminescence quantum efficiencies were calculated by
comparison of the emission intensities (integrated areas) of
a standard sample and the unknown sample according to equation
(1) [30].
2. Experimental
2.1. Materials and measurements
Carbazole, ruthenium (III) chloride trihydrate and 2,20-bipyr-
idine were purchased from Yuan Hang Reagent Company, Kunming
Bo Rui metal material Ltd. and Sinopharm Chemical Reagent Co.
Ltd. (China), respectively. 1,4-Dibromobenzene, benzoyl hydrazine,
2-(2-pyridyl) benzimidazole (Pybm) and 1,3-dimethyl-3,4,5,6-ter-
ahydro-2(1H)-pyrimidinone (DMPU) were brought from Acros,
Aldrich and Alfa Companies. All of them were used as received. The
IR spectra were taken on a Vector 22 Bruker spectrophotometer
(400e4000 cmꢀ1) with KBr pellets. NMR spectra were measured on
a Bruker AM 500 spectrometer. Mass spectra were determined with
an Autoflex IITM instrument for MALDI-TOF-MS or on a Varian MAT
311A instrument for ESIeMS. Elemental analyses for C, H, and N
were performed on a PerkineElmer 240C analyzer. Absorption
spectra were measured on a UV-3100 spectrophotometer. Photo-
luminescence measurements were carried out on Hitachi F4600
luminescence spectrophotometer. The lifetime measurements
were measured with an Edinburgh Instruments FLS920P fluores-
cence spectrometer in solid powder and degassed acetonitrile
solution. All the luminescence experiments were prepared in
spectroscopic grade solvents. Cyclic voltammetry measurements
were conducted on a CHI660b electrochemical analytical instru-
ment, with a polished Pt plate as the working electrode, platinum
thread as the counter electrode and Ag/0.1 M AgNO3 in acetonitrile
as the reference electrode, tetra-n-butylammonium hypher-
chlorate was used as the supporting electrolyte, using Fcþ/Fc as the
internal standard, the scan rate was 0.1 V/s.
ꢀ
ꢁꢀ
ꢁꢀ
ꢁ
2
Is
Istd
Astd
As
hs
hstd
Fs
¼
Fstd
(1)
where Fs is the luminescence quantum yield of the unknown
sample, Fstd is the luminescence quantum yield of the standard
substance, the hs and hstd terms represent the refractive indices of
the corresponding solvents (pure solvents were assumed), I is the
wavelength-integrated area of the corrected emission spectrum,
and A is the absorbance value at the excitation wavelength. We take
air-free and air-saturated acetonitrile solution of [Ru(bpy)3]2þ$2Clꢀ
as standard samples. The Fstd has been revalued to be 9.4%
(degassed) or 1.8% (air) [31], ruthenium complexes synthesized
were also dissolved in acetonitrile, then were detected under
degassed and air-saturated conditions, respectively.
2.2. Synthesis
The chemical structures of the materials used in this work and
the synthetic routes were depicted in the Scheme 1. The ligand
precursors 2-(4-bromophenyl)-5-phenyl-1,3,4-oxadiazole (1) and
1-carbazolyl-4-bromobenzene (2) were synthesized as described in
literatures [32,33]. Ru(bpy)2Cl2$2H2O was synthesized in advance
[34] to be used as the precursor to synthesize all the ruthenium (II)
complexes. In preparation of ruthenium (II) complexes, the Schlenk
technology was used.
The crystal of [Ru(bpy)2L1]Cl2 suitable for single-crystal X-ray
analysis was obtained by diffusion diethyl ether into acetonitrile
solution of [Ru(bpy)2L1]Cl2. The data were collected on a Bruker
O
O
O
C
O
C
O
i
ii
Br
+
Br
CNHNH
CNHNH2
Br
Cl
N
N
1
iii
N
Br
Br
+
Br
NH
170 oC,13h
2
N
N
iii
iv
R
N
N
v
HN
N
N
R
N
N
N
R-Br +
N
230 oC, 48h
R
N
N
N
2Cl-
N
2X-
Ru
Ru
N
N
N
N
N
L
[Ru(bpy)2L]X2 (L = L1, L2, X- = PF6 , SCN-)
-
O
L=L1,
[Ru(bpy)2L]Cl2 (L = L1, L2)
R=
N
R=
L=L2,
N N
.
(i) Et3N, CHCl3, RT; (ii) POCl3, reflux ; (iii) CuI, 18-Crown-6, K2CO3, DMPU, in reactor; (iv) Ru(bpy)2Cl2 2H2O, ethylene glycol, 120oC, 6h; (v) KPF6 or KSCN, ethanol, RT or reflux, 2h.
Scheme 1. Synthetic routes for ligands and complexes.

2050
J. Wu et al. / Journal of Organometallic Chemistry 695 (2010) 2048e2056
Fig. 1. ORTEP view of complex [Ru(bpy)2L1]Cl2 with the atom-numbering scheme. Hydrogen atoms are omitted for clarity. Ellipsoids are drawn at the 30% probability level.
2.2.1. Synthesis of 2-(4-bromophenyl)-5-phenyl-1,3,4-oxadiazole
(1)
2.2.2. Synthesis of 1-carbazolyl-4-bromobenzene (2)
Similar methods (see Scheme 1) are used to prepare 2, L1 and L2.
A mixture of carbazole (16.72 g, 0.1 mol), 1,4-dibromobenzene
(23.59 g, 0.1 mol), CuI (1.90 g, 0.01 mol), 18-Crown-6 (0.88 g,
0.0033 mol), K2CO3 (27.67 g, 0.2 mol) and DMPU (3 mL) was put into
a reactor, then keep it heating at 170 ꢁC for 13 h under nitrogen. After
cooling to room temperature, the mixture was quenched with 1 N
HCl, the precipitate was filtered and washed with NH3$H2O and
water. The brown solid was purified with column chromatography
using hexane as eluant (10.95 g, yield: 34%). M. p.: 152e154 ꢁC. IR
(KBr, cmꢀ1): 3056, 1496, 1452,1230, 751. 1H NMR (CDCl3, 500 MHz):
4-Bromobenzoyl chloride (21.95 g, 0.1 mol) was added dropwise
to a solution of benzoyl hydrazine (13.62 g, 0.1 mol) and triethyl-
amine (10.10 g, 0.1 mol) in chloroform (150 mL) at room temper-
ature (RT). The resulting mixture was stirred for 1 h and then
filtered. The collected solid was washed with water and ethanol to
give the product N0-benzoyl-4-bromobenzohydrazide (30.32 g,
yield: 95%). A mixture of N0-benzoyl-4-bromobenzohydrazide
(20.00 g) and POCl3 (250 mL) in a 500 mL flask was refluxed under
nitrogen for 5 h. The excessive POCl3 was then distilled out, and the
residue was poured into water. The crude solid product was
collected by filtration and purified by recrystallization from
chloroform/hexane to give 2-(4-bromophenyl)-5-phenyl-1,3,4-
oxadiazole (1) as white needlelike crystals (16.04 g, yield: 85%). M.
p.: 164e168 ꢁC. IR (KBr, cmꢀ1): 3060, 1600, 1546, 1474, 1073, 728,
d
8.175 (d, 2H, J ¼ 7 Hz), 7.757 (d, 2H, J ¼ 8.5 Hz), 7.495 (d, 2H,
J ¼ 8.5 Hz), 7.431 (t, 2H, J ¼ 7 Hz), 7.411 (d, 2H, J ¼ 9 Hz), 7.342 (t, 2H,
J ¼ 7.5 Hz). MS(MALDI-TOF): m/z 321.035 [M]þ. Anal. Calcd. for
C18H12NBr: C, 67.10; H, 3.75; N, 4.35. Found: C, 66.93; H, 3.71; N, 4.31.
689. 1H NMR (CDCl3, 500 MHz):
(d, 2H, J ¼ 9 Hz), 7.710 (d, 2H, J ¼ 8.5 Hz), 7.570 (m, 3H). MS(ESI): m/z
301.08 [M]þ. Anal. Calcd for C14H9N2OBr: C, 55.84; H, 3.01; N, 9.30.
Found: C, 55.87; H, 3.11; N, 9.27.
d
8.159 (d, 2H, J ¼ 7 Hz), 8.040
2.2.3. Synthesis of 1-(4-50-phenyl-1,3,4-oxadiazolylphenyl)-2-
pyridinylbenzoimidazole (L1)
The procedure is similar to that of compound 2 with the
materials of 1 (3.01 g, 0.01 mol) and Pybm (1.95 g, 0.01 mol) at the
temperature of 230 ꢁC (2.50 g, yield: 60%). M. p.: 186e189 ꢁC. IR
(KBr, cmꢀ1): 3050,1606,1500,1442,1385, 773, 755, 741, 708, 691. 1H
Table 1
Crystallographic Data for [Ru(bpy)2L1]Cl2.
NMR (CDCl3, 500 MHz):
d
8.380 (d, 3H, J ¼ 7.5 Hz), 8.200 (d, 2H,
J ¼ 7.5 Hz), 7.987 (t,1H, J ¼ 7.5 Hz), 7.603e7.577 (m, 7H), 7.525 (t, 2H,
J ¼ 7.5 Hz), 7.405 (t, 1H, J ¼ 6 Hz), 7.321(d, 1H, J ¼ 8.5 Hz). MS
(MALDI-TOF): m/z 416.232 [M]þ. Anal. Calcd. for C26H17N5O: C,
75.17; H, 4.12; N, 16.86. Found: C, 75.11; H, 4.21; N, 16.81.
[Ru(bpy)2L1]Cl2
Formula
FW
C46H33N9OCl2Ru
899.78
T (K)
271(2)
Wavelength (Å)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
0.71073
Monoclinic
P 21/c
11.320(4)
35.314(12)
13.017(4)
90.00
105.481(6)
90.00
5015(3)
4
2.2.4. Synthesis of 1-(4-carbazolylphenyl)-2-
pyridinylbenzimidazole (L2)
The procedure is similar to that of compound 2 with the
materials of 2 (3.22 g, 0.01 mol) and Pybm (1.95 g, 0.01 mol) at the
temperature of 230 ꢁC (2.93 g, yield: 67%). M. p.: 225e228 ꢁC. IR
(KBr, cmꢀ1): 3044, 1728, 1593, 1514, 1446, 740. 1H NMR (CDCl3,
a
b
g
(deg)
(deg)
(deg)
V (Å3)
500 MHz):
d
8.489 (d, 2H, J ¼ 4.5 Hz), 8.203 (d, 2H, J ¼ 7.5 Hz), 8.074
Z
(d, 1H, J ¼ 8 Hz), 7.906 (t, 1H, J ¼ 7.5 Hz), 7.762 (d, 2H, J ¼ 8.5 Hz),
7.614 (d, 2H, J ¼ 9 Hz), 7.550 (d, 2H, J ¼ 7.5 Hz), 7.502 (t, 3H, J ¼ 7 Hz),
7.472 (m, 2H), 7.357 (t, 3H, J ¼ 7 Hz). MS (MALDI-TOF): m/z 437.130
[M]þ. Anal. Calcd for C30H20N4: C, 82.55; H, 4.62; N, 12.84. Found: C,
82.54; H, 4.69; N, 12.83.
rcalcd (g/cm3)
1.192
0.459
m
(Mo K
a
) (mmꢀ1
)
F (000)
1832
Range of transm factors (deg)
Reflns collected
Unique
2.31e19.35
27 313
9781
Data/restraints/params
9781/0/532
0.873
0.0559, 0.1311
0.1157, 0.1475
759 108
GOF on F2
2.2.5. Synthesis of Ru(bpy)2Cl2$2H2O
Ra1; wRb2½I > 2
s
ðIÞꢂ
The following modified method [34] was utilized to prepare this
complex with good yields. Commercial RuC13$3H2O (3.92 g,
15.0 mmol), bipyridine (4.69 g, 30.0 mmol), and LiCl (3.04 g,
100.0 mmol) were refluxed and stirred in reagent grade
Ra1; wRb2ðall dataÞ
CCDC No.
P
P
P
P
Ra1 ¼ j jjFoj ꢀ jFcj= Fojj. wRb2 ¼ ½ wðFo2 ꢀ Fc2Þ2= wðFo2Þꢂ1=2

J. Wu et al. / Journal of Organometallic Chemistry 695 (2010) 2048e2056
2051
Table 2
(0.23 g, 2.4 mmol), and the mixed solution was refluxed 2 h. The
solution was concentrated to get the crude product which was puri-
fied by alumina column chromatography with methanol/dichloro-
methane (v/v ¼ 0e5%) as eluant to get [Ru(bpy)2L](SCN)2 complexes.
Selected bond lengths (Å) and angles (ꢁ) for [Ru(bpy)2L1]Cl2.
Ru(1)eN(6)
Ru(1)eN(9)
Ru(1)eN(2)
2.054(4)
2.061(4)
2.069(4)
172.3(2)
78.9(2)
95.2(2)
95.8(2)
101.5(2)
89.2(2)
175.8(2)
77.7(1)
Ru(1)eN(8)
Ru(1)eN(7)
Ru(1)eN(1)
N(6)eRu(1)eN(9)
N(6)eRu(1)eN(7)
N(9)eRu(1)eN(7)
N(8)eRu(1)eN(2)
N(7)eRu(1)eN(2)
N(8)eRu(1)eN(1)
N(7)eRu(1)eN(1)
2.054(4)
2.069(4)
2.074(4)
95.0(2)
79.4(2)
85.0(2)
90.1(2)
172.4(2)
96.9(2)
96.1(2)
N(6)eRu(1)eN(8)
N(8)eRu(1)eN(9)
N(8)eRu(1)eN(7)
N(6)eRu(1)eN(2)
N(9)eRu(1)eN(2)
N(6)eRu(1)eN(1)
N(9)eRu(1)eN(1)
N(2)eRu(1)eN(1)
2.2.9. General preparation of [Ru(bpy)2(Pybm)]X2
(X ¼ Clꢀ, PFꢀ6 , SCNꢀ)
The processes resemble the preparations of [Ru(bpy)2L]X2. It is
needed to point out that because of the light sensitivity of [Ru
(bpy)2(Pybm)]X2, the purified products were gained through
recrystallization twice from diethyl ether and acetonitrile instead of
using chromatograph.
[Ru(bpy)2L1]Cl2 (0.05 g, yield: 46.0%) 1H NMR (500 MHz, D2O)
d
8.66e8.59 (m, 3H), 8.59e8.50 (m, 3H), 8.27e8.20 (m, 2H), 8.18 (d,
dimethylformamide (50 mL) for 8 h. After the reaction mixture was
cooled to room temperature, 250 mL of reagent grade acetone was
added and the resultant solution was kept at 0 ꢁC overnight.
Filtering yielded a dark green-black microcrystalline product. The
solid was washed three times with 25-mL portions of water, three
25-mL portions of diethyl ether, and then dried by suction to give
4.82 g of Ru(bpy)2Cl2.2H2O (yield: 61.8%).
J ¼ 8.0 Hz, 1H), 8.12 (t, J ¼ 8.6 Hz, 2H), 8.09e8.03 (m, 2H), 8.00 (t,
J ¼ 6.0 Hz, 2H), 7.87 (dd, J ¼ 13.1, 4.1 Hz, 2H), 7.83 (d, J ¼ 5.4 Hz, 1H),
7.81e7.78 (m, 1H), 7.76 (d, J ¼ 8.2 Hz, 1H), 7.70e7.62 (m, 3H),
7.55e7.41 (m, 5H), 7.37 (t, J ¼ 6.7 Hz, 3H), 7.32 (d, J ¼ 8.4 Hz,1H), 7.16
(t, J ¼ 7.8 Hz, 1H). MS(ESI): m/z 864.17 [M ꢀ Cl]þ.
[Ru(bpy)2L1](PF6)2 (0.04 g, yield: 31.1%) 1H NMR (500 MHz,
CD3CN)
d
8.56e8.47 (m, 6H), 8.21 (d, J ¼ 7.5 Hz, 2H), 8.15 (t,
J ¼ 7.5 Hz, 1H), 8.08 (t, J ¼ 9.0 Hz, 3H), 8.03 (d, J ¼ 9.0 Hz, 2H), 7.97
(dd, J ¼ 2, 2.5 Hz, 2H), 7.84 (m, 2H), 7.77e7.74 (m, 2H), 7.72e7.71
(m, 1H), 7.67e7.62 (m, 3H), 7.48e7.39 (m, 5H), 7.34e7.28 (m, 3H),
7.14 (t, J ¼ 8.25 Hz, 1H). MS(ESI): m/z 974.17 [M ꢀ PF6]þ.
2.2.6. General preparation of [Ru(bpy)2L]Cl2 (L ¼ L1, L2)
Ru(bpy)2Cl2$2H2O (0.06 g, 0.12 mmol) and L (0.15 mmol) were
heated under N2 atomsphere at 120 ꢁC for 6 h in ethylene glycol
until the color of the solution thoroughly changed to be red. After
the mixture was cooled to RT, the solvent was distilled out. The
resulting red solid was purified by alumina column chromatog-
raphy with methanol/dichloromethane (v/v ¼ 0e5%) as eluant to
get [Ru(bpy)2L]Cl2 complexes.
[Ru(bpy)2L1](SCN)2 (0.05 g, yield: 44.9%) 1H NMR (500 MHz,
CD3CN)
d
8.62e8.46 (m, 6H), 8.20 (dd, J ¼ 12.1, 5.5 Hz, 2H),
8.17e8.11 (m, 1H), 8.10e8.05 (m, 2H), 8.03 (dd, J ¼ 6.6, 2.7 Hz, 2H),
7.97 (dd, J ¼ 11.7, 3.5 Hz, 2H), 7.88e7.81 (m, 2H), 7.80e7.70 (m, 3H),
7.68e7.59 (m, 3H), 7.51e7.46 (m, 3H) 7.44e7.41 (m, 3H), 7.36e7.25
(m, 3H), 7.12 (t, J ¼ 7.8 Hz, 1H). MS(ESI): m/z 887.17 [M ꢀ SCN]þ.
[Ru(bpy)2L2]Cl2 (0.04 g, yield: 38.8%) 1H NMR (500 MHz, D2O)
2.2.7. General preparation of [Ru(bpy)2L](PF6)2 (L ¼ L1, L2)
The crude product [Ru(bpy)2L]Cl2 (0.12 mmol) used as precursor
complex was resolved in 10 mL ethanol. KPF6 (0.22 g, 1.2 mmol)
aqueoussolutionwasaddeddropwiseintotheethanol solutionof[Ru
(bpy)2L]Cl2. The solutionwas stirred for 2 h at room temperature, and
then filtered to get the precipitation. This crude product was purified
by alumina column chromatography with methanol/dichloro-
methane (v/v ¼ 0e5%) as eluant to get [Ru(bpy)2L](PF6)2 complexes.
d
8.66e8.60 (m, 3H), 8.56 (d, J ¼ 8.1 Hz, 1H), 8.26 (d, J ¼ 7.7 Hz, 2H),
8.20 (td, J ¼ 8.1, 1.2 Hz, 1H), 8.12 (t, J ¼ 7.9 Hz, 2H), 8.09e7.99 (m,
6H), 7.92e7.83 (m, 4H), 7.81 (d, J ¼ 5.2 Hz, 1H), 7.72 (d, J ¼ 8.3 Hz,
2H), 7.58e7.52 (m, 4H), 7.52e7.43 (m, 5H), 7.42e7.35 (m, 4H),
7.21e7.14 (m, 1H). MS(ESI): m/z 909.00 [M ꢀ Cl þ Na]2þ
.
[Ru(bpy)2L2](PF6)2 (0.09 g, yield: 65.4%) 1H NMR (500 MHz,
CD3CN)
d
8.57e8.53 (m, 3H), 8.49 (d, J ¼ 7.5 Hz, 1H), 8.24 (d,
J ¼ 8 Hz, 2H), 8.16 (t, J ¼ 7.75 Hz, 3H), 8.08e8.02 (m, 5H), 8.01e7.95
(m, 3H), 7.86e7.83 (m, 3H), 7.79 (d, J ¼ 4.5 Hz, 1H), 7.76
(d, J ¼ 5.5 Hz, 1H), 7.53e7.50 (m, 4H), 7.48e7.43 (m, 3H), 7.41e7.39
2.2.8. General preparation of [Ru(bpy)2L](SCN)2 (L ¼ L1, L2)
The synthesis of [Ru(bpy)2L](SCN)2 is similar to the process of [Ru
(bpy)2L](PF6)2, the aqueous solution of KPF6 was replaced by KSCN
2.0
2.0
2.0
a
b
c
1.5
1.0
0.5
0.0
1.5
1.0
0.5
0.0
1.5
1.0
0.5
0.0
200
300
400
500
200
300
400
500
200
300
400
500
Wavelength (nm)
Wavelength (nm)
Wavelength (nm)
Fig. 2. Electronic absorption spectra of all the ruthenium (II) complexes in acetonitrile solution at room temperature.

2052
J. Wu et al. / Journal of Organometallic Chemistry 695 (2010) 2048e2056
Table 3
and angles are given in Table 2. Crystal of [Ru(bpy)2L1]Cl2 was
found to be monoclinic and the crystallographic data were refined
in space group P21/c. The geometry of the ruthenium (II) center is
distorted octahedral. A slight distortion from octahedral geometry
is reflected in trans-N-Ru-N bond angles below 180ꢁ (175.8(2),172.4
(2) and 172.3(2), respectively) and cis-N-Ru-N angles below 90ꢁ
(77.7(1), 79.4(2) and 78.9(2), respectively) which agree with the
reported literature [35]. The NeRueN “bite” angles for the biden-
tate ligands are typical of 5-membered chelate rings formed by
such ligands. The two RueN bond distances for the same diimine
ligand are similar (2.074(4) Å for RueN(1) and 2.069(4) Å for RueN
(2), for example). The RueN bond lengths found in [Ru(bpy)2L1]Cl2
(2.054(4)-2.074(4) Å) are in agreement with those for related
structures [36e39]. There are lattice water molecules in this
complex which are significantly disordered and could not be
modeled properly with the program SQUEEZE [40], a part of the
PLATON package [41]. The number of lattice water molecules can be
calculated to be four depending on the TGA curve of this complex
(Fig. S3).
Absorption and photoluminescence data of ruthenium (II) complexes in solution
and solid state at room temperature.
Complex
Medium labs,max
Emission Lifetime
Efficiency
(nm)
lmax
s
F
(%)
3
( ꢃ 105 (nm)a
M cmꢀ1
)
f
[Ru(bpy)2L1]Cl2
Solid
670b
2.003 m
sd
c2 ¼ 0.976
CH3CN
Solid
288, 2.01 648c
650b
264.18 nse 5.2g
c2 ¼ 0.997 1.4h
f
[Ru(bpy)2L1](PF6)2
[Ru(bpy)2L1](SCN)2
[Ru(bpy)2L2]Cl2
2.280 m
sd
c2 ¼ 0.980
CH3CN
Solid
286, 1.95 650c
660b
269.90 nse 3.4g
c2 ¼ 0.997 0.84h
2.214 m
sd
f
c2 ¼ 0.982
CH3CN
Solid
288, 1.69 647c
653b
257.20 nse 5.6g
c2 ¼ 0.997 1.8h
2.236 m
sd
f
c2 ¼ 0.980
CH3CN
Solid
287, 1.80 643c
654b
263.70 nse 4.8g
c2 ¼ 0.997 1.2h
f
[Ru(bpy)2L2](PF6)2
[Ru(bpy)2L2](SCN)2
2.340 m
sd
3.2. Photoluminescence properties
c2 ¼ 0.980
CH3CN
Solid
289, 1.91 643c
663b
247.68 nse 3.7g
c2 ¼ 0.998 0.92h
The electronic absorption spectra of all the nine ruthenium (II)
complexes studied in acetonitrile solution are shown in Fig. 2 and
all the peaks data are listed in Table 3. The presence of different
acceptor levels in the complexes may be responsible for the
observed multiple absorptions [42]. All compounds show a strong
2.222 m
sd
f
c2 ¼ 0.979
CH3CN
288, 1.90 643c
643b
238.79 nse 9.7g
c2 ¼ 0.998 2.6h
f
[Ru(bpy)2(Pybm)]Cl2 Solid
CH3CN
Solid
2.402 m
sd
c2 ¼ 0.981
ligand centered
transfer (d (Ru) /
The band at w285 nm has been assigned to LC
p
/
p
* transition and two metal-to-ligand charge-
*, MLCT) transitions in the UV-visible range.
* transitions
289, 1.29 638c
651b
151.44 nse 1.8g
p
p
c2 ¼ 0.997 0.71h
p
/ p
f
[Ru(bpy)2(Pybm)]
(PF6)2
2.257 m
sd
c2 ¼ 0.982
by comparison with the spectrum of protonated bipyridine [43] and
corresponding free ligands (L1, L2 and Pybm, see Supporting
Information). The two remaining intense bands at w240 and 460
CH3CN
Solid
287, 1.63 628c
625b
125.07 nse 3.2g
c2 ¼ 0.998 0.75h
f
[Ru(bpy)2(Pybm)]
(SCN)2
2.044 m
sd
nm have been assigned to MLCT d
respect to the C2 axis of the bipyridine ligand, there are two
different kinds of bipyridine acceptor orbitals, one symmetric (
and one antisymmetric ( ) and the transitions from metal-filled d
orbitals to these two * orbitals result in the above-mentioned
p (Ru) / p* transitions. With
c2 ¼ 0.978
CH3CN
289, 1.74 634c
114.31 nse 3.3g
c2 ¼ 0.997 0.66h
c)
j
p
a
Emission maxima from not corrected spectra.
Be excited at 495 nm.
Be excited at 376 nm.
Be detected at lex ¼ 495 nm and the maximal emission bands of the ruthenium
b
c
p
bands. Thus these are believed to represent MLCT transitions and
are expected for low-spin ruthenium (II) complexes. The lower-
d
(II) complexes in solid state.
energy band at w460 nm is considered to be the d
transition and the higher-energy band near 240 nm due to the d
(Ru) / *(
p
(Ru) /
p
*(
j
)
e
Be detected at lex ¼ 405 nm and the maximal emission bands of the ruthenium
p
(II) complexes in degassed acetonitrile solution.
f
p
c
) transition [43]. The MLCT absorption maxima of all
Not detected.
Calculated by Fs
g
¼
Fstd(IsAstdh2s)/(Istd shs2td) using degassed acetonitrile solution
A
the compounds with replaced new diimine ligand(s) show little red
shift from 451 nm of the pristine [Ru(bpy)3]2þ to longer wave-
lengths. From the Fig. 2, it is also observed that the absorption
intensities of all the [Ru(bpy)2L]X2 (L ¼ L1, L2, X ¼ Clꢀ, PF6ꢀ, SCNꢀ)
are stronger than the reference complexes [Ru(bpy)2(Pybm)]X2
(X ¼ Clꢀ, PFꢀ6 , SCNꢀ). It is reasonable to infer that the addition of
carrier-transporting groups (oxadiazole and carbazole) is useful to
enhance the electronic absorption of ruthenium (II) ploypyridine
complexes. This benefit is certified in quantum efficiency in
following discussion.
of [Ru(bpy)3]2þ$2Clꢀ as a standard sample (Fstd ¼ 9.4%), the error in this method is
estimated to be approximately 10% of the measured value.
h
Calculated by Fs
¼
Fstd(IsAstdh2s)/(Istd shs2td
A ) using air-saturated acetonitrile
solution of [Ru(bpy)3]2þ$2Clꢀ as a standard sample (Fstd ¼ 1.8%), the error in this
method is estimated to be approximately 10% of the measured value.
(m, 3H), 7.38e7.33 (m, 3H), 7.15 (t, J ¼ 7.25 Hz, 1H). MS(ESI): m/z
995.33 [M ꢀ PF6]þ.
[Ru(bpy)2L2](SCN)2 (0.05 g, yield: 40.4%) 1H NMR (500 MHz,
CD3CN)
d
8.65 (d, J ¼ 8.2 Hz, 3H), 8.58 (d, J ¼ 8.1 Hz, 1H), 8.25
(d, J ¼ 7.8 Hz, 2H), 8.23e8.18 (m, 1H), 8.13 (t, J ¼ 8.0 Hz, 2H),
8.11e8.07 (m, 2H), 8.06e8.00 (m, 4H), 7.93e7.84 (m, 4H), 7.82 (d,
J ¼ 5.5 Hz, 1H), 7.72 (d, J ¼ 8.2 Hz, 2H), 7.54 (dd, J ¼ 8.1, 7.3 Hz, 4H),
7.51e7.45 (m, 5H), 7.44e7.34 (m, 4H), 7.18 (t, J ¼ 7.7 Hz, 1H). MS
(ESI): m/z 908.92 [M ꢀ SCN]þ.
Fig. 3 demonstrates the emission spectra of the nine ruthenium
(II) complexes in air-equilibrated acetonitrile solution and in solid
state excited at 376 nm and 495 nm at room temperature, respec-
tively. Emission band maxima (lmax), emission quantum yield (
F),
and lifetime ( ) values are also collected in Table 3. It is easily to find
s
that the ruthenium (II) complexes in acetonitrile solution excited at
376 nm lead to the emissions around 630e650 nm and these
complexes in solid state excited at 495 nm lead to the emissions
around 640e670 nm which are the typical MLCT emission of
ruthenium (II) polypyridine complexes. Unlike the absorption
spectra, the emission spectra of these compounds show bigger
variation in both intensity and peak position. From Fig. 3 we can
3. Results and discussion
3.1. Crystallograph
The X-ray crystal structure of [Ru(bpy)2L1]Cl2 is shown in Fig. 1,
and the crystal data are presented in Table 1, selected bond lengths

J. Wu et al. / Journal of Organometallic Chemistry 695 (2010) 2048e2056
2053
200
150
100
50
600
a
b
500
400
300
200
100
0
0
600
700
800
900
500
600
700
800
900
Wavelength (nm)
Wavelength (nm)
Fig. 3. Emission spectra of all the ruthenium (II) complexes in acetonitrile solution (a, lex ¼ 376 nm) and solid (b, lex ¼ 495 nm) state at room temperature.
observe that the complexes with two novel diimine ligands [Ru
(bpy)2L]X2 (L ¼ L1, L2, X ¼ Clꢀ, PFꢀ6 , SCNꢀ) show higher intensities
than the reference complexes [Ru(bpy)2(Pybm)]X2 (X ¼ Clꢀ, PF6ꢀ,
SCNꢀ). After introducing the carrier-transporting groups into the
Pybm the derivatives become much more rigid and also can provide
efficient shielding of the Ru (II) core towards external quenching
which are favorable for the light emission. Compared to the emis-
sion band at 606 nm of [Ru(bpy)3]2þ in acetonitrile solution [43],
the emission bands of all the ruthenium (II) complexes in this
article have a little red shift. A similar red shift in the absorption
and the emission has been detected in several mixed-ligand Ru
complexes in which the emitting ligand has lower p* energies than
c
b
a
d
e
f
h
g
i
Fig. 4. Decay curves of all the ruthenium (II) complexes in solid state at room temperature.

2054
J. Wu et al. / Journal of Organometallic Chemistry 695 (2010) 2048e2056
a
b
c
Ru(bpy) L1(SCN)
2
1000
800
600
400
200
0
Ru(bpy) L1( PF )
1000
800
600
400
200
0
2
Ru(bpy) L1Cl
2
1000
800
600
400
200
0
2
6 2
2
τ =257.20 ns
τ =269.90 ns
1
τ =264.18 ns
1
1
2
2
2
χ =0.997
χ =0.997
χ =0.997
0
1000 2000 3000 4000 5000
Time (ns)
0
1000 2000 3000 4000 5000
Time (ns)
0
1000 2000 3000 4000 5000
Time (ns)
d
e
f
Ru(bpy) L2(SCN)
2
Ru(bpy) L2( PF )
1000
800
600
400
200
0
1000
800
600
400
200
0
Ru(bpy) L2Cl
2
2
2
6 2
1000
800
600
400
200
0
2
τ =238.79 ns
τ =247.68 ns
τ =263.70 ns
1
1
1
2
2
2
χ =0.998
χ =0.998
χ =0.997
0
1000 2000 3000 4000 5000
Time (ns)
0
1000 2000 3000 4000 5000
Time (ns)
0
1000 2000 3000 4000 5000
Time (ns)
g
h
i
Ru(bpy) (Pybm)(SCN)
2
Ru(bpy) (Pybm)( PF )
1000
800
600
400
200
0
1000
800
600
400
200
0
2
Ru(bpy) (Pybm)Cl
2
1000
800
600
400
200
0
2
6 2
2
τ =114.31 ns
τ =125.07 ns
1
τ =151.44 ns
1
1
2
2
2
χ =0.997
χ =0.998
χ =0.997
0
1000 2000 3000 4000 5000
Time (ns)
0
1000 2000 3000 4000 5000
Time (ns)
0
1000 2000 3000 4000 5000
Time (ns)
Fig. 5. Decay curves of all the ruthenium (II) complexes in degassed acetonitrile solution at room temperature. The black lines are experimental lines and the red lines are
fitting lines.
the ligand it replaced [44,45]. The replaced ligands in our case are
the ones with electron-accepting groups (oxadiazole) or electron-
donating groups (carbazole). By compared with the reference
complexes [Ru(bpy)2(Pybm)]X2 (X ¼ Clꢀ, PF6ꢀ, SCNꢀ), the red shift
also exists, so both of the oxadiazole and carbazole can increase the
ground state (t2g) energy level of the complex. These two novel
diimine ligands lose the excellent symmetry of bipyridine. The
resulting degeneration of the excited states also seems to lead to
red-shifted emission [46].
noticed that the quantum efficiencies of [Ru(bpy)2L]X2 (L ¼ L1, L2)
are higher than that of the reference complexes [Ru(bpy)2(Pybm)]
X2 either in degassed solutions or in air-saturated ones, and similar
to the emission intensity sequence as the above description.
However, the change of anions, X ¼ Clꢀ, PF6ꢀ, SCNꢀ, has no distinct
effect in emission intensity and quantum efficiency yield suggest-
ing that the anions did not affect emission process greatly. We think
that because the anions are located at outside of the Ru-core and
the strengths of RueX bonds are weaker than that of RueN. We also
observe a significant decrease in the quantum efficiencies of these
complexes relative to the standard sample, [Ru(bpy)3]2þ$2Clꢀ,
except the sample [Ru(bpy)2L2](SCN)2. Because there were also
The luminescence quantum yield, defined as the ratio of the
number of photons emitted to the number of photons absorbed,
gives the efficiency of the luminescence process. From Table 3 it is
30
40
20
a
b
C
15
20
10
0
-15
-30
-45
-60
0
-10
-20
-30
-40
-50
0
-20
-40
-60
-80
-2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0
E (v) versus AgNO (10 mM)/Ag
3
-2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0
E (v) versus AgNO (10 mM)/Ag
3
-2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0
E (v) versus AgNO (10 mM)/Ag
3
Fig. 6. Cyclic voltammograms of ruthenium (II) complexes in acetonitrile solution at 298 K.

J. Wu et al. / Journal of Organometallic Chemistry 695 (2010) 2048e2056
2055
Table 4
electrochemically accessible LUMO [51]. Since all the complexes
have two bipyridine units, four one-electron reductions are there-
fore expected. However, in practice we have observed only one
reduction process in the range ꢀ1.60 w ꢀ1.80 V. Other expected
reductions could not be seen possibly due to solvent cut-off. Other
irreversible reduction waves in some figures may be due to the
presence of water and impurities in acetonitrile.
Electrochemical data of ruthenium (II) complexes at 298 K.
Complex
Ru(III)-Ru(II) Ligand
reduction
D
Eo(v)a nMLCT (cmꢀ1
)
Eo
(v)
Eo
(v)
Cal.b Obs.c
298
298
(DEp (mv))
[Ru(bpy)2L1]Cl2
0.83 (80)
0.84 (60)
0.85 (70)
0.85 (60)
0.84 (90)
0.82 (100)
0.81 (90)
ꢀ1.60
ꢀ1.60
ꢀ1.63
ꢀ1.64
ꢀ1.66
ꢀ1.60
ꢀ1.80
ꢀ1.80
ꢀ1.78
2.43
2.44
2.48
2.49
2.50
2.42
2.61
2.61
2.60
22 598 21 834
22 679 21 786
23 001 21 834
23 082 21 786
23 163 21 786
22 517 21 834
24 050 21 881
24 050 21 834
23 969 21 929
[Ru(bpy)2L1](PF6)2
[Ru(bpy)2L1](SCN)2
[Ru(bpy)2L2]Cl2
[Ru(bpy)2L2](PF6)2
[Ru(bpy)2L2](SCN)2
[Ru(bpy)2(Pybm)]Cl2
The lowest energy MLCT transition involves excitation of the
electron from the filled t26g orbital of ruthenium (II) to the lowest
p*
orbital of the bipyridine ligand. Now the associated energy of the
MLCT band for each complex can be predicted from the experi-
mentally observed electrochemical data by considering the
following two eqns (2) and (3) [52,53].
[Ru(bpy)2(Pybm)](PF6)2 0.81 (90)
[Ru(bpy)2(Pybm)](SCN)2 0.82 (80)
a
nMLCT ¼ 8065ð
D
EÞ þ 3000
(2)
Calculated by using eqn (3) of the text.
Calculated by using eqn (2) of the text.
In acetonitrile solution.
b
c
D
E ¼ E298ðRuðIIIÞ=RuðIIÞÞ ꢀ E298ðLÞ
(3)
Here, E298 (Ru(III)/Ru(II)) and E298 (L) are the formal potentials (in
V) of the ruthenium (III)eruthenium (II) couple and the first ligand
reduction, respectively. The nMLCT is the frequency of the lowest
energy MLCT transition (in cmꢀ1). The factor 8065 in eqn (2) is used
significant red shifts in the emission of these complexes, these
decreased quantum yields are probably a direct consequence of the
energy gap law [47].
to convert potential difference D
E from volt to cmꢀ1 and the term
The decay of an excited state takes place by competitive radia-
tive and non-radiative processes, which is an important parameter
for practical applications of luminescence. In this study, the lumi-
nescence decay curves of all the complexes in solid state were
obtained from time-resolved luminescence experiments at the
MLCT excitation and maximal emission wavelengths at room
temperature (Fig. 4), the luminescence decay curves of all the
samples in degassed acetonitrile solution were also obtained from
time-resolved luminescence experiments using the laser lamp as
the light source (lex ¼ 405 nm) and emitting at the maximal
wavelength (Fig. 5). From the figures we can find that the emission
decay curves of the nine complexes are best fitted by mono-
exponential, which lie on the microsecond timescale. If a decay is
not single exponential then that implies that there are different
sites for the ion and that each site has a different lifetime. So, from
our results we can conclude that all ruthenium ions occupy the
same average local environment within each sample. Fig. 5 also
shows the mono-exponential decay curves, but the lifetimes in
degassed acetonitrile solution are much shorter than in solid state,
the quenching of solvent may account for this. The lifetimes of the
reference samples are shorter than [Ru(bpy)2L]X2, that support the
sequence of quantum efficiency.
3000 cmꢀ1 is of empirical origin. The calculated values accord with
the experimental observed MLCT energies (Table 4) in a certain
degree. This agreement is previously reported in the other mixed
ligand ruthenium bipyridine complexes and other related systems
[54e56].
4. Conclusion
The noteworthy feature of our work is success in introducing
two diimine ligands with carrier-transporting units of oxadiazole
and carbazole into ruthenium (II) bipyridine complexes. The
comparisons of PL and quantum efficiency between the [Ru(bpy)2L]
X2 (L ¼ L1, L2, X ¼ Clꢀ, PF6ꢀ, SCNꢀ) and [Ru(bpy)2(Pybm)]X2 (X ¼ Clꢀ,
PFꢀ6 , SCNꢀ) suggest these ligands containing carrier-transporting
groups are more benefit to the luminescence of the ruthenium (II)
complexes than the based starting ligand (Pybm) due to the more
rigid structure and more efficient shielding of the Ru (II) core
towards external quenching. However, the different anions, X ¼ Clꢀ,
PFꢀ6 , SCNꢀ, did not affect the emission process greatly due to the
long distance between the anions and Ru core. One reversible
oxidation process in the range 0.80e1.00 V exists in each of the
complexes which is assigned to the metal oxidation, [Ru(III)
(bpy)2L]2þ þ eꢀ#[Ru(II)(bpy)2L]þ.
3.3. Redox properties
Acknowledgments
Using a platinum working electrode, redox properties of the
complexes have been studied in acetonitrile solution by cyclic
voltammetry (CV). Complexes are electroactive with respect to
metal as well as ligand centers. Representative voltammograms are
shown in Fig. 6 and the electrochemical data are depicted in Table 4.
One reversible oxidation process in the range 0.80e1.00 V exists
in each of the complexes which is assigned to the metal oxidation,
[Ru(III)(bpy)2L]2þ þ eꢀ#[Ru(II)(bpy)2L]þ. Under the experimental
condition using saturated calomel electrode (SCE) as inner refer-
ence electrode, the Ru (III)eRu (II) reduction potential of [Ru
This work was supported by the National Natural Science
Foundation of China (Grant 20971067 and 20721002), the Natural
Science Foundation of Jiangsu Province (Grant BK2008257), the
Major State Basic Research Development Program (2006CB806104
and 2007CB925103).
Appendix. Supporting information
(bpy)3]2þ appears at 1.29
reasonable.
V [48,49], so this assignment is
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jorganchem.2010.04.037.
In some voltammograms of these complexes (Fig. 6 and Fig. S2),
some other oxidation processes could be found in the range
0e1.5 V. These irreversible oxidation processes may be due to
either Ru (III)eRu (IV) oxidation or oxidation of the coordinated
ligand [50]. 2,20-bipyridine is a well known potential electron-
transfer center and each bipyridine can accept two electrons in one
References
[1] B.S. Brunschwig, C. Creutz, N. Sutin, Coord. Chem. Rev. 177 (1998) 61e79.
[2] E.M. Kober, T.J. Meyer, Inorg. Chem. 21 (1982) 3967e3977.
[3] E.M. Kober, J.C. Marshall, W.J. Dressick, B.P. Sullivan, J.V. Caspar, T.J. Meyer,
Inorg. Chem. 24 (1985) 2755e2763.

2056
J. Wu et al. / Journal of Organometallic Chemistry 695 (2010) 2048e2056
[4] T.J. Meyer, Pure Appl. Chem. 58 (1986) 1193e1206.
[5] P.A. Anderson, F.R. Keene, T.J. Meyer, J.A. Moss, G.F. Strouse, J.A. Treadway,
J. Chem. Soc. Dalton Trans. (2002) 3820e3831.
[6] A.D. Guerzo, S. Leroy, F. Fages, R.H. Schmehl, Inorg. Chem. 41 (2002) 359e366.
[7] T.M. Dixon, J.P. Colin, J.P. Savage, L. Flamigini, S. Encinas, F. Barigelletti, Chem.
Soc. Rev. 29 (2000) 385e391.
[29] K. Koike, S. Naito, S. Sato, Y. Tamaki, O. Ishitani, J. Photochem, Photobiol. A 207
(2009) 109e114.
[30] D.P. Rillema, D.G. Taghdiri, D.S. Jones, C.D. Keller, L.A. Worl, T.J. Meyer, et al.,
Inorg. Chem. 26 (1987) 578e585.
[31] K. Suzuki, A. Kobayashi, S. Kaneko, K. Takehira, T. Yoshihara, H. Ishida, et al.,
Phys. Chem. Chem. Phys. 42 (2009) 9850e9860.
[8] A. Vogler, H. Kunkely, Coord. Chem. Rev. 177 (1998) 81e96.
[9] J.M. Lehn, Supramolecular Chemistry Concepts and Perspecties. VCH, New
York, 1995.
[10] V. Balzani, P. Ceroni, M. Maestri, C. Saudan, V. Vicinilli, Top. Curr. Chem. 228
(2003) 159e191.
[11] V. Balzani, F. Scandola, Supramolecular Photochemistry. Horwood, Chichester
U.K., 1991.
[12] G.R. Newkome, E. He, C.N. Moorefield, Chem. Rev. 99 (1999) 1689e1746.
[13] S. Serroni, S. Campagna, F. Puntoriero, C. di Pietro, N.D. McClenaghan,
F. Loiseau, Chem. Soc. Rev. 30 (2001) 367e375.
[32] Q. Zhang, J.S. Chen, Y.X. Cheng, L.X. Wang, D.G. Ma, X.B. Jing, et al., J. Mater.
Chem. 14 (2004) 895e900.
[33] Z. Peng, Z. Bao, M.E. Galvin, Adv. Mater. 10 (1998) 680e684.
[34] B.P. Sullivan, D.J. Salmon, T.J. Meyer, Inorg. Chem. 17 (1978) 3334e3341.
[35] N. Nickita, G. Gasser, P. Pearson, M.J. Belousoff, L.Y. Goh, A.M. Bond, et al.,
Inorg. Chem. 48 (2009) 68e81.
[36] N. Nickita, A.I. Bhatt, A.M. Bond, G.B. Deacon, G. Gasser, L. Spiccia, Inorg. Chem.
46 (2007) 8638e8651.
[37] P. Pearson, A.M. Bond, G.B. Deacon, C. Forsyth, L. Spiccia, Inorg. Chim. Acta 361
(2008) 601e612.
[14] M. Sommovigo, G. Denti, S. Serroni, S. Campagna, C. Mingazzini, C. Mariotti,
et al., Inorg. Chem. 40 (2001) 3318e3323.
[38] R. Caspar, H. Amouri, M. Gruselle, C. Cordier, B. Malezieux, R. Duval, et al., Eur.
J. Inorg. Chem. 3 (2003) 499e505.
[15] J.A. Barron, S. Bernhard, P.L. Houston, H.D. Abruna, J.L. Ruglovsky, G.
G. Malliaras, J. Phys. Chem. A 107 (2003) 8130e8133.
[39] R. Caspar, L. Musatkina, A. Tatosyan, H. Amouri, M. Gruselle, C. Cordier, et al.,
Inorg. Chem. 43 (2004) 7986e7993.
[16] J.F. Callan, A.P. de Silva, N.D. McClenaghan, Chem. Commun. (2004) 2048e2049.
[17] D.C. Magri, G.J. Brown, G.D. McClean, A.P. de Silva, J. Am. Chem. Soc. 128
(2006) 4950e4951.
[40] P. van der Sluis, A.L. Spek, Acta Crystallogr. A 46 (1990) 194e201.
[41] A. Juris, V. Balzani, F. Barigelletti, S. Campagna, P. Belser, A.V. Zelewsky, Coord.
Chem. Rev. 84 (1988) 85e277.
[18] J.D. Badijic, V. Balzani, A. Credi, S. Silvi, J.F. Stoddart, Science 303 (2004)
1845e1849.
[19] M. Gratzel, Inorg. Chem. 44 (2005) 6841e6851 (and references cited therein).
[20] M.K. Nazeeruddin (Ed.), Coord. Chem. Rev., 248, 2004, pp. 1161e1164.
[21] H.B. Baudin, J. Davidsson, S. Serroni, A. Juris, V. Balzani, S. Campagna, et al.,
J. Phys. Chem. A 106 (2002) 4312e4319.
[22] M. Nowakowska, V.P. Fovle, J.E. Guillet, J. Am. Chem. Soc. 115 (1993)
5975e5981.
[23] S.I. Gorelsky, E.S. Dodsworth, A.B.P. Lever, A.A. Vlcek, Coord. Chem. Rev. 174
(1998) 469e496.
[42] F.E. Lytle, D.M. Hercules, J. Am, Chem. Soc. 91 (1969) 253e257.
[43] M. Zhou, G.P. Robertson, J. Roovers, Inorg. Chem. 44 (2005) 8317e8325.
[44] P.A. Anderson, G.B. Deacon, K.H. Haarman, F.R. Keene, T.J. Meyer, D.A. Reitsma,
et al., Inorg. Chem. 34 (1995) 6145e6157.
[45] A.E. Curtright, J.K. McCusher, J. Phys. Chem. A 103 (1999) 7032e7041.
[46] Y. Shen, B.P. Maliwal, J.R. Lakowicz, J. Fluorescence 13 (2003) 163e168.
[47] J.V. Casper, T.J. Meyer, Inorg. Chem. 22 (1983) 2444e2453.
[48] R. Alsfasser, R.V. Eldik, Inorg. Chem. 35 (1996) 628e636.
[49] B.J. Coe, T.J. Meyer, P.C. White, lnorg. Chem. 34 (1995) 593e602.
[50] K.D. Keerthi, B.K. Santra, G.K. Lahiri, Polyhedron 17 (1998) 1387e1396.
[51] S. Bhattacharya, Polyhedron 12 (1993) 235e240.
[24] G. Albano, P. Belser, C. Daul, Inorg. Chem. 40 (2001) 1408e1413.
[25] J.A. Treadway, B. Loeb, R. Lopez, P.A. Anderson, F.R. Keene, T.J. Meyer, Inorg.
Chem. 35 (1996) 2242e2246.
[52] S. Goswami, R.N. Mukherjee, A. Chakravorty, Inorg. Chem. 22 (1983)
2825e2832.
[26] A.A. Vlcek, E.S. Dodsworth, W.J. Pietro, A.B.P. Lever, Inorg. Chem. 34 (1995)
1906e1913.
[27] S. Le Gac, S. Rickling, P. Gerbaux, E. Defrancq, C. Moucheron, A. Kirsh-De
Mesmaeker, Angew. Chem. Int. Ed. 48 (2009) 1122e1125.
[28] L. Moriggi, A. Aebischer, C. Cannizzo, A. Sour, A. Borel, J.C.G. Bünzli, et al.,
J. Chem. Soc. Dalton Trans. (2009) 2088e2095.
[53] B.K. Ghosh, A. Chakravorty, Coord. Chem. Rev. 95 (1989) 239e294.
[54] B.P. Sullivan, J.V. Caspar, S.R. Johnson, T.J. Meyer, Organometal. 3 (1984)
1241e1251.
[55] E.S. Dodsworth, A.B.P. Lever, Chem. Phys. Lett. 124 (1986) 152e158.
[56] M.A. Greaney, C.L. Coyle, M.A. Harmer, A. Jordan, E.I. Stiefel, Inorg. Chem. 28
(1989) 912e920.